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Digilock 110

1. DCC 110 3A implemented System GND la le Digital Signals not usea D 0 2a 2c D 1 D 2 3a 3c D 3 D 4 4a Ac D 5 D 6 5a 5c D 7 Analog Signals DA 0 6a 6c DA 1 DA 2 7a KS DA 3 Address Lines not used A 0 10a 10c A A 2 lla lle A 3 A 4 12a 12c A 5 A 6 13a 13c A 7 read write r w 14a 14c Address Enable AEN Indicated Parameter Photo Diode Channel 1 DCC 8a 8c DCC Photo Diode Channel 2 Umax Channel 1 DCC 9a 9c DCC Umax Channel 2 TEC max Channel 1 DTC 15a 15c DTC I TEC max Channel 2 Tmax Channel 1 DTC 16a 16c DTC Tmax Channel 2 max Channel 1 DCC 17a 17c DCC Imax Channel 2 Tmin Channel 1 DTC 18a 18c DTC Tmin Channel 2 set Channel 1 DCC 19a 19c DCC ket Channel 2 Tse Channel 1 DTC 20a 20c DTC Tat Channel 2 aa ES 1 DEC 21a 216 DCC lact Channel 2 Tee Chicininel DIC 22a 22c DTC Tact Channel 2 tec Channel DTC 23a 23c DTC hec Channel 2 VO 24a 24c VO Power typ 6 8 V GND floating if no 25a 25G Power typ 6 8 V GND floating if DCC 110 3A implemented no DCC 110 3A implemented V Supply 26a 26c V Supply Error beep 27a QC Error LED on when GND Blink Reference GND 28a 28c Remote On Off low Power down Uret 29a 29c Uret General supply lines 15 V stabilized 30a 30c 15 V stabilized 3la 31c Power typ 6
2. 3 Operator Controls and Connections 3 1 Front Panel 1 13 12 O TRIG A _ 11 L O eng _ o ell 7 10 AO2 SO Gi Ze e 9 Figure 4 Front Panel of the DigiLock 110 1 ON OFF switch and indicator 6 Main 11 DIO LED 2 Precise analog input 3 Aux high speed analog input 4 Main high speed analog input 5 Error output high speed analog output 7 Aux high speed analog output 8 Sum input 9 Al02 General purpose analog input output 2 AlO 1 General purpose analog input output 1 General purpose digital input output 12 Trigger output 13 USB connector ing Trigger output 1 CAUTION All high speed inputs are 50 Ohm terminated by default and all high speed outputs includ 2 are able to drive 50 Ohm loads If needed the inputs can be con figured to high impedance by changing internal jumpers for details see Paragraph 9 1 Page 8 Status 9 6 09 TOPTICA PHOTONICS 3 Operator Controls and Connections 3 2 Description of Front Panel Operator Controls and Connectors NOTE The values in the default configuration are set in bold letters Range V Impedance Q 1 ON OFF Switch ON OFF Switch for the main e Switch and LED power supply of the DigiLock 110 module 2 Precise input Precision analog input 2V 10
3. P Proportional gain Sign Sign of the controller input signal General Slope Sign of the slope the system is locked to Lock Turns the controller ON OFF e TOPTICA PHOTONICS Page 24 Status 9 6 09 8 DigiLock User Interface DUI 8 2 1 7 Lock In Lock In PDH Modulation SE Hz 1195 31k Hz Zomm Y pp J Main out L gt OFF J Main in Set freq Act freq Amplitude Output rel Ll error signal a Input Adjust Phase shift LA Offset Left Lock in Module Right Schematic Error Signal of a Single Resonance generated with the Lock In Modulation Technique Figure 15 q uorssiuusuna 181 detuning linewidth The Lock In module can be used to generate an error signal for the PID controller with the Lock in modu lation demodulation scheme Since it generates the derivative of the original signal i stabilize a system to a peak or a valley allows the user to Modulation A frequency modulation is applied to one of the outputs to generate an error signal by mixing the detected signal with the internal local oscilla tor The modulation is automatically switched on for locking It can be switched manually with the ON OFF button Manual activation is only needed to adjust the phase shift or in manual lock mode Set freq The desired modulation frequency in Hz Act freq The actual modulation frequency in Hz Due to signal processing
4. Figure 12 PID 1 Controller The PID 1 is a standard PID controller with the special feature that the user can set a cut off frequency cut off below which the integral part is limited as illustrated by the transfer function Paragraph 8 2 2 This limitation of the integral part is important in case PID 1 is used together with PID 2 in one control sys tem lt prevents the controllers from accumulating offsets in opposite directions NOTE In case the controller is not selected for AUtoLock it can be used as an independent con troller Manual Mode Input nput source for the controller Main in Aux in Ll out or PDH out Cannot be changed when this controller is active for AUtoLock Locked LED This indicator is on when the controller is active Sign Defines the polarity of the PID output with respect to the Sean module output In the typical setup the PID 2 output is directed to lt SC 110 out gt he PID 1 output to the current modulation input of the laser head and he lt SC110 out gt used for scanning In this case the PID 2 sign is positive The sign of PID 1 is defined by the polarity of the current controller DCC 110 It is positive negative if the polarity of the DCC 110 is nega ive positive respectively For details see Paragraph 9 4 Gain Overall gain P Proportional gain I ntegral gain cut off Frequency in Hz below which the integrator is limited Activated by the checkbox D Deriva
5. As common to any digital signal sampling the Dig quency componenis faster than half the samp frequency The sampling rate of the DigiLock 110 is the sampled signals have fre into the frequency band from zero to this Nyquis iLock 110 oscilloscope shows effects of aliasing When ing rate they will be folded automatically set to make full Use of the number of acquired points Therefore in Scope and AutoLock display the sampling rate is given by the number chosen According to the Ny Because of the aliasing e ion applied On the other h ower value Le modulus the Undersampled oscillation wil rom shot to shot This effect i of points per trace 1000 divided by the time range quist theorem the sampling rate in the frequency analysis FFT is set to twice he selected maximum frequency fects it is hence irritating to look at the input signal with frequency modula and the non demodulated signal can serve as an example to discuss the possible effects observed In the Spectrum display the modulation frequency will be observed at a sampling rate For a sampling rate lower than the modulation frequency an be observed i e a rather fast noisy signal that can breathe in amplitude s well known from digital oscilloscopes In the case of the DigiLock 110 there is an additional effect to be observed for sampling rates well below the Nyquist frequency especially using PDH modul
6. NOTE The turn off behavior i e whether the PID controller is reset to its original value when the lock was initiated can be configured by the user see Paragraph 8 2 5 1 Page 22 Status 9 6 09 TOPTICA PHOTONICS 8 DigiLock User Interface DUI 8 2 1 5 PID 2 CH fa fm Cf f T Figure 13 PID 2 Controller The PID 2 controller is identical to PID 1 PID 2 does not have an integral cut off frequency because when combining two PID controllers this is only needed at the controller which has to drive the output with the higher bandwidth usually PID 1 Instead it comprises an additional low pass output filter see System in Paragraph 8 2 4 NOTE In case the controller is not selected for AutoLock it can be used as an independent con troller Manual Mode TOPTICA pensa Page 23 Status 9 6 09 Feedback Controlyzer Digilock 110 8 2 1 6 Analog Controller Figure 14 Analog Controller In order to overcome the signal delay introduced by digital signal processing the Digilock 110 features a very fast analog path lts high bandwidth allows the experienced user to achieve further improvements particularly in demanding locking situations Note that an improvement of the lock relies on a corre spondingly high error signal and actuator bandwidth NOTE In case the controller is not selected for AutoLock it can be used as an independent con troller Manual Mode
7. 8 2 5 5 Visibility Modules included in the software that are not used in a specific application might distract the user Therefore the visibility status of some modules can be configured Figure 24 Visibility Tab in the Settings Function Module and Function visibility Show or hide the respective functions and modules Advanced Functions Autolock Show or hide advanced settings in the AutoLock tab that give the user access to additional functionality This features are not needed for stan dard operation scenarios and are only recommended for experienced users 8 2 5 6 Profiles NOTE Loading profiles is only possible when the PID controllers are off see Status display The user can save and load profiles A profile is a set of system parameters e g all settings of the different modules display settings etc Profiles are useful and save time if the user has to change between different control tasks LS Load profile Figure 25 Load and Save Profiles If the user saves a profile all system parameters are recorded To load a profile a dialog window opens in which the desired parameters to be imported can be selected see Figure 26 TOPTICA pensa Page 33 Status 9 6 09 Feedback Controlyzer Digilock 110 F Open DigiLock Profile D DigiLock_default pro 14 04 2008 12 50 par Figure 26 Dialog Window to select the Profile Source File and the Parameters to be imported TOPTICA Page 34 O
8. Isolator PBC es rb Cavity FPI 100 PBC Polarizing Beam Cube 2 4 Quarter wave Plate Isolator Optical Isolator Figure 51 Experimental Setup of a Pound Drewer Hall PDH Stabilization to a Cavity Note that the modulation is directly added to the lt Main out gt channel of the Digilock 110 Alternatively the modulation can be applied to the mod AC input of the DLpro The initial setup is the same as in the other examples see Paragraph 10 1 steps 1 to 12 Once the spec troscopy signal is obtained the following steps are analogous to the case of the Doppler free absorption spectroscopy see Paragraph 10 2 steps 13 and 14 Figure 53 shows the expected signal for scanning across a resonance of the cavity lt can directly be used for side of fringe locking analogous to Para graph 10 2 1 15a To generate the error signal for locking to the maximum of the resonance use the PDH module The PDH module provides a number of higher modulation frequencies in the MHz range In the case of the cavity with well separated modes modulation frequencies much larger than the characteris tic linewidth combine steep slopes with a large capture range TOPTICA pensa pages Status 9 6 09 Feedback Controlyzer Digilock 110 The parameters of the PDH module are analogous to the Ll module and are listed in the following table Name Description Value to set to Input Signal input to
9. Low pass filter Low pass filter of given frequency and order bypass box checked 1 path also Table 4 Input Signal Path Settings TOPTICA PHOTONICS The signal can also be inverted by using the controller polarity i e the inversion is mostly needed when using the analog Page 49 Status 9 6 09 Feedback Controlyzer Digilock 110 10 2 Doppler Free Saturation Spectroscopy After realizing the initial setup in Paragraph 10 1 this section describes t he stabilization to an atomic tran sition by Doppler free saturation spectroscopy of Rb Figure 37 shows the experimental setup Connection via backplane t DC DigiLock110 DCC110 DTC110 Mon110 DC110 Gas Cell AE Rb Cs Figure 37 Experimental Setup for Doppler free Saturation Spectroscopy Once the Doppler free saturation spectroscopy is adjusted and the transition the photodetector signal at the Main in connector 4 in Fig ning the laser wavelength across the desired resonance 13 Toscan the laser with the piezo use the Sean module of the Digi ure 9 Select lt SC 110 out gt as output set the signal type to tria aser is tuned to the appropriate ure 4 can be optimized by scan Lock User Interface DUI see Fig ngle the frequency to 10 Hz and the amplitude in the order of 10 Volts Depending on the laser his corresponds to several GHz of freque
10. Table 8 Ca Page 66 L ste Status 9 6 09 11 Appendix 11 4 Directories of the Digilock 110 Software NOTE ZsystemDrive refers to the harddrive partition where Windows and the user specific application data are installed typically CAM lt UserProfile gt is the currently active Windows User account English version German version Standard installation directory system Drive Programs system Drive Toptica DigiLock Programme Toptica DigiLock Default configuration files system Drive Documents A SystemDrive Dokumente and Settings und Einstellungen lt UserProfile gt Application lt UserProfile gt Anwendungs Data Toptica DigiLock daten Toptica DigiLock Program Files Profiles Program Files Profiles Module dependent calibration SystemDrive Documents system Drive Dokumente files and Settings und Einstellungenx lt UserProfile gt X Application lt UserProfile gt Anwendungs Data Toptica DigiLock daten Toptica DigiLock Program Files Calibration Program Files Calibration Table 9 TOPTICA pensa pages Status 9 6 09 Feedback Controlyzer Digilock 110 11 5 Pin Assignment of the Digilock 110 Backplane Actual pins needed for normal operation of the Digilock 110 Module are marked with a grey back ground color VG 64 a b c standard connector according to IEC 60603 2 Figure 59 VG 64 a b c Standard Connector 32
11. e Two separate PID controllers e Lock in error signal generator e Pound Drever Hall PDH error signal generator e Computer assisted hardware zoom e Lock detection Click and Lock e Configurable reset and relock e Integrated multi channel digital oscilloscope etwork analyzer e Spectrum analyzer e Controller simulation 1 1 Package Contents DigiLock 110 plug in module Installation CD containing software and drivers DigiLock 110 Manual color version is provided on the installation CD USB cable 3 BNC SMB cables 1 1 1 1 TOPTICA Qi Page 3 Status 9 6 09 Feedback Controlyzer Digilock 110 1 2 Design and Operating Principle of the Digilock 110 Error out Main in Precise in PC with USB USB to SPI User Interface gt JTAG Software Converter EE gt DAC L t Dass gt ADC FPGA Sum in qT Main out 2 CH ib gt High Speed DAC WEE Aux out Pp c I ac KE kacht c 4 ac 7 t Backplane Circuit Power Supply gt Sr eg D o e At og E D 8 S lt i lt 8 lt 5 lt 3 A Fa EE Do Or DC110 Backplane Figure 1 Schematic Block Diagram of the Digilock 110 Module For Details of Backplane Connections see Figure 3 Page 4 Status 9 6 09 FPGA Field Programmable Gate Array e TOPTICA P
12. 2 Doppler Free Saturation Spectroscopy 50 10 2 1 Side of Fringe Locking 51 10 2 2 Top of Fringe Locking Lock In 56 10 3 Pound Drewer Hall Stabilization to a Cavity 59 TOPTICA PHOTONICS Status 9 6 09 Feedback Controlyzer Digilock 110 11 Appendix 1 Internal Jumpers 2 Digilock 110 PCBs 11 21 Baseboard 11 2 2 Plug On Board 3 Specifications of Digilock 110 Connections 4 Directories of the Digilock 110 Software 5 Pin Assignment of the DigiLock 110 Backplane 12 Guarantee and Service Status 9 6 09 63 63 64 64 65 66 67 68 69 e TOPTICA PHOTONICS Feedback Controlyzer Digilock 110 1 The Feedback Controlyzer DigiLock 110 Stabilized lasers see an increasing number of applications in research and development To meet the dif ferent requirements a number of locking techniques have been developed So far the different schemes require a corresponding set of adapted electronics The Digilock 110 integrates fast analog and digital electronics into a versatile general purpose locking module lts Up to date digital hardware allows to implement the scan generator PID controllers and optional frequency modulation techniques all into one plug in module Together with a graphical user interface running on a PC the module facilitates the procedure of laser locking enormously and provides features to analyze and optimize the control system Digilock 110 features e Generation of scan waveforms
13. 8 V floating if no 32a 32c Power typ 6 8 V floating if no DCC 110 3A implemented lines connected on backplane Page 68 Status 9 6 09 TOPTICA PHOTONICS 12 Guarantee and Service 12 Guarantee and Service To obtain information concerning factory service contact your local distributor or TOPTICA Photonics AG directly On the following pages you find the Guarantee Registration Form and the Service and Technical Support Form Please fill in the Guarantee Registration Form immediately after you have received your device and return it to TOPTICA Photonics AG by mail or fax In case your device has to be returned to TOPTICA Photonics AG for service or technical support first call ToPTICA Photonics AG for a Return Authorization Number which you should use as a reference in your shipping documents and mark clearly on the outside of the shipping container Then fill in the Service and Technical Support Form and return it to TOPTICA Photonics AG together with the device Please spec ify the problems with the device as detailed as possible TOPTICA pensa Bage Status 9 6 09 Guarantee Registration Form amp TOPTICA PHOTONICS Status of form 22 02 05 return to sender QM form F 015 TOPTICA Photonics AG Customer Service Lochhamer Schlag 19 D 82166 Graefelfing Munich Germany FAX 49 89 85837 200 Guarantee Conditions The products of TOPTICA Photoni
14. A reasonable choice is about 1 10 of the characteristic linewidth In this example a frequency of about 100 kHz is used Due to ing Scope display with optimized phase splitting from the main beam Page 56 Status 9 6 09 he specific architecture of the DigiLock 110 only discrete frequencies are possible Type in the desired one and the system will automatically determine the nearest one available Act freq Turn on the modulation by pressing the ON OFF button The second trace should now display the error signal derived from the frequency modulation The modulation amplitude is a trade off between the desired lock in signal strength and the allowed frequency modulation of the laser The larger the amplitude the larger the lock in signal but note that at the same time the side bands on the laser increase 13 This tradeoff can be eliminated by using an additional electro optical modulator EOM in the locking beam path after TOPTICA PHOTONICS 10 Application Examples Name Description Value to set to Input Signal input to be demodulated lt Main In gt Set freq Modulation set frequency is the user selected 100 kHz modulation frequency Act freq Modulation act frequency is automatically set to the automatically set nearest possible discrete frequency Mod amplitude Amplitude of the modulation 0 01 Vp Phase shift Phase shift of the local oscillator with respect to the O to be opti
15. Hold Creld cs m ma Fee Lakes SG TTC Mean ror LI out a u Gilet ant 50k 100k 150k 200k 250k 300k 350k 400k 450k 500k Frequency Hz Figure 2 Spectrum Display The Spectrum displays the fast fourier transform FFT of the signal The functionality is similar to the Scope display but in the frequency domain NOTE The selected frequency range defines the sampling rate of the signal used for the FFT CH 1 Signal displayed on channel 1 CH 2 Signal displayed on channel 2 Hold Freezes the trace for this channel Ovid Indicates whether the selected channel was at its limits during the last acquisition f scale Frequency span displayed on the frequency axis Within this range 500 measurement points are calculated from a time signal of 1000 measure ment points sample rate 2 x f scale Mean Mean value calculated from the time signal for channel 1 and channel 2 respectively RMS error RMS value calculated from the difference between the time signal and its mean value for channel 1 and channel 2 respectively Show Shows or hides the trace Avg Option to average consecutive frequency spectra of a channel the number of traces for the average can be set in the Advanced Settings see Paragraph 8 2 5 3 Sm Smoothing trace using nearest neighbor averaging The number of points for the average can be set in the Advanced Settings see Para graph 8 2 5 3 Dc Include DC contribut
16. PHOTONICS Status 9 6 09 8 DigiLock User Interface DUI 8 3 Display Area The lower part of the screen shows three different displays that are accessible through the buttons on the left hand side 8 3 1 Scope Main in Y Figure 27 Scope Display Signal Hold Ovid SH SE RE E m2 Di 5110 out de W 20m 30m Time s Two channel digital oscilloscope to display different available system signals CH 1 Signal displayed on channel 1 CH 2 Signal displayed on channel 2 CH x Signal on the x axis Only available in x y mode Hold Freezes the trace of the respective channel Ovid ndicates that the signal has reached the limits of the channel during he last acquisition Timescale Timescale displayed on the time axis Mean Mean value calculated from the trace for channel 1 and channel 2 respectively RMS error RMS value calculated from the difference between the displayed trace and its mean value Show Shows or hides the trace Avg Average Sm Smooth e TOPTICA PHOTONICS Average consecutive scans of a channel The number of traces for the average can be set in the Advanced Settings see Paragraph 8 2 5 3 Smoothing trace using nearest neighbor averaging The number of points for the average can be set in the Advanced Settings see Para graph 8 2 5 3 Page 35 Status 9 6 09 Feedback Controlyzer Digilock 110 8 3 2 Autolock Main in Y Figure 28 Auto
17. be demodulated lt Main In gt Set freq Modulation set frequency can be selected for a set of 12 5 MHz 5 discrete modulation frequencies Amplitude Amplitude of the modulation 0 1 Vop Phase shift Phase shift of the local oscillator with respect to the O 9 to be optimized applied modulation see text Output Output to which the modulation is added lt Main out gt Table 5 Note that the capture range is given by the modulation frequency but a larger modulation amplitude is needed with increasing modulation frequency For standard applications a modulation frequency of 12 5 MHz or less is preferred because at 25 MHz the analog electronics bandwidth additionally reduces the signal strength 16a Set the input of the Autolock module to lt PDH out gt To view the PDH error signal use the AUtoLock display In the Sean tab set the scan frequency to 10 Hz and the output to lt SC 110 out gt Jism Yo2000 Manot e Figure 52 PDH Module with typical Parameters Phase and offset should be optimized to the specific setup dtrane Ao u ze A GES 17a To obtain an error signal the modulation amplitude has to be set The amplitude is a trade off between the signal to noise ratio and the tolerated frequency modulation of the laser The larger the amplitude the larger the error signal and the frequency modulation of the laser Turn on the modulation and start to scan the laser with the Sean module In Figure 53 t
18. due to the hysteresis the limits should be chosen symmetrically to define reasonable bounds nput signal to be compared to the window Lower upper bound of the comparator window Time to wait between detecting the unlocked state signal outside win dow and initialization of a reset relock procedure This Delay allows for an immediate relock e g after the system was subject to a temporary disturbance Enables the PID reset Slope in Volt second when resetting the outputs of PID and PID 2 respectively Finite rates restrict the reset soeed of the PID outputs to avoid destabilization due to rapid changes e g creep of piezos after a sudden voltage step This option is only available if the Use Window and the Relock check boxes are selected since is relies on the detection of the lock state see above In case the window signal is out of bounds i e the system is not locked the relock option scans the output channel of the selected PID controller with the chosen values for frequency and amplitude wave form type is a symmetrical triangle Once the Window signal is within the specified limits again the scan is turned off and the controllers are activated Frequency of the relock scan Amplitude of the relock scan NOTE The tabs General Window for the individual PID and Analog controller are only visible when the respective controller is not selected for AUtoLock Manual Mode
19. limitations only discrete modulation frequen cies are possible even fractions of 781 25 kHz The closest frequency is chosen automatically Amplitude Peak to peak amplitude of the modulation signal in Volts Output Output channel for the modulation signal Modulation ON OFF Modulation switched ON OFF Input Input source for the module Main in Aux in Phase shift Phase shift in degrees between the output and the local oscillator Offset Offset in units corresponding to the oscilloscope display The offset is substracted from the demodulated signal Adjust Adjusts the phase of the demodulated error signal to match the deriva tive of the spectrum signal The progress is indicated on the progress bar in the status display In order for the algorithm to work properly be sure that the resonance of interest is visible in the AUtoLock display during operation NOTE Due to signal processing limitations it is recommended to optimize the lock e g minimal rms error or spectrum analysis using the demodulated lt LI out gt signal and not the input signal which is modulated see Paragraph 9 6 TOPTICA PHOTONICS Page 25 Status 9 6 09 Feedback Controlyzer Digilock 110 8 2 1 8 PDH Lock In PDH Modulation Set freq J 12 50M Hz Amplitude 10 2000 pp Output fy main out C OFF Input ey main in Adjust Phase shift EP e r r r r i Offset Jo detuning linewidth rel PDH er
20. so the associated backplane channels have to be activated by setting the corresponding internal jumpers see Paragraph 11 1 Ca Page 46 Gu PHOTONICS Status 9 6 09 10 Application Examples The laser frequency can be adjusted to the desired resonance by several means with increasing preci sion e Coarse tuning in the 0 1 nm range usually only required for the initial setup can be achieved by modifying the angle of the grating with the fine thread screw e Change the current and if necessary the temperature of the laser to tune the frequency and achieve single mode operation The built in piezo allows mode hop free scanning of the laser over several 10 GHz The DigiLock 110 generates the scan signal that drives the piezo using the SC 110 as a high voltage amplifier The output is the sum of the voltage specified in the DigiLock 110 software and the offset of the SC 110 The SC 110 offset can hence additionally be used to scan the laser Ja In the Scan module of the DigiLock 110 you can choose the parameters for the scan signal gener ation Name Description Value to set to Signal type type of scan ramp triangle Frequency frequency of full scan back and forth 10 Hz Amplitude scan amplitude peak peak 10 V2 Output output to which the scan signal is added lt SC 110 out gt The numerical values are guidelines and depend on the individual setup 2 The scan amplitu
21. type S H triangle Frequency y 10 Hz Amplitude 15 0000 Yop Scan gt OFF Output 5c110 out Figure 9 Scan Module The Scan module is used to generate periodic waveforms with user adjustable parameters The signal can be directed to different output channels Signal type Type of the generated waveform sine triangle square or sawtooth Frequency Repetition frequency of the chosen waveform in Hz Amplitude Peak to peak amplitude in Volts Scan button Turn signal generation on off indicated by the green light Output Output channel to which the generated signal is directed 8 2 1 2 Offset Offset Value 0 0000 Y Output 15C110 out Figure 10 Offset Adjustment With the Offset Adjustment module it is possible to view and change the DC voltage level of the selected output channel Offset Signal level in Volts Output Output channel to which the offset voltage applies TOPTICA pensa SE Status 9 6 09 Feedback Controlyzer Digilock 110 8 2 1 3 AutoLock NOTE The AutoLock features are intended to work with a triangle waveform only _ PDH out mania O KEES Figure 11 The AutoLock Module combines several Controllers to one with Advanced Locking Features Advanced Options can be found in four Subtabs some have to be activated see Para graph 8 2 5 5 The AutoLock module is used in combination with the AutoLock display see Paragraph 8 3 2 in the low
22. unchecked the current PID value is transferred to the offset value of its output channel box Unchecked or the PID output is simply set to zero box checked In this case the scan will be centered around the last output value which is suitable when the PID controller offset has been compensating an offset drift DIO output port DIO output port Function Configures the function of the DIO digital input output port when jum pered as output factory setting Four different modes are available manual operation PID 1 within Lock Window range PID 2 within Lock Window range PID 1 and PID 2 within Lock Window range Manual state When the function selector above is in position manual operation the state of the DIO output port can be set manually e g for testing Rena Page 30 O PHOTONICS Status 9 6 09 8 DigiLock User Interface DUI 8 2 5 2 LI PDH Figure 21 LI PDH Tab in the Settings Function Modulation signal type Type of the waveform used for modulation and demodulation First filter notch LI Module The Ll module only works properly if a low pass filter is applied to the demodulated signal in order to filter frequency components located at the modulation frequency This filter is implemented as a moving aver age filter in the digital domain The first notch of such a filter is at the modulation frequency In order to reduce noise this first filter notch can be set to lower frequencies It
23. zm eee Ce PS E r a 2190 5 satan ES amt e a b 30 SI NW A SR Go Se W LO fern Ro a Bisa Ea st comp E em anr Ess ae 8 N Zagal e ele a B ss BE 8 Real S 25 ma E sl d n g gt E Sog p E kO Figure 57 DigiLock 110 Jumpers on Baseboard Page 64 Status 9 6 09 JPZ E e de ll S z m 232 3 E ES ae Sty H SI i A gr e A e Ze ES 8 Er ER em Bi on e E JP8 JP9 TOPTICA PHOTONICS 11 Appendix 11 2 2 Plug On Board f g lal v d a a Zom eemo 949 DE 1 zerio Fem en Se eau 33 WC Fdoe De oe la BF r Sco E S i sn om RR 940 1840 z e V i GAN a T gt Soe Lal Ze a Ca e899 E a N H H A Pda eD s Se WE ve Ek E nza a aa IE o Ceol o o ren A qn esI AT o e um en La en He SEN a a o a 0 D Ee Sg seu Ss l D Gre zen am y am wao n 21m am en Status 9 6 09 Page 65 PHOTONICS Figure 58 Digilock 110 Plug On Board TOPTICA Feedback Controlyzer Digilock 110 11 3 Specifications of Digilock 110 Connections Power Supply Value Supply Voltage 15 V Supply Current 700 mA 15V max Supply Current 200 mA 15V max Input Resolution Sample Bandwidth Range Input Comment Channel bit Rate Hz 3dB Hz V Impedance Ohm Main in 14 100 M 14M 2 0 50 nput signal at lt Mai
24. 110 relies on a con sistent choice of polarity and sl the relocking and signal analys ope the determination of which is discussed in Paragraph 9 4 Details on is features can be found in Paragraph 9 4 and 9 5 respectively 9 1 Signal to Noise and Bandwidth Considerations To take full advantage of the possible bandwidth of the con a true 50 Ohms wave guide and to avoid extra cable length in the signal path The fast inputs and out puts of the Digilock 110 are 50 Ohms in the standard setting upon delivery If necessary they can be changed to high impedance by appropriate settings of internal jumpers for details please see Para graph 11 1 Bandwidths and sampling rates of the inputs and outputs are listed in Table 8 Due to the limited gain bandwidth product in analog amplification a higher gain generally reduces the bandwidth In the DigiLock 110 the digital signal paths do not show this effect but instead every pro cessing step inherently contributes a fixed delay The implementation of extra filters e g low pass filters to clean up the error signal usually has a negative influence by introducing extra phase lag and should hence be avoided Improvements based on filters usually rely on a detailed analysis of the frequency response of the control loop and have to be designed carefully In case of the digital filters in the DigiLock 110 the phase lag is due to additional signal delay For most cases it is hence recommended to b
25. Digilock 110 Feedback Controlyzer Manual Manual M 031 Version 04 Copyright 2009 TopticA Photonics AG TOPTICA Photonics AG Lochhamer Schlag 19 D 82166 Graefelfing Munich Tel 49 89 85837 0 Fax 49 89 85837 200 email info toptica com http www toptica com June 2009 Subject to changes without notice Feedback Controlyzer Digilock 110 Dear Customer welcome to the TOPTICA community We have designed this product to be easy to use and reliable so that you can focus on your actual work Should you anyway have questions regarding its Use or need advice on how to integrate it into your setup please do not hesitate to ask We will provide you with quick and competent help through our ser vice staff and product managers You can contact us in the following ways internet www toptica com In our support section you can find a list of frequently asked ques tions and a service contact form email serviceOtoptica com phone 49 89 85837 0 Please have your product ID serial number ready when contacting Us so we can quickly retrieve all rele vant information from our databases We are constantly refining and improving our products and therefore highly valuate feedback from our customers We would therefore like to encourage you to let Us know what you like about our products and of course also if there is something we could improve Best regards How Harald Ellmann Service Manager TOPTICA Ph
26. ECDL Since the DigiLock 110 provides the scan capability set the trigger switch on the front panel of the SC 110 to position ext external 4 The fast feedback via the Main out 6 SMB connector of the DigiLock 110 is applied to the DC coupled modulation input of the DLpro 5 The output of the photodetector is connected to the Main in 4 connector of the DigiLock 110 CAUTION To allow for high bandwidth the Main in 4 connector of the DigiLock 110 is jumpered as a 50 Ohm input factory setting Check that the photodetector amplifier can drive the 50 Ohm input Alternatively the input can be jumpered to high impedance see Paragraph 11 1 6 When all connections are established switch on the DigiLock 110 connect the USB port to the PC and start the software Afterwards turn on the Temperature and Current Control DTC 110 and DCC 110 as well as the SC 110 and switch on the laser After a few minutes the laser will thermally stabilize Adjust the parameters Iet and Tse in order to get stable single mode cw operation Fig ure 35 shows the user interface software after startup All parameters of the DigiLock 110 can be reset by loading the default profile Functions Setup gt Load profile For the standard path to the default profile DigiLock Profile_default pro see Paragraph 11 4 10 The current and temperature settings of the laser can be remotely controlled via the DigiLock 110 module To do
27. HOTONICS 1 The Feedback Controlyzer Digilock 110 a o S Trigger omman p can gt Interpreter PEEN Module DAC gt DAC DDS 2 i Modulation DAG Aux in DAC DDS Direkt Digital Synthesizer LI Lock in PDH Pound Drever Hall ADC Analog to Digital Converter DAC Digital to Analog Converter FPGA Field Programmable Gate Array Figure 2 Schematic Block Diagram of the DigiLock 110 Functional Units and their Interaction FPGA 2 CH 2 CH 2 CH 2 CH ADC DAC DAC DAC y Filter Filter lact Tact JP 301 E JP 300 H TM DAO DA3 T set DC110 Backplane Figure 3 Schematic Block Diagram of the Connections to the DC 110 Backplane TOPTICA PHOTONICS Page 5 Status 9 6 09 Feedback Controlyzer Digilock 110 2 Safety Instructions and Warnings 2 1 General Safety Terms The following safety terms are used in this manual The DANGER heading in this manual explains danger that could result in personal injury or death The CAUTION heading in this manual explains hazards that could damage the instrument In addition instrument DANGER CAUTION DANGER DANGER DANGER DANGER DANGER CAUTION CAUTION Page 6 Status 9 6 09 a NOTE heading provides infor
28. Lock Display Tg IER EEN 50110 out Y This display is Used in conjunction with the AutoLock module in the Upper part of the screen In this display the user can handle two major tasks e Search the desired lock point via panning and zooming the displayed signal e Initiate the locking procedure with the help of the context menu CH 1 CH 2 CH x Hold Ovid Mean RMS error Can not be modified Spectrum signal chosen in the AutoLock tab see Figure 11 Can not be modified Input signal chosen in the AutoLock tab see Figure 11 Signal displayed on the x axis Given by the output of the Sean module Freezes the trace Indicates whether the selected channel was at its limits during the last acquisition Mean value calculated from the trace for channel 1 and channel 2 respectively RMS value calculated from the difference between the displayed trace and its mean value The following shortcuts AUtoLock display only allow a more convenient operation CTRL lt arrow left gt CTRL lt arrow right gt CTRL lt arrow down gt CTRL lt arrow up gt Page 36 Status 9 6 09 increases the offset of the x channel by scan range 0 1 decreases the offset of the x channel by scan range 0 1 increases the scan range of the x channel to scan range 1 2 decreases the scan range of the x channel to scan range 1 2 TOPTICA PHOTONICS 8 DigiLock User Interface DUI 8 3 3 Spectrum Signal
29. OPTICA Photonics AG by mail or fax 49 0 89 85837 200
30. S automatically detects multiple DigiLock 110 modules connected to the computer via USB It can start and manage one instance of the DigiLock User Interface DU for each of the detected modules The user can thus contro the DigiLocks via independent DUIs NOTE The Remote Control Interface RCI and the DigiLock Module Server DMS are only imple mented in software versions 1 5 4 70 and higher If you are still running an earlier version please contact TOPTICA Photonics AG for a software update The DigiLock 110 is always controlled via the dedicated software running on a Windows PC However to allow for the implementation of application specific features like scripting and the integration into the general software environment of a larger experiment the DigiLock Module Server DMS and each instance of the DUI has a built in Remote Control Interface RCI Nearly all controls of the DMS and DUI can be accessed remotely by sending corresponding commands via a TCP IP connection A detailed description of the RCI can be found in the DigiLock 110 RCI Manual which can be downloaded from the ToPTICA Photonics AG website NOTE The Digilock 110 RCI is a supplementary free add on developed by ToPTICA Photonics AG on customers requests However due to the complexity of individual hard and software configurations there is no support provided for the DigiLock 110 RCI LabVIEW Custom Interface Remo Cont Remote Control
31. Telnet Client Solution Vis Interface Local Ethernet Internal Communication Remote Control Remote Control Remote Control Interface Interface Interface DigiLock 1 DigiLock 2 DigiLock 3 User Interface User Interface User Interface Figure 6 Overview of the DigiLock 110 Control Architecture TOPTICA pensa Page 13 Status 9 6 09 Feedback Controlyzer Digilock 110 7 DigiLock Module Server DMS Ei DigiLock Module Server DigiLock Module Server 192 168 50 191 TP Address 5 REI Update module list A 60000 Module list module name serial number connection SC PID1 PID2 Ana LI PDH port status number Module 01043 disconnected DigiLock Dummy DCD disconnected Status display Figure 7 DigiLock Module Server Front End Figure 7 shows the front end of the Digilock Module Server lt automatically detects ER lists all Digilock 110 modules that are connected to the computer when the software starts up The li st is Updated by pressing the Update module list button A specific module can be selected by clicking any where on the corresponding row in the list The selected module is indicated by the highlighted module DigiLoc again wi By cli name The modules are identified by their serial number and can be given a name by double clicking he module name column for editing To connect to the selected Digilock 110 press the Connect button This wil
32. allation Start the program setup exe located in the folder Installer on the installation CD The installer wil guide you through the installation process NOTE The DigiLock 110 software consists of two parts the DigiLock Module Server DMS and the DigiLock User Interface s DUI The DMS handles the access to all the DigiLock 110 mod ules physically connected to the computer For each of the connected physical modules an instance of the DigiLock User Interface DUI can be started from the DigiLock Module Server DMS If no DigiLock 110 module is connected to the computer via USB a dummy module is displayed in the DMS NOTE The Remote Control Interface RCI and the DigiLock Module Server DMS are only imple mented in software versions 1 5 4 70 and higher If you are still running an earlier version please contact TOPTICA Photonics AG for a software update Rena Page 12 PHOTONICS Status 9 6 09 6 Digilock 110 Control Architecture 6 DigiLock 110 Control Architecture The DigiLock 110 Feedback Controlyzer is a very fast and flexible controller solution based on FPGA tech nology The combination of a fast FPGA with a dedicated PC software package allows to implement the advanced locking capabilities An overview of the DigiLock 110 control architecture is shown in Figure 6 It consists of two levels The DigiLock 110 software initially starts the DigiLock Module Server DMS The DM
33. an Av cp Pound Drever Hall Paragraph 10 3 will lead to an error signal and hence capture range that extends from one sideband to the other vo Vmod Vo Vmod The latter situation is preferable and used in situations where the resonance is well isolated e g on a Fabry Perot cavity where no frequency also provides a high The phase of the local oscil neighboring resonances spoil the signal In this case a higher modulation er bandwidth error signal after mixing with the local oscillator LO ator has to be adjusted to obtain a large error signal with steep slopes at 3 Note that the analog preamp 4 corresponding chapters of LIR 1 Page 38 Status 9 6 09 ifiers in the DigiLock 110 have a fixed bandwidth independent of the selected gain Some details on the generation of the error signal by frequency modulation can be found in the SYS DC 110 manual in the 10 and PDD 110 respectively TOPTICA PHOTONICS 9 Notes on Feedback Control Loops with the Digilock 110 the resonance of the spectral signal The sign of the error signal can be inverted by changing the phase by 180 It should be adjusted such that the Lock in PDH signal is the derivative of the input signal with the correct sign The sign is correct when a positive slope in the error signal corresponds to an increase in the spectrum NOTE As of software versions 1 5 4 70 the Digilock 110 frequency modulat
34. an Control SC 110 with a signal via the backplane Therefore the external control of he SC 110 has to be configured to DA2 by appropriately setting the jumpers dip switches on the SC 110 board For detailed description on the SC 110 please see the Sys DC 110 user manual 2 Make sure that the laser head is properly connected to the Temperature Controller DTC 110 and he Current Controller DCC 110 In these examples a DLpro extended cavity diode laser ECDL is used The same setup can equally well be realized with the DL 100 and translated to other diode based laser systems like the tapered amplifier TA 100 DLX 110 RockSolid and SHG 110 For the DL 100 laser head the corresponding connections are labelled as follows DLpro DL 100 Comment mod DC zu mod DC coupled current feedback is used for the fast feed d back in addition to the slow feedback to the piezo AC coupled fast current feedback can optionally be d used for feedback or modulation at high frequencies in mod AC bias t the MHz range or to apply the modulation frequency independenily from the current feedback CAUTION Check the maximum current Imax of the current controller DCC 110 to prevent damage of the laser diode To do so turn on the key switch but leave the modules and laser switches off and check the Imax setting on the DC 110 Monitor Unit 3 Connect the output of the Scan Control SC 110 to the piezo of the
35. an be figured out by comparing the signals of he regular Sean module output e g SC 110 out with the signal observed while scanning the controller output To determine the directionality of the resulting effect one can look at a characteristic part of the error signal e g close to the lock point or use the wavemeter reading if available The slope is defined by the displayed graph at the lock point during the scan It is automatically cho sen in AutoLock mode If the controller is used in manual mode the user can define the lock point by selecting the corresponding slope direction A general method to verify the correct overall polarity is to compare the signals during scan with the controller switched on and off while using just the proportional part To do so only activate the PID con troller in question Set the integrator and differentiator parts to zero and the P part and overall gain to some finite value e g 10 Use the System input offset see Paragraph 8 2 4 to center the signal around zero Switch on the PID controller while scanning across the characteristic lock point Increase the pro portional part and or overall gain until you see a significant distortion of the signal To check the observed effect you can compare with the cases of the other polarity as well as the controller being switched off The cases of side of fringe locking and locking to a lamb dip of saturated absorption signal are illustrated in Figure 31 and Figure 32
36. aph 9 for details The RMS error value in the right panel quantifies the residual excursions of the laser As PID 2 is only responsible for the low frequency compo nents this controller can be left at moderate gains The performance of the lock is predominanily deter mined by the settings of PID 1 connected to the fast actuator Mod input of the DLpro A helpful tool in the optimization process is the Spectrum display see Figure 46 Here the result of the Fourier transformation of the sampled time signal is shown In our case select lt Main in gt as CH 1 The fre quency scale has to be chosen according to the bandwidths of the experiment Typical bandwidth of he gratings are in the range of a few kHz while the DC modulation input has bandwidths of a few 100 kHz to MHz Turn off the DC component of CH 1 because normally a high DC offset dominates and herefore small signal amplitudes may not be observed Alternatively the autoscale option can be deactivated and an appropriate amplitude range chosen by setting the upper bound of the y axis see Paragraph 8 1 to resolve all peaks in the frequency spectrum as desired Signal Hold Ovid 1 E Cayo n Main in Y o D 200k 400k 600k 800k 1M 1 2M 1 4M 1 6M 1 8M 2M 2 2M 2 5M Frequency Hz Figure 46 Spectrum Display of the Photodiode Signal at lt Main in gt In this example the frequency analysis clearly shows the onset of an oscillation at about 650 kHz due to high gain set
37. are upload at startup Disable all pop up windows Sample when hidden Page 32 Status 9 6 09 By default the firmware of the DigiLock 110 is uploaded at startup of the software This Upload takes some seconds and resets the module During a module reset all analog output channels are set to O V before they are loaded with the values specified in the interface software The firm ware must be uploaded each time the Digilock 110 is switched on If he module is already configured and running e g you already worked with the system but you closed down the interface software for a while he upload and reset are not necessary With this option you can con igure the upload behavior at startup This option is only useful when controlling the user interface remotely and should be used with care Pop up windows can not be handled via he remote control which is why they should be suppressed in this case The DigiLock Module Server DMS has the option to show hide each DigiLock User Interface DUI By default the acquisition of data indi cated by the option Sampling in the Display area is disabled when the DUI is hidden in order to avoid unnecessary traffic on the USB However or some reasons it is desired to acquire data nevertheless e g operat ing the DUI remotely see Digilock 110 RCI Manual which can be down oaded from the ToPTICA Photonics AG website TOPTICA PHOTONICS 8 DigiLock User Interface DUI
38. ation Due to the complete synchrony of the sampling with the applied m odulation the undersampled signal can show as a noisy line at a finite off set that varies from shot to shot Note that this is not an indication of the performance of the lock but merely an artifact of sampling the input signal including the applied modulation and explains why it is highly recommended to use the demodulated signal for analysis 9 By additionally applying the signal to the Aux input a low passed signal for analysis can be derived using the built in digital filter see Paragraph 8 2 4 Page 44 Status 9 6 09 TOPTICA PHOTONICS 10 Application Examples 10 Application Examples There are numerous different schemes to stabilize lasers for example to atomic or molecular resonances and cavities The Digilock 110 is designed to cover a large range of locking scenarios This paragraph describes step by step how to implement some of the most common ones with the DigiLock 110 NOTE This chapter assumes that the user has some basic knowledge of the laser system and the electronics involved For further information see the Sys DC 110 manual 10 1 General System Setup The general setup for the stabilization is shown in Figure 34 All locking schemes are based on a spectro scopic signal provided by the experimental setup which serves as a reference The Digilock 110 is capa ble of supplyi
39. cs AG are produced with the greatest possible care using high quality components and are checked in detail before being delivered Therefore as the manufacturer TOPTICA Photonics AG gives a guarantee of durability according to the following terms 1 TOPTICA Photonics AG guarantees the buyer that there will be no defects in the product based on defective material or processing for a period of 12 months from first delivery guarantee period Natural wear and tear as well as defects resulting from improper use or use contrary to the specifications from failure to observe operating instructions from insufficient maintenance and care or from modifications interventions or attempted repairs that are neither carried out nor authorized by TOPTICA Photonics AG are not covered by the guarantee 2 Unless expressively stated in the order acknowledgement or the invoice semiconductor light emitting devices like laser diodes tapered amplifier chips etc whether sold as single parts or integrated in systems are not covered by the guarantee de If a defect covered by the guarantee arises during the guarantee period TOPTICA Photonics AG shall rectify such defect within a reasonable period at its own discretion by repairing or replacing the product or the defective part 4 The guarantee period shall commence upon delivery of the product by TOPTICA Photonics AG or by a third party that obtained the product directly from TOPTICA Photonics AG for the purpose of sell
40. ction the crosshairs will follow the current trace Once chosen the crosshairs will auto matically track the lock point while the laser might slowly drift To engage the lock click the right mouse button and choose PID Lock to slope from the context menu see Figure 43 Starting with the next trigger the trace captured is displayed in a different color here yellow while the held trace is visible here blue Once the lock point is reached the trace stops and the lock is acti vated Figure 44 shows the AutoLock display some seconds after the lock has been triggered 11 The output of the controllers can be restricted using the Limits settings Paragraph 8 2 1 4 and 8 2 1 5 e g to about the scan range This helps to avoid destabilization of the laser by driving it very far from the lock point especially during initial setup and optimization 12 The colors of the traces can be changed by the user To restore the factory settings load the default profile TOPTICA pensa Page 53 Status 9 6 09 Feedback Controlyzer Digilock 110 Signal PID Lock to slope Mean RMS error D Main in Clear Graph Export Data Export Simplified Image 6 1 5C110 out Y Figure 43 Initiating the AUtoLock to a Slope of the Absorption Signal Signal Hal Mean Main in Y 6 1 5C110 out v Figure 44 Autolock Display just after the Lock is engaged PID lock to slope 20 After some time the y
41. de can be enlarged or reduced to correspond to the application Table 3 DigiLock 110 Scan Module Settings The maximum scan range of the DigiLock 110 module is obtained in the following way 8 Choose lt SC 110 out gt in the Offset tab see Figure 10 of the of the DigiLock User Interface DUI and set the Offset value to O V 9 Set the Offset adjust ten turn potentiometer on the SC 110 front panel to half the available output range 5 which corresponds to an output voltage of 75 V The DigiLock 110 software can now access the full output range 0 150 V 10 All the relevant signals can be analyzed through the DigiLock 110 computer interface However the Digilock 110 also provides a trigger output TRIG which can be used for monitoring with an auxiliary external oscilloscope CAUTION The SC 110 output can deliver high voltages up to 150 V Please make sure that your oscilloscope has suitable inputs Now all the hardware is set Up and the system can be completely controlled by the Digilock 110 soft ware 11 The photodetector signal connected to the Main in 4 connector on the Digilock 110 front panel can be examined in the Scope display shown in the lower part of Figure 35 TOPTICA pensa pagez Status 9 6 09 Feedback Controlyzer Digilock 110 DigiLock 110 SN 01012 Module_1012 File Yew Help Function ee weld E m 2 e Functions gt Escort Display Ej Di
42. digit use the arrow keys left right digit to modify Engineering units All input fields in this software are capable of handling engineering units For example U micro 1 0 m milli 1073 k kilo 10 M mega 10 Graph display Dynamic range scaling The axes of the graphs have a dynamic range scaling optimized for the data displayed If this behavior is not desired it can be turned on or off by clicking on the button marked in the figure below Autoscale off PDH out a u ei Si Autoscale on Graph Display Setting the scale of a graph When the dynamic range scaling option is deactivated the limits of the scaling of an axis can be modified manually To change the lower upper limit click on the value in the graph and modify it by typing a new value upper limit lower limit Description of controls To get information about a control move the mouse pointer across the desired control and a brief description appears Ca Page 16 O PHOTONICS Status 9 6 09 8 DigiLock User Interface DUI 8 2 Functions In the upper part of the screen all the available functions and options of the Digilock 110 are displayed on different layers With the buttons on the left hand side you can select the desired function and then browse the corresponding options and parameters 8 2 1 Lock This function comprises all the modules needed for scanning and locking of the laser 8 2 1 1 Scan Scan Signal
43. e Figure 39 AutoLock Setup for the PID Controllers TOPTICA pensa pages Status 9 6 09 Feedback Controlyzer Digilock 110 15 First the AutoLock module is activated and the controllers PID 1 and PID 2 are selected by check ing the corresponding boxes see Figure 39 PID 1 will handle the high frequencies by controlling he laser current via the modulation option in the laser head whereas PID 2 will be responsible for he lower frequencies by controlling the piezo voltage As input channel select lt Main in gt where he photodetector signal enters the module In AUtoLock mode the input channel chosen in the AutoLock tab see Figure 11 is taken as input for all the selected controllers 16 To use the AutoLock change the display from Scope to AutoLock The x axis of the display is the output of the Sean module and the y axis is the corresponding value of the selected AutoLock input channel In the AutoLock mode the software will actually perform a hardware zoom and pan i e modify the scan amplitude of the Sean module and the offset of the corresponding output channel according to the dis played x axis To graphically and interactively magnify the part of the absorption spectrum in the vicinity of the desired lock point Select the x axis Zoom tool see Figure 40 place the cursor left of the desired x value hold the left mouse button move the mouse to the right of the desired x value and release the left mouse but
44. e automatically updated throughout the whole system The filters three low pass and one high pass are either configured via the corresponding input fields fc cut off frequency order of the filter Alternatively pressing the filter symbol opens a screen which shows the simulation of the transfer function of the filter with the specified parameters By modifying the parameters fc order you can change this transfer function Pressing OK confirms the parameters and transfers them to the setup Note that the filters introduce additional phase lags and delays corresponding to the processing time The processing time for an active low pass filter is 2 order x10 ns for an active high pass filter I order x 10 ns TOPTICA pensa Page 29 Status 9 6 09 Feedback Controlyzer Digilock 110 8 2 5 Settings The Settings function enables the user to access additional options of the DigiLock 110 lt is splitted into the following six tabs according to the affected functionality 8 2 5 1 PID 1 On this tab all advanced parameters for the PID modules can be set E manual operation rr Figure 20 PID Tab in the Settings Function Turn off Behavior PID 1 and PID 2 Manual Autolock Controls the behavior of the PID controllers when switching off the lock Both PID controllers can be set individually for AUtoLock as well as Man ual Mode When checked the PID output is set to zero hence the out put returns to the initial offset If
45. e graph TOPTICA pensa page Status 9 6 09 Feedback Controlyzer Digilock 110 600 400 200 200 Ll error signal a u o 400 600 120 80 i correct unlocked 40 40 Sat Absorption Signal mV o 80 Figure 32 Polarity of the PID Controller using Frequency Modulation The graph shows the characteristic distortions of the error signal as well as the saturated absorption signal of a top of fringe lock for different polarities The undistorted signal solid black is given for reference For the correct overall polarity dashed red the slope of the error signal at the peak is shallower while the peak itself is broader see boxed part of the graph In contrast for the wrong polarity dotted green the slope is steeper and the peak narrower If the overall sign is correct incorrect a resonance should become wider narrower as compared to the case of the controller being inactive The slope of the error signal e g in frequency modulation should become flatter steeper when the overall sign is correct incorrect f the overall gain is too high oscillations will be observed which will be either at the original position with multiple zero crossings or repelled from the original position with oscillations positive and or negative at different parts of the signal for correct and incorrect overall polarity respectively To suppress the oscillations reduce the overall gain Generally the cha
46. ellow trace disappears and a scatter plot is left which indicates both the input signal y axis and the current output of the PID 2 which in this case coincides with the scan see Figure 45 on the x axis The calculated rms deviation from the setpoint value displayed in the right panel can be used to optimize the lock To turn the lock off perform a right mouse click in the AUtoLock display graph and select either Unlock to just release the lock or Unlock amp Restart scan to release the lock and immediately start scanning again NOTE The behavior of the output value of the PID controllers when switching off the lock can be configured by the user in Settings PID Turn off reset behavior for Manual and AutoLock respectively Either the PID controller output is set to zero or its current value is transferred to the offset value of its output channel The latter setting leads to the scan being cen tered at the last output value see Paragraph 8 2 5 1 for details Rena Page 54 PHOTONICS Status 9 6 09 10 Application Examples Signal Hold Ovid Main in Y 18 2 18 3 4 18 5 18 5 C110 out v Figure 45 AutoLock Display while the Lock is active The yellow scatter plot indicates signal input and regulator output PID 2 Parameter optimization To obtain a good lock it is necessary to increase the gain settings of the PID controllers to the highest possible values without oscillations see Paragr
47. er part of the screen This module combines the PID and the Analog controllers see below and enables the user to interactively select the desired locking point and lock the system click and lock In addi tion several options are available to detect out of lock states as well as to reset and to relock the sys tem Checkbox Input Spectrum Auto Controllers checkboxes Activate Deactivate the AutoLock module Common signal input for all selected controllers In Autolock mode the inputs of all selected PID controllers PID 1 PID 2 are set according to this selection Input Channel of the Spectrum which corresponds to the error signal selected for input The Spectrum is useful when the error signal is gener ated by frequency modulation to select the peak valley to lock to If the error signal is generated in the Digilock 110 the Spectrum can be automatically selected to be the input of the frequency modulation module Since the auto setting see below relies on the fact that the FM signal also carries the DC part it is possible to manually select a different spectrum input Uncheck the auto checkbox to select the spectrum channel manually Select the controllers to be combined for the Autolock mode Once selected for AutoLock the input channels of the controllers are set to the selected common input see above and can hence no longer be modified in the corresponding controller tabs The same holds true for the s
48. es Number of measurement points between the start and stop frequency Scaling Method to distribute the measurement points between the start and stop frequency logarithmic or linear Averaging Number of measurements to average for one resulting measurement value Modulation Amplitude Amplitude peak to peak of the stimulus signal Output Output channel for the stimulus signal Input Input channel for the response signal Start Starts the measurement Show reference tracks Option to display reference tracks saved before Show time signal during analysis Option to view the response signal in the Scope display during the mea surement the Scope display has to be selected manually by the user NOTE Any filters applied to the signal path see Figure 19 will affect the measured transfer func tion Besa Page 28 W PHOTONICS Status 9 6 09 8 DigiLock User Interface DUI 8 2 4 System Main out do a Main in Dua rain out Dua Home Figure 18 System Overview of the Current Configuration of the Signal Path Particularly allows to con figure the Main Input Offset and Gain as well as Filters Schematic of the high speed signal path inside the DigiLock 110 module indicating the current configu ration Some parameters can only be set on this screen lt Main in gt input offset lt Main in gt gain invert sig nal all kinds of filters All parameters set here ar
49. eter adjustment is obtained in an iterative process l Set the integral gain K to a finite value all others to zero and increase the overall gain until the system locks 2 Alternate between increasing the proportional Kp and the integral gain Kj and Kp each until the eedback loop oscillates then reduce the gains until the oscillation definitely stops Standard opti mization procedures set the proportional Kp gain to about half the value at which oscillation starts 3 Alternate between increasing the differential Kp and the integral kj and Kp gain each until the eedback loop just oscillates increase one and the other until the oscillation will not stop by further increase At that point reduce the gain until the oscillation definitely stops Note that the optimized parameters depend on the slope of the error signal at the current lock point and the actuator response Therefore there is usually a trade off between a good locking result and a reason able robustness against oscillations due to additional external disturbance and variations in the overall response The DigiLock 110 features a build in network analyzer see Paragraph 8 2 3 which can be used to analyze the frequency dependent amplitude and phase response of the actuators and control loop ele ments In particular it can be used to do an in loop analysis of the stability of the closed lock In addition the frequency response of the controller can be analyzed using the Simulatio
50. etpoint 2 This is e g the case when locking to a cavity using an AC coupled photodiode for the Pound Drever error signal in reflec tion and a DC coupled photodiode for the spectrum in transmission cp Paragraph 10 3 Page 18 Status 9 6 09 e TOPTICA PHOTONICS 8 DigiLock User Interface DUI General Setpoint Mode Window Use Window Channel Max Min Delay Reset checkbox Reset rates Relock Output Frequency Amplitude TOPTICA PHOTONICS Since all PID controllers selected share a common error input signal they also share a common setpoint Displays the operating mode of the AutoLock If the AutoLock module is configured such that the feature to lock to slope peak valley may be chosen manually see Advanced Smart Assistance Engage this con trol can be changed Activates a window comparator to determine the lock state The selected input channel is compared to the window defined by the Min Max range This option specifies boundaries for the selected channel If he signal leaves the window the controllers associated with the AutoLock module are on hold They are reactivated when the signal is back in the selected range taking into account a 10 hysteresis for fur her details see Paragraph 9 5 Note that due to the hysteresis the limits should be chosen symmetrically to define reasonable bounds nput signal to be compared to the window Lower upper bound of
51. g allows to configure the automatic features of the DigiLock 110 in detail There are two functional subsets Display is concerning the selection and the tracking of the lockpoint before activation of the lock Smart Assistance concerns the configuration of the lock parameters when the lock is engaged drifts Defines the trace noise on the signa Track the selected cursor position from scan to scan e g if the laser Only allow points that match the selected setpoint value In FM modula ion schemes only peaks and valleys are allowed Note that due to the the actual setpoint will fluctuate on which the lock point is selected with the cursor i e nput signal or spectrum Based on the settings pos neg slope ex automatically con remum the DigiLock 110 is figured to lock to the nearest matching point Engage Uses an adapted trigger mechanism to engage the lock at the right moment to make the process insensitive to fluctuations Setpoint Automatic determination of the setpoint at the time when the lock is engaged NOTE To further customize the lock the individual settings for the selected PID s are found on the corresponding tabs i e besides gain and PID parameters also limits for the PID output can be set see below for details Ca Page 20 PHOTONICS Status 9 6 09 8 DigiLock User Interface DUI 8 2 1 4 PID 1 Duc E Dien zz Hanow
52. has to be taken into account that a mov ing average filter introduces a linear phase shift to the output signal of the Ll module At the first notch frequency the phase shift is 180 As a consequence lowering the filter frequency reduces the maximum available regulation bandwidth 8 2 5 3 Display On this tab the settings for displaying the data can be chosen Figure 22 Display Tab in the Settings Function Update rate Rate at which new data sets are displayed in the various graphs Scope trace average Number of averaged data sets if the Avg option is used in the Scope display Scope smooth average Number of adjacent data points in one data set that are averaged if the Sm option is used in the Scope display TOPTICA pensa Page 31 Status 9 6 09 Feedback Controlyzer Digilock 110 Spectrum trace average tf Spectrum smooth average tf 8 2 5 4 General Number of averaged data sets if the Avg option is used in the Spectrum display Number of adjacent data points in one data set that are averaged if the Sm option is used in the Spectrum display General system settings can be accessed on this tab PID LIPDH Response Display L Sample when hidden General visibility Firmware upload at startup J upload Disable all pop up windows Caution This option is only useful when the user interface is controlled remotely Figure 23 General Tab in the Settings Function Firmw
53. he resulting Scope display with optimized phase is shown 15 This trade off can be eliminated by using an additional electro optical modulator EOM in the locking beam path after splitting from the main beam Page 60 Status 9 6 09 TOPTICA PHOTONICS 10 Application Examples Signal Hold Ovid E e Mean 11 9 11 9 11 9 12 C110 out Figure 53 AutoLock Display of the Reflection Signal of a Fabry Perot Cavity upper yellow trace with 18a the corresponding PDH Signal lower red trace The phase between the modulation and the reference signal has to be adjusted to obtain a large symmetric error signal with steep slopes at the maximum of the spectral signal The sign of the error signal can be inverted by changing the phase by 180 The sign should be adjusted such that the lock in signal is the derivative of the input signal NOTE As of software versions 1 5 4 70 the DigiLock frequency modulation modules feature an automatic phase adjust see Paragraph 8 2 1 7 and 8 2 1 8 for details 20a Please see Paragraph 9 2 on how to manually adjust the phase Once the phase is adjusted compensate for any residual offset at the corresponding control of the PDH module and check the parameters of the PID controllers To find the correct settings of the sign for each PID controller please see Paragraph 9 4 For optimization of the PID parameters see Paragraph 9 3 Now you can
54. i Hz of samples E Scaling Averaging qo Modulation AS Amplitude efjo 200 V pp BR Output Grain out eis mE Input A PDH out Figure 18 Response of the System to an additional Sinosoidal Pertubation Network Analysis lola Magnitude dB 3seyd 1 I 10k 100k Frequency Hz Magnitude Phase Kiel Mag ref Ea Ea Phase ref Cursors x 3 BA Cursor 0 Magnitude 4 Show reference tracks Show time signal during analysis 100 56 3 In order to determine the dynamic behavior of a system it is a common strategy to perform a network analysis i e to measure the frequency response to a swept sinosoidal pertubation The result of such an analysis is the transfer function of the device under test DUT defined by the amplitude and phase values with respect to the frequency of the stimulus In particular it is possible to analyze the complete feedback loop comprising of frequency discriminator detector controller and actuator How it works An additional modulation is applied to the DUT via the selected output The response of the DUT is ana lyzed in amplitude and phase with respect to the applied stimulus The resulting transfer function is dis played with respect to the frequency of the stimulus Frequency Sweep Start Start frequency of the stimulus Stop Stop frequency of the stimulus of sampl
55. ing it to the buyer The claim under the guarantee shall be excluded if the defect is not notified to TOPTICA Photonics AG in writing immediately after having been discovered and no later than one month after expiry of the guarantee period For the purpose of rectifying a defect covered by the guarantee the product or the relevant part shall be sent to TOPTICA Photonics AG at the expense and risk of the buyer The product shall be returned at the expense and risk of TOPTICA Photonics AG 5 No claims may be derived from this guarantee other than claims for rectification of the defects falling within the scope hereof in accordance with the present terms In particular the buyer is not entitled under this guarantee to claim damages or a reduction in price from TOPTICA Photonics AG or to rescind the contract Potential more far reaching claims of the buyer against its seller shall not be affected by this guarantee 6 Important The obligation of TOPTICA Photonics AG under this guarantee is subject to the condition that the buyer gives his her express consent to them by sending the signed duplicate of this form to TOPTICA Photonics AG immediately after delivery also truthfully indicating the model number the serial number and the date on which the product was delivered L The buyer may not assign claims under this guarantee to third parties without the prior written consent of TOPTICA Photonics AG 8 This guarantee is governed by substantive Ger
56. iode Laser Head The user must not open the Diode Laser Supply Electronics Sys DC 110 or any of the plug in modules during operation Internal tuning as well as the replacement of components may only be carried out by authorized and specially trained service personnel Under certain cir cumstances there may be dangerous voltages even if the device is disconnected from the mains supply Special precautions are necessary if the Diode Laser Supply Electronics Sys DC 110 is to be operated in surroundings of high electro magnetic radiation such as close to a plasma dis charge Please refer to TOPTICA Photonics AG for technical support Please assure with particular care that the electrical safety conditions are met especially concerning the high voltage outputs Also carefully read the instruction for operation of the Supply Rack DC 110 before using the device TOPTICA PHOTONICS 2 Safety Instructions and Warnings 2 2 Identification of Manufacturer Manufacturer name and address serial number article number compliance with CE standards are given by the identification label j Lochhamer Schlag 19 1 TOPTICA D 32166 Graefelfing Made in Germany Product ID No DigiLock 110_1V3_01001 Size 46 mm x 25 mm Color Silver black Location Rear Panel of the plug in module TOPTICA Qi Page 7 Status 9 6 09 Feedback Controlyzer Digilock 110
57. ion modules feature an automatic phase adjust see Paragraph 8 2 1 7 and 8 2 1 8 for details The optimum phase can be found by first adjusting to the minimum signal at a phase shift of 90 to the optimum setting l Change the phase value until you get the minimum signal in the vicinity of the carrier 2 Then subtract 90 to obtain the maximum signal 3 If you observe the wrong sign add or subtract 180 to the current phase value Note that the phase should always be adjusted on the local oscillator as implemented in the DigiLock 110 because any additional phase in the signal path deteriorates the control loop perfor mance Once the optimum phase is found and the offset is properly adjusted the control loop can be closed and the controller parameters can be optimized 9 3 Controller Parameter Adjustment and Optimization Once a suitable error signal is at hand the feedback loop can be closed and optimized The general working principle of the Proportional Integral Derivative PID controller is to minimize the deviation of a physical measure process variable from a selected set value by modifying the actuator drive manipu lated variable accordingly The output of the controller is a weighted sum of the integral I proportional P and differential D paths scaled by the overall gain The digital PIDs in the DigiLock 110 allow for a precise and reproducible control of the gain settings The three contribution
58. ion of the frequency analysis Note that the DC part is usually much bigger than the signal in the frequency range of interest Hence suppressing the DC part allows to use the autoscaled signal for analysis 8 4 Status Display On the bottom of the window the status bar displays the current state of the most important modules sys tem messages and a progress bar used for time consuming processes Status display sM emana ana u ea fo fo j Figure 30 Status Display TOPTICA pensa Fee Status 9 6 09 Feedback Controlyzer Digilock 110 9 Notes on Feedback Control Loops with the Digilock 110 The Digilock 110 is a universal module to realize different locking scenarios It provides two PID controllers means for frequency modulation techniques as well as tools for analyzing the lock This paragraph is indented as a starting point for more detailed information on the implementation of control loops and their optimization For application examples see Paragraph 10 Before discussing the adjustment of the controller parameters Paragraph 9 3 it is helpful to consider a few signal path issues Paragraph 9 1 Frequency modulation is necessary to generate an error signal for top of fringe locking It also offers advantages in terms of insensit ivity with respect to amplitude modulation and frequency noise and can provide a larger capture range Paragraph 9 2 The AutoLock mode of the DigiLock
59. k e SMB connector 3 Auxin High speed analog input 2V 50 e SMB connector 4 Mainin Versatile high speed analog 2V 50 e SMB connector input 5 Error output Output of the error signal Main 1 7 V 50 e SMB connector in Input offset x Gain 2 6 Main out Versatile high speed analog 1V 50 e SMB connector output 7 Aux out High speed analog output 1V 50 e SMB connector 8 Sum input Signal input is added to Main 1V 50 e SMB connector OU 9 AlO2 General purpose analog input Input 125V Input 47k e SMB connector output Output 6 5 V Output high 10 AlO 1 General purpose analog input Input 125V Input 47k e SMB connector output Output 6 5 V Output high 11 DIO General purpose digital input 0V 2 6 V TIL Input 47k e SMB connector output Output 50 12 Trigger output Trigger output 0V 2 6 V TIL 50 e SMB connector 13 USB connector Connector for Computer Con trol NOTE The ON OFF switch 1 should only be used when the laser is switched off NOTE For detailed connector specifications please see Paragraph 11 3 TOPTICA O PHOTONICS Page 9 Status 9 6 09 Feedback Controlyze r DigiLock 110 3 3 Backplane Connections The DigiLock 110 module is capable of accessing several analog signals on the backplane of the Sys DC 110 rack On the one hand analog signals can be set in order to remote control other modules see Table below On the other hand actual parameters of modules can be read DCC 110 lact DTC 110 lact Currentl
60. l open an instance of the User Interface DUI Once connected the button changes to Disconnect Pressing the button ll close the DUI and disconnect the Digilock 110 cking the Show Hide module button the DigiLock Interface can be un hidden from the user Hiding the DUI is Useful to clean up the desktop or to avoid excessive traffic on the USB system When a DUI is hidden the sampling is disabled by default This setting can be changed in the Settings General ab of the DUI The IP Address and Port Number fields display the corresponding values for the RCI of the DMS which are defined in the configuration file This configuration file DigiLock ModuleServer Profile pro is found in he profile directory see Paragraph 11 4 The Port Numbers of the RCls of the DUIs are listed in the last column port number For details on the remote control see the DigiLock 110 RCI Manual which can be downloaded from the TOPTICA Photonics AG website 1 In addition to the physically present DigiLocks it also lists a dummy to allow to start a DUI with no DigiLock 110 present Page 14 Status 9 6 09 TOPTICA PHOTONICS 8 DigiLock User Interface DUI 8 DigiLock User Interface DUI NOTE This DigiLock 110 manual refers to the software version 1 5 4 70 Visit www toptica com for information about the most recent software version The Digilock User Interface DUI consists of two main areas and a status bar In the Upper
61. man law to the exclusion of the provisions of the UN Convention on Contracts for the International Sale of Goods CISG The Regional Court Landgericht Munich shall be the court of exclusive international local and subject matter jurisdiction for legal disputes arising under or in connection with this guarantee request the above mentioned guarantee for the purchased products and herewith consent to the above mentioned Guarantee Conditions Model No Date Serial No Signature Date of Delivery Name Title To be completed by the buyer and returned to TOPTICA Photonics AG by mail or fax 49 89 85837 200 Version 01 02 05 Service and Technical Support Form amp TOPTICA PHOTONICS QM form F 008 Status of form 22 7 05 Page lof 1 Return to Sender TOPTICA Photonics AG Customer Service Lochhamer Schlag 19 D 82166 Graefelfing Muenchen Germany FAX 49 89 85837 200 Return Authorization number RMA VB Before goods are returned please ask the TOPTICA Customer Service for a RMA number Products model ID numbers S N Located on the back panel of the device S N S N Please give us a detailed description of your problems e g what the symptoms are and under which circumstances they occur Additional information e g modifications additional equipment etc Mains voltage V Hz Did you notice irregularities spikes etc 18 To be completed by the customer and returned to T
62. match the deriva tive of the spectrum signal The progress is indicated on the progress bar in the status display In order for the algorithm to work properly be sure that the resonance of interest is visible in the AUtoLock display during operation NOTE Due to signal processing limitations it is recommended to optimize the lock with the demodulated lt PDH out gt signal and not the modulated input signal see Paragraph 9 6 Ca Page 26 PHOTONICS Status 9 6 09 8 DigiLock User Interface DUI 8 2 2 Simulation Controller Frequency Response Selected PID PID 1 Get parameters Input van in Gain 21 P 10000 SE l 4 active i mE 1 cut off freg Jo Hz 10k 100k al D go Frequency Hz IO Output gman out Y Frequency Start Ss Unit Jrz i d send parameters parameters to lt FIDi 74 6 Stop SES f lela Magnitude dB aseyd Cursors xX EN Cursor 0 Phase Magnitude Ez Phase Ea azik Figure 17 Simulation of the Frequency Response for Optimization of the Controller Design This function visualizes the transfer function of the selected PID controller according to the parameters chosen The transfer function graph consists of two traces the magnitude and the phase which are plot ted versus the frequency It also includes filters and signal delay e g ADC conversion FPGA calcula tions This information is
63. mation to the user that may be beneficial in the use of the Before operating the DigiLock 110 plug in module please read this manual carefully to prevent from damage to the electronics connected diode lasers and injury to persons The following safety instructions must be followed aft all times The electrical units should not be operated in a hazardous environment Any plug in module should only be opened by trained personnel Before exchanging and opening any module the Sys DC 110 Supply Electronics must be switched off and discon nected from the mains supply Do not look into the beam from the laser diode under conditions which exceed the limits specified by the United States Food and Drug Administration Department of Health and Human Services Center for Devices and Radiological Health 21 CFR 1040 10 and 2 CFR 1040 11 Take precautions to eliminate exposure to a direct or reflected beam It is essential to check the adjusted parameters of the supply units before switching on the modules Therefore the operator must make sure that the ON OFF switches of the modules are in position OFF before the Key Switch of the DC 110 monitor Unit is switched to position ON In particular pay attention to the Imax limitation the POS NEG switch and the CURRENT POWER switch of the Current Control DCC 110 As long as the ON OFF switches are set to position OFF the laser diode is short circuited by the relay integrated in the Toptica D
64. mized applied modulation see text Mod Output Output to which the modulation is added lt Main out gt Signal Hold vid 283 8 36 1m 597 0 show Main in Y 11 3 11 4 5C110 out Y Figure 48 AutoLock Display of the Doppler free Rb spectrum upper yellow trace with the correspond ing Lock in Signal lower red trace Note that the sign phase of the error signal is chosen to be the derivative of the absorption signal Le it is positive negative on positive negative slopes respectively 24 The phase between the modulation and the reference signal has to be adjusted to obtain a large error signal with steep slopes and zero crossings at the maxima of the spectral signal The sign o the error signal can be inverted by changing the phase by 180 The sign should be adjusted such that the lock in signal is the derivative of the input signal Le positive error signal on positive signa slope and vice versa NOTE As of software versions 1 5 4 70 the DigiLock 110 frequency modulation modules feature an automatic phase adjust see Paragraph 8 2 1 7 and 8 2 1 8 for details Please see Paragraph 9 2 on how to manually adjust the phase 25 Once the phase is adjusted turn off the modulation of the Lock In module Check the parameters of the PID controllers Now you can position the crosshairs to either a peak or a valley and it will automatically track the lock point To find the correct settings
65. n and Max values should be chosen within reasonable range Choosing one to be extremely far from the expected signal level will result in a shifted hysteresis window and hence to a disfunctional detection of reentering EE Ed Max Mean Max Min 2 epicenter cap EE At Figure 23 Relock Window The relock window is defined by the Min and Max values When the signal leaves this window the out of lock state is detected and the output of the controller is frozen Once the signal has reentered the inner 80 window the system is considered to be locked again The time between detection of the out of lock state and the activation of the relock scan is defined by the delay set in the AutoLock Window tab Before starting the relock scan the controllers can optionally be reset to zero using a finite slope defined by the reset rates see Paragraph 8 2 1 3 and 8 2 1 4 for details TOPTICA pensa pageda Status 9 6 09 Feedback Controlyzer Dig iLock 110 9 6 Signal Limitations in Analyzing the Locking Performance NOTE provided by the PDH and Ll modules it is highly recommended to use the demodulated signal lt PDH out gt or lt LI out gt respectively to observe residual excursions in the Scope dis play as well as using the frequency analysis Spectrum display To analyze the performance of a lock based on a frequency modulation technique as ools
66. n function see Paragraph 8 2 2 This allows to identify reasonable relative gains for the different contributions in particular an advantageous influence of the D part on the phase at higher frequencies 9 4 Identification of Signal Polarity and Slope To support the AutoLock features the DigiLock User Interface DUI takes a consistent approach to the definition of the signal polarity of each controller and the slope of the error signal The polarity of the controller is used to match the action of the corresponding output to the direction of the scan lt should be chosen such that an increased controller output acts in the same direction as an increase of the Sean module output Hence if the output of the controller is identical to the Sean module output the polarity is positive Otherwise the direction has to be determined for the particular actuator used For example if the DigiLock 110 Sean module scans the laser via the Scan Control SC 110 and the output of PID 2 is also chosen to be the SC 110 its polarity is trivially positive If the output of PID 1 is then directed to the current of the laser diode the polarity of the controller will depend on the polarity of the aser diode as defined by the DCC 110 current control see Sys DC 110 manual for details In this case he polarity of PID 1 has to be opposite to the polarity of the laser diode The polarity of the controller output for any actuator c
67. n in gt has to be between 3 5 V it can be shifted with the lt Input Offset gt and ampli ied with the input gain Aux in 4 100 M 15M 2 0 50 Precise in 6 200 k 50 k 2 0 10k DCC lact 6 100 k 15k 13 1 40 k Backplane default not connected DTC Tact 6 100 k 15k 13 1 gt 500 k Backplane 40 kin Ver default not connected sion 1V1 AIO 1 in 6 100 k 15k 12 5 47 k Default not connected AIO 2 in 6 100 k 15k 12 5 47 k Sum in 27M 1 0 50 Banawidth value refers to signal path between lt Sum in gt and lt Main out gt DIO in 1 0 2 6 47k Default not connected TTL Level Output Resolution Sample Bandwidth Range 50 Ohm Comment Channel bit Rate Hz 3dB Hz V Driver Main out 14 100 M 19M 1 0 Yes Sum of lt Sum in gt and Analog P branch Aux out 14 100 M 19M 1 0 Yes SC110 out 21 100 k 18k 6 5 No Backplane amplification by 15 with SC110 DCC Let 21 100 k 18k 6 5 No backplane DIC Tet 16 100 k 18k 6 5 No backplane AIO 1 out 16 100 k 16k 6 5 No AIO 2 out 16 100 k 16k 6 5 No default not connected Error out 20M 1 7 Yes Error out lt Main in gt lt Input Off set gt Gain 2 bandwidth value refers to signal path between lt Main in gt and lt Error out gt TRIG 1 0 2 6 Yes TTL Level DIO out 0 2 6 Yes TTL Level Internal Resolution Sample Bandwidth Range Comment Signal bit Rate Hz 3dB Hz V Input Offset 16 100 k 2 5 Analog P 16 100 k 0 58
68. ncy tuning Switch on the scan by pressing the Scan button 14 The Scope display provides a two channel oscilloscope and is a general tool to view a variety of signals of the DigiLock 110 To display the spectroscopy signal use a timescale of 50 ms corre sponding to the 10 Hz scan frequency choose lt Main in gt as CH 1 and lt SC 110 out gt as CH 2 The scope triggers on the rising slope of the internal scan ramp The signal expected after the adjustment will look similar to the one shown in Figure 38 Page 50 Status 9 6 09 e TOPTICA PHOTONICS 10 Application Examples Signal ob CH 3 5C110 out isciidout 10 out ode W Mean RMS error 1121 5m show avg sm Main in 20m 30m Time s Figure 38 Absorption Signal of a Doppler free Rb Spectroscopy Once the laser scans across the spectral function two different locking schemes can be implemented using the AutoLock module of the DigiLock 110 First locking to the side of a fringe is presented Para graph 10 2 1 then the use of frequency modulation demodulation to lock to a maximum or minimum is explained Paragraph 10 2 2 10 2 1 Side of Fringe Locking We are now ready to use the AutoLock module to lock the laser to the slope of a Doppler free absorp tion line AutoLock PID 1 PID 2 Analog Input Ei main in Controllers PID 1 PID 2 L Analog General Window Relock Advanced Mode Setpoint SE pos slop
69. ng the scan to find the resonance and lock point derive the error signal and it provides the controllers for the feedback loop lt can optionally generate an error signal by means of a frequency modulation technique Furthermore the graphical user interface supports both a user friendly AutoLock mode as well as intuitive access to all locking parameters The integrated frequency analysis Spectrum display allows to optimize the regulators in advanced applications This section introduces the common setup for the different locking scenarios described in the following paragraphs DC DTC110 Mon110 DC110 Connection via backplane DigiLock110 DCC110 Isolator Experimental Setup Figure 34 Typical Setup for Laser Locking The signal from the photo detector PD is fed into the lt Main in gt input of the Digilock 110 The two PID controllers act via the backplane and SC 110 on the grating piezo and via the lt Main out gt on the laser diode current mod DC TOPTICA pensa page 45 Status 9 6 09 Feedback Controlyzer Digilock 110 Initial setup CAUTION Make sure that the laser current is switched off while installing or exchanging the Digilock 110 or any other module Take care of proper personal grounding while han dling the laser head e g when connecting cables l Switch off all modules in the DC 110 electronics to install the DigiLock 110 The DigiLock 110 pro vides the Sc
70. nge in slope as explained earlier is easier to inter pret NOTE The AutoLock mode of the Digilock 110 expects a consistent choice of the polarity setting for all PID controllers involved see above Once the overall polarity is found a correction of the polarity can be compensated by changing the slope also Ca Page 42 Gu PHOTONICS Status 9 6 09 9 Notes on Feedback Control Loops with the Digilock 110 9 5 Relock Feature The basis of the relock feature of the DigiLock 110 is the out of lock detection It is based on a window comparator which is defined by the minimum and maximum bounds The laser is considered in loc when the signal of the selected channel is within these bounds 100 window Once the signal has left his window the corresponding PID controller is in hold state i e its output is frozen Reentering the com parator window takes into account a 10 hysteresis Le the input signal has to be within the 80 win dow see Figure 33 Once the signal has been within these bounds the PID controller is reactivated The ime between the detection of the unlocked state and the activation of the relock sean can be set by he delay on the PID Window tab of the Settings function see Paragraph 8 2 1 5 The output channel requency and amplitude of the relock scan are defined in the AutoLock Window tab or the corre sponding PID controller NOTE Due to the 10 hysteresis both Mi
71. ns P D to zero Now increase the integral part until the system locks Generally speaking at this point he quality of the lock improves with increasing gain on the controller until the feedback loop starts to oscillate This is the case when the feedback loop reaches a gain of 1 at a 180 phase shift Therefore the usable bandwidth of many actuators e g piezos is limited by their characteristic frequencies In any case phase shifts due to finite bandwidths and signal propagation times in the control loop lead to phase lags which increase with frequency The appearance of oscillations can be observed in the oscil oscope display of the error signal see Paragraph 9 6 for details However the frequency analysis Spec rum display is better suited because it is more sensitive and directly shows the resonance peak at its 5 In analog controller circuits the integral part is sensitive to persistent DC deviations of the error signal e g internal OPAmp IC offsets Therefore the integral gain E in analog PID controllers should always be kept at a finite setting to reduce resid ual offsets 6 If the system does not lock check the polarity i e try the opposite polarity or consult Paragraph 9 4 TOPTICA pensa pages Status 9 6 09 Feedback Controlyzer Digilock 110 frequency Usually it is helpful to drive the system into oscillation and note the characteristic frequencies for reference A simple param
72. of the sign for each PID controller please see Paragraph 9 414 Here we assume the following AutoLock settings Cursor Track on Snap to setpoint on Smart Assistance Engage on Setpoint off When the error signal offset is compensated the PID set point can be set to zero TOPTICA pensa pages Status 9 6 09 Feedback Controlyzer Digilock 110 26 To initiate the lock perform a right mouse click to access the context menu and select LI PDH Lock to extremum The trace changes its color here from yellow to blue to show that the actual trace is captured in the background During the next scan the lock is triggered Figure 50 shows the AutoLock display while the lock is triggered The blue trace is the captured signal of the last scan The yellow trace is the scan during which the lock is triggered You can see that the trace stops at the selected peak After a while the yellow trace disappears and there is only a scatter plot left The interpretation of this plot and the optimization of the lock can be found in Paragraph 10 2 1 For optimization of the PID parameters see Paragraph 9 3 LI PDH Lock to extremum Clear Graph Export Data Export Simplified Image 11 3 11 4 C110 out Figure 49 Initiating the automatic Ll lock to a Peak Select the lock point by positioning the crosshairs When the Lockpoint tracker is on it snaps to the nearest peak or dip and if the laser drifts the lock point i
73. on NOTE The installation of the USB driver and the control software requires administrator privileges Please uninstall any previously installed DigiLock 110 software as otherwise the installations may interfere Read the Readme html file located on the installation CD for up to date information about the installation procedure and the current software version 5 1 System Requirements Processor x86 Platform e g Pentium Ill 4 M min 800 MHz recommended gt 1 2 GHz RAM min 256 MB recommended 512 MB Screen resolution min 1024 x 768 Operating System Windows XP SP2 Windows 2000 SP4 not tested with Windows Vista nterface 1 x USB 1 1 or USB 2 0 To view the user manual provided in the Help Menu installation of Adobe Acrobat Reader is necessary 5 2 USB Driver Installation The DigiLock 110 provides a USB connection to load the firmware and to control the module via the sup plied PC based software In order to communicate with the DigiLock 110 the USB driver has to be installed before the installation of the application software The driver is located in the directory Driv ers USB on the installation CD supplied with the DigiLock 110 module Run the exe file to install the driver on the PC After the driver is installed successfully connect the Digilock 110 module to the PC with the appropri ate USB cable The operating system will recognize the new hardware 5 3 Software Inst
74. or the high frequency feedback therefore its output channel is lt Main out gt which is con nected to the modulation input of the laser PID 2 is Used for large range low frequency feedback to the piezo To prevent the controllers from mutual interaction the PID 1 features an cut off fre quency The cut off frequency defines the corner frequency below which the integral gain of the controller is limited A reasonable choice is in the order of 100 Hz The values of the gain parameters for the PIDs shown in Figure 42 are set in the corresponding tabs Their settings depend on the slope of the error signal and the actuator response For the given setup the error signal amplitude should be on the order of 100 MVpp See above for input offset and gain In most cases the low frequency feedback of PID 2 is sufficient to achieve a first lock It is advisable to start with conservative gain settings To find the correct settings of the sign for each PID controller please see Paragraph 9 4 Once locking is accomplished the parameters can be optimized see Paragraph 9 3 She l 2 as oe EE far a a a 4 Main out E 7 h E Figure 42 PID Setup for Locking to the Slope of a Doppler free Rb Peak 19 Before the lock is initiated the lock point has to be selected by dragging the crosshairs in the graph of the AutoLock display to the desired position When you drag the vertical line in the hori zontal dire
75. otonics AG TOPTICA PHOTONICS Status 9 6 09 Feedback Controlyzer Digilock 110 Contents 1 The Feedback Controlyzer Digilock 110 3 1 1 Package Contents 3 1 2 Design and Operating Principle of the DigiLock 110 4 2 Safety Instructions and Warnings D 2 1 Generol Safety Terms 6 2 2 Identification of Manufacturer 7 3 Operator Controls and Connections 8 3 1 Front Panel 8 3 2 Description of Front Panel Operator Controls and Connectors 9 33 Backplane Connections 10 4 Digilock 110 Hardware Installation 11 5 Digilock 110 Software Installation 12 5 1 System Requirements 12 5 2 USB Driver Installation 12 5 3 Software Installation 12 6 Digilock 110 Control Architecture 13 7 DigiLock Module Server DMS 14 8 Digilock User Interface DUI 15 8 1 General 16 8 2 Functions 17 8 2 1 Lock 17 8 2 2 Simulation Controller Frequency Response 27 8 2 3 Response Network Analysis 28 8 2 4 System 29 8 2 5 Settings 30 8 3 Display Area 35 8 3 1 Scope 35 8 3 2 Autolock 36 8 3 3 Spectrum 37 8 4 Status Display 37 9 Notes on Feedback Control Loops with the Digilock 110 38 9 1 Signal to Noise and Bandwidth Considerations 38 9 2 Frequency Modulation Techniques 38 9 3 Controller Parameter Adjustment and Optimization 39 9 4 Identification of Signal Polarity and Slope 40 9 5 Relock Feature 43 9 6 Signal Limitations in Analyzing the Locking Performance 44 10 Application Examples 45 10 1 General System Setup 45 10
76. output input Pos 2 Jumper Channel Closed Open Factory JP 300 DTC 110Tset connected to open DA3 JP 301 not used open JP 302 DCC 110 Let connected to open DAI JP 303 SC 110 out connected to closed DA2 Table 6 Baseboard Jumper Settings Plug on board Jumper Channel Pos 1 Pos 2 Open Factory JIP 2 Aux in 50 Ohm connection to high Pos 1 terminated ain in impedance JP 3 Precise in 50 Ohm connection to high open terminated ain in impedance JP 5 Sum in 50 Ohm connection to high Pos 1 terminated ain in impedance Jumper Channel Closed Open Factory JP 1 Main in 50 Ohm high imped closed terminated ance JP 4 not used closed Table 7 Plug on board Jumper Settings TOPTICA pensa pagar s Status 9 6 09 Feedback Controlyzer Digilock 110 11 2 Digilock 110 PCBs 11 2 1 Baseboard JP 300 JP 302 JP 303 E D N n O POT 7p eS A Ile anc oo e ga 38 Se JP 301 gel Bo FS eat ali at oll BS Se Se g 5 asen S o reset gd gl S igg Zeus 8 go F XC el y 2e A ky 8 Ge 8 D z ZS E Al oi ui Pr D83 el gs l pes O DO zi ag P H y LR SZ SS E a 3 3 Be E ESTA Ba e E d SR a E rios wm S 8 8 Be o a7 g 58 a a sie rs DS 88 E H o zi BS 3 o gan pi o i FT IR i 7 al gel gl S E E Bes i d Be d d o En 5 F H 3 8 Le ae eH TE g Se R DI SS a5 E go EM mm hu PL eN 5 B a ED S E
77. part of the screen the user can set the appropriate operation parameters of the selected function The lower part is used to display various signals by means of an oscilloscope or a spectrum analyzer DigiLock 110 SN 01012 Module_1012 ER SE Function EAN Lock In Signal type yi Input ivan in Modulation PT a Frequency Spectrum Main in Set freq EES He SEA Controllers Ferme S SS a PID 1 Amplitude 20 2700 mp Functions J PID2 Output manou Es J 5C110 out H Analog La OFF General Window Relock Advanced Input SG Ee in Meds Phaseshit Ur Value E e Setpoint Dm SES Offset C Dutput Dacun out Display Sampling Main in Display fis ke rd pre EL pak ER 5C110 out Y Status Statusdisplay ESM pw pw2 ana ir Pon Figure 8 DigiLock User Interface DUI Example Autolock mode displaying a Saturated Absorption Spectrum TOPTICA pensa pagers Status 9 6 09 Feedback Controlyzer Digilock 110 8 1 General To operate the software efficiently it is necessary to be familiar with the DUI Some helpful remarks are presented in the following Changing numeric input controls Set the focus on the desired numeric control left click on the field A cursor appears in the input field The digit to the left of the cursor can be incremented decremented with the up down arrow keys To select the desired
78. position the crosshairs to either a peak or a valley and they will auto matically track the lock point Here we assume the following settings Cursor Track on Snap to setpoint on Smart Assistance Engage on Setpoint off When the error signal offset is compensated the PID set point can be set to zero To initiate the lock perform a right mouse click to access the context menu and select LI PDH Lock to extremum The trace changes its color here from yellow to blue to show that the actual trace is captured in the background During the next scan the lock is triggered Figure 55 shows the AutoLock display while the lock is triggered The blue trace is the captured signal of the last scan The yellow trace is the scan during which the lock is triggered You can see that the trace stops at he selected peak After a while the yellow trace disappears and there is only a scatter plot left The interpretation of this plot and the optimization of the lock can be found in Paragraph 10 2 1 IS 16 17 Residual offsets in the demodulated error signal are mostly due to unintended intensity modulations that come with the phase modulation The output of the controllers can be restricted using the Limit settings Paragraph 8 2 1 4 and 8 2 1 5 e g to about the scan range This helps to avoid destabilization of the laser by driving it far from the lock point especially during initial setup and optimization TOPTICA pensa pagesi S
79. respectively 7 Alternatively there are several optimization methods for PID controllers which mostly originate from slow temperature type controller applications The Ziegler Nichols method gives rule of thumb values derived from the proportional gain Kp osc where oscillation of fre QUENCY Vosc Starts Kp 0 6 x Kpose K 2 Kpose Vosc Ki Kose X Voso 8 8 The overall polarity is given by the product of the PID controller polarity and the sign of the slope Ca Page 40 Gu PHOTONICS Status 9 6 09 9 Notes on Feedback Control Loops with the Digilock 110 0 10 d neg slope unlocked pos slope 2 e a Saturated Absoption Signal V 2 8 0 05 0 75 1 00 1 25 1 50 1 75 Figure 31 Polarity of the PID Controller for Side of Fringe Lock The graph shows the characteristic distortions of the error signal of a side of fringe lock for dif ferent polarities The displayed example is a zoom into the saturated absorption spectros copy of Rb The undistorted signal solid black is given for reference When the polarity is chosen to lock on a negative slope dashed red the negative slopes are shallower broader while the positive slopes are steeper narrower The opposite is true for locking onto the posi tive slopes dotted green The traces have successively been exported from the Scope dis play of the DigiLock 110 right click on Scop
80. ror signal a q UOIssILUSUDI 194 Figure 16 Left PDH Module Right schematic Error Signal of a Single Resonance generated with the Pound Drever Hall Modulation Technique The Sidebands exaggerated for Illustration can be seen at about 10 MHz The principle of operation is similar to the Lock In module but the modulation frequencies are typically higher than the characteristic linewidth of the resonance The available modulation frequencies are given by fractions of 25 MHz 25 MHz 12 5 MHz 6 25 MHz 3 13 MHz 1 56 MHz Modulation A frequency modulation is applied to one of the outputs to generate an error signal by mixing the detected signal with a local oscillator The modulation is automatically switched on for locking It can be switched manually with the ON OFF button Manual activation is only needed to adjust the phase shift or in manual lock mode Set freq Modulation frequency in Hz Amplitude Peak to peak amplitude of the modulation signal in Volts Output Output channel to which the modulation signal is applied Modulation ON OFF Modulation switched ON OFF Input Input source for the module Main in Aux in Phase shift Phase shift in degrees between the output and the local oscillator sig nal Offset Offset in units corresponding to the oscilloscope display The offset is substracted from the demodulated signal Adjust Adjusts the phase of the demodulated error signal to
81. s differ in their frequency dependence l The integral I part is given by the time integral of the error signal Therefore its gain increases to ower frequencies and it is responsible for the compensation of dc offset changes The residual deviation of the error signal from zero or respectively the difference between the physical mea sure and the set point decreases with increasing integral gain 2 The proportional P part has a flat frequency response and is limited by the bandwidth of the con rol loop A larger proportional gain Kp reduces the deviation from the set point and is limited by he onset of oscillations 3 The differential D part reacts on sudden changes to reduce deviations e g an over shoot in the ransient response lts frequency response increases with frequency and is limited to higher fre quencies by the bandwidth of the control loop Since it provides a phase lead the differential D part can help to improve the phase response at higher frequencies which in turn allows to increase the gain on the and P parts before inducing oscillations Note that due to the high bandwidth transient resoonse the differential part is also particularly prone to amplification of noise Before adjusting the parameters of the controllers the correct phase and polarity should be chosen for details see Paragraph 9 2 and 9 4 respectively To start select a low input gain and set all contributio
82. s tracked automatically Acti vate the lock by selecting LI PHD Lock to extremum from the context menu 120m Signal Hold Ould 110m i 5 100m d A g m LG e 60m Om 60m 50m 40m Main in Y 30m 20m 10m 0 11 1 11 2 11 3 SC110 out Figure 50 AutoLock Display while the lock is triggered LI PDH Lock to extremum The background trace blue displays the last scan before The trace yellow captured dur ing the engagement of the lock stops at the selected lock point where the scan stops and the selected controllers are switched on 14 The output of the controllers can be restricted using the Limit settings Paragraph 8 2 1 4 and 8 2 1 5 e g to about the scan range This helps to avoid destabilization of the laser by driving it far from the lock point especially during initial setup and optimization Besa Page 58 O PHOTONICS Status 9 6 09 10 Application Examples 10 3 Pound Drewer Hall Stabilization to a Cavity The second important application described here is the stabilization of a laser to a cavity with the Pound Drever Hall technique Figure 51 shows an overview of the setup used for a Pound Drever Hall stabiliza tion onto a cavity in reflection In this example the cavity is a FPI 100 Fabry Perot interferometer available from TOPTICA Photonics AG Connection via backplane DigiLock110 C110 DCC110 DTC110 DC Mon110 Main in Main out
83. sed to adjust for stable single mode operation using the computer aser diode temperature via DTC 110 Tet DAS is of particular interest for scan The Digilock 110 can read the DCC 110 lact and DTC 110 Tact parameters via the backplane see ls This readout only works for modules installed on channel 1 of the rack slot 2 3 and 6 It is recommended to install the DigiLock 10 in slot 6 see Figure 5 For further information on DC 110 manual Backplane Line Adressed Module Parameter lact Channel 1 DCC 110 lact Tact Channel 1 DTC 110 Tact Table 2 Backplane inputs accessible by the DigiLock 110 and their assignment Page 10 Status 9 6 09 TOPTICA PHOTONICS 4 DigiLock 110 Hardware Installation 4 DigiLock 110 Hardware Installation The Digilock 110 module is designed as a plug in module for the ToPTICA DC 100 or DC 110 supply rack Before installation switch off the laser and all other modules and disconnect the supply rack from the mains supply The Digilock 110 can be plugged into any slot of a 19 or 12 rack except the one reserved for the DC 110 Mon on the right a lll SS i vc A E Se Greg gg en Slot 5 Slot 3 Slot 1 SC 110 DTC 110 DCC 110 Mon Slot 6 Slot 4 Slot 2 Digilock110 DCC 110 Figure 5 DigiLock 110 installed in Supply Rack DC 110 TOPTICA Qi Page 11 Status 9 6 09 Feedback Controlyzer Digilock 110 5 Digilock 110 Software Installati
84. splay 16 18 20 5C110 out Y Estatus Statsdloply Dt zial pi Figure 35 Digilock User Interface DUI after Startup Here the laser is scanned across the saturated absorption lines of Rb at 780 24 nm see Para graph 10 2 error out sum in Main out Main in Grain cue Dua cut eit Aux in z Figure 36 Graphical Overview of the Signal Path through the Controller System Function 12 The System function Figure 36 shows a block diagram of the control loop Here several options for the analog gain and offset as well as different filters for the lt Main in gt signal path can be set Their function and default setting are given in the following table The default values are a good starting point and can later be optimized for the specific application by the user Please refer to Para graph 9 for further information Seen Page 48 Miro Status 9 6 09 10 Application Examples Name Description Standard Value Input offset Offset to be subtracted from the input signal before digitalization to reduce the signal offset or further analog amplification 0 0V Analog gain to amplify the signal to take advan Gain age of the maximum input range of the analog o digital converter ADC and hence its resolu ion 2 V Invert nverts the input signal off box not checked High pass filter High pass filter of given frequency and order bypass box checked
85. tatus 9 6 09 Feedback Controlyzer Digilock 110 380m md pas A ML ir gom o t db ten le o o ir rr d 940m 920m V 900m L L o slo 880m LI POH Lock to extremum we 860m 840m 820m Clear Graph 800m Main in Y i Export Data 780m Export Simplified Image 760m f 740m 720m 680m 272m 250m 200m 150m 75 3m 50110 out Figure 54 Initiating the automatic PDH Lock to extremum Signal Ht _ 3554m WE Input 950m deg AER UE 950m 925m 300m e E 375m 350m 25m 800m Main in Ti5m 750m 725m 150m 100m SC110 out DEE 625 on RMS error Wain in Y PDH out a u Figure 55 AutoLock display after triggering the lock LI PDH Lock to extremum Page 62 Status 9 6 09 TOPTICA O PHOTONICS 11 Appendix 11 Appendix 11 1 Internal Jumpers The Digilock 110 module is shipped with a standard configuration of its inputs and outputs The internal jumpers allow to modify this configuration The table below shows all jumpers and their function For loca tion of the jumpers please see Figure 57 and Figure 58 Pos CT 000 Pos 2 Figure 56 Description of Jumper Positions Pos 1 is always near the angled corner Baseboard Jumper Channel Pos 1 Pos 2 Factory JP 7 DIO input output Pos 2 JP8 AIO 1 output input Pos 1 JP 9 AlO 2
86. the comparator window Time to wait between detecting the unlocked state signal outside win dow and initialization of a reset relock procedure This Delay allows for an immediate relock e g after the system was subject to a temporary disturbance Enables the corresponding PID reset Slope in Volt second when resetting the outputs of PID 1 and PID 2 respectively Finite rates restrict the reset speed of the PID outputs to avoid destabilization due to rapid changes e g creep of piezos after a sudden voltage step This option is only available if the Use Window checkbox is selected since is relies on the detection of the lock state see above In case the window signal is out of bounds Le the system is not locked the relock option scans the output channel of the selected PID controller with the chosen values for frequency and amplitude waveform type is a sym metrical triangle Once the window signal is within the specified limits again the scan is turned off and the controllers are activated Select one of the PID outputs to be scanned to relock with the given fre quency and amplitude Frequency of the relock scan Amplitude of the relock scan Page 19 Status 9 6 09 Feedback Controlyzer Digilock 110 Advanced Display Track Snap to setpoint Active trace Smart Assistance Dependent on the nature of the lock task and the error signal available the advanced settin
87. tings To improve the lock performance you can now increase the gain of the P and D parts of the PID in turn to values well below the point at which the control loop starts to oscillate The general strategy for opti mizing the P land D parameters is described in Paragraph 9 3 TOPTICA pensa pages Status 9 6 09 Feedback Controlyzer Digilock 110 10 2 2 Top of Fringe Locking Lock In To lock the laser to a maximum of the Doppler free absorption signal a zero crossing slope is generated using frequency modulation The Lock In module uses a modulation frequency smaller than the charac teristic resonance width to obtain the derivative of the absorption signal by demodulation For the setup follow the initial steps 1 AutoLock module SE to 18 described above but choose lt LI out gt as input to the To view the error signal switch to AutoLock display Set the scan frequency of the Sean module to 10 Hz the output to lt SC 110 out gt and switch on the scan Figure 47 22 23 Figure 48 shows the resul Lock In PDH Modulation Set freq took Hz Act freq 97 66k Hz Amplitude Zeen pp Output main out i ER OFF Phase shift fso A Offset Ajo Input Afman in Adjust Lock In Module with typical Parameters Configure the parameters for the Lock In module see Figure 47 The modulation set frequency Set freq has to be chosen depending on the spectral resonance
88. tive gain NOTE If the gain parameters are out of range an error message is displayed in the controller tab Note that the maximum response is a combination of all PID parameters Output Output channel of the controller Limits Voltage values to which the PID output is limited relative to the initial off set of the output channel Activated by the checkbox TOPTICA pensa Page 21 Status 9 6 09 Feedback Controlyzer Digilock 110 General Setpoint Slope Lock Window Use Window Channel Max Min Delay Reset PID checkbox Reset rate Relock Frequency Amplitude These parameters are intended to manually operate the controller In he AutoLock mode these parameters are set automatically Since the interactive AutoLock covers most standard locking situations the man val options should only be needed in special cases Setpoint of the controller Sign of the slope to which the system is locked to Turns the controller ON OFF Activates a window comparator to determine the lock state The selected input channel is compared to the window defined by the Min Max range This option specifies boundaries for the selected channel If he signal leaves the window the controllers associated with the AutoLock module are on hold They are reactivated when the signal is back in the selected range taking into account a 10 hysteresis for fur her details see Paragraph 9 5 Note that
89. ton Cursor Pan Mm Zoom x axis Zoom 4 Zoom in Figure 40 Available Tools for the Graph Displays To increase the scan range again use the Zoom out tool The graph will zoom as long as you press the left mouse button To shift the spectrum to the left or right i e modifying the offset use the Pan hand tool In our example the 85Rb D2 transitions at 780 nm are used Figure 41 and the locking point is chosen to be at the rising slope of the second peak by dragging the crosshairs Note that the behavior of the lockpoint selection can be customized in detail in the settings of the Autolock Advanced tab see Figure 11 The options are explained in Paragraph 8 2 5 1 Here the following settings are assumed Cursor Track on Snap to Setpoint off Smart Assistance Engage on Setpoint on Main in Y 18 2 18 3 50110 out v Figure 41 85Rb D2 transitions at 780 nm The Crosshairs mark the currently selected Locking Point Ca Page 52 PHOTONICS Status 9 6 09 10 Application Examples To configure the PID controllers select the PID 1 PID 2 tab see Figure 11 and Figure 13 to access the corresponding parameters see Figure 42 A valid strategy is to first implement PID 2 for initial locking setting the Gain of PID 1 to zero and then add PID 1 to improve the lock at higher fre quencies In Autolock mode the input channel of the PIDs is defined by the AutoLock input PID 1 is used f
90. very helpful in designing the control loop to the frequency response of the actuators and to get an idea of reasonable relative gains of the different PID contributions In particular it allows to identify the derivative gain needed to significantly reduce the phase lag at higher frequencies Selected PID PID controller to which the parameter set belongs Get parameters Actual parameters of the selected PID are transferred to the controller design environment PID input nput channel to the controller Main in Aux in Ll out PDH out Gain Overall gain P Proportional gain l ntegral gain cut off Frequency in Hz at which the integral part is limited only applies to PID 1 D Derivative gain PID output Output channel of the controller Send parameters Sends the above parameters to the selected PID controller see Para graph 8 2 1 Frequency Scale Settings Start Start frequency of the simulation Stop End frequency of the simulation Unit Units used on the frequency axis When the parameters are changed the transfer function graph will be updated automatically If you are satisfied with the displayed transfer function you can send the parameters to the selected PID controller see Paragraph 8 2 1 TOPTICA pensa page za Status 9 6 09 Feedback Controlyzer Digilock 110 8 2 3 Response Network Analysis Frequency Sweep Start CJ 100 1 He Stop S
91. y only the actual values of the channel 1 modules Figure 5 slots 2 3 can be read by the Digilock 110 see Sys DC 110 manual for details Backplane Line Adressed Module Parameter Comment FDA 1 DCC 110 lset not jumpered by default FDA 2 SC 110 Offset jumpered by default FDA 3 DTC 110 Tset not jumpered by default Table 1 Backplane outputs of the DigiLock 110 and their assignment NOTE The assignment of the DA lines to the respective parameter is fixed inside the DigiLock 110 module Be sure that the jumpers of the corresponding modules are set according to the table above For detailed information please see the appropriate para graphs in the Sys DC 110 manual Make sure that no module other than the SC 110 uses the DA 2 analog backplane line By default the ion to the SC 110 outpu DA3 which can be Generally theses outpu Digilock 110 communicates via DA 2 with the SC connect DA 2 from the backplane by removing t there is are two more bac 1 he appropriate jumper see Paragraph 11 1 In addi 10 If you do not need this functionality you can dis plane outputs DCC 110 let ADA 1 and DTC 110 Tet interface Adjusting the ning the wavelength of DFB laser diodes Paragraph 11 3 for detai he arrangement of the modules please see the Sys activated by setting the corresponding internal jumper see Paragraph 11 1 ts can be u
92. ypass the digital input filters in the System see Paragraph 8 2 4 To optimize the signal to noise ratio of the input subtract the dc offset from the input signal by setting the input offset in the System see Figure 19 to the mean value as read from the oscilloscope display or the negative if inversion is activated in the System The gain can now be increased to take advantage of the full 2 V range of the analog to digital converter trol loop care should be taken to implement NOTE Due to the specific design the input analog gain does not contribute an additional band width reduction 9 2 Frequency Modulation Techniques Frequency modulation techniques are applied to obtain an error signal with a steep slope at the lock point The typical spectroscopy signal in transmission or absorption consists of a resonance line e g a Lorenzian or Gaussian or multiple thereof see application examples in Paragraph 10 To lock to the max imum of the resonance a dispersive signal is needed which is generated by frequency modulation and subsequent demodulation There are two regimes depending on the choice of the modulation fre quency with respect to the characteristic line width Dn of the resonance A modulation frequency Vmog smaller than Av leads to the derivative of the resonance signal as obtained from the Lock In module cp Paragraph 10 2 2 4 A modulation frequency much larger th

Digilock 110

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