141,3,4,5X HSPD revD TS (Page 3)
Contents
1. Using a voltmeter or oscilloscope measure the output voltage from the Bias Monitor on the front panel With no light on the detector the Bias Monitor voltage should be lt 10 mV 3 Couple some CW light into the photodetector 4 With the voltmeter or oscilloscope you should observe a DC output voltage If you know the optical power and wavelength you can calculate the expected output voltage Vu using the expression Pin R G where P is the input optical power watts R is the photodetector s responsivity A W and G is the amplifier s transimpedance gain V A The gain of the bias monitor port is 1000 V A If the output voltage appears to be low then the fiber connector might be dirty If a dirty connector is suspected see Cleaning the Fiber Connector below Cleaning the Fiber Connector The high speed photodetectors have an internal fiber connector and a fiber pigtail that brings the input light to the detector If the fiber connector is dirty this can block the input light so that light TROUBLESHOOTING sent into the detector will produce little or no output voltage Note also that if the fiber types are not compatible single mode with multi mode and vice versa this can also be the cause of a very low output voltage To clean the fiber 1 Turn off the module 2 Blow filtered air or another inert gas such as nitrogen into the input fiber connector This will help to remove any dust or dirt pa2. frequency impulse response of the detector will degrade as will the responsivity See Checking the Battery below Dirty fiber optic connector A dirty fiber optic connector can cause an apparent degradation of responsivity See Basic Optical Test below Tests Procedures and Solutions DC Offset Voltage With no light on the photodetector turn the detector on and use a voltmeter to measure the Bias Monitor output voltage This voltage is the DC offset plus dark current If the output is gt 10 mV then the detector is probably damaged and will need to be returned to New Focus Checking the Battery 1 Turn on the module using the power switch 2 Connect the Bias Monitor port to a voltmeter 3 Press and hold the Batt Chk button and observe the bias mon itor output The photodiode bias voltage is momentarily applied to the Bias Monitor SMA connector A reading of 5 V on this connector is typical with a new battery the battery should be replaced when the voltage reaches 3 5 V 13 0 TROUBLESHOOTING Replacing the Battery 1 Turn off the module and remove the two screws on the back panel with a Phillips screwdriver See Fig 1 2 Remove the back panel and replace the battery 3 Replace the back panel 4 Check the battery level as described above Basic Optical Test To quickly test whether a photodetector appears to be working you can perform a simple DC optical test 1 Turn the detector on 2
3. 0 mW Detector Material InGaAs Detector Type Schottky 16 DETECTOR CHARACTERISTICS Fig 3 Responsivity vs wavelength for a Models 143X and145X and b Models 141X and 144X Responsivity A W Responsivity increases from 0 0 52 A W over the range of 950 970 m 500 700 900 1100 1300 1500 1700 Wavelength nm 17 1 WARRANTY SERVICE amp SUPPORT New Focus Inc guarantees its products to be free of defects for one year from the date of shipment This is in lieu of all other guarantees expressed or implied and does not cover incidental or consequential loss TECHNICAL SUPPORT Information and advice about the operation of your New Focus products is available from our technical support engineers Engineers on duty from 8 00 5 00 PST Monday through Friday excluding holidays For quickest response ask for Technical Support and know the model number for your product Phone 408 980 8088 Fax 408 980 8883 Support is also available by email Email techsupport newfocus com We typically respond to email within one business day SERVICE In the event that your translation stage malfunctions or becomes damaged please contact New Focus for a return authorization number and instructions on shipping the unit back for evaluation and repair
4. Models I41X 143X 144X amp 145X FIBER COUPLED ULTRAHIGH SPEED PHOTODETECTOR MODULES USER S MANUAL Vv TABLE OF CONTENTS HANDLING PRECAUTIONS 3 QUICK START 4 INTRODUCTION 5 OPERATION 6 APPENDIX 1 USING AN OPTICAL FIBER 10 APPENDIX 2 USING THE CORRECT MICROWAVE 11 APPENDIX 3 INSIDE THE PHOTODETECTOR MODULE 12 TROUBLESHOOTING 13 DETECTOR CHARACTERISTICS s tten 16 WARRANTY SERVICE amp SUPPORT 18 v Is a registered trademark of 141522 Rev D New Focus Inc HANDLING PRECAUTIONS The detector is sensitive to electrostatic discharges and could be permanently damaged if subjected even to small discharges Prior to handling or making connections be sure to ground yourself adequately ground strap provides the most effective grounding and minimizes the likelihood of electrostatic discharge Do not over torque the microwave K connector Excessive torque can damage connectors Make sure the optical connector is clean and undamaged before connecting to the detector module QUICK START The Models 141X and 144X are hi
5. as voltage is applied to bias monitor port 2 25 57 1 J 2 00 50 8 Power Switch 3 27 82 9 Shown with ST connector for optic input Remove two screws 1411 ST connector to replace 9V battery 1414 FC connector 1431 ST connector 1434 FC connector 1441 ST connector 1444 FC connector 1451 ST connector 1454 FC connector APPENDICES APPENDIX 1 USING AN OPTICAL FIBER Single mode optical fiber can provide low loss and low distortion if attention is paid to a few important details First if more than one mode is allowed to propagate in a step index fiber the bandwidth will be degraded to approximately fsa cn 2L NA where c is the speed of light in free space n is the index of the core L is the length of the fiber and NA is the numerical aperture of the fiber Modal distortion can be eliminated by using a fiber with a core small enough that only a single mode will propagate In this case the bandwidth of the fiber will be limited by material dispersion which is a property of the glass used in the fiber core In this limit the bandwidth is approximately 543 1 LMA where L is the fiber length in kilometers M is the material dispersion in ps nm x km and AA is the line width of the optical source in nm This bandwidth limitation can be ignored for glass fibers less than 10 meters in length but can be serious for longer fibers and spectrally broad sources Palais C J Fiber Optic Communicati
6. cy circuitry This housing is bolted to a printed circuit board which regulates the bias for the photodiode and amplifies the DC photocurrent for the monitor port The optical signal is brought from the front panel connector to the microwave housing with a 0 2 meter 9 um core fiber Although the material and modal dispersion per unit length of this fiber can be high at certain wavelengths there is no degradation in frequency response since the fiber is only 0 2 meters long The fiber is protected by a sheet metal flange to prevent damage while changing the battery A simplified schematic is provided in Fig 2 for your reference Fig 2 Simplified schematic diagram of the 141X 143X 144X and 145X series photodetector modules Microwave Output Microwave Connector Housing pe Vv oN Photodiode Bias _ Monitor Batt Chk T On Off i V i Le te et i v ali 112 TROUBLESHOOTING Several problems which can arise with the detector modules and procedures to check for them are outlined below Problems Damaged photodiode Excessive offset voltage The photodi ode can be damaged by electrostatic discharge or excessive optical power and both causes lead to an increased dark or offset voltage A damaged photodiode can result in a degraded respon sivity and frequency impulse response See DC Offset Voltage below Low bias voltage If the photodiode bias voltage is too low the
7. els 141X and 143X are optimized for a flat frequency response and the Models 144X and 145X are optimized to achieve an impulse response with minimal ringing All models are 50 Q termi nated to reduce reflections in 50 Q systems and to make them compatible with 50 Q receiver filters All detectors have single mode FC or ST fiber connectors and an option 50 is available for a 50 um core multimode fiber input Each models characteristics are listed and their responsivity vs wavelength curves are shown in the Detector Characteristics section of this manual OPERATION Checking the battery and offset voltage The battery and offset voltage should be checked regularly to ensure proper functioning of the detector 1 Turn on the module using the power switch 2 Connect the Bias Monitor port to a voltmeter 3 Press and hold the Batt Chk button and observe the bias monitor output The photodiode bias voltage is momentarily applied to the Bias Monitor SMA connector reading of 5 V on this connector is typical with a new battery the battery should be replaced when the voltage reaches 3 5 V 4 Release the Batt Chk button and observe the voltage level the voltmeter Without an optical input this voltage is the DC offset plus dark current This dark voltage should be less than 10 mV 5 If needed keep the voltmeter connected to the module to optimize coupling to the fiber Making the Micro
8. etector module The Bias Monitor may be used to optimize coupling to the fiber OPERATION Table 1 Fiber optic cable assembly selection table Optical Input Fiber Assembly Required lt 2 mm diameter collimated beam at 830 nm wavelength Model 1233 collimator FC 2 meters for 1434 1454 1 3 um wavelength Model 1237 collimator FC 2 meters for 1414 1444 1 55 um wavelength Model 1238 collimator FC 2 meters for 1414 1444 Other wavelengths and beam types 600 to 900 nm wavelength Model 1223 pigtail FC assembly 2 meters for 1434 1454 1 1 to 1 6 um wavelength Model 1232 pigtail FC assembly 2 meters for 1414 1444 Patch Cable 1 1 to 1 6 um wavelength Model 1222 ST FC 2 meters These assemblies are available from New Focus Collimators require an Opti Claw tilt mount such as the Model 9854 Pigtail assemblies require a fiber aligner such as the Model 9091 0 APPENDICES Replacing the battery 1 Turn off the module and remove the two screws on the back panel with a Phillips screwdriver See Fig 1 2 Remove the back panel and replace the battery 3 Replace the back panel 4 Check the battery level as described above Fig 1 Front side and rear views of the Models 141X 143X 144X and 145X fiber coupled photodetector modules Bias monitor port Output K connector Output is equal to photodiode current times 1000 ohms for one millivolt Battery Check Button per microamp When depressed bi
9. gh speed InGaAs photodetector modules for detection of light of wavelengths 950 to 1650 nm The 143X and 145X are high speed InGaAs photodetector modules for detection of light of wavelengths 400 to 1650 nm All the models are 50 Q terminated An internal battery and bias circuitry make the modules self contained so that no additional power supplies or bias circuitry are needed To operate the modules follow these instructions 1 Take proper precautions to avoid electrostatic damage to the photodiode See the Handling Precautions above 2 Remove module from its case 3 Turn on power using the Off On switch QUICK START Perform steps 4 5 and 6 if using the detector for the first time or you wish to check the battery and DC offset 4 5 Connect a voltmeter to the Bias Monitor SMA connector Press Batt Chk button The voltage should be at least 3 5 V Release the Batt Chk button Without an optical input the voltage should be less than 10 mV Connect the photodetector module to your measurement instrument being careful not to over torque the K connector The instrument must have a 50 Q input impedance Check that the optical power emerging from your fiber is below the Max Pulse Power or cw Saturation Power as appropriate see the Detector Characteristics section of this manual to ensure detector linearity and to avoid detector damage Connect your optical fiber to the connector on the detec
10. ons Prentice Hall Inc Englewood Cliffs NY 1984 110 v APPENDICES 11 APPENDIX 2 USING THE CORRECT MICROWAVE CONNECTOR The performance you obtain from the Model 14XX photodetector modules will depend largely on the instrument you use to mea sure its microwave output and how the connection is made to this instrument The male connector of the photodetector module should be connected directly to the female connector of the instrument If an intervening coaxial cable is used care must be exercised in selecting a cable that has sufficiently low loss in the frequency range of interest Even if a coaxial cable is not used performance can be degraded if an improper adapter is chosen for mating to the instrument Common SMA connectors for example are intended for use to only 18 GHz Table 2 is a list of a few con nectors and the frequency range in which they may be used Table 2 Common RF connectors and the corresponding frequency ranges in which they are useful Connector Type Frequency Range Compatibility BNC DC 18G Wiltron 3 5 mm Z New Focus also offers the following products Model 1224 Female V to Male K Model 1225 Male SMA to Female BNC Model 1226 Female SMA to Male BNC Model 1227 40 GHz Flex Cable Female K to Male K APPENDICES APPENDIX 3 INSIDE THE PHOTODETECTOR MODULE Inside the photodetector module is a gold plated microwave housing that contains the high frequen
11. rticles that might be blocking the input light If more cleaning is needed proceed with steps 3 8 3 Wear a grounding strap 4 Remove the two screws on the back panel with a Phillips screwdriver Remove the back panel 5 Remove the two screws on the bottom of the detector using an Allen key 1 16 or 1 5 mm and carefully slide the detector housing off Steps 6 8 Be extremely careful not to pull on the fiber Stress applied to the fiber where it attaches to the microwave hous ing can cause the fiber to misalign from the photodiode resulting in degraded detector performance 6 Carefully disconnect the fiber connector from the fiber receptacle attached to the front panel of the detector 7 The front surface of the fiber can be cleaned using acetone or alcohol and lens tissue 8 Carefully reconnect the fiber to the front panel receptacle re install the detector housing be careful not to pinch or damage the fiber and re install the back panel 15 fu DETECTOR CHARACTERISTICS Wavelength Range 950 1650 nm 400 1650 nm 950 1650 nm 400 1650 nm multimode versions 950 1650 nm 550 1330 nm 950 1650 nm 550 1330 nm Max Full Width at Half Maximum 5 195 Ps Min 3 dB Bandwidth 25 GHz 25 GHz Electrical zz Single mode Specify the 50 option for a 50 micron core multimode fiber a et 3 D a 5 A 2 0 2m Power Max Pulse Power 10
12. tor module 10 When finished using the module turn off power to preserve battery life If any of these steps present problems or you would like more information please consult the remainder of this manual 0 INTRODUCTION Ultrahigh speed measurements are easy with the Models 141X 143X 144X and 145X high speed photodetector modules These modules convert your optical signals to electronic signals in effect g an optical input The modules are connected directly to the test iving every high speed high frequency instrument in your lab instrument or amplifier eliminating the need for coaxial cables fol lowing the photodetector which can seriously distort picosecond pulses and attenuate microwave signals The optical signal is delivered to the Schottky photodiode in the module through a single mode or multi mode optical fiber Moreover the photodi ode bias circuit and battery are self contained eliminating the hassle of external power supplies and expensive bias networks and reducing the possibility of photodiode damage due to over voltage New Focus offers a total of eight models allowing you to match your wavelength of interest and the connector style of your instru mentation The Models 141X and 144X are high speed InGaAs photodetector modules for detection of light of wavelengths 950 to 1650 nm and the Models 143X and 145X are also high speed InGaAs photodetectors designed for 400 1650 nm operation Mod
13. wave Connection Connect the microwave output connector of the photodetector module to a 50 Q input test instrument such as an oscilloscope or spectrum analyzer or other 50 Q load using the proper torque To avoid connector damage and signal distortion be sure that the instrument you intend to connect to the module has a compatible connector See Appendix 2 Using the Correct Microwave Connector for a list of connector compatibilities Aligning the Photodetector to the Optical Input To avoid signal distortion the optical fiber used to deliver the optical signal to the photodetector module should be single mode at the operating wavelength and the cable length should be no longer than necessary OPERATION 1 If you do not currently have an ST or FC terminated optical fiber use either a pigtail assembly or a fiber collimator see Table 1 and align the fiber so that light exits the output fiber connector With a pigtail assembly use a fiber aligner such as the Model 9091 and its accessories with a collimator use the Model 9854 Opti Claw or the Model 9016 tiny fiber positioner 2 Measure the power in the fiber prior to connection to the module to be sure it is within the safe operating range see the Detector Characteristics section of this manual The Models 20X1 FC and 20X1 ST are useful for this purpose and have the sensitivity to aid in fiber alignment 3 Connect the fiber optic cable to the fiber optic input on the d
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