1417 & 1437 Rev B (Page 20)
Contents
1. 2x 8 32 M4 lt 3 Type K connector mounting holes Connecting wire to bias supply not shown Photodetector Module For connection to tiny detector Nd oF N Bias monitor port Output is equal to photodiode current times 1000 Ohms for one millivolt per microamp 3 03 76 9 Battery check button When depressed bias 0 72 18 3 m voltage is applied to bias monitor port T E 0 75 19 0 aJ Power switch ey ay 0 84 21 3 NJ Battery cover screws 1 NET 2x 1 4 20 M6 a0 e Thread far side Bias Supply Operation Vv NOTE Prior to handling New Focus detectors we recommend you ground yourself to prevent elec trostatic damage Checking the battery and offset voltage 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 SMB 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 4 Release the Batt Chk button and observe the voltage level on the voltmeter This voltage is the DC offset plus dark current This dark voltage should be less than 10 mV 5 Keep the voltmeter connected to the module while optimizing the optical coupling to the detecto2. and reducing the possibility of photodiode damage due to overvoltage New Focus offers two direct illumination models to match your wavelength and bandwidth requirements Table 1 pg 6 lists each model s characteristics In the Models 1417 and 1437 the InGaAs Schottky photodiode is located in the center of the glass window near the K connector output For proper microwave performance the optical beam must be focused on the 25 pm Schottky diode Fig 1 pg 7 shows the front and back of the photodetector mod ules You can significantly improve the minimum detectable optical signal by using a broadband amplifier such as the Model 1421 or Model 1422 5 Table 1 Models 1417 and 1437 modules Vv 1417 1437 Wavelength nm Min 950 400 Max 1650 1650 Bandwidth GHz Min 25 25 Photodetector Material InGaAs InGaAs Microwave Connector K K Full width at half max impulse response can be estimated from pulse width in picoseconds 400 bandwidth in GHz K Connector is a trademark of Wiltron Co Vv Fig 1 Front side and rear views of Models 1417 and 1437 photodetector modules 0 218 5 53 0 18 4 5 distance flat ik from mounting M l hole center to 0 50 075 __ 0 185 4 69 detector center 12 7 19 1 I window to detector aoe iie rt 030107 8 f 0 30 0 76 window thickness 4 2 f 0 75 m a 19 1 it 0 31 0 31 8 0 8 0
3. Models 1417 and 1437 User s Manual High Speed Photodetector Modules Vv Handling Precautions 141702 Rev B 2 Vv The detector is sensitive to electrostatic discharges and could be permanently damaged if subjected even to small discharges Prior to handling the detector or making connections be sure to ground yourself adequately A ground strap pro vides the most effective grounding and minimizes the likelihood of electrostatic damage v Is a registered trademark of New Focus Inc Warranty Vv New Focus Inc guarantees its products to be free of defects for one year from the date of ship ment This is in lieu of all other guarantees expressed or implied and does not cover inci dental or consequential loss Contents Handling Precautions Warranty Introduction Operation Appendix 1 Focusing on the Detector Appendix 2 Using the Correct Microwave Connector Appendix 3 Inside the Photodetector Module Specifications References Vv oO MN Ww N 12 14 16 18 20 Vv Introduction The Models 1417 and 1437 high speed photo detector modules convert your optical signals to electronic signals in effect giving every high speed high frequency instrument in your lab an optical input High speed measurements are easy with these modules The photodiode bias circuit and battery are self contained eliminating the hassle of external power supplies and expensive bias networks
4. and the corresponding frequency ranges in which they are useful Connector Type Frequency Range Compatibility BNC DC 2 GHz SMA DC 18 GHz Wiltron K Wiltron K DC 40 GHz SMA 2 4mm DC 55 GHz Wiltron V Wiltron V DC 65 GHz 24mm ew Focus also offers the following products odel 1224 Female V to Male K odel 1225 Male SMA to Female BNC odel 1226 Female SMA to Male BNC odel 1227 40 GHz Flex Cable Female K to Male K 15 16 Appendix 3 Inside the Photodetector Module Vv Inside the photodetector module is the gold plated microwave housing that contains the high fre quency circuitry A simplified schematic is provided on page 17 for your reference Vv Fig 3 Simplified schematic diagram of the Models 1417 and 1437 photodetector modules Photodetector Mi icrowave Output Connector VW gt Bias Monitor Batt Chk yt On Off Socket Ws rear panel v l V v Ww j vifi 17 v Model 1417 Specifications 18 Conversion Gain photodiode responsivity x 25 Q 50 Q internal in parallel with 50 Q external Frequency Response Max Safe Optical Power Limit of Linear Operation Max Pulse Power Bias Monitor DC Gain DC Offset Output Impedance Bandwidth Battery Battery Battery Life See enclosed data sheet accuracy 1 5 dB 5 mW average 2 mW average 100 mW 1 mV pA of phot
5. gnals off much longer than they are on the voltmeter reading will be too low to be useful unless used with a chopper wheel and a lock in ampli fier The bandwidth of the bias monitor output is high enough for use with a lock in and chopper wheel Method 2 Projection Follow the first two steps in Method 1 except place an optical flat before the lens where the optical beam is well collimated See Fig 2 pg 13 Remember that a fairly good optical quality flat is required since it will introduce aberrations which may limit your focusing ability p 2 Place the flat at an angle so that you can conve niently observe the reflection from the photodi ode surface on a white piece of paper 3 Bring the module into focus so that you get a clear image Refering to the illustration in Fig 2 pg 13 center the photodetector in the image and move the module so that the illuminated area and the image becomes smaller At this point you should have a signal on the voltmeter 4 Follow steps 4 5 from Method 1 Note As the signal is being optimized attenuation should be added to the optical beam to prevent the photodetector output from exceeding 0 5 V peak or 0 05 V average 15 dBm RF power out 11 Focusing on the 12 Vv The Models 1417 and 1437 consist of a 25 um diameter photodetector For optimal performance the spot size of the optical beam striking the detec tor should be 20 pm Tighter beam focus will resu
6. lt in excessive optical power density Loose beam focus will result in reduced detector efficiency and bandwidth degradation For a diffraction limited Gaussian beam the focal length of the focusing lens should be d D an f where f is the focal length d is the focused beam diameter 20 pm D is the diameter of the colli mated beam striking the lens and A is the optical wavelength v Fig 2 Using a good optical flat project the reflected image onto a sheet of paper Note The 1417 chip is mounted upside down so the front side is visible only with gt 950 nm illumination Alumina Y Photodiode 4 InGaAs 13 Vv Appendix 2 Using the Correct Microwave Connector The performance you obtain from the Models 1417 and 1437 photodetector modules will depend largely on the instrument you use to measure their microwave output and how the connection is made to the instrument 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 exam ple are intended for use to only 18 GHz Table 2 lists a few connectors and the frequency ranges in which they may be used For more information request Application Note 1 Table 2 Vv Common RF connectors
7. ocurrent lt 10 mV 1kQ 50 kHz 9 V alkaline approx 500 hours v Model 1437 Specifications Conversion Gain photodiode responsivity x 25 Q 50 Q internal in parallel with 50 Q external Frequency Response See enclosed data sheet accuracy 1 5 dB Max Safe Optical Power 10 mW average Limit of Linear Operation 10 mW average Max Pulse Power 200 mW Bias Monitor DC Gain 1 mV pA of photocurrent DC Offset lt 10 mV Output Impedance 1kQ Bandwidth 50 kHz Battery Battery 9 V alkaline Battery Life approx 500 hours 19 Vv References 1 Siegman S E Lasers University Science Books Mill Valley CA 1986
8. placing the detector in the optical beam ensure that the optical power is within spec ified limits pp 18 19 1 Position the module on an x y adjustment stage in front of the focusing lens For a discussion on how to choose a proper lens see Appendix 1 Focusing on the Detector pg 12 2 Once the module has been roughly positioned in front of the lens and all of the RF connections have been made connect a voltmeter to the Bias Monitor output and turn it on The volt age displayed when no light is striking the detec tor is an electrical offset voltage and dark cur rent This dark voltage should be less than 10 mV 3 With the detector slightly out of focus so as to increase the spot size in the plane of the detector move the detector slowly back and forth while watching the voltmeter reading Note As the signal is being optimized attenuation should be added to the optical beam to prevent the photodetector output from exceeding 0 5 V peak or 0 05 V average 15 dBm RF power out 4 The moment the voltmeter reading increases by 5 mV or more stop the coarse adjustment and use a fine adjustment screw to adjust x y posi tion and focus to maximize the voltage reading Vv A voltage reading above 200 mV should be suffi cient for observation of cw signals on a spectrum analyzer 5 As soon as the actual RF signal is observable this should be optimized instead of the voltmeter reading With very low duty cycle si
9. r Replacing the battery 1 Turn off the module and remove the two screws on the battery cover with a Phillips screwdriver See Fig 1 pg 7 2 Remove the battery cover 3 Replace the battery and battery cover 4 Check the battery level as described above Vv Microwave connection and set up 1 Due to the small size of the detector active area you will need to bolt the detector housing to a fine positioning device such as the New Focus Models 8062 or 9062 or any x y adjustment stage that is compatible with 8 32 M4 screws 2 Plug the bias cable on the detector housing into the microconnector on the rear of the bias hous ing 3 Connect the microwave connector of the pho todetector module to a 50 Q input test instru ment such as an oscilloscope or spectrum ana lyzer or other 50 Q load using the high fre quency cable To avoid connector damage and signal distortion be sure that the cable and the instrument you intend to connect to the module have compatible connectors See Appendix 2 Using the Correct Microwave Connector pg 14 for a list of connector compatibilities Model 1227 male to female K connector cables are available from New Focus to simplify this matter 4 Turn the power switch to On 5 Connect the Bias Monitor to a voltmeter Check the battery level as described on page 8 9 10 Vv Aligning the Photodetector to the Optical Input Method 1 Defocusing Note Before
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