Avalanche photodiode (APD) questions
时间：04-06
整理：3721RD
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I'm planning to build a photodetector to sense the return photons of a laser beam reflection. It will be part of a rangefinder project, but for now it will be "standalone", catching reflected pulses with the APD through a transimpedance amplifier, into a programmable gain amplifier and into my oscilloscope.
I've been looking at different APDs and have not settled yet. Eye safe 1.5μm InGaAs devices seem so hideously expensive so I'm shooting for a sub-1μm Si-device, either something like a S2383 or possibly a S4315-02 if I can justify the ~5x price tag for built-in thermistor and peltier cooler.
I'm pretty blank at both APDs and optics, so I need a primer;
1) Pros and cons of a large photosensitive area
Larger dies have a larger dark current and terminal capacitance, and lower cut-off frequency. What are the pros of larger dies besides the fact they are easier to focus the light onto? Range is more important to me than speed/accuracy, will a larger photosensitive area provide better sensitivity?
2) Temperature sensing
Is the thermal coupling die-to-casing in an APD good enough that I'll get precise measurements slabbing a thermistor onto the casing, or is there an advantage having the thermistor integrated in the device and thus closer to the die?
3) Advantages of cooling
Simpler bias supply as I can temperature regulate the device instead of adjusting the bias over a huge range, but that's really just a practical benefit. Any performance benefits by operating the device at lower temperatures? How fast do these devices normally heat up?
4) Lens(es)
Will it do with a single plano-convex lens with the APD in it's focal point? To get optimum focus onto the APD, I was thinking of using a finely adjustable focus tube with set screw to lock it in position.
5) Optical bandpass filter
Looking at the optical filters at Edmund I have a hard time sorting out which bandpass filter would do best in my application. Am I simply looking for any filter with a narrow bandpass and high rejection outside its passband, or are there different types/properties I should know about and take into account?
Sincerely,
Kjetil
I've been looking at different APDs and have not settled yet. Eye safe 1.5μm InGaAs devices seem so hideously expensive so I'm shooting for a sub-1μm Si-device, either something like a S2383 or possibly a S4315-02 if I can justify the ~5x price tag for built-in thermistor and peltier cooler.
I'm pretty blank at both APDs and optics, so I need a primer;
1) Pros and cons of a large photosensitive area
Larger dies have a larger dark current and terminal capacitance, and lower cut-off frequency. What are the pros of larger dies besides the fact they are easier to focus the light onto? Range is more important to me than speed/accuracy, will a larger photosensitive area provide better sensitivity?
2) Temperature sensing
Is the thermal coupling die-to-casing in an APD good enough that I'll get precise measurements slabbing a thermistor onto the casing, or is there an advantage having the thermistor integrated in the device and thus closer to the die?
3) Advantages of cooling
Simpler bias supply as I can temperature regulate the device instead of adjusting the bias over a huge range, but that's really just a practical benefit. Any performance benefits by operating the device at lower temperatures? How fast do these devices normally heat up?
4) Lens(es)
Will it do with a single plano-convex lens with the APD in it's focal point? To get optimum focus onto the APD, I was thinking of using a finely adjustable focus tube with set screw to lock it in position.
5) Optical bandpass filter
Looking at the optical filters at Edmund I have a hard time sorting out which bandpass filter would do best in my application. Am I simply looking for any filter with a narrow bandpass and high rejection outside its passband, or are there different types/properties I should know about and take into account?
Sincerely,
Kjetil