Comparison of linear-mode avalanche photodiode lidar receivers for use at one micron wavelength

Silicon avalanche photodiode (APD) detectors have been used in most space lidar receivers to date with a sensitivity that is typically hundreds of photons per pulse at 1064 nm, and is limited by the quantum efficiency, APD gain noise, dark current, and preamplifier noise. We have purchased and tested InGaAs avalanche photodiode based receivers from several US vendors as possible alternatives. We present our measurement results and a comparison of their performance to our baseline silicon APD. Using a multichannel scalar instrument, we observed undesired dark counts in some devices, even though the APDs were biased below the breakdown voltage. These effects are typically associated with over-biased Geiger-mode photon-counting, but we demonstrate that the probability distribution indicates their necessity at the high gains typically associated with operation slightly below the breakdown voltage. We measured the following parameters for our 0.8 mm diameter baseline silicon APD receiver: excess noise factor 2.5, bandwidth 210 MHz, minimum detectable pulse (10 ns) in incident photons 110 photons, noise equivalent power 30 fW/rt-Hz. We present our test procedures and results for the InGaAs based APD receivers.