HgCdTe APDs for free space optical communications

HgCdTe avalanche photodiode single element detectors have been developed for a large scope of photon starved applications. The present communication is dedicated to use of these detectors for free space optical communications. In this perspective we present and discuss the sensitivity and bandwidth that has been measured directly on HgCdTe APDs and on detector modules. In particular, we report on the performance of TEC cooled large area detectors with sensitive diameters ranging from 30- 200 μm, characterised by detector gains of 2- 20 V/μW and noise equivalent input power of 0.1-1 nW for bandwidths ranging from 20 to 400 MHz. One of these detectors has been used during the lunar laser communication demonstration (LLCD) and the results The perspectives for high data rate transmission is estimated from the results of impulse response measurements on HgCdTe APDs. These results indicate that bandwidths close to 10 GHz can be achieved in these devices. The associated sensitivity at an APD gain of 100 is estimated to be below 4 photons rms (NEP<10 nW) for APDs operated at 300 K.