Sensitivity analysis of an HgCdTe based photoconductive receiver for long-wavelength free space optical communication systems

In this paper we examine theoretically the performance of an optical receiver based on an Hg_0.77Cd_0.23Te photoconductive detector for its possible application at 9.6 mum free space optical communication system at moderate bit rate. A rigorous noise model of the receiver has been developed for this purpose. It is found that the mean square value of the total noise current of the photoconductive receiver is dominated at all bit rates B < 1 Gb/s by Johnson noise in the conductive channel. At bit rates -10 Gb/s and above, the FET channel noise current is found to be comparable to Johnson noise current and total noise overrides the Johnson noise. Our analysis reveals that the photoconductive receiver exhibits sensitivity of -50 dBm at a bit rate of 100 Mb/s and -45 dBm at a bit rate of lGb/s and total mean-square noise current = 10^-14 A² at a bit rate of 100 Mb/s and 10^-13 A² at bit rate of 1 Gb/s for a photoconductor gain of 10 and 3dB bandwidth of 120 MHz.