Research on the optimal optical attenuation in a laser radar using a Geiger-mode APD

摘要

For a laser radar (LADAR) system using a Geiger-mode avalanche photodiode (GmAPD), attenuating echo and background noise simultaneously affect the original data output from the GmAPD and eventually affect detection performance. In this study, we established a model that applies to the GmAPD-based LADAR with optical attenuation and also applies to any typical single photon detector that has a dead time (e.g., the photomultiplier tube); thus, a comprehensive and fundamental study is performed for the mathematical expectation of the number of signal detections (ES), the mathematical expectation of the number of noise detections (E-N), the signal-to-noise ratio (SNR), and the range bias (absolute error, R-b) and precision (standard deviation, R-p) under various attenuation levels with different dead times and signal noise conditions. We observed the following: on the one hand, there exists an optimum attenuation level at which E-S and SNR are maximized; on the other hand, there exists another optimum attenuation level for shorter dead times, at which R-p is minimized. The phenomenon of the maximum E-S, SNR, or minimum R-p disappears gradually as the echo or noise decreases from high levels (e.g., 10 photoelectrons/echo or an equivalent background noise of 10 photoelectrons/range gate). Further, higher attenuation, which shows advantages under strong echo or noise conditions, yields a larger improvement in E-S for longer dead times; and, with the reduction of the dead time or the noise, the maximum E-S gradually increases, and the corresponding optimum attenuation level becomes slighter. Additionally, we found that, as the optical attenuation increases, E-N decreases to 0, R-b changes from a negative value to 0, and R-p is minimized, becomes slightly worse, and reaches a constant. Moreover, the shorter dead times, which show advantages when they are shorter than the end time of the echo, lead to a larger E-S, better R-b, and slightly worse R-p than the longer ones. (C) 2018 Optical Society of America