Sensitivity and Signal to Noise Ratio Improvement of a One Micron Ladar System Incorporating a Neodymium Doped Optical Fiber Preamplifier. Laser Radar Testbed.

摘要

In an effort to increase the signal to noise ratio of a continuous wave, one micrometer all solid state ladar system, a rare earth doped optical fiber amplifier has been investigated as a preamplifier for ladar return signals. This details the experimental system used and provides a theoretical analysis of the fiber amplifier's effect on heterodyne and direct detection. The SNR is plotted as a function of the return signal power, and a SNR threshold defines a minimum detectable signal power. The return signals required to attain the SNR threshold are compared for four cases: direct detection with and without the fiber amplifier, and heterodyne detection with and without the fiber amplifier. For direct detection, these results predict a sensitivity increase of 21.0 dB, yet for heterodyne detection the predicted sensitivity increase is only 4.0 dB. These SNR equations are then used to predict experimental improvements of 42.0 dB and 4.0 dB for the direct detection and heterodyne detection experiments, respectively. Experimentally measured increases in SNR are then compared to these predictions. Specifically, for direct detection a SNR increase of 36.5 dB has been measured, and for heterodyne detection the experimental work yielded an increase of 8.0 dB. Ladar, Lidar, Fiber Amplifier, SNR.