SENSITIVITY IMPROVEMENT OF A 1-MU-M LADAR SYSTEM INCORPORATING AN OPTICAL-FIBER PREAMPLIFIER

In an effort to increase the SNR of a continuous wave, 1-mu m all soli d state ladar system, a rare-earth-doped optical fiber amplifier is in vestigated as a preamplifier for radar return signals. The experimenta l system is detailed and a theoretical analysis of the fiber amplifier 's effect on both heterodyne and direct detection schemes is provided. Beginning with the optical powers incident on the detector, the signa l and noises are analyzed, through the detector electronics, to predic t the SNR. The SNR is then plotted as a function of the return signal power, and a SNR threshold is defined to determine a minimum detectabl e signal power. The return signals required to attain the SNR threshol d are then compared for four cases: direct detection with and without the fiber amplifier and heterodyne detection with and without the fibe r amplifier. For the direct detection scheme considered, our results p redict a sensitivity increase of 20.6 dB with the addition of the fibe r amplifier, yet for heterodyne detection the predicted sensitivity in crease is only 3.1 dB.