OPTICAL-FIBER PREAMPLIFIERS FOR LADAR DETECTION AND ASSOCIATED MEASUREMENTS FOR IMPROVING THE SIGNAL-TO-NOISE RATIO

In an effort to increase achievable postdetection signal-to-noise rati os (SNRs) of continuous-wave, 1-mu m all-solid-state radar systems, a prototype rare-earth-doped optical-fiber amplifier has been included i n the optical return signal path of both a heterodyne and a direct det ection ladar system. We provide numerical predictions for SNR increase s according to our previously developed theory. We also detail our exp erimental efforts and provide the results of SNR measurements for four distinct cases: direct radar detection with and without a fiber ampli fier, and heterodyne ladar detection with and without a fiber amplifie r. Experimentally measured increases in SNRs for ladar systems incorpo rating an optical-fiber amplifier are then compared with our earlier p redictions. Specifically, we have found that for direct detection with a fiber amplifier in place, the predicted SNR increase is 42.0 dB, an d we have measured an increase of 36.5 dB. Similarly, for heterodyne l adar detection with a fiber amplifier, the predicted SNR increase is 3 .8 dB, and we have measured an increase of 8.0 dB.