Continuously Operating Laser Range Finder Based on Incoherent Pulse Compression: Noise Analysis and Experiment

A continuously operating laser range-finder setup based on the incoherent compression of periodic binary unipolar sequences is analyzed and demonstrated experimentally. The periodic cross-correlation between the directly detected echoes and a properly chosen reference sequence exhibits perfect zero sidelobes. An approximate analytic model for the peak-to-noise-sidelobe ratio in the presence of additive detector noise is established. Tradeoffs among transmitted power, measurement range, aperture size, and acquisition time are addressed. Performance is compared against that of time-of-flight measurements, and scenarios in which each protocol is advantageous are discussed. Outdoor ranging measurements at a distance of 270-m and with a ranging resolution of 15 cm are reported. The range to a Lambertian reflector target at that distance could be measured using a peak transmission power of only 800 mW, at a low signal-to-noise ratio (SNR) of -25 dB and with an acquisition time of 50 mu s.