Anti-aliasing techniques in photon-counting depth imaging using GHz clock rates

Nils J. Krichel; Aongus McCarthy; Robert J. Collins; Gerald S. Buller

doi:10.1117/12.850900

21 April 2010 Anti-aliasing techniques in photon-counting depth imaging using GHz clock rates

Nils J. Krichel, Aongus McCarthy, Robert J. Collins, Gerald S. Buller

Proceedings Volume 7681, Advanced Photon Counting Techniques IV; 768108 (2010) https://doi.org/10.1117/12.850900
Event: SPIE Defense, Security, and Sensing, 2010, Orlando, Florida, United States

Abstract

Single-photon detection technologies in conjunction with low laser illumination powers allow for the eye-safe acquisition of time-of-flight range information on non-cooperative target surfaces. We previously presented a photon-counting depth imaging system designed for the rapid acquisition of three-dimensional target models by steering a single scanning pixel across the field angle of interest. To minimise the per-pixel dwelling times required to obtain sufficient photon statistics for accurate distance resolution, periodic illumination at multi- MHz repetition rates was applied. Modern time-correlated single-photon counting (TCSPC) hardware allowed for depth measurements with sub-mm precision. Resolving the absolute target range with a fast periodic signal is only possible at sufficiently short distances: if the round-trip time towards an object is extended beyond the timespan between two trigger pulses, the return signal cannot be assigned to an unambiguous range value. Whereas constructing a precise depth image based on relative results may still be possible, problems emerge for large or unknown pixel-by-pixel separations or in applications with a wide range of possible scene distances. We introduce a technique to avoid range ambiguity effects in time-of-flight depth imaging systems at high average pulse rates. A long pseudo-random bitstream is used to trigger the illuminating laser. A cyclic, fast-Fourier supported analysis algorithm is used to search for the pattern within return photon events. We demonstrate this approach at base clock rates of up to 2 GHz with varying pattern lengths, allowing for unambiguous distances of several kilometers. Scans at long stand-off distances and of scenes with large pixel-to-pixel range differences are presented. Numerical simulations are performed to investigate the relative merits of the technique.

Citation Download Citation

Nils J. Krichel, Aongus McCarthy, Robert J. Collins, and Gerald S. Buller "Anti-aliasing techniques in photon-counting depth imaging using GHz clock rates", Proc. SPIE 7681, Advanced Photon Counting Techniques IV, 768108 (21 April 2010); https://doi.org/10.1117/12.850900

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