Kilometre-range, high resolution depth imaging using 1560 nm wavelength single-photon detection

Single-photon time-of-flight ranging offers shot-noise limited detection and excellent surface-to-surface resolution. Infrared operation is advantageous in terms of improved eye safety and reduced solar background. Despite a number of recent advances in semiconductor infrared single photon detectors [1] little is available in the open literature in terms of long-range single-photon depth imaging. Previously, superconducting nanowire single photon detectors were used for ranging [2] from cooperative targets, however, we present recent depth imaging measurements using a state-of-the-art scanning time-of-flight system which has made measurements on non-cooperative targets in bright daylight conditions. This system was based on time-correlated single-photon counting (TCSPC), employing a 1560 nm source (50 MHz mode-locked fibre laser with a pulse width of <;1 ps) and a superconducting nanowire single-photon detector (SNSPD). We employed a niobium titanium nitride SNSPD on an oxidized silicon substrate, which formed a resonant optical cavity to achieve improved detection efficiency at telecom wavelengths [3]. The SNSPD was coupled using single-mode telecommunications optical fibre (9 μm diameter core) and mounted inside a closed-cycle refrigerator at an operating temperature of ~3 K [4]. Output pulses from the SNSPD were amplified at room temperature and routed to the TCSPC module. The SNSPD system detection efficiency is 17.5% at a wavelength of 1560 nm when biased for 1 kHz dark count rate. The overall system timing jitter was ~100 ps full-width at-half-maximum (FWHM). Depth profiling measurements were successfully performed under bright daylight conditions on a variety of targets. Field trial results are shown in Fig. 1. Uniquely, the performance of the system enabled a 1 mrad field-of-view depth profile movie of a moving object to be recorded at a standoff distance of 325 meters using a pixel dwell time of 1 ms. We will present the centimetre resolution depth profile movie, which was captured at 10 frames per second, each frame having 10 × 10 pixels.