Ranging performance of a SWIR laser rangefinder using a free-running InGaAs/InP single-photon avalanche diode detector

We demonstrate the use of a free-running InGaAs/InP single-photon avalanche diode (SPAD) as the detector for a laser rangefinder (LRF). The bi-static LRF employs a laser with a wavelength of 1550 nm coupled to the transmit channel, and a receive channel fibre-coupled to the SPAD detector. The range measurement is based on the Time-Correlated Single-Photon Counting (TCSPC) technique with the Time-of-Flight (ToF) of the transmitted pulses being stored in a timing histogram. This has a time window of 134 µs, allowing a full detection range of up to ~ 20 km, with a distance resolution of ~ 30 cm. Due to its single-photon detection capabilities, the LRF can obtain long-range measurements in sub-second acquisition times using pulse energies as low as nano-Joules, requiring an average of 9 detected photons per target to achieve over 99% success rate. Here, we present the false alarm rate analysis of the SPAD detector based LRF. We also provide examples of range measurements of non-calibrated targets at distances of up to 18.9 km, using periodic pulses, as well as pseudo-random pulse patterns with a maximum average optical power of 9.8 mW and pulse energies between 3 nJ and 1.3 μJ.