We demonstrate a portable system integrated with time comparison, absolute distance ranging, and optical communication (TRC) to meet the requirements of space gravitational wave detection. A 1 km free-space asynchronous two-way optical link is performed. The TRC realizes optical communication with 7.7×10-5 bit error rate with a Si avalanche photodiode single-photon detector, while the signal intensity is 1.4 photons per pulse with the background noise of 3×104 counts per second. The distance measurement uncertainty is 48.3 mm, and time comparison precision is 162.4 ps. In this TRC system, a vertical-cavity surface-emitting laser diode with a power of 9.1 µW is used, and the equivalent receiving aperture is 0.5 mm. The TRC provides a miniaturization solution for ultra-long distance inter-satellite communication, time comparison, and ranging for space gravitational wave detectors.

We demonstrate a multi-channel pseudo-random coding single-photon ranging system. A pseudo-random multiplexing technique is proposed, which realizes multi-channel pseudo-random ranging only by using one single-photon detector and processing circuit. Compared with the time division multiplexing technique, it will not reduce the maximum unambiguous range while increasing the number of the ranging channel. Eight-channel pseudo-random coding single-photon ranging was realized with the ranging accuracy better than 2 cm. Moreover, photon counting imaging was realized through scanning the laser beams of the eight-channel pseudo-random ranging system. There is no crosstalk between channels, which is suitable for multi-beam long-distance single-photon Lidar.

We report a method to reduce the detection delay temperature drift for a single-photon detector based on the avalanche photodiode (SPAD). Both the SPAD and the comparator were temperature stabilized, resulting in an ultra-low temperature drift at 0.01 ps/°C. A stable time deviation as 0.15 ps over 1000 s was realized, while the ambient temperature fluctuated rapidly from 24°C to 44°C. To the best of our knowledge, this is the first report on the ultra-stable delay SPAD detector in the case of rapid increase or decrease of ambient temperature. It is helpful to improve the stability of onboard detectors for optical laser time transfer between ground and space.

Solar-blind ultraviolet detection is of great importance in astronomy and industrial and military applications. Here, we report enhanced solar-blind ultraviolet single-photon detection by a normal silicon avalanche photodiode (Si APD) single-photon detector with a specially designed photon-collecting device. By re-focusing the reflected photon from the Si chip surface on the detection area by the aluminum-coated hemisphere, the detection efficiency of the Si APD at 280 nm can be improved to 4.62%. This system has the potential for high-efficiency photon detection in the solar-blind ultraviolet regime with low noise.