In this study, to achieve high-speed, high-sensitivity, and low-cost laser communication, we optimized and improved a new InGaAs/InP single-photon avalanche diode (SPAD) to better apply to the near-infrared laser communication system detected using a single single-photon detector (SPD). Compared with the previous generation, we added a dielectric-metal reflective layer and improved the double Zn diffusion process while optimizing the structure of each layer. The fabricated InGaAs/InP SPAD achieved a photon detection efficiency (PDE) of 30%, a dark count rate (DCR) of 3 kHz, and an afterpulsing probability (P-ap) of 2. 4% under a high-frequency sine-wave gate (SWG) operating mode with a frequency of 1. 25 GHz, temperature of 225 K, and bias of 6 V. A free-running negative feedback avalanche diode (NFAD) prepared based on the high-performance SPAD was used as a receiver in the real-time spatial laser communication system. The performance parameters of the laser communication system with the NFAD were experimentally obtained. The experimental results show that the InGaAs/InP NFAD with a bit rate of 1 Mbit/s using the 4-pulse position modulation (4PPM) scheme has a bit error rate of 1. 1x10(-5) and sensitivity of -69. 6 dBm.

Free-running InGaAs/InP single-photon detectors (SPDs) based on negative-feedback avalanche diodes (NFADs) are the key components for applications requiring asynchronous single-photon detection in the near-infrared region. From the perspective of practical applications, the features of SPDs in terms of high photon detection efficiency (PDE), low noise, large sensitive area, and compactness are highly desired for system integration and performance enhancement. Here, we present the implementation of a compact four-channel multimode fiber coupling free-running InGaAs/InP SPD, with the best overall performance to date. On the one hand, we design and fabricate structure-optimized InGaAs/InP NFAD devices with 25 $\mu$m diameter active area and integrated thin film resistors to enhance the maximum achievable PDE. On the other hand, we apply a compact thermoacoustic cryocooler to regulate the operating temperature of NFADs within a large range, and design a dedicated readout circuit with minimized parasitic parameters and tunable settings of hold-off time to suppress the afterpulsing effect. The SPD is then characterized to achieve remarkable overall performance simultaneously at 1550 nm, i.e., 40% PDE, 2.3 kcps dark count rate, 8% afterpulse probability and 49 ps timing jitter (full width at half maximum) under the conditions of 5.9 V excess bias voltage, 10 $\mu$s hold-off time and 213 K operation temperature. Such performance and the results of the long-term stability tests indicate that the SPD could be a favorable solution for practical applications.