The optical frequency comb serves as a powerful tool for distance measurement by integrating numerous stable optical modes into interferometric measurements, enabling unprecedented absolute measurement precision. Nonetheless, due to the periodicity of its pulse train, the comb suffers from measurement dead zones and ambiguities, thereby impeding its practical applications. Here, we present a linear group delay spectral interferometer for achieving precise full-range distance measurements. By employing a carefully designed linear group delay (LGD) device for phase modulation of the comb modes, interference can occur and be easily measured at any position. Our approach effectively eliminates the dead zones and ambiguities in comb-based ranging, without the need for cumbersome auxiliary scanning reference devices or reliance on complex high-repetition-rate combs or high-resolution spectrometers. We conducted length metrology experiments using a mode-locked comb referenced to a rubidium clock, achieving a large nonambiguity range up to 0.3 m, covering the entire measurement period. The maximum deviation compared to a laser interferometer was less than 1.5 μm, and the minimum Allan deviation during long-term measurements reached 5.47 nm at a 500 s averaging time. The approach ensures high accuracy while maintaining a simple structure, without relying on complex external devices, thereby propelling the practical implementation of comb-based length metrology.

The quantum key distribution (QKD) network is a promising solution for secure communications. In this paper, we proposed a polarization-independent phase-modulated polarization encoding module, and it can be combined with a dense wavelength division multiplexer (DWDM) to achieve multi-user QKD. We experimentally test the encoding module with a repetition rate of 62.5 MHz, and its average quantum bit error rate (QBER) is as low as 0.4%. Finally, we implement a principle verification test for simultaneous QKD for 1 to 2 users in 100 min, and the average QBER of two users under the transmission distance of 1 km and 5 km is kept below 0.8%. Due to the use of polarization encoding, the module can also realize scalable network architecture in free-space QKD systems in the future.

为降低可见光通信系统中的额外功耗，对可见光通信中发光二极管结电容充放电导致的额外功耗进行了理论分析，给出了通信速率、结电容和调制方式对额外功耗的影响.基于此，提出了新型的双电平脉冲宽度调制技术，从额外功耗、带宽需求和差错性能三方面对双电平脉冲宽度调制进行了理论分析，并与非归零开关键控调制、脉冲位置调制和数字脉冲间隔调制进行了对比。结果表明，双电平脉冲宽度调制和非归零开关键控调制误时隙率相同，但额外功耗仅为非归零开关键控调制的M/2，（M为调制阶数）；虽然相比于脉冲位置调制和数字脉冲间隔调制，双电平脉冲宽度调制需要更高的信噪比，但额外功耗仅为脉冲位置调制和数字脉冲间隔调制的1/2，带宽需求也小于脉冲位置调制和数字脉冲间隔调制，在功耗和带宽敏感的可见光通信系统中有较大优势。

Laser-based light detection and ranging (lidar) plays a significant role in both scientific and industrial areas. However, it is difficult for existing lidars to achieve high speed, high precision, and long distance simultaneously. Here, we demonstrate a high-performance lidar based on a chip-scaled soliton microcomb (SMC) that can realize all three specialties simultaneously. Aided by the excellent properties of ultrahigh repetition rate and the smooth envelope of the SMC, traditional optical frequency comb (OFC)-based dispersive interferometry is heavily improved and the measuring dead zone induced by the mismatch between the repetition rate of the OFC and resolution of the optical spectrum analyzer is totally eliminated. Combined with an auxiliary dual-frequency phase-modulated laser range finder, the none-dead-zone measurable range ambiguity is extended up to 1500 m. The proposed SMC lidar is experimentally implemented in both indoor and outdoor environment. In the outdoor baseline field, real-time, high-speed (up to 35 kHz) measurement of a long distance of ～1179m is achieved with a minimum Allan deviation of 5.6 μm at an average time of 0.2 ms (27 nm at an average time of 1.8 s after high-pass filtering). The present SMC lidar approaches a compact, fast, high-precision, and none-dead zone long-distance ranging system, aimed at emerging applications of frontier basic scientific research and advances in industrial manufacturing.