分析了多抖动算法的工作原理，通过波动光学原理以2-11路相干合成系统作为数学模型进行仿真模拟，引入了动态噪声模型，以总合成光束的均方根相位误差作为评价函数，分析了不同阵列规模下的相干合成系统中噪声频率以及噪声振幅对系统相位锁定效果的影响，当噪声频率或噪声振幅过大，超出算法补偿相位噪声的能力时，便会锁相失败。证明了增益系数与调制振幅存在一个最优区间且只有处于该区间内时，才能快速完成锁相。引入有效控制带宽概念，用以直观评价多抖动算法的锁相性能，研究表明，有效控制带宽与采样频率、第一路调制频率成正比例，与噪声振幅成反比例，且随着阵列规模增大，有效控制带宽降低。

Stable operation is one of the most important requirements for a laser source for high-precision applications. Many efforts have been made to improve the stability of lasers by employing various techniques, e.g., electrical and/or optical injection and phase locking. However, these techniques normally involve complex experimental facilities. Therefore, an easy implementation of the stability evaluation of a laser is still challenging, especially for lasers emitting in the terahertz (THz) frequency range because the broadband photodetectors and mature locking techniques are limited. In this work, we propose a simple method, i.e., relative phase locking, to quickly evaluate the stability of THz lasers without a need of a THz local oscillator. The THz laser system consists of a THz quantum cascade laser (QCL) frequency comb and a single-mode QCL. Using the single-mode laser as a fast detector, heterodyne signals resulting from the beating between the single-mode laser and the comb laser are obtained. One of the heterodyne beating signals is selected and sent to a phase-locked loop (PLL) for implementing the relative phase locking. Two kinds of locks are performed by feeding the output error signal of the PLL, either to the comb laser or to the single-mode laser. By analyzing the current change and the corresponding frequency change of the PLL-controlled QCL in each phase-locking condition, we, in principle, are able to experimentally compare the stability of the emission frequency of the single-mode QCL (f_s) and the carrier envelope offset frequency (f_CEO) of the QCL comb. The experimental results reveal that the QCL comb with the repetition frequency injection locked demonstrates much higher stability than the single-mode laser. The work provides a simple heterodyne scheme for understanding the stability of THz lasers, which paves the way for the further locking of the lasers and their high-precision applications in the THz frequency range.

We report a long-term frequency-stabilized optical frequency comb at 530–1100 nm based on a turnkey Ti:sapphire mode-locked laser. With the help of a digital controller, turnkey operation is realized for the Ti:sapphire mode-locked laser. Under optimized design of the laser cavity, the laser can be mode-locked over a month, limited by the observation time. The combination of a fast piezo and a slow one inside the Ti:sapphire mode-locked laser allows us to adjust the cavity length with moderate bandwidth and tuning range, enabling robust locking of the repetition rate (f_r) to a hydrogen maser. By combining a fast analog feedback to pump current and a slow digital feedback to an intracavity wedge and the pump power of the Ti:sapphire mode-locked laser, the carrier envelope offset frequency (f_ceo) of the comb is stabilized. We extend the continuous frequency-stabilized time of the Ti:sapphire optical frequency comb to five days. The residual jitters of f_r and f_ceo are 0.08 mHz and 2.5 mHz at 1 s averaging time, respectively, satisfying many applications demanding accuracy and short operation time for optical frequency combs.

报道了实验室内56 km光纤微波频率传递的实验研究，在56 km的传递距离上实现了1.8×10^-15/s，4×10^-18/10⁴s的传递稳定度。系统通过环回法比较往返传递的微波信号相位获得链路上的相位扰动量，并实时控制本地发射端的微波发射信号相位实现预补偿。在环回往返传递的不同方向上，系统方案采用不同频率的微波调制信号，这种方法极大避免了光寄生反射效应的影响，同时利用色散补偿光纤改善探测信号相噪等措施，提高了系统的传递稳定度。

We analyze a feasible high-sensitivity homodyne coherent optical receiver for demodulating optical quadrature phase-shift keying (QPSK). A fourth-power phase-lock loop based on a digital look-up table is used. Considering the non-negligible loop delay, we optimize the loop natural frequency. Without error correction coding, a sensitivity of ?37 dBm/?35 dBm is achieved, while the bit error rate is below 10^?9 at 2.5 Gbaud/5 Gbaud rate. For the QPSK communication system, the bit rate is twice the baud rate. The loop natural frequency is 0.647 Mrad/s, and the minimized steady-state phase-error standard deviation is 3.83°.