We demonstrate a high-performance acousto-optic modulator-based bi-frequency interferometer, which can realize either beating or beating free interference for a single-photon level quantum state. Visibility and optical efficiency of the interferometer are (99.5±0.2)% and (95±1)%, respectively. The phase of the interferometer is actively stabilized by using a dithering phase-locking scheme, where the phase dithering is realized by directly driving the acousto-optic modulators with a specially designed electronic signal. We further demonstrate applications of the interferometer in quantum technology, including bi-frequency coherent combination, frequency tuning, and optical switching. These results show the interferometer is a versatile device for multiple quantum technologies.

In an acousto-optic modulator, the electrode shape plays an important role in performance, since it affects the distribution of the acoustic field. The acousto-optic modulator based on the conventional rectangular electrode has the problems of low energy efficiency and small modulation bandwidth due to an imperfect acoustic field. In this paper, a new serrated periodic electrode has been proposed for using acousto-optic modulator transducers. The proposed electrode has the following advantages. By using serrated periodic electrodes to suppress the sidelobes, the collimation of the acoustic field in the direction perpendicular to the light incidence is improved. This makes the acousto-optic modulator have a stable diffraction efficiency fluctuation and high energy efficiency. In addition, the electrode has a large divergence angle in the direction of light incidence, so a large bandwidth can be obtained. The simulations and experiments demonstrate that the serrated periodic electrode has an increased bandwidth and high energy efficiency.

传统光时域反射仪（OTDR）技术是通过背向瑞利散射功率来进行光纤检测的，在带有光中继放大的传输线路中，大多采用掺铒光纤放大器（EDFA）来补偿信号光的损耗，延长信号光的传输距离，由于EDFA在对信号进行放大的同时会产生自发辐射噪声，噪声的不断累积会使OTDR测量的信噪比快速下降，导致无法测量。文章主要阐述了相干光时域反射仪（C-OTDR）的技术原理，通过相干探测方法把探测到的信号光功率集中到中频，通过对该频率信号进行带通滤波即可滤除大部分噪声，使其能穿过EDFA不断延伸探测距离。文章同时提出采用频移键控方式来消除海缆长距离传输多级中继器级联带来的光浪涌问题，以便将其应用于海缆长距离传输系统中。通过自研C-OTDR研制，在模拟海缆多跨传输系统中，C-OTDR技术的实际测试达到3 000 km，完全具备实用条件。

基于声光调制器作为反馈器件设计了原子钟常用波段780 nm激光器的功率锁定构型。通过低噪声设计和参数优化实现了关键噪声源的抑制和激光器功率锁定。实验结果表明，在20~10 000 Hz频偏范围内，激光的相对强度噪声得到有效抑制。尤其在1 300 Hz频率处，RIN抑制达到20 dB。同时，中期（9 000 s）功率相对稳定性由±0.754%提升78倍至±0.009 68%。根据CPT原子钟的典型参数，激光相对强度噪声对原子钟频率稳定度影响仅为2.1×10^–14@1 s。另外，中期稳定度由无锁定情况下的4.67×10^-2提高到锁定状态下的8.67×10^-5，得到了较好的改进，有利于改善原子钟中期频率稳定度。