Li Hao-Jie, Qi Hong-Xing, Liang Xin-Dong, Zeng Li-Xiao, Yao Wei-Lai, Yang Yi-Chao, Wang Jian-Yu
Appl Opt. 2022 Aug 10;61(23):6915-6923. doi: 10.1364/AO.462411.
We developed a digital optical phase locking loop (OPLL) with three advantages, including high precision of phase locking, high control bandwidth up to 2.8 MHz, and automatic laser locking strategy. Spaceborne laser interferometers will be used to measure tiny displacements caused by gravitational waves in millions of kilometers range. A slave laser will be heterodyne phase locked to the incoming weak light at the end of an arm, emitting a higher power light back to the other satellite to measure pathlength variations at the picometer level. Such accuracy requires extremely precise OPLL. We report an experiment to demonstrate a digital OPLL that can automatically lock two independent free-running Nd:YAG lasers with residual phase error below 1/ above 0.01 Hz, which is the best performance recorded for digital servos, to our knowledge. Such performance tested under a normal laboratory environment will be highly improved in a vacuum environment with temperature and vibration well controlled. Both the digital OPLL and the automatic strategy were implemented on a field programmable gate array that could be potentially used for future gravitational-wave detection. Our experiment might change the thinking of scientists who study phasemeters of gravitational-wave detection because we are aware that the digital phase locking loop used for "optical phase tracking" is differently designed from "optical phase locking."
我们开发了一种数字光学锁相环（OPLL），它具有三个优点，包括锁相精度高、高达2.8 MHz的高控制带宽以及自动激光锁定策略。星载激光干涉仪将用于测量数百万公里范围内由引力波引起的微小位移。在臂的末端，一个从激光器将与入射的弱光进行外差锁相，发射更高功率的光回到另一颗卫星，以测量皮米级别的光程变化。如此高的精度需要极其精确的OPLL。我们报告了一项实验，展示了一种数字OPLL，它能够自动锁定两台独立的自由运行的Nd:YAG激光器，在高于0.01 Hz时残余相位误差低于1/，据我们所知，这是数字伺服记录的最佳性能。在正常实验室环境下测试的这种性能，在温度和振动得到良好控制的真空环境中将得到极大提升。数字OPLL和自动策略都在现场可编程门阵列上实现，这可能会用于未来的引力波探测。我们的实验可能会改变研究引力波探测相位计的科学家们的想法，因为我们意识到用于“光学相位跟踪”的数字锁相环与“光学锁相”的设计不同。
