基于微腔光梳的低噪声微波合成

Low-noise microwave synthesis based on microcombs

光学频率梳(简称光频梳或光梳)能够实现光波和微波的直接连接,自其发明以来深刻影响了精密测量与激光技术的发展.传统光频梳基于固体或者光纤锁模激光器,而基于高品质因数光学微腔非线性四波混频效应产生的微腔光频梳是近年来实现的一类新型光频梳.相比于传统光频梳,微腔光频梳具有尺寸小、功耗低、集成化程度高和重频范围大等优势.微腔光频梳可广泛应用于精密测量、微波光子学等领域,吸引了科学界和工业界越来越多的关注.在微波光子学领域,基于光梳合成的微波具有比直接电学合成的微波更优越的噪声性能,同时微腔光频梳集成化程度高的优势使得基于微腔光梳的低噪声微波合成成为研究热点.本文综述了基于微腔光梳合成低噪声微波的方法与现状,并对这一领域的未来发展方向进行了展望.

Microwave technology has played a pivotal role in advancing global science and technology,profoundly impacting human life over the past few centuries.The evolution of microwave technology has not only enabled wireless communication,transforming interpersonal interaction and catalyzing the emergence of mobile internet technology,but also opened up new frontiers in radio astronomy and precision measurement,among other fields.In contemporary applications,there is a growing demand for low-noise,high carrier frequency microwaves.This poses a challenge for traditional electrical microwave synthesis methods to meet these requirements effectively.However,the innovative approach of microwave photonics provides a solution,where low-noise microwave signals are generated through the beat signal of optical components.The core of microwave photonics is the utilization of optical frequency combs(OFC),serving as a key component that establishes a direct link between optical and microwave frequencies.Microwaves synthesized by downconversion of ultra-stable optical frequencies based on traditional optical frequency combs typically exhibit ultra-low noise.However,the generation of traditional optical frequency combs often relies on solid-state or fiber mode-locked lasers,which are characterized by large volume and high power consumption.These factors have hindered the large-scale application of traditional optical frequency comb-synthesized microwaves,confining them to laboratory settings.Recently,a groundbreaking class of optical frequency combs has emerged to address the longstanding challenges—Microcombs.Microcombs are generated through the non-linear four-wave mixing effect in high-quality factor microresonators.In the time domain,they achieve mode-locking by forming dissipative temporal solitons through a delicate balance of dispersion and nonlinearity,as well as gain and loss.In comparison to their traditional counterparts,microcombs offer several advantages,including small size,low power consumption,high integration capabilities,and a wide range of repetition rates.These features make microcombs highly attractive for applications in precision measurement and microwave photonics,garnering increasing attention from both the scientific and industrial communities.Leveraging the high integration advantages of microcombs,low-noise microwave synthesis has emerged as a prominent and active research area.Microcombs can be utilized to directly synthesize microwaves or by means of optical frequency division.In the direct synthesis of microwaves using microcombs,employing techniques like quiet point operation and injection locking becomes crucial to suppress the repetition frequency noise of microcombs,ensuring the generation of lower-noise microwave signals.On the other hand,when employing the optical frequency division method,a common practice is the use of two-point locking to simplify the system.Additionally,the common mode suppression effect is utilized to suppress the relative frequency noise of the two lasers.This paper aims to provide a comprehensive overview of the methodologies and current status of low-noise microwave synthesis based on microcombs,offering insights into its potential and future development.