光电振荡器:从分立到薄膜铌酸锂光集成(特邀)

Optoelectronic Oscillator:From Discrete to Photonic Integration on Thin Film Lithium Niobate(Invited)

光电振荡器(OEO)可以产生高频、宽带可调、低相位噪声的射频(RF)信号,可应用于5G通信、雷达探测和传感等领域。OEO的基本结构主要包括激光器、调制器、储能介质、光电探测器、RF放大器和RF滤波器,实现低相位噪声的关键是高Q储能介质,例如低损耗的长光纤或者高Q因子的光学谐振腔。自姚晓天博士在1996年首次提出OEO至今,已经衍生出各种OEO结构,但它们大多都由分立器件组成,体积庞大、价格昂贵且使用不便。随着各种集成光学材料平台的成熟,小尺寸、低成本和更可靠的集成OEO成为可能,例如绝缘体上硅(SOI)OEO、磷化铟(InP)OEO和硫化物OEO等,但由于这些材料本身高损耗、非线性和温度敏感等特性,难以实现OEO所需的高性能电光调制器和高Q的储能介质,而薄膜铌酸锂(TFLN)由于宽透明窗口、大线性电光系数和低损耗特性在实现高性能的电光调制器和高Q微腔中已经得到广泛应用,有望实现高频、宽带可调、低相位噪声的RF信号。本文回顾过去30年从分立OEO到集成OEO的发展历程并展望未来集成OEO的发展前景。

Optoelectronic oscillators(OEOs)can generate high frequency,broadband tunable,and low phase noise radio frequency(RF)signals that can be applied in 5G communication,radar detection,and sensing.The basic structure of an OEO includes lasers,modulators,energy storage media,photodetectors,RF amplifiers,and RF filters.The key to achieve low phase noise is high-Q energy storage media,such as low loss long fibers or high-Q optical resonators.As Dr.Yao Xiaotian proposed OEOs in 1996,various OEO structures have emerged;however,a majority of these are composed of discrete devices,making them bulky,expensive,and inconvenient to use.With the development of various integrated optical material platforms,it has become possible to construct small-sized,low-cost,and more reliable integrated OEOs,such as silicon-on-insulator(SOI),indium phosphide,and chalcogenide OEOs.However,due to high loss,nonlinearity,and temperature sensitivity of these materials,it is difficult to achieve the high-performance electro-optic modulators and high-Q energy storage media required for OEOs.Consequently,thin-film lithium niobate(TFLN)has been widely used for achieving high-performance electro-optic modulators and high-Q microcavities due to its wide transparent window,large linear electro-optic coefficient,and low loss characteristics;thus,it achieves high frequency,broadband tunable,and low phase noise RF signals.This article reviews the development process of OEOs over the past 30 years,from discrete OEOs to integrated OEOs.It also discusses future development prospects of integrated OEOs.