基于光纤布里渊腔双波长激光的宽频、低相噪、长时稳频毫米波生成

Microwave photonics technology has great potential in the field of millimeter wave generation due to its unique properties such as high bandwidth and low transmission loss. Stimulated Brillouin Scattering (SBS)-based signal generation technique offers excellent phase noise suppression, but requires coherent pumping inputs, resulting in a limited frequency range over which millimeter wave can be generated. Moreover, there is a vacuum of study regarding investigating and improving the long term stability, which is another crucial aspect as it determines the practicability and reliability of the systems in the application of, for example, high-capacity wireless communication. This project aims at, on one hand, through two incoherent CW laser pumps, breaking the pumping input coherency restriction and increasing the frequency range of the generated signal. In the meantime, lowering the SBS threshold, increasing the energy efficiency and suppressing phase noise by deploying a fiber cavity. On the other hand, improving the stability of the generated millimeter wave in a large time scale through investigating and incorporating active frequency stabilization technique. This project is expected to generate millimeter wave signals with phase noise lower than -120dBc/Hz at 10kHz offset and frequency drift smaller than 100mHz, in the frequency range of 1-300GHz, realizing the synthesis of long-term stable, low phase noise, broad frequency range millimeter wave generation through SBS. In addition, the system enhancement by deploying the proposed millimeter wave generation method is planned to be verified through a preliminary wireless communication demonstration.

微波光子技术因其高带宽、低传输损耗等优点在高频毫米波生成方向拥有巨大的应用潜力。基于受激布里渊散射效应的微波光子毫米波生成技术有着良好的相噪压制效果，但由于其在泵浦光源相干性方面的要求而使信号生成的频率范围受限。同时由于对大时间尺度上的频率稳定度缺乏有效的控制，降低了这类技术在诸如超大容量无线通信等实际应用中的实用性与可靠性。因此本项目拟一方面通过使用两个互不相干的激光源，打破基于受激布里渊散射效应系统的泵浦相干性限制，产生双波长激光，显著扩大生成毫米波的频率范围，同时利用布里渊腔的结构降低激发阈值，提高能效并压制相噪；另一方面，引入光纤腔主动稳频技术，大幅提高生成毫米波的长时频稳度。力争在1-300GHz范围内生成相噪在10kHz频偏低于-120dBc/Hz、 频率漂移小于100mHz的毫米波，突破长时频稳、低相噪、大频率范围的微波光子毫米波生成技术，并通过大容量无线通信演示验证其性能。

高质量的毫米波信号可推动高精度分子光谱学、超大容量无线通信、高精度雷达等领域的进一步发展，其研究的重点之一是降低输出信号的相噪和提高其长时频稳度。本项目主要针对基于受激布里渊散射的低相噪毫米波生成技术中输出多波长激光相干性不足、长期稳定性低的问题，主要对光纤布里渊腔结构设计、单波长泵浦-谐振腔锁定技术、双波长共振泵浦与共腔激射、光纤布里渊腔长稳定控制与光生毫米波应用展开研究，通过设计的双独立光源共振泵浦+双波长共腔激射的光信号生产架构，实现了大频差、低线宽、高稳定的光载射频信号生成，经过光电转换后实现了宽频、低相噪、高长时频稳的毫米波/太赫兹波源。在实验中，获得了最大频率300 GHz, 相噪不随频率增大恶化（-90 dBc/Hz @ 10 kHz频偏），长时频漂小于0.5 mHz的光生毫米波/太赫兹信号，并在300 GHz实时无线通信演示实验中验证了高质量波源对于通信能力的提升，基本实现了所有研究目标。研究结果证明了共振泵浦对于布里渊阈值的降低作用和对于光信号频谱纯度的优化作用，证实了受激布里渊散射效应对于光信号线宽的抑制、以及共腔激射对于双波长光信号间相干性的提升，验证了项目所提基于共腔布里渊激光方案带来的太赫兹载波信噪比的提升和相噪的抑制，为高稳定时频信号合成、多维大容量光子无线通信、跨波段频率协同等应用提供了基础理论与关键技术的支撑。