基于光电混合振荡的窄线宽光源研究

Narrow-linewidth optical source have found significant and a large number of applications in optical communications, sensing, as well as advanced scientific researches where the precise measurement is critical. As a result, the ultra-narrow linewidth has been globally attractive and pursued, especially for linewidth less than 1 kHz. The tunability is also greatly demanded. However, linewidth around hundreds of Hz is difficult to achieve. Though the linewidth can be narrowed in theory by extending the cavity length, the interval between adjacent longitudinal modes is also accordingly reduced. As a result, multimode oscillation or unstable mode hopping occurs. The single mode oscillation under ultra-long optical cavity is then the key issue. In this applications, we try to employ a novel “optics-electronics-hybrid oscillation” instead of the traditional pure-optics cavity, in order to get the demanded high-quality (high-Q) factor. In the hybrid oscillator, part of the oscillation is carried by electronics rather than optics, so that the high-Q delay and narrow (~MHz level or less) mode-selecting filter can be achieved by the mature electronics devices. Under the enlarged Q factor, we would like to solve the following key problems. Firstly, how do the multiple longitudinal mode oscillations compete in a long-delay cavity, and how to select a single one? Secondly, how does the noise accumulate? And thirdly, how to suppress the low-Fourier-frequency noise, and how to fine tune the wavelength? The above studies are believed to suppress the high-Fourier-frequency spurs, high-Fourier-frequency noise, and low-Fourier-frequency noise, respectively. Finally, we try to obtain optical source with linewidth less than 500 Hz. We try to employ commercial available and mature parts, both in optics and in electronics, to achieve the ultra-narrow linewidth. Note that the current narrow-linewidth lasers are all based on key but specially-fabricated components. Our study tries to find a feasible way that can be implemented by ordinary laboratories, so that the studies on ultra-narrow-linewidth lasers and their applications can be greatly broadened.

窄线宽激光器在通信、传感、以及基于精密测量的先进科学研究等领域中有重要的应用前景。目前线宽在1 kHz以下的可调谐激光器广受国内外重视，也是该领域的难点。大延时光谐振腔导致的可激射纵模密集、多模式振荡或者跳模等，是需要解决的首要问题。项目拟采用创新性的“光—电混合振荡”替代传统的单纯的光振荡来实现高Q值腔；该结构的部分振荡被射频承载，成熟的射频器件提供了高Q值和单纵模选择滤波。随着谐振腔Q值的提高，项目将解决如下科学问题：（1）长延时谐振腔内纵模竞争机理与单模选择机制，（2）腔内噪声累积机理，以及（3）低频噪声抑制与波长调谐机制；这些研究将分别抑制激光器的高频杂散、高频噪声、和低频噪声，实现激光器线宽降低至百Hz量级。项目拟利用当前商用或成熟化的光纤器件，打破窄线宽激光器受特殊光器件制约的现状，寻找简单可行、容易被常规实验室所采纳的结构，以大幅推广窄线宽、尤其是极窄线宽激光器的应用研究。

对窄线宽低相位噪声激光器的研究有重要的学术意义。现有激光器的线宽很难降低到1 kHz以下；众多努力表明，只靠激光器的封装、与环境隔离等技术是不够的。针对高端窄线宽激光器、展开线宽压缩机制的深入研究是非常有价值、有必要的。本项目针对未来信息电子系统在超宽带覆盖、高频谱纯度、以及快速调谐需求，力求解决百Hz量级窄线宽光纤激光器产生、可调谐问题，重点开展了长延时谐振腔内纵模竞争机理与单模选择机制、长延时谐振腔内噪声累积机理、窄线宽激光器低频噪声抑制与波长调谐机制技术研究；突破高Q值激光腔技术、激光器噪声抑制技术；研制了基于光电混合振荡的可调谐低噪声光纤激光器原理样机，达到了单纵模激光器线宽小于500Hz；相对强度噪声小于-135dBc/Hz@1MHz、小于-145dBc/Hz@1GHz；输出功率大于0dBm；可调谐范围大于20nm等指标；完成了项目合同规定的所有研究内容，达到了合同规定的技术指标。基于该项目研究基础，项目负责人牵头承担了国防创新特区的相关项目；其中，项目提创新性提出的“光—电混合振荡”替代传统的单纯的光振荡来实现高Q值激光腔等功能相对“十二五”均为首创。