Rayleigh backscattering: a method to highly compress laser linewidth

Ultra-narrow linewidth laser with several hundred hertz at room temperature has attracted a great deal of attention in recent years and played a critical role in both optical sensing and communication fields. In this paper, a new method based on Rayleigh backscattering to highly compress the laser linewidth was proposed and demonstrated theoretically and experimentally. By theoretical analysis and simulation, Rayleigh backscattering can be collected in any waveguide structure and all wave bands, which could have a revolutionary impact on the field of laser. A single-longitudinal mode fiber ring laser with 130-Hz linewidth was achieved with self-injection feedback structure at normal atmospheric temperature. The linewidth compression based on Rayleigh backscattering lies in the fact that laser linewidth after scattering is narrower than that of incident light in high Rayleigh scattering structure. The self-rejection feedback method expanding free spectra range of laser cavity simultaneously was used to further suppress the mode-hopping and stabilizing output. Experimental results showed that the laser linewidth can be easily narrowed to hundreds of hertz with side-mode suppression up to 75 dB. This agrees with the theoretical analysis and simulation results qualitatively.摘要频率线宽低至数百赫兹的超窄激光器具有极低的频率噪声和超长的相干长度, 在光原子钟、引力波探测、低噪声微波信号产生、高精度激光测距以及光纤传感等领域有重要的应用. 论文首次提出了基于后向瑞利散射的激光线宽压缩模型, 实验中利用瑞利散射机制和自注入反馈结构得到了线宽低至130 Hz, 边摸抑制比高达75 dB的超窄线宽激光输出. 基于后向瑞利散射能够对任意波段的单波长或多波长激光线宽产生压缩效果, 并且通过制作和优化产生瑞利散射的波导结构, 能实现常温常态下工作的便携式超窄线宽激光装置.