级联光栅反馈半导体激光器混沌机制与非线性优化

Chaotic semiconductor lasers under optical feedback are particularly interesting because they are typically random-like, broadband, high-dimensional, and synchronizable. These unique properties inspired a number of emerging applications such as LiDAR, secure communication, random number generation, secure key distribution, etc. However, performances of chaos-based applications are generally degraded by two fundamental limitations. One is chaotic time-delay signature which threatens the system security. The other is laser’s relaxation resonance which restricts chaos bandwidths. In this proposal, a novel implementation of chaos generation and optimization will be explored. Optical chaos is generated by optical feedback from cascaded gratings, while chaos optimization is conducted by all-optical processing based on fiber nonlinearity. Firstly, cascaded gratings are utilized to provide tailored optical feedback for generating intensity time-delay signatures suppressed chaotic dynamics. In addition, the fiber Kerr nonlinearity induced self-phase modulation is applied to the generated chaos for suppressing phase time-delay signatures. Finally, the interaction between fiber dispersion and self-phase modulation are further investigated for generating bandwidth enhanced chaos with time-delay signature suppression in both intensity and phase. Completion of the project will deepen the fundamental understanding of the interaction between nonlinear laser dynamics and fiber nonlinearity, which significantly contributes to the theory development and application innovation of laser chaos.

光反馈混沌半导体激光器具有输出波形随机、宽带、高维、可同步等优势，已广泛应用于激光雷达、保密通信、随机数生成、安全密钥分发等领域。然而，反馈时延特征对混沌安全性的威胁、激光器弛豫振荡对混沌带宽的限制逐渐成为阻碍其发展与应用的两个关键因素。在此背景下，本项目提出利用级联光栅反馈实现半导体激光器混沌生成，再结合光纤非线性处理实现混沌优化。首先，设计级联光栅反馈结构抑制混沌幅度时延特征；继而，借助光纤中自相位调制非线性抑制混沌相位时延特征；进而，结合光纤非线性和色散相互作用扩展混沌带宽，最终生成幅度与相位均无时延特征的大带宽混沌信号。本项目的研究工作及成果将推进半导体激光器动力学与光纤非线性的融合以及相互作用的认知，并对激光混沌的理论发展和方法创新具有重要理论意义和应用价值。

光反馈下半导体激光器可呈现出混沌动力学状态，具有波形随机、宽带、高维、可同步等诸多优势，已在激光雷达、保密通信、随机数生成、安全密钥分发等新兴领域得到了广泛应用。随着技术的发展，激光混沌的相关应用已逐渐触及到两个关键限制：一是反馈时延特征对混沌安全性的威胁，二是激光器弛豫振荡对混沌带宽的限制。争对这两个关键限制，本项目主要基于频谱裁剪的光栅反馈实现半导体激光器混沌产生，再结合光纤参量非线性实现混沌优化，并取得了一系列研究成果。首先，从理论和实验上研究了带通滤波反馈下半导体激光器的非线性动力学特性，发现了窄带滤波可抑制弛豫振荡，大幅度提升非线性动力学稳定性，使激光器即使在强反馈下依然能维持稳定单周期振荡；继而，从理论和实验上研究了带阻滤波反馈下半导体激光器的混沌产生机制，借助光反馈下激光器谐振红移特性，基于负失谐频率实现了激光混沌的产生及外腔模式的抑制，从而使幅度和相位的时延特征均得到十倍以上的抑制；最后，结合光纤参量非线性，实现混沌功率从中心波段往边带的转移，进而将混沌带宽扩展到100GHz以上。本项目建立了基于窄带带通滤波与带阻滤波的光反馈激光器动力学平台，实现了半导体激光器动力学与光纤非线性的技术融合，相关成果对突破激光混沌的原理限制，推进相关应用向前发展具有一定贡献。