高功率随机光纤激光器光谱特性演化动力学及调控方法研究

As the performance improvement of rare earth doped fiber based high power fiber laser is limited by the key scientific and technical problems of self-pulse and photon darkening effects, this proposal focus on the high power random fiber laser (RFL) featured with cavity-free, longitudinal-mode-free and spectral flexibility. Systematical investigations will be done for the evolutionary dynamics and control methods of output spectrum. Firstly, a spatial and spectral dimensions fused theoretical model based on nonlinear Schrödinger equation and power balanced equation for high power random fiber laser will be established to describe the spectral evolutionary dynamics of large-mode-area passive fiber based high power RFL. Then, the spectral characteristics of output laser will be predicted effectively. Then, the influences of passive fiber, spectral reflection device, pump source and other factors on the spectral characteristics of high-power RFL will be clarified with the aid of theoretical and experimental studying. The comprehensive management strategies of nonlinear effects will be explored. Additionally, the power distribution characteristics of pump light and Stokes light in high-power RFL will be revealed. And the control mechanism and implementation methods of its spectral parameters will be mastered. At last, the optimization goals and methods of system parameters of high power RFL will be proposed. And a center wavelength and linewidth adjustable RFL with kilowatt-level output power will be realized.

本项目针对常规基于稀土掺杂光纤的高功率光纤激光器性能提升受限于自脉冲、光子暗化等效应这一关键科学、技术难题，以无谐振腔结构、无纵模特性、光谱调控灵活的高功率随机光纤激光器（random fiber laser, RFL）为研究对象，聚焦其光谱特性演化动力学及调控方法开展系统研究。首先，基于非线性薛定谔方程和功率平衡方程建立空频域维度融合的高功率RFL理论模型，描述基于大模场面积无源光纤的高功率RFL输出光谱特性演化动力学过程，实现对高功率RFL输出光谱特性的有效预测；在此基础上，通过理论和实验研究厘清无源光纤、光谱反射器件、泵浦光源等因素对高功率RFL输出光谱特性的影响，探索非线性效应综合管理策略，揭示高功率RFL中泵浦光、Stokes光的功率分布特点，掌握其光谱参数调控机理与实施方法；最终提出高功率RFL系统工作参数优化设计目标和方法，实现千瓦级高功率RFL中心波长、线宽同时可调控输出。

高功率随机光纤激光器（random fiber laser, RFL）基于无源光纤中分布式瑞利散射提供反馈实现激光输出，具有无谐振腔结构、无纵模特性、光谱调控灵活等优点，在中红外激光泵浦、超连续谱产生、光学传感等领域具有重要应用。本项目聚焦高功率RFL光谱特性演化动力学及调控方法开展系统的理论和实验研究，主要研究内容和结果如下：. （1）高功率RFL光谱特性演化动力学描述。基于广义非线性薛定谔方程组建立空域与频域融合的理论模型，考虑光纤损耗、拉曼增益、群速度色散、时域走离、自相位调制和交叉相位调制等因素，研究泵浦光源时域稳定性、时域走离效应等对高功率RFL输出光谱、功率、时序等的影响。. （2）高功率RFL系统工作参数优化设计。研制光谱中心波长、线宽均可调谐的高性能超荧光源，实现3 kW功率输出。基于自研的高性能泵浦源，探索泵浦光源波长、线宽、半腔结构RFL光栅参数等对RFL寄生振荡、功率转化、光谱纯度、光谱信噪比等输出特性的影响。. （3）高功率RFL光谱特性调控方法探索。基于高功率RFL中的功率分布特性，开展基于宽谱泵浦光源的高功率多波长RFL研究，当泵浦光源线宽从0.5 nm增大至40 nm时，输出波长数量可从9通道增加至18通道（波长间隔0.57 nm）；基于级联拉曼效应首次实现了1.3 μm波段可调谐多波长随机拉曼激光输出，输出功率高达4.67 W；基于混合增益和泵浦时域调控高功率RFL中输出中心波长、线宽，实现2 kW级高光谱纯度RFL，为目前RFL的最高输出功率。