基于多模干涉波导结构的自组织相干合束半导体激光器的机理研究

To fulfill the demands on narrow absorption linewidth and high stability absorption peak for the gain medium of diode pumped alkali vapor lasers, it becomes a most promising solution to obtain GHz-scale narrow linewidth semiconductor laser pumping source with high power, high beam quality, high frequency stability. The existing studies mainly focus on the volume holographic grating external cavity semiconductor laser, which have the drawbacks of low efficiency, low integration level and poor stability. And traditional monolithic integrated high beam quality semiconductor lasers, such as taper lasers and DFB lasers, have the disadvantage of beam quality degradation under high injection current and high cost of grating preparation. In order to solve these problems, we propose a novel self-organized coherent combination semiconductor laser based on multi-mode interference waveguide structures. This work will be carried out on the basis of frequency selectivity with low-loss high order gratings, beam splitter and self-organized coherent combination using MMI waveguide structures. And the studies on the preparation of low-loss high order gratings and integrated device are essential. This novel device is expected to implement high beam quality laser output with the power ≥ 5 W, 3 dB linewidth ≤ 0.4 nm (~200 GHz), and beam quality factor M2 ≤ 3. This project will extend the applications of the MMI waveguide structures in monolithic integrated semiconductor laser field and provide a more efficient pumping source for high performance diode pumped alkali vapor lasers.

针对碱金属激光器增益介质吸收谱线窄、吸收峰稳定性高的需求，高功率、高光束质量、频率稳定的GHz量级窄线宽半导体激光泵浦源成为最有前景的方案。现有研究主要集中在体全息光栅外腔激光器，其劣势是效率低、集成度低、稳定性差。而传统单片集成高光束质量半导体激光器，如锥形激光器、DFB激光器等，存在高电流注入下光束质量劣化和光栅制备成本高的问题。针对上述问题，本项目创新性提出基于多模干涉波导(MMI)结构的自组织相干合束半导体激光器。该工作将在高阶光栅低损耗选频机制、MMI波导分束机制、自组织波导相干耦合机理，以及低损耗高阶光栅和集成器件的制备研究基础上开展。预计该新颖器件可实现输出功率≥5 W，3 dB光谱线宽≤0.4 nm（~200 GHz），光束质量因子M2≤3的高光束质量激光输出。本项目的研究将拓展基于MMI波导结构在单片集成半导体激光器领域的应用，并为高性能碱金属激光器提供更高效的光泵浦源。

先进激光制造技术是“中国制造2025”国家战略的重要组成部分，半导体激光器（LD）具有体积小、重量轻、电光转换效率高等优势，是稀土掺杂单模光纤激光器等先进激光制造光源的核心泵浦元件。稀土掺杂单模光纤具有纤径尺寸小和泵浦吸收谱窄的特性，因此改善LD的激光光束质量和线宽性能对提高光纤激光器的泵浦效率具有显著影响。本项目通过开展低损耗光栅设计方法、脊形波导周期性电流调制结构设计、增益耦合型分布反馈（DFB）激光器、双锥形主振荡光放大（MOPA）激光器、单片集成MOPA激光器等研究工作。开发出高光束质量和窄线宽的单片集成MOPA激光器，实现了激光波长为976.6 nm，输出功率达到3.1 W@5.5 A，3dB光谱线宽＜0.16 nm（50.3 GHz），慢轴发散角＜19.48º ，光束质量因子M2≈2.51，光电效率32%的高功率、高光束质量激光。本项目的研究工作拓展了高阶光栅和锥形光放大结构在单片集成高光束质量半导体激光器领域的应用，并为高性能单模光纤激光器领域提供更高效的光泵浦源。