基于模式选择的高亮度单模外腔半导体激光器

High power diode lasers are very efficient, compact, wavelength versatile, low cost, and highly reliable. Diode lasers for high output powers are usually embodied as broad stripe laser. Owing to the comparatively large lateral extent of the active region, generally a large number of transverse modes can establish oscillation in the case of diode lasers of this type. This results in higher order transverse modes to be amplified which impairs the beam quality and increases the beam divergence. The in-plane beam quality of broad stripe lasers is mainly limited by the onset of many higher order lateral modes. Transverse fundamental mode operation of the diode laser cannot be achieved. A method of improving the beam quality of diode lasers while maintaining the high output power is the use of relatively narrow stripe and external resonator. When the stripe is arrowed, higher order modes are cut off, improving beam quality, leading eventually to lower order transverse modes operation. The main goal of the external cavity laser is going to be the improvement of the lateral beam quality of the laser, while maintaining the same output power levels. The principles underlying the spatial mode filtering process inside the laser and their validity at high power operation are studied. The theoretical model is refined in order to accommodate thermal lensing, the main contribution to non-linear effects thatgain in influence inside the gain medium. Subsequently, an additional lens is included inside the setup in order to optimize the mode filtering. Through these studies, 3W CW-power with the diffraction-limited narrow linewidth will be reached from external cavity laser with mode feedback control.

半导体激光器具有输出功率大，效率高，体积小等优点，但是半导体激光器的大功率输出一般是通过增加激光器的条宽实现，随着条宽的增加，激光器的横向波导限制变弱，高阶横向模式增多，光束质量下降，从而使激光器不能在近衍射极限下工作，同时半导体激光器还存在输出光谱宽、波长稳定性差等缺陷，制约其应用。本项目提出采用大光腔、相对窄脊形半导体激光器增益芯片，有效的利用折射率引导机制，控制增益引导机制，使半导体激光器增益芯片在自由激射时，只在有限的低阶模式起振，同时采用外腔反馈结构抑制其他的低阶模式，只让基横模近衍射极限激射，相应的改善激光器的光谱线宽及波长稳定性。具体研究大光腔、相对窄脊形结构引入的有效折射率变化对高阶横向模式的限制机制，外腔反馈基横模近衍射极限输出控制。通过以上研究，掌握外腔反馈半导体激光器的模式控制关键技术，实现3W以上的近衍射极限、窄线宽输出。

半导体激光器具有体积小、质量轻、结构紧凑、光电转换效率高、模块化、寿命长等技术优势。在实际应用过程中，亮度代替功率成为一个重要因素，为得到更大亮度的激光输出，可通过改善输出功率和光束质量实现：在功率不变的情况下，通过提高光束质量，获得较高功率密度。高功率近衍射极限半导体激光器逐渐引起人们的关注。研制出一种基于MCC封装的高密度多单元激光芯片，其单元条宽为10μm，单元数为96，输出功率达到17.7W，光束质量M2≤3.1；研制出一种基于高阶Bragg光栅和锥形光放大结构的主振荡功率放大（MOPA）半导体激光芯片，实现激射波长为976.6nm，输出功率达到3.1W@5.5A，3dB光谱线宽小于0.16nm，慢轴发散角小于19.48º ，光束质量因子M2≈2.51，光电效率32%的高光束质量激光的高功率、高光束质量激光；研制出一种基于增益耦合光栅和双锥形光放大结构的分布反馈（DFB）半导体激光芯片，实现激射波长为996nm，输出功率达到2.5W@3.5A，3dB光谱线宽小于1.95pm，边模抑制比大于33dB，慢轴发散角小于15.22º，光束质量因子 M2≈2.8，最高光电转换效率35%的高功率、高光束质量激光。培养博士毕业生2名，在读博士生1名。发表相关论文7 篇（其中，第一标准2 篇，第二标注4 篇，第三标准1篇），授权发明专利1 项，授权国家发明专利1 项，申请国家发明专利7项，获得中科院科技促进发展奖，中国专利优秀奖1项。