同轴双波长室温连续波量子级联激光器关键技术研究

High performance, dual-wavelength, single mode mid-infrared lasers are very demanding for mid-infrared laser absorption spectroscopy and other applications. In this project, we design a low modal loss, co-axial, dual-wavelength, single mode quantum cascade laser (QCL) structure based on two specially designed distributed Bragg reflectors (DBRs), and research on the related key technologies to realize room temperature continuous wave (cw) operation of such devices. By optimizing the design of the dual-wavelength heterogeneously cascaded QCL active-region and the two DBR structures with different periods, as well as the adoption of electrical isolation trenches and separately integrating two micro-heaters, we can control the two wavelengths precisely and independently, meanwhile reducing the thermal cross-talk between the two wavelengths. Through the skillful design of the reflection spectra of the two DBRs, the optimization of active-region doping level, and using the buried DBR grating to achieve strong coupling, low modal loss can be realized. By using selective-area regrowth of Fe doped semi-insulating InP and high thermal conductivity, patterned heat sink to improve the thermal management of the dual-wavelength device, room temperature cw operation of the device can be achieved. After accomplishing this project, we will be capable of developing high performance, co-axial, dual-wavelength DBR-QCLs, which can be operated in cw mode at room temperature and the two wavelengths can be controlled precisely and independently. The achievements of this project will greatly promote the development of related spectral techniques and realizing high sensitivity detection of two gases simultaneously.

本项目围绕中红外激光吸收光谱等领域对高性能双波长单模激光器的需求，提出了一种基于双分布布拉格反射镜（DBR）结构的低模式损耗、同轴、双波长可控输出的单模量子级联激光器（QCL）结构，并开展相关关键技术研究，实现其室温连续波工作。通过双波长QCL有源区堆叠结构和双DBR结构的优化设计、以及采用电隔离沟道和分别集成微加热器，实现在相同的热沉温度下对双波长同时进行精确控制，并减小两个波长之间的热串扰；通过优化有源区掺杂浓度、巧妙设计DBR反射谱、采用掩埋DBR结构实现强耦合，来降低模式损耗；通过选区外延掺Fe的半绝缘InP、采用图形化高热导率热沉实现倒装焊，来提高器件热管理水平，实现双波长DBR-QCL器件室温连续波工作。通过本项目研究，可以掌握高性能双波长DBR-QCL研制的关键技术，并实现同轴、双波长可独立控制的单纵模DBR-QCL的室温连续波工作，推动两种气体同时检测等光谱技术的发展。

随着基于单模中红外量子级联激光器（QCL）的可调谐激光吸收光谱技术的发展，人们希望能利用同轴输出的、双波长可独立控制的单模QCL实现两种或者多种气体的同时检测，这样既能简化数据采集和分析过程，又无需进行光束耦合从而简化多种气体检测装置，实现其小型化。本项目围绕中红外激光吸收光谱等领域对高性能双波长单模激光器的需求，设计并制备了两种同轴、双波长可独立控制的单模QCL：（1）设计并制备了一种新颖的双分布布拉格反射镜（DBR）QCL。该器件结构包括前、后两个增益区和两个周期不同的DBR用于选择两个不同的布拉格波长，四个区域采用三个电隔离沟分开。通过分区加电驱动，可实现两个单模波长的选择性输出。研制的7.6微米和8.2微米双波长可独立控制的双DBR-QCL，室温单模输出光功率分别达到275 mW和218 mW，边模抑制比超过25 dB。（2）设计并制备了一种新型的双波长可灵活控制的双分布反馈（DFB）光栅叠加的QCL。通过优化束缚态到连续态跃迁的有源区设计，在较大的电压动态范围内均可实现对激光跃迁上能级的有效注入；并在波导上限制层的同一区域，利用叠加两个不同周期的DFB光栅来实现对两个不同波长的选择性输出。通过采用窄脊、并在双沟中填充掺Fe的半绝缘InP作为绝缘介质来提高侧向散热能力，以及后腔面镀高反射膜来降低镜面损耗等手段，实现了双DFB叠加QCL的室温连续波工作。研制的同轴双波长室温连续波工作QCL，当注入电流小于1.27Ith时，仅波长约7.61微米单模激射；而当注入电流大于1.66Ith时，仅波长约7.06微米单模激射。两个单模波长随温度和电流均可线性调谐。在20 ℃连续波工作时，单模7.61微米和单模7.06微米的最大输出功率分别超过30 mW和75 mW。该双DFB叠加QCL，只需要一个驱动电源就可以灵活控制双波长输出，波长的切换仅通过改变注入电流（偏压）的大小即可完成。通过本项目研究，我们成功设计并制备了两种同轴、双波长可独立控制的单模QCL，有力推动了双波长QCL研究以及多种气体同时检测等光谱技术的发展。