硅光子平台上混合集成VCSEL的制备及其偏振稳定性与热效应的研究

With the rapid growth of Internet, the number of data centers is increasing exponentially. Optical interconnects play a key role in realizing the communication links in the data centers. The vertical-cavity surface-emitting laser (VCSEL) is one of the most promising light source candidates for the high-speed optical interconnects. VCSELs can also leverage the benefits of the CMOS compatible silicon photonics which is featured by excellent scalability, tiny footprint and low cost. Integrating VCSELs with silicon photonics may enable the next generation of low power consumption and high-speed on-chip optical interconnects to address the growing demands for Internet and data center networks. This field attracts intense research interest at present. .We propose a new method for the hybrid integration of a VCSEL with a silicon photonic chip, in which a silicon grating coupler is integrated with the VCSEL to control the polarization dynamics of the laser. The oxide aperture structure and the strain in the active region of the VCSEL will also be engineered to maintain the single polarization lasing and suppress thermal effects in the VCSEL. The highly thermal conductive thermal fillers will be applied during the hybrid integration processes. We will explore the key performances of the hybrid VCSELs using the modified classical model. The revised model will include the multi-physical fields coupling effects, such as the coupling among photons, carriers, heat and strain in the hybrid VCSEL. The mechanisms of the polarization switching and the degradation of thermal stabilities in the hybrid VCSEL will be investigated based on the improved model. By optimizing the device structure and integration processes, the project aims to realize a stable hybrid VCSELs on silicon photonics. This work will support the on-chip optical interconnects and provide key solutions for the silicon-based on-chip laser that uses VCSEL as the light source.

互联网高速发展驱动数据中心数量大幅增长，光互连是数据中心最主要的信号互连技术，而垂直腔面发射激光器（VCSEL）则是光互连系统中最有前景的光源器件，因此成为当前国际研究前沿热点。VCSEL与硅光子器件集成，有望借助硅光子技术扩展性强、集成度高、成本低的优势，为低功耗、宽带片上光互连技术带来突破。本项目将制备一种新型硅基混合集成VCSEL，提出利用硅基光栅耦合器、非对称氧化孔径结构、有源区应力控制及拥有高导热系数固化胶的集成工艺来提升VCSEL的偏振稳定性和热稳定性。为分析VCSEL性能，将修改经典激光器模型以考察器件中光、电、热、力多物理场耦合，探索硅基混合集成VCSEL偏振态跳变机理及其热稳定性下降根源。进而优化器件结构与集成工艺，既使VCSEL维持稳定偏振态，又能抑制使器件性能恶化的热效应。本项目针对VCSEL提出的硅基混合集成方法将为研制高性能片上光互连芯片提供重要支持。

互联网高速发展驱动数据中心数量大幅增长，光互连是数据中心最主要的信号互连技术，而垂直腔面发射激光器（VCSEL）则是光互连系统中最有前景的光源器件，因此成为当前国际研究前沿热点。本课题围绕VCSEL与硅基光子集成回路之间的先进集成方法展开。我们探索了混合集成方案所涉及的关键理论与核心技术。借助硅基光子集成技术在系统可扩展性、集成密度、制备工艺与CMOS兼容上的优势，可以使硅基VCSEL性能获得大幅提升，成为一种性能优异的片上低功耗光源。我们建立了集成VCSEL理论模型，考虑光、电、热、力多物理场耦合效应，解释了硅基混合集成VCSEL偏振态跳变机理，找到了光源热稳定性下降的原因。.在研制长波长VCSEL芯片时，我们采用基于空气隙的台面结构、采用应力补偿多量子阱调控技术使激光器易于实现单模单偏振输。测得VCSEL在室温的阈值电流为2mA，中心波长1539nm，最大输出光功率1mW，单模抑制比30dB。随后，我们演示了采用硅基偏振分束光栅耦合器的混合集成方法，能将VCSEL芯片的偏振态控制在单TE态并将光功率从VCSEL耦合到硅波导中，BCB胶和导电纳米银胶用于混合集成。VCSEL经过硅波导输出光波的偏振抑制比超过15dB, 同时激光器输出光功率，阈值和温度特性并未出现明显劣化。最后，我们演示了基于SOI衬底的多层SiN/Si光子集成平台：在1550nm波长附近，测得平台中的双层五尖端SiN 端面耦合器与激光器的耦合效率约为76%，垂直1-dB对准容差约为±0.6μm。利用SiN/Si多层结构设计了完美垂直耦合GC，多层层间耦合器的在Si波导和SiN波导之间的垂直耦合效率约为91%。SiN/Si多层光子集成平台中的耦合器能有力地支持混合集成方案，因为与纯硅材料构成的耦合器相比，它们具有更高的耦合效率、更宽的光学工作带宽，以及更低的材料吸收损耗。.本项目取得的成果可以用来深入阐释或者有效调控硅基片上VCSEL光源的光电特性，也将为开发高性能光互连芯片、光传感芯片提供支持。

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