基于双向光栅垂直耦合和VCSEL 混合集成的硅基光发射机研究

As silicon is extremely inefficient in light emitting, silicon-based light emission hinders the realization of silicon photonic interconnect as the biggest obstacle. To overcome this problem, optical transmitters based on Ⅲ-Ⅴ/silicon heterogeneous integration become a research hot topic. In this proposal, VCSEL laser is employed as off-chip light source and light is vertically coupled through the bidirectional grating structure; an on-chip optical modulator based on the bidirectional grating structure is built as the external modulator of the VCSEL source and finally a silicon-based optical transmitter is realized. The research task is arranged as follows：Ⅰ. Build the FDTD simulation model of the VCSEL-bidirectional grating coupling structure and then fully optimize this structure through co-simulation with FDTD method. Ⅱ. Enhance the coupling efficiency of the vertical optical interface by introducing the substrate metal mirror and the anti-reflection cladding film using CMOS-compatible post-processing technology. Ⅲ.Design and realize the on-chip quasi Mach-Zehnder type optical modulator based on the bidirectional grating structure. Ⅳ.Realize the hybrid integration between the VCSEL laser and the silicon photonic chip by surface mounting or flip-chip bonding. Related research results is believed to provide a promising solution for low-cost and high-bandwidth silicon optical transmitter and offer novel and feasible ideas and technologies for future silicon photonic interconnects.

由于硅材料发光效率低下，硅基光发射成为硅基光互连面临的最大障碍。为解决这一难题，采用高光效的Ⅲ-Ⅴ族材料和硅材料异质混合集成的光发射机成为研究热点。本课题提出：采用VCSEL激光器作为片外光源并通过双向光栅耦合器实现垂直光耦合，同时基于双向耦合光栅构建片上电光调制器对VCSEL光源进行外调制，实现硅基混合光发射机。具体包括：Ⅰ. 建立VCSEL-双向耦合光栅光学仿真模型，采用时域有限差分算法（FDTD）对该结构进行协同仿真优化；Ⅱ.结合CMOS后工艺设计实现衬底金属反射镜以及上包层增透/减反膜进一步提高光耦合效率；Ⅲ.基于双向光栅结构设计类马赫-曾德调制器, 实现高速片上电光调制功能；Ⅳ.利用表面贴装或者倒装焊的方式实现VCSEL激光器和硅基光电子芯片之间的混合集成。本课题的研究有望提供一个低成本、高带宽的硅基光发射机解决方案，从而为硅基光互连提供新颖、可行的技术。

由于硅材料发光效率十分低下，硅基光发射成为硅基光互连面临的最大障碍。为解决这一难题，我们采用VCSEL激光器作为片外光源并通过双向光栅耦合器实现垂直光耦合，同时基于双向耦合光栅构建片上电光调制器对VCSEL光源进行外调制，实现硅基混合光发射机。主要研究内容和重要结果包括：1. 采用FDTD算法对双向光栅耦合器以及基于双向光栅结构的类马赫-曾德干涉仪结构进行了光学仿真优化，分析了光栅后工艺中衬底金属反射镜和双包层减反膜对于光栅性能的影响，基于双包层减反膜实现双向光栅实测耦合效率为50%。2. 基于CMOS兼容的硅基光电子工艺设计并制作了双向光栅耦合器、电光调制器、锗波导探测器等关键光电子器件，通过实验测试验证了器件的功能并对器件特性进行了表征，实现了具有点到点光互连功能的光电子集成回路，最高互连速率达7Gb/s。3. 基于激光器倒装焊工艺和胶接键和工艺，我们实现了VCSEL激光器和硅基光电子芯片之间的混合集成和高效光耦合，实测显示在电压为2V、电流为3mA时混合集成VCSEL在1534.5nm波长处的出射光功率可以达到-17dBm，其中光栅耦合归一化插入损耗约为6.5dB，换算VCSEL光栅耦合效率达到22.4%。该项目研究成果初步探索并实现了VCSEL激光器和硅基光电子芯片之间的高效光耦合和混合集成，为硅基混合光源研究提供了一个新颖思路以及可行的技术方案，具有重要的科学意义。