InP基单片集成少模光发射芯片的研究

Mode division multiplexing (MDM) is an effective technique to increase the transmission bandwidth of the optical communication system and on-chip optical interconnect system. Currently, the optical transmitters in the MDM systems are normally based on discrete components which often involves complex free space optical elements or fiber optic devices. Such a system requires precise and usually difficult adjustment of the discrete elements. Besides, the insertion loss, stability, footprint and mass-production possibility are also practical problems faced by such system. In optical interconnect systems, it is difficult to integrate light sources and optical amplifiers. By using photonic integration technology, it is possible to integrate the directly modulated light source, mode converters, and multiplexers into a single chip. From the perspective of the guide mode generation and control, the excitation, transmission and conversion of waveguide modes will be more effective. From a system perspective, the overall insertion loss, module size, power consumption of the light transmitter and receiver will be greatly reduced. In this proposal, we will develop a multimode interference (MMI) coupler and Y-waveguide based integrated few-mode optical transmitter chip, which integrate the functions of optical carrier generation, signaling modulation, mode conversion and multiplexing. The design of the chip is compatible with future InP-based generic foundry model, and is a promising candidate for low cost MPW run in such foundry models. The few mode transmitter is not only applicable to fiber optic communication systems, but also suitable for on-chip interconnection system.

模分复用技术是提升光通信系统和片上光互连通信带宽的有效手段。目前，光纤模分复用系统的光发端送多采用分立器件，涉及复杂的空间光路或光纤器件，系统调试难度大、插入损耗高、稳定性差、不适于批量生产。硅基片上光互连中，光源和光放大器也难以与模式转换复用器集成。本项目提出采用磷化铟（InP）光子集成技术将直调光源、模式转换器、复用器等集成在一起，实现集成化少模光发射芯片。从模式产生和控制角度，集成芯片中导波模式的激励、传输和转换将更为有效。从系统角度、光发射和接收端的工作稳定性、插损也将大为改善，收发模块体积、功耗也将有效降低。本项目将以分布半导体反馈激光器作为直调光源，以多模干涉耦合器和Y波导结构为模式转换/复用器，实现基模信号与高阶模信号的转换、复用和光发射功能。器件设计面向InP基标准代工工艺，有望实现低成本、多晶圆(MPW)生产。该光发射器不仅适用于光纤通信系统，也适用于片上光互连系统。

模分复用技术是提升光通信系统和片上光互连系统通信带宽的有效手段。采用分立器件组成的模分复用系统往往涉及空间光路或光纤器件，系统调试难度大。在插入损耗、稳定性和体积方面也有许多问题需要解决。而采用集成技术，则可通过精准的加工工艺将光源、模式转换、复用器等集成在一起。从模式产生和控制角度，集成芯片中导波模式的激励、传输和转换将更为有效。从系统角度、光发射和接收端的整体插损也将大为减小，收发模块体积、功耗也将有效降低。在本项目中，我们研制了一种集成式少模光发射芯片，在同一芯片上实现光载波产生、调制、模式转换和复用功能。该方案采用InP基材料体系，可以实现有源无源的单片集成，有利于减小工艺复杂度和器件尺寸。..项目的具体研究内容包括基于多模干涉耦合器（MMI）的模式转换复用器研制、高速直调激光器与模式转换复用器的集成方案和工艺研究、少模光发射芯片模式产生与表征研究。项目中模式转换/复用器采用了MMI结构，具有设计和工艺容差大，对波长和偏振不敏感的优点，同时MMI结构作为标准工艺中的基本单元结构，可以兼容多项目晶圆（MPW）设计，适于批量低成本生产。直调激光器采用分布反馈DFB激光器，可以实现单波长高速调制功能。..在本项目中，课题组制备了集成双路直调DFB激光器与模式转换复用器集成的少模光发射芯片。芯片中DFB激光器的阈值25~30 mA，功率>9 mW ，波长在1536 nm，激光器的小信号带宽约为15 GHz；该发射芯片每路DFB激光器可以达到10Gbps的调制速率；成功实现了TE0和TE1模式产生和调制，并在少模光纤中激发出LP01和LP11模；实现了2×10Gbps少模光发射功能。可以获得清晰的背靠背眼图和并实现了零误码测试。