Heterogeneous Photonic Integrated Circuits for Microwave Photonics

微波光子学（MWP）是利用光子学研究微波信号的产生、处理、控制和分布的跨学科领域，在宽带无线通信、雷达、高速传感、高分辨率成像和现代仪器仪表等领域都有广泛的应用。在过去的几年中，各种MWP系统已经被提出并证明。然而，这些系统是基于离散光子元件实现的，这使得系统体积大，重量大，成本高，性能相对较差。为了克服这些限制，人们对使用光子集成电路（PICs）来实现MWP系统的片上集成越来越感兴趣。目前，有三种主要的材料系统正在研究集成MWP的实现：1)磷化铟（InP）， 2)氮化硅（Si3N4）和3)硅光子学（Si）。采用标准且成熟的CMOS制造工艺来开发和制造基于绝缘体上硅（SOI）平台的光学器件的硅基PICs被认为是集成微波光子系统的潜在解决方案。主要优势包括更小的占地面积，低功耗和与CMOS技术兼容的制造工艺，这也具有与微电子无缝集成的巨大潜力。然而，限制硅用于单片集成的一个关键因素是缺乏光源和放大器，因为硅是一种非直接带隙材料。一个潜在的解决方案是通过异质集成将基于inp的光源和放大器集成在硅芯片上。这种方法结合了两种不同材料系统的优点，为光的产生和放大提供了独特的解决方案。提出的研究动机是研究使用异构集成技术开发完全集成的MWP系统，用于高频和频率可调谐微波信号的产生和处理。基于inp和si的PICs的结合将显著提高微波光子系统的性能，并为实际应用开辟了新的途径。

Microwave photonics (MWP) is an interdisciplinary field to study the generation, processing, control and distribution of microwave signals by means of photonics, which can find applications such as broadband wireless communications, radar, high-speed sensing, high-resolution imaging, and modern instrumentation. Various MWP systems have been proposed and demonstrated in the past few years. These systems, however, were implemented based on discrete photonic components, which makes the systems bulky, heavy and costly with relatively poor performance. To overcome these limitations, there is an ever-increasing interest in using photonic integrated circuits (PICs) to realize on-chip integration of MWP systems. Currently, there are three major material systems that are being studied for integrated MWP implementations: 1) Indium Phosphide (InP), 2) Silicon Nitride (Si3N4) and 3) Silicon photonics (Si). Si-based PICs using the standard and well-developed CMOS fabrication process to develop and manufacture optical devices on silicon-on-insulator (SOI) platforms has been considered a potential solution for integrated microwave photonic systems. The key advantages include much smaller footprint, low power consumption and compatible fabrication process with CMOS technology, which also holds a significant potential for seamless integration with microelectronics. However, one key factor limiting the Si for monolithic integration is the lack of light sources and amplifiers, since silicon is a non-direct bandgap material. A potential solution is to integrate InP-based light sources and amplifiers on a silicon chip through heterogeneous integration. This approach combines the benefits of two different material systems to provide a unique solution to light generation and amplification. The motivation of the proposed research is to study the use of the heterogeneous integration technology to develop fully integrated MWP systems for the generation and processing of high-frequency and frequency-tunable microwave signals. The combination of the InP-based and Si-based PICs would significantly boost the performance of microwave photonic systems and opens up new avenues toward real applications.