Heterogeneous Photonic Integrated Circuits for Microwave Photonics

微波光子学是利用光子学方法研究微波信号的产生、处理、控制和分布的一门交叉学科，在宽带无线通信、雷达、高速传感、高分辨率成像和现代仪器等领域有着广泛的应用。在过去的几年里，各种MWP系统被提出和展示。然而，这些系统是基于分立的光子组件实现的，这使得系统体积大、重量重、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(PIC)实现MWP系统的片上集成越来越感兴趣。目前，用于集成MWP实现的主要材料系统有三种：1)磷化铟(InP)，2)氮化硅(Si3N4)和3)硅光子学(Si)。硅基PIC采用标准和成熟的CMOS制造工艺，在绝缘体上硅(SOI)平台上开发和制造光学器件，被认为是集成微波光子系统的潜在解决方案。其主要优势包括占地面积小得多，低功耗，以及与CMOS工艺兼容的制造工艺，这也具有与微电子无缝集成的巨大潜力。然而，限制单片集成硅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。一种潜在的解决方案是通过异质集成将InP基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。这项研究的目的是研究利用异质集成技术开发完全集成的MWP系统，用于产生和处理高频和频率可调的微波信号。基于InP和基于Si的PIC的结合将显著提高微波光子系统的性能，并为真正的应用开辟新的途径。

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.