Germanium Mid-Infrared Integrated Photonic Circuits

该项目涉及将III-V光源与光子集成电路集成在一起，以开发一个全面的中红外硅光子平台，该平台可能用作气体传感器。第四组光子学是近十年来研究的一个新兴课题，其重点是在近红外（NIR）和中红外（MIR）波长范围内工作的光子器件的发展。然而，这项工作只侧重于MIR设备的开发。这些设备适用于许多应用，包括化学，生物和环境传感，安全，通信以及天文学。整个项目的主要目标是开发可以集成在单个硅芯片上的集成光子器件。本报告介绍了过去8个月为实现这一目标所开展的工作。更具体地说，这包括MIR波长范围的低损耗波导的发展。这些波导使用悬浮的锗-硅-绝缘体（Ge-on-SOI）平台进行了演示。波导最初是使用流形模式解决方案设计的。在由220 nm厚的硅（Si）层和3 m厚的二氧化硅（SiO2）层（也称为埋藏氧化物（BOX））构成的硅绝缘体（SOI）衬底上生长400 nm和1 m厚的锗（Ge）肋波导进行了模拟。测量到的传输损耗为16.7 dB/cm。然后用氢氟酸（HF）湿蚀刻步骤去除BOX，使波导悬浮。通过在波导旁边设计亚波长孔来实现对BOX的访问。去掉BOX后，在3.8 m处的传输损耗为（2.82 dB/cm）。测得的弯曲损耗为0.13 dB/弯曲。1微米锗- soi的样品也已制成，并将进行测量。量子级联激光器（qcl）在硅上的集成也进行了研究。qcl -波导重叠分析表明，横向偏移1 m对应的插入损耗约为0.34 dB，而横向偏移5.5 m则增加到10 dB。垂直偏差值在1 m和1.9 m时分别为2.71 dB和10 dB。

This project involves the integration of III-V light sources with photonic integrated circuits for the development of a comprehensive mid-infrared silicon photonic platform which can be potentially used as a gas sensor.Group IV photonics has been an emerging topic of research over the last decade which focuses on the development of photonic devices which operate in the Near-Infrared (NIR) Mid-Infrared (MIR) wavelength range. However, this work focuses only in the development of devices for MIR.These devices are suitable for numerous applications including chemical, biological and environmental sensing, security, communications, as well as astronomy. The main point which the overall project aims to achieve is the development of integrated photonic devices that can potentially be integrated on a single silicon chip.This report presents the work that has been carried out towards this aim, over the last 8 months. More specifically, this includes the development of low loss waveguides for the MIR wavelength range. These waveguides were demonstrated using the platform of suspended Germanium-on-Silicon-on-Insulator (Ge-on-SOI). The waveguides were initially designed using Lumerical Mode Solutions. The simulations were carried out for 400 nm and 1 _m thick Germanium (Ge) rib waveguides grown on an Silicon on Insulator (SOI) substrate formed of a 220 nm thick Silicon (Si) layer and a 3 _m thick Silicon Dioxide (SiO2) layer (also known as the Buried Oxide (BOX)). The measured propagation loss was 16.7 dB/cm at 3.8 _m. Then the waveguides were suspended by removing the BOX using a wet etch step with Hydrofluoric Acid (HF). Access to the BOX was achieved by designing subwavelength holes alongside the waveguides. After removing the BOX, a propagation loss of (2.82 dB/cm) at 3.8 _m was observed. The measured bend loss was 0.13 dB/bend. Samples of 1 _m Ge-on-SOI have also been fabricated and are due to be measured. Integration of Quantum Cascade Lasers (QCLs) on Si has also been investigated. A QCL-waveguide overlap analysis has been carried out showing that a lateral misalignment of 1 _m corresponds to an insertion loss of approximately 0.34 dB which is increased to 10 dB for 5.5 _m of misalignment. The respective values of the vertical misalignment are 2.71 dB for 1 _m and 10 dB for 1.9 _m.