Monolithic integrated-photonic sensors in the molecular fingerprint region

本项目旨在开发中红外集成光子学材料平台，创建十亿分之一灵敏度的中红外光子晶体传感器。这样的平台和传感器目前还不存在。利用狭缝光子晶体波导中的慢光原理，瞄准中红外光谱范围内化学成分的强基本振动吸收谱线（也称为分子指纹区），实现高灵敏度。光子晶体波导将与中红外量子级联激光器和探测器单片集成，使用外延转移技术生产高度紧凑的集成光子化学传感器，在中红外光谱区域工作，用于广泛的应用，如化学和生物医学传感，环境监测和安全应用。本课题的科学目标是研究一种跨越分子指纹区域（3-14微米）的中红外光子波导平台，并在分子指纹区域开发集成光子传感器。由于SiO2的中红外吸收，绝缘体上硅器件不能在超过3.5微米的波长范围内工作；由于蓝宝石的吸收，蓝宝石上硅平台的波长限制在5微米以下，而硅本身只能在7-8微米内透明。目前，缺乏合适的光子波导平台限制了台式红外光谱系统的便携式吸收光谱仪替代品的实现，该光谱仪可以有效探测1500 cm-1以下的分子指纹区域。外延生长的GaAs/AlGaAs波导为整个3-14微米波长范围内的低损耗光学电路提供了完善的晶格匹配，非常低的缺陷密度和高折射率对比度平台。本项目旨在开发一个GaAs/AlGaAs集成光子学平台，用于跨越整个中红外光谱范围（包括分子指纹区域）的片上中红外光子学，并利用该平台在分子指纹区域展示高灵敏度低十亿分之一的片上吸收传感。采用开槽光子晶体波导器件可实现高灵敏度。拟议的平台预计在各自的峰值吸收波长分别为4.23微米和13.8微米时，二氧化碳和甲苯的检测极限分别为十亿分之0.3和十亿分之1。

This project is to develop a materials platform for mid-infrared integrated photonics and create mid-infrared photonic crystal sensors with parts per billion sensitivity. Such a platform and sensors do not currently exist. High sensitivity will be achieved by targeting strong fundamental vibrational absorption lines of chemical components in the mid-infrared spectral range, also known as the molecular fingerprint region, and employing the principle of slow light in slotted photonic crystal waveguides. The photonic crystal waveguides will be monolithically integrated with mid-infrared quantum cascade lasers and detectors using epitaxial transfer techniques to produce highly compact integrated-photonic chemical sensors operating in the mid-infrared spectral region for a wide range of applications, such as chemical and biomedical sensing, environmental monitoring, and security applications.The scientific objective of this project to investigate a mid-infrared photonic waveguideing platform spanning molecular fingerprint region (3-14 micrometer) and develop integrated-photonic sensors in the molecular fingerprint region. Silicon-on-insulator devices cannot be operated beyond 3.5 micrometer wavelength range owing to mid-infrared absorption in SiO2, silicon-on-sapphire platform is limited to wavelengths below 5 micrometer owing to sapphire absorption, and silicon itself is only transparent down to 7-8 micrometers. The lack of a suitable photonic waveguiding platform currently limits the realization of a portable absorption spectrometer surrogate of benchtop infrared spectroscopic systems that can effectively probe the molecular fingerprint region below 1500 cm-1. Epitaxially-grown GaAs/AlGaAs waveguides offer a well-established lattice-matched, very low defect density and high index contrast platform for low loss optical circuits in the entire 3-14 micrometer wavelength range. This project aims at developing a GaAs/AlGaAs integrated photonics platform for on-chip mid-infrared photonics spanning the entire mid-infrared spectral range, including the molecular fingerprint region, and using this platform to demonstrate high sensitivity low parts per billion on-chip absorption sensing in the molecular fingerprint region. High sensitivity will be achieved using slotted photonic crystal waveguide devices. The proposed platform is expected to have a detection limit of 0.3 parts per billion for CO2 and 1 part per billion for toluene at their respective peak absorbance wavelengths at 4.23 micrometer and at 13.8 micrometer, respectively.