Monolithic integrated-photonic sensors in the molecular fingerprint region

该项目是开发中红外集成光子学的材料平台，制造灵敏度为十亿分之一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。通过在中红外光谱范围内瞄准化学成分的强基本振动吸收线，也称为分子指纹区，并利用缝隙光子晶体波导中的慢光原理，将获得高灵敏度。利用外延传输技术，将光子晶体光波导与中红外量子级联激光器和探测器进行单片集成，制成高度紧凑的集成光子化学传感器，应用于化学和生物医学传感、环境监测、安防等领域。本项目的科学目标是研究一种跨越分子指纹区(3-14微米)的中红外光子光波导平台，并开发分子指纹区的集成光子传感器。绝缘体上的硅器件由于二氧化硅的中红外吸收而不能超过3.5微米的波长范围，蓝宝石上的硅平台由于蓝宝石吸收而被限制在5微米以下的波长，而硅本身只是7-8微米的透明波长。目前，由于缺乏合适的光子波导平台，限制了便携式吸收光谱仪替代台式红外光谱系统的实现，该系统可以有效地探测1500 cm-1以下的分子指纹区域。外延生长的GaAsAlGaAs光波导为整个3-14微米波长范围内的低损耗光路提供了良好的晶格匹配、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覆盖包括分子指纹区在内的整个中红外光谱范围的片上中红外光子学集成光子学平台，并利用该平台展示高灵敏度、低亿分之一分子指纹区的片上吸收传感。利用缝隙光子晶体光波导器件将获得高灵敏度。在二氧化碳和甲苯的峰值吸收波长分别为4.23微米和13.8微米时，拟议的平台预计对二氧化碳和甲苯的检测下限分别为百万分之0.3和百万分之一。

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.