A terahertz spectrometer on a chip, at the thermodynamical limits

太赫兹光谱法为远距离和非破坏性检测微量化学物质和气体、爆炸物、病原体和生物制剂提供了一个平台。这些分子和有害物质在太赫兹频率上具有独特的吸收光谱，能够从远处识别隐藏的有害物质。外差光谱仪是高光谱分辨率太赫兹光谱法的前沿。通过许多不同的技术，如肖特基二极管的非线性频率混合，超导体-绝缘体-超导体结构，或热电子辐射热计，它们的线宽与中心频率比降低到百万分之一。然而，这些最先进的外差光谱仪和混频器体积庞大（重达数十公斤），受到远离基本噪声限制的电子噪声的限制，并且通常需要低温冷却才能达到可观的灵敏度。本课题提出了一种基于芯片级激光频率梳与芯片级光度计模块集成的芯片级太赫兹光谱仪。激光频率梳由离散的光学频率线组成，可在一个倍频程范围内广泛调谐。光电混合器是基于一个等离子体增强吸收衬底，直接耦合到一个太赫兹天线收集入射太赫兹辐射。所提出的单片太赫兹接收器具有1-8太赫兹的光谱带宽，光谱分辨率优于1 kHz，并且接近热力学噪声极限。高性能、低成本和紧凑的太赫兹光谱仪在空间科学、生物分析、环境研究、制药和工业质量控制方面带来了宝贵的应用。拟议的科学努力与一项推广和教育计划相结合。这包括向代表性不足的高中学生和教师伸出援手，改进研究生和本科课程，并向公众伸出援手，重点关注代表性不足的女性和少数民族学生在本科生暑期研究经历中的表现。本文提出的外差芯片级光谱仪由三个相互关联的推力组成。在Thrust 1中，该项目将展示一种片上频率梳状振荡器，其调谐范围为1-8太赫兹，在参考光载波时，梳状振荡器的线对线不均匀性为千万亿分之0.2。在推力2中，该项目将开发一个片上集成泵浦激光器和放大器，用于光电混合器和频率梳的异构集成。在推力3中，该项目将展示基于天线耦合等离子体光电混合器的集成芯片级外差接收器。该团队试图测量具有接近基本边界的双边带噪声灵敏度的外差photomixer。频率敏捷方法是通过他们最近的初步研究和接近或接近热力学噪声极限的测量而实现的。提议的太赫兹光谱结构和科学推力可以将太赫兹波的平台转化为大气研究，空间探索和安全-工业-环境质量控制系统。科学推进与教育推广和跨学科培训工作相结合。这个为期三年的项目将在精密芯片级频率梳和等离子体光电混合器的界面上培养新一代的科学家，用于接近基本边界的变换器太赫兹光谱。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Terahertz spectrometry offers a platform for long-distance and non-destructive detection of trace chemicals and gases, explosives, pathogens, and biological agents. These molecules and hazardous agents have unique absorption spectra in the terahertz frequencies, enabling identification of concealed hazardous substances from remote distances. Heterodyne spectrometers are at the frontier for high spectral resolution terahertz spectrometry. Achieved through a number of different techniques such as nonlinear frequency mixing in Schottky diodes, superconductor-insulator-superconductor structures, or hot electron bolometers, they have linewidth-to-center frequency ratios down to one part in a million. These state-of-the-art heterodyne spectrometers and mixers, however, are bulky (weighing tens of kilograms), are bounded by electronic noise far from the fundamental noise limits, and often require cryogenic cooling to reach appreciable sensitivities. This project proposes a chip-scale terahertz spectrometer based on modular integration of a chip-scale laser frequency comb with a chip-scale photomixer. The laser frequency comb consists of discrete optical frequency lines, widely tunable over an octave. The photomixer is based on a plasmonically-enhanced absorbing substrate, directly coupled to a terahertz antenna to collect the incident terahertz radiation. The proposed single-chip terahertz receiver has spectrometry bandwidth of 1-8 THz with spectral resolution better than a kHz, and operates close to the thermodynamical noise limits. The high-performance, low-cost, and compact terahertz spectrometer brings valuable applications in space sciences, biological analysis, environmental studies, pharmaceuticals, and industrial quality control. The proposed scientific efforts are coupled with an outreach and education plan. This involves outreach to underrepresented high-school students and teachers, improvements to the graduate and undergraduate curriculum, and outreach to the general public with focus on underrepresented women and minority students in summer research experiences for undergraduates. The proposed advancement on the heterodyne chip-scale spectrometer consists of three cross-related Thrusts. In Thrust 1, the project will demonstrate an on-chip frequency comb oscillator with wide tuning range of 1-8 THz and comb line-to-line non-uniformity at 0.2 parts per quadrillion when referenced to the optical carrier. In Thrust 2, the project will develop an on-chip integrated pump laser and amplifier, for heterogeneous integration with the photomixer and frequency comb. In Thrust 3, the project will demonstrate the integrated chip-scale heterodyne receiver based on an antenna-coupled plasmonic photomixer. The team seeks to measure a heterodyne photomixer with double-sideband noise sensitivities close to the fundamental bound. The frequency-agile approach is enabled by their recent preliminary studies and measurements close to or at the thermodynamical noise limits. The proposed terahertz spectrometry architecture and scientific Thrusts can transform the platform of terahertz waves for atmospheric studies, space explorations, and safety-industrial-environmental quality control systems. The scientific Thrusts are integrated with educational outreach and cross-disciplinary training efforts. This three-year project will educate a new generation of scientists at the interface of precision chip-scale frequency combs and plasmonic photomixers for transformative terahertz spectrometry near the fundamental bounds.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.