Integrated THz Spectroscopy exploiting On-chip Scattering and Device Nonlinearity

太赫兹（THz）光谱在成像、无损质量控制、生物医学、化学和空气污染传感、细胞生物学、晶体工程、爆炸物和假药识别等方面具有广泛的潜在应用。然而，在这一光谱区域缺乏足够和具有成本效益的仪器开发，导致了它被称为“太赫兹”差距，并对其应用空间的发展产生了不利影响。然而，随着纳米技术、材料科学和光学的新发展，对这一频率范围的研究兴趣重新活跃起来，研究团体正在从广泛的科学学科领域接近技术发展。该项目的成功可以为上述应用提供强大的、低成本的集成太赫兹光谱系统。这种针对太赫兹频率区域的低成本解决方案将使从事该领域的研究人员和科学家能够快速创新新技术，这些新技术可以在我们的日常生活中得到广泛应用。PI还希望这项研究能够吸引和培养多学科领域的研究生和本科生，这对于解决未来具有挑战性的研究问题至关重要。PI还将与当地学校的高中毕业生合作，通过他提议的两门课程以及出版物、研讨会和讲习班广泛传播知识。太赫兹光谱在生物医学和化学分析中有着广泛的应用。目前在时域执行太赫兹光谱的技术主要依赖于昂贵的光学元件，包括飞秒激光器，光导衬底，非线性光学元件和机械部件，使系统昂贵，笨重且不适合集成。另一方面，固态技术使用经典的下转换架构执行频域光谱。它需要大量的频率合成器和乘法器，覆盖整个太赫兹范围，使其不适合集成。本文提出了一种电磁-电路-非线性估计横切方法，通过从电磁散射中提取光谱信息，在室温下实现芯片级太赫兹光谱。关键的想法是，片上接收器和传入太赫兹波之间的电磁接口创造了对入射信号进行频谱分析的机会，而不需要传统接收器跟随它。本提案旨在通过测量片上电磁散射来建立光谱估计的分析框架。提出了通过测量芯片上由于太赫兹波入射而在平面天线结构上产生的感应表面电流分布的大小来估计这种散射的技术。此外，本提案还寻求利用检测器的非线性来提取入射信号频谱的时域特征或相位信息。这有可能使电池供电的芯片级太赫兹光谱仪用于广泛的传感和成像应用。

Terahertz (THz) spectroscopy has a wide range of potential applications in imaging, non-destructive quality control, biomedical, chemical and air pollution sensing, cell biology, crystal engineering, identification of explosives and counterfeit drugs. However, lack of adequate and cost-effective instrumentation development in this spectral region has contributed to it being called the 'THz' gap, and has adversely affected the development of its application space. However, with new developments in nanotechnology, material science and optics, there has been a resurgence of active research interest in this frequency range and the research community are approaching the technology development from a broad range of scientific disciplines. The success of this project can enable robust, low-cost integrated, THz spectroscopic systems for the aforementioned applications. Such low-cost solutions for the THz frequency region will enable researchers and scientists engaged in this field to rapidly innovate on new technologies that can find extensive use in our daily lives. The PI also expects that this research will engage and train both graduate and undergraduate students in multi-disciplinary fields, which are vitally important for solving challenging research problems for the future. The PI will also engage high-school seniors from local schools and broadly disseminate the knowledge through his proposed two courses and through publications, seminars and workshops.THz-based spectroscopy is purported to have a wide range of applications in biomedical and chemical analysis. Current technology to perform THz spectroscopy in the time domain mostly relies on expensive optics including femtosecond lasers, photoconductive substrates, nonlinear optical elements and mechanical components making the system expensive, bulky and not amenable to integration. On the other hand, solid-state technology performs frequency domain spectroscopy using the classical down-conversion architecture. It requires a large bank of frequency synthesizers and multipliers covering the entire THz range making it unsuitable for integration. This proposal presents an electromagnetics-circuits-nonlinear estimation crosscut approach to enable chip-scale THz spectroscopy at room temperature through extraction of spectral information from electromagnetic scattering. The key idea is that an electromagnetic interface between the on-chip receiver and the incoming THz wave itself creates an opportunity to perform spectral analysis of the incident signal, without requiring the traditional receiver following it. This proposal seeks to establish the analytical framework for spectral estimation by measuring on-chip electromagnetic scattering. It proposes techniques to estimate such scattering by measuring on-chip the magnitude of the induced surface current distribution on the planar antenna structure due to the incidence of the THz wave. In addition, this proposal also seeks to exploit nonlinearity of the detectors to extract time-domain signature or phase information of the spectrum of the incident signal. This can potentially enable battery-powered, chip-scale THz spectroscopes for a wide range of sensing and imaging applications.