Integrated THz Spectroscopy exploiting On-chip Scattering and Device Nonlinearity

Princeton University, Princeton NJ

Investigators

Abstract

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.