Polarization-Resolved Integrated Detectors and Optical Switching Technology for Advanced Terahertz Imaging System

In this dissertation, novel device and circuit technologies for advanced terahertz (THz) imaging systems have been developed and investigated. In order to fully exploit the polarization information available in the THz regime, a polarization-resolved integrated THz detector has been developed and utilized in a THz imaging system. In this single-pixel detector design, zero-biased heterostructure backward diodes (HBDs) were monolithically and orthogonally integrated with a planar dual-polarization annular-slot antenna (ASA) for highly sensitive detection and superior polarization imaging performance. The two linearly polarized components of the incident THz wave have been demonstrated to be individually detected, from which the polarization direction can be obtained. In addition to the polarimetric detection, the polarization-resolved images of THz beams, as well as birefringent crystal samples, have been obtained from the THz imaging system using the integrated HBD detectors. From the imaging measurements, the polarization angular resolution of the THz imaging system has been demonstrated to be as small as 3°.

In addition to the polarization-resolved capability, THz imaging system with frequency selectivity is also of great importance. The employment of high performance optically controlled THz switches is critical to enable such a feature. In this approach, the significant change in conductivity associated with the photogenerated carriers within semiconductor is utilized to develop high performance THz switches. An additional thin layer of insulator has been included between the active semiconductor film and the metal contact to further enhance the carrier concentration by reducing the recombination near the contact. Coplanar waveguide-based switches in series configuration have been modeled and investigated at the frequencies from 140 GHz to 220 GHz. The proposed optically controlled switches outperform both conventional solid-state switches and phase-change material-based switches in the THz regime. On the basis of the high-performance switches, additional tunable and reconfigurable filters have also been proposed, designed, and studied, which shows great promise in developing advanced THz spectroscopic imaging system.