Development of compact continuous-wave terahertz (THz) sources by photoconductive mixing

Abstract

The electromagnetic terahertz (THz) frequency range is typically defined as 0.1 THz to 10 THz. This frequency range remains as the least developed part of the EM spectrum range, due to the lack of efficient emitters, detectors and transmission technology. Nonetheless, myriad applications of THz waves have been found or proposed, for example: spectroscopy, ultra large bandwidth communications, astrophysics and atmospheric science, biological and medical imaging, security screening and illicit material detection, and non-destructive evaluation. A highly desirable component for many applications is a compact, coherent, continuouswave (cw) solid-state source of THz radiation. Semiconductor-based devices have been known to be highly compact and efficient, as apparent in the productions of integrated-circuits (ICs) and diode lasers. Unfortunately, approaches using traditional semiconductors electronics devices are limited by the significant roll off in output power at such high frequencies due to both transit-time and resistance– capacitance (RC) effects. On the other hand, photonic approaches are limited by the lack of semiconductor materials with sufficiently small bandgaps (1 THz ~ 4 meV). Recently, more techniques to generate THz waves using semiconductor materials are developed. One of such techniques is the photoconductive mixing (photomixing) of two near infrared lasers with THz beat frequency in ultra-fast semiconductor materials. This technique is promising for realization of compact, semiconductor-based and efficient CW THz emitters. This paper discusses on our efforts to develop compact and efficient continuous-wave THz photomixers