Characterization and Analysis of Continuous Wave Terahertz Photomixers

Abstract

In recent years, Terahertz (THz) technology has become a very active field of research in regards to its wide range of potential applications such as biosensing, biomedical imaging, pharmaceutical, security, and many others. There are different methods to generate THz radiation. Photomixing is one of the Continuous Wave (CW) THz generation methods in which the output of two single-mode lasers or the output of a dual-mode laser with different center frequencies are combined in a nonlinear medium such as photoconductors or superconductors. The photomixing system is designed such that the difference of the laser frequencies falls in the THz range. The generated THz wave can be coupled to an integrated antenna or waveguide. The CW THz photomixer sources are potentially compact, low cost, low power consuming, coherent, and highly tunable. However, the primary disadvantage of using photomixers is that the output power is relatively low compared with other THz sources. Photomixer modeling requires solving both semiconductor and electromagnetic problems. In contrast to most of the researches which only report either experimental results or simple analytical model to characterize the photomixers, in this research, a computational simulation method is presented to analyze and model the photomixer devices. The proposed computational method combines a semiconductor solver and a full-wave electromagnetic simulator to rigorously analyze and optimize an integrated THz photomixer antenna device. In this method, by solving Maxwell’s equations and then the drift-diffusion charge carrier transport model, the generated THz photo-current inside the photomixer device is obtained. This THz photo-current is modeled as a current source in the antenna feed to find the radiated THz power. Using the proposed simulation method the effects of photomixer parameters on the THz photo-current and radiated power is accurately investigated and the results of a parametric study on various parameters such as carrier lifetime of material, incident optical power density, applied bias voltage, the THz beat frequency, and the gap size are presented.