Abstract

Compact, cost-effective and frequency-tunable continuous-wave (CW) THz systems are preferable for spectroscopic applications such as atmospheric remote sensing and molecular spectral analysis [1]. Usually, one uses two distributed feedback (DFB) lasers with slightly different frequencies and photomixing [2]. Conventional photomixers such as photoconductive antennas require high bias voltage and have low optical-to-THz conversion efficiency due to low photoconductive gain. In this work we present a THz spectroscopy system that combines a single 1.55 µm two-color semiconductor laser providing up to 3 THz beat frequency with an InP-based high-speed photodiode (PD) as the photomixer [3]. To our knowledge, we were the first to build an external-cavity two-color laser at 1.55 µm and to use it for THz spectroscopy systems. Moreover, the PD chip maintains the photomixing efficiency by optimizing the transit time to increase the speed. With this compact spectroscopy setup, we show preliminary results in water absorption measurements.

© 2017 IEEE