Broadband photonic terahertz-wave emitter based on planar-antenna-integrated UTC-PD

The uni-traveling-carrier photodiode (UTC-PD) is a promising device for generating continuous terahertz (THz) waves by photomixing since it simultaneously operates at very high frequencies and generates relatively high output powers. These features are due to its unique operation mode utilizing only electrons as the active carriers. To utilize the performance of the UTC-PD fully, monolithic integration of an appropriate broadband antenna is essential. We fabricated devices integrating several types of planar antennas and compared their characteristics. Although all the modules exhibited broadband output characteristics at frequencies up to 1.6 THz, the behaviors at the lower frequency side as well as their polarization characteristics were quite different. Using a device integrating a novel planar antenna, we could detect output powers at frequencies from 30 GHz to 1.6 THz with almost constant polarization. Typical detected output powers were 120 μW at 200 GHz, 17 μW at 500 GHz, and 2.9 μW at 1 THz for a photocurrent of 10 mA with a bias voltage of only -0.6 V.