Photonic THz-wave generation by UTC-PD and its related device

Abstract

The generation of continuous THz-waves by photomixing has several promising features, such as extremely-wide frequency tunability, very narrow linewidth, good frequency stability, and the ability to transmit high-frequency signals through low-loss optical fibers. To make such a scheme work effectively, we developed an InP/InGaAs uni-traveling-carrier photodiode (UTC-PD) [1, 2]. The UTC-PD has a unique mode of operation where only electrons are the active carriers that travel through the device. This feature provides several advantages over the conventional photodiode, such as higher operation speed, larger output saturation current, and lower operation voltages. Several kinds of planar antennas were integrated with the UTC-PDs for emitting THz-waves. Use of a self-complementary antenna could generate broadband signals at frequencies of up to 3 THz. Resonant antennas were utilized to increase the output power from the UTC-PDs. We could enhance the THz-wave output powers by factors of up to about four while restricting the operational bandwidths due to the resonant design. A comprehensive solution with a relatively wide bandwidth and enhanced output power was also designed for practical use. Furthermore, for measurements that require polarization discrimination, we developed antenna-integrated UTC-PDs to generate stable and linearly polarized signals with broad bandwidth. To make the best use of the photomixer, we also developed a THz-wave detector called a Fermi-level managed barrier (FMB) diode [3]. The FMB diode has a very low barrier height (below 100 meV), and this feature simultaneously enables a broad bandwidth and low noise-equivalent-power (NEP). The fabricated device could detect THz waves at frequencies from 200 GHz to 1 THz with large current and voltage sensitivities.