We show that phohtonic technologies developed for conventional fiber-optic communications have potential for use in
contemporary terahertz-wave applications, such as remote sensing and wireless communications. Advanced unitravelling
photodiodes (UTC-PDs) can produce output power of 0.5 mW at 350 GHz and 10 μW at 1 THz. Using the
UTC-PD and other optical devices, we demonstrate a time-continuous terahertz-wave signal generator that can tune the
output signal over a wide frequency range with very narrow spectral linewidth and gas-sensing with the terahertz-wave
source. We also show some preliminary results for terahertz-wave wireless communications using photonic technologies.
We developed an active gas sensing system with a highly- sensitive sub-terahertz (THz) wave receiver consisting of a
superconductor-insulator-superconductor mixer and a photonics-based THz-wave local oscillator. Continuous
monitoring of the gas contents in the gas cell was successfully carried out with the developed system. The high
sensitivity of the developed THz-wave receiver makes it possible to extend the detection range up to 30 m.