The photomixer transceiver

Summary form only given. In the time domain, terahertz photoconductive sampling has been used by many groups for spectroscopy in free space and on transmission lines over several THz of instantaneous bandwidth. These systems consist of two fast photoconductive switches that are excited by a mode-locked laser and are coupled to each other via antennas or transmission line. In the frequency domain, photomixers that use low-temperature-grown GaAs photoconductors illuminated by two cw diode lasers have generated cw difference-frequency radiation from 200 MHz to 5 THz. These sources have application as local oscillators and for high-resolution gas spectroscopy when coupled to a cryogenic detector such as a bolometer. Until now, there has not been a demonstration of photoconductive sampling using photomixers. This paper describes a general technique for performing photoconductive sampling in the frequency domain. For spectroscopy applications that require narrow-resolution linewidth (<1 MHz), this technique can offer significant improvement over time-domain sampling in spectral brightness (/spl sim/10/sup 6/ times higher). Furthermore, the system is coherent, widely tunable, and can be compact-using inexpensive diode lasers that are fiber coupled to photomixer transmitter and receiver chips.