Distributed photomixers

Summary form only given.The photomixer is a solid-state, tunable source capable of producing coherent radiation in the millimeter-wave and submillimeter-wave frequency range. Photomixers have been demonstrated as local oscillators for heterodyne astronomy and as sources for terahertz (THz) spectroscopy. Photomixers generate coherent radiation at the difference frequency of two lasers by performing optical heterodyne downconversion in low-temperature-grown gallium arsenide (LTG-GaAs). The conductance of a dc-biased LTG-GaAs switch is modulated by the optical beat signal of the beam-combined output of two lasers. In the new distributed design, the switch is no longer a lumped element but is distributed along the length of a THz coplanar strip waveguide. The optical beat signal is guided by a dielectric ridge waveguide and is evanescently coupled to the switch and coplanar strips (CPS) fabricated on top of the ridge waveguide. A larger switch allows for greater power handling capability, because the optical signal is absorbed more gradually. The distributed design offers the possibility of higher output power and broader band performance. We present measurements from the first generation of these devices.