In the successful approach to millimeter-wave and particularly submillimeter wave circuity, it has become apparent the techniques commonly used in the microwave region are inapplicable. It has recently been demonstrated that laser-excited highly conductive bulk semiconductor (silicon or gallium arsenide) can be used for high-speed optoelectronic controlled devices getting signals up to the submillimeter-wave region . The advantages of optical control include short response time, high modulation rates, inherent high dc and reverse-signal isolation, compatibility with optical fibers, immunity to electromagnetic interference and low cost. With the rapid development of solid-state millimeter devices and electrooptics, it became apparent that this devices and systems can be controlled by optical illumination.
V. V. Gusakov,
"Light controlled millimeter-wave devices", Proc. SPIE 1576, 16th International Conference on Infrared and Millimeter Waves, 157642 (1 October 1991); doi: 10.1117/12.2297859; https://doi.org/10.1117/12.2297859