An optically controllable millimeter-wave phase shifter

In this research, an optically controllable millimeter-wave phase shifter is introduced and its fabrication and measurements are reported. Optical controlling of millimeter-wave devices has the advantage of high isolation between the controlling signal and the controlled RF signals. The proposed device has high power handling capability. The phase shift is achieved by changing the complex relative permittivity of a high-resistivity crystalline silicon (HR c-Si) slab as a result of optical induction of plasma. A low-cost high-power LED is used as the optical source whose parameters are measured in a first step. Moreover, the impact of the optical source parameters on the characteristics of the induced plasma is studied. An insertion phase shift of 32 degrees is demonstrated in the frequency range of 26.5 to 28.5 GHz with an RMS phase error of 5 degrees.