Theory of optically controlled millimeter-wave phase shifters

In this paper the millimeter-wave propagation characterstics of a dielectric waveguide containing a plasma-dominated region are analyzed. Such a device presents a new method for controlling millimeter-wave propagation in semiconductor waveguides via either optical or electronic means resulting in ultrafast switching and gating. The phase shift and attenuation resulting from the presence of the plasma are calculated. Higher order modes, both TE and TM, as well as millimeter-wave frequency variation, are studied in both Si and GaAs dielectric waveguides. A surface plasma model that is a good approximation to the more elaborate volume plasma model is formulated. Phase shifts are predicted to be as high as 1400 deg/cm for modes operating near cutoff. These modes suffer very little attenuation when the plasma region contains a sufficiently high carrier density.