Optical modulation by surface states

In this paper, the effect of two-dimensional electron plasma formed on the surface of a semiconductor on the refraction phase of an optical beam is investigated. Both the density and effective mass of the surface state electrons can be controlled by a transverse electric field. While the surface density of electrons varies slowly with the applied field, their effective mass changes instantaneously. Therefore, a high bandwidth for the phase modulation can be obtained. It is expected that the device operates in the far-infrared region with a semiconductor as the base material. GaAs is one of the best candidates having both large dynamic range, and large ratio of free electron to the crystal effective mass. The device operates in a waveguide configuration, as discussed throughout the paper. The electron effective mass is found through quantum mechanical calculations, and the interaction with the incident light beam is treated classically. Finally, a waveguide light phase modulator is proposed.