Ultrafast, all-silicon light modulator

An ultrafast, all-silicon light-intensity modulator is proposed. The carrier-refraction effect is used to modulate the refractive index of silicon. An electric-field-induced Bragg reflector on a silicon-on-insulator optical waveguide efficiently converts the small modulation of the index of refraction into light-intensity modulation. A modulator with 300-microm interaction length is expected to have a modulation depth of ~40% with 5-V bias. Being based on free-carrier depletion, this modulator is expected to have a bandwidth limited only by the RC time constant, which is calculated for a sample device to be ~40 GHz.