US Patent 5067828: Transferred electron effective mass modulator

An optical modulator having a waveguide region comprising first and second layers of material having differing effective masses for free charge carriers at a predefined band edge energy disposed immediately adjacent to each other and covered by a lower refractive index cladding. A preferred embodiment employs a semiconductor system such as Aly Ga1-y As for the first and second material layers with the value of y adjusted between the layers so that the conduction band edge energies of the direct band in one layer is about the same as that of the indirect condition band in the other layer. A mechanism is provided for moving charge carriers between the first and second layers, such as metal contacts and a power source for applying electrical fields to the waveguide structure in a desired modulation pattern. The material layers may be deposited as a series of quantum wells with limited disordering or a ridge structure used to obtain lateral confinement. In addition, the optical modulator can comprise a photodetector or a second control waveguide positioned adjacent to the waveguide region and electrically connected to the waveguide to alter electrical fields applied to the waveguide in response to optical signals.