Abstract: Modulation-doped quantum well heterostructures are cascaded in a semiconductor device to achieve high speed operation while obtaining large index of refraction or absorption coefficient changes for modulating lightwave signals without significant increases in the operating potentials over prior quantum well structures. Each modulation-doped quantum well heterostructure exhibits substantially equal boundary conditions in an unbiased condition for efficient cascading or stacking. Each quantum well has associated with it a barrier layer to minimize leakage current. As a result, each quantum well has associated with it a separate charge reservoir. This aspect contributes to the speed of the cascaded structure. When incorporated within a waveguide structure, cascaded modulation-doped quantum well heterostructures can act as an external modulator, or as an intra-cavity wavelength tuning element, or as an intra-cavity modulator, or even as an optically-pumped laser.

Abstract: Information borne by an optical signal at a first wavelength is transferred intact to another optical signal at a second wavelength and vice versa via an optoelectronic circuit employing quantum well devices connected serially to facilitate self electrooptic effects therein. The optoelectronic circuit accepts two input signals and provides two output signals wherein an input signal and its corresponding output signal are at the same wavelength. Bidirectional information transfer with bidirectional wavelength conversion is permitted by the optoelectronic circuit.

Abstract: Optical apparatus is disclosed wherein narrow line width light from a source is directed through the substrate of a semiconductor structure and reflected from the gate electrode of a field effect transistor element fabricated on the surface of the semiconductor structure. A quantum well layer serves as the current channel for the field effect transistor, and charge carries from a doped semiconductor layer provide high mobility carriers in the quantum well layer. Changes in the potential between the gate and source electrodes of the field effect transistor causes the normal pinchoff of carriers in the quantum well layer thereby causing changes in the absorption characteristic presented by the quantum well layer.