Multi-wavelength demultiplexer for fiber optical communication

Abstract

A multi-wavelength optical demultiplexer includes at least three relatively thick layers of direct band gap semiconductor material deposited on a substrate. The various thick layers are separated by respective, individual, relatively thin layers of lattice matched material having a larger band gap than the materials in the thick layers. The thin layers, deposited on the thick layers, serve as a potential barrier to prevent photo-electrons generated in one layer from entering another. Ohmic contacts of donor impurity diffusion are provided at opposite ends of each relatively thick layer. With a substrate of gallium arsenide, the relatively thick layers can be aluminum gallium arsenide of varying compositions, in which the proportions of aluminum to gallium decreases from the layer distal to the substrate to the layer proximal to the substrate. Each of the relatively thin layers can be aluminum arsenide; the relatively thick layers are on the order of ten microns thick; the relatively thin layers are on the order of 100 Angstroms thick. When the substrate is indium phosphide, the relatively thick layers are indium gallium arsenide phosphide in which the relatively thick layers are in the order In.sub.x Ga.sub.1-x As.sub.y P.sub.1-y for x=2.16(1-x) where each of the layers can be produced by the process of molecular beam epitaxy.