Monolithic dual mode emitter-detector terminal for optical waveguide

Abstract

There is disclosed a monolithic dual mode emitter-detector terminal for optical waveguide transmission lines such as optical data busses or links which terminal serves in one mode to introduce an optical signal onto the line for transmission from one point and in its other mode to read a signal off of the line at the same point. The line includes a plurality of such terminals each of which is a monolithic device having the dual functions or dual modes of sending and receiving. Each terminal comprises a P-N junction diode positioned in optical signal transmissive relationship to the waveguide element. Associated with the diode are switching means to selectively D-C bias the diode in the forward direction for the emitter mode of operation and in the reverse direction for the detector mode of operation. The diode is formed in a direct bandgap semiconductor having overlapping absorption and emission spectra and being doped to produce maximum emission at the shorter wavelengths of the absorption spectrum to increase the efficiency of the diode as an emitter at the expense of its efficiency as a detector which detector efficiency is increased by the Franz-Keldysh effect which shifts the edge of the absorption spectrum to longer wavelengths in the presence of an electric field such as that produced by reverse biasing the diode.