Isolators, polarizers, and other optical waveguide devices using a resonant-layer effect

This paper investigates the effect of a high-refractive-index layer added onto the clad layer of an optical waveguide. With proper design, the value of the fundamental mode´s confinement factor in the added layer can exhibit a resonance. This resonance depends on the added layer´s location, thickness, complex index, and wavelength of operation. If loss is incorporated into this added layer, relatively small changes in waveguide properties can result in large changes in loss. This phenomenon is referred to in this paper as the resonant-layer effect (RLE). A number of devices, including isolators, polarizers, and modulators, can be made and/or improved by using the RLE. As examples, this paper describes an integratable isolator giving 240-dB/cm isolation and 13-dB/cm insertion loss, an integratable polarizer with 90-dB/cm rejection and about 0.8-dB/cm insertion loss, and a 300-μm-long modulator requiring electric fields of ±5 V/μm for ∼45% intensity modulation. In general, the resonant layer need not be epitaxial with the waveguide, allowing for integration with a variety of material systems.