Apparatus using two-mode optical waveguide with non- circular core

Abstract From the Canadian patent

An apparatus utilizes a two-mode optical waveguide with a non-circular core to provide stable spatial intensity patterns in both propagation modes for light propagating therein. The light has a wavelength and the, non-circular core has cross-sectional dimensions selected such that (1) the waveguide propagates light at that wavelength in a fundamental mode and a higher order mode and (2) substantially all of the light in the higher order mode propagates in only a single, stable intensity pattern. Embodiments of the invention include for, example, modal couplers, frequency shifters mode, selectors, and interferometers. One of the interferometer embodiments may be used as a strain gauge. …