Bending-induced phase shifts in dual-mode planar optical waveguides

Abstract

We examine the manner in which the effective index for each of the two modes of a bent dual-mode planar waveguide changes with curvature. We find that the bending-induced changes in the effective indices depend strongly on core-cladding index contrast and the value of V. For waveguides with large contrast, the changes in effective indices are such that the change in the phase difference between the modes is positive (or negative) at large (or small) values of V. The change becomes zero at a V value that depends on the waveguide parameters and curvature. If the index contrast is small, the bending-induced phase difference may change sign with increase in curvature. This might help in ultimately explaining the bipolar phase shift seen in a recent experiment. The results of our study can be used to increase or decrease the bending sensitivity of dual-mode optical-waveguide sensors and devices.