An optical device comprises a first optical coupler configured to receive a light signal and provide a first output and a second output, a first optical waveguide in optical communication with the first output and configured to provide a first optical path for a first portion of the light signal, and a second optical waveguide in optical communication with the second output and configured to provide a second optical path for a second portion of the light signal, wherein the first optical waveguide is configured to provide a phase differential between the first optical path and the second optical path, wherein the second optical waveguide is positioned according to a lateral thermal diffusion length associated with the first optical waveguide, and wherein the lateral thermal diffusion length is a spreading distance of a thermal effect in a direction about perpendicular to the first optical path.