A temperature-insensitive Bragg grating sensor—Using orthogonal polarisation modes for in situ temperature compensation

An exposed Bragg grating incorporated into a planar waveguide forms an optical device that acts as a refractive index sensor. The exposed evanescent field causes the Bragg peak to be sensitive to the refractive index of its surroundings and can be used to detect changes in this environment. The method reported is able to provide accurate temperature compensation by applying a scaling factor derived from measurement of the birefringence of the transverse electric (TE) and transverse magnetic (TM) modes of the Bragg reflection. For a fluid sensor, fluctuations in ambient temperature can be both accounted for and compensated to produce a temperature-insensitive sensor.