Incorporated bragg filter temperature compensated optical waveguide

Abstract

A temperature compensated embedded grating optical waveguide light filtering device includes an optical fiber having an elongated core in which light is guided toward a core portion of a predetermined limited length that has embedded therein a multitude of grating elements extending with a substantially equal longitudinal spacing substantially normal to the longitudinal axis and collectively constituting a grating that reflects, of the light propagating in the path toward and reaching the grating elements, that of a wavelength within a narrow range about a central wavelength determined by the spacing of the grating elements and by the index of refraction of the material of the core as influenced by the temperature of and longitudinal strains applied to the grating, back into the path for longitudinal propagation therein opposite to the original propagation direction. Each end of the fiber portion is attached to a different one of two compensating members made of materials with such coefficients of thermal expansion relative to one another and to that of the fiber material as to apply to the fiber longitudinal strains the magnitude of which varies with temperature in such a manner that the changes in the central wavelength that are attributable to the changes in the longitudinal strains substantially compensate for those attributable to the changes in the temperature of the grating.