Strain-isolated bragg grating temperature sensor

Abstract

A strain-isolated bragg grating temperature sensor includes an optical sensing elementwhich includes an optical fiberhaving at least one Bragg gratingdisposed therein which is encased within and fused to at least a portion of a glass capillary tubeand/or a large diameter waveguide gratinghaving a core and a wide cladding and having the gratingdisposed therein, which senses temperature changes but is substantially not sensitive to strains on the element caused by the fiber or other effects. Lightis incident on the gratingand lightis reflected at a reflection wavelength λ1. The shape of the sensing elementmay be other geometries and/or more than one concentric tube may be used or more than one grating or pair of gratings may be used or more than one fiber or optical core may be used. At least a portion of the elementmay be doped between a pair of gratings, disposed therein to form a temperature tunable laser or the gratingor gratingsmay be constructed as a temperature tunable DFB laser disposed in the element. Also, the element may have an inner or outer tapered regions, respectively, to provide strain relief and/or added pull strength for the fiber. Further, the fiberand the tubemay be made of different coefficients of thermal expansion for increased sensitivity.