Analysis of thermal phase noise in fiber-optic sensors

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Abstract
An analysis is conducted of the thermally induced phase noise in a fiber‐optic interferometer. This phase noise will represent the lower detection limit of fiber‐optic sensors used for detecting low‐ level magnetic fields. The method herein uses a statistical approach to find the general form of the solution, and then relates this solution to the thermal properties of the fiber. Phase noise spectra are calculated over the region of 0.01–10 Hz. The spectral power density is found to vary as ω−7/2 over this spectral range. The analysis also shows that the major portion of the noise arises in the uncoated fiber. Noise may be reduced by using metallic coatings of low emissivity and, to some extent, by increasing the fiber diameter.