General treatment of the thermal noises in optical fibers

A general framework based on the fluctuation-dissipation theorem has been outlined for the study of the spontaneous thermal fluctuations in optical fibers. The goal is to seek a unified scheme to analyze the two types of intrinsic noises found in fiber lasers and interferometric fiber-optic sensors, namely, the thermoconductive noise and the thermomechanical noise. Some outstanding questions in the current theories are addressed. These include: (a) the underlying relation between the thermoconductive and the thermomechanical noises, (b) the lack of a fully disclosed theory for the thermoconductive noise in passive fibers, and (c) the low-frequency restriction in the current theory of the thermomechanical noise. Specific analyses based on the proposed approach find excellent agreement with existing theories.