ABSTRACT
Optical fiber sensors are now widely used as parts of measuring systems for monitoring various technical and natural systems. Optical fiber sensors that implement the frequency shift of the transmitted radiation are much more resistant to interference due to the fundamental nature of the wavelength. Interference-aided converters commonly utilize a pair of single-mode optical fibers, with one fiber exposed to an external physical influence and the other used as a reference. For higher-order modes, which are nearer to the cutoff frequency, the light energy is confined closer to the fiber core boundaries, which means that the transfer to the unguided modes takes place at smaller external influences, compared to the lower-order modes. The physical principle behind the design of an optical fiber converter is mode coupling due to fiber deformations, which leads to the energy being redistributed between the modes and partially transferred to non-propagating modes.
