AXIAL STRAIN INSENSITIVITY OF WEAKLY GUIDING OPTICAL FIBERS

A numerical model was developed to calculate the modal phase shift of a circular step index profile weakly guiding optical fiber under axial strain. Whenever an optical fiber is under stress, the optical path l ength, the index of retraction, and the propagation constants of each mode change. In consequence, the phase of each mode is also modified. A relationship for the modal phase shift is presented. This relation i s applied to both single-mode and two-mode fibers to determine the sen sitivity characteristics of strained fibers. It was found that the pha se shift is strongly dependent on the core refractive index n(co). It was also found that it is possible to design fibers that are insensiti ve to axial strain. Practical applications of strain-insensitive fiber s are discussed.