BIREFRINGENCE MEASUREMENT UNDER HYDROSTATIC-PRESSURE IN TWISTED HIGHLY BIREFRINGENT FIBERS

A new method of birefringence measurement in highly birefringent fiber s influenced by hydrostatic pressure conditions up to 100 MPa is prese nted. The birefringence measurement method is based on twist-induced e ffects and has never been applied before in a high-pressure environmen t. The experiments were conducted using a specially designed pressure facility, which made it possible to simultaneously generate several me chanical perturbations, including twist and hydrostatic stress, and to investigate their effects on mode transmission in optical fibers. The results indicate that in the case of HE single-mode bow-tie fibers, h ydrostatic pressure up to 100 MPa increased birefringence with a mean coefficient of (1/Delta beta(0))(Delta beta)/dp = 0.,2%/MPa which is i n very dose agreement,vith our previous measurement based on Rayleigh scattering.