Effect of external relative pressure on phase shift in Sagnac interferometer

Abstract

Subject of Research. The paper considers the effect of a relative pressure change on the H-parameter value in a birefringent optical fiber with ESC-4 elliptical straining cladding and in Sagnac coil with 140 mm diameter and 700 m length. We analyze the effect of a relative pressure change on the phase shift in Sagnac interferometer. Method. The broadband interferometry method was used for the H-parameter estimation. Michelson polarizing scanning interferometer with a broadband source with a 1560 nm central wavelength and a 45 nm bandwidth was applied. The relative pressure was varied in a special pressure chamber in the range from –80 kPa to +300 kPa. Main Results. It is found out that when the relative pressure changes, random phase jumps occur in Sagnac interferometer. Such random phase jumps are not observed under normal conditions. It is also shown that the effect of increased relative pressure on Sagnac phase shift is more pronounced than the effect of reduced relative pressure; the frequency of phase jumps is greater in case of increased relative pressure. Practical Relevance. Analysis of research results is focused on the problem of high-quality winding and laying of birefringent optical fiber in Sagnac coil, which will improve the accuracy characteristics of fiber- optic sensors based on Sagnac interferometers.