Modeling of Influence of Shupe Effect on Fiber-Optic Goniometer with different coil winding types

Abstract

One of key errors of the classic interference-type fiber-optic goniometer is the thermo-optical zero shift. Its caused by the non-uniform change of temperature of different fiber sections in the loop under the influence of temperature; as a result of that, counter-rotating waves get different phase incursions during stretching of fiber in the loop, thus creating thermo-optical zero shift (Shupe effect). Difference of the phase incursions of counter-rotating waves is the bigger the higher speed of fiber length change is, and the higher difference of delay time of those waves. The current study is focused on the modeling of influence of the Shupe effect on on the precision of the fiber optic goniometer. The key features of the goniometer mentioned are use of the copper coil carcass and compound with high thermal conductivity (use of nanotubes is desired). Different coil winding types (simple, dipole quadrupole, modified quadrupole, bifilar, octupole) are considered from the point of view of minimizing the thermo-optical zero shift under self-heating and influence of the ambient temperature changes. Analysis is based on the transient thermal analysis of finite element model of the goniometer performed in ANSYS environment with subsequent data import and integration of phase incursion, calculated based on temperature data, along the fiber length. Study results show that best results during self-heating gives the use of quadrupole winding, at that goniometer's zero shift changes insignificantly (about 0.08°, compared to 1,35° for the simple winding). Change of ambient temperature for a given design has almost no influence on the zero shift, as device is heated uniformly. One should note that as during modeling not all factors could be taken into account, the result obtained should be checked and qualified during FOG tests.