Assessment of magneto-optic Faraday effect-based drift on interferometric single-mode fiber optic gyroscope (IFOG) as a function of variable degree of polarization (DOP)

Abstract

In this study, a novel interferometric fiber optic gyroscope (IFOG), which has a different depolarizer structure, is designed in TUBITAK UME (National Metrology Institute of Turkey) to experimentally and relatively evaluate the effect of the degree of polarization on the Faraday effect-based drift of the light waves injected into both arms of a Sagnac interferometer. In order to observe whether or not any change occurs in the Faraday-based drift, depending on the variations in degree of polarization (DOP), a triple structure-depolarizer IFOG possessing adjustable DOP is firstly designed and prototyped. The minimum DOP achieved with triple structure-depolarizers is typically 0.15% for both clockwise (CW) and counterclockwise (CCW) light waves at both arms of the Sagnac interferometer. The experimental evaluations about the drift are given for DOP changes extending from 78.00% to 0.15% together with two main and different theoretical approaches in the literature. According to the experimental evaluations given herein, it is experimentally proved that the Faraday-based drift does not change depending on DOP values of both CW and CCW light waves injected into the single-mode (SM) sensing coil and it is impossible to state a concept of a depolarized IFOG by considering the polarization state at the entrance arms of the SM sensing coil.

Design and applications of drilling trajectory measurement instrumentation in an ultra-deep borehole based on a fiber-optic gyro

“…Furthermore, geothermal energy and shale gas are considered to be new "green energies" that can maintain sustainable development, which is of both domestic and foreign concern. Therefore, the development of drilling engineering, in the field of high-temperature geothermal energy and shale gas, is included in the development plan of China (Chen et al, 2015). With increases in borehole depths, there is also an increase in temperature.…”

“…With increases in borehole depths, there is also an increase in temperature. In general, the temperature gradient for a normal formation is about 3 • C/100 m; the maximum temperature of a 3000 m deep oil and gas well can reach over 100 • C. When the borehole depth reaches around 8000 m, the temperature will reach 250 • C. In hot dry rock, areas of high geothermal energy, and other areas with anomalous geothermal gradients, the temperature will be higher (Osipova et al, 2015;Chen et al, 2015). When the depth of the borehole (well) increases, the degree of borehole deviation also increases.…”

Nonreciprocity in single-mode fiber coil induced by orthogonal magnetic field

“…Because each turn of the coil has a certain helix angle, the axial component B A should be decomposed into a parallel unit B A parallel to the light propagating direction and an orthogonal unit B A⊥ orthogonal to the direction. B R induces magnetic drift to IFOGs due to the Faraday effect, the twisting and the residual birefringence from the drawing and winding process of a fiber coil [1][2][3][4]. According to the different birefringence of the fiber used in the sensing coil, IFOGs can be separated into polarized interferometric fiber optic gyroscopes (P-IFOGs) and depolarized interferometric fiber optic gyroscopes (D-IFOGs).…”

Nonreciprocal phase shift caused by magnetic-thermal coupling of a polarization maintaining fiber optic gyroscope

“…Under the action of a radial magnetic field B R , which is perpendicular to the sensing axes of the FOG, the nonreciprocal phase shift Δϕ F generated by the FOG is caused by the combined action of fiber birefringence after winding a coil, fiber twist, and Faraday circular birefringence produced by the magnetic field. The nonreciprocal phase shift Δϕ F is closely related to fiber birefringence Δβ, fiber twist rate φ, fiber length L, and magnetic field B R [2][3][4][5].…”