Research On Mechanism And Suppression Measures Of Magnetic Field Error Of Fiber Optic Gyroscope

The interferometric fiber optic gyroscope(IFOG)is used in a variety of applications,including ship and submarine and satellite,along with missile for their advantages of truly solid-state,without moving parts,light weight,small size and flexible structure.With the expansion of its application scope,the deterioration of precision in the harsh environment(thermal perturbations,magnetic field and vibration transients)has became an important factor that restricts the development of IFOG.Under the action of magnetic field,magnetic field error of IFOG may occur through the magneto-optic Faraday effect and magneto-optic nonreciprocal phase shift in the fiber.Therefore,analyzing its generation mechanism and exploring the effective suppression measures are particularly significant.Up to now,most of the models of magnetic field error are built at room temperature.Actually,the working environment of IFOG is often accompanied by a wide range of temperature changes.Besides,although the current suppression measures of magnetic field error can reduce the magnetic field sensitivity of IFOG to some extent,there are still some defects.In view of the above-described situation,this dissertation further researches the mechanism and suppression measures of magnetic field error to improve environmental adaptability and precision of IFOG.In terms of the mechanism of magnetic field error,the models of magnetic field error at room temperature are built by Jones matrix method,and the relationship between the parameters of fiber and fiber coil and the magnetic field error is analyzed based on these models.After that,based on the magnetic field error models at room temperature,the relationship between the magnetic field error and temperature in IFOG with non-skeleton coil is deduced by Jones matrix method.Theoretical results show that the magnetic field error changes with the temperature,which is result from the temperature dependence of linear birefringence and Verdet constant of polarization maintaining fiber(PMF).Finally,experiments of testing the radial magnetic field error under the temperature range of-40oC to 60oC are carried out,and the experimental results support these theoretical predictions.In the aspect of the suppression measures,a series of suppression measures are proposed for enhancing the interference immunity to magnetic field based on the magnetic field error models.The following four parts are included in this aspect:(1)The optical compensation method is proposed to suppress the magnetic field error of IFOG at the system level.Jones matrix method is utilized to formulize the magnetic field error in dual-polarization IFOG under room temperature and variable temperature.Theoretical results indicate that the radial magnetic field error in two orthogonal polarizations of PMF have opposite polarities at room temperature.When the two orthogonal polarizations of PMF are utilized simultaneously,the radial magnetic field error can be optically compensated.Particularly,the temperature dependence of radial magnetic field error in two orthogonal polarizations is the same,and the optical compensation method is still valid regardless of the variation of temperature.Experiments of measuring radial magnetic field error of dual-polarization IFOG under room temperature and variable temperature are performed,and the experimental results confirm the validity of these theoretical predictions.(2)On account of the potential error that caused by calculating magnetic shielding effectiveness with the magnetic field intensity at the central point,the mean value of magnetic field intensity at the space of fiber coil is proposed to calculate magnetic shielding effectiveness accurately at the magnetic shielding level.On this basis,the relationships between the parameters of magnetic shielding and magnetic shielding effectiveness are analyzed by finite element method(FEM),and a single-layer magnetic shielding which has magnetic shielding effectiveness of 40 dB under radial magnetic field and axial magnetic field is proposed.(3)The radial magnetic field error of IFOG is inversely proportional to the birefringence of PMF.To overcome the defect of low birefringence of traditional PMF,a novel pentagonal photonic crystal fiber(PCF)with high birefringence is proposed at the fiber level.The relationships between birefringence properties and structure parameters of pentagonal PCF are researched by FEM.A pentagonal PCF with high birefringence,which can suppress the radial magnetic field error effectively,is proposed.(4)In order to eliminate the temperature drift caused by the compensation fiber coil,an IFOG with dicyclic coils is proposed at the winding method level of fiber coil.By adjusting the radial magnetic field sensitivity axis of the dicyclic coils,the radial magnetic field error in IFOG with dicyclic coils can be compensated effectively.More importantly,due to the same length of fiber coils,the additional temperature drift will disappears when the dicyclic coils are assembled in an appropriate heat-off spool.