Analysis Of Thermally Induced Nonreciprocity In Fogs And Sensing Of Temperature Distribution In The Optical Fiber Coil

FOGs (Fiber Optic Gyroscopea), very important inertial instruments, have wide applications in armaments and civil vehicles Shupe effect is one of main factors affecting FOGs' accuracy. Ideally, the quadrupolar winding of the optical fiber coil can restrain thermally induced nonreciprocity obviously, however, various nonideal factors severely limit the advantage of the quadrupolar winding. In this theme, the analyses were performed, for the damages induced by the midpoint deviation and the fiber diameter to the symmetry between the counterpropagating lights coming from the quadrupolar winding. A formula was derived and given to calculate the Shupe effect in the quadrupolar winding including the effects of the midpoint deviation and the fiber diameter. This formula, compared with that considering only the ideal situation, can not only be used to account the thermally induced nonreciprocal phase shift under different midpoint deviations and fiber diameters, but also indicate the effects of the fiber coil's structure when there exist nonideal factors. Numerical calculations of the Shupe effect under given environmental temperatures showed that the Shupe effect introduced by the midpoint deviation and the fiber diameter has significant restrains to the performance of FOGs. Some guidance conclusions were gotten also.The temperature distribution sensing of the optical fiber coil is the precondition of the temperature compensation of FOGs In this paper, two schemes of the temperature sensing were designed by using the optical fiber gratings according to the structural characteristics of the optical fiber coils, and their feasibilities were analyzed. The scheme using appended optical fiber gratings has some advantages, such as, accurately measuring at real time, multipliable at different points, free of impact on the normal working of the gyroscopes, etc.. A novel scheme of demodulating grating's sensing wavelength adopting a piece' of polarization-maintaining fiber was designed. Through introducing a Sagnac loop, the polarization dependant problem of output of the polarization-maintaining fiber was overcome. An experimental system of temperature sensing using an optical fiber grating was set up. The temperature sensitivity of a sensitivity-enhanced fiber Bragg grating was tested. An experiment using a long period grating to demodulate the sensing wavelength was performed.The present study in this paper can be expected to provide fundamentals for the control and compensation of Shupe effect of FOGs.