Analysis of the errors in free space coupling setup used in an air-core photonic bandgap fiber ring resonator for rotation sensing

The fiber ring resonator is the key component of resonator fiber optic gyros. The configuration of an air-core photonic bandgap fiber (air-core PBF) ring resonator is proposed based on a kind of free space coupling setup (FSCS). The Mathematical model of such kind of ring resonator is derived. With relevant model derivation, the effects of different parameters, including fiber coupling efficiency, alignment of fiber polarization axis and backscattering of fiber end faces, on the performance of ring resonator are simulated. It is clarified that the performance of air-core PBF ring resonator can be greatly influenced by radial linear alignment of air-core PBFs, angular alignment of air-core PBFs, the difference of incident polarization angles and the angle of air-core PBF end faces. According to the simulation, the theoretical model of the FSCS has been established. Furthermore, the solutions to three errors in the FSCS have been advanced, respectively.