Research On Novel Hybrid Hollow-core Micro-structured Polarization-maintaining Fiber

Fiber Optic Gyroscopes（FOGs）,as optical fiber sensors,have the advantages of all-solid state,long life and high reliability,etc.And FOGs have become high-precision angular velocity sensors which are widely used in the fields of inertial navigation and guidance,such as sea,land,air and space.The polarization-maintaining fiber ring is the core component of the current FOG.Due to the performance limitations of traditional solid-core polarization-maintaining fibers,non-reciprocal optical noises,caused by backscattering,nonlinear effects,Faraday effects,and polarization crosstalk limits the improvement of precision and long-term stability of FOG.Hollow-core polarization-maintaining fiber（HC-PMF）can guide light in a hollow core,and has unique advantages such as low nonlinearity,low backscattering,and high temperature stability.The HC-PMF replaces the traditional solid-core polarization-maintaining fiber to construct a fiber loop,which is expected to break through the current bottleneck of FOG’s accuracy and long-term stability improvement.And it is of great significance and application potential to the development of high-precision FOG.In this thesis,the light guiding mechanism and new structure design of hollow-core micro-structure polarization maintaining fiber are studied,aiming at improving the birefringence or single polarization performance of polarization maintaining fiber.The main research achievements in this thesis are as follows:1.The research progress of HC-PMF is overviewed.And the designed methods and challenges of HC-PMF are summarized.The finite element analysis model is introduced.Combined with the characteristic analysis of the hollow core photonic bandgap fiber（HC-PBGF）and the hollow core anti-resonant fiber（HC-ARF）,the accuracy and validity of the finite element analysis model are verified,which lays a theoretical foundation for the subsequent development of new structure of hollow-core micro-structure polarization maintaining fibers.2.A novel hybrid hollow-core micro-structure polarization-maintaining fiber with hybrid light guiding mechanism is proposed by combining the advantage of photonic bandgap effect and anti-resonant effect.High birefringence can be achieved by introducing a pair of negative curvature anti-resonant layers into the air core of a 7-cell HC-PBGF to obtain two-fold rational symmetry.The results show that the birefringence can reach 10^-3 and the single-mode can be obtained within the 200 nm bandwidth covering the wavelength range from 1.45μm to 1.65μm.Especially,the birefringence is up to 3.38×10^-3 atλ=1.55μm.The structure also exhibits strongly bending resistance.The bending radius can be maintained in the magnitude order of millimeters,and the fiber properties are insensitive to bending direction.3.A low-loss single-polarization single-mode HC-PBGF with anti-resonant tubes in the core and defect holes in the cladding is proposed.The single-polarization can be achieved by introducing the small defect holes in the horizontal direction of 19-cell HC-PBGF’s cladding.By introducing evenly distributed anti-resonant tubes in the fiber core,the coupling between the core modes and the surface modes in HC-PBGF is limited,thus the loss is effectively reduced.Single polarization and single-mode operation can be realized simultaneously.The results show that the surface scattering loss is reduced from 6.12 d B/km to 2.6 d B/km,and the polarization loss ratio is up to 1.84×10⁵ atλ=1.55μm.And the single-mode bandwidth is as high as 240 nm.