Characteristic Research Of The Polarization Maintaining Photonic Crystal Fibers With Near-elliptic Inner Cladding Structure

Photonic crystal fibers (PCFs) consisting of a central defect region surrounded by multiple air holes running along its length have been the subject of much interest in recent years because of their unique properties which are not realized in conventional optical fibers. Using PCFs, highly birefringent fibers, even single mode single polarization fibers, can be easily realized, because the index contrast is higher than conventional fibers and the fabrication process permits the formation of the required asymmetric microstructure near the fiber core. So far, various highly birefringent PCFs have been presented. It has been shown that their birefringence is of the order of 10^-3, which is at least one order of magnitude larger than that of conventional fibers. These highly birefringent PCFs have great application potential in the field of optical communication, e.g. polarization-sensitive optical modulators and in the field of fiber sensing, e.g. fiber gyros. However, the birefringence and dispersion properties of those actual PCFs are different from the idealized ones because of the unpredictable perturbations of the microstructures which are induced by the practical fabrication process. In this dissertation, the properties of the polarization-maintaining PCFs are investigated deeply, such as modal birefringence, dispersion and polarization stability.The main achievements of this dissertation are summarized in two parts:1. Four kinds of reported polarization-maintaining PCFs are analyzed by using a full-vector finite element method, of which the modal birefringence curves and dispersion curves are provided. From the numerical results, it is confirmed that the highly modal birefringence is realized as the reported microstructures promised. Further more, the analyses of the polarization stabilities of those PCFs are proposed in this dissertation, which is meaningful for the designing and fabricating of the polarization-maintaining PCFs with higher error tolerance.2. A new polarization-stable highly birefringent photonic crystal fiber designed for fiber gyros is proposed. By varying the diameters of the air holes near the fiber core gradually, a new inner cladding structure with near elliptic refractive index distribution is proposed. The theoretical analyses confirm that the proposed small MFD PCF promises highly modal birefringence with high polarization stability, which can be applied in highly accurate fiber gyros.