Highly birefringent photonic crystal fibers and sensors

A novel class of material, known as photonic crystal, has opened up new ways to guide the flow of light. In the early 1990s, Photonic Crystal Fibers (PCFs), an optical fiber using photonic crystal cladding, were developed. The pioneering experimental works on these fibers showed that they have inherently unprecedented properties and overcome many limitations of conventional optical fiber. Among the many unique properties of PCFs, this thesis is most concerned with the polarization and modal properties of highly birefringent (Hi-Bi) PCFs with asymmetric core and different hole-sizes along the two orthogonal axes.; The basic properties of an asymmetrical core PCF are theoretically investigated by using the full-vector finite element method (FEM). The calculated birefringence is in good agreement with the measured value. The influence of fiber structural parameters on modal birefringence, mode field diameter (MFD), half divergence angle, and group velocity dispersions are investigated in detail.; The full-vector FEM is also used to calculate the electrical fields and to evaluate the equivalent MFD of endlessly single mode PCFs. An empirical formula is proposed for estimating the MFD. The results calculated by using the formula deviates less than 1% from those obtained from FEM for 0.25 ≤ d/Λ ≤ 0.45. With the help of the MFD, the connection loss between a single mode fiber and a PCF can be evaluated by using the classical method based on the MFD.; Through the analysis of a Hi-Bi PCF by FEM with anisotropic perfectly matched layers (PMLs), we proposed a general design methodology for an asymmetrical core PCF to achieve single polarization single mode (SPSM) operation at an arbitrary operating wavelength. Specifically we optimized the PCF structure for SPSM operation around 1.30mum and 1.55mum. The coupling losses between the proposed SPSM fibers and single mode fibers were also calculated by using the overlap integral method and found to be ∼78% and ∼77% at 1.55mum and 1.30mum, respectively.; A similar Hi-Bi PCF but with different parameters is found to support only the LP01 and L11 (even) modes from 543m to 1310nm. With the special modal properties of the Hi-Bi PCF, we experimentally demonstrated a two-mode PCF interferometer based on the modal interference between the LP01 and LP11 (even) modes propagating in the same length of PCF. The responses of the interferometer to axial strain and temperature were experimentally investigated. For the strain sensor, the fiber elongations needed to produce 27pi phase change decrease with the wavelength, indicating higher strain sensitivity at longer wavelengths. The temperature sensitivity of the two-mode PCF sensor was measured and it showed a non-monotonic dependence on the operating wavelength. A mathematical model was developed to explain the non-monotonic temperature dependence, and found to agree in trends with the experimentally measured results.