Coupling And Sensing Mechanisms In Dual-core Photonic Crystal Fibers

In this dissertation, the mechanisms of dual-core coupling in photonic crystal fibers (PCFs) are analyzed and its applications in novel designs of fiber couplers, dispersion compensating and refractive index sensing are also discussed.A new type of paratactic symmetrical dual-core PCFs based on two guiding mechanisms of total internal reflection and photonic bandgap effects simultaneously is proposed, whose coupling properties are investigated numerically and theoretically. There are several special coupling features such as the existences of local maxima, alternative cutoffs of supermodes, mode decoupling between the two cores and so on. It is found that the relative change between the symmetries of supermodes and inclusion resonant modes play an important role in the coupling.A splitting ratio tunable directional coupler and a dual-wavelength coupler with tunable work stations are proposed and their work principles are illuminated. The relations between their work parameters and the refractive index of high-index inclusion are also presented.The conditions of complete coupling between leaky modes in PCFs are put forward. By investigating the coupling properties of proposed concentric dual-core PCFs, it is proved that complete coupling between leaky modes in PCFs requires not only satisfying the phase matching condition, but also that the difference between imaginary parts of mode propagation constant is less than two times of the coupling strength coefficient.Based on the coupling in concentric dual-core PCFs, a new dual-core PCF with optional mode coupling is proposed. Its coupling modes can be selected according to the requirements, and as high as -36000ps/nm/km negative dispersion and as large as 34.8μm~2 mode field area can be obtained at the same time. This merit is helpful to decrease the disadvantageous influence of nonlinear effects during the dispersion compensating.The confinement loss of index-guiding PCFs with finite outer cladding is analyzed. It is found that there are coupling-induced loss peaks for the core mode and the locations of loss peaks are related with the diameter of outer cladding and the refractive index of external medium. It is suggested that the refractive index of external medium can be surveyed by measuring the variations of loss peaks of the core mode.The research results have important reference value for the further study on dual-core coupling mechanisms and relevant applications.