| The polarization unstability of optical fibers and the narrow bandwidth of the optical fiber devices restrict the transmission rate and capacity of the optical fiber communication system,and further delay the development of the coherent all-optical network.The polarization-maintaining photonic crystal fibers(PM-PCFs)and their related polarization-dependent devices have significant potential applications for fiber sensors,tunable fiber laser,in the future coherent communication system due to their advantage properties of much better polarization stability and much more flexible structure designing.For its theory and application requirements for polarization stability,wide band transmission,and the miniaturization of passive devices in coherent optical communication system,the high polarization stability PM-PCFs and their related polarization dependent devices with miniaturization and high-bandwidth are studied and analyzed based on the full vectorial finite element method in this dissertation.The main achievements of the dissertation are listed below:1.Based on the mode cut-off method,an ultra-wide spectral range(bandwidth)single-polarization single mode photonic crystal fiber(SPSM-PCF)is proposed.The SPSM operation bandwidth of the proposed PCF structure can be up to 1610 nm with confinement loss lower than 0.01 dB/km.Moreover,the dual-core SPSM PCF has also been investigated based on the single core SPSM PCF,enabling potential applications in a coarse wavelength-division demultiplexer,which can split firstly the wavelength bands of 1.31 and 1.55 ?m at a short fiber length of 1.629 mm with SPSM operation in the coarse wavelength-division multiplexing system.2.Based on the coupled-mode theory and the surface plasmon resonance effect,an ultrabroadband polarization splitter based on square-lattice dual-core photonic crystal fiber with gold wire is designed.At the wavelength of 1.55 ?m,the extinction ratio can reach 78.2 dB,and the 4.036 mm-long dual-core PCF can split the two polarized lights from each other.The polarization splitter has an extinction ratio better than 20 dB with a broad bandwidth of 430 nm in a 1.25 ?m-1.68 ?m wavelength range.3.Based on the surface plasmon resonance effect,a gold-filled photonic crystal fiber with ultra-broadband polarization-dependent filter characteristics is designed.The loss of x-polarized core mode is better than 248.95 dB/cm in a 1.25 ?m-2.1 ?m wavelength range,while the corresponding loss of y-polarized core mode is lower than 0.21 dB/cm for the first time,enabling potential applications in a wide polarization-dependent filter at a fiber length of 1 mm with a broad bandwidth of 850 nm with extinction ratio higher than 20 dB.4.Based on the surface plasmon resonance effect,a dual-band orthogonal single polarization filtering single-core PCF is proposed.The incoming light at wavelength bands of 1.31 ?m and 1.55 ?m can propagate through orthogonal single polarization operation based on the proposed PCF,enabling potential applications in a wavelength-division multiplexing polarization-dependent filter,which can split the wavelength bands of 1.31 and 1.55 ?m at a short fiber length of 0.3 mm in the coarse wavelength division multiplexing system.5.Based on the surface plasmon resonance effect,three kinds of gold-coated PCF with good polarization-dependent filter properties in the wavelength of 1.31 ?m or 1.55 ?m are proposed.The effects of asymmetric factor introduced in the core mode and the surface plasmon mode on the polarization-dependent filter properties are studied in detail.The resonance loss of 412.91 dB/cm can be achieved for y polarized mode at 1.31 ?m,where the loss of x-polarized core mode is only 2.02 dB/cm.The Full Width at Half Maximum(FWHM)of the resoance strength is 21 nm.The proposed PCF can be used in a single band polarization-dependent filter. |
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