Structural Design And Propagation Properties Analysis Of Novel Microstructured Polymer Optical Fiber

Microstructured polymer optical fibers (MPOFs) possess not only the unusualproperties of microstructured optical fibers (MOFs), including endlessly single modetransmission, highly tunable dispersion, ultra low nonlinearity and high birefringence,but also the characteristics of polymer optical fibers (POFs), such as lower processingtemperature, variety of processing methods, flexibleness and lower cost etc. MPOFs anddevices with new structures or new materials can be extensively applied on optical fibercommunications, sensing, nonlinear optics, terahertz waveguide technology and so on.In this thesis, several kinds of novel MPOFs are designed, and propagation properties ofthe designed MPOFs are analyzed theoretically. The details are described as follows:(1) The theory model based on finite element method is used to analyze the singlemode property, dispersion and transmission losses of MPOFs. Based on Topas CyclicOlefin Copolymers (Topas COC), MPOFs with triangular lattice, guiding light by thetotal inner reflaction are designed. The effective index of the fundamental mode, themode area and the numerical aperture are calculated. Effects of fiber structureparameters upon the mode field distribution, single mode property and dispersionproperty are discussed. Structure parameters corresponding to very large/small effectivemode area and endlessly single mode are obtained. The conclusions demonstrate thattheory model and calculation method we adopt is accurate and effective.(2) Index guiding MPOF with defected core and elliptical cladding holes isdesigned based on Topas COC. The extra small defected hole in fiber core and theelliptical holes in cladding are capable of enhancing the waveguide dispersion andintroducing birefringence, respectiveky. The designed MPOF has ultra flattened nearzero chromatic dispersion and high birefringence. Dispersion values between±0.5ps/km/nm over the wavelength1.1~1.7μm and high birefringence of the order of10-3 are obtained for the optimized fiber structure. The results provide theoretical referencesfor applications of MPOFs in dispersion controlling, polarization maintaining andnonlinear optics.(3) A hollow core photonic bandgap MPOF based on Topas COC is designed. Therhombic hollow core with rounded corners is formed by omitting four central air holesof the cladding structure. The guided modes, birefringence and confinement loss of thefiber are investigated. A high phase birefringence of the order of10-3, a groupbirefringence of the order of10-2and confinement loss less than0.1dB/km are obtainedat the central wavelength range of the bandgap for the designed fiber.(4) Thermally tunable bandgap guiding MPOFs are designed by infiltrating thecladding air holes with high index nematic liquid crystals. The MPOF filled with liquidcrystal E7has a bandgap centered at approximately1.55μm, with bandwidth about600nm. Thermal tuning sensitivity of-5.5nm/°C is achieved at the long wavelength edge ofthe bandgap from15°C to35°C. The MPOF filled with liquid crystal5CB has a highthermal tuning sensitivity of27.8nm/°C at the long wavelength edge of the bandgapfrom25.1°C to34.8°C. By using the full vector finite element method, modeproperties and effective mode area of the fundamental mode are investigated. Thedesigned liquid crystal filled MPOFs have high power transmission coefficient (~99%)between the index guiding modes and the bandgap guiding modes around the centerwavelength of the bandgap. Our results provide theoretical references for applicationsof MPOFs in sensing and tunable fiber optic devices.(5) Porous polymer fiber and hollow core photonic bandgap microstructuredpolymer fibers used for Terahertz guiding are designed respectively based on TopasCOC which has both low absorbtion loss and low material dispersion in the Terahertzrange. The designed fiber structures are able to minimize the power distribution indielectric region while guiding the Terahertz frequencies along the waveguide. A largefraction of the mode field can be distributed in the sub-wavelength air holes in core for the porous fiber. Low loss smaller than0.2cm-1and low dispersion of1.8±0.3ps/THz/cm are obtained within0.4~1.5THz. The hollow core photonic bandgapmicrostructured fiber has a continuous low loss bandgap about0.2THz in widthcentered at1.47THz. Minimum loss of0.13cm-1is obtained near1.51THz. Structureof the designed THz microstructured polymer fibers are relatively simple and feasiblefor fabrication by the thermo-drawing techniques of polymer preforms invented by ourgroup.