| With the development of optic fiber communication and sensing, special fibers are utilized more and more widely. Microstructure optic fiber (MOF), also named photonic crystal fiber(PCF), is a novel special fiber proposed about20years ago. The emergence of PCFs is a major change in the development of optic fibers. PCFs have many advantageous properties, such as endless single-mode property, high birefringence, flexible dispersion properties, and so on.Polarization is an important property for a fiber. Highly birefringent fibers can realize polarization-maintaining. In order to obtain high birefringence, geometrical asymmetry of the fibers in two vertical directions should be enlarged. Conventional polarization-maintaining fibers such as PANDA fiber obtain high birefringence mainly depend on stress effect, which can only amount to10-4.The birefringence of10-3even10-2can be obtained by use of PCFs, which is one order or two of magnitude higher than conventional polarization-maintaining fibers. In this dissertation, we proposed a novel highly birefringent PCF based on elliptical holes. The birefringence doubled compared with circular-hole PCFs. which amount to3.5×x10-3. In addition, we studied the properties of this PCF with one, two and three defects respectively. We found that the birefringences changed little but the coupling efficiency with single mode fiber (SMF) of PCF with two defects is higher than that with one or three defects. Furthermore, we studied the confinement loss, bend loss and other properties of the optimized PCF. Simulation results show that the confinement loss and bend loss are very small, which is promising in such fields as polarization-maintaining, and so on.In optic fiber communications, dispersion is a key factor to confine the transmission bandwidth. The structures of PCFs are flexible and we can alter the parameters to realize dispersion compensation and flattening. In this dissertation, we proposed a dispersion compensation fiber and a dispersion-flattened fiber and calculated them with the finite element method (FEM) respectively. The proposed dispersion compensating fibers have an octagonal dual-concentric-core structure. Simulation results reveal that this kind of PCF can realize a very large negative dispersion about-840ps/nm/km at1550nm. This PCF can compensate the dispersions of a SMF of about50times its length and also its slope, which can be used as a C-band broadband compensating fiber. Our proposed dispersion-flattened PCF is circular-ringed, and we reduce the radius of the center seven holes to form a fiber core and enlarge the effective mode area. Calculation results show that the dispersion of this PCF fluctuates between±0.9ps/nm/km in S+C+L band (1460nm-1625nm). This PCF can couple with SMF-28fibers efficiently, and the effective mode area is relatively large (42μm2). The nonlinear coefficient is2.92W-1·km-1, which is relatively low. In addition, the confinement loss of this PCF is10-7dB/km at1550nm, and the bend loss is very low. This PCF is quite suitable for optic fiber communication systems.The design of microstructure optic fibers is flexible. According to the arrangement of air holes, microstructure optic fibers can be designed as different structures, such as hexagonal structure, octagonal structure, circular stucture and so on. Microstructure optic fibers with different structures can perform various characteristics, and we can choose optimized structures to obtain requisite properties. In this dissertation, the dispersion properties of abovementioned three structures are theoretically studied by use of FEM with perfectly matched layers by contrast. An octagonal dispersion compensating microstructure optic fiber near1550nm is proposed, which can obtain a negative dispersion about-3020ps/nm/km. Furthermore, many beneficial results have been obtained, which is very useful for researching and utilizing dispersion compensating fibers. |
PDF Full Text Request