A.G. Rozhnev, A.V. Sadovnikov, M.P. Chernyaev

The optical fiber with photonic crystal cladding provide new approaches for achieving single transverse mode guiding in large core fibers. Such fiber often is named microstructured fibers (MF). There are many applications of MF in fiber-optic communications, fiber lasers, nonlinear devices, high-power transmission devices, ultrabroad supercontinuum generation and broadband dispersion compensation. MF with a solid core, which has a higher average index than the microstructured cladding, can operate on the same index-guiding principle as an ordinary optical fiber. Such fiber exhibit novel dispersion properties such as ultra-flat dispersion over broad wavelength range. We considered the MF with the hexagonal lattice of rods with finite wall thickness in the fiber cladding. Thereby we assumed the complicated triangle-form area in the transverse section of MF that usually appears during the manufacture of such fiber. The control of dispersion in fiber has been demonstrated by variation of geometrical parameters of fiber such as size of an air-hole defect in the fiber core and distance between holes. The effect of varying cladding parameters is estimated to find the trends of the decrease of dispersion slope and control of absolute value of dispersion coefficient and then applied to the design of an ultralow, ultra-flattened chromatic dispersion photonic-crystal fiber. The numerical modeling of microstructured fiber was performed using two methods, namely finite-element method (FEM) and the plane-wave method (PWM). The former assumed the explicit frequency or wavelength dependence of the refractive index. The latter was applied with the supercell modification and the material dispersion wasn-t assumed explicitly. For the computation with finite-element method the program for calculation of eigenmodes dispersion of the transmission line with complicated transverse section was applied. The plane-wave simulation was done by MPB (MIT Photonic Bands) package, developed in Massachusetts Institute of Technology. We have shown that the variation of geometrical parameters of optical microstructured fiber can modify the dispersion properties of such system. We have demonstrated that dispersion slope and absolute value of dispersion coefficient of MFs can be controlled with a change of size of an air-hole defect in the fiber core, with variation of interval between holes and with a doping the center part of the fiber with germanium dioxide. Simulations and estimations shows that one can construct a system based on microstructured-fibers with minute difference of dispersion coefficient in the operating range of wavelength and dispersion control can help to improve transmission speeds and distances.