Research On Coupling Characteristics Of Dual-core Photonic Crystal Fiber With Rectangular Lattice Structure

Coupler based on Photonic Crystal Fiber (PCF) has some superiorities such as simple structure,micro-size, convenient parameter adjusting, high coupling ratio, lower loss, flexible designing,these superiorities will be used in optical powerless devices which can be integrated in otherdevices easily, for example: directional coupler and polarization splitter based on photonic crystalfiber.Mode distribution and coupling characteristics of photonic crystal fiber with rectangularstructure are analyzed by Finite Element Method (FEM) based on transverse mode coupling theoryin this paper, the research demonstrate that, due to the relationship between high birefringence andhole structure array, the coupling length and ratio of devices can be adjusted by changing thestructure parameter, and enlarging hole pitch in vertical or reducing hole pitch in horizontal anddecreasing hole diameter can shorten the coupling length of fiber and the difference of couplinglength in x-and y-polarization simultaneously. Two dual-core PCF-Coupler unrelated topolarization with different structure parameter are designed based on this structure and identicalcoupling length in the two orthotropic directions, when upright pitch is1.7μm, hole pitch0.728μmand transverse pitch1.02μm, the bandwidth over410nm with power coupling greater than90%canbe realized near the center operating wavelength1.55μm in the coupler designed. A newpolarization splitter is proposed by inserting elliptical holes with parameter w and Λ setting as1.1μm and1.7μm respectively, the performances of coupling length and extinction ratio arenumerical simulated and analyzed via Beam Propagation Method(BPM), and short couplinglength(125μm) and high extinction ratio(-38dB) are realized also, and the bandwidth with extinctionratio below-20dB exceeding80nm.