Research On The Dispersion Characteristics Of Photonic Crystal Fibers

Photonic Crystal Fibers (PCFs) possess dispersion properties significantly different from those of the conventional fibers because the novel cladding structures consisting of an array of micrometer-sized air-holes allows for flexible tailoring of the dispersion curves. Dispersion characteristics of PCFs are very important for realistic applications of optical fiber communications, dispersion compensation and nonlinear optics.The finite-element method (FEM) is a powerful tool able to cope with any hole distribution in the cross section of PCFs with high accuracy. In this thesis, the FEM formulas are derived from the wave equation of magnetic field vector by using the variational principle. Furthermore, the FEM programs are modified to calculate the fundamental mode of PCFs for different polarization in a quarter or half domain.Nearly-zero flattened dispersion is a crucial factor for wide-band high speed WDM systems. So far, the nearly zero flattened dispersion PCFs with different structures have been designed. In this thesis, a new kind of three-fold symmetry core PCF with nearly zero flattened dispersion is designed. Because the structure parameters of PCFs manufactured in the actual situation always deviate from their designed values, the dispersions are different from the corresponding designed values. For this reason, the stability of nearly zero flattened dispersion for different PCF structures are analyzed. Numerical results show that around the wavelength of 1550nm, when the structure parameters deviate from their designed values, the dispersion deviations of both the three-fold symmetry core PCF and the hexagonal PCF are much less than those of the PCFs with different hole diameters in different rings. Therefore, the stabilities of nearly zero flattened dispersion of the first two kinds of PCFs are much better. Considering the confinement loss, the three-fold symmetry core PCF is preferable to practical use.Non-zero dispersion-shifted fibers (NZDSFs) have been widely used in optical transmission systems. Due to their low dispersion at the communication window of 1550nm, extra dispersion compensation is usually not needed. However, with the increasing bit rate for transmission, the specialized dispersion-compensating fibers are needed to compensate the dispersion of NZDSFs. For this reason, the PCFs which can compensate the NZDSFs with low and ultra-low dispersion slope at 1550nm are designed in this thesis. The designed PCFs, which have depressed-index core, not only can provide dispersion compensation in the whole C band (1530-1565nm), but also have the mode areas of more than 20μm~2. Compared with other dispersion-compensating PCFs, the designed PCFs have the advantage of wide-band dispersion compensation and low nonlinearity.