Modal solutions of photonic crystal fibers by finite element method

Abstract

ABSTRACT Modal solutions of photonic crystal fibers with both circular and rectangular air holes are presented by using a rigorous full vectorial finite element-based approach. The effective indices, mode field profiles, spot-sizes, power confinements, modal hybridness, beat lengths and group velocity dispersions are shown for the fundamental and higher order modes of the quasi-TE and TM polarizations. 1. INTRODUCTION The photonic crystal fiber (PCF) (which is also known as ‘holey’ fiber), is a micro-structured fiber, where arrays of holes run along the waveguide length, having a more controllable fabrication parameters than standard single mode fiber. Increasing interest is being shown in such PCFs for a range of applications in optical communications, sensing and signal processing. These include the control and guidance of optical beams, taking advantage of their unique transmission characteristics, which include being continuously single-moded, with controllable spot-sizes and with tailored group velocity dispersion (GVD) characteristics. The optical properties of standard fibers are mostly controlled by two key parameters, the radius and the index difference between core and cladding. Single mode fiber can be designed by balancing these two parameters for different applications, for example in conventional low-loss telecommunication grade fibers or specialized fibers such as doped fibers with a smaller spot-size. However, the adjustment of the GVD properties is severely limited. By contrast in a PCF, the number of holes, their sizes, orientations and placements can provide an additional degree of freedom which is not present for conventional fiber. A wide range of potential applications is anticipated, exploiting the ability to tailor the GVD, the large spot-size for high power applications, and the smaller spot-size for improved nonlinear interactions, Raman amplification, Brillouin lasers, second harmonic generation, four-wave mixing, and creating polarization maintaining PCFs with higher modal birefringence and super continuum generation.