Chapter 4 - Photonic Bandgap-Guided Bragg Fibers

Abstract

This chapter describes the history, underlying physics, modeling of propagation characteristics, design issues, and fabrication of 1D photonic bandgap-guided bragg fibers (PBGF). It has indeed emerged as a specialty fiber with the potential for several attractive applications. In a conventional optical fiber, light is guided by total internal reflection because of the refractive index contrast that exists between a finite-sized cylindrical core and the cladding of lower refractive index that surrounds it. Whereas, in a PBGF, light of certain frequencies cannot propagate along directions perpendicular to the fiber axis but instead are free to propagate along its length confined to the fiber core. This phenomenon that forbids the propagation of photons transverse to the axis of micro-structured fibers, led to the christening of these specialty fibers as photonic bandgap-guided optical fibers, in analogy with the electronic bandgaps encountered by electrons in semiconductors. In contrast to the electronic bandgap that is the consequence of periodic arrangement of atoms/molecules in a semiconductor crystal lattice, photonic bandgap arises due to a periodic distribution of refractive index in certain dielectric structures, generically referred to as photonic crystals.