TECHNOLOGY TUTORIAL - INTRODUCTION

Photonic crystal fibers (PCFs) were first demonstrated in 1996 and have generated much attention since then. PCFs are optical fibers that employ a microstructured arrangement of low-index material in a background material of higher refractive index. The background material is often undoped silica and the low index region is typically provided by air voids running along the length of the fiber.

PCFs may be divided into two categories, high index guiding fibers and low index guiding fibers. Similar to conventional fibers, high index guiding fibers are guiding light in a solid core by the Modified Total Internal Reflection (M-TIR) principle. The total internal reflection is caused by the lower effective index in the microstructured air-filled region.

Low index guiding fibers guide light by the photonic bandgap (PBG) effect. The light is confined to the low index core as the PBG effect makes propagation in the microstructured cladding region impossible.

The strong wavelength dependency of the effective refractive index and the inherently large design flexibility of the PCFs allow for a whole new range of novel properties. Such properties include endlessly single-moded fibers, extremely nonlinear fibers and fibers with anomalous dispersion in the visible wavelength region.

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