Coupling in Core-Ring Photonic Crystal Fibers

Abstract

Over the past few years, a substantial effort has been made in fabricating photonic crystal fibres (PCFs) — new dielectric structures with a refractive index that varies periodically in the transverse plane, with a period of the order of an optical wavelength [1]. PCFs constitute a new kind of lightguides that possess huge possibility of parameters tailoring [2–5]. It seems that a new generation of optical fibres can outperform conventional germanium-doped fibres especially for sensing applications. We propose PCF which can transmit light in the two independent regions — a core in the middle of the fibre and ring — around the core. The SiO2-based fibre comprises: defect in the centre (SiO2 core), 3 rings of air holes, 3 rings of defects — rods (SiO2) and 3 rings of air holes. Both defect regions (the core and the ring) guide light by modified total internal reflection [1]. We can change the effective refractive index of the photonic regions by means of a hole diameter (d) to a pitch (Λ) ratio. In this fibre modes with similar phase constants can couple from core into ring in the presence of microbendings. Selective pulse excitation of the mode in ∗corresponding author; e-mail: mszustakowski@wat.edu.pl