Photonic-Crystal Fibres with Suspended Core — Numerical Analyses

1. The photonic-crystal fibres In conventional optical fibres, electromagnetic modes are guided by a phenomenon of total internal reflection on a core-cladding border. The core refractive index is higher than the refractive index of a cladding which is achieved by adequate doping of a central part of the based material [1]. After over 20 years of intense researches on optical fibres, including special type optical fibres, it is currently apparent that transmission capabilities of conventional optical fibres reach their limit. Over the past few years, essential efforts have been directed toward elaboration of photonic-crystal fibres (PCF) [2]. The photonic-crystal fibres are new optical structures in which a refractive index varies periodically in the transverse plane with geometrical disturbances of the order of an optical wavelength. Morphological microstructure induces into the fibre core radically modification of optical properties of such fibre [3]. In general, two types of guiding mechanisms are distinguished in photonic-crystal fibres, which classify the photonic-crystal fibres as: index-guiding photonic-crystal fibres and the photonic band-gap fibres [2–4]. For index-guiding fibres a waveguide consists of a glass core and a cladding with an array of airholes. The optical modes are guided through the fibres in the core of a higher refractive index than an effective refractive index of the cladding. The index-guiding fibres are an excellent example of two-dimensional structures because their properties are invariable in the third dimension, i.e., along the length of a fibre. Qualitatively, propagation of modes in the index-guiding photonic∗corresponding author; e-mail: [email protected]