Two octave spanning supercontinuum generation in hexagonal spiral photonic crystal fiber

Abstract

ABSTRACT In th is paper, we propose a relatively new PCF structure made of silica with a very high nonlinearity i.e. ~343 W -1 km -1 @1060 nm. We have also demonstrated two -octave spanning supercontinuum generation from 5 00 nm ± 168 0 nm using 50 fs pulse with peak power of 2 kW. Keywords: Hexagonal spiral, photonic crystal fiber, supercontinuum, octave spanning, nonlinear optics. 1. INTRODUCTION Due to intensity dependence of refractive index and stimulated inelastic scattering, various nonlinear effect like self phase modulation (SPM) , cross phase modulation (XPM), four wave mixing (FWM), stimulated Raman scattering (SRS), self steepening (SS) and stimulated Brillouin scattering (SBS) can be observed as the light propagates through a nonlinear medium [1]. The interaction of one or more of these effects and their interplay with dispersion leads to extreme spectral broadening of optical pulses when launched into a nonlinear dispersive medium such as an optical fiber [1]. This phenomenon of generating broadband light with narrowband optical sources such as a laser is called as supercontinuum (SC) generation [1]. The l ight so generated is highly intense, spatially coherent and its spectral width can be several hundreds of nanometers. Due to these properties, SC sources are used in wide range of telecom applications such as pulse compression, short pulse generation, desi gn of multi ± wavelength sources, TDM to WDM conversion and vice versa, fiber characterization etc. as well as non ± telecom applications like frequency metrology, optical coherence tomography (OCT), spectroscopy of materials, chemical sensing etc [2 -7] . R ecently, PCFs have emerged as a potential candidate for SC generation because of reduced input power requirements which can be achieved by reducing the effective area and thus enhancing the nonlinear properties [2]. In case of standard optical fibers, the power requirements are almost double than that in case of PCFs [8] . Thus, highly bright and broad supercontinuum can be generated by launching input pulse with relatively low intensity in PCFs. Moreover, PCFs offer greater design flexibility which allows the tailoring of dispersion properties such as shifting the zero dispersion wavelength(s) (ZDW) according to the wavelength of the pump source and to achieve a flat dispersion profile in anomalous region, which is a desirable condition for a flat and broad SC generation [9 -14] . In this direction, a significant amount of effort has been put to tailor the dispersion characteristics and to enhance the nonlinear properties by developing novel PCF structures [1 1] [15 -16] .