Mid-infrared supercontinuum generation in suspended-core chalcogenide and tellurite optical fibers

Abstract

Summary form only given. The generation of optical supercontinua in the mid-infrared region and especially their expansion beyond the intrinsic limit dictated by fused silica is currently a subject of high interest. Tellurite and chalcogenide glasses have serious advantages because of their wide transmittance window which can reach more than 10 μm while the Kerr nonlinearity can be 500 times stronger than fused silica. These different features make them serious candidates for broad mid-infrared supercontinuum generation. For example, supercontinuum as broad as 4000-nm bandwidth has been generated in a sub-cm long Tellurite microstructured fiber by Domachuk et al. in ref. [1] by means of a femtosecond regime pumping. In this work, two kinds of soft-glasses, Tellurite and As2S3 chalcogenide suspended-core fibers with nearly 3-μm core diameter have been designed and pumped in their anomalous dispersion regime by means of an optical parametric oscillator delivering 200-fs pulses between 1700 and 2500 nm [2]. Figure 1a shows the resulting supercontinua obtained at the output of a 40-cm long sample of our tellurite fiber characterized by a 3.4-μm triangular core size. The nonlinear coefficient was evaluated to γ = 175 W <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> .km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , linear losses to 1.5 dB/m at 1550 nm and the zero dispersion wavelength (ZDW) was measured near 1660 nm. The pump wavelength was fixed to 1745 nm and resulting spectra have been recorded as a function of injected power. The broadest 112-mW supercontinuum is characterized by a 2000-nm bandwidth, corresponding to almost 2 octaves and is remarkably flat (a 1900-nm span contained in a -20 dB range). Figure 1b presents the corresponding numerical simulations, which reproduce quite well the dynamics highlighted during our experiments [2]. Figure 2a illustrates the experimental results obtained from a 45-mm long sample of our 3.2-μm suspended-core chalcogenide fiber. The nonlinear Kerr coefficient was estimated to Ȗ = 1175 W-1.km-1, linear losses to 1 dB/m at pump wavelength and a ZDW close to 2330 nm. Figure 2a shows the resulting spectrum for a pump wavelength of 2300 nm and an injected power of 70 mW. The supercontinuum extends from 1200 nm to 3200 nm in the -20 dB range. Note however that large residual OH absorption bands are clearly visible around 2.9 μm and beyond 3.2 μm and thus limiting supercontinuum expansion. Taking into account these extra losses, the corresponding numerical simulations illustrated in Fig. 2b are in good agreement with our experimental recordings.