An As2S3 fiber-based supercontinuum source that covers 3500 nm, extending from near visible to the midinfrared, is successfully reported by using a 200-fs-pulsed pump with nJ-level energy at 2.5 μm. The main features of our fiber-based source are two-fold. On the one hand, a low-loss As2S3 microstructured optical fiber has been fabricated, with typical attenuation below 2 dB/m in the 1–4 μm wavelength range. On the other hand, a 20-mm-long microstructured fiber sample is sufficient to enable a spectral broadening, spreading from 0.6 to 4.1 μm in a 40 dB dynamic range.
We analyze optical and structural aging in As₂S₃ microstructured optical fibers (MOFs) that may have an impact on mid-infrared supercontinuum generation. A strong alteration of optical transparency at the fundamental OH absorption peak is measured for high-purity As₂S₃ MOF stored in atmospheric conditions. The surface evolution and inherent deviation of corresponding chemical composition confirm that the optical and chemical properties of MOFs degrade upon exposure to ambient conditions because of counteractive surface process. This phenomenon substantially reduces the optical quality of the MOFs and therefore restrains the spectral expansion of generated supercontinuum. This aging process is well confirmed by the good matching between previous experimental results and the reported numerical simulations based on the generalized nonlinear Schrödinger equation.
We report the manufacturing and characterization of Tellurite micro structured fibres (MOFs) with low OH content. The different purification processes used during the fabrication of the TeO2 - ZnO - Na2O glass allowed us to reduce the hydroxyl compounds concentration down to 1ppm mass. A suspended core MOF was drawn from this material and then pumped by nanojoule-level femtosecond pulses at 1.7μm, its zero dispersion wavelength (ZDW), and well above it at 2.5μm. We show the related supercontinuum (SC) generated in the two distinct dispersion regimes of the waveguide. Moreover, the SC spanning was extended in both visible and mid-IR regions (between 600nm up to 3300nm) by the taperisation of the previously tested MOFs.
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 -1 .km -1 , 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.
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