34 research outputs found
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Mid-infrared supercontinuum generation using dispersion-engineered Ge11.5As24Se64.5 chalcogenide channel waveguide
We numerically investigate mid-infrared supercontinuum (SC) generation in dispersion-engineered, air-clad, Ge11.5As24Se64.5 chalcogenide-glass channel waveguides employing two different materials, Ge11.5As24S64.5 or MgF2 glass for their lower cladding. We study the effect of waveguide parameters on the bandwidth of the SC at the output of 1-cm-long waveguide. Our results show that output can vary over a wide range depending on its design and the pump wavelength employed. At the pump wavelength of 2 µm the SC never extended beyond 4.5 µm for any of our designs. However, supercontinuum could be extended to beyond 5 µm for a pump wavelength of 3.1 µm. A broadband SC spanning from 2 µm to 6 µm and extending over 1.5 octave could be generated with a moderate peak power of 500 W at a pump wavelength of 3.1 µm using an air-clad, all-chalcogenide, channel waveguide. We show that SC can be extended even further when MgF2 glass is used for the lower cladding of chalcogenide waveguide. Our numerical simulations produced SC spectra covering the wavelength range 1.8-7.7 µm (> two octaves) by using this geometry. Both ranges exceed the broadest SC bandwidths reported so far. Moreover, we realize it using 3.1 µm pump source and relatively low peak power pulses. By employing the same pump source, we show that SC spectra can cover a wavelength range of 1.8-11 µm (> 2.5 octaves) in a channel waveguide employing MgF2 glass for its lower cladding with a moderate peak power of 3000 W
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Design and modeling of dispersion-engineered all-chalcogenide triangular-core fiber for mid-infrared-region supercontinuum generation
An ultrabroadband mid-infrared supercontinuum (SC) source has been designed and modeled using a 10-mm-long all-chalcogenide triangular-core fiber (TCF). The TCF structure can be fabricated from Ge11.5As24Se64.5 chalcogenide glass as a core and Ge11.5As24S64.5 chalcogenide glass for its cladding running along the length of the fiber instead of air holes. Assuming the pump operates at 4 μm, the TCF is optimized by varying its side length using both anomalous-dispersion and all-normal-dispersion SC generation. Mid-infrared-region SC spectral broadening spanning beyond 15 μm could be generated with a low peak power of 3 kW by the proposed TCF structure optimized with varying its side length between 7 and 8 μm in anomalous-dispersion pumping. On the other hand, the TCF side length has to be decreased to 5.5 μm and below to optimize it for pumping in all-normal-dispersion-region SC generation. A coherent flat-top SC evolution in the mid-infrared region of up to 7 μm could be observed by this design with the same pump peak power and pulse duration applied before. The ultrawide optical bandwidth obtained by the proposed TCF design can be an effective tool for mid-infrared-region applications such as optical coherence tomography, molecular fingerprint spectroscopy, and biomedical imaging
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Ultra-broadband mid-infrared supercontinuum generation through dispersion engineering of chalcogenide microstructured fibers
We demonstrate numerically that the use of dispersion-engineered microstrucured fibers made with chalcogenide glasses allows one to generate ultrabroadband supercontinuum spectra in the mid-infrared region by launching optical pulses at a suitable wavelength. As a specific example, numerical simulations show that such a 1 cm long fiber, made with Ge11.5As24Se64.5 glass and pumped at a wavelength of 3.1 μm using short pulses with a relatively modest peak power of 3 kW, can produce a spectrum extending from 1.3 μm to beyond 11 μm (more than 3 octaves). We consider three fiber structures with microstrucured air holes in their cladding and find their optimum designs through dispersion engineering. Among these, equiangular spiral microstrucured fiber is found to be the most promising candidate for generating an ultrawide supercontinuum in the mid-infrared region
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Ultra-broadband mid-infrared supercontinuum generation using chalcogenide rib waveguide
The ultrabroadband mid-infrared (MIR) supercontinuum (SC) generation using dispersion-tailored Ge11.5As24Se64.5 chalcogenide (ChG) glass rib-waveguide has been investigated numerically. An air-clad 1-cm-long rib-waveguide employing MgF2 glass for its lower cladding shows that an ultrabroadband MIR SC spanning from 1.8 to 8 μm and extending over more than 2 octave could be generated with a relatively low peak power of 0.5 kW pumped at a wavelength of 3.1 μm. Our estimated bandwidth is the largest reported so far for SC generated using ChG rib-waveguide pumped at a wavelength of 3.1 μm with a low peak power of 0.5 kW. We carry out simulations by varying peak power ranges between 0.1 and 3 kW. Our analysis through rigorous numerical simulations show that SC can be extended further into the MIR up to 10 μm using the same pump pulses with a relatively modest peak power of 3 kW
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Dispersion engineered Ge11.5As24Se64.5 nanowire for supercontinuum generation: A parametric study
A promising design of Ge11.5As24Se64.5 nanowires for supercontinuum generation is proposed through numerical simulations. It can be used for generating a supercontinuum with 1300-nm bandwidth. The dispersion parameters upto eighth-order are obtained by calculating the effective mode index with the finite-element method. We have investigated dispersion curves for a number of nanowire geometries. Through dispersion engineering and by varying dimensions of the nanowires we have identified a promising structure that shows possibility of realizing a wideband supercontinuum. We have found significant variations in its bandwidth with the inclusion of higher-order dispersion coefficients and indicated the possibility of obtaining spurious results if the adequate number of dispersion coefficients is not considered. To confirm the accuracy of dispersion coefficients obtained through numerical computations, we have shown that a data-fitting procedure based on the Taylor series expansion provides good agreement with the actual group velocity dispersion curve obtained by using a full-vectorial finite-element mode-solver
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Generation of an ultrabroadband supercontinuum in the mid-infrared region using dispersion-engineered GeAsSe photonic crystal fiber
An ultrabroadband mid-infrared (MIR) region supercontinuum (SC) is demonstrated numerically through dispersion-engineered traditional chalcogenide (ChG) photonic crystal fiber (PCF). By varying structural parameters pitch (hole to hole spacing) and air-hole diameter to pitch ratio, a number of 10-mm-long hexagonal PCFs made employing GeAsSe ChG glass as a core and air-holes of hexagonal lattice running through their lengths as a cladding are optimized to predict an efficient mid-infrared region SC spectral emission by pumping them using a tunable pump source between 2.9 and 3.3 µm. Simulations are carried out using an ultrashort pump pulse of 100-fs duration with a low pulse peak powers of between 3 and 4 kW into the optimized designs. It is found through numerical analysis that efficient SC spectral broadening with flattened output can be obtained by increasing the PCF pitch rather than increasing the PCF cladding containing air-hole diameter although a larger nonlinear coefficient could be obtained through increasing air-hole diameter of an optimized design. Simulation results show that the SC spectra can be broadened up to 12.2 µm for a certain design with a peak power of 3 kW. Using a peak power of 4 kW, it is possible to obtain SC spectral broadening beyond 14 µm with an optimized design spanning the wavelength range from 1.8 to 14 µm which covers the electromagnetic spectrum required for MIR molecular fingerprint region applications such as sensing and biological imaging
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Dispersion-engineered silicon nitride waveguides for mid-infrared supercontinuum generation covering the wavelength range 0.8-6.5 mu m
We numerically demonstrate the generation of a mid-infrared supercontinuum (SC) through the design of an on-chip complementary metal oxide semiconductor (CMOS) compatible 10-mm-long air-clad rectangular waveguide made using stoichiometric silicon nitride (Si 3 N 4 ) as the core and MgF 2 glass as its lower cladding. The proposed waveguide is optimized for pumping in both the anomalous and all-normal dispersion regimes. A number of waveguide geometries are optimized for pumping at 1.55 μ m with ultrashort pulses of 50-fs duration and a peak power of 5 kW. By initially keeping the thickness constant at 0.8 μ m, four different structures are engineered with varying widths between 3 μ m and 6 μ m. The largest SC spectral evolution covering a region of 0.8 μ m to beyond 6.5 μ m could be realized by a waveguide geometry with a width of 3 μ m. Numerical analysis shows that increasing width beyond 3 μ m by fixing thickness at 0.8 μ m results in a reduction of the SC extension in the long wavelength side. However, the SC spectrum can be enhanced beyond 6.5 μ m by increasing the waveguide thickness beyond 0.9 μ m with the same peak power and pump source. To the best of our knowledge, this is first time report of a broad SC spectral evolution through numerical demonstration in the mid-infrared region by the silicon nitride waveguide. In the case of all-normal dispersion pumping, a flatter SC spectra can be predicted with the same power and pump pulse but with a reduced bandwidth spanning 950–2100 nm
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All-Normal Dispersion Chalcogenide PCF for Ultraflat Mid-Infrared Supercontinuum Generation
We numerically study the dispersion-engineered chalcogenide photonic crystal fiber (PCF), which allows us to generate ultraflat broadband supercontinuum (SC) spectra in all-normal dispersion regime. A 1-cm-long chalcogenide hexagonal PCF made using Ge11.5As24Se64.5 glass pumped at 1.55 μm produced an SC bandwidth 700 nm at a peak power of 1 kW. By shifting pump at 2 μm, SC spectra can be extended with a bandwidth of 1900 nm at the same peak power level. In both cases, nonuniform spectral power distribution observes over the entire output bandwidth owing to the lower dispersion slop on the long wavelength side of the dispersion curve. To spanning SC further in the mid-infrared as well as to reduce the spectral asymmetry, we optimize another design for pumping at 3.1 μm in such a way that the pump source can be employed vicinity to the peak of the dispersion curve. Employing the largest pump peak power up to 5 kW, SC can be extended up to 6 μm (1.5 octaves), and the power distribution among the spectral components over the entire SC bandwidth can be improved significantly by this design. To enhance the spectral flatness, we optimize a second PCF geometry by reducing its pitch length, and it is possible to obtain ultraflat coherent SC spanning from 2 to 5.5 μm (>1 octave) by this structure maintaining nearly symmetric power distribution between both side of its spectral components
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All-Normal-Dispersion Chalcogenide Waveguides for Ultraflat Supercontinuum Generation in the Mid-Infrared Region
We show numerically, how a chalcogenide planar waveguide designed to exhibit normal dispersion over a wide spectral range around the pump wavelength can produce relatively flat supercontinuum in the mid-infrared regime. A 1-cm-long channel waveguide, made using Ge11.5As24Se64.5 glass and pumped at 1.55 gm using short optical pulses with only 25 W peak power, produced a supercontinuum that was nearly 600 nm wide. Employing the same pump source with a peak power of 100 W, the supercontinuum could be extended to beyond 2.2 gm with a bandwidth of 1000 nm. By shifting the pump wavelength to 3.1 gm and using pulses with peak powers of up to 3 kW, the resulting ultraflat supercontinuum extended from 2 to 5.5 gm. Even a wider spectral range (1.8-6 gm) can be realized if MgF2 glass is used for the lower cladding while maintaining power variations below 5 dB over the entire bandwidth
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Design of dispersion-engineered As2Se3 channel waveguide for mid-infrared region supercontinuum generation
In recent years, low cost and scalable integrated optics compatible planar waveguides have emerged for an ultrabroadband supercontinuum generation between ultraviolet and mid-infrared region applications. A 20-mm-long integrated photonics compatible highly nonlinear As2Se3 channel waveguide, which exhibited wider as well as lower magnitude and nearly flat anomalous dispersion region, designed and modeled by employing GeAsSe glass for its upper and lower claddings. Using pump source at 6 μm with a pulse duration of 170-fs, an ultrabroadband long wavelength region supercontinuum broadening covering the wavelength from 3.5 μm to 15 μm could be predicted with the largest input peak power of 10 kW. Increasing the power further to 20 kW does not enhance the supercontinuum expansion noticeably beyond 15 μm. This numerical demonstration could be the longest supercontinuum generation by an on-chip integrated photonics compatible planar waveguide which can be used for a variety of mid-infrared region applications