Mid-infrared supercontinuum generation in tapered As2S3 chalcogenide planar waveguide

Abstract

We numerically demonstrate mid-infrared supercontinuum generation in a non-uniformly tapered chalcogenide planar waveguide. This planar rib waveguide of As₂S₃ glass on MgF₂ is 2 cm long with increasing etch depth longitudinally to manage the total dispersion. This waveguide has zero dispersion at two wavelengths. The dispersion profile varies along the propagation distance, leading to continuous modification of the phase-matching condition for dispersive wave emission and enhancement of energy transfer efficiency between solitons and dispersive waves. Numerical simulations are conducted for secant input pulses at a wavelength of 1.55 μm with a width of 50 fs and peak power of 2 kW. Results show this proposed scheme significantly broadens the generated continuum, extending from ~1 to ~7 μm.     

Ultra-broadband,coherent mid-IR supercontinuum expanding from 1.5 to 12.2 μm in new design of AsSe2 photonic crystal fibre

We propose a new design of AsSe₂ photonic crystal fibre (PCF) with all-normal dispersion, nearly zero flat-top used to generate an ultra-broadband supercontinuum spanning from 1.5 to 12.2 μm. Simulated results show that, when we use only 1 mm of AsSe₂ PCF, a broadband mid-infrared supercontinuum with the specrum extent from 1.5 to 12.2 μm is obtained with a very low input energy of E = 1.3 nJ at the wavelength of 3.5 μm and pulse duration of 100 fs. We study the temporel and spectral impact of optical wave breaking in the development of the continuum. The influence of the fibre length, the input energy and the full width at half maximum is investigated. Compared to previous research works, we have obtained the broadest, coherent supercontinuum, which could be applicable in biomolecular sensing, cancer diagnostics, infrared spectroscopy and free space communication.     

Design of an As2Se3-based photonic quasi-crystal fiber with highly nonlinear and dual zero-dispersion wavelengths

We propose an As₂Se₃-based highly nonlinear photonic quasi-crystal fiber with dual zero-dispersion wavelengths (ZDWs). Using a full-vector finite element method, the proposed fiber is optimized to obtain high nonlinear coefficient, low confinement loss and two zero-dispersion points by optimizing the structure parameters. Numerical results demonstrate that the proposed photonic quasi-crystal fiber (PQF) has dual ZDWs and the nonlinear coefficient up to 2600 W^?1 km^?1 within the wavelength range from 2 to 5.5 μm. Due to the introduction of the large air holes in the third ring of the proposed fiber, the ability of confining the fundamental mode field can be improved effectively and thus the low confinement loss can be obtained. The proposed PQF with high nonlinearity and dual ZDWs will have a number of potential applications in four-wave mixing, super-continuum generation, and higher-order dispersion effects.     

Study of the structure of As0.3Se0.2S0.4Ge0.1 chalcogenide glass using the radial distribution function

In the present work, the structure of As_0.3Se_o.3S_0.4Ge_0.1 chalcogenide glass has been studied using the radial distribution function (RDF). Moreover, the effect of annealing temperature on the short range order of this glass has been investigated. The results revealed that the short range order structure of the as-prepared and annealed As_0.3Se_0.2S_0.4Ge_0.1 chalcogenide glass is close to a regular tetrahedron. The medium range order of As_0.3Se_0.4S_0.4Ge_0.1 chalcogenide glass is topology order. The topological structure of the medium range order can be described by the Phillips model. The structure of As_0.3Se_0.2S_0.4Ge_0.1 chalcogenide glass is stable in the annealing temperature range 324–523 K.     

Determination of the optical constants of As–Se–Ag chalcogenide thick films with high precision for optoelectronics applications

Thin films of (As₅₀Se₅₀)_100?xAg_x (with 0?≤?x?≤?25 s) metal-chalcogenide glasses were deposited onto glass substrates by thermal evaporation technique under high vacuum (10^?6 mbar). The optical constants as well as the average thickness of the studied films are determined by the Swanepoel envelope method which is based on the optical transmission spectra measured in the spectral range 300–2500 nm. This method enables the transformation of the optical-transmission spectrum of a thin film of wedge-shaped thickness into the spectrum of a uniform film, whose thickness is equal to the average thickness of the non-uniform layer. The dispersion of the refractive index is discussed in terms of the Wemple–DiDomenico single-oscillator model. The optical absorption edge is described using the non-direct transition model proposed by Tauc relation. Analysis of the optical data revealed that an addition of Ag in the range from 0 to 25 at.% to the (As₅₀Se₅₀)_100?x binary alloys affected the optical parameters of the investigated thin films. For instance, the optical band gap decreased from 1.661 to 1.441 eV with increasing the Ag content from 0 to 25 at.%. The results were discussed in terms of Mott and Davis model as well as chemical-bond approach.     

Line–plane-switching infrared bundle for push-broom sensing fiber imaging

We reported line–plane-switching infrared (IR) fiber bundle with high-resolution of 0.027 μm⁻¹, small numerical aperture (NA) of 0.20 (±0.02), high filling-factor, and bending radius of around 5.0 mm, i.e. extremely good flexibility. This fiber bundle is made from chalcogenide glass fibers, possessing core (As₄₀S₅₈Se₂) of 45 μm, cladding (As₄₀S₆₀) of 50 μm, and error of 1% in diameter. Based on the lens used to demonstrate IR push-broom imaging, the format of matching fiber bundle we chose is 64 × 9 in system to implement 192 × 3 format linear array imaging. By principle-demonstrating system incorporated this fiber bundle coupled with small scale Infrared Focal Plane Array (IRFPA), wide-field and long-array IR push-broom image was successfully demonstrated.     

Maximizing the bandwidth of coherent,mid-IR supercontinuum using highly nonlinear aperiodic nanofibers

We describe in detail a new procedure of maximizing the bandwidth of mid-infrared (mid-IR) supercontinuum (SC) in highly nonlinear microstructured As₂Se₃ and tellurite aperiodic nanofibers. By introducing aperiodic rings of first and secondary air holes into the cross-sections of our microstructured fiber designs, we achieve flattened and all-normal dispersion profiles over much broader bandwidths than would be possible with simple periodic designs. These fiber designs are optimized for efficient, broadband, and coherent SC generation in the mid-IR spectral region. Numerical simulations show that these designs enable the generation of a SC spanning over 2290?nm extending from 1140 to 3430?nm in 8?cm length of tellurite nanofiber with input energy of E?=?200?pJ and a SC bandwidth of over 4700?nm extending from 1795 to 6525?nm generated in only 8?mm-length of As₂Se₃-based nanofiber with input energy as low as E?=?100?pJ. This work provides a new type of broadband mid-IR SC source with flat spectral shape as well as excellent coherence and temporal properties by using aperiodic nanofibers with all-normal dispersion suitable for applications in ultrafast science, metrology, coherent control, non-destructive testing, spectroscopy, and optical coherence tomography in the mid-IR region.     

Optically addressed As<Subscript>50</Subscript>Se<Subscript>50</Subscript>-liquid crystal structure highly sensitive to He-Ne laser radiation

An optically addressed structure of the As _x Se_1-x -liquid crystal (LC) type, with the photoconductor composition deviating from stoichiometry toward excess arsenic, has been tested using holographic techniques. It is established that the As₅₀Se₅₀-LC structure (with maximum possible arsenic content in the photoconductor) exhibits record high sensitivity (2.2 × 10^?7 W/cm²) at a He-Ne laser radiation wavelength. Based on this structure, it is possible to implement nonlinear optical data-processing algorithms employing the entire transmission characteristic including the inversion region. The maximum diffraction efficiency achieved with the As₅₀Se₅₀-LC structure amounts to 36.5%.     

Tapered chalcogenide–tellurite hybrid microstructured fiber for mid-infrared supercontinuum generation

Fibers exhibiting flattened and decreasing dispersion are important in nonlinear applications. Such fibers are difficult to design, particularly in soft glass. In this work, we develop a preliminary design of a highly nonlinear tapered hybrid microstructured optical fiber (TH-MOF) with chalcogenide glass core and tellurite glass microstructure cladding. We then numerically studied its dispersion, loss, and nonlinearity-related optical properties under fundamental mode systematically using the infinitesimal method. The designed TH-MOF exhibits low chromatic dispersion that is similar to a convex function with two zero-dispersion wavelengths and decreases with fiber length from 2 to 5 μm band. The potential use of the TH-MOF in nonlinear applications is demonstrated numerically by a supercontinuum spectrum of 20 dB bandwidth covering 1.96–4.76 μm generated in 2-cm-long TH-MOF using near 3.25-μm fs-laser pump.     

Composition dependence of UV–visible and MID-FTIR properties of Se98−x Zn2In x (x = 0, 2, 4, 6 and 10) chalcogenide glasses

The UV–VIS absorption spectra of thin film of Se_98?x Zn₂In _x (x = 0, 2, 4, 6 and 10) chalcogenide glasses were measured in the wavelength range of 200–1100 nm by using spectrophotometer. It is observed from UV–VIS absorption measurements that the optical energy gap (E _g ) decreases with In content and it found a minimum for the Se₉₂Zn₂In₆ system. The refractive index (n), extinction coefficient (k), real dielectric constant (?′) imaginary dielectric constant (?″), absorption coefficient (α) are evaluated maximum for the Se₉₂Zn₂In₆ composition. However, FTIR spectra were recorded in the wavenumber range 4000–400 cm^?1. The FTIR recorded spectrum was shown to be a broad spectrum with increasing transmission in the MID (6–25 m) infrared region. The MID-IR spectrum transmittance percentage was also found to be considerably high for the Se₉₂Zn₂In₆ system.     

Optical nonlinearity in glasses: the origin and photo-excitation effects

Linear and nonlinear optical properties in oxide and chalcogenide glasses have been studied comparatively. Applying a semiconductor concept to these glasses, we show that maximal nonlinear refractive-index at optical communication wavelengths is ～10^?4 cm²/GW, which can be obtained in materials with bandgap energy of ～1.6 eV. It is also shown for SiO₂ and As₂S₃ that linear and nonlinear optical excitations induce different photostructural changes, which are attributable to different photo-electronic transition probabilities.     

Visible to mid-infrared supercontinuum generated in novel GeS2–Ga2S3–CsI step-index fibre

In this work, two kinds of GeS₂–Ga₂S₃–CsI chalcogenide glasses had been fabricated in conventional meltquenching method, and these glasses express excellent transmittance (0.52–10.5?µm), low refractive index difference, high Raman gain and good thermal stability against crystallization. We designed a highly nonlinear step-index fibre consisting of a 72GeS₂–18Ga₂S₃–10CsI core and a 73GeS₂–15Ga₂S₃–12CsI cladding with the zero dispersion wavelength in near-infrared (<1?µm), and theoretically analysed the optical and nonlinear characteristics of this fibre in detail. Substantial simulation results revealed that wide ultra-flat supercontinuum broadening from the visible to the mid-infrared range can be achieved by pumping this fibre at 1064?nm.     

Efficient generation of ultra broadband supercontinuum in a mid-infrared field

We theoretically investigate the generation of ultra broadband supercontinuum from helium atoms exposed to a linearly polarized mid-infrared field. By adopting a UV trigger pulse to the mid-infrared field, the continuous harmonic yields are significantly enhanced by 3.5 orders, and a supercontinuum with the width of 230?eV is observed. The spectrum can support a sub-20 as pulse, which is below one atomic unit of time (24 as). The short quantum path is selected by adjusting the time delay between the UV pulse and the mid-infrared pulse, then broadband single 70 as pulses with tunable central wavelengths are obtained, which can be extended to the ‘water window’ region (284–543?eV).     

Photo-induced changes in optical properties of As2S3 and As2Se3 films deposited at normal and oblique incidence

Photostructural transformations in amorphous chalcogenide films have been a subject of intensive research so far. In this paper we discuss the changes in the optical properties of typical As-based chalcogenide glasses (As₂S₃ and As₂Se₃) on exposure to ultraviolet (UV) light. An attempt has been made to systematically investigate the optical parameters like extinction coefficient, refractive index and optical bandgap of the films by measuring the same for as-grown and UV-exposed amorphous films of As₂S₃ and As₂Se₃ prepared by vacuum evaporation technique.     

Selenium modified GeTe4 based glasses optical fibers for far-infrared sensing

This study reports on the synthesis of telluride glasses that have transmission far beyond the second atmospheric window and are stable enough toward crystallisation to be drawn into optical fiber. These glasses are based on the GeTe₄ initial composition which has been stabilized by the introduction of few percents of Se and a modified the Te/Ge ratio. In that domain, Ge₂₁Se₃Te₇₆ constitute the optimum composition and some mono index optical fibers have been successfully drawn. It is shown that their optical transparencies extend from 5 to almost 16 μm in the mid-infrared, establishing a record for chalcogenide glass fibers. These fibers have been used to implement Fiber Evanescent Wave Spectroscopy experiments, permitting to detect infrared molecule signatures beyond 12 μm, infrared domain that was unreachable by now. These innovative fibers are also used to detect the broad absorption band of gaseous CO₂ lying from 13 to 16 μm and therefore hold promises in the framework of the Darwin mission of the European Space Agency. Both of these results suggest that these new optical fibers will become essential in the field of infrared remote sensing.     

Fabrication of Ultrasensitive TES Bolometric Detectors for HIRMES

The high-resolution mid-infrared spectrometer (HIRMES) is a high resolving power (R ~?100,000) instrument operating in the 25–122 μm spectral range and will fly on board the Stratospheric Observatory for Far-Infrared Astronomy in 2019. Central to HIRMES are its two transition edge sensor (TES) bolometric cameras, an 8 × 16 detector high-resolution array and a 64 × 16 detector low-resolution array. Both types of detectors consist of Mo/Au TES fabricated on leg-isolated Si membranes. Whereas the high-resolution detectors, with a noise equivalent power (NEP) ~ 1.5 × 10^?18 W/rt (Hz), are fabricated on 0.45 μm Si substrates, the low-resolution detectors, with NEP ~ 1.0 × 10^?17 W/rt (Hz), are fabricated on 1.40 μm Si. Here, we discuss the similarities and differences in the fabrication methodologies used to realize the two types of detectors.     

Infrared spectroscopic characterization of Na5Lu9F32 single crystals doped with various Er3+ concentrations

This work reports on optical spectra of Na₅Lu₉F₃₂ single crystals doped with various Er³⁺ concentrations from 0.5 to 5 mol%. In our improved Bridgman method, the X-ray powder diffractions were investigated and optical parameters were also calculated by the Judd–Ofelt theory. Results showed that Er³⁺ ions entered the Lu³⁺ sites successfully without causing any obvious peak changes, and the doping concentration of Er³⁺ had important influence on the Er³⁺ local structure in Na₅Lu₉F₃₂ crystals. The maximum emission intensities of ~1.5 and ~2.7 μm were obtained in present research when the doping concentration of Er³⁺ were 4 and 5 mol%, respectively, under the excitation of 980 nm LD. In these doping concentration, the maximum emission cross-sections were calculated to be 1.37 × 10^?20 cm² (~1.5 μm) and 2.1 × 10^?20 cm² (~2.7 μm). The gain cross-section at 2.7 μm was also estimated according to the absorption and emission cross section spectra. All these spectroscopic characterizations suggested that this fluoride crystal would possess promising applications in infrared lasers.     

Luminescence at 2.8 μm: Er3+-doped chalcogenide micro-waveguide

This paper reports the fabrication of luminescent optical rib/ridge waveguides made of erbium doped Ga-Ge-Sb-S films deposited by RF magnetron sputtering. Several fluorescence emissions of Er³⁺ ions from the visible to the middle infrared spectral domain were clearly observed within the films. The study of the ⁴I_13/2 level lifetime enabled development of a suitable annealing treatment of the films to reach the value of the bulk counterpart while the variation in surface roughness was limited, thus ensuring reasonable optical losses (0.7–0.9 dB/cm). Amplification experiments were carried out at 1.54 μm leading to complete characterization of the erbium-doped micro-waveguide with ∼3.4 dB/cm on/off gain. A demonstration of mid-IR photoluminescence from Er³⁺-doped chalcogenide micro-waveguide was recorded at ∼2.76 μm. The multi-luminescence from the visible to mid-IR generated using erbium doped chalcogenide waveguiding micro-structures might find easy-to-use applications concerning telecommunication technologies or on-chip optical sensors for which luminescent sources or amplifiers operating at different wavelengths are required.     

Enhancement of photoinduced transformations in amorphous chalcogenide film via surface plasmon resonances

Laser-matter coupling results specific structural changes in amorphous chalcogenide semiconductor layers which originate from electron-hole excitations, defect creation or modification and subsequent atomic motions. These changes can be influenced by plasmon fields. Plasmon enhanced photo-darkening and bleaching, optical recording in thin As_xSe_1 − x films have been demonstrated in this paper, specifically in As₂₀Se₈₀ and As₂Se₃ compositions which revealed the best effects of stimulated expansion or optical darkening respectively due to the He-Ne laser (λ = 633 nm) illumination. Gold nanoparticles deposited on the silica glass substrate and covered by an amorphous chalcogenide film satisfy the conditions of efficient surface plasmon resonance in this spectral region. These experimental results support the importance of localized electric fields in photo-structural transformations of chalcogenide glasses as well as suggest better approaches for improving the performance of these optical recording media.     

Mechanochemically driven amorphization of nanostructurized arsenicals,the case of β-As<Subscript>4</Subscript>S<Subscript>4</Subscript>

The amorphization is studied in mechanically activated β-As₄S₄ using high-energy ball milling in a dry mode with 100–600 min^?1 rotational speeds, employing complementary methods of X-ray powder diffraction (XRPD) related to the first sharp diffraction peak, positron annihilation lifetime (PAL) spectroscopy, and ab initio quantum-chemical simulation within cation-interlinking network cluster approach (CINCA). The amorphous substance appeared under milling in addition to nanostructurized β-As₄S₄ shows character XRPD halos parameterized as extrapolation of the FSDPs, proper to near-stoichiometric amorphous As–S alloys. The structural network of amorphized arsenicals is assumed as built of randomly packed multifold cycle-type entities proper to As₄S₄ network. The depressing and time-enhancing tendency in the PAL spectrum peak is direct indicative of milling-driven amorphization, associated with free-volume evolution of interrelated positron- and Ps-trapping sites. At lower speeds (200–500 min^?1), these changes include Ps-to-positron trapping conversion, but they attain an opposite direction at higher speed (600 min^?1) due to consolidation of β-As₄S₄ crystallites. In respect of CINCA modeling, the effect of high-energy milling is identified as destruction–polymerization action on monomer cage-type As₄S₄ molecules and existing amorphous phase, transforming them to amorphous network of triple-broken As₄S₄ derivatives. These findings testify in a favor of “shell” kinetic model of solid-state amorphization, the amorphous phase continuously generated under speed-increased milling being identified as compositionally authentic to arsenic monosulfide, different in medium range ordering from stoichiometric As₂S₃.