As2S3 Layers Research Articles

Numerical analysis of a compact all-fiber polarization beam splitter based on dual-core photonic crystal fiber with As2S3 thin layer

Modern-day optical systems are evolving towards miniaturization and integration, leading to higher performance demands for polarizing beam splitters (PBSs). A simple-structure and high-performance PBS based on dual-core photonic crystal fiber (DC-PCF) with As2S3 layer is proposed. The finite element method (FEM) and classical coupled-mode theory (CMT) are utilized to investigate the performance of this PBS. Simulation results demonstrate that the proposed PBS can achieve a minimum length of 2.65 mm, a minimum extinction ratio of −64 dB, an operating bandwidth of 420 nm, and a minimum insertion loss of 0.03 dB when the optimal parameters include cladding hole diameter of 1.0 μm, central hole diameter of 2.0 μm, lattice spacing of 2.0 μm, and As2S3 ring layer thickness of 50 nm. Moreover, it also possesses a high birefringence of 3.58 × 10−3 and a negative dispersion of −30 ps/km/nm at 1.55 μm. It is believed that the proposed PBS holds great potential to become a critical device in optical multiplexing technologies.

Numerical Investigation of a Short Polarization Beam Splitter Based on Dual-Core Photonic Crystal Fiber with As2S3 Layer.

A polarization beam splitter is an important component of modern optical system, especially a splitter that combines the structural flexibility of photonic crystal fiber and the optical modulation of functional material. Thus, this paper presents a compact dual-core photonic crystal fiber polarization beam splitter based on thin layer As2S3. The mature finite element method was utilized to simulate the performance of the proposed splitter. Numerical simulation results indicated that at 1.55 μm, when the fiber device length was 1.0 mm, the x- and y-polarized lights could be split out, the extinction ratio could reach −83.6 dB, of which the bandwidth for extinction ratio better than −20 dB was 280 nm. It also had a low insertion loss of 0.18 dB for the x-polarized light. In addition, it can be completely fabricated using existing processes. The proposed compact polarization beam splitter is a promising candidate that can be used in various optical fields.

RECORDING OF DIFFRACTION GRATINGS WITH AN ACTIVE STABILIZATION SCHEME OF INTERFERENCE FIELD

The paper describes a modernized optoelectronic system for stabilizing the interference pattern during exposure of a holographic grating. The results of applying the extreme control system to stabilize the interference field when recording holographic gratings of high optical quality are presented. Thin chalcogenide layers of the composition As2S3 were used as the recording medium. When using the stabilization system, a monotonic increase in the diffraction efficiency of the gratings from the recording time is observed and a low level of spurious scattering is recorded for the recorded gratings. The scheme was experimentally tested when recording holographic gratings up to 60x60 mm2 in size and exposure time up to 30 minutes. The use of an active stabilization scheme will make it possible to record large-size gratings using low-power lasers without the use of additional complex systems for protecting optical circuits from vibration.

Efficient Er:Ti:LiNbO3 ridge waveguide amplifier by patterning As2S3 layer

In this study, the effect of As2S3 waveguide layer on propagation gain for Er:Ti:LiNbO3 ridge waveguide amplifiers is investigated. In comparison with a typical titanium in-diffused channel waveguide, the three side Erbium in-diffusion of a 6 μm wide ridge waveguide and the better light confinement has improved the overlap between Er concentration and guided mode profiles up to 2.58 times. Our simulation demonstrates that by purposely adjusting the thickness of the three side As2S3 layer it is possible to pull the guided mode towards the ridge/air interface where Er concentration is higher. Consequently in this new configuration by taking advantage of the high refractive index As2S3 layer and mode de-shaping, the overlap relative to a ridge free of As2S3 layer has increased by 1.5 times thereby gain coefficient has been improved from 3.2 to 4.28 dB/cm at a coupled pump power of 200 mW. In comparison with a typical Ti channel waveguide amplifier, the relative overlap has increased by 3.88 times resulting in noticeable gain improvement from 0.65 to 4.28 dB/cm under the same Er diffusion conditions.

Optical properties of As2S3 layers deposited from solutions obtained by chemical reaction

This paper deals with three approaches for the preparation of arsenic sulfide layers from solutions. First approach employs arsenic sulfide solutions obtained by dissolving powder of arsenic sulfide glass in n-propylamine. Second approach, a novel one, employs amorphous arsenic sulfide precipitated by chemical reaction of arsenic trichloride and ammonium sulfide. The precipitate was dissolved in n-propylamine. Third original approach relays on the same chemical reaction carried out in a mixture of n-propylamine and water that prevents the precipitation. By using all the approaches input arsenic sulfide solutions with a concentration of 0.33 mol/l were fabricated and applied onto glass slides by dip-coating method with withdrawing velocities of 50, 100, 200, and 250 mm/min. Applied layers dried in vacuum at 60 °C for 1 h and thermally treated at 180 °C for 30 s were characterized by optical and atomic force microscopy as well as by transmission spectroscopy in a wavelength range of 300–2500 nm. Refractive indices, thicknesses and band gaps were estimated from measured spectra. A maximum refractive index of about 2.15 at 600 nm and thicknesses up to 220 nm were determined on layers fabricated from input solutions obtained by dissolving of arsenic sulfide glass. Arsenic sulfide layers prepared on the basis of the arsenic sulfide precipitation exhibit refractive indices up around 1.90 and thicknesses up to 410 nm. Photonic band gap values on a level of 2.2 eV have been determined on these layers. On the other hands, composite layers prepared by reaction of arsenic trichloride and ammonium sulfide in the solution of n-propylamine and water exhibited low transparencies, refractive indices around 1.7 and thicknesses of about 2 µm.

Fabrication and characterization of microstructures created in thermally deposited arsenic trisulfide by multiphoton lithography

A detailed study of multiphoton lithography (MPL) in arsenic trisulfide (As2S3) films and the effects on nanoscale morphology, chemical networking, and the appearance of the resulting features by the chemical composition, deposition rate, etch processing, and inclusion of an antireflection (AR) layer of As2Se3 between the substrate and the As2S3 layer is reported. MPL was used to photo-pattern nanostructured arrays in single- and multilayer films. The variation in chemical composition for laser-exposed, UV-exposed, and unexposed films is correlated with the etch response, nanostructure formation, and deposition conditions. Reflection of the focused beam at the substrate back into the film produces standing wave interference that modulates the exposure with distance from the substrate and produces nanobead structures. The interference and the modulation can be controlled by the addition of an AR layer of As2Se3 deposited between the substrate and the As2S3 film. Relative to structures produced in a single-layer As2S3 film having no AR layer, photo-patterning in the multilayer As2S3-on-As2Se3 film yields pillar-shaped structures that are closer to the targeted shape and are narrower (120 versus 320 nm), more uniform, and better adhering to the substrate. Processing methods are demonstrated for fabricating large-area arrays with diffractive optical function.

Contamination of glassy arsenic sulfide by SiO2 particles during melt solidification in silica glassware

It is found that the content of SiO2 inclusions in the As2S3 volume is increased during chalcogenide glass melting in silica glassware with subsequent cooling to solid sample and separation from the container walls. The experiment consisted in repetition of cycles of “chalcogenide ingot melting and heating to 450–600°C - cooling the melt to a glass transition temperature - separation of the sample from the silica-glass container walls - cooling to room temperature”. Content and size of the inclusions in the initial glass and the samples after the “melting–solidification” cycles was controlled by means of laser ultramicroscopy and optical microscopy. The concentration of micrometer-sized particles was found to increase with cycles of melting and solidification.The increase of particles concentration is explained by the combined effect of a number of factors such as high adhesion of glassy arsenic sulfide to silica glass and strong radial and longitudinal shrinkage of the chalcogenide ingot during cooling compared with silica-glass container due to significant differences in their linear coefficients of thermal expansion. It leads to destruction of the adhesion contact along the boundary of solid phases and the surface layers of glasses with separation of microprotrusions and fragments of silica glass surface and their fixation in the surface layers of As2S3 glass.The excess optical losses in glassy arsenic sulfide, caused by this type of contaminating action of apparatus, have been estimated.

The Sensing Characteristics of a Bragg Fiber Based Plasmonic Biosensor Using an As<sub>2</sub>S<sub>3</sub> Chalcogenide Layer

The sensing performances of a four layer Bragg fiber based plasmonic biosensor for aqueous solutions using an As2S3 chalcogenide layer are investigated with an analytical method. In comparison with a previously considered fiber structure with a GaP layer, the new geometry has the advantages of a smaller value of the full width at half maximum and a larger value of the signal-to-noise ratio; however, the maximum of amplitude sensitivity is smaller when an As2S3 layer is used in the place of the GaP layer. If the thickness of the As2S3 layer is increased to the value for which it is quarter wavelength, the power fraction carried at the resonant wavelength by the core guided mode in the analyte layer becomes comparable with the value obtained in an optical fiber with the GaP layer, evidencing that the higher value of the refractive index for the GaP layer is compensated by a larger value of the thickness for the As2S3 layer. Taking into account the 0.04 photoinduced refractive index change obtained by illumination the chalcogenide As2S3 layer with a laser beam, the resonant wavelength is decreased by 0.128 nm and the loss for the core mode is increased by 41dB/cm.

Investigation of structural features of As2S3–Se multilayer nanostructure by Raman spectroscopy

The focus of this research is on the investigation of structural changes in the As2S3–Se multilayer nanostructure and on the examination of a relative contribution of As2S3 and Se layers to nanostructuring by measuring the Raman spectra. The formation of the As2S3-Se nanostructure by an alternate As2S3 and Se layers deposition was applied. The diffraction efficiency dependence on the exposure of a CW DPSS laser were monitored in a transmission mode of the1st order diffracted beam intensity and measured in real-time at the normal incidence of the laser diode beam (λ = 650 nm). From the comparison of these dependences for a set of samples we have chosen the multilayer nanostructure As2S3–Se with optimal recording properties meaning maximum both the value and the rate of diffraction efficiency. Our results are found to be of practical interest as they allow a significant improvement of the diffraction efficiency of the directly recorded relief gratings.

Ultra-flat and broad optical frequency combs generation based on novel dispersion-flattened double-slot microring resonator

In this paper, a novel double-slot microring resonator is proposed to produce flat dispersion of 0–3.8 ps/(nm km) over 1150 nm wavelength range. Moreover, the dispersion tailoring with different structural parameters of the proposed microring resonator is analyzed and simulated. The simulation results show that the dispersion fluctuation can be tailored by the height of the central and bottom As2S3 layer, and the slope can be adjusted by the waveguide width and lower SiO2 slot thickness. Furthermore, by means of the Lugiato–Lefever equation, an ultra-flat and broad optical frequency comb with 7-dB bandwidth of 1155 nm (1855–3010 nm) is obtained based on such dispersion-optimized resonator. The proposed double-slot microring resonator shows potential application in both telecommunication and mid-infrared research domain.

Optical properties of As2S3 layers deposited from solutions

This paper presents results of the preparation and optical characterization of As2S3 layers by using spin or dip-coating technique and As2S3 solutions in ethylenediamine and n-propylamine as solvents. These solutions were prepared from arsenic sulfide powders obtained from laboratory-prepared bulk glasses. Ethylenediamine and n-propylamine solutions with the same As2S3 concentration of 0.7mol/l were used for the layer preparation.Layers were prepared by both the dip-coating and spin-coating techniques with velocity of 0.2–30cm/min and 2000rpm for 90s, respectively. Substrates used in these experiments were microscopic slides (refractive index of about 1.49). All applied As2S3 layers were dried in vacuum for 60min and then heat-treated at 180°C for 60s in nitrogen atmosphere.Prepared As2S3 layers were characterized by transmission spectroscopy in the wavelength range of 200–100nm. Thicknesses of applied layers in the range of 200–1500nm and their refractive indices ranging from 1.7 to 2.3 at 800nm were estimated from interference bands in measured transmission spectra using Swanepoel's method. Dispersion curves of the refractive index are shown in the paper. Optical band gaps of prepared layers in the range of 2.15–2.35eV were determined from measured transmission spectra by using Tauc's extrapolation.

Photoinduced formation of Ag nanoparticles on the surface of As2S3/Ag thin bilayer

In this article, we demonstrate the combined effect of photodoping and photoinduced-surface deposition in a bilayer of chalcogenide glass (ChG) and Ag as an alternative method to optically synthesize Ag nanoparticles (AgNP) on the surface of ChG. In our experiment, AgNP formation occurs through two distinct stages: In the first stage, Ag is transported through the As2S3 layer as Ag+ ions, and in the second stage Ag+ ions are photo-deposited as AgNP. The ex situ x-ray photoelectron spectroscopy measurements and AFM observations show photoinduced Ag mass transport and the formation of AgNP.

Asymmetric one-dimensional photonic crystal for optical sensing in the visible spectral range

A gas sensor based on an asymmetric one-dimensional (1D) photonic band gap structure with one defect layer was designed and fabricated through layer-by-layer deposition of spin-coated poly methyl methacrylate (PMMA) and vacuum-deposited As2S3. Initially, the thickness variations, Δd, were determined of the thin films resulting from the poly methyl methacrylate exposure to chloroform vapor in the concentration range 100 – 9000 ppm. It was found that the value of Δd depends on the gas concentration and the exposure time. A two-layer structure was prepared consisting of PMMA and vacuum-deposited As2S3. Further, the permeability of thin As2S3 films to chloroform vapors was investigated. The asymmetric photonic structure consisted of 11 alternating layers of As2S3 and PMMA. The defect PMMA layer was located before the last high-refractive-index film of chalcogenide glass. The thickness of the defect layer of PMMA was pre-calculated so that the pass band be centered at the wavelength of 550 nm. An offset was observed of the position of the pass band to the larger wavelengths after exposure to chloroform vapor. The multilayered structure proposed is promising for optical sensor applications.

Effect of broadband light on Ag/As2S3 multilayers

A sandwich structure of four double layers of Ag (5nm)/As2S3 (82.7nm) has been prepared by Pulsed Laser Deposition (PLD) method. The effect of broadband light on the multilayer structure has been investigated. The X-ray reflectivity (XRR) patterns after different irradiation times have been measured. Although the fully intermixing of Ag and As2S3 layers should be expected during irradiation with visible light, however even after 5h of irradiation the intermixing is not completed. The characteristic features of XRR diagrams for long irradiation times have been interpreted by scattering of X-ray radiation on clusters of Ag or Ag–As2S3.

Gain Improvement of $\hbox{Er-Ti:LiNbO}_{3}$ Waveguide Amplifier by an $\hbox{As}_{2}\hbox{S}_{3}$ Overlay Waveguide

A new configuration consisting of an arsenic trisulfide (As2S3) channel waveguide on top of an erbium (Er)-doped titanium-diffused x-cut lithium niobate (Er:Ti:LiNbO3) waveguide has been investigated by simultaneous analytical expressions, numerical simulations, and experimentation. Both simulation and experimental results have shown that this structure can enhance the optical gain, as predicted by the analytical expressions. An As2S3 channel waveguide has been fabricated on top of a conventional Er:Ti:LiNbO3 waveguide, where the higher refractive index As2S3 waveguide is used to pull the optical mode toward the substrate surface where the higher Er concentration yields an improved propagation gain. The relationship between the gain and As2S3 layer thickness has been evaluated, and the optimal As2S3 thickness was found by simulation and experimentation. Side integration was applied to reduce the extrapropagation loss caused by the titanium diffusion bump. The propagation gain has been improved from 1.1 to 2 dB/cm.

Silver doped As2S3 chalcogenide films: A diffusion study

AbstractPhoto‐diffusion of silver across an As2S3 thin film layer is studied, as continuing some earlier work about surface morphology modifications in double‐layer structures of Ag and As2S3, and some qualitative preliminary results on lateral Ag diffusion in As2S3 thin films. An estimation of the Ag film's dissolution rate and the diffusion front's advancement rate in As2S3 is given based on cross‐section measurements.In order to understand better the diffusion mechanism of Ag in As2S3, a structural model of the As2S3 matrix is used to estimate the amount of silver which might be hosted by an As2S3 layer in terms of molar ratio, and an interaction mechanism of the Ag with the chalcogenide matrix is proposed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Direct surface patterning of homogeneous and nanostructured chalcogenide layers

AbstractInvestigations of direct one‐step optical recording of surface optical and geometrical patterns in homogeneous and nanostructured chalcogenide layers were extended towards e‐beam recording. Our aim was to establish the common features of the two processes, and to develop some optimum materials for prototypic micro‐ and nanosized elements for optoelectronics. Experiments were conducted on Se/As2S3 and Sb/As2S3 nanolayered structures (NLS) as well as on uniform Se, Sb and As2S3 layers. Both green laser light (λ = 535 nm) and e‐beam (5‐20 pA, 10‐30 keV) induced bleaching in all NLS. The optical change was more efficient in Sb‐containing NLS. In contrast, volume expansion occurred only in chalcogenide‐chalcogenide NLS and the homogeneous Se or As2S3 layers. Its magnitude was larger for the NLS (Δd /d ≥10%); no volume change was detected in Sb layer. A comparison of the two types of recording revealed the role of interdiffusion and induced free volume aggregation in a giant relief formation under the increased fluidity conditions. It was shown that these effects could be used to fabricate micro lenses, amplitude‐phase optical modulating and guiding elements. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Mechanism of photoinduced nanodimensional expansion/contraction in glassy thin layers of As2S3

The mechanism of photoinduced expansion/contraction in glassy As2S3 has a photochemical nature. Photostructural transformation is connected with rearrangement of As4S4 molecules and similar non-stoichiometric compounds, As4S4+x. These molecules are believed to exist in clusters which correspond to the second glass-forming region of As–S systems, including the As56S44 eutectic.

Kinetics and chemical analysis of photoinduced interdiffusion in nanolayered Se/As2S3 films

We have studied the kinetics of photoinduced effects in nanolayered Se/As2S3 film by in situ optical absorption measurements, which reveal that photodarkening in these films is followed by photoinduced diffusion. An increase in disorder during photodarkening and its subsequent decrease during photoinduced diffusion were also observed. The observation of photodarkening of Se at room temperature when confined between As2S3 layers suggests that the glass transition temperature of Se shifts to higher energy. The analysis shows that the atoms which take part in photodarkening play a vital role in photoinduced diffusion. The x-ray photoelectron spectroscopy measurements show the atomic movements during photoinduced diffusion. It also shows that some of the As–S bonds are converted into As–Se bonds. Since it is energetically difficult to break an As–S bond to form an As–Se bond, we assume that the new bond formations are taking place by the bond rearrangement mechanism.

Fabrication of holographic diffraction gratings based on As2S3 Layers

The formation of holographic diffraction gratings based on As2S3 layers is investigated. The variation of the groove profiles with exposure is studied by atomic force microscopy. The spectral curves of the diffraction efficiency are taken, and a relationship between these curves and grating surface relief is analyzed.