A. Tverjanovich

Supercontinuum generation in chalcogenide-silica step-index fibers

We explore the use of a highly nonlinear chalcogenide-silica waveguide for supercontinuum generation in the near infrared. The structure was fabricated by a pressure-assisted melt-filling of a silica capillary fiber (1.6 µm bore diameter) with Ga4Ge21Sb10S65 glass. It was designed to have zero group velocity dispersion (for HE11 core mode) at 1550 nm. Pumping a 1 cm length with 60 fs pulses from an erbium-doped fiber laser results in the generation of octave-spanning supercontinuum light for pulse energies of only 60 pJ. Good agreement is obtained between the experimental results and theoretical predictions based on numerical solutions of the generalized nonlinear Schrödinger equation. The pressure-assisted melt-filling approach makes it possible to realize highly nonlinear devices with unusual combinations of materials. For example, we show numerically that a 1 cm long As2S3:silica step-index fiber with a core diameter of 1 µm, pumped by 60 fs pulses at 1550 nm, would generate a broadband supercontinuum out to 4 µm.

Bandgap guidance in hybrid chalcogenide–silica photonic crystal fibers

We report a hybrid chalcogenide-silica photonic crystal fiber made by pressure-assisted melt-filling of molten glass. Photonic bandgap guidance is obtained at a silica core placed centrally in a hexagonal array of continuous centimeters-long chalcogenide strands with diameters of 1.45 μm. In the passbands of the cladding, when the transmission through the silica core is very weak, the chalcogenide strands light up with distinct modal patterns corresponding to Mie resonances. In the spectral regions between these passbands, strong bandgap guidance is observed, where the silica core transmission loss is 60 dB/cm lower. The pressure-assisted fabrication approach opens up new ways of integrating sophisticated glass-based devices into optical fiber circuitry with potential applications in supercontinuum generation, magneto-optics, wavelength selective devices, and rare-earth-doped amplifiers with high gain per unit length.

Raman spectra of gallium sulfide based glasses

Abstract Raman investigation of glasses x GeS 2 -Ga 2 S 3 - y MCl, Ga 2 S 3 2MCl (where M = Ag, Tl, Rb, Cs) and melt Ga 2 S 3 2CsCl has been carried out for various x and y . Raman spectra have been interpreted in the frame of the model that gallium is fourfold coordinated in the chalcogenide/halide glasses and forms complex anions such as [ GaS 3 2 Cl] 1 − . Stability of these units and type of their interconnection (corner shared or edge shared tetrahedra) depends on cation radius of a metal and correlates with glass-forming ability.

Up-conversion fluorescence in Er-doped chalcogenide glasses based on GeS2-Ga2S3 system

Abstract The up-conversion fluorescence excited with 813 and 1550 nm light is investigated in glasses of the Ga2S3–GeS2–Er2S3 system. The influence of the glassy matrix composition and Er concentration on the luminescence and absorption spectra is studied. Increasing the Ga content relative to Ge decreases the erbium concentration quenching effect. The efficiency of up-conversion fluorescence has a strong dependence on thermal history of the sample. Annealing of the glasses and decreasing the synthesis temperature increase the luminescence intensity.

Up-conversion luminescence efficiency in Er-doped chalcogenide glasses

Abstract The efficiency of up-conversion luminescence of Er 3+ ions (excited by laser light operating at 810 nm) in the GeS 2 –Ga 2 S 3 :Er 2 S 3 system strongly depends on the energy position of the fundamental absorption edge. This dependence is due to non-radiative energy exchange between the electronic subsystem of the glassy matrix and excited levels of Er 3+ ions. In chalcogenide glasses Ge and Ga atoms are fourfold coordinated. Except for the M (M=Ge, Ga)–S heterobonds, the rest are M–M homobonds. These homobonds can be detected with Raman spectroscopy. The energy position of the absorption tail of the fundamental band depends on the concentration of M–M homobonds. When the concentration of these bonds increases the absorption edge shifts to longer wavelengths and the intensity of up-conversion luminescence decreases. The relative concentration of M–M bonds depends not only on composition of the glassy matrix but also on the synthesis and on concentration of extrinsic impurities such as OH − , SH − and –CH 2 –. Another cause of reduction of up-conversion luminescence intensity is the inhomogeneous distribution of REI in the Ga 2 S 3 –GeS 2 glasses. The simple model describing dependence of luminescence intensity on type of REI distribution in the glassy matrix is discussed.

Heat of structural transformation at the semiconductor-metal transition in As2Te3 liquid

Abstract A reversible transition at 780 K with an enthalpy of 25 kJ/kg was found by a differential scanning calorimetry study of the As 2 Te 3 liquid. The investigation of density and magnetic susceptibility of the same compound proves that the effect is due to the semiconductor-metal transformation.

Deposition of Er3+ doped chalcogenide glass films by excimer laser ablation

Abstract The Ga2S3–GeS2:Er2S3 films of various thicknesses (from 0.3 to 5 μm) were prepared by laser ablation. The deposed films were characterized with various diagnostic techniques: optical absorption spectroscopy, X-ray fluorescence spectroscopy, secondary ion mass spectroscopy and luminescence spectroscopy. Concentrations of rare-earth ions, gallium and germanium in the target bulk glass and in the films were similar. The composition of deposited films was uniform. The location of the fundamental absorption edge was in the range from about 350 to 550 nm and depended on deposition conditions. The UV irradiation led to a large photo bleaching effect. The luminescence spectrum of the deposited film was measured.

Glasses of the Ga2S3-GeS2 system doped with rare-earth ions (Nd3+,Er3+) as active optical materials

Physical-chemical and optical properties of glassy system Ga-Ge-S, doped with Nd3+, Er3+ were treated from viewpoints of differential-temperature analysis, Raman and luminescence spectroscopy. Strong correlation between network structure and luminescence efficiency of Ga-Ge-S:Nd, Er system is established. Increase of Ga2S3 contents in Ga-Ge-S:Nd, Er system leads to forming of ternary structure units and enhances luminescence efficiency.

Structure of As2Te3 glass, influence thermal processing

Abstract A comparison of atom radial density distribution curves for quenched and annealed As 2 X 3 (X = Se, Te) glasses shows that quenched and annealed As 2 Se 3 and annealed As 2 Te 3 have a similar structure, but the local order in quenched As 2 Te 3 glass differs. This result is explained by a semiconductor-metal transition in As 2 Te 3 liquid.

Low-Crosstalk 3 × 3 Optical Cross-Connect Using Fiber Bragg Gratings

A power-compensated, 3×3 reconfigurable, multiwavelength and bidirectional optical cross-connect (RMB-OXC) for all-optical networks is proposed using strain-tunable fiber Bragg gratings (ST-FBG) and several optical circulators. The paper presents the experimental study for the induced crosstalk due to the OXC. The RBM-OXC operation and performance are experimentally demonstrated and crosstalk is determined to confirm the low penalty incurred. In overall the selective RBM-OXC offers high reconfigurable capability, flexibility and survivability in an optical network.