Chalcogenide infrared As2−xSe3+x glass fibers

Chalcogenide glasses As_2?xSe_3+x have been prepared. A new technique of preparing the raw material and subsequently drawing fibers has been developed in order to avoid the formation of oxygen compounds. The fibers have been drawn by the crucible and rod method from oxygen free raw material inside an Ar atmosphere glove box. The fibers drawn to date have a diameter of 50–500 μm and lengths of several meters. Preliminary attenuation measurements indicate that the attenuation is better than 0.1 dB/cm at 10.6 μm. The attenuation is not affected even when the fiber is bent to a circular radius of 2 cm. By improving the preparation of materials and the drawing technique, we expect to achieve a better transmission.     

Fine embossing of chalcogenide glasses – a new fabrication route for photonic integrated circuits

For the first time embossing of ribs, from 1 to 10 μm wide and ∼10 mm long, has been carried out in chalcogenide glass layers sputtered onto semiconductor wafer substrates, with potential to act as monomode waveguides; these features have been similarly embossed in the surface of bulk chalcogenide glasses. The embossing shows very good replication of the GaAs mould patterning to 1 μm definition, with evidence also for sub-micron replication. For the embossing, thin coatings of the chalcogenide glasses were sputtered onto wafer substrates as follows: (i) a 6 μm layer of Ge₁₇As₁₈Se₆₅ (at.%) onto porous Si-on-Si wafer substrates and (ii) a 4 μm layer of Ge₁₅As₁₅Se₁₇Te₅₃ onto uncoated GaAs substrates. The Ge₁₇As₁₈Se₆₅ sputtered glass layer on porous Si-on-Si was demonstrated to slab waveguide at 1.55 μm wavelength; it was designed to achieve monomode waveguiding at 1.55 μm after embossing, for the 5 μm wide rib. The series of ribs, 1–10 μm wide, were successfully embossed in the Ge₁₇As₁₈Se₆₅ glass sputtered layer on porous Si-on-Si, but cracking of the glass layer occurred during the embossing process. Successful embossing of ribs without the glass layer cracking was achieved for the Ge₁₅As₁₅Se₁₇Te₅₃ sputtered glass layer on uncoated GaAs. Due to its relative simplicity, it is likely that hot embossing of this type of glass-based matrix offers an extremely promising route for producing high-resolution, guided-wave optical components and circuitry at low-cost, high-volume, and for a wide wavelength range.     

Recent advances in preparation of high-purity glasses based on arsenic chalcogenides for fiber optics

The processes of production of high-purity glasses based on arsenic chalcogenides and optical fibers with low optical losses in the middle IR have been analyzed. Physical–chemical, technological and methodological factors determining the degree of purity of glasses and the level of optical losses in optical fibers are considered. Dominant factors, rational actions and approaches optimizing the manifestation of these factors in glasses formed by arsenic chalcogenides are discussed. Vitreous As₂S₃ is produced with the content of hydroxyl groups not more than 1 ppb wt, of hydrogen in the form of SH-groups — 75 ppb mol, of silicon — 0.2 ppm wt. From this glass a multi-mode optical fiber was manufactured with optical losses of 12 and 14 dB/km at 3.0 and 4.8 μm, respectively, which is the best result published in literature for chalcogenide glass optical fibers.     

Ultrasonic wave velocities and attenuation in IVb-Vb-VIb chalcogenide glasses: 2–300 K

The velocities and attenuation of longitudinal and shear ultrasonic (12 MHz) waves have been measured for several chalcogenide glasses (Ge₁₀Si₁₂As₃₀Te₄₈, Ge₂₀As₃₀Se₅₀, Si₂₀As₃₂Te₄₈, Ge₁₀Si₁₂As₂₉Te₄₉, Ge₁₂S₁₄As₃₅Te₄₉). The bulk, shear and Young's moduli and the Poisson ratio are found to be insensitive to the glass composition. The temperature dependences of the longitudinal and shear-wave velocities are negative at higher temperatures and approach 0 K with a zero slope. The ultrasonic attenuation does not exhibit either the broad loss peak or the smaller low-temperature peak found in many other glasses: the elastic and anelastic behaviour is quite different from that of oxide glasses — no evidence for the existence of two-level systems has been obtained from the ultrasonic measurements.     

Bulk and impurity infrared absorption in 0.5 As2Se30.5 GeSe2 glass

A study of infrared absorption in the 250–4000 cm^?1 region has been carried out for 0.5 As₂Se₃0.5 GeSe₂ glasses quantitatively doped with oxide impurity. The frequencies of the intrinsic 2- and 3-phonon absorption bands at 490 and 690 cm^?1 correspond well to those predicted from combinations of the high frequency bands in the first order IR and Raman spectra of As₂Se₃ and GeSe₂ glasses.Glasses doped with As₂O₃ exhibit the same oxide impurity absorptionbands as those doped with GeO₂. Unlike As₂Se₃ glass, at impurity concentrations up to 1000 ppm As₂O₃, 0.5 As₂Se₃0.5 GeSe₂ glass exhibits only one major oxide impurity species, characterized by absorption bands at 780 and 1260 cm^?1 and due to oxygen bonded to network Ge. The observation of a much weaker network AsO vibration band at 670 cm^?1 confirms that oxygen bonds preferentially to Ge in this glass. The same minor oxide species appears to determine excess IR absorption at the CO₂ laser wavelength of 10.6 μm in both As₂Se₃ and 0.5 As₂Se₃ 0.5 GeSe₂ glasses. The frequencies and intensities of absorption bands due to hydrogen impurities are also quite comparable for these two materials.     

Polynary silicon arsenic chalcogenide glasses with high softening temperatures

The introduction of Ag in SiAsTe glasses permits the incorporation of Se, otherwise volatile and/or degradable as a constituent in Si-containing chalcogenide glasses. SiAsAgTeSe glasses exhibit much higher softening ranges and glass transition temperatures than encountered in known chalgogenide systems. A glass Si₃₅As₁₅Ag₁₀Te₂₀Se₂₀ had the viscosity log ν = 13 at about 500°C, as compared to 370°C for the base glass Si₃₅As₂₅Te₄₀, the viscosity of log ν = 9.8 at about 560°C, as compared to 442°C for the base glass. Phase separation occurs in the system SiAsAgTeSe and becomes manifest in two glass transitions indicated by changes in the slopes of the expansion curves and breaks in the softening point-composition relations. The existence and behavior SiAsAgTeSe glasses suggests the possible development of higher T_g i.r. transparencies and higher T_g semiconductor glasses than described so far.     

Infrared absorption of some high-purity chalcogenide glasses

New compouning techniques were devised to prepare high-purity Ge₂₈Sb₁₂Se₆₀ (TI 1173)and Ge₃₃As₁₂Se₅₅ TI 20). The methods were based on the combination of the reactant purification and compounding steps. The goal of the program was to establish the absorption limit for the glasses and to lower the absorption at 10.6 μm. At the present purity level, the GeSbSe glass is found to have an absorption level of about 0.01 cm^?1 at 10.6 μm while the absorption level for the GeAsSe glass is 0.05 cm^?1. Underlying causes for the limits are discussed along with the possibilities for improvement.     

Non-linear properties of chalcogenide glasses and fibers

High purity chalcogenide glasses were prepared in the series As₂S_(3?x)Se_x where x = 0 to 3. The measured third order non-linearities increase with the value of x, and are up to about 1000 times larger than silica for As₂Se₃ glass. We show that the anharmonic oscillator model, using the normalized photon energy, gives an excellent fit to the data over three orders of magnitude. Single mode optical fibers based on As₂S₃ and As₂Se₃ glasses have been fabricated using the double crucible technique and the Stimulated Brillouin Scattering (SBS) investigated. The threshold intensity for the SBS process was measured and used to estimate the Brillouin gain coefficient. Preliminary results indicate record high values for the figure of merit and theoretical gain, compared to silica, which bodes well for slow-light based applications in chalcogenide fibers.     

Effect of some manufacturing conditions on the optical loss of compound glass fibers

The effect of the use of platinum crucibles and gas flow at glass melting and fiber drawing on the optical loss of compound silicate glass fibers have been investigated for the purpose of obtaining low-loss optical fibers. In concentrations of more than 50 ppm, platinum impurity dissolved into the glass from a platinum crucible increases the optical loss. The flow of oxidizing gas decreases the optical loss due to the Fe²⁺ ions. The flow of dry gas also decreases the absorption loss at 0.96 μm by water. The improvement based on these results lowers the total loss of clad fibers to 9.5 dB/km at 0.84 μm and 15 dB/km at 1.06 μm.     

Te-rich Ge–As–Se–Te bulk glasses and films for future IR-integrated optics

Ge₁₅As₁₅Se_70−xTe_x materials with x = 56, 60 and 63, of potential use in IR-integrated optics, were prepared by the classical melt-quenching method. A macroscopic phase separation was observed with a crystalline phase on the top and an amorphous one at the bottom. The glasses from the bottom were transparent from 1.9 to 16 μm without any purification of the elemental precursors Ge, As, Te and Se. The higher the Te/Se content in the glasses the lower their glass transition temperature and thermal stability. Films 7–12 μm thick of the above stated compositions were deposited by thermal evaporation. The higher the tellurium content, the larger the optical band gap shift of the films in the infra-red and the higher the refractive index.     

Infrared studies of Se-based polynary chalcogenide glasses (II): YxZxSe100−2x (Y = Ge,As; Z = As,Te)

The infrared (IR) absorption spectra for Y_xZ_xSe_100?2x glasses (Y = Ge, As;Z = As, Te), x = 2.5 and 5.0 are measured in the wavenumber region 700-60 cm^?1 at room temperature. These IR spectra are explained by comparing with the IR spectra already reported for the binary glasses such as Ge–Se, As–Se and Se–Te. In Ge_xAs_xSe_100-2x glasses (x ? 5.0), the main spectral features as well explained by both the spectra of Ge_xSe_100?x and As_xSe_100?x glasses. Main structural units in these glasses are considered to be GeSe₄ tetrahedra and AsSe₃ pyramids, and Se₈ rings and Se_n chains which are the units in pure glassy Se. In Ge_xTe_xSe_100?2x glasses (x ? 5.0) and IR band which cannot be explained by either the spectra of Ge_xSe_100?x or Se_100?xTe_x glasses appears at 210 cm^?1. This band is considered to be due to Ge–Te bonds. The IR spectra of As_xTe_x Se_100?2x glasses (x ? 5.0) are well explained by both the spectra of As_xSe_100?x and Se_100?xTe_x glasses. It is concluded that As and Te atoms combine with Se atoms in the forms of AsE₃ pyramids and Se₅Te₃ mixed rings, respectively.     

Optical properties of thin films of system (As2Se3)80−x(As2Te3)x(SnTe)20 prepared by PLD

Thin amorphous films from system (As₂Se₃)_80−x(As₂Te₃)_x(SnTe)₂₀ were prepared by pulsed laser deposition (PLD) from their bulk glasses and their optical properties were studied by spectral ellipsometry. Spectral dependencies of refractive index, absorption and extinction coefficient and optical gap (1.41–1.66 eV for (As₂Se₃)_80−x(As₂Te₃)_x(SnTe)₂₀ with x = 20 resp. x = 0) were calculated from optical tansmittance, from ellipsometric data by Tauc method. High values of refractive index n₀ (2.49–2.60) and of non-linear χ⁽³⁾ coefficient of index of refraction (4.9–7.5 × 10⁻¹² esu for the glass (As₂Se₃)_80−x(As₂Te₃)_x(SnTe)₂₀ with x = 0 resp. x = 20) made studied thin films of system (As₂Se₃)_80−x(As₂Te₃)_x(SnTe)₂₀ promising candidates for application in optics and optoelectronics.     

Study of As―Se―Te glasses by neutron-, X-ray diffraction and optical spectroscopic methods

The atomic structures of amorphous As₄₀Se_(60?x)Te_x (x = 10 and 15) and As₄₀Se₆₀ glasses have been investigated by neutron and high energy X-ray diffraction methods. The two datasets were modeled simultaneously by reverse Monte Carlo (RMC) simulation technique. The RMC simulations revealed a glassy network built-up from As(Se, Te)₃ pyramids in which Te atoms substitute Se atoms. The As―Se correlation function shows a strong and sharp first peak at 2.4 Å and two broad and much less intense peaks at 3.7 and 5.6 Å, related to 1st, 2nd and 3rd neighbor distances of the As―Se bonds, respectively. They are an evidence for existence of short and medium ordering in the studied glasses. The similarity of Θ_Te―As―Te and Θ_Se―As―Se bond distributions suggests that Te atoms have a similar role in the structure formation as Se atoms. The FTIR spectra analysis revealed impurity bonds of Se―H, As―O, Se―O, and Te―O in the glasses which contributed to enhanced absorption in visible spectral range. From the ellipsometric data analysis the optical constants and the energetic parameters of the studied glasses were established. The compositional variation of these parameters is explained in terms of chemical bonds formation and change in the density of charged defects.     

Electrical and optical properties of the AsTeIn and GeSeIn chalcogenide systems

The influence of indium on the optical and properties of As_2−xTe_3−xxIn_2x, As_20−xTe_80−xIn_2x and Ge_20−xSe_80−xIn_2x is described. In Te-containing glasses the Fermi level is shifted by 0.05 eV and in Se-containing glasses by 0.2 eV towards the valence band.     

Thermoelectric power of AsSeTe glasses

The result of the measurement of the thermoelectric power of glasses in the As₂Se₃As₂Te₃ system are reported. The results indicate that towards the As₂Te₃ end of the composition, there is an anomalous increase in thermoelectric power, the origin of which is not clear. Polaron hopping seems to contribute to conductivity in tellurium rich glasses. Structural restrictions on polaron hopping, such as the availability of AsTeAsTe chains seems to be important in discussing transport behaviour.     

Mechanical damping of silver-containing SiAsChalcogenide glasses

Mechanical damping measurements were used to study the structural conditions responsible for the increase in thermal stability that has been observed when Ag and Se are substituted simultaneously in Si₃₅As_25?xAg_xTe_40?ySe_y glasses. Glasses containing Ag exhibited a mechanical damping peak whose magnitude was approximately proportional to the Ag content and which was absent in the more completely cross-linked Si₃₅As₂₅Te₄₀ base glass. This peak shifted to lower temperatures and split into two overlapping peaks with increasing Se content. The splitting of the peak has been tentatively attributed to phase separation which has been postulated to occur at higher Se contents.     

Electron diffraction RDF analysis of amorphous As2Se3,AAs2Se2Te,As2SeTe2 and As2Te3 films

The local order in amorphous films of As₂Se₃, As₂Se₂Te, As₂SeTe₂, and As₂Te₃ has been examined by scanning electron diffraction with direct recording of the intensity of the elastically scattered electrons. The radial distribution functions indicate that there is a systematic increase in mean nearest neighbor distance as the Te concentration is increased, butthe mean coordination number increases slightly around 2.4. Pair function calculation of models shows that the 3-aand 2-fold coordinations of arsenic and chalcogens are retained in these glasses and the interatomic distances are close to those predicted from the Pauling covalent atomic radii of the constituent atomic species. The short range order appears to be similar in amorphous and crystalline As₂Se₃, but different in the case of As₂Te₃ as found by previous workers on bulk materials.     

Photoconductivity of oxychalcogenide glasses in the system As2Se3CdO

The photoconductivity of oxychalcogenide glasses in the system As₂Se₃CdO was investigated. When 2–3 mol % CdO was added, the photoresponse peak of the parent glass As₂Se₃ in the vicinity of 740 nm became broader and a little weaker. The addition of more than about 4 mol % CdO brought about a sharp and strong peak at 720 nm and a broad peak at 860 nm. X-ray diffraction and electron microscopic observations revealed the presence of crystalline CdSe in the glass matrix, indicating that the reaction As₂Se₃ + 3CdO → As₂O₃ + 3CdSe took place in the melting process of these glasses. Tempeature and light intensity dependences of the photocurrent lead to the conclusion that the above spectral photoresponse is greatly affected by the presence of the dispersed crystalline CdSe.     

Infrared studies of Se-based polynary chalcogenide glasses (III): YxZxSxSe100−3x (Y = Ge,As; Z = As,Te)

The infrared (IR) absorption spectra for Y_xZ_xS_xSe_100?3x glasses (Y = Ge, As; Z = As, te), with x = 2.5 and 5.0, are measured in the wavenumber region 700-60 cm^?1 at room temperature. These IR spectra are qualitatively explained by comparing with the IR spectra of the binary and ternary glasses. In Ge_xAs_xS_xSe_100?3x glasses (x ? 5.0), the main spectral features are explained by both spectra of the two ternary glasses Ge_xS_xSe_100?2x and As_xS_xSe_100?2x. In Ge_xS_xTe_xSe_100?3x glasses (x ? 5.0), the main spectral features are well explained by both spectra of the two ternary glasses Ge_xS_xSe_100?2x and Ge_xTe_xSe_100?2x. On the other hand, main spectral features in As_xS_xTe_xSe_100?3x glasses (x ? 5.0) are well explained by both spectra of the ternary glasses As_xS_xSe_100?2x and the binary glasses Se_100?xTe_x. In these glasses with low concentrations (x ? 5.0) some chemical bonds are confirmed and some structural units estimated.     

ESR study of structural changes in chalcogenide glasses

Structural changes in chalcogenide glasses induced by various processes such as annealing, illumination or application of a high pressure were investigated from a microscopic viewpoint by measuring changes of the ESR spectrum from Mn doped as a probe. Here, Mn incorporated in the glass network exhibits a characteristic ESR signal with g = 4.3 having a hyperfine structure. It is found that the above-mentioned processes cause a change of the lineshape of the hyperfine line and a change of the hyperfine structure constant A, both of which reflect the bonding characteristics around Mn. One of the annealing effects for bulk glasses is the increase of the A-value. The change of the A-value for well-annealed As₂Se₃ and As₄Se₅Ge₁ films occurs reversibly in sequential illumination and annealing cycles, as does the shift of the optical gap. The reversible change of the lineshape is observed for well-annealed As₂Se₃ films in the illumination and annealing cycles. Application of a high pressure to bulk glasses causes changes similar to those by illumination for annealed films. From these results it is concluded that the randomness of amorphous structure decreases by annealing and increases by illumination or application of high pressure.