Multiphonon Edge Research Articles

Structure-properties relationship study in niobium oxide containing GaO3/2-LaO3/2-KO1/2 gallate glasses

The investigation has been devoted to the effect of the KNbO3 in a gallate based glasses of composition (100-x) (69GaO3/2-11LaO3/2-20KO1/2) – x KNbO3 with x varying from 0 to 20 mol.% allowing the use of standard melt technique. The thermal and optical properties were characterized and the local structure has been investigated by Raman spectroscopy. The gallium ions are mostly found in tetrahedra thanks to charge balancing of potassium and lanthanum ions. The continuous increase of the KNbO3 concentration gives rise to the progressive formation of a niobate subnetwork composed of corner shared NbO6 octahedra which does not depolymerize the gallate glass network. This addition has a limited impact on the multiphonon edge in the infrared while it causes a significant increase of the refractive index. For KNbO3 concentrations above 14 mol.% a phase separation occurs due to the absence of formation of a mixed gallo-niobate glass skeleton.

Comparative study on three highly sensitive absorption measurement techniques characterizing lithium niobate over its entire transparent spectral range.

We employ three highly sensitive spectrometers: a photoacoustic spectrometer, a photothermal common-path interferometer and a whispering-gallery-resonator-based absorption spectrometer, for a comparative study of measuring the absorption coefficient of nominally transparent undoped, congruently grown lithium niobate for ordinarily and extraordinarily polarized light in the wavelength range from 390 to 3800 nm. The absorption coefficient ranges from below 10(-4) cm(-1) up to 2 cm(-1). Furthermore, we measure the absorption at the Urbach tail as well as the multiphonon edge of the material by a standard grating spectrometer and a Fourier-transform infrared spectrometer, providing for the first time an absorption spectrum of the whole transparency window of lithium niobate. The absorption coefficients obtained by the three highly sensitive and independent methods show good agreement.

The decisive role of oxide content in the formation and crystallization of gallium-lanthanum-sulfide glasses

A series of gallium-lanthanum-sulfide (GLS) glasses of different oxide concentration has been made and their spectroscopic properties, thermal properties, and the crystallization behavior of the glasses have been studied. It was revealed that the formability of GLS glasses relies on the existence of a certain amount of oxide content. The thermal stability of GLS glasses changes as a function of oxide concentration. The results have also shown that increasing oxide content caused a shift of the visible absorption edge to shorter wavelengths and an increase of absorption intensity in the infrared region at the multiphonon edge. Two closely related crystalline phases have been identified in the crystallized GLS glasses. For the first time it has been revealed that thermally stable GLS glasses can be made near the eutectic point of these two crystal phases by introducing an optimized amount of oxide.

Rare-earth-doped cadmium-based chlorofluoride glasses with improved durability

Glass formation is investigated in mixed-halide systems based on CdF 2, NaF, BaF 2, ZnF 2, and CdCl 2. The compositions are optimized for the best compromise between glass stability and low sensitivity to hydrolysis. Addition of 1 mol % rare-earth fluoride does not affect significantly the glass stability. The multiphonon edge is found to depend directly on the chlorine content. Located beyond 9 μm, the position of the IR edge is indicative of low phonon-energy, as compared to pure fluorides. Fundamental vibrations of the host are obtained by means of Raman and far-IR transmission spectroscopies.

New fluoroindate glass compositions

New multicomponent InF 3-based bulk glasses have been investigated. The molar composition of the base glass is 28% InF 3–20% ZnF 2–16.5% BaF 2–12% GaF 3–9% PbF 2–6% NaCl–5% SrF 2–3% CaF 2–0.5% PrF 3. A number of variations of the base glass were prepared and their refractive indices and densities measured. Resistance to crystallization allowed the preparation of large pieces of the base glass. The infrared and Raman spectra show that the base composition has a longer wavelength multiphonon edge at 10 μm and a phonon energy of 509 cm −1, in comparison with 8 μm and 574 cm −1 for ZBLAN, which reveals that the present glasses have a lower phonon energy and a greater transparency in the infrared than ZBLAN. Reduction of PbF 2 concentration in the base composition provided glasses with smaller refractive indices than the base glass.

The effects of Sn and Bi additions on properties and structure in Ge-Se-Te chalcogenide glass

The effects of Sn and Bi additions on the properties and structure in Ge 2Se 5Te 3 glass have been studied by X-ray diffractometry, differential thermal analysis (DTA), analysis of weight-loss in solution, infrared (IR) transmission spectra and far Fourier-transform infrared (far FTIR) spectra for the purpose of expanding the IR transparency region of the Ge-Se-Te system glass and to decrease the fibre's attenuation at 10.6 μm. The additional Sn atom, which has formed [SnSe 4] tetrahedra, another type of network former in the glass network, increased the glass transition and crystallization temperatures, T g and T c, respectively, anti-crystallisation stability, chemical durability and IR multiphonon edge. The optimum glass composition in this quaternary system has a quantitative ratio (mol) of Ge/Sn ≈ 2. The most outstanding advantages of the Ge-Se-Te-Bi glass system are its excellent chemical durability and broad IR transparency region (the multiphonon absorption edge has been extended to 17.6 μm, 1.2 μm longer compared with the Ge-Se-Te system glass). Meanwhile, other properties of this glass are still somewhat better than the original Ge-Se-Te glass. These two chalcogenide glasses are candidates for drawing fibres for far-infrared transmission, especially for CO 2 laser radiation (10.6 μm) delivery in various environments.

A review of fluoride fibres for optical amplification

This paper reviews the current world-wide status of fibres based on the fluoride glass system for optical amplification, with particular emphasis on telecom applications. The key feature of fluorozirconate glasses, with the very long wavelength multiphonon edge, is the accompanying relatively low non-radiative decay rate of excited rare-earth dopant ions. This gives unique opportunities compared with the better known oxide glass systems. Amplifiers with high gains have been demonstrated at important wavelengths such as 0.8, 1.3 and 1.5 μm. Improvements to allow the fabrication of more efficient fibres are also discussed.

Optical properties of sodium alminosilicate glass

Optical properties of sodium alminosilicate (NAS) glasses are investigated theoretically and experimentally. Rayleigh ratio and infrared absorption loss are measured for various compositions of NAS glasses prepared by melting. These measurements show that Rayleigh scattering loss of SiO 2 glass is greatly reduced when Na 2O and Al 2O 3 are added to it, which results in reduction of the glass fixation temperature and the photoelastic constant. The multiphonon edge absorption in the 2.5–6 μm region is also measured and the infrared edge wavelength is found to be the same as that of pure silica. The total loss of a NAS glass is found to be 0.055 dB/km at a wavelength of 1.56 μm. This value is about one-third that of pure silica core fiber and it indicates the potential of NAS glasses as a low loss fiber material.

The tellurium halide glasses

The reaction of tellurium with the halogens Cl, Br and I leads to a new family of halide glasses which are structurally related to Se. These chain-like materials are characterized by a broad optical window lying from 1 to 13 μm or 1 to 20 μm, depending on the weight of the halogen. When combined with S or specially Se, many of these new IR glasses exhibit a strong resistance towards devitrification and water corrosion. Infrared optical fibers have been prepared from these so-called TeX glasses. The position and the dependence of the multiphonon edge as well as the bandgap have been investigated by measuring the attenuation spectra. It has been shown that these glasses exhibit low optical losses in the 8–12 μm atmospheric window. Thin layers of TeX glasses have been deposited by sputtering on silica or fluoride glass substrates, and antireflection coatings deposited on bulk TeX glasses allow the reduction of optical losses by reflection.

Chalcogenide glasses Ge–Sn–Se, Ge–Se–Te, and Ge–Sn–Se–Te for infrared optical fibers

Chalcogenide glasses of the systems Ge–Sn–Se, Ge–Se–Te, and Ge–Sn–Se–Te have been prepared. Several compositions were found suitable for drawing fibers for CO2 laser radiation (λ = 10.6 μm) transmission. The glasses were characterized by x-ray diffraction, DSC (Differential Scanning Calorimetry), SEM with EDX analysis, FTIR spectrometry, density, and microhardness measurements. The glass transition temperature and microhardness of Ge–Se–Sn and Ge–Sn–Se–Te glasses decreased with increasing Sn content, for most of the samples. The region of high IR transparency of Ge–Se–Sn, Ge–Se–Te, and Ge–Sn–Se–Te glasses was slightly expanded (1–2 μm) toward longer wavelengths, compared to Ge–Se glasses, mainly for the glasses containing 70 at.% Se. The intensity of the impurity absorption peak of Ge–O (at λ ∼ 12.8 μm), which usually appears in Ge–Se glasses, was reduced or absent in Ge–Sn–Se–Te glasses. The best fibers were produced with the glass composition Ge–0.8Sn0.2Se3.5Te0.5. An attenuation of 20 dB/m at 10.6 μm, and a transmitted maximum power density of 2.4 ⊠ 106 W/m2 were measured. The mechanical and optical characteristics of these glasses have been related to the glasses structure. Corresponding to the reduced masses of the bonds formed in the Ge–Sn–Se–Te system (in the amorphous region), it is expected that the multiphonon edge is slightly shifted. As a consequence, as was measured, the transparency region has been expanded by less than 2 μm toward longer wavelengths.

Calcium aluminate glasses as pontential ultralow-loss optical materials at 1.5–1.9 μm

The suggestion made in an earlier paper, that the calcium aluminate (CA) family of glasses should exhibit intrinsic optical losses at 1.55 μm, markedly lower than the 0.16 dB/km of SiO 2, is confirmed by scattering measurements. The total (i.e. Rayleigh, Brillouin and Raman) scattering losses are found to be ≈ 0.04 dB/km at 1.55 μm with a projected minimum total attenuation for pure silica-free samples of as low as 0.015 dB/km at ≈1.9 μm. Measurements are also made of multiphonon edge absorption in the 4–6 μm regime and a preliminary assessment given of the materials outlook for the preparation of ultralow-loss CA-glass fibers.

Progress in Halide Glass Fibers

ABSTRACTFluoride glasses are being considered for use in long distance, mid-infrared transmitting optical fibers. The multi-phonon edge of these fibers is shifted to longer wavelengths compared to silica fibers. The intrinsic loss is therefore lower (< 0.01 dB/km) and occurs at about 2.5 microns. Applications for these fibers include ultra-low loss communication links, radiation resistant links, remoting of IR focal plane arrays and IR power delivery. In addition, this ultra low loss optical fiber may be used for fiber guided missiles with capability for distances longer than 500 km. Most of the interest however, has been focused on development of ultra long (thousands of kilometers), repeaterless communication links. Such repeaterless links may decrease system cost and cable weight, while increasing overall reliability and ease of repair compared to silicate optical fibers.

A new family of vitreous materials: The cesium aluminum or gallium thiohalide glasses

A new class of non-oxide glasses with the general composition CsAXY 2 (A  Al, Ga; X  S, Se; Y  Cl, Br) has been isolated and characterized. Raman spectroscopy, investigations of the I.R. multiphonon edge, Differential Thermal Analysis measurements show that these glasses contain a giant polymeric tetrahedra-based anion and have a good stability towards devitrification. Their chemical durability in normal atmosphere is very poor and affects severely their optical properties, specially in the I.R. multiphonon region.

New zirconium free multicomponent fluoride glasses

Systematic investigations of indium based heavy metal fluoride glasses have led to the discovery of a fluoride composition with a low devitrification rate. The glass BIZYbT with the composition 30 BaF 2−30 InF 3−20 ZnF 2−10 YbF 3−10 ThF 4 is characterized by a difference Tc−Tg = 123° C and an I.R. multiphonon edge lying in the 8 μm region, about 1 μm longer than for the fluorozirconate. Investigations of the T.T.T. curve and various optical properties indicate that this composition is a good candidate for I.R. fluoride fibers of wide transmission range.