Properties of As40S(60–x) Sex Glasses for IR Fiber Optics

The physical and optical properties of glasses in the As₄₀S₍₍₆₀-_x:)Se_x system where x = 0, 5,10,15, and 20 at. % Se have been investigated. The changes in the glass transition temperature, density, hardness, IR edge, and refractive index can be attributed to the presence of Se, which simply replaces S in these glasses. The glasses do not exhibit crystallization under the conditions used in this study, which is a desirable property from the viewpoint of flberization. Appropriate core and cladding glass compositions have been identified for fabrication of optical fibers with known numerical apertures. Furthermore, it has been shown that these glasses will not impart additional thermal or mechanical stresses in optical fibers made from these compositions.     

Use of CsCl to Enhance the Glass Stability Range of Tellurite Glasses for Er3+-Doped Optical Fiber Drawing

Tellurite glasses are important as a host of Er³⁺ ions because of their good solubility and because they present broadband optical gain compared with Er³⁺-doped silica, with the potential to increase the bandwidth of communication systems. However, the small glass stability range (GSR) of tellurite glasses compromises the quality of the optical fibers. We show that the addition of CsCl to tellurite glasses can increase their GSR, making it easier to draw good-quality optical fibers. CsCl acts like a network modifier in glass systems, weakening the network by forming Te–Cl bonds. We show that the thermal expansion coefficient mismatch is in the right direction for optical fiber fabrication purposes and that the Bi₂O₃ content can be used to control the refractive index of clad and core glasses. Single-mode and multi-mode Er³⁺-doped optical fibers were produced by the rod-in-tube method using highly homogeneous TeO₂–ZnO–Li₂O–Bi₂O₃–CsCl glasses.     

Influence of As2O3 on the Optical Properties of Ultrapure Multicomponent Silicate Glasses and Optical Fibers

To obtain low transmission loss optical fibers from ultrapure multicomponent silicate glasses, it is necessary to add small quantities of As₂O₃ (or Sb₂O₃). In optical fibers prepared from glasses without these agents, a significant increase in loss is observed. To investigate this effect, the influence of As₂O₃ (added to the batch and present in the glass as As₂O₅) on the optical properties of ultrapure silicate glasses was studied. These properties are the Rayleigh scattering loss coefficient, transition metal absorption, and position of the uv absorption edge. This study showed that the increase in loss of As₂O₃-free glass cannot be assigned to any of these contributions and was attributed to absorption by electrons, trapped in relatively shallow traps in the glass network. The As⁵⁺ ions serve as deep traps and therefore remove the additional absorption. The same phenomenon, although much more pronounced, was observed in optical fibers prepared from alkali borosilicate glasses.     

The Glass System SiO2-B2O3-Bap-Na2O for High-Numerical-Aperture Optical Fibers

The glass system SiO₂-B₂O₃-BaO-Na₂O was investigated to obtain high-refractive-index glasses for high-numerical-aperture (N.A.) optical fibers. Compositions having a mole ratio [B₂O₃]/[BaO+Na₂O]=2 have unique properties. They are both highly viscous and chemically durable despite the fact that they contain highly alkaline metals and alkaline-earth metals. Glass properties at this mole ratio are favorable for optical fibers. It is proposed that the composition for core glass of high-N. A. optical fibers be based on this mole ratio.     

Formation and Properties of GeSe2–Ga2Se3–PbI2 Novel Chalcohalide Glasses

The glass-forming region of the GeSe₂–Ga₂Se₃–PbI₂ system was determined and homogeneous glasses were prepared. The maximum dissolvable PbI₂ can be up to 50 mol%. The structures of glasses were characterized by Raman spectroscopy. The thermal, optical, and some basic physical properties of the glasses were investigated. The results show that GeSe₂–Ga₂Se₃–PbI₂ glasses have a wide region of transmission window (0.7–16 μm) and high refractive index (∼2.5) with the addition of PbI₂. The glasses have good glass-forming ability and high glass transition temperatures. Consequently, these novel glasses may be promising candidate materials for infrared optics and nonlinear optical field.     

Ultrafast Optical Switches and Wavelength Division Multiplexing (WDM) Amplifiers Based on Bismuth Oxide Glasses

Glasses with a high refractive index exhibit interesting properties. All optical switching and broadband amplification performances have been demonstrated using glasses based on bismuth oxide (Bi₂O₃). Optical Kerr shutter (OKS) switching and degenerated four-wave mixing experiments for nonresonant-type Bi₂O₃–B₂O₃–SiO₂ glasses have been performed using femtosecond lasers. This glass exhibits an ultrafast response (<150 fs) in OKS operation. Moreover, terahertz-range (THz-range) optical switching has been successfully performed with this glass, using a 1.5-THz pulse train. Erbium-doped bismuth-based oxide glasses also have been prepared for wavelength division multiplexing (WDM) amplifiers. These glasses exhibit broadband emission and negligible concentration quenching, which indicates that the bismuth-based glass is suitable for broadband amplifiers and highly doped short-length fiber applications for metro use.     

Preparation and Properties of Heavy-Metal Fluoride Glasses Containing Ytterbium or Lutetium

Beginning with a 19BaF₂−27ZnF₂−27YbF₃−27ThF₄ (mol%) base glass, compositional modifications were made to improve optical properties and glass-forming ability. Replacement of YbF₃ by LuF₃ removed a strong near-ir electronic absorption band, and small additions of LiF and NaF improved glass quality. The multicomponent BaF₂/ThF₄ glasses had higher refractive indices and lower expansion coefficients than fluorozirconate and fluorohafnate glasses. In the 6 to 10 μm region, these materials exhibit absorption coefficients an order of magnitude lower than those reported for other heavy-metal fluoride glasses.     

La2O3-Al2O3-SiO2 Glasses for High-Power, Yb3+-Doped, 980-nm Fiber Lasers

Single-mode semiconductor pumps have failed to keep pace with the increasing power requirements of Er-doped fiber amplifiers (EDFAs), so there is a need for high-powered 980-nm sources. Yb³⁺-doped tapered fiber lasers can provide high-power output by conversion of a low-brightness, high-powered, 920-nm, multimode broad stripe laser diode to a high-brightness, 980-nm, single-mode output. The tapered fiber laser requires a fiber with high numerical aperture (NA) (>0.4), a rectangular core, and good Yb³⁺ spectroscopy for efficient operation. CVD-based fiber fabrication methods are incapable of delivering fibers with an NA > ∼0.3 or with good efficiency at 980 nm so a new method of high-NA fiber fabrication was developed. The core glass composition is critical for maintaining a high-NA fiber with good power extraction while avoiding phase separation, loss, and clustering. The SiO₂ level controlled the NA and interdiffusion between core and clad, while the Al₂O₃/La₂O₃ ratio controlled phase separation. A La₂O₃-Al₂O₃-SiO₂ glass was developed that is compatible with a pure SiO₂ cladding glass and has a laser slope efficiency of 70% at 980 nm. The optimized fiber composition yielded 450 mW of 980-nm power in a single-mode fiber.     

Structure, Thermal Behavior, Chemical Durability, and Optical Properties of the Na2O–Al2O3–TiO2–Nb2O5–P2O5 Glass System

The FTIR, Raman, UV-Vis, ³¹P MAS-NMR, DTA, and refractive index measurements have been combined to investigate a series of glasses with the general formula 20Na₂O–5Al₂O₃− x TiO₂–(45− x )Nb₂O₅–30P₂O₅, 15≤ x ≤45. The glass structure, as well as thermal, optical, and chemical durability properties, were then described as functions of the f _Nb/ f _Ti ratio. An increase of the f _Nb/ f _Ti ratio correlates with a decrease in length of the average phosphate chains linked through Nb–O–P and Ti–O–P bonds, with an increase in the glass stability and with increase in the linear refractive indices at 632.8 nm from 1.79 to 1.89. Furthermore, niobium is more effective than titanium in improving chemical durability.     

Rare-Earth Aluminosilicate Glasses

Rare-earth aluminosilicate glasses of the general formula 20R₂O₃· 20Al₂O₃· 60SiO₂ have been formed for 10 of the 14 possible rare-earth oxides. Two series of "mixed-rare-earth" glasses were also formed (Nd/Er and Nd/Y). These glasses exhibit exceptionally high glass transformation temperatures, moderate thermal expansion coefficients, and refractive indices of approximately 1.65. The glass transformation temperature and thermal expansion coefficients vary linearly with the field strength of the rare-earth ion. No evidence of a "mixed-rare-earth effect" was observed. MAS-NMR indicates that the aluminum ions are tetrahedrally coordinated in at least some of these glasses.     

Structure and Properties of Long-Wavelength-Transmitting Halide Glasses

The lower halides of zinc, namely, ZnCl₂, ZnBr₂, and ZnI₂, may act as network formers in glasses that also contain modifying alkali halides such as KCI, KBr, KI, NaI, or CsI. Compositions which contain only Br⁻ or I⁻ anions are of particular interest because of their extended infrared transmission, which includes the ∼10-μm region, in addition to full visible transparency. A series of modified zinc halide glasses were prepared and characterized by differential scanning calorimetry, middle and far Fourier transform infrared spectroscopy, and polarized Raman spectroscopy. T _g values were characteristically low, around 40°C. Bulk glass infrared transmission up to 15 to 20 μm was recorded. The most probable glass structures are discussed and compared to oxide glass models. An attenuation of  0.001 dB/km has been projected as a possible intrinsic minimum for optical fibers operating near ∼6 μm.     

Effects of the Weak Absorption Tail on the Transmission Loss of Ge–Sb–Se Optical Fibers

Selenide glass optical fibers were fabricated for Ge₃₀Sb₁₀Se₅₈S₂ and Ge₂₀Sb₁₀Se₇₀ glasses. Their transmission loss has been measured and compared with the theoretical attenuation loss that was calculated taking into account the electronic transition absorption, Rayleigh scattering, and multiphonon absorption. A low attenuation loss of the Ge₂₀Sb₁₀Se₇₀ glass composition in 1.2–1.7 μm range has been expected due to its high optical band gap energy compared with the Ge₃₀Sb₁₀Se₅₈S₂ glass. However, the measured attenuation loss of the Ge₃₀Sb₁₀Se₅₈S₂ glass fiber was ∼13 dB/m at 1.5 μm while Ge₂₀Sb₁₀Se₇₀ glass showed ∼82 dB/m. An enhanced weak absorption tail due to the localized states of the Ge₂₀Sb₁₀Se₇₀ glass was responsible for this behavior. Structural defects are related to the localized states and discussed for the present glass compositions.     

Binary Titania-Silica Glasses Containing 10 to 20 Wt% TiO2

A series of glasses in the TiO₂-SiO₂ system was prepared by the flame hydrolysis boule process. Clear glasses containing as much as 16.5 wt% TiO₂ were obtained. More TiO₂ caused opacity due to phase separation and anatase/rutile crystallization during glass boule formation. Glasses in the 12 to ∼17 wt% TiO₂ range were metastable and showed structural rearrangements on heat treatment at temperatures as low as 750CEC (∼200° below the annealing point). These changes were accompanied by large changes in thermal expansion. Thermal treatment can be designed to produce almost any desired expansion between α_-200+700=−5 × 10^-7/°C and +10 × 10^-7/°C. Zero expansion between 0 and 550°C was obtained. Evidence that these changes are due to phase separation and anatase formation is presented. Viscosity data in the glass transition range, refractive index, and density are also presented.     

Fabrication of Transparent Tellurite Glasses Containing Potassium Niobate Crystals by an Incorporation Method

To fabricate transparent oxide glasses containing ferroelectric KNbO₃ crystals, a new method in which KNbO₃ particles are directly incorporated into TeO₂─K₂O─Nb₂O₅ glasses has been developed. Transparent TeO₂-based glasses containing KNbO₃ crystals with a diameter of ∼ 10 μm have been first successfully fabricated by adjusting temperature and time for incorporation. A small difference in the refractive indexes, n , between TeO₂-based matrix glasses ( n = 2.0) and incorporated KNbO₃ crystals ( n = 2.21) is a significant reason for the transparency. This new method is applicable for the fabrication of new transparent glasses containing other functional materials with high refractive indexes.     

Properties and Structure of Glasses in the Binary Systems Alkali—TiO2

Glasses corresponding to mole formulas R₂TiO₃ and R₂Ti₂O₅ were prepared in 1- to 5-g quantities by quenching in a platinum crucible. K₂O, Rb₂O, and Cs₂O formed fairly stable glasses with TiO₂. On heat treatment, these glasses nucleated readily and formed opal-like glasses. Li₂O and Na₂O, however, did not form glasses with TiO₂ in 1-g quantities. Hygroscopicity increased with the alkali content and decreased with the increase in TiO₂ concentration. The refractive indices of the glasses ranged from 1.66 to 1.90. These facts indicate that TiO₂ is a glass former in its own right and that Ti⁴⁺ exists in sixfold coordination in these glasses.     

Cation Effects in NaPO3 Glasses Doped with Metal Nitrides and Oxides

Oxynitride glasses were prepared by doping a NaPO₃ melt with either AIN, Mg₃N₂, or Ca₃N₂ NaPO₃ glasses doped with AI₂O₃, MgO, or CaO, so as to contain the same weight percent of each cation as in the oxynitride glasses were also prepared. The dissolution rate in water and the thermal expansion coefficient both decreased while the dilatometric softening point, glass transition temperature, and refractive index increased with increasing nitride or oxide dopant concentration. The properties of the corresponding oxide- or nitride-doped glasses were essentially equal, which indicated that the cation was primarily responsible for the change in each property.     

Tellurite Glasses for Broadband Amplifiers and Integrated Optics

The present investigation discusses the advantage of using RE-ion-doped (Nd³⁺, Tm³⁺, and Er³⁺) TeO₂ glasses for developing fiber and planar broadband amplifiers and lasers. The spectroscopy of RE-ion-doped fibers and glasses is discussed along with the thermal properties of glass hosts. The results of emission from the ³H₄ level in single-mode Tm³⁺-doped tellurite fiber show that the emission band overlaps with Er³⁺ emission from the ⁴I_13/2 level and Nd³⁺ emission from the ⁴F_3/2 level in silicate and tellurite glasses, thereby enabling the development of amplifiers and lasers between 1350 and 1650 nm. Recent results using Z-scan measurements of nonlinear refractive index and absorption demonstrate that the third-order nonlinearity in undoped TeO₂ glasses is of the order of 2 × 10⁻¹⁵ to 3 × 10⁻¹⁵ cm²·W⁻¹ between 1300 and 1550 nm. These results are briefly discussed in view of an amplifier operation combined with ultrafast all-optical switching.     

Compound-Glass Waveguides Fabricated by a Metal Evaporation Technique

Glass fiber optical waveguides consisting of a potassium silicate glass core and SiO₂ cladding were produced by a potassium metal evaporation technique. An evacuated fused-silica tube containing an evaporated deposit of K was heated to temperatures sufficient to form a uniform potassium silicide layer on its inner surface. This layer was oxidized and reacted with the SiO₂tubing at high temperatures to form a potassium silicate glass. The tube was then collapsed to give a solid rod preform with a potassium silicate core. Fibers drawn from such preforms exhibit moderately low optical loss. The fabrication technique is described, and a representative loss spectrum is presented.     

Structure and Mechanism of Conduction of Semiconductor Glasses

The area of glass formation in the system GeO₂-P₄O₁₀-V₂O₅ and the properties of the glasses in this area were determined. The glasses displayed electronic conduction at room temperature (25°C). Resistivity ranged from 500 ohm-cm to 10⁹ ohm-cm at 25°C. Some of the glasses had unusual negative temperature coefficients of resistance of the order of -760,000 ppm °C⁻¹ in the range 25° to -55°C. Volt-ampere characteristics indicated nonlinearity suitable for thermistor application. Other unusual properties included high refractive indices from 1.6 to >2.0 and dielectric constants from 6 to 33 at 1 Mc and 25°C. Values of loss-tangents, however, were high. Infrared spectra indicated that the V⁵⁺ ion existed in sixfold coordination in the glassy state as well as in the devitrified crystalline state. The normal vibrational frequency of the V–O bond at 1015 cm⁻¹ was observed for all glasses in the system. Property versus composition curves indicated that density, refractive index, and dielectric constant of ternary glasses in the system do not obey the additivity rule. The density versus mole % V₂O₅ curve goes through a minimum. Derived quantities from experimental data indicate pronounced influence of V₂O₅ on oxygen packing in the system. Addition of SiO₂, even in small quantities, destroys glass formation. The structure of these glasses, which differs from that of silicate glasses, is discussed. A mechanism of conduction is suggested, based on evidence from magnetic susceptibility, chemical analysis, activation energy, and infrared spectra.     

Dispersion of Thermooptic Coefficients of Soda–Lime–Silica Glasses

The thermooptic coefficients, i.e., the variation of refractive index with temperature (d n /d T ), are analyzed in a physically meaningful model for two series of soda–lime–silica glasses, 25Na₂O· x CaO·(75 – x )SiO₂ and (25 – x )Na₂O· x CaO·75SiO₂. This model is based on three physical parameters—the thermal expansion coefficient and excitonic and isentropic optical bands that are in the vacuum ultraviolet region—instead of on consideration of the temperature coefficient of electronic polarizability, as suggested in 1960. This model is capable of predicting and analyzing the thermooptic coefficients throughout the transmission region of the optical glasses at any operating temperature.