Fluoride glass fibers have been intensively developed for the last 20 years. A major effort was devoted to the fabrication of low loss fibers for repeaterless long haul telecommunications. This step which ended in the late eighties provided the basic technology for the manufacturing of multimode and single mode fibers with minimum losses below 10 dB/km. Such fibers area now used for various passive applications requiring the handling of IR signal. In this respect, fluoride fibers are complementary to silica fibers when wavelength exceeds 2 micrometers . Some practical set ups are operating for IR imaging, remote spectroscopy and thermometry. Special fibers such as polarization maintaining fibers have been developed for interferometric astronomy, which could also apply to sensors. UV transmission has still to be developed. Laser power delivery is another field of application for these fibers. YAG:Er laser at 2.9 micrometers attracts a growing interest for medical applications, ophthalmology and dentistry, while prospects for CO laser are positive. Active fibers are based on rare earth doped single mode fibers. They lead to the definition of numerous new laser lines and emphasized the potential of up conversion for the generation of visible light using IR pumping laser diodes. High power output has been achieved in the blue and the red light, which open prospects for compact and all solid state fiber lasers for a wide range of applications, from displays to medical uses. Optical amplification makes another field of R and D centered on telecommunication needs. Pr3+ doped fluoride fibers have been used for the 1.3 micrometers band, and Er based fluoride fiber amplifiers exhibit wider and flatter gain than those made from silica. Optical amplification may be implemented at other wavelengths for more general purposes.
The availability of a relatively low-cost miniature integrate dIR spectrometer facilitates the application of IR spectroscopy to numerous spectral analysis and identification tasks. Recent advances in semiconductor material processing now provide the technology for the development of planar optical waveguides that exhibit good transmission characteristics in the mid-IR spectral range. Chalcogenide and fluoride glass fibers are commercially available which allows their use for coupling light to the integrated spectrometer. Integration of the slab waveguide structure with an input IR fiber and an output IR detector array thus results in a very compact device that can be used in numerous field and industrial applications such as gas detection, water analysis, chemical process monitoring, geological and agricultural surveys, and pollution monitoring. In the present work, these new materials and technologies have been exploited for the implementation of a miniature integrated optic SPECtrometer (IOSPEC) for the 2 to 6 micrometers spectral range. In the developed miniature spectrometer, broadband light is coupled into the spectrometer through an IR fiber, then subsequently dispersed into its spectral components by a diffraction grating made by anisotropic etching of silicon and finally focused on an IR detector array. This paper discusses some of the performance and design aspects of the current third generation IOSPEC technology; namely the use of IR fiber arrays in order to improve the device throughput and resolution, and the coupling of IOSPEC to advanced linear IR detector array technology.
Monitors specifically designed to measure hydrogen fluoride (HF) have been tested and evaluated over a period of 4 years in a very demanding industrial environment. These instruments use a non-dispersive IR spectroscopy (NDIR) technique and IR optical fibers as light guides between the central unit and the remote measurement points. In this application, the use of optical fiber provides two great advantages: 1) The central unit can be left in a control room where the conditions are much less difficult and, 2) the capability of the central unit to process the optical information coming from two probe heads significantly reduces the overall costs by measurement points. Since all- fiber components are not common for these fibers, special optical components were designed and built. We have found that the limits of this, and probably most other similar techniques, have more to do with long term stability than short-term sensitivity. In that respect, special attention to the fiber cable assembly and mounting is critical and some examples and mounting is critical and some examples will illustrate this point. Results of test for monitors use din roof top vents of aluminum smelters are given.
Extrusion of glass rods, tubes and core/clad performs of melt-derived, special glasses is being investigated to satisfy demand for preforms from which optical fiber can be drawn. These glasses include: heavy metal oxide, chalcogenide, halide as well as mixed systems such as oxyhalide, chalcohalide, and oxychalcogenide. Extruder equipment has been commissioned and progress in extrusion of rods, core/clad preforms and multimode, and monomode, proportioned tubes is described extruding water soluble sodium borosilicate glasses, for convenience. The extrusion process has been shown to produce good quality glass rods of close to 5mm diameter and tubes of sodium borosilicate glasses with OD of the order 10mm and OD/ID equals 2.5, 4.1, 7.1 and 11.0. The latter ratio approaches that required for a monomode proportioned preform. Tolerances on OD were within +/- 0.32mm and on ID were within +/- 0.19mm over at least 160mm of tube. The tube orifice out-of-round was <EQ 0.13mm at a measured point along the tubes. Also reported is the successful extrusion of Ga-La-S glasses which have potential as host glasses for rare earth doped optical devices.
Glass samples have been synthesized from sulfide and tellurite glasses. General chemical compositions are Ge0.25Ga0.10S0.65, Ge0.25Ga0.05As0.05S0.65, (TeO2)-(PbCl2)1-x with x equals 0.4 to 0.6 and (TeO2x-(ZnO)1-x with x equals 0.75 to 0.80. Samples doped with 500 to 12000 ppm rare earth in weight were also prepared. Sulfide glasses were made from pure components using a reactive atmosphere, which lead to glasses with a low OH content. Rare earth doped glasses are homogeneous when RE concentration is less than 3000 ppm. Heterogeneous inclusions arise beyond 1000 ppm RE when doping is made with chloride or oxide. Absorption and fluorescence measurements have been made. A YAG:Nd laser was used for excitation. The evolution of the fluorescence lifetime shown that the emission from the Pr3+1G4 level at 1.3 micrometers shows some concentration quenching above 1000 ppm Pr3+. The color and the optical quality of the tellurite glasses depend on crucible materials. Colorless samples are obtained with gold crucible while various colorations or defects are observed with Pt, SiO2 and Al2O3. Rare earth doping result in visible defects or inhomogeneities when concentration is larger than 1000 ppm. The chemical composition and the optical absorption of doped and undoped samples was examined. Fluorescence intensity of Pr and Dy is smaller in these HMO glasses than in the sulfide glasses, this results from higher phonon energy and higher OH concentration. Further development is required for future applications.
Double-crucible, rod-in-tube and preform drawing techniques were applied for the preparation of different fiber structures based on arsenic sulfide. Because of the low crystallization tendency and the high mechanical and chemical stability, this glass is favored for passive and active fiber applications. By modification the base glass with small amounts of germanium, gallium, surplus-sulfur and other elements, both optical properties and thermal properties can be controlled in a wide range. Moreover, the solubility of rare earth elements is influenced by the co- dopants. The interplay of these parameters in the drawing process was studied and described by mathematical models which enable the defined preparation of fiber geometry and refractive index structure. Besides the basic glass properties, microscopic defects and inclusions in the material are important for the fiber properties. The origin of such imperfections and their role in the different drawing technologies were demonstrated. Possibilities and limitations of the fiber preparation with special regard of active fibers are discussed.
TeX glass fibers with monoindex structure are routinely achieved with a minimum attenuation, less than 1dB/m, in the 8-12 micrometers strategic window. Their exceptional properties in the IR allow to investigate many potential applications such as laser power delivery, temperature sensing as well as remote chemical monitoring. Chalcohalide fibers having optical losses of 0.5dB/m between 7 and 9 micrometers have been obtained by the preform drawing technique. These optical fibers are generally protected with an appropriate coating, thermal and/or UV plastic. Such materials show clearly improved mechanical properties and a high flexibility suitable for industrial manipulations. A high sensitivity of TeX glass fibers for chemical analysis by remote evanescent wave spectroscopy has been demonstrated. The detection efficiency has been studied as a function of various parameters especially the fibers' diameter. TeX glass fibers with a tapered shape have allowed to detect very low concentrations of less than 1 percent vol. in ethanol.
The scientific and applied interest for so-called IR glasses, the very subject of this conference, are exclusively linked to such glass low phonon energy. It provides their IR transparency and good quantum efficiency when doped, trough reduced multiphonon interactions. Recently we have shown that multiphonon decay in oxide glasses could be reduced at high excitation level and that this was linked with a saturation of the accepting vibration modes. The saturation coming from a common phonon diffusion volume for two excited ions. In this paper, after recalling the basics of multiphonon nonradiative decay, we shall present recent result on rare-earth doped halide glasses in comparison with oxide glasses brings a different behavior with respect to oxide glasses: sometimes no saturation ca be observed for certain levels because accepting modes seem not to be excited whatever the phonon diffusion volume in the halide glass. In fact we show that up-conversion do play a role in fluoride glasses partially masking the phonon bottleneck. Because the key parameter for such multiphonon process is the ratio between inter electronic levels energy gap and the phonon energy, halide glasses can be said to behave homothetically with oxide glasses. This confirms a likely generalization for our theoretical approach and allows to predict likely similar behavior for other multiphonon processes described by energy gap laws such as sidebands and RI absorption bleaching, phonon assisted energy transfer saturation.
An investigation has been undertaken to explore various compositions of erbium doped heavy metal fluoride glasses for 1.55 micrometers optical amplifiers. The optical fluorescence of Er3+ in various glasses at 1.55 micrometers was measured and compared to standard Er3+ doped ZBLAN. The focus of the investigation was a broader flatter emission for wavelength division multiplexing optical amplifiers. Various InF3 and ZrF4 based glasses were characterized. ZrF4 glasses containing LiF have been found to exhibit a broader and flatter emission at 1.55 micrometers .
Doping of arsenic sulfide with small amounts of germanium and gallium ca be used to improve the rare-earth ion solubility, whereby optical nd thermal properties are modified.Here the influence of germanium and gallium on refractive index, fluorescence and glass transition temperature is systematically studied and discussed. It is shown that material properties suitable for variable lightguide structures can be tailored. In addition, we present our studies of properties of lead germanate glasses. Variations of the matrix composition were made an the effects in glass transition temperature, crystallization behavior, refractive index, solubility of rare earths and UV-VIS-IR transmission were studied. Reducing the lead content and partial substitution of oxides by fluorides causes a shift of the optical bandgap of bulk material. First fluorescence investigations on Tm3+ doped lead germanate glasses show blue, red and IR emission under 980 nm excitation.
In this paper the glass formation, physical and spectroscopic properties of phospho-tellurate and germano- tellurate glasses are systematically studied. Yb3+- doped laser glasses with high stimulated emission cross- section are discussed.
The prospect of using optical fiber amplifiers made of rare- earth doped glasses other than the very familiar silica glass opens new applications and new amplifications windows. A literature survey has been conducted in order to assess the current situation in regards to these alternative technologies. Clearly, despite the amount of efforts, the 1.3 micrometers spectral region is still looking for a more efficient candidate. So far, Pr3+-doped ZBLAN is the technology of choice, offering quantum efficiencies of about 1.5 percent only. On the other hand, the current 1.55 micrometers fiber amplifiers offer nearly unbeatable performances. Other than rare-earth silica fiber amplifiers, only fluoride and tellurite glasses rare-earth doped fiber amplifiers applications is currently in a prospective state, although the potential of these technologies is undeniable. In these cases, the huge step between bulk glass and fiber fabrication remains to be made and/or optimized.
Nd3+-doped 1.3micrometers fiber amplifier has many inherent advantages, but two major problems must be overcome to achieve a device: signal excited-state absorption (ESA), and amplified spontaneous emission (ASE). Signal ESA around 1300 nm prevents gain in that region, and so red-shifts and gain out of the second telecom window. The ASE at 1050 nm has a branching ratio 5 time larger than the 1.3 micrometers transition; as a result it clamps signal gain at low values. Moreover, in many Nd3+-doped glass hosts the peak of emission lies at wavelengths above 1320 nm. In this paper we present new highly ionic fluoroaluminate glasses developed as hosts for the 1.3 micrometers -doped fiber amplifier and discuss aspects of glass design. (Formula available in paper) emission peaks between 1310 and 1317 nm were demonstrated in bulk glasses, and gain in the 1310-1320 nm region was measured in fiber. The gain and emission spectra show evidence of significantly reduced ESA. ASE filtering is discussed, focusing on Bragg grating filters and on absorbing co-dopants, such as (formula available in paper) The paper also assesses thermal and viscous properties of the core and cladding glasses for fiber drawing.
At Southampton, our work has focused on gallium lanthanum glass and fiber, for both active and passive applications. As part of our ongoing program, optical, thermal and mechanical properties of these glasses are under study. In parallel with this, fiber drawing is being refined in a quest for practical fibers. Over the past year, improvements have been made in understanding and eliminating the sources of loss in these glasses. In this paper, we describe the current specifications of fibers based on this material group. Recent progress in several applications, in particular those extending into the IR will be reported and the prospects for a future generation of sulphide-fiber based devices examined.
Spectroscopic study on super-fluorescence of Nd-doped glass fibers has been carried out. The laser emission characteristics around 910nm, 1060nm and 1350nm of Nd-doped glass fibers pumped by Ar+ laser and Ti:sapphire laser have been reported and analyzed. Up-conversion emission in Nd-doped glass fibers has been studied. The mechanism of up-conversion has been proposed too.
Rare earth ion doped fiber devices can achieve high efficiencies and high output powers due to their advantages of high optical pump power densities over long interaction lengths. With the advent of fluoride-based fibers, breakthroughs into both the short- and long-wavelength regions not possible with silica-based fibers have achieved. The low phonon energy and high rare earth ion doping concentrations of fluorides allow multi-level transition processes such as upconversion. This paper reviews some of the recent advances in fluoride-based fiber lasers and amplifiers, and takes a look at the major issues, mainly from an industrial viewpoint. The primary issue of cost has hampered commercialization and widespread acceptance of these devices. The future prospects of fluoride-based fiber devices will be discussed from the viewpoint of industrial applications.
Experimental results on the realization of microlasers at 1.05 micrometers with Nd-doped ZBLAN spheres are described. A microwave plasma torch process was developed to produce spheres with very low ellipticities. Laser oscillation was obtained using properties of whispering gallery modes. These modes were excited with an evanescence wave coupling which provided a low threshold and an oscillation with only few modes.
The upconverted fluorescence dots which appear under photon- avalanche excitation in a Er:ZBLAN fiber are quantitatively analyzed with respect to the pump mode structure into the fiber. By computing the modes propagation constants, we show that the main luminescent structures periods correspond to beatings between low order pump modes. The observed luminescent dots result from these interferences combined with the excitation intensity threshold of avalanche upconversion. An unusual dynamical effect in which the same final incident power leads to two different long-lived population states is also reported. This effect is mainly attributed to the long time required to build up a strong absorption near the avalanche threshold.
Growing applications of optical fibers in remote sensing applications, such as evanescent wave spectroscopic monitoring of composite cure kinetics, has created a need for mid-IR fiber with the often incompatible properties of high glass transition temperature and high refractive index. A family of glasses in the Bi-Pb-Ga-Ge oxide system has been investigated for this application. The substitution of Ge into the base Bi-Pb-Ga ternary produces an increase in glass transition temperature and a decrease in refractive index, although the later remains high. Novel glass compositions having substantially higher stability than the base ternary are described.
The viscosity of two fluoroindate glasses was measured as a function of temperature in the range of 310 degrees C - 362 degrees C. In such interval,the viscosity values were found to be similar to those reported for fluorozirconate glasses. The log (eta) - 1/T plots had an unexpected behavior: two viscosity regions that seem to obey Arrhenius equation were identified and the activation energy for viscous flow for the region near Tg is smaller than the value found above the transition range. This behavior is probably due to structural changes occurred around Tg. The low values of the activation energy for viscous flow obtained for the indium fluoride-based glasses studied, suggests a good resistance against the devitrification process, what can make them suitable for fiber preparation.
High-speed all-optical signal routing is achievable by designing new materials with fast response optical nonlinearities; in this context, third-order high nonlinear refractive index glasses are the best candidates. In this work, the characterization of the third-order nonlinear optical properties of a new chalcohalide glass and its application for the fabrication of high-efficiency nonlinear optical devices are presented. We report the measured values of high third-order optical nonlinear refractive index n2 and the two-photon absorption (beta) of a new ternary GeS2-Ga2S3-CsI chalcohalide glass. Improvements in the glass third-order optical nonlinearity were achieved by the inclusion of Ag-ions in the ternary glass composition. A theoretical analysis of signal propagation along a nonlinear directional coupler (NLDC) in twin-core fiber geometry and the interaction between the signal electromagnetic field and the waveguiding medium were considered in order to estimate the performance of the considered device for all-optical switching applications. All-optical switching, by controlling the optical pulse intensity in NLDC, has been numerically modeled in the second telecommunication window, and preliminary result support the suitability of this glass for these applications.
New glasses have been obtained in the system InF3-BaF2-ErPO4. Glass compositions with up to 30 percent mol Er3+ were shown to exist and characterized by thermal analysis, x-ray diffraction, IR absorption and electronic spectroscopy. The systems with high Er3+ content were studied recording IR and visible emission spectral characteristics. A specially elaborated technique allowed the preparation of a high purity phosphate precursor ErPO4. X-ray identification of the crystalline phases appearing during thermal treatment have been carried out and parameters of a mixed fluoride Ba4In3-nErnF17 calculated.
Glasses containing lutetium fluoride have been prepare in the system BaF2 - SrF2 - ZnF2 - LuF3 - InF3. The composition of the phases crystallizing out of these glasses suggests octahedral pre-arrangement comprising (LuF6) and [Sr(Ba)F2] structural fragments.
Silver halide and Chalcogenide fibers are tow major mid-IR fibers that are used in gas sensing and light transmission. For both purposes, especially for power transmission, it is important to increase the launching efficiency from the mid- IR source (Globar) to fiber so that the signal-to-noise ratio of the while system will be improved. However, due to the shape of the Globar, it is often difficult to get a uniform and small spot image with ordinary lens or mirror. In this paper, a 'mid-IR cavity' has been designed to increase the collecting ratio of IR radiation from a Globar. Comparing with direct forward collection method, the cavity offers not only higher power, more important, but also the uniform Gaussian and smaller spot. As result, higher signal to noise ratio has been obtained in the fiber ends. This can be used to improve the spectral resolution, signal processing time for FT-IR based real-time Chemical Vapor Deposition processing and other type of applications.
Novel step-tunable single-frequency fiber lasers in ring or linear configurations are presented. The frequency discriminating elements are periodic filters, either sampled fiber Bragg gratings or Fabry-Perot micro-etalons. The lasers can be step-tuned to exact multiples of 100 GHz and they find applications in frequency referencing for DWDM communication systems.
New heavy halide glasses without fluorine have been synthesized as Pr3+ host materials for optical amplification at 1.3 micrometers or other active applications which require a phonon energy as low as possible. A relatively stable composition is 15CdCl2-10CdI2- 20PbI2-40PbBr2-15CsBr. However, this glass still undergoes the devitrification during fiber drawing process. A small amount of oxides and sulfides have been introduced in this system to decrease the crystallization tendency. The incorporation of 3 mole percent PbO in the base glass composition enlarges the thermal stability range. The stabilizing effect of CdO is more limited than that of PbO. Optimum results are observed when PbO substitutes PbBr2 rather than PbI2. The influence of several sulfides on glass stability was also investigated in the same glass. The additions of 5 mole percent of HgS, As2S3 and Sb2S3 appear favorable to glass formation. By comparison, attempts implemented with SeS2, PbS and CdS had no significant effect. An additional benefit of the introduction of oxides and sulfides is the decrease of the hygroscope character of the base glass. The optical transmission in the visible-IR spectrum shows no absorption at the pump and emission wavelengths, e.g. 1.0 and 1.3 micrometers , while the cut-off wavelength exceeds 10 micrometers for sample of 3 mm in thickness.
Optical parallel logic operations were studied using IR light as a signal beam. The optical system was constructed with a planar heat source, a liquid crystal switch array, a chalcogenide glass fiber bundle, and a PtSi CCD sensor array. A variety of logic operations, e.g., AND, NAND, OR, NOR, and XOR, were demonstrated successfully by this optical system.
Aluminophosphate glasses doped with rare-earth ions have recently attracted a large interest owing to their relevant non-linear optical properties. Until now, all studies were done over the glasses doped with rare-earth ions in which the rare-earth ions were into a vitreous silica matrix. Our study was made as for rare-earth ions into a vitreous aluminophosphate matrix. In the first step, the sample of rare-earth doped glasses were obtained by melting the raw materials batch and then by adding rare-earth oxides. In the second step, the resulted glass was annealed. By mean of a spectrophotometer, were drawn absorption and transmission spectra, in UV - visible domain. For IR domain we used a SHIMADZU-FTIR-8001PC spectrophotometer.
Cadmium fluorochloride glass (CdFCl) is considered as a more favorable host for Pr3+1G4-3H5 transition than all-fluoride hosts, but it cannot be drawn easily into fibers. This critical problem is largely correlated with its special devitrification behavior and temperature dependence of viscosity. The high Avrami coefficients of crystallization obtained by isothermal method and by non-isothermal method suggest that nucleation rate increases during the crystallization. Meanwhile Avrami coefficients and activation energy values vary with the crystalline fraction. This corresponds to the formation of different phases during crystallization. The the ram XRD measurements performed from 210 to 320 degrees C confirm that chlorine-rich phases appear first at low temperature while the fluoride phases form lately. Comparison with fluorozirconate glass shows that CdFCl glass has a lower log (eta) - T slope. As a result the drawing temperature of the CdFCl glass is well above Tg, in the crystallization thermal range. These two factors explain the difficulties encountered in drawling CdFCl fibers from a preform. Drawing fibers directly from the melt should be an alternative method for CdFCl glasses.