A new class of I.R. transmitting glasses have been discovered in the binary systems Te-Cl and Te-Br and in the ternary systems Te-Cl-S, Te-Cl-Se, Te-Br-S, Te-Br-Se, Te-I-Se. The ternary glasses have a very high resistance towards devitrification. The glass temperature Tg is ranging from 50 to 80° C depending on the composition. The S or Cl containing glasses have their I.R. edge located in the 13 pm region while the compositions not containing those light elements have their multiphonon edge near 20 μm. A typical glass composition such as Te₃Br₂Se has a potential high transparency of about 10 dB/km at 10.6 μm estimated from band-gap and multiphonon absorption. Samples prepared from high purity compounds show no parasitic absorption bands due to OH, SH, and so on.

Stable glasses composed of two or more of the oxides of bismuth, lead, gallium, and cadmium have been previously reported as having infrared cut-offs of about 8pm, significantly more transmissive than any other oxide glass. They are yellow, having a lower absorption edge at about 470 nm. Refractive indices are about 2.4 at 0.6μm and 2.2 at 5μm. The material dispersion and cross-over wavelength are favorable for low-loss optical fibers operating near 3μm.

We report here two studies relevant to these phenomena. Phase separation was unambiguously shown to occur in a ZrF₄-based glass containing a small amount of PbF₂ and prepared under a chloride-containing reactive atmosphere. Partial replacement of ZrF₄ by HfF₄ in a ZBLAN glass appears to improve the resistance to crystallization. The reason for this improvement seems to be a change in the crystalline phases and compositions first appearing on reheating.

Fast and slow fracture of chalcogenide and fluoride glasses in air are compared and contrasted to silicate glasses as represented by silica glass. The fracture toughness, elastic modulus and hardness of silicates are, in general, superior to both chalcogenide and fluoride glasses. Thus, improvements are needed in these properties to successfully use these materials in a structural environment. The present and past studies have shown that changes in composition will not be sufficient to improve the desired mechanical property. Thus, some external techniques such as compressive surface stress, coatings, or additions of second phase will have to be employed to improve the strength and hardness of these materials. Slow crack growth due to stress corrosion processes were measured in two ways: direct measurement of crack extension using the double cantilever beam (DCB) technique and the strength-stressing rate (S-SR) technique. The former technique uses large cracks travelling at a constant stress intensity and the latter technique, used for fibers, uses small cracks propagated to failure during loading at a constant stressing rate. Both of these techniques result in a value of the stress corrosion susceptibility constant, n. In general, the higher the "n" the more resistant to stress corrosion. Values of n obtained from bulk glass (DCB) and fibers (S-SR) for chalcogenide glasses were found to be in the same range ( e.g. for As₂S₃ the values were between 17 & 20) but for fluoride glasses, the values were considerably different. Also, the n values were more dependent on composition than they were for toughness, elastic modulus or hardness. However, for both types of glasses, more data are needed in different environments to fully asses the structural reliability.

A small amount of oxygen is shown to be necessary to form CdF₂-LiF-A1F₃-PbF₂ (CLAP) glasses. Too little oxygen produces order of magnitude increases in crystallization, too much oxygen produces liquid-liquid phase separation. A microcrystallite structure is suggested to explain these results.

In this paper a discussion on the design of single-mode mid-IR optical fibers operating in the 2-5 μm wavelength range for use in repeaterless telecommunication systems is made. First, the different factors affecting the single-mode fiber design are identified and then applied to the mid-IR materials case. Then, theoretical evaluations are made for the chromatic dispersion, both material and waveguide, and the excess losses caused by microbending, macrobending and fiber splicing, for several single-mode step-index fiber structures having different fluoride-glass compositions. Optimum fiber parameters such as material composition, core and cladding diameters and relative index difference are obtained based on these evaluations which lead to various fiber designs either from the minimum dispersion or the minimum loss point of view, or a tradeoff between these two.

In this paper we report, for the first time, on the chromatic dispersion, in the 1.9 - 5.2 μm region, of single-mode, mid-IR, heavy metal fluoride (HMF) fibers with a-profiles. Excellent dispersion-flattened characteristics are obtained with a range of a-profiles, core diameters and relative index differences. Small variations in these three parameters are not critical.

The primary objective for the development of infrared fibres based on fluorozirconate glasses has been the that of long distance repeaterless telecommunications, and sufficient progress has been made to suggest that this target should be reached in the not too distant future. The quality of the fibre has improved dramatically over the past two years, to the extent that moderate losses ( 3 - 5 dB/km ) are possible over lengths in excess of 200 m, and although not yet suitable for telecommunications, this type of fibre has many other commercial uses. In this work we will review the progress that has been made in reducing losses and improving reproducibility and mechanical properties. We will discuss the types of fibre that it is now possible to fabricate and finally descibe some preliminary applications that these fibres are already able to meet.

Optical and mechanical properties of commercially available chalcogenide glasses (AsSe, AsGeSe, AsGeSeTe and SbGeSe) are reported. The measured optical properties include: bulk transmittance (between 0.5 and 25 μm) and the attenuation (at 10.6 μm) of core and optically clad fibers. The measured mechanical properties include: bending and tensile strength testing of coated, uncoated, core and optically clad fibers. In addition to the measured physical characteristics, some potential applications of chalcogenide fibers are mentioned.

Improved infrared fibers of As₂Se₃ were fabricated by the rod method. Losses values of less than 7dB/m at 10.6μm, about 1dB/m at 9.6 μm and about 0.1dB/m around 3.6μm were measured. The IR absorption spectra of the fibers and the glass preforms were studied in the range of 2.2-25 μm and exhibited similar absorption coefficient. The losses obtained by means of both tuneable CO₂ laser and FTIR spectrometer measurements agrees very well.

Theoretical analysis has been made to see the possibility of realization of low-loss hollow core optical fiber made of a glass functioning as the cladding whose refractive index is lower than unity. It is shown that such total reflection-type waveguide can be realized only when the refractive index of the cladding is near unity not far from unity and also the absorption loss is extremely small.

The infra-red optical constants of certain ceramics and glasses have been determined in the wavelength range 5-55 μm to assess their potential as hollow waveguides at 10.6 μm. Materials have been selected which are likely to exhibit significant anomalous dispersion at this wavelength, and glasses based on germanium dioxide are shown to be candidate materials for development into hollow flexible waveguides. It is demonstrated that modifying oxide additions to the base glass, Ge0₂, increase the predicted waveguide loss at 10.6 μm. Devitrification of these glasses is proposed as a means of further reducing waveguide loss and some supporting data are presented. Experimental CO2 laser power transmission measurements on hollow fibers fabricated from Ge02 and SiO₂ based glasses are presented for both straight and curved guides. The data demonstrates that considerable improvement in transmission is derived in both configurations when the refractive index of the glass is significantly less than unity at 10.6 μm.

The CO₂ laser radiation (λ=10.6) is very useful in many fields especially in medicine. For this application plastic hollow waveguides are very suitable, since they are flexible and nontoxic. Such plastic tubes were devised and the obtained results are given in this paper. The transmission of infrared radiation was made possible by covering the inside with metallic films. To achieve high transmission, even when the waveguides were bent, an inside dielectric film was added over the metallic one. Theoretical and experimental investigation of the energy transmission and the output power distribution was done. The theoretical results were obtained based on a ray model calculation. Experimental results have shown an attenuation of about 1.5 dB/m for a straight waveguide and a transmitted power up to 14 watts for 55 cm length and 3.5 mm inner diameter of the waveguide. For a bent waveguide (radius of bending 15 cm) attenuation of 5-6 dB/m and maximum of 6 watts was achieved.

Optical aging in bulk and extruded fibers of thallium bromo-iodide is discussed. In particular, changes in optical attenuation with age are correlated with the physical properties of the material.

A series of mixed silver halide crystals of composition AgCl_xBr_1-x (0≤x≤1) have been extruded into 0.9 mm diameter fibers of several meters length. The intrinsic absorption edges that define the infrared spectral window of these crystalline solids, namely band-to-band transitions in the U.V.-visible, and multiphonon processes in the infrared, have been measured as a function of composition. Optical losses have been measured at a wavelength of 10.6 μm in these fibers. The average loss at this wavelength totals about 0.15 dB per meter, of which about 0.08 is attributable to bulk scatter, 0.04 to "hot spots" (which we relate to macroscopic defects), and 0.03 to extrinsic absorption. The far field power distribution of the fiber output, and the total light scatter were measured and were found to vary with fiber length. These results are consistent with a model that postulates the presence of large scale scatterers in the fiber which cause diffusion of power between guided rays until steady state is reached.

The mechanisms of light scattering losses ∝_s in fibers fabricated by plastic deformation of silver and thallium halide crystals have been analysed. It was found that the power index 7 in the loss dependence on wavelenght λ(∝_s~λ^-7) continuosly changes in the range -0.5< η(λ)≤3, depending on the crystal material and its history, manufacturing conditions and evolution of fibers. On the basis of this and on the consideration of the plastic deformation we suggested that vacancy micropores or voids are the fundamental phisical reason which determines the scattering losses in polycrystalline fibers. The crossection of scattering and η(λ) is calculated for inclusions and voids with the relative refractive index 0.2≤ m ≤0.2. We explain the behaviour of ∝_s and η by evolution of the micropores distribution and by exsistence of vacancy excess in fibers. The average diameter D of effective micropores and their concentration N are determined from the spectra We observed these micropores in KRS-5 and KRS-13 polycrystalline fibers.

Backward stimulated Brillouin scattering (sBs) in optical fibers has been extensively investigated in the visible and near infrared both as an intrinsic power limiting factor in signal transmission through fibers and as a means of implementing phase conjugation and optical switching. We propose to study these effects in mid infrared (MIR) transparent fibers. Fibers transparent in this spectral region (5-10μm) hold great promise to have their intrinsic losses reduced to the theoretical limit of Rayleigh-Brillouin scattering, which varies inversely with wavelength to the fourth power. The theoretical loss limit of MIR fibers can thus be several orderslower than that in fused silica fibers. It is expected that such a significant reduction in the low-power Brillouin loss will be accompanied by a corresponding lowering in the high power sBs threshold, making it achievable in fibers through increased interaction length, while lowering incident laser power density. The inherent capability of optics for parallel processing can be fully utilized in optical computing, in which optical switching is a key element. Optical NAND gate has been demonstrated using sBs in fibers in the visible with a switching time of the order of ~100 ns. With our proposal of phonon tuning, simultaneous operation of multiple gates is possible in the same fiber. Experiments are designed for the observation of sBs in the currently most promising AgC1 and KRS-5 fibers by monitoring pump transmission through these fibers and acoustooptic radiative effects simultaneously. sBs shifted scattered light spectrum will be analyzed by laser heterodyne spectroscopy using HgCdTe and very fast metal-oxide-metal diode broadband mixers. These experimental schemes will also permit the detection of optical switching.

Sapphire fibers doped with 0.05 atomic % trivalent titanium were made by the laser-heated pedestal growth method with diameters from 500 to 1000-μm. The fibers were used as gain media in a tunable laser oscillator. They were end pumped by 532-nm frequency-doubled Nd:YAG radiation and produced up to 2-mJ in 4-ns pulses at 1-Hz with 1-nm linewidth from 790 to 840 nrn.

Recent advances in mid-IR (2-12 μm) optical fibers require that more serious consideration be given to the development of measurement techniques and the design of equipment to characterize these fibers and measure the propagation characterostics. In this paper, a review of the measurement techniques for characterizing mid-IR fibers is presented. The important properties of the sources and detectors suitable for these measurements are summarised. Currently used measuring systems and the typical measurement made on infrared fibers are reviewed.

Room-temperature bromine is a liquid with index of refraction of the order of 1.66. It is composed of homonuclear diatomic molecules, possessing only a single vibrational normal mode for which infrared transitions are approximately dipole forbidden. Hence, it offers the prospect for very low absorption in the region from 1pm to 30μm. This would be particularly attractive for broadly tunable sources, such as free-electron lasers.

The transmission of laser energy over long lengths of optical fiber is being utilized for numerous applications including materials processing, medical surgery, powering of remote devices and sensors, and data transmission. Motivated by the development of ultra-low loss non-oxide optical fibers and potential novel applications for laser power delivery in the mid-infrared, we have undertaken a program to study the power handling capabilities of fluoride and chalcogenide fibers. Fluoride fibers based on the ZrF₄ glass system and chalcogenidefibers based on the SbGeSe and GeAsSeTe systems have been evaluated. Using a Nd:YAG laser operating CW, the radiation effects on both commercial and developmental fibers have been determined. The test measurement matrix for power delivery consisted of variable power, power density and fiber length at wavelengths of 1.06 and 1.32 microns. A database has been generated on coupling efficiency, transmission efficiency, damage mechanisms, and physical handling which could influence the choice of fiber for a particular task. Work is continuing to extend the optical power transfer/radiation effects research to longer wavelengths corresponding to regions of lower total attenuation for these fibers.

The silver halide fiber for transmitting a CO₂ laser beam using the mixture crystal of silver bromide and silver chloride is described. The silver halide is purified by zone melting. The absorption coefficient of its preformed crystal measured by a CO₂ laser calorimeter is less than 1.0x10^-4 cm^-1 . The silver halide fibers whose diameters are 0.5 to 0.7mm are made by hot extrusion. The transmission loss of silver halide fiber is 0.07dB/m when measured by a CO₂ laser beam. The measured spectral transmission lgss due to scattering inside and on the surface of the fiber is nearly proportional to λ ^-2 where λ is the wavelength, and it is low in the infrared wavelength region, ranging from a few microns to over ten microns. Because of its excellent resistance to optical damage and bending as well as other characteristics important to practical application, silver halide fiber is suitable for use in CO₂ laser power transmission. It is also expected to he an optical waveguide in the field of infrared optic sensors.

Infrared fiber optic pyrometry has become a practical reality using improved strength fluoride glass fibers. The addition of a plastic coating and rugged cabling allows the fibers to be used in the field. A detailed theoretical model of the infrared fiber optic pyrometer (non-contact or radiative thermometer) has been derived and compared with data produced by a prototype fluoride glass fiber radiative thermometer. Excellent agreement was obtained between theory and experiment over a temperature range of 30 to 700° C.

The paper deals with the investigation of optical and mechanical properties of polycrystalline fibers from silver and thallium halide crystals. The dependence of the fiber properties on the fabrication conditions as well as the influence of the stretching stresses and UV irradiation on the optical losses and also their resistance to the pulsed CO₂ -laser radiation are discussed. The fabrication of the first AgCl-cladded KRS-13 fibers isreported.