The sources of scattering losses in fluorozirconate glasses and fibers are reviewed. Results are presented which show that the predominant mechanism responsible for the presence of fluoride crystals is heterogeneous nucleation. The nature and origin of the different nuclei are discussed and possible ways to eliminate them from the glasses assessed. It is proposed that extreme care be employed in the processing of the glasses with particular emphasis on the preform fabrication step as this is critical to the design of ultra-low loss fibers.

Several glass systems based on AIF3 have been synthesized and fabricated into preforms by controlled melting and rotational casting. High optical quality preforms have been drawn into fibers using a specially modified drawing facility. The drawing tower is enclosed with a vertical glove box in which the levels of both moisture and oxygen are kept below 1 ppm during the drawing. The AIF3 -based fibers have shown dramatically superior chemical durability relative to the ZrF4 -based glass fibers. Selected optical, mechanical and thermal properties of these fibers will be presented. AIF3 -based glass fibers offer interesting opportunities for short range applications in the 2–4 micron region of the infrared such as sensing, remote spectroscopy and laser power delivery.

The authors will review the methods used to characterize infrared transmitting optical fibers. The use of FTIR spectroscopic techniques for the measurement of fiber loss will be discussed. Fiber end preparation and fiber cleaving techniques will be reviewed. Data will be presented on silica fiber in the extended IR region, heavy metal fluoride, chalcogenide, silver halide fibers and sapphire crystalline fiber.

Numerical calculations of losses due to polymer coatings and macrobending have been made for step index multimode fluoride fibers. To avoid such losses, fiber core and cladding diameters and numerical aperture must be chosen carefully.

Chalcogenide and chalcohalide glasses were prepared and the resulting glass Tg's and spectra were investigated. Some chalcogenide glasses were prepared from thermally and chemically pretreated raw materials. Pretreatment steps produced a reduction in impurity absorptions caused by oxygen bonding to the constituent elements. Additions of small amounts of iodine improved attenuations by acting as a hydrogen getter material which eliminated H-Se absorptions. Due to low transition temperatures, chalcohalide glasses containing iodine may not meet commercial requirements.

While the utility of solid state NMR to provide structural information in amorphous systems is well established in silicate and borate glasses, the systematic application of modern NMR techniques to non-oxidic systems has just begun. One of the central issues in these types of glasses is the question of the chemical bond distribution and the existence of short range order. The present study utilizes the selective measurement of homonuclear 31p.31P dipole-dipole couplings via spin echo decay to address this issue in the glass systems P-Se, PSe- Ge and CdGeAs2-xPx. The results indicate that the first two systems are characterized by a high degree of chemical ordering. The chemical bond distribution in CdGeAs2-xPx glasses is found to deviate considerably from that in the stoichiometry-analog crystalline materials.

In-depth studies of property-composition relationship in chalcogenide glasses have revealed some interesting structural features. For example, specific discoveries in the Ge-Se-Sb and similar systems were of (i) meta-stable phase separation for glasses with a high Se or S content ( >70 at.% ), and (ii) abnormal behavior of some structure-sensitive properties ( e.g. optical band-gap energy ) for glasses with Se or S in the range of 60–70 at.%. In carefully studying the Ge-Se system, the liquidus curve ( reported by H. Ipser et al, 1982 ).was reexamined; this was found to have an S-shape at the phase-separation region. Another interesting finding was the dependence of the band-gap energy on composition in (1−x)GeSe2 xSb2Se3 glasses; this was not a linear relation but a curve with a maximum band-gap energy at 9 at.% Sb.

Glasses in the Te-Br-Se and Te-I-Se systems show potential low losses in the 8–12 μm region. They are very stable against crystallization and against moisture. The lowest losses of a fiber at 10.6 μm, measured using a CO2 laser, is about 3 dB/m. The essential diffusion centers in these fibers have been proved to be bubbles. A power delivery experiment was made using a fiber having an attenuation of 5 dB/m. The power density of about 40 kw/cm2 can be injected into the fiber without damaging this fiber.

Iodide glasses presently being investigated suffer from their poor glass forming abilities, thermal instabilities and general lack of chemical durability. Glasses in the Cd-As-I and Cd-As-Ge-I systems are investigated in this study for the purpose of developing water-resistant, thermally stable iodide glasses and optical fibers. Differential scanning calorimetry(DSC) showed that glasses in these systems have glass transition temperature(Tg) values above 300°C. Devitrification of glasses during cooling and reheating can be suppressed by incorporating small amount of Ge atoms into ternary Cd-As-I glasses. They are transparent up to 14μm in the infrared region with excellent durability against liquid water at 90°C.

In quantitative studies of the structural stability of Te-Cl and Te-Br glasses, specific attention has been devoted to determining the kinetics of their overall crystallization process and the glass composition range in which chemical decomposition occurs at elevated temperatures. The calorimetric studies reveal that the tendency of crystallization or thermal decomposition of these glasses is related to phase-diagram characteristics. It seems that the structure of these glasses is not an idealized random arrangement as described by the classic model. Underlaying causes for this deviation from a perfect random arrangement to one involving a degree of ordering ( structural group ) is discussed.

We have studied the effect of laser irradiation on Te-Se-Br thin films. The major effects were found to be dominated by changes in composition because of the complete loss of Br and variable loss of Se. These losses are measured by EIDS and are reasonable in view of the temperatures obtained from a heat flow calculation. The remaining Te-Se material can be made crystalline under specific conditions of laser pulse length and laser power (which determine the cooling rate). We have been able to establish that the crystallization starts with surface filamentary growth exhibiting fractal network formation. With higher laser energy it tends to coalesce to form three dimensional crystals.

Chalcogenide glasses present a unique opportunity for the study of the effect of dimensionality of the properties of amorphous systems. Presented here are preliminary results of experiments on fibers of these materials. Strength in these fibers is related both to dimensionality, which is a continuously variable function of composition and to drawing conditions, which produce ordering. A simple theoretical model for the ordering effect is proposed and discussed.

Plastic optical fibers (so called POF) are already in wide use in a large number of fields. This paper gives an overview of the field including the advantages of plastic optical fibers, the various types of fibers and the materials in them.

Then, the properties of three types of fibers which have recently been developed, are discussed. The first is fibers with a poly-methyl-methacrylate (PMMA) core, which have a low transmission loss. Another is heat resistant fibers for use in automobiles. And the third is the multi-fiber type for image guides. And finally, the applications of these fibers and their future prospect are discussed.

A low-loss GI plastic optical fiber in which the attenuation of transmission was about 130 dB/km at 650 nm wavelength was successfully obtained by a new interfacial-gel copolymerization technique. Novel optical functional polymer glasses, such as birefringence-free copolymers for any degree of orientation and optically active amorphous polymers which act as polarization modulators, were synthesized and characterized.

Low-loss silica-based single-mode waveguides are fabricated on Si substrates by flame hydrolysis deposition and reactive ion etching. The waveguide loaded with a thin film heater operates as a phase shifter due to the refractive index dependence on temperature. The phase shifter can afford optical switching and/or tuning functions for silica-based integrated-optic devices. The waveguides have large stress-induced birefringence due to the difference in thermal expansion coefficients between SiO2 and Si. Waveguide birefringence control techniques are proposed for constructing various polarization insensitive and sensitive devices.

The infrared transmission, and possible high nonlinear optical susceptibility of Bi(Pb)-Ca- Sr-Cu-O glasses as well as their being the precursors for high temperature superconductors make them potential materials for integrated optical fibers. In this work, the glass formation and the fabrication of glass fibers have been investigated. The properties of the glasses have been studied. The infrared cutoff of the glasses is above 7 μm, and a high refractive index (˜ 2.9) and a high density (˜ 6 g/cm3) indicate the possible high nonlinear optical susceptibility. After being heat treated at high temperatures, the glasses become superconductors which show the response to the optical radiation due to the bolometric effect. Fabrication of an integrated optical fiber system incorporating the transmitting medium, optical modulator and detectors is possible.

Void-free sapphire single crystal fibers with diameters of 110 μm and 60 μm and lengths of over 2 m have been grown by the laser-heated pedestal growth method. The growth dynamics of the floating zone was studied and shows the features expected from a simple theoretical model. Optical losses have a minimum of 0.5 dB/m in the near infrared at 1064 nm. An absorption band centered at 400 nm results in losses of up to 20 dB/m in the visible. The fibers have potential applications in high temperature thermometry and in delivery systems for laser surgery. Absorption losses of 0.88 dB/m with a damage threshold higher than 1.2 kJ/cm2 at 2936 nm made tissue ablation feasible with fibers several meters in length.

The growth of SrxBal−xNb2O6 solid solution single crystal fibers has been achieved using a modified float zone technique. The technique is described and the results of several property measurements are presented.

Evidence supporting the temperature dependent defect mechanism of nonstoichiometry on the potassium and oxygen sublattices in KTP is presented. The primary compensating defects for the formation of vacant potassium sites in typical flux grown KTP are vacant oxygen sites. Protons (OH-) are the principal defect compensating for the formation of vacant potassium sites in high temperature hydrothermal KTP. A model of the ionic conductivity in high temperature hydrothermal KTP is proposed in which specific protons participate in cooperative motion over a limited distance with the potassium vacancies migrating along the “channels” in the structure in the Z-direction. The higher activation energy measured for ionic conductivity in flux grown KTP (0.5 eV) relative to high temperature hydrothermal (0.3 eV) is suggested to be due to the energy required to dissociate from a defect complex, such as a (VO - VK). The correlation of ionic conductivity to damage susceptibility appears to be due to the levels of compensating defects for vacant potassium sites in KTP, which are related to the concentrations of Ti3+ formed in the crystals. Further study is ongoing to understand the specific mechanisms involved in the ionic conductivity and damage in KTP grown by the flux and hydrothermal techniques.

Extended x-ray absorption fine structure (EXAFS) of potassium niobate (KnbO3 ) was measured at the K edge of Nb, at various temperatures to include all phases of the material. The first shell data were analyzed to determine the distances between the niobium atom and its oxygen neighbors. The single shell amplitude almost vanishes around k-7.5 A−1 at all temperatures, suggesting two distances with a separation of about 0.21 A. Nonlinear fitting was used to determine the structure more carefully and the data at all temperatures can be fit reasonably well with two Nb-O ditances. This is in disagreement with the displacive model which implies only one Nb-O distance in the cubic phase. This result suggests that the niobium atom is displaced along the (111) direction relative to the oxygen atom in all phases. Thus, the transitions are not displacive, but have a strong order-disorder character.