The current stktus of worldwide research in the use of polymers as active lightwave transmission media is examined. Applications include plastic optical fibers, plastic optical components, polymeric optical fiber sensors and non-linear optical polymers.

Technology coupling fast ultraviolet (UV) cure response with elastomeric properties in silicone formulations has been developed. Rapid photocure was obtained through addition of mercaptan to vinyl on silicon via a free radical chain reaction resulting in a monosulfide link. One optical fiber coating based on the technology, OPTIGARD™ X3-6662, is a onepart formulation which can be cured very rapidly (≤0.1 sec) upon UV exposure (≥25 mJ/cm2) to provide a low refractive index (RI=1.42), elastomeric film exhibiting good low temperature properties. A high refractive index counterpart (RI=1.51), OPTIGARD™ X3-6663, was obtained through incorporation of a controlled amount of phenyl groups into the polymer backbone. The technology, an IR-100 Award winner in 1985, is being used by the fiber optic industry to satisfy their need for coatings which will cure fast, perform over a wide temperature range, and be moisture insensitive.

An emerging growth market for integrated optic devices and data transmission is in non-metallic composite aircraft structures. There is a regional need to identify optical fiber coatings which are suitable for embedment in composite structures. This paper assesses fibers with various coatings for the following: 1) critical structural test performance, 2) reproducibility, and 3) low attenuation when subjected to representative manufacturing and service conditions. A brief discussion of follow-on system verification tests, and an overview of desirable fiber and coating developments to meet future application requirements are also included.

Organic/polymeric materials remain the most prevalent protective coatings for optical fibers. Many studies have chronicled significant differences inn the levels of protection against moisture and other adverse environments by such coatings. Recently an attempt was made to identify those coating properties which correlate with these protective characteristics. Water absorption and adhesion between the coating and fused silica were proposed to correlate the best.

In this study a series of coatings have been prepared with varying levels of adhesion to fused silica substrates, without significant differences in water absorption or in water permeation properties. The tensile strength, static fatigue and dynamic fatigue properties of the coated fibers were measured and correlated with the lap shear strengths of correspondingly coated slides. As the adhesion of the coating/silica glass interface increases, the corresponding fiber's strength and fatigue properties improve also.

The strong positive correlation between the coating's adhesion and the fiber's strength/fatigue properties will be reported for a number of coating/fiber combinations. Effects on lifetime predictability will also be addressed.

The properties necessary for a material to be useful as a fiber cladding (appropriate Δn) and/or coating (provide mechanical protection) were evaluated for an organosilsesquioxane (Owens-Illinois Resin GR 650). The samples were 120 μm silica fibers coated with 12 μm of the cured organosilicon polymer. We observe, from an index profile of the clad fiber, that Δn = 0.04. The tensile strength measured in air (65% RH, 25 °C) was 765 ksi and the dynamic fatigue constant determined under the same ambient conditions was 29, both of which are typical of a mechanically protected fiber. From aging experiments in 90 °C distilled water we observe that the onset for a marked loss of strength with time is ∼1 day for an epoxy-acrylate coated fiber and slightly more than a week for the organosilicon polymer coated fiber, a notable improvement.

The incorporation of atomic fluorine into flame synthesized silica boules has been investigated. Soot boules were doped with fluorine using three different methods: (A) in a low temperature process, using XeF2 as the fluorinating agent prior to consolidation, (B) utilizing SiF4 or SF6 in the reagent gas mix during the combustion synthesis and soot deposition step and (C) in situ treatment with SF6 during the dehydration/ consolidation step at elevated temperatures. All three methods produced uniformly down-doped glass after consolidation, although the maximum fluorine incorporation and level of down-doping for each method followed A <B <C. Fluorine incorporation mechanisms are proposed for each method.

Owing to their opacity to visible light porous soot boules cannot be analyzed by standard optical methods. Yet it would be of considerable help to the preform maker to be able to measure the density and dopant concentration profiles of an unsintered soot boule. This realization prompted the development of a non-destructive soot boule characterization method.

This method amounts to a three step measurement process based on Xray tomography. First the attenuation of a well collimated X-ray beam is measured as it is scanned across the boule perpendicular to the boule axis. Next the linear attenuation coefficient profiles of the boule are reconstructed for a certain number of distinct X-ray energies. Finally, the mass density and dopant concentration profiles of the soot boule are obtained from the attenuation coefficient profiles. Hence, the method reported here allows a fairly complete analysis of the macroscopic structure of a soot boule before sintering.

Photo-luminescence(PL) in VAD silica preforms sintered under reducing or oxidizing condition was observed. Two types of diamagnetic luminescence centers and the Si-E′ center were found in pure silica glass. The intensity of photoluminescence was strongly dependent on the sintering atmosphere. This observation suggests that reduced Si species, Si(III) and Si(II), are responsible for the luminescence.

We report the use of CO2 laser heating for inducing an increase in the refractive index of germania doped silica films. UV absorption spectroscopy and XPS analysis have confirmed that the index change is a result of GeO2 being reduced to GeO. The technique has been successfully used for the direct writing of integrated optical strip waveguides.

The mechanical behavior of wet silica gels formed by various sol-gel processes has been studied. Samples were analyzed with a beam-bending apparatus specifically designed for accurate measurements of very low strength solids. Breaking strength, viscosity and relaxation measurements were made on gelled bodies. Specimens were studied in an undried gel state, molded in shapes suitable for the particular experiments. Tests were made in several ambient conditions including immersion in a liquid bath. The mechanical properties of gels are dependent upon the gel composition, gel age and other formation parameters such as pH, temperature and pressure. An understanding of these properties is particularly important in determining the nature of subsequent processing steps. Models for the structures of the various gels are proposed which explain variation in mechanical behavior.

A new method for optical fiber production is shown. Hydrolytic polycondensation of tetramethoxysilane using a low concentration of α-picoline, 1.56×10−3% in water, gives SiO2 gel which was dried at 22 °C to a transparent amorphous material.

The densification process shows an exponential time dependence with a final value of 2.253 g/cm3 after 30 days. The specific surface area of the porous gel varies from 500 to 600 m2/g but pores are eliminated by the sintering process. Before sintering the gel, it is treated under an oxidizing atmosphere above 700 °C. At 1200 °C the pores are eliminated and a solid glass rod obtained.

After the sintering process a fiber is obtained from the rod which shows a transmission loss as low as 5.5 dB/km at 840nm.

LiNbO3 is the best substrate for modulators and switches for integrated optics. Efficient low loss waveguides for light in LiNbO3 are formed by introducing Ti-ions into its lattice, thus increasing locally the ordinary and the extraordinary indices of refraction. We are the first to use the very versatile technique of ion-implantation to administer Ti into LiNbO3. This implantation process offers the possibility to introduce significantly more Ti into a well-defined volume than conventional diffusion techniques. During this process first an amorphous non-equilibrium phase is generated, which has to be kept at low temperatures in order to prevent segregation. Subsequent thermal treatment leads to solid phase epitaxy and restores the desired stable crystalline state. We have used this technique to fabricate excellent planar waveguides, channel waveguides and Mach-Zehnder modulators.

Nonlinear optical glasses with fast responding nonlinearities and very low absorption are promising materials for use in ultra-fast (picosecond) all-optical switches. We have synthesized a TiO2 Nb2O5. B2O3 Na2O SiO2 glass with the intention of optimizing both the third order optical nonlinearity and suitability for fabrication of optical waveguides. The nonlinear index coefficient n2 for this glass composition was found to be 4X 10-19 m2/W, a factor of two greater than the largest value previously reported for commercially available TiO2-silicate glasses. Optical waveguides with a maximum index change of Δn = 0.12 were made using silver-sodium ion exchange. These waveguides may become building blocks for future all-optical logic elements and circuits.

Optical fibers with attenuations much lower than those attainable in present-day silicate waveguides are possible in theory if mid-infrared operating wavelengths are used. The loss mechanisms, materials, and problems inherent in obtaining such fibers are discussed. Among several candidates, heavy metal fluoride glasses are suggested as being must suited to low and moderate loss fiber applications in the 2-5 micrometer spectral region.

The temperature dependence of the viscosity of heavy metal fluoride glasses is important for determining processing temperatures for procedures such as fiber drawing and in understanding crystallization behavior in these systems. Viscosity data in the glass transition region and in the liquid region have been measured by several different laboratories for ZBLA (58 ZrF4-33 BaF2-5 LaF3-4 AlF3) and ZBLAN viscosity-temperature curves for these two compositions are highly non-Arrhenius in nature, and cannot be described by the Fulcher equation; however the Cohen-Crest equation fits the data very well. On a reduced temperature scale (Tg/T), the viscosity curves nearly coincide, suggesting the possibility of a master viscosity equation for fluorozicronate glasses. Crystallization temperatures for these compositions have been measured by differential scanning calorimetry. On reheating, the first crystallization product for both compositions is a barium fluorozicronate phase. However, ZBLAN glass does not crystallize until a much lower viscosity is reached, compared to ZBLA. These results indicate that the devitrification behavior for ZBLAN is due to additional entropy of mixing from the addition of NaF.

Lanthanum chloride was synthesized by reacting La2O3 with CCl4. Purification carried out by zone refining resulted in reduction of Nd and Eu concentrations by at least a factor of 103. Impurity segregation coefficients were calculated from the concentration profiles in the charge measured by neutron activation analysis. Values of 0.85, 0.5, and 0.15 were found for Ce, Nd and Eu while a value of 0.65 was obtained for Pr from a plot of measured distribution coefficient versus ionic radius. These results show the feasibility of removing rare earth impurities to the ppb level from LaCl3. After purification, LaC13 is converted to LaF3

A technique is presented which addresses the problem of analyzing impurities in heavy metal fluoride glass optical fibers at the extremely low levels required for long distance applications. The procedure uses selectively excited fiber impurity luminescence (SEFIL), and is extremely sensitive due to the zero-background nature of luminescence and the long interaction lengths afforded by optical fiber. The technique has been rendered quantitative through the use of standards and the normalization of the impurity emission by the Raman scattering intensity. A SEFIL analysis of two fibers with differing origins and designs is reported. The ultimate detection limits are estimated to be <1 ppb-wt for Fe3+ and ≤ 0.001 ppb-wt for Nd3+ and Pr3+.

The heavy metal fluoride glasses (HMFG) have attracted considerable attention in recent years because of their unusual physical and chemical properties which allow potential use in numerous electrical and optical applications. The HMFG are transparent over a wide range of the optical spectrum (from 220 nm to 8,μ) and have sufficient chemical stability to make them a suitable optical material middle IR fibers optics. Their high anionic conductivity permits their application as solid electrolytes. They are also of interest scientifically since their structure is different from that of other inorganic glasses. The high coordination number of the network formers ions is the principal structural peculiarity of the HMFG.

Motivated by the benefits of optical data transmission, materials for the electromagnetic spectral window from approximately 0.6 to 4.0 microns are being explored by many investigators. I will review materials for the spectral regions surrounding this window. In these spectra regions a primary interest is optical power transmission. Optical power transmission in the UVand far IR has significant application for materials and device fabrication and characterization. Sources such as eximer and CO2 lasers provide potential sources of very high power.

Based on bonding and atomic mass considerations, materials for transmission in these windows can be approximated. Methods for taking advantage of the properties of materials such as reflectivity have the potential for interesting lightguiding structures such as hollow core lightguides. Materials currently contemplated for use in these wavelength regions and properties of potential materials will be discussed.

Raman, IR transmission, and reflectance spectra have been measured for a series of zirconium fluoride glasses deliberately doped with 0.4, 0.8 and 1.2 mole % lanthanum oxide. The effect of such impurities on the attenuation near the loss minimum in these glasses is discussed. In addition the utilization of Raman and IR spectroscopy to quantify the oxide contamination levels and optical absorption respectively, in heavy metal fluoride glasses is demonstrated.