Hydrogen doping of optical fibers has been examined as an approach to increase the radiation hardness of optical fibers for high dosage (107 rad) space applications. A systematic study has been performed on 4 types of optical fibers designed to operate at 1.31 and 1.55 μm and doped with up to 8200 ppm H2. For low dosages, the most significant reductions m radiation-induced losses were obtained with low H2 concentrations (<10 ppm). Spectral loss measurements for hydrogen-doped fibers containing GeO2 show a radiation-induced loss peak at 1.45 μm and a broad absorption band around 0.6–0.8 μm. These bands are not observed in the pure silica-core fibers.

Fibers were fabricated to permanently trap 2.7 ppm H2 and the radiation-induced losses in these fibers are 35 to 85% that of the untreated fibers. Experimental data are used to delineate the γ-T-α operating limits which define the maximum gamma radiation (γ) dosages at different temperatures (T) while still meeting a requirement of α<150 dB/km. Among the four fiber types, hydrogen-doped silicacore fibers show the widest operating range and smallest radiation-induced loss for space applications. However, hydrogen-doped fibers with moderately high GeO2-doped core offer the best tradeoff between the bending and radiation-induced losses.

The radiation response of a series of optical fibers with pure silica cores, that differed as to residual hydroxide and chloride content and as to preform formation, have been measured after exposure to pulsed electron beam radiation to 10 krads [100 Gys]. The irradiations were carried out at both ambient temperature and at −50°C and with two different operating power levels at each temperature. The responses have been analyzed seeking to identify correlations between the differences in the residual chemical contents or preform formation and the observed differences in the initial response and the recovery behavior among the optical fibers in the series.

A novel kind of hydroxyl formation during the processing of quartz glass tubes with oxy-hydrogen burners was found and studied in detail by high-resolution laser spectroscopy. The formation mechanism involving hydrogen penetration from the flame and following reactions is discussed.

Oxygen or chlorine was incorporated into silica glasses by sintering porous soot rods under 02/He or C12/He atmosphere. In case of oxygen, the Schumann-Runge band of 02 molecule was found in VUV region. An absorption band at 4. 8eV having 1. 9eV emission was generated with irradiation of excimer laser. We proposed that such optical properties were due to 02 molecule trapped in glass because they were similar to photochemistry of 02 molecule in the gas phase which could be shown as:

When silica glasses were fabricated under chlorine ambient, a minor fraction was found to be present as Cl2 molecule trapped in the glass, which gives the absorption band at 3.8eV.

Characteristics of ArF laser induced luminescence, and absorption bands in soot remelted silica, before and after annealing in various atmospheres, were investigated. A soot remelted silica containing no OH has an absorption band at 5.1 eV which can be annealed out with H2, but an absorption band at 5.8 eV is induced by subsequent the ArF laser irradiation. In a soot remelted silica containing 50 ppm of OH, an emission band at 1.9 eV was induced by the ArF laser irradiation. The 1.9 eV band can be annealed out with He and H2, but, by annealing in H2, the 5.8 eV absorption band was induced by the ArF laser irradiation as in the case of the silica containing no OH.

Characteristics of ArF excimer laser induced 1.9 eV emission and 5.8 eV absorption bands in type III and soot remelted silicas were investigated. In a type III silica synthesized in a reducing condition, an absorption band at 5.8 eV band is induced. The creation of this band can be prevented by annealing in an atmosphere of He. In the soot remelted silicas with and without OH, the creation of the 5.8 eV band is strongly promoted by annealing in H2. An emission band at 1.9 eV is induced in a type III fused silica synthesized in an oxydizing condition and soot remelted silica containing OH. When annealing in He, creation of the 1.9 eV band is strongly promoted in the former but suppressed in the latter sample. This difference is derived from the difference of higher order structures between the type III and the soot remelted silicas.

The effect of varying single mode fiber fabrication factors such as core and clad dopant concentrations, deposition conditions, and draw parameters on the recovery of the nuclear radiation-induced attenuation at 1.3 μm has been studied. Statistically significant correlations of core factors have been established with a 24 experimental design, and separate one-dimensional experiments revealed the effect of clad [Ge] and [F].

Ge-associated defect centers induced by 5 eV (∼ 245 nm) photons of various intensities in Ge-doped silica were studied using electron spin resonance (ESR). We found that Ge E' centers observed in Bragg grating Ge-doped silica core fibers are induced and bleached by one- and two-photon absorption processes, respectively. The observation that Ge E's are the only paramagnetic centers induced by low intensity 5 eV photons supports the proposal that the Ge E' center is responsible for the photoinduced structures observed in both Bragg grating and second-harmonic-generation (SHG) fibers.

Permanent X(2) gratings can be written in doped silica fibers by coherent irradiation with light at ω and 2ω. The X(2) gratings give rise to phase-matched second harmonic generation (SHG), i.e. subsequent irradiation of the prepared fiber with light at ω results in an output at 2ω. The efficiency with which the gratings can be written depends on the nature and concentration of defect states induced by dopants in the, glass. We present results for fibers doped with Ge and rare earth ions and discuss the implications of our results for the various mechanisms that have been proposed to explain photoinduced SHG in fibers.

Permanent refractive index gratings were holographically photowritten into rare earth doped glasses using the 488 rn line of a Ar Ion laser. The rare earths Pr3+, Tb3+, and Eu2+ were examined. Experiments were performed to elucidate the mechanism responsible for the photoinduced index change. A model is presented in which the index change is accomplished through photoionization of the rare earth dopant and subsequent trapping of the free carrier. The viability of these materials for use in optical fiber grating devices is discussed.

The mechanical properties of silica and titania-doped silica glasses, in bulk and fiber forms, are presented. These include the elastic properties (E and ν), strength distribution (in tension and bending), fatigue behavior (dynamic and static loading) and fracture toughness. Following a brief review of above properties for fused silica and ULE™ glasses (Coming Codes 7940 and 7971), used primarily for space applications, the mechanical properties data for silica and titania-doped silica-clad optical fibers are presented. The enhancement of mechanical performance of titania-doped silica clad fiber is also discussed.

The effect of titania doping on fundamental properties like stress-free activation energy, crack tip pH, and deformation mode of Si-O-Si bond is discussed. In addition, the crack velocity data obtained from DCDC specimens of homogeneous silica and titania-doped silica glasses are compared in an attempt to understand the role titania plays in improving the fatigue resistance of optical fibers.

This paper describes four key measurements of critical coating performance attributes which can affect coated optical fiber performance. The four measurement methods to be described are: 1) primary coating adhesion, 2) coating toughness, 3) primary coating equilibrium modulus, and 4) primary coating glass transition temperature.

Chemical kinetics is applied to the fatigue (stress assisted corrosion) of silica fibers in NaOH solutions. The thermodynamic parameters are determined and compared to measurements in water; the zero stress activation energy is the same for the two systems (∼25kcal/mol), but the activation volume in aqueous NaOH solutions is smaller (∼11cm3/mol) than that in water (∼27cm3/mol). The accelerated fatigue rate is dominated by a three decade decrease in the pre-exponential factor; it is shown that this decrease can be attributed to an increase in the entropy of the system.

The influence of residual moisture under a metal coating on strength and fatigue of silica optical fibers was investigated. It was shown that for the fabrication of metalcoated fibers with strength – 10 GPa and low static fatigue it is necessary that the water content in the atmosphere during the freezing process should be less than 40 ppm.

Several chalcogenide glass fibers with Teflon cladding and glass cladding were prepared for infrared optical application. A minimum transmission loss, at C02 laser wavelength, of 0.9 dB/m was attained in SeTel glass fiber. The CO and CO2 laser power transmission characteristics of fibers were investigated. Selenide and telluride glass fibers yielded damage thresholds lower than sulfide glass fiber because of their large temperature dependence of refractive index and transmission loss. Deliveries of 80 W of CO laser light in AsS glass fiber, and 10 W of CO2 laser light in GeSeTe glass fiber, were attained. An AsS fiber bundle of 8400 cores was prepared, which could deliver a clear thermal image below 100 °C. Prepared fibers were also found useful for low temperature monitoring and gas sensing in narrow or restricted spaces.

Alkaline earth gallogermanate glasses are a possible low-loss oxide optical material which would be able to operate in the 1.6–2 μm wavelength range. Processing techniques investigated to date and pertinent optical property data are presented.

ZrF4-based binary glass film is synthesized for the first time by plasma-enhanced chemical vapor deposition (PCVD). The optical transmission spectrum is measured and the effects of oxygen doping on the glass forming ability are clarified. No absorption band caused by OH or other impurities is observed in the near IR region. Weak absorption bands attributed to defect centers are observed in the UV to visible region. The glass forming region in the ZrF4-BaF2 system is significantly improved by oxygen doping. Oxygen ions are distributed homogeneously in the fluoride glass film by PCVD and improve its stability against crystallization.

Zirconium fluoride (ZrF4 ) thin films were formed by plasma CVD and evaporation for thin-film optical wave guide. In the case of plasma CVD, ZrF4 compound was actually observed to be synthesized from the vapour of Zr and CF4 gas according to. ESCA measurement, even if the film contained impurities. As for evaporation, transparent and amorphous film was obtained and optical transmission loss was measured by scattering detection method, and the loss was calculated to be 9.5 dB/cm. But when only ZrF4 was deposited, thin film was tarnished to be white because of adsorption of moisture. Therefore, simultaneous evaporation of ZrF4 and BaF2 was performed and the charastaristic was stabilized.

Optical amplifiers promise to revolutionize optical communication. Erbium-doped silica fiber amplifiers operating at 1.5 μm are now commercially available while the performance of devices using neodymium or praseodymium doped fiber in the 1.3 gtm telecommunications window are improving rapidly. This review discusses the importance of host material on amplifier characteristics.

Efficient 1.54 μm emission under 1064nm excitation of Er3+/Yb3+ codoped silica fibre is reported. The energy transfer efficiency from Yb3+ to Er3+, of at least 85%, even under high inversion, is comparable to that in multicomponent glass fibres. Fibre design parameters are discussed and results presented. Small signal gain of ˜ 45dB is also measured and a power amplifier giving 145mW output power demonstrated.