Low OH Content Research Articles

Effect of deposition rate on spectral loss of GeO 2 -P 2 O 5 -SiO 2 graded index fibres

Low loss, low OH content 0.23 n.a. graded index germanium phosphosilicate fibres have been fabricated using the m.c.v.d. process at rates up to 0.34 g/min with deposited layer thicknesses up to 16 μm. The deposition rate did not affect achievement of low loss in the spectral range 0.7 μm–1.7 μm.

Investigation of the silica surface via electron-energy-loss spectroscopy

Various aspects of the electronic structure of the silica surface and its response to electron irradiation have been studied. Electron-energy-loss spectra (ELS) were obtained for bulk high-purity synthetic Si${\mathrm{O}}_{2}$ with either high or low OH content, crystalline $\ensuremath{\alpha}$-quartz, and compacted aerosil powder. All show peaks at ${E}_{\mathrm{loss}}=3.3, 5.0, \mathrm{and} 6.8$ eV for excitation of valence-band electrons with low-energy (${E}_{p}=175$ eV) primary beams. Aside from small changes in relative intensity, these features are independent of: (i) exposure to different atmospheres, (ii) electron irradiation up to levels of 5 \ifmmode\times\else\texttimes\fi{} ${10}^{20}$ electrons/${\mathrm{cm}}^{2}$ at 5 keV, (iii) in situ annealing in vacuum, ${\mathrm{O}}_{2}$ or ${\mathrm{H}}_{2}$, and (iv) ${\mathrm{Ar}}^{+}$ sputtering at either 0.5 or 2 keV. Assignment of these transitions to intrinsic surface electronic states (as distinct from chemisorbed species or radiation-induced point defects) is discussed qualitatively. Electron irradiation is known to cause oxygen desorption, leading to a surface region of the form $\mathrm{Si}{\mathrm{O}}_{x}$ ($1lxl2$). After irradiation sufficient to produce $x=1.5$, as indicated by Auger spectroscopy, no strong evidence is found for interband or plasmon excitations characteristic of bulk elemental silicon. These results tend to favor the random-mixture model over the phase-separation model of the damage region. Arguments are also presented against the participation of surface point defects in the 70-100-eV Auger spectrum of electron-irradiated Si${\mathrm{O}}_{2}$.

Very low OH content P 2 O 5 -doped silica fibres

Very low OH content optical fibres consisting of P2O5-doped silica core and GeO2-P2O5-B2O3-doped silica cladding were fabricated by the m.c.v.d. technique. The relation between the OH absorption loss and the deposition temperature was clarified. The OH content in this fibre could be reduced to about seven parts per billion (∼ 7 × 10−9) by using a low deposition temperature.

Radiation response of fiber optic waveguides in the 0.4 to 1.7 μ region

The response of fiber optic waveguides to ionizing radiation has been studied. Measurements of the growth and decay of the radiation-induced loss at 0.82μ have revealed that fibers with low OH are more susceptible to damage than those with high OH. The addition of P to Ge-doped silica core fibers has been found to suppress an intense transient absorption. Spectral measurements of the radiation-induced absorption between 0.4 - 1.7μ have shown an increase in the OH overtone and combination band intensity with irradiation so that the induced loss at 1.3μ is actually less in the low OH content silica core fibers than in the high OH content fibers. Real time spectral measurements of the damage following a pulsed irradiation have lead to an identification of the absorption bands and damage mechanisms responsible for the radiation-induced absorption.

Low loss and low OH content soda-lime-silica glass fibre

Low loss soda-lime-silica glass fibres of minimum loss of 4.23 dB/km at 0.85 μm were prepared with 6.5 dB/km extra absorption loss due to OH radicals at 0.97 μm. The loss factors were analysed from the impurity contents and scattering loss. These fibres have been developed by unique preparation techniques of wet mixing of raw materials and dry gas flow at glass melting.

Improved mercury arc lamps

The devitrification problem of capillary high pressure mercury lamps is shown to be caused by impurities in the natural quartz. It is shown that this problem may be solved by using synthetic quartz of low OH-content. An improvement of lamp life by an order of magnitude appears to be possible.

Three Anisotropies in Vitreous Silica

Plasma‐torch fused‐silica boules of low OH content showed an optical anisotropy in the as‐grown state which disappeared after annealing in O2; this behavior was related to an EPR anisotropy which also depended on annealing, probably involving Fe2+ and Fe3+, respectively. High‐temperature (1200° to 1500°C) deformation experiments performed in a modified DTA machine on slabs cut parallel and perpendicular to the preparation symmetry axis also showed an anisotropy, corresponding approximately to a factor of 2 in the viscosity. This anisotropy was also observed in commercial worked fused silica of high and low OH (water) content, made from purified Si compounds or natural quartz, and was not removed by annealing for 5 days at 1200°C in O2. The deformation rate of fused silica decreases as water content is reduced from high to medium, but there is little further change when water content is decreased to a very low level.

Drawing-induced defect centers in a fused silica core fiber

The process of fiber drawing has been found to produce defect centers in optical fibers with a silica core of low OH content (Suprasil W-1), but not in fibers with a silica core of high OH content (Suprasil 1). At least one center gives rise to the drawing-induced optical absorption, which is identical to the 630-nm band created by ionizing radiation in bulk samples of Suprasil W-1. By means of electron-spin-resonance techniques, additional drawing-induced defect centers have been observed; these centers are identical to the radiation-induced oxygen-associated hole centers in bulk fused silica.