Vapor-phase Axial Deposition Method Research Articles

Control of optical properties of silica glass synthesized by VAD method for photonic components

High-purity silica glass (SiO 2) synthesized by vapor-phase methods has been extensively used as optical material for photolithography due to its high transmittance in the UV range. Furthermore, low birefringence is an essential property in order to attain distortion-free images of fine IC patterns. This research reports the development of low birefringence silica glass for photonic components that excludes the annealing requirement by controlling the processing parameters of the VAD (Vapor-phase Axial Deposition) method. Nanoparticles size radial homogeneity of silica soot boules was characterized by scanning electron microscopy (SEM). It was established a relationship with the birefringence of consolidated boules characterized through polarization spectrophotometry. As the most interesting results, low birefringence silica glass (⩽ 2 nm/cm) was synthesized with reduced fabrication time and cost besides simple processing stages by controlling the silica boule bottom shape during deposition processing in correlation with the consolidation time.

Effect of the Nanostructure Control on the Novel Optical Properties of Silica Photonic Glass Synthesized by VAD Method

This research reports the development of high homogeneity silica glass for photonic components synthesized by the VAD (Vapor-phase Axial Deposition) method. Structural radial homogeneity of silica soot were characterized by scanning electron microscopy (SEM) and small angle X-ray scattering (SAXS). It was established a relationship with the refractive index homogeneity, n, and the birefringence of consolidated boules characterized through interferometry, optical spectrometry, and polarization spectrophotometry. By controlling the silica soot nanostructure during the deposition stage, a material with high radial homogeneity of refractive index of 1 ppm and birefringence of 2 nm/cm can be synthesized.

Effect of processing parameters on control of defect centers associated with second-order harmonic generation and photosensitivity in SiO2:GeO2 glass preforms

In this research, the effect of the H2/O2 ratio and the processing temperature parameters on the inducing and enhancement of the defect centers associated to the second-order optical non-linearity in SiO2:GeO2 glass preforms, prepared by vapor-phase axial deposition method, have been investigated. The formation of germanium oxygen deficient centers and the development of paramagnetic structures induced in the glass preforms after X-ray irradiation were investigated using UV–Vis absorption spectroscopy and electronic spin resonance. The results indicate that the concentration of germanium oxygen deficient centers increases exponentially when the H2/O2 ratio decreases, while the processing temperature increases, simultaneously. The electronic spin resonance spectra profiles, shows that defects of the electron trapped centers type [Ge(1), Ge(2)] are induced by the effect of X-ray irradiation. An efficient generation of defect centers associated to the second-order optical non-linearity in SiO2:GeO2 glass preforms, occurring in samples prepared with low H2/O2 ratios and high processing temperatures, have been observed.

Dependence of H 2/O 2 ratio and GeO 2 content on the enhancement of second-order non-linearity related defects in Ge-doped optical fiber preforms

In this research, we studied the influence of the process conditions through the H 2/O 2 ratio and the GeO 2 content, on the formation of germanium oxygen deficient centers and paramagnetic defects center induced by X-ray irradiation in SiO 2:GeO 2 glass preform prepared by the vapor-phase axial deposition method. The absorption band at around 5.1 eV, characteristic of germanium oxygen defect center was observed in all glass preform sample absorption spectra. The absorption coefficient increased when the GeO 2 concentration increased, however, the absorption was higher in samples prepared with high H 2/O 2 ratio. The electronic spin resonance spectrum profiles suggest that paramagnetic structures, such as, electron trapped centers and positively charged germanium oxygen deficient centers, assigned as Ge(1) and Ge(2), respectively, are induced in all samples after being X-ray irradiated for 1 h. It was found that the concentration of induced paramagnetic centers is linearly proportional to germanium oxygen defect center concentration and that the efficiency in the enhancement of paramagnetic defect centers associated with second-order optical non-linearity increased as H 2/O 2 ratio used in the fabrication process was decreasing. It was concluded that SiO 2:GeO 2 glass preform with low H 2/O 2 ratio and higher GeO 2 content must be prepared for the enhancement of the second-order non-linearity.

Dependence of H2/O2 ratio and GeO2 content on the enhancement of second-order non-linearity related defects in Ge-doped optical fiber preforms

In this research, we studied the influence of the process conditions through the H2/O2 ratio and the GeO2 content, on the formation of germanium oxygen deficient centers and paramagnetic defects center induced by X-ray irradiation in SiO2:GeO2 glass preform prepared by the vapor-phase axial deposition method. The absorption band at around 5.1 eV, characteristic of germanium oxygen defect center was observed in all glass preform sample absorption spectra. The absorption coefficient increased when the GeO2 concentration increased, however, the absorption was higher in samples prepared with high H2/O2 ratio. The electronic spin resonance spectrum profiles suggest that paramagnetic structures, such as, electron trapped centers and positively charged germanium oxygen deficient centers, assigned as Ge(1) and Ge(2), respectively, are induced in all samples after being X-ray irradiated for 1 h. It was found that the concentration of induced paramagnetic centers is linearly proportional to germanium oxygen defect center concentration and that the efficiency in the enhancement of paramagnetic defect centers associated with second-order optical non-linearity increased as H2/O2 ratio used in the fabrication process was decreasing. It was concluded that SiO2:GeO2 glass preform with low H2/O2 ratio and higher GeO2 content must be prepared for the enhancement of the second-order non-linearity.

Local structure and persistent spectral hole burning of Sm 2+ in silica-based fibers

Silica-based glasses doped with Sm 2+ have been prepared by using vapor-phase axial deposition method under a reducing atmosphere. The fluorescence spectra reveal that the reduction of Sm 3+ to Sm 2+ ions is accomplished in the silica glass codoped with Al 2O 3, while the Sm 2+ ions are not incorporated into the silica glass without Al 2O 3. The effects of Al 2O 3 codopant on the coordination change around divalent rare-earth ions are discussed according to our previous studies of 151Eu Mössbauer effects. It is assumed that the divalent rare-earth ions are preferentially coordinated by Al polyhedra, resulting in the stability of the lower valence state of the rare-earth ions. Persistent spectral hole burning is also demonstrated at room temperature for the 7F 0– 5D 0 transition of Sm 2+ in the aluminosilicate glass fiber. A hole width of 6 cm −1 is much narrower than the inhomogeneous width of 100 cm −1 , leading to the ratio of inhomogeneous-to-homogeneous width of ∼40.

Photochemical reactions of Ge-related defects in 10GeO 2·90SiO 2 glass prepared by sol–gel process

Germanosilicate glasses (10GeO 2–90SiO 2) were prepared by a sol–gel method and the ultraviolet-photosensitivity of glasses was investigated by optical absorption, electron spin resonance, and photoluminescence measurements. A one order larger intensity in the 5-eV absorption band was observed in the sol–gel glass sintered under an atmosphere at pressure <10 −2 Torr, compared to a fiber preform of the same composition formed by a vapor phase axial deposition method. Changes in optical absorption were observed in the sol–gel derived glass by ultraviolet laser irradiation; a decrease in 5-eV band and increases in absorption around 4.5 and >5.7 eV were also noted. Photoluminescence intensity under 248-nm excitation decreased with an increase in laser fluence and with a corresponding decrease in the 5-eV band. This result implies that an ultraviolet-induced photochemical reaction from Ge 2+ to Ge E′ in the glass had occurred.

Ultraviolet-photosensitive effect of sol–gel-derived GeO2–SiO2 glasses

Germanosilicate glasses are prepared by a sol–gel method and the ultraviolet (UV) photosensitivity of the glasses is investigated by optical absorption, electron spin resonance, and photoluminescence measurements. A KrF pulsed laser and a Hg lamp are used as UV light sources. The concentrations of intrinsic germanium-related oxygen-deficient centers in the glasses are successfully controlled by sintering conditions; in air or under reduced pressure. One-order larger intensity of the 5 eV absorption band is observed in the sol–gel glass sintered under the latter condition, as compared to a fiber preform of almost the same composition, which is formed by the vapor-phase axial deposition method. The effect of irradiation with KrF laser pulses on sol–gel glass is different from that on preform glass. On the other hand, the Hg-lamp illumination has the same effect on both sol–gel glass and preform glass. Based on these results, we discuss the defect states in sol–gel-derived glass and fiber preform glass and also the mechanisms of photochemical reactions under these two UV light sources.

Nanometer-scale heterogeneity in SiO2–GeO2 glass preforms and fibers prepared by vapor phase axial deposition method

Nanometer-scale heterogeneity of Ge ions in SiO2:GeO2 (10–15 mol %) glass preforms prepared by vapor phase axial deposition method and in optical fibers drawn from the preform was found by transmission electron microscopic observation. Both preforms and fibers were comprised of 8–10 nm sized Ge-rich and Si-rich phases. Observation of Ge E′ centers in the as-prepared state and the formation of Ge E′ centers with light illumination with 5 eV-light may be understood by the occurrence of these heterogeneity.

Chlorination and vaporization of GeO2 component in SiO2:GeO2 porous preform in dehydration process by VAD method and spontaneous formation of SiO2 cladding layer during the dehydration by selective vaporization of GeO2

Abstract In order to prepare silica-based graded index fibers of uniform transmission quality and low OH content by the vapor phase axial deposition (VAD) method, the halogenation rates of various types of GeO2 as a function of the molar ratio of oxygen to chlorine and of temperature were measured. As a result, the behavior of both the hexagonal GeO2 and the solid solution GeO2 in the dehydration and consolidation processes has become clear, that is, the solid solution GeO2 having SiOGe bonds which is formed in the high temperature region is very stable in the dehydration and consolidation processes. On the other hand, the crystalline hexagonal GeO2 which is formed in the low temperature region is unstable for chlorination reaction in the dehydration process and for volatilization in the consolidation process. This effect has been applied for OH content, and bandwidth control of fibers and VAD fibers of low OH content with losses less than 1 dB/km at 1.39 μm without any cladding deposition process and also those of highly uniform bandwidth fluctuations within ± 100 MHz km in the longitudinal direction of the fibers were obtained.

O2 molecules dissolved in synthetic silica glasses and their photochemical reactions induced by ArF excimer laser radiation

Silica glasses were prepared by three different techniques, vapor phase axial deposition method, oxidation of SiCl4 in O2-H2 flame, and O2 or O2-Ar plasma method with changing preparation conditions. This was done with the expectation that O2 molecules dissolve in the glasses with different concentrations by using a wide variety of preparation conditions. O2 molecules were found to be dissolved in the order of 1017 cm−3 and give an optical absorption above 7 eV, the so-called Schumann–Runge bands. The estimations of concentrations were done by using a molar absorption coefficient of ≡SiOH at 0.46 eV formed under a reaction of O2 with H2 diffusing from atmosphere at high temperature, 1/2 O2+H2+≡Si−O−Si≡ →2≡Si−OH. The concentration directly estimated from the absorption intensity at above 7 eV was consistent with those estimated from the IR band of ≡SiOH. On the ArF excimer laser irradiation of the glasses which possess the absorption band above 7 eV, the well-known absorption band at 4.8 eV was induced. This band was assigned to the Hartley bands of the O3 molecule. The reaction model was proposed to be O2(trapped)→2O(hν&amp;gt;5.1 eV) and O+O2→O3(trapped). On exciting the induced 4.8 eV band, a photoluminescence at 1.9 eV was observed. The photoluminescence excitation spectrum of the band was agreed closely with the quantum yield curve of O(1D) on the excitation of Hartley bands of ozone. This suggests that the luminescence is due to the radiative relaxation of O(1D) to O(3P). The total reaction was proposed to be O3→O(1D)+O2 and O(1D)→O(3P)+1.9 eV.

Collection and Characterization of Soot from an Optical Fiber Preform Torch

To follow the development of particle morphology, silica soot is extracted from four axial positions in the flame of a torch used to manufacture optical fiber preforms by the vaporphase axial deposition method. The soot, collected by three extraction techniques, is analyzed by transmission electron microscopy and gas adsorption to identify which characteristics of the soot morphology are dependent on the sampling technique and which upon the position in the flame. Comparison is also made to other work in which silica soot was extracted from a nondiffusion flame.

Bottom shape control of optical fiber soot preform by modified VAD method

Control of the bottom shape of an optical fiber soot preform fabricated by a modified vapor-phase axial deposition (VAD) method is proposed as a way to realize indirect control of the refractive index profile exponent during soot deposition. The technique is based on the close correlation between the profile and the bottom shape. Diameter and refractive index profile fluctuations of the preform with and without control are analyzed. In the case of no control, the fluctuations are larger, and unstable growth of the preform is observed. By controlling the bottom shape, axial fluctuations in the refractive index profile of a transparent preform are reduced to half the magnitude for preforms with no control, and axial diameter fluctuations of the soot and transparent preform are reduced to below +or-0.5%. As a result, fibers with a bandwidth of about 1 GHz km at a wavelength of 0.85 mu m can be stably fabricated. >

Germanate Glass Optical Fibers For 2 To 3 µm Band Fabricated By Vapor-Phase Axial Deposition Method

Germanate glass (Ge02-Sb203) optical fiber has been drawn from a preform glass rod prepared by the vapor-phase axial deposition (VAD) method. Transmission loss as low as 13 dB/km at the 1.1 Am wavelength has been obtained for a silicone resinclad fiber, and 5 dB/km at 2 Am and 23 dB/km at 2.4 Am have been obtained for a fiber with germanate glass cladding. If a germanate glass fiber of ideal design with a water content as low as 1 ppb (as has already been achieved for high-silica fiber prepared by the VAD method) is prepared, a loss of less than 0.1 dB/km is anticipated around the 2.2 to 2.4 Am wavelength.

Preparation of Germanate Glass by Vapor-Phase Axial Deposition

Antimony-doped germanate-glass rods for fabricating optical fibers, which transmit up to ∼3 μm, were prepared by the vapor-phase axial deposition method.

Germanium-oxide glass optical fibre prepared by VAD method

Germanium-oxide glass optical fibre doped with antimony for transmission of the 2 to 3 ?m band has been prepared by the vapour-phase axial deposition (VAD) method. An attenuation loss of 13 dB/km at 2.05 ?m and 70 dB/km at 2.4 ?m has been achieved.

Low-OH-content optical fibre fabricated by vapour-phase axial-deposition method

A low-OH-content and long-length optical fibre has been made by the v.a.d. method. The OH content in the rod preform was reduced to about 0.4 p.p.m. utilising the chemical reactions of SOCl2 or CCl4 with OH ions and H2O molecules In the porous glass rod. The minimum loss of the fibre, 20km long, was 1.0±0.1 dB/km at 1.2μm.