Takao Edahiro

Raman spectra of binary high-silica glasses and fibers containing GeO2, P2O5 and B2O3

Abstract The Raman spectra of binary high-silica glasses have been studied. The main peaks at 808 cm −1 and 710 cm −1 in vitreous B 2 O 3 and vitreous P 2 O 5 , respectively, are greatly reduced in binary high-silica glass, whereas a peak at 425 cm −1 due to GeOGe vibration and a peak at 1320 cm −1 due to P = O vibration remain strong, increasing in intensity with decreasing SiO 2 concentration. In the stimulated Raman spectra of a P 2 O 5 -SiO 2 glass fiber pumped by a mode-locked and Q-switched Nd:YAG laser at 1.064 μm, strong Stokes emissions due to the P = O vibration have been observed at 1.24 μm and 1.48 μm. In the spectra for a GeO 2 -SiO 2 glass fiber, four narrow-width Stokes emissions due to the GeOGe vibration have been observed at 1.115, 1.172, 1.235 and 1.305 μm.

Deposition Properties of High-Silica Particles in the Flame Hydrolysis Reaction for Optical Fiber Fabrication

Deposition properties of SiO2-GeO2 particles synthesized by the flame hydrolysis reaction of SiCl4-GaCl4 (10 mol%) were investigated with emphasis on the effect of the substrate temperature Ts. Deposited GeO2 was found to be formed with hexagonal crystalline structure for Ts 500°C ; the dissolved GeO2 concentration increased with increasing Ts from 500°C to 800°C. This is of practical interest in relation to the soot processes for optical fiber fabrication.

Possibility of Use of Liquid Crystals as Optical Waveguide Material for 1.3 µm and 1.55 µm Bands

This letter describes an experimental investigation on the transmission characteristics of a liquid crystal optical waveguide in the 0.7 µm–1.7 µm spectral range. The scattering loss decreases from 10 dB/cm to about 2 dB/cm as the wavelength is increased from 0.7 µm to more than 1.3 µm. This indicates the potential use of liquid crystals as an active waveguide material for integrated optics operating at 1.3 µm and 1.55 µm, at which wavelengths the liquid crystals also have low absorption loss windows.

Transmission characteristics of VAD multimode optical fibers

The influence of convex striations of vapor phase axial deposition (VAD) optical fibers on transmission characteristics has been analyzed. These convex striations are inherent in optical fibers made by VAD and cause refractive-index fluctuations in both radial and axial directions. The phase of the sinusoidal fluctuations in the radial direction varies periodically along the fiber axis. Numerical analysis shows that bandwidth degradation due to sinusoidal fluctuations in the radial direction can be alleviated by a periodic phase variation in the axial direction.

Threshold Gas Flow Rate of Halide Materials for the Formation of Oxide Particles in the VAD Process for Optical Fiber Fabrication

The state of oxides produced by the flame hydrolysis reaction of halide materials, in particular whether the oxides exist as vapor or as solid particles in the oxy-hydrogen flame, is investigated because of its connection with the VAD process for optical fiber fabrication. Each halide gas is found to have a threshold flowrate below which the oxide product does not form solid particles in the flame but remains in the vapor state. The threshold flowrate of halide materials examined in this work is in the order TiCl4, SiCl4<GeCl4, BBr3<SnCl4<PCl3. This peculiar order is dominated by the saturated vapor pressure values of the oxides produced at high temperatures in the flame. The relation between the experimental results and the refractive-index formation mechanism in the VAD process is discussed.

Invited) Recent Progress in VAD Fiber Fabrication Process

Since the development of the Vapor-phase Axial Deposition (VAD) process in 1977, rapid progress has been made in the improvement of transmission properties by the analysis of the above process. This paper describes the progress in the fabrication process for attaining better transmission characteristics and future aspects of this process. Specific characteristics obtained in this process are: reduction in the transmission loss of fibers by the optimal material composition and dehydration technique, the realization of less than 1 ppb of OH content, a bandwidth that now exceeds 6 GHz-km at 1.3 µm, which was attained through the analytical studies of the profile formation mechanism and the controlling of the deposition condition, and the production of long low-loss graded-index fibers.

Stimulated Raman generation in two-mode long-length fibers pumped by a mode-locked laser

Single-pass Raman generation pumped by a mode-locked Nd:YAG laser has been investigated for two-mode fibers each 35 km long. From input power dependence of stimulated Raman scattering, it was found that the peak wavelength of the first Stokes jumps dramatically from 1.114 to 1.12 microm at 1.65-W input power and that total output power of the first Stokes also increases rapidly at this power for a fiber with a 1.27-microm cutoff wavelength, when the fiber is pumped at the LP(11) mode exciting condition. These experimental results can be explained by the group delay for LP(01) and LP(11) modes. The maximum interaction length and the threshold power were determined from the group delay, which showed fairly good agreement with the experimental results.

Refractive-index profiling of preform rods by a photoelastic method: application to VAD single-mode fiber preforms

An automatic and nondestructive method for measuring the refractive-index profile of optical fiber preforms using the photoelastic effect is presented. The method is applied to single-mode fiber preforms fabricated by the VAD technique. A collimated beam of linearly polarized light is passed transversely through the preform. The transmitted light is detected with a video camera equiped with a large diameter lens, a quarter-wave plate, and an analyzer. The refractive-index profile is computed from the light intensity distribution. Excellent agreement is obtained with core diameters and profiles determined from interference microscopic observation on preform slab samples.