Masao Kawachi

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.

Hysteresis Behavior of Texture in the Field-Induced Nematic-Cholesteric Relaxation

The effects of bias voltages on the field-induced nematic-cholesteric relaxation are investigated both for samples with perpendicular boundaries and for ones with parallel boundaries, and are discussed in relation to the hysteresis behavior of texture. When the applied voltage is reduced from a value above the threshold to a bias voltage below the threshold a relaxation from the field-induced nematic to a Grandjean-like cholesteric state occurs, the relaxation time of which increases as the bias voltage approaches a certain value Vc↓; the ratio of Vc↓ to the threshold voltage Vc for cholesteric-to-nematic transition is about 0.5 irrespective of the boundary conditions. When the bias exceeds Vc↓, the transformation shows a hysteresis behavior such that the nematic state is kept for a long time until gradually replaced by focal conic domains nucleating from some local defect points; the boundary condition is found to play no essential role in the hysteresis behavior. An interpretation of the results is presented.

Flame hydrolysis deposition of SiO2-TiO2 glass planar optical waveguides on silicon

Extension de la methode decrite precedemment au depot de verres sur des substrats en silicium cristallin. Cette methode est utilisable pour la construction de differents dispositifs en optique et electronique integres

Organic crystals growth for optical channel waveguides

Abstract Optical channel waveguides of meta-nitroaniline (m-NA) crystal, which has potential applications to nonlinear optical devices, have been fabricated on glass substrates having fine grooves. The crystal growth was performed by zone-melting, scanning a CO 2 laser beam along the grooves filled with the polycrystal m-NA. Optical and X-ray observations showed that zone-melting changed the polycrystalline state to a single crystalline state with the 〈001〉 direction along the groove. The scattering loss for a 5 mm-long m-NA crystal waveguide (100 μm both in width and in depth) was found to decrease from 50 dB to 2.5 dB with this process.

Light Scattering Characteristics in Nematic-Cholesteric Mixtures with Positive Dielectric Anisotropy

The angular dependence of light scattering in nematic-cholesteric mixtures with positive dielectric anisotropy was measured; the quiescent transparent satate S, the focal-conic state F, the storage focal-conic state F0, and the field-induced nematic state H were investigated. The F0 state showed Bragg scattering peaks caused by the lattice spacing of P0/2 where P0 was the helical pitch of the mixture used. While, the light scattering profile for the F state under an applied electric voltage was found to be characterized by scattering peaks caused by the optical lattice spacing of P0 itself, though the detailed physical reason has not yet been fully understood. The contrast ratio of the light scattering between F0 and S was also discussed in connection with application to storage-type liquid crystal displays.

Nondestructive Structure Measurement of Optical-Fiber Preforms with Photoelastic Effect

The photoelastic effect is used to measure nondestructively the structure parameters of optical-fiber preforms. An He–Ne laser beam is introduced perpendicular to the preform axis, the transmitted beam is optically retarded by residual stresses in the preform, and the optical retardation is measured. A procedure for determining the core diameter and the refractive-index profile from the measured optical retardation is presented. It is applied to a step-index preform and a graded-index preform fabricated by the M.C.V.D. (Modified Chemical Vapour-phase Deposition) technique.

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.

OH-Ion Distribution in Preforms of High-Silica Optical Fiber

The OH-ion distribution in preforms of high-silica optical fibers was investigated and related to the OH-contamination mechanism in the preform fabrication processes of the C.V.D method. The OH-ion distribution profiles were measured optically at 2.73 µm with a high spatial resolution of about 90 µm. It was confirmed from the OH-ion distribution profiles that one of the OH-contamination processes is the thermal diffusion of OH-ions from the supporting silica tube into the deposited glass layers during deposition. No significant difference was observed in the OH-ion diffusivity between nondoped silica glass and B2O3-doped silica glass. The OH-contamination in the center of the preform was attributed to the dissolution of the water vapor due to an accidental leak from the outlet of the deposited tube during the collapsing procedure. Based on this result, the OH-ion solubility in silica glass at a high temperature of 1900°C is estimated to be about 1.4×1020 OH/cm3atm.1/2

Second Harmonic Generation in Inclusion Complexes

Second harmonic generation in inclusion complexes between dimethyl β-cyclodextrin and nitroaniline derivatives having a non-centrosymmetric crystal structure occurs.

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.