Osamu Fukuda

Photorefractive effect of BaTiO 3 single crystals grown in inert atmospheres

BaTiO3 single crystals were grown by the top-seeded solution growth technique in inert atmospheres of nitrogen gas and of argon gas and in air. They were then annealed at 1200°C in air. These crystals, prepared from a mixture of 99.999% pure BaCO3 powder and 99.99% pure TiO2 powder, contained virtually equal amounts of transition-metal impurities (Fe, Co, Ni, etc.). The maximum beam-coupling gain of the two crystals grown in inert atmospheres was 6 cm−1, and that of the crystal grown in air was 3 cm−1; the sign of the beam-coupling gain of the crystals was positive. We found that the crystals grown in inert atmospheres exhibited high gains without having been doped with any transition-metal elements.

Polarimetric Strain And Pressure Sensors Using Temperature-Independent Polarization Maintaining Optical Fiber

A polarimetric fiber sensors stabilized against the ambient temperature change has been developed by cancelling the temperature dependence of the intrinsic fiber birefringence with the thermal stress of a multi-layer plastic jacket.

Transmission characteristics of long spliced graded-index optical fibers at 1.27µm

Transmission characteristics of graded-index fibers at 1.27 μm are investigated. Bandwidth measurements are made in the frequency domain by using a CW GaInAsP laser diode modulated by a sinusoidal signal. For a germanium pbosphosilicate fiber, the optimum index profile at 1.27 μm is determined as 1.98. It is shown that optimum profile at 0.83 μm is 2.08 and there exists a large profile dispersion effect: for example, the experimental maximum 3-dB bandwidth at 1.27 μm decreases to one-third at 0.83 μm. Length dependence of bandwidth is investigated for 48 km long spliced graded-index fibers at 1.27 μm. It is verified that using a simplified transmission model in which mode conversion is assumed at splicing points, the bandwidths of long spliced fibers are predicted with satisfactory accuracy in terms of unit fiber transfer functions.

Superconducting Bi‐Sr‐Ca‐Cu‐O crystalline fibers prepared by the micro‐Czochralski method

Superconducting Bi‐Sr‐Ca‐Cu‐O crystalline fibers were successfully prepared by the micro‐Czochralski method from Bi2Sr2 CaCu2 Ox source ceramic rods. The maximum length of the fibers obtained was 55 mm (0.3 mm diameter). The fiber crystal grains were oriented with the current carrying a‐b basal planes parallel to the fiber axis. The values of Tc (zero) and Jc (77 K and zero magnetic field) for these fibers were ∼84 K and ∼3170 A/cm2 , respectively.

Vapor axial deposition single-mode fibers with ultimate low-core eccentricity

Introduction of single-mode fibers into subscriber loops is being studied from the viewpoint of technical feasibility.1 The technique of low-loss mass splicing is a major problem, and core eccentricity seems to limit the reduction of splice loss. We describe newly developed VAD single-mode fibers with ultimate tow-core eccentricity. Using the VAD process a core and a whole cladding have been synthesized with a high deposition rate.

Ultralow-crosstalk splicing of polarization-maintaining optical fibers by a local end-image monitoring technique

Polarization-maintaining optical fibers (PMFs), which maintain a state of polarization over a long length, have many applications from coherent transmission systems to fiber-optic sensors.1·2 For putting PMFs into practical use, PMFs must be easily spliced with a low loss and low crosstalk. When a usual splicing technique is used for PMFs a polarized light power monitoring is required for polarization axis matching. However, it would be hard to apply this technique to an installed PMF cable. If the monitored polarized light power is unstable, high-quality splicing of PMF becomes difficult.

Fabrication of 1.55-μm dispersion-shifted polarization-maintaining optical fiber

Polarization-maintaining optical fiber (PMF), which maintains a state of polarization over a long length, has many applications from coherent transmission systems to fiber-optic sensors. Especially, in a long coherent transmission system, it is necessary that a PMF have low loss and low dispersion in the 1.55-µm wavelength region.1

Refractive-index profile measurement of large preforms: a new technique

A number of techniques have been developed to measure the refractive- index profile of optical fiber preforms: interferometric,1,2 focusing,3 and spatial filtering4 methods. Among those techniques, the method described in Ref. 5, which traces the deflection angle of a scanning laser beam injected laterally to preform, is widely used in preform characterization.

Effect of an additional ring profile on transmission characteristics of 1.55-µm dispersion-shifted fibers

Various types of 1.55-μm dispersion-shifted fiber have been presented. Among them, triangular core1 and similar fibers have the advantage in terms of optical loss. Recently, a triangular profile with a ring in the cladding was proposed to minimize the bending loss.2 Our paper now describes the effect of the ring on the transmission characteristics of triangular and Gaussian core fibers.3

Polarimetric sensing of fiber strain in plastic-jacketed high-birefringence optical fibers

It is important to measure quantitively the initial compressive strain and fiber axis deformation in plastic-jacketed optical fibers induced by the jacketing process,1 since these are serious factors which are related to the thermal characteristics for optical cable design. Usually thermal characteristics of fiber strain in plastic-jacketed optical fibers are measured by using the phase shift of the modulation signal or delay time of the launched optical pulse. Our measurements used the birefringence change in nylon-jacketed high-birefringence optical fibers.