Chromatic dispersion distribution measurement along a single-modeoptical fiber

A nondestructive measurement technique, which uses a four-wavelength bidirectional optical time domain reflectometer (OTDR) to measure the chromatic dispersion distribution along a single-mode fiber, is compared with the destructive interferometric technique. The experimental results obtained by this technique are in good agreement with those obtained by the interferometric technique. In addition, a measurement procedure is proposed for a transmission line composed of different types of single-mode fiber. These results show that this technique is extremely useful for the design of wavelength division multiplexer (WDM) and finite difference multiplexer (FDM) optical communication systems     

Effects of intraventricular and intraspinal 6-hydroxydopamine on blood pressure of renal hypertensive rats

6-Hydroxydopamine (6-OH-DA) was administered into the lateral brain ventricle of normal rats and of rats with renal hypertension produced by unilateral clipping of the renal artery, and was also administered into the spinal cord of normal rats. Intraventricular administration of 6-OH-DA prevented the development of renal hypertension in rats, but was ineffective in developed renal hypertension. The development of renal hypertension was not affected by pretreatment with intraspinal injection of 6-OH-DA, which produced a marked reduction only in spinal cord noradrenaline. These data suggest that brain adrenergic neurones may participate in the production of renal hypertension but the noradrenergic projections in the spinal cords are not essential for this process.     

Method for separation of particles using a rotating titled liquid column (RTC). II. Closed and open-bottom column systems

A new method for selective separation of particulate materials has been developed, using a rotating tilted liquid column (RTC) with closed or open bottom. As particles move with RTC velocities determined by pseudo-circular loci which approach eccentrically to the inside wall of RTC, the most influential factor for the separation is the interaction between the particles and the column wall. To evaluate the influence of the interaction, we calculated the loci with a parameter Aω/V₀ (where A is the radius of the column, ω is the angular velocity of the column, and V₀ is the sedimentation velocity).Exploratory tests in closed column indicate that RTC velocity V(ω, θ) is represented by the following equation: V(ω, θ)/sin θ = uV₀ ? bAω/V₀, where θ is the inclination of the column to the horizontal, u = 1.103, and b = 0.16 [LT^?1] (at θ = 30 – 45°, 26 – 30 °C).In a practical application of this method, the open-bottom column was used for separation of fine particles such as starch particles.     

Characteristics of dispersion-shifted dual shape core single-mode fibers

The structural design, bending loss, and dispersion characteristics of the dual shape core (DSC) single-mode fiber with zero dispersion at 1.55 μm are described. It is clarified that the bending loss of the DSC fiber is less than one tenth of that of a step-index fiber, and that the dispersion sensitivity due to a small change of the core radius is less than half of that of a step-index fiber. The explanation for the small bending loss is presented. A greater reduction of bending loss is expected from the replacement of the center core profile with a Gaussian or triangular profile.     

Evaluation of the performance of polished mirror surfaces for the TAMA gravitational wave detector by use of a wave-front tracing simulation

We evaluated the performance of polished mirror surfaces for the TAMA interferometric gravitational wave detector by comparing the experimental results with a wave-front tracing simulation. The TAMA mirror surfaces were polished to a roughness of a few nanometer rms. We confirmed that these polished mirrors do not limit the present TAMA sensitivity and that the target shot-noise sensitivity will be achieved with these mirrors, even if a power-recycling technique is introduced in the next stage of the TAMA.     

Evaluation and improvement of optical-grade LiTaO3 single crystals by the LFB ultrasonic material characterization system

This paper describes the first demonstration for feeding back the results obtained by the line-focus-beam ultrasonic material characterization (LFB-UMC) system to the crystal growth conditions for optical-grade LiTaO₃ crystals and for achieving much improved homogeneity of chemical composition. We evaluated a commercially available optical-grade LiTaO₃ single crystal with a nominally congruent composition in detail, by measuring distributions of the velocities of leaky surface acoustic waves (LSAW) along the Y-axis direction for a Z-cut specimen plate prepared from the crystal grown in the Y-axis direction. We detected an increment of 0.66 m/s in LSAW velocity along the pulling axis direction corresponding to 0.024 mol% in Li₂O content, and the compositional gradient was +0.346×10^-3 (Li₂O-mol%)/mm. By experimentally obtaining the starting material composition dependence of the gradients, we developed a method of estimating the proper composition ratio that would lead to a more homogeneous crystal. We grew a new crystal with a Li₂O content of 48.47 mol%, resulting in a very small compositional gradient of +0.046×10^-3 (Li ₂O-mol%)/mm and a compositional homogeneity of less than 0.012 Li₂O-mol% in a Z-cut area of 50 mm×50 mm used for device substrates