Laser-trimming adjustment of waveguide birefringence in optical FDMcomponents

Laser trimming of amorphous-silicon stress-applying films deposited on silica-based single-mode waveguides is demonstrated for controlling waveguide birefringence. Successful applications to polarization-insensitive operation of an optical ring resonator and a Mach-Zehnder interferometer are presented. A phase difference of less than π/100 between TE and TM modes has been attained. It is noted that this laser trimming method can also be applicable to other material devices such as LiNbO₃ and yttrium-aluminum-garnet (YAG), where waveguide birefringence control is a crucial factor in achieving the practical performance of the device     

Single-pass Raman generation pumped by a mode-locked laser

Single-pass Raman generation pumped by a mode-locked Nd:YAG laser is investigated for long-span and low-loss fibres. The peak wavelength of the first Stokes jumps dramatically from 1.114 ?m to 1.12 ?m at 1.65 W average input power. The first Stokes increases rapidly between the inputs of 1.65 W and 2.1 W. These characteristics of single-pass stimulated Raman scattering are discussed in terms of group velocity matching.     

OH-ion distribution profiles in rod preforms of high-silica optical waveguide

To investigate the OH-contamination mechanism in high-silica optical waveguide, we have measured optically OH-ion distribution profiles in rod preforms prepared by the c.v.d. technique. The contamination due to OH diffusion from the supporting silica tube was clarified in relation to the deposited barrier-glass-layer thickness.     

Real-time measurement of implanted deuterons by using the nuclear reaction H(d,p)H

We propose a method for real-time measurement of the density of implanted deuterons in solid materials during deuterium implantation. In this method, the density of implanted deuterons is measured by detecting the emitted protons from the deuteron fusion reaction between the incident deuterons and the implanted deuterons. A negative deuterium beam with an energy of 90 keV is used both for the implanted atoms and a probe beam to measure the implanted deuterons. The density of the implanted deuterium atoms was observed to be drastically different between the single crystal and poly-crystal in Ta.     

Effectiveness and limitations of the fallback I algorithm for transient supraventricular tachyarrhythmias in DDD pacing

To examine the function of the fallback I algorithm (Chorus I, Ela Medical Inc., Montrouge, France), which automatically changes the DDD mode to VDI during transient supraventricular tachyarrhythmias to prevent high-rate tracking of the venticule, a total of 45 patients who were preoperatively diagnosed with sick-sinus syndrome (SSS) (Group 1; n = 19) or with advanced or complete atrioventricular block (AVB) (Group 2; n = 26) were followed up and analyzed. Mean follow-up times (mean +/- SD) were 22.4 +/- 9.7 and 12.4 +/- 10.9 months, respectively. Each of the groups was further divided into subgroups according to the preoperative existence of of paroxysmal atrial fibrillation (PAF) or paroxysmal supraventricular tachyarrhythmia (PSVT). During follow-up, the fallback started through a given cycle of ventricular pacing at a upper-rate limit (URL) to avoid a continuous high-rate tracking during the arrhythmias specifically in the patients with PSVT (0/4) (p = 0.0004). The fallback, however, sometimes started in the patients who had AVB not associated with either PAF or PSVT (4/21) during normal exercise because the fallback algorithm did not distinguish a normal P wave from the abnormal atrial waves. To further clarify the behavior of the fallback, a treadmill test was conducted in 25 of the 45 patients. The fallback start was observed in 12 of the 17 patients with AVB (Group 2). In such patients, the use of a long fallback delay and/or a high URL setting prevented the fallback starts during normal exercise. These results suggest that, in DDD pacing, the algorithm in Chorus I is useful in patients with SSS or AVB to avoid highrate tracking of the ventricle during transient supraventricular tachyarrhythmias, but special care must be taken to avoid the fallback starts during the normal exercise in AVB patients.     

VAD single-mode fibres with high ?n values

VAD single-mode fibres even with relative refractive-index difference ?n higher than 0.5% show low-loss properties, indicating the high potential of the VAD method to produce zero-dispersion fibres in the 1.55 ?m wavelength region.     

Nucleation mechanism of polyhydroxybutyrate and poly(hydroxybutyrate‐co‐hydroxyhexanoate) crystallized by orotic acid as a nucleating agent

The mechanism involved in the crystallization of bacterial polyhydroxybutyrate (PHB) and poly(hydroxybutyrate‐co‐hydroxyhexanoate) P(HB‐co‐HH) induced by orotic acid as a nucleant was investigated by using differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and proton nuclear magnetic resonance spectroscopy (¹H‐NMR). GPC measurements both carried on solvent cast and hot pressed samples did not show any significant drop of the molecular weight caused by the addition of the nucleant, indicating that no chemical reaction happened during the nucleation process. This result was confirmed by ¹H‐NMR analysis of oligohydroxybutyrate (OHB) treated with an excess amount of orotic acid. The possibility of epitaxial growth of the polymer crystal on the surface of the nucleant crystal was then investigated. It was found that there is an outstanding crystalline lattice matching between the plane (100) of the PHB crystal and the plane (001) of the orotic acid crystal. In comparison, the matching obtained with conventional nucleating agents, such as boron nitride and talc, was worse. Moreover, some regular hydrogen bonds between the polyester and orotic acid could stabilize the physical process. According to these results, the physical mechanism involving the epitaxial matching between orotic acid and PHB appears to be the most probable nucleation mechanism. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010