Hiroo Kanamori

Long-period fiber grating in a pure-silica-core fiber written by residual stress relaxation

Summary form only given. Long-period fiber gratings (LPFGs) have recently been attracting much attention for their possible applications such as gain-flattening filters for erbium-doped fiber amplifiers. Most LPFGs have been written in germanosilicate optical fibers because periodic structures can be easily obtained using UV-induced refractive-index changes due to the photosensitivity of Ge-related glass defects. This technique requires that fibers for LPFGs should contain photosensitive sites, and thus it cannot be applied to those which have no photoreaction centers inside such as pure-silica core optical fibers. Here we report the efficient fabrication of LPFGs in pure-silica-core optical fibers by residual stress relaxation. We also present the thermal dependence of the loss peak of the LPFG.

High-performance dispersion-compensating fibers

Abstract An optimum fiber structure for a practical dispersion-compensating fiber (DCF) has been explored theoretically and experimentally, taking dispersion, attenuation, bending loss characteristics, polarization mode dispersion, and nonlinear effects into account. A high figure of merit (FOM) of 280 ps/nm/dB has been successfully achieved with a simple matched cladding design. Furthermore, it was confirmed that the optimized structure with enhanced FOM also benefits self-phase modulation (SPM) suppression.

Ultra-Low-Loss Pure-Silica-Core Single-Mode Fiber and Transmission Experiment

A single mode (SM) fiber with extremely low loss and sufficient long term reliability is indispensable for the coming ultra long span optical transmission system. As a promising candidate for such a high grade fiber, a pure silica core SM fiber has been introduced.(1) Owing to the absence of additional metal oxide to the core region, the proposed fiber features the low transmission loss due to low Rayleigh scattering and the increased chemical stability against hydrogen.

Optimization of dispersion-compensating fibers considering self-phase modulation suppression

Summary form only given. In summary, we have explored the optimized structure of dispersion compensated fibers (DCFs) based on actual performances considering self phase modulation (SPM) in DCFs, and it was confirmed that optimized structure with enhanced figure of merit (FOM) also benefits SPM suppression.

Characterization of fluoride glasses for single-mode optical fibers with large refractive index difference

Abstract In order to obtain fluoride glass optical fibers with large refractive index difference between the core and the cladding, refractive indices and viscosities of PbF2-doped core glasses and HfF4-incorporated cladding glasses were systematically investigated. From the point of view of viscosity matching, it was found that the 9 mol% PbF2-doped core glass containing 14 mol% NaF was the most adequate choice in combination with the 43 mol% HfF4-incorporated cladding glass containing 22 mol% NaF. Using a casting method, single-mode fluoride glass fibers with relative refractive index difference of 2.9% were successfully fabricated.

Thermal and mass analyses of fluorination process with ammonium bifluoride

Mixtures of ZrO 2 or ZBLAN/NH 4 FHF were mainly analyzed in the range of room temperature to 600 o C by TG-DTA and mass spectroscopy simultaneously in order to determine the best temperature for the fluorination process. Four endothermic peaks with weight reduction were found by TG-DTA, and clearly assigned by mass spectrum. The first peak around 100 o C is caused by the ZrO 2 /NH 4 FHF reaction, and the second to fourth peaks are attributed to decomposition of (NH 4 ) x-4 ZrF x

Adequate aging condition for fiber Bragg grating based on simple power law model

Summary form only given. In summary, we have examined thermal decay of fibre Bragg gratings (FBG) for wide temperature and time range. Decay fitted well to a simple power law, and temperature dependence of decay suggests that the accelerated aging condition can be used to test for long-term reliability. This analysis is simpler than previous models and useful for decay estimation.

Study of fluorine doping during vapour-phase axial deposition sintering process

The fluorine doping process of pure silica “soot” with various type of fluorine gases in the vapour-phase axial deposition (VAD) sintering process was investigated in detail. This investigation showed that the doping level is proportional to the 1/4 power of the concentration of the fluorine gas, and the achievable reduction of relative refractive index is −0.75% with this process. The kinetic investigation clarified that the fluorine doping process consists of the doping and dissociation reactions; the former reaction obeys the 1/2 power of the SiF4 partial pressure and the latter the two power of fluorine content [SiO1.5F], where SiO1.5F represents a silicon tetrahedron consisting of one fluorine and three bridging oxygen atoms in glass. The fluorine content is proportional to the 1/4 power of the SiF4 partial pressure at an equilibrium where the doping reaction is in competition with the dissociation reaction.

Fluorine doping in the VAD sintering process

Fluorine is an attractive dopant for silica based optical fibers because it reduces the refractive index of silica glass without any additional loss as opposed to a boron dopant.1 A typical example of the fluorine-doped fiber Is a depressed cladding single-mode fiber. The fiber was fabricated by a direct flame hydrolysis of SiCl4 in the presence of fluorine containing dopant in the VAD method. The maximum depression of the refractive index [Δn(F)] was −0.22%.2

Dispersion-shifted fibers with fluorine-added cladding by the vapor phase axial deposition method

Dispersion-shifted single-mode fibers operated in the 1.5-μm region, where silica-based fibers exhibit the lowest loss and zero chromatic dispersion simultaneously, are extremely attractive for high-bit-rate transmission systems with a long repeater spacing. Recently, several research institutions have reported structure designs of dispersion-shifted single-mode fibers based on a triangular-index profile core to reduce microbending sensitivity.1,2 These designs require a high level of GeO2, which leads to increased Rayleigh scattering loss. The fiber structure with a cladding depressed by adding fluorine can reduce the level of GeO2 but results in a leakage loss increase of the fundamental mode.