Gotaro Tanaka

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.

Preparation of Large Single Crystal Thin Film of Polydiacetylene by Graphoepitaxy

The crystal growth of a diacetylene monomer was investigated by graphoepitaxy, an orientation-controlled crystal growth using a substrate with an artificial surface pattern. The direction of crystal growth was controlled by grooves prepared on a part of a fused-silica substrate surface and single crystal growth followed it on a non-grooved area next to the grooves. A large single crystal thin film with the domain size of approximately 2 x 2 mm was finally obtained. The thin film could be polymerized by UV light irradiation without any morphological change. The obtained polydiacetylene thin film was large enough to apply in an optical waveguide for nonlinear optical devices.

Characteristics of pure silica core single-mode fiber

Abstract Single-mode fibers with low attenuation and sufficient reliability are especially important for long-span optical transmission systems. Conventionally, GeO2 has been added to the fiber core region in order to make a refractive index difference between the core and cladding. However, the addition of GeO2 increases Rayleigh scattering loss [1], and deteriorates the chemical stability against hydrogen atmosphere and γ-ray irradiation to bring about an increase in attenuation. [2][3] Therefore, pure silica core single-mode fiber was considered to be an ideal type of fiber, and it was succeeded in being fabricated by utilizing fluorine containing SiO2 cladding.

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.

Radiation-resistant characteristics of image fiber

γ ray irradiated characteristics of radiation resistant image fiber was mainly studied, and also core material and cladding material were investigated. We have got the following result.