Nobuo Inagaki

Formation and disappearance of defect centers in GeO 2 -doped silica fibers with heat treatments

Electronic state changes of defect centers in Ge-doped SiO 2 fibers were investigated using ESR technique. The germanium associated defects, especially Ge(3) centers, are mainly produced during the drawing process and are quenched in the fibers. The heat treatment of the Ge-doped fiber causes a remarkable decrease in the Ge(3) ESR intensity, subsequently causing OH absorption loss increase. The mechanism of this OH loss increase is proposed, in relation to the interactions between the Ge(3) centers and hydrogen.

Fabrication of dispersion-free VAD single-mode fibers in the 1.5-µm wavelength region

Low-loss and low-dispersion single-mode fibers in the 1.5- μm wavelength region were fabricated by the VAD method. Causes for loss increase in these fibers were investigated. By improving uniformities in the refractive index, both in core section and along the core axis, minimum loss of 0.35 dB/km at 1.55 μm was obtained. Bending loss of the 1.5-μm optimized single-mode fiber was also discussed.

On-line monitoring technique of the refractive-index profile in the VAD process

A nondestructive on-line monitoring method to estimate the refractive-index profile in vapor-phase axial deposition (VAD) processing has been developed. This technique is developed on the basis of the deposition properties of a SiO 2 -GeO 2 glass particles in the flame hydrolysis reaction. The profile monitoring accuracy is pm 7 times 10^{-5} in refractive-index difference. The estimated profiles during the porous preform fabrication are well coincided with those of the consolidated preform. The average bandwidth properties of graded-index fibers produced by adjusting the fabrication conditions, to be optimized with using present method, is 2.5 GHz . km0.9at 1.3-μm wavelength.

Invited) Recent Progress in VAD Fiber Fabrication Process

Since the development of the Vapor-phase Axial Deposition (VAD) process in 1977, rapid progress has been made in the improvement of transmission properties by the analysis of the above process. This paper describes the progress in the fabrication process for attaining better transmission characteristics and future aspects of this process. Specific characteristics obtained in this process are: reduction in the transmission loss of fibers by the optimal material composition and dehydration technique, the realization of less than 1 ppb of OH content, a bandwidth that now exceeds 6 GHz-km at 1.3 µm, which was attained through the analytical studies of the profile formation mechanism and the controlling of the deposition condition, and the production of long low-loss graded-index fibers.

High-speed coating and coating materials for optical fibers

The performance properties of optical fibers, e.g., transmission losses and strength, are strongly influenced by the fiber drawing, coating, and jacketing processes and by the coating and Jacketing materials used. Also the cost reduction of optical fibers requires the speedup of these processes and the use of inexpensive coating and jacketing materials together with the speedup of fiber preform production.