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Structural relaxations in fiber cores and claddings with various fluorine concentrations were investigated. It was found that structural relaxation in the core is strongly affected by that in the cladding and this effect leads to an approach to control structural relaxation in fiber core for reducing the Rayleigh scattering loss in optical fibers.

Limit of the Rayleigh scattering loss in Ge-doped silica core fiber was estimated from the results of structural relaxation and the Rayleigh scattering measurements, and the most suitable fiber-drawing condition to reduce the Rayleigh scattering loss was determined. An annealing furnace, which could be attached to a fiber-drawing tower, was developed for realizing the optimum fiber-drawing condition. Drawing tests with this furnace confirmed our estimation of the loss. [ABSTRACT FROM AUTHOR]

Long-period fibre grating (LPFG) writing by a CO2 laser-annealing using a fibre-drawing process is demonstrated. The fibre in the drawing process was irradiated periodically by a CO2 laser to modify the refractive index. An LPFG with transmission loss of -10 dB and full width at half-maximum of 13 nm has been fabricated. Results show that the refractive index change was induced by stress at the moment of laser annealing. [ABSTRACT FROM AUTHOR]

The limit of the Rayleigh scattering and total losses in silica fiber was determined from the results of the Rayleigh scattering and structural relaxation measurements. Annealing condition during fiber drawing was optimized, and much potential to reduce the Rayleigh scattering loss has been verified. Total loss can be reduced below 0.15 dB/km at 1.55 μm, for example, even when annealing time is 0.1 s. Total loss below 0.14 dB/km can be realized by increasing the annealing time. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]