Refractive Index Variations and Long-Period Fiber Gratings Made by the Glass Structure Change

Katsumi MORISHITA
Shi Feng YUAN
Yoshihiro MIYAKE
Takahiro FUJIHARA

Publication
IEICE TRANSACTIONS on Electronics   Vol.E86-C    No.8    pp.1749-1758
Publication Date: 2003/08/01
Online ISSN: 
DOI: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Optoelectronics
Keyword: 
refractive index change,  fiber grating,  glass structure,  rapid solidification,  optical device fabrication,  

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Summary: 
It is shown that the glass structure change is a simple and widely applicable method to modify refractive index locally in various glass fibers. A small part of a glass fiber is heated immediately to above its melt temperature by arc discharge, and then the molten fiber undergoes rapid cooling, which freezes the change of the glass structure. Therefore the refractive index of the fiber is decreased partially by the glass structure change induced by rapid solidification. The index reduction in a fiber fabricated from multicomponent glasses is estimated to be more than 0.006. To clarify that rapid solidification works for various glasses including silica glasses, long-period gratings are written in a standard telecommunication fiber with various discharge currents and times. The peak loss of more than 25 dB is obtained within only 6 periods. The index change can be adjusted by the discharge conditions. The gratings are not degraded by heating the whole gratings at 700C for 2 hours, and are highly temperature-stable. It is shown that resonance wavelengths can be tuned by controlling the heating temperature and heating time.