Abstract

Processes that remove water and/or prevent it from diffusing into the silica matrix are required for the production of “low-water peak” optical fiber (LWPF). As demand for LWPF increases, fiber makers have resorted to new materials and manufacturing steps to reach more difficult attenuation specifications for this fiber type.

The appearance of the “water peak” in conventional optical fibers has historically eliminated wavelengths between 1360 and 1460 nm, about 30% of the available channels, due to high light attenuation. The water peak appears because hydrogen, which readily diffuses through the glass matrix of an optical fiber, is trapped at defects in the glass structure, forming hydroxyl groups that cause attenuation at these wavelengths. Many fiber manufacturers are focused on making LWPF as a means to provide the most light-carrying capacity for their products. Production volumes of LWPF are expected to show a compound annual growth rate of greater than 20% from 2004–2007.

A concentration of several parts per billion (ppb) of hydroxyl groups in a conventional single mode fiber core causes the attenuation for wavelengths around the water peak to be several times higher than that at lower or higher wavelengths. Process improvements that allow the manufacture of low-water peak fiber require water levels in the glass to be reduced from 10 ppb to less than 1 ppb.

© 2005 Optical Society of America