Extra-High Pressure in the Core of Silica-Based Optical Fiber Preforms during the Manufacturing Process

Abstract

The core refractive index n2 of silica-based optical fiber preform heated to 2000 °C was determined experimentally for the first time. The measurements were carried out in the process of preform temperature reduction. It was shown that n2 could increase up to ~1.75 in the visible spectral range at temperatures of ~2000 °C (n2 ≈ 1.46 at room temperature). This fact suggests that pressures close to or exceeding the ultimate strength of silica glass (~20 GPa) occur in the preform core region. The local extra pressure is argued to be a possible cause of the well-known “starburst” phenomenon at the core–cladding interface of preforms with certain core compositions. The observed effect of radial cracks can be interpreted as the result of silica cladding destruction under the action of extra-high pressure in the core.

Keywords

• MCVD technology
• FCVD technology
• core–cladding interface
• refractive index of core
• silica glass
• “starbursts” in fiber preforms