<title>All-silica optical fibers with reduced losses beyond two microns</title>

Abstract

The newly developed optical fibers are described designed to transmit intense radiation in the visible and near IR spectral regions. The main characteristic feature of the fibers is a core made of unique purity silica with extremely low OH content not exceeding 20 ppb. As a result, the fiber spectral attenuation in the infrared is substantially reduced: the absorption spectrum is a smooth monotonously rising curve with typical loss levels of less than 0.2 dB/m at 2.1, 10 dB/m--at 2.7 and 27 dB/m--at 2.8 microns. Thin (approx. 10% of the fiber diameter) fluorinated silica cladding together with the high purity core ensure excellent optical damage resistivity of the fibers and greatly facilitate their coupling to high power lasers. The plasma outside deposition technology used for clad fabrication can provide fluorine doping levels sufficient to produce the fibers with numerical aperture NA up to 0.24. The fibers can have either hermetic metal (In, Sn, Pb, Zn, Al) or plastic protective coating. For the Al-coated fibers the mechanical properties and environmental durability are characterized by the following figures: tensile strength--more than 7 GPa, minimal bend radius--40 times the fiber radius (long term), operating environment--from--196 up to 400 degree(s)C, 100% humidity.