Influence of fusing on the uniformity of the distribution of Yb^3+ ions and the formation of clusters in silica with phosphorus admixture synthesized by SPCVD

Abstract

The loss spectra of slab lightguides with Yb-activated P-doped silica cores are studied in the 320-1050 nm wavelength range. Two or three layer lightguiding structures were synthesized by surface-plasma chemical vapor deposition (SPCVD) of doped SiO2 on the inner surface of a substrate silica tube. The glass in the first and the third layer contained ~3.5 mol. % fluorine and functioned as reflecting cladding. The second (intermediate) layer contained ~0.5 mol. % phosphorus and ytterbium and served as a lightguiding core. Slab lightguides 20 mm in length were cut lengthwise from the wall of the substrate tube with the deposited silica layers before and after their fusing by external heating in the flame of an oxygen-hydrogen burner at a temperature of ~1600°C. The fusing of the synthesized SPCVD amorphous silicon dioxide with phosphorous leads to an increase in the size of clusters constituting YbPO4, which is responsible for the significant increase of the scattering loss of the lightguides.