PROCESS FOR FABRICATION OF YTTERBIUM DOPED OPTICAL FIBER

摘要

The present invention provides a process for fabrication of ytterbium (Yb) doped optical fiber through vapor phase doping technique. The method comprises deposition of Al2O3 and Yb2O3 in vapor phase simultaneously in combination with silica during formation of sintered core layer. This is followed by collapsing at a high temperature in stepwise manner to produce the preform and drawing of fibers of appropriate dimension. The process parameters have been optimized in such a way that Al and Yb-chelate compounds can be transported to the reaction zone without decomposition and condensation of precursor materials. Thus variations of dopants concentration along the length of the preform have been minimized to <1% and good repeatability of the process has also been achieved. The resulting fibers also have smooth core-clad boundary devoid of any star-like defect. The process can be reliably adopted for fabrication of large core Yb doped optical fibers. The fibers also show low loss, negligible center dip and good optical properties suitable for their application as fiber lasers.

主权项

1. A process for fabrication of ytterbium (Yb) doped optical fiber through vapor phase doping technique, said process comprising the steps of:
depositing pure silica cladding layers inside a silica glass substrate tube at a temperature in the range of 1900 to 1980° C. using MCVD process; (ii) sublimating AlCl3 and Yb(thd)3 in their respective sublimator chamber at a temperature in the range of 100 to 170° C. and 180 to 260° C. respectively to obtain Al-precursors and Yb-precursors; (iii) introducing preheated Helium in the sublimator chamber of step (ii) at a flow rate in the range of 10 to 50 sccm for Al precursors and 100 to 300 sccm for Yb precursors; (iv) transporting Al and Yb precursors with Helium obtained in step (iii) to the substrate tube with the adjustment of temperature of a ribbon burner in the range of 180-370° C.; (v) passing O2 gas into a SiCl4 bubbler at a temperature in the range of 15 to 40° C. and a flow rate in the range of 80 to 150 sccm to transport SiCl4—O2 gas mixture to the substrate tube; (vi) mixing SiCl4, O2, Al precursors, Yb-precursors, and Helium in the substrate tube followed by concurrent oxidation to form SiO2, Al2O3 and Yb2O3; (vii) depositing a sintered core layer comprising SiO2—Al2O3—Yb2O3 with targeted Al2O3 and Yb2O3 concentrations to obtain a deposited tube; (viii) collapsing the deposited tube at a temperature in the range of 1900 to 2300° C. to obtain a fabricated preform; and (ix) drawing fibers from the fabricated preform obtained in step (viii) to obtain ytterbium (Yb) doped optical fiber.