Process of fabrication of Erbium and Ytterbium-co-doped multi-elements silica glass based cladding-pumped fiber

A process for fabricating erbium and ytterbium-co-doped multi-elements silica glass based cladding-pumped fiber for use as an optical amplifier, the process comprising the steps of:

• a) depositing a pure SiO2 synthetic cladding within a silica glass substrate tube to obtain match clad structure;
• b) forming a porous core layer inside the silica glass substrate tube by depositing a fluorinated-phospho silica porous soot layer using a flow of O2/POCl3 in a range of 800 to 900 sccm and SF6 in a range of 25 to 35 sccm, at a temperature in a range of 1420-1455° C. and maintaining a burner speed a range of 28-35 mm/min;
• c) pre-sintering the deposited fluorinated-phospho silica porous soot layer at a temperature in a range of 1075-1125° C. by keeping the burner speed in a range of 305-315 mm/min in a forward direction to maintain a uniform porosity;
• d) soaking the pre-sintered fluorinated-phospho silica porous soot layer into an alcoholic solution for one hour, wherein the alcoholic solution comprises AlCl3 6H2O in a range of 0.12 to 0.15 (M), ErCl3 6H2O in a range of 0.02 to 0.023(M), YbCl3 6H2O in a range of 0.25 to 0.28 (M), CeCl3 7H2O in a range of 0.003 to 0.0035(M) and H3BO3 in a range of 0.5 to 0.75(M);
• e) drying the soaked fluorinated-phospho silica porous soot layer under flow of an inert Ar gas for 30 to 45 minutes;
• f) incorporating Er2O3, Yb2O3, P2O5, F, CeO2, Al2O3 and B2O3 into the dried fluorinated-phospho silica porous soot layer in the presence of O2 and He at a temperature within a range of 700-850° C. for efficient oxidation to form the core layer;
• g) dehydrating the core layer at a temperature in a range of 850 to 900° C. in presence of Cl2 and O2 to form a porous dried core layer;
• h) sintering the porous core layer in presence of a mixture of O2 and He at a temperature in a range of 1350 to 1890° C. with flow of O2/GeCl4 and O2/POCl3 to form a final core layer;
• i) repeating steps (b) to (h) 2-3 times to form the final core layer of a thickness in a range of 10.0-11.5 μm;
• j) collapsing the silica glass substrate tube having the final core layer at a temperature in a range of 2000 to 2250° C. with the flow of POCl3 to obtain an Er/Yb codoped multi-elements silica glass based optical preform of 10.0±0.1 mm diameter;
• k) increasing the preform diameter from 10.0±0.1 mm to 18.5±0.1 mm through an overcladding process using a thick silica tube at a temperature in a range of 2200 to 2400° C. to form an overcladded preform;
• l) grinding the overcladded preform to a grinding length in a range of 0.72-0.75 mm from a periphery of the overcladded preform at each point of eight positions separated by equal distances followed by polishing of each grinded sides to form an octagonal shaped preform;
• and
• m) drawing an octagonal cladding shaped Er/Yb doped fiber from the octagonal shaped preform using a PC 375L AP compound as a low RI resin coating at a preform feed down speed in a range of 0.6 to 0.7 mm/min and at a fiber drawing speed in a range of 20-25 m/min.