Process for fabrication of ytterbium doped optical fiber

Patent metadata

Field	Value
Publication number	US-10040714-B2
Application number	US-201414888930-A
Country	US
Kind code	B2
Filing date	Mar 26, 2014
Priority date	May 3, 2013
Publication date	Aug 7, 2018
Grant date	Aug 7, 2018

Abstract

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.

First claim

We claim:

1. A process for fabrication of ytterbium (Yb) doped optical fiber through vapor phase doping technique, said process comprising the steps of:
(i) depositing pure silica cladding layers inside a silica glass substrate tube at a main burner temperature in the range of 1900 to 1980° C. using MCVD process;
(ii) sublimating AlCl 3 and Yb(thd) 3 in their respective sublimator chambers at a temperature in the range of 100 to 170° C. and 180 to 260° C. respectively to obtain vapors of Al-precursors and Yb-precursors;
(iii) introducing preheated Helium in the sublimator chambers 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 silica glass substrate tube with the adjustment of temperature of a ribbon burner in the range of 180-370° C., wherein the ribbon burner is fixed before the input end of the silica glass substrate tube;
(v) passing O 2 gas into a SiCl 4 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 SiCl 4 —O 2 gas mixture to the silica glass substrate tube;
(vi) mixing SiCl 4 , O 2 , Al precursors, Yb-precursors, and Helium in the silica glass substrate tube followed by concurrent oxidation to form SiO 2 , Al 2 O 3 and Yb 2 O 3 ;
(vii) depositing a sintered core layer comprising SiO 2 —Al 2 O 3 —Yb 2 O 3 with targeted Al 2 O 3 and Yb 2 O 3 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.

2. The process as claimed in claim 1 , wherein in step (i) 4-10 pure silica cladding layers are deposited in the silica glass substrate tube.

3. The process as claimed in claim 1 , wherein in step (i) the main burner temperature is in the range of 1910-1960° C.

4. The process as claimed in claim 1 , wherein in step (ii) the sublimating temperature for AlCl 3 is in the range of 120 to 160° C.

5. The process as claimed in claim 1 , wherein in step (ii) the sublimating temperature for Yb(thd) 3 is in the range of 200 to 240° C.

6. The process as claimed in claim 1 , wherein in step (iv) the temperature of the ribbon burner is in the range of 200-350° C.

7. The process as claimed in claim 1 , wherein in step (vii) the number of core layers is in the range of 1 to 40.

8. The process as claimed in claim 1 , wherein in step (vii) the main burner temperature of deposition of sintered core layer is in the range of 1770 to 1920° C.

9. The process as claimed in claim 8 , wherein in step (vii) the main burner temperature of deposition of sintered core layer is in the range of 1820-1880° C.

10. The process as claimed in claim 1 , wherein in step (vii) the sintered core layer is deposited with the main burner traverse speed in the range of 9 to 14 cm/min, wherein the main burner traverses along the length of the silica glass substrate tube.

11. The process as claimed in claim 1 , wherein in step (ix) the NA (Numerical aperture) of the core glass is in the range of 0.06 to 0.32.

12. The process as claimed in claim 1 , wherein in step (ix) the Al 2 O 3 content of the fiber is in the range of 0.5 to 18 mol %.

13. The process as claimed in claim 1 , wherein in step (ix) the Yb 2 O 3 concentration of the fiber is in the range of 0.2 to 2.0 mol %.

14. The process as claimed in claim 1 , wherein in step (ix) the Yb 2 O 3 concentration of the fiber is in the range of 0.25 to 1.25 mol %.

15. The process as claimed in claim 1 , wherein in step (viii) the collapsing temperature is in the range of 2050-2250° C.

16. The process as claimed in claim 1 , wherein the length of the fabricated preforms is up to 45 cm.

17. The process as claimed in claim 1 , wherein the core diameter of the fabricated fiber is in the range of 10 to 50 μm out of 125 μm overall diameter.

Assignees

• Council Scient Ind Res
• Department Of Electronics And Information Tech

Inventors

• Sen Ranjan
• Saha Maitreyee

Classifications

• C03B37/025

  from reheated softened tubes, rods, fibres or filaments {, e.g. drawing fibres from preforms (draw-down of tubes, rods or preforms to reduced diameter preforms C03B37/0124)} · CPC title

• C03B2207/50

  Multiple burner arrangements · CPC title

• C03B2207/81

  Constructional details of the feed line, e.g. heating, insulation, material, manifolds, filters · CPC title

• C03B2201/36

  doped with rare earth metals and aluminium, e.g. Er-Al co-doped · CPC title

• C03B37/01815

  Reactant deposition burners or deposition heating means · CPC title