Tapered composite optical fiber and method of making the same

• US 5,729,643 A
• Filed: 05/12/1997
• Issued: 03/17/1998
• Est. Priority Date: 04/05/1996
• Status: Expired due to Term

• Current Assignee: Lumenis Incorporated (Boston Scientific Corporation)
• Original Assignee: Coherent Inc (Coherent Corp.)
• Inventors: Lovato, Paul, Mehl, Ron C., Hmelar, Michael
• Primary Examiner(s): Lee, John D.
• Assistant Examiner(s): KIM, ELLEN E
• Application Number:
  US08/855,770
• Time in Patent Office: 309 Days
• Field of Search: 385/43, 385/51, 385/95-99
• US Class Current: 385/43
• CPC Class Codes: G02B 6/2551 using thermal methods, e.g. fusion welding by arc discharge, laser beam, plasma torch
• CPC Class Codes: G02B 6/2552 reshaping or reforming of light guides for coupling using thermal heating, e.g. tapering, forming of a lens on light guide ends
• CPC Class Codes: G02B 6/262 Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements

Abstract

A composite optical fiber including a first optical fiber having a first core with a first diameter being optically fused to a second optical fiber having a second core with a second diameter that is smaller than the first diameter. The first optical fiber has an output end with a tapered end section. The first core tapers down in diameter in the tapered end section from the first diameter and terminates at the output end with a third diameter that is smaller than the first diameter and substantially equal to or smaller than the second diameter. The second fiber has an input end that is optically fused to the output end of the first fiber. The composite optical fiber of the present invention is formed by heating the output end of the first optical fiber, and then pulling the output end of the first optical fiber to form the tapered end section. The output end of the first optical fiber is then optically fused to the input end of the second optical fiber.

Claims

1. A composite optical fiber, comprising:

a first optical fiber having a first core made of a first core material surrounded by a first cladding made of a first cladding material, said first core and cladding having a main body and a tapered end section that terminates in an output end, with the output end having first core and cladding diameters that are smaller than the first core and cladding diameters respectively of the main body; and

a second fiber having a second core made of a second core material surrounded by a second cladding made of a second cladding material with second core and cladding diameters that are substantially equal to or greater than the first core and cladding diameters respectively of the output end of the first optical fiber, but are less than the first core and cladding diameters respectively of the first optical fiber main body, and having an input end that isoptically fused to the output end of the first fiber;

wherein each of said first and second fibers having an intrinsic numerical aperture of at least 0.29 as defined by;

(n²_core -n²_cladding)^1/2, where n_core is the refractive index of the fiber core material for light having a wavelength of 2.1 um, and n_cladding is the refractive index of the fiber cladding material for light having a wavelength of 2.1 um.

2. The composite optical fiber of claim 1, further comprising:

a first buffer surrounding the first cladding that terminates before the tapered end section of the first fiber;

a second buffer surrounding the second cladding that terminates before the input end of the second fiber; and

a protective layer surrounding the first and second claddings and extending from the first buffer to the second buffer.

3. The composite optical fiber of claim 2, wherein the first and second fibers are made of the same materials.

4. The composite optical fiber of claim 3, wherein the first and second cores are made of germanium oxide doped quartz, and the first and second claddings are made of pure silica.

5. The composite optical fiber of claim 1, further comprising:

a third optical fiber having a third core surrounded by a third cladding, said third core and cladding having a second main body and a second tapered end section that terminates in a second input end, with the second input end having third core and cladding diameters that are smaller than the third core and cladding diameters respectively of the second main body, wherein said second core and cladding diameters of said second fiber being substantially equal to or less than the third core and cladding diameters respectively of the second input end of the third optical fiber, said second fiber having an output end that is optically fused to the second input end of the third fiber.

6. A method of forming a composite optical fiber, comprising the steps of:

heating an output end of a first optical fiber having a first core made of a first core material with a first core diameter surrounded by a first cladding made of a first cladding material with a first cladding diameter;

pulling the heated output end of the first optical fiber to form a tapered end section of the first optical fiber wherein the first core and cladding terminate at the output end with a second core diameter and a second cladding diameter that are smaller than the first core diameter and first cladding diameter respectively; and

optically fusing the output end to an input end of a second optical fiber that has a second core made of a second core material with a third core diameter surrounded by a second cladding made of a second cladding material with a third cladding diameter, the third core and cladding diameters are substantially equal to or greater than the second core and cladding diameters respectively, but are less than the first core and cladding diameters respectively, of the first optical fiber;

wherein each of said first and second fibers having an intrinsic numerical aperture of at least 0.29 as defined by;

(n²_core -n²_cladding)^1/2, where n_core is the refractive index of the fiber core material for light having a wavelength of 2.1 um, and n_cladding is the refractive index of the fiber cladding material for light having a wavelength of 2.1 um.

7. The method of claim 6 further comprising the step of:

stripping back a first buffer surrounding the first fiber away from the output end before the heating step.

8. The method of claim 7 further comprising the step of:

cleaving the output end of the first fiber before the optically fusing step.

9. The method of claim 7 further comprising the step of:

polishing the output end of the first fiber before the optically fusing step.

10. The method of claim 7 further comprising the step of:

cleaving and polishing the output end of the first fiber before the optically fusing step.

11. The method of claim 7 further comprising the step of:

forming a protective layer around the tapered section of the first fiber.

12. The method of claim 6 further comprising the steps of:

heating an input end of a third optical fiber having a third core with a fourth core diameter surrounded by a third cladding with a fourth cladding diameter;

pulling the heated output end of the third optical fiber to form a tapered end section of the third optical fiber wherein the third core and cladding terminates at the input end of the third optical fiber with fifth core and cladding diameters that are smaller than the fourth core and cladding diameters respectively; and

optically fusing the input end of the third fiber to an output end of the second optical fiber, wherein the third core and cladding diameters of the second core and cladding are substantially equal to or less than the fifth core and cladding diameters respectively of the third optical fiber.

13. A method of forming a composite optical fiber that includes a first optical fiber having a first core made of a first core material with a first core diameter surrounded by a first cladding made of a first cladding material with a first cladding diameter and a first buffer, and a second optical fiber having a second core made of a second core material with a second core diameter surrounded by a second cladding made of a second cladding material with a second cladding diameter and a second buffer, the first core and cladding diameters are greater than the second core and cladding diameters respectively, the first fiber having an output end and the second fiber having an input end, each of said first and second fibers having an intrinsic numerical aperture of at least 0.29 as defined by:

(n²_core -n²_cladding)^1/2, where n_core is the refractive index of the fiber core material for light having a wavelength of 2.1 um, and n_cladding is the refractive index of the fiber cladding material for light having a wavelength of 2.1 um, comprising the steps of;

heating the first optical fiber adjacent the output end;

pulling the heated output end of the first optical fiber to form a tapered end section wherein the first core and cladding terminate at the output end with third core and cladding diameters that are smaller than the first core and cladding diameters respectively and substantially equal to or less than the second core and cladding diameters respectively of the second optical fiber; and

optically fusing the output end of the first optical fiber to the input end of the second optical fiber.

14. The method of claim 13 further comprising the steps of:

stripping back a portion of the first buffer adjacent to the output end of the first fiber; and

stripping back a portion of the second buffer adjacent to the input end of the second fiber.

15. The method of claim 14 further comprising the steps of:

cleaving the output end of the first fiber before the optically fusing step.

16. The method of claim 14 further comprising the steps of:

polishing the output end of the first fiber before the optically fusing step.

17. The method of claim 14 further comprising the steps of:

cleaving and polishing the output end of the first fiber before the optically fusing step.

18. The method of claim 14 further comprising the step of:

forming a protective layer around the tapered section of the first fiber.