Optical fiber coupling arrangement

• US 20060187541A1
• Filed: 03/15/2006
• Published: 08/24/2006
• Est. Priority Date: 02/11/2003
• Status: Active Grant

• Current Assignee: Andrei Starodoumov
• Original Assignee: Andrei Starodoumov
• Inventors: Starodoumov, Andrei
• Granted Patent: US 7,286,283 B2
• Time in Patent Office: Days
• US Class Current: 359/341.320
• CPC Class Codes: H01S 3/06708 Constructional details of the fibre, e.g. compositions, cross-section, shape or tapering optical fibres as passive waveguides G02B6/02
• CPC Class Codes: H01S 3/094003 the pumped medium being a fibre

Abstract

Apparatus for optically pumping a clad amplifier fiber includes one or more transmission fibers arranged and configured to insert pump-light from a pump light source such as a diode-laser into the cladding of the amplifier fiber. The pump light propagates through the cladding and a portion of the pump light is absorbed in the doped core of the amplifier fiber. At least one of the transmission fibers is arranged to receive an unabsorbed portion of the propagated pump light from the amplifier cladding and re-insert the unabsorbed portion of the pump-light into the cladding for re-propagation through the cladding. This provides that pump light that would otherwise be wasted is circulated through the amplifier fiber for further absorption by the amplifier core.

Claims

1. An optical amplification apparatus comprising:

a source of light to be amplified, the light having a first wavelength;

a optical fiber isolator for transmitting said first wavelength light;

a conversion fiber for receiving said first wavelength light from the first fiber isolator and converting at least a portion of said first wavelength light into light at a second wavelength;

a second optical fiber isolator for receiving light transmitted from said conversion fiber and for transmitting said second wavelength light while directing unconverted first wavelength light out of the apparatus; and

a power amplifier for receiving and amplifying said converted light and wherein said first optical fiber isolator also functions to prevent any light at said second wavelength reflected from or generating by the power amplifier from reaching said light source.

2. An apparatus as recited in claim 1, wherein said first optical fiber isolator includes a fiber having a core surrounded by a cladding and configured so that the light at said second wavelength is directed out of the core.

3. An apparatus as recited in claim 2, wherein said first optical isolator is one of a blazed fiber Bragg grating, a slanted fiber Bragg grating, and a long period fiber Bragg grating.

4. An apparatus as recited in claim 1, wherein said first fiber isolator includes an optical fiber doped with ions that absorb light at said second wavelength and transmit light at said first wavelength.

5. An optical amplification apparatus comprising:

a fiber laser generating light having a first wavelength;

a optical fiber isolator for transmitting said first wavelength light;

an conversion fiber for receiving said first wavelength light from the first fiber isolator and converting at least a portion of said first wavelength light into light at a second wavelength by a stokes shift;

a second optical fiber isolator for receiving light transmitted from said conversion fiber and for transmitting said second wavelength light while directing unconverted first wavelength light out of the apparatus; and

a power fiber amplifier for receiving and amplifying said converted light and wherein said first optical fiber isolator also functions to prevent any light at said second wavelength reflected from or generating by the power amplifier from reaching said light source.

6. An apparatus as recited in claim 5, wherein said first optical fiber isolator includes a fiber having a core surrounded by a cladding and configured so that the light at said second wavelength is directed out of the core.

7. An apparatus as recited in claim 6, wherein said first optical isolator is one of a blazed fiber Bragg grating, a slanted fiber Bragg grating, and a long period fiber Bragg grating.

8. An apparatus as recited in claim 5, wherein said first fiber isolator includes an optical fiber doped with ions that absorb light at said second wavelength and transmit light at said first wavelength.

9. A method for amplifying light from a source thereof, the light having a first wavelength, the method comprising the steps of:

coupling the light into a first optical fiber having a core surrounded by cladding such that the first-wavelength light propagates along said core in a forward direction;

converting, in a first length of said first optical fiber, at least a portion of the first-wavelength light to light having a second wavelength, different from the first wavelength;

selectively coupling said second-wavelength light from said core of said first optical fiber into a second optical fiber in a manner such that coupling of first wavelength light into said second optical fiber is minimized;

transmitting said second wavelength light along said second optical fiber to an optical amplifier;

amplifying said second wavelength light in said optical amplifier, said amplification causing second wavelength light to be reflected, and amplified spontaneous emission at said second wavelength be to emitted, propagating in a reverse direction along said second optical fiber back into said core of said first optical fiber; and

selectively coupling at least at least a portion of said reflected second wavelength light and emitted amplified spontaneous emission out of said core of said first optical fiber, thereby preventing said portion of said reflected second wavelength light and emitted amplified spontaneous emission from reaching the source of the first wavelength light.

10. The method of claim 9, wherein said portion of said second-wavelength light is coupled into said second optical fiber via a wavelength-selective fiber coupler having first and second output arms, said second-wavelength light being coupled into said second optical fiber through said first arm of said wavelength-selective fiber coupler, with residual first-wavelength light being directed out of said first optical fiber via said second arm of said a wavelength-selective fiber coupler, thereby preventing said residual first-wavelength light from reaching the optical amplifier.

11. The method of claim 9, wherein at least a portion of said reflected second-wavelength light and amplified spontaneous emission is coupled out said core of said first optical fiber via a wavelength-selective device located in said first optical fiber between the light source and the length of said first optical fiber in which first-wavelength light is converted to second wavelength light.

12. The method of claim 11, wherein said wavelength selective device is a wavelength-selective fiber coupler and said portion of said reflected second-wavelength light and amplified spontaneous emission is coupled out said core of said first optical fiber via an unconnected output arm of said wavelength-selective fiber coupler.

13. The method of claim 11, wherein said wavelength-selective device is a fiber Bragg grating written into said core of said first optical fiber and arranged to direct said portion of said reflected second-wavelength light and amplified spontaneous emission out of said core into said cladding of said first optical fiber.

14. The method of claim 13, wherein said fiber Bragg grating is a blazed fiber Bragg grating.

15. The method of claim 13, wherein said fiber Bragg grating is a long-period fiber Bragg grating.

16. The method of claim 13, wherein said fiber Bragg grating is a slanted fiber Bragg grating.

17. The method of claim 11, wherein said wavelength-selective device is provided by a second length of said first optical fiber wherein said core thereof is doped with ions that absorb said portion of said reflected second-wavelength light and amplified spontaneous emission.

18. The method of claim 17, wherein said ions are samarium ions.

19. Optical amplification apparatus comprising:

a source of light to be amplified, the light having a first wavelength;

a first optical fiber having a core surrounded by cladding and arranged to transmit light along said core to a second optical fiber, said second optical fiber being arranged to convert at least a portion of the first wavelength light to light having a second wavelength, different from the first wavelength;

an optical fiber isolator formed in said first optical fiber between said light source and said second optical fiber and arranged to direct second wavelength light out of said first optical fiber core;

said second optical fiber being connected to a wavelength selective fiber coupling device arranged to couple second wavelength light into a third optical fiber for transmission to an optical amplifier, while directing unconverted first wavelength light out of the apparatus; and

wherein one of said second wavelength light reflected from said optical amplifier and amplified spontaneous emission emitted by said optical amplifier having a wavelength about equal to said second wavelength, propagates back along said third optical fiber, is coupled by said wavelength selective coupler into said second optical fiber, propagates through said second optical fiber into said first optical fiber core, and at least a portion thereof is prevented by said fiber isolator from propagating further in said first optical fiber core.

20. The apparatus of claim 19, wherein said optical isolator is one of a blazed fiber Bragg grating, a slanted fiber Bragg grating, and a long period fiber Bragg grating.