S-band light sources using erbium-doped fiber with depressed cladding

1. A source of light in an S-band of wavelengths comprising:

a) a fiber having:

1) a core doped with Erbium and having a core cross-section and a refractive index n o ;

2) a depressed cladding surrounding said core, said depressed cladding having a depressed cladding cross-section and a refractive index n 1 ;

3) a secondary cladding surrounding said depressed cladding, said secondary cladding having a secondary cladding cross-section and a refractive index n 2 ;

b) a pump source for pumping said Erbium contained in said core to a high relative inversion D, such that said Erbium exhibits positive gains in said S-band and high gains in a long wavelength band longer than said S-band;

wherein said core cross-section, said depressed cladding cross-section, and said refractive indices n o , n 1 , and n 2 are selected to produce losses at least comparable to said high gains in said long wavelength band and losses substantially smaller than said positive gains in said S-band.

2. The source of claim 1 , further comprising a wavelength-selecting means for selecting an output wavelength of said light.

3. The source of claim 2 , wherein said wavelength-selecting means comprises a wavelength-selecting feedback mechanism.

4. The source of claim 3 , wherein said wavelength-selecting feedback mechanism comprises a fiber Bragg grating.

5. The source of claim 2 , wherein said wavelength-selecting means consists of a filter selected from the group consisting of tilted etalons, strain-tuned fiber Bragg gratings, temperature-tuned fiber Bragg gratings, interferometers, arrays waveguide gratings, diffraction gratings and tunable coupled cavity reflectors.

6. The source of claim 2 , wherein said wavelength-selecting means comprises a pump source adjustment for tuning said high relative inversion D.

7. The source of claim 2 , wherein said wavelength-selecting means comprises a coiling diameter of said fiber.

8. The source of claim 7 , wherein said coiling diameter is continuously variable.

9. The source of claim 1 , further comprising a master oscillator for seeding said fiber.

10. The source of claim 9 , wherein said master oscillator is an optical source selected from the group consisting of distributed feedback laser, Fabry-Perot laser, external cavity diode laser, distributed Bragg reflector laser, vertical cavity surface emitting laser, semiconductor laser, a fiber laser, a broadband source.

11. The source of claim 1 , wherein said fiber comprises:

a) a first section having a first coiling diameter; and

b) a second section having a second coiling diameter larger than said first coiling diameter.

12. The source of claim 11 , wherein said first section is positioned before said second section for seeding said second section.

13. The source of claim 12 , further comprising an isolator installed between said first section and said second section.

14. The source of claim 1 , wherein said fiber comprises:

a) a first section wherein said core cross-section, said depressed cladding cross-section, and said refractive indices n o , n 1 , and n 2 are selected to produce a first cutoff wavelength λ c1 ;

b) a second section wherein said core cross-section, said depressed cladding cross-section, and said refractive indices n o , n 1 , and n 2 are selected to produce a second cutoff wavelength λ c2 longer than said first cutoff wavelength λ c1 .

15. The source of claim 14 , wherein said first section is positioned before said second section for seeding said second section.

16. The source of claim 15 , further comprising an isolator installed between said first section and said second section.

17. The source of claim 1 , wherein said pump source comprises a laser diode providing pump light at about 980 nm.

18. The source of claim 1 , further comprising an optical cavity for containing said fiber.

19. The source of claim 18 , wherein said optical cavity is a ring cavity.

20. A method for generating light in an S-band of wavelengths comprising:

a) providing a fiber having a core doped with Erbium and having a core cross-section and a refractive index n o ;

b) surrounding said core with a depressed cladding having a depressed cladding cross-section and a refractive index n 1 ;

c) surrounding said depressed cladding with a secondary cladding having a secondary cladding cross-section and a refractive index n 2 ;

d) pumping said Erbium contained in said core to a high relative inversion D, such that said active material exhibits positive gains in said S-band and high gains in a long wavelength band longer than said S-band;

wherein said core cross-section, said depressed cladding cross-section, and said refractive indices n o , n 1 , and n 2 are selected to produce losses at least comparable to said high gains in said long wavelength band and losses substantially smaller than said positive gains in said S-band.

21. The method of claim 20 , wherein said step of pumping comprises counter-propagating pumping.

22. The method of claim 20 , further comprising seeding said fiber.

23. The method of claim 22 , wherein said fiber comprises a first section and a second section, and said method comprises seeding said second section by said first section.

24. The method of claim 20 , wherein said pumping is performed in a pulsed mode.

25. The method of claim 20 , wherein said light in said S-band is combined with a light outside said S-band.