Semiconductor laser device having a diffraction grating on a light reflection side

• US 20020154665A1
• Filed: 10/23/2001
• Published: 10/24/2002
• Est. Priority Date: 04/19/2001
• Status: Active Grant

• Current Assignee: Furukawa Electric Company Limited
• Original Assignee: Furukawa Electric Company Limited
• Inventors: Tsukiji, Naoki, Yoshida, Junji, Funabashi, Masaki
• Granted Patent: US 6,614,823 B2
• Time in Patent Office: Days
• US Class Current: 372/45
• CPC Class Codes: H01S 3/094003 the pumped medium being a fibre
• CPC Class Codes: H01S 3/09415 the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
• CPC Class Codes: H01S 5/1021 Coupled cavities H01S5/14 takes precedence
• CPC Class Codes: H01S 5/1039 Details on the cavity length
• CPC Class Codes: H01S 5/125 Distributed Bragg reflector [DBR] lasers
• CPC Class Codes: H01S 5/141 using a wavelength selective device, e.g. a grating or etalon H01S5/146 takes precedence
• CPC Class Codes: H01S 5/146 using a fiber as external cavity

Abstract

A semiconductor device includes an active layer configured to radiate light, a light reflecting facet positioned on a first side of the active layer, a light emitting facet positioned on a second side of the active layer thereby forming a resonant cavity between the light reflecting facet and the light emitting facet, and a partial diffraction grating having a predetermined length and positioned on a light reflecting side of the resonator. The predetermined length of the partial diffraction grating is selected such that the semiconductor device emits a light beam having a plurality of longitudinal modes within a predetermined spectral width of an oscillation wavelength spectrum of the semiconductor device. The predetermined length of the partial diffraction grating may be set in relation to a length of the resonant cavity, or in relation to a coupling coefficient of the diffraction grating. The semiconductor device may also include another partial diffraction grating positioned on the light emitting side of the laser device.

Claims

1. A semiconductor device comprising:

an active layer configured to radiate light;

a light reflecting facet positioned on a first side of said active layer;

a light emitting facet positioned on a second side of said active layer thereby forming a resonant cavity between said light reflecting facet and said light emitting facet; and

a partial diffraction grating having a predetermined length and positioned on a light reflecting side of said resonator, wherein said predetermined length of said partial diffraction grating is selected such that said semiconductor device emits a light beam having a plurality of longitudinal modes within a predetermined spectral width of an oscillation wavelength spectrum of the semiconductor device.

2. The semiconductor device of claim 1, wherein said light reflecting facet is configured to have a reflectivity of no more than 5%.

3. The semiconductor device of claim 1, wherein said light reflecting facet is configured to have a reflectivity of no less than 80%.

4. The semiconductor device of claim 1, wherein said light emitting facet is configured to have a reflectivity of no more than 5%.

5. The semiconductor device of claim 1, wherein said predetermined length of said partial diffraction grating is set in relation to a length of said resonant cavity.

6. The semiconductor device of claim 5, wherein said predetermined length of said partial diffraction grating is set to meet the inequality:

Lgr≦

1/2L,

where Lgr is the predetermined length of the partial diffraction grating in μ

m, and

L is the length of the resonant cavity in μ

m.

7. The semiconductor device of claim 6, wherein said predetermined length of said partial diffraction grating is approximately ½

L.

8. The semiconductor device of claim 1, wherein said predetermined length of said partial diffraction grating is set in relation to a coupling coefficient of said diffraction grating.

9. The semiconductor device of claim 8, wherein said predetermined length of said partial diffraction grating is set to meet the inequality:

κ

i·

Lgr≧

2,

where κ

i is the coupling coefficient of the partial diffraction grating, and

Lgr is the length of the partial diffraction grating.

10. The semiconductor device of claim 9, wherein said predetermined length of said partial diffraction grating is set such that κ

i·

Lgr is approximately equal to 2.

11. The semiconductor device of claim 8, wherein

said partial diffraction grating has a thickness tgr, a distance from the active layer dsp, and a diffraction grating composition wavelength λ

gr, and

at least one of the parameters tgr, dsp, and λ

gr is a predetermined value such that the coupling coefficient λ

i is set in relation to the grating length Lgr.

12. The semiconductor device of claim 1, wherein said partial diffraction grating comprises a plurality of grating elements having a predetermined pitch such that said oscillation wavelength spectrum has a center wavelength in the range of 1100 nm-1550 nm.

13. The semiconductor laser device of claim 12, wherein said pitch of said partial diffraction grating is configured such that said center wavelength is a shorter wavelength than a peak wavelength of the gain spectrum determined by said active layer.

14. The semiconductor laser device of claim 12, wherein said pitch of said partial diffraction grating is configured such that said center wavelength is a longer wavelength than a peak wavelength of the gain spectrum determined by said active layer.

15. The semiconductor device of claim 1, further comprising another partial diffraction grating positioned on the light emitting side of the laser device.

16. The semiconductor device of claim 15, wherein a reflectivity of each of said light reflecting and light emitting facets is no greater than 5%.

18. The method of claim 17, wherein said step of providing a light reflecting facet comprises providing a light reflecting facet having a reflectivity of no more than 5%.

19. The method of claim 17, wherein said step of providing a light reflecting facet comprises providing a light reflecting facet having a reflectivity of no less than 80%.

20. The method of claim 17, wherein said step of providing a light emitting facet comprises providing a light emitting facet having a reflectivity of no more than 5%.

21. The method of claim 17, wherein said step of selecting said predetermined length comprises setting said predetermined length of said partial diffraction grating in relation to a length of said resonant cavity.

22. The method of claim 21, wherein said step of setting said predetermined length comprises setting the predetermined length to meet the inequality:

Lgr≦

1/2L,

where Lgr is the predetermined length of the partial diffraction grating in μ

m, and

L is the length of the resonant cavity in μ

m.

23. The method of claim 22, wherein said step of setting said predetermined length comprises setting the predetermined length to be approximately equal to ½

L.

24. The method of claim 17, wherein said step of selecting said predetermined length comprises setting said predetermined length of said partial diffraction grating in relation to a coupling coefficient of said diffraction grating.

25. The method of claim 24, wherein said step of setting the predetermined length comprises setting the predetermined length of said partial diffraction grating to meet the inequality:

κ

i·

Lgr≧

2,

where κ

i is the coupling coefficient of the partial diffraction grating, and

Lgr is the length of the partial diffraction grating.

26. The method of claim 25, wherein said step of setting the predetermined length comprises setting the predetermined length of said partial diffraction grating approximately equal to 2.

27. The method of claim 24, further comprising setting at least one of a thickness tgr the partial diffraction grating, a distance dsp from the active layer to the partial diffraction grating, and a diffraction composition wavelength λ

gr of the partial diffraction grating such that a coupling coefficient κ

i is set to a predetermined value.

28. The method of claim 17, wherein said step of providing a partial diffraction grating comprises providing a plurality of grating elements having a predetermined pitch such that said oscillation wavelength spectrum has a center wavelength in the range of 1100 nm-1550 nm.

29. The method of claim 28, wherein said step of providing a plurality of grating elements having a predetermined pitch comprises setting the predetermined pitch such that said center wavelength is a shorter wavelength than a peak wavelength of the gain spectrum determined by said active layer.

30. The method of claim 28, wherein said step of providing a plurality of grating elements having a predetermined pitch comprises setting the predetermined pitch such that said center wavelength is a longer wavelength than a peak wavelength of the gain spectrum determined by said active layer.

31. The method of claim 17, further comprising providing another partial diffraction grating positioned on the light emitting side of the laser device.

32. The method of claim 31, wherein said steps of providing a light reflecting facet and providing a light emitting facet comprise providing a light reflecting facet and a light emitting facet each having a reflectivity of no more than 5%.

17. A method for providing light from a semiconductor device comprising:

radiating light from an active layer of said semiconductor device;

providing a light reflecting facet positioned on a first side of said active layer;

providing a light emitting facet positioned on a second side of said active layer thereby forming a resonant cavity between said light reflecting facet and said light emitting facet;

providing a partial diffraction grating having a predetermined length and positioned on a light reflection side of said resonator; and

selecting said predetermined length of said partial diffraction grating such that said semiconductor device emits a light beam having a plurality of longitudinal modes within a predetermined spectral width of an oscillation wavelength spectrum of the semiconductor device.

33. A semiconductor device comprising:

means for radiating light;

means for reflecting said radiated light positioned on a first side of said means for radiating light;

means for emitting light positioned on a second side of said means for radiating light to thereby form a resonant cavity between said means for reflecting light and said means for emitting light; and

means for selecting a portion of said radiated light to be emitted by said semiconductor laser device as an output light beam; and

means for ensuring said output light beam has an oscillation wavelength spectrum having a plurality of longitudinal modes located within a predetermined spectral width of the oscillation wavelength spectrum.

34. The semiconductor device of claim 33, further comprising means for ensuring that each of the plurality of longitudinal modes within a predetermined spectral width of an oscillation wavelength spectrum of the semiconductor device has substantially the same threshold gain.

36. The semiconductor laser module of claim 35, further comprising an internal isolator interposed between said semiconductor laser device and said waveguide device.

37. The semiconductor laser module of claim 35, further comprising a temperature control device configured to control a temperature of the semiconductor laser device.

35. A semiconductor laser module comprising:

a semiconductor laser device comprising;

an active layer configured to radiate light;

a light reflecting facet positioned on a first side of said active layer;

a light emitting facet positioned on a second side of said active layer thereby forming a resonant cavity between said light reflecting facet and said light emitting facet; and

a partial diffraction grating having a predetermined length and positioned on a light reflecting side of said resonator, wherein said predetermined length of said partial diffraction grating is selected such that said semiconductor device emits a light beam having a plurality of longitudinal modes within a predetermined spectral width of an oscillation wavelength spectrum of the semiconductor device; and

a waveguide device for guiding said laser beam away from the semiconductor laser device.

38. An optical fiber amplifier comprising:

a semiconductor laser device comprising;

an active layer configured to radiate light;

a light reflecting facet positioned on a first side of said active layer;

a light emitting facet positioned on a second side of said active layer thereby forming a resonant cavity between said light reflecting facet and said light emitting facet; and

a partial diffraction grating having a predetermined length and positioned on a light reflecting side of said resonator, wherein said predetermined length of said partial diffraction grating is selected such that said semiconductor device emits a light beam having a plurality of longitudinal modes within a predetermined spectral width of an oscillation wavelength spectrum of the semiconductor device; and

an amplifying fiber coupled to said semiconductor laser device and configured to amplify a signal by using said light beam as an excitation light.

39. A wavelength division multiplexing system comprising:

a transmission device configured to provide a plurality of optical signals having different wavelengths;

an optical fiber amplifier coupled to said transmission device and including a semiconductor laser device comprising;

an active layer configured to radiate light;

a light reflecting facet positioned on a first side of said active layer;

a light emitting facet positioned on a second side of said active layer thereby forming a resonant cavity between said light reflecting facet and said light emitting facet; and

a partial diffraction grating having a predetermined length and positioned on a light reflecting side of said resonator, wherein said predetermined length of said partial diffraction grating is selected such that said semiconductor device emits a light beam having a plurality of longitudinal modes within a predetermined spectral width of an oscillation wavelength spectrum of the semiconductor device; and

a receiving device coupled to said optical fiber amplifier and configured to receive said plurality of optical signals having different wavelengths.

40. A Raman amplifier comprising:

a semiconductor laser device comprising;

an active layer configured to radiate light;

a light reflecting facet positioned on a first side of said active layer;

a light emitting facet positioned on a second side of said active layer thereby forming a resonant cavity between said light reflecting facet and said light emitting facet; and

a partial diffraction grating having a predetermined length and positioned on a light reflecting side of said resonator, wherein said predetermined length of said partial diffraction grating is selected such that said semiconductor device emits a light beam having a plurality of longitudinal modes within a predetermined spectral width of an oscillation wavelength spectrum of the semiconductor device; and

a fiber coupled to said semiconductor laser device and configured to carry a signal that is amplified based on said light beam being applied to said fiber.