Tunable diode laser system, apparatus and method

• US 20020018496A1
• Filed: 08/27/2001
• Published: 02/14/2002
• Est. Priority Date: 09/14/1998
• Status: Active Grant

• Current Assignee: Inter Science GmbH
• Original Assignee: Inter Science GmbH
• Inventors: Gutin, Mikhail A.
• Granted Patent: US 6,671,295 B2
• Time in Patent Office: Days
• US Class Current: 372/20
• CPC Class Codes: H01S 3/105 by controlling the mutual position or the reflecting properties of the reflectors of the cavity , e.g. by controlling the cavity lengthH01S3/10076, H01S3/13 take precedence
• 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 5/143 Littman-Metcalf configuration, e.g. laser - grating - mirror

Abstract

Disclosed herein, in all embodiments of the invention, is a tunable laser system comprising wavelength separation means for separating incoming light into wavelength-separated light; optical focusing means for focusing the wavelength-separated light into a plurality of single-wavelength focal spots; and locally-controllable reflectivity array means comprising a plurality of individually-controllable localized reflective elements each corresponding to and reflecting one of the plurality of single-wavelength focal spots. A frequency matching embodiment further comprises wavelength filtering means for substantially allowing wavelengths the incoming light which are separated from one another by a specified optical frequency difference to emerge as filtered light, while substantially barring all other wavelengths. The light separated the wavelength separation means comprises this filtered light. A CW embodiment further comprises focal spot elongation means for elongating the wavelength-separated light into a plurality of elongated, single-wavelength focal spots; and the locally-controllable reflectivity array means comprises a plurality of sets of a plurality of individually-controllable localized reflective elements; each set corresponding to and reflecting one of the elongated, single-wavelength focal spots.

Claims

1. A tunable laser system, comprising:

wavelength filtering means for substantially allowing wavelengths of incoming light emitted from an active media which are separated from one another by a specified optical frequency difference to emerge therefrom as filtered light, and for substantially barring all other said wavelengths of said incoming light from emerging therefrom;

wavelength separation means for separating said filtered light emerging from said wavelength filtering means, into wavelength-separated light comprising a plurality of separate component wavelengths of said filtered light;

optical focusing means for focusing said separate component wavelengths of said wavelength-separated light into a plurality of single-wavelength focal spots, wherein each one of said single-wavelength focal spots is focused, but is displaced from, all others of said single-wavelength focal spots, within a common focal plane of said optical focusing means; and

locally-controllable reflectivity array means comprising a plurality of individually-controllable localized reflective elements residing substantially within said common focal plane of said optical focusing means, each of said localized reflective elements corresponding to and reflecting one of said plurality of said single-wavelength focal spots in a manner determined by a setting of said localized reflective element.

2. The system of claim 1, further comprising control module means for:

determining which of said single-wavelength focal spots is to be selected for retro-reflection back toward said active media;

causing each localized reflective element for which the corresponding wavelength is selected for retro-reflection to be set such that said corresponding selected wavelength is retro-reflected back toward said active media, as a retro-reflecting reflective element; and

causing each localized reflective element for which the corresponding wavelength is not selected for retro-reflection to be set such that said corresponding not-selected wavelength is not retro-reflected back toward said active media, as a non-retro-reflecting reflective element.

3. The system of claim 1, said wavelength filtering means comprising a Fabry-Perot etalon.

4. The system of claim 1, said wavelength filtering means comprising a tunable Fabry-Perot interferometer.

5. The system of claim 1, said wavelength filtering means comprising means for tuning said specified optical frequency difference and thus said filtered light emerging therefrom.

6. The system of claim 1, wherein said specified optical frequency difference of said wavelength filtering means is chosen so as to substantially match frequencies of a laser light output of said system to a predetermined set of optical frequencies.

7. The system of claim 6, wherein said specified set of optical frequencies is predetermined according to requirements of a telecommunications standard.

8. The system of claim 1, wherein:

a focal length f of said optical focusing means is chosen to be substantially equal to;

$f=\frac{a}{\mathrm{\Delta <br><br>\beta <br><br>}}=\frac{a·<br><br>c·<br><br>d·<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}}{{\mathrm{\lambda <br><br>}}^2·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>v},$

where Δ

ν

is a desired frequency difference for a laser light output of said system, d is a period of said wavelength separation means, a is a pitch of said locally-controllable reflectivity array means, λ

is a central wavelength of said incoming light, m is an order of said wavelength separation means used for separating said filtered light into said wavelength-separated light, and β

is deduced according to

$\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\alpha <br><br>}+\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}=m<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{\mathrm{\lambda <br><br>}}{d},$

where α

is a angle of incidence of said filtered light onto said wavelength separation means;

a distance between said wavelength separation means and said optical focusing means is chosen to be substantially equal to said focal length f; and

a distance between said optical focusing means and said locally-controllable reflectivity array means is chosen to be substantially equal to said focal length f.

9. The system of claim 1, said locally-controllable reflectivity array means further comprising a plurality of localized selective elements also residing substantially within said common focal plane of said optical focusing means, each said localized selective element corresponding with one of said localized reflective elements, and said localized selective elements separated from said corresponding localized reflective elements by no more than a maximum coplanarity separation distance h;

wherein;

said maximum coplanarity separation distance h is determined by maintaining an ambiguity Δ

ν

of an optical frequency ν

of said system to be less than a threshold percentage of an output frequency spacing of said system;

wherein

$\mathrm{\Delta <br><br>\upsilon <br><br>}=\frac{c}{{\mathrm{\lambda <br><br>}}^2}·<br><br>d<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}·<br><br>\frac{\mathrm{Dh}}{f^2}$

And wherein;

λ

Is a central wavelength of said incoming light, c is the speed of light, d is a period of said wavelength separation means, D is a diameter of said optical focusing means, f is focal length of said optical focusing means, and β

is a diffraction angle of said wavelength-separated light from said wavelength separation means; and

wherein

said threshold percentage is equal to approximately 15 percent.

10. The system of claim 2, used for simultaneously selecting a plurality of wavelengths for lasing;

further comprising control module means for;

determining a plurality of said single-wavelength focal spots to be selected for simultaneous retro-reflection back toward said active media;

causing the localized reflective elements corresponding to said wavelengths so-selected for simultaneous retro-reflection back toward said active media to be set such that said corresponding wavelength is retro-reflected back toward said active media; and

causing the remaining localized reflective elements corresponding to said wavelengths not so-selected for simultaneous retro-reflection back toward said active media to be set such that said corresponding wavelength is not retro-reflected back toward said active media.

11. The system of claim 2, used for sequentially selecting a plurality of sets of wavelengths for lasing;

further comprising control module means for;

determining a plurality of sets of at least zero of said single-wavelength focal spots to be selected for sequential retro-reflection back toward said active media, as sequential selected wavelength sets;

at a first given moment, and again at a different, second given moment, causing the localized reflective elements corresponding to said wavelengths so-selected at the given moment for retro-reflection back toward said active media to be set such that said corresponding wavelengths are retro-reflected back toward said active media; and

at said first given moment, and again said second given moment, causing the remaining localized reflective elements corresponding to said wavelengths not so-selected at the given moment for retro-reflection back toward said active media to be set such that said corresponding wavelengths are not retro-reflected back toward said active media.

12. The system of claim 1, said active media comprising a laser diode.

13. The system of claim 1, wherein at least one of said localized reflective elements is set to retro-reflect one of said single-wavelength focal spots back toward said active media, further comprising:

amplification means for amplifying said single-wavelength focal spots retro-reflected by said locally-controllable reflectivity array means, for lasing at the wavelengths of the retro-reflected light.

14. The system of claim 1, said wavelength separation means comprising diffraction means for diffracting said filtered light into said wavelength-separated light.

15. The system of claim 1, said optical focusing means comprising a focusing element selected from the focusing element group consisting of lenses and mirrors.

16. The system of claim 1:

said locally-controllable reflectivity array means comprising a micromirror array; and

said plurality of individually-controllable localized reflective elements comprising a plurality of individually-controllable micromirrors.

17. The system of claim 2:

said locally-controllable reflectivity array means comprising a micromirror array;

said plurality of individually-controllable localized reflective elements comprising a plurality of individually-controllable micromirrors;

said control module means for causing each said retro-reflecting reflective element to be set comprising control module means for causing each micromirror for which the corresponding wavelength is selected for retro-reflection to be set in a first state such that said corresponding selected wavelength is retro-reflected back toward said active media; and

said control module means for causing each said non-retro-reflecting reflective element to be set comprising control module means for causing each micromirror for which the corresponding wavelength is not selected for retro-reflection to be set in a second state such that said corresponding not-selected wavelength is not retro-reflected back toward said active media.

19. The system of claim 18, further comprising control module means for:

determining which of said elongated, single-wavelength focal spots is to be selected for retro-reflection back toward said active media;

causing at least one localized reflective element within each set of localized reflective elements for which the corresponding wavelength is selected for retro-reflection to be set such that its portion of its corresponding selected wavelength is retro-reflected back toward said active media, as a retro-reflecting reflective element set;

causing at least one localized reflective element within each set of localized reflective elements for which the corresponding wavelength is not selected for retro-reflection to be set such that its portion of its corresponding not-selected wavelength is not retro-reflected back toward said active media, as non-retro-reflecting reflective element sets; and

within any retro-reflecting reflective element set, determining which of said localized reflective elements are caused to be set to retro-reflect based upon at least one power output characteristic of a laser light output of said system.

20. The system of claim 18, wherein said at least one power output characteristic comprises maintaining substantially constant output power of said laser light output.

21. The system of claim 18, wherein said at least one power output characteristic comprises controlling a power output for at least one wavelength of said laser light output.

22. The system of claim 19, said control module further comprising means for causing at least one first localized reflective element within each said retro-reflecting reflective element set to be set such that it does not retro-reflect its said corresponding wavelength back toward said active media at a first given time, and for causing at least one second localized reflective element different from said first localized reflective element within each said retro-reflecting reflective element set to be set such that it does not retro-reflect its said corresponding wavelength back toward said active media at a second given time different from said first given time, thereby exercising said first and second localized reflective elements to avoid stiction that would otherwise result from continuously maintaining said first and second localized reflective elements in a retro-reflecting state.

23. The system of claim 19, said control module further comprising means for causing at least one first localized reflective element within each said non-retro-reflecting reflective element set to be set such that it does retro-reflect its said corresponding wavelength back toward said active media at a first given time, and for causing at least one second localized reflective element different from said first localized reflective element within each said non-retro-reflecting reflective element set to be set such that it does retro-reflect its said corresponding wavelength back toward said active media at a second given time different from said first given time, thereby exercising said first and second localized reflective elements to avoid stiction that would otherwise result from continuously maintaining said first and second localized reflective elements in a non-retro-reflecting state.

24. The system of claim 18, said optical focusing means and said focal spot elongation means comprising a single optical element.

25. The system of claim 24, said single optical element comprising an aspheric lens.

26. The system of claim 18, further comprising:

wavelength filtering means for substantially allowing wavelengths of said incoming light emitted from said active media which are separated from one another by a specified optical frequency difference to emerge therefrom as filtered light, and for substantially barring all other said wavelengths of said incoming light from emerging therefrom;

wherein;

said incoming light separated by said wavelength separation means comprises said filtered light.

27. The system of claim 18, wherein:

a focal length f of said optical focusing means is chosen to be substantially equal to;

$f=\frac{a}{\mathrm{\Delta <br><br>\beta <br><br>}}=\frac{a·<br><br>c·<br><br>d·<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}}{{\mathrm{\lambda <br><br>}}^2·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>v},$

where Δ

ν

is a desired frequency difference for a laser light output of said system, d is a period of said wavelength separation means, a is a pitch of said locally-controllable reflectivity array means, λ

is a central wavelength of said incoming light, m is an order of said wavelength separation means used for separating said filtered light into said wavelength-separated light, and β

is deduced according to

$\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\alpha <br><br>}+\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}=m<br><br>\frac{\mathrm{\lambda <br><br>}}{d},$

where α

is a angle of incidence of said filtered light onto said wavelength separation means;

a distance between said wavelength separation means and said optical focusing means is chosen to be substantially equal to said focal length f; and

a distance between said optical focusing means and said locally-controllable reflectivity array means is chosen to be substantially equal to said focal length f.

28. The system of claim 18, said locally-controllable reflectivity array means further comprising a plurality of localized selective elements also residing substantially within said common focal plane of said optical focusing means, each said localized selective element corresponding with one of said localized reflective elements, and said localized selective elements separated from said corresponding localized reflective elements by no more than a maximum coplanarity separation distance h;

wherein;

said maximum coplanarity separation distance h is determined by maintaining an ambiguity Δ

ν

of an optical frequency ν

of said system to be less than a threshold percentage of an output frequency spacing of said system;

wherein

$\mathrm{\Delta <br><br>\upsilon <br><br>}=\frac{c}{{\mathrm{\lambda <br><br>}}^2}·<br><br>d<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}·<br><br>\frac{\mathrm{Dh}}{f^2}$

and wherein;

λ

is a central wavelength of said incoming light, c is the speed of light, d is a period of said wavelength separation means, D is a diameter of said optical focusing means, f is focal length of said optical focusing means, and β

is a diffraction angle of said wavelength-separated light from said wavelength separation means; and

wherein

said threshold percentage is equal to approximately 15 percent.

29. The system of claim 19, used for simultaneously selecting a plurality of wavelengths for lasing;

further comprising control module means for;

determining a plurality of said elongated, single-wavelength focal spots to be selected for simultaneous retro-reflection back toward said active media, using a plurality of said reflective element sets corresponding with said focal spots so-selected;

causing at least one localized reflective element within each reflective element set selected for retro-reflection to be set such that its portion of its corresponding single-wavelength focal spot is retro-reflected back toward said active media; and

causing at least one localized reflective element within each reflective element set not selected for retro-reflection to be set such that its portion of its corresponding single-wavelength focal spot is not retro-reflected back toward said active media.

30. The system of claim 19, used for sequentially selecting a plurality of sets of wavelengths for lasing;

further comprising control module means for;

determining a plurality of sets of at least zero of said elongated, single-wavelength focal spots to be selected for sequential retro-reflection back toward said active media, as sequential selected wavelength sets;

at a first given moment, and again at a different, second given moment, causing at least one localized reflective element within each retro-reflecting reflective element set corresponding to the wavelengths so-selected at the given moment for retro-reflection to be set such that its portion of its corresponding single-wavelength focal spot is retro-reflected back toward said active media; and

at said first given moment, and again said second given moment, causing at least one reflective element within each non-retro-reflecting reflective element set corresponding to the wavelengths not so-selected at the given moment for retro-reflection back toward said active media to be set such that its portion of its corresponding single-wavelength focal spot is not retro-reflected back toward said active media.

31. The system of claim 18, said active media comprising a laser diode.

32. The system of claim 18, wherein at least one of said localized reflective elements is set to retro-reflect a portion of one of said elongated, single-wavelength focal spots back toward said active media, further comprising:

amplification means for amplifying said single-wavelength focal spots retro-reflected by said locally-controllable reflectivity array means, for lasing at the wavelengths of the retro-reflected light.

33. The system of claim 18, said wavelength separation means comprising diffraction means for diffracting said incoming light into said wavelength-separated light.

34. The system of claim 18, said optical focusing means comprising a focusing element selected from the focusing element group consisting of lenses and mirrors.

36. The system of claim 19:

said locally-controllable reflectivity array means comprising a micromirror array;

said plurality of sets of a plurality of individually-controllable localized reflective elements comprising a plurality of sets of a plurality of individually-controllable micromirrors;

said control module means for causing at least one localized reflective element within said retro-reflecting reflective element set to be set comprising control module means for causing at least one of said micromirrors within each said set of micromirrors for which the corresponding wavelength is selected for retro-reflection to be set in a first state such that its portion of its corresponding single-wavelength focal spot is retro-reflected back toward said active media; and

said control module means for causing at least one localized reflective element within said non-retro-reflecting reflective element sets to be set comprising control module means for causing at least one of said micromirrors for which the corresponding wavelength is not selected for retro-reflection to be set in a second state such that its portion of its corresponding single-wavelength focal spot is not retro-reflected back toward said active media.

38. The system of claim 37, further comprising control module means for:

determining which of said single-wavelength focal spots is to be selected for retro-reflection back toward said active media;

causing each micromirror for which the corresponding wavelength is selected for retro-reflection to be set in a first state such that said corresponding selected wavelength is retro-reflected back toward said active media, as a retro-reflecting micromirror; and

causing each micromirror for which the corresponding wavelength is not selected for retro-reflection to be set in a second such that said corresponding not-selected wavelength is not retro-reflected back toward said active media, as a non-retro-reflecting micromirror.

39. The system of claim 37, wherein said micromirror array is angled such that the micromirrors in said first state are substantially normal relative to a path of said single-wavelength focal spots.

40. The system of claim 39, wherein said micromirror array is angled at θ

degrees relative to said micromirrors in said first state and thus at 90-θ

degrees relative to said path of said single-wavelength focal spots, wherein said angle θ

is non-zero; and

said optical focusing means is oriented to be substantially parallel to said micromirrors in said first state and is thus angled at substantially 90-θ

degrees relative to said wavelength-separated light.

41. The system of claim 37, said optical focusing means comprising focus-improving means for substantially converting any elongation of a cross section of said single-wavelength focal spots into a substantially circular cross-section thereof.

42. The system of claim 41, said optical focusing means and said focus-improving means comprising a single optical element.

43. The system of claim 42, said single optical element comprising an aspheric lens.

44. The system of claim 37, wherein:

at least one of said micromirrors is set to retro-reflect one of said single-wavelength focal spots back toward said active media;

a laser light output of said system emerges from a zero order of said wavelength separation means; and

light retro-reflected by said micromirror array back toward said wavelength separation means emerges from a first order of said wavelength separation means back toward said active media.

45. The system of claim 37, wherein a laser light output thereof emerges from a rear facet of said active media.

46. The system of claim 37, wherein:

a focal length f of said optical focusing means is chosen to be substantially equal to;

$f=\frac{a}{\mathrm{\Delta <br><br>\beta <br><br>}}=\frac{a·<br><br>c·<br><br>d·<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}}{{\mathrm{\lambda <br><br>}}^2·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>v},$

where Δ

ν

is a desired frequency difference for a laser light output of said system, d is a period of said wavelength separation means, a is a pitch of said micromirror array, λ

is a central wavelength of said incoming light, m is an order of said wavelength separation means used for separating said filtered light into said wavelength-separated light, and β

is deduced according to

$\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\alpha <br><br>}+\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}=m<br><br>\frac{\mathrm{\lambda <br><br>}}{d},$

where α

is a angle of incidence of said filtered light onto said wavelength separation means;

a distance between said wavelength separation means and said optical focusing means is chosen to be substantially equal to said focal length f; and

a distance between said optical focusing means and said micromirror array is chosen to be substantially equal to said focal length f.

48. The method of claim 47, further comprising the steps of:

determining which of said single-wavelength focal spots is to be selected for retro-reflection back toward said active media;

causing each localized reflective element for which the corresponding wavelength is selected for retro-reflection to be set such that said corresponding selected wavelength is retro-reflected back toward said active media, as a retro-reflecting reflective element; and

causing each localized reflective element for which the corresponding wavelength is not selected for retro-reflection to be set such that said corresponding not-selected wavelength is not retro-reflected back toward said active media, as a non-retro-reflecting reflective element.

49. The method of claim 47, said wavelength filtering means comprising a Fabry-Perot etalon.

50. The method of claim 47, said wavelength filtering means comprising a tunable Fabry-Perot interferometer.

51. The method of claim 47, further comprising the step of tuning said specified optical frequency difference and thus said filtered light emerging from said wavelength filtering means.

52. The method of claim 47, further comprising the step of choosing said specified optical frequency difference of said wavelength filtering means so as to substantially match frequencies of a laser light output of said laser to a predetermined set of optical frequencies.

53. The method of claim 52, further comprising the step of predetermining said specified set of optical frequencies according to requirements of a telecommunications standard.

54. The method of claim 47, further comprising the steps of:

choosing a focal length f of said optical focusing means to be substantially equal to;

$f=\frac{a}{\mathrm{\Delta <br><br>\beta <br><br>}}=\frac{a·<br><br>c·<br><br>d·<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}}{{\mathrm{\lambda <br><br>}}^2·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>v},$

where Δ

ν

is a desired frequency difference for a laser light output of said laser, d is a period of said wavelength separation means, a is a pitch of said locally-controllable reflectivity array means, λ

is a central wavelength of said incoming light, m is an order of said wavelength separation means used for separating said filtered light into said wavelength-separated light, and β

is deduced according to

$\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\alpha <br><br>}+\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}=m<br><br>\frac{\mathrm{\lambda <br><br>}}{d},$

where α

is a angle of incidence of said filtered light onto said wavelength separation means;

choosing a distance between said wavelength separation means and said optical focusing means to be substantially equal to said focal length f; and

choosing a distance between said optical focusing means and said locally-controllable reflectivity array means to be substantially equal to said focal length f.

55. The method of claim 47, said locally-controllable reflectivity array means further comprising a plurality of localized selective elements also residing substantially within said common focal plane of said optical focusing means, each said localized selective element corresponding with one of said localized reflective elements, and said localized selective elements separated from said corresponding localized reflective elements by no more than a maximum coplanarity separation distance h;

further comprising the step of;

determining said maximum coplanarity separation distance h by maintaining an ambiguity Δ

ν

of an optical frequency ν

of said laser to be less than a threshold percentage of an output frequency spacing of said laser;

wherein

$\mathrm{\Delta <br><br>\upsilon <br><br>}=\frac{c}{{\mathrm{\lambda <br><br>}}^2}·<br><br>d<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}·<br><br>\frac{\mathrm{Dh}}{f^2}$

and wherein;

λ

is a central wavelength of said incoming light, c is the speed of light, d is a period of said wavelength separation means, D is a diameter of said optical focusing means, f is focal length of said optical focusing means, and β

is a diffraction angle of said wavelength-separated light from said wavelength separation means; and

wherein

said threshold percentage is equal to approximately 15 percent.

56. The method of claim 48, further comprising the step of simultaneously selecting a plurality of wavelengths for lasing, in turn comprising the steps of:

determining a plurality of said single-wavelength focal spots to be selected for simultaneous retro-reflection back toward said active media;

causing the localized reflective elements corresponding to said wavelengths so-selected for simultaneous retro-reflection back toward said active media to be set such that said corresponding wavelength is retro-reflected back toward said active media; and

causing the remaining localized reflective elements corresponding to said wavelengths not so-selected for simultaneous retro-reflection back toward said active media to be set such that said corresponding wavelength is not retro-reflected back toward said active media.

57. The method of claim 48, further comprising the step of sequentially selecting a plurality of wavelengths for lasing, in turn comprising the steps of:

determining a plurality of sets of at least zero of said single-wavelength focal spots to be selected for sequential retro-reflection back toward said active media, as sequential selected wavelength sets;

at a first given moment, and again at a different, second given moment, causing the localized reflective elements corresponding to said wavelengths so-selected at the given moment for retro-reflection back toward said active media to be set such that said corresponding wavelengths are retro-reflected back toward said active media;

at said first given moment, and again said second given moment, causing the remaining localized reflective elements corresponding to said wavelengths not so-selected at the given moment for retro-reflection back toward said active media to be set such that said corresponding wavelengths are not retro-reflected back toward said active media.

58. The method of claim 47, said active media comprising a laser diode.

59. The method of claim 47, further comprising the steps of:

setting at least one of said localized reflective elements to retro-reflect one of said single-wavelength focal spots back toward said active media; and

amplifying said single-wavelength focal spots retro-reflected by said locally-controllable reflectivity array means, for lasing at the wavelengths of the retro-reflected light.

60. The method of claim 47, said wavelength separation means comprising diffraction means for diffracting said filtered light into said wavelength-separated light.

61. The method of claim 47, said optical focusing means comprising a focusing element selected from the focusing element group consisting of lenses and mirrors.

63. The method of claim 48:

said locally-controllable reflectivity array means comprising a micromirror array; and

said plurality of individually-controllable localized reflective elements comprising a plurality of individually-controllable micromirrors;

said step of causing each said retro-reflecting reflective element to be set comprising the step of causing each micromirror for which the corresponding wavelength is selected for retro-reflection to be set in a first state such that said corresponding selected wavelength is retro-reflected back toward said active media; and

said step of causing each said non-retro-reflecting reflective element to be set comprising the step of causing each micromirror for which the corresponding wavelength is not selected for retro-reflection to be set in a second state such that said corresponding not-selected wavelength is not retro-reflected back toward said active media.

18. A tunable laser system, comprising:

wavelength separation means for separating incoming light emitted from an active media, into wavelength-separated light comprising a plurality of separate component wavelengths of said incoming light;

optical focusing means for focusing said separate component wavelengths of said wavelength-separated light into a plurality of single-wavelength focal spots, wherein each one of said single-wavelength focal spots is focused, but is displaced from, all others of said single-wavelength focal spots, within a common focal plane of said optical focusing means;

focal spot elongation means for elongating each of said separate component wavelengths of said wavelength-separated light into a plurality of elongated, single-wavelength focal spots; and

locally-controllable reflectivity array means comprising a plurality of sets of a plurality of individually-controllable localized reflective elements residing substantially within said common focal plane of said optical focusing means;

each of said sets of said plurality of localized reflective elements corresponding to and reflecting one of said elongated, single-wavelength focal spots;

each of said elongated, single-wavelength focal spots impinging on the plurality of localized reflective elements comprising its corresponding set of localized reflective elements; and

each said localized reflective element within each of said sets reflecting a portion of its associated elongated, single-wavelength focal spots in a manner determined by a setting of said localized reflective element.

35. The system of claim 18:

said locally-controllable reflectivity array means comprising a micromirror array; and

said plurality of sets of a plurality of individually-controllable localized reflective elements comprising a plurality of sets of a plurality of individually-controllable micromirrors.

37. A tunable laser system, comprising:

wavelength separation means for separating incoming light emitted from an active media, into wavelength-separated light comprising a plurality of separate component wavelengths of said incoming light;

optical focusing means for focusing said separate component wavelengths of said wavelength-separated light into a plurality of single-wavelength focal spots, wherein each one of said single-wavelength focal spots is focused, but is displaced from, all others of said single-wavelength focal spots, within a common focal plane of said optical focusing means; and

a micromirror array comprising a plurality of individually-controllable micromirrors residing substantially within said common focal plane of said optical focusing means, each of said micromirrors corresponding to and reflecting one of said plurality of said single-wavelength focal spots of said separated light in a manner determined by a setting of said micromirror.

47. A method for tuning a laser, comprising the steps of:

substantially allowing wavelengths of incoming light emitted from an active media which are separated from one another by a specified optical frequency difference to emerge as filtered light from wavelength filtering means, and substantially barring all other said wavelengths of said incoming light from emerging from said wavelength filtering means;

separating said filtered light emerging from said wavelength filtering means, into wavelength-separated light comprising a plurality of separate component wavelengths of said filtered light, using wavelength separation means;

focusing said separate component wavelengths of said wavelength-separated light into a plurality of single-wavelength focal spots, wherein each one of said single-wavelength focal spots is focused, but is displaced from, all others of said single-wavelength focal spots, within a common focal plane of optical focusing means, using said optical focusing means; and

reflecting each of said plurality of said single-wavelength focal spots in a manner determined by a setting of an individually-controllable localized reflective element corresponding thereto, using locally-controllable reflectivity array means comprising a plurality of said localized reflective elements residing substantially within said common focal plane of said optical focusing means.

62. The method of claim 47:

said locally-controllable reflectivity array means comprising a micromirror array; and

said plurality of individually-controllable localized reflective elements comprising a plurality of individually-controllable micromirrors.

64. A method of tuning a laser, comprising:

separating incoming light emitted from an active media, into wavelength-separated light comprising a plurality of separate component wavelengths of said incoming light, using wavelength separation means;

focusing said separate component wavelengths of said wavelength-separated light into a plurality of single-wavelength focal spots, wherein each one of said single-wavelength focal spots is focused, but is displaced from, all others of said single-wavelength focal spots, within a common focal plane of said optical focusing means, using optical focusing means;

elongating each of said separate component wavelengths of said wavelength-separated light into a plurality of elongated, single-wavelength focal spots, using focal spot elongation means;

impinging each of said elongated, single-wavelength focal spots on one of a plurality of sets of a plurality of individually-controllable localized reflective elements corresponding thereto; and

reflecting each of said elongated, single-wavelength focal spots from its corresponding set of localized reflective elements, each said localized reflective element within each of said sets reflecting a portion of its associated elongated, single-wavelength focal spot in a manner determined by a setting of said localized reflective element, using locally-controllable reflectivity array means comprising said plurality of said sets of said plurality of localized reflective elements residing substantially within said common focal plane of said optical focusing means.

65. The method of claim 64, further comprising the steps of:

determining which of said elongated, single-wavelength focal spots is to be selected for retro-reflection back toward said active media;

causing at least one localized reflective element within each set of localized reflective elements for which the corresponding wavelength is selected for retro-reflection to be set such that its portion of its corresponding selected wavelength is retro-reflected back toward said active media, as a retro-reflecting reflective element set;

causing at least one localized reflective element within each set of localized reflective elements for which the corresponding wavelength is not selected for retro-reflection to be set such that its portion of its corresponding not-selected wavelength is not retro-reflected back toward said active media, as a non-retro-reflecting reflective element set; and

within any retro-reflecting reflective element set, determining which and how many of said localized reflective elements are caused to be set to retro-reflect based upon at least one power output characteristic of a laser light output of said laser.

66. The method of claim 64, said at least one power output characteristic comprising maintaining substantially constant output power of said laser light output.

67. The method of claim 64, said at least one power output characteristic comprising controlling a power output for at least one wavelength of said laser light output.

68. The method of claim 65, further comprising the step of:

exercising at least one first localized reflective element and at least one second localized reflective element different from said first localized reflective element within each said retro-reflecting reflective element set to avoid stiction that would otherwise result from continuously maintaining said first and second localized reflective elements in a retro-reflecting state, in turn comprising the steps of;

at a first given time, causing said at least one first localized reflective element to be set such that it does not retro-reflect its said corresponding wavelength back toward said active media; and

at a second given time different from said first given time, causing said at least one second localized reflective element to be set such that it does not retro-reflect its said corresponding wavelength back toward said active media.

69. The method of claim 65, further comprising the step of:

exercising at least one first localized reflective element and at least one second localized reflective element different from said first localized reflective element within each said non-retro-reflecting reflective element set to avoid stiction that would otherwise result from continuously maintaining said first and second localized reflective elements in a non-retro reflecting state, in turn comprising the steps of;

at a first given time, causing said at least one first localized reflective element to be set such that it does retro-reflect its said corresponding wavelength back toward said active media; and

at a second given time different from said first given time, causing said at least one second localized reflective element to be set such that it does retro-reflect its said corresponding wavelength back toward said active media.

70. The method of claim 64, said optical focusing means and said focal spot elongation means comprising a single optical element.

71. The method of claim 70, said single optical element comprising an aspheric lens.

72. The method of claim 64, further comprising the steps of:

substantially allowing wavelengths of said incoming light emitted from said active media which are separated from one another by a specified optical frequency difference to emerge as filtered light from wavelength filtering means, and substantially barring all other said wavelengths of said incoming light from emerging from said wavelength filtering means;

wherein;

said incoming light separated by said wavelength separation means comprises said filtered light.

73. The method of claim 64, further comprising the steps of:

choosing a focal length f of said optical focusing means to be substantially equal to;

$f=\frac{a}{\mathrm{\Delta <br><br>\beta <br><br>}}=\frac{a·<br><br>c·<br><br>d·<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}}{{\mathrm{\lambda <br><br>}}^2·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>v},$

where Δ

ν

is a desired frequency difference for a laser light output of said laser, d is a period of said wavelength separation means, a is a pitch of said locally-controllable reflectivity array means, λ

is a central wavelength of said incoming light, m is an order of said wavelength separation means used for separating said filtered light into said wavelength-separated light, and β

is deduced according to

$\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\alpha <br><br>}+\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}=m<br><br>\frac{\mathrm{\lambda <br><br>}}{d},$

where α

is a angle of incidence of said filtered light onto said wavelength separation means;

choosing a distance between said wavelength separation means and said optical focusing means to be substantially equal to said focal length f; and

choosing a distance between said optical focusing means and said locally-controllable reflectivity array means to be substantially equal to said focal length f.

74. The method of claim 64, said locally-controllable reflectivity array means further comprising a plurality of localized selective elements also residing substantially within said common focal plane of said optical focusing means, each said localized selective element corresponding with one of said localized reflective elements, and said localized selective elements separated from said corresponding localized reflective elements by no more than a maximum coplanarity separation distance h;

further comprising the step of;

determining said maximum coplanarity separation distance h by maintaining an ambiguity Δ

ν

of an optical frequency ν

of said laser to be less than a threshold percentage of an output frequency spacing of said laser;

wherein

$\mathrm{\Delta <br><br>\upsilon <br><br>}=\frac{c}{{\mathrm{\lambda <br><br>}}^2}·<br><br>d<br><br>\text{\hspace{1em}<br><br>}<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}·<br><br>\frac{\mathrm{Dh}}{f^2}$

and wherein;

λ

is a central wavelength of said incoming light, c is the speed of light, d is a period of said wavelength separation means, D is a diameter of said optical focusing means, f is focal length of said optical focusing means, and β

is a diffraction angle of said wavelength-separated light from said wavelength separation means; and

wherein

said threshold percentage is equal to approximately 15 percent.

75. The method of claim 65, further comprising the step of simultaneously selecting a plurality of said wavelengths, in turn comprising the steps of:

determining a plurality of said elongated, single-wavelength focal spots to be selected for simultaneous retro-reflection back toward said active media, using a plurality of said reflective element sets corresponding with said focal spots so-selected;

causing at least one localized reflective element within each reflective element set selected for retro-reflection to be set such that its portion of its corresponding single-wavelength focal spot is retro-reflected back toward said active media; and

causing at least one localized reflective element within each reflective element set not selected for retro-reflection to be set such that its portion of its corresponding single-wavelength focal spot is not retro-reflected back toward said active media.

76. The method of claim 65, further comprising the step of sequentially selecting a plurality of sets of said wavelengths, in turn comprising the steps of:

determining a plurality of sets of at least zero of said elongated, single-wavelength focal spots to be selected for sequential retro-reflection back toward said active media, as sequential selected wavelength sets;

at a first given moment, and again at a different, second given moment, causing at least one localized reflective element within each retro-reflecting reflective element set corresponding to the wavelengths so-selected at the given moment for retro-reflection to be set such that its portion of its corresponding single-wavelength focal spot is retro-reflected back toward said active media;

at said first given moment, and again said second given moment, causing at least one reflective element within each non-retro-reflecting reflective element set corresponding to the wavelengths not so-selected at the given moment for retro-reflection back toward said active media to be set such that its portion of its corresponding single-wavelength focal spot is not retro-reflected back toward said active media.

77. The method of claim 64, said active media comprising a laser diode.

78. The method of claim 64, further comprising the steps of:

setting at least one of said localized reflective elements to retro-reflect a portion of one of said elongated, single-wavelength focal spots back toward said active media; and

amplifying said single-wavelength focal spots retro-reflected by said locally-controllable reflectivity array means, for lasing at the wavelengths of the retro-reflected light.

79. The method of claim 64, said wavelength separation means comprising diffraction means for diffracting said incoming light into said wavelength-separated light.

80. The method of claim 64, said optical focusing means comprising a focusing element selected from the focusing element group consisting of lenses and mirrors.

81. The method of claim 64:

said locally-controllable reflectivity array means comprising a micromirror array; and

said plurality of sets of a plurality of individually-controllable localized reflective elements comprising a plurality of sets of a plurality of individually-controllable micromirrors.

82. The method of claim 65:

said locally-controllable reflectivity array means comprising a micromirror array;

said plurality of sets of a plurality of individually-controllable localized reflective elements comprising a plurality of sets of a plurality of individually-controllable micromirrors;

said step of causing at least one localized reflective element within said retro-reflecting reflective element set comprising the step of causing at least one of said micromirrors within each said set of micromirrors for which the corresponding wavelength is selected for retro-reflection to be set in a first state such that its portion of its corresponding single-wavelength focal spot is retro-reflected back toward said active media; and

said step of causing at least one localized reflective element within said non-retro-reflecting reflective element sets to be set comprising the step of causing at least one of said micromirrors for which the corresponding wavelength is not selected for retro-reflection to be set in a second state such that its portion of its corresponding single-wavelength focal spot is not retro-reflected back toward said active media.

83. A method for tuning a laser, comprising the steps of:

separating incoming light emitted from an active media, into wavelength-separated light comprising a plurality of separate component wavelengths of said incoming light, using wavelength separation means;

focusing said separate component wavelengths of said wavelength-separated light into a plurality of single-wavelength focal spots, wherein each one of said single-wavelength focal spots is focused, but is displaced from, all others of said single-wavelength focal spots, within a common focal plane of said optical focusing means, using optical focusing means; and

reflecting one of said plurality of said single-wavelength focal spots of said separated light in a manner determined by a setting of said micromirror corresponding thereto, using a micromirror array comprising a plurality of individually-controllable micromirrors residing substantially within said common focal plane of said optical focusing means.

84. The method of claim 83, further comprising the steps of:

determining which of said single-wavelength focal spots is to be selected for retro-reflection back toward said active media;

causing each micromirror for which the corresponding wavelength is selected for retro-reflection to be set in a first state such that said corresponding selected wavelength is retro-reflected back toward said active media, as a retro-reflecting micromirror; and

causing each micromirror for which the corresponding wavelength is not selected for retro-reflection to be set in a second such that said corresponding not-selected wavelength is not retro-reflected back toward said active media, as a non-retro-reflecting micromirror.

85. The method of claim 83, further comprising the step of:

angling said micromirror array such that the micromirrors in said first state are substantially normal relative to a path of said single-wavelength focal spots.

86. The method of claim 85, further comprising the steps of:

angling said micromirror array at θ

degrees relative to said micromirrors in said first state and thus at 90-θ

degrees relative to said path of said single-wavelength focal spots, wherein said angle θ

is non-zero; and

orienting said optical focusing means to be substantially parallel to said micromirrors in said first state and thus angled at substantially 90-θ

degrees relative to said wavelength-separated light.

87. The method of claim 83, said optical focusing means comprising focus-improving means for substantially converting any elongation of a cross section of said single-wavelength focal spots into a substantially circular cross-section thereof.

88. The method of claim 87, said optical focusing means and said focus-improving means comprising a single optical element.

89. The method of claim 88, said single optical element comprising an aspheric lens.

90. The method of claim 83, further comprising the steps of:

setting at least one of said micromirrors to retro-reflect one of said single-wavelength focal spots back toward said active media;

emerging a laser light output of said laser from a zero order of said wavelength separation means; and

emerging light retro-reflected by said micromirror array back toward said wavelength separation means from a non-zero order of said wavelength separation means back toward said active media.

91. The method of claim 83, further comprising the step of emerging a laser light output of said laser from a rear facet of said active media.

92. The method of claim 83, further comprising the steps of:

choosing a focal length f of said optical focusing means to be substantially equal to;

$f=\frac{a}{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}}=\frac{a·<br><br>c·<br><br>d·<br><br>\cos <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}}{{\mathrm{\lambda <br><br>}}^2·<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>v},$

where Δ

ν

is a desired frequency difference for a laser light output of said laser, d is a period of said wavelength separation means, a is a pitch of said micromirror array, λ

is a central wavelength of said incoming light, m is an order of said wavelength separation means used for separating said filtered light into said wavelength-separated light, and β

is deduced according to

$\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\alpha <br><br>}+\sin <br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\beta <br><br>}=m<br><br>\frac{\mathrm{\lambda <br><br>}}{d},$

where α

is a angle of incidence of said filtered light onto said wavelength separation means;

choosing a distance between said wavelength separation means and said optical focusing means to be substantially equal to said focal length f; and

choosing a distance between said optical focusing means and said micromirror array to be substantially equal to said focal length f.