Micro-cavity laser

• US 20010033587A1
• Filed: 03/09/2001
• Published: 10/25/2001
• Est. Priority Date: 03/09/2000
• Status: Active Grant

• Current Assignee: California Institute of Technology, Cquint Communications Corporation
• Original Assignee: California Institute of Technology
• Inventors: Cai, Ming, Painter, Oskar, Vahala, Kerry J., Sercel, Peter C.
• Granted Patent: US 6,741,628 B2
• Time in Patent Office: Days
• US Class Current: 372/6
• CPC Class Codes: G02B 6/2821 using lateral coupling between contiguous fibres to split or combine optical signals
• CPC Class Codes: G02B 6/2852 using tapping light guides arranged sidewardly, e.g. in a non-parallel relationship with respect to the bus light guides (light extraction or launching through cladding, with or without surface discontinuities, bent structures)
• CPC Class Codes: H01S 3/06 Construction or shape of active medium
• CPC Class Codes: H01S 3/0604 in the form of a plate or disc
• CPC Class Codes: H01S 3/0627 the resonator being monolithic, e.g. microlaser
• CPC Class Codes: H01S 3/08 Construction or shape of optical resonators or components thereof
• CPC Class Codes: H01S 3/083 Ring lasers fibre ring lasers H01S3/06791
• CPC Class Codes: H01S 3/094 by coherent light
• CPC Class Codes: H01S 3/1628 characterised by a semiconducting matrix
• CPC Class Codes: H01S 3/163 characterised by a crystal matrix
• CPC Class Codes: H01S 3/17 amorphous, e.g. glass
• CPC Class Codes: H01S 5/10 Construction or shape of the optical resonator , e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region H01S5/20 takes precedence
• CPC Class Codes: H01S 5/1032 Coupling to elements comprising an optical axis that is not aligned with the optical axis of the active region
• CPC Class Codes: H01S 5/1042 Optical microcavities, e.g. cavity dimensions comparable to the wavelength
• CPC Class Codes: H01S 5/1075 Disk lasers with special modes, e.g. whispering gallery lasers

Abstract

The present invention is a micro-cavity laser and methods related thereto. In the preferred embodiments, the micro-cavity laser comprises a laser pump signal in a fiber waveguide which is optically coupled to a micro-cavity resonator through a fiber taper. The micro-resonator includes a gain medium necessary for lasing action. The lasing frequency can be determined based upon the gain medium, the micro-cavity structure, as well as frequency selective elements such as gratings incorporated into the micro-cavity. The tapered fiber waveguide permits the micro-cavity laser to operate without a break in the fiber waveguide. In the preferred embodiments, the micro-cavity resonator is constructed from a doped silica or a semiconductor material. The present invention provides a compact laser with improved emissions and coupling efficiencies. Alternative configurations include multiple micro-cavities on a single fiber waveguide and/or utilizing multiple waveguides attached to one or more micro-cavity resonators. The laser can be made to operate in a continuous-wave as opposed to self-pulsing mode.

Claims

1. A micro-cavity laser comprising:

a. A fiber waveguide, said fiber waveguide having a tapered coupling region, said tapered coupling region being positioned between said first end and said second end of said fiber waveguide;

b. A micro-cavity optical resonator, said micro-cavity optical resonator being arranged so as to provide optical coupling between said tapered coupling region of said fiber and said micro-cavity optical resonator, said micro-cavity optical resonator having at least one optical resonance at a desired frequency output, said micro-cavity including an active medium capable of providing optical gain upon pump excitation; and

,

c. At least one laser pump, the output of said laser pumps being optically connected to said first end of said fiber waveguide to couple optical pump power into said resonator to excite at least one resonance to pump said active medium, and induce lasing action such that laser output power is coupled to said fiber waveguide.

2. A micro-cavity laser of

claim 1

further including a second fiber waveguide, said second fiber waveguide having a coupling region between a first end and a second end of said second fiber waveguide, said second fiber waveguide being optically coupled to said micro-cavity optical resonator.

3. The micro-cavity laser of

claim 2

further including a second set of at least one laser pumps, the output of at least one of said second set of laser pumps is optically connected to said first end of second fiber waveguide and the output of said second set of laser pumps excites at least one resonance in said micro-cavity optical resonator and thereby pumps the active medium to induce lasing action.

4. The micro-cavity laser of

claim 3

wherein the output of at least one of said second set of laser pumps excites at least one resonance in said micro-cavity optical resonator at a frequency different from the resonance excited by the output of said laser pumps optically connected to said first fiber waveguide.

5. The micro-cavity laser of

claim 2

wherein the said first fiber waveguide and said second fiber waveguide are optically coupled to the same micro-cavity resonances.

6. The micro-cavity laser of

claim 5

wherein the said first fiber waveguide preferentially couples laser pump power from said fiber waveguide to the micro-cavity to attain lasing and said second fiber waveguide preferentially couples laser output power from said micro-cavity to said second fiber waveguide.

7. The micro-cavity laser of

claim 1

wherein said micro-cavity optical resonator is one of a microsphere, disk, ring, and racetrack.

8. The micro-cavity laser of

claim 1

wherein said micro-cavity is based on silica.

9. The micro-cavity laser of

claim 8

wherein said silica-based micro-cavity is doped with a rare earth element to provide an active medium.

10. The micro-cavity laser of

claim 9

wherein said rare earth element is at least one of erbium, ytterbium, praseodymium, neodymium, holmnium, and thulium.

11. The micro-cavity laser of

claim 1

wherein said micro-cavity optical resonator is a semiconductor, said semiconductor being arranged to be pumped electrically.

12. The micro-cavity laser of

claim 1

wherein the material composition of said micro-cavity includes phosphate glass.

13. The micro-cavity laser of

claim 1

wherein said micro-cavity optical resonator includes a plurality of micro-rings in a semiconductor.

14. The micro-cavity laser of

claim 1

wherein said micro-cavity optical resonator includes a plurality of micro-rings on an optical fiber.

15. The micro-cavity laser of

claim 1

wherein said micro-cavity optical resonator includes a plurality of photonic crystal cavities.

16. The micro-cavity laser of

claim 1

wherein said micro-cavity optical resonator is fabricated on a substrate.

17. The micro-cavity laser of

claim 1

wherein the micro-cavity optical resonator includes Bragg gratings in the resonant mode path so as to provide increased spectral purity of the lasing output.

18. The micro-cavity laser of

claim 17

wherein the Bragg gratings in the resonant mode path are defined holographically.

19. The micro-cavity laser of

claim 1

wherein the micro-cavity optical resonator has at least one preferred output frequency, and further including a frequency selector in the mode path of the micro-cavity optical resonator of at least one of the preferred output frequencies of the micro-cavity optical resonator.

20. A system for producing laser emission in a desired wavelength band, the system comprising:

a. A fiber waveguide, said waveguide having a first end and a second end and a tapered region therebetween, said tapered region having a tapered diameter;

b. A micro-cavity optical resonator, said resonator having a mode path diameter, said micro-cavity resonator being constructed from a silica material doped with at least one dopant;

c. Optical gratings, said optical gratings being position in the mode path of at least one resonant frequency of said micro-cavity optical resonator;

d. An alignment structure, said alignment structure being arranged to locate said microcavity optical resonator and said fiber waveguide in proximity to one another so as to enable coupling between said tapered region of said fiber waveguide and said micro-cavity optical resonator; and

,

e. A laser pump, said laser pump being optically connected to said first end of said fiber waveguide and being arranged so as to launch one or more signals into said fiber waveguide, said optical pump signals having frequencies which excite resonances in the micro-cavity optical resonator to thereby pump at least one silica dopant to induce lasing emission within a desired output frequency band of the system.

21. The system of

claim 20

wherein at least one of the laser pump source signals is in the 980 nanometer emission band.

22. The system of

claim 20

wherein the lasing emission is in the range of 1300-1600 nanometers.

23. The system of

claim 22

wherein the output of the system is used in a telecommunications application.

24. The system of

claim 20

wherein said taper section diameter and said mode path diameter are selected to provide optimal phased matching such that the coupling efficiency for pump and laser emission is maximized.

25. The system of

claim 20

wherein said fiber waveguide includes at least one additional optical resonator optically coupled thereto at the tapered section. Said at least one additional optical resonator doped so as to enable operation as a laser and optically pumped by coupling to said fiber waveguide.

26. The system of

claim 25

wherein said fiber waveguide has at least one additional taper coupling sections therein and at least one of said additional doped resonators is coupled to at least one of said additional taper sections in said fiber waveguide.

27. The system of

claim 20

wherein the system includes at least one additional fiber waveguide, each said additional fiber waveguide is optically coupled to said micro-cavity resonator and arranged so as to permit additional laser pumping of or laser emission coupling from said micro-cavity optical resonator.

28. The laser of

claim 20

wherein said micro-cavity is a sphere, disk, ring or racetrack.

29. The system of

claim 20

wherein optical gratings increase the spectral purity of the laser emission by forcing laser oscillation at a desired frequency.

30. The system of

claim 20

wherein said dopants include at least one of erbium, ytterbium, praseodymium, neodymium, holmnium, and thulium.

31. The system of

claim 20

wherein said fiber waveguide is a panda fiber.

32. A micro-cavity laser comprising:

a. A first fiber waveguide, said first fiber waveguide having an evanescent coupling region, said evanescent coupling region being positioned between a first end and a second end of said fiber waveguide;

b. A micro-cavity optical resonator, said micro-cavity optical resonator being positioned in proximity to said coupling region of said first fiber so as to evanescently couple said fiber coupling region and said micro-cavity optical resonator, said micro-cavity optical resonator having at least one optical resonance at a desired frequency output, said micro-cavity optical resonator comprising an active medium capable of providing optical gain when excited; and

c. A laser pump, said laser pump being optically connected to said first end of said fiber waveguide for the purpose of exciting said gain medium.

33. The laser of

claim 32

wherein said micro-cavity resonator is fabricated on a chip or substrate.

34. The laser of

claim 33

wherein said fiber waveguide is an etched fiber.

35. The system of

claim 33

wherein said fiber waveguide is a D-fiber.

36. The system of

claim 33

wherein said fiber waveguide includes polished fiber half-blocks.

37. The system of

claim 33

wherein said fiber waveguide is a panda fiber.

38. The system of

claim 33

wherein said waveguide coupling section is phased matched to said resonator such that the pump coupling and laser emission collection efficiency are maximized.

39. The micro-cavity laser of

claim 33

wherein the micro-cavity optical resonator has at least one preferred output frequency, and further including frequency modifier gratings, said gratings being disposed in the mode path of the micro-cavity optical resonator of at least one of the preferred output frequencies of the micro-cavity optical resonator.

40. The micro-cavity laser of

claim 33

wherein said micro-cavity optical resonator includes at least one of a micro-disk, ring and racetrack.

41. A micro-cavity laser comprising:

a. A fiber waveguide, said waveguide having a first end and a second end and a tapered region therebetween, said tapered region having a tapered diameter;

b. A highly doped Erbium;

Ytterbium phosphate silica micro-sphere, said microsphere being arranged so as to enable weak optical coupling between said microsphere and said tapered region of said fiber waveguide; and

c. A laser pump signal, said laser pump signal being transmitted in said fiber waveguide through said tapered region, said laser signal including a frequency which excites a resonance in said silica microsphere and pumps the erbium gain medium to induce laser emission.

42. A micro-cavity laser system comprising:

a. A fiber waveguide, said fiber waveguide having at least one tapered coupling region, said tapered coupling regions being located between said first end and said second end of said fiber waveguide;

b. A plurality of micro-cavity optical resonators including a first micro-cavity resonator, each said micro-cavity optical resonator being arranged in proximity to at least one of said tapered coupling regions so as to provide optical coupling between said micro-cavity optical resonator and said fiber waveguide through at least one said tapered coupling region of said fiber waveguide, at least one of said micro-cavity optical resonators having at least one optical resonance at a desired frequency output, said first micro-cavity optical resonator including an active medium associated therewith capable of providing optical gain upon pump excitation; and

c. At least one laser pump, the output of said laser pump being optically connected to said first end of said fiber waveguide to couple optical pump power into at least said first micro-cavity resonator to excite said active medium associated with said first micro-cavity optical resonator and induce lasing action such that laser output power is coupled to said fiber waveguide.

43. The micro-cavity laser system of

claim 42

wherein the laser system includes at least a second micro-cavity optical resonator, said at least a second micro-cavity resonator including an active medium, said active medium associated with said at least a second micro-cavity optical resonator providing optical gain upon pump excitation at a frequency different than in said first micro-cavity optical resonator.

44. The micro-cavity laser system of

claim 42

wherein at least one of said micro-cavity optical resonators is one of a microsphere, disk, ring, and racetrack.

45. The micro-cavity laser system of

claim 42

wherein said micro-cavity is based on silica.

46. The micro-cavity laser system of

claim 45

wherein said silica-based micro-cavity is doped with a rare earth element to provide an active medium.

47. The micro-cavity laser system of

claim 46

wherein said rare earth element is at least one of erbium, ytterbium, praseodymium, neodymium, holmnium, and thulium.

48. The micro-cavity laser system of

claim 42

wherein said plurality of micro-cavity optical resonators are semiconductor based, said semiconductor being arranged to be pumped electrically.

49. The micro-cavity laser system of

claim 42

wherein the material composition of at least one micro-cavity resonator includes phosphate glass.

50. The micro-cavity laser of

claim 42

wherein said plurality of micro-cavity optical resonators are fabricated on a substrate.

51. The micro-cavity laser system of

claim 42

wherein said plurality of micro-cavity optical resonator includes a plurality of micro-rings on an optical fiber.

52. The micro-cavity laser system of

claim 42

wherein said plurality of micro-cavity optical resonator includes a plurality of photonic crystal cavities.

53. The micro-cavity laser system of

claim 42

wherein said plurality of micro-cavity optical resonator is fabricated on a substrate material which is a semiconductor.

54. A method of creating a laser signal of a desired frequency, the steps comprising:

Launching at least one signal into a fiber waveguide, said waveguide having a tapered coupling region, said tapered coupling region being optically coupled to a micro-cavity resonator, said micro-cavity resonator containing a gain medium and being resonant and critically coupled to the signal so as to permit excitation of the gain medium and lasing in a desired emission band.

57. The method of producing a microsphere of

claim 54

wherein said phosphorus glass material is doped with a rare earth element.

55. A method of obtaining a laser signal within a desired frequency range, the steps comprising:

Receiving a laser signal in a waveguide, said waveguide being optically connected to a fiber waveguide, said fiber waveguide having a fiber tapered coupling region therein, said tapered coupling region being optically coupled to a micro-cavity resonator, said micro-cavity resonator having a resonance at the desired output frequency, and said micro-cavity resonator containing a gain medium capable of amplification at the desired output frequency and excitation from the said laser signal.

58. The method of

claim 55

wherein said dopant includes Erbium.

59. The method of

claim 55

wherein said dopant includes Ytterbium.

56. A method of fabricating a phosphorus glass microsphere for use in a micro-cavity resonator, the steps comprising:

Melting a small piece of phosphorus glass material in a crucible,

Stabilizing the temperature of said molten phosphorus glass,

Placing the tip of a silica fiber taper into the molten phosphorus glass,

Extracting the silica fiber so that a small phosphate taper is formed on the end of the silica fiber taper;

Melting the end of the phosphate taper until a spheroid forms under surface tension,

Quickly cooling the phosphate sphere in a manner which avoids crystallization of the phosphate in the spheroid to an extent which would interfere with the refractive properties of the spheroid as a micro-cavity optical resonator.