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A tunable laser and laser tuning method based on the use of a tunable etalon in reflection as a mirror within a laser cavity. The laser emission wavelength is not necessarily at a wavelength of peak etalon reflectivity. A preferred embodiment makes use of a microelectromechanical etalon to tune an e

A tunable laser and laser tuning method based on the use of a tunable etalon in reflection as a mirror within a laser cavity. The laser emission wavelength is not necessarily at a wavelength of peak etalon reflectivity. A preferred embodiment makes use of a microelectromechanical etalon to tune an external cavity semiconductor laser.

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1. A tunable laser comprising:(a) a laser pump; (b) a resonant optical cavity having a round trip light path, said optical cavity having an odd number of reflective surfaces and comprising: i) a gain medium responsive to pumping by said laser pump, one face of said gain medium forming a first reflec

1. A tunable laser comprising:(a) a laser pump; (b) a resonant optical cavity having a round trip light path, said optical cavity having an odd number of reflective surfaces and comprising: i) a gain medium responsive to pumping by said laser pump, one face of said gain medium forming a first reflective endface of the resonant optical cavity: and ii) a tuning etalon, positioned within the resonant optical cavity, said tuning etalon comprising two spaced apart mirrors having a controllable mirror-to-mirror separation distance, and forming the other reflective endface of said resonant optical cavity, so that light traveling on said round trip light path is reflected from said tuning etalon, and whereby the emission wavelength of the rain medium is determined by a selected separation distance of the etalon mirrors. 2. A tunable laser comprising:(a) a laser pump; (b) a resonant optical cavity having a round trip light path, said optical cavity having an odd number of reflective surfaces and comprising: i) a gain medium responsive to pumping by said laser pump, one face of said gain medium forming a first reflective endface of the resonant optical cavity: and ii) a tuning etalon, positioned within the resonant optical cavity, said etalon comprising two spaced apart mirrors having a controllable mirror-to-mirror separation distance, and forming the other reflective endface of said optical cavity so that light traveling on said round trip light path is reflected from the etalon, and whereby the emission wavelength of the gain medium is determined by a selected separation distance of the etalon mirrors and is selected to have a value that differs from a wavelength of peak reflectivity of the etalon. 3. The laser of claim 2, wherein said gain medium comprises a semiconductor structure providing vertical emission of radiation.4. The laser of claim 2, wherein said etalon comprises a microelectromechanical device with an electrically adjustable free spectral range.5. The laser of claim 2, wherein said optical resonator further comprises a grid fixing etalon.6. The laser of claim 2, wherein said round trip light path has a preselected path length value that is chosen to achieve discrete tunability.7. The laser of claim 2, wherein said gain medium comprises an electrically pumped, single-mode, semiconductor optical waveguide contiguous with a semiconductor substrate.8. The laser of claim 7, wherein said etalon further comprises a microelectromechanical device with an electrically adjustable free spectral range.9. The laser of claim 8, further comprising a lens positioned between said gain medium and said etalon.10. The laser of claim 8, further comprising an optical fiber and coupling optics positioned between said gain medium and said optical fiber.11. The laser of claim 8, further comprising an optical fiber and coupling optics positioned between said etalon and said optical fiber.12. The laser of claim 8, further comprising means for generating a wavelength reference signal.13. The laser of claim 8, further comprising means for generating an output power reference signal.14. The laser of claim 8, wherein said pump has an output power that is variable in response to receipt of a data signal to provide a modulated pump output signal.15. The laser of claim 8, further comprising an optical fiber and an optical modulator positioned between said resonator and said optical fiber.16. The laser of claim 15, wherein said optical modulator is contiguous with said semiconductor substrate.17. The laser of claim 15, wherein said optical modulator is butt-coupled to said gain medium.18. A laser emitting light at a selected wavelength λ1 said laser comprising a resonant optical cavity having a round trip light path, said cavity having an odd number of reflective surfaces and comprising:(a) a laser pump; (b) a gain medium, responsive to pumping by said laser pump, the gain medium comprising a single-mode optical waveguide having first and second end faces, wherein the first optical waveguide end face is an output coupler which forms one reflective endface of the resonant optical cavity and wherein the second end face emits a beam including a selected wavelength λ1 and having a selected power Pa; (c) a lens that receives the emitted beam and transmits it as a focused beam to; (d) a tuning etalon; which forms the other reflective endface of the resonant optical cavity, said etalon comprising two spaced apart mirrors; having a controllable mirror-to-mirror separation distance, which receives and reflects the focused beam as a distorted and attenuated beam; wherein the extent of the beam distortion and beam attenuation depends upon the focused beam wavelength and wherein the reflected beam is received at the second waveguide endface with an optical power Pb and issues from the second endface into the waveguide with an optical power P0, where the ratio P0/Pa has a maximum value at a wavelength λ0 that is determined by a selected separation distance of the etalon mirrors, and wherein the wavelength λ1 differs from a wavelength of peak reflectivity of the etalon and is selected to be approximately equal to λ0. 19. A method for generating tunable laser light, the method comprising the steps of:(a) pumping a laser gain medium, positioned within a resonant optical cavity having a round trip light path and having an odd number of reflective surfaces and wherein one face of said gain medium forms the first reflective endface of said resonant optical cavity; (b) positioning in the round trip light path a tuning etalon which forms the second reflective endface of said resonant optical cavity and wherein said etalon comprises two spaced apart mirrors having a controllable mirror-to-mirror separation distance; (c) receiving and reflecting light traveling in the round trip light path at the etalon, whereby an emission wavelength of the laser is determined by a selected separation distance for the etalon mirrors. 20. A method for generating tunable laser light, the method comprising:(a) using a laser pump to pump a laser gain medium positioned within a resonant optical cavity having a round trip light path and having an odd number of reflective surfaces and wherein one face of said gain medium forms the first reflective end face of said resonant optical cavity; (b) positioning in the round trip light path a tuning etalon, which forms the second reflective endface of said resonant optical cavity and wherein said etalon comprises two spaced apart mirrors having a controllable mirror-to-mirror separation distance, (c) receiving and reflecting light traveling in the round trip list path at the etalon, whereby the emission wavelength of the laser is determined by a selected separation distance for the etalon mirrors and has a value that differs from a wavelength of peak reflectivity of the etalon. 21. The method of claim 20, wherein said gain medium comprises a semiconductor structure adapted for vertical emission of radiation.22. The method of claim 20, wherein said tuning etalon is a microelectromechanical device with an electrically adjustable free spectral range.23. The method of claim 20, further comprising the step of receiving and passing said light traveling along said round trip light path through a grid fixing etalon.24. The method of claim 20, further comprising choosing a path length for said round trip light path to provide discrete tunability.25. The method of claim 20, further comprising providing, as said gain medium, an electrically pumped, single-mode semiconductor optical waveguide having a semiconductor substrate.26. The method of claim 25, further comprising providing, as said tuning etalon, is a microelectromechanical device with an electrically adjustable free spectral range.27. The method of claim 26, further comprising receiving and passing said light traveling alone said round trip, light path through a grid fixing etalon.28. The method of claim 26, further comprising the steps of:(d) emitting light from said gain medium, and directing the emitted light away from said tuning etalon; (e) passing said emitted light through coupling optics to provide a focused beam; and (f) coupling said focused beam into a single-mode optical fiber. 29. The method of claim 26, further comprising the steps of:(d) emitting light from said tuning etalon, and directing the emitted light away from said gain medium; (e) passing the emitted light through coupling optics to provide a focused beam; and (f) coupling the focused beam into a single-mode optical fiber. 30. The method of claim 26, further comprising the step of generating a wavelength reference signal.31. The method of claim 26, further comprising the step of generating an output power reference signal.32. The method of claim 26, further comprising the step of varying the output power from said pump in response to receipt of a data signal to provide a modulated pump output sigal.33. The method of claim 26, further comprising the steps of:(d) emitting light from said gain medium, and directing said emitted light away from said tuning etalon; (e) passing said emitted light through an optical modulator to thereby generate modulated light; and (f) coupling said modulated light into a single-mode optical fiber. 34. The method of claim 33, further comprising locating said gain medium and said optical modulator on said semiconductor substrate.35. The method of claim 33, wherein said optical modulator is butt-coupled to said gain medium.36. A method for generating tunable laser lights of a wavelength λ1 comprising the steps of:(a) pumping a gain medium, positioned within a resonant optical cavity having a round trip light path and an odd number of reflective surfaces, said gain medium comprising a single-mode optical waveguide having first and second endfaces, wherein the first endface is the first reflective end face of said resonant optical cavity and serves as an output coupler for the resonant optical cavity and wherein the second endface emits a beam including a selected wavelength λ1 and having a selected power Pa; (b) passing said emitted beam through a lens to provide a focused beam; and (c) receiving and reflecting said focused beam from a tuning etalon, which forms the second reflective endface of the resonant optical cavity, said etalon comprising two spaced apart mirrors having a controllable mirror-to-mirror separation distance, to generate a distorted and attenuated version of the focused beam, where the extent of the distortion and attenuation depends upon the wavelength λ1, where the reflected beam is received at the second endface with an optical power Pb and issues from the second endface into the waveguide with an optical power P0, where the ratio P0/Pa has a maximum value at a wavelength λ0 which is determined by a selected separation distance of the etalon mirrors, and wherein the wavelength λ1 differs from a wavelength of peak reflectivity of the etalon and is selected to be approximately equal to λ0.