Alignment and wavelength selection in external cavity lasers

• US 7,822,096 B2
• Filed: 12/12/2008
• Issued: 10/26/2010
• Est. Priority Date: 12/12/2008
• Status: Expired due to Fees

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Kuksenkov, Dmitri Vladislavovich
• Primary Examiner(s): Harvey; Minsun
• Assistant Examiner(s): Zhang; Yuanda
• Application Number:
  US12/334,082
• Publication Number:
  US 20100150184A1
• Time in Patent Office: 683 Days
• Field of Search: 372/21, 372/22, 372/24, 372/29.01, 372/29.011, 372/29.014, 372/29.02, 372/93, 372/102, 372/20, 359/196.1, 359/201.2, 359/204.5, 359/211.5
• US Class Current: 372/102
• CPC Class Codes: H01S 3/101 Lasers provided with means to change the location from which, or the direction in which, laser radiation is emitted
• CPC Class Codes: H01S 3/1055 one of the reflectors being constituted by a diffraction grating
• CPC Class Codes: H01S 3/109 Frequency multiplication, e.g. harmonic generation
• CPC Class Codes: H01S 5/041 Optical pumping
• CPC Class Codes: H01S 5/0687 Stabilising the frequency of the laser
• 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 5/183 having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
• CPC Class Codes: H04N 9/3155 for controlling the light source light source control per se H05B35/00 – H05B47/00; control of an illumination source for displays in general G09G3/3406
• CPC Class Codes: H04N 9/3161 using laser light sources using laser beams scanning the display screen H04N9/3129
• CPC Class Codes: H04N 9/3194 including sensor feedback

Abstract

A method of operating a laser projection system is provided. The projection system comprises an external cavity laser, an optical intensity monitor, laser projection optics, and a controller. The external cavity laser comprises a laser diode, an intra-cavity wavelength conversion device, and a wavelength selective element. According to the method, the position of the wavelength selective element is adjusted relative to an optical axis Z of the external cavity laser to optimize output intensity. Specifically, the position of the wavelength selective element is adjusted by (i) tilting the wavelength selective element about its wavelength selective axis Y to reflect a wavelength of interest along an optimum path in an XZ plane of the external laser cavity and (ii) tipping the wavelength selective element about its wavelength insensitive axis X to reflect the wavelength of interest along an optimum path in a YZ plane of the external laser cavity. Additional embodiments are disclosed and claimed.

Claims

1. A method of operating a laser projection system comprising an external cavity laser, an optical intensity monitor, laser projection optics, and a controller, wherein the external cavity laser comprises a laser diode, an intra-cavity wavelength conversion device, and a wavelength selective element for wavelength selection and beam steering through the wavelength conversion device and the method comprises:

monitoring an output intensity of the external cavity laser; and

adjusting the position of the wavelength selective element relative to an optical axis Z of the external cavity laser to optimize the output intensity, wherein the position of the wavelength selective element is adjusted by

tilting the wavelength selective element about its wavelength selective axis Y to reflect a wavelength of interest along an optimum path in an XZ plane of the external laser cavity and

operating the wavelength selective element as an adaptive mirror to maintain optimal coupling of light within the wavelength conversion device by tipping the wavelength selective element about its wavelength insensitive axis X to reflect the wavelength of interest back along a beam axis along an optimum path through the wavelength conversion device in a YZ plane of the external laser cavity, wherein the wavelength selective element is configured such that a given degree of tipping about the wavelength insensitive axis X changes the path of the back-reflected wavelength of interest, relative to the wavelength conversion device, to maintain optical coupling of light with the wavelength conversion device.

2. A method as claimed in claim 1 wherein the wavelength selective element is tilted about the wavelength selective axis Y such that the reflected wavelength of interest matches an optimum phase matching wavelength of the intra-cavity wavelength conversion device.

3. A method as claimed in claim 1 wherein the wavelength selective element is configured such that a given degree of tipping about the wavelength insensitive axis X yields an insignificant degree of wavelength tuning relative to that which would be generated under a corresponding degree of tilting about the wavelength selective axis Y.

4. A method as claimed in claim 1 wherein the wavelength selective element is tipped such that the path of the reflected wavelength of interest is directed back through the intra-cavity wavelength conversion device with sub-micron precision.

5. A method as claimed in claim 1 wherein the method alternates between tilting and tipping of the wavelength selective element in an iterative process until the wavelength of interest is reflected along the optimum path in the XZ and YZ planes.

6. A method as claimed in claim 1 wherein the method executes the tilting and tipping of the wavelength selective element simultaneously until the wavelength of interest is reflected along the optimum path in the XZ and YZ planes.

7. A method as claimed in claim 1 wherein:

the wavelength selective element is tilted about the wavelength selective axis Y until the wavelength of interest is reflected along the optimum path in the XZ plane of the external laser cavity; and

the wavelength selective element is subsequently tipped about the wavelength insensitive axis X until the wavelength of interest is reflected along the optimum path in the YZ plane of the external laser cavity.

8. A method as claimed in claim 1 wherein the method executes the tilting and tipping of the wavelength selective element such that the wavelength selective element serves both as a wavelength tuning element and as an adaptive mirror to maintain optimal coupling of light within the external cavity laser.

9. A method as claimed in claim 1 wherein the method executes the tilting and tipping of the wavelength selective element while monitoring a wavelength-converted output intensity of the external cavity laser or a native wavelength output intensity of the external cavity laser.

10. A method as claimed in claim 1 wherein the method further comprises operating the laser projection optics to generate a scanned laser image using an output beam of the external cavity laser and the tilting and tipping of the wavelength selective element is executed while generating the scanned laser image.

11. A method as claimed in claim 1 wherein the external cavity laser is driven by a sinusoidally varying or pulsed current such that the laser operates in a pulsed mode to increase the wavelength conversion efficiency.

12. A method as claimed in claim 1 wherein the external cavity laser comprises a Fabry-Perot laser diode comprising a continuous active waveguide divided into gain and absorber sections, and the method comprises operating the laser in a Q-switched or mode-locked pulsed mode without external modulation by applying a DC bias to the gain section of the laser diode and by shorting or reverse biasing the absorber section of the laser diode.

13. A method as claimed in claim 1 wherein the wavelength selective element comprises a ruled, multi-layer dielectric or holographic diffraction grating, a prism with a highly reflective coating on one of its sides, or a combination of a prism and a grating.

14. A method as claimed in claim 1 wherein the wavelength selective element is coupled to a multi-axial actuator to enable tilting and tipping about the X and Y axes.

15. A method as claimed in claim 1 wherein the laser diode, the intra-cavity wavelength conversion device, and the wavelength selective element are assembled as an optically pumped, external cavity Littrow configuration.

16. A method as claimed in claim 1 wherein the laser diode, the intra-cavity wavelength conversion device, and the wavelength selective element are assembled as a folded external cavity semiconductor laser comprising an external cavity formed between highly reflective dielectric coatings at the rear facet of the laser diode and the output face of the wavelength conversion device.

17. A method as claimed in claim 16 wherein a dichroic coating is deposited on the input face of the wavelength conversion device to increase the effective optical path length of the wavelength conversion device, the dichroic coating being highly transmissive at the native lasing wavelength of the laser diode and highly reflective at the frequency converted output of the wavelength conversion device.

18. An external cavity laser comprising a laser diode, an intra-cavity wavelength conversion device, a wavelength selective element for wavelength selection and beam steering through the wavelength conversion device, and a multi-axial actuator, wherein:

the laser diode, the intra-cavity wavelength conversion device, and the wavelength selective element are assembled as a folded external cavity semiconductor laser comprising an external cavity formed between highly reflective dielectric coatings at the rear facet of the laser diode and the output face of the wavelength conversion device;

the wavelength selective element is coupled to the multi-axial actuator to enable operation of the wavelength selective element as an adaptive mirror to maintain optimal coupling of light within the wavelength conversion device through adjustment of the position of the wavelength selective element relative to an optical axis Z of the external cavity laser by tilting and tipping the wavelength selective element about a wavelength insensitive axis X and a wavelength selective axis Y;

the tilting of the wavelength selective element about its wavelength selective axis Y reflects a wavelength of interest along an optimum path in an XZ plane of the external laser cavity;

the tipping of the wavelength selective element about its wavelength insensitive axis X reflects the wavelength of interest back along a beam axis along an optimum path through the wavelength conversion device in a YZ plane of the external laser cavity; and

the wavelength selective element is configured such that a given degree of tipping about the wavelength insensitive axis X changes the path of the back-reflected wavelength of interest, relative to the wavelength conversion device, to maintain optical coupling of light with the wavelength conversion device.

19. A system for generating a projected laser image, the system comprising an external cavity laser, an optical intensity monitor, laser projection optics, and a controller, wherein:

the controller, the external cavity laser, and the laser projection optics are configured to generate a projected laser image utilizing an output beam of the external cavity laser;

the external cavity laser comprises a laser diode, an intra-cavity wavelength conversion device, and a wavelength selective element for wavelength selection and beam steering through the wavelength conversion device;

the external cavity laser, the optical intensity monitor, and the controller form at least a portion of a feedback loop configured to control the wavelength selective element as a function of optical intensity;

the system is programmed to operate the wavelength selective element as an adaptive minor to maintain optimal coupling of light within the wavelength conversion device by adjusting the position of the wavelength selective element relative to an optical axis Z of the external cavity laser to optimize the output intensity by tilting the wavelength selective element about its wavelength selective axis Y to reflect a wavelength of interest along an optimum path in an XZ plane of the external laser cavity and tipping the wavelength selective element about its wavelength insensitive axis X to reflect the wavelength of interest back along a beam axis along an optimum path through the wavelength conversion device in a YZ plane of the external laser cavity; and

the wavelength selective element is configured such that a given degree of tipping about the wavelength insensitive axis X changes the path of the back-reflected wavelength of interest, relative to the wavelength conversion device, to maintain optical coupling of light with the wavelength conversion device.