Monochromatic R,G,B laser light source display system and method

• US 6,304,237 B1
• Filed: 05/27/1999
• Issued: 10/16/2001
• Est. Priority Date: 11/29/1996
• Status: Expired due to Term

• Current Assignee: Corporation For Laser Optics Research, Christie Digital Systems USA Incorporated (Ushio Incorporated)
• Original Assignee: Corporation For Laser Optics Research
• Inventors: Karakawa, Masayuki
• Primary Examiner(s): NGUYEN, CHANH DUY
• Application Number:
  US09/319,058
• Time in Patent Office: 873 Days
• Field of Search: 345/85, 345/32, 345/84, 345/102, 345/88, 345/139, 345/153, 345/44, 345/46, 345/39, 345/82, 345/83, 359/621, 359/619, 372/22, 372/23, 372/26, 372/31, 353/31, 348/661, 348/760
• US Class Current: 345/84
• CPC Class Codes: G02F 1/3532 Arrangements of plural nonlinear devices for generating multi-colour light beams, e.g. arrangements of SHG, SFG, OPO devices for generating RGB light beams
• CPC Class Codes: G02F 1/3534 Three-wave interaction, e.g. sum-difference frequency generation G02F1/3532 takes precedence
• CPC Class Codes: G02F 1/354 Third or higher harmonic generation
• CPC Class Codes: G02F 1/3542 Multipass arrangements, i.e. arrangements to make light pass multiple times through the same element, e.g. using an enhancement cavity
• CPC Class Codes: G02F 1/37 for second-harmonic generation G02F1/3532 takes precedence
• CPC Class Codes: G02F 1/39 for parametric generation or amplification of light, infrared or ultraviolet waves
• CPC Class Codes: H04N 9/3129 scanning a light beam on the display screen scanning a light beam on a screen in displays other than projection devices G09G3/02; scanning systems in general G02B26/10; projectors using laser light sources in general H04N9/3161

Abstract

A monochromatic red (R), green (G), blue (B) pulsed laser light source (FIG. 2) for use in a full color video/image display system particularly an LCD display system (FIG. 3), the light source generating R,G,B laser beams with minimum speckle noise, and having digital color space conversion incorporated within.

Claims

1. An R,G,B pulsed laser light source with reduced speckle noise adapted for use with a display system, which light source generates R, G and B beams and comprises:

a laser with a laser medium producing a pulsed laser output beam of selected pulse width and wavelength;

an R-channel receiving a first portion of the output beam and generating the R beam, with the R-channel including a resonant cavity with a first nonlinear crystal producing optical radiation having a first wavelength that is greater than the wavelength of the output beam and a spectral width that is greater than a spectral width of the output beam, and a second nonlinear crystal that combines the radiation of the first wavelength with the first portion of the output beam to generate the R beam by sum frequency mixing, said R-beam having a spectral width determined by the spectral width of the optical radiation of the first wavelength;

a G-channel receiving a second portion of the output beam and generating the G beam, with the G-channel including a resonant cavity with a third nonlinear crystal producing second harmonic optical radiation of the output beam, with the cavity of the G-channel further including an etalon that produces a plurality of longitudinal G-channel resonant cavity modes which define a spectral width of the G-channel; and

a B-channel receiving a third portion of the output beam and generating the B beam, with the B-channel including a fourth nonlinear crystal that frequency-doubles the third portion of the output beam, and a lasing cavity having a Ti;

S laser crystal pumped with the frequency-doubled output beam and producing a lasing wavelength that is twice the wavelength of the B-beam, said lasing wavelength being frequency-doubled by a fifth nonlinear crystal located in the lasing cavity and producing the B-beam;

with the spectral width of the R-channel and the G-channel reducing the speckle noise of the R,G,B pulsed laser light source.

2. The source of claim 1 wherein a pulse rate of the output beam is greater than 40 kHz.

3. The source of claim 1 wherein the laser medium comprises a neodymium-yttrium crystal.

4. The source of claim 1 wherein the G beam has a wavelength of approximately 532 nm or 523.5 nm.

5. The source of claim 1 wherein the R beam has a wavelength of approximately 626 nm to 629 nm.

6. The source of claim 1 wherein the B beam has a wavelength of approximately 452 nm or 447 nm.

7. The source of claim 1 wherein the laser comprises:

a) a neodymium-yttrium vanadate laser medium with a pump end with an active mirror;

b) a diode laser bar with output wavelength of 807 nm;

c) an optical fiber means to deliver the diode laser bar output to the pump end of the laser medium;

d) a Q-switch means to pulse the laser beam from the laser medium; and

e) an output beam coupler to transmit a pulsed laser beam.

8. The source of claim 1 wherein the laser comprises:

a) a neodymium-yttrium vanadate laser medium;

b) a single or multiple diode laser bar with an output wavelength of 807 nm;

c) means to focus the diode laser bar output to one or both sides of the laser medium;

d) a Q-switch means to pulse the laser beam from the laser medium; and

e) an end mirror and an output beam coupler to resonate and transmit a pulsed laser beam.

9. The source of claim 1 wherein the output laser beam wavelength is 1047 nm or 1064 nm.

10. The source of claim 1, further including:

means to divide the output signal into the three separate portions of the output beams.

11. The source of claim 1 which includes active modelock means to produce quasi-cw operation of the R,G,B laser light source.

12. The source of claim 1, further including a laser power amplifier means to amplify the power of the output beam.

13. The source of claim 1, wherein the first nonlinear crystal comprises a potassium titanyl arsenate (KTA) and the second nonlinear crystal is selected from the group consisting of KTA or lithium triborate (LBO).

16. The system of claim 13, further comprising:

a first optical means to receive and shape the R,G,B beams;

a spatial light modulator means to receive the R,G,B beams from the optical means, and to modulate the R,G,B beams to produce a full color video image;

electronic means to operate the spatial light modulator means; and

a second optical means to relay, combine, and project a full color video image on a screen.

17. The system of claim 16 wherein the spatial light modulator means comprises three transmissive or reflective LCD panels, one for each R,G,B beam.

18. The system of claim 16 wherein the first optical means includes expander, collimator and micro-array lens means to receive the R,G,B beams and to increase the R,G,B light transmission efficiency and minimize diffraction.

19. The system of claim 16 wherein the spatial light modulator means comprise three transmissive LCD panels, one for each R,G,B beam, and which system includes:

a) a first optical means which comprises a beam expander, collimator and micro-array lens means to expand, to collimate, and to increase transmission efficiency of the R,G,B beams from the light source and incident on the LCD panels;

b) a second optical means which comprises an optical means to re-collimate the R,G,B beams on the opposite side of the LCD panels; and

c) projection means to project the re-collimated R,G,B beams onto a screen.

20. The system of claim 16 wherein the electronic means includes digital color space conversion means to translate electronic input video chromatic signals into electronic signals within R,G,B laser color space.

21. The system of claim 16 wherein the output laser beam wavelength is 1047 nm, 1064 nm or 1342 nm.

14. A color image video display system comprising:

an R,G,B pulsed laser light source with reduced speckle noise, which light source generates R, G and B beams and includes

a laser with a laser medium producing a pulsed laser output beam of selected pulse width and wavelength;

an R-channel receiving a first portion of the output beam and generating the R beam, with the R-channel including a resonant cavity with a first nonlinear crystal producing optical radiation having a first wavelength that is greater than the wavelength of the output beam and a spectral width that is greater than a spectral width of the output beam, and a second nonlinear crystal that combines the radiation of the first wavelength with the first portion of the output beam to generate the R beam by sum frequency mixing, said R-beam having a spectral width determined by the spectral width of the optical radiation of the first wavelength;

a G-channel receiving a second portion of the output beam and generating the G beam, with the G-channel including a resonant cavity with a third nonlinear crystal producing second harmonic optical radiation of the output beam, with the cavity of the G-channel further including an etalon that produces a plurality of longitudinal G-channel resonant cavity modes which define a spectral width of the G-channel; and

a B-channel receiving a third portion of the output beam and generating the B beam, with the B-channel including a fourth nonlinear crystal that frequency-doubles the third portion of the output beam, and a lasing cavity having a Ti;

S laser crystal pumped with the frequency-doubled output beam and producing a lasing wavelength that is twice the wavelength of the B-beam, said lasing wavelength being frequency-doubled by a fifth nonlinear crystal located in the lasing cavity and producing the B-beam.

15. The system of claim 14, further comprising three LCD panels, each panel optically and electronically coupled with one of the R,G,B beams to provide a full color LCD display system.

22. A method of producing a pulsed laser R, G, B light source of reduced speckle noise useful in a full color display system, which method comprises:

a) providing a pulsed laser output beam;

b) generating by crystal-based, non-linear frequency conversion, a G beam with spatial incoherency, by multi-longitudinal mode operation produced by an etalon located in a G-channel cavity, from the output beam;

c) generating, by optically pumping a Ti;

S laser crystal with frequency-doubled output beam radiation to produce an intermediate lasing wavelength and crystal-based, intra-cavity non-linear frequency conversion of the intermediate lasing wavelength, a B beam from the output beam;

d) generating from the output beam, by crystal-based, non-linear frequency conversion, an intermediate beam having a spectral width substantially greater than a spectral width of the output beam and a wavelength longer than the wavelength of the output beam, and subsequent crystal-based, non-linear sum frequency mixing of the intermediate beam with the output beam an R beam with a spectral width determined by the spectral width of the intermediate beam; and

e) mixing the generated R,G and B beams to provide a full color beam with reduced speckle noise.

23. The method of claim 22, wherein the mixed full color beam produces a well color balanced, white laser light source.

24. The method of claim 22, further including modulating an intensity of the R, G, B beams and projecting the modulated beams on a projection screen to provide a full color video image.

25. The method of claim 22 wherein the output beam wavelength is a 1047 nm, 1064 nm or 1342 nm.

26. The method of claim 22 which includes generating an R beam of 626-629 nm, a G beam of 532 nm or 523.5 nm, and a B beam of 452 nm or 447 nm.

27. The method of claim 22, further including:

a) amplifying the pulsed laser output beam by a power amplifier means having a neodymium-yttrium vanadate laser medium; and

b) side-pumping the neodymium-yttrium vanadate laser medium with a single or multiple diode laser bar.

28. The method of claim 22 which includes generating the output laser beam at a wavelength of 1047 nm or 1064 nm.