Color laser display employing excitation solid laser unit,...

Details Color laser display employing excitation solid laser unit,... Color laser display employing excitation solid laser unit,...

2001-03-14

2004-07-20

Adams, Russell (Department: 2851)

Optics: image projectors

Composite projected image

Multicolor picture

C372S075000, C362S035000, C359S430000, C359S204200

Reexamination Certificate

active

06764183

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a color laser display of a type where a screen is scanned with three-color laser light, and more particularly to a color laser display in which an excitation solid laser unit with a Pr
3+
-doped solid-state laser crystal, or a fiber laser unit with a fiber having a Pr
3+
-doped core, or a semiconductor laser unit with a GaN semiconductor laser element for exciting a surface-emitting semiconductor element, is employed as a laser light source.
2. Description of the Related Art
There is a conventional color laser display in which an image is projected onto a screen, which displays each color when irradiated with red, green, and blue light, by scanning the screen with laser light modulated based on each color image signal. In another conventional color laser display, an image obtained by modulating laser light with a spatial modulation element is projected onto a screen by a projection optics system. These types of color laser displays require a laser light source, whose output is of the order of W (watt), in order to meet the high-brightness requirement. Because of this, a high-output gas laser, such as an Ar
+
gas laser, a Kr
+
gas laser, etc., has been used as the laser light source. However, the gas laser has the disadvantage that its device size is increased and manufacturing costs are considerably high, because the energy conversion efficiency is low such as about 0.1% and a cooling mechanism is necessary.
Hence, excitation second-harmonic-generation (SHG) solid lasers have recently been used as visible short-wavelength laser light sources, as described in Jpn. J. Laser Focus World, p.52 (December 1997). For instance, an yttrium aluminum garnet (YAG) laser unit, which employs an excitation solid laser element of oscillating wavelength 1064 nm to emit laser light of green wavelength 532 nm, is higher in energy conversion efficiency than the aforementioned gas laser.
However, noise due to a conflict of longitudinal modes will occur as the aforementioned excitation SHG laser unit generates higher output. For example, Jpn. J. Laser Focus World (p 243, May 1998) discloses that an amount of noise due to the blue and green solid laser elements is 3% or less, while an amount of noise due to the red solid laser element is as much as 50%.
To control these longitudinal modes, it is conceivable to insert, for example, an etalon as a wavelength selecting element. However, in such a case, realization of perfect single mode oscillation results in a great loss in efficiency, and consequently, high output is no longer obtainable and there arises a problem that the laser display will not able to have high brightness. Thus, in the case of employing the excitation SHG solid laser unit as a light source for a laser display, a reduction in the size is attainable, but numerous problems remain unsolved with respect to high efficiency, device performance, and costs.
SUMMARY OF THE INVENTION
The present invention has been made in view of the problems found in the prior art. Accordingly, it is the primary object of the present invention to provide a color laser display that is capable of realizing size reduction, high efficiency, and noise reduction.
To achieve this end and in accordance with an important aspect of the present invention, there is provided a first color laser display comprising:
a red laser light source for emitting red laser light;
a green laser light source for emitting green laser light;
a blue laser light source for emitting blue laser light;
modulation means for modulating the red laser light, the green laser light, and the blue laser light, based on a red image signal, a green image signal, and a blue image signal;
a screen for displaying red, green, and blue when irradiated with the red laser light, the green laser light, and the blue laser light; and
projection means for projecting the red laser light, the green laser light, and the blue laser light onto the screen so that an image, carrying the red, green, and blue image signals, is displayed on the screen;
wherein an excitation solid laser unit, having a solid-state laser crystal doped with Pr
3+
and a GaN semiconductor laser element for exciting the solid-state laser crystal, is employed as at least one of the red laser light source, the green laser light source, or the blue laser light source.
In the first color laser display, the excitation solid laser unit may emit laser light of wavelength 600 to 660 nm by a transition of
3
P
0
→
3
F
2
or
3
P
0
→
3
H
6
, and this laser unit can be satisfactorily employed as the red laser light source. The excitation solid laser unit may also emit laser light of wavelength 515 to 555 nm by a transition of
3
P
1
→
3
H
5
, and this laser unit can be satisfactorily employed as the green laser light source. Furthermore, the excitation solid laser unit may emit laser light of wavelength 465 to 495 nm by a transition of
3
P
0
→
3
H
4
, and this laser unit can be satisfactorily employed as the blue laser light source.
In accordance with another important aspect of the present invention, there is provided a second color laser display comprising:
a red laser light source for emitting red laser light;
a green laser light source for emitting green laser light;
a blue laser light source for emitting blue laser light;
modulation means for modulating the red laser light, the green laser light, and the blue laser light, based on a red image signal, a green image signal, and a blue image signal;
a screen for displaying red, green, and blue when irradiated with the red laser light, the green laser light, and the blue laser light; and
projection means for projecting the red laser light, the green laser light, and the blue laser light onto the screen so that an image, carrying the red, green, and blue image signals, is displayed on the screen;
wherein a fiber laser unit, having a fiber with a Pr
3+
-doped core and a GaN semiconductor laser element for exciting the fiber, is employed as at least one of the red laser light source, the green laser light source, or the blue laser light source.
As with the first color laser display, the excitation solid laser unit of the second color laser display may emit laser light of wavelength 600 to 660 nm by a transition of
3
P
0
→
3
F
2
or
3
P
0
→
3
H
6
, and this laser unit can be satisfactorily employed as the red laser light source. In addition, the excitation solid laser unit of the second color laser display may emit laser light of wavelength 515 to 555 nm by a transition of
3
P
1
→
3
H
5
, and this laser unit can be satisfactorily employed as the green laser light source. Furthermore, the excitation solid laser unit of the second color laser display may emit laser light of wavelength 465 to 495 nm by a transition of
3
P
0
→
3
H
4
, and this laser unit can be satisfactorily employed as the blue laser light source.
In accordance with still another important aspect of the present invention, there is provided a third color laser display comprising:
a red laser light source for emitting red laser light;
a green laser light source for emitting green laser light;
a blue laser light source for emitting blue laser light;
modulation means for modulating the red laser light, the green laser light, and the blue laser light, based on a red image signal, a green image signal, and a blue image signal;
a screen for displaying red, green, and blue when irradiated with the red laser light, the green laser light, and the blue laser light; and
projection means for projecting the red laser light, the green laser light, and the blue laser light onto the screen so that an image, carrying the red, green, and blue image signals, is displayed on the screen;
wherein a semiconductor laser unit is employed as at least one of the red laser light source, the green laser light source, or the blue laser light source, and the semiconductor laser unit includes an excitation light source constructed of a semiconductor lase

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