30-05-2012, 12:42 PM
Laser TV for Home Theater
[attachment=23501]
INTRODUCTION
As the multimedia society has come, the needs for large area display is increasing more rapidly. So many kinds of
projection displays are now developed and are developing, such as LCD, DMD, LCOS and so on. Most projection
displays are now using the lamp as a light source, so the effort for using the laser as a light source is continued for its
merits of laser1, 2. The advantages of using the laser light for projection displays are come from the original
characteristics of laser. The main advantages of scanning laser projection displays are high contrast ratio, excellent
expression of natural color and infinite depth of focus. Laser light is polarized, so it can yield a higher contrast ratio by
using the proper polarized optics. The monochromatic property and color saturation of the laser light can increase the
color space about three times larger than that of the conventional phosphor system3, 4. The wavelengths of lasers cover
more than 90% of all colors which can be perceived by the human eye. Laser has a long coherence length and a low
beam divergence, so one can achieve infinite depth of focus with the proper display technology, such as a raster
scanning. Projection image is no longer limited to a flat screen and it can be projected at any other surface. In spite of
these excellent characteristics, laser TV for home theater could not realized yet, for the lack of laser-related
technologies. The most obstacle for home theater of laser display is the compact, high power blue and green laser
sources. It is however clear that we can use the diode laser sources within several years due to the rapid progress of the
semiconductor laser technologies. The successful development of compact laser TV will open a new area of home
application of the laser light.
LASER TV
a schematic drawing of the basic layout of the laser TV. It is mainly composed of blue, green and red
laser light sources, three acousto-optic modulators, a laser beam combining part (a high-reflection mirror and two
dichroic mirrors), a polygon scan mirror, a galvanometer and optical lenses.
Blue, green diode-pumped solid state (DPSS) lasers and a red diode laser are used as a light source. The wavelengths of
the blue, green and red are 457 nm, 532 nm and 648 nm, and the output powers are 350 mW, 700 mW and 500 mW,
respectively. The power levels of lasers are adjusted for white color balance. Diode-pumped solid state (DPSS) lasers
are an exciting tool that combines the beam quality of a gas laser, small size and efficiency of a diode laser with single
line output.
BREWSTER-ANGLE TYPE AOM
The acousto-optic modulator (AOM) is fabricated for laser beam modulation. The carrier frequency of the AOM is 350
MHz for XGA resolution. The entrance window is cut at Brewster angle, so the laser beam is incident on the crystal
surface with the Brewster angle. TeO2 crystal is used as an optical medium and 36°-Y cut LiNbO3 (LN) is attached as a
transducer. In case of Brewster-angle type AOM, any optical coating does not needed on the crystal surface, but the
transmittance of 99% can be acquired.
MEMS OPTICAL SCANNER
To use the scanning mirror for laser display, the size of a scanning mirror must be larger than that of the laser beam and
the laser beam must be scanned linearly with analog operation to make an image without distortion. To control the
scanning mirror of such large size, the large driving force is also required. But the conventional electrostatic scanning
mirror with two parallel electrode plates are not easy to control linearly, because the driving force is related to the
square of the applied voltage and inversely related to the square of the electrode gap, which varies according to the
movement of the mirror plate. Though the mirror size becomes larger, the driving force can not be increased so much
in the conventional electrostatic scanning mirror, because the electrode gap must be increased also for the same tilting
angle9. As the method to satisfy such requirements for laser display, the scanning mirror having vertical comb fingers
has been designed and fabricated10, 11. As the mirror size becomes larger, the driving force generated by vertical comb
fingers becomes larger than that of the conventional scanning mirror. The driving force is only related to the square of
the applied voltage with the same electrode gap, so this scanning mirror can be controlled very linearly according to the
applied voltage12.
[attachment=23501]
INTRODUCTION
As the multimedia society has come, the needs for large area display is increasing more rapidly. So many kinds of
projection displays are now developed and are developing, such as LCD, DMD, LCOS and so on. Most projection
displays are now using the lamp as a light source, so the effort for using the laser as a light source is continued for its
merits of laser1, 2. The advantages of using the laser light for projection displays are come from the original
characteristics of laser. The main advantages of scanning laser projection displays are high contrast ratio, excellent
expression of natural color and infinite depth of focus. Laser light is polarized, so it can yield a higher contrast ratio by
using the proper polarized optics. The monochromatic property and color saturation of the laser light can increase the
color space about three times larger than that of the conventional phosphor system3, 4. The wavelengths of lasers cover
more than 90% of all colors which can be perceived by the human eye. Laser has a long coherence length and a low
beam divergence, so one can achieve infinite depth of focus with the proper display technology, such as a raster
scanning. Projection image is no longer limited to a flat screen and it can be projected at any other surface. In spite of
these excellent characteristics, laser TV for home theater could not realized yet, for the lack of laser-related
technologies. The most obstacle for home theater of laser display is the compact, high power blue and green laser
sources. It is however clear that we can use the diode laser sources within several years due to the rapid progress of the
semiconductor laser technologies. The successful development of compact laser TV will open a new area of home
application of the laser light.
LASER TV
a schematic drawing of the basic layout of the laser TV. It is mainly composed of blue, green and red
laser light sources, three acousto-optic modulators, a laser beam combining part (a high-reflection mirror and two
dichroic mirrors), a polygon scan mirror, a galvanometer and optical lenses.
Blue, green diode-pumped solid state (DPSS) lasers and a red diode laser are used as a light source. The wavelengths of
the blue, green and red are 457 nm, 532 nm and 648 nm, and the output powers are 350 mW, 700 mW and 500 mW,
respectively. The power levels of lasers are adjusted for white color balance. Diode-pumped solid state (DPSS) lasers
are an exciting tool that combines the beam quality of a gas laser, small size and efficiency of a diode laser with single
line output.
BREWSTER-ANGLE TYPE AOM
The acousto-optic modulator (AOM) is fabricated for laser beam modulation. The carrier frequency of the AOM is 350
MHz for XGA resolution. The entrance window is cut at Brewster angle, so the laser beam is incident on the crystal
surface with the Brewster angle. TeO2 crystal is used as an optical medium and 36°-Y cut LiNbO3 (LN) is attached as a
transducer. In case of Brewster-angle type AOM, any optical coating does not needed on the crystal surface, but the
transmittance of 99% can be acquired.
MEMS OPTICAL SCANNER
To use the scanning mirror for laser display, the size of a scanning mirror must be larger than that of the laser beam and
the laser beam must be scanned linearly with analog operation to make an image without distortion. To control the
scanning mirror of such large size, the large driving force is also required. But the conventional electrostatic scanning
mirror with two parallel electrode plates are not easy to control linearly, because the driving force is related to the
square of the applied voltage and inversely related to the square of the electrode gap, which varies according to the
movement of the mirror plate. Though the mirror size becomes larger, the driving force can not be increased so much
in the conventional electrostatic scanning mirror, because the electrode gap must be increased also for the same tilting
angle9. As the method to satisfy such requirements for laser display, the scanning mirror having vertical comb fingers
has been designed and fabricated10, 11. As the mirror size becomes larger, the driving force generated by vertical comb
fingers becomes larger than that of the conventional scanning mirror. The driving force is only related to the square of
the applied voltage with the same electrode gap, so this scanning mirror can be controlled very linearly according to the
applied voltage12.