AbstractâA Spectral multiplex 3D cinema projector is realized by inserting a color-band modulator between the light source and the optical engine of the ...
Proceedings of 3DSA2013, P5-1
Spectral Multiplex 3D Cinema Projector Junejei Huang1, Yuchang Wang1 and Chien-Cheng Kuo2 2
1 Display Solution Business Unit, Delta Electronics, Inc., Taoyuan, Taiwan Thin Film Technology Center, National Central University, Chungli, Taiwan
Abstract—A Spectral multiplex 3D cinema projector is realized by inserting a color-band modulator between the light source and the optical engine of the projector. The color-band modulator comprises a multi-band filter, a TIR prism, a relay lens system and a mirror wheel. The rotation of the mirror wheel is synchronized with the frame rate of the projector. The input light is passing or reflected by the mirror wheel and then guided to be reflected or passing the multiband filter. Two groups of RGB lights are selected with the transmission or reflection of the multi-band filter.
waveband R2, green light beams of a waveband G2 and blue light beams of a waveband B2. The part of light selected by the reflection of the multiband filter is used to pass one lens of the eye glasses while the other part of light selected by the transmission of the multiband filter is used to pass the other lens of the eye glasses.
Keywords- spectral multiplex; wavelength multiplex; band filter; 3D projector; mirror wheel; color-band modulator
I.
INTRODUCTION
In recent years, stereoscopic display technology has become one of the most important technologies. The stereoscopic display technology use active shutter glasses or passive glasses. Passive glasses are better than active shutter glasses. As for passive glasses, it can further be categorized into polarization passive glasses and multi-band filter passive glasses. Multi-band filter passive glasses are better since it does not require operating with a silver screen, could be applied in an Ultra Short Throw (UST) projectors and compatible to most existing optical engine [1-3]. Conventionally, spectral multiplex 3D cinema projector uses rotating band-filter wheel. Because of the dichroic angle shift, a rotating band-filter wheel has the problems of big size and light loss. To overcome these difficulties, a color band modulator that moves the band-filter from the wheel position to the telecentric light path is proposed. II.
Figure 1. Multi-band filter
Figure 2 and 3 shows the structure of the color band modulator. The mirror wheel with one half reflected and the other half transparent is disposed at the stop position of the relay lens. The ring of the wheel is at one half part of the stop while the other half part of the stop is the air. A TIR prism is set after the input light beam. Neighbor to it is a right angle prism. Between the TIR prism and the right angle prism, the multi-band filter is set. The output light goes out from the output side of the TIR prism. The wheel rotates with a sequence synchronizes with the frame rate of the projector.
THE COLOR BAND MODULATOR
The core component in the color band modulator is the multi-band filter. The multi-band filter may be a transparent plate on which a plurality of optical coatings are disposed to allow the light beams of a plurality of specific wavebands to pass and reflect the light beams of a plurality of other specific wavebands. A typical multi-band filter is shown in figure 1. The light beams that transmitted by the multiband filter are defined as the first light beam, while the light beams that reflected by the multiband filter are defined as the second light beam. With reference to figure 1, the multiband filter can allow the red light beams of a waveband R1, green light beams of a waveband G1 and blue light beams of a waveband B1 to pass through, but reflect the red light beams of a
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Proceedings of 3DSA2013, P5-1 With two time sequences, the light source system is converted into light beams of two groups of wavebands and sent to the light valve of the projector, which could thus project a right-eye view image and a left-eye view image to the viewers to form a stereoscopic image.
Figure 2. The structure of the color band modulator and the light path reflected from the mirror wheel
Figure 4. Multi-band filters for eye-glasses
While receiving the first view angle image and the second view angle image projected by the projector, a viewer must wear a pair of passive glasses. Two sets of band filters for left and right eyes can be coated on the glasses, as shown in figure 4. The right lens of the passive glasses only allows the light beams of the waveband R1, the waveband G1 and the waveband B1 to pass, while the left lens of the passive glasses only allows the light beams of the waveband R2, the waveband G2 and the waveband B2 to pass. III. Figure 3. The structure of the color band modulator and the light path transmitted through the mirror wheel
TWO GROUPS OF RED, GREEN AND BLUE LIGHT SOURCES
The color band modulator is disposed between the light source and the light engine of the projector. It converts the original white light in the light source into two groups of white lights. These two groups of white lights are further divided into two groups of red, green and blue lights by the dichroic mirrors in the 3-chip projector.
Figure 2 shows the light path when the ring of the mirror wheel rotates to the position of the mirror part. The incoming light is converged by the first part of the relay lens to the ring of the mirror wheel and reflected by the mirror ring, made collimated by passing again the first part of the relay lens, entering into the right angle prism next to TIR prism and passing through the multi-band filter. The (R1, G1 and B1) group of light is selected by the transmission of the multi-band filter and going out from the TIR prism.
Figure 5 shows the spectrum of the original UHP lamp and the red, blue and green filters that used in the 3-chip projector. Figure 6 shows the results when the original white light in the UHP lamp is filtered by the red, green and blue dichroic mirrors in the 3-chip projector.
Figure 3 shows the light path when the ring of the mirror wheel rotates to the position of the transparent part. The light converges and passes at the ring positon of the mirror wheel, converges again at the other half part of the stop by passing the second part of the relay lens, made collimated by the first part of the relay lens, coming into the TIR prism and reflected by the multi-band filter. The (R2, G2 and B2) group of light is selected by the reflection of the multi-band filter and going out from the TIR prism
When a color band modulator is used between the UHP lamp and the 3-chip projector, the original white light is converted into two groups of white lights. Figure 7 shows the result when the first group of white light passes the red, green and blue filters in the 3-chip projector. Figure 8 shows the
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Proceedings of 3DSA2013, P5-1 result when the second group of white light passes the red, green and blue filters in the 3-chip projector.
Figure 8. Reflected part from the multi-band filter shown in figure 1 Figure 5. Spectrum of the UHP lamp and the spectral distribution of the dichroic mirrors in the 3-chip projector
The color coordinates of the two groups of the white light can be calculated. Figure 9 shows the color gamut of these two groups of red, green and blue lights.
Figure 6. Spectral distribution of red, green and blue part of the original light source after filterd by the the dichroic mirrors in the 3-chip projector
Figure 9. Color gamut of two groups of red, blue and green light sources
Figure 7. Transmitted part from multi-band filter shown in figure 1
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Proceedings of 3DSA2013, P5-1 IV.
CONCLUSION
The spectral multiplex 3D cinema projector can be realized by using a color band modulator disposed between the original light source and the existing optical engine of the cinema projector. A multi-band filter in the color band modulator is used to convert the original light source into light source of two groups of wavebands. A high efficiency can be obtained because the multi-band filter is placed in the telecentric light path of the color band modulator. Other advantages include: a low manufacturing cost, a simplified optical structure, a miniaturized volume and wide color gamut when used in 2D mode.
REFERENCES
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[1]
Ernst Lueder, 3D Displays, John Wiley & Sons, SID series in display technology, 1997, pp. 41-48.
[2]
Jorke, H., "Advanced stereo projection using interference filters," J. SID, 17.5, 2009, p 407.
[3]
Bart Maximus, Koen Malfalt, Koenraad Vermerirsch, "Method and device for performing stereoscopic image display based on color selective filters," US patent 2007/0127121, Jun. 7 2007.
