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Liquid-crystal–on–silicon (LCOS) technology can be regarded
a hybrid technology, with features of both digital light processing
(DLP) and high temperature polysilicon (HTPS).
DLP is based on microelectromechanical systems (MEMS)
technology and consists of an array of electrically oriented
aluminum mirrors (one per pixel). It is operated in reflection,
allowing binary images to be created depending upon
the local deflection of light. |
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Liquid-crystal–on–silicon (LCOS) microdisplay technology
offers the greatest performance/cost ratio of all display technologies
by combining the high resolution and performance
of silicon VLSI with controlled liquid-crystal optical modulation.
To view directly in the form of a conventional TV-like
display, one or more LCOS display panels need to be projected
onto a viewable screen, as shown in Fig. 1.1 LCOS
projection is non-trivial since the panels are reflective.
Modulated light forms a reflected beam with a spatially
varying polarization state, which occupies the same region
of space as the uniform input illuminating light. |
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A novel RYGB four-panel liquid-crystal-on-silicon (LCOS) projection system is presented that utilizes the otherwise discarded yellow emission of the industry standard UHP mercury illumination source. The system uses all four available ports of the successful 4xPBS/polarization filter architecture with system output estimated at ~75% brighter than EBU standard gamut RGB systems and with a larger than NTSC color gamut. |
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Contrast limits are investigated for MacNeille PBS based LCOS projection systems that use retarder stack filters (RSF). The two contributing factors are considered separately; namely the color management system and the panel port. To enhance performance of the former, skew ray compensated RSFs are introduced. For the latter, a general methodology is presented to optimize contrast by compensating the LCOS panel. It is shown that the orientation of the LCOS panel and compensator, relative to the MacNeille PBS, is critical. The significant impact of AR coating performance on system contrast is also revealed. A high contrast architecture will be presented by way of example. |
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A general three-step methodology is presented to optimize contrast when compensating
LCoS panels. The first step acts to compensate the in-plane residual retardation, while the second one
improves the field of view (FOV) using either MacNeille-type or wire-grid polarizing beamsplitters (PBS).
The orientation of the LCoS panel and compensator, relative to the MacNeille PBS, are critical to achieve
good system contrast. The final step is to account for reflections from anisotropic material, which can contribute
field componenets that appear as on-state light, limiting contrast. |
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A general three-step methodology is presented to optimize contrast when compensating LCoS panels. The first step acts to compensate the in-plane residual retardation, while the second one improves the field of view (FOV) using either MacNeille-type or wire-grid polarizing beamsplitters (PBS). The orientation of the LCoS panel and compensator, relative to the MacNeille PBS, are critical to achieve good system contrast. The final step is to account for reflections from anisotropic materials, which appear as on-state light, limiting contrast. |
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Presented is an optimization strategy for three-panel, LCoS projection systems based on a shared PBS/polarization filter approach. It first considers the optical elements within the projection path and gradually works backward towards the illumination, finally proposing two optimal system designs. Specific trade-offs between component performances within the two systems are then considered, and an analytic model described. Measured system results are compared to the model output. |
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A full-color sequencer is described, based on a color management kernel used in two-panel liquid crystal on silicon (LCOS) projection systems. A polarizing beam-splitter (PBS) creates two modulation paths. Retarder stack filters are used for color control, and single-pixel LC devices are used to modulate the state of polarization of each primary. |
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Novel color splitting and combining solutions are now possible with ColorSelect® filters developed by ColorLink Inc., which utilize polarization rather than thin film interference or absorption effects for controlling color. ColorSelect® based on ColorLink’s proprietary retarder stack technology and efficiently rotates the state of polarization of a primary color band by 900, while the complementary color band retains the input state of polarization. The combination of PBS and our ColorSelect® results in novel color management systems, such as ColorQuad®, which has become a benchmark for color management in high performance LCoS projection systems. The basic functionalities of ColorSelect® will be reviewed. Many feasible color management architectures will be explored. |
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A novel compensation scheme for correcting geometrical depolarization affects in cube polarizing beamsplitters is presented.
The low cost, oblique, uniaxial birefringent components used can significantly improve system performance, e.g. the contrast
of LCoS projection systems. The scheme is generally applicable to all mirror-like beamsplitting elements whose performance
can be improved by minimizing geometric polarization mixing. |
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The paper describes the methodology behind designing color management systems for 1,2 and 3 panel LCoS video projection systems.
Examples of architectures are described in detail, which include ColorLink’s 2-panel system and the ColorQuad Filter design and fabrication issues are presented relating to overall system performance. |
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Compact liquid crystal on silicon (LCOS) based projection engines have been demonstrated that use retarder stack filters with polarizing
beamsplitters as the basis of a color management system. A new class of retarder stack filter compensates for the geometrical rotation characteristic of polarizing beamsplitters, further improving attainable system performance. |
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A new two-panel architecture is discussed for projection systems based on liquid crystal on silicon (LCOS) panels. It is enabled by ColorLink's ColorSwitchTM and ColorSelectTM technologies. A first prototype has demonstrated performance of 325:1 contrast and 400 lumens using a UHP 120W lamp. This paper will cover system design and function, and will include a comparison of performance to alternative single and three panel approaches. |
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Based on ColorLink's ColorSelect polarization filter technology, and used in conjunction with polarizing beamsplitters, the system
gives excellent performance. |
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The ColorSwitch developed specifically for projection systems uses a unique two-polarizer additive-mode design. Three retarder stack based stages are cascaded, each independently operating on an additive primary. |
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A technology for manipulating color is presented which utilizes polarization, rather than thin-film interference or absorption effects. Retarder stack technology produces high performance filtering, color separation/combining, and chromatic polarization control operations. These structures are light efficient and provide saturated colors when used in sequential and subtractive (stacked-panel) display modes. |
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We report on recent progress in the development of a new liquid crystal color shutter technology that provides high throughput and saturated color. These devices, when combined with high frame rate displays or imagers, convert monochrome to color using the sequential color technique. The current focus is on designs that are compatible with low cost nematic liquid crystal switches. |
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We report a new switchable RGB color shutter that provides better color saturation, a 400% improvement in color band transmission over dye-based shutters, and sub-millisecond transition times. The improvements are achieved via a complementary color polarizers and achromatic LC polarization rotator technologies.
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Field-sequential color display and digital color cameras require tunable filters with high-throughput, saturated colors, rapid switching between bands. ColorLink has developed a new digital tunable filter technology that provides >37% average transmission of unpolarized light in each primary band, saturated colors, sub-millisecond transition between colors, and view-angles exceeding +30°. Performance improvements are derived from proprietary color polarizer and achromatic liquid crystal switch technologies.
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