Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/10—Beam splitting or combining systems
  • G02B27/1006—Beam splitting or combining systems for splitting or combining different wavelengths
  • G02B27/102—Beam splitting or combining systems for splitting or combining different wavelengths for generating a colour image from monochromatic image signal sources
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
  • G02B26/0808—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more diffracting elements
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/10—Beam splitting or combining systems
  • G02B27/1006—Beam splitting or combining systems for splitting or combining different wavelengths
  • G02B27/102—Beam splitting or combining systems for splitting or combining different wavelengths for generating a colour image from monochromatic image signal sources
  • G02B27/104—Beam splitting or combining systems for splitting or combining different wavelengths for generating a colour image from monochromatic image signal sources for use with scanning systems
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/10—Beam splitting or combining systems
  • G02B27/14—Beam splitting or combining systems operating by reflection only
  • G02B27/145—Beam splitting or combining systems operating by reflection only having sequential partially reflecting surfaces
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/10—Beam splitting or combining systems
  • G02B27/14—Beam splitting or combining systems operating by reflection only
  • G02B27/148—Beam splitting or combining systems operating by reflection only including stacked surfaces having at least one double-pass partially reflecting surface
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/10—Beam splitting or combining systems
  • G02B27/14—Beam splitting or combining systems operating by reflection only
  • G02B27/149—Beam splitting or combining systems operating by reflection only using crossed beamsplitting surfaces, e.g. cross-dichroic cubes or X-cubes
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
  • H04N9/3129—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] scanning a light beam on the display screen

Definitions

• the present invention is related to a scanning line color display system, and particularly to a modulator device for use in a single path color projection system comprising a 5 plurality of dichroic plates in optical contact with a corresponding plurality of locations on a surface of at least one tunable light modulator unit.
• Projection display systems have recently become increasingly popular for a multiple of applications, ranging from e.g., rear projection consumer TV's to front projector Q products for presentation purposes.
• Several different light modulator technologies exist for projection displays and the light modulator is currently typically based on Digital Micro mirror device (DMD), Liquid Crystal on Silicon (LCOS) or Liquid Crystal Display (LCD) technology.
• DMD Digital Micro mirror device
• LCOS Liquid Crystal on Silicon
• LCD Liquid Crystal Display
• Several new technologies have also recently been proposed, based on one-dimensional light modulator arrays for line scanning projection using laser s illumination, e.g., Grating Light Valve (GLV), Grating Electromechanically System (GEMS), and DxP.
• GLV Grating Light Valve
• GEMS Grating Electromechanically System
• DxP DxP
• a typical scheme is to use systems with multiple light paths and multiple light modulators.
• the light from the illumination source is divided into separate optical paths with different spectral bands, each optical path being individually modulated by separate light valves, and the resulting light output from the different paths being merged together at the screen by projection optics in order to achieve images with color information.
• Examples of such approaches are three-channel LCD, LCOS, and DMD 5 projectors.
• Fig. 2 is an illustration of a prior art modulator used in a color projection system.
• Three different modulators, 6R, 6G, and 6B, are illuminated with red, green, and blue laser light respectively.
• Each modulator is preceded by beam-shaping relay optics, 5R, 5G, Q and 5B respectively.
• the modulated beams are coaxially aligned into a single path with an X-prism, 7.
• the projection system comprises projection optics, 8, a schlieren stop, 9, followed by a rotating mirror, 10, that projects (scans) the modulated light beam across a screen surface, 11, to generate a 2D-image.
• the light valve modulates the separate spectral bands using time sequential differentiation in combination with a synchronized adaptive color filter in the optical path, like e.g., in a single-channel DMD projector with color wheel.
• the solution provides a system with low complexity and the use of a single modulator, the drawback of the solution is much reduced brightness efficiency compared to multiple-path solutions, due to the spectral filtering of the light.
• the solution reduces time slots that are available for displaying each image frame, which for digital pulse width modulated display systems in particular, reduces the dynamic range and gray scale resolution of the system, hi addition, the solution requires increased bandwidth, and hence the cost and complexity of the corresponding high bandwidth driving electronics.
• a different solution is to apply color filters directly on the pixel structure on the display, with one pixel dedicated to an individual spectral band, which selectively reflect, absorb, or transmits the incoming light and passes on a spatially separated modulated color image.
• An example of such a solution is a single-channel transmissive LCD projector.
• the drawback with single-channel transmissive LCD projectors is that the brightness efficiency is low due to color filtering of the incoming light, hi addition, the light modulator must have an increased resolution, as each pixel is dedicated to an individual color, which typically significantly increases both the size and cost of the modulator chip.
• the modulator in such a single-chip system must have three times the resolution of a comparable modulator in a three-channel system in order to achieve the same color resolution on a display screen.
• a larger chip area based modulator increases also the aperture size and cost of the optical system.
• Another prior art approach for single-channel color images with two dimensional micro- displays is to apply spatially separated spectral bands on the display, typically by means of angular differentiation, where each pixel is dedicated to individual spectral bands, but where the pixels of the light modulator itself does not perform any spectral filtering.
• This method could be significantly more efficient compared to the previous described solutions above involving color filtering.
• the cost and complexity of the system optics is typically increased, and with same increased pixel number requirements as above, the cost is also increased.
• EP 0606136 A discloses a micro mechanical light modulator (62) and accompanying printer system.
• the printing system comprises a laser (51) that meets a first and split light beam (52).
• a first dichroic mirror (56) is the unsplit light beam (52) divides in a first light beam (58) and a second light beam (59) with different wave length.
• the disadvantages of prior art solutions as described above is solved by arranging a plurality of dichroic plates in optical contact with a corresponding plurality of locations on a surface of at least one tunable light modulator unit in a modulator device.
• An example of embodiment of the present invention is based on tunable diffraction gratings. Such gratings have been disclosed in the literature, refer for example Guscho: Physics of reliefography, 1992 Nauka Moscow. The basic principles of these modulators are well known to a person skilled in the art and have been used for projection applications since the introduction of the Eidophor project over 60 years ago.
• the working principle of a tunable diffraction grating is based on light diffraction due to surface modulation in a thin gel layer or a membrane (elastomer) with equal optical and functional characteristics.
• a modulator comprises a thin layer of gel (or membrane, elastomer) 1, attached to a transparent modulator prism 2.
• the gel membrane is index matched to the prism glass, and the gel has low light absorption (less than 2 % in a typical system).
• the gel layer is 15-30 ⁇ m thick.
• Electrodes, 3 are processed on a flat substrate layer separated from the gel surface by a thin air gap (5-10 ⁇ m thick). The spacing can be arranged differently as known to a person skilled in the art.
• An ITO (indium tin oxide) layer, 4 is used to apply a bias voltage across the gel and the air gap. As a result, a net force acts on the gel surface (membrane) due to the electric field. In addition it is possible to individually address each signal electrode. By applying a local signal voltage, forces are applied to the gel surface (membrane), resulting in a surface modulation.
• Electrodes may be grouped together in patterns providing local surface modulation of the gel or membrane due to the applied signal voltage on those electrodes, thus providing control and geometric arrangement of individual modulator pixels and/or groups of pixels.
• such a light modulator provides the opportunity to design different individual modulators defined by their corresponding arrangement of the adjacent located electrodes on the same gel or membrane surface.
• this modulator design may be utilized in a modulator device according to the present invention.
• separate modulator units may be used in the modulator device according to the present invention.
• different colors of the light path in an RGB projector system is split/recombined by the same component according to the present invention, thereby reducing size and improving tolerances. Furthermore, the assembly process is much easier since the RGB modulator components can be aligned against each other on a chip level.
• Figure 1 depicts a modulator design according to prior art.
• Figure 2 depicts a color projection system according to prior art.
• Figure 3 illustrates an example of embodiment of a modulator device according to present invention.
• Figure 4 illustrates an example of embodiment of a color projection system comprising a modulator design according to figure 3
• Figure 5 is an illustration of another example of embodiment of the present invention.
• Figure 6 is an illustration of another example of embodiment of the present invention.
• Figure 3 depicts an example of embodiment of the present invention.
• Red, green, and blue laser light, 12 is incident on a modulator prism 50.
• the light is reflected off a stack of dichroic plates, 13, which is in optical contact with the modulator prism 50.
• the effect of said reflection is that the incident light, 12, is divided into three separate beams of different colors (red, green, and blue), 12R, 12G, and 12B.
• Each beam is then incident on separately modulating parts of the modulator gel surface, 2.
• Different patterns of the electrodes, 3R, 3 G, and 3B makes it possible to control the angles of the diffracted light at the different wavelengths.
• FIG. 4 An example of color projection system using a modulator according to the example of embodiment illustrated in figure 3 is depicted in figure 4.
• the different laser colors, R, G, and B (red, green, and blue) are coaxially aligned with the aid of two dichroic filters (other components, e.g., an X-prism can also be used to perform this alignment), 14R and 14G and directed through beam-shaping relay optics (common to all colors), 5, to the modulator, 15, which modulates the different beams individually and directs them towards the projection optics, 8.
• a schlieren stop, 9, is used to filter out unwanted diffraction orders and a scanning mirror, 10, is used to generate a 2D-image on the screen, 11.
• the screen 11 is not necessary a canvas screen.
• the screen can be for example the retina of a human eye, where said display system is denoted as a retina display system. Any kind of device, material or system that can provide an imaging effect of the light outgoing form said modulator device according to the present invention may be used in a display system according to the present invention.
• Torodial projection optics may be used to make the projected images of the individual colors coincide on the screen. Using ordinary optics will cause the projected line images of the different colors to be separated spatially in the scanning direction (defined by the direction of movement of the mirror 10) on the screen. This means that the modulator controls the color information in different parts of the image at any given time. To compensate for this a time delay is introduced in the electronics controlling the image color information sent to the modulator.
• Red, green, and blue laser light, 12 is incident on a modulator prism.
• the light is reflected off an area of a stack of dichroic plates, 13a, which is in optical contact with the modulator prism.
• the effect of said reflection is that the incident light, 12, is divided into three separate beams of different colors (red, green, and blue), 12R, 12G, and 12B.
• Each beam is then incident on separately modulating parts of the modulator gel surface, 2.
• Different patterns of the electrodes, 3R, 3G, and 3B makes it possible to control the angles of the diffracted light at the different wavelengths.
• the modulated beams are directed back to another area of the dichroic stack, 13b.
• the two areas of the dichroic stack, 13a and 13b differ from each other by the applied dichroic coatings performing the wavelength selection at the reflective interfaces. This makes the modulated beams coaxially aligned prior to be outgoing from the modulator prism.
• An advantage of this embodiment is that the embodiment removes the need for toroidal optics or time delay processing of the image signal as necessary in prior art solutions as described above.
• the modulator depicted in figure 3 can be used in a reversed mode where the incident light is spatially separated and is directly directed onto different modulating components after which the light is directed to the dichroic stack which coaxially aligns the modulated beams into a single beam path achieving much the same benefits as the modulator depicted in figure 5.
• the incident light are three separate beams reaching the modulator device on the right hand side of the partitioning, while the output from the device is on the left hand side of the modulator device.
• FIG. 6 Another example of embodiment of the present invention is depicted in figure 6, where an additional (with respect to the modulator depicted in figure 3) prism part is in optical contact with both the dichroic stack and the part of the modulator prism on which the modulating components are attached.
• the incident beam 12 is divided into its wavelength components by the dichroic stack, 13.
• the separate beams are incident on separately modulating parts of the modulator gel surface, 2 after which the modulated beams are directed through the additional prism part back to the dichroic stack, 13, to be coaxially aligned prior to be outgoing from the modulator.
• the advantage of this solution is that only one set of dichroic coatings is needed for the dichroic stack.
• the additional prism part can be manufactured by optically connecting two right-angle prisms together.
• all three colors may be modulated at the same time using only one modulator device.
• the reduction of components in the system makes the assembly process much easier and less expensive as the alignment between the different modulator components are already made with high accuracy on the modulator chip.
• the same beam- shaping relay optics can be used for all three colors, again saving space and money.
• handling the color separation/combination using a dichroic stack is preferable compared to using any kind of color combining prism.
• the color combining prism e.g., the x-prism depicted in figure 2
• the dichroic stack consists of plane-parallel dichroic filters with no need of specific alignment procedure during the assembly. In addition, it is easier to achieve tight tolerances when manufacturing plane-parallel optics than manufacturing optical components having specific angles.
• the modulating unit which in a preferred example of embodiment of the present invention is a TDG type of modulator, may be of another type of modulator as known to a person skilled in the art.
• the unit used either has separate modulating surfaces for said respective ones of the separated beams, ore that a specific type of modulator unit is used for each separate beam, and that are combined into one functional unit located the same way as described for the TDG unit in the preferred example of embodiment.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• General Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Projection Apparatus (AREA)

Applications Claiming Priority (2)

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Cited By (4)

Citations (4)

• 2005
  • 2005-10-19 NO NO20054834A patent/NO20054834D0/no unknown
• 2006
  • 2006-10-18 WO PCT/NO2006/000363 patent/WO2007046710A1/en active Application Filing

Patent Citations (4)

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