WO1999042898A9 - Image generating system - Google Patents
Image generating systemInfo
- Publication number
- WO1999042898A9 WO1999042898A9 PCT/US1999/003347 US9903347W WO9942898A9 WO 1999042898 A9 WO1999042898 A9 WO 1999042898A9 US 9903347 W US9903347 W US 9903347W WO 9942898 A9 WO9942898 A9 WO 9942898A9
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- compensator
- light modulator
- spatial light
- liquid crystal
- state
- Prior art date
Links
Classifications
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
- G02F1/139—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
- G02F1/141—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent using ferroelectric liquid crystals
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1347—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
- G02F1/13471—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells in which all the liquid crystal cells or layers remain transparent, e.g. FLC, ECB, DAP, HAN, TN, STN, SBE-LC cells
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/1336—Illuminating devices
- G02F1/133616—Front illuminating devices
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/13363—Birefringent elements, e.g. for optical compensation
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/13363—Birefringent elements, e.g. for optical compensation
- G02F1/133638—Waveplates, i.e. plates with a retardation value of lambda/n
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
- G02F2201/34—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 reflector
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2203/00—Function characteristic
- G02F2203/02—Function characteristic reflective
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2203/00—Function characteristic
- G02F2203/12—Function characteristic spatial light modulator
Definitions
- the present invention is a continuation-in-part of United States Patent Application Serial Number 09/025,160 (Attorney Docket Number DIS-P01 1 ) entitled "OPTICS ARRANGEMENT INCLUDING A COMPENSATOR CELL AND STATIC WAVE 5 PLATE FOR USE IN A CONTINUOUSLY VIEWABLE, REFLECTIVE MODE, FERROELECTRIC LIQUID CRYSTAL SPATIAL LIGHT MODULATING SYSTEM" (as Amended), filed February 18, 1998, which application is incorporated herein by reference.
- compensator arrangements for a continuously viewable, DC field-balanced, reflective, ferroelectric liquid crystal display system.
- the present invention relates generally to image generating systems including a 5 reflective type, ferroelectric liquid crystal (FLC) spatial light modulator (SLM). More specifically, the invention relates to an optics arrangement including an FLC compensator cell for allowing the system to generate a substantially continuously viewable image while DC-balancing the FLC material of both the SLM and the compensator cell.
- FLC ferroelectric liquid crystal
- SLM spatial light modulator
- FLC materials may be used to provide a low voltage, low power reflective spatial light 0 modulator due to their switching stability and their high birefringence.
- a problem with FLC materials, and nematic liquid crystal materials is that the liquid crystal material may degrade over time if the material is subjected to an unbalanced DC electric field for an extended period of time.
- liquid crystal spatial light modulators SLMs
- Nematic liquid crystal materials respond to positive or negative voltages in a similar manner regardless of the sign of the voltage. Therefore, nematic liquid crystals are typically switched ON by applying either a positive or negative voltage through the liquid crystal material. Nematic liquid crystal materials are typically switched OFF by not applying any voltage through the material.
- nematic liquid crystal materials respond to voltages of either sign in a similar manner
- DC balancing for nematic liquid crystal materials may be accomplished by simply applying an AC signal to create the voltage through the material.
- the use of an AC signal automatically DC balances the electric field created through the liquid crystal material by regularly reversing the direction of the electric field created through the liquid crystal material at the frequency of the AC signal.
- the materials are switched to one state (i.e. ON) by applying a particular voltage through the material (i.e. +5 VDC) and switched to the other state (i.e. OFF) by applying a different voltage through the material (i.e. -5 VDC).
- FLC materials respond differently to positive and negative voltages, they cannot be DC-balanced in situations where it is desired to vary the ratio of ON time to OFF time arbitrarily. Therefore, DC field-balancing for FLC SLMs is most often accomplished by displaying a frame of image data for a certain period of time, and then displaying a frame of the inverse image data for an equal period of time in order to obtain an average DC field of zero for each pixel making up the SLMs.
- the image produced by the SLM during the time in which the frame is inverted for purposes of DC field-balancing may not typically be viewed. If the system is viewed during the inverted time without correcting for the inversion of the image, the image would be distorted. In the case in which the image is inverted at a frequency faster than the critical flicker rate of the human eye, the overall image would be completely washed out and all of the pixels would appear to be half on. In the case in which the image is inverted at a frequency slower than the critical clicker rate of the human eye, the viewer would see the image switching between the positive image and the inverted image. Neither of these situations would provide a usable display.
- the light source used to illuminate the SLM is switched off or directed away from the SLM during the time when the frame is inverted.
- This type of system is described in copending United States Patent Application serial number 08/361 ,775, filed December 22, 1994, entitled DC FIELD-BALANCING TECHNIQUE FOR AN ACTIVE MATRIX LIQUID CRYSTAL IMAGE GENERATOR, which is incorporated herein by reference.
- this approach substantially limits the brightness and efficiency of the system.
- the magnitude of the electric field during the DC field-balancing and the time when the frame is inverted is equal to the magnitude of the electric field and the time when the frame is viewed, only a maximum of 50% of the light from a given light source may be utilized. This is illustrated in Figure la which is a timing diagram showing the relationship between the switching on and off of the light source and the switching of the SLM image data.
- the light source is switched on for a period of time indicated by Tl .
- the SLM is switched to form a desired image.
- the SLM is switched to form the inverse of the desired image during a time period T2.
- the light source is switched off during the time T2 as shown in Figure la.
- Figure lb shows pixel 10 when it is in its bright state
- Figure lc shows pixel 10 when it is in its dark state.
- a light source 12 directs light, indicated by arrow 14, into a polarizer 16.
- Polarizer 16 is arranged to allow, for example, horizontally linearly polarized light, indicated by the reference letter H and by arrow 18, to pass through polarizer 16.
- polarizer 16 blocks any vertically linearly polarized component of the light and thereby directs only horizontally linearly polarized light into pixel 10. This arrangement insures that only horizontally linearly polarized light is used to illuminate pixel 10.
- pixel 10 includes a reflective backplane 22 and a layer of FLC material 24 which is supported in front of reflective backplane 22 and which acts as the light modulating medium.
- the various components would typically be positioned adjacent one another, however, for illustrative purposes, the spacing between the various components is provided.
- the FLC material has a thickness and a birefringence which cause the material to act as a quarter wave plate for a given wavelength.
- the FLC material is typical of those readily available and has a birefringence of 0.142. Therefore a thickness of 900 nm causes the SLM to act as a quarter wave plate for a wavelength of approximately 510 nm.
- FLC material 22 has accompanying alignment layers (not shown) at the surfaces which have a buff axis or alignment axis that controls the alignment of the molecules of the FLC material.
- the SLM is oriented such that the alignment axis is rotated 22.5 degrees relative to the polarization of the horizontally linearly polarized light being directed into the SLM.
- the FLC also has a tilt angle of 22.5 degrees associated with the average optic axis of the molecules making up the FLC material. Therefore, when FLC material 24 of the pixel is switched to its first state, in this case by applying a +5 VDC electric field across the pixel, the optic axis is rotated to a 45 degree angle relative to the horizontally linearly polarized light.
- the pixel acts as a quarter wave plate for horizontally linearly polarized light at 510 nm.
- the optic axis is rotated to a zero degree angle relative to the horizontally linearly polarized light. This causes the pixel to have no effect on the horizontally linearly polarized light directed into the pixel.
- the tilt angle is the angle that the FLC optic axis is rotated one side or the other of the buff axis when the FLC material is switched to its first and second states.
- the light is monochrome at the wavelength at which the SLM acts as a quarter wave plate, in this case 510 nm.
- FLC material 24 converts the 510 nm wavelength horizontally linearly polarized light directed into the pixel and indicated by arrow 18 into circularly polarized light indicated by the reference letters C and arrow 26.
- Reflective backplane 22 reflects this circularly polarized light as indicated by arrow 28 and directing it back into FLC material 24.
- FLC material 24 again acts on the light converting it from circularly polarized light to vertically linearly polarized light as indicated by reference letter V and arrow 30.
- the vertically linearly polarized light 30 is directed into an analyzer 32 which is configured to pass vertically linearly polarized light and block horizontally polarized light. Since analyzer 32 is arranged to pass vertically linearly polarized light, this vertically linearly polarized light indicated by arrow 30 passes through analyzer 32 to a viewing area indicated by viewer 34 causing the pixel to appear bright to the viewer.
- FLC material 24 has no effect on the horizontally linearly polarized light directed into the pixel when the pixel is in its second state, which will be referred to hereinafter as its B state. This is the case regardless of the wavelength of the light. Therefore, the horizontally linearly polarized light passes through FLC material 24 and is reflected by reflective backplane 22 back into FLC material 24. Again, FLC material 24 has no effect on the horizontally linearly polarized light. And finally, since analyzer 32 is arranged to block horizontally linearly polarized light, the horizontally linearly polarized light is prevented from passing through to viewing area 34 causing the pixel to appear dark.
- Solid line 36 corresponds to the first case when the pixel is in its A state as illustrated in Figure 1 b and the dashed line 38 corresponds to the second case when the pixel is in its B state as illustrated in Figure lc.
- the resulting output of this configuration varies substantially depending on the wavelength of the light as indicated by line 36. In fact, only a little more than 50% of the horizontally linearly polarized light at 400 nm that is directed into the SLM is converted to vertically linearly polarized light using this configuration.
- polarizer 16 blocks vertically linearly polarized light and analyzer 32 blocks horizontally linearly polarized light.
- polarizer 16 and analyzer 32 must be different elements or must be provided as a polarizing beam splitter as will be described in more detail hereinafter. If both polarizer 16 and analyzer 32 were configured to pass the same polarization of light, they would be referred to as parallel polarizers and could be provided by the same element.
- a polarizing beam splitter may be used to replace both the polarizer and the analyzer.
- Figures 1 e and 1 f illustrate such a system when pixel 10 is in its A and B states respectively.
- light from light source 12 is directed into a polarizing beam splitter (PBS) 40 as indicated by arrow 42.
- PBS 40 is configured to reflect horizontally linearly polarized light as indicated by arrow 44 and pass vertically linearly polarized light as indicated by arrow 46.
- the horizontally linearly polarized light indicated by arrow 44 is directed into SLM 24.
- SLM 24 acts as a quarter wave plate as described above converting the horizontally linearly polarized light to circularly polarized light and reflective backplane 22 reflects this light back into SLM 24. Again. SLM 24 converts this circularly polarized light into vertically linearly polarized light as described above for Figure lb and as indicated by arrow 48. Since PBS 40 is configured to pass vertically linearly polarized light, this light passes through PBS 40 into viewing area 34 causing pixel 10 to appear bright.
- FIG. 1 illustrates a transmissive mode system 200 which includes an SLM 202, a compensator cell 204. a polarizer 206, and an analyzer 208.
- SLM 202 and compensator cell 204 each include an FLC layer which is switchable between an A and a B state. This results in four possible combinations of states for the SLM and compensator cell. For purposes of consistency in comparing various configurations described herein, these four cases will be defined as follows: Case 1 - compensator cell in B state, SLM pixel in A state Case 2 - compensator cell in B state. SLM pixel in B state Case 3 - compensator cell in A state.
- Cases 1 and 2 correspond to the normal operation of the system during which the compensator cell is in its B state and the SLM pixels are switched between their A and B states to respectively produce a bright or dark pixel.
- Figure 2b is a timing diagram showing the states of the light source, the SLM, and the compensator cell. As shown in Figure 2b. the light source remains ON throughout the operation of the system. During the first half of the time illustrated in Figure 2b, the pixels of the SLM are switched between their A and B states to produce a desired image.
- Cases 3 and 4 correspond to the time during which the frame is inverted for purposes of DC field balancing (i.e. the SLM pixel states must be reversed) and the compensator cell is switched to its A state to compensate for the inversion. This is illustrated by the second half of the diagram of Figure 2b.
- Case 1 and Case 3 must give the same results and Case 2 and Case 4 must give the same results. That is, for this configuration, Cases 1 and 3 must both produce a bright pixel and Cases 2 and 4 must both produce a dark pixel.
- both the FLC layer of the SLM pixel and the compensator cell are 1800 nm thick which causes them to act as a half wave plate for a wavelength of 510 nm when in the A state.
- the polarizer and analyzer perform the functions performed by polarizer 16 and analyzer 32, or alternatively PBS 40, of the reflective mode systems described above.
- Polarizer 206 is positioned optically in front of compensator cell 204 and the SLM pixel 202 such that it allows only horizontally linearly polarized light to pass through it into compensator cell 204.
- analyzer 208 which only allows vertically linearly polarized light to pass through is positioned optically behind SLM 202.
- Figures 2c and 2d illustrate the net result the above described transmissive system configuration has on light directed in to the system.
- Figure 2c shows the results for Case 1 and 2 during which the compensator cell is in its B state and the SLM is switched between its A state for Case 1 and its B state for Case 2.
- Case 1 is indicated by solid line 210 and Case 2 is indicated by dashed line 212.
- Figure 2d shows the results for Case 3 and 4 during which the compensator cell is in its A state and the SLM is switched between its B state for Case 3 and its A state for Case 4.
- Case 3 is represented by solid line 214 and Case 4 is represented by dashed line 216.
- this transmissive configuration produces identical results, that is a bright pixel, for Case 1 and 3 as indicated by lines 210 and 214, respectively. It also produces identical results for Cases 2 and 4 as indicated by lines 212 and 216, respectively. It should also be noted that this configuration produces relatively good results over the entire wavelength range from 400 nm to 700 nm. The worst results are at 400 nm where approximately 80% of the horizontally linearly polarized light is converted to vertically polarized light.
- a reflective type display system 300 including a reflective type SLM 302 having a reflective backplane 303, a compensator cell 304, a polarizer 306, and an analyzer 308 will be described.
- Compensator cell 304 is positioned adjacent to SLM 302.
- polarizer 306 is positioned to direct only horizontally linearly polarized light into compensator cell 304.
- the FLC material of SLM 302 and compensator cell 304 are configured to act as quarter wave plates for a wavelength of 510 nm rather than half wave plates as described above for the transmissive system of Figure 2a.
- the FLC materials of both SLM 302 and compensator cell 304 are 900 nm thick and both have a tilt angle of 22.5 degrees.
- the buff axis of the SLM is aligned with the horizontally linearly polarized light directed into the system by polarizer 306.
- the buff axis of compensator cell 304 is positioned perpendicular to the buff axis of SLM 302.
- Figures 3b and 3c illustrate the net result that system 300 has on light directed in to the system.
- Figure 3b shows the results for Case 1 and 2 during which the compensator cell is in its B state and the SLM is switched between its A state for Case 1 and its B state for Case 2.
- Case 1 is indicated by solid line 310
- Case 2 is indicated by dashed line 312.
- Figure 3c shows the results for Case 3 and 4 during which the compensator cell is in its A state and the SLM is switched between its B state for Case 3 and its A state for Case 4.
- Case 3 is represented by solid line 314 and Case 4 is represented by dashed line 316.
- system 300 produces identical results, that is, a bright pixel for Case 1 and 3 as indicated by lines 310 and 314, respectively. It also produces identical results for Cases 2 and 4 as indicated by lines 312 and 316, respectively.
- this configuration does not produce very good results over the entire wavelength range from 400 nm to 700 nm. The worst results are at 400 nm where only approximately 5% of the horizontally linearly polarized light is converted to vertically polarized light. At a wavelength of about 500 nm about 50% of the horizontally linearly polarized light is converted to vertically linearly polarized light.
- the display system includes a reflective ferroelectric liquid crystal spatial light modulator having a layer of ferroelectric liquid crystal light modulating medium divided into an array of individually controllable pixels Each pixel is switchable between a first pixel state and a second pixel state
- a polarizer arrangement includes a polarizer for polarizing the light entering the system and directing the polarized light into the spatial light modulator along an optical path having an optical path axis
- the reflective spatial light modulator acts on the polarized light to produce an optical output that is directed from the spatial light modulator back into the polarizing arrangement along substantially the same optical path axis that the polarized light is directed into the spatial light modulator
- the polarizing arrangement also includes an analyzer configured to receive and analyze the optical output of the spatial light modulator and to direct the analyzed optical output out of the system
- the polarizing arrangement is a polarizing beam splitting cube that acts as both the polarizer
- a compensator is positioned in the optical path between the pola ⁇ zer of the pola ⁇ zing arrangement and the spatial light modulator and in the optical path between the spatial light modulator and the analyzer
- the compensator includes a layer of ferroelectric liquid crystal light modulating medium switchable between a first compensator state and a second compensator state
- the compensator is used to invert the optical output of the spatial light modulator when the compensator is switched to the second compensator state
- the layer of ferroelectric liquid crystal light modulating medium of the compensator and the spatial light modulator have single pass retardances that are substantially different than one another
- the layer of ferroelectric liquid crystal light modulating medium of the compensator has a thickness substantially different than the thickness of the layer of ferroelectric liquid crystal light modulating medium of the spatial light modulator
- the compensator and the spatial light modulator combine so as to cause the display system to operate such that each pixel is capable of producing four different optical intensities for a display output corresponding to that pixel
- the display output corresponding to that pixel is a first optical intensity Du ⁇ ng
- the display output corresponding to that pixel is a second optical intensity.
- the display output corresponding to that pixel is a third optical intensity
- the first and fourth optical intensities being substantially equal and the second and third optical intensities being substantially equal
- the layer of ferroelectric liquid crystal light modulating medium of the compensator is a thickness and retardance that causes the compensator to function as approximately a half wave plate for visible.
- the layer of ferroelectric liquid crystal light modulating medium associated with a pixel of the spatial light modulator is a thickness and retardance that causes the pixel to function as approximately a quarter wave plate for visible light.
- the polarizing arrangement of the display system has a primary axis and the polarizer allows substantially only linearly polarized light aligned with the primary axis of the pola ⁇ zer to pass through the polarizer toward the spatial light modulator.
- the layer of ferroelect ⁇ c liquid crystal light modulating medium of both the compensator and the spatial light modulator each have an associated buff axis and tilt angle.
- the ferroelectric liquid crystal material is aligned generally at the tilt angle in a particular direction from the buff axis.
- the ferroelectric liquid crystal material is aligned generally at the tilt angle in a direction opposite the particular direction from the buff axis.
- the tilt angle of the layer of ferroelectric liquid crystal light modulating medium of the compensator is approximately one half that of the tilt angle of the layer of ferroelectric liquid crystal light modulating medium of the spatial light modulator.
- the polarizer arrangement acts as crossed polarizers.
- the buff axis associated with the layer of ferroelectric liquid crystal light modulating medium of the spatial light modulator is o ⁇ ented pe ⁇ endicular to the buff axis associated with the layer of ferroelect ⁇ c liquid crystal light modulating medium of the compensator.
- the buff axis associated with the layer of ferroelectric liquid crystal light modulating medium of either the compensator or the spatial light modulator is aligned with the primary axis of the pola ⁇ zer.
- the polarizer arrangement again acts as crossed polarizers.
- the buff axis associated with the layer of ferroelectric liquid crystal light modulating medium of the spatial light modulator is now oriented 1 12.5 degrees relative to the primary axis of the polarizer while the buff axis associated with the layer of ferroelectric liquid crystal light modulating medium of the compensator is oriented 11.25 degrees relative to the primary axis of the polarizer.
- the system includes a heating arrangement for heating the layer of ferroelectric liquid crystal light modulating medium of the compensator in order to maintain the layer of ferroelectric liquid crystal light modulating medium of the compensator at a substantially constant temperature.
- the compensator includes a transparent ITO layer that acts as the heating arrangement.
- the compensator and the spatial light modulator are positioned adjacent one another and in direct contact with one another.
- the heating arrangement is configured to maintain the layers of ferroelectric liquid crystal light modulating medium of both the compensator and the spatial light modulator at a substantially constant temperature.
- the layer of ferroelectric liquid crystal light modulating medium of the compensator has a tilt angle approximately one half that of the layer of ferroelectric liquid crystal light modulating medium of the spatial light modulator at the constant temperature maintained by the heating arrangement.
- the layer of ferroelectric liquid crystal light modulating medium of the compensator and the spatial light modulator are switched to and maintained in their first and second states by establishing and maintaining certain drive voltages through the layers of ferroelectric liquid crystal light modulating medium.
- the system uses lower compensator drive voltages to maintain the layer of ferroelectric liquid crystal light modulating medium of the compensator in the first and second compensator states compared to the drive voltages used to maintain the layer of ferroelectric liquid crystal light modulating medium of the spatial light modulator in the first and second pixel states.
- the lower compensator drive voltages cause the tilt angle of the layer of ferroelectric liquid crystal light modulating medium of the compensator to be approximately one half that of the tilt angle of the layer of ferroelectric liquid crystal light modulating medium of the spatial light modulator.
- the compensator drive voltages used to maintain the layer of ferroelectric liquid crystal light modulating medium of the compensator in the first and second compensator states include a leading edge spike of voltage at a voltage greater than the compensator d ⁇ ve voltages. This leading edge spike of voltage improves the speed at which the layer of ferroelectric liquid crystal light modulating medium of the compensator may be switched between the first and second compensator states.
- Figure la is a timing diagram illustrating the timing at which a light source for a prior art DC-balanced display system is switched ON and OFF.
- Figures lb and lc are diagrammatic cross sectional views of a pixel of a prior art reflective type SLM display system illustrating how the pixel acts on light when the pixel is in the ON and OFF states.
- Figure Id is a graph illustrating the effects the system of Figure lb and lc has on light after it passes through the system.
- Figures le and If are diagrammatic cross sectional views of a pixel of a prior art reflective type SLM display system including a polarizing beam splitter.
- Figure 2a is a diagrammatic cross sectional view of a prior art transmissive SLM display system.
- Figure 2b is a timing diagram illustrating the timing at which a light source for a prior art DC-balanced display system is switched ON and OFF.
- Figures 2c and 2d are graphs illustrating the effects the system of Figure 2a has on light after it passes through the system.
- Figure 3a is a diagrammatic cross sectional view of a prior art reflective SLM display system.
- Figures 3b and 3c are graphs illustrating the effects the system of Figure 3a has on light after it passes through the system.
- Figure 4a is a diagrammatic cross sectional view of a first embodiment of a reflective SLM display system designed in accordance with the present invention.
- Figures 4b-c are graphs illustrating the effects the system of Figure 4a has on light after it passes through the system
- Figure 5a is a diagrammatic cross sectional view of a second embodiment ot a reflective SLM display system designed in accordance with the present invention
- Figures 5b-c are graphs illustrating the effects the system of Figure 5a has on light after it passes through the system
- Figure 6 is a diagrammatic cross sectional view of a third embodiment of a reflective SLM display system designed in accordance with the present invention
- Figures 7a-b are diagrammatic cross sectional views of a fourth embodiment of a reflective SLM display system designed in accordance with the present invention
- Figure 8 is a diagrammatic cross sectional view of a fifth embodiment of a reflective SLM display system designed in accordance with the present invention
- Figure 9 is a diagram illustrating the relative rotational positions of the various components making up a first configuration of the system of Figure 8
- Figures 1 Oa-g are diagrams illustrating the relative rotational positions of the various components making up additional possible configurations of the system of Figure 8
- Figure 1 1 is a diagrammatic partial cross sectional view of a portion of a compensator cell including a first embodiment of heater arrangement designed in accordance with the present invention
- Figure 12 is a diagrammatic partial cross sectional view of a portion of a compensator cell and SLM including a second embodiment ot heater arrangement designed in accordance with the present invention
- Figure 13 is a graph illustrating the relative effects temperature has on the tilt angle of two different types of FLC material
- Figure 14 is a graph illustrating the relative effects that temperature and drive voltage have on the tilt angle of a typical FLC material
- Figure 15 is illustrates the use of a drive voltage waveform having a leading edge spike to improve the switching speed of a compensator cell that uses reduced drive voltage to reduce the tilt angle of the FLC material of the compensator cell
- Figure 16 is a graph indicating the effect that the compensator d ⁇ ve voltage has on the optical output of the system
- Figure 17 is a diagrammatic illustration of another embodiment of a spatial light modulator panel designed in accordance with the invention.
- Figure 18 is a schematic diagram illustrating a servomechanism circuit designed in accordance with the invention.
- An invention for providing methods and apparatus for producing a substantially continuously viewable reflective type SLM display system which is DC field-balanced and which is more efficient or brighter than would be possible using a reflective type SLM display system which simply turns off the light source during the DC field balancing portion of each image frame.
- numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, based on the following description, it will be obvious to one skilled in the art that the present invention may be embodied in a wide variety of specific configurations. Also, well known processes for producing various components and certain well known optical effects of various optical components will not be described in detail in order not to unnecessarily obscure the present invention.
- system 400 includes an SLM 402 having a reflective backplane 403, a compensator cell 404, a polarizer 405, and an analyzer 406.
- crossed polarizer 405 and analyzer 406 may be replaced with a polarizing beam splitter.
- System 400 is configured in a manner similar to that described above for system 300 of Figure 3a. That is, compensator cell 404 is positioned adjacent SLM 402. Also, polarizer 405 is positioned to direct only horizontally linearly polarized light into compensator cell 404.
- system 400 also includes a static quarter wave plate 408 positioned optically between compensator cell 404 and polarizer 405 and analyzer 406.
- SLM 402 may be made up of an array of any number of individually controllable pixels which are individually switchable between two states. For pu ⁇ oses of consistency, it will be assumed that each pixel is switched to its A state by applying a +5 VDC electric field through the pixel and each pixel is switched to its B state by applying a -5 VDC electric field through the pixel. It should be understood that the present invention is not limited to these specific voltages and would equally apply regardless of the voltages used to switch the pixels.
- System 400 further includes a light source 410 for directing light into the system in a manner similar to that described above for Figures lb and lc.
- light source 410 directs light into polarizer 405 as indicated by arrow 412.
- Polarizer 405 blocks any vertically linearly polarized portions of the light from passing through polarizer 405 an allows only horizontally linearly polarized portions of the light to pass through polarizer 405 into static quarter wave plate 408.
- This light passes through static quarter wave plate 408, compensator cell 404, and SLM 402 and is then reflected by reflective backplane 403 back through SLM 402, compensator cell 404, and static wave plate 408 to analyzer 406 as illustrated in Figure 4a.
- Analyzer 406 then blocks any horizontally linearly polarized portions of the light and allows only vertically linearly polarized portions of the light to pass through it to a viewing area indicated by viewer 416. Since polarizer 405 blocks vertically linearly polarized light and analyzer 406 blocks horizontally linearly polarized light, this type of system is referred to as using crossed polarizers.
- the FLC material of SLM 402 and compensator cell 404 are configured to act as quarter wave plates for a wavelength of 510 nm.
- the FLC materials of both SLM 402 and compensator cell 404 are 900 nm thick and both have a tilt angle of 22.5 degrees.
- the buff axis of the SLM is positioned at a 22.5 degree angle relative to the horizontally linearly polarized light directed into the system.
- the buff axis of compensator cell 404 is positioned pe ⁇ endicular to the buff axis of SLM 402.
- the buff axis of the SLM is described as being positioned at 22.5 degrees relative to the horizontally linearly polarized light directed into the system, this is not a requirement. In fact, this configuration works equally as well regardless of the orientation of the SLM buff axis relative to the horizontally linearly polarized light directed into the system so long as the buff axis of the compensator cell is oriented pe ⁇ endicular to the buff axis of the SLM. This freedom in orienting the buff axis of the SLM relative to the horizontally linearly polarized light directed into the system makes this overall system easier to produce than other conventional systems because only the orientation of the SLM relative to the compensator cell must be precisely controlled.
- static quarter wave plate 408 has a primary axis which is oriented at a 45 degree angle to the horizontally linearly pola ⁇ zed light directed into the quarter wave plate.
- tilt angles in the range of 22.5 to 25.5 degrees provides optimum dark state extinction, with the choice of tilt angle at the low end of the range providing best extinction over a narrow range of wavelengths centered on the wavelength for which the SLM and compensator have quarter-wave retardance and with the choice of tilt angle towards the upper end of the range providing good extinction over a more extended range of wavelength.
- Increasing the tilt angle past 25.5 degrees eventually reduces dark state extinction.
- Figures 4b and 4c illustrate the net result that system 400 has on light directed in to the system.
- Figure 4b shows the results for Case 1 and 2 du ⁇ ng which the compensator cell is in its B state and the SLM is switched between the A state for Case 1 and the B state for Case 2.
- Case 1 is indicated by solid line 420 and Case 2 is indicated by dashed line 422.
- Figure 4c shows the results for Case 3 and 4 during which the compensator cell is in its A state and the SLM is switched between the B state for Case 3 and the A state for Case 4.
- Case 3 is represented by solid line 424 and Case 4 is represented by dashed line 426
- Cases 1 -4 correspond to Cases 1 -4 for the systems described above in the background.
- Cases 1 and 3 result m a dark pixel rather than a bright pixel and Cases 2 and 4 result in a bright pixel rather than a dark pixel. This is the opposite of the results desc ⁇ bed in the background.
- this inversion of the bright and the dark states may be compensated for in a variety of ways such as reversing the A and the B states for the SLM (i.e. using a -5 VDC to switch the pixel to the A state and using a 5 VDC to switch the pixel to the B state).
- the results of Cases 1 and 3 are identical and the results of Cases 2 and 4 are identical.
- static quarter wave plate 408 is preferably a readily providable achromatic quarter wave plate.
- the use of an achromatic static quarter wave plate provides the best results over a broad color spectrum because it flattens out the curves 422 of Figure 4b and 426 of Figure 4c representing the bright states obtained by Case 1 and Case 2. This flattening out of the curve improves the optical throughput of system 400 by increasing the amount of light which passes through the system for a given pixel when the combination of that pixel and the other elements are switched to produce a b ⁇ ght state.
- FIG. 5a- c illustrate a system 500 which utilizes parallel polarizers.
- system 500 includes a SLM 502, a reflective backplane 503, a compensator cell 504, a polarizer 505, a static quarter wave plate 508, and a light source 510.
- Light source 510 directs light into polarizer 505 which blocks any vertically linearly polarized light and allows only horizontally linearly polarized light to pass through This horizontally linearly polarized light then passes through and is acted upon by static quarter wave plate 508, compensator cell 504, SLM 502, and reflective backplane 503 in the same way as described above for Figure 4a.
- polarizer 505 also acts as the analyzer for the system. This use of polarizer 505 for both the polarizer and the analyzer is what makes this system a parallel polarizer system.
- polarizer 505 acts as the analyzer by blocking any vertically linearly polarized light and allowing any ho ⁇ zontally linearly polarized light to pass into the viewing area. This is the opposite of the polarizations of light blocked and passed by analyzer 406 in system 400. This has the effect of reversing the bright and dark states of the system and results in the net effects illustrated in Figures 5b and 5c.
- Figure 5b shows the results for Case 1 and 2 during which the compensator cell is in its B state and the SLM is switched between the A state for Case 1 and the B state for Case 2. Case 1 is indicated by solid line 520 and Case 2 is indicated by dashed line 522.
- Figure 5c shows the results for Case 3 and 4 during which the compensator cell is in its A state and the SLM is switched between the B state for Case 3 and the A state for Case 4.
- Case 3 is represented by solid line 524 and Case 4 is represented by dashed line 526.
- Cases 1-4 correspond to Cases 1-4 for the systems described above in the background and Cases 1-4 described above for Figure 4.
- system 500 produces identical results, that is, a bright pixel for Case 1 and 3 as indicated by lines 520 and 524, respectively. It also produces identical results for Cases 2 and 4 as indicated by lines 522 and 526, respectively.
- This configuration also produces very good results over the entire wavelength range from 400 nm to 700 nm. In fact, as illustrated by lines 522 and 526, this configuration provides substantially uniform blockage of the entire range of wavelengths of the light that is directed into the spatial light modulator. Also, in both Cases 1 and 3, a large portion of the horizontally linearly polarized light passes through the system for the entire range of 400 nm to 700 nm.
- a birefringent element may be added to system 400 in order to provide results very similar to the results obtained by system 500 of Figure 5a.
- Figure 6 illustrates a system 600 including SLM 402, reflective backplane 403, compensator cell 404, polarizer 405. analyzer 406, static quarter wave plate 408. and light source 410.
- SLM 402 reflective backplane 403, compensator cell 404
- polarizer 405. analyzer 406, static quarter wave plate 408.
- light source 410 As described above for Figure 4, polarizer 405 and analyzer 406 are crossed polarizers.
- system 600 further includes an additional birefringent element 612 which can be positioned between SLM 402 and compensator cell 404, as shown here, or alternately, can be positioned between compensator cell 404 and static quarter wave plate 408.
- birefringent element 612 is a commercially available polycarbonate film having a retardance of approximately one half of the wavelength of the light for which the system is optimized, for example a wavelength of 510 nm.
- birefringent element 612 may be any birefringent material capable of providing the desired retardance such as poly vinyl alcohol or any other optically clear birefringent material.
- the buff axes of SLM 402 and compensator cell 404 are parallel to one another and birefringent element 612 has a primary axis which is oriented pe ⁇ endicular to the buff axis of both SLM 402 and compensator cell 404.
- polarizer 405 directs horizontally linearly polarized light into quarter wave plate 408 and quarter wave plate 408 is oriented at a 45 degree angle to the horizontally linearly polarized light.
- SLM 402, compensator cell 404, and birefringent element 612 may be oriented in any way relative to quarter wave plate 408 so long as the buff axes of SLM 402 and Compensator cell 404 are parallel to one another and the primary axis of birefringent element 612 is pe ⁇ endicular to the buff axes of SLM 402 and compensator cell 404.
- FIGS. 7a and 7b illustrate one embodiment of an off axis display system 700 As illustrated in Figures 7a and 7b.
- system 700 includes a SLM 702, a reflective backplane 703, a compensator cell 704, a pola ⁇ zer 705, an analyzer 706, and a light source 710
- the light is directed into the SLM at an angle and reflected back into a viewing area indicated by viewer 720 such that the light directed into the system only passes through the compensator cell once rather than passing through the compensator cell twice as described above for the previously described embodiments
- the thickness of compensator cell 704 is configured to be twice the thickness of the SLM Generally, SLM 702 has a thickness which causes SLM 702 to act as a quarter wave plate when switched to its A state and compensator cell 704 has a thickness which causes it to act as a half wave plate when it is switched to its A state Therefore, in the case in which an FLC material is used for both the SLM and compensator cell that has a birefringence of 0 142, the thickness FLC material for the SLM would be approximately 900 nm and the thickness of the FLC material for the compensator cell would be approximately 1800 nm Both SLM 702 and compensator cell are configured to have substantially no effect on the polarization of the light passing through them when they are switched to their B states
- polarizer 705 is configured to allow only horizontally linearly polarized light to be directed into the system
- Analyzer 706 is configured to allow only vertically linearly polarized light to pass into the viewing area
- the buff axis of compensator cell 704 is o ⁇ ented pe ⁇ endicular to the buff axis of SLM 702 and the buff axis of SLM 702 is advantageously o ⁇ ented parallel to horizontally linearly pola ⁇ zed light directed into the system.
- Other o ⁇ entations of the buff axes are also effective provided that the SLM and compensator cell buff axes remain pe ⁇ endicular to one another.
- system 700 is also able to provide a continuously viewable system which more effectively utilizes light from the light source when compared to the conventional reflective systems illustrated in Figures lb-c and Figure 3a.
- system 800 includes an SLM 802 having a reflective backplane 803, a compensator cell 804, a polarizer 805, and an analyzer 806.
- crossed polarizer 805 and analyzer 806 may be replaced with a polarizing beam splitter.
- System 800 is configured in a manner similar to that desc ⁇ bed above for system 400 of Figure 4a. That is, compensator cell 804 is positioned adjacent SLM 802. Also, polarizer 805 is positioned to direct only horizontally linearly polarized light into compensator cell 804. Similarly, analyzer 806 allows only vertically linearly pola ⁇ zed light to pass through it and into the viewing area after the light directed in to the system has passed through compensator cell 804 and SLM 802 and been reflected back through SLM 802 and compensator cell 804. However, in accordance with this aspect of the invention, compensator cell 804 has a thickness and retardance that is substantially different than that of SLM 802. In the embodiment being described, compensator cell 804 has a thickness and retardance that is twice that of SLM 802.
- System 800 further includes a light source 810 for directing light into the system in a manner similar to that desc ⁇ bed above for Figures lb and l c. With this configuration, light source 810 directs light into pola ⁇ zer 805 as indicated by arrow 812.
- Polarizer 805 blocks any vertically linearly pola ⁇ zed portions ot the light from passing through pola ⁇ zer 805 and allows only horizontally linearly polarized portions of the light to pass through polarizer 805 into compensator cell 804 This light passes through compensator cell 804, and SLM 802 and is then reflected by reflective backplane 803 back through SLM 802 and compensator cell 804 to analyzer 806 as illustrated in Figure 8 Analyzer 806 then blocks any horizontally linearly pola ⁇ zed portions ot the light and allows only vertically linearly pola ⁇ zed portions of the light to pass through it to a viewing area indicated by viewer 816 Since polarizer 805 blocks vertically linearly polarized light and analyzer 806 blocks horizontally linearly pola ⁇ zed light, this type of system is referred to as using crossed polarizers
- the FLC material of SLM 802 is configured to act as a quarter wave plate for a wavelength of 510 nm
- compensator cell 804 has a thickness and retardance that is twice that of SLM 802 Therefore, compensator cell 804 is configured to act as a half wave plate for a wavelength of 510 nm
- the FLC matenal of SLM 802 is 900 nm thick and has a tilt angle of 22.5 degrees
- the FLC material of compensator cell 804 is 1800 nm thick and has a tilt angle of half that of the FLC mate ⁇ al of SLM 802, that is, 11.25 degrees
- the buff axis of SLM 802 (indicated by dashed line 817) is aligned with or parallel with the ho ⁇ zontally linearly pola ⁇ zed light directed into the system
- the buff axis of compensator cell 804 (indicated by dashed line 818) is positioned pe ⁇ endicular to the buff axis 817 of SLM 802
- the system works equally well when configured with the buff axis 817 of the SLM aligned pe ⁇ endicular to the horizontally polarized light and the buff axis 818 of the compensator cell still pe ⁇ endicular to the buff axis of the SLM This configuration is illustrated in Figure 10a
- the buff axes 817 and 818 can be o ⁇ ented at 45 degrees to the horizontally polarized incident light as illustrated in Figure 10b
- the buff axes 817 and 818 of the SLM and the compensator cell can be parallel to each other and aligned either both parallel to the horizontally pola ⁇ zed light, as shown in Figure 10c, or both pe ⁇ endicular to the horizontally polarized light as shown in Figure lOd.
- the same components can even be configured with both buff axis 817 and 818 being oriented at 45 degrees relative to the honzontally polarized light, as illustrated in Figure lOe.
- the buff axis 817 of the SLM can be oriented at 1 12.5 degrees relative to 5 the horizontally polarized light with the FLC material of the SLM again having a tilt angle of 22.5 degrees).
- the buff axis 818 of the compensator cell is oriented 1 1.25 degrees to the horizontally polarized light with the FLC material of the compensator cell again having a tilt angle of 1 1.25 degrees, or half that of the material of the SLM. This configuration is shown in Figure lOf.
- Figure 1 Of can be oriented relative to the vertically polarized analyzer instead of relative to the horizontal polarizer without changing the results of the system.
- the buff axis of the SLM can be oriented 22.5 degrees from the horizontally polarized input light while the buff axis of the compensator cell is oriented nearly parallel to the buff
- tilt angles of SLM 802 and compensator cell 804 are described as being 22.5 degrees and 1 1.25 degrees respectively for the above described configurations, this is not a requirement.
- the configurations described above for this embodiment work for a range of tilt angles, but work best when the tilt angle of the compensator cell is half that of
- the SLM buff axis is preferably oriented at 90 degrees plus the SLM tilt angle from the horizontally polarized input light.
- the compensator is preferably made from an FLC material having half the tilt of the SLM material, and the compensator buff axis of the compensator cell is
- the solutions identified by the equation result in a system configuration that produces two relatively bright states and two relatively good dark states.
- the equation is used to determine the required buff angle P (measured in degrees from the primary axis of the polarized light directed into the system) for the SLM for any given compensator buff angle C (also measured in degrees from the pola ⁇ zed light directed into the system) where N is an integer.
- the retardance of the FLC material of the SLM is a quarter wave for visible light and that the retardance of the compensator cell is a half wave for visible light. It also assumes that the tilt angle B of the FLC material of the compensator cell is half that of the tilt angle D of the FLC material of the SLM.
- N an odd integer
- the dark states will be most tolerant to the same variations of tilt angles B and D.
- the buff angle C of the compensator cell is 90 degrees.
- the buff angle P of the SLM is oriented a multiple of 90 degrees from the buff angle C of the compensator as required by the equation thus making the buff angles either pe ⁇ endicular to or parallel to one another.
- the equation results in an SLM buff angle that is rotated 45 degrees one way or the other relative to buff angle C of the compensator cell.
- the compensator buff angle C is 1 1.25 degrees. Therefore, when N is equal to 2, the resulting SLM buff angle P is 1 12.5 degrees as described above. In the configuration of Figure 10 g, the compensator buff angle C is 168 75. Therefore, when N is equal to 1 , the resulting SLM buff angle P is 382.5 degrees which is the same as 22.5 degrees as described above for Figure lOf Now that the physical configuration of system 800 has been described, its effect on light directed into system 800 will be described.
- the one with the SLM buff axis oriented with the vertically polarized output light, but the compensator buff axis still pe ⁇ endicular to the SLM buff axis) gives the bright and dark states of the same characteristics as the configuration of Figure 10(a).
- the other configurations generally give bright states with more throughput variation over the wavelength range and a less spectrally uniform dark state, but all provide the contrast reversal necessary for continuous viewing of the display system, and all provide high bright state throughput and a good dark state over at least a narrow range of wavelengths.
- system 800 has been described as using crossed polarizers, this is not a requirement of the invention. Instead, parallel polarizes may be utilized. However, the use of parallel polarizers reverses the light and dark states and results, for the configuration described with reference to Figure 10(a), in curves similar to those of Figures 4b and 4c. Although this configuration provides identical results for Cases 1 and 3 and Cases 2 and 4, it does not provide as good of a contrast ratio as system 800 using crossed polarizers.
- FIG. 1 1 illustrates a first embodiment of a heater arrangement designed in accordance with the invention for heating compensator cell 804 for this purpose.
- compensator cell 804 is made up of three layers of glass substrate 820, 822, and 824.
- Glass layers 820 and 822 have inner faces 821 and 823 that respectively support electrodes 826 and 828.
- Electrodes 826 and 828 are transparent electrodes, such as Indium-Tin-Oxide (ITO), that allow a voltage to be applied to control the state of compensator cell 804.
- the FLC material of the compensator cell indicated by reference numeral 830, is sandwiched between ITO electrodes 826 and 828.
- the third layer of glass, layer 824 has an inner surface 825 that supports a layer 832 of ITO material. Two electrical leads (not shown) are connected at opposite ends of ITO layer 832.
- ITO layer 832 which ITO layer 832 dissipates as heat.
- the electrical leads are connected to opposite edges of ITO layer 832 along the entire length of each edge. This configuration causes ITO layer 832 to be uniformly heated so that it heats the entire compensator cell including FLC material 830.
- Compensator cell 804 further includes a temperature sensor 834 that is used to control the power provided to ITO layer 832. Therefore, the temperature of compensator cell 804 and FLC material 830 may be readily controlled.
- ITO layer 832 is described as being attached to the inner surface 825 of glass layer 824, it should be understood that this is not a requirement. Instead. ITO layer 832 may be attached to the outside surface of glass layer 824 or alternatively to any of the glass layers.
- a combined compensator cell and SLM panel configuration where the SLM and compensator cell are maintained at substantially the same temperature
- Figure 12 illustrates one embodiment of such a configuration.
- compensator cell 804 is attached directly to SLM 802.
- compensator cell 804 includes a heater arrangement, such as a layer of ITO material, that is used to maintain the temperamre of the combination of compensator cell 804 and SLM 802 at a particular temperamre.
- a variety of other heater arrangements may be used to maintain compensator cell 804 and SLM 802 at a constant temperature.
- Figure 13 illustrates the tilt angle vs. temperature characte ⁇ stics of two exemplary FLC materials that may be used in the immediately above described configuration.
- a high temperature FLC mate ⁇ al with the tilt angle vs. temperature characte ⁇ stics indicated by curve 840 is used in SLM 802.
- a different, lower temperature FLC mate ⁇ al with tilt angle vs. temperature characte ⁇ stic indicated by curve 842 is used in the compensator cell.
- a curve showing half the tilt angle of the SLM FLC mate ⁇ al of curve 840 is shown as curve 844.
- Both FLC materials illustrated are of the common type having a zero-tilt smectic A phase at temperatures above the ferroelectric smectic C phase.
- the smectic A to smectic C phase transition temperature T AC has a value of about 90 °C (the temperature where the tilt goes to zero), while the material used in the compensator cell has a T AC value of about 55 °C.
- the compensator tilt angle indicated by curve 842 has a value equal to half the SLM FLC tilt indicated by curve 844 at a temperature of about 40 °C (i.e. at the temperature where curve 842 and curve 844 intersect).
- the temperature of both cells together can be controlled, for example, by attaching a temperature sensor 834 to the combined compensator cell and SLM.
- a resistive heater 846 may be attached to the back of the SLM and a temperamre control servomechanism 848 may be used to supply electrical current to resistive heater 846 in a manner to maintain sensor 834 at a desired set-point temperature.
- the operation of such a temperature-controlled combined compensator/ SLM can be achieved by filling the compensator cell with an FLC material having, at some temperamre, a tilt angle substantially equal to half the tilt angle of the FLC material used in the SLM at that temperature. Specifically, this can be accomplished by filling the compensator cell with an FLC material having a T AC suitably lower than the T AC of the
- Another method of controlling the tilt angle of an FLC material is to control the drive voltage used to switch and maintain the FLC material in its A and B states.
- FLC materials are switched to and maintained in their A and B states by establishing and maintaining certain drive voltages through the layers of FLC
- Figure 14 illustrates how the combination of drive voltage and temperature effect the tilt angle of a typical FLC material.
- the tilt angle of FLC material varies in a predictable way as the drive voltage used to maintain the FLC material in their A and B states, the tilt angle of compensator cell
- the drive voltages for the compensator cell and the SLM may be controlled such that the resulting tilt angle of the compensator cell is half that of the SLM.
- the switching speed of the FLC material is also effected by the drive 0 voltage used to establish and maintain the FLC material in the desired state.
- the drive voltage used to establish and maintain the FLC material in the desired state may include a leading edge spike.
- Figure 15 illustrates a drive voltage waveform 850 including a leading edge spike 852 that may be used to overcome the reduction of switching speed which may occur when a
- V hold is a low voltage, e.g. 0.5 - 2.0 Volts, which is adjusted to tune the FLC tilt angle of compensator cell 804 to exactly half of the tilt angle of the FLC in associated SLM 802.
- V hold is too low a voltage to cause the FLC of compensator cell 804 to switch quickly between its two states.
- V is a high voltage, e.g. 6 Volts, which drives the FLC material of compensator cell 804 quickly between its two states. If left on the compensator, V k would produce a tilt angle that is much too high. Thus, the applied voltage is reduced from V k to V hold after the fast switching has been accomplished.
- any combination of the above described two approaches may be used to controlling the tilt angle of the FLC material of the compensator cell or the combination of the compensator cell and the SLM.
- relatively low drive voltages may be used to drive the compensator cell while the compensator cell is maintained at an elevated temperature compared to the SLM.
- the combination of these two approaches may be used to cause the FLC material of the compensator cell to have a tilt angle half that of the FLC material of the SLM. It may be desirable to implement an SLM plus compensator display system according to one of the above configurations where it is not necessary to know exactly at what voltage or temperamre the desired tilt angle of the FLC compensator material is obtained.
- the display system dark state output intensity should vary with compensator cell drive voltage as shown in Figure 16 when the pixel state is such that a positive compensator-cell drive voltage produces a display system dark state.
- FIG. 18 A servomechamsm that can automatically keep the compensator cell tilt at its optimum value is shown in Figure 18
- the pixel array, indicated by region 870 in Figure 17, of SLM 802 has an adjacent or surrounding apron area 872 Apron area 872 functions in exactly the same way that the pixels function, but is not part of the desired image
- the apron area is d ⁇ ven so that it should always produce a dark output state, even as the compensator cell is switched to accomplish DC balancing of both the pixel area and the apron area Display system output light from this apron area is imaged onto a photodetector 880 (shown in Figure 18) that provides an input signal 882 for the servomechamsm
- the compensator cell is d ⁇ ven from a signal source 884 that adds a small high-frequency dither signal 886 to a lower-frequency alternating pola ⁇ ty d ⁇ ve signal 888 For example, if the display system were performing DC balance such that an image data
- the output of the photodetector is detected by a phase-sensitive detector or lock-in amplifier 890 whose reference input is d ⁇ ven by the dither signal 886
- this type of detection scheme produces a positive output when the input signal (the photodetector output) is in phase with the reference signal (the compensator dither signal) and a negative output when the input signal is out of phase with the reference signal
- This output signal can be low-pass filtered using low pass filter 892 to remove unwanted noise
- the sign of the lock-in amplifier output signal indicates whether the compensator tilt angle is too much or too little, and the magnitude of the signal indicates the degree of error
- the servomechamsm feeds this lock-in amplifier output signal back to control the level of the compensator cell drive voltage in such a way as to reduce the error signal to zero If the error signal is positive (dark-state output intensity increasing with compensator drive voltage), then the amplitude of the lower- frequency compensator drive voltage is reduced. If the error signal is negative (dark-state output intensity decreasing with compensator drive voltage), then the amplitude of the lower-frequency compensator drive voltage in increased.
- the description above characterizes the performance of the servo system during the phase when the apron (or dark pixels) are driven such that a positive compensator cell drive voltage produces a display system output dark state.
- the servo system operates similarly during the other phase when the compensator is driven with a negative voltage, but the feedback sense is reversed to accommodate the fact that reversal of the change in output intensity with variation of compensator drive voltage.
- the servomechanism need not constrain the positive and negative compensator drive voltages to be equal in magnitude; different magnitudes can be used to correct for small compensator buff-axis misorientations that arise, for example, as a result of non-zero manufacturing assembly tolerances.
- the servomechanism was described above as operating on the compensator cell drive voltage.
- the servo could equally well operate on the compensator temperature. In the case of operating on temperature, if the lock-in detected that the compensator tilt was larger than optimum, a feedback signal could be supplied to the compensator temperature controller that would cause the compensator temperature to be increased, and vice versa.
Abstract
Description
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Priority Applications (5)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2000532773A JP2002504714A (en) | 1998-02-18 | 1999-02-17 | Image generation system |
AU28687/99A AU2868799A (en) | 1998-02-18 | 1999-02-17 | Image generating system |
CA002321252A CA2321252A1 (en) | 1998-02-18 | 1999-02-17 | Image generating system |
KR1020007008981A KR20010034497A (en) | 1998-02-18 | 1999-02-17 | Image generating system |
EP99909497A EP1057074A1 (en) | 1998-02-18 | 1999-02-17 | Image generating system |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/025,160 US6016173A (en) | 1998-02-18 | 1998-02-18 | Optics arrangement including a compensator cell and static wave plate for use in a continuously viewable, reflection mode, ferroelectric liquid crystal spatial light modulating system |
US09/025,160 | 1998-02-18 |
Publications (2)
Publication Number | Publication Date |
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WO1999042898A1 WO1999042898A1 (en) | 1999-08-26 |
WO1999042898A9 true WO1999042898A9 (en) | 1999-11-04 |
Family
ID=21824391
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1999/003347 WO1999042898A1 (en) | 1998-02-18 | 1999-02-17 | Image generating system |
Country Status (7)
Country | Link |
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US (6) | US6016173A (en) |
EP (1) | EP1057074A1 (en) |
JP (1) | JP2002504714A (en) |
KR (1) | KR20010034497A (en) |
AU (1) | AU2868799A (en) |
CA (1) | CA2321252A1 (en) |
WO (1) | WO1999042898A1 (en) |
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-
1998
- 1998-02-18 US US09/025,160 patent/US6016173A/en not_active Expired - Lifetime
-
1999
- 1999-02-17 CA CA002321252A patent/CA2321252A1/en not_active Abandoned
- 1999-02-17 KR KR1020007008981A patent/KR20010034497A/en not_active Application Discontinuation
- 1999-02-17 WO PCT/US1999/003347 patent/WO1999042898A1/en not_active Application Discontinuation
- 1999-02-17 JP JP2000532773A patent/JP2002504714A/en active Pending
- 1999-02-17 US US09/251,627 patent/US6100945A/en not_active Expired - Fee Related
- 1999-02-17 AU AU28687/99A patent/AU2868799A/en not_active Abandoned
- 1999-02-17 EP EP99909497A patent/EP1057074A1/en not_active Withdrawn
- 1999-09-04 US US09/391,087 patent/US6075577A/en not_active Expired - Lifetime
-
2000
- 2000-02-19 US US09/507,450 patent/US6144421A/en not_active Expired - Fee Related
- 2000-09-13 US US09/661,249 patent/US6310664B1/en not_active Expired - Fee Related
-
2001
- 2001-09-24 US US09/960,535 patent/US6426783B2/en not_active Expired - Fee Related
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US6310664B1 (en) | 2001-10-30 |
US20020012081A1 (en) | 2002-01-31 |
US6075577A (en) | 2000-06-13 |
KR20010034497A (en) | 2001-04-25 |
US6100945A (en) | 2000-08-08 |
EP1057074A1 (en) | 2000-12-06 |
JP2002504714A (en) | 2002-02-12 |
US6016173A (en) | 2000-01-18 |
CA2321252A1 (en) | 1999-08-26 |
AU2868799A (en) | 1999-09-06 |
US6144421A (en) | 2000-11-07 |
US6426783B2 (en) | 2002-07-30 |
WO1999042898A1 (en) | 1999-08-26 |
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