# US 7,477,206 B2 · Enhanced ZScreen modulator techniques > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,477,206 B2 - Document ID: US7477206B2 - Status: Granted - Kind: B2 - Application number: 11/430,598 - Filed: 2006-05-08 - Published: 2007-11-08 - Granted: 2009-01-13 - Earliest claimed: 2005-12-06 - Assignees: Real D - Inventors: Matt Cowan; Josh Greer; Lenny Lipton; Joseph Chiu - Web page: https://patentgrep.com/patent/US7477206B2 ## CPC - G02F 1/0136: {for the control of polarisation, e.g. state of polarisation [SOP] control, polarisation scrambling, TE-TM mode conversion or separation (G02F1/0353 takes precedence)} - G02F 1/13471: {in which all the liquid crystal cells or layers remain transparent, e.g. FLC, ECB, DAP, HAN, TN, STN, SBE-LC cells (G02F1/13475 takes precedence)} - G03B 21/56: Projection screens - H04N 13/341: using temporal multiplexing - H04N 13/363: using image projection screens (volumetric display H04N13/388) - G02F 1/13306: {Circuit arrangements or driving methods for the control of single liquid crystal cells (G02F1/132, G02F1/133382 take precedence)} - 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 - G03B: APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR (optical parts of such apparatus G02B; photosensitive materials or processes for photographic purposes G03C; apparatus for processing exposed photographic materials G03D) - H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION ## Abstract A method and system for use in conjunction with a push-pull liquid crystal modulator system for creating circularly polarized light of alternating handedness is provided. The method and system comprise a pair of surface mode liquid crystal cells and a driver electrically coupled to the cells. The driver is configured to move an electrical charge using a quenching pulse comprising a relatively brief voltage spike at a beginning of a waveform period. Multiple additional improvements are provided, including reducing the thickness of the LC gap (the distance between cell electrode plates), creating a charge connection or wiring connection to the cell electrodes, employing anti-reflection coating technology, thinner ITO and ITO index matched to the LC material, bonding all possible air to material surfaces, using superior glass, employing more efficient polarizers, and reducing projector blanking time. ## Claims ### Claim 1 A method of displaying a stereoscopic video image, comprising: positioning a push-pull liquid crystal modulator that includes a pair of surface mode liquid crystal cells with orthogonal rub axes and a linear polarizer having an absorption axis bisecting the orthogonal rub axes, so that light comprising the stereoscopic video image propagates therethrough; and driving the modulator in synchronization with fields of a field sequential image so that a transmitted image emerging from the modulator consists of right-handed circularly polarized fields alternating at field rate with left-handed circularly polarized fields; wherein said driving comprises moving an electrical charge using a waveform comprising at least one quenching pulse in association with a holding voltage comprising a relatively brief voltage spike opposite in polarity to the holding voltage and lower in absolute voltage than the holding voltage at a beginning of a holding voltage period. ### Claim 2 (depends on 1) The method of claim 1, further comprising positioning a left-handed circular polarizer analyzer and a right-handed circular polarizer analyzer so that circularly polarized light emerging from the modulator propagates through space and is reflected by a polarizing conserving screen through space and then through one circular polarizer analyzer while being blocked by a complementary circular polarizer analyzer. ### Claim 3 (depends on 1) The method of claim 1, wherein the modulator comprises a first surface mode liquid crystal cell and a second surface mode liquid crystal cell, and wherein the first cell is driven by a first voltage signal that alternates at field rate between a low voltage square wave and a high voltage square wave, and the second cell is driven by a second voltage signal having substantially the same amplitude as the first voltage signal but having phase opposite to the first signal's phase. ### Claim 4 (depends on 1) The method of claim 1, wherein each field includes at least two subfields, each subfield having a duration, the modulator includes a first surface mode liquid crystal cell and a second surface mode liquid crystal cell, and including: driving the first cell with a first voltage signal; and driving the second cell with a second voltage signal, in such a manner that the absolute magnitude of the envelope of the first voltage signal and the absolute magnitude of the envelope of the second voltage signal decrease substantially simultaneously during each subfield. ### Claim 5 (depends on 1) The system of claim 1, wherein each field includes at least two subfields, and each subfield having a duration, the modulator includes a first surface mode liquid crystal cell and a second surface mode liquid crystal cell, and comprising: driving the first cell with a first carrier-less voltage signal; and driving the second cell with a second carrier-less voltage signal, in such a manner that the absolute magnitude of the first voltage signal and the absolute magnitude of the second voltage signal decrease substantially simultaneously during each subfield. ### Claim 6 (depends on 1) The method of claim 1, wherein the modulator includes a first surface mode liquid crystal cell and a second surface mode liquid crystal cell, and wherein the first cell is driven by a first voltage signal that alternates at field rate between a low AC voltage portion and a high AC voltage portion, and the second cell is driven by a second voltage signal having substantially the same amplitude as the first voltage signal but having phase opposite to the first signal's phase. ### Claim 7 (depends on 6) The method of claim 6, wherein each of the AC voltage portions is a 2 KHz sinusoidal wave, the low AC voltage portion has peak to peak amplitude in the range from zero volts to ten volts, and the high AC voltage portion has peak to peak amplitude in the range from 40 volts to 80 volts. ### Claim 8 (depends on 1) The method of claim 1, wherein the push-pull liquid modulator comprises a dyestuff polarizer. ### Claim 9 (depends on 1) The method of claim 1, wherein the push-pull liquid crystal modulator has air to material surfaces bonded. ### Claim 10 (depends on 1) The method of claim 1, wherein liquid crystal used in the push-pull liquid crystal modulator comprises water clear Borofloat. ### Claim 11 (depends on 1) The method of claim 1, wherein the push-pull liquid crystal modulator is employed in connection with a screen, and persons viewing the screen employ eyewear comprising polarizing elements matched to the push-pull liquid crystal modulator. ### Claim 12 A method of displaying a stereoscopic video image, comprising: driving a push-pull liquid crystal modulator comprising: a pair of surface mode liquid crystal cells with orthogonal rub axes; and a linear polarizer having an absorption axis bisecting the orthogonal rub axes, the push-pull liquid crystal modulator positioned so that light comprising the stereoscopic video image propagates therethrough; wherein said driving occurs in synchronization with fields of a field sequential image so that a transmitted image emerging from the modulator comprises right-handed circularly polarized fields alternating at field rate with left-handed circularly polarized fields; and further wherein said driving comprises moving an electrical charge using a waveform comprising at least one quenching pulse in association with a holding voltage comprising a relatively brief voltage spike opposite in polarity to the holding voltage and lower in absolute voltage than the holding voltage at a beginning of a holding voltage period. ### Claim 13 (depends on 12) The method of claim 12, further comprising positioning a left-handed circular polarizer analyzer and a right-handed circular polarizer analyzer so that circularly polarized light emerging from the modulator propagates through space and is reflected by a polarizing conserving screen through space and then through one circular polarizer analyzer while being blocked by a complementary circular polarizer analyzer. ### Claim 14 (depends on 12) The method of claim 12, wherein the modulator comprises a first surface mode liquid crystal cell and a second surface mode liquid crystal cell, and wherein the first cell is driven by a first voltage signal that alternates at field rate between a low voltage square wave and a high voltage square wave, and the second cell is driven by a second voltage signal having substantially the same amplitude as the first voltage signal but having phase opposite to the first signal's phase. ### Claim 15 (depends on 12) The method of claim 12, wherein each field includes at least two subfields, each subfield having a duration, the modulator includes a first surface mode liquid crystal cell and a second surface mode liquid crystal cell, and including: driving the first cell with a first voltage signal; and driving the second cell with a second voltage signal, in such a manner that the absolute magnitude of the envelope of the first voltage signal and the absolute magnitude of the envelope of the second voltage signal decrease substantially simultaneously during each subfield. ### Claim 16 (depends on 12) The system of claim 12, wherein each field includes at least two subfields, and each subfield having a duration, the modulator includes a first surface mode liquid crystal cell and a second surface mode liquid crystal cell, and comprising: driving the first cell with a first carrier-less voltage signal; and driving the second cell with a second carrier-less voltage signal, in such a manner that the absolute magnitude of the first voltage signal and the absolute magnitude of the second voltage signal decrease substantially simultaneously during each subfield. ### Claim 17 (depends on 12) The method of claim 12, wherein the modulator includes a first surface mode liquid crystal cell and a second surface mode liquid crystal cell, and wherein the first cell is driven by a first voltage signal that alternates at field rate between a low AC voltage portion and a high AC voltage portion, and the second cell is driven by a second voltage signal having substantially the same amplitude as the first voltage signal but having phase opposite to the first signal's phase. ### Claim 18 (depends on 17) The method of claim 17, wherein each of the AC voltage portions is a 2 KHz sinusoidal wave, the low AC voltage portion has peak to peak amplitude in the range from zero volts to ten volts, and the high AC voltage portion has peak to peak amplitude in the range from 40 volts to 80 volts. ### Claim 19 (depends on 12) The method of claim 12, wherein the push-pull liquid modulator comprises a dyestuff polarizer. ### Claim 20 (depends on 12) The method of claim 12, wherein the push-pull liquid crystal modulator has air to material surfaces bonded. ### Claim 21 (depends on 12) The method of claim 12, wherein liquid crystal used in the push-pull liquid crystal modulator comprises water clear Borofloat. ### Claim 22 (depends on 12) The method of claim 12, wherein the push-pull liquid crystal modulator is employed in connection with a screen, and persons viewing the screen employ eyewear comprising polarizing elements matched to the push-pull liquid crystal modulator. ### Claim 23 A stereoscopic video image display system, comprising: a push-pull liquid crystal modulator comprising: a pair of surface mode liquid crystal cells with orthogonal rub axes; and a linear polarizer having an absorption axis bisecting the orthogonal rub axes, the push-pull liquid crystal modulator positioned so that a stereoscopic image propagates therethrough; wherein said push-pull liquid crystal modulator is driven in synchronization with fields of a field sequential image so that a transmitted image emerging from the modulator comprises right-handed circularly polarized fields alternating at field rate with left-handed circularly polarized fields; and further wherein said push-pull liquid crystal modulator is driven by moving an electrical charge using a waveform comprising at least one quenching pulse in association with a holding voltage comprising a relatively brief voltage spike opposite in polarity to the holding voltage and lower in absolute voltage than the holding voltage at a beginning of a holding voltage period. ### Claim 24 (depends on 23) The system of claim 23, wherein the modulator comprises a first surface mode liquid crystal cell and a second surface mode liquid crystal cell, and wherein the first cell is driven by a first voltage signal that alternates at field rate between a low voltage square wave and a high voltage square wave, and the second cell is driven by a second voltage signal having substantially the same amplitude as the first voltage signal but having phase opposite to the first signal's phase. ### Claim 25 (depends on 23) The system of claim 23, wherein the modulator includes a first surface mode liquid crystal cell and a second surface mode liquid crystal cell, and wherein the first cell is driven by a first voltage signal that alternates at field rate between a low AC voltage portion and a high AC voltage portion, and the second cell is driven by a second voltage signal having substantially the same amplitude as the first voltage signal but having phase opposite to the first signal's phase.