Optical stack for privacy display
a technology of optical stack and privacy display, applied in the field of illumination, can solve the problems of increasing inventory and cost, high loss of film head-on illumination, moiré artefacts, etc., and achieve the effect of high efficiency
Active Publication Date: 2018-11-08
REALD SPARK LLC
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AI Technical Summary
Benefits of technology
The present invention is about a display device that can switch between a narrow angle and wide angle mode of operation. It includes a backlight, a transmissive spatial light modulator, a display polarizer, an additional polarizer, and plural retarders. The retarders include a switchable liquid crystal retarder and passive compensation retarders. The technical effect of this invention is to provide a display device with high efficiency and privacy, which can display information without exposing its contents to stray light.
Problems solved by technology
However such films have high losses for head-on illumination and the micro-louvres may cause Moiré artefacts due to beating with the pixels of the spatial light modulator.
The pitch of the micro-louvre may need selection for panel resolution, increasing inventory and cost.
Method used
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Embodiment Construction
[0097]Terms related to optical retarders for the purposes of the present disclosure will now be described.
[0098]In a layer comprising a uniaxial birefringent material there is a direction governing the optical anisotropy whereas all directions perpendicular to it (or at a given angle to it) are optically equivalent.
[0099]Optical axis refers to the direction of propagation of an unpolarised light ray in the uniaxial birefringent material in which no birefringence is experienced by the ray. For light propagating in a direction orthogonal to the optical axis, the optical axis is the slow axis when linearly polarized light with an electric vector direction parallel to the slow axis travels at the slowest speed. The slow axis direction is the direction with the highest refractive index at the design wavelength. Similarly the fast axis direction is the direction with the lowest refractive index at the design wavelength.
[0100]For positive dielectric anisotropy uniaxial birefringent materia...
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Abstract
A privacy display comprises a spatial light modulator and a compensated switchable liquid crystal retarder arranged between first and second polarisers arranged in series with the spatial light modulator. In a privacy mode of operation, on-axis light from the spatial light modulator is directed without loss, whereas off-axis light has reduced luminance. The visibility of the display to off-axis snoopers is reduced by means of luminance reduction over a wide polar field. In a wide angle mode of operation, the switchable liquid crystal retardance is adjusted so that off-axis luminance is substantially unmodified.
Description
TECHNICAL FIELD[0001]This disclosure generally relates to illumination from light modulation devices, and more specifically relates to switchable optical stacks for providing control of illumination for use in a display including a privacy display.BACKGROUND[0002]Privacy displays provide image visibility to a primary user that is typically in an on-axis position and reduced visibility of image content to a snooper, that is typically in an off-axis position. A privacy function may be provided by micro-louvre optical films that transmit some light from a display in an on-axis direction with low luminance in off-axis positions. However such films have high losses for head-on illumination and the micro-louvres may cause Moiré artefacts due to beating with the pixels of the spatial light modulator. The pitch of the micro-louvre may need selection for panel resolution, increasing inventory and cost.[0003]Switchable privacy displays may be provided by control of the off-axis optical output...
Claims
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IPC IPC(8): G02F1/13G02F1/1343G02F1/1335G02F1/1337G02B6/122G02B27/30
CPCG02F2001/133635G02F1/133634G02F1/1323G02F1/1343G02F1/1337G02B27/30G02F1/133536G02B6/122G02F1/133602G02B3/005G02B6/0048G02B6/0051G02B6/0055G02F1/13363G02F1/13471G02F2413/10G02F1/133633G02F1/133635
Inventor ROBINSON, MICHAEL G.WOODGATE, GRAHAM J.RAMSEY, ROBERT A.HARROLD, JONATHAN
Owner REALD SPARK LLC