A compound retarder that creates independent control of R.sub.e and R.sub.th. This can be done by forming a three-layer compound retarder, including a pair of matched −A-plates, combined with single +A-plate. The +A-plate is typically an MD-stretched film, with retardation that is specific to the in-plane requirements (R.sub.e) of the application. The pair of −A-plates have their optic axes crossed, such that R.sub.e=0, with an optic axis aligned parallel to the +A-plate. A single retardation value for the −A-plate can produce improved field-of-view performance over a broad range of R.sub.e values, making it a very practical means of universal compensation. While R.sub.th is typically associated with a single retarder, retarder stacks with a diverse range of optic-axis orientations can be considered to have a compound (or composite) R.sub.th value (R.sub.th.sup.c). The three-layer compound retarder has the practical benefit of enabling field-of-view compensation across a broad range of normal-incidence polarization transformations.

A compound retarder that creates independent control of R.sub.e and R.sub.th. This can be done by forming a three-layer compound retarder, including a pair of matched −A-plates, combined with single +A-plate. The +A-plate is typically an MD-stretched film, with retardation that is specific to the in-plane requirements (R.sub.e) of the application. The pair of −A-plates have their optic axes crossed, such that R.sub.e=0, with an optic axis aligned parallel to the +A-plate. A single retardation value for the −A-plate can produce improved field-of-view performance over a broad range of R.sub.evalues, making it a very practical means of universal compensation. While R.sub.this typically associated with a single retarder, retarder stacks with a diverse range of optic-axis orientations can be considered to have a compound (or composite) R.sub.th value (R.sub.th.sup.C). The three-layer compound retarder has the practical benefit of enabling field-of-view compensation across a broad range of normal-incidence polarization transformations.

A switchable privacy display apparatus comprises a polarised output spatial light modulator, and an additional polariser. A reflective polariser, switchable liquid crystal polar control retarder, passive polar control retarders and air gap are arranged between the display output polariser and additional polariser. The passive retarders are arranged to provide no phase difference to polarised light from the spatial light modulator for on-axis light; and simultaneously provide a non-zero phase difference for polarised light in off-axis directions. The polar control retarders are further arranged to achieve low reflectivity for light propagating through the air gap. A switchable privacy display that can be conveniently assembled at low cost can be provided with high contrast images for display users while maintaining high visual security level for off-axis snoopers.

A switchable privacy display apparatus comprises a polarised output spatial light modulator, and an additional polariser. A reflective polariser, switchable liquid crystal polar control retarder, passive polar control retarders and air gap are arranged between the display output polariser and additional polariser. The passive retarders are arranged to provide no phase difference to polarised light from the spatial light modulator for on-axis light; and simultaneously provide a non-zero phase difference for polarised light in off-axis directions. The polar control retarders are further arranged to achieve low reflectivity for light propagating through the air gap. A switchable privacy display that can be conveniently assembled at low cost can be provided with high contrast images for display users while maintaining high visual security level for off-axis snoopers.

A display comprises a polarised output spatial light modulator, switchable liquid crystal retarder, absorbing polariser and touch panel electrodes. The switchable liquid crystal layer is stabilised by a cured reactive mesogen material during application of an applied voltage. Light scatter in privacy mode is reduced and visual security level enhanced. Visibility of disclinations during application of applied pressure, for example from a finger on a touch screen is minimised.

Provided are a retardation film that has a high heat resistance, has excellent formability and handleability even in a single-layer structure, has a negative thickness-direction retardation Rth value, and is suitable as a negative A-plate or a positive C-plate and a method for producing the film. The retardation film is formed of a stretched film of a polyester resin, contains a unit (A1) represented by the formula (1) as a diol unit (A) and a unit (B1) represented by the formula (2a) or (2b) as a dicarboxylic acid unit (B), and is a negative A-plate or a positive C-plate.

##STR00001##

In the formulae, Z.sup.1 and Z.sup.2 represent an aromatic hydrocarbon ring, R.sup.1, R.sup.2a, R.sup.2b, R.sup.3a and R.sup.3b represent a substituent, k, p1 and p2 denotes an integer of 0 to 8, q denotes an integer of 0 to 4, m1, m2, n1 and n2 denotes an integer of not less than 0, A.sup.1a and A.sup.1b represents an alkylene group, and A.sup.2a, A.sup.2b and A.sup.3 represents a divalent hydrocarbon group.

An optical device includes a first layer including a first birefringent material having a negative birefringence dispersion property. The optical device also includes a second layer including a second birefringent material having a positive birefringence dispersion property. The first layer and the second layer are structurally patterned to provide at least one predetermined optical function.

An optical element is provided. The optical element includes a positive-C film including a liquid crystal (“LC”) layer. The optical element also includes a positive-A film. The optical element also includes a negative biaxial retardation film disposed between the positive-A film and the positive-C film.

An electronic device is provided. The electronic device includes a first substrate and a second substrate. The second substrate is disposed opposite to the first substrate. A light control layer is disposed between the first substrate and the second substrate, and the light control layer includes a first optical axis. A negative phase retardation layer is disposed between the first substrate and the second substrate. The negative phase retardation layer includes a second optical axis. The first optical axis and the second optical axis are parallel to each other.

A control system for a switchable privacy display apparatus comprises an ambient light sensor and a display luminance controller arranged to control the luminance of the display in response to measured illuminance. High image visibility is provided for public mode operation while in privacy mode visual security level above a perceived privacy threshold may be obtained by means of control of image luminance, in response to the output of the ambient light sensor.