Reflective optical stack for privacy display

A view angle control optical element for application to the output side of a display device for use in ambient illumination comprising a spatial light modulator (SLM) arranged to output light;

• wherein the SLM comprises an output polariser arranged on the output side of the SLM;
• the view angle control optical element comprising:
• an additional polariser;
• a reflective polariser arranged between the output polariser and the additional polariser on application of the view angle control optical element to the display device;
• and
• plural polar control retarders arranged between the reflective polariser and the additional polariser, there being no further polarisers between the reflective polariser and the additional polariser, wherein the plural polar control retarders comprise a switchable liquid crystal retarder comprising a layer of liquid crystal material and a passive polar control retarder,
• wherein the plural polar control retarders are arranged, in a switchable state of the switchable liquid crystal retarder, simultaneously to introduce no net relative phase shift to orthogonal polarisation components of light passed by the reflective polariser along a first axis and to introduce a net relative phase shift to orthogonal polarisation components of light passed by the reflective polariser along a second axis inclined at a different angle to the first axis;
• wherein the passive polar control retarder is arranged to introduce no net relative phase shift to orthogonal polarisation components of light passed by the reflective polariser along an axis along a normal to the plane of the passive polar control retarder and to introduce a net relative phase shift to orthogonal polarisation components of light passed by the reflective polariser along an axis inclined to a normal to the plane of the passive polar control retarder;
• wherein the passive polar control retarder comprises a pair of passive retarders which have optical axes in the plane of the retarders that are crossed;
• wherein the pair of retarders have optical axes that extend at 45° and 135°, respectively, with respect to an electric vector transmission direction of the output polariser.

A view angle control optical element for application to the output side of a display device for use in ambient illumination comprising a spatial light modulator (SLM) arranged to output light;

• wherein the SLM comprises an output polariser arranged on the output side of the SLM;
• the view angle control optical element comprising:
• an additional polariser;
• a reflective polariser arranged between the output polariser and the additional polariser on application of the view angle control optical element to the display device;
• plural polar control retarders arranged between the reflective polariser and the additional polariser, there being no further polarisers between the reflective polariser and the additional polariser, wherein the plural polar control retarders comprise a switchable liquid crystal retarder comprising a layer of liquid crystal material and a passive polar control retarder;
• and
• at least one further polar control retarder arranged between the output polariser and the reflective polariser,
• wherein the plural polar control retarders are arranged, in a switchable state of the switchable liquid crystal retarder, simultaneously to introduce no net relative phase shift to orthogonal polarisation components of light passed by the reflective polariser along a first axis and to introduce a net relative phase shift to orthogonal polarisation components of light passed by the reflective polariser along a second axis inclined at a different angle to the first axis;
• wherein the switchable liquid crystal retarder is a first switchable liquid crystal retarder comprising a first layer of liquid crystal material, and the at least one further polar control retarder comprises a second switchable liquid crystal retarder comprising a second layer of liquid crystal material;
• wherein the passive polar control retarder comprises a pair of passive retarders which have optical axes in the plane of the retarders that are crossed and extend at 45° and 135°, respectively, with respect to an electric vector transmission direction of the output polariser;
• wherein the at least one further polar control retarder comprises a further pair of passive retarders which have optical axes in the plane of the retarders that are crossed and extend at 45° and 135°, respectively with respect to the electric vector transmission direction of the output polariser;
• and
• wherein the optical axes of the one of the first-mentioned pair of passive retarders and the one of the further pair of passive retarders that are closest to each other extend in the same direction.