Optical film, illuminator and display

An illuminator comprising:

• a light source having an exit surface;
• and an optical film disposed adjacent the exit surface and comprising a light-tranmissive substrate of a material having a refractive index greater than one, said substrate having first and second major surfaces, one of which has a first surface relief on which is formed a mirror structure, said mirror structure comprising a plurality of transmissive surfaces and a plurality of reflective surfaces each having a specularly reflective layer which are specularly reflective towards said material of said substrate, first groups of said reflective surfaces alternating in at least one direction with second groups of said transmissive surfaces, where each of said first groups comprises at least one said reflective surface and each of said second groups comprises at least one said transmissive surface, all of said reflective surfaces being non-parallel to a first plane in which said first surface relief extends and at least some of said reflective surfaces being non-perpendicular to said first plane, the transmissive surfaces being parallel to the first plane, and reflective surfaces adjacent to and on opposite sides of a transmissive surface being asymmetrical in a second plane perpendicular to said first plane and parallel to the direction in which said first surface relief extends, such that, for light propagating through said film from said first surface to said second surface, light in a first angular input range in said second plane passes through said film without reflection into a first angular output range in said second plane and light in a second angular input range on a first side of said first input range is reflected by said mirror structure so as to exit said second surface in a second angular output range, which is in said second plane and which at least partially overlaps said first output range.

A display comprising a spatial light modulator, a light source having an exit surface, and an optical film comprising a light-transmissive substrate of a material having a refractive index greater than one, said substrate having first and second major surfaces, one of which has a first surface relief on which is formed a mirror structure, said mirror structure comprising a plurality of transmissive surfaces and a plurality of reflective surfaces each having a specularly reflective layer which are specularly reflective towards said material of said substrate, first groups of said reflective surfaces alternating in at least one direction with second groups of said transmissive surfaces, where each of said first groups comprises at least one said reflective surface and each of said second groups comprises at least one said transmissive surface, all of said reflective surfaces being non-parallel to a first plane in which said first surface relief extends and at least some of said reflective surfaces being non-perpendicular to said first plane, the transmissive surfaces being parallel to the first plane, and reflective surfaces adjacent to and on opposite sides of a transmissive surface being asymmetrical in a second plane perpendicular to said first plane and parallel to the direction in which said first surface relief extends, such that, for light propagating through said film from said first surface to said second surface, light in a first angular input range in said second plane passes through said film without reflection into a first angular output range in said second plane and light in a second angular input range on a first side of said first input range is reflected by said mirror structure so as to exit said second surface in a second angular output range, which is in said second plane and which at least partially overlaps said first output range.