Optical devices and methods for their manufacture

An optical device, comprising:

• a colour layer which comprises elongate strips of at least two different colours alternating with one another periodically along a direction of colour periodicity, the elongate strips extending along the direction which is orthogonal to the direction of colour periodicity;
• and
• a light redirecting layer overlapping the colour layer, and defining at least a first image to be exhibited by the optical device, the light redirecting layer comprising at least a first array of refractive and/or reflective anisotropic light redirecting elements extending across a first region of the light redirecting layer and being absent elsewhere, the anisotropic light redirecting elements of the first array each having a primary axis orientated along a first direction lying in the plane of the optical device and being configured such that an incident light beam lying in a plane perpendicular to the first direction and from a light source off the normal of the optical device will be redirected by the anisotropic light redirecting elements towards the normal of the optical device but within the same plane, whereas an incident light beam lying in a plane which is not perpendicular to the first direction and from a light source off the normal of the optical device will either not be redirected, or will be redirected by the anisotropic light redirecting elements out of the plane of the incident light beam;
• whereby for a viewer substantially on the normal of the optical device, when the incident light beam lies in a plane perpendicular to the first direction and is from a light source off the normal of the optical device, portions of the colour layer which overlap the first region of the light redirecting layer are illuminated by the anisotropic light redirecting elements relative to the remainder of the colour layer;
• and wherein the first region is arranged such that, at each location across the first region, the relative proportions of the at least two different colours of the colour layer which are illuminated by the anisotropic light redirecting elements are configured to exhibit in combination a colour of a corresponding pixel of the first image;
• such that for a viewer substantially on the normal of the optical device, when the incident light beam lies in a plane perpendicular to the first direction and is from a light source off the normal of the optical device, a colour version of the first image will be exhibited by the device.

A method of manufacturing an optical device, comprising:

• (a) providing a colour layer which comprises elongate strips of at least two different colours alternating with one another periodically along a direction of colour periodicity, the elongate strips extending along the direction which is orthogonal to the direction of colour periodicity;
• (b) generating a template for a light redirecting layer, which template defines at least a first region thereof, corresponding to a first image to be exhibited by the optical device, by:
• (b1) providing a version of the first image comprising a plurality of image pixels, each image pixel exhibiting a uniform colour;
• (b2) for each image pixel of the first image, creating a corresponding 1 template pixel based on the colour of the respective image pixel, each template pixel comprising an arrangement of one or more illumination zones and/or one or more non-illumination zones, different arrangements of the of one or more illumination zones and/or one or more non-illumination zones in different ones of the template pixels defining different respective colours;
• (b3) arranging the template pixels in accordance with the positions of their corresponding image pixels in the first image to form the template for the light receiving layer, the illumination zones of the template pixels in combination forming the first region thereof which defines the first image;
• (c) forming a light redirecting layer in accordance with the generated template, the light redirecting layer comprising at least a first array of refractive and/or reflective anisotropic light redirecting elements extending across a first region of the light redirecting layer corresponding to the first region of the template and being absent elsewhere, the anisotropic light redirecting elements of the first array each having a primary axis orientated along a first direction lying in the plane of the optical device and being configured such that an incident light beam lying in a plane perpendicular to the first direction and from a light source off the normal of the optical device will be redirected by the anisotropic light redirecting elements towards the normal of the optical device but within the same plane, whereas an incident light beam lying in a plane which is not perpendicular to the first direction and from a light source off the normal of the optical device will either not be redirected, or will be redirected by the anisotropic light redirecting elements out of the plane of the incident light beam;
• and
• (d) overlapping the colour layer and the light redirecting layer to form the optical device;
• whereby for a viewer substantially on the normal of the optical device, when the incident light beam lies in a plane perpendicular to the first direction and is from a light source off the normal of the optical device, portions of the colour layer which overlap the first region of the light redirecting layer are illuminated by the anisotropic light redirecting elements relative to the remainder of the colour layer, such that for a viewer substantially on the normal of the optical device, when the incident light beam lies in a plane perpendicular to the first direction and is from a light source off the normal of the optical device, a colour version of the first image will be exhibited by the device.