A method of forming a security device includes: a holographic image layer, diffusion element, and barrier layer. A region of the barrier layer includes a heat-transformable material. The method further includes selectively applying heat at a plurality of positions within the region of the barrier layer, in accordance with a predetermined pattern, so as to modify the heat-transformable material such that the region of the barrier layer is selectively rendered passable to the diffusible substance at each of the plurality of positions, thereby permitting diffusion of the diffusible substance between the regions of the diffusion element and the holographic image layer such that, at a plurality of positions within the region of the holographic image layer and corresponding to the predetermined pattern, the volume hologram is dimensionally modified so as to become viewable in a second observable colour, different from the first observable colour.

A matrix-array optical component that includes, superposed, a holder, a matrix-array of reflectors and at least one matrix-array of holographic lenses with the holder placed between the matrix-array of reflectors and the at least one matrix-array of holographic lenses. The holographic lenses are each formed by at least one reflection hologram, and each includes a through-aperture for letting light pass. Each individual cell of the matrix-array optical component includes one reflector of the matrix-array of reflectors and one holographic lens of the matrix-array of holographic lenses, which are arranged opposite one another on either side of the holder with respective reflective faces of the reflector and of the holographic lens located facing. Thus, a planar matrix-array optical component with a focusing efficiency higher than or equal to 50% and able to focus an incident light beam axially is produced.

An optical device (100) for forming a distribution of a three-dimensional light field comprises: an array (102) of unit cells (104), a unit cell (104) being individually addressable for switching the optical property of the unit cell (104) between a first and a second condition; wherein the unit cells (104) are configured to be selectively active or inactive and wherein the array (102) comprises at least a first and a second disjoint subset (110; 112; 114; 116), and wherein the unit cells (104) in a subset (110; 112; 114; 116) are configured to be jointly switched from inactive to active, wherein the active unit cells (104) are configured to interact with an incident light beam (106) for forming the distribution of the three-dimensional light field; and wherein the optical device (100) is configured to address inactive unit cells (104) for switching the optical property of unit cells (104).

An optical device (100) for forming a distribution of a three-dimensional light field comprises: an array (102) of unit cells (104), a unit cell (104) being individually addressable for switching the optical property of the unit cell (104) between a first and a second condition; wherein the unit cells (104) are configured to be selectively active or inactive and wherein the array (102) comprises at least a first and a second disjoint subset (110; 112; 114; 116), and wherein the unit cells (104) in a subset (110; 112; 114; 116) are configured to be jointly switched from inactive to active, wherein the active unit cells (104) are configured to interact with an incident light beam (106) for forming the distribution of the three-dimensional light field; and wherein the optical device (100) is configured to address inactive unit cells (104) for switching the optical property of unit cells (104).