Device with anti-counterfeiting diffractive structure
AssigneeOptaglio Limited
InventorJohn Drinkwater
Life of this patent
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Abstract
An optical device for security and anti-counterfeit applications comprises a diffractive structure comprising a discrete region that in response to white light illumination generates an image by a process of diffraction in close angular proximity to the specular reflection and which is thus substantially non-visible to an observer, and which under coherent illumination generates a laser projection covert image which forms an image in an image plane located away from the physical plane of the device and which is angularly co-located in close proximity to the direction and position of the specular reflection.
Claims28
An optical device comprising at least one discrete region comprising diffractive structure wherein the diffractive structure is arranged to replay in response to white light illumination exhibiting specular reflection a first image in close angular proximity to the specular reflection of the white light such that the said first image is non-visible to an observer, and wherein the diffractive structure is arranged to replay in response to coherent light illumination exhibiting specular reflection a second covert image visible to an observer when imaged on a separate image plane located away from the physical plane of the optical device and replaying in close angular proximity to the specular reflection of the said coherent light.
An optical device as claimed in any one of the preceding claims wherein the second covert image comprises any one of, or any combination of, alphanumeric characters, graphical indica or continuous tone images.
An optical device as claimed in any one of the preceding claims comprising a plurality of discrete regions of diffractive structure.
An optical device as claimed in any one of the preceding claims wherein the diffractive structure is in the form of a reflective surface relief structure.
An optical device as claimed in any one of the preceding claims wherein the diffracted light forming the second image subtends an angle of 7 degrees or less from the discrete specular reflection.
An optical device as claimed in any one of the preceding claims wherein the diffractive structure is combined with a visual holographic or diffractive device, wherein the additional diffractive structure replays in response to white light illumination a holographic or diffractive image visible to an observer for authentication.
An optical device as claimed in any one of the preceding claims wherein the optical device is formed as a single continuous structure.
An optical device as claimed in any one of the preceding claims wherein the visible second image is asymmetric in form.
An optical device as claimed in any one of the preceding claims including at least one additional diffractive structure comprising a substantially smaller diffraction grating carrier pitch arranged to replay under white light illumination a respective additional first image which is non-visible to an observer and arranged to replay under coherent light illumination in a Littrow geometry a respective additional second covert image visible to an observer when imaged on a plane located in a direction near the direction of illumination and imaging on a separate image plane located away from the physical plane of the optical device.
An optical device substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.
Dependencies are inferred from the claim text.