Optically variable device

Abstract

An optically variable device and method of manufacturing the device is disclosed, the device including a plurality of zero-order diffraction grating elements some of which are modulated such that a coloured at least partially polarised image is visible to a person viewing the device, observing a first optically variable effect when the device is rotated about an axis substantially perpendicular to the plane, and a second optically variable effect when the device is viewed under polarised light and rotated about an axis substantially perpendicular to or parallel with the plane. The device is particularly suitable for security documents such as bank notes. Preferably, the first optically variable effect is produced by a change in brightness and/or colour of the grating elements and the second optically variable effect may likewise be produced by a change in brightness and/or colour of the grating elements. The device advantageously provides two different types of optically variable effect may be provided in a single device. This is possible due to the use of zero-order grating elements as the “pixels” of the coloured image. Each pixel, under illumination by unpolarised light, produces reflected light of a defined colour which is also at least partially polarised.

Dependencies are inferred from the claim text.