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 polarized 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 polarized 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 color of the grating elements and the second optically variable effect may likewise be produced by a change in brightness and/or color of the grating elements.

Abstract: An optical device, preferably for use in security devices and documents, comprising an arrangement of wavelength dependant optical phase, and optionally amplitude, modifying optical elements on a first surface of a substrate, each of the optical elements being in the form of an optical antenna and configured to produce a local phase change to reflected and/or transmitted electromagnetic waves, the arrangement configured such that the combined action of each of the optical elements produces a pre-defined optical effect on reflection and/or transmission observable by a viewer when the arrangement is illuminated by an external electromagnetic source.

Abstract: A hybrid security device for security documents and the like, with the microstructure for a first optically variable device (OVD) and the microstructure for a second OVD mutually interlace or interspersed. The first microstructure has a height profile that differs from that of the second microstructure by more than 0.5 microns. Suitable fabrication processes for the hybrid security device are also disclosed.

Abstract: An optical device comprising an at least substantially transparent substrate having a first side comprising a source layer having an arrangement of source elements and a second side comprising an Optically Variable Device (OVD) layer having a corresponding arrangement of diffractive elements, wherein each source element is configured to, upon illumination of the first side, provide an embedded light source for an associated diffraction element, and wherein the diffractive elements are configured for producing an optical effect observable when the diffractive elements are viewed by a viewer, such as the naked eye, upon illumination by the source elements.

Abstract: A hybrid security device for security documents and the like, with the microstructure for a first optically variable device (OVD) and the microstructure for a second OVD mutually interlace or interspersed. The first microstructure has a height profile that differs from that of the second microstructure by more than 0.5 microns. Suitable fabrication processes for the hybrid security device are also disclosed.

Abstract: A polarising security element for polarising light of a predetermined wavelength including a first dielectric material having a refractive index nb and at least one polarising region of mutually parallel segments of a second material having a refractive index np which is different from nb, the second material being a dielectric or conducting material. The segments of the second material are in contact with the first material and the segments have a width and/or an average spacing which is less than a predetermined range of wavelengths. A method of manufacturing such a security element in which a relief structure is embossed in the layer of the first dielectric material, the relief structure includes mutually parallel peaks and troughs, and the second layer of dielectric or conducting material is applied on the relief structure to form the at least one polarising region of mutually parallel segments.

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.

Abstract: An optical device which generates an optically variable image, the image being optically variable in that it varies according to the position of observation, is manufactured by dividing an optically invariable image into multiple pixels. Color component values are determined for each pixel. For each of the pixels of the optically invariable image, there is determined an associated pixel surface structure which has a three-dimensional surface shape and curvature which is related via a mathematical of computer algorithm to the color component values of the associated pixel in the optically invariable image, each pixel surface structure being an individual reflective or diffractive surface structure which produces an observable optical effect. An assembly of the reflective or diffractive pixel surface structures is produced which when illuminated generates a plurality of observable optical effects which combine to form an optically variable reproduction of the optically invariable image.

Abstract: An optical device which generates an optically variable image, the image being optically variable in that it varies according to the position of observation, is manufactured by dividing an optically invariable image into multiple pixels. Color component values are determined for each pixel. For each of the pixels of the optically invariable image, there is determined an associated pixel surface structure which has a three-dimensional surface shape and curvature which is related via a mathematical of computer algorithm to the color component values of the associated pixel in the optically invariable image, each pixel surface structure being an individual reflective or diffractive surface structure which produces an observable optical effect. An assembly of the reflective or diffractive pixel surface structures is produced which when illuminated generates a plurality of observable optical effects which combine to form an optically variable reproduction of the optically invariable image.

Abstract: A diffractive device has a surface relief structure which, when illuminated by a light source, generates one or more diffraction images which are observable from particular ranges of viewing angles around the device. The device includes background diffractive structural elements and interstitial diffractive structural elements. The interstitial elements are interspersed between the background elements such that the diffractive action of the background elements is modulated by the interstital elements, with differing interstitial element configuration in differing parts of the surface relief structure producing differing diffraction effects in corresponding parts of the diffraction images.

Abstract: A pixellated diffractive device includes a multiplicity of pixels (12,22) in turn divided into multiple sub-pixels (13,23). The device is related to one or more pixellated diffraction surface structures which when illuminated generate respective corresponding optically variable images. The sub-pixels (13,23) of each pixel of the diffractive device include diffractive elements (13a,23a) arranged in one or more groups, the diffractive elements of each group matching diffractive elements of a corresponding single pixel of the respective pixellated diffraction surface structures. In each pixel of the device the diffractive elements (13a,23a) of the or each said group are intermixed with other sub-pixels and cooperatively contribute a single element of the corresponding optically variable image which is generated on illumination of the diffractive device.

Abstract: A diffractive device has a surface relief structure which, when illuminated by a light source, generates one or more diffraction images which are observable from particular ranges of viewing angles around the device. The device includes background diffractive structural elements and interstitial diffractive structural elements. The interstitial elements are interspersed between the background elements such that the diffractive action of the background elements is modulated by the interstital elements, with differing interstitial element configuration in differing parts of the surface relief structure producing differing diffraction effects in corresponding parts of the diffraction images.

Abstract: A three-dimensional microstructure includes a plurality of structure elements, each structure element having a width, a length and a height, wherein a significant proportion of the structure elements have height dimensions which exceed their width and length dimensions. A method of fabricating such a microstructure includes the steps of: forming a mask with a plurality of regions, each region having a predetermined degree of transparency to UV radiation; providing a substrate (5) coated with a thick layer (6) of UV resist material; using UV radiation to irradiate through each of the regions of the mask a corresponding region of the layer of UV resist; and developing the layer of UV resist to remove irradiated regions, wherein the depth of each region is dependent upon the degree of transparency of the corresponding region of the mask.

Abstract: A diffractive device has a surface relief structure which when illuminated by a light source, generates one or more diffraction effects which are observable from a range of viewing angles around the device. At least part of the surface relief structure is arranged in a series of tracks, each track being less than 0.25 mm in width. The device, which may be embossed onto a metallised foil, is suitable for use as an anti-forgery authentication element on valuable documents.

Abstract: Diffractive indicia for a surface (1) comprising a plurality of small separate diffractive elements (2) and means for a adhering the diffractive elements to the surface. Each diffractive element has a diffractive surface relief structure and is not separately resolvable to the human eye. The appearance of the diffractive indicia, when applied to the surface, changes when the viewing angle and/or angle of illumination relative to the surface changes. In preferred arrangements, the diffractive indicia, are incorporated in an ink or a transfer medium. A palette of diffractive indicia with different characteristic colours and other optical properties may be provided.

Abstract: A pixellated diffractive device includes a multiplicity of pixels in turn divided into multiple sub-pixels. The device is related to one or more pixellated diffraction surface structures which when illuminated generate respective corresponding optically variable images. The sub-pixels of each pixel of the diffractive device include diffractive elements arranged in one or more groups, the diffractive elements of each group matching diffractive elements of a corresponding single pixel of the respective pixellated diffraction surface structures. In each pixel of the device the diffractive elements of the or each said group are intermixed with other subpixels and cooperatively contribute a single element of the corresponding optically variable image which is generated on illumination of the diffractive device.

Abstract: A diffractive device having a surface relief structure which, when illuminated by a light source, generates one or more diffraction images which are observable from particular ranges of viewing angles around the device, wherein at least part of the surface relief structure (1) is arranged in a series of tracks (2), each track (4, 5) having a diffracting surface (3) which generates a component of a diffraction image, such that at least one of the diffraction images generated by the diffractive device is formed from image components generated by a plurality of the tracks.

Abstract: An optical data element includes a plurality of diffraction zones wherein each zone contains a multiplicity of diffraction gratings. These zones may be illuminated and the resultant one or more diffracted beams detected to provide a signature for the element consisting of a series of discrete signature signals each generated by the plurality of zones and each including portions or relatively different intensities. At least one of the diffraction zones has a segment thereof modified whereby to discernibly alter at least one of the discrete signature signals of the signature and to thereby form a data segment of the optical data element.