Abstract: Disclosed herein is a display device using a single-panel diffractive light modulator. The display device includes a light source unit, a condensing unit, an illumination unit, a diffractive light modulator, a projection unit, a filter unit, and a distortion correcting means.

Abstract: A conventional diffractive optical element (DOE), which consists of repetition of a unit pattern , has an advantage of applicability of the Fast Fourier Transform algorithm to calculate diffraction beam spots intensities on lattice points on an image plane. But, the conventional DOE has a drawback of impossibility of diffracting a laser beam off the lattice points. This invention designs a DOE by giving arbitrary complex amplitude transmittance {tmn} to every pixel (m, n), calculating actual Fourier transform from {tmn} to intensity W(?, ?), and obtaining intensity of a diffraction beam directing in any ? and ? direction. Since ?, ? are not necessary to be on lattice points, the FFT is of no use. Angular resolutions U and V satisfy inequalities U<?/aR and V<?/bS, where ? is a wavelength, aR and bS are the size of the DOE. The DOE can produce multidiffracted beams anywhere on an image and can irradiate a plurality of arbitrary arranged points simultaneously with high precision.

Abstract: A product with a surface relief grating (SRG) image effect has a surface with rotational cuts effected therein to create the SRG image effect. The SRG image has an effect based on a rotational speed of a cutting tool effecting the cuts, a travel speed of a cutting tool effecting the cuts, and a depth of the cuts. A light source can be used to emit light on the surface of the product. In an SRG image machining process, a material and a cutting tool are provided. The material is contacted by the cutting tool to a predetermined depth. The cutting tool is rotated to cut the material at a predetermined rotational speed. The cutting tool is moved to cut the material at a predetermined travel speed. A SRG image effect is produced in the material through the contacting, rotating, and moving steps.

Abstract: A virtual image display device is provided which displays a two-dimensional image for viewing a virtual image in a magnified form by a virtual optical system. The virtual image display device includes an optical waveguide (13) to guide, by internal total reflection, parallel pencil groups meeting a condition of internal total reflection, a first reflection volume hologram grating (14) to diffract and reflect the parallel pencil groups incident upon the optical waveguide from outside and traveling in different directions as they are so as to meet the condition of internal total reflection inside the optical waveguide and a second reflection volume hologram grating (15) to project the parallel pencil groups guided by internal total reflection inside the optical waveguide as they are from the optical waveguide by diffraction and reflection thereof so as to depart from the condition of internal total reflection inside the optical waveguide.

Abstract: The invention relates to a device for generating a periodical array of light spots from an input light beam, said device comprising—a periodical array of apertures (202) forming a plurality of interlaced sub-arrays of apertures,—phase shifter elements (PSi) placed in front of said apertures for imposing a phase shift to said input light beam so that each light spot is constructed as the superposition of a plurality of light spots generated by said plurality of interlaced sub-arrays of apertures. Use: Light spot generation.

Abstract: Laser information is prepared which indicates the irradiation interval and intensity level to be irradiated on an optical disc in advance. Then, when image drawing is indicated together with the indication of the forming spacing for pits, a laser is controlled so as to achieve the irradiation interval and intensity level indicated by the laser information that corresponds to the indicated formation spacing to fabricate pits in the optical disc.

Abstract: A surface relief grating (SRG) image machining process and/or product. For the SRG image machining process a material and a cutting tool are provided. The material is contacted by the cutting tool to a predetermined depth. The cutting tool is rotated to cut the material at a predetermined rotational speed. The cutting tool is moved to cut the material at a predetermined travel speed. A SRG image effect is produced in the material through the contacting, rotating, and moving steps. A product with a SRG image effect has a surface with rotational cuts effected therein to create the SRG image effect. The SRG image has an effect based on a rotational speed of a cutting tool effecting the cuts, a travel speed of a cutting tool effecting the cuts, and a depth of the cuts. A light source can be used to emit light on the surface of the product.

Abstract: A display element includes a display substrate that comprises a liquid crystal; and a plurality of diffraction gratings having different diffraction modes, arranged in regions of the single display substrate that are different from one another.

Abstract: A security device includes an optically variable device (OVD) having diffraction-based micro-optics including at least one moiré magnified visual representation of a micro-object. A diffractive structure provides micro-objects with unique optical effects when the OVD is viewed through the micro-object structure from a predetermined relative observation point. In addition to magnifying the micro-objects, the diffractive structure can impart optical effects such as change in observed color, enhanced contrast, animation of the observed visual representation, and change in size or shape of the observed visual representation. The micro-objects and the diffractive structure can be disposed on the same or different portions of a substrate. A method of making OVDs, and an article employing such OVDs are also disclosed.

Abstract: An optical layer comprises a sheet of material having a surface. The surface comprises a plurality of optical elements. The optical elements are comprised of microscopic patterns in the surface that cooperate to produce an image. Each of the elements has a focal length. At least some of the focal lengths are significantly different from other focal lengths, such that some portions of the surface appear to be closer to a viewer than other portions of the surface.

Abstract: Disclosed herein is a color display apparatus using a one-panel diffractive-type optical modulator. The color display apparatus includes a plurality of light sources, an illumination lens system, a diffractive-type optical modulator, a filter system, and a projection system. The light sources simultaneously emit the light beams of corresponding wavelengths. The illumination lens system allows respective light beams to be converted into linear parallel light. The diffractive-type optical modulator forms diffractive light by diffracting incident light when the locations of at least two neighboring reflection parts vary to a predetermined distance by an actuating means. The filter system allows diffractive light having a desired diffractive order for respective wavelengths to pass therethrough when diffractive light having a plurality of diffractive orders for the respective wavelengths enters from the diffractive-type optical modulator.

Abstract: A method for forming fine concavo-convex patterns by using a relief formation material 3 having a relief formation layer 2 composed of a resin having thermoplasticity and a relief pattern sheet 6 having on a surface thereof fine concavo-convex patterns 5, wherein a photothermal conversion layer 7 is formed in the relief formation material 3 or the relief pattern sheet 6; the photothermal conversion layer 7 is irradiated with light 8 to make the photothermal conversion layer 7 generate heat in the state that the relief formation layer 2 is brought into contact with the fine concavo-convex patterns 5; and the fine concavo-convex patterns 5 are formed on the relief formation layer 2.

Abstract: In one embodiment, a light modulator includes a substrate and a number of modulator elements disposed above and spaced apart from the substrate. Each modulator element has an optically active portion adapted to receive light incident thereon, and a support portion on either side of the active portion to support the modulator element above the substrate. The modulator elements include at least one deflectable modulator element. To shorten damping time, the deflectable modulator element has a lower surface in the support portion that is closer to the substrate than a lower surface under the optically active portion.

Abstract: Tire made of a rubber-based material of black color comprising at least one design on an outer surface of the said tire, the material being a diene elastomer or rubber, the design having on its outer surface at least one light diffraction grating formed of a plurality of ridges or grooves of height H arranged parallel to one another with a period P. The process for obtaining a design of variable color on an article made of a rubber-based material of black color, the design being visible in at least one color different from black.

Abstract: An optical device for security and anti-counterfeit applications has a holographic diffractive structure that includes a discrete region that in response to white light illumination generates a holographic image by a process of diffraction of light in one embodiment combined with a paper substrate which also contains a secure mark produced by laser ablation of the structure, the mark being characterised by various attributes: variable cut width and pattern, being visible both in reflected light and also in transmitted light, variable depth of cut, variable perforation visible in transmission, variable reflection characteristics. In one embodiment when combined with paper based laser mark has elements in both metallised diffractive region and paper region, the marks on different regions showing different characteristics and thereby securely linking diffractive structure and paper substrate and also showing different characteristics of marking pattern on the different materials.

Abstract: A light pipe includes a surface provided with a pattern that has diffractive properties, where the pattern has uniform, mutually different areas on the surface such that some of the areas are configured to distribute light from a light input end of the light pipe to form macroscopically uniform distribution of light and some other areas are configured to couple light out from the light pipe in order to produce lighting, and where the relative proportion of surface covered by areas configured to distribute light is arranged to decrease in relation to increase of distance from the light input end.

Abstract: A microscope including a source of light, adjustable in frequency and intensity, a method of operating such a microscope, and a method for manufacturing such a microscope are described. Typically, there is provided a microscope comprising an illumination source for illuminating a subject, the illumination source comprising: a source of polychromatic light; elements for selecting a combination of frequencies from among the frequencies of the polychromatic light at selected respective relative intensities to one another, to provide non-white, polychromatic light for illuminating a subject.

Abstract: An optical structure includes a light transmissive substrate having a surface relief pattern applied thereon, such as a hologram. A patterned layer of a reflective material is applied over portions of the surface relief pattern so as to form alphanumeric characters, bars codes, or pictorial or graphical designs. An optically active coating is applied over the patterned layer of reflective material and exposed portions of the surface relief pattern in order to provide desirable optical effects to the exposed portions of the surface relief pattern. In some embodiments, the optically active coating is a color shifting thin film, or contains color shifting flakes. Optionally, the material of the optically active coating is index matched to the light transmissive substrate in order to optically erase the effect of the surface relief pattern in the portions of the surface relief pattern not covered by the reflective material.

Abstract: A label (1) made from a layer composite (15) includes at least one machine-readable diffractive bar code (3) consisting of narrow rectangular fields (4) occupied by the optically active structures and intermediate surfaces (5). The optically active structures which are covered by a reflection layer are embedded between layers of the layer composite (15). The diffractive relief structure used in the diffractive bar code (3) for the fields (4) diffracts and polarizes incident light and scatters the diffracted light into a half-space above the diffractive relief structure. A second diffractive relief structure differs at least in respect of the polarization of the polarizedly backscattered light with respect to the first diffractive relief structure. The second diffractive relief structure can be used for example for field surfaces of a second bar code in the bar code field (9) on the label (1) or for the intermediate surfaces (5).

Abstract: A security element (2) comprising a plastic laminate has a surface pattern (12) composed mosaic-like from surface elements (13; 14; 15). Shaped into at least two of the surface elements (14; 15) is a respective diffraction structure {B(x, y, T)} produced from a superimposition of a low-frequency grating structure {G(x, y)} with a high-frequency relief structure {R(x, y)}. In the one surface element (14) a grating vector of the grating structure {G(x, y)} and a relief vector of the relief structure {R(x, y)} are parallel and in the other surface element (15) the grating vector (16) and the relief vector (17) include a substantially right angle. In addition the grating vectors (16) of the grating structures {G(x, y)} in the two surface elements (14; 15) are parallel. A common boundary (18) of the two surface elements (14; 15) is visible only upon lighting with linearly polarized light, in daylight both surface elements (14; 15) have the same surface brightness.

Abstract: A light-diffractive binary grating structure has a microscopic mesa structure (2) whose plateaux (5) are separated by valleys (4) of substantially rectangular cross-section, wherein the arrangement of the valleys (4) is periodically repeated. Within a period (T) of the mesa structure (2) at least N valleys (4) separate the plateaux (5), N being an integer and greater than 2. The mesa structure (2) is an additive superimposition of N phase-shifted rectangular structures which have the same period (T) of the mesa structure (2). Each of the rectangular structures has a phase shift such that the plateaux (5) of the one rectangular structure fall into the valleys (4) of the N?1 other rectangular structures. In addition the resulting mesa structure (2) has only a single valley between two plateaux (5), which is of a width greater than a seventh of the period (T).

Abstract: A security device has a substrate formed with a surface relief defining an optically variable effect generating structure. At least two different reflection enhancing materials are provided on, or on the same side of, substrate with respect to the surface relief, whereby the optically variable effect can be viewed against a background defined by the reflection enhancing materials.

Abstract: The present invention is directed to an improvement in a diffractive display suitable for presenting graphic and the like displays. Broadly, a novel embodiment is realized from a holographic diffraction pattern carried by a magnet or element and an electrically energizable coil magnetically coupled with said magnet that is energizable for movement of the magnet. Rotation of the holographic diffraction pattern generates a display using the diffracted light from the holographic diffraction grating. Another novel embodiment is realized from a faceted rotatable element (FRE) having an array of facets each bearing a diffraction grating and a source energizable for rotation of the FRE from a resting station to a viewing station. Rotation of the FRE generates a display using the diffracted light from the diffraction gratings.

Abstract: The invention relates to an optical feature, in particular for documents of value, having at least one at least dual-channel hologram for the holographic reconstruction of different images from different directions of gaze, wherein different regions of the hologram are associated with the different channels and the regions of the hologram reconstructing the respective image under incident light have sub-regions which do not take part in the image reconstruction, to a data carrier having at least one optical feature of the invention and to a method for the manufacture of an optical feature, in particular for documents of value.

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: Invisible different monochromatic images are inscribed in a diffractive optical element. Each of the images appears when a specific light source is on and image disappears when the specific light is off. The light sources for the different monochromatic images are spaced at different positions with respect to the diffractive optical element. A dynamic image is produced by time-varying and electronically controlling the intensity and on/off of the different light sources.

Abstract: A multilevel optical phase element is illuminated with a light source having a plurality of wavelengths of interest. The multilevel phase element disperses light from the light source by diffraction and focuses the dispersed light onto an imaging plane. A light modulating display in the imaging plane having a plurality of pixel elements is actuated. Each pixel element is assigned to transmit a predetermined spectral region within the near field region of the multilevel display element so as to receive the dispersed and focused light from the multilevel optical phase element. A system for displaying a color image includes a light source emitting a plurality of wavelengths of interest, a multilevel optical phase element, and a light modulating electronic display.

Abstract: An optical device for security and anti-counterfeit applications comprises a holographic diffractive structure (8) that generates a holographic optically variable image by diffraction that consists of at least two separate substantially co-located linear regions that generate in response to white light illumination a visually observable holographic image consisting of at least two defined graphical elements and which generates in response to coherent illumination (1) at least two covert images (5, 6, 7) focussed at a separate image plane a distance away from the real physical plane of the device, each covert image (5, 6, 7) corresponding to the replay from one of the linear regions, each covert image (5, 6, 7) being separated on its image plane from the adjacent covert image (5, 6, 7) by at least its own dimensions.

Abstract: Invisible diff&rent monochromatic images are inscribed in a diffractive optical element. Each of the images appears when a specific light source is on and image disappears when the specific light is off. The light sources for the different monochromatic images are spaced at different positions with respect to the diffractive optical element. A dynamic image is produced by time-varying and electronically controlling the intensity and on/off of the different light sources.

Abstract: A security element (1) is embedded in a layer composite of plastic material and has reflecting, optically variable surface patterns (11) which can be visually recognised from predetermined observation directions and which are formed from a mosaic of surface elements (12; 13; 14) occupied by optically active structures. A part of the surface pattern (11) is additionally covered by a regularly arranged matrix (18) of unit cells (15). Each unit cell (15) is occupied by a single elementary surface (16) or a group of identical surface portions (17), wherein the elementary surfaces (16) and the surface portions (17) contain optically active structures (4) which are independent of the mosaic of the surface pattern (11).

Abstract: The invention relates to a pattern (18) which is designed as a visually perceptive mosaic consisting of a plurality of surface elements (8; 9; 15; 16; 17) and which is embedded in a laminate (1) consisting of at least one transparent outer layer (2) and one protective layer (5). The surface elements (8; 9; 15; 16; 17) are transparent, scatter or reflect incident light (10) or diffract the incident light (10) to microscopic relief structures covered with a reflecting layer (3). An area (16) corresponding to at least one of the surface elements provided with a microscopic relief structure (4) has a ZOM structure (4′) with a profile height h which can be slowly modified in a pre-determined manner and a spatial frequency f. The product of a predetermined critical wavelength &lgr;G of the visible spectrum and the spatial frequency f is greater than or equal to 1.

Abstract: In order to improve a structure arrangement comprising a plurality of portions having a relief structure with an optical-diffraction effect, in particular for visually identifiable optical security elements for value-bearing documents, for example banknotes, credit cards, passes or cheque documents, or other articles to be safeguarded, in such a way that it can give a viewer an image impression which in particular is more homogenous and more brilliant than is possible with known structure arrangements, it is proposed that a predominant number of the portions is of strip or band configuration.

Abstract: A lamellar volume grating operating in reflection and transmission and providing a substantially wavelength- and polarization-independent diffraction efficiency is disclosed. The lamellar grating has an approximately rectangular grating profile with a height-to-width ratio of the grooves or “teeth” advantageously greater than 2. The grating operates preferably in first order and can be implemented as an immersion grating. In particular, the lamellar volume grating described herein can be employed in an optical multiplexer/demultiplexer arrangement with small overall dimensions.

Abstract: Reflective diffraction grating. A focused ion beam (FIB) micromilling apparatus is used to store color images in a durable medium by milling away portions of the surface of the medium to produce a reflective diffraction grating with blazed pits. The images are retrieved by exposing the surface of the grating to polychromatic light from a particular incident bearing and observing the light reflected by the surface from specified reception bearing.

Abstract: Reflective diffraction grating. A focused ion beam (FIB) micromilling apparatus is used to store color images in a durable medium by milling away portions of the surface of the medium to produce a reflective diffraction grating with blazed pits. The images are retrieved by exposing the surface of the grating to polychromatic light from a particular incident bearing and observing the light reflected by the surface from specified reception bearing.

Abstract: Disclosed is a curved surface element (e.g., light bulb, ornament, light pipe, etc.) which has at least a portion thereof (inner or outer surface) covered with a holographic diffraction grating which was constructed to be essentially distortion free on said curved surface, whereby such diffraction grating diffracts light to emit color to the observer. The diffraction grating can take for form of a holographic optical element (HOE) attached to the curved surface or a diffractive holographic optical pattern (HOP) embossed into the curved surface.

Abstract: A tube has walls consisting totally or partially of a first diffraction grating with its ruled surface aligned perpendicular to the length of the tube to disperse a field of rainbow colored light when illuminated with a light source aimed through or along the length of the tube.

Abstract: Disclosed is an illumination system using optical feedback to maintain a predetermined illumination output. The illumination system employs an electrically controllable optical filter for filtering light incident thereon. The illumination system also includes a light detector for detecting at least a portion of the light filtered by the electrically controllable optical filter. The light detector is in data communication with the electrically controllable optical filter. Some or all light filtered by the electrically controllable optical filter is detected by the light detector, which, in turn generates a corresponding signal that is compared to at least one predetermined value. If the signal generated by the light detector differs when compared to the at least one predetermined value, one or more filtering characteristics of electrically controllable optical filter are varied which, in turn, varies the amount of light filtered by the electrically controllable optical filter.

Abstract: A system for projecting images is provided having a group of diffractive phase plates each encoded with different image information which have phase shifts aligned to reconstruct visible images in a Fraunhofer diffraction region. The plates are arranged along a path, and may represent successive frames of animation. A light source illuminates the plates and provides, when multiple plates are illuminated, a composite image representing image information encoded in such multiple plates. This composite image is a coincident superposition of reconstructed images from the multiple plates. A mechanism is provided for moving the plates along their path such that images projected from the system in the Fraunhofer diffraction region represent the composite image from successively different illuminated multiple plates or the reconstructed image from a single plate. Both monochromatic and multi-color channel phase plates may be used in the system.

Abstract: A viewing device comprising a media having a lineal pattern of alternating transparent and non-transparent regions printed thereon, wherein the non-transparent regions comprise edges having an Edge Roughness greater than about 2 micrometers.

Abstract: This invention pertains to the design of optimized far field viewing devices that simultaneously produce bright far field holographic light patterns and achieve good see-through performance to present a well focused scene. A far field transmission hologram recorded on a transparent substrate has regions having high diffraction efficiency juxtaposed with regions having low diffraction efficiency. The high diffraction efficiency regions contribute to production of bright far field holographic light patterns, whereas the low diffraction efficiency regions contribute to see-through performance.

Abstract: A multilevel optical phase element is illuminated with a light source having a plurality of wavelengths of interest. The multilevel phase element disperses light from the light source by diffraction and focuses the dispersed light onto an imaging plane. A light modulating display in the imaging plane having a plurality of pixel elements is actuated. Each pixel element is assigned to transmit a predetermined spectral region within the near field region of the multilevel display element so as to receive the dispersed and focused light from the multilevel optical phase element. A system for displaying a color image includes a light source emitting a plurality of wavelengths of interest, a multilevel optical phase element, and a light modulating electronic display.

Abstract: A surface pattern is made up of surface elements (1 to 7) which are arranged in a mosaic-like fashion and which have microscopic relief structures. The surface elements (2 to 6) which are divided at least into first and second surface portions (8; 9) have in the first and second surface portions (8; 9) asymmetrical diffraction gratings (12; 13) with an optical diffraction effect, wherein in each divided surface element (2 to 6) adjacent first surface portions (8) are separated by at least one second surface portion (9). The grating vectors of the asymmetrical diffraction gratings (12) of the first surface portions (8) of all divided surface elements (2 to 6) have the same first value in respect of azimuth and the asymmetrical diffraction gratings (13) of the second surface portions (9) of all divided surface elements (2 to 6) have the same second value in respect of azimuth.

Abstract: An illumination system for a color projection display. In one embodiment a broad spectrum light source illuminates a multilevel optical phase element which disperses the broad spectrum light from the light source by diffraction. A display having a number of pixel elements, each capable of transmitting a predetermined spectral region, is positioned within the near field region of the multilevel optical phase element so as to receive the light dispersed by the multilevel phase element.

Abstract: A dot matrix hologram with a hidden image is disclosed, wherein the hidden image technology is applied to a dot matrix hologram. Although the hidden image technology has been used in a conventional hologram, it has not been used in a dot matrix hologram. Although the above two kinds of hologram both can show hidden images with illuminating laser light, the disclosed dot matrix hologram with a hidden image and the conventional hologram with a hidden image use different working principles and have different detailed characteristics to create hidden image regions.

Abstract: A diffraction surface and a method of making the surface. The surface may be applied to labels and other items to identify the origin of the goods to which the label is attached. The surface can include a block grating including ridges and recesses in the enclosed squares or rectangles. The diffraction grating manufactured by processing a data stream indicative of the image including obtaining a Fourier Transform of the data stream and preferably clipping and quantising the data stream, and deforming a plate surface in accordance with the data stream. Also claimed is a diffraction grating having spaced first and second portions each producing an image on a receiving surface in response to illumination by a reading light beam, configured such that when the reading light beam moves from the first to the second portion, a change occurs in the first image to produce the second image.

Abstract: A surface pattern (1) has N visually recognizable patterns which are composed of optically diffractive, microscopically fine relief structures, plane mirror faces or absorbing or scattering structures. The N patterns share at least one independent common surface element (11). The surface element (11) is subdivided into surface parts and has an arrangement of the surface parts which is independent of the N patterns, which has a predetermined structure, and which is not recognizable to the naked eye. A single microscopically fine diffraction structure or a structure which has an absorbing or scattering property or is a plane mirror is applied to each surface part. The relief structures, diffraction structures and other structures are embedded in a plastic laminate (20) and can have their optical performance enhanced by a reflection layer (21). The surface pattern (1) is applied as a security element to a document (2) and allows the document (2) to be identified by machine in a reading machine.

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 surface pattern (1) is composed of elements (2 to 5) which are arranged in a mosaic-like fashion and of which at least one pattern is formed from a background element (4) and a pixel (2) with microscopically fine relief structures diffracting visible light. The surface elements (3) and the element portions (5) either contain the microscopically fine relief structures diffracting visible light or they comprise reflecting or scattering surfaces. Arranged in the pixel (2) is a first diffraction grating B1 and arranged in the background element (4) is a second diffraction grating B2, wherein the first diffraction grating B1 and the second diffraction grating B2 are a superimposition of at least two different, microscopically fine relief structures F1 and F2 diffracting visible light. The first diffraction grating B1 and the second diffraction grating B2 differ only by virtue of a relative phase shift &Dgr;&phgr; between the relief structure F1 and the relief structure F2.

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.