Abstract: A skew mirror is an optical reflective device, such as a volume holographic optical element, whose reflective axis forms an angle (the skew angle) with the surface normal. A skew illuminator is a skew mirror that expands a narrow beam into a wide beam without changing the angular bandwidth of the illumination. Because the skew angle can form a relatively large angle with the surface normal (e.g., about 45), a skew illuminator can be fairly compact, making it suitable for directing light onto a spatial light modulator (SLM) in a small package. In some cases, the skew illuminator is formed as a waveguide, with a holographic layer sandwiched between a pair of substrates. A grating structure in the holographic core diffracts light out of the waveguide and, e.g., onto the active area of an SLM, which modulates the incident light and either transmits it or reflects it back through the waveguided skew illuminator.

Abstract: A depth camera assembly (DCA) has a light source assembly, a mask, a camera assembly, and a controller. The light source assembly includes at least one light source. The mask is configured to generate an interference pattern that is projected into a target area. The mask has two openings configured to pass through light emitted by the at least one light source, and the light passed through the two openings forms an interference pattern across the target area. The interference pattern has a phase based on a position of the light source. The camera assembly is configured to capture images of a portion of the target area that includes the interference pattern. The controller is configured to determine depth information for the portion of the target area based on the captured images.

Abstract: An optical assembly may include a waveguide and a Bragg grating configured to couple light into or out of the waveguide. The Bragg grating may include a plurality of layer pairs, wherein at least one layer pair comprises a first material having a first refractive index and a second layer having a second refractive index, and wherein properties of the Bragg grating are selected so that the Bragg grating exhibits a substantially similar diffractive efficiency and diffraction angle for light of at least two colors.

Abstract: An electronic device may have a reflective display with a pixel array that generates images. The reflective display may be illuminated by an illumination system. Light from the illumination system may be reflected by the pixel array as image light. The image light may be provided to a viewer using a waveguide with diffractive input and output couplers. The illumination system may have a waveguide. The illumination system may also have a light source such as one or more light-emitting diodes. Light from the light source may be coupled into the waveguide of the illumination system by a diffractive coupler such as volume hologram that serves as an input coupler. Light from the light source may be routed to the display to illuminate the display using the waveguide in the illumination system and a diffractive coupler such as a volume hologram that serves as an output coupler.

Abstract: An optical combiner includes an optical substrate. An in-coupler grating is positioned to receive an incident light with a FOV and couple a first portion of the incident light into a first propagation path within the optical substrate and a second portion of the incident light into a second propagation path within the optical substrate. The first light portion includes light of a first color, while the second light portion excludes light of the first color. The optical combiner includes fold gratings to expand the first light portion and second light portion and direct the expanded light towards an out-coupler grating, which couples the expanded light out of the optical substrate at multiple exit pupils.

Abstract: A backlight module and display device are provided. The backlight module includes: a light source module including a transparent block, a light source and a first grating group, and a light emergent module including a light guide plate and a second grating group. The light source emits initial lights to the first grating group which diffracts initial into first diffracted lights, and transmits first diffracted lights in light guide plate to second grating group; the second grating group diffracts the first diffracted lights into second diffracted lights, and enables the second diffracted lights to be emergent from backlight module. When an included angle between initial lights and side surface of light guide plate is greater than 0°, an angle between second diffracted lights and side surface is smaller than an angle between initial lights and side surface, thereby improving collimation degree of lights emergent from backlight module.

Abstract: An optical device or display is disclosed for use in an augmented reality or virtual reality device. The display includes a waveguide (2), an output element (4) and a plurality of input diffraction gratings (6, 8, 10, 12). Light from a plurality of projectors (16, 18, 20, 22) is diffracted by the input gratings (6, 8, 10, 12) so that it is coupled into the waveguide (2) by total internal reflection. The input gratings (6, 8, 10, 12) are provided in a staggered configuration in relation to the output element (4), with respect to a y-axis. Each input grating is adjacent another input grating that has a different separation distance from the output element (4). This can improve the evenness of illumination from the output element (4).

Abstract: An optical waveguide includes an input diffractive optical element arranged for being aligned with an optical projector for diffracting light beams therefrom, a waveguide substrate n, and an output diffractive optical element. Light beams diffracted by the output diffractive optical element are coupled out of the waveguide substrate towards users' eyes. The output diffractive optical element has an effective area arranged to maintain a constant output flux per unit area therein for providing an uniform image in brightness when the image is being projected out of the waveguide substrate.

Abstract: An optical waveguide includes an input diffractive optical element arranged for being aligned with an optical projector for diffracting light beams therefrom, a waveguide substrate, and an output diffractive optical element. Light diffracted by the output diffractive optical element is projected out of the waveguide substrate towards users' eyes. The output diffractive optical element has an effective area arranged to maintain a constant output flux per unit area therein for providing an uniform brightness of the light when the light is being projected out of the waveguide substrate.

Abstract: The present disclosure relates to a flat panel display embedding an optical imaging sensor such as a fingerprint image sensor.

Abstract: A system installed on an aircraft. The system includes a memory storing static information in one or more optical fibre gratings; and an interrogator. The interrogator includes a light source configured to transmit interrogation light to the memory, a receiver configured to receive return light from the memory, and an analyser configured to analyse the return light to obtain the static information.

Abstract: A VCSEL may include a bottom DBR mirror and a top DBR mirror above the bottom DBR mirror. The VCSEL may include a vertical optical cavity located within a portion of the bottom and top DBR mirrors. The vertical optical cavity may be configured to emit an optical signal. The VCSEL may include a lateral feedback optical cavity located within a different portion of the bottom and the top DBR mirrors configured to receive a feedback bias signal configured to bias the lateral feedback optical cavity to adjust the optical signal. The VCSEL may include an active region formed between the bottom and the top DBR mirrors that may include an oxide layer defining an oxide aperture. The VCSEL may include an isolation implant configured to electrically isolate the vertical optical cavity from the feedback optical cavity and to create a first and a second aperture within the oxide aperture.

Abstract: A holographic radar reflector includes a surface with a plurality of substantially microwave wavelength scale patterns along one or more portions of the surface. The holographic radar reflector can be a non-specular reflector, where the plurality of substantially microwave wavelength scale patterns have varying reflectivity. The holographic radar reflector can reflect electromagnetic radiation emitted from a fixed feed point in varying directions depending on the portion of the surface reflecting the electromagnetic radiation.

Abstract: The present disclosure relates to a flat panel display embedding an optical imaging sensor such as a fingerprint image sensor. The present disclosure suggests a flat panel display embedding an image sensor comprising: a display panel including a display area and a non-display area; and a directional optical unit having a length and a width corresponding to the display panel and a thickness, and attached on a top surface of the display panel, wherein the directional optical unit provides a sensing light to the display area, and wherein the sensing light is collimated and directionized to a predetermined direction.

Abstract: The present disclosure relates to a flat panel display embedding an optical imaging sensor such as a fingerprint image sensor. The present disclosure suggests a flat panel display embedding an image sensor comprising: a display panel including a display area and a non-display area; and a directional optical unit having a length and a width corresponding to the display panel and a thickness, and attached on a top surface of the display panel, wherein the directional optical unit provides a sensing light beam to the display area, and wherein the sensing light is collimated and directionized to a predetermined direction.

Abstract: An optical device is disclosed for expanding input light in two dimensions in an augmented reality display. The device comprises a waveguide (12) and three linear diffraction grat-ings H0, H1, H2. An incident beam from a projector illuminates an input grating H0 with polychromatic light, and the light is coupled into the waveguide (12). The other two gratings H1, H2 are overlaid on top of one another. Light can be diffracted by one grating H1 into a first diffracted order and towards the other grating H2 which can couple the light out of the waveguide (12) towards a viewer. In another arrangement the crossed gratings H1, H2 may be replaced by a photonic crystal (19) having a regular array of pillars (20) which create a number effective diffraction gratings.

Abstract: An optical device is disclosed for expanding input light in two dimensions in an augmented reality display. The device comprises a waveguide (12) and three linear diffraction gratings H0, H1, H2. An incident beam from a projector illuminates an input grating H0 with polychromatic light, and the light is coupled into the waveguide (12). The other two gratings H1, H2 are overlaid on top of one another. Light can be diffracted by one grating H1 into a first diffracted order and towards the other grating H2 which can couple the light out of the waveguide (12) towards a viewer. In another arrangement the crossed gratings H1, H2 may be replaced by a photonic crystal (19) having a regular array of pillars (20) which create a number effective diffraction gratings.

Abstract: An arrangement and method that compensates for variation in grating strength associated with forming multiple gratings in multicore fiber is proposed where the writing efficiency of the beam(s) used to form the gratings is controlled to compensate for fiber lensing effects. In one case, a spacing between the multicore optical fiber and the beam source is controlled such that the writing efficiency (which decreases as a function of the space between the source and the fiber) compensates (at least in part) for the increased beam intensity attributed to the lensing effect of the fiber itself. The width of beam itself may also be controlled to modify the writing efficiency.

Abstract: Embodiments of the present invention provide a variable optical attenuator. The variable optical attenuator includes: a collimator, a switchable polarization grating, a reflector, and a voltage controller for adjusting a voltage between electrodes at both ends of a liquid crystal layer of the switchable polarization grating, where the collimator, the switchable polarization grating, and the reflector are disposed successively; the collimator is configured to receive incident light and output the incident light to the switchable polarization grating; the switchable polarization grating is configured to diffract the incident light for one time and then perform emission onto the reflector; the switchable polarization grating is further configured to diffract, for one time, a beam reflected back by the reflector, and then emit resulting diffracted light; and the collimator is further configured to receive the diffracted light and output the diffracted light.

Abstract: An optical coupling system and method are provided for coupling light from a light source into an optical fiber that reduce back reflection of light into the light source and provide controlled launch conditions that improve forward optical coupling. The optical coupling system comprises at least one flat surface having perturbations formed therein over at least a portion of the flat surface that intersects an optical pathway. The perturbations have a lateral width and a height that are preselected to increase forward optical coupling efficiency and to decrease back reflection of the light beam from the optical fiber end face into the light source. The perturbations improve forward optical coupling by creating a complex light beam shape that is preselected to better match a spatial and angular distribution of a plurality of light modes of the optical fiber.

Abstract: A retro-focus type imaging-optical system is disclosed. The imaging-optical system comprises, in order from an object side to an image side a first lens group, an aperture stop, and a second lens group. The first lens group includes, in order from the object side, a positive first F lens group and a negative first R lens group. The first F lens group includes a positive meniscus lens having a convex surface on the object side. The first R lens group includes a negative meniscus lens having a convex surface on the object side and a positive lens. The second lens group includes, in order from the object side, a positive second F lens group and a second R lens group, and the second F lens group includes a positive lens element having a convex meniscus shape on the image side.

Abstract: A heat assisted magnetic recording (HAMR) write apparatus is described. The HAMR write apparatus is coupled with a laser that provides energy. The HAMR writer has a media-facing surface (MFS) and a laser-facing surface. The HAMR write apparatus includes a free-standing reflector and at least one waveguide. The free-standing reflector resides on the laser-facing surface and has a concave reflective surface oriented to receive the energy from the laser. The waveguide(s) are optically coupled with the free-standing reflector and direct energy from the laser toward the MFS.

Abstract: A security document comprises a substrate (1) and an optical waveguide (7). Couplers (10a, 10b) are provided in the waveguide (7) for coupling light into and out of the waveguide. The couplers (10a, 10b) can e.g. by gratings, scattering objects, holograms, luminescent dyes or perforations. The authenticity of the document can be verified using methods based on the properties of the waveguide.

Abstract: The invention concerns a method for generating a laser beam (3) with different beam profile characteristics, whereby a laser beam (2) is coupled into one fiber end (1a) of a multi-clad fiber (1), in particular a double-clad fiber, and emitted from the other fiber end (1b) of the multi-clad fiber (1) and whereby, to generate different beam profile characteristics of the output laser beam (3), the input laser beam (2) is electively coupled either at least into the inner fiber core (4) of the multi-clad fiber (1) or at least into at least one outer ring core (6) of the multi-clad fiber (1), as well as a corresponding arrangement (10).

Abstract: A solar light concentration plate comprises a plurality of holograms diffracting incident light wherein each of the plurality of the holograms has a thickness, at least one intermediate light guide plate disposed between the plurality of the holograms, and a pair of external light guide plates disposed on outer surfaces of outermost holograms of the plurality of the holograms, wherein at least one of the pair of the external light guide plates has an inner surface and an outer surface inclined relative to the inner surface.

Abstract: Holographic display apparatuses are provided. The holographic display apparatus may include a light source module generating coherent light, at least two input optical systems converging the light generated from the light source module on at least two converging points, an output optical system mixing the lights provided from the at least two input optical systems to provide a hologram image, and a spatial light modulating module modulating the light.

Abstract: A solar light concentration plate comprises a first hologram which receives solar light and diffracts incident light in a range of an incident angle, and first and second light guides respectively disposed on both sides of the first hologram, wherein at least one of the first and second light guides has an outer surface substantially inclined to an inner surface of the at least one of the first and second light guides.

Abstract: An optical element is provided with: first polarization-separation layer (13) that is laminated on first surface (12b) of light guide body (12) and that, of the light incident from light guide body (12), transmits X-polarized light and reflects Y-polarized light that is orthogonal to the X-polarized light; polarization hologram layer (14) that is laminated on first polarization-separation layer (13) and that diffracts to a prescribed diffraction angle the X-polarized light that is incident within a prescribed range of angles of incidence and converts the X-polarized light to Y-polarized light; second polarization-separation layer (15) that is laminated on polarization hologram layer (14) and that, of the light incident from polarization hologram layer (14) transmits Y-polarized light and reflects X-polarized light; reflection layer (18) provided on second surface (12c) side of light guide body (12); and phase difference layer (17) that is provided between first surface (12b) of light guide body (12) and refle

Abstract: Technologies are generally described for generating an image in a holographic imaging device by causing multiple reflections of a hologram reconstruction light on one side of a display panel in the holographic imaging device. An example device may include a display panel, a semi-transparent mirror layer on the display panel, a mirror layer at a side of the semi-transparent mirror layer opposite to the display panel, and a light irradiation unit opposite to the semi-transparent mirror layer. The light irradiation unit may irradiate a hologram reconstruction light on the semi-transparent mirror layer at a predetermined incident angle. The semi-transparent mirror layer may reflect a portion of the hologram reconstruction light such that the reflected portion of the hologram reconstruction light may be incident on the mirror layer. The semi-transparent mirror layer may transmit the other portion of the hologram reconstruction light to cause interference in the hologram.

Abstract: A security device including a zero order diffractive microstructure buried within a substrate. One or more optical structures, such as microlenses, may be formed on a surface of the substrate. The optical structures modify the optical characteristics of the zero order diffractive microstructure. Various alternatives or additional optical structures and methods of producing the security device are described in additional embodiments.

Abstract: An optical device includes: a light guide plate receiving, for each of N types of wavelength bands, a plurality of parallel light beams with different incident angles each corresponding to view angles, and guiding the received parallel light beams; a first and a second volume hologram gratings of reflection type having a diffraction configuration which includes N types of interference fringes each corresponding to the N types of wavelength bands, and diffracting/reflecting the parallel light beams. The optical device satisfies for each wavelength band, a relationship of ‘P>L’, where ‘L’ represents a central diffraction wavelength in the first and second volume hologram gratings, defined for a parallel light beam corresponding to a central view angle, and ‘P’ represents a peak wavelength of the parallel light beams.

Abstract: A light emitting apparatus includes a first rod integrator and a second rod integrator supported by a support substrate and a light emitting device disposed between the first rod integrator and the second rod integrator. The light emitting device emits a plurality of light beams to be incident on the first rod integrator and a plurality of light beams to be incident on the second rod integrator. Each of the rod integrators has a light incident surface on which the plurality of light beams are incident, a bent portion that changes the propagating direction of the plurality of incident light beams, and a light exiting surface through which the plurality of light beams mixed with each other exit.

Abstract: An image display device includes an image forming device, collimating optical system, and optical device, with the optical device including a light guide plate, first diffraction grating member and second diffraction grating member which are made up of a volume hologram diffraction grating, and with central light emitted from the pixel of the center of the image forming device and passed through the center of the collimating optical system being input to the light guide plate from the near side of the second diffraction grating member with a certain angle. Thus, the image display device capable of preventing occurrence of color irregularities, despite the simple configuration, can be provided.

Abstract: A polarization element includes: a substrate; and a plurality of grid sections arranged on the substrate, wherein the grid sections each have protruding sections and recessed sections alternately arranged in a longitudinal direction of the grid sections at a pitch shorter than a wavelength of incident light, in the plurality of grid sections, the arrangement pitch P of the protruding sections is the same, and a proportion (D=L/P) of a length L of the protruding section to the arrangement pitch P of the protruding sections is the same, and a height of the protruding sections is different between the grid sections adjacent to each other.

Abstract: An electronic device includes an instrument panel that includes a display opening, where the instrument panel is located in a first plane; a circuit board located inside the electronic device, where the circuit board includes a display device that includes a display area, and where the display area is located in a second plane that is different from the first plane; and a waveguide that couples the display area to the display opening and guides light, and/or an image displayed in the display area, from the display area to the display opening.

Abstract: The present patent application comprises a method and apparatus to compile a superposition coded packet by compiling user candidates for superposition coding, ranking the user candidates based on a result of an evaluation function, selecting a deserving user candidate from among the user candidates, and compiling a superposition coded packet by adding other user data packets to a packet of the deserving user data packet, wherein the data packets for the user candidates may conform to a plurality of different formats and wireless communication standards.

Abstract: A video image display device (1) is provided with an ocular optical system (12) that guides video image light from a display element (11) to the pupil of an observer through an ocular prism (21) and at the same time guides ambient light to the pupil of the observer through the ocular prism (21). The eyepiece optical system (12) has reflection planes set in the ocular prism (21) that are provided with three or more planes to fold down three or more times an optical path for the video image light from the display element (11), wherein an HOE (23) is formed on at least one plane of the reflection planes. The video image display device (1) satisfies a conditional equation that properly prescribes the relationship between an incident range of the video image light incident on the HOE (23) formed plane in the ocular prism (21) and a display screen size of the display element (11).

Abstract: The frontlight illumination system is intended for enhancing illumination of a reflective display having pixels arranged in a matrix pattern and using monochromatic laser lights as light sources. The unit contains a network of light-distributing planar ridge waveguides with holograms arranged in a matrix pattern that corresponds to the matrix pattern of the reflective display. The light-distributing holograms of the system are formed on opposite sides of each core of respective light-distributing planar ridge waveguides. Neighboring holograms located on opposite sides of the core are combined into pairs and are arranged on each core in positions at which they interact with a predetermined phase shift that doubles the intensity of light directed to the reflective display and extinguishes light directed to the external surface.

Abstract: The invention relates to an optical element for guiding and forming a laser beam, and to a method for recording beam parameters, particularly in a laser system, comprising a carrier substrate (40) and a coating (39), which is applied to at least one side of the carrier substrate (40), and comprising at least one temperature sensor (38). The temperature sensor (38) is comprised of a number of pixels arranged in a matrix, and each respective pixel has at least one temperature-sensitive element (39). The at least one temperature-sensitive element (39) of the pixel is constructed inside the carrier substrate (40) made of silicon.

Abstract: A virtual-image projector comprises a laser configured to form a narrow beam, first and second dilation optics, first and second redirection optics each having a diffraction grating, and a controller. The first dilation optic is arranged to receive the narrow beam and to project a one-dimensionally dilated beam into the second dilation optic. The second dilation optic is arranged to receive the one-dimensionally dilated beam and project a two-dimensionally dilated beam. The first and second redirection optics are each operatively coupled to a transducer. The first redirection optic is arranged to direct the narrow beam into the first dilation optic at a first entry angle. The second redirection optic is configured to direct the one-dimensionally dilated beam into the second dilation optic at a second entry angle. The controller is configured to bias the transducers to vary the first and second entry angles.

Abstract: A near-eye display of a type having an image generator for generating a succession of angularly related beams and waveguide for propagating the angularly related beams to an eyebox within which a virtual image is visible includes a controllable output aperture for such purposes as reconstructing a better defined pupil within the eyebox while also preserving the possibility for viewing the ambient environment from the eyebox through the controllable output aperture.

Abstract: A light emitting apparatus includes a first rod integrator and a second rod integrator supported by a support substrate and a light emitting device disposed between the first rod integrator and the second rod integrator. The light emitting device emits a plurality of light beams to be incident on the first rod integrator and a plurality of light beams to be incident on the second rod integrator. Each of the rod integrators has a light incident surface on which the plurality of light beams are incident, a bent portion that changes the propagating direction of the plurality of incident light beams, and a light exiting surface through which the plurality of light beams mixed with each other exit.

Abstract: A 3D display device with controllable device for tracking visibility regions is disclosed, and includes a controllable device for tracking a visibility region, generated by way of superposition of light source images, in a observer plane of the display device. In preferred embodiments, the cladding of a waveguide comprises at least one material with optical properties of an anisotropic liquid, or at least two materials with optical properties of an isotropic liquid; a matrix arrangement of control electrodes defines multiple positions to be generated for local exit points in the cladding of the waveguide at which the total reflection is locally cancelled; and a system controller modifies positions of the output coupling points for superposing the output-coupled light through the lens array to the visibility region by displacing an output coupling point, or by switching off one output coupling point and switching on another one.

Abstract: A virtual image display device with an optical waveguide to guide, by internal total reflection, parallel pencil groups meeting a condition of internal total reflection, a first reflection volume hologram grating 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 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: A method for reducing speckle patterns of a three-dimensional holographic reconstruction is disclosed. A controllable light modulator into which a hologram of a three-dimensional scene is coded is illuminated by coherent light, a reconstruction lens transforms the modulated light into an eye position and reconstructs the three-dimensional scene in a reconstruction space and a control means controls the illumination. This provides a holographic reproduction device in which the speckle patterns occurring during reconstruction of a three-dimensional scene are reduced. According to one embodiment, a next-to-real time method is presented using a carrier medium of conventional image refresh rate.

Abstract: A method for reducing speckle patterns of a three-dimensional holographic reconstruction is disclosed. A controllable light modulator into which a three-dimensional scene is coded is illuminated by coherent light, a reconstruction means projects the modulated light close to an eye position into a space of observation and a control means controls the illumination. This provides a holographic reproduction device in which the speckle patterns occurring during reconstruction of a three-dimensional scene are reduced. Also provided is a next-to-real time method using a carrier medium of conventional image refresh rate.

Abstract: A diffractive beam expander (50) comprises a substantially planar waveguiding substrate, an input grating (10) to provide an in-coupled beam (B1) propagating within said substrate, and an output grating (30) to provide an out-coupled beam. The expander (50) comprises also four or more further grating portions to expand the height of the in-coupled beam (B1). A part of the in-coupled light is diffracted by a first deflecting grating portion (21a) to provide a first deflected beam. A part of the in-coupled light is diffracted by a second deflecting grating portion (22a) to provide a second deflected beam. The first deflected beam propagates downwards and the second deflected beam propagates upwards with respect to the in-coupled beam (B1). The first deflected beam impinges on a first direction-restoring grating portion (21b) and the second deflected beam impinges on a second direction-restoring grating portion (22b).

Abstract: A recycling system and method for increasing the brightness of light output using at least one recycling light pipe with at least one light source. The output end of the recycling light pipe reflects a first portion of the light back to the light source, a second portion the light to the input end of the recycling light pipe, and transmits the remaining portion of the light as output. The recycling system is incorporated into a projector to provide color projected image with increased brightness. The light source can be white LEDs, color LEDs, and dual paraboloid reflector (DPR) lamp.

Abstract: A display apparatus includes: a light modulator having translucent windows; a light emitter having a light source; a light guide having a tubular reflecting surface guiding light source light to the light modulator; and a light separator having a light separation surface separating guided light into transmitted and reflected light. The tubular reflecting surface narrows from the light modulator toward the light emitter to guide the reflected light to the windows. Denoting a lateral cross-sectional area of an inside area of the tubular reflecting surface at a light source end as S1, a lateral cross-sectional area of the tubular reflecting surface at a light separation surface end as S2, and a maximum incident angle at which light from the light source reflected by the tubular reflecting surface is input to the light separation surface as ?, ?×?(S2/S1)?110.

Abstract: A security device comprises a zero order diffractive microstructure buried within a substrate. One or more further optical structures, such as microlenses, may be formed on a surface of the substrate. The further optical structures modify the optical characteristics of the zero order diffractive microstructure such as by enhancing or reducing the color effect produced by the zero-order diffractive microstructure upon tilting the security device.