Abstract: A fiber optic assembly is provided including a support substrate having a substantially planar surface, a signal-fiber array supported on the planar surface of the support substrate. The signal-fiber array including a plurality of optical fibers and an adhesive disposed on the plurality of optical fibers and the support substrate. Each of the optical fibers is spaced from adjacent optical fibers of the plurality of optical fibers at a precise pitch.

Abstract: An illumination optical system for endoscope includes a rod lens as an optical element. The optical element includes a proximal end surface through which light enters and a distal end surface configured to emit the light. The distal end surface includes a diffusion region configured to diffuse emitted light. The diffusion region includes a plurality of concave portions and a plurality of peripheral regions surrounding the concave portions. Each concave portion includes a plurality of inclined surfaces as total reflection surfaces that are inclined with respect to the distal end surface. Each peripheral region includes a transmission surface configured to emit light totally reflected by the total reflection surfaces after passing through the proximal end surface and light not totally reflected by the total reflection surfaces.

Abstract: A display may have an array of display pixels that generate an image. A coherent fiber bundle may be mounted on the display pixels. The coherent fiber bundle may have a first surface that is adjacent to the display pixels and a second surface that is visible to a viewer. The coherent fiber bundle may contain fibers that carry light from the first surface to the second surface. The second surface may be planar or may have a central planar region and curved edge regions that run along opposing sides of the central planar region. The fibers may have cross-sectional surface areas with a first aspect ratio on the first surface and a second aspect ratio that is greater than the first aspect ratio on the second surface.

Abstract: A method is disclosed for manufacturing, by injection molding with use of a mold, a light guide plate in which a first region having a curvature in a first direction and a second region having a predetermined curved surface are connected. The mold includes a first member for forming the first region and a second member for forming the second region. The first member is manufactured by bending a first electroforming stamper on which a predetermined structure is formed by electroforming in a direction corresponding to the first direction.

Abstract: A homogenizing element includes a light incident end, a light exit end, a first surface, a second surface, a reflective layer and a first dichroic layer. The first surface extends from the light incident end to the light exit end. The second surface extends from the light incident end to the light exit end, and the second surface overlaps the first surface and is non-parallel to the first surface. The first dichroic layer is disposed on the first surface and configured to allow a first beam to pass therethrough and reflect a second beam. The reflective layer is disposed on the second surface and configured to reflect the first beam. A projection device adopting the homogenizing element is also provided. The homogenizing element and the projection device provided can adjust the beam angles of different color beams respectively.

Abstract: A light guide is described that includes a thermoplastic light channeling layer having at least a first segment, at least a second segment, and at least one groove dividing the thermoplastic light channeling layer into the first segment and second segment. The light guide further includes one or more light sources at least at the first segment. The at least one groove is shaped to block light from leaking between the first segment and the second segment. A method of forming the light guide is described that includes: providing a thermoplastic light channeling layer, thermoforming the at least one groove to divide the light guide into the first and second segments, and providing one of more light sources to at least the first segment.

Abstract: Systems and methods for holographic waveguide backlights in accordance with various embodiments of the invention are illustrated. One embodiment includes an optical illumination device including at least one waveguide, a source of light optically coupled to the at least one waveguide configured to emit light having a first polarization state, a first plurality of grating elements for diffracting the light having the first polarization state out of the at least one waveguide into a first set of output paths, a second plurality of grating elements for diffracting the light having the first polarization state light out of the at least one waveguide into a second set of output paths, and at least one input coupler configured to couple at least a portion of the light having the first polarization state towards the first and second pluralities of grating elements.

Abstract: A diffusion element is configured by combining: a structure for diffusion constituted by combining periodic surface structures having multiple periods to achieve a light intensity distribution in which the light intensity is uniform at angles less than or equal to a predetermined diffusion angle ? and the light intensity is as close as possible to zero intensity at angles greater than the diffusion angle ?; and a diffractive structure having a period of 1 or more and 2 or less times of ?max, where ?max is the maximum period of the structure for diffusion.

Abstract: A class of fibers is described that have a non-circular cross section on one or both ends that can by optimized to capture the optical radiation from a laser diode or diode array and deliver the light in the same or different shape on the opposite end of the fiber. A large multimode rectangular waveguide may be provided which can accept the radiation from a high-power diode bar and transform it into a circular cross section on the opposite end, while preserving brightness.

Abstract: A waveguide for plastic welding has an entry end, an exit end as well as a first and a second inner face arranged between the entry end and the exit end, which are arranged opposite to each other and by means of which laser light can be reflected. A first distance between the entry end and the exit end defines a length of the waveguide and a second distance between the first and the second inner face defines a thickness of the waveguide. The exit end may be arranged opposite to the entry end and a central plane of the waveguide may extend centrally from the entry end to the exit end. The first inner face comprises a continuously curved, concave shape so that a third distance between the first inner face and the central plane varies continuously from the entry end in the direction of the exit end.

Abstract: An illumination device includes a light source and a first light guide. The first light guide includes a first light guide portion and a second light guide portion, and the second light guide portion includes a light-emitting surface. Light emitted by the light source couplingly enters the first light guide portion, and is emitted from the light-emitting surface of the second light guide portion. The cross-sectional area of the second light guide portion is perpendicular to the center line of the first light guide and gradually decreases along the optical axis direction of the light source. The light-emitting surface does not have rotational symmetry. By means of the illumination device, light rays emitted from the light-emitting surface are distributed unevenly in a space. Modifying the distribution of light emitted by the illumination device helps to reduce light loss and increase the utilization of the light.

Abstract: An optical system including a light guide and a turning film that includes a first major surface, where the first major surface is substantially smooth and a second major surface including a plurality of asymmetric microstructures each respective asymmetric microstructure including a first side, where the first side is substantially planar, and a second side including a first surface segment defining a substantially planar surface and a second surface segment defining a non-planar surface.

Abstract: A backlight unit for a binocular-holographic display device and a holographic display device including the same are provided. The backlight unit includes a light source unit which outputs light, a first beam expansion unit which expands, in a first direction, the light output from the light source unit, a second beam expansion unit which expands, in a second direction perpendicular to the first direction, the light output from the first beam expansion unit, and a beam deflection unit which diffracts light incident on the first beam expansion unit. The holographic display device includes the backlight unit, a field lens, and a spatial light modulator.

Abstract: A unified imaging device used for detecting and classifying objects in a scene including motion and micro-vibrations by receiving a plurality of images of the scene captured by an imaging sensor of the unified imaging device comprising a light source adapted to project on the scene a predefined structured light pattern constructed of a plurality of diffused light elements, classifying object(s) present in the scene by visually analyzing the image(s), extracting depth data of the object(s) by analyzing position of diffused light element(s) reflected from the object(s), identifying micro-vibration(s) of the object(s) by analyzing a change in a speckle pattern of the reflected diffused light element(s) in at least some consecutive images and outputting the classification, the depth data and data of the one or more micro-vibrations which are derived from the analyses of images captured by the imaging sensor and are hence inherently registered in a common coordinate system.

Abstract: A method of manufacturing a light emitting module according to the present disclosure includes: preparing a light guide plate that comprises a first main surface serving as a light-emitting surface and a second main surface opposite to the first main surface; respectively providing light emitting elements on the second main surface so as to correspond to each of a plurality of optically functional portions provided on the first main surface of the light guide plate; and forming wires electrically connecting the plurality of light emitting elements.

Abstract: An optical element includes a rectangular light guide plate, a light source setting portion, a parallel light lens group, and a total reflection lens group, disposed between the parallel light lens group and the first side surface, a part of the parallel light from the parallel light lens group is subjected to total reflection at least once to form a first parallel light parallel to the front surface, and the first parallel light enters the first side surface to make the second side surface emit light; another part of the parallel light from the parallel light lens group is totally reflected at least twice to form a second parallel light oblique to the front surface, and the second parallel light enters the first side surface to make the front surface emit light.

Abstract: A light guide plate includes a main body, first stripe structures and second stripe structures. The main body has an optical surface, a light-incident surface and an opposite light-incident surface. The main body has a hole passing through the optical surface, and the optical surface has a first region and a second region which are separated by an imaginary line. The imaginary line intersects the hole. The hole has a first side near the opposite light-incident surface and a second side near the light-incident surface. A portion of each of the first stripe structures is disposed in the first region. The second stripe structures are disposed in the second region. An extending direction of at least one portion of each first stripe structure is vertical to the light-incident surface, and a portion of the second stripe structures extends to the first side of the hole near the opposite light-incident surface.

Abstract: A method of fabricating a light guide plate (LGP), an LGP fabricated thereby, and an illumination device having the same. The method includes preparing an LGP and fabricating a light-scattering layer by printing a printing solution including light-scattering particles on an overall bottom surface of the LGP. The light-scattering layer may be fabricated by at least one of a first method of controlling the printing such that the density of the light-scattering particles gradually increases with increases in a distance from the light-emitting diode facing a side surface of the LGP and a second method of controlling the printing such that the thickness of the light-scattering layer gradually increases with increases in the distance from the light-emitting diode. A luminous point through can be prevented from being viewed by a front observer, a process can be simplified, and light distribution similar to Lambertian distribution can be obtained.

Abstract: A method for locally introducing a light emitter or a plasmonic element into a light guide is provided. The method (300) comprising the acts of: applying (302) a printing head (100) to a surface (204) of the light guide (202, 404), the printing head (100, 200) comprising an insertion portion (102) comprising the light emitter (106) or the plasmonic element and a heating element (108), heating (304) the heating element (108) such that a portion (205) of the surface (204) of the light guide (202, 404) is locally heated, pressing (306) the printing head (100, 200) into the light guide (202, 404) such that at least a portion (208) of the insertion portion (102) is inserted into the light guide (202, 404), introducing (308) the light emitter (106) or the plasmonic element (500) into the light guide (202, 404) via the insertion portion (102). A printing head (100, 200) for locally introducing a light emitter (106) or a plasmonic element (500) into a light guide (202, 404) is also provided.

Abstract: The present disclosure discloses a lens, a light source module and a lighting device. The lens includes a bottom surface, an inner surface, an outer surface, and a first accommodating chamber configured for accommodating a light-emitting assembly, a wall face of the first accommodating chamber being an inner surface of the lens; where, the inner surface has a sawtooth shape, and a first light incident surface, a second light incident surface and a third light incident surface, the outer surface includes a first light-emitting surface, a second light-emitting surface and a third light-emitting surface.

Abstract: A plurality of waveguide display substrates, each waveguide display substrate having a cylindrical portion having a diameter and a planar surface, a curved portion opposite the planar surface defining a nonlinear change in thickness across the substrate and having a maximum height D with respect to the cylindrical portion, and a wedge portion between the cylindrical portion and the curved portion defining a linear change in thickness across the substrate and having a maximum height W with respect to the cylindrical portion. A target maximum height Dt of the curved portion is 10?7 to 10?6 times the diameter, D is between about 70% and about 130% of Dt, and W is less than about 30% of Dt.

Abstract: A lighting device (100) for use in a luminaire (200) comprising: —a base (101) having a longitudinal axis (LA) and comprising an electrical connector (102) for connecting the lighting device (100) to a luminaire socket (201) of the luminaire (200), —at least one LED-filament (103) comprising a substrate (104) having an elongated body and a plurality of light sources (105) mechanically coupled to the substrate (104), the plurality of light sources (105) configured for emitting light (106) in a first spatial light distribution, —at least one light guide (107) having an elongated body, comprising at least one light in-coupling portion (108) at at least on the external periphery of the at least one light guide (107) for coupling light (106) into the at least one light guide (107), a plurality of light out-coupling portions (109) for coupling light (106) out of the at least one light guide (107) in a second spatial light distribution, —an at least in part light-transmissive envelope (110) at least partly encapsula

Abstract: A connector comprises a cage and a light pipe. The cage has a top wall, a bottom wall, and a pair of side walls between the top wall and the bottom wall. The light pipe is mounted on an outer surface of at least one of the pair of side walls.

Abstract: A lighting device with a multiple light function includes an optical component (1) which includes a transparent segment (1a) having a primary transparent part (2) and a secondary transparent part (3) which parts are connected to each other by an interconnecting channel (4). A non-transparent segment (1b) is connected to the transparent segment (1a). A primary lighting unit (2a) illuminates the primary transparent part (2) and a secondary lighting unit (3a) illuminates the secondary transparent part (3). Leading-out optics are formed by prismatic elements (6) in the interconnecting channel (4) of the transparent segment (la) of the optical component (1). Against the leading-out optics, a light absorber (8) is formed in the part of the non-transparent segment (1b) overlapping the interconnecting channel (4). The light absorber (8) being adapted to convert light energy into thermal energy.

Abstract: Displays having a viewing area are described. In particular, displays including a lightguide, a turning film, a liquid crystal module including two polarizers, and a diffuser disposed proximate the top polarizer are described. Light extracted from the lightguide and emitted through the viewing area is specularly transmitted between the planar side of the turning film and the bottom absorbing polarizer. Displays that may be useful as switchable displays are described.

Abstract: A light emission display device according to an aspect of the present invention includes: a light guide member that converts rays of incident light from a back face thereof to produce diffused light and emits the diffused light from the front face; a plurality of point light sources that are arranged at intervals on a side of the back face of the light guide member, in which the light guide member includes a light shield structure that partitions the front face into a plurality of light emission regions each corresponding to at least one point light source of the plurality of point light sources immediately below the front face, such that transmission of the rays of light to an adjacent light emission region is reduced.

Abstract: There is provided a new and improved optical body, a new and improved method for manufacturing an optical body, and a new and improved light emitting device that can emit light derived from a light source in more various manners. The optical body includes: a base material; and a first concave-convex structure that is formed on at least one surface of the base material and that extracts internally propagating light that is injected into an inside of the base material from a side surface of the base material. An average period of concavity and convexity of the first concave-convex structure is more than or equal to a minimum value of a visible light wavelength band and less than or equal to 10 ?m.

Abstract: An automotive light guide that displays subsurface engraved indicia to create an optical branding feature or another illuminated design element. In one implementation, the light guide has a body with a primary viewing outer side and a plurality of microablation sites located within the body. From a first viewing angle with respect to the primary viewing outer side, the plurality of microablation sites are configured to appear in a first indicia pattern, and from a second viewing angle, the plurality of microablation sites are configured to appear in a second indicia pattern. In another implementation, the light guide has a body with a planar engraving outer side and a rounded primary viewing outer side. The plurality of microablation sites are etched through the planar engraving side and are viewable as an indicia pattern through the rounded primary viewing outer side.

Abstract: A display device is provided with: a light guide plate having a light exit surface that emits light; a display panel; an optical sheet that is interposed between the light guide plate and the display panel and that comprises a plurality of rectangular unit sheets; and a holding frame section that surrounds the optical sheet and that holds the optical sheet. The holding frame section comprises a first side for holding the optical sheet, and a second side and a third side that intersect the first side at the two ends of the first side. A first protrusion and a second protrusion are provided to the two ends of the first side in the lengthwise direction thereof. A first unit sheet and a second unit sheet are each fixed by the first protrusion and the second protrusion. The second side faces an end side of the first unit sheet; and is in contact with all of said end side. The third side faces an end side of the second unit sheet and is in contact with all of said end side.

Abstract: Light redirecting film articles include a microstructured optical film, such as a daylight redirecting film, bonded to another film. This type of assembly may serve various purposes. For example, the assembly may protect the structured film, provide additional functionality, such as diffusion or infrared reflection, and/or facilitate attachment of the microstructured optical film to a mounting surface, such as a glazing or window pane.

Abstract: A planar solar concentrator includes a light collecting assembly and a light condensing unit. The light collecting assembly includes a light collecting unit and a waveguide slab extending in a longitudinal direction. The light collecting unit includes a light collector having an input surface, an output surface, and a curved surface to direct an incident light toward a collecting zone on the output surface. The light condensing unit is slidably coupled to a rear end of the waveguide slab for condensing the incident light from the waveguide slab, and is coupled such that based on an elevation angle of the light source, the light condensing unit is permitted to be driven to slide in a transverse direction.

Abstract: A planar lighting device according to an embodiment includes a light guide plate and a reflecting member. The light guide plate has an incident surface that receives light output from a light source and an output surface that outputs the light received by the incident surface. The reflecting member faces an end surface opposite to the incident surface of the light guide plate and reflects light leaking from the end surface. A plurality of first prisms are formed on an opposite surface opposite to the output surface-of the light guide plate to be away from the output surface stepwise from the incident surface to the end surface.

Abstract: A method of manufacturing a light emitting module according to the present disclosure includes: preparing a light guide plate that comprises a first main surface serving as a light-emitting surface and a second main surface opposite to the first main surface; respectively providing light emitting elements on the second main surface so as to correspond to each of a plurality of optically functional portions provided on the first main surface of the light guide plate; and forming wires electrically connecting the plurality of light emitting elements.

Abstract: A light emitting module and a planar light source reduced in thickness are provided. A light emitting module includes: a light guide plate including a first main surface serving as a light emitting surface, a second main surface provided on a side opposite to the first main surface, and a recess provided at the second main surface; a first fluorescent material layer provided in the recess; a light emitting element provided at the first fluorescent material layer on the second main surface side; and a second fluorescent material layer provided at the second main surface.

Abstract: A light assembly including a light pipe and a plurality of light sources. The light pipe is an elongated, single, unitary piece having a generally linear light-exiting surface along one edge. The light pipe includes a plurality of lens portions along its length. Each lens portion forms a portion of the light existing surface. Each light source is associated with one of the lens portions to emit light into the lens portion and, therefore, the light pipe as a whole. The light from the light sources mixes within the light pipe before exiting the light pipe through the light-exiting surface in a generally linear pattern.

Abstract: A solar cell module manufacturing method is provided. This method includes: arranging a printing plate over a solar cell element in proximity to a surface of the solar cell element; providing a coating material on the printing plate; and moving a squeegee in a first direction so as to push out the coating material via the printing plate to the solar cell element, thereby applying the coating material in an outer peripheral area of the surface of the solar cell element.

Abstract: An optical device is provided. The optical device includes a first surface that defines a concave light incident surface facing a central axis and a light source; a second surface disposed opposite the first surface which is configured to reflect light incident on the concave light incident surface; and an inclined light exit surface between the first surface and the second surface. The second surface includes a concave first reflective portion curving toward the first surface, and a substantially flat second reflective portion which portion is interposed between a first reflective portion edge of the first reflective portion and an outer second surface edge of the second surface. The first reflective portion is configured to totally reflect light incident at a predetermined angle or more with respect to a top surface of the light source once to the light exit surface.

Abstract: An integrated CMOS-MEMS device includes a first substrate having a CMOS device, a second substrate having a MEMS device, an insulator layer disposed between the first substrate and the second substrate, a dischargeable ground-contact, an electrical bypass structure, and a contrast stress layer. The first substrate includes a conductor that is conductively connecting to the CMOS devices. The electrical bypass structure has a conducting layer conductively connecting this conductor of the first substrate with the dischargeable ground-contact through a process-configurable electrical connection. The contrast stress layer is disposed between the insulator layer and the conducting layer of the electrical bypass structure.

Abstract: The present disclosure provides a display device and a method of manufacturing the same. In one embodiment, a display device includes: an optical waveguide; at least one transparent display module disposed on the optical waveguide, each transparent display module corresponding to one display pattern; an optical source disposed at a light incident side of the optical waveguide, a light emitted by the optical source being transmitted in the optical waveguide, passing through the at least one transparent display module, and exiting the display device; and a lightproof medium disposed on regions of the optical waveguide excepting regions where the transparent display module and the optical source are located.

Abstract: A substrate has a first surface and a second surface facing each other. A photoelectric conversion region includes a plurality of photoelectric conversion devices provided in the substrate. An interlayered insulating layer is provided on the first surface of the substrate. A plurality of wires is provided on the interlayered insulating layer. An inter-wire insulating layer covers the plurality of wires. A plurality of micro lenses is provided on the second surface of the substrate. A grid pattern is provided in at least one of the interlayered insulating layer and the inter-wire insulating layer. The grid pattern, when viewed in a plan view, overlaps a region between two adjacent photoelectric conversion devices of the plurality of photoelectric conversion devices.

Abstract: In various embodiments, an illumination apparatus includes an air gap between a sub-assembly and a waveguide attached thereto at a plurality of discrete attachment points, as well as a bare-die light-emitting diode encapsulated by the waveguide.

Abstract: A surgical retractor comprising a handle and a blade extending at an angle from the handle; an illumination assembly having a plurality of direct light sources provided on the blade, at least one of the light sources being angled differently relative to the blade than another one of the light sources; and a cover configured to enclose the illumination assembly, wherein the cover comprises a plurality of openings, each opening corresponding in position to a respective light source of the illumination assembly when the cover is attached to the blade.

Abstract: Provided is a display device that can prevent light emitted from, a light guide plate from arriving at a display panel via a gap in an optical sheet and a gap between the optical sheet and a holding frame member. The display device is provided with: a light guide plate having a light exit surface; an optical sheet that is arranged facing the light exit surface, that is configured from a plurality of stacked unit sheets, and in which a plurality of flanges are arranged in each of the unit sheets so as to extend along the sheet surface of the unit sheet from the side edge of the unit sheet toward the exterior; and a holding frame member having formed therein a plurality of accommodating sections in which the flanges of the optical sheet are accommodated when holding the optical sheet. One or more of the plurality of flanges in each of the unit sheets is a matching flange having a shape that matches the shape of the accommodating section along the sheet surface.

Abstract: A lighting assembly that includes an LED source that generates a light cone (solid angle); and a transparent near field lens having a front surface, a collimating surface, and an aspherical groove. The collimating surface collimates the light cone into a beam that reflects off of the front surface toward the aspherical groove, and the aspherical groove directs the beam away from the lens as an exit cone from a virtual focal point, positive virtual focal ring or a negative virtual focal ring. The exit cone may be evenly distributed, substantially forward or substantially rearward from the virtual focal point or virtual focal ring. Parabolic or aparabolic reflectors can be employed with lighting assemblies having a virtual focal point or virtual focal ring, respectively, to reflect the exit cone in a vehicular exterior lighting pattern.

Abstract: Techniques are provided for a high dynamic range panel that includes an array of light sources (202,203) illuminating a corresponding array of light guides (204, 206). A light source (202) of the array illuminates a first light guide (204). The light source directly underlies, such as in a cavity (208), a second light guide (206) that is adjacent to the first light guide. The light source (202) does not extend below a bottom side (214) of either the first light guide or the second light guide to reduce thickness of the panel. The light source (202) and the first light guide (204) can be integrated as a tile assembly. Alternatively, the light source (202) and the second light guide (206) can be an integrated tile assembly. In a specific embodiment, the light source emits a blue or ultraviolet light, which is converted by quantum dots to a different color.

Abstract: A ferrule has a receiving area for receiving and securing an optical waveguide and an optical element for receiving light from an optical waveguide received and secured at the receiving area and changing at least one of a divergence and a propagation direction of the received light. A plurality of registration features are configured to permit a stacking of the ferrule in a stacking direction such that the ferrules in the stack are aligned relative to each other along a length of the ferrule and along a direction perpendicular to the stacking direction.

Abstract: A light emission device is used for a casing of the game device. This light emission device comprises a light source disposed in the casing, and a light guiding member having a plate-like shape, the light guiding member being configured to guide light emitted from the light source and being attached to the casing. The light guiding member comprises a reflecting unit configured to reflect the light incident from a first direction along a thickness direction of the light guiding member to a direction different from the first direction to diffuse the light in the interior of the light guiding member; and a light emission part configured to transmit the light reflected from the reflecting unit to outside from a surface of the light guiding member.

Abstract: A screen for operation in a free viewing mode or a restricted viewing mode, comprising: an image reproduction unit, a plate-shaped transparent light guide in front of the image reproduction unit and luminous means arranged on sides of the light guide. The image reproduction unit is arranged behind the light guide. In the free-viewing mode, the luminous means are switched off, with the result that the light which comes from the image reproduction unit and onto which image information is modulated passes through the light guide substantially without influence. The luminous means are switched on in the restricted-viewing mode. A light emission characteristic is generated either on the basis of scattering particles which are distributed spatially and/or in terms of the concentration in the light guide or on the basis of coupling elements arranged on at least one of the large surfaces of the light guide.

Abstract: A backlight assembly uses one or more lighting elements and a light guide to provide backlight with a reduced number of lighting elements. The light guide is optically coupled with the one or more lighting elements and is configured to receive light at one or more locations, internally reflect the light at the extremities of the light guide, extract the light from the light guide, and radiate the light from a surface of the light guide to backlight an area.

Abstract: A backlight unit includes a light guide layer including a plurality of extraction features disposed along a rear face of the light guide layer, a first cladding layer adhesively secured to the rear face of the light guide layer, a plurality of turning structures disposed along the first cladding layer, and a second cladding layer adhesively secured to a front face of the light guide layer. The first cladding layer has a first refractive index lower than a guide refractive index of the light guide layer. The second cladding layer has a second refractive index lower than or equal to the first refractive index.