Patent Description:
Glasses-based methods and glasses-free methods are widely commercialized and used for displaying three-dimensional (3D) images. Glasses-based methods include polarized glasses methods and shutter glasses methods, and glasses-free methods include lenticular methods and parallax barrier methods. These methods use the binocular parallax of the two eyes, and since there is a limit to the increase of the number of viewpoints and also the depth of the brain and the focus of the eye do not match each other, viewers who see a 3D image via these methods may feel tired.

As a 3D image display method capable of providing full parallax wherein the depth perceived by the brain and the focus of the eyes match each other, a holographic display method is gradually becoming practical. The holographic display method uses the principle of reproducing an image of an original object by radiating and diffracting reference light onto a hologram pattern on which an interference pattern obtained by interfering the object light reflected from the original object and the reference light is recorded. The holographic display method currently in practical use provides a computer generated hologram (CGH) as an electrical signal to a spatial light modulator rather than directly exposing the original object to obtain a holographic pattern. According to the inputted CGH signal, the spatial light modulator forms a hologram pattern and diffracts the reference light, thereby generating a 3D image.

However, in order to implement a complete holographic display method, a spatial light modulator having very high resolution and processing of a very large amount of data are required. Recently, in order to alleviate the conditions of data throughput and resolution, a binocular hologram method has been proposed whereby holographic images are provided only in the viewing area corresponding to both eyes of an observer. For example, only a holographic image having a viewpoint corresponding to the viewer's left eye field of view and a holographic image having a viewpoint corresponding to the observer's right eye field of view are generated and provided to each of the observer's left and right eyes. In this case, since it is not necessary to generate holographic images for the remaining viewpoints, data throughput can be greatly reduced and even with the currently commercialized display apparatus, the resolution condition of the spatial light modulator can be satisfied.

On the other hand, compared to a backlight unit (BLU) used in a liquid crystal display (LCD), a BLU used in holographic displays uses light with high coherence. Regarding the BLU, grating is used to maintain the coherence of light emitted from the waveguide tube.

The BLU should emit light with uniform intensity. In order to match the uniformity of the emitted light, the light extraction efficiency of the output grating can be set differently for each area. For example, output grating in which light extraction efficiency increases along one direction may be used for the BLU. However, it is difficult to implement an output grating in which the light extraction efficiency is precisely adjusted due to problems in the manufacturing process. <CIT> discloses a polarized-light-emitting waveguide comprising: an entry side face via which, in operation, light from a light source arranged adjacent the entry side face enters the waveguide; a waveguiding layer for waveguiding light entered via the entry surface; an exit surface via which, in operation, polarized light exits the waveguide; a polarization-selection layer provided adjacent to the waveguiding layer and, preferably, opposite the exit surface; a planar polarization-selective beam-splitting interface formed at an interface of the waveguiding layer and the polarization-selection layer; and a relief-structured surface which is situated on the polarization-selection layer side of and is spatially separated from the polarization-selective beam-splitting interface, the relief-structured surface being adapted to redirect light polarized by the beam-splitting interface and incident on the relief-structured surface, via the exit surface, out of the waveguide. <CIT> discloses an optical component for a display apparatus comprising: an optical waveguide part arranged to guide light there along between surface parts thereof by internal reflection thereat; an input part arranged to receive light and direct the received light into the optical waveguide part; and, an output part comprising a partially transmissive angularly reflective optical coating arranged upon a said surface part of the optical waveguide part and optically coupled to the input part by the optical waveguide part to receive said guided light and to transmit some but not all of said guided light out from the optical waveguide part; wherein the angularly reflective optical coating extends along a dimension of the optical waveguide part to expand the guided light in said dimension along the output part by repeated partial transmission thereof for output. <CIT> discloses a method of displaying an image, the method comprising: generating an image; providing a beam of substantially collimated light carrying said image; and replicating said image by reflecting said substantially collimated light along a waveguide between substantially parallel planar optical surfaces defining outer optical surfaces of said waveguide, at least one of said optical surfaces being a mirrored optical surface, such that light escapes from said waveguide through one of said surfaces when reflected to provide a replicated version of said image on a said reflection.

The invention relates to a waveguide structure according to claim <NUM>. BRIEF DESCRIPTION OF THE DRAWINGS.

The above and other aspects, features, and advantages of example embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:.

Accordingly, the example embodiments are merely described below, by referring to the figures, to explain aspects of the present description.

Hereinafter, example embodiments of the disclosure will be described in detail with reference to the accompanying drawings. In the following drawings, the same reference numerals refer to the same components, and the size of each component in the drawings may be exaggerated for clarity and convenience of description. Further, the example embodiments described below are merely example, and various modifications are possible from these example embodiments.

Hereinafter, what is described as "on" may include not only those directly above by contact, but also those above non-contact.

The terms of a singular form may include plural forms unless otherwise specified. In addition, when a certain part "includes" a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

In addition, terms such as ". unit" described in the specification mean a unit that processes at least one function or operation.

<FIG> is a perspective view of a waveguide structure <NUM> according to an example embodiment. <FIG> is an exploded perspective view of <FIG>. <FIG> is a plan view of <FIG>. <FIG> is a cross-sectional view taken along line A-A' of the waveguide structure of <FIG>. <FIG> is a cross-sectional view taken along line A-A' of <FIG> illustrating the path of light in the waveguide structure <NUM> of <FIG>.

Referring to <FIG>, the waveguide structure <NUM> may be provided. The waveguide structure <NUM> may include a first waveguide layer <NUM>, a second waveguide layer <NUM>, a first input grating <NUM>, a second input grating <NUM>, a third input grating <NUM>, a first polarization separation element <NUM>, a first polarization conversion element <NUM>, and an output grating <NUM>. The first waveguide layer <NUM> and the second waveguide layer <NUM> may guide light through total internal reflection. The first waveguide layer <NUM> and the second waveguide layer <NUM> may be stacked along a height direction (i.e., z direction). The first waveguide layer <NUM> and the second waveguide layer <NUM> may include resin or glass that transmits light in the range of about <NUM> to about <NUM>. The first waveguide layer <NUM> and the second waveguide layer <NUM> may have a refractive index in the range of about <NUM> to about <NUM>. The first waveguide layer <NUM> and the second waveguide layer <NUM> may have substantially the same refractive index.

The first input grating <NUM> may be provided on the upper surface 120u of the second waveguide layer <NUM>. The first input grating <NUM> may face a light source outside the waveguide structure <NUM>. The first input grating <NUM> may diffract light provided from a light source and provide the diffracted light to the second waveguide layer <NUM>. For example, from a viewpoint along the z direction, light incident on the first input grating <NUM> along the -z direction may travel in the x direction by the first input grating <NUM>. The first input grating <NUM> may provide light to the second input grating <NUM>. Light may travel from the first input grating <NUM> to the second input grating <NUM> using total internal reflection.

The second input grating <NUM> may be provided on the bottom surface 110b of the first waveguide layer <NUM>. From the viewpoint along the z direction, the second input grating <NUM> may be spaced apart from the first input grating <NUM> along the x direction. The second input grating <NUM> may convert a path of light transmitted from the first input grating <NUM>. From the viewpoint along the z direction, the path of light may be changed from the x direction to the y direction by the second input grating <NUM>. The second input grating <NUM> may transmit the light in the x direction. The second input grating <NUM> may provide light to the third input grating <NUM>. Light may travel from the second input grating <NUM> to the third input grating <NUM> using total internal reflection.

The third input grating <NUM> may be provided on the bottom surface of the first waveguide layer <NUM>. The third input grating <NUM> may be spaced apart from the second input grating <NUM> along the y direction. The third input grating <NUM> may reflect light Li transmitted from the second input grating <NUM>. From the viewpoint along the z direction, the third input grating <NUM> may change the path of the light Li from the y direction to the -x direction. The third input grating <NUM> may provide light Li to the first polarization separation element <NUM>. The third input grating <NUM> may transmit the light Li in the y direction.

The first polarization separation element <NUM> may transmit light L1 having a first polarization direction among the light Li provided from the third input grating <NUM>, and reflect light L2 having a second polarization direction different from the first polarization direction. For example, the first polarization separation element <NUM> may include a reflective wire-grid polarizer. For example, the first polarization direction may be parallel to the y direction, and the second polarization direction may be parallel to the x direction. Light L1 having a first polarization direction may be provided to the output grating <NUM>, and light L2 having a second polarization direction may be provided to the first polarization conversion element <NUM>.

The first polarization separation element <NUM> may include a first area <NUM>, a second area <NUM>, a third area <NUM>, and a fourth area <NUM> having different transmission/reflection ratios. The transmission/reflection ratio may be a ratio of the intensity of light reflected by the first polarization separation element <NUM> and the intensity of light transmitted by the first polarization separation element <NUM>. The transmission/reflection ratio corresponds to a transmission efficiency of each of the first area <NUM>, the second area <NUM>, the third area <NUM>, and the fourth area <NUM>. The transmission/reflection ratio can be expressed by the following Equation <NUM>.

The first area <NUM>, the second area <NUM>, the third area <NUM>, and the fourth area <NUM> may be arranged along the y direction. The first area <NUM> may be closest to the third input grating <NUM>, and the fourth area <NUM> may be disposed farthest from the third input grating <NUM>. For example, the transmission/reflection ratio may increase from the first area <NUM> to the fourth area <NUM>. Light reflected from the third input grating <NUM> may be provided to the first area <NUM>. Accordingly, light of the strongest intensity may be provided to the first area <NUM>. Light of the weakest intensity may be provided to the fourth area <NUM>. The transmission/reflection ratio of each of the first to fourth areas <NUM>, <NUM>, <NUM>, and <NUM> may be determined so that the first to fourth areas <NUM>, <NUM>, <NUM>, and <NUM> emit light having a constant intensity.

The first polarization conversion element <NUM> may be provided on the bottom surface 110b of the first waveguide layer <NUM>. The first polarization conversion element <NUM> may face the first polarization separation element <NUM>. For example, the first polarization conversion element <NUM> may be disposed parallel to the first polarization separation element <NUM>. The first polarization conversion element <NUM> may be spaced apart from the third input grating <NUM> in the -x direction. The first polarization conversion element <NUM> may change and reflect a polarization direction of light incident on the first polarization conversion element <NUM> (i.e., light L2 having a second polarization direction). For example, the first polarization conversion element <NUM> may include a half wave plate or a full wave plate. When light L2 having a second polarization direction is provided to the first polarization conversion element <NUM>, the polarization direction of the light L2 having the second polarization direction is rotated by a predetermined angle, so that light L3 having a third polarization direction different from the first polarization direction and the second polarization direction may be generated. Light L3 having a third polarization direction may be provided to the first polarization separation element <NUM>. The light L3 having a third polarization direction may be separated into light L1 having a first polarization direction and light L2 having a second polarization direction by the first polarization separation element <NUM>. Rotation of polarization of light L2 by the first polarization conversion element <NUM> and separation of polarization of light L3 by the first polarization separation element <NUM> may be repeated. As light travels in the -x direction within the first waveguide layer <NUM>, the intensity may gradually decrease in the -x direction. Accordingly, the light of the highest intensity may be provided to the first area <NUM> and the light of the weakest intensity may be provided to the fourth area <NUM>.

The output grating <NUM> may be provided on the upper surface 120u of the second waveguide layer <NUM>. The output grating <NUM> may output the light L1 provided from the first polarization separation element <NUM> to the outside of the backlight unit <NUM>. The output grating <NUM> may have uniform light extraction efficiency. For example, the output grating <NUM> may have a light extraction efficiency of substantially <NUM>%. The actual <NUM>% light extraction efficiency may include not only the light extraction efficiency of exactly <NUM>%, but also the light extraction efficiency close to <NUM>%. The output grating <NUM> may emit all of the light L1 provided from the first polarization separation element <NUM>. Since the first to fourth areas <NUM>, <NUM>, <NUM>, and <NUM> provide light of uniform intensity to the output grating <NUM>, the output grating <NUM> may emit light LO of uniform intensity.

The first input grating <NUM>, the second input grating <NUM>, the third input grating <NUM>, and the output grating <NUM> may be formed of various types of surface gratings or volume gratings. The surface grating is a grating formed directly on the surface of a substrate, and may include, for example, a diffractive optical element (DOE) such as a binary phase grating, a blazed grating, or the like. A plurality of grating patterns of the DOE act as a diffraction grating to diffract incident light. For example, depending on the size, height, period, duty ratio, shape, etc. of the grating patterns, the incident light is diffracted in a specific angular range to cause extinction and constructive interference, so that the direction of light can be changed. The volume grating can be formed separately from the substrate, and may include, for example, a holographic optical element (HOE), a geometric phase grating, a Bragg polarization grating, a holographically formed polymer dispersed liquid crystal (H-PDLC), and the like. This volume grating may include periodic fine patterns of materials having different refractive indices.

The example embodiment may provide a waveguide structure <NUM> including a first polarization separation element <NUM> having different transmission/reflection ratios for each area of the first polarization separation element <NUM> and an output grating <NUM> having uniform light extraction efficiency. The waveguide structure <NUM> may emit light of uniform intensity.

<FIG> is a cross-sectional view corresponding to line A-A' in <FIG> illustrating a waveguide structure <NUM> according to an example embodiment. <FIG> is a cross-sectional view corresponding to line A-A' of <FIG> illustrating the path of light in the waveguide structure of <FIG>. For the concise description, contents substantially the same as those described with reference to <FIG> may not be described.

Referring to <FIG>, <FIG>, the waveguide structure <NUM> may include the first waveguide layer <NUM>, the second waveguide layer <NUM>, the first input grating <NUM>, the second input grating <NUM>, the third input grating <NUM>, the first polarization separation element <NUM>, a second polarization conversion element <NUM>, and the output grating <NUM>. The first waveguide layer <NUM>, the second waveguide layer <NUM>, the first input grating <NUM>, the second input grating <NUM>, the third input grating <NUM>, the first polarization separation element <NUM>, and the output grating <NUM> may be substantially the same as those described with reference to <FIG>.

The second polarization conversion element <NUM> may be provided on the bottom surface 110b of the first waveguide layer <NUM>. The second polarization conversion element <NUM> may face the first polarization separation element <NUM>. For example, the second polarization conversion element <NUM> may be disposed parallel to the first polarization separation element <NUM>. The second polarization conversion element <NUM> may be spaced apart from the third input grating <NUM> in the -x direction. The second polarization conversion element <NUM> may change and reflect a polarization direction of light incident on the second polarization conversion element <NUM>, for example, light L2 having a second polarization direction. For example, the second polarization conversion element <NUM> may include an active wave plate. The second polarization conversion element <NUM> may be controlled by a controller to adjust the degree of polarization rotation of light incident on the second polarization conversion element <NUM>. When light L2 having a second polarization direction is provided to the second polarization conversion element <NUM>, the polarization direction of the light L2 having the second polarization direction is rotated by a predetermined angle, so that light L3 having a third polarization direction different from the first polarization direction and the second polarization direction may be generated. Light L3 having a third polarization direction may be provided to the first polarization separation element <NUM>. The light L3 having a third polarization direction may be separated into light L1 having a first polarization direction and light L2 having a second polarization direction by the first polarization separation element <NUM>. Rotation of polarization of light L2 by the second polarization conversion element <NUM> and separation of polarization of light L3 by the first polarization separation element <NUM> may be repeated. As light travels in the -x direction within the first waveguide layer <NUM>, the intensity may gradually decrease in the -x direction. Accordingly, the light of the highest intensity may be provided to the first area <NUM> and the light of the weakest intensity may be provided to the fourth area <NUM>.

The present disclosure may provide a waveguide structure <NUM> including a first polarization separation element <NUM> having different transmission/reflection ratios for each area and an output grating <NUM> having uniform light extraction efficiency. The waveguide structure <NUM> may emit light of uniform intensity.

<FIG> is a cross-sectional view corresponding to line A-A' in <FIG> for explaining a waveguide structure <NUM> according to an example embodiment. <FIG> is a cross-sectional view corresponding to line A-A' of <FIG> for explaining the path of light in the waveguide structure <NUM> of <FIG>. For the concise description, contents substantially the same as those described with reference to <FIG> may not be described.

Referring to <FIG>, <FIG>, the waveguide structure <NUM> may include the first waveguide layer <NUM>, the second waveguide layer <NUM>, the first input grating <NUM>, the second input grating <NUM>, the third input grating <NUM>, a second polarization separation element <NUM>, the first polarization conversion element <NUM>, a circularly polarized light-linearly polarized light conversion element <NUM>, and the output grating <NUM>. The first waveguide layer <NUM>, the second waveguide layer <NUM>, the first input grating <NUM>, the second input grating <NUM>, the third input grating <NUM>, the first polarization conversion element <NUM>, and the output grating <NUM> may be substantially the same as those described with reference to <FIG>.

The second polarization separation element <NUM> may transmit light L1 having a first polarization direction among the light Li provided from the third input grating <NUM>, and convert the polarization of the light L1 having the first polarization direction into circular polarization. The second polarization separation element <NUM> may provide light having circular polarization to the circularly polarized light-linearly polarized light conversion element <NUM>. For example, the second polarization separation element <NUM> may include polarization grating.

The second polarization separation element <NUM> may include a first area <NUM>, a second area <NUM>, a third area <NUM>, and a fourth area <NUM> having different transmission/reflection ratios. The first area <NUM>, the second area <NUM>, the third area <NUM>, and the fourth area <NUM> may be arranged along the -x direction. The first area <NUM> may be closest to the third input grating <NUM>, and the fourth area <NUM> may be disposed farthest from the third input grating <NUM>. For example, the transmission/reflection ratio may increase from the first area <NUM> to the fourth area <NUM>. Light reflected from the third input grating <NUM> may be provided to the first area <NUM>. Accordingly, light of the strongest intensity may be provided to the first area <NUM>. Light of the weakest intensity may be provided to the fourth area <NUM>. The transmission/reflection ratio of the first to fourth areas <NUM>, <NUM>, <NUM>, and <NUM> may be determined so that the first to fourth areas <NUM>, <NUM>, <NUM>, and <NUM> emit light having a constant intensity.

A circular polarization-linear polarization conversion element <NUM> may be provided between the second polarization separation element <NUM> and the output grating <NUM>. The circularly polarized light-linearly polarized light conversion element <NUM> may convert the polarization of light to have linear polarization from circular polarization. For example, the circularly polarized light-linearly polarized light conversion element <NUM> may include a quarter wave plate. The circularly polarized light-linearly polarized light conversion element <NUM> may provide light having linear polarization to the output grating <NUM>.

The example embodiment may provide a waveguide structure <NUM> including a second polarization separation element <NUM> having different transmission/reflection ratios for each area and an output grating <NUM> having uniform light extraction efficiency. The waveguide structure <NUM> may emit light of uniform intensity.

Referring to <FIG>, the waveguide structure <NUM> may include the first waveguide layer <NUM>, the second waveguide layer <NUM>, the first input grating <NUM>, the second input grating <NUM>, the third input grating <NUM>, a third polarization separation element <NUM>, the first polarization conversion element <NUM>, and the output grating <NUM>. The first waveguide layer <NUM>, the second waveguide layer <NUM>, the first input grating <NUM>, the second input grating <NUM>, the third input grating <NUM>, the first polarization conversion element <NUM>, and the output grating <NUM> may be substantially the same as those described with reference to <FIG>.

The third polarization separation element <NUM> may transmit light having a first polarization direction among light Li provided from the third input grating <NUM> as light L1, and reflect light having a second polarization direction different from that of the first polarization direction as light L2. For example, the first polarization direction may be parallel to the y direction, and the second polarization direction may be parallel to the x direction. The third polarization separation element <NUM> may include a dielectric coating. For example, the third polarization separation element <NUM> may include a surface dielectric multilayer coating. The third polarization separation element <NUM> may have a different transmission/reflection ratio for each area. For example, the third polarization separation element <NUM> may have a transmission/reflection ratio increasing along the -x direction. For example, the transmission/reflection ratio of the third polarization separation element <NUM> may be adjusted by varying the number of multilayer films to be coated for each area. Light L1 having a first polarization direction may be provided to the output grating <NUM>, and light L2 having a second polarization direction may be provided to the first polarization conversion element <NUM>.

The example embodiment may provide a waveguide structure <NUM> including a third polarization separation element <NUM> having different transmission/reflection ratios for each area and an output grating <NUM> having uniform light extraction efficiency. The waveguide structure <NUM> may emit light LO of uniform intensity.

Referring to <FIG>, <FIG>, the waveguide structure <NUM> may include the first waveguide layer <NUM>, the second waveguide layer <NUM>, a third waveguide layer <NUM>, the first input grating <NUM>, the second input grating <NUM>, the third input grating <NUM>, the first polarization separation element <NUM>, the first polarization conversion element <NUM>, and the output grating <NUM>. The first waveguide layer <NUM>, the second waveguide layer <NUM>, the first input grating <NUM>, the second input grating <NUM>, the third input grating <NUM>, the first polarization separation element <NUM>, the first polarization conversion element <NUM>, and the output grating <NUM> may be substantially the same as those described with reference to <FIG>. However, the third input grating <NUM> and the first polarization conversion element <NUM> may be provided on the bottom surface 130u of the third waveguide layer <NUM>.

The third waveguide layer <NUM> may be provided between the first waveguide layer <NUM> and the first polarization conversion element <NUM>. The third waveguide layer <NUM> may extend between the first waveguide layer <NUM> and the third input grating <NUM> and may be provided between the first waveguide layer <NUM> and the third input grating <NUM>. The third waveguide layer <NUM> may include resin or glass that transmits light in the range of about <NUM> to about <NUM>. The third waveguide layer <NUM> may have a refractive index in the range of about <NUM> to about <NUM>. The third waveguide layer <NUM> may have a larger refractive index than the first waveguide layer <NUM>. For example, the third waveguide layer <NUM> may have a refractive index greater than <NUM> or more than the first waveguide layer <NUM>.

Due to the difference in refractive index between the third waveguide layer <NUM> and the first waveguide layer <NUM>, a portion of light L5 (hereinafter, the first light L5) of the light Li reflected from the third input grating <NUM> passes through the interface between the third waveguide layer <NUM> and the first waveguide layer <NUM>, and another portion of light L4 (hereinafter, second light L4) is reflected towards the first polarization conversion element <NUM>.

The first polarization separation element <NUM> can transmit light L1 having a first polarization direction among the first light L5 and reflect light L2 having a second polarization direction different from the first polarization direction. Light L1 having a first polarization direction may be provided to the output grating <NUM>, and light L2 having a second polarization direction may be provided to the third waveguide layer <NUM>. The light L2 having the second polarization direction may pass through the third waveguide layer <NUM> as light the second L4 and reach the first polarization conversion element <NUM>. The first polarization conversion element <NUM> may rotate and reflect the polarization direction of the light L2 having the second polarization direction by a predetermined angle. As described above, a polarization direction rotated by a predetermined angle from the second polarization direction may be a third polarization direction, and light having a third polarization direction is indicated as L3. Light L3 having a third polarization direction may pass through the third waveguide layer <NUM> and the first waveguide layer <NUM> and reach the first polarization separation element <NUM>.

The second light L4 may travel along the third waveguide layer <NUM>. The second light L4 may be reflected by the interface between the first waveguide layer <NUM> and the third waveguide layer <NUM> and the first polarization conversion element <NUM> and travel. Since a part of the second light L4 passes through the interface between the first waveguide layer <NUM> and the third waveguide layer <NUM>, the intensity of the second light L4 may gradually decrease each time it reaches the interface. In <FIG>, the second light passing through the interface between the first waveguide layer <NUM> and the third waveguide layer <NUM> is indicated as L4'. Since the second lights L4 and L4 ' are unpolarized light, the unpolarization state may be maintained regardless of the first polarization conversion element <NUM>. The second light L4' may pass through the first waveguide layer <NUM> and reach the first polarization separation element <NUM>.

The first polarization separation element <NUM> may pass light L1 having a first polarization direction and reflect light L2 having a second polarization direction in the light L3 and the second light L4' having the third polarization direction. The reflection of light and conversion of the polarization direction described above may be repeated.

When the light is separated by using the third waveguide layer <NUM> and the first waveguide layer <NUM>, the boundary of the beams emitted from the output grating may be blurred.

The example embodiment may provide a waveguide structure <NUM> including a first polarization separation element <NUM> having different transmission/reflection ratios for each area and an output grating <NUM> having uniform light extraction efficiency. The waveguide structure <NUM> may emit light LO of uniform intensity.

<FIG> is a perspective view of a waveguide structure <NUM> according to an example embodiment. <FIG> is an exploded perspective view of <FIG>. <FIG> is a cross-sectional view taken along line B-B' of the waveguide structure <NUM> of <FIG>. <FIG> is a cross-sectional view taken along line B-B' of <FIG> for explaining the path of light in the waveguide structure <NUM> of <FIG>. For the concise description, contents substantially the same as those described with reference to <FIG> may not be described.

Referring to <FIG>, the waveguide structure <NUM> may be provided. The waveguide structure <NUM> includes a fourth waveguide layer <NUM>, a fifth waveguide layer <NUM>, the first input grating <NUM>, the second input grating <NUM>, the third input grating <NUM>, and the output grating <NUM>. The first input grating <NUM>, the second input grating <NUM>, and the third input grating <NUM> may be substantially the same as the first input grating <NUM>, the second input grating <NUM>, and the third input grating <NUM> described with reference to <FIG>, respectively.

The fourth waveguide layer <NUM> and the fifth waveguide layer <NUM> may guide light Li through internal reflection. The fourth waveguide layer <NUM> and the fifth waveguide layer <NUM> may be stacked along a height direction (i.e., z direction). The fourth waveguide layer <NUM> and the fifth waveguide layer <NUM> may include resin or glass that transmits light Li in the range of about <NUM> to about <NUM>. The fourth waveguide layer <NUM> and the fifth waveguide layer <NUM> may have a refractive index in the range of about <NUM> to about <NUM>. The fourth waveguide layer <NUM> may have a larger refractive index than the fifth waveguide layer <NUM>.

The third input grating <NUM> may reflect light Li provided from the second input grating <NUM> and provide the light Li to the interface BS between the fourth waveguide layer <NUM> and the fifth waveguide layer <NUM>. The third input grating <NUM> may reflect light Li such that light Li is incident on the interface BS between the fourth waveguide layer <NUM> and the fifth waveguide layer <NUM> at an angle greater than the critical angle. Accordingly, the light Li may be totally reflected at the interface BS between the fourth waveguide layer <NUM> and the fifth waveguide layer <NUM>.

When light Li is totally reflected at the interface BS between the fourth waveguide layer <NUM> and the fifth waveguide layer <NUM>, evanescent waves Le may flow into the fifth waveguide layer <NUM>. Evanescent waves Le may be weak electromagnetic files that pass through an interface where total reflection occurs. In general, evanescent waves can be abruptly attenuated from the interface where total reflection occurs and then disappear. According to the example embodiment, the thickness of the fifth waveguide layer <NUM> may be sufficiently thin so that evanescent waves Le may be emitted to the outside of the backlight unit by the output grating <NUM>. For example, the thickness of the fifth waveguide layer <NUM> may be determined so that evanescent waves Le reach the output grating.

A waveguide structure <NUM> including an output grating <NUM> having uniform light extraction efficiency may be provided. The waveguide structure <NUM> may emit light LO of uniform intensity.

<FIG> illustrates a holographic display apparatus <NUM> according to an example embodiment. For the concise description, contents substantially the same as those described with reference to <FIG> may not be described.

The holographic display apparatus <NUM> may include a light source <NUM> for providing light, a waveguide structure <NUM> for guiding light from the light source <NUM>, and a spatial light modulator <NUM> for diffracting light from the waveguide structure <NUM> to reproduce a holographic image. The light source <NUM> may provide a coherent light beam. The light source <NUM> may include, for example, a laser diode. However, if the light has a certain degree of spatial coherence, light can be diffracted and modulated by a spatial light modulator to be coherent light, so other light sources can be used if light having a certain degree of spatial coherence is emitted. The light source <NUM> may include a plurality of light sources that emit light of different wavelengths. For example, a first light source that emits light of a first wavelength band, a second light source that emits light of a second wavelength band different from the first wavelength, and a third light source that emits light of a third wavelength different from the first and second wavelengths may be included. Light of the first, second, and third wavelengths may be red, green, and blue light, respectively. As for the waveguide structure <NUM>, any one of the waveguide structures <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> described with reference to <FIG> may be applied, and detailed descriptions are omitted here.

A field lens <NUM> for focusing a holographic image reproduced by the spatial light modulator <NUM> on a predetermined space may be further provided between the waveguide structure <NUM> and the spatial light modulator <NUM>. In addition, first beam steerer <NUM> and second beam steerer <NUM> for controlling a traveling direction of light emitted from the waveguide structure <NUM> two-dimensionally may be further provided. The first and second beam steerers <NUM> and <NUM> may adjust the position of the output light beam according to the position of the pupil of the viewer. For example, the first beam steerer <NUM> may adjust the horizontal position of the light beam, and the second beam steerer <NUM> may adjust the vertical position of the light beam. The first and second beam steerers <NUM> and <NUM> may be implemented as, for example, a liquid crystal layer or an electrowetting element.

In <FIG>, the position of the field lens <NUM> is illustrated as being located between the second beam steerer <NUM> and the spatial light modulator <NUM>, but is not limited thereto. For example, the field lens <NUM> may be disposed between the spatial light modulator <NUM> and the viewer.

A beam expander <NUM> may be further provided between the light source <NUM> and the waveguide structure <NUM>. For example, the beam expander <NUM> may expand and collimate a one point light provided from the light source <NUM>. The beam expander <NUM> may include, for example, a collimating lens. As the divergence angle of the light beam becomes closer to <NUM> degrees by collimating the light beam, the coherence of light can be increased. Accordingly, the optical beam is collimated by the beam expander <NUM>, so that the quality of the holographic image may be improved.

The holographic display apparatus <NUM> may further include an eye tracking sensor <NUM> that recognizes a viewer's position, and may further include a control unit <NUM> that controls the first and second beam steerers <NUM> and <NUM> depending on the position detected by the eye tracking sensor <NUM>. The eye tracking sensor <NUM> may include an infrared camera, a visible light camera, or various other sensors.

The controller <NUM> may also control driving of the light source <NUM>. For example, the control unit <NUM> may sequentially control the radiation direction of the light beam so that the holographic image is formed in the left eye and the right eye of the viewer in chronological order.

The holographic display apparatus <NUM> according to the example embodiment may provide holographic images having different viewpoints to the left eye LE and the right eye RE of the observer in a binocular hologram method. For example, the holographic display apparatus <NUM> provides a holographic image for the left eye to the viewer's left eye LE viewing area, and provides a holographic image for the right eye with a different viewpoint than the holographic image for the left eye to the viewer's right eye RE viewing area. The holographic image for the left eye and the hologram image for the right eye provided by the holographic display apparatus <NUM> can provide a three-dimensional effect to the observer independently unlike the left eye image and the right eye image of the stereoscopic method, and only the viewpoints may be different. In the case of the stereoscopic method, when a 2D image for the left eye and a 2D image for the right eye with different viewpoints are perceived by the observer's left and right eyes, respectively, a three-dimensional effect is provided using binocular parallax. Therefore, in the stereoscopic method, a three-dimensional effect does not occur with only one of the left-eye image and the right-eye image, and the depth perception perceived by the brain and the focus of the eyes do not match, which can cause the observer to feel tired. On the other hand, in the holographic display apparatus <NUM> according to the example embodiment, since a hologram image for the left eye and a hologram image for the right eye are formed at the position in a predetermined space, that is, the viewer's left eye LE and right eye RE, the depth perceived by the brain and the focus of the eye can be consistent and complete parallax can be provided. The reason why the holographic display apparatus <NUM> according to the example embodiment provides only binocular viewpoints is that since the observer can only recognize two viewpoints with the left eye LE and the right eye RE, this is to reduce the amount of data processing by removing the remaining viewpoint information except for the viewpoint information that can be recognized by the observer. However, the holographic display apparatus according to various embodiments may provide more viewpoints.

The position at which the holographic image is focused may be adjusted by the first and second beam steerers <NUM> and <NUM>. For example, by the first and second beam steerers <NUM> and <NUM>, a left eye position at which the left eye hologram image is focused and a right eye position at which the right eye hologram image is focused may be adjusted. Each viewer's unique left-eye and right-eye spacing may be detected by the eye tracking sensor <NUM>, and a change in the position of the left and right eyes due to the viewer's movement may be detected. According to the detected information, the first and second beam steerers <NUM> and <NUM> may control the traveling direction of the light beam.

One of the first beam steerer <NUM> and the second beam steerer <NUM> may be a liquid crystal deflector that diffracts incident light to generate two light beams traveling at different angles. When any one of the first and second beam steerers <NUM> and <NUM> spatially separates light toward the left and right eyes at the same time, time-sequential driving of the light source LS may not be required.

The field lens <NUM> may focus light direction-controlled by the first and second steerers <NUM> and <NUM> into a predetermined space. The field lens <NUM> may include a Fresnel lens, a liquid crystal lens, and a holographic optical element.

The light controlled in the direction by the first and second beam steerers <NUM> and <NUM> is incident on the spatial light modulator <NUM> through the field lens <NUM>. The spatial light modulator <NUM> may play a role of forming a hologram pattern having an interference fringe for modulating incident light. Incident light is diffracted and modulated by the hologram pattern formed by the spatial light modulator <NUM>, so that a holographic image may be reproduced at a location in a predetermined space.

The holographic display apparatus according to an example embodiment may be applied to, for example, a mobile phone. By using the eye tracking element <NUM> and a beam steerer, when the user views the screen of the mobile phone, the movement of the user's eye can be tracked to display a 3D image according to the eye position.

<FIG> is a diagram showing a holographic display apparatus <NUM> according to another example embodiment.

The holographic display apparatus <NUM> may include a light source <NUM> for providing light, a waveguide structure <NUM> for guiding light from the light source <NUM>, and a spatial light modulator <NUM> for reproducing a holographic image by diffracting light provided from the waveguide structure <NUM>. The light source <NUM> may provide a coherent light beam. In the waveguide structure <NUM>, the example described with reference to <FIG> may be applied, and detailed descriptions are omitted here.

A field lens <NUM> for focusing a holographic image reproduced by the spatial light modulator <NUM> on a predetermined space may be further provided between the waveguide structure <NUM> and the spatial light modulator <NUM>.

A beam expander <NUM> may be further provided between the light source <NUM> and the waveguide structure <NUM>. The beam expander <NUM> may expand and collimate one point light provided from the light source <NUM>.

In addition, first and second beam steerers <NUM> and <NUM> may be further provided between the light source <NUM> and the waveguide structure <NUM> to control the traveling direction of light in two dimensions. The first and second beam steerers <NUM> and <NUM> may adjust the position of the output light beam according to the position of the pupil of the viewer. For example, the first beam steerer <NUM> may adjust the horizontal position of the light beam, and the second beam steerer <NUM> may adjust the vertical position of the light beam.

The holographic display apparatus <NUM> may further include an eye tracking sensor <NUM> that recognizes a viewer's position, and may further include a control unit <NUM> that controls the first and second beam steerers <NUM> and <NUM> depending on the position detected by the eye tracking sensor <NUM>.

When comparing <FIG>, the beam steerer is positioned differently, and components having the same numbers perform substantially the same functions and operations, and thus detailed descriptions thereof will be omitted.

The backlight unit according to the example embodiment may be applied to a holographic display, a mobile phone, a 3D TV, or the like. In the holographic display apparatus according to the example embodiment, light uniformity may be improved and band patterns may be reduced by a waveguide structure in which a plurality of layers are stacked.

The example embodiments may provide a waveguide structure including output grating that has a constant light extraction efficiency and emits light of a uniform intensity.

The example embodiments may provide a back light unit including output grating that has a constant light extraction efficiency and emits light of a uniform intensity.

The example embodiments may provide a display apparatus including a backlight unit that emits light of uniform intensity.

However, the effects of the disclosure are not limited to the above descriptions.

Claim 1:
A waveguide structure (<NUM>; <NUM>; <NUM>; <NUM>; <NUM>) comprising:
an output grating (<NUM>);
a polarization conversion element (<NUM>; <NUM>) disposed parallel to the output grating (<NUM>);
a polarization separation element (<NUM>) provided between the output grating (<NUM>) and the polarization conversion element (<NUM>; <NUM>); and
a first input grating (<NUM>) provided on the surface of the polarization conversion element (<NUM>; <NUM>), wherein the first input grating is configured to provide light to the polarization separation element (<NUM>),
wherein the polarization separation element (<NUM>) is configured to:
transmit, to the output grating (<NUM>), light having a first polarization direction among light incident on the polarization separation element (<NUM>), and
reflect, to the polarization conversion element (<NUM>; <NUM>), light having a second polarization direction different from the light having the first polarization direction among the light incident on the polarization separation element (<NUM>), and
characterized in that
the polarization separation element (<NUM>) comprises a first area having a first light transfer efficiency, and a second area having a second light transfer efficiency that is greater than the first light transfer efficiency, wherein the first area is closer to the first input grating than the second area.