KR102349960B1 - Backlight unit for holographic display - Google Patents

Abstract

A backlight unit for a holographic display is disclosed.
The disclosed backlight unit includes at least one light source unit; at least one input coupler; light guide plate to guide the light; a first holographic element located on a first surface of the light guide plate; and a second holographic element positioned on the second surface of the light guide plate, wherein the input coupler is configured to uniformly illuminate the light beam emitted from the light source unit to the first holographic element through the light guide plate, the light guide plate comprising: configured to transmit the light beam to the first holographic element without total internal reflection, the first holographic element collimating the light beam and redirecting the light beam to the second holographic element, the second holographic element emits the light beam to the outside of the light guide plate.

Description

Backlight unit for holographic display

The disclosed embodiments relate to a backlight unit for realizing a 3D holographic display using coherent collimated light from a laser light source.

Recently, a lot of 3D movies have been released, and accordingly, a lot of technology related to a 3D image display device is being studied. A three-dimensional image display device that is currently commercialized uses binocular parallax of both eyes. By providing a left-eye image and a right-eye image from different viewpoints, respectively, the viewer can feel a three-dimensional effect. let it be Such a 3D image display device includes a glasses-type 3D image display device that requires special glasses and a glasses-type 3D image display device that does not require glasses.

However, when viewing a 3D image displayed in the binocular disparity method, the user experiences great eye fatigue, and the 3D image display device that provides only two views of the left-eye image and right-eye image reflects the change in viewpoint according to the movement of the viewer. Because it cannot, there is a limit to providing a natural three-dimensional effect.

In order to display a more natural three-dimensional image, a holographic display is being studied.

A backlight system capable of providing parallel light with high uniformity and reducing light loss due to reflection during light guiding is provided.

According to one type of backlight unit, at least one light source unit; at least one input coupler; light guide plate to guide the light; a first holographic element located on a first surface of the light guide plate; and a second holographic element positioned on a second surface of the light guide plate, wherein the input coupler is configured to uniformly illuminate the light beam emitted from the light source unit to the first holographic element through the light guide plate, the light guide plate comprising: configured to transmit the light beam to the first holographic element without total internal reflection, the first holographic element collimating the light beam and redirecting the light beam to the second holographic element, the second holographic element emits the light beam to the outside of the light guide plate.

The second holographic element may be located on an upper surface or a lower surface of the light guide plate.

The light source unit may include at least one of a light emitting diode, a laser diode, a solid laser, and an optical fiber.

The input coupler may include at least one of a concave lens, a convex lens, a transmissive hologram element, and a reflective hologram element.

The light guide plate may include at least one of a high transmittance plastic, an optical glass, and a quartz glass.

The second holographic element may emit parallel rays to the outside of the light guide plate.

The second holographic element may form at least two focused viewing areas at a predetermined distance.

The light guide plate may have a constant cross-sectional area along its length.

A cross-section of the light guide plate may have a rectangular shape.

The first holographic element and the second holographic element may include a diffraction grating.

The first holographic element and the second holographic element may be formed of an optically transparent material.

A front surface, a bottom surface, an upper surface, and a rear surface of the light guide plate may be formed of flat surfaces.

In addition, the backlight unit according to one type may further include an eye-tracking unit for tracking the user's pupil position.

A backlight unit according to an exemplary embodiment may generate coherent collimated light.

Also, the backlight unit according to the exemplary embodiment may create at least two viewing zones.

In addition, the backlight unit according to the exemplary embodiment may increase the efficiency and uniformity of illumination.

Also, the backlight unit according to the exemplary embodiment may reduce the thickness of the backlight unit.

1 is a configuration diagram schematically illustrating a configuration of a backlight unit emitting parallel light according to an embodiment.
2 is a configuration diagram schematically illustrating a configuration of a backlight unit forming two focused viewing zones at a predetermined distance according to an exemplary embodiment.
3 is a block diagram schematically showing a hologram recording apparatus for recording a hologram provided by a second holographic element that emits parallel light to the upper surface of the light guide plate.
4 is a block diagram schematically showing a hologram recording apparatus for recording a hologram provided by a second holographic element that forms a viewing area focused at a predetermined distance.
5 is a block diagram schematically showing a hologram recording apparatus for recording a hologram provided by a first holographic element that parallels incident light and converts a direction to a second holographic element.
6 is a cross-sectional view of the hologram recording apparatus shown in FIG. 5 as viewed from A. Referring to FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily implement them. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part is "connected" with another part, this includes not only the case of being "directly connected" but also the case of being "electrically connected" with another element interposed therebetween. . Also, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

1 is a block diagram schematically showing the configuration of a backlight unit 100 emitting parallel light according to an embodiment, and FIG. 2 is a backlight unit 100 forming two focused viewing areas at a constant distance according to the embodiment. It is a configuration diagram schematically showing the configuration.

Referring to FIG. 1 , the backlight unit 100 includes two light source units 10 , two input couplers 20 , a light guide plate 30 , a first holographic element 40 , and a second holographic element 50 . may include

The light guide plate 30 may include a front surface 31 , a bottom surface 32 , an upper surface 33 , and a rear surface 34 .

The first holographic element 40 may be positioned on the rear surface 34 of the light guide plate 30 , and the second holographic element 50 may be positioned on the lower surface 32 of the light guide plate 30 .

The light source unit 10 may emit light toward the input coupler 20 . The light source unit 10 may include a light emitting diode (LED), a laser diode, a solid laser, or an optical fiber. However, the light source unit 10 is not limited thereto, and any type of light source suitable for the backlight unit 100 may be included.

The input coupler 20 may use light emitted from the light source unit 10 to provide uniform light to the first holographic element 40 . Each input coupler 20 may include a concave lens, a convex lens, a transmissive hologram element, a reflective hologram element, or a combination thereof, but is not limited thereto.

In FIG. 1 , two light source units 10 and two input couplers 20 are illustrated, but the present invention is not limited thereto, and other numbers may be used.

The light guide plate 30 may transmit the light incident from the light source unit 10 toward the first holographic element 40 without total reflection inside the light guide plate 30 . That is, light incident into the light guide plate 30 may not be totally reflected on the front surface 31 , the bottom surface 32 , the side surfaces and the upper surface 33 of the light guide plate 30 . The light guide plate 30 may have any shape suitable for transmitting incident light. For example, as shown in FIG. 1 , the cross-section of the light guide plate 30 may have a rectangular shape or a square shape. However, the shape of the cross-section of the light guide plate 30 is not limited thereto. Also, the light guide plate 30 may be formed to have a constant cross-sectional area along the entire length of the light guide plate 30 . The light guide plate 30 may be made of highly transparent plastic, optical glass, or quartz glass. However, the shape and material of the cross-sectional area of the light guide plate 30 are not limited thereto, and may be formed of other shapes and materials.

The first holographic element 40 may parallel the light rays incident from the light source unit 10 , and may change the direction toward the second holographic element 50 located on the bottom surface 32 of the light guide plate 30 .

The second holographic element 50 may reflect the light beam redirected by the first holographic element 40 . The light beam reflected by the second holographic element 50 may be emitted from the light guide plate 30 through the upper surface 33 of the light guide plate 30 .

The first holographic element 40 and the second holographic element 50 may include a diffraction grating. The distance between the diffraction gratings so that the first holographic element 40 parallels the light rays incident from the light source unit 10 and changes the direction toward the second holographic element 50 located on the bottom surface 32 of the light guide plate 30 . and the inclined angle may be appropriately adjusted. In addition, the second holographic element 50 reflects the light beam redirected by the first holographic element 40 and diffracts it so that it can be emitted from the light guide plate 30 through the upper surface 33 of the light guide plate 30 . The spacing between the grids and the inclined angle may be appropriately adjusted.

The angle formed by the rear surface 34 of the light guide plate 30 on which the first holographic element 40 is located and the lower surface 32 of the light guide plate 30 on which the second holographic element 50 is located does not need to be 90 degrees, Various angles can be achieved. In this case, the distance between the diffraction gratings and the inclined angle may be appropriately adjusted to parallelize the light rays incident on the first holographic element 40 and change the direction toward the second holographic element 50 . In addition, the second holographic element 50 reflects the light beam redirected by the first holographic element 40 and diffracts it so that it can be emitted from the light guide plate 30 through the upper surface 33 of the light guide plate 30 . The spacing between the grids and the inclined angle may be appropriately adjusted.

The second holographic element 50 may have two embodiments.

As a first embodiment, referring to FIG. 1 , the second holographic element 50 transmits the light rays from the first holographic element 40 to at least two parallel rays through the upper surface 33 of the light guide plate 30 . can be emitted as

As a second embodiment, referring to FIG. 2 , the second holographic element 50 operates like an objective lens, so that at least two beams from the first holographic element 40 are transmitted at a predetermined distance from the light guide plate 30 . It can be emitted to form a focused field of view.

In addition, according to an embodiment of the second holographic element 50 , a light beam emitted in parallel or a light beam directed to a point may illuminate the holographic display.

The backlight unit 100 according to the present embodiment may have at least two optical channels. In particular, the backlight unit 100 may form left and right viewing areas. Each viewing area may be formed from the light source unit 10 , one input coupler 20 , the light guide plate 30 , the first holographic element 8 , and the second holographic element 9 . The angle 2φ between the two optical channels may be determined by the angle between the two light rays incident from the light source unit 10 . In general, the average distance between the user's eyes is about 62 mm, and based on this numerical value, at least two light sources 10 may be positioned so that an angle of 2 phi between the two optical channels is formed. However, depending on the user, the distance between the eyes may be slightly different, and when the user's viewpoint is moved, the holographic image created based on the average value may be perceived somewhat unnaturally.

To solve this, the backlight unit 100 may further include an eye tracking unit 60 and a control unit 70 . The eye tracking unit 60 is for sensing the user's eye position. To this end, the eye tracking unit 60 may include an infrared camera, a visible light camera, or other various sensors. The eye tracking unit 60 may obtain an image of the user through, for example, a camera, detect the user's pupil in the image, and analyze the position thereof. In addition, when the observer's eyes cannot be found due to blinking or obstacles, the eye position may be predicted, and the movement of the eye position may be predicted according to the user's movement. The eye tracking unit 60 may track a change in the user's pupil position in real time and provide the result to the control unit 70 . When the position of the user's pupil is changed according to the information sensed by the eye tracking unit 60 , the control unit 70 moves the light source unit 10 so that the image generation position is adjusted to the changed pupil position of the user. ) can control the light output direction.

3 is a block diagram schematically showing a hologram recording apparatus 300 for recording a diffraction pattern on the second holographic element 50 that emits parallel light to the upper surface of the light guide plate. Referring to FIG. 3 , the hologram recording apparatus 300 includes a light source unit 302 , a shutter 320 , reflective members M1 , M2 , M3 , a first half-wave plate 310 , a second half-wave plate 311 , and polarization Beam splitter 304, apertures D1, D2, pinhole 312, micro lenses O1, O2, lens 314, light guide plate 30, photosensitive medium 316, and cover glass 318 may include

The light beam incident from the light source unit 302 may be separated into a reference beam passing through the reference section 306 and a signal beam passing through the signal section 308 by a polarizing beam splitter 304, respectively. .

The intensity of the reference light and the signal light may be adjusted by the first half-wave plate 310 . By rotating the first half-wave plate 310, the intensity of the reference light and the signal light may be adjusted.

The reference light and the signal light separated by the polarization beam splitter 304 may have different polarization states. For example, the reference light may be in a P-polarized (or S-polarized) state, and the signal light may be in an S-polarized (or P-polarized) state. Since the reference light and the signal light must have the same polarization state for hologram recording, a second half-wave plate 311 may be added to change the polarization state of either the reference light or the signal light. Although the second half-wave plate 311 is added to change the polarization state of the reference light in FIG. 3 , the second half-wave plate 311 may be added to change the polarization state of the signal light.

In the reference portion 306 , the reference light is filtered by the pin hole 312 and parallelized by the lens 314 . The parallel reference light may pass through the side surface of the light guide plate 30 and travel toward the photosensitive medium 316 . The photosensitive medium 316 may be positioned in contact with the lower surface 32 of the light guide plate 30 .

In the signal portion 308 , the signal light is filtered by the pin hole 312 and parallelized by the lens 314 . The parallelized signal light may be reflected by the reflective member M3 and travel toward the photosensitive medium 316 .

Signal light may be lost due to reflection from the lower surface of the light guide plate 30 on which the photosensitive medium 316 is located. In order to reduce loss due to reflection, the cover glass 318 may be positioned in contact with the photosensitive medium 316 .

The shutter 320 may adjust the exposure time of the light incident from the light source 302 .

4 is a block diagram schematically illustrating a hologram recording apparatus 400 for recording a diffraction pattern on a second holographic element 50 that forms a viewing area focused at a predetermined distance. Referring to FIG. 4 , the recording apparatus shown in FIG. 3 may further include an objective lens 322 positioned in the signal part 308 . The objective lens 322 may serve to focus light, and when the hologram recording apparatus 400 is reproduced, a viewing area focused at a predetermined distance may be formed.

5 is a configuration schematically showing a hologram recording apparatus 500 for recording a hologram provided by a first holographic element 40 that parallels incident light and redirects it to a second holographic element 50 FIG. 6 is a cross-sectional view of the hologram recording apparatus shown in FIG. 5 as viewed from A. As shown in FIG.

Referring to FIG. 5 , the hologram recording apparatus 500 includes a light source unit 502 , a shutter 522 , reflective members M1 , M2 , M3 , a first half-wave plate 510 , a second half-wave plate 511 , and polarization. Beam splitter 504, aperture D1, D2, pin hole 512, micro lens O1, O2, lens 514, light guide plate 30, square aperture 516, photosensitive medium 517, It may include a slit 518 and a cylindrical concave lens 520 .

A light beam incident from the light source unit 502 may be separated into a reference light passing through the reference portion 506 and a signal light passing through the signal portion 508 by the polarization beam splitter 504 .

The polarization state of the light beam may be adjusted by the first half-wave plate 510 . By rotating the first half-wave plate 510, the intensity of the reference light and the signal light may be adjusted.

The reference light and the signal light separated by the polarization beam splitter 504 may have different polarization states. For example, the reference light may be in a P-polarized (or S-polarized) state, and the signal light may be in an S-polarized (or P-polarized) state. Since the reference light and the signal light must have the same polarization state for hologram recording, a second half-wave plate 511 may be added to change the polarization state of either the reference light or the signal light. In FIG. 5 , the second half-wave plate 511 is added to change the polarization state of the reference light, but a second half-wave plate 511 may be added to change the polarization state of the signal light.

In the signal portion 508 , the signal light is filtered by the pin hole 512 and parallelized by the lens 514 . The parallelized signal light may be absorbed into the slit 518 located in the signal portion 508 and may travel in the direction of the photosensitive medium 517 .

In the reference portion 506 , the reference light is filtered by the pin hole 512 and may be parallelized by the lens 514 . The parallelized signal light may be reflected by the reflective member M3 to be absorbed by the rectangular opening surface 516 , and may travel toward the photosensitive medium 517 . The photosensitive medium 517 may be positioned in contact with the rear surface 34 of the light guide plate 30 .

When the reference light from the reference portion 506 is incident into the light guide plate 30 , a cylindrical concave lens 520 may be used to uniformly spread the light rays into the light guide plate 30 . Referring to FIG. 6 , the signal light may be uniformly spread into the light guide plate 30 by the cylindrical concave lens 520 .

The shutter 522 may adjust the exposure time of the light incident from the light source unit 502 .

The light source unit 10 may include at least two laser diodes, but the use of several laser diodes may overheat the backlight unit. In order to minimize overheating of the backlight unit, an optical material having a very low absorption rate may be used. The optical material may be, but is not limited to, highly transparent plastic, optical glass, or quartz glass.

The first holographic element 40 located on the rear surface 34 of the light guide plate 30 and the second holographic element 9 located on the lower surface 32 of the light guide plate 30 may be recorded independently of each other. Through this, it is possible to adjust the output parameters of the entire system by adjusting the parameters of each of the holographic elements 40 and 50 .

The backlight unit 100 may be applied to a holographic display, a smart phone, or a 3D TV.

In the above, the backlight unit has been described with reference to the embodiment shown in the drawings, but this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the disclosed embodiments are to be considered in an illustrative rather than a restrictive sense. The scope of the present invention is indicated in the claims rather than the foregoing description, and all differences within the scope equivalent thereto should be construed as being included in the present invention.

100 … Backlight unit 300, 500 … hologram recorder
10 … Light source 20 . input coupler
30 … light guide plate 31 … the front side of the light guide plate
32 … The underside of the light guide plate 33 … upper surface of the light guide plate
34 … The back side of the light guide plate 40 … first holographic element
50 … The second holographic element 60 . eye tracker
70 … Controls 302, 502 . light source
304, 504... Polarizing beam splitters 310, 510 ... first half-wave plate
311, 511 … Second half-wave plates 312, 512 ... pin hole
314, 514 . Lens 316, 517 … photosensitive medium
318 … Cover Glass 322 … objective lens
308, 508 … Signal parts 306, 506 ... reference part
320, 522 . Shutter 516 … square aperture
518 … slit 520 … cylindrical concave lens
M1, M2, M3 … Reflective members O1, O2 ... micro lens
D1, D2 … iris

Claims (13)

at least two light sources;
at least two input couplers;
light guide plate to guide the light;
a first holographic element located on a first surface of the light guide plate;
a second holographic element located on a second surface of the light guide plate; and
A control unit for controlling an angle between the light rays output from the at least two light source units by moving the at least two light source units;
The at least two input couplers are configured to uniformly illuminate the light rays output from the at least two light source units to the first holographic element through the light guide plate,
the light guide plate is configured to transmit the light beam to the first holographic element without total internal reflection;
the first holographic element collimates and redirects the light beam to the second holographic element;
The second holographic element emits the light beam to the outside of the light guide plate,
The light beam passing through the second holographic element forms two different viewing zones, and an angle between the two viewing zones is determined by an angle between the two beams output from the at least two light sources. The method of claim 1,
The second holographic element is a backlight unit positioned on an upper surface or a lower surface of the light guide plate. The method of claim 1,
The light source unit includes at least one of a light emitting diode, a laser diode, a solid laser, and an optical fiber. The method of claim 1,
The input coupler is a backlight unit including at least one of a concave lens, a convex lens, a transmissive hologram element, and a reflective hologram element. The method of claim 1,
The light guide plate is a backlight unit including at least one of a high-transmittance plastic, optical glass, and quartz glass. The method of claim 1,
The second holographic element is a backlight unit that emits parallel rays to the outside of the light guide plate. The method of claim 1,
The second holographic element is a backlight unit that forms at least two focused viewing areas at a predetermined distance. The method of claim 1,
The light guide plate has a constant cross-sectional area along a length of the backlight unit. 9. The method of claim 8,
A cross section of the light guide plate has a rectangular shape. The method of claim 1,
The first holographic element and the second holographic element are a backlight unit including a diffraction grating. The method of claim 1,
The first holographic element and the second holographic element are formed of an optically transparent material. The method of claim 1,
The front, bottom, top, and back surfaces of the light guide plate are formed of flat surfaces. The method of claim 1,
The backlight unit further comprising an eye-tracking unit for tracking the user's pupil position.

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