KR102643176B1 - Variable-depth holographic display device providing expandable eyebox - Google Patents

Abstract

A variable depth holographic display device providing an expandable eyebox is provided. A holographic display device according to an embodiment of the present invention includes a plurality of light sources emitting light of a plurality of wavelengths; And a spatial light modulator that functions as a panel of a holographic display using light emitted from a plurality of light sources, wherein the spatial light modulator is configured to provide an expanded eye box with an expanded eye box size compared to the existing eye box, By placing a plurality of scattering layers in the target depth plane at different depths, the divergence angle of individual holographic pixels can be enlarged compared to when the scattering layers are located in the target depth plane at a single depth. As a result, by increasing the eyebox through which holographic content can be observed, it is possible to enable the user to observe holographic content in a wider range.

Description

Variable-depth holographic display device providing expandable eyebox

The present invention relates to a holographic display device, and more specifically, to a variable depth holographic display device that provides an expandable eyebox.

Holographic display is a technology that expresses three-dimensional images by reproducing the light waves of an object propagating in space using the diffraction phenomenon of light. It expresses both intensity and phase information, which are the unique characteristics of object light, and is the most ideal It is accepted as the ultimate form of three-dimensional display. Each pixel of a holographic display panel has a diffraction angle that is inversely proportional to the size of the pixel's opening, and the diffraction angle determines the eye box of the entire holographic display.

Specifically, as illustrated in FIG. 1, when individual pixels of a spatial light modulator (SLM) serving as a panel of a holographic display have a size of p, the diffraction angle θ of each pixel is as follows. It is decided.

(Formula 1)

At this time, λ is the illumination wavelength, θ determines the divergence angle of the holographic pixel in the target virtual depth plane, and a collimated or enlarged virtual image is formed through the eyepiece lens.

As illustrated in FIG. 1, the width w of the eyebox, which is an observable viewing area in a holographic display device that forms an enlarged virtual image, is as follows.

(Formula 2)

Since the pixel size p of the currently technically available spatial light modulator is about 4um or more, the theoretical maximum diffraction angle obtained based on green light is about 7.8 degrees, assuming that the eyepiece lens is at a typical level (focal length 20mm~30mm) In this case, the width w of the eyebox is limited to about 2.7mm to 4mm.

In reality, a person's pupil diameter is approximately 4 mm, and considering pupil movement and binocular spacing that vary from user to user, the eye box may act as a factor limiting the general use of augmented reality devices.

In summary, holographic display-based augmented reality devices have the advantage of producing the same three-dimensional effect as the real thing by reproducing the wavefront of virtual content, but have a very narrow eyebox as a limitation, so it is necessary to find ways to improve this. It is required.

The present invention was devised to solve the above problems, and the purpose of the present invention is to achieve narrow diffraction without losing the ability to express content over various variable depths in a holographic display reproduced through a spatial light modulator, etc. The aim is to provide a variable depth holographic display device that can expand the limited eye box due to the angle.

According to an embodiment of the present invention for achieving the above object, a holographic display device includes: a plurality of light sources emitting light of a plurality of wavelengths; And a spatial light modulator that functions as a panel of a holographic display using light emitted from a plurality of light sources, wherein the spatial light modulator is configured to provide an expanded eye box with an expanded eye box size compared to the existing eye box, By placing a plurality of scattering layers in the target depth plane at different depths, the divergence angle of individual holographic pixels can be enlarged compared to when the scattering layers are located in the target depth plane at a single depth.

And each scattering layer can respond individually to each wavelength and selectively serve as a scattering layer.

Additionally, each scattering layer can use a passive optical element that can selectively respond to each wavelength without a separate active element.

And the holographic image expressed by the spatial light modulator is reproduced taking into account each wavelength and the distance to the scattering layer, and the width of the eyebox that can be provided by the spatial light modulator is the width of the eyebox that can be provided by each scattering layer. It may be equal to the minimum value.

Additionally, each scattering layer is arranged to have different distances from the eyepiece lens according to the imaging characteristics of the eyepiece lens, thereby providing different depths of the virtual image imaging plane.

And each scattering layer may be implemented with at least one of a holographic optical element, a surface relief grating, and a meta surface so that it responds individually to each wavelength. .

In addition, the plurality of light sources are switched according to different operation cycles and may emit light through a common optical path through a combiner, which is a single entity.

Meanwhile, according to another embodiment of the present invention, an apparatus for manufacturing a holographic optical element includes: a plurality of light sources emitting light of a plurality of wavelengths; a splitting unit that divides individual holographic pixels with enlarged divergence angles into reference beams and signal beams to emit light in different directions; a first direction adjustment unit that adjusts the direction of the signal beam divided by the splitting unit and emitted; It is implemented in plural, and is located in target depth planes of different depths, and when a signal beam whose direction is adjusted by the first direction adjustment unit enters the light, the signal beam in the form of incident parallel light is modulated into the shape of a scattered light wave, a first optical element that causes the divergence angle of the individual holographic pixels of the incident signal beam to be enlarged compared to the case where the optical element serving as a scattering layer is located in the target depth plane of a single depth; a second direction adjustment unit that adjusts the direction of the reference beam that is divided by the splitting unit and emitted; It is implemented in plural, and is located in the target depth plane at different depths, passing through a reference beam whose direction is adjusted by the second direction adjustment unit, and the divergence angle of the individual holographic pixel of the incident reference beam serves as a scattering layer. a second optical element that causes the optical element to be enlarged compared to the case where the optical element is located in the target depth plane of a single depth; and a recording medium storing the interference pattern of the reference beam that passed through the second optical element and the signal beam modulated by the first optical element.

As described above, according to embodiments of the present invention, it is possible to enable the user to observe holographic content in a wider range by increasing the eye box through which holographic content can be observed.

1 is a diagram illustrating an existing holographic display;
2 to 3 are diagrams provided to explain a holographic display device according to an embodiment of the present invention;
4 is a diagram provided to explain the change in virtual screen depth according to the distance between the scattering layer and the eyepiece lens;
5 is a diagram provided to explain time-division driving of a light source according to an embodiment of the present invention;
FIG. 6 is a diagram provided to explain an embodiment of operating by dividing one frame of a holographic image into three light sources using the light source shown in FIG. 5;
7 is a diagram provided to explain the wavelength selectivity of a typical holographic optical element, and
FIG. 8 is a diagram provided to explain an apparatus for manufacturing a holographic optical element according to another embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

FIGS. 2 and 3 are diagrams provided to explain a holographic display device according to an embodiment of the present invention, and FIG. 4 is a diagram showing a diagram between each of the scattering layers 210-1 to 210-N and the eyepiece lens 220. This diagram is provided to explain the change in virtual screen depth according to distance.

The holographic display device according to this embodiment is a holographic display reproduced through a spatial light modulator 200, etc., without losing the ability to express content across various variable depths, while maintaining a limited eye box due to a narrow diffraction angle. It is designed to expand beyond the existing one.

For this purpose, the present holographic display device uses a plurality of light sources (100-1 to 100-N) that emit light of a plurality of wavelengths and light emitted from the plurality of light sources (100-1 to 100-N). , may include a spatial light modulator 200 that serves as a panel of a holographic display.

The spatial light modulator 200 positions a plurality of scattering layers (210-1 to 210-N) in the target depth plane at different depths to provide an expanded eye box with an expanded eye box size than before. The divergence angle of the individual holographic pixels can cause the scattering layer to be magnified compared to if it were located in a single depth target depth plane. Here, the plurality of scattering layers (210-1 to 210-N) are from the scattering layer (210-1) of P1, which has the shallowest depth, to Pn, which has the deepest depth (210-N). ) can be composed of.

Each scattering layer (210-1 to 210-N) reacts individually only to each wavelength (λ1 to λn) and can selectively serve as a scattering layer (210-1 to 210-N). It has the characteristic of not reacting to light of other wavelengths.

For example, when a plurality of light sources (100-1 to 100-N) emit light (laser) of wavelengths corresponding to each color of RGB (Red-Green-Blue), the scattering layer (210-1 to 210- N) is composed of three, and each scattering layer (210-1 to 210-N) is an R scattering layer that responds only to red-colored wavelengths, a G-scattering layer that responds only to green-colored wavelengths, and a blue-colored layer. It can be implemented as a B scattering layer that responds only to wavelengths of

For another example, when a plurality of light sources (100-1 to 100-N) emit light (laser) of wavelengths corresponding to each color of RGB (Red-Green-Blue), the scattering layer (210-1 to 210) -N) is composed of 9, and in this case, R1, R2, and R3 scattering layers, which react only to red-colored wavelengths, but react to slightly different wavelengths from each other, and react only to green-colored wavelengths, but to each other. It can be implemented as G1, G2, and G3 scattering layers that respond to slightly different wavelengths, and B1, B2, and B3 scattering layers that respond only to blue-colored wavelengths, but react to slightly different wavelengths.

Through this, the divergence angle of individual holographic pixels can be enlarged compared to the case where the scattering layer is located in the target depth plane at a single depth.

Each of these scattering layers (210-1 to 210-N) uses a holographic optical element, a surface relief grating, and a meta surface to individually react only to each wavelength. surface) can be implemented with at least one of the following:

Additionally, each scattering layer (210-1 to 210-N) can use a passive optical element that can selectively respond to each wavelength without a separate active element.

As shown in Figure 2, the holographic image reproduced at wavelength λ1 passes through all of the scattering layers (210-1 to 210-N) from P2 to Pn and is scattered at P1, and at this time, the scattering angle θ1 is that of the existing SLM. By providing a very large value compared to the diffraction angle, an eyebox of sufficient size can be provided.

Likewise, when a holographic image is reproduced with a wavelength of λn as illustrated in FIG. 3, the image is scattered at Pn and passes through the scattering layers (210-1 to 210-N) of P1 to Pn-1 to the user. It can be delivered.

At this time, the holographic image expressed by the spatial light modulator 200 can be reproduced taking into account each wavelength and the distance to the scattering layers 210-1 to 210-N. The final width of the eyebox that can be provided is equal to the minimum value of the eyebox that can be provided in each scattering layer (210-1 to 210-N).

In addition, each scattering layer (210-1 to 210-N) is arranged to have different distances from the eyepiece lens 220 according to the imaging characteristics of the eyepiece lens 220, so as to provide different depths of the virtual image imaging plane. can be provided.

Specifically, each scattering layer (210-1 to 210-N) is arranged with different intervals from g1 to gn from the eyepiece lens 220, and the spacing is small depending on the imaging characteristics of the eyepiece lens 220. Even the scattering layers (210-1 to 210-N) arranged with each other can provide different depths of virtual image formation surfaces over a wide range.

For example, as illustrated in FIG. 4, even if scattering layers 210-1 to 210-N having a spacing of less than 1 mm are used, the virtual image surface enlarged through the eyepiece lens 220 is similar to that of a typical augmented reality user. It can cover the entire depth of field range (approximately 25 cm in front of the user to infinity).

Therefore, the present invention can provide a wide eye box using the scattering layers 210-1 to 210-N without losing the three-dimensional effect due to the variable depth that can be provided by existing holographic displays.

FIG. 5 is a diagram provided to explain time-division driving of the light source 100 according to an embodiment of the present invention.

Referring to FIG. 5, the light source 100 according to an embodiment of the present invention includes a controller 110 and a combiner to select and provide wavelengths based on the (laser) light source 100 of a plurality of wavelengths. It may include (120).

Specifically, as illustrated in Figure 5, a plurality of light sources (100-1 to 100-N) may emit light through a common optical path through one combiner 120 through optical fiber or freespace coupling.

At this time, before each light source (100-1 to 100-N) is coupled to the (laser) combiner 120, an individual controller 110 (can be implemented as a short-circuit switch, optical block, etc.) It switches quickly on the time axis and can perform the function of providing wavelengths corresponding to λ1 to λn by time division.

Through this, the plurality of light sources (100-1 to 100-N) are switched according to different operation cycles and can emit light through a common optical path through the combiner 120, which is a single entity.

FIG. 6 shows one frame of a holographic image for a combiner 120 operating through time division driving switched according to different operation cycles using the light source 100 shown in FIG. 5 with a total of three lasers. This is a diagram showing an example of operation by dividing into light sources 100.

Referring to FIG. 6, in accordance with the operation cycle of the light source 100, the hologram pattern on the spatial light modulator 200 is also generated differently depending on the designed wavelength and the distance of the wavelength selective scattering layers 210-1 to 210-N. It must change quickly.

FIG. 7 is a diagram provided to explain the wavelength selectivity of a typical holographic optical element, and FIG. 8 is a diagram provided to explain an apparatus for manufacturing a holographic optical element according to another embodiment of the present invention.

Meanwhile, the scattering layer (210-1 to 210-N) (wavelength selective scattering layer) according to an embodiment of the present invention can be applied to a holographic optical device.

Specifically, the holographic optical element is manufactured by recording the interference pattern of two plane waves (reference beam and signal beam) incident from different directions on the recording medium 360 (e.g. photopolymer, photorefractive polymer, silver halide, etc.) It can be.

At this time, the recorded interference pattern forms a periodically repeating volume grating in the holographic recording medium 360, and the incident beam in the later reproduction stage meets the Bragg condition of the volume grating. If satisfactory, the reproduction beam can be output through the diffraction phenomenon.

If the incident light deviates from the Bragg condition of the recorded volume grating, it has the characteristic of being transmitted as is without any separate diffraction, which is called wavelength and angle selectivity.

In the present invention, the wavelength selectivity of this holographic optical device can be utilized.

Figure 7 shows the wavelength selectivity of a typical holographic optical device. It can be seen that even if there is only a wavelength deviation of about +/- 7.5 nm compared to the designed wavelength (λr in Figure 7), the diffraction efficiency is reduced by less than half.

Therefore, the present invention can be implemented by applying a plurality of holographic optical element scattering layers (210-1 to 210-N) having a wavelength interval greater than the corresponding value.

Referring to FIG. 8, the apparatus for manufacturing a holographic optical element according to this embodiment uses a signal beam and a reference beam to record wavelength-selective scattering layers (210-1 to 210-N) based on the holographic optical element. It is designed to cause interference at the location of the holographic medium by consisting of two types of paths, and for this purpose, the light source 100, the dividing part 310, the first direction adjusting part 320, and the first optical element 330 ), a second direction adjustment unit 340, a second optical element 350, and a recording medium 360.

The light source 100 may be implemented as a plurality of light sources and may emit light with a wavelength corresponding to λ1 to λn. However, in some cases, the light source 100 may be implemented singly (a single wavelength laser) rather than as a plurality of light sources. When recording a selective scattering layer (210-1 to 210-N) in λ1 to λn using a single wavelength laser, the recording grid must be angularly compensated according to the wavelength deviation between the recording and reproducing wavelengths.

The splitter 310 may divide individual holographic pixels with enlarged divergence angles into reference beams and signal beams, so that they emit light in different directions.

The first direction adjustment unit 320 is provided to adjust the direction of the signal beam that is divided and emitted by the splitter 310, and the first optical elements 330 are implemented in plural, with targets of different depths. When a signal beam located in the depth plane and whose direction has been adjusted by the first direction adjustment unit 320 enters the light, the signal beam in the form of incident parallel light is modulated into the shape of a scattered light wave, but The divergence angle of the graphic pixel can be enlarged compared to the case where the optical element serving as a scattering layer is located in the target depth plane of a single depth.

Specifically, the first optical element 330 is mounted on the first direction adjustment unit 320 and is made of a film-type diffuser, ground diffuser, ground glass, or ultraviolet light to modulate the incident parallel light into the shape of a scattered light wave. It can be implemented with a small pitch microlens array, etc.

The second direction adjustment unit 340 is provided to adjust the direction of the reference beam that is divided and emitted by the splitter 310, and the second optical elements 350 are implemented in plurality, with targets of different depths. It is located in the depth plane and can pass the reference beam whose direction is adjusted by the second direction adjustment unit 340, and the divergence angle of the individual holographic pixel of the incident reference beam is used to create a single optical element that serves as a scattering layer. The depth can be enlarged compared to the case where it is located in the target depth plane.

And the second direction adjustment unit 340 must support a fine rotation function of at least one axis to support rotational movement up, down, left, and right, and adjusts the projection angle and wave front of the holographic display through the second optical element 350. It must be modulated so that it can be copied. At this time, the second optical element 350 may be implemented as a two-axis motorized scanning device using a galvo mirror, MEMS mirror, etc.

The recording medium 360 can store the interference pattern of the reference beam that passed through the second optical element 350 and the signal beam modulated by the first optical element 330.

In the above, preferred embodiments of the present invention have been shown and described, but the present invention is not limited to the specific embodiments described above, and may be used in the technical field to which the invention pertains without departing from the gist of the present invention as claimed in the claims. Of course, various modifications can be made by those skilled in the art, and these modifications should not be understood individually from the technical idea or perspective of the present invention.

100: light source
110: controller
120: Combiner
200: Spatial light modulator (SLM)
210: scattering layer
220: Eyepiece lens
310: division part
320: First direction adjustment unit
330: first optical element
340: Second direction adjustment unit
350: second optical element
360: recording medium

Claims (8)

A plurality of light sources emitting light of a plurality of wavelengths; and
A spatial light modulator that functions as a panel of a holographic display using light emitted from a plurality of light sources,
The spatial light modulator,
In order to provide an expanded eyebox with an expanded eyebox size than before, a plurality of scattering layers are placed in the target depth plane at different depths, so that the divergence angle of each holographic pixel changes the scattering layer to a target depth plane of a single depth. Make it larger than when it is located in,
Each scattering layer is,
It responds individually to each wavelength and selectively acts as a scattering layer.
Each scattering layer is,
Using passive optical elements that can selectively respond to each wavelength without a separate active element,
The holographic image expressed by the spatial light modulator is,
It is regenerated considering each wavelength and the distance to the scattering layer,
The width of the eyebox that can be provided by the spatial light modulator is:
It is equal to the minimum value of the eyebox that can be provided in each scattering layer,
Each scattering layer is,
Implemented with at least one of a holographic optical element, a surface relief grating, and a meta surface to respond individually to each wavelength,
Each scattering layer is,
When multiple light sources emit light of wavelengths corresponding to each RGB (Red-Green-Blue) color, it consists of 3 or 9 light sources.
When composed of three, it consists of an R scattering layer that responds only to red-colored wavelengths, a G-scattering layer that responds only to green-colored wavelengths, and a B-scattering layer that responds only to blue-colored wavelengths.
When composed of 9, scattering layers R1, R2, and R3 react only to red-colored wavelengths, but react to different wavelengths; G1, which responds only to green-colored wavelengths, but reacts to different wavelengths; It consists of G2, G3 scattering layers and B1, B2, and B3 scattering layers that react only to blue color wavelengths, but react to different wavelengths.
Multiple light sources,
It is switched according to different operation cycles and is emitted into a common optical path through a single entity, the combiner.
Each scattering layer is,
Depending on the imaging characteristics of the eyepiece lens, they are arranged at different distances from the eyepiece lens to provide different depths of the virtual image forming plane.
The virtual image plane magnified through the eyepiece lens is
A holographic display device, characterized in that when using individual scattering layers having different intervals of less than 1 mm from the eyepiece lens, the entire depth of field usage range of the user corresponding to 25 cm or more in front of the user is included. delete delete delete delete delete delete delete