WO2023197115A1

WO2023197115A1 - Display system

Info

Publication number: WO2023197115A1
Application number: PCT/CN2022/086170
Authority: WO
Inventors: Tatsuya Nakatsuji; Yoji Okazaki; Takashi Hashimoto
Original assignee: Guangdong Oppo Mobile Telecommunications Corp., Ltd.
Priority date: 2022-04-11
Filing date: 2022-04-11
Publication date: 2023-10-19

Abstract

A display system according to one aspect of the present invention includes: a micro Light Emission Diode (microLED) including a set of light emitting units of Red (R), Green (G), and Blue (B) colors, the set of light emitting units having a stacked structure; a shifter configured to shift emitted light from the microLED; and an optical system configured to convert the emitted light having passed through the shifter into collimated light.

Description

DISPLAY SYSTEM

TECHNICAL FIELD

The present invention relates to a display system.

BACKGROUND

As one of display systems, there are known augmented reality (AR) glasses. In a case of achieving high resolution equal to or higher than 2K or 4K with a compact full-color display system such as AR glasses, it is needed a display device having a compact size, a high brightness, a low power consumption, and a high frame rate. Types possible to achieve such a display device include Liquid crystal on-silicon (LCOS) (registered trademark) , Digital Micromirror Device (DMD) , LBS, or micro Light Emission Diode (microLED) , etc. Among them, as for LCOS and DMD, size is large; and LBS type has to be a frame rate of 60 Hz because of physical limits of micro electro mechanism systems (MEMS) ; thus, microLED having a large number of microLED chips arranged thereon can be a potential candidate. However, because the microLED needs to rearrange microLED chips, it is difficult to achieve a small microLED and, at the same time, it is difficult to achieve compact size and high resolution.

SUMMARY

Technical Problem

However, microLED needs to rearrange small microLED chips for R (Red) , G (Green) , and B (Blue) colors like Bayer arrangement, for example, and mount them, which is extremely difficult to fabricate. Moreover, in microLED, because pixels of respective R, G, and B colors are on the same surface, a reduction in emitter size is needed to achieve the same resolution. This reduces an active area and thus, under influence of a damage layer on a side wall, decreases brightness efficiency of the microLED. A larger power supply is needed to compensate the decrease in brightness efficiency, and a heat radiation fin is also needed. Accordingly, it is difficult to fabricate a Bayer-arranged small microLED, while obtaining a sufficient efficiency of light emittance, and its size may further increase because of the decrease in brightness, which is hindering of compactness.

There is another approach to achieve a full-color microLED, in which waves from respective single-color microLED chips of the R, G, and B colors are combined through a prism to achieve full color. Because of the necessity of a prism, this approach may increase size. In addition, the combining of waves through a prism may generate deviation among R, G, B optical axes, and pixel deviation may be likely to occur.

Whereas, in recent years, there has been developed a technique for a display device used in a large-size projector, the technique achieving high resolution by doubling low resolution. However, even when high resolution is achieved by the doubling with a conventional configuration, it is difficult to achieve high image quality because colors are mixed and clear colors cannot be obtained, for example. In addition, even with the resolution doubling process, there is difficulty in final achievement to a small high-resolution device suitable for AR glasses, because of non-existence of small display devices. A high-resolution display device may be larger than a low-resolution one, and its collimated lens may have a smaller light-receiving angle; thus, light-collecting efficiency tends to drop down. Therefore, it is important increase the light-receiving angle of the collimated lens, keeping the size of the display device small, thereby increasing the light-collecting efficiency. The technology of achieving high resolution by doubling low resolution is very effective in achieving a display device having small size, high resolution, and high efficiency.

The present invention has been made in view of such a situation, and an object of the present invention is to provide a display system used for, for example, AR glasses that can obtain high image quality with a high resolution even in a case in which the size thereof is made compact.

Solution to Problem

To solve the above problems and achieve the object, a display system according to one aspect of the present invention includes: a micro Light Emission Diode (microLED) including a set of light emitting units of Red (R) , Green (G) , and Blue (B) colors, the set of light emitting units having a stacked structure; a shifter configured to shift emitted light from the microLED; and an optical system configured to convert the emitted light having passed through the shifter into collimated light.

Advantageous Effects of Invention

According to one aspect of the present invention, high image quality can be obtained with a high resolution even in a case in which the size of the display system is made compact.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a configuration of a display system according to an embodiment.

FIG. 2 is a perspective view illustrating an example of a configuration of a microLED according to the embodiment.

FIG. 3 is an explanatory diagram of a stacked structure of the microLED according to the embodiment.

FIG. 4 is a diagram illustrating an example of a configuration of a glass-type pixel shifter unit according to the embodiment.

FIG. 5 is a principle explanatory diagram of a beam shifter according to the embodiment.

FIG. 6 is an explanatory diagram of control for a pixel shift according to the embodiment.

FIG. 7 is a diagram illustrating an example of the configuration of the display system provided with an optical system according to the embodiment.

FIG. 8 is a diagram illustrating an example of a configuration of the optical system according to the embodiment.

FIG. 9 is a diagram explaining an image displayed on a display surface of the display system according to the embodiment.

FIG. 10 is a diagram illustrating an example of a configuration of a display system according to a first modification.

FIG. 11 is a diagram illustrating an example of a configuration of a pixel shifter unit 20 according to the first modification.

FIG. 12 is a diagram illustrating an example of a configuration of a display system according to a second modification.

FIG. 13 is a cross-sectional view illustrating a configuration of a microLED according to a third modification.

FIG. 14 is a diagram illustrating an example of an AR glass to which the display system according to the embodiment and modifications is applied.

DETAILED DESCRIPTION

The following describes a display system and an AR glass according to embodiments in detail with reference to the attached drawings. The present invention is not limited to the embodiments.

(Embodiments)

A display system according to an embodiment includes a display device, a shifter, and an optical system. The display system according to the embodiment can be applied to a compact display system such as AR glasses that implements an augmented reality (AR) image. Applications of the display system are not limited to AR glasses. The display system can be appropriately applied to other display systems.

In the following description, the shifter is assumed to be a pixel shifter unit, but the shifter is not limited to such a unit. Moreover, the display device is described as a microLED in the following. The microLED enables full-color display and is configured with, for example, three colors: R (Red) , G (Green) , and B (Blue) .

FIG. 1 is a diagram illustrating an example of the configuration of a display system 1 according to the embodiment. The display system 1 includes a microLED 10, a pixel shifter unit 20, and an optical system 30.

The microLED 10 emits light for forming an image by light emission from a large number of light emitting units arranged on one surface 10-1 on one side. The respective light emitting units on the surface 10-1 emit light rays of a plurality of colors, and an optical axis P of emitted light of each color is common in the light emitting units. For explanation, the optical axis P illustrated in FIG. 1 schematically illustrates an optical axis of light emitted from one certain light emitting unit.

The pixel shifter unit 20 doubles pixels by shifting light of pixel emitted from each of the light emitting units of the microLED 10. When an optical path of light of pixel is shifted to be positioned between adjacent pixels by the pixel shifter unit 20, the number of pixels of an image to be emitted is doubled. A specific method of shifting the pixel will be described later.

The optical system 30 receives incident light shifted by the pixel shifter unit 20, and emits collimated light to a display surface. Various display surfaces can be used depending on the configuration, and one example thereof is a screen.

By way of example, in the configuration illustrated in FIG. 1, the pixel shifter unit 20 is provided in a direction in which the microLED 10 emits light. The arrangement and configuration of the pixel shifter unit 20 are not limited thereto.

FIG. 2 is a perspective view illustrating an example of a configuration of the microLED 10. The microLED 10 illustrated in FIG. 2 includes sets of light emitting units 10a having a stacked structure. The sets of light emitting units 10a are arranged in a pixel array 10b on a substrate 11. In FIG. 2, a direction perpendicular to an upper surface of the drive-circuit substrate 11 made of a semiconductor is assumed to be the Z direction, and two directions orthogonal to each other in a plane perpendicular to the Z direction are assumed to be the X direction and the Y direction. Only part of the entire pixel array 10b is illustrated. The pixel array 10b further expands in the XY direction.

The microLED 10 emits light of each pixel corresponding to an image in the Z direction by light emission from the sets of light emitting units 10a in the pixel array 10b.

In the set of light emitting units 10a, light emitting units 12 corresponding to respective colors of RGB are stacked in the Z-axis direction. In FIG. 2, a position in the pixel array 10b is represented as (m, n) , and the light emitting units of the respective R, G, and B colors in the set of light emitting units 10a at the position (m, n) are respectively represented as an R pixel 12r (m, n) , a G pixel 12g (m, n) , and a B pixel 12b (m, n) . A group of the R pixel 12r (m, n) , the G pixel 12g(m, n) , and the B pixel 12b (m, n) is a pixel group 13. Additionally, m and n are natural numbers.

In each set of light emitting units 10a, the R pixel 12r, the G pixel 12g, and the B pixel 12b emit light from a first surface 100a of the set of light emitting units 10a by light emission of the respective colors, and emitted light rays of respective colors have the same optical axis. Stacking order of the R pixel 12r, the G pixel 12g, and the B pixel 12b is shown in FIG. 2 as an example, depending on relationship among bandgaps of the respective layers. One method to achieve this stacking includes: bonding an R layer in epi film form to the substrate and process the film for each pixel; then, bonding a G layer and a B layer thereto, thereby easily forming each of the R, G, and B layers; and then, electrically connecting each layer to the circuit substrate 11 using a through electrode. It is noted that a micro lens is mounted after that, although no explanation is provided herein.

As illustrated in FIG. 3, in the

pixels

12r, 12g, and 12b, P-type semiconductor films 12rp, 12gp, and 12bp extending in the XY direction and N-type semiconductor films 12rn, 12gn, and 12bn extending in the XY direction are stacked in the Z direction. The

pixels

12r, 12g, and 12b are applied with a voltage in a forward direction from a control circuit, and thus emit light from bonded

interfaces

15r, 15g, and 15b between the P-type semiconductor films 12rp, 12gp, and 12bp and the N-type semiconductor films 12rn, 12gn, and 12bn. At this time, in each set of light emitting units 10a, red light generated from the bonded interface 15r in the R pixel 12r is transmitted through the

pixels

12g and 12b and emitted from the first surface 100a, green light generated from the bonded interface 15g in the pixel 12g is transmitted through the pixel 12b and emitted from the first surface 100a, and blue light generated from the bonded interface 15b in the pixel 12b is emitted from the first surface 100a. Emission intensities of the

pixels

12r, 12g, and 12b may be respectively adjusted by the control circuit in accordance with colors to be displayed.

Note that protective films and reflecting

members

14R and 14L may be arranged on

side walls

13R and 13L of the pixel group 13 as illustrated in FIG. 3. The protective films and the reflecting

members

14R and 14L may be given reflecting characteristics by a protective film or dielectric multi-layer that protects a damage layer on the side wall during dry-etching by atomic layer deposition (ALN) between the P-type semiconductor films 12rp, 12gp, and 12bp and the N-type semiconductor films 12rn, 12gn, and 12bn, respectively. As a result, the protective layer and the reflecting member 14R is arranged on the side wall 13R of the pixel group 13 to be able to form a protective film and a reflective interface on the side wall 13R. The reflecting member 14L is arranged on the side wall 13L of the pixel group 13 to be able to form a reflective interface on the side wall 13L.

As illustrated in FIG. 2 and FIG. 3, in the microLED 10, the R pixel, the G pixel, and the B are mounted in film form and each is formed as a chip; thereby, a set of light emitting units stacked is provided. Thus, as compared with the Bayer arrangement and the like in which chips are mounted thereon, the mounting method is easier and the same number of pixels can be provided for each microLED without reducing an emitter diameter. The respective colors are stacked, so that the emitter diameter can be relatively increased in a range from about 1 μm to about 2 μm, and an active area can by maximally used at a level of not lowering brightness. Accordingly, the number of pixels per unit area can be increased while suppressing lowering of brightness. As in this example, the configuration in which light rays of respective colors have the same optical axis, can achieve high resolution of the microLED 10, and is suitable for size reduction.

Dissimilar to LCOS, DMD, and LBS types, the microLED is self-luminous; therefore, it has a high refresh rate, and can achieve a high-speed frame rate such as 120 Hz or 240 Hz. Thus, resolution can be easily doubled by combining the microLED with the pixel shifter unit 20 as follows, while the frame rate keeps high (for example, 60 Hz or higher) .

FIG. 4 is a diagram illustrating an example of the configuration of the glass-type pixel shifter unit 20. The pixel shifter unit 20 illustrated in FIG. 4 is a beam shifter. When the control circuit inputs a control signal to an input unit 220, an actuator inside a housing is driven to tilt a glass window 210 in uniaxial or biaxial directions. Due to this tilt, beam shift is performed on a light beam that is light incident on the glass window 210. The light forming an image having first image resolution emitted from the microLED 10 passes through the glass window 210, and is combined with an image having second image resolution on the display surface to double the resolution by control for tilting the glass window 210.

The beam shifter can be configured by a magnetic circuit, for example. The beam shifter includes a first support member for oscillating a glass plate as the glass window 210 in the uniaxial direction and a second support member for oscillating the glass plate in the biaxial direction, and an actuator for oscillating the first support member and an actuator for oscillating the second support member are provided using the magnetic circuit.

FIG. 5 is a principle explanatory diagram of the beam shifter. Incident light P is refracted when the glass window 210 is tilted, and emitted through an optical path deviating by Δy. Assuming that n is a refractive index, θ is a tilt angle, and t is a thickness of glass of the glass window 210, Δy is calculated by the expression 1.

FIG. 6 is an explanatory diagram of control for a pixel shift. With reference to FIG. 6, the following describes the pixel shift when tilt is performed in the biaxial direction as the X-axis direction and the Y-axis direction. By way of example, in the following description, an image is assumed to be emitted from the microLED 10 at a frame rate that is four times a display frame rate. This example is merely an example for clarifying the explanation, and the embodiment is not limited thereto. For example, the control circuit decomposes an image having the second image resolution, which is high resolution, as an original into frame images of pixel arrangements A, B, C, and D to have low resolution, and outputs the frames having the first image resolution to the microLED 10 in order. The microLED 10 emits the frame image of the pixel arrangement A, the frame image of the pixel arrangement B, the frame image of the pixel arrangement C, and the frame image of the pixel arrangement D each having the first image resolution from the microLED 10 in this order at the frame rate four times the display frame rate described above.

The beam shifter performs tilt control assuming four frames as one cycle. FIG. 6 illustrates a state of a pixel shift at a certain point of each frame as a representative. The pixel shift illustrated in FIG. 6 is assumed to be similarly performed for all other pixels.

The beam shifter first emits a pixel of the incident light P in the frame of the pixel arrangement A to a position of a pixel p1. Subsequently, the beam shifter tilts the pixel of the incident light P in the frame of the pixel arrangement B in a positive direction of the Y-axis to be emitted to a position of a pixel p2. Subsequently, the beam shifter tilts the pixel of the incident light P in the frame of the pixel arrangement C in a positive direction of the X-axis to be emitted to a position of a pixel p3. Subsequently, the beam shifter tilts the pixel of the incident light P in the frame of the pixel arrangement D in a negative direction of the Y-axis to be emitted to a position of a pixel p4. The beam shifter then tilts the pixel of the incident light P in a frame corresponding to the next frame of the pixel arrangement A in a positive direction of the X-axis to be emitted to the position of the pixel p1 similarly to the previous frame of the pixel arrangement A. In this way, pixel shifts from the pixel arrangement A to the pixel arrangement B, from the pixel arrangement B to the pixel arrangement C, from the pixel arrangement C to the pixel arrangement D, and from the pixel arrangement D to the pixel arrangement A are repeatedly performed as one cycle. Each of shift positions of the pixels p2 to p4 is assumed to be positioned between pixels of the image having the first resolution.

When such pixel shifts are repeatedly executed, an image having high resolution can be obtained in which the four frames of the respective pixel arrangements are combined with each other on the display surface.

In this example, when the four frames on which pixel shifts have been executed are combined with each other on the display surface to be displayed as one frame, a high resolution image in which the pixels are doubled can be obtained. With such a configuration, images having the first resolution as a low resolution image can be converted into an image having second resolution as an image having higher resolution on the display surface.

The images of the respective pixel arrangements output from the microLED 10 are merely examples, and the embodiment is not limited thereto. The control for the pixel shift by the beam shifter is not limited thereto. In this example, the pixels are increased two times by shifting the pixel between the pixels by 1/2 like the pixel arrangement A, the pixel arrangement B, the pixel arrangement C, and the pixel arrangement D. Alternatively, a method may be taken in which shifting from the pixel arrangement A (p1 position) to the pixel arrangement B (p2 position) doubles the pixels and increases the frame rate. Still alternatively, the control for the pixel shift may be modified such that the pixels are increased three times by shifting the pixel between the pixels by 1/3, or the pixels are further increased four times.

(Example of optical system 30)

The following describes an example of the optical system 30.

FIG. 7 is a diagram illustrating an example of the configuration of the display system 1 provided with the optical system 30. The pixel shifter unit 20 illustrated in FIG. 7 is arranged between the microLED 10 and the optical system 30. As illustrated in FIG. 7, the optical system 30 is configured to convert light emitted from the pixel shifter unit 20 into collimated light.

In this configuration, regarding light having the first image resolution emitted from the microLED 10, pixels are doubled by the pixel shifter unit 20. Furthermore, light rays having the first image resolution emitted from the pixel shifter unit 20 in a time-division manner are respectively incident on the optical system 30, and the collimated light is emitted.

By combining the display system 1 with the optical system 30, a shift amount between a lens center position and a peripheral position can be reduced.

FIG. 8 is a diagram illustrating an example of the configuration of the optical system 30. The optical system 30 illustrated in FIG. 8 may be employed. The optical system 30 includes a lens group 20a. The lens group 20a has an incident surface 20b and an exit pupil surface 20c. The incident surface 20b faces the first surface 100a. The optical system 30 receives light emitted from the first surface 100a of the microLED 10 on the incident surface 20b, refracts the light to convert the light into collimated light substantially parallel to an optical axis PA, and emits the collimated light from the exit pupil surface 20c.

The lens group 20a includes a plurality of lenses 21 to 26 and a lens diaphragm 27 in sequence from an object side to an image side. The plurality of lenses 21 to 26 and the lens diaphragm 27 are arranged along the optical axis PA, and each of them intersects with the optical axis PA. An incident surface of the lens 21 closest to the object side among the plurality of lenses 21 to 26 forms the incident surface 20b of the optical system 30. The lens diaphragm 27 is arranged on the exit pupil surface 20c of the optical system 30.

The lenses 21 to 26 are formed of translucent material, and are formed of, for example, glass, quartz, translucent plastic, or the like. The lens diaphragm 27 may be formed of a light-shielding material, or may be formed of an arbitrary material to paint a color suitable for light shielding such as black color on its surface.

The plurality of lenses 21 to 26 are configured by combining a lens having positive refractive power and a lens having negative refractive power to correct an aberration of the lens group 20a. The plurality of lenses 21 to 26 may have different cross-sectional shapes including the optical axis PA.

It is desirable that the number of lenses included in the lens group 20a is 5 or more and 8 or less. When the number of lenses is 4 or less, it may be difficult to correct aberration characteristics so as to be within an allowable range. When the number of lenses is 9 or more, the optical system 30 may grow in size beyond an allowable range.

The lens group 20a may include a convex lens on the image side. The lens group 20a may include a meniscus lens or a concave lens on the object side. In FIG. 8, the image-side lens 26 is a convex lens, and the object-side lens 21 is a meniscus lens.

In the lens group 20a, the diameter of the lens close to the incident surface 20b may be larger than the diameter of the lens close to the exit pupil surface 20c. In FIG. 8, the diameter of the lens 21 is larger than the diameter of the lens 26. In this case, it is possible to use a display device having a high resolution and a relatively large size, and the entire length of lenses can be short.

The lens diaphragm 27 has an aperture 27a. The aperture 27a is a substantially circular shape in an XY plan view.

(Effect of embodiment)

FIG. 9 is a diagram explaining an image displayed on the display surface of the display system 1 according to the embodiment. FIG. 9 schematically illustrates a state of an image on a display surface 40 such as a screen. For ease of explanation, FIG. 9 illustrates a state of an image on the display surface 40 in a case of doubling the pixels in the uniaxial direction by the pixel shift.

As illustrated in FIG. 9, the R pixel, the G pixel, and the B pixel of the RGB light emitted with the same optical axis are overlapped on substantially the same pixel to be displayed. As illustrated in FIG. 9, regarding light of pixel emitted from center and peripheral positions of an optical lens of the optical system 30, shift amount differs between the center position and the peripheral position. Due to this, with a structure in which the R, G, and B colors are on different optical axes, if a beam shifter that uses glass refraction is employed, the shift amount may differ depending on R, G, and B colors, and emitted light from the collimated lens may be affected by chromatic aberration, and thus the colors may be mixed in the peripheral part. In contrast, with the structure of the present embodiment in which the R, G, and B colors are on the same optical axis, because the R, G, B colors are shifted to the same position, color deviation is very unlikely to occur. Due to this, if the R, G, and B lights are on the same optical axis, it is possible to suppress mixing of colors, for example, overlapping of adjacent pixels when shift occurs, so that an image having clear colors and high image quality can be obtained.

(First modification of embodiment)

The embodiment describes the configuration in which the beam shifter executes the pixel shift on the light emitted from the microLED 10 as an example of the pixel shifter unit 20, but a configuration in which the microLED 10 itself performs sub-pixel shift may be employed. For example, a shift mechanism of an image sensor employed as a shake correction technology for a camera module is employed as the pixel shifter unit 20, in which a shape-memory alloy, a magnetic circuit, a piezoelectric element, etc., are used as an actuator. By employing this shift mechanism, the microLED 10 itself is sub-pixel shifted in the biaxial directions (the X-axis direction and the Y-axis direction) orthogonal to the optical axis. A conventional technology to achieve full color with a microLED takes a method in which respective waves of three R, G, and B colors from single-color microLED chips are combined together through a prism; therefore, it is required to mount a shifter for each of the R, G, and B colors and perform position alignment for the shifter on sub-pixel basis. It is thus impossible to use the pixel shift technology. Employment of this pixel shift is possible only with, among various microLEDs that are self-luminous, a microLED that has a high frame rate of 240 Hz or higher and that achieves full color with a single plate by sets of microLED chips having R, G, and B colors on the same optical axis. Furthermore, because the R, G, and B colors are on the same optical axis, it is possible to easily increase the pixels twofold, threefold, or fourfold with no color mixing by sub-pixel shift, without any complicated movement.

FIG. 10 is a diagram illustrating an example of a configuration of a display system according to a first modification. As illustrated in FIG. 10, the microLED 10 is arranged on the pixel shifter unit 20. The optical system 30 is the same as that in the embodiment except that the light emitted from the microLED 10 is converted into collimated light.

In this configuration, for example, the pixel shifter unit 20 is a shift mechanism 20-1 as illustrated in FIG. 11. When the shift mechanism 20-1 is driven, a cycle of driving the microLED 10, being stationary with respect to the optical system 30, in the uniaxial direction or the biaxial direction is repeated. When the shift mechanism 20-1 is driven, the cycle of driving the microLED 10 in the uniaxial direction or the biaxial direction with respect to the optical system 30 is repeated, the light of pixel having the first image resolution emitted from the microLED 10 is incident on the optical system 30 while being repeatedly subjected to the sub-pixel shift, and the collimated light is emitted.

This configuration is modified to cause the microLED 10 to shift; but, this configuration enables zero shift deviation among the R, G, and B colors because the R, G, and B light rays on the same optical axis is shifted directly, and the each light ray of the image having the first image resolution is incident on the optical system 30. Thus, the configuration of the first modification can reduce the influence of color deviation, more than the first embodiment, to almost zero.

(Second modification of embodiment)

A second modification describes a configuration in a case of using a liquid crystal shifter as the pixel shifter unit 20. FIG. 12 is a diagram illustrating an example of the configuration of the display system 1 according to the second modification. As illustrated in FIG. 12, in the display system 1 according to the second modification, the microLED 10, a polarizer 20-2, liquid crystal 20-3, and the optical system 30 are arranged in this order. The liquid crystal shifter includes the liquid crystal 20-3 and the polarizer 20-2 that is an element for rotating a polarization direction.

Light incident on the liquid crystal 20-3 from the microLED 10 is polarized in a predetermined direction. In a case in which the microLED 10 does not include a polarizing unit, the polarizer 20-2 such as a polarizing plate is arranged between the microLED 10 and the liquid crystal 20-3. Additionally, the polarizer 20-2 is arranged so that the polarization direction of the polarizer 20-2 is perpendicular to an orientation direction of the liquid crystal 20-3.

When a predetermined voltage is applied to the liquid crystal 20-3 and a liquid crystal director is inclined with respect to the substrate, an optical path of light incident on the liquid crystal 20-3 is shifted in a direction of the liquid crystal director.

Accordingly, the liquid crystal director is inclined at a predetermined angle when the liquid crystal 20-3 is driven by voltage, and the light emitted from the liquid crystal 20-3 is shifted. That is, the liquid crystal 20-3 functions as a pixel shifter, and enables doubling of the pixels.

As described above, also in the configuration according to the second modification, the liquid crystal 20-3 functions as the pixel shifter unit 20, so that the same effect as that of the embodiment can be obtained. Additionally, the liquid crystal is driven in the second modification, so that it is possible to largely reduce sound or vibration at the time when the pixel shifter unit 20 is driven.

(Third modification of embodiment)

A third modification of the embodiment describes a specific method of mounting a micro lens.

FIG. 13 is a cross-sectional view illustrating a configuration of the microLED 10 according to the third modification. As illustrated in FIG. 13, the microLED 10 has micro lenses 14 disposed on the first surfaces 100a of the sets of light emitting units. Specifically, the microLED 10 has the micro lenses 14 (1, 1) to 14 (m, n) corresponding to pixel groups 13 (1, 1) to 13 (m, n) , respectively. Each of the micro lenses 14 is also called an on-chip lens.

Among the plurality of pixel groups 13 (1, 1) to 13 (m, n) , the pixel group 13 (1, 1) is the pixel group 13 near a first maximum image-height position of the peripheral part, and has a central axis AX (1, 1) . The central axis AX (1, 1) substantially coincides with axes parallel to the Z-axis through the centers of light emitting surfaces of the pixel 12b (1, 1) , the pixel 12g (1, 1) , and the pixel 12r (1, 1) .

Among the plurality of micro lenses 14 (1, 1) to 14 (m, n) , the micro lens 14 (1, 1) is the micro lens 14 near a maximum image-height position of the center part, and has an optical axis OA (1, 1) . Compared to the central axis AX (1, 1) , the optical axis OA (1, 1) shifts in the +X direction and the +Y direction so as to be closer to the center. The direction of the shift means that an emission direction of light from the micro lens 14 (1, 1) to the optical system 30 is inclined from the +Z direction to the +X direction and the +Y direction.

Among the plurality of pixel groups 13 (1, 1) to 13 (m, n) , the pixel group 13 (j, k) is the pixel group 13 near the center and has a central axis AX (j, k) . "j" is an integer number that is larger than 1 and smaller than m. "k" is an integer number that is larger than 1 and smaller than n. The central axis AX (j, k) substantially coincides with axes parallel to the Z-axis through the centers of the light emitting surfaces of the pixel 12b (j, k) , the pixel 12g (j, k) , and the pixel 12r (j, k) .

Among the plurality of micro lenses 14 (1, 1) to 14 (m, n) , the micro lens 14 (j, k) is the micro lens 14 near the center and has an optical axis OA (j, k) . The optical axis OA (j, k) substantially coincides with the central axis AX (j, k) .

Among the plurality of pixel groups 13 (1, 1) to 13 (m, n) , the pixel group 13 (m, n) is the pixel group 13 near a second maximum image-height position of the peripheral part and has a central axis AX (m, n) . With respect to the vicinity of the maximum image-height position of the center part, the vicinity of the first maximum image-height position and the vicinity of the second maximum image-height position are at positions of the peripheral part opposed to each other.

The central axis AX (m, n) substantially coincides with axes parallel to the Z-axis through the centers of the light emitting surfaces of the pixel 12b (m, n) , the pixel 12g (m, n) , and the pixel 12r (m, n) .

Among the plurality of micro lenses 14 (1, 1) to 14 (m, n) , the micro lens 14 (m, n) is the micro lens 14 near a maximum image-height position and has an optical axis OA (m, n) . Compared to the central axis AX (m, n) , the optical axis OA (m, n) shifts in the -X direction and the -Y direction so as to be closer to the center CP. The direction of the shift means that the emission direction of light from the micro lens 14 (m, n) to the optical system 30 is inclined from the +Z direction to the -X direction and the -Y direction.

As described above, in the microLED 10, a distance between the optical axis OA of the micro lens 14 and the central axis AX of the corresponding pixel group 13 is larger than a distance between the optical axis OA of any micro lens 14 closer to the center part and the central axis AX of the corresponding pixel group 13. As a result, the emission direction of light from the pixel group 13 can be inclined by the shifting of the micro lens 14 of the pixels in the peripheral part, conforming with the direction of light proceeding to the optical system 30 in accordance with the position of the pixel group 13, and thus the light emitted from the microLED 10 can be efficiently entered into the optical system 30.

(Application examples of embodiment and modifications)

FIG. 14 is a diagram illustrating an example of an AR glass to which the display system 1 is applied. As illustrated in FIG. 14, an AR glass 1a includes the microLED 10, the pixel shifter unit 20, the optical system 30, and a light guide plate 300 as an example of a light guide member.

The light guide plate 300 is arranged on the image side of the optical system 30. The optical system 30 is arranged between a side surface 31c of the light guide plate 300 and the first surface 100a of the microLED 10. The side surface 31c of the light guide plate 300 substantially coincides with the exit pupil surface of the optical system 30. The side surface 31c has a wedge shape in which the side surface inclines toward a back surface 31b as the side surface heads from the front surface 31a to the back surface 31b. By employing such a wedge shape, the light collimated by the optical system 30 can be incident into the light guide plate 300 to be guided by the total reflection. Note that, instead of a wedge shape, by arranging a diffractive optical element DOE, a holographic optical element HOE, or the like on the front surface 31a or the back surface 31b, for example, the light collimated by the optical system 30 may be incident to the DOE and HOE and make the DOE and HOE change an angle for guide so as to guide the light within the light guide plate 300 by the total reflection.

The AR glass 1a can transmit light from the outside world toward an eyeball 1000 of a user by using the light guide plate 300. Along with that, the AR glass 1a can convert the light from the microLED 10 into collimated light by using the optical system 30, and guide the collimated light toward the eyeball 1000 of the user by using the light guide plate 300. The collimated light injected from the side surface 31c of the light guide plate 300 proceeds through the light guide plate 300 while being reflected by the front surface 31a and the back surface 31b of the light guide plate 300. The diffractive optical element DOE is formed in a region indicated by a thick line on the front surface 31a of the light guide plate 300. The diffractive optical element DOE has a diffraction grating structure such as periodic unevenness, and is configured so that light having a predetermined wavelength injected by a predetermined angle among light rays proceeding through the light guide plate 300 is reflected toward the eyeball 1000. The light diffracted by the diffractive optical element DOE among the light rays proceeding through the light guide plate 300 may be guided toward the eyeball 1000 of the user. As a result, the user distant from the light guide plate 300 can visually recognize the AR image according to the image of the microLED 10 without chipping. Moreover, the light guide plate 300 can easily expand an image to cause the user to visually recognize the image as the AR image by receiving the image of the microLED 10 as the collimated light.

The configuration of the AR glass 1a described herein is merely an example, and the configuration may be appropriately modified. While being typically required to be lightweight and compact, the AR glass has been required to have high brightness and high image quality. In the AR glass 1a to which the present embodiment and modifications are applied, the sets of light emitting units 10a may be arranged on the microLED 10 with a small number of pixels, which results in low resolution. In such a case, high brightness can be obtained with low power consumption, so that there is no need to supply high electric power or to provide a heat radiation fin, and a compact size can be achieved. For example, a total weight is expected to be smaller than 100 g. Additionally, power consumption is expected to reduce to about 0.5 W.

Thus, due to the application to the AR glass, it is expected that full-color, high brightness, high resolution, and a high frame rate can be achieved at the same time in the AR glass.

Typically, when a display frame rate is 240 Hz, implementation is made so that a black frame is input to the entire display. Due to this, a shift rate can be reduced in the pixel shift by using a black display timing, so that a pixel shift frame rate becomes 120 Hz.

Generally speaking displays should be very small size and low power consumption under high resolution. Especially, high resolution such as 2k/4K needs very compact size display under very low power consumption. Thus, a microLED display with stacked structure is most suitable.

1) The microLED with stacked structure can have a larger pixel size which can realize lower power consumption than another type of microLED.

2) The microLED with stacked structure can use high precise micro lens array which can easily realize the same optical axis in an RGB light source.

3) The microLED with stacked structure can realize the most compact size under high resolution.

4) The microLED with stacked structure can realize large FOV (> 50 deg) and compact size collimated lens under low power consumption.

The microLED with stacked structure can implement many kind of pixel shift technology easily under a high frame rate, and can realize higher resolution such as 2K/4K under low power consumption and a high frame rate.

(Reasons)

1) Using only one pixel shift direction (same optical axis in RGB) , high resolution and low power consumption at microLED/Pixel shift simultaneously can be realized in "many kinds of pixel shift technologies" .

2) As the microLED with stacked structure has the same optical axis in RGB, the shifted beam position difference in RGB each pixel (color mixing problem) can be reduced easily, even though using many kinds of pixel shift technologies.

3) Even though the pixel shift technology is implemented, the total display size including the pixel shift can realize both high resolution and a compact size, because of compact size microLED using a stacked structure.

(Other effects of embodiment and modifications)

As microLED with stacked structure can realize high directivity in RGB light using a micro lens array, the pixel shifter can be set between the microLED and the collimated lens. The brightness loss and pixel shift difference in RGB light (color mixing) become very low.

As sensor shift allows a device moving from the sensor to the display to operate as a pixel shifter, that device can be used as a half pixel shifter (doubling resolution) and a 1/3 pixel shifter (tripling resolution) without complicated moving due to the same optical axis in RGB. In addition, as compared to a glass shifter, high image quality and high resolution can be obtained due to less difference for shift amount between a center position and a peripheral position in the display.

High brightness, high resolution, high image quality and low power consumption can be obtained under very compact size microLED + pixel shifter. The reasons are as follows.

1. Half resolution microLED can be used and it can realize a half size.

2. A large emitter size can be used and realize high brightness under low power consumption.

3. Color balance is not changed while the pixel shift because of the same axis in RGB light.

4. RGB optical shift does not occur by heat cycle and drop damage etc. It means a good pixel shifter can be obtained.

5. The microLED can realize a high frame rate such as 240 Hz. The pixel shift can be executed under 240 Hz.

The embodiment and modifications of the present invention have been described above. These embodiment and modifications are merely examples, and do not intend to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and can be variously omitted, replaced, or modified without departing from the gist of the invention. These embodiment and modifications are encompassed by the scope and the gist of the invention, and also encompassed by the invention described in CLAIMS and an equivalent thereof.

Reference Signs List

1 display system

10 microLED

20 pixel shifter unit

30 optical system

10a set of light emitting units

Claims

A display system comprising:

a micro Light Emission Diode (microLED) including a set of light emitting units of Red (R) , Green (G) , and Blue (B) colors, the set of light emitting units having a stacked structure;

a shifter configured to shift emitted light from the microLED; and

an optical system configured to convert the emitted light having passed through the shifter into collimated light.
The display system according to claim 1, wherein the microLED has the set of light emitting units of the R, G, and B colors on a surface of the microLED, each of the light emitting units being a pixel, and

light rays of the R, G, B colors in the pixels have the same optical axis.
The display system according to claim 2, wherein the microLED includes a protective film and a reflecting member on a side wall of each of the pixels.
The display system according to claim 2, wherein the light emitting units of the R, G, and B colors are formed as chips for each of the pixels.
The display system according to claim 4, wherein, in the microLED, an emitter diameter of the microLED chip is from about 1 μm to about 2 μm.
The display system according to claim 2, wherein

the set of light emitting units of the R, G, and B colors includes a first light emitting unit of a first color among the R, G, and B colors, a second light emitting unit of a second color among the R, G, and B colors, and a third light emitting unit of a third color among the R, G, and B colors,

the set of light emitting units of the R, G, and B colors has structure in which a light ray of the first light emitting unit transmits through the second light emitting unit, the light ray of the first light emitting unit and a light ray of the second light emitting unit transmit through the third light emitting unit, and

the light ray of the first light emitting unit the light ray of the second light emitting unit, and a light ray of the third light emitting unit emit from the third light emitting unit.
The display system according to claim 6, further comprising a control circuit configured to adjust an emission intensity of each of the first, second, and third light emitting units in accordance with a color to be displayed.
The display system according to any one of claims 1 to 7, wherein

the shifter is configured to shift light incident on glass by structure for tilting the glass in uniaxial or biaxial directions, and

the shifter is arranged between the microLED and the optical system on an optical path of the emitted light emitted by the microLED.
The display system according to any one of claims 1 to 7, wherein the microLED is arranged on the shifter, and shifts the emitted light from the microLED by sub-pixel shift of the microLED itself.
The display system according to any one of claims 1 to 7, wherein the shifter comprises a combination of a polarizer and a liquid crystal shifter.
The display system according to any one of claims 1 to 7, wherein a micro lens is arranged on a light emitting surface of the microLED, and the micro lens is shifted in a peripheral pixel.
The display system according to any one of claims 1 to 7, further comprising:

a light guide member configured to guide light emitted from the optical system and light from an outside world toward an eyeball of a user.
The display system according to any one of claims 1 to 7, wherein the shifter at least doubles or triples the pixels.
The display system according to any one of claims 1 to 7, wherein a resolution of a low-resolution image of the microLED is increased by pixel shift of the shifter to 2K or 4K, at least.
The display system according to claim 1, wherein the optical system is a lens group including a plurality of lenses, and the plurality of lenses have different cross-sectional shapes including an optical axis of the optical system.
The display system according to claim 15, wherein the number of lenses included in the lens group is 5 or more and 8 or less.
The display system according to claim 15, wherein the lens group includes a convex lens on an image side.
The display system according to claim 15, wherein the lens group includes a meniscus lens or a concave lens on an object side.
The display system according to claim 15, wherein, a diameter of an object-side lens included in the lens group is larger than a diameter of an image-side lens included in the lens group.
The display system according to claim 12, wherein the light guide member is configured to allow the light from the outside world to transmit toward the eyeball of the user and allow the light emitted from the optical system to be guided toward the eyeball of the user.