OPTICAL EXPANSION WAVEGUIDE

Abstract

An optical expansion waveguide is disclosed that may comprise a first waveguide substrate (1) and a second waveguide substrate (2). The first waveguide substrate (1) allows the light entering the first waveguide substrate to expand in a first dimension direction, and the first waveguide substrate (1) comprises a plurality of first reflecting surfaces (101) arranged in sequence. The second waveguide substrate (2) allows the light entering the second waveguide substrate to expand in a second dimension direction, and the second waveguide substrate (2) comprises a plurality of second reflecting surfaces (201) arranged in sequence. At least one of the first reflecting surface (101) and the second reflecting surface (201) is at least partially curved so as to change an emission angle of light, such that the image distance of the image formed by the light emitted by the second waveguide substrate (2) meets the preset requirement.

Description

The present application claims the priority to Chinese Patent Application No. 202210065286.6, titled “OPTICAL EXPANSION WAVEGUIDE”, filed with the China National Intellectual Property Administration on Jan. 20, 2022, the entire disclosure of which is incorporated herein by reference.

FIELD

The present disclosure relates to the field of optical devices, and in particular to an optical expansion waveguide.

BACKGROUND

Near-eye display is a technology field that attracts widespread attention nowadays, and its optical system includes a micro-display and an optical element. At present, there are many different optical solutions for near-eye display on the market.

In an array waveguide solution, a semi-transparent and semi-reflective optical surface is used to achieve light expansion and exit pupil, and according to the reflection law that an incident angle is equal to a reflection angle, there is no dispersion effect on three-primary-color incident light that constitute full-color display. Therefore, the resulting image can be guaranteed to have no obvious color deviation, which can meet most basic requirements of a display device and has obvious advantages in optimizing a design and beautifying an appearance of the head-mounted display.

However, due to the solution has a characteristic that an image is imaged at infinity, the display device applying this solution is suitable for people with a visual acuity of about 1.2, while the visual acuity of the general population (including with corrected vision) is about 1.0. Therefore, when using such a display device, a wearer cannot see a clear and good image, which causes great trouble to the wearer. In order to solve this problem, in a popular solution, an external device is used to assist in adjustment, which not only increases a volume and weight of the display device, but also reduces comfort and feeling experience of a user.

SUMMARY

In view of this, an object of the present disclosure is to provide an optical expansion waveguide, which can be applied to an optical display device to change an image distance of a resulting image, can be applicable for a user with an abnormal vision, and has a thin and light structure.

To achieve the above object, the present disclosure provides the following technical solutions.

An optical expansion waveguide includes a first waveguide substrate and a second waveguide substrate, where,

• • the first waveguide substrate is configured for expanding a light beam entering the first waveguide substrate in a first dimensional direction, and the first waveguide substrate includes a plurality of first reflective surfaces arranged in sequence, the plurality of first reflective surfaces being configured for at least partially reflecting light incident on the first reflective surfaces, such that at least part of the light is coupled into the second waveguide substrate; and
  • the second waveguide substrate is configured for expanding a light beam entering the second waveguide substrate in a second dimensional direction, and the second waveguide substrate includes a plurality of second reflective surfaces arranged in sequence, the plurality of second reflective surfaces being configured for at least partially reflecting light incident on the second reflective surfaces, such that at least part of the light is emitted out of the second waveguide substrate; and
  • where at least one of the first reflective surfaces and the second reflective surfaces is at least partially curved, such that an image distance of an image formed by emitted light from the second waveguide substrate meets a preset requirement.

Preferably, a first reflective surface is at least partially curved, and enables light reflected by the first reflective surface to diverge; or

• • a second reflective surface is at least partially curved, and enables light reflected from the second reflective surface to diverge

Preferably, each of the first reflective surfaces forms an inclination angle with respect to the first dimensional direction.

Preferably, the first waveguide substrate further includes at least a first set of opposite surfaces, and light entering the first waveguide substrate is reflected on each surface of the first set of opposite surfaces to propagate forward.

Preferably, at least one surface of the first set of opposite surfaces is at least partially curved, to change an incident angle of reflected light from the surface when incident on the first reflective surfaces, so as to assist in achieving that the image distance of the image formed by the light emitted from the second waveguide substrate meets the preset requirement.

Preferably, at least one surface of the first set of opposite surfaces enables reflected light from the surface to diverge.

Preferably, the second waveguide substrate further includes at least a third set of opposite surfaces, and light entering the second waveguide substrate is reflected on each surface of the third set of opposite surfaces to propagate forward.

Preferably, each of the second reflective surfaces forms an inclination angle with respect to any surface of the third set of opposite surfaces.

Preferably, an inclination angle formed by a second reflective surface with respect to a surface, serving as an out-coupling surface, in the third set of opposite surfaces is greater than 0° and less than or equal to 45°, where the inclination angle of the second reflective surface with respect to the surface is positive when the second reflective surface rotates counterclockwise with respect to this surface.

Preferably, at least one surface of the third set of opposite surfaces is at least partially curved, to change an incident angle of reflected light from the surface when incident on the second reflective surfaces, so as to assist in achieving that the image distance of the image formed by the light emitted from the second waveguide substrate meets the preset requirement.

Preferably, at least one surface of the third set of opposite surfaces enables reflected light from the surface to diverge.

Preferably, the first waveguide substrate further includes a first out-coupling surface through which the reflected light of the first reflective surface is emitted out of the first waveguide substrate, and the second waveguide substrate further includes a second in-coupling surface through which the emitted light from the first waveguide substrate enters the second waveguide substrate, where the first out-coupling surface and the second in-coupling surface are optically coaxial.

Preferably, the first out-coupling surface is a plane, an inclined plane, a serrated surface, or a curved surface, and the second in-coupling surface is a plane, an inclined plane, a serrated surface, or a curved surface.

Preferably, the first waveguide substrate is placed in front of, behind or above the second waveguide substrate.

It can be seen from the above technical solutions that an optical expansion waveguide provided by the present disclosure includes a first waveguide substrate and a second waveguide substrate, where the first waveguide substrate is configured for expanding a light beam entering the first waveguide substrate in a first dimensional direction, and the first waveguide substrate includes a plurality of first reflective surfaces arranged in sequence, the plurality of first reflective surfaces being configured for at least partially reflecting light incident on the first reflective surfaces, such that at least part of the light is coupled into the second waveguide substrate; and the second waveguide substrate is configured for expanding a light beam entering the second waveguide substrate in a second dimensional direction, and the second waveguide substrate includes a plurality of second reflective surfaces arranged in sequence, the plurality of second reflective surfaces being configured for at least partially reflecting light incident on the second reflective surfaces, such that at least part of the light is emitted out of the second waveguide substrate. At least one of the first reflective surfaces and the second reflective surfaces is at least partially curved to change an emission angle of the light through the first reflective surfaces and/or the second reflective surfaces, such that an image distance of an image formed by the light emitted from the second waveguide substrate meets a preset requirement. Therefore, the optical expansion waveguide of the present disclosure can be applied to an optical display device to change the image distance of the resulting image, can be applicable for the user with an abnormal vision, and has a light and thin structure.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solutions in embodiments of the present disclosure or the existing technologies, the accompanying drawings for use in description of the embodiments or the existing technologies will be briefly introduced below. Apparently, the accompanying drawings described below are only some embodiments of the present disclosure, and other drawings may be obtained by ordinary technicians in this field based on these drawings without creative effort.

FIG. 1 is a schematic diagram of light propagation on a first reflective surface in an embodiment of the present disclosure;

FIG. 2-1 is a left view of an optical expansion waveguide shown in FIG. 2-2;

FIG. 2-2 is a front view of an optical expansion waveguide provided in an embodiment of the present disclosure;

FIG. 3 is a schematic diagram of light propagation in a first waveguide substrate in an embodiment of the present disclosure;

FIG. 4 is a schematic diagram of light propagation on a surface of a first set of opposite surfaces and a first reflective surface in an embodiment of the present disclosure;

FIG. 5 is a schematic diagram of light propagation in a second waveguide substrate in an embodiment of the present disclosure;

FIG. 6 is a schematic diagram in which an effective aperture is formed for light propagation in the second waveguide body in an embodiment of the present disclosure;

FIG. 7 is a schematic diagram of structural parameters of a reflective surface and a surface, each of which is a curved surface, in any waveguide substrate in an embodiment of the present disclosure;

FIG. 8-1 is a schematic diagram of a curved surface used in any of the opposite surfaces of any waveguide substrate in an embodiment of the present disclosure;

FIG. 8-2 is a schematic diagram of another curved surface used in any of the opposite surfaces of any waveguide substrate in an embodiment of the present disclosure;

FIGS. 9-1 to 9-4 are schematic diagrams of four implementations of a first out-coupling surface of the first waveguide substrate and a second in-coupling surface of the second waveguide substrate in an embodiment of the present disclosure, respectively; and

FIGS. 10-1 to 10-3 are schematic diagrams of three implementations of arrangement positions of the first waveguide substrate and the second waveguide substrate in an embodiment of the present disclosure, respectively.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In order to enable a person skilled in the art to better understand the technical solutions in the present disclosure, the technical solutions in the embodiments of the present disclosure will be described clearly and completely in combination with the accompanying drawings in the embodiments of the present disclosure as below. Apparently, the described embodiments are only part of the embodiments of the present disclosure, not all of them. Based on the embodiments of the present disclosure, all other embodiments obtained by the ordinary person skilled in the art without creative effort should fall within the protection scope of the present disclosure.

An optical expansion waveguide is provided in the present embodiment, including a first waveguide substrate and a second waveguide substrate.

Here, the first waveguide substrate is configured for expanding a light beam entering the first waveguide substrate in a first dimensional direction, and the first waveguide substrate includes multiple first reflective surfaces arranged in sequence. The first reflective surfaces are configured for at least partially reflecting light incident on the first reflective surfaces, such that at least part of the light is coupled into the second waveguide substrate.

The second waveguide substrate is configured to expand a light beam entering the second waveguide substrate in a second dimensional direction, and the second waveguide substrate includes multiple second reflective surfaces arranged in sequence. The second reflective surfaces are configured for at least partially reflecting light incident on the second reflective surfaces, such that at least part of the light is emitted out of the second waveguide substrate.

At least one of the first reflective surfaces and the second reflective surfaces is at least partially curved, such that an image distance of an image formed by emitted light from the second waveguide substrate meets a preset requirement.

The light beam entering the first waveguide substrate propagates through the first waveguide substrate, and each part of the light beam is respectively incident on each of the first reflective surfaces. Each first reflective surface enables at least part of incident light on itself to be reflected, such that at least part of the light is coupled into the second waveguide substrate, and the light beam entering the first waveguide substrate is expanded in the first dimensional direction.

The light beam entering the second waveguide substrate propagates through the second waveguide substrate, and each part of the light beam is respectively incident on each of the second reflective surfaces. Each second reflective surface enables at least part of incident light on itself to be reflected, such that at least part of the light is emitted out of the second waveguide substrate, and the light beam entering the second waveguide substrate is expanded in the second dimensional direction.

The image distance of the image formed by the light emitted from the second waveguide substrate refers to a distance from a virtual image corresponding to the image formed by the light emitted by the second waveguide substrate to a viewing position.

Here, if a first reflective surface of the first waveguide substrate is at least partially curved, a reflective angle of the light on the first reflective surface may be changed due to a curved surface, an incident angle of light when coupled into the second waveguide substrate may be changed, thus enabling an emission angle of the light when emitted from the second waveguide substrate to be changed. If a second reflective surface of the second waveguide substrate is at least partially curved, a reflective angle of light on the second reflective surface may be changed due to a curved surface, and an emission angle of light when emitted from the second waveguide substrate can be changed. Therefore, by setting at least one of the first reflective surfaces and the second reflective surfaces to be a curved surface, the present optical expansion waveguide can change the emission angle of the emitted light, and change the image distance of the image formed by the emitted light of the present optical expansion waveguide, thus obtaining a resulting image with an image distance meeting the preset requirement.

Therefore, by applying the optical expansion waveguide of the present embodiment to an optical display device, it is possible to change the image distance of the resulting image, to be applicable to the user with an abnormal vision, so that the user with an abnormal vision can see a clear and good image. Moreover, the optical expansion waveguide structure in the present embodiment is thin and light.

If a first reflective surface of the first waveguide substrate is at least partially curved, in the present embodiment, a shape of the curved surface and an area size of the curved surface included in the first reflective surface are not specifically limited, as long as the emission angle of the light emitted from the second waveguide substrate can be changed such that the image distance of the image formed by the light emitted from the second waveguide substrate meets the preset requirement. The curved surface included in the first reflective surface may be a curved surface with a fixed curvature or a free-form curved surface. Optionally, if the first reflective surface is a curved surface, it may cause the light reflected by the first reflective surface to diverge or converge.

If a second reflective surface of the second waveguide substrate is at least partially curved, in the present embodiment, a shape of the curved surface and an area size of the curved surface area included in the second reflective surface are not specifically limited, as long as the emission angle of the light emitted from the second waveguide substrate can be changed such that the image distance of the image formed by the light emitted from the second waveguide substrate meets the preset requirement. The curved surface included in the second reflective surface may be a curved surface with a fixed curvature or a free-form curved surface. Optionally, if the second reflective surface is a curved surface, it can cause the light reflected by the second reflective surface to diverge or converge.

For example, reference may be made to FIG. 1. FIG. 1 is a schematic diagram of light propagation on a first reflective surface in an embodiment. As shown in the figure, light L1 and light L2 reflected by a surface 100 of a first waveguide substrate are respectively incident on a first reflective surface 101, and the first reflective surface 101 is a curved surface. Reflected lights L1′ and L2′ are formed through the first reflective surface 101. Compared with the reflected lights L1″ and L2″, formed through a reference plane 102 of the first reflective surface 101, of the lights L1 and L2, the reflected lights L1′ and L2′ become divergent. This reduces the image distance of the image formed by the light emitted from the second waveguide substrate. For the user with an abnormal vision, the resulting image can be converged on the retina of the user with an abnormal vision.

Based on FIG. 1, the above-mentioned light propagation on the first reflective surface of the first waveguide substrate is taken as an example to illustrate a principle in which a curved surface is used as the first reflective surface to change the image distance. Similarly, for the second waveguide substrate, a change of the image distance is achieved by a second reflective surface thereof provided as a curved surface based on the above principle.

In the first waveguide substrate, an inclination angle is formed by each of first reflective surfaces with respect to the first dimension direction. The inclination angle being formed by the first reflective surface with respect to the first dimensional direction refers to the chord of the first reflective surface is not parallel and not perpendicular to the first dimensional direction. Correspondingly, the inclination angle formed by the first reflective surface with respect to the first dimensional direction refers to an angle between the chord of the first reflective surface and the first dimensional direction. When the light propagating through the first waveguide substrate is incident on the first reflective surface, part of the light energy is transmitted through the first reflective surface and continues to propagate, and part of the light energy is reflected and coupled into the second waveguide substrate.

In this embodiment, a degree of the inclination angle formed by each first reflective surface with respect to the first dimensional direction is not limited, as long as, when the light propagating in the first waveguide substrate is incident on the first reflective surface, at least part of the light is reflected and coupled into the second waveguide substrate. In practical applications, it can be set according to a size of the first waveguide substrate, a size of the second waveguide substrate, and expansion requirements for the light in the first dimensional direction. It is preferred to provide the optical expansion waveguide with a thin and light structure while meeting the expansion requirements for the light.

A projection surface of the first reflective surface on a plane parallel to the first dimensional direction determines an aperture of the emitted light of the optical expansion waveguide in the first dimensional direction, where the plane parallel to the first dimensional direction is located at a side, from which the reflected light is emitted, of the first reflective surface. By applying the optical expansion waveguide in an optical display device, the aperture of the outgoing light of the optical expansion waveguide in the first dimensional direction is required to ensure that an image from an image source can be fully expanded, that is, the image formed by the emitted light of the optical expansion waveguide contains complete information of the image in the first dimensional direction.

The first waveguide substrate further includes at least a first set of opposite surfaces, and the light entering the first waveguide substrate is reflected on each surface of the first set of opposite surfaces to propagate forward. Specifically, the light incident on each surface of the first set of opposite surfaces meets the total reflection condition. Surfaces of the first set of opposite surfaces may be parallel or non-parallel to each other, as long as the light can be reflected on each surface of the first set of opposite surfaces to propagate forward.

Preferably, the first waveguide substrate may further include a second set of opposite surfaces, where the second set of opposite surfaces and the first set of opposite surfaces form a closed section, and the light entering the first waveguide substrate is reflected on each surface of the first set of opposite surfaces and the second set of opposite surfaces to propagate forward. Specifically, light incident on each surface of the second set of opposite surfaces meets the total reflection condition. Surfaces of the second set of opposite surfaces may be parallel to each other or may not be parallel, as long as the light can be reflected on each surface of the second set of opposite surfaces to propagate forward.

For example, reference may be made to FIGS. 2-1, 2-2 and 3. FIG. 2-1 is a left view of the optical expansion waveguide as shown, FIG. 2-2 is a front view of the optical expansion waveguide provided in an embodiment, and FIG. 3 is a schematic diagram of the light propagation in the first waveguide substrate in an embodiment. As shown in the figures, the light entering the first waveguide substrate 1 will be reflected on each surface of four surfaces 1-A, 1-B, 1-C and 1-D of the first waveguide substrate 1 and propagated forward, as shown in a cross section formed by these four surfaces. Upon reaching the first reflective surface 101 during the propagation, a part of the light energy is reflected at a certain energy ratio, and then coupled into the second waveguide substrate 2.

In the first waveguide substrate 1 shown in FIG. 3, illustration is made by taking a case in which surfaces of the first set of opposite surfaces, i.e., 1-A and 1-B, are parallel to each other and surfaces of the second set of opposite surfaces, i.e., 1-C and 1-D, are parallel to each other as an example. It can be understood that FIG. 3 is only an example. In other embodiments, the surfaces of the first set of opposite surfaces may not be parallel, and the surfaces of the second set of opposite surfaces may not be parallel.

In a preferred embodiment, at least one surface of the first set of opposite surfaces is at least partially curved, so as to change an incident angle of the reflected light on the surface when incident on the first reflective surfaces, to assist in achieving that the image distance of the image formed by the light emitted from the second waveguide substrate meets the preset requirement. If at least one surface of the first set of opposite surfaces is at least partially curved, a reflective angle of the light obtained through the surface may be changed, and an incident angle of the reflected light from the surface when incident on the first reflective surfaces may be changed, thereby assisting in changing the image distance of the image formed by the light emitted from the present optical expansion waveguide.

In the present embodiment, a shape of the curved surface and an area size of the curved surface included in any surface of the first set of opposite surfaces are not specifically limited, as long as the emission angle of the light emitted from the second waveguide substrate can be changed such that the image distance of the image formed by the light emitted from the second waveguide substrate meets the preset requirement. The curved surface included in any surface of the first set of opposite surfaces may be a curved surface with a fixed curvature or a free-form curved surface. Optionally, the curved surface included in any surface of the first set of opposite surfaces may cause the reflected light of the surface to diverge or converge.

For example, reference may be made to FIG. 4. FIG. 4 is a schematic diagram of light propagation on a surface of a first set of opposite surfaces and a first reflective surface in an embodiment. As shown in the figure, a surface 100 is any surface of the first set of opposite surfaces of the first waveguide substrate 1, and the surface 100 is a curved surface (its reference plane is surface 103), so that the reflected lights of incident lights L3 and L4 on the surface 100 become divergent, the reflected lights L3′ and L4′ obtained after lights being reflected by the first reflective surface 101 become divergent, and an image distance of an image formed by the light emitted from the second waveguide substrate 2 is finally reduced.

The second waveguide substrate further includes at least a third set of opposite surfaces, and light entering the second waveguide substrate is reflected on each surface of the third set of opposite surfaces to propagate forward. Specifically, the light incident on each surface of the third set of opposite surfaces meets the total reflection condition. Surfaces of the third set of opposite surfaces may be parallel or non-parallel to each other, as long as the light can be reflected by each surface of the third set of opposite surfaces to propagate forward.

Optionally, each of the second reflective surfaces forms an inclination angle with respect to any surface of the third set of opposite surfaces. If an inclination angle is formed by a second reflective surface with respect to a surface, it means that the chord of the second reflective surface is not parallel and not perpendicular to the surface, and correspondingly, the inclination angle formed by the second reflective surface with respect to the surface refers to an angle between the chord of the second reflective surface and the surface. If a surface is a curved surface, an inclination angle of a second reflective surface with respect to the surface refers to an angle between the chord of the second reflective surface and the chord of the surface. When the light propagating through the second waveguide substrate is incident on the second reflective surface, part of the light energy is transmitted through the second reflective surface and continues to propagate, and part of the light energy is reflected and emitted out of the second waveguide substrate.

For example, reference may be made to FIGS. 2-1, 2-2 and 5. FIG. 5 is a schematic diagram of the light propagation of the second waveguide substrate in an embodiment. As shown in the figures, the light coupled into the second waveguide substrate 2 from the first waveguide substrate 1 may be reflected on the surfaces 2-A and 2-B of the second waveguide substrate 2 to propagate forward. When light reaches the second reflective surfaces 201 during the propagation, part of the light energy is reflected at a certain energy ratio, such that part of the light is emitted out of the second waveguide substrate 2.

In the present embodiment, a degree of an inclination angle of each of the second reflective surfaces with respect to any surface of the third set of opposite surfaces is not limited, as long as it is possible to achieve that when the light propagating in the second waveguide substrate is incident on the second reflective surface, at least part of the light is reflected and emitted out of the second waveguide substrate. In practical applications, it may be set according to the size of the first waveguide substrate, the size of the second waveguide substrate, and the expansion requirements for the light in the second dimensional direction.

For example, reference may be made to FIG. 6, which is a schematic diagram of forming an effective aperture by the light propagation in the second waveguide substrate in an embodiment. The light propagating through the second waveguide substrate 2 is reflected when reaching each second reflective surface S1, S2, S3, S4 and S5, so that at least part of the light is emitted out of the second waveguide substrate 2. A total projection surface S of the second reflective surface S1, S2, S3, S4 and S5 on the surface 2-A determines the effective aperture of the optical expansion waveguide. When applied to an optical display device, the effective aperture of the optical expansion waveguide is required to ensure that an image from an image source may be fully expanded, that is, the image formed by the emitted light of the optical expansion waveguide contains complete information of the image in the first and second dimensional directions.

Preferably, an inclination angle of the second reflective surface with respect to a surface, serving as an out-coupling surface, in the third set of opposite surfaces is greater than 0° and less than or equal to 45°, which may be expressed as 0°<β≤45°, where, the inclination angle of the second reflective surface with respect to the surface is positive when the second reflective surface rotates counterclockwise with respect to this surface. The surface, serving as the out-coupling surface, in the third set of opposite surfaces refers to a surface through which the light reflected by the second reflective surface is emitted out of the second waveguide substrate. In this way, the light is expanded through the second reflective surface, while a thickness of the second waveguide substrate may be reduced, and the entire waveguide may be thin and light.

In a preferred embodiment, at least one surface of the third set of opposite surfaces is at least partially curved, to change an incident angle of the reflected light of the surface when incident on the second reflective surfaces, so as to assist in achieving that an image distance of an image formed by the light emitted from the second waveguide substrate meets the preset requirement. At least one surface of the third set of opposite surfaces is at least partially curved, a reflective angle of the light may be changed through the surface, and an incident angle of the reflected light from the surface when incident on the second reflective surfaces may be changed, thereby achieving to change the image distance of the image formed by the light exiting the optical expansion waveguide in combination with a first reflective surface provided as a curved surface or a second reflective surface provided as a curved surface.

In the present embodiment, a shape of the curved surface and an area size of the curved surface included in any surface of the third set of opposite surfaces are not specifically limited, as long as an emission angle of the light emitted from the second waveguide substrate can be changed such that the image distance formed by the light emitted from the second waveguide substrate meets the preset requirement. The curved surface included in any surface of the third set of opposite surfaces may be a curved surface with a fixed curvature or a free-form curved surface. Optionally, the curved surface included in any surface of the third set of opposite surfaces can cause the light reflected by the surface to diverge or converge.

When the optical expansion waveguide is applied to an optical display device during optical design, in order that resolution, contrast, clarity, or the like of a resulting image meet requirements, if a first reflective surface of the first waveguide substrate is a curved surface and at least one surface of the first set of opposite surfaces is a curved surface, curved surface parameters of the first reflective surface of the first waveguide substrate and any surface of the first set of opposite surfaces should satisfy a certain relationship. If a second reflective surface of the second waveguide substrate is a curved surface and at least one surface of the third set of opposite surfaces is a curved surface, curved surface parameters of the second reflective surface of the second waveguide substrate and any surface of the third set of opposite surfaces should satisfy a certain relationship. Reference may be made to FIG. 7, which is a schematic diagram of structural parameters of a reflective surface and a surface, each being a curved surface, in any waveguide substrate in an embodiment. The optical design is performed with reference to the collimated main axis beam emitted by an on-axis object point. When the main axis beam is vertically incident on an in-coupling surface of the waveguide substrate, a corresponding relationship between various parameters is as follows:

${\alpha }_{R2}={\alpha }_{R1}-{\beta }_o;$ ${\alpha }_{R1}=\pi /2-{\beta }_i;$

• • where β_i represents an angle between the in-coupling surface and a horizontal reference plane of a surface of the waveguide substrate, β_o represents an angle between a plane where the chord of the curved reflective surface is located and the horizontal reference plane of the surface of the waveguide substrate, α_R1 represents an angle between main-axis light and a normal of the horizontal reference plane of the surface of the waveguide substrate, and α_R2 represents an angle between the main-axis light and a normal of a reference plane of the out-coupling surface; and

$h_s=h_r=N*\left(\lambda /2\right);$ $H_r=H/\left(\sin \left({\beta }_o\right)\right);$ $H_s=H/\left(\tan \left({\beta }_o\right)\right);$

• • where h_s represents a partially-curved surface sag of a curved waveguide corresponding to a single reflective surface, H_s represents a curved-part chord length of the curved waveguide corresponding to the single reflective surface, h_r represents a partially-curved surface sag corresponding to the curved reflective surface itself, H_r represents a curved-part chord length corresponding to the curved reflective surface itself, N is F-number for adjustment according to an image distance, and λ is a reference wavelength selected during optical design. According to adjustment requirements of a specific image distance, calculation can be made based on a corresponding sag and chord length, and thus it is possible to obtain a required curved-part curvature of the curved reflective surface and a required curved-part curvature radius of the curved surface of the waveguide substrate.

For example, reference may be made to FIGS. 8-1 and 8-2, which are schematic diagrams of curved surfaces used in any surface of the opposite surfaces of any waveguide substrate in the present embodiment respectively. As shown in the figures, any surface of the opposite surfaces of the waveguide substrate may be a free-form surface, a concave surface or a convex surface.

Further, the first waveguide substrate further includes a first out-coupling surface through which the reflected light of the first reflective surface is emitted out of the first waveguide substrate, and the second waveguide substrate further includes a second in-coupling surface through which the emitted light from the first waveguide substrate enters the second waveguide substrate. The first out-coupling surface and the second in-coupling surface are optically coaxial. The first out-coupling surface and the second in-coupling surface being optically coaxial means that an optical axis of a part of the first out-coupling surface and an optical axis of a corresponding part of the second in-coupling surface are parallel.

In the present embodiment, a shape of the first out-coupling surface of the first waveguide substrate is not limited, and a shape of the second in-coupling surface of the second waveguide substrate is not limited, as long as the first out-coupling surface and the second in-coupling surface are optically coaxial. The first out-coupling surface may be, but not limited to, a plane, an inclined plane, a serrated surface, or a curved surface, and the second in-coupling surface may be, but not limited to, a plane, an inclined plane, a serrated surface, or a curved surface. For example, reference may be made to FIGS. 9-1 to 9-4, which show four implementations of the first out-coupling surface of the first waveguide substrate and the second in-coupling surface of the second waveguide substrate in the present embodiment, respectively.

In the present embodiment, a relative position of the first waveguide substrate and the second waveguide substrate is not limited, as long as the light emitted from the first waveguide substrate for in-coupling can enter the second waveguide substrate. For example, reference may be made to FIGS. 10-1 to 10-3, which show three implementations of arrangement positions of the first waveguide substrate and the second waveguide substrate of the present embodiment, respectively. As shown in the figures, the first waveguide substrate 1 may be placed in front of, behind or above the second waveguide substrate 2.

The optical expansion waveguide of the present embodiment may be applied to a near-eye display device, such as a head-mounted device, which can change the image distance of the resulting image, be applicable for the user with an abnormal vision, and has a thin and light structure, which improves the comfort and feeling experience of the user.

An optical expansion waveguide provided by the present disclosure has been introduced in details as above. Specific examples are used herein to set forth the principles and implementations of the present disclosure, and the description of the above embodiments is only used to help in understanding the method and core idea of the present disclosure. It should be pointed out that, for ordinary technicians in this field, without departing from the principles of the present disclosure, several improvements and modifications can be made to the present disclosure, and these improvements and modifications also fall within the claimed protection scope of the present disclosure.

Claims

1. An optical expansion waveguide, comprising a first waveguide substrate and a second waveguide substrate, wherein, the first waveguide substrate is configured for expanding a light beam entering the first waveguide substrate in a first dimensional direction, and the first waveguide substrate comprises a plurality of first reflective surfaces arranged in sequence, the plurality of first reflective surfaces being configured for at least partially reflecting light incident on the first reflective surfaces, such that at least part of the light is coupled into the second waveguide substrate; andthe second waveguide substrate is configured for expanding a light beam entering the second waveguide substrate in a second dimensional direction, and the second waveguide substrate comprises a plurality of second reflective surfaces arranged in sequence, the plurality of second reflective surfaces being configured for at least partially reflecting light incident on the second reflective surfaces, such that at least part of the light is emitted out of the second waveguide substrate, andwherein at least one of the first reflective surfaces and the second reflective surfaces is at least partially curved, such that an image distance of an image formed by emitted light from the second waveguide substrate meets a preset requirement.

2. The optical expansion waveguide according to claim 1, wherein a first reflective surface is at least partially curved, and enables light reflected by the first reflective surface to diverge; or a second reflective surface is at least partially curved, and enables light reflected from the second reflective surface to diverge.

3. The optical expansion waveguide according to claim 1, wherein each of the first reflective surfaces forms an inclination angle with respect to the first dimensional direction.

4. The optical expansion waveguide according to claim 1, wherein the first waveguide substrate further comprises at least a first set of opposite surfaces, and light entering the first waveguide substrate is reflected on each surface of the first set of opposite surfaces to propagate forward.

5. The optical expansion waveguide according to claim 4, wherein at least one surface of the first set of opposite surfaces is at least partially curved, to change an incident angle of reflected light from the surface when incident on the first reflective surfaces, so as to assist in achieving that the image distance of the image formed by the light emitted from the second waveguide substrate meets the preset requirement.

6. The optical expansion waveguide according to claim 5, wherein at least one surface of the first set of opposite surfaces enables reflected light from the surface to diverge.

7. The optical expansion waveguide according to claim 1, wherein the second waveguide substrate further comprises at least a third set of opposite surfaces, and light entering the second waveguide substrate is reflected on each surface of the third set of opposite surfaces to propagate forward.

8. The optical expansion waveguide according to claim 7, wherein each of the second reflective surfaces forms an inclination angle with respect to any surface of the third set of opposite surfaces.

9. The optical expansion waveguide according to claim 8, wherein an inclination angle formed by a second reflective surface with respect to a surface, serving as an out-coupling surface, in the third set of opposite surfaces is greater than 0° and less than or equal to 45°, wherein the inclination angle of the second reflective surface with respect to the surface is positive when the second reflective surface rotates counterclockwise with respect to this surface.

10. The optical expansion waveguide according to claim 7, wherein at least one surface of the third set of opposite surfaces is at least partially curved, to change an incident angle of reflected light from the surface when incident on the second reflective surfaces, so as to assist in achieving that the image distance of the image formed by the light emitted from the second waveguide substrate meets the preset requirement.

11. The optical expansion waveguide according to claim 10, wherein at least one surface of the third set of opposite surfaces enables reflected light from the surface to diverge.

12. The optical expansion waveguide according to claims 1, wherein the first waveguide substrate further comprises a first out-coupling surface through which the reflected light of the first reflective surface is emitted out of the first waveguide substrate, and the second waveguide substrate further comprises a second in-coupling surface through which the emitted light from the first waveguide substrate enters the second waveguide substrate, wherein the first out-coupling surface and the second in-coupling surface are optically coaxial.

13. The optical expansion waveguide according to claim 12, wherein the first out-coupling surface is a plane, an inclined plane, a serrated surface, or a curved surface, and the second in-coupling surface is a plane, an inclined plane, a serrated surface, or a curved surface.

14. The optical expansion waveguide according to claim 1, wherein the first waveguide substrate is placed in front of, behind or above the second waveguide substrate.