Patent Description:
VR (Virtual Reality) technology is a computer simulation system that can create and experience a virtual world. It uses a computer to generate a simulation environment, and enables users to immerse in the simulation environment by interactive three-dimensional dynamic visualization with multi-source information fusion and system simulation with the behavior of an entity. With the development of technology, VR head-mounted display devices have been widely used in various fields, such as games, real estates, tourism and the like.

Currently, one type of VR head-mounted display device employs a screen used by a mobile phone as a display device, and the size of such a screen is generally larger, about <NUM>-<NUM> inches. In the existing head-mounted display devices, eyepiece optical systems that fit with such larger display devices generally have a long axial distance. Eyepieces with long axial distances fail to satisfy the demand for lighter and thinner head-mounted display devices. Prior art document D1 (<CIT>) discloses an ocular optical system, which includes a first lens element and a second lens element from an eye-side to a display-side in order along an optical axis; the first lens element and the second lens element each include an eye-side surface and a display-side surface; the eye-side surface of the first lens element has a convex portion in a vicinity of the optical axis; the second lens element has negative refracting power (see ABSTRACT of D1). Prior art document D2 (<CIT>) discloses a VR/MR optical system of dual-element convex-concave lens and VR/MR device, which comprises a lens group module formed by a first convex lens approaching a diaphragm and a second concave lens at a distance to the first convex lens; the first convex lens is a positive-focal-length lens and the second concave lens is a negative-focal-length; the surface, opposite to the diaphragm, of the first convex lens is a spherical surface and the radius of curvature is R1 that is larger than <NUM> and is smaller than <NUM>; the surface, opposite to the second concave lens, of the first convex lens is a dual-curve aspheric surface; the surface, opposite to the first convex lens, of the second concave lens is a spherical surface is a dual-curve aspheric surface; and the surface, opposite to the screen, of the second concave lens is a spherical surface and the radius of curvature is R2 that is larger than <NUM> and is smaller than <NUM> (see ABSTRACT of D2). Prior art document D3 (<CIT>) discloses an aberration corrected optical system for near-eye displays, where the optical system includes, from an image side to an object side, a first lens having a positive refractive power, a second lens having a positive refractive power, and a third lens having a negative refractive power (see ABSTRACT of D3).

There are provided an eyepiece and a head-mounted display device in various aspects of the present disclosure, which realizes an ultrathin eyepiece optical system and facilitates a miniaturized and lighter head-mounted display device.

There is provided in the present disclosure an eyepiece, including: a positive lens and a negative lens arranged sequentially and coaxially;.

Further optionally, the light emergent surface of the positive lens is a convex aspheric surface.

Further optionally, a refractive index n1 and a dispersion v1 of the positive lens satisfy the following conditions: <NUM><n1<<NUM>, <NUM><v1<<NUM>; a refractive index n2 and a dispersion v2 of the negative lens satisfy the following conditions: <NUM><n2<<NUM>, and <NUM><v2<<NUM>.

According to the claimed in invention, there is provided a head-mounted display device comprising an eyepiece as specified in appended claim <NUM>.

Optionally, a focal length F of the device satisfies the following condition: <NUM> TTL< F<<NUM> TTL.

Further optionally, a Fresnel curvature radius R of the light incident surface of the positive lens satisfies the following condition: -<NUM>. 6F<R<-<NUM>.

Further optionally, a focal length of the negative lens satisfies the following condition: -<NUM> <F2<<NUM>; and a focal length F1 of the positive lens is less than F.

In the eyepiece and head-mounted display device provided by the present disclosure, the eyepiece optical system is constituted by positive and negative lenses with simple structure. Herein, the light emergent surface of the positive lens is a convex surface, and the light incident surface is a planar Fresnel surface; the light incident surface of the negative lens is a concave surface, and the light emergent surface is a convex surface. In the case of ensuring good optical performance of the positive and negative lenses, such an eyepiece arrangement greatly reduces the thickness of the lenses, realizes an ultrathin eyepiece optical system and facilitates a miniaturized and lighter head-mounted display device.

To make the principles and advantages of the present disclosure more apparent, the technical solutions of the present disclosure will be described more clearly and fully hereinafter with reference to specific embodiments and corresponding drawings of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all of the embodiments.

<FIG> is a schematic diagram of a structure of an eyepiece according to an embodiment of the present disclosure. As shown in <FIG>, an optical system of the eyepiece includes:
a positive lens <NUM> and a negative lens <NUM> arranged sequentially and coaxially, a light incident surface Si1 of the positive lens <NUM> being close to the light emergent surface Se2 of the negative lens.

Herein, a light incident surface Si2 of the negative lens <NUM> is a concave surface, and a light emergent surface Se2 is a convex surface. When the light to be observed is incident, the concave surface of Si2 can ensure that the negative lens <NUM> has higher light collection efficiency and can receive and transmit the light to be observed as much as possible. Se2 is a convex surface, which can refract light with large angle and enables light with larger divergence angle to be incident on the light incident surface Si1 of the positive lens <NUM> with a larger incident height and a smaller divergence angle. Furthermore, the marginal lights and the principal lights incident on Si1 have a larger opening angle and a lower incident height of the rays with respect to the human eyes, thereby achieving the purpose of increasing the field angle.

Herein, the light incident surface Si1 of the positive lens <NUM> is a planar Fresnel surface, and the light emergent surface Se1 is a convex surface. When light is incident on Si1, Si1 may collect light incident thereon and reshape the light to make it reach Se1 at a required angle. Se1 is a convex surface, which can refract light with a large angle and further increase the field angle.

Optionally, Se1 can be designed as a convex aspheric surface. The curvature radius of the convex aspheric surface undergoes a specific change from the center to the edge continuously, and the direction of each emergent light can be accurately controlled so that the emergent light is emitted to the human eyes at a set angle to perform aberration correction while increasing the field angle.

In some embodiments, after determining the requirements for aberration correction and the deflection degree of the light, a reverse design may be performed to obtain a convex aspheric surface Se1 with a varying curvature radius. In an alternative embodiment, in order to ensure the convenience of processing and detection, the surface shape of Se1 can be designed as an even aspheric surface. The surface shape of Se1 can be designed according to the equation for the even aspheric surface shown below: <MAT>.

Herein, z represents a coordinate along the direction of the optical axis, and r represents a radial coordinate along the height direction of the lens; c is a quadratic coefficient related to the curvature of the center point of the aspheric surface, c=<NUM>/r0, and r0 is the curvature radius of the center point of the aspheric surface; k is a conic coefficient, and k=-e<NUM>; and ai is coefficients of each even-order term. Optionally, in the practical design of the present embodiment, N=<NUM> may be selected, that is, the even-order term may be up to the sixth power.

In some embodiments, the surface shape of Se1 may also be designed as an odd-order aspheric surface. The surface shape of Se1 can be designed based on the odd-order aspheric surface equation, as shown below: <MAT>.

Herein, βi is a coefficient of each odd-order term.

In an optional embodiment, when the positive lens <NUM> and the negative lens <NUM> are processed, a plastic material may be selected. Plastic materials are easy to process and lay a foundation for the light weighting of the eyepiece optical system. Herein, the refractive index n1 and the dispersion v1 of the positive lens <NUM> can satisfy the following conditions: <NUM><n1<<NUM>, <NUM><v1 <<NUM>; the refractive index n2 and the dispersion v2 of the negative lens <NUM> can satisfy the following conditions: <NUM><n2<<NUM>, <NUM><v2<<NUM>. Optionally, in the actual processing, positive and negative lenses processed by K26R type plastic materials can be selected in the some embodiments. The K26R type plastic materials have a refractive index of <NUM> and a dispersion of <NUM>.

The eyepiece provided in the present embodiment is composed of positive and negative lenses with simple structures. Herein, the light emergent surface of the positive lens is a convex surface, and the light incident surface is a planar Fresnel surface; the light incident surface of the negative lens is a concave surface, and the light emergent surface is a convex surface. In the case of ensuring good optical performance of the positive and negative lenses, such an eyepiece arrangement greatly reduces the thickness of the lenses, realizes an ultrathin eyepiece optical system and facilitates a miniaturized and lighter head-mounted display device. Secondly, the light emergent surface of the positive lens <NUM> is a convex aspheric surface, which corrects the aberration of the overall eyepiece optical system to a certain extent, so that the eyepiece has an excellent imaging quality and clear images. In addition, the eyepiece composed of positive and negative lenses can correct the chromatic aberration of the overall optical system of the eyepiece, improve the imaging quality, and has the advantages of simple structure and low cost.

<FIG> is a schematic diagram of a structure of a head-mounted display device according to an embodiment of the present disclosure. As shown in <FIG>, the head-mounted display device includes:
a positive lens <NUM> and a negative lens <NUM> arranged sequentially and coaxially, and a display device <NUM>. Herein, the light incident surface Si1 of the positive lens <NUM> is close to the light emergent surface Se2 of the negative lens, and the light incident surface Si2 of the negative lens is close to the display device <NUM>.

Optionally, in the present embodiment, the display device <NUM> may be a display device with a larger size, such as a display device of a mobile phone or an LCD (Liquid Crystal Display), etc..

As shown in <FIG>, a distance from the center point of the display screen of the display device <NUM> to the center point of the light emergent surface Se1 of the positive lens <NUM> is defined as TTL (total track length). In the head-mounted display device provided in the present embodiment, since the positive lens <NUM> and the negative lens <NUM> have a strong refractive power and a thinner volume, TTL can reach <NUM> or less. Compared with the existing head-mounted display device with a large display screen, the smaller TTL in the present embodiment greatly reduces the volume of the head-mounted display device.

As shown in <FIG>, after the user wears the head-mounted display device provided in the present embodiment, the position of the human eyes is the exit pupil position of the eyepiece optical system. A distance from the center point of the light emergent surface Se1 of the positive lens <NUM> to the human eyes is defined as T0. In order to ensure that the user can watch a better image after wearing the head-mounted display device, the length of T0 can be set to satisfy the following condition: <NUM> TTL<T0<<NUM> TTL. Optionally, the length of T0 may be controlled by providing an adjustable support component on the head-mounted display device in consideration of different head shapes of different users.

In some embodiments, in order to ensure that the two lenses in the eyepiece have a thinner thickness and a better optical performance, the center thickness T1 of the positive lens <NUM> can be designed to satisfy the following condition: <NUM> TTL<T1 <<NUM> TTL; the center thickness T2 of the negative lens <NUM> satisfies the following condition: <NUM> TTL<T2<<NUM> TTL; and the focal length F of the device satisfies the following condition: <NUM> TTL<F<<NUM> TTL. Optionally, the Fresnel curvature radius R of the light incident surface Si1 of the positive lens <NUM> can be designed to satisfy the following condition: -<NUM>. 6F<R<-<NUM>. 65F; the focal length F1 of the positive lens <NUM> satisfies the following condition: F1<F, and the focal length F2 of the negative lens <NUM> satisfies the following condition: -<NUM><F2<<NUM>. For example, after iterative optimization, when the pixel size of the display chip of the display device <NUM> is <NUM>, it can be selected that F=<NUM>, F1=<NUM>, and F2=-<NUM>.

In some embodiments, the above-mentioned structure and parameter design can make the half field angle θ of the eyepiece optical system reach about <NUM>°, that is, tanθ is between <NUM> and <NUM>. In addition, when the user wears the head-mounted display device to watch the virtual scene, the wearing pressure is small, and a deep sense of immersion and realism can be generated.

In the present embodiment, the eyepiece-fitted display device can achieve a shorter axial distance and a field angle of about <NUM>°, which is smaller and lighter while ensuring that the head-mounted display device has a field angle which is large enough.

In the following section, a specific example will be provided to explain in detail the optical system of the head-mounted display device provided by the embodiment of the present disclosure with reference to Tables <NUM> and <NUM>. A possible design result is shown in Table <NUM>. In Table <NUM>, Surface represents the optical surface numbered sequentially from the human eyes to the display device, Type represents the surface shape of each optical surface, C represents the curvature of each optical surface, T represents the distance between each optical surface and the subsequent optical surface, Glass represents the material of each optical surface, Semi-Diameter represents the aperture of each optical surface, and Conic represents the quadric surface constant.

In Table <NUM>, Surface1 is the plane where the human eyes are located, Surface2 is the light emergent surface Se1 of the positive lens <NUM>, Surface3 is the light incident surface Si1 of the positive lens <NUM>, Surface <NUM> is the light emergent surface Se2 of the negative lens <NUM>, Surface <NUM> is the light incident surface Si2 of the negative lens <NUM>, and Surface <NUM> is the display screen of the display device <NUM>.

As shown in Table <NUM>, in a possible design, a thickness of the positive lens <NUM> is <NUM>, a distance from the center point of the light emergent surface Se1 of the positive lens <NUM> to the human eyes is <NUM>, the curvature radius of the center point of Se1 is <NUM>, and the Fresnel curvature radius of Si1 is -<NUM>. A thickness of the negative lens <NUM> is <NUM>, a curvature radius of the center point of the light emergent surface Se2 of the negative lens <NUM> is <NUM>, a distance between the center points of Se2 and Si1 is <NUM>, and a curvature radius of the center point of the light incident surface Si2 is <NUM>. A distance between Si2 and the display screen of the display device <NUM> is <NUM>, and a thickness of the display device is <NUM>.

In such a design, the TTL of the optical system is calculated as follows: TTL=<NUM>+<NUM>+<NUM>+<NUM>=<NUM>, and the axial length is greatly reduced with respect to the prior art.

In this design, the even-order aspheric coefficients α2, α3 and α4 can be as shown in the following table:.

Based on the above design, the imaging quality of the designed optical system can be analyzed by drawing MTF (Modulation Transfer Function) curves, optical field curvature, distortion graphs, spot diagrams and the chromatic aberration graphs.

<FIG> is a schematic diagram of MTF curves of an eyepiece optical system provided in an embodiment of the present disclosure at a limit resolution of the display device, and <FIG> is a schematic diagram of MTF curves at a <NUM>/<NUM> limit resolution of a display device. In <FIG> and <FIG>, each color represents each of the field lights, the horizontal coordinate represents a distance from the point on the optical system to the center of the optical system, and the vertical axis represents a percentage of the imaging quality close to the object. The MTF can comprehensively reflect the imaging quality of the optical system, the smoother the shape of the curve thereof, and the higher the height relative to the axis X (i.e. closer to <NUM>), the better the imaging quality of the optical system. In <FIG> and <FIG>, the curves in various colors are relatively smooth and compact, and the MTF values represented by the curves are high. In <FIG>, in the case of a half of the limit resolution of a display device, the MTF within <NUM> field of view has reached <NUM> or more, indicating that the aberration of the optical system has been well corrected.

<FIG> is a schematic diagram of an optical field curvature and a distortion of an eyepiece optical system provided by an embodiment of the present disclosure. The left diagram of <FIG> shows a field curvature, in which different colors represent different wavelengths, a solid line represents a tangential field curvature, and a dashed line represents a sagittal field curvature, and the astigmatism of the optical system can be obtained by the subtraction of the above two field curvatures. The astigmatism and field curvature are important aberrations affecting off-axis field lights. An excessively large astigmatism may greatly affect the imaging quality of off-axis lights of the system, and the field curvature may lead to the situation that central and edge optimal imaging are not on the same plane. As can be seen from the left diagram of <FIG>, the field curvature and astigmatism of the optical system provided in the present embodiment are corrected within <NUM>. As can be seen from the right diagram of <FIG>, the distortion (F-Tan(theta)distortion) of the optical system provided in the present embodiment is less than <NUM>%.

<FIG> is a spot diagram of an eyepiece optical system according to an embodiment of the present disclosure. The spot diagram shows the dispersion light spots formed by various field lights of the optical system that converge on the image plane. A smaller RMS (Root Mean Square) radius of the spot diagram demonstrates a better imaging quality of the system. As can be seen from <FIG>, the RMS diameter of the diffuse spot of the optical system provided in the present embodiment is less than <NUM>, which indicates that the aberration correction has been corrected very well.

<FIG> is a schematic diagram of a system chromatic aberration curve of an eyepiece optical system according to an embodiment of the present disclosure. In <FIG>, the horizontal axis represents the chromatic aberration, and the vertical axis represents the field angle. The deviation of the curve from the vertical axis indicates the change in chromatic aberration, and a greater deviation means a larger chromatic aberration. In <FIG>, the maximum half field angle is <NUM>°, and the chromatic aberration can be controlled within <NUM>.

It should be noted that the descriptions of "first" and "second" herein are used to distinguish different messages, devices, modules, etc., and do not represent the sequential order and not define that "first" and "second" are different types.

It should also be noted that the terms "including", "comprising" or any other variations thereof are intended to cover non-exclusive inclusions, so as to make processes, methods, goods or devices which include a series of elements to include not only the series of elements but also other elements that are not explicitly listed, or other elements that are inherent to such processes, methods, goods or devices. In the case of no more limitation, the element defined by the sentence "including a. " does not exclude a case that there are additional identical elements in the processes, methods, goods or devices which include the elements.

Claim 1:
A head-mounted display device, comprising: an eyepiece, and a display device coaxial with the eyepiece, the eyepiece comprising a positive lens (<NUM>) and a negative lens (<NUM>) arranged sequentially and coaxially;
wherein a light incident surface (Si1) of the positive lens (<NUM>) is a planar Fresnel surface, and a light emergent surface (Se1) of the positive lens (<NUM>) is a convex surface; a light incident surface (Si2) of the negative lens (<NUM>) is a concave surface, and a light emergent surface (Se2) of the negative lens (<NUM>) is a convex surface; and
light to be observed is incident on the light incident surface (Si2) of the negative lens (<NUM>), and is refracted by the negative lens (<NUM>) to the light incident surface (Si1) of the positive lens (<NUM>), and emitted by the positive lens (<NUM>);
screen light emitted by the display device is adapted to enter human eyes after being refracted by the eyepiece; characterised in that
a distance TTL from a center point of the light emergent surface (Se1) of the positive lens (<NUM>) to a center point of a display screen of the display device is less than <NUM>;
a distance T0 from a center point of the positive lens (<NUM>) to the exit pupil position of the eyepiece satisfies a condition of <NUM> TTL<T0<<NUM> TTL;
a center thickness T1 of the positive lens (<NUM>) satisfies a condition of <NUM> TTL<T1<<NUM> TTL; and
a center thickness T2 of the negative lens (<NUM>) satisfies a condition of <NUM> TTL<T2<<NUM> TTL.