Optical systems and virtual reality devices

Abstract

An optical system (20) includes a first lens (210), a second lens (220) and a third lens (230) arranged sequentially from the image side to the object side with their principal optical axes collinear. The first lens (210) is a convex lens, and at least one of the second lens (220) and the third lens (230) is a meniscus lens.

Description

Technical Field

[0001] This disclosure relates to the field of display technology, and more particularly to an optical system and a virtual reality device. Background Technology

[0002] In recent years, virtual reality (VR) has become one of the most popular research topics in the field of computer technology, and the corresponding technology has developed rapidly. Virtual reality is a human-computer interface that enables natural interaction between humans and a computer-generated virtual environment. Its application development prospects are very broad, and its market potential is immeasurable. Currently, virtual reality has been initially applied in many fields such as mechanical design, scientific computing, film and television entertainment, chemical medicine, and military training, and many of these applications are irreplaceable by other technologies. Summary of the Invention

[0003] On one hand, an optical system is provided, including a first lens, a second lens, and a third lens arranged sequentially from the image side to the object side with their principal optical axes collinear; wherein the first lens is a convex lens; and at least one of the second lens and the third lens is a meniscus lens.

[0004] In some embodiments, the refractive index of the second lens is not equal to the refractive index of the third lens.

[0005] In some embodiments, the ratio of the refractive index of the second lens to the refractive index of the third lens ranges from 0.85 to 1.15; and / or, the absolute value of the difference between the refractive index of the second lens and the refractive index of the third lens is greater than or equal to 0.1.

[0006] In some embodiments, the ratio of the Abbe number of the second lens to the Abbe number of the third lens ranges from 0.3 to 3 and is not equal to 1; and / or, the absolute value of the difference between the Abbe number of the second lens and the Abbe number of the third lens is 30 to 40.

[0007] In some embodiments, the ratio of the refractive index of the first lens to the refractive index of the second lens is 0.85 to 1.15.

[0008] In some embodiments, the ratio of the Abbe number of the first lens to the Abbe number of the second lens is 0.3 to 3.

[0009] In some embodiments, at least one of the surfaces of the first lens, the second lens, and the third lens is an aspherical surface.

[0010] In some embodiments, the aspherical surface is an even-order aspherical surface.

[0011] In some embodiments, the first lens and the second lens do not contact each other; along the extension direction of the principal optical axis, the distance between the surfaces of the first lens and the second lens that are close to each other is 0.5mm to 3mm.

[0012] In some embodiments, the second lens and the third lens do not contact each other; and along the extension direction of the principal optical axis, the distance between the surfaces of the second lens and the third lens that are close to each other is 0.5mm to 3mm; or, the surfaces of the second lens and the third lens that are close to each other are in contact.

[0013] In some embodiments, the surfaces of the second lens and the third lens that are close to each other are in contact with each other, and the surfaces in contact are both spherical.

[0014] In some embodiments, the focal lengths of the first lens, the second lens, and the third lens are all less than or equal to 50 mm.

[0015] In some embodiments, the focal length of the optical system is 25mm to 32mm.

[0016] In some embodiments, the field of view of the optical system is 60°~70°.

[0017] In some embodiments, the first lens is a biconvex lens or a meniscus lens with positive optical power.

[0018] In some embodiments, the optical power of the second lens is positive, the optical power of the third lens is negative, and the sum of the optical powers of the second lens and the third lens is negative.

[0019] On the other hand, a virtual reality device is provided, including an optical system as described in any of the above embodiments; it also includes a microdisplay screen, the microdisplay screen being perpendicular to the principal optical axis of the optical system; along the extension direction of the principal optical axis of the optical system, the distance between the surface of the first lens away from the microdisplay screen and the microdisplay screen is greater than or equal to the focal length of the optical system.

[0020] In some embodiments, the relative positions of the first lens, the second lens, and the third lens are fixed; the third lens is close to the surface of the microdisplay and the distance between the third lens and the microdisplay is 11.5mm to 15.8mm.

[0021] On the other hand, another virtual reality device is provided, including an optical system as described in any of the above embodiments; it also includes a mounting component configured to detachably mount a display terminal such that the display surface of the display terminal is perpendicular to the main optical axis of the optical system, and the distance between the surface of the first lens away from the mounting component and the display surface of the display terminal along the extension direction of the main optical axis of the optical system is greater than or equal to the focal length of the optical system.

[0022] In some embodiments, the relative positions of the first lens, the second lens, and the third lens are fixed; the distance between the surface of the third lens close to the display surface of the display terminal and the display surface of the display terminal is 11.5mm to 15.8mm. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in this disclosure, the accompanying drawings used in some embodiments of this disclosure will be briefly described below. Obviously, the drawings described below are only drawings of some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings. In addition, the drawings described below can be regarded as schematic diagrams and are not intended to limit the actual size of the product, the actual flow of the method, the actual timing of the signals, etc. involved in the embodiments of this disclosure.

[0024] Figure 1 This is a structural diagram of a virtual reality device according to some embodiments;

[0025] Figure 2 An optical path diagram of a virtual reality device according to some embodiments;

[0026] Figure 3 This is a structural diagram of an optical system according to some embodiments;

[0027] Figure 4 This is a structural diagram of an optical system according to some other embodiments;

[0028] Figure 5 A modulation transfer function graph of an optical system according to some embodiments;

[0029] Figure 6 A lateral chromatic aberration curve of an optical system according to some embodiments;

[0030] Figure 7 This is a dot diagram of an optical system according to some embodiments. Detailed Implementation

[0031] The technical solutions in some embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments provided in this disclosure are within the scope of protection of this disclosure.

[0032] Unless the context otherwise requires, throughout the specification and claims, the term "comprise" and its other forms, such as the third-person singular "comprises" and the present participle "comprising," are interpreted as open-ended and encompassing, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiments," "example," "specific example," or "some examples," etc., are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this disclosure. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics mentioned may be included in any suitable manner in any one or more embodiments or examples.

[0033] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more.

[0034] "At least one of A, B and C" has the same meaning as "at least one of A, B or C", both including the following combinations of A, B and C: only A, only B, only C, combinations of A and B, combinations of A and C, combinations of B and C, and combinations of A, B and C.

[0035] As used herein, descriptions such as “about,” “approximately,” or “approximately” include the value stated and the average value within an acceptable range of deviation from the given value, wherein the acceptable range of deviation is determined by a person skilled in the art taking into account the measurement under discussion and the error associated with the measurement of the given quantity (i.e., the limitations of the measurement system).

[0036] As used herein, descriptions such as “parallel,” “perpendicular,” and “equal” include the described situation and situations that are similar to the described situation, within an acceptable range of deviation, which is determined by those skilled in the art taking into account the measurement under discussion and the errors associated with the measurement of a particular quantity (i.e., the limitations of the measurement system). For example, “parallel” includes absolute parallelism and approximate parallelism, where an acceptable range of deviation for approximate parallelism may be, for example, within 5°; “perpendicular” includes absolute perpendicularity and approximate perpendicularity, where an acceptable range of deviation for approximate perpendicularity may also be, for example, within 5°; “equal” includes absolute equality and approximate equality, where an acceptable range of deviation for approximate equality may be, for example, a difference between the two equals being less than or equal to 5% of either one.

[0037] This document describes exemplary embodiments with reference to cross-sectional views and / or plan views, which are idealized exemplary drawings. In the drawings, the thickness of layers and regions is enlarged for clarity. Therefore, variations in shape relative to the drawings are contemplated due to, for example, manufacturing techniques and / or tolerances. Thus, exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing processes. For example, etched regions shown as rectangular would typically have curved features. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to show the actual shapes of the regions of the device, nor are they intended to limit the scope of the exemplary embodiments.

[0038] In related technologies, the optical system of a pancake-style VR device generally includes a lens group (consisting of at least two lenses) and a catadioptric assembly (including optical components such as polarizing reflectors). By reflecting light and changing its polarization state, a folded optical path is formed, significantly reducing the thickness of the optical system in the VR device and achieving a thinner and lighter design. However, due to factors such as materials and manufacturing processes, the lenses in the folded optical path exhibit birefringence, causing undesirable polarization state changes in the light passing through the lenses. When the light first reaches the polarizing reflector, a significant amount of light passes through, creating ghosting. When the light reaches the polarizing reflector again along the transmission path, it cannot completely pass through, resulting in effective light loss and low light efficiency in the VR device. Furthermore, some solutions use Fresnel lenses to replace the lenses in the lens group to reduce the thickness of the optical system. However, Fresnel lenses are difficult to design and manufacture, costly, and suffer from severe glare problems, also failing to achieve satisfactory imaging results.

[0039] To solve the above problem, see Figure 1 and Figure 2Some embodiments of this disclosure provide a virtual reality device 1, which can be an all-in-one virtual reality device, including at least one (e.g., two) microdisplays 10 for displaying images and at least one (e.g., two) optical systems 20. The microdisplays 10 are displays with a size ranging from about 0.2 inches to about 2.5 inches, but are not limited thereto. It is understood that the microdisplays 10 can also be displays with a smaller size, such as less than or equal to 0.2 inches. The optical systems 20 include multiple (e.g., three) lenses that transmit the image displayed on the microdisplays 10 to the human eye. The human eye traces the received light in the opposite direction, seeing a magnified virtual image of the displayed image, thus creating a sense of immersion. The specific arrangement of the microdisplays 10 and the optical systems 20 will be described later. Furthermore, the specific form of the virtual reality device 1 is not limited in many ways; for example, the virtual reality device 1 can be a VR headset, headband, glasses, or hat.

[0040] For example, the microdisplay 10 can be a liquid crystal display (LCD), a liquid crystal on silicon (LCOS) display, or a self-emissive display, such as an OLED (Organic Light Emitting Diode) display, a QLED (Quantum Dot Light Emitting Diodes) display, or a micro LED (including Mini LED or Micro LED) display.

[0041] See Figure 3Some other embodiments of this disclosure provide an optical system 20 that can be applied to the aforementioned virtual reality device 1. The optical system 20 includes a first lens 210, a second lens 220, and a third lens 230 arranged sequentially from the image side to the object side, with their principal optical axes collinear. Collinear principal optical axes mean that the principal optical axes of the first lens 210, the second lens 220, and the third lens 230 extend in the same direction and are all on the same straight line. Correspondingly, their optical centers are also on the same straight line. The collinearity of the principal optical axes helps reduce the design difficulty of the optical system 20 and improves its imaging quality. For this optical system 20, the image side refers to the side where the optical system 20 ultimately forms the image, i.e., the side where the user views it; the object side refers to the side where the image is generated, i.e., the side where the microdisplay is located. A first lens 210, a second lens 220, and a third lens 230 are sequentially arranged between the user and the microdisplay (i.e., from the image side to the object side). Light rays emitted from the microdisplay pass through the third lens 230, the second lens 220, and the first lens 210 in sequence before being transmitted to the user. The optical system 20 does not require the setting of optical structures such as polarizing reflectors, and the light transmission path is direct, which can avoid the generation of stray light such as ghosting and glare, improve the imaging quality, and at the same time avoid the influence of optical structures such as polarizing reflectors on the amount of light emitted, resulting in high light efficiency.

[0042] For example, see [link to previous article] Figure 3The first lens 210 is a convex lens. Specifically, the first lens 210 can be a biconvex lens, a plano-convex lens, or a meniscus lens with positive optical power. At least one (e.g., both) of the second lens 220 and the third lens 230 is a meniscus lens. For example, the second lens 220 can be a meniscus lens and the third lens 230 can be a biconcave lens; or the second lens 220 can be a convex lens and the third lens 230 can be a meniscus lens; or both the second lens 220 and the third lens 230 can be meniscus lenses. The second lens 220 and the third lens 230 that meet the above constraints can also have other configurations, which will not be elaborated here. When one of the lens surfaces is not a plane, it can be a spherical surface, an aspherical surface, a freeform surface, etc., without much restriction. Along the extension direction of the principal optical axis, the distance between the two surfaces of the lens is the thickness of the lens. When the thickness of the lens is much smaller than the focal length of the lens, the lens is a thin lens. According to the lens grinder's formula, for thin lenses, the greater the curvature, the smaller the focal length. In this disclosure, the first lens 210, the second lens 220, and the third lens 230 are all thin lenses. At least one of the second lens 220 and the third lens 230 is a meniscus lens. Meniscus lenses have a small radius of curvature, and a large curvature results in a small focal length. Therefore, the equivalent focal length when the second lens 220 and the third lens 230 are used together is also small. Compared to using other types of lenses, setting at least one of the second lens 220 and the third lens 230 to be a meniscus lens enables the achievement of a smaller optical system focal length 20 (this focal length is the equivalent focal length when the first lens 210, the second lens 220, and the third lens 230 are used together).

[0043] The optical system 20 in a virtual reality device can be equivalent to a convex lens (hereinafter referred to as the equivalent convex lens). The object distance of this equivalent convex lens is the distance between the microdisplay and the optical center of the equivalent convex lens along the extension direction of the principal optical axis of the equivalent convex lens (i.e., the principal optical axis of the optical system 20). According to the imaging principles of convex lenses, in order to achieve imaging at the human eye, the object distance needs to be greater than the focal length of the equivalent convex lens (i.e., the focal length of the optical system 20). The larger the focal length of the equivalent convex lens, the greater the distance between the microdisplay and the optical center of the equivalent convex lens needs to be. Correspondingly, the overall length of the microdisplay and the equivalent convex lens also increases, resulting in a thicker and heavier virtual reality device. In this embodiment, the first lens 210 is a convex lens, and at least one of the second lens 220 and the third lens 230 is a meniscus lens. The focal length of the optical system 20 formed by this is relatively small, and a smaller object distance is sufficient to achieve imaging, thereby enabling the virtual reality device to be thinner and lighter.

[0044] When light of different colors passes through the same lens, because the wavelengths of the light are different, they have different refractive indices. Therefore, the focal points of the different colors of light are at different positions along the optical axis of the lens, resulting in chromatic aberration (also known as dispersion). To correct this chromatic aberration, for example, the refractive index of the second lens 220 can be set to be unequal to that of the third lens 230. The ratio of the refractive index of the second lens 220 to that of the third lens 230 can range from 0.85 to 1.15, and / or the absolute value of the difference between the refractive indices of the second lens 220 and the third lens 230 can be greater than or equal to 0.1. Specifically, the ratio of the refractive index of the second lens 220 to that of the third lens 230 can be 0.9, 0.95, 1.05, 1.1, 1.12, 1.14, etc.; the absolute value of the difference between the refractive indices of the second lens 220 and the third lens 230 can be 0.15, 0.2, 0.35, 0.5, 0.55, etc. For example, the refractive index of the second lens 220 is less than that of the third lens 230; the refractive index of the second lens 220 is 1.55, and the refractive index of the third lens 230 is 1.67. The ratio of the refractive index of the second lens 220 to that of the third lens 230 is approximately 0.93, and the absolute value of the difference between the refractive indices of the second lens 220 and the third lens 230 is 0.12.

[0045] The higher the refractive index of a lens, the more severe the chromatic aberration and the lower the Abbe number; conversely, the lower the refractive index, the less severe the chromatic aberration and the higher the Abbe number. Taking the third lens 230, whose refractive index is greater than that of the second lens 220, as an example, the Abbe number of the third lens 230 is less than that of the second lens 220. The combination of the second lens 220 and the third lens 230 allows the chromatic aberration produced by either lens to be compensated by the other, thus minimizing the overall chromatic aberration. The same principle applies when the refractive index of the second lens 220 is greater than that of the third lens 230. To achieve different refractive indices for the second lens 220 and the third lens 230, they can be made from different materials; no further restrictions are placed here.

[0046] For example, the ratio of the Abbe number of the second lens 220 to the Abbe number of the third lens 230 ranges from 0.3 to 3 and is not equal to 1, and / or the absolute value of the difference between the Abbe numbers of the second lens 220 and the third lens 230 is 30 to 40. Specifically, the ratio of the Abbe number of the second lens 220 to the Abbe number of the third lens 230 can be 0.5, 0.65, 0.8, 1.2, 1.5, 1.8, 2.2, 2.5, 2.7, etc.; the absolute value of the difference between the Abbe numbers of the second lens 220 and the third lens 230 can be 32, 34, 35, 38, etc. The larger the difference in Abbe numbers, the smaller the optical power of the lens combination and the larger the equivalent focal length; the smaller the difference in Abbe numbers, the larger the optical power of the lens combination and the smaller the equivalent focal length. Corresponding to this disclosure, when the Abbe number difference between the second lens 220 and the third lens 230 is too large (greater than 40, for example, 60), the combined optical power of the second lens 220 and the third lens 230 is small, the equivalent focal length is large, and the focal length of the corresponding optical system 20 is also large, which is not conducive to the thinning and lightening of virtual reality devices. Conversely, when the Abbe number difference between the second lens 220 and the third lens 230 is too small (less than 30, for example, 10), the combined optical power of the second lens 220 and the third lens 230 is large, which will produce serious aberrations and affect image quality. Therefore, this disclosure sets the ratio of the Abbe numbers of the second lens 220 and the third lens 230 to a range of 0.3 to 3 and not equal to 1, and / or the absolute value of the difference between the two is 30 to 40, which can better reduce overall chromatic aberration and avoid the adverse effects caused by excessively large or small Abbe number differences.

[0047] For example, similar to the above, the ratio of the refractive index of the first lens 210 to the refractive index of the second lens 220 can be set to 0.85 to 1.15, and / or the ratio of the Abbe number of the first lens 210 to the Abbe number of the second lens 220 can be 0.3 to 3. Specifically, the ratio of the refractive index of the first lens 210 to the refractive index of the second lens 220 can be 0.9, 0.95, 1.05, 1, 1.1, 1.12, 1.14, etc.; the ratio of the Abbe number of the first lens 210 to the Abbe number of the third lens 230 can be 0.5, 0.65, 0.8, 1, 1.1, 1.2, 1.5, 1.8, 2.2, 2.5, 2.7, etc. The beneficial effects produced by this setting are similar to those produced by the aforementioned settings of the second lens 220 and the third lens 230, and will not be repeated here.

[0048] For example, see Figure 4, the two adjacent lenses are not in contact with each other, that is, the first lens 210 and the second lens 220 are not in contact with each other, and the second lens 220 and the third lens 230 are not in contact with each other either. The intersection point of the main optical axis and the lens surface is the vertex of the lens surface. The distance between the surfaces of two adjacent lenses that are close to each other is the distance between the vertices of the surfaces of the two lenses that are close to each other. When the distance between the surfaces of two adjacent lenses that are close to each other is too large, the overall length of the optical system 20 is relatively large, which is not conducive to the realization of the thin and light of the virtual reality device. When the distance between the surfaces of two adjacent lenses that are close to each other is too small, the assembly process of the optical system 20 is more difficult, which is not conducive to the control and optimization of production costs. Therefore, in the present disclosure, along the extension direction of the main optical axis, the distance d1 between the surfaces of the first lens 210 and the second lens 220 that are close to each other is 0.5 mm to 3 mm, for example, specifically 0.5 mm; the distance d2 between the surfaces of the second lens 220 and the third lens 230 that are close to each other is also 0.5 mm to 3 mm, for example, specifically 3 mm, so as to avoid the above problems.

[0049] On the above premise, exemplarily, at least one (for example, each) surface of the first lens 210, the second lens 220, and the third lens 230 is an aspherical surface. Using an aspherical lens can correct aberrations such as coma and astigmatism that affect imaging quality without affecting the light flux, which is conducive to improving the imaging quality. In addition, the use of an aspherical lens has a positive impact on the improvement of the optical performance of the optical system 20, the expansion of the viewing angle, and the thin and light of the optical system 20.

[0050] Furthermore, the type of the aspherical surface can be set as an even aspherical surface. The design and processing of an even aspherical surface are less difficult, which is conducive to reducing production costs. When the lens surface is an even aspherical surface, its shape satisfies the following surface formula:

[0051]

[0052] where Z is the sag of the lens, c is the curvature corresponding to the vertex of the aspherical surface, r is the distance from the vertex of the aspherical surface to any point on the aspherical surface, A 2i is the coefficient of the polynomial term. k is the conic coefficient. When k < -1, the surface curve of the lens surface is a hyperbola; when k = -1, the surface curve of the lens surface is a parabola; when -1 < k < 0, the surface curve of the lens surface is an ellipse; when k = 0, the surface curve of the lens surface is a circle; when k > 0, the surface curve of the lens surface is a flattened circle.

[0053] Also exemplarily, see Figure 3The first lens 210 and the second lens 220 do not contact each other, while the surfaces of the second lens 220 and the third lens 230 that are close to each other are bonded together. The shapes of the bonded surfaces of the second lens 220 and the third lens 230 are pre-designed, and the shapes of the two bonded surfaces are basically consistent. Under the current technological conditions, the distance between the two bonded surfaces should be as small as possible. The specific method used to bond the close-to-close lens surfaces of the second lens 220 and the third lens 230 is not overly restricted. For example, a mechanical method can be used to combine the two into an optical component using mechanical parts such as spacers and pressure rings; another example is the optical adhesive method, which relies on the attraction between the molecules of the two surfaces to be bonded to combine them into an optical component; yet another example is the adhesive method, which uses an adhesive bond to form a double-sided lens. The optical adhesive used can be at least one of silicone, acrylic resin, unsaturated polyester, polyurethane, epoxy resin, etc. The surfaces of the second lens 220 and the third lens 230 are closely fitted together, making the overall structure of the optical system 20 more compact and facilitating the thinning and lightening of virtual reality devices. Simultaneously, light emitted from the third lens 230 directly illuminates the second lens 220, eliminating air gaps and improving the stability of light transmission, thus enhancing the imaging quality of the optical system 20. Under this premise, the distance d1 between the surfaces of the first lens 210 and the second lens 220 along the extension direction of the principal optical axis can be set to 0.5mm to 3mm, for example, 0.5mm. This setting ensures that the distance between the surfaces of the two lenses is within a reasonable range, achieving the aforementioned beneficial effects, which will not be elaborated further here.

[0054] For example, the surfaces of the second lens 220 and the third lens 230 that are close to each other are bonded together, and both bonded surfaces are spherical. Spherical surfaces are easier to design and fabricate, and easier to bond, thus reducing fabrication difficulty and controlling production costs. Apart from the bonded surfaces of the second lens 220 and the third lens 230, at least one (e.g., each) of the other lens surfaces in the optical system 20 is aspherical. For example, the other lens surfaces can all be even-order asphericals, the surface shape formula of which is consistent with the aforementioned formula, and the beneficial effects produced by this arrangement are similar to those described above, and will not be repeated here.

[0055] For details, see Figure 3 and Figure 4When the surfaces of the first lens 210, the second lens 220, and the third lens 230 are spherical or aspherical, from the image side to the object side, the two surfaces of the first lens 210 are the first surface 211 and the second surface 212, the two surfaces of the second lens 220 are the third surface 221 and the fourth surface 222, and the two surfaces of the third lens 230 are the fifth surface 231 and the sixth surface 232. The radius of curvature of the first surface 211 is -500mm to -100mm; the radius of curvature of the second surface 212 is -50mm to -10mm, convex towards the side where the microdisplay is located; the radius of curvature of the third surface 221 is 20mm to 100mm, and the radius of curvature of the fourth surface 222 is 50mm to 200mm; the radius of curvature of the fifth surface 231 is 50mm to 200mm, and the radius of curvature of the sixth surface 232 is 50mm to 200mm, convex towards the side where the user is located. The radius of curvature of the sixth surface 232 is 0 mm to 200 mm.

[0056] For example, the focal lengths of the first lens 210, the second lens 220, and the third lens 230 are all less than or equal to 50 mm. The small focal length of each lens in the optical system 20 ensures that the optical system 20 has a small focal length, thereby facilitating the thinning and lightening of virtual reality devices.

[0057] Under the aforementioned limitations, the optical system 20 in this disclosure has a relatively small focal length, ranging from 25mm to 32mm, making it a short-focal-length optical system 20. Furthermore, the width of the Eye Box (eye movement range diameter) is not less than 8mm, which enables the virtual reality device to be made thinner and lighter while ensuring imaging quality.

[0058] For example, see Figure 2The field of view θ of the optical system 20 is 60°~70°. Among the light rays passing through the first lens 210 from the object side to the image side, the angle between the outermost ray and the principal optical axis of the optical system 20 is half of the field of view. For the optical system 20, the smaller the focal length, the larger the field of view θ, and vice versa. When the field of view of the optical system 20 is too small (less than 60°, for example, 30°), the focal length of the optical system 20 is large, and a large distance needs to be set between the optical system 20 and the microdisplay 10, which is not conducive to achieving the thinness of the virtual reality device. At the same time, a small field of view θ will reduce the immersive experience of using the virtual reality device 1, affecting the user experience. When the field of view θ of the optical system 20 is too large (greater than 70°, for example, 90°), when observing through the optical system 20, the displayed image is prone to perspective distortion, which will have an adverse effect on the imaging effect. Therefore, the field of view θ of the optical system 20 in this disclosure is set to 60°~70°. This angle value is within a reasonable range and can take into account both the imaging effect and the size of the device.

[0059] For example, see Figure 2 , Figure 3 and Figure 4 The first lens 210 can be configured as a biconvex lens or a meniscus lens with positive optical power. For example, the optical power range of the first lens 210 can be 0.02 to 0.1. Both surfaces of the first lens 210 are curved surfaces with a certain curvature. During the transmission of light, both curved surfaces can deflect the light to compensate for the aberrations generated, thereby better eliminating aberrations and achieving better imaging results.

[0060] For example, in the second lens 220 and the third lens 230, the optical power of the second lens 220 is positive, the optical power of the third lens 230 is negative, and the sum of the optical powers of the second lens 220 and the third lens 230 is negative. The optical power range of the second lens 220 can be 0.02 to 0.1, and the optical power range of the third lens 230 can be -0.2 to -0.02. The second lens 220 and the third lens 230 can be equivalent to a lens with negative optical power. The first lens 210 is a convex lens with positive optical power. The entire optical system 20 can be equivalent to a combination of a lens with positive optical power and a lens with negative optical power. The combination of positive and negative lenses can correct aberrations such as spherical aberration, field curvature, and distortion while obtaining a larger field of view, thereby improving the resolution of the virtual reality device and ensuring full-field high-definition display.

[0061] For example, the materials of each lens in the optical system 20 can be glass, plastic, or other optional materials. The materials of the three lenses can be all the same or all different; there are no major limitations on this, and various arrangements can achieve the aforementioned beneficial effects. For instance, at least one (e.g., all three) of the first lens 210, second lens 220, and third lens 230 may be made of plastic. Specifically, these could be acrylic resin, polycarbonate resin, polystyrene resin, vinyl chloride resin, diethylene glycol diallyl carbonate, etc. Using plastic as the material for each lens in the optical system 20 allows for a lighter device weight and improves the user experience.

[0062] To verify the improvement in imaging performance of the optical system 20 in this disclosure, see [link to relevant documentation]. Figure 2 and Figure 3 The optical system 20 was designed according to the aforementioned constraints, and a corresponding microdisplay 10 was set up. Relevant parameters were obtained through simulation for evaluation. Specifically, the settings of the aperture (simulating the pupil size of the human eye), the optical system 20, and the microdisplay 10 are shown in the figure. The design parameters of the aperture and the optical system 20 are shown in Table 1 below. The lens surface type in the optical system 20 includes spherical and aspherical surfaces, with the aspherical surface type being even-order aspherical, and the aforementioned surface type formula is applicable. The selected microdisplay 10 can be a liquid crystal display (LCD). The diagonal length of the microdisplay 10 is 2.1 inches, and the resolution is 2160*2160. The calculated length of each pixel is approximately 17.5 μm.

[0063] Table 1

[0064]

[0065] In the table above, F is the focal length of the optical system 20, TL is the distance between the vertex of the first surface 211 of the first lens 210 and the microdisplay 10 along the extension direction of the principal optical axis of the optical system 20, and R is the radius of curvature corresponding to the vertex of the lens surface. For a surface (including the surface of the aperture stop), T is the distance between the surface and its immediate neighbor along the extension direction of the principal optical axis of the optical system 20 from the aperture stop to the microdisplay 10. For example, for the aperture stop, the corresponding T value is the distance between the aperture stop and the vertex of the first surface 211; for the first surface 211, the corresponding T value is the distance between the vertex of the first surface 211 and the vertex of the second surface 212, and so on for other surfaces. For each aspherical surface, except for A4 and A6, whose values ​​are shown in Table 1, the coefficients of the other polynomial terms are all 0.

[0066] Since the principal optical axes of all lenses in the optical system 20 are collinear and the surfaces of the lenses are spherical or aspherical, the optical system 20 is an axisymmetric optical system 20. When detecting various parameters, it is only necessary to detect the angular range of 0° to 1 / 2 field of view. Figure 5 The diagram shows the modulation transfer function (MTF) curve of the optical system 20 in this disclosure. This curve represents the percentage of the contrast of the image displayed on the microdisplay 10 relative to the contrast of the image displayed on the microdisplay 10 within the spatial frequency range of 0 lp / mm to 30 lp / mm (OTF modulus). The different line shapes (curves A to N) correspond to the MTF curves at different field of view angles. The MTF curves corresponding to each field of view angle are smooth and compact, and when the spatial frequency is 30 lp / mm, the OTF modulus corresponding to each curve is not less than 0.2, indicating that the optical system 20 has high imaging quality.

[0067] See Figure 6 The lateral color difference curve shown has the horizontal axis representing lateral color difference and the vertical axis representing the field of view (Angle in Degrees). It can be seen that within a field of view of 0° to 35°, the lateral color difference of this system does not exceed 17μm. For a microdisplay 10 with a corner length of 2.1 inches and a resolution of 2160*2160, this lateral color difference is smaller than the pixel size of the microdisplay 10 and therefore will not be perceived by the user, resulting in a significant color difference improvement effect.

[0068] Figure 7 The diagram shows the points at seven field of view angles (or object heights): 0°, 5.83°, 11.67°, 17.5°, 23.33°, 29.17°, and 35.0°. The maximum root mean square radius at multiple field of view angles is only 22 μm, indicating that a clear image can be seen at each field of view angle, and the imaging quality is high.

[0069] As can be seen from the above, the optical system provided in this disclosure not only helps to make virtual reality devices thinner and lighter, but also enables full-field high-definition display with high imaging quality.

[0070] In some embodiments of this disclosure, see Figure 1 and Figure 2 The virtual reality device 1 may include two microdisplays 10 and two optical systems 20, each optical system 20 corresponding to one microdisplay 10. The microdisplay 10 is perpendicular to the main optical axis of its corresponding optical system 20, and the image formed by each optical system 20 is transmitted to one of the user's eyes.

[0071] For example, along the extension direction of the principal optical axis of the optical system 20, the distance TL between the surface of the first lens 210 away from the microdisplay 10 and the microdisplay 10 is greater than or equal to the focal length of the optical system 20. Specifically, the distance TL between the vertex of the first surface of the first lens 210 and the center of the microdisplay 10 can be set to be greater than or equal to the focal length of the optical system 20. In conjunction with the foregoing, the optical system 20 can be regarded as an equivalent convex lens. This setting can ensure that the distance between the microdisplay 10 and the optical center of the equivalent convex lens is greater than the focal length of the equivalent convex lens (i.e., the focal length of the optical system 20), thereby ensuring the imaging effect.

[0072] For example, along the extension direction of the principal optical axis of the optical system 20, the distance TL between the surface of the first lens 210 away from the microdisplay 10 and the microdisplay 10 is equal to the focal length of the optical system 20. This minimizes the overall length of the optical system 20 and the microdisplay 10 while ensuring imaging, thereby maximizing the thinness and lightness of the virtual reality device 1. Under this premise, when the focal length of the optical system 20 is 25mm~32mm and the field of view of the optical system 20 is 60°~70°, the diagonal length of the microdisplay 10 can be selected in the range of 1.5 inches~2.5 inches. Furthermore, the pixel density of the microdisplay 10 can be set to be no less than 1500 PPI so that the size of the pixels in the microdisplay 10 is no less than the lateral chromatic aberration of the optical system 20, thereby ensuring the chromatic aberration correction effect.

[0073] For example, see Figure 2 and Figure 3 The relative positions of the first lens 210, the second lens 220, and the third lens 230 are fixed. The third lens 230 is close to the surface of the microdisplay 10, and the distance S between it and the microdisplay 10 is 11.5mm to 15.8mm. That is, along the extension direction of the principal optical axis of the optical system 20, the optical system 20 can move back and forth relative to the microdisplay 10. When users with different vision conditions use it, they only need to adjust the distance between the optical system 20 and their eyes to a suitable position to see the display screen clearly, thereby improving the practicality of the virtual reality device and making it available to a wider user group. For the aforementioned optical system 20, when the distance S between the sixth surface 232 of the third lens 230 and the surface of the microdisplay 10 is adjusted within the range of 15.8mm to 11.5mm, the virtual reality device equipped with this optical system 20 is suitable for users with myopia ranging from 0 degrees to 600 degrees (corresponding to a refractive power of 0D to -6D).

[0074] Other embodiments of this disclosure provide another type of mobile phone box-style virtual reality device, also including the aforementioned optical system and a mounting component. The mounting component is configured to detachably mount a display terminal, such that the display surface of the display terminal is perpendicular to the principal optical axis of the optical system. Along the extension direction of the principal optical axis, the distance between the surface of the first lens away from the mounting component and the display surface of the display terminal is greater than or equal to the focal length of the optical system. Specifically, the display surface of the display terminal is the surface of the display terminal closest to the optical system. The display terminal can be an electronic device such as a mobile phone capable of independently displaying images. This virtual reality device with an optical system can also achieve a thin and light design while maintaining good imaging performance.

[0075] For example, in this mobile phone box-style virtual reality device, the relative positions of the first lens, the second lens and the third lens are fixed. The third lens is close to the surface of the display terminal, and the distance between the third lens and the display terminal is 11.5mm~15.8mm, so that the virtual display device is also suitable for users with different vision conditions.

[0076] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. An optical system, comprising a first lens, a second lens and a third lens which are collinear with a main optical axis and arranged in order from an image side to an object side; at least one of the second lens and the third lens is a meniscus lens; From the image side to the object side, two surfaces of the first lens are a first surface and a second surface respectively, two surfaces of the second lens are a third surface and a fourth surface respectively, and two surfaces of the third lens are a fifth surface and a sixth surface respectively; wherein, a curvature radius of the first surface is -500mm~ -100mm, a curvature radius of the second surface which is convex to the object side is -50mm~ -10mm, a curvature radius of the third surface and the fourth surface which are convex to the image side is 20mm~100mm and 50mm~200mm respectively, and a curvature radius of the fifth surface and the sixth surface which are convex to the image side is 50mm~200mm and 0mm~20mm respectively. 2.The optical system according to claim 1, wherein a refractive index of the second lens is not equal to a refractive index of the third lens. 3.The optical system according to claim 2, wherein a ratio of the refractive index of the second lens to the refractive index of the third lens is in a range of 0.85~1.15 and not equal to 1; and / or, an absolute value of a difference between the refractive index of the second lens and the refractive index of the third lens is greater than or equal to 0.

1. 4.The optical system according to claim 1, wherein a ratio of an Abbe number of the second lens to an Abbe number of the third lens is in a range of 0.3~3 and not equal to 1; and / or, an absolute value of a difference between the Abbe number of the second lens and the Abbe number of the third lens is in a range of 30~40. 5.The optical system according to claim 1, wherein a ratio of a refractive index of the first lens to a refractive index of the second lens is in a range of 0.85~1.

15. 6.The optical system according to claim 1, wherein a ratio of an Abbe number of the first lens to an Abbe number of the second lens is in a range of 0.3~3. 7.The optical system according to claim 1, wherein at least one surface of each surface of the first lens, the second lens and the third lens is an aspheric surface. 8.The optical system according to claim 7, wherein the aspheric surface is an even aspheric surface. 9.The optical system according to claim 1, wherein the first lens and the second lens are not in contact with each other; a distance between surfaces of the first lens and the second lens which are close to each other along an extension direction of the main optical axis is in a range of 0.5mm~3mm. 10.The optical system according to claim 1, wherein the second lens and the third lens are not in contact with each other; and a distance between surfaces of the second lens and the third lens which are close to each other along an extension direction of the main optical axis is in a range of 0.5mm~3mm; or, the surfaces of the second lens and the third lens which are close to each other are in contact. 11.The optical system according to claim 10, wherein the surfaces of the second lens and the third lens which are close to each other are in contact, and each of the surfaces in contact is a spherical surface. 12.The optical system according to claim 1, wherein The focal length of the first lens, the second lens and the third lens is less than or equal to 50mm.

13. The optical system of claim 12, wherein, The focal length of the optical system is 25mm-32mm.

14. The optical system of claim 1, wherein, The field of view angle of the optical system is 60°-70°.

15. The optical system of claim 1, wherein, The first lens is a meniscus lens with positive optical power.

16. The optical system of any one of claims 1-15, wherein, The second lens has positive optical power, the third lens has negative optical power, and the sum of the optical power of the second lens and the third lens is negative.

17. A virtual reality device, comprising: The optical system of any one of claims 1-16; A micro display screen perpendicular to the principal optical axis of the optical system; In the extension direction of the principal optical axis of the optical system, the distance between the surface of the first lens away from the micro display screen and the micro display screen is greater than or equal to the focal length of the optical system.

18. The virtual reality device of claim 17, wherein, The relative positions of the first lens, the second lens and the third lens are fixed; The distance between the surface of the third lens close to the micro display screen and the micro display screen is 11.5mm-15.8mm.

19. A virtual reality device, comprising: The optical system of any one of claims 1-16; A mount configured to detachably mount a display terminal such that the display surface of the display terminal is perpendicular to the principal optical axis of the optical system, and in the extension direction of the principal optical axis of the optical system, the distance between the surface of the first lens away from the mount and the display surface of the display terminal is greater than or equal to the focal length of the optical system.

20. The virtual reality device of claim 19, wherein, The relative positions of the first lens, the second lens and the third lens are fixed; The distance between the surface of the third lens close to the display surface of the display terminal and the display surface of the display terminal is 11.5mm-15.8mm.

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