Optical System of Head-Mounted Display

Abstract

An optical system of a head-mounted display, comprising a first lens and a second lens arranged in sequence from the human eye to the display screen. The first lens and the second lens are lenses with a first refractive index and a second refractive index respectively, and only one of the first lens and the second lens is a Fresnel lens, and it satisfies #imgabs0# where f1 and f2 are the focal lengths of the first lens and the second lens respectively. Through the setting of the Fresnel lens, the present invention can achieve field curvature correction in the design of a large viewing angle on a small screen, which helps to improve the quality of the peripheral image, can reduce the weight and volume of the lens group. At the same time, because only a single Fresnel lens is used, stray light can be effectively suppressed to improve the viewing effect of the virtual reality experience.

Description

Technical Field

[0001] The present invention relates to a technology of optical elements, and particularly to an optical system of a head-mounted display. Background Art

[0002] Virtual reality (VR) is a technology that uses computer technology to generate a virtual image in a three-dimensional space and projects its image into the user's eyes, enabling the user to feel immersive. Currently, most of the technologies used to implement virtual reality are such that the user wears a virtual reality device on the head, and at the same time, the display screen in the virtual reality device is close to the user's eyes, and the user can see a magnified display image at a short distance.

[0003] Generally, a head-mounted display (HMD) transmits a three-dimensional effect signal with binocular parallax, that is, different image data for both eyes, to display screens arranged in front of both eyes and projects it onto an optical system. After that, the optical system can adjust the focusing position of the image to project the image close to the user's eyes at a short distance, enabling the user to view a wide-angle picture through the head-mounted display and generate a virtual reality image.

[0004] However, the current disadvantage of virtual reality devices is that in the implementation of a large field of view (FOV) design for their optical systems, it is necessary to increase the screen size to ensure image quality, resulting in a much larger volume of the virtual reality device, which is relatively bulky and causes discomfort for the user when wearing, leading to problems such as the user being unable to wear it for a long time. For this reason, an optical system composed of Fresnel lenses has a larger field of view and takes into account the miniaturization of virtual reality devices. However, for a general single-piece Fresnel lens optical system, the larger the field of view, the greater the aberration; in addition, for existing optical systems using multiple Fresnel lenses, due to the more serious interaction of stray light, the viewing experience is affected, so it is not easy to design and implement on virtual reality devices. Summary of the Invention

[0005] In view of this, the main object of the present invention is to provide an optical system of a head-mounted display, which has a two-piece lens design, can significantly reduce the aberration at a large field of view and correct the field curvature, helps to improve the quality of peripheral images, can reduce the weight and volume of the lens group, and only one of the two lenses uses a Fresnel lens, which can effectively avoid the generation of stray light and make the imaging clearer.

[0006] To achieve the above object, the present invention provides an optical system for a head-mounted display, which includes a first lens and a second lens. The first lens is a lens with a first refractive index, and the first side of the first lens faces the human eye. The second lens is a lens with a second refractive index, and the first side of the second lens faces the second side of the first lens, and the second side of the second lens faces the display screen; wherein, the optical system of the head-mounted display satisfies the following conditions:

[0007] Only one of the first lens and the second lens is a Fresnel lens, and f1 and f2 are the focal lengths of the first lens and the second lens respectively.

[0008] According to an embodiment of the present invention, the second side of the second lens is a Fresnel surface, and the first side of the second lens, and the first and second sides of the first lens are spherical or aspherical.

[0009] According to an embodiment of the present invention, the second side of the first lens is a Fresnel surface, and the first side of the first lens, and the first and second sides of the second lens are spherical or aspherical.

[0010] According to an embodiment of the present invention, the first and second sides of the second lens are Fresnel surfaces, and the first and second sides of the first lens are spherical or aspherical.

[0011] According to an embodiment of the present invention, the optical system further satisfies n1 is the first refractive index, and n2 is the second refractive index.

[0012] According to an embodiment of the present invention, the optical system further satisfies 0 ≤ S ≤ 20, where S is the distance between the first lens and the second lens.

[0013] According to an embodiment of the present invention, the optical system further satisfies SD2 is the optical effective radius of the second side of the first lens, and SD3 is the optical effective radius of the first side of the second lens.

[0014] According to an embodiment of the present invention, the optical system further satisfies F is the effective focal length of the optical system, and H is the radius of the visible range.

[0015] According to an embodiment of the present invention, the optical system further satisfies F is the effective focal length of the optical system, and SD2 is the optical effective radius of the second side of the first lens.

[0016] According to an embodiment of the present invention, the optical system further satisfies Vd1 is the dispersion coefficient of the first lens, and Vd2 is the dispersion coefficient of the second lens.

[0017] The following will be described in detail through specific embodiments, so that the purpose, technical content, features and achieved effects of the present invention can be more easily understood. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the first embodiment of the optical system of the head-mounted display of the present invention.

[0019] Figure 2 It is a schematic diagram of the second embodiment of the optical system of the head-mounted display of the present invention.

[0020] Figure 3 It is a schematic diagram of the third embodiment of the optical system of the head-mounted display of the present invention.

[0021] Description of the reference numerals: 1, 1', 1'' - optical system; 10 - first lens; 101 - first side; 102 - second side; 12 - second lens; 121 - first side; 122 - second side; 50 - display screen; 52 - human eye; H - visible range radius; S - spacing; SD2 - optical effective radius; SD3 - optical effective radius; ω - half field of view angle of the optical system; TTL - total length of the optical system. Detailed Description of the Embodiments

[0022] Please refer to Figure 1 , which shows a schematic diagram of the first embodiment of the optical system of the head-mounted display of the present invention. The optical system 1 of this embodiment includes a first lens 10 and a second lens 12 arranged side by side between the human eye 52 and the display screen 50. Among them, the first lens 10 is closer to the human eye 52 side, and it is a lens with a first refractive index n1, and the second lens 20 is closer to the display screen 50 side, and it is a lens with a second refractive index n2. Specifically, the first refractive index n1 and the second refractive index n2 of the optical system 1 satisfy Furthermore, the spacing S between the first lens 10 and the second lens 12 of the optical system 1 can satisfy 0 ≤ S ≤ 20 mm.

[0023] In the present invention, the first lens 10 includes a first side surface 101 and a second side surface 102. The first side surface 101 is the surface facing the human eye 52, and the second side surface 102 is the surface facing the display screen 50. The second lens 12 includes a first side surface 121 and a second side surface 122. The first side surface 121 is the surface facing the second side surface 102 of the first lens 10, and the second side surface 122 is the surface facing the display screen 50. In the present invention, only one of the first lens 10 and the second lens 12 is a Fresnel lens. For example, the second side surface 122 of the second lens 12 can be a Fresnel surface, and the other three surfaces are non-Fresnel surfaces, that is, the first side surface 121 of the second lens 12 and the first side surface 101 and the second side surface 102 of the first lens 10 are spherical or aspherical. Or, the second side surface 102 of the first lens 10 is a Fresnel surface, and the other three surfaces are non-Fresnel surfaces, that is, the first side surface 101 of the first lens 10 and the first side surface 121 and the second side surface 122 of the second lens 12 are spherical or aspherical. Or, the first side surface 121 and the second side surface 122 of the second lens 12 are both Fresnel surfaces, and the other two surfaces are non-Fresnel surfaces, that is, the first side surface 101 and the second side surface 102 of the first lens 10 are spherical or aspherical.

[0024] The structure of the optical system 1 of the present invention preferably satisfies any one or more of the following conditions (1) to (5):

[0025] (1)

[0026] where f1 and f2 are the focal lengths of the first lens 10 and the second lens 12 respectively.

[0027] (2)

[0028] where SD2 is the optical effective radius of the second side surface 102 of the first lens 10, and SD3 is the optical effective radius of the first side surface 121 of the second lens 12.

[0029] (3)

[0030] where F is the effective focal length of the optical system 1, and H is the radius of the visible range.

[0031] (4)

[0032] where F is the effective focal length of the optical system 1, and SD2 is the optical effective radius of the second side surface of the first lens.

[0033] (5)

[0034] Where Vd1 is the dispersion coefficient (or Abbe number) of the first lens 10, and Vd2 is the dispersion coefficient (or Abbe number) of the second lens 12.

[0035] The above conditions (1), (2), and (3) can effectively increase the viewing angle and achieve a good aberration balance. Condition (4) can increase the viewing angle and achieve a thinner and lighter design, while condition (5) can produce good chromatic aberration correction and effectively improve the viewing contrast.

[0036] Next, please refer to the following experimental data to prove that the optical system of the present invention has good imaging effects.

[0037] In Figure 1 the first embodiment, the second lens 12 is a Fresnel lens, and the second side surface 122 of the second lens 12 is a Fresnel surface, and the surfaces of the other three sides that are not Fresnel surfaces are aspherical surfaces. Under the conditions that the effective focal length F of the optical system 1 of this embodiment is 21.2 mm, the half field of view angle 2ω in the horizontal direction is 100°, the effective focal length f1 of the first lens 10 is 765 mm, the effective focal length f2 of the second lens 12 is 21.6 mm, the total length TTL of the optical system 1 is 49.5 mm, and the viewing range radius H is 22.8 mm, the first lens 10 and the second lens 12 are respectively represented as L1 and L2, and the lens parameters (Table 1) and aspherical coefficients (Table 2) are as follows:

[0038]

[0039] Table 1. Lens parameters

[0040] Lens surface K A B C D E 2 0.000 -1.606E-05 7.241E-08 -9.589E-11 3.453E-14 0.000E+00 3 46.949 -1.699E-05 8.694E-08 -4.692E-10 5.471E-13 0.000E+00 4 0.000 1.020E-05 -2.574E-09 1.420E-12 3.320E-16 0.000E+00 5 -0.976 1.087E-05 -4.975E-09 1.955E-10 -2.023E-13 0.000E+00

[0041] Table 2. Aspherical coefficients

[0042] A, B, C, D, E, K, etc. in Table 2 above are parameters in the aspherical formula, and the aspherical formula is where C = 1 / R, R is the radius of curvature, and K is the conic coefficient.

[0043] Figure 2 Shown is the optical system 1' of the second embodiment of the present invention. The first lens 10 is a Fresnel lens, and the second side surface 102 of the first lens 10 is a Fresnel surface, and the surfaces of the other three sides that are not Fresnel surfaces are aspherical surfaces. Under the conditions that the effective focal length F of the optical system 1' of this embodiment is 22.8 mm, the half field of view angle 2ω in the horizontal direction is 100°, the effective focal length f1 of the first lens 10 is 27.9 mm, the effective focal length f2 of the second lens 12 is 119.8 mm, the total length TTL of the optical system 1' is 43.6 mm, and the viewing range radius H is 22.8 mm, the lens parameters (Table 3) and aspherical coefficients (Table 4) are as follows:

[0044]

[0045] Table III. Lens Parameters

[0046] Lens surface K A B C D E F 2 82.492 1.360E-08 3.434E-09 2.342E-11 -5.449E-14 7.438E-17 0.000E+00 3 -0.707 -3.312E-08 -3.691E-08 2.035E-11 6.881E-14 2.022E-16 0.000E+00 4 9.171 4.608E-08 -3.033E-10 -3.999E-13 5.419E-17 1.692E-18 0.000E+00 5 0.000 3.398E-06 2.502E-08 4.134E-11 -6.001E-16 -1.135E-16 0.000E+00

[0047] Table IV. Aspherical Coefficients

[0048] Figure 3 Shown is the optical system 1” of the third embodiment of the present invention. The second lens 12 is a Fresnel lens, and the first side 121 and the second side 122 of the second lens 12 are both Fresnel surfaces, and the surfaces of the other two sides that are not Fresnel surfaces are aspherical surfaces. Under the conditions that the effective focal length F of the optical system 1” of this embodiment is 24.22 mm, the half field of view angle 2ω in the horizontal direction is 110°, the effective focal length f1 of the first lens 10 is 83.2 mm, the effective focal length f2 of the second lens 12 is 36.6 mm, the total length TTL of the optical system 1” is 51.2 mm, and the radius of the visible range H is 25.9 mm, the lens parameters (Table V) and the aspherical coefficients (Table VI) are as follows:

[0049]

[0050] Table V. Lens Parameters

[0051] Lens surface K A B C D E F 2 -76.413 4.897E-06 9.814E-10 -4.692E-12 -9.310E-15 0.000E+00 0.000E+00 3 -6.789 3.181E-06 -9.423E-09 2.552E-12 -3.199E-15 0.000E+00 0.000E+00 4 0.000 -3.554E-06 -6.227E-10 3.257E-12 7.712E-15 0.000E+00 0.000E+00 5 -0.658 -1.155E-05 8.124E-09 1.245E-11 1.286E-14 0.000E+00 0.000E+00

[0052] Table VI. Aspherical Coefficients

[0053] The structures of the first to third embodiments of the present invention are summarized in the following Table VII for the data in the various condition formulas:

[0054]

[0055] Table VII. Data Summary List

[0056] In summary, the optical system of the head-mounted display provided by the present invention uses a combination of two lenses, and only one of the lenses is set as a Fresnel lens to adjust the focal length. It can achieve good aberration correction under the design of a small screen and a large field of view angle, and can reduce the weight and volume of the lens group. At the same time, it can effectively suppress stray light, thereby optimizing the image quality and enhancing the visual experience of the user's virtual reality. Furthermore, the visible range of the optical system of the head-mounted display provided by the present invention is: Ф28 mm to Ф52 mm, suitable for screens of 2 inches to 3 inches, and is particularly applicable to wide-angle lenses or wide-angle eyepieces on products such as head-mounted displays and game consoles.

[0057] The above are only the preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. Therefore, all equivalent changes or modifications made in accordance with the features and spirit described in the scope of the claims of the present invention shall be included within the protection scope of the present invention.

Claims

1. An optical system of a head-mounted display, characterized in that, It consists of two lenses, which are: A first lens, which is a lens with a first refractive index, and a first side of the first lens faces a human eye; and a second lens, which is a lens with a second refractive index, a first side of the second lens faces a second side of the first lens, and a second side of the second lens faces a display screen; The optical powers of both the first lens and the second lens are positive; Among them, the optical system of the head-mounted display satisfies the following conditions: Only one of the first lens and the second lens is a Fresnel lens, and f1 and f2 are the focal lengths of the first lens and the second lens respectively; This optical system better meets F is the effective focal length of this optical system, and H is the radius of the visible range; This optical system better satisfies F is the effective focal length of this optical system, and SD2 is the optical effective radius of the second side surface of the first lens.

2. The optical system of the head-mounted display according to claim 1, wherein The second side of the second lens is a Fresnel surface, and the first side of the second lens, the first side and the second side of the first lens are spherical or aspherical surfaces.

3. The optical system of the head-mounted display according to claim 1, wherein, The second side of the first lens is a Fresnel surface, and the first side of the first lens, the first side and the second side of the second lens are spherical or aspherical surfaces.

4. The optical system of the head-mounted display according to claim 1, characterized in that, The first side and the second side of the second lens are Fresnel surfaces, and the first side and the second side of the first lens are spherical or aspherical surfaces.

5. The optical system of the head-mounted display according to claim 1, characterized in that, This optical system better satisfies n1 is the first refractive index and n2 is the second refractive index.

6. The optical system of the head-mounted display according to claim 1, characterized in that, The optical system further satisfies 0 ≤ S ≤ 20 mm, where S is the distance between the first lens and the second lens.

7. The optical system of the head-mounted display according to claim 1, wherein This optical system better satisfies SD2 is the optical effective radius of the second side of the first lens, and SD3 is the optical effective radius of the first side of the second lens.

8. The optical system of the head-mounted display according to claim 1, characterized in that, This optical system better satisfies Vd1 is the dispersion coefficient of the first lens, and Vd2 is the dispersion coefficient of the second lens.

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