Optical system

Abstract

To provide an optical system.SOLUTION: An optical system is provided, comprising, in order from a rear side to a front side, an aperture stop, first lens, second lens, third lens, circularly polarizing plate, and image surface. The circularly polarizing plate is provided on a rear side of the image surface. A front surface of the first lens or a rear surface of the second lens is provided with a composite film comprising a reflective polarizing film and a 1 / 4 wavelength plate, where the reflective polarizing film is provided on the rear side of the 1 / 4 wavelength plate. The optical system satisfies the following conditional expressions: 5.00≤f2 / f≤9.00, 1.30≤(R1+R2) / (R1-R2)≤4.80, 0.90≤R5 / R6≤2.80, and SDmax≤23.00 mm, where f represents a focal length of the optical system, f2 represents a focal length of the second lens, R1 represents a central curvature radius of a rear surface of the first lens, R2 represents a central curvature radius of the front surface of the first lens, R5 represents a central curvature radius of a rear surface of the third lens, R6 represents a central curvature radius of a front surface of the third lens, and SDmax represents a maximum effective radius of each lens of the optical system.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to the field of eyepiece display technology, and in particular to optical systems. [Background technology]

[0002] In recent years, the technology related to smart head-mounted devices has been developing rapidly, and the applications of electronic devices equipped with optical lenses have become more widespread, resulting in more diverse requirements for optical lenses. Applications in fields such as virtual reality, augmented reality, and mixed reality have grown rapidly, and from the perspective of user experience, there is an urgent need for optical systems that combine small size with excellent imaging methods. Summary of the Invention [Problem to be solved by the invention]

[0003] In view of the above problems, an object of the present invention is to provide an optical system that has excellent optical performance and satisfies the design requirements of being small and lightweight. [Means for solving the problem]

[0004] In order to solve the above technical problems, an embodiment of the present invention provides an optical system, the optical system comprising, from the back side to the front side, in order: a diaphragm located on the back side of the optical system; a first lens; a second lens; a third lens; a circular polarizer; and an image plane; wherein the circular polarizer is attached to the back surface of the image plane; and a composite film is provided on the front surface of the first lens or the back surface of the second lens; the composite film includes a reflective polarizer and a quarter wave plate; the reflective polarizer is provided on the back side of the quarter wave plate; the focal length of the optical system is defined as f; the focal length of the second lens is defined as f2; the central radius of curvature of the back surface of the first lens is defined as R1; the central radius of curvature of the front surface of the first lens is defined as R2; the central radius of curvature of the back surface of the third lens is defined as R5; the central radius of curvature of the front surface of the third lens is defined as R6; and the maximum effective radius of each lens in the optical system is defined as SDmax, the following relationship is satisfied: 5.00≦f2 / f≦9.00 1.30≦(R1+R2) / (R1-R2)≦4.80 0.90≦R5 / R6≦2.80 SDmax≦23.00mm

[0005] Preferably, when the size of the eyebox of the optical system is defined as Eyebox, the following relational expression is satisfied: Eyebox≧12.00mm

[0006] Preferably, when the on-axis distance from the human eye to the back surface of the first lens is defined as eyerelief, the following relational expression is satisfied: Eye relief≦16.50mm

[0007] Preferably, when the axial distance from the back surface of the first lens to the image plane is defined as TL, the following relational expression is satisfied: TL≦18.40mm

[0008] Preferably, when the total optical length of the optical system is defined as TTL, the following relational expression is satisfied: TTL≦34.80mm

[0009] Preferably, the back and front surfaces of the first lens, the back and front surfaces of the second lens, and the back and front surfaces of the third lens are all aspherical.

[0010] Preferably, when the angle of view of the optical system is defined as FOV, the following relational expression is satisfied: 85.00°≦FOV≦95.00°

[0011] Preferably, the front surface of the second lens is plated with a semi-transmissive, semi-reflective film.

[0012] Preferably, the transmittance and reflectance of the semi-transmitting semi-reflective film are both 40.00% to 60.00%.

[0013] Preferably, the reflective polarizing film has a transmittance of 95% or more.

[0014] Preferably, when the distortion of the optical system is defined as MIST, the following relational expression is satisfied: MIST≦35.00%

[0015] Preferably, when the chromatic aberration of the optical system is defined as LC, the following relational expression is satisfied: LC≦100μm

[0016] Preferably, when the total optical length of the optical system is defined as TTL, the following relational expression is satisfied: TTL / f≦2.10

[0017] Preferably, the image surface is a display, and its size is 1.0 to 1.3 inches. [Effects of the Invention]

[0018] The beneficial effects of the present invention are as follows: A composite film consisting of a reflective polarizing film and a quarter-wave plate is provided on the front surface of the first lens or the back surface of the second lens, and a semi-transmissive semi-reflective film is provided on the front surface of the second lens, allowing the two lenses to participate in a folded optical path structure, significantly shortening the total optical length TTL of the optical system and reducing the volume of the optical imaging module, thereby meeting the design requirements for compactness and lightweight VR devices. At the same time, the optical system provided by the present invention allows users to view the optimal display effect at the optimal position without the need for tedious adjustments, and the optical system combines compactness with excellent imaging performance. [Brief explanation of the drawings]

[0019] To more clearly describe the technical solutions in the embodiments of the present invention, the following will briefly describe the drawings necessary for describing the embodiments. Obviously, the following description of the drawings is only for describing some embodiments of the present invention, and those skilled in the art can derive other drawings from these drawings without any creative efforts. [Figure 1] FIG. 1 is a diagram showing the configuration of an optical system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a spot diagram of the optical system shown in FIG. [Figure 3] FIG. 3 is a diagram showing chromatic aberration of magnification of the optical system shown in FIG. [Figure 4] FIG. 4 is a diagram showing the field curvature and distortion of the optical system shown in FIG. [Figure 5] FIG. 5 is a schematic diagram showing the optical system shown in FIG. 1 having a film layer structure. [Figure 6] FIG. 6 is a diagram showing the configuration of a part of an optical system according to the second embodiment of the present invention. [Figure 7] FIG. 7 is a spot diagram of the optical system shown in FIG. [Figure 8] FIG. 8 is a diagram showing chromatic aberration of magnification of the optical system shown in FIG. [Figure 9] FIG. 9 is a diagram showing the field curvature and distortion of the optical system shown in FIG. [Figure 10]FIG. 10 is a schematic diagram showing the optical system shown in FIG. 6 having a film layer structure. DETAILED DESCRIPTION OF THE INVENTION

[0020] In order to clarify the objectives, technical solutions, and advantages of the present invention, the following detailed description of each embodiment of the present invention will be given with reference to the drawings. Although many technical details are described in each embodiment of the present invention to facilitate understanding of the present invention, it is obvious to those skilled in the art that the technical solutions protected by the present invention can be realized without these technical details and various changes and modifications based on the following embodiments.

[0021] As shown in FIGS. 1 to 10, the technical solution of the present invention provides optical systems 100 and 200. FIGS. 1 and 6 show the optical systems 100 and 200 of the present invention, each of which includes three lenses. Specifically, from the back to the front, the optical systems 100 and 200 include, in order, an aperture 11, a first lens 12, a reflective polarizing film 13, a quarter-wave plate 14, a second lens 15, a semi-transmissive semi-reflective film 16, a third lens 17, a circular polarizer 18, and an image plane 19. In this embodiment, the image plane 19 is a display, and its size is 1.0 to 1.3 inches. In this invention, the back side refers to the side facing the human eye, and the front side refers to the side facing the display in the direction of the optical axis. The front surface refers to the surface facing the human eye in the direction of the optical axis. The back surface refers to the surface facing the human eye in the direction of the optical axis.

[0022] Specifically, the light beam emitted from the image plane 19 passes through the circular polarizer 18, and then forms left-handed circularly polarized LCP, which then enters the third lens 17. The front surface of the second lens 15 is plated with a semi-transmissive semi-reflective film 16, and the left-handed circularly polarized LCP emitted from the back surface of the third lens 17 enters the semi-transmissive semi-reflective film 16, and some of the light beam is reflected, and some of the light beam enters the second lens 15. At this time, the light beam incident on the second lens 15 is left-handed circularly polarized LCP.

[0023] When a composite film consisting of a reflective polarizing film 13 and a quarter-wave plate 14 is provided on the front surface of the first lens 12, the reflective polarizing film 13 is closer to the front surface of the first lens 12 than the quarter-wave plate 14, and the left-handed circularly polarized light LCP emitted from the second lens 15 is converted into linearly polarized light S after passing through the quarter-wave plate 14 for the first time, and then reflected by the reflective polarizing film 13. The reflected light is still linearly polarized light S, and after passing through the quarter-wave plate 14 for the second time, it is converted into left-handed circularly polarized light LCP. The light is then incident on the second lens 15 for the second time, partially reflected by the semi-transmissive semi-reflective film 16, the reflected light is converted into right-handed circularly polarized light RCP, and incident on the second lens 15 for the third time. The right-handed circularly polarized light RCP exits the second lens 15, then incidents on the quarter-wave plate 14, which converts it into linearly polarized light P, and incidents on the reflective polarizing film 13. Since the reflective polarizing film 13 has the property of reflecting linearly polarized light S and transmitting linearly polarized light P, the linearly polarized light P passes through the first lens and then incidents on the diaphragm 19. The diaphragm 11 is positioned to simulate the surface of the human eye.

[0024] When a composite film consisting of a reflective polarizing film 13 and a quarter-wave plate 14 is provided on the rear surface of the second lens 15, the reflective polarizing film 13 is farther from the rear surface of the second lens 15 than the quarter-wave plate 14, and the left-handed circularly polarized light LCP emitted from the second lens 15 is converted into linearly polarized light S after passing through the quarter-wave plate 14 for the first time, and then reflected by the reflective polarizing film 13. The reflected light is still linearly polarized light S, and after passing through the quarter-wave plate 14 for the second time, it is converted into left-handed circularly polarized light LCP. The right-handed circularly polarized light RCP is then incident on the second lens 15 for the second time, and is then partially reflected by the semi-transmissive semi-reflective film 16. The reflected light is converted into right-handed circularly polarized light RCP and incident on the second lens 15 for the third time. The right-handed circularly polarized light RCP is then emitted from the second lens 15, and is then incident on the quarter-wave plate 14, which converts it into linearly polarized light P and incidents on the reflective polarizing film 13. Since the reflective polarizing film 13 has the property of reflecting linearly polarized light S and transmitting linearly polarized light P, the linearly polarized light P passes through the first lens and then enters the aperture 19.

[0025] A composite film consisting of a reflective polarizing film 13 and a quarter-wave plate 14 is attached to the front surface of the first lens 12, and a folded optical path structure is used to reduce the volume of the optical system. In addition, a semi-transmissive semi-reflective film 16 is attached to the front surface of the second lens 15, and the first lens 12 and the second lens 15 are simultaneously involved in the folded optical path design, which significantly reduces the overall optical length of the optical system and is advantageous for the development of smaller and lighter VR devices.

[0026] When the focal length of the optical system is defined as f and the focal length of second lens 15 is defined as f2, the relational expression 5.00≦f2 / f≦9.00 is established, which defines the ratio of the focal length of second lens 15 to the total focal length of the optical system. By allocating focal lengths within the range of this relational expression, it is advantageous to correct aberration problems at off-axial angles of view.

[0027] If the central radius of curvature of the back surface of first lens 12 is defined as R1 and the central radius of curvature of the front surface of first lens 12 is defined as R2, the relationship 1.30≦(R1+R2) / (R1-R2)≦4.80 is established to define the shape of the first lens. By rationally controlling the surface shape within this relationship, it is advantageous to correct aberrations of light rays during the reflection process and to shorten the overall length of the optical system.

[0028] When the central radius of curvature of the back surface of the third lens 17 is defined as R5 and the central radius of curvature of the front surface of the third lens 17 is defined as R6, the relational expression 0.90≦R5 / R6≦2.80 is established. Within the range of this relational expression, by controlling the surface shape of the third lens 17, the emission angle of the light rays from the third lens 17 can be effectively increased, so that the optical system has a wide field of view and can provide a wide range of eye movement.

[0029] When the maximum effective radius of each lens in the optical system is defined as SDmax, the relation SDmax≦23.00 mm is established, and if it is within this range, it helps to reduce the volume of the optical system.

[0030] When the size of the eyebox of an optical system is defined as Eyebox, the relationship Eyebox ≥ 12.00mm is established. Within this range, users can view the optimal display effect at the optimal position without tedious adjustments. The FOV can be increased to reach 90°. For easier understanding, the eyebox size can be considered as the sum of the entrance pupil diameter ENPD ±4mm of the optical system and the eye movement range eyeshift ±4mm. Setting Eyebox ≥ 12mm improves the full field of view performance of the optical system and improves the user's viewing experience when glasses are poorly adjusted.

[0031] When the axial distance from the human eye to the rear surface of the first lens 12 is defined as eyerelief, i.e., the axial distance from the aperture 11 to the rear surface of the first lens 12 (this is the space in which other structures, such as mechanical mechanisms or glasses, can be placed), the relational expression eyerelief≦16.50 mm is established, and if it falls within the range of this relational expression and satisfies the eye's normal condition, the overall optical length of the optical system can be made shorter, which is advantageous for miniaturization.

[0032] When the axial distance from the back surface of the first lens 12 to the image plane 19 is defined as TL, the relational expression TL≦18.40 mm is established, and being within the range of this relational expression is advantageous for making the optical system compact.

[0033] When the total optical length of the optical system (the axial distance from the human eye to the image plane 19, i.e., the axial distance from the aperture 11 to the image plane 19) is defined as TTL, the relational expression TTL≦34.80 mm is established, and being within the range of this relational expression is advantageous for miniaturizing the optical system.

[0034] The rear and front surfaces of the first lens 12, the second lens 15, and the third lens 17 are all aspheric. The aspheric design allows for adjustment of the focus position of the displayed image, reduction of chromatic aberration and distortion of the displayed image, and improvement of imaging quality.

[0035] In the present invention, the transmittance and reflectance of the semi-transmitting semi-reflective film 16 are both 40.00% to 60.00%, and may be, for example, 50:50, 40:60, 60:40, etc. in each embodiment.

[0036] In the present invention, the transmittance of the reflective polarizing film 13 is 95% or more, and a higher transmittance can improve the light efficiency of the optical system and increase the display brightness.

[0037] When the optical distortion of an optical system is defined as MIST, the relational expression MIST≦35.00% is established. If the value falls within the range of this relational expression, the distortion of the optical system will be small, and a more realistic VR environment can be provided to the user.

[0038] When the chromatic aberration of an optical system is defined as LC, the relational expression LC≦100μm is established. If the chromatic aberration of the optical system is within the range of this relational expression, the chromatic aberration of the optical system will be small, and a more realistic VR environment can be provided to the user.

[0039] The focal length of the optical system is defined as f, and the relation TTL / f≦2.10 is established. If the focal length is within this relation, it is advantageous to reduce the volume of the optical system. (First embodiment)

[0040] The optical system 100 of the present invention will be described below using examples. The symbols used in each example are as follows: focal length, axial distance, central radius of curvature, axial thickness, inflection point position, and stationary point position are all in mm.

[0041] 1 and 5 show an optical system 100 according to a first embodiment of the present invention.

[0042] As shown in FIG. 5, in the first embodiment, a composite film made up of the reflective polarizing film 13 and the quarter-wave plate 14 is provided on the front surface 122 of the first lens 12.

[0043] Tables 1 and 2 show setting data for the optical system 100 according to the first embodiment of the present invention.

[0044] [Table 1]

[0045] Here, the meaning of each symbol is as follows: R: Radius of curvature at the center of the optical surface R1: central radius of curvature of the back surface of the first lens 12 R2: central radius of curvature of the front surface of the first lens 12 R3: central radius of curvature of the back surface of the second lens 15 R4: central radius of curvature of the front surface of the second lens 15 R5: central radius of curvature of the rear surface of the third lens 17 R6: central curvature radius of the front surface of the third lens 17 d: Axial thickness of lens, axial distance between lenses (To make the optical path easier to understand, a positive value indicates that light is propagating from the back side to the front side, and a negative value indicates that light is propagating from the front side to the back side) d0: the axial distance from the aperture stop 11 to the rear surface 121 of the first lens 12 d1: axial thickness of the first lens 12 d2: On-axis thickness of the reflective polarizing film 13 d3: On-axis thickness of the quarter-wave plate 14 d4: the axial distance from the front surface 141 of the quarter-wave plate 14 to the back surface 151 of the second lens 15 d5: Axial thickness of the second lens 15 d6: Negative value of the axial thickness of the second lens element 15 d7: a negative value of the on-axis distance from the front surface 141 of the quarter-wave plate 14 to the back surface 151 of the second lens 15 d8: Negative value of the axial thickness of the quarter wave plate 14 d9: the axial distance from the front surface 152 of the second lens 15 to the back surface 171 of the third lens 17 d10: Axial thickness of the third lens element 17 d11: the axial distance from the front surface 172 of the third lens 17 to the back surface 181 of the circular polarizer 18 d12: On-axis thickness of the circular polarizer 18 nd: Refractive index of the d line (d line is green light with a wavelength of 540 nm) nd1: refractive index of the first lens 12 at the d line nd2: refractive index of the d line of the second lens 15 nd3: refractive index of the third lens 17 at the d line ng: refractive index of the d line of the circular polarizer 18 vd: Abbe number v1: Abbe number of the first lens 12 v2: Abbe number of the second lens 15 v3: Abbe number of the third lens element 17 vg: Abbe number of circular polarizer 18

[0046] Table 2 shows the aspheric data of each lens of the optical system 100 according to the first embodiment of the present invention.

[0047] [Table 2]

[0048] For convenience, the aspherical surface of each lens surface is expressed by the following formula (1): However, the present invention is not limited to the aspherical polynomial format expressed by formula (1). z=(cr 2 ) / {1+[1-(k+1)(c 2 r 2 )] 1 / 2}+A4r 4 +A6r 6 +A8r 8 +A10r 10 +A12r 12 +A14r 14 +A16r 16 (1)

[0049] Here, k is the conic coefficient, A4, A6, A8, A10, A12, A14, and A16 are aspheric coefficients, c is the curvature of the center of the optical surface, r is the perpendicular distance between a point on the aspheric curve and the optical axis, and z is the aspheric depth (the perpendicular distance between a point on the aspheric surface that is a distance r from the optical axis and a tangent plane that touches the vertex on the aspheric optical axis).

[0050] 2 and 3 are diagrams showing spot diagrams and chromatic aberration of magnification, respectively, after light having wavelengths of 470 nm, 540 nm, and 630 nm has passed through optical system 100 of the first embodiment. Fig. 4 is a diagram showing curvature of field and distortion aberration after light having a wavelength of 540 nm has passed through optical system 100 of the first embodiment, where curvature of field S in Fig. 4 is the curvature of field in the sagittal direction and T is the curvature of field in the meridional direction.

[0051] In this embodiment, the optical system 100 has an entrance pupil diameter ENPD of 4.00 mm, a full field of view image height IH of 11.500 mm, and a diagonal angle of view FOV of 89.94°. The optical system 100 satisfies the design requirements for compactness and light weight, and its on-axis and off-axis chromatic aberrations are sufficiently corrected, providing excellent optical characteristics. (Second embodiment)

[0052] The second embodiment is basically the same as the first embodiment, and the symbols have the same meanings as in the first embodiment, so only the differences will be listed below.

[0053] 6 and 10 show an optical system 200 according to a second embodiment of the present invention.

[0054] As shown in FIG. 10, in the optical system 200 of the second embodiment, a composite film made up of the reflective polarizing film 13 and the quarter-wave plate 14 is provided on the back surface 151 of the second lens 15.

[0055] Tables 3 and 4 show setting data for the optical system 200 according to the second embodiment of the present invention.

[0056] In this second embodiment, the installation position of the composite film is different from that of the first embodiment, and therefore, what differs from the first embodiment is that d4 in Table 3 represents the axial distance from the front surface 122 of the first lens 12 to the back surface 131 of the reflective polarizing film 13.

[0057] [Table 3]

[0058] Table 4 shows the aspheric data of each lens of the optical system 200 according to the second embodiment of the present invention.

[0059] [Table 4]

[0060] 7 and 8 are diagrams showing spot diagrams and chromatic aberration of magnification, respectively, after light with wavelengths of 470 nm, 540 nm, and 630 nm has passed through the optical system 200 of the second embodiment. Fig. 9 is a diagram showing curvature of field and distortion aberration after light with a wavelength of 540 nm has passed through the optical system 200 of the second embodiment. In Fig. 9, curvature of field S is the curvature of field in the sagittal direction, and T is the curvature of field in the meridional direction.

[0061] In this embodiment, the optical system 10 has an entrance pupil diameter ENPD of 4.00 mm, a full field of view image height IH of 11.200 mm, and a diagonal angle of view FOV of 94.95°. The optical system 200 satisfies the design requirements for compactness and light weight, and its on-axis and off-axis chromatic aberrations are sufficiently corrected, resulting in excellent optical characteristics.

[0062] [Table 5]

[0063] The above-described embodiments are specific embodiments for realizing the present invention, but it should be understood by those skilled in the art that in actual applications, various changes in form and details that do not deviate from the spirit and scope of the present invention will all fall within the scope of protection of the present invention.

Claims

1. The optical system includes, in order from the rear side to the front side, a diaphragm located on the rear side of the optical system, a first lens, a second lens, a third lens, a circular polarizer, and an image surface; wherein the circular polarizer is attached to a rear surface of the image plane, and a composite film is provided on a front surface of the first lens or a rear surface of the second lens, the composite film including a reflective polarizing film and a quarter wave plate, and the reflective polarizing film is provided on the rear side of the quarter wave plate; an optical system characterized by satisfying the following relational expression, wherein a focal length of the optical system is defined as f, a focal length of the second lens is defined as f2, a central radius of curvature of the back surface of the first lens is defined as R1, a central radius of curvature of the front surface of the first lens is defined as R2, a central radius of curvature of the back surface of the third lens is defined as R5, a central radius of curvature of the front surface of the third lens is defined as R6, and a maximum effective radius of each lens in the optical system is defined as SDmax: 5.00≦f2 / f≦9.00 1.30≦(R1+R2) / (R1-R2)≦4.80 0.90≦R5 / R6≦2.80 SDmax≦23.00mm

2. 2. The optical system according to claim 1, wherein the following relational expression is satisfied when the size of the eyebox of the optical system is defined as Eyebox: Eyebox≧12.00mm

3. 2. The optical system according to claim 1, wherein the following relational expression is satisfied when the on-axis distance from a human eye to the back surface of the first lens is defined as eyerelief: eye relief≦16.50mm

4. 2. The optical system according to claim 1, wherein the following relational expression is satisfied when an axial distance from the back surface of the first lens to the image plane is defined as TL: TL≦18.40mm

5. 2. The optical system according to claim 1, wherein the following relational expression is satisfied when the total optical length of the optical system is defined as TTL: TTL≦34.80mm

6. 2. The optical system according to claim 1, wherein the back and front surfaces of the first lens, the back and front surfaces of the second lens, and the back and front surfaces of the third lens are all aspheric.

7. 2. The optical system according to claim 1, wherein the following relational expression is satisfied when the angle of view of the optical system is defined as FOV: 85.00°≦FOV≦95.00°

8. 2. The optical system according to claim 1, wherein a semi-transmissive, semi-reflective film is plated on the front surface of said second lens.

9. 9. The optical system according to claim 8, wherein the transmittance and reflectance of the semi-transmissive semi-reflective film are both 40.00% to 60.00%.

10. 2. The optical system according to claim 1, wherein the transmittance of the reflective polarizing film is 95% or more.

11. 2. The optical system according to claim 1, wherein the following relational expression is satisfied when the distortion of the optical system is defined as MIST: MIST≦35.00%

12. 2. The optical system according to claim 1, wherein the following relational expression is satisfied when chromatic aberration of the optical system is defined as LC: LC≦100 μm

13. 2. The optical system according to claim 1, wherein the following relational expression is satisfied when the total optical length of the optical system is defined as TTL: TTL / f≦2.10

14. 2. The optical system according to claim 1, wherein the image surface is a display, and the size thereof is 1.0 to 1.3 inches.

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