Pancake optical system

Abstract

The present invention discloses a Pancake optical system in the field of optical imaging technology, comprising an object side and an image side of the Pancake optical system that are relatively arranged along the extension direction of the optical axis. The Pancake optical system is provided with three plastic aspheric lenses, namely a first lens, a second lens and a third lens, in sequence from the object side to the image side. The image side of the first lens is provided with a polarizer, a reflective polarizer, a phase delay plate and an anti-reflection plate from the inside to the outside, and the image side of the second lens is provided with a semi-reflective lens. The present invention can fully expand the field of view by controlling parameters such as the curvature radius, refractive index, and Abbe number of the lens, so that the screen performance is fully utilized, and the dispersion problem is effectively reduced. There is no need for post-processing color correction, no need for frequent adjustments to correct spatial cognition, and no destruction of user immersion or dizziness.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging technology, and in particular to a Pancake optical system. Background Art

[0002] With the widespread popularity of VR, the optical solutions for VR are also being updated. Currently, the main optical solution in the VR market is the Fresnel lens solution. However, the Fresnel lens solution is heavy, the module is thick, and the image quality is poor. With the development of the consumer market, the Pancake solution with a better experience is becoming the first choice of leading companies. The Pancake solution mainly uses the principle of polarized light and adopts a folded optical path design. After the image source enters the semi-reflective and semi-transparent beam splitter, the light is reflected back and forth multiple times between the lens, phase delay plate and reflective polarizing film, and finally emitted from the reflective polarizing film into the human eye.

[0003] The module thickness of the Pancake solution is greatly reduced. Through the lens combination, the imaging quality of the lens edge is improved, image distortion is reduced, and the imaging contrast, clarity and fineness are improved. Moreover, the Pancake solution is a combined lens, and the diopter can be adjusted by controlling one of the lenses. The currently generally supported adjustment range is 0° to 700°.

[0004] However, the main problem with the Pancake solution is its small market potential. Although the theoretical upper limit of the Pancake solution's field of view is relatively high, the actual field of view of the current mass-produced solution is basically between 60 and 90 degrees, which is lower than that of the Fresnel solution. In addition, due to the birefringence of light, the image is easily distorted. The birefringence is related to the lens material.

[0005] Based on this, the present invention designs a Pancake optical system to solve the above problems. Summary of the Invention

[0006] The object of the present invention is to provide a Pancake optical system to solve the problems raised in the above background technology.

[0007] To achieve the above objectives, the present invention provides the following technical solutions: a Pancake optical system, comprising an object side and an image side of the Pancake optical system that are oppositely arranged along an optical axis extension direction; the Pancake optical system is provided with three plastic aspheric lenses, namely, a first lens, a second lens, and a third lens, in sequence from the object side to the image side; the image side of the first lens is provided with a polarizer, a reflective polarizer, a phase delay plate, and an anti-reflection plate in sequence from the inside to the outside; and the image side of the second lens is provided with a semi-reflective lens;

[0008] The lens power distribution method satisfies the following conditional formula:

[0009] -150mm <f1<-50mm;

[0010] 5mm <f2<45mm;

[0011] -1000mm <f3<-700mm;

[0012] f is the effective focal length of the lens module, where f(a) is the lens number;

[0013] The lens satisfies:

[0014] 1.51<|Nd1|<1.62,40<|Vd1|<65;

[0015] 1.51<|Nd2|<1.62,40<|Vd2|<65;

[0016] 1.51<|Nd3|<1.62,40<|Vd3|<65;

[0017] Where Nd(a) represents the refractive index of a lens, Vd(a) represents the Abbe number of a lens, and a is the lens serial number.

[0018] As a further solution of the present invention, the lens satisfies:

[0019] 10mm<|R11|<70mm, 60mm<|R12|<120mm;

[0020] 110mm<|R21|<200mm,10mm<|R22|<70mm;

[0021] 200mm<|R31|<1000mm,500mm<|R32| <inf;

[0022] Where R(ab) represents the radius of curvature of a certain surface of a lens, a is the lens number, b is the surface number, and inf is infinity.

[0023] As a further embodiment of the present invention, f(a) satisfies:

[0024] 0.05 <f1 / f3<0.25;

[0025] 5 <f3 / (f1+f2)<15;

[0026] f / EPD<2;

[0027] Wherein, f is the effective focal length of the lens module, and EPD is the entrance pupil diameter.

[0028] As a further solution of the present invention, the module of the Pancake optical system also satisfies the following conditional formula:

[0029] 11.5mm ≤ Ts ≤ 13mm;

[0030] Where Ts is the total thickness of the Pancake optical system.

[0031] As a further solution of the present invention, the Pancake optical system achieves myopia diopter adjustment of 0 to 500° by dynamically adjusting the distances between the first lens, the second lens, and the third lens, and the total thickness of the module is not changed during the diopter adjustment process.

[0032] As a further solution of the present invention, the entrance pupil diameter of the Pancake optical system is not less than 14 mm.

[0033] As a further solution of the present invention, the field of view angle of the Pancake optical system is not less than FOV 100°.

[0034] As a further solution of the present invention, the full-field lateral chromatic aberration of the Pancake optical system is less than 0.6 μm.

[0035] As a further solution of the present invention, when the circularly polarized light of the polarization state of the light emitted from the display is left-handed polarized light LCP, it enters the optical system through a half-mirror, maintains the left-handed polarized light LCP through the second lens and the third lens, and is converted into S-polarized light through a phase delay plate. At this time, the polarization direction is parallel to the Y-axis. After being reflected by the reflective polarizing film, the S-light polarization state is maintained. After passing through the phase delay plate again, it is converted into left-handed polarized light LCP. After reaching the second lens, it is reflected by the half-mirror and converted into right-handed polarized light. After passing through the second lens and the first lens, it continues to pass through the phase delay plate and becomes P-polarized light. At this time, the polarization direction is parallel to the X-axis and reaches the exit pupil through the reflective polarizing film and the polarizer.

[0036] Another object of the present invention is to provide a smart wearable device, comprising any one of the above-mentioned Pancake optical systems.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. By controlling lens parameters such as radius of curvature, refractive index, and Abbe number, this invention can fully expand the field of view, fully utilizing screen performance and effectively reducing chromatic aberration. It eliminates the need for post-processing color correction and frequent adjustments to correct spatial perception, and will not disrupt user immersion or cause dizziness.

[0039] 2. By setting the curvature radius of the lens' object and image sides, the present invention ensures that each aspheric surface is not excessively curved or undulating, facilitating molding while facilitating the attachment of polarizing film layers, thereby improving production yield.

[0040] 3. This invention ensures that the lenses are made of high-refractive-index, low-dispersion materials by adjusting the Abbe number and refractive index of the lenses. This reduces dispersion and distortion, improves image quality, and avoids post-processing color correction, thereby reducing CPU power consumption. Furthermore, high-refractive-index, low-dispersion materials help reduce the overall weight and volume of VR glasses, improving wearing comfort.

[0041] 4. The optical power distribution method provided by the present invention satisfies the - + - structure, resulting in an initial low-stress lens structure with uniform optical power distribution and a flat surface, thereby improving the stability of the film and shortening the optical path length. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of the overall structure of the present invention, wherein: first lens G1; object-side surface S1 of the first lens G1; image-side surface S2 of the first lens; second lens G2; object-side surface S3 of the second lens G2; image-side surface S4 of the second lens G2; third lens G3; object-side surface S5 of the third lens G3; image-side surface S6 of the third lens G3; quarter-wave plate (QWP) 11; anti-reflection plate (AR) 12; reflective polarizer (RP) 13; polarizer (POL) 14; semi-reflective plate (BS) 15;

[0043] Figure 2 Schematic diagram of the modulation transfer function in Example 1;

[0044] Figure 3 Schematic diagram of the modulation transfer function in Example 2. DETAILED DESCRIPTION

[0045] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limiting the present invention.

[0046] The present invention provides a technical solution:

[0047] A pancake optical system, comprising an object side and an image side of the pancake optical system that are arranged opposite to each other along an optical axis. The pancake optical system is provided with three plastic aspheric lenses, namely, a first lens, a second lens, and a third lens, in sequence from the object side to the image side. The image side of the first lens is provided with a polarizer, a reflective polarizer, a phase delay film, and an anti-reflection film in sequence from the inside out. The image side of the second lens is provided with a semi-reflective lens.

[0048] The lens power distribution method satisfies the following conditional expressions:

[0049] -150 mm < f1 < -50 mm;

[0050] 5 mm < f2 < 45 mm;

[0051] -1000 mm < f3 < -700 mm;

[0052] where f is the effective focal length of the lens module, f(a), and a is the lens serial number; according to this power distribution method, a - + - type structure is satisfied, and an initial structure of a low-stress lens with uniform power distribution and a gentle surface shape is obtained, improving the stability of film sticking and shortening the optical path length; according to the above content, it should also satisfy 0.05 < f1 / f3 < 0.25, 5 < f3 / (f1 + f2) < 15, f / EPD < 2; where f is the effective focal length of the lens module, and EPD is the entrance pupil diameter;

[0053] The lens satisfies:

[0054] 1.51 < |Nd1| < 1.62, 40 < |Vd1| < 65;

[0055] 1.51 < |Nd2| < 1.62, 40 < |Vd2| < 65;

[0056] 1.51 < |Nd3| < 1.62, 40 < |Vd3| < 65;

[0057] [[ID=2"]]where Nd(a) represents the refractive index of a certain lens, Vd(a) represents the Abbe number of a certain lens, and a is the lens serial number; for example, Nd1 represents the refractive index of the first lens G1, and Vd2 represents the Abbe number of the second lens; when the VR lens satisfies the above relational expressions, it is ensured that the lens uses high-refractive-index and low-dispersion materials, thereby reducing dispersion and distortion problems, improving imaging quality, avoiding post-processing color correction, and thus reducing CPU power consumption. At the same time, high-refractive-index and low-dispersion materials help to reduce the overall weight and volume of the VR glasses and improve the wearing comfort.

[0058] Among them, the lens satisfies:

[0059] 10 mm < |R11| < 70 mm, 60 mm < |R12| < 120 mm;

[0060] 110 mm < |R21| < 200 mm, 10 mm < |R22| < 70 mm;

[0061] 200 mm < |R31| < 1000 mm, 500 mm < |R32| < inf;

[0062] Here, R(ab) represents the radius of curvature of a lens surface, a represents the lens number, b represents the surface number, and inf represents infinity. For example, R11 represents the object-side surface of the first lens G1, and R22 represents the image-side surface of the second lens G2. When a VR lens satisfies this relationship, controlling the lens curvature radius ensures that each aspheric surface is not excessively curved or fluctuating, facilitating molding and facilitating the attachment of a polarizing film, thereby improving production yield.

[0063] The module of the Pancake optical system also satisfies the following conditional formula:

[0064] 11.5mm ≤ Ts ≤ 13mm;

[0065] Where Ts is the total thickness of the Pancake optical system.

[0066] The Pancake optical system achieves myopia diopter adjustment of 0 to 500° by dynamically adjusting the distances between the first lens, the second lens, and the third lens, and the total thickness of the module is not changed during the diopter adjustment process.

[0067] Wherein, the entrance pupil diameter of the Pancake optical system is not less than 14 mm.

[0068] Wherein, the field of view angle of the Pancake optical system is not less than FOV 100°.

[0069] The full-field lateral chromatic aberration of the Pancake optical system is less than 0.6 μm.

[0070] Among them, when the circularly polarized light of the polarization state of the light emitted from the display is left-handed polarized light LCP, it enters the optical system through a half-mirror, maintains the left-handed polarized light LCP through the second lens and the third lens, and is converted into S-polarized light through the phase delay plate. At this time, the polarization direction is parallel to the Y axis. After being reflected by the reflective polarizing film, the S light polarization state is maintained. After passing through the phase delay plate again, it is converted into left-handed polarized light LCP. After reaching the second lens, it is reflected by the half-mirror and converted into right-handed polarized light. After passing through the second lens and the first lens, it continues to pass through the phase delay plate and becomes P-polarized light. At this time, the polarization direction is parallel to the X axis and reaches the exit pupil through the reflective polarizing film and the polarizer.

[0071] Another object of the present invention is to provide a smart wearable device, comprising the above-mentioned Pancake optical system. Example 1

[0072] The system surface data meets the conditions in Table 1 below:

[0073] Table 1

[0074]

[0075] Among them, T(3), T(5), and T(7) meet the conditions in Table 2 below:

[0076] Table 2:

[0077]

[0078] in:

[0079] R (mm): radius of curvature of each surface;

[0080] T (mm): the distance between lenses and the thickness of the lenses;

[0081] K: cone coefficient;

[0082] α1: second-order aspheric coefficient;

[0083] α2: fourth-order aspheric coefficient;

[0084] α3: sixth-order aspheric coefficient;

[0085] α4: eighth-order aspheric coefficient;

[0086] α5: tenth-order aspheric coefficient;

[0087] α6: twelfth-order aspheric coefficient;

[0088] Aspheric surface formula:

[0089] ;

[0090] Nd: refractive index of each glass at d line;

[0091] Vd: Abbe number of glass;

[0092] Among them, surface number 1 is the aperture, surface number 2 corresponds to the object-side surface S1 of the first lens G1, surface number 3 corresponds to the image-side surface S2 of the first lens, surface number 4 corresponds to the object-side surface S3 of the second lens G2, surface number 5 corresponds to the image-side surface S4 of the second lens G2, surface number 6 corresponds to the object-side surface S5 of the third lens G3, and surface number 7 corresponds to the image-side surface S6 of the third lens G3;

[0093] Among them, T corresponding to surface number 1 is the distance between the aperture and the first lens G1, T corresponding to surface number 2 is the thickness of the first lens G1, T corresponding to surface number 3 is the distance between the first lens G1 and the second lens G2, T corresponding to surface number 4 is the thickness of the second lens G2, T corresponding to surface number 5 is the distance between the second lens G2 and the third lens G3, T corresponding to surface number 6 is the thickness of the third lens G3, and T corresponding to surface number 7 is the distance between the third lens G3 and the OLED;

[0094] See also Figure 1-2 A pancake optical system specifically consists of three plastic aspheric lenses. The first, second, and third lenses, G1, G2, and G3, are all made of APL5014XH. The system has a focal length of f=11.3301mm, with the first lens G1 having a focal length of f1=-126.8952mm, the second lens G2 having a focal length of f2=10.3729mm, and the third lens G3 having a focal length of f3=-941.4295mm. The system has a total thickness of less than 13.5mm, enabling diopter adjustment from 0 to 500 degrees of myopia. This adjustment process does not change the total thickness of the module, meeting the needs of most myopic patients who can use VR glasses without wearing glasses. The field of view (FOV) is 100°, fully utilizing the screen's performance. The traditional 3P Pancake dispersion is approximately 100-200μm. This design adopts a 3P structure and uses low-dispersion materials. The lateral chromatic aberration across the entire field of view is less than 1.0μm, eliminating the need for post-processing color correction.

[0095] Due to barrel or pincushion distortion in aspheric lenses, the distortion rate of the peripheral field of view can reach 15%-20%. If the interpupillary distance (IPD) and the center distance (ICD) of the lens are mismatched (e.g., the difference is greater than ±2mm), the binocular images will produce double vision (double vision) due to the misalignment of the visual axes. The user's pupils must be forced to focus through compensatory shifts, resulting in blurred vision. In this design, the entrance pupil diameter is 14mm, which can accommodate the normal pupil drift of ±5mm. This eliminates the need for frequent adjustments to correct spatial cognition, does not disrupt user immersion, and does not cause dizziness.

[0096] like Figure 1 As shown, the Z axis is the optical axis direction, the polarization direction of the transmitted light of the POL film is parallel to the X axis; the RP film transmits the light with the polarization direction parallel to the X axis and reflects the light with the polarization direction parallel to the Y axis; the fast axis of the 1 / 4 wave plate QWP is at an angle of 45° with the X axis.

[0097] Circularly polarized light (assuming left-handed polarized light, LCP) emitted from the display enters the optical system through a half-mirror (BS). It passes through the second and third lenses, G2 and G3, maintaining the left-handed polarized light (LCP). It is converted to S-polarized light by a quarter-wave plate (QWP), with the polarization direction parallel to the Y axis. After reflecting off the RP reflective film, it maintains its S polarization state and passes through the QWP again, converting it to LCP. After reaching the second lens, G2, it is reflected off the half-mirror (BS), converting it to RCP. After passing through the second lens, G2, and then the first lens, G1, it passes through the QWP again, converting it to P-polarized light, with the polarization direction parallel to the X axis. It then passes through the RP reflective film and the POL film to reach the exit pupil.

[0098] This system can adjust the diopter from 0° to 500°. For example, when adjusting from -1D to -5D, the distance the third lens G3 moves toward the second lens G2 is 0.5817mm (according to Table 4: 0.7792 - 0.1975 = 0.5817). Furthermore, the diopter adjustment process does not change the overall thickness of the lens module, meeting the needs of most myopic patients for glasses-free use.

[0099] The modulation transfer function (MTF) of Example 1 is as follows: Figure 2 As shown, TS represents the field of view angle, for example, TS-11.00 represents a field of view angle of 11 degrees. Example 2

[0100] The system surface data meets the conditions in Table 3 below:

[0101] Table 3

[0102]

[0103] Among them, T(3), T(5), and T(7) meet the conditions in Table 4 below:

[0104] Table 4

[0105]

[0106] in:

[0107] R (mm): radius of curvature of each surface;

[0108] T (mm): the distance between lenses and the thickness of the lenses;

[0109] K: cone coefficient;

[0110] α1: second-order aspheric coefficient;

[0111] α2: fourth-order aspheric coefficient;

[0112] α3: sixth-order aspheric coefficient;

[0113] α4: eighth-order aspheric coefficient;

[0114] α5: tenth-order aspheric coefficient;

[0115] α6: twelfth-order aspheric coefficient;

[0116] Aspheric surface formula:

[0117] ;

[0118] Nd: refractive index of each glass at d line;

[0119] Vd: Abbe number of glass;

[0120] Among them, surface number 1 is the aperture, surface number 2 corresponds to the object-side surface S1 of the first lens G1, surface number 3 corresponds to the image-side surface S2 of the first lens, surface number 4 corresponds to the object-side surface S3 of the second lens G2, surface number 5 corresponds to the image-side surface S4 of the second lens G2, surface number 6 corresponds to the object-side surface S5 of the third lens G3, and surface number 7 corresponds to the image-side surface S6 of the third lens G3;

[0121] Among them, T corresponding to surface number 1 is the distance between the aperture and the first lens G1, T corresponding to surface number 2 is the thickness of the first lens G1, T corresponding to surface number 3 is the distance between the first lens G1 and the second lens G2, T corresponding to surface number 4 is the thickness of the second lens G2, T corresponding to surface number 5 is the distance between the second lens G2 and the third lens G3, T corresponding to surface number 6 is the thickness of the third lens G3, and T corresponding to surface number 7 is the distance between the third lens G3 and the OLED.

[0122] A pancake optical system consists of three plastic aspheric lenses. The first, second, and third lenses (G1, G2, and G3) are all made of APL5014XH. The system has a focal length of f=11.3373mm, with the first lens (G1) having a focal length of f1=-127.8564mm, the second lens (G2) having a focal length of f2=10.3711mm, and the third lens (G3) having a focal length of f3=-797.9630mm. The system's total thickness is less than 13.1mm, enabling diopter adjustment from 0° to 500°. This adjustment process dynamically adjusts the distances between G1 and G2, G2 and G3, and G3 and the image plane without changing the overall module thickness, meeting the needs of most myopic patients for using VR glasses without wearing glasses. The field of view (FOV) is 100°, fully utilizing the screen's performance. The dispersion of a traditional 3PP pancake is approximately 100-200μm. This design adopts a 3P structure and uses low-dispersion materials. The lateral chromatic aberration of the entire field of view is less than 1.1μm, and no post-processing color correction is required.

[0123] Due to barrel or pincushion distortion in aspheric lenses, the distortion rate of the peripheral field of view can reach 15%-20%. If the interpupillary distance (IPD) and the center distance (ICD) of the lens are mismatched (e.g., the difference is greater than ±2mm), the binocular images will produce double vision (double vision) due to the misalignment of the visual axes. The user's pupils must be forced to focus through compensatory shifts, resulting in blurred vision. In this design, the entrance pupil diameter is 14mm, which can accommodate the normal pupil drift of ±5mm. This eliminates the need for frequent adjustments to correct spatial cognition, does not disrupt user immersion, and does not cause dizziness.

[0124] This system can adjust the diopter from 0° to 500°. For example, when adjusting from -1D to -5D, the distance the third lens G3 moves toward the second lens G2 is 0.5780mm (according to Table 4: 0.7754 - 0.1974 = 0.5780). Furthermore, the diopter adjustment process does not change the overall thickness of the lens module, meeting the needs of most myopic patients for glasses-free use.

[0125] The modulation transfer function (MTF) of Example 2 is as follows: Figure 3 As shown, TS represents the field of view angle, for example, TS-11.00 represents a field of view angle of 11 degrees.

Claims

1. A pancake optical system, comprising an object side and an image side disposed opposite each other along an optical axis. The pancake optical system comprises three plastic aspheric lenses, namely, a first lens, a second lens, and a third lens, disposed sequentially from the object side to the image side. The image side of the first lens is sequentially disposed, from the inside out, with a polarizer, a reflective polarizer, a phase delay film, and an anti-reflection film. The image side of the second lens is disposed with a semi-reflective lens. The lens satisfies the following conditional formula: -150mm <f1<-50mm; 5mm <f2<45mm; -1000mm <f3<-700mm; Where f(a) is the effective focal length of the lens, and a is the lens number; The lens satisfies: 1.51<|Nd1|<1.62,40<|Vd1|<65; 1.51<|Nd2|<1.62,40<|Vd2|<65; 1.51<|Nd3|<1.62,40<|Vd3|<65; Where Nd(a) represents the refractive index of a lens, Vd(a) represents the Abbe number of a lens, and a is the lens number; The lens satisfies: 10mm<|R11|<70mm, 60mm<|R12|<120mm; 110mm<|R21|<200mm, 10mm<|R22|<70mm; 200mm<|R31|<1000mm,|R32|=inf; Where R(ab) represents the radius of curvature of a certain surface of a lens, a is the lens number, b is the surface number, and inf is infinity.

2. The Pancake optical system according to claim 1, wherein: The f(a) satisfies: 0.05 <f1 / f3<0.25; 5 <f3 / (f1+f2)<15; f / EPD<2; Where f is the effective focal length of the optical system and EPD is the entrance pupil diameter.

3. The Pancake optical system according to claim 2, wherein: The module of the Pancake optical system also satisfies the following conditional formula: 11.2313mm ≤ Ts ≤ 13mm; Where Ts is the total thickness of the Pancake optical system.

4. The Pancake optical system according to claim 1, wherein: The Pancake optical system achieves myopia diopter adjustment of 0 to 500 degrees by dynamically adjusting the distances between the first lens, the second lens, and the third lens, and the total thickness of the module is not changed during the diopter adjustment process.

5. The Pancake optical system according to claim 1, wherein: The entrance pupil diameter of the Pancake optical system is not less than 14 mm.

6. A Pancake optical system according to any one of claims 1 to 5, characterized in that: The field of view of the Pancake optical system is not less than FOV 100°.

7. The Pancake optical system according to claim 1, wherein: The full-field lateral chromatic aberration of the Pancake optical system is less than 0.6 μm.

8. The Pancake optical system according to claim 1, wherein: When the circularly polarized light emitted from the display is left-handed polarized light LCP, it enters the optical system through a half-mirror, maintains the left-handed polarized light LCP through the second lens and the third lens, and is converted into S-polarized light through the phase delay plate. At this time, the polarization direction is parallel to the Y axis. After being reflected by the reflective polarizing film, the S light polarization state is maintained. After passing through the phase delay plate again, it is converted into left-handed polarized light LCP. After reaching the second lens, it is reflected by the half-mirror and converted into right-handed polarized light. After passing through the second lens and the first lens, it continues to pass through the phase delay plate and becomes P-polarized light. At this time, the polarization direction is parallel to the X axis and reaches the exit pupil through the reflective polarizing film and the polarizer.

9. A smart wearable device, comprising a Pancake optical system according to any one of claims 1 to 8.

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