Pancake optical system

Abstract

The invention discloses a Pancake optical system in the technical field of optical imaging, and the Pancake optical system comprises an object side and an image side which are oppositely arranged along the extension direction of an optical axis, the Pancake optical system is sequentially provided with three plastic aspheric lenses from the object side to the image side, namely a first lens, a second lens and a third lens, the image side of the first lens is sequentially provided with a polaroid, a reflective polaroid, a phase delay sheet and an anti-reflection sheet from inside to outside, and the image side of the second lens is provided with a half-reflection lens; the field angle can be fully expanded by controlling the curvature radius, the refractive index, the Abbe number and other parameters of the lens, the screen performance is fully utilized, the dispersion problem is effectively reduced, post-processing color correction is not needed, space cognition correction through frequent adjustment is not needed, and immersion of a user cannot be damaged or dizziness cannot be caused.

Description

Technical Field

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

[0002] With the wide popularization of VR, the optical solutions of VR are also being updated day by day. Currently, the main optical solution in the VR market is the Fresnel lens solution. However, the Fresnel lens solution has a large weight, a thick module, and poor imaging quality. With the development of the consumer market, the Pancake solution with a better experience is becoming the first choice of leading enterprises. The Pancake solution mainly utilizes the principle of polarized light and adopts a folded optical path design. After the image source enters the beam splitter with semi-reflective and semi-transmissive functions, the light is reflected back and forth multiple times between the lens, the phase retarder, and the reflective polarizing film, and finally exits from the reflective polarizing film and enters the human eye.

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

[0004] However, the main problem of the Pancake solution at present is its small market angle. Although the theoretical upper limit of the field of view angle of the Pancake solution is relatively high, the actual field of view angle of the currently mass-produced solutions is basically between 60° and 90°, which is lower than that of the Fresnel solution. Moreover, due to the birefringence phenomenon of light, the image is prone to distortion, and the birefringence phenomenon 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 purpose of the present invention is to provide a Pancake optical system to solve the problems raised in the above background art.

[0007] To achieve the above purpose, the present invention provides the following technical solution: A Pancake optical system, the Pancake optical system has an object side and an image side that are oppositely arranged along the optical axis extension direction. The Pancake optical system is sequentially provided with three plastic aspherical lenses, namely a first lens, a second lens, and a third lens, from the object side to the image side. On the image side of the first lens, a polarizer, a reflective polarizer, a phase retarder, and an anti-reflection film are sequentially arranged from the inside to the outside. A semi-reflective lens is arranged on the image side of the second lens; The lens focal power distribution method satisfies the following conditional formula: -150mm < f1 < -50mm; 5mm < f2 < 45mm; -1000mm < f3 < -700mm; f is the effective focal length of the lens module, where f(a), a is the lens serial 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 certain lens, Vd(a) represents the Abbe number of a certain lens, and a is the lens serial number.

[0008] As a further solution of the present invention, the lens satisfies: 10mm < |R11| < 70mm, 60mm < |R12| < 120mm; 110mm < |R21| < 200mm, 10mm < |R22| < 70mm; 200mm < |R31| < 1000mm, 500mm < |R32| < inf; Where R(ab) represents the curvature radius of a certain surface of a certain lens, a is the lens serial number, b is the surface serial number, and inf is infinity.

[0009] As a further solution of the present invention, 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 lens module, and EPD is the entrance pupil diameter.

[0010] As a further solution of the present invention, the module of the Pancake optical system also satisfies the following conditional formula: 11.5mm ≤ Ts ≤ 13mm; Where Ts is the total thickness of the Pancake optical system.

[0011] As a further solution of the present invention, the Pancake optical system realizes 0 - 500° myopic diopter adjustment through dynamic adjustment of the distance between the first lens, the second lens and the third lens, and the total thickness of the module remains unchanged during the diopter adjustment process.

[0012] As a further solution of the present invention, the entrance pupil diameter value of the Pancake optical system is not less than 14mm.

[0013] As a further solution of the present invention, the field of view angle of the Pancake optical system is not less than FOV 100°.

[0014] As a further solution of the present invention, the lateral chromatic aberration of the full field of view of the Pancake optical system is less than 0.6 μm.

[0015] 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 the half-reflecting mirror, and the left-handed polarized light LCP is maintained through the second lens and the third lens, and is converted into S-polarized light through the phase retardation 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, and it is converted into left-handed polarized light LCP again after passing through the phase retardation plate. After reaching the second lens, it is reflected by the half-reflecting mirror. At this time, it is converted into right-handed polarized light, and then passes through the second lens and the first lens and continues to pass through the phase retardation plate to become P-polarized light. At this time, the polarization direction is parallel to the X axis, and it passes through the reflective polarizing film and the polarizer to reach the exit pupil.

[0016] Another object of the present invention is to provide a smart wearable device, including any one of the above-mentioned Pancake optical systems.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. By controlling parameters such as the radius of curvature, refractive index, and Abbe number of the lens, the present invention can fully expand the field of view angle, make full use of the screen performance, effectively reduce the chromatic dispersion problem, without post-processing color correction, without frequent adjustment to correct spatial perception, and will not destroy the user's immersion or cause dizziness; 2. By setting the radius of curvature of the object side and the image side of the lens, the present invention can ensure that each aspherical surface will not be too curved or fluctuating, which is conducive to attaching the polarizing film layer while being easy to form, thereby improving the production yield; 3. By setting the Abbe number and refractive index of the lens, the present invention ensures that the lens uses a high refractive index and low dispersion material to reduce chromatic dispersion and distortion problems, improve the imaging quality, avoid post-processing color correction, and thus reduce the CPU power consumption. At the same time, the high refractive index and low dispersion material helps to reduce the overall weight and volume of the VR glasses and improve the wearing comfort; 4. The optical power distribution method set by the present invention satisfies the - + - type structure, and obtains an initial structure of a low-stress lens with uniform optical power distribution and a flat surface shape, improves the stability of film sticking, and shortens the optical path length. Description of the Drawings

[0018] Figure 1Schematic diagram of the overall structure during the implementation of the present invention, where: the first lens G1; the object side S1 of the first lens G1; the image side S2 of the first lens; the second lens G2; the object side S3 of the second lens G2; the image side S4 of the second lens G2; the third lens G3; the object side S5 of the third lens G3; the image side S6 of the third lens G3; a quarter-wave plate (QWP) 11; an anti-reflection film (AR) 12; a reflective polarizer (RP) 13; a polarizer (POL) 14; a semi-reflective film (BS) 15; Figure 2 Schematic diagram of the modulation transfer function in Embodiment 1; Figure 3 Schematic diagram of the modulation transfer function in Embodiment 2. Detailed implementation manners

[0019] The following details the implementation manners of the present invention. Examples of the implementation manners are shown in the drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The implementation manners described below with reference to the drawings are exemplary and are only used to explain the present invention and should not be construed as a limitation of the present invention.

[0020] The present invention provides a technical solution: A Pancake optical system, including an object side and an image side that are oppositely arranged along the optical axis extension direction of the Pancake optical system. Along the object side to the image side of the Pancake optical system, three plastic aspherical lenses are sequentially arranged, namely the first lens, the second lens, and the third lens. On the image side of the first lens, a polarizer, a reflective polarizer, a phase retardation plate, and an anti-reflection film are sequentially arranged from the inside out. A semi-reflective lens is arranged on the image side of the second lens; The lens focal power distribution method satisfies the following conditional equations: -150mm < f1 < -50mm; 5mm < f2 < 45mm; -1000mm < f3 < -700mm; Where f is the effective focal length of the lens module, f(a), and a is the lens serial number; according to this focal power distribution method, a - + - type structure is satisfied, obtaining an initial structure of a low-stress lens with uniform focal power distribution and a gentle surface shape, 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; 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 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 high refractive index and low dispersion materials are used for the lens, so as to reduce the chromatic aberration and distortion problems, improve the imaging quality, avoid post-processing color correction, thereby reducing the CPU power consumption. At the same time, the high refractive index and low dispersion materials help to reduce the overall weight and volume of the VR glasses and improve the wearing comfort.

[0021] Among them, the lens satisfies: 10mm < |R11| < 70mm, 60mm < |R12| < 120mm; 110mm < |R21| < 200mm, 10mm < |R22| < 70mm; 200mm < |R31| < 1000mm, 500mm < |R32| < inf; Where R(ab) represents the curvature radius of a certain surface of a certain lens, a is the lens serial number, b is the surface serial number, and inf is 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 the VR lens satisfies the above relational expressions, controlling the curvature radius of the lens can ensure that each aspherical surface is not overly curved or fluctuating, which is conducive to attaching the polarization film layer while being easy to mold, thereby improving the production yield.

[0022] Among them, the module of the Pancake optical system also satisfies the following conditional expressions: 11.5mm ≤ Ts ≤ 13mm; Where Ts is the total thickness of the Pancake optical system.

[0023] Among them, the Pancake optical system realizes 0 - 500° myopic diopter adjustment through the dynamic adjustment of the distances between the first lens, the second lens and the third lens, and the total thickness of the module remains unchanged during the diopter adjustment process.

[0024] Among them, the entrance pupil diameter value of the Pancake optical system is not less than 14mm.

[0025] Among them, the field of view angle of the Pancake optical system is not less than FOV 100°.

[0026] Among them, the lateral chromatic aberration of the full field of view of the Pancake optical system is less than 0.6 μm.

[0027] 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 the half-reflecting mirror, maintains the left-handed polarized light LCP through the second lens and the third lens, is converted into S polarized light through the phase retardation plate. At this time, the polarization direction is parallel to the Y axis, and the S light polarization state is maintained after being reflected by the reflective polarizing film. After passing through the phase retardation plate again, it is converted into left-handed polarized light LCP, and is reflected by the half-reflecting mirror after reaching the second lens. At this time, it is converted into right-handed polarized light, and then passes through the second lens and the first lens and continues to pass through the phase retardation plate to become P polarized light. At this time, the polarization direction is parallel to the X axis, and it reaches the exit pupil through the reflective polarizing film and the polarizer.

[0028] Another object of the present invention is to provide a smart wearable device, including a Pancake optical system as described above. Embodiment 1

[0029] The system surface type data satisfies the conditions in Table 1 below: Table 1

[0030] Among them, T(3), T(5), and T(7) satisfy the conditions in Table 2 below: Table 2:

[0031] Among them: R(mm): The radius of curvature of each surface; T(mm): The intervals between lenses and the lens thicknesses; K: Conic coefficient; α1: Second-order aspheric coefficient; α2: Fourth-order aspheric coefficient; α3: Sixth-order aspheric coefficient; α4: Eighth-order aspheric coefficient; α5: Tenth-order aspheric coefficient; α6: Twelfth-order aspheric coefficient; Aspheric surface type formula: ; Nd: The refractive index of each glass for the d line; Vd:: The Abbe number of the glass; Among them, surface serial number 1 is the aperture stop, surface serial number 2 corresponds to the object side S1 of the first lens G1, surface serial number 3 corresponds to the image side S2 of the first lens, surface serial number 4 corresponds to the object side S3 of the second lens G2, surface serial number 5 corresponds to the image side S4 of the second lens G2, surface serial number 6 corresponds to the object side S5 of the third lens G3, and surface serial number 7 corresponds to the image side S6 of the third lens G3; Among them, the T corresponding to surface serial number 1 is the interval distance between the aperture stop and the first lens G1, the T corresponding to surface serial number 2 is the thickness of the first lens G1, the T corresponding to surface serial number 3 is the interval distance between the first lens G1 and the second lens G2, the T corresponding to surface serial number 4 is the thickness of the second lens G2, the T corresponding to surface serial number 5 is the interval distance between the second lens G2 and the third lens G3, the T corresponding to surface serial number 6 is the thickness of the third lens G3, and the T corresponding to surface serial number 7 is the interval distance between the third lens G3 and the OLED; Please refer to Figure 1-2 , a Pancake optical system, specifically composed of three plastic aspherical lenses. The materials of the three aspherical lenses of the first lens G1, the second lens G2, and the third lens G3 are all APL5014XH. The system focal length f = 11.3301mm, among which the focal length f1 of the first lens G1 is -126.8952mm, the focal length f2 of the second lens G2 is 10.3729mm, and the focal length f3 of the third lens G3 is -941.4295mm; the total thickness of the system is less than 13.5mm, and it can achieve myopia diopter adjustment from 0 to 500 degrees, and the total thickness of the module does not change during the diopter adjustment process, meeting the needs of most myopic patients to use VR glasses without wearing glasses. The field of view angle FOV is 100°, making full use of the screen performance. The traditional 3P Pancake chromatic dispersion is about 100 - 200μm. This design uses a 3P structure and low-dispersion materials, and the lateral chromatic aberration of the full field of view is less than 1.0μm, without the need for post-processing color correction.

[0032] Due to the barrel or pincushion distortion of the aspherical lens, the edge field distortion rate can reach 15% - 20%. If the interpupillary distance (IPD) and the lens optical center distance (ICD) are mismatched (such as the difference > ±2mm), double images (diplopia) will occur due to the non-coincidence of the visual axes of the binocular images, and the user's pupils need to be forced to focus through compensatory offset, resulting in visual blurring. In this design, the entrance pupil diameter value is 14mm, which can meet the normal pupil drift of ±5mm, without the need to frequently adjust to correct spatial perception, and will not destroy the user's immersion or cause dizziness.

[0033] As Figure 1 shown, where 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 light with a polarization direction parallel to the X-axis and reflects light with a polarization direction parallel to the Y-axis; the fast axis of the 1 / 4 wave plate QWP makes an angle of 45° with the X-axis.

[0034] Circularly polarized light with a polarization state of the light emitted from the display (assuming left-handed polarized light LCP) enters the optical system through a half mirror (BS), and the left-handed polarized light LCP is maintained by the second lens G2 and the third lens G3. It is converted into S-polarized light by a quarter-wave plate (QWP). At this time, the polarization direction is parallel to the Y-axis. After being reflected by the RP reflective film, the S-light polarization state is maintained. After passing through the QWP again, it is converted into left-handed polarized light LCP. After reaching the second lens G2, it is reflected by the half mirror BS. At this time, it is converted into right-handed polarized light RCP. After passing through the second lens G2 and the first lens G1 in sequence, it continues to pass through the QWP and becomes P-polarized light. At this time, the polarization direction is parallel to the X-axis, and it reaches the exit pupil through the RP reflective film and the POL film.

[0035] This system can achieve myopia diopter adjustment from 0 to 500 degrees. For example, when adjusting from -1D to -5D, the distance that the third lens G3 moves towards the second lens G2 is: 0.5817 mm (according to Table IV: 0.7792 - 0.1975 = 0.5817). And the total thickness of the lens module does not change during the diopter adjustment process, meeting the needs of most myopic patients who can use it without wearing glasses.

[0036] The modulation transfer function (Modulus of the OTF, MTF) of Example 1 is as Figure 2 shown, where TS represents the field angle. For example, TS-11.00 represents the case where the field angle is 11 degrees. Example 2

[0037] The system surface type data meets the conditions in Table III below: Table III

[0038] Among them, T(3), T(5), and T(7) meet the conditions in Table IV below: Table IV

[0039] Among them: R(mm): The radius of curvature of each surface; T(mm): The spacer and thickness of each lens; K: Conic coefficient; α1: Second-order aspheric coefficient; α2: Fourth-order aspheric coefficient; α3: Sixth-order aspheric coefficient; α4: Eighth-order aspheric coefficient; α5: Tenth-order aspheric coefficient; α6: Twelfth-order aspheric coefficient; Aspheric surface formula: ; Nd: Refractive index of each glass of the d-line; Vd:: Abbe number of the glass; Among them, surface number 1 is the diaphragm, surface number 2 corresponds to the object side S1 of the first lens G1, surface number 3 corresponds to the image side S2 of the first lens, surface number 4 corresponds to the object side S3 of the second lens G2, surface number 5 corresponds to the image side S4 of the second lens G2, surface number 6 corresponds to the object side S5 of the third lens G3, and surface number 7 corresponds to the image side S6 of the third lens G3; Among them, the T corresponding to surface number 1 is the interval distance between the diaphragm and the first lens G1, the T corresponding to surface number 2 is the thickness of the first lens G1, the T corresponding to surface number 3 is the interval distance between the first lens G1 and the second lens G2, the T corresponding to surface number 4 is the thickness of the second lens G2, the T corresponding to surface number 5 is the interval distance between the second lens G2 and the third lens G3, the T corresponding to surface number 6 is the thickness of the third lens G3, and the T corresponding to surface number 7 is the interval distance between the third lens G3 and the OLED.

[0040] A Pancake optical system consists of three plastic aspherical lenses. Among them, the materials of the three aspherical lenses of the first lens G1, the second lens G2, and the third lens G3 are all APL5014XH. The system focal length f = 11.3373mm, where the focal length f1 of the first lens G1 is -127.8564mm, the focal length f2 of the second lens G2 is 10.3711mm, and the focal length f3 of the third lens G3 is -797.9630mm; the total thickness of the system is less than 13.1mm, and it can achieve myopia diopter adjustment from 0 to 500 degrees. During the diopter adjustment process, the distances between G1 and G2, G2 and G3, and G3 and the image plane are dynamically adjusted without changing the total thickness of the module, meeting the needs of most myopic patients to use VR glasses without wearing glasses. The field of view angle FOV is 100°, making full use of the screen performance. The traditional 3P Pancake chromatic aberration is about 100 - 200μm. This design uses a 3P structure and low-dispersion materials, and the lateral chromatic aberration of the full field of view is less than 1.1μm, without the need for post-processing color correction.

[0041] Due to the barrel or pillow distortion of the aspherical lens, the edge field of view distortion rate can reach 15% - 20%. If the pupil distance (IPD) is mismatched with the lens optical center distance (ICD) (such as the difference > ±2mm), double images (diplopia) will occur due to the non-coincidence of the visual axes of the two eyes, and the user's pupils need to be forced to focus through compensatory offset, resulting in visual blurring. In this design, the entrance pupil diameter value is 14mm, which can meet the ±5mm drift of the normal pupil, without the need for frequent adjustment to correct spatial perception, and will not destroy the user's immersion or cause dizziness.

[0042] This system can achieve myopia diopter adjustment from 0 degree to 500 degrees. For example, when adjusting from -1D to -5D, the third lens G3 moves towards the second lens G2 by a distance of: 0.5780 mm (according to Table 4: 0.7754 - 0.1974 = 0.5780). And during the diopter adjustment process, the total thickness of the lens module remains unchanged, meeting the needs of most myopic patients who can use it without wearing glasses.

[0043] The modulation transfer function (MTF) of Example 2 is as Figure 3 shown, where TS represents the field angle. For example, TS - 11.00 represents the case where the field angle is 11 degrees.

Claims

1. A Pancake optical system, including an object side and an image side that are relatively arranged along the extending direction of the optical axis of the Pancake optical system. Along the object side to the image side of the Pancake optical system, three plastic aspherical lenses are sequentially arranged, namely a first lens, a second lens, and a third lens. On the image side of the first lens, a polarizer, a reflective polarizer, a phase retardation plate, and an antireflection film are sequentially arranged from the inside out. A semi-reflective lens is arranged on the image side of the second lens; The lens optical power distribution method satisfies the following conditional expressions: -150mm < f1 < -50mm; 5mm < f2 < 45mm; -1000mm < f3 < -700mm; f is the effective focal length of the lens module, where f(a), a is the lens serial 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 certain lens, and Vd(a) represents the Abbe number of a certain lens, and a is the lens serial number.

2. The Pancake optical system according to claim 1, wherein: The lens satisfies: 10mm < |R11| < 70mm, 60mm < |R12| < 120mm; 110mm < |R21| < 200mm, 10mm < |R22| < 70mm; 200mm < |R31| < 1000mm, 500mm < |R32| < inf; Where R(ab) represents the curvature radius of a certain surface of a certain lens, a is the lens serial number, b is the surface serial number, and inf is infinity.

3. The Pancake optical system according to claim 2, characterized in that: 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 lens module, and EPD is the entrance pupil diameter.

4. The Pancake optical system according to claim 3, characterized in that: The module of the Pancake optical system also satisfies the following conditional expression: 11.5mm ≤ Ts ≤ 13mm; Where Ts is the total thickness of the Pancake optical system.

5. The Pancake optical system according to claim 1, characterized in that: The Pancake optical system realizes 0 - 500° myopic diopter adjustment through the dynamic adjustment of the distances between the first lens, the second lens, and the third lens, and the total thickness of the module remains unchanged during the diopter adjustment process.

6. The Pancake optical system according to claim 1, characterized in that: The entrance pupil diameter value of the Pancake optical system is not less than 14mm.

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

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

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

10. An intelligent wearable device, comprising a Pancake optical system according to any one of claims 1-9.

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