Imaging optical system

Abstract

The invention, which relates to the technical field of desktop display, discloses an imaging optical system comprising a curved mirror, an image source and a spectroscope. The curved mirror is provided with a first side and a second side which are oppositely arranged, and a first light splitting surface is arranged on the surface of the first side or the second side; the image source is arranged on the first side of the curved mirror, and imaging light emitted by the image source is circularly polarized light capable of penetrating through the first light splitting surface when reaching the first light splitting surface; the spectroscope is arranged on the second side of the curved mirror, a first quarter-wave plate and a first reflection type polaroid are arranged on the side, facing the first light splitting surface, of the spectroscope, and the first reflection type polaroid reflects linearly polarized light penetrating through the first quarter-wave plate to the first light splitting surface; and the imaging light is reflected by the first light splitting surface again, penetrates through the first quarter-wave plate and the first reflective polarizer, and is emitted from the imaging optical system. According to the technical scheme provided by the invention, the thickness of the optical system can be effectively reduced while virtual image imaging is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of desktop display, and in particular to an imaging optical system. Background Art

[0002] In my country, the prevention and control of myopia among children and adolescents is a serious issue. According to a 2018 survey, the overall myopia rate among children and adolescents aged 6 to 18 in my country was 53.6%, with the rate exceeding 80% among high school students. Globally, myopia among children and adolescents is increasing, a common problem in all regions of the world. Surveys show that the proportion of the global myopic population increased from 28.4% to 33.9% between 2010 and 2020, and this proportion is projected to approach 50% by 2050. Scientific research shows that myopia is the result of a combination of genetic and environmental factors. Close eye use causes a small, temporary myopic shift in the eye's refractive state, known as near-use-induced transient myopia. Prolonged, continuous close eye use is considered a key contributing factor to the development of myopia.

[0003] To address the shortcomings of near-sighted products, desktop virtual image displays have been developed. These utilize an optical telephoto imaging solution, magnifying a small, near-sighted screen into a large, distant virtual image within a compact desktop space. This telephoto image reduces the diopter required for focusing, thereby reducing eye fatigue and the risk of myopia.

[0004] For general optical imaging systems, including reflective imaging systems, the basic object-image relationship can be referred to thin lens imaging. A thin lens is one in which the thickness of the lens itself can be ignored in the imaging calculation. For a thin lens in air, its object-side and image-side focal lengths are equal, i.e. The imaging formula is Where s and s' are the object distance and image distance respectively. When the object is a physical object, that is, s>0, there may be several imaging possibilities, as shown in Table 1.

[0005]

[0006]

[0007] Table 1 Thin lens imaging analysis

[0008] VR optics based on the imaging principle of the thin lens imaging system has gone through three stages: aspheric lens, Fresnel lens and Pancake folded optical path. Figure 16Fresnel lenses have the advantages of low cost and controllable imaging quality. Their design principle is to remove the portion of light that propagates in a straight line in the lens, retaining only the curved surface of the lens used to refract light. While retaining the optical characteristics of conventional lenses, the thickness of the lens is greatly compressed, achieving lightweight lenses. However, since this solution requires the screen to be placed near the focal plane of the lens, the distance between the lens and the screen is long, resulting in a larger volume for the entire optical module. In addition, since the Fresnel lens uses a single-layer lens design, its physical properties lead to problems such as blurred image edges, easy distortion, and inability to adjust the diopter.

[0009] Against this backdrop, the Pancake optical solution emerged and gradually became the development and evolutionary direction of consumer VR optics. Based on the principle of a folded optical path, this solution not only achieves ultra-short optical focus imaging, significantly reducing lens thickness and headset size, but also overcomes the edge blur and distortion of traditional Fresnel lens optical solutions, achieving a distortion-free, full-range HD visual experience.

[0010] The core design idea of the Pancake optical solution is to fold the optical path through the reflection and refraction of polarized light. The Pancake optical solution, also known as the folded optical path solution, is a type of VR short-focus optical solution. The principle of this solution is that after the image source emitted by the display enters the lens with a semi-transparent and semi-reflective function, the light is folded back and forth multiple times between the lens, the 1 / 4 phase delay plate and the reflective polarizer, and finally enters the human eye after being emitted from the reflective polarizer. Figure 17 In other words, this solution uses folded optical elements to allow light to travel the same distance in a narrower space, "folding" the original optical path. This compresses the space between the optical lens and the display, significantly reducing the size of the VR headset. This optical solution can theoretically reduce the size of a VR headset to 1 / 4 that of a Fresnel lens solution.

[0011] The optical path principle of the desktop virtual image display device based on the above Pancake optical solution is as follows: Figure 1 As shown, a light beam of a specific polarization state emitted by an image source 1' (such as a liquid crystal screen) is reflected by a beam splitter 3' and then irradiated onto a curved reflector 2'. After further reflection by the curved reflector 2', the imaging light passes through the beam splitter 3' and enters the human eye at the observation position 4'. The human eye focuses the light onto the virtual image plane against the light, and based on the experience that light propagates in a straight line, it is believed that the light is emitted from the virtual image plane.

[0012] This technology is inspired by the more mature Birdbath coaxial catadioptric optical solution used in AR (Augmented Reality) displays. The project's product technical architecture can be considered an enlarged version of the Birdbath solution used in AR glasses. Traditional AR glasses, as head-mounted products, pursue small size in terms of performance, so the size of Birdbath curved mirrors is generally small. The curved mirrors used in AR glasses cannot meet the 10-inch to 20-inch aperture requirement for desktop designs. In recent years, the increasingly mature head-up display market has promoted the industrialization of large-aperture curved mirrors in order to achieve a larger viewing angle. The currently mature and mass-produced free-form mirrors that meet the imaging accuracy requirements make desktop optical solutions with large fields of view, large exit pupil distances, and large eye boxes possible.

[0013] Because image source 1' is designed to be within one focal length of curved reflector 2' and close to the focal point of a desktop virtual image display device utilizing the aforementioned technology, the virtual image has a longer image distance, and thus a longer distance from the human eye. Typical virtual image distances are designed to exceed 5 meters, compared to a close reading distance of approximately 30 cm. When viewing a display device, the crystalline lens's accommodation force is significantly reduced, maintaining a more relaxed state, thereby reducing visual fatigue and the risk of myopia.

[0014] The distance from the observation position 8' to the beam splitter 3' is the exit pupil distance; the angle between the two connecting lines with the observation position 8' as the vertex and the observation position 8' reaching the opposite edges of the light-emitting end of the image source 1' is the field of view angle; and the distance from the beam splitter 3' to the light-emitting end of the image source 1' is the thickness of the optical system. When the exit pupil distance or the field of view angle increases, in order to achieve the same display effect, a beam splitter 3' with a larger area is required. The beam splitter 3' and the curved reflector 2' are tilted, and the larger beam splitter 3' increases the thickness of the entire optical system. Generally speaking, when the exit pupil distance is about 200mm and the diagonal field of view angle is about 30°, the thickness of the optical design is generally above 150mm, and the thickness of the optical design increases with the increase of the exit pupil distance and the field of view angle, thereby limiting the use of desktop display devices. Therefore, how to reduce the thickness of the desktop display system is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0015] The main purpose of the present invention is to provide an imaging optical system to reduce the thickness of a desktop display system.

[0016] To achieve the above-mentioned object, the imaging optical system proposed in the present invention includes a curved mirror, an image source and a beam splitter; the curved mirror has a first side and a second side arranged opposite to each other, the first side of the curved mirror is configured as a convex surface, and the second side of the curved mirror is configured as a concave surface, and a first beam splitter surface is provided on the surface of the first side or the second side of the curved mirror;

[0017] an image source, disposed on the first side of the curved mirror, wherein the imaging light emitted by the image source is circularly polarized light that can pass through the first beam splitting surface when reaching the first beam splitting surface; and

[0018] A beam splitter is provided on the second side of the curved mirror, and a first quarter-wave plate and a first reflective polarizer are sequentially provided on the side of the beam splitter facing the first beam splitting surface. The first quarter-wave plate converts circularly polarized light from the first beam splitting surface into linearly polarized light. The first reflective polarizer reflects the linearly polarized light that has passed through the first quarter-wave plate to the first beam splitting surface. The imaging light is reflected again by the first beam splitting surface, then passes through the first quarter-wave plate and the first reflective polarizer, and then exits the imaging optical system.

[0019] The focal length of the curved mirror is f, the object distance between the image source and the curved mirror is s, and s<f.

[0020] Light emitted by the image source passes through the first beam splitter surface, where the imaging light is circularly polarized. It then passes through the first quarter-wave plate located inside the beam splitter, becoming linearly polarized. It is then reflected back to the first beam splitter surface by the first reflective polarizer located inside the beam splitter. After reflecting again, it passes through the first reflective polarizer inside the beam splitter and is then transmitted from the side of the beam splitter away from the first beam splitter surface. (Because the imaging light passes through the first quarter-wave plate twice after being reflected by the first reflective polarizer, the polarization direction of the imaging light is perpendicular to its polarization direction when reflected by the first reflective polarizer, allowing it to pass through the first reflective polarizer.) A distant virtual image can be observed at the observation position. The aforementioned overall polarization folded optical path utilizes the polarization properties of light to achieve multiple folding and multiplexing of the optical path, compressing the beam propagation path without significantly increasing the number of optical components, thereby effectively reducing the overall thickness of the optical system.

[0021] Furthermore, in order to convert the imaging light emitted by the image source into circularly polarized light, the light output end of the image source includes a first linear polarizer and a second quarter-wave plate sequentially arranged in a direction from inside to outside.

[0022] According to one aspect of the present invention, in order to achieve the light path folding effect, the angle between the absorption axis direction of the first linear polarizer and the slow axis direction of the second quarter-wave plate is set to 45°, and the angle between the slow axis direction of the first quarter-wave plate and the reflection axis direction of the first reflective polarizer is set to 45° or 90°.

[0023] According to one aspect of the present invention, in order to achieve the light path folding effect, the beam splitter extends along the first direction, the angle between the absorption axis of the first linear polarizer and the second direction is θ, the slow axis direction of the second quarter-wave plate is θ±45°, the slow axis direction of the first quarter-wave plate on the beam splitter is θ±90°, the angle between the reflection axis direction of the first reflective polarizer on the beam splitter and the second direction is θ, and the first direction and the second direction are perpendicular.

[0024] According to one aspect of the present invention, in order to achieve the light path folding effect, the beam splitter extends along the first direction, the angle between the absorption axis of the first linear polarizer and the second direction is θ, the slow axis direction of the second quarter wave plate is θ±45°, and the slow axis direction of the first quarter wave plate on the beam splitter is θ±45°. The angle between the reflection axis direction of the first reflective polarizer on the beam splitter and the second direction is θ, and the first direction and the second direction are perpendicular.

[0025] Furthermore, in order to reduce ghost images formed by light leakage during reflection from the first reflective polarizer, a second linear polarizer is provided on a side of the first reflective polarizer away from the first quarter-wave plate.

[0026] Furthermore, in order to reduce reflection of ambient light by the beam splitter, a third quarter wave plate and a third linear polarizer are sequentially arranged on a side of the beam splitter away from the first beam splitting surface in a direction away from the first beam splitting surface.

[0027] Furthermore, in order to reduce ghost images reflected by the first beam splitter, a fourth quarter wave plate and a fourth linear polarizer are sequentially arranged on the side of the third linear polarizer away from the beam splitter in a direction away from the beam splitter.

[0028] Preferably, a first beam-splitting film is provided on the first side or the second side surface of the curved mirror to form the first beam-splitting surface.

[0029] Furthermore, the transmittance of the first prismatic film is t, where t≤50%. Thus, the contrast of the imaging light compared to the image source ghost image is improved, thereby reducing the impact of the image source ghost image on the display effect.

[0030] In the technical solution of the present invention, light emitted by the image source passes through the first beam splitting surface. At this time, the imaging light is circularly polarized light. It then passes through the first quarter-wave plate provided inside the beam splitter to become linearly polarized light. It is then reflected by the first reflective polarizer provided inside the beam splitter to the first beam splitting surface. After being reflected again, it is reflected to the first reflective polarizer inside the beam splitter and then transmitted from the side of the beam splitter away from the first beam splitting surface (because the imaging light passes through the first quarter-wave plate twice after being reflected by the first reflective polarizer, the polarization direction of the imaging light is perpendicular to its polarization direction when reflected by the first reflective polarizer, allowing it to pass through the first reflective polarizer). A distant virtual image can be observed at the observation position. The above-mentioned overall polarization folded optical path utilizes the polarization characteristics of light to achieve multiple folding and multiplexing of the optical path, compressing the light beam propagation path without significantly increasing the number of optical components, thereby effectively reducing the overall thickness of the optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0032] Figure 1 An imaging optical system in the related art;

[0033] Figure 2 A schematic structural diagram of Example 1 provided by the present invention;

[0034] Figure 3 A schematic diagram of the optical path of Example 1 provided by the present invention;

[0035] Figure 4 for Figure 2 Schematic diagram of membrane material stacking;

[0036] Figure 5 This is a light path grid distortion diagram of Example 1 provided by the present invention;

[0037] Figure 6 The optical path binocular parallax of embodiment 1 provided by the present invention;

[0038] Figure 7 Schematic diagram of the beam splitter film stacking according to Example 2 of the present invention;

[0039] Figure 8 Schematic diagram of the optical path of the ghost image reflected by the image source and the ghost image reflected by the curved mirror;

[0040] Figure 9Schematic diagram of the beam splitter film stacking according to Example 3 of the present invention;

[0041] Figure 10 Schematic diagram of the optical path of the image source ghost image;

[0042] Figure 11 Schematic diagram of the relationship between the luminous brightness of the image source and the pixel luminous angle;

[0043] Figure 12 This is a schematic diagram of the structure of Example 6 provided by the present invention;

[0044] Figure 13 This is a schematic diagram of angle adjustment of Example 6 provided by the present invention;

[0045] Figure 14 This is a schematic structural diagram of Example 7 provided by the present invention;

[0046] Figure 15 This is a schematic diagram of the structure of Example 8 provided by the present invention;

[0047] Figure 16 A schematic diagram for comparing virtual imaging solutions in the prior art;

[0048] Figure 17 Schematic diagram of the propagation path of polarized light in the Pancake folded light path.

[0049] Description of Figure Numbers:

[0050] 100. Imaging optical system; 1. Image source; 11. First linear polarizer; 12. Second quarter-wave plate; 13. First antireflection coating; 2. Curved mirror; 21. First beam splitter; 3. Beam splitter; 31. Second antireflection coating; 32. First quarter-wave plate; 33. First reflective polarizer; 34. Second linear polarizer; 35. Third quarter-wave plate; 36. Third linear polarizer; 37. Fourth quarter-wave plate; 38. Fourth linear polarizer; 39. Third antireflection coating; 4. Reflector; 5. Lens; 6. Plano-convex lens; 7. Flat glass; 8. Observation position;

[0051] 200. Related art imaging optical system; 1', image source; 2', curved reflector; 3', beam splitter; 4', observation position.

[0052] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0053] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0054] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0055] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of such features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0056] In order to reduce the thickness of a desktop virtual image display device, the present invention proposes an imaging optical system 100 .

[0057] See also Figure 2 In one embodiment of the present invention, the imaging optical system 100 includes: a curved mirror 2, an image source 1 and a beam splitter 3; the curved mirror 2 extends along a first direction to have a first side and a second side arranged opposite to each other in a second direction, the first side of the curved mirror 2 is set to a convex surface, the second side of the curved mirror 2 is set to a concave surface, and a first beam splitter surface is provided on the surface of the first side or the second side of the curved mirror 2; the image source 1 is provided on the first side of the curved mirror 2, the light output end of the image source 1 faces the first side of the curved mirror 2, and the imaging light emitted by it can pass through the curved mirror 2; the beam splitter 3 extends along the first direction and is provided on the second side of the curved mirror 2, the beam splitter 3 and the curved mirror 2 are arranged at intervals in the second direction, the beam splitter 3 is used to reflect the imaging light to the first beam splitter surface of the curved mirror 2, and the imaging light is reflected again by the first beam splitter surface of the curved mirror 2 and then emitted from the imaging optical system through the beam splitter 3; wherein the focal length of the curved mirror 2 is f, the object distance between the image source 1 and the curved mirror 2 is s, and s<f.

[0058] In the technical solution of the present invention, the image source 1 and the beam splitter 3 are respectively arranged at the two ends of the curved mirror 2. The curved mirror 2 and the beam splitter 3 both extend along the first direction. The beam splitter is not tilted relative to the curved mirror. Under the premise of satisfying virtual image formation, the length of the beam splitter 3 in the second direction is shortened, thereby reducing the thickness of the optical system.

[0059] The object distance S is approximately equal to the sum of the distance from the center of the image source 1 to the center of the curved mirror 2 and the distance from the center of the 2x curved mirror 2 to the center of the beam splitter 3.

[0060] The light emitted by the image source 1 passes through the curved mirror 2 and is incident on the beam splitter 3. It is reflected at the portion of the beam splitter 3 near the curved mirror 2, reflected to the curved mirror 2, reflected again at the first beam splitting surface of the curved mirror 2, and after being reflected to the beam splitter 3, it passes through the side of the beam splitter 3 away from the curved mirror 2 and reaches the observation position 8. At the observation position 8, the observer can observe a virtual image at a long distance.

[0061] See also Figures 2 to 4 In the first embodiment of the present invention, in order to achieve the above-mentioned light path folding effect, the light output end of the image source 1 includes a first linear polarizer 11 and a second quarter-wave plate 12 arranged in sequence from the inside to the outside; a curved mirror 2 ( Figure 4 A first dichroic film 21 is provided on the first side or the second side surface of the curved mirror 2 (not shown) to form a first dichroic surface, and the surface opposite to the first dichroic surface of the curved mirror 2 may not be processed; on the side of the dichroic mirror 3 facing the curved mirror 2, a first reflective polarizer 33 and a first quarter-wave plate 32 are sequentially provided in the direction close to the curved mirror 2.

[0062] In the technical solution of the present invention, in order to enhance the light transmission effect of the imaging optical system 100 and reduce unnecessary reflections, a first anti-reflection film 13 is provided on the side of the second quarter-wave plate 12 away from the first linear polarizer 11, and a second anti-reflection film 31 is provided on the side of the first quarter-wave plate 32 away from the first reflective polarizer 32, and an anti-reflection film can be provided on the side surface of the first splitter surface of the curved mirror 2.

[0063] Following the direction of light propagation, the imaging light is emitted from the image source 1 and passes through the first linear polarizer 11 on the surface of the image source 1 to become linearly polarized light. It then passes through the second quarter-wave plate 12 to become circularly polarized light. The imaging light then passes through the first anti-reflection film 13 and reaches the curved mirror 2.

[0064] The circularly polarized light can pass through the first beam splitter film 21 on the curved mirror 2, so the imaging light reaches the beam splitter 3 after passing through the first beam splitter film 21;

[0065] When the imaging light enters the beam splitter 3, it becomes linearly polarized light after passing through the second anti-reflection film 31 and the first quarter-wave plate 32. The linearly polarized light can be reflected by the first reflective polarizer 33. The imaging light propagates in the reverse direction after being reflected by the first reflective polarizer 33.

[0066] During the propagation in the reverse direction, the imaging light passes through the first quarter-wave plate 32 and the second anti-reflection film 31 and reaches the curved mirror 2. The linearly polarized light can be reflected by the first beam splitter film 21. Therefore, the imaging light is reflected by the first beam splitter film 21 on the curved mirror 2 and propagates in the forward direction again.

[0067] During the second forward propagation process, the imaging light again passes through the second anti-reflection film 31 and the first quarter-wave plate 32 to reach the first reflective polarizer 33;

[0068] From the beginning of the reverse propagation of the imaging light to the second forward propagation to the first reflective polarizer 33, it passes through the first quarter-wave plate 32 twice. The polarization direction of the imaging light is perpendicular to its polarization direction when it is reflected by the first reflective polarizer 33, and is able to pass through the first reflective polarizer 33, exit the optical system, and reach the observation position 8.

[0069] Specifically, the angle between the absorption axis direction of the first linear polarizer 11 and the slow axis direction of the second quarter wave plate 12 is set to 45°, and the angle between the slow axis direction of the first quarter wave plate 32 and the reflection axis direction of the first reflective polarizer 33 is set to 45° or 90°.

[0070] To achieve the light path folding effect, alternatively, the angle between the absorption axis of the first linear polarizer 11 and the second direction is θ, the slow axis direction of the second quarter wave plate 12 is θ±45°, the slow axis direction of the first quarter wave plate 32 is θ±90°, and the angle between the reflection axis direction of the first reflective polarizer 33 and the second direction is θ. Alternatively, the slow axis direction of the first quarter wave plate is The angle between the reflection axis direction of the first reflective polarizer and the second direction is θ.

[0071] Preferably, an anti-reflection film is provided on the second side surface of the curved mirror 2 to increase the transmittance of the light emitted by the image source 1 through the curved mirror 2 .

[0072] Furthermore, during use, the beam splitter 3, the curved mirror 2, and the image source 1 can be moved along the second direction to adjust the virtual image display position.

[0073] Using the solution of Example 1, when the virtual image distance is 2000 mm, the exit pupil distance is 200 mm, the horizontal field angle is about 34°, the vertical field angle is about 20°, and the diagonal field angle is about 39°, the corresponding optical thickness is about 65 mm.

[0074] See also Figure 5 The maximum value of the grid distortion corresponding to the center eye point of the system in Example 1 (the center position of the left eye point and the right eye point) is about 3.1%.

[0075] During the optimization process, the front and rear surfaces of the curved mirror 2 maintain the same surface shape to ensure compatibility with the hot bending process of the flat glass 7, and the optimization goal is to minimize the RMS diameter of the imaging spot in each field of view while keeping the entrance pupil diameter larger than the general pupil distance of 65 mm, thereby ensuring the binocular parallax index.

[0076] See also Figure 6 The binocular disparity between the left eye point (X coordinate 32.5 mm) and the right eye point (X coordinate -32.5 mm) in Example 1 is as follows: Figure 5 As shown in the figure. Biocular Dipvergence represents the vertical binocular parallax, and the horizontal axis represents the Y-angle of view, ranging from -10° to +10°. Each line in the curve represents a different X-angle of view. Biocular Convergence represents the horizontal binocular parallax, and the vertical axis uses an offset of 25 mrad.

[0077] See also Figure 7 In Example 2, a second linear polarizer 34 is provided on the side of the first reflective polarizer 33 away from the first quarter-wave plate 32; a third quarter-wave plate 35 and a third linear polarizer 36 are provided in sequence on the side of the beam splitter 3 away from the curved mirror 2 in the direction away from the curved mirror 2.

[0078] Similar to the first embodiment, in order to enhance the light transmission effect of the imaging optical system 100 and reduce unnecessary reflection, a third anti-reflection film 39 is provided in the direction of the third linear polarizer 36 away from the third quarter-wave plate 35 .

[0079] In the technical solution of the present invention, a second linear polarizer 34 is provided on the side of the first reflective polarizer 33 away from the first quarter-wave plate 32 to reduce ghost images formed by light leakage during reflection from the first reflective polarizer 33 .

[0080] When the first reflective polarizer 33 reflects polarized light whose polarization direction is parallel to its reflection axis, the reflection axis extinction ratio of the first reflective polarizer 33 is insufficient, which causes a portion of the light to be transmitted. To reduce this type of reflection, the absorption axis of the second linear polarizer 34 is set parallel to the reflection axis of the first reflective polarizer 33.

[0081] In the technical solution of the present invention, on the side of the beam splitter 3 away from the curved mirror 2, a third quarter-wave plate 35, a third linear polarizer 36 and a third anti-reflection film 39 are arranged in sequence in the direction away from the curved mirror 2 to reduce the reflection of ambient light by the beam splitter 3.

[0082] When ambient light is incident on the beam splitter 3 and then reflected, the light passes through the third linear polarizer 36 and the third quarter-wave plate 35 in sequence before reaching the surface of the beam splitter 3 and being reflected. The light passes through the third quarter-wave plate 35 and the third linear polarizer 36 again. The light that passes through the third polarizer for the first time is linearly polarized light with a polarization direction perpendicular to the absorption axis direction of the third polarizer. The linearly polarized light passes through the third quarter-wave plate 35 twice. At this time, the polarization direction of the light is perpendicular to the polarization direction of the light transmitted through the third polarizer, and the light cannot pass through the third polarizer again, thereby reducing the reflection of ambient light by the beam splitter 3.

[0083] Furthermore, to ensure that the above solution does not affect light emitted from the optical system, the slow axis of the third quarter-wave plate 35 can be set at a 45° or 135° angle relative to the absorption axis of the second linear polarizer 34, while the absorption axis of the third linear polarizer 36 can be set at any angle relative to the absorption axis of the second linear polarizer 34. When light from within the optical system is transmitted through the glass surface, it first passes through the third quarter-wave plate 35 to become circularly polarized light, then passes through the third linear polarizer 36 and the third anti-reflection film 39, exits the optical system, and reaches the observation position 8.

[0084] See also Figure 8 The light emitted by the image source 1 is not directly transmitted at the first prismatic film 21 but is reflected, forming a source reflection ghost image; the external ambient light passes through the prismatic mirror 3 and is reflected by the curved mirror 2 and then emitted through the prismatic mirror 3 again, forming a curved mirror 2 reflection ghost image.

[0085] In Example 3, to reduce the ghost image reflected by the image source, based on Example 2, an AG film is further provided at the light output end of the image source 1. Preferably, the AG film is provided on the side of the first antireflection film 13 away from the second quarter-wave plate 12;

[0086] See also Figure 9 To reduce ghost images reflected by the curved mirror 2, a fourth quarter-wave plate 37 and a fourth linear polarizer 38 are sequentially disposed on the side of the third linear polarizer 36 facing away from the beam splitter 3, in a direction away from the beam splitter 3. Preferably, the fourth quarter-wave plate 37 and the fourth linear polarizer 38 are sequentially disposed between the third linear polarizer 36 and the third anti-reflection film 39, in a direction away from the beam splitter 3.

[0087] In the technical solution of the present invention, an AG film is added to the first antireflection film 13, so that the light from the image source and falling on the screen of the image source 1 after one reflection by the curved mirror 2 is scattered and the intensity is reduced and can no longer be strictly imaged.

[0088] Furthermore, the higher the haze of the AG film, the better the effect of reducing the ghost image reflected by the image source, but at the same time, the more serious the degradation of the imaging clarity will be. Therefore, an AG film with a haze greater than 3% is preferred.

[0089] In the technical solution of the present invention, a layer of circular polarizer, namely a fourth quarter-wave plate 37 and a fourth linear polarizer 38, is added to the side of the beam splitter 3 away from the curved mirror 2 in Example 2, which can effectively reduce the transmittance of the beam splitter 3 to ambient light and reduce ghost images reflected by the curved mirror 2.

[0090] See also Figure 10 Due to the dispersion of the second quarter-wave plate 12 and the first quarter-wave plate 32 themselves, and the phase delay of the second quarter-wave plate 12 and the first quarter-wave plate 32 for non-normally incident large-angle light deviates from the strict 1 / 4 wavelength phase difference, and the first linear polarizer 11 and the second linear polarizer 34 are not strictly orthogonal to the non-normally incident large-angle light, the large-angle light emitted from the image source screen will directly pass through the curved mirror 2 and the beam splitter 3, resulting in light leakage, thereby causing image source ghost images.

[0091] In the fourth embodiment, the transmittance of the first prismatic film 21 is t, where t≤50%.

[0092] In the technical solution of the present invention, when the transmittance t of the first prismatic film 21 is less than or equal to 50%, the contrast of the imaging light compared to the image source ghost image will be improved, thereby reducing the influence of the image source ghost image on the display effect.

[0093] The transmittance of the first prismatic film 21 is t, and the reflectance r is r=1-t. Then the imaging brightness is lower than that of the scheme with a transmittance of 50%. The brightness ratio of the image source ghost image becomes The contrast of the imaging light compared to the image source ghost image becomes 2×(1-t) of the contrast of the solution with a transmittance of 50%. It can be seen that when the transmittance of the dichroic film is lower than 50%, the contrast of the imaging light compared to the image source ghost image will be improved.

[0094] The transmittance of the first prismatic film 21 is preferably 10%. Compared with the first prismatic film 21 with a transmittance of 10%, the brightness of the image source ghost light is reduced to 1 / 5 of the original, and the corresponding imaging light brightness is reduced to the original The brightness contrast between the imaging light and the image source ghost image will become Therefore, the imaging light ghost is more prominent than the image source ghost, while the image source ghost is less obvious than the imaging light.

[0095] Image source ghosting becomes more obvious as the viewing angle increases. In Example 5, to avoid the appearance of large-angle light, a collimating backlight film is provided between the first polarizer and the image source 1 .

[0096] In the technical solution of the present invention, a collimating backlight film is provided between the first polarizer and the image source 1 to control the light emitting angle of the image source 1, thereby avoiding the occurrence of large-angle light and reducing image source ghost images.

[0097] See also Figure 11 , where the ordinate L is the luminance of the image source 1, and the abscissa is the pixel luminous angle of the image source 1, where θ max It indicates that the combination of polarizing film materials in the optical path can achieve a light-emitting angle with better ghost image elimination.

[0098] For LCD-type image source screens, the above effect can be achieved by adjusting the exit angle of the backlight. Common solutions include adding collimating backlight film 3M BEF (Brightness Enhancement Film) or ALCF (Advanced Light Control Film), or using a collimating light guide plate with a micro-nano structure, or using a direct-type backlight superimposed with a collimating lens 5. For uLED self-luminous image source screens, a solution of combining uLED with a matching collimating lens 5 array can be used.

[0099] In one embodiment, to further reduce the thickness of the optical system, the image source 1 extends along the first direction and is spaced apart from and arranged in parallel with the curved mirror 2 in the second direction.

[0100] When the window size of the desktop display becomes larger, the curvature radius of the curved mirror 2 that can form a better image will increase accordingly, and the object distance required for imaging will also increase accordingly, thereby increasing the distance between the beam splitter 3 and the image source screen, making it appear thicker in appearance and adding restrictions on the actual structural placement.

[0101] See also Figure 12 In Example 6, in order to further reduce the thickness of the optical system, the image source 1 is extended along the second direction and is located on the side of the curved mirror 2 in the first direction; the imaging optical system 100 also includes a reflector 4 arranged on the first side of the curved mirror 2, and the reflector 4 and the image source 1 are arranged opposite to each other in the second direction, and are used to reflect the light emitted by the image source 1 to the first side of the curved mirror 2.

[0102] In the technical solution of the present invention, the optical path between the curved mirror 2 and the image source 1 is folded by the reflector 4 to form a back-folded optical path, thereby increasing the optical path distance between the curved mirror 2 and the image source 1 in an optical path system of the same volume.

[0103] Furthermore, the distance between the beam splitter 3 and the curved mirror 2 can be reduced, the distance between the curved mirror 2 and the image source 1 can be increased, and the light path between the curved mirror 2 and the image source 1 can be deflected by the reflector 4 to further reduce the thickness of the optical system.

[0104] See also Figure 13 In Example 6, in order to enable the reflector 4 to effectively reduce the thickness of the optical system, the angle formed between the extension direction of the reflector 4 and the second direction is α, where α≥45°.

[0105] In the technical solution of the present invention, the overall volume of the imaging optical system 100 is made smaller by adjusting the angle of the reflector 4. When α ≥ 45°, the image source 1 does not increase the overall thickness of the imaging optical system 100, and as α increases, the length of the reflector 4 in the thickness direction will gradually decrease, further reducing the overall thickness. In this embodiment, α = 50°.

[0106] Since the degrees of freedom that can be optimized for imaging using a single curved mirror 2 are limited, especially due to the current process limitations of the curved mirror 2, the surface shape of the curved mirror 2 is mostly spherical, and the field curvature and distortion of the actual virtual image may exceed the required specifications.

[0107] See also Figure 14 In Example 7, based on Example 6, the imaging optical system 100 further includes at least one lens 5 arranged between the image source 1 and the reflecting mirror 4.

[0108] In the technical solution of the present invention, at least one lens 5 is provided between the image source 1 and the reflector 4, and the field curvature and distortion of the real image are optimized by increasing the number of lenses 5 in the optical path.

[0109] See also Figure 15 In Example 8, to reduce the distance between the image source 1 and the reflector 4, flat glass 7 and plano-convex lenses 6 are disposed between the image source 1 and the reflector 4, spaced apart along a first direction. The plano-convex lenses 6 are disposed between the flat glass 7 and the reflector 4, with the plano-convex sides of the plano-convex lenses 6 facing the flat glass 7 and the convex sides of the plano-convex lenses 6 facing the reflector 4. A second reflective polarizer and a fifth quarter-wave plate are sequentially disposed on the plano-convex side of the plano-convex lens 6 in the direction closer to the image source 1. A fourth antireflection coating may be added to the surface of the fifth quarter-wave plate to reduce unwanted reflections. The flat glass 7 has a first side and a second side disposed opposite each other in the first direction. A second beam splitter surface is disposed on the first or second side of the flat glass 7. Preferably, the second beam splitter surface of the flat glass 7 is a second beam splitter coating.

[0110] The light emitted from the image source 1 passes through the flat glass 7 and is reflected on the plane side of the plano-convex lens 6, thereby propagating in the reverse direction. During the reverse propagation process, the light reaches the second side of the flat glass 7 and is reflected. The light propagates forward for the second time and then passes through the plano-convex lens 6, thereby reducing the thickness of the imaging optical system 100.

[0111] At the same time, in order to match the polarization folding optical path of the next stage, it is preferred to add a sixth quarter-wave plate between the plane side of the plano-convex lens 6 and the second reflective polarizer, so that the polarized light emitted from the plano-convex lens 6 is circularly polarized light that matches the polarization folding optical path of the next stage.

[0112] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformation made by utilizing the contents of the present invention's description and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. An imaging optical system, characterized in that: The imaging optical system comprises: A curved mirror (2) having a first side and a second side arranged opposite to each other, the first side of the curved mirror (2) being arranged as a convex surface, the second side of the curved mirror (2) being arranged as a concave surface, and a first light splitting surface being arranged on the surface of the first side or the second side of the curved mirror (2); An image source (1) is provided on a first side of the curved mirror, and the imaging light emitted by the image source is circularly polarized light that can pass through the first splitting surface when it reaches the first splitting surface; and A beam splitter (3) is provided on the second side of the curved mirror, and a first quarter-wave plate (32) and a first reflective polarizer (33) are sequentially provided on the side of the beam splitter (3) facing the first beam splitting surface. The first quarter-wave plate (32) converts circularly polarized light from the first beam splitting surface into linearly polarized light, and the first reflective polarizer (33) reflects the linearly polarized light passing through the first quarter-wave plate (32) to the first beam splitting surface. The imaging light is reflected again by the first beam splitting surface and then passes through the first quarter-wave plate (32) and the first reflective polarizer (33), and then exits from the imaging optical system. The focal length of the curved mirror is f, the object distance between the image source and the curved mirror is s, and s<f.

2. The imaging optical system according to claim 1, wherein: The light-emitting end of the image source (1) comprises a first linear polarizer (11) and a second quarter-wave plate (12) which are sequentially arranged in a direction from inside to outside.

3. The imaging optical system according to claim 2, wherein: The angle between the absorption axis direction of the first linear polarizer (11) and the slow axis direction of the second quarter-wave plate (12) is set to 45°, and the angle between the slow axis direction of the first quarter-wave plate (32) and the reflection axis direction of the first reflective polarizer (33) is set to 45° or 90°.

4. The imaging optical system according to claim 2, wherein: The beam splitter (3) extends along a first direction, the angle between the absorption axis of the first linear polarizer (11) and the second direction is θ, the slow axis direction of the second quarter-wave plate (12) is θ±45°, the slow axis direction of the first quarter-wave plate (32) on the beam splitter (3) is θ±90°, the angle between the reflection axis direction of the first reflective polarizer (33) on the beam splitter (3) and the second direction is θ, and the first direction and the second direction are perpendicular.

5. The imaging optical system according to claim 2, wherein: The beam splitter (3) extends along a first direction, the angle between the absorption axis of the first linear polarizer (11) and the second direction is θ, the slow axis direction of the second quarter wave plate (12) is θ±45°, and the slow axis direction of the first quarter wave plate (32) on the beam splitter (3) is θ±45°. The angle between the reflection axis direction of the first reflective polarizer (33) on the beam splitter (3) and the second direction is θ, and the first direction is perpendicular to the second direction.

6. The imaging optical system according to claim 1, wherein: A second linear polarizer (34) is provided on a side of the first reflective polarizer (33) facing away from the first quarter-wave plate (32).

7. The imaging optical system according to claim 1, wherein: On the side of the beam splitter (3) facing away from the first beam splitting surface, a third quarter wave plate (35) and a third linear polarizer (36) are sequentially arranged in a direction away from the first beam splitting surface.

8. The imaging optical system according to claim 7, wherein: On the side of the third linear polarizer (36) facing away from the beam splitter (3), a fourth quarter-wave plate (37) and a fourth linear polarizer (38) are sequentially arranged in a direction away from the beam splitter (3).

9. The imaging optical system according to any one of claims 1 to 8, wherein: A first light-splitting film is provided on the first side or the second side surface of the curved mirror to form the first light-splitting surface.

10. The imaging optical system according to claim 9, wherein: The transmittance of the first prismatic film (21) is t, wherein t≤50%.

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