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, a reflector and a spectroscope. The curved mirror is provided with a first side and a second side which are oppositely arranged, the first side is a convex surface, the second side is a concave surface, and a first light splitting surface is arranged on the surface of the first side or the second side; an image source; the reflecting mirror is used for reflecting light rays emitted by the image source to the first side of the curved mirror; and the spectroscope is arranged on the second side of the curved mirror, the spectroscope is used for reflecting the imaging light rays penetrating through the curved mirror to the first light splitting surface of the curved mirror, and the imaging light rays are reflected by the first light splitting surface of the curved mirror again, penetrate through the spectroscope and are 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 particularly relates to an imaging optical system. Background Art

[0002] Scientific research shows that myopia is the result of the combined action of genetic and environmental factors. After near vision, there is a small and temporary myopia shift in the refractive state of the human eye, which is called transient myopia induced by near vision, and long-term continuous near vision is considered to be the key inducing factor for the occurrence of myopia.

[0003] To solve the deficiencies of near-vision products, desktop virtual image display products have been proposed. Desktop virtual image display adopts an optical tele-imaging scheme to magnify a small-size screen at a short distance into a huge virtual image at a long distance in a small-volume space on the desktop. The long-distance virtual image can reduce the diopter required for eye focusing, thereby reducing visual fatigue and the risk of myopia.

[0004] Generally, an optical imaging system, including a reflection imaging system, the basic object-image relationship can refer to thin lens imaging. A thin lens refers to a lens whose own thickness can be ignored in imaging calculations. For a thin lens in air, its object-side and image-side focal lengths are equal, that is

[0005] where s and s ′ are the object distance and the image distance respectively. The lateral magnification

[0006] The imaging formula is

[0007] When the object is a real object, that is, s>0,

[0008] There are several possible imaging situations, as shown in Table 1.

[0009]

[0010]

[0011] Table 1 Thin lens imaging analysis

[0012] Based on the imaging principle of the above thin lens imaging system, VR optics has successively gone through three stages: aspherical lens, Fresnel lens, and Pancake folded optical path. See Figure 17, Fresnel Lenses have the advantages of low cost and controllable imaging quality. Its design principle is to remove the part where light travels in a straight line in the lens and only retain the lens surface used to refract light. While retaining the optical characteristics of a conventional lens, it greatly compresses the lens thickness and realizes the lightweight of the lens. However, since this solution requires the screen to be placed at the near focal plane of the lens, the distance between the lens and the screen is relatively long, resulting in a relatively large volume of the entire optical module. In addition, due to the single-layer lens design of the Fresnel lens, its physical properties lead to problems such as blurred imaging edges, easy distortion, and inability to adjust diopter.

[0013] In this context, the Pancake optical solution emerged and gradually became the development and evolution direction of consumer-grade VR optics. Based on the principle of folded optical paths, this solution can not only achieve ultra-short optical focusing imaging, thus greatly compressing the lens thickness and the volume of the head-mounted display, but also overcome the edge blurring and distortion phenomena of the traditional Fresnel lens optical solution, realizing a zero-distortion full-field high-definition visual experience.

[0014] 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, belongs to a type of VR short-focus optical solution. The principle of this solution is that after the image source emitted by the display screen enters the lens with semi-transmissive and semi-reflective functions, the light travels back and forth multiple times between the lens, the 1 / 4 wave plate, and the reflective polarizer, and finally exits from the reflective polarizer and enters the human eye, as Figure 18 shown. That is to say, this solution uses folded optical elements to make the light travel the same distance in a narrower space, "folding" the original optical path, thereby realizing the compression of the space between the optical lens and the display screen, and then significantly reducing the volume of the VR head-mounted display. Through this optical solution, theoretically, the volume of the VR head-mounted display can be reduced to 1 / 4 of that of the Fresnel lens solution.

[0015] For the desktop virtual image display device based on the above Pancake optical solution, its optical path principle is as Figure 1 shown. The light with a specific polarization state emitted by the image source 1' (such as a liquid crystal screen) is reflected by the beam splitter 3' and then irradiated onto the curved mirror 2'. After being reflected by the curved mirror 2', the imaging light passes through the beam splitter 3' and then enters the human eye at the observation position 4'. The human eye focuses against the light on the virtual image imaging surface and believes that the light is emitted from the virtual image surface based on the experience that light travels in a straight line.

[0016] This technology is inspired by the relatively mature Birdbath coaxial catadioptric optical scheme in AR (Augmented Reality) displays. The technical architecture of the project product can be considered an enlarged version of the Birdbath scheme in AR glasses. As a head-mounted product, traditional AR glasses pursue a small volume in terms of performance. Therefore, the size of the Birdbath curved mirror is generally small. The curved mirror used in AR glasses cannot meet the requirements of a clear aperture of 10 inches to 20 inches in a desktop design. 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 field of view. The currently mature and mass-produced free-form curved mirrors that meet the imaging accuracy requirements make it possible to have a desktop optical scheme with a large field of view, a large exit pupil distance, and a large eye box.

[0017] For the desktop virtual image display device using the above technology, since the design position of the image source 1' is within one focal length of the curved mirror 2' and close to the focal point, the image distance of the virtual image is relatively far, and thus the distance between the virtual image and the human eye is also relatively far. The designed image distance of the virtual image of general products is greater than 5m, compared with the close reading distance of about 30cm. When a person views the display device, the accommodation power required by the lens in the eye is greatly reduced, and the lens is always in a relatively relaxed state, thereby reducing visual fatigue and the risk of myopia.

[0018] The distance from the observation position 8' to the beam splitter 3' is the exit pupil distance; the angle with the observation position 8' as the vertex and the two connecting lines from the observation position 8' to the relative edges of the light-emitting end of the image source 1' as the sides is the field of view angle; 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 becomes larger, in order to achieve the same display effect, a beam splitter 3' with a larger area needs to be used, and the beam splitter 3' is inclined with respect to the curved mirror 2'. 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 increase of the field of view angle. This restricts the use of desktop display devices. Therefore, how to reduce the thickness of the desktop display system is an urgent problem for those skilled in the art to solve. Summary of the Invention

[0019] The main object of the present invention is to propose an imaging optical system to reduce the thickness of the desktop display system.

[0020] To achieve the above object, the imaging optical system proposed by the present invention includes a curved mirror, an image source, a reflector 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 set as a convex surface, the second side of the curved mirror is set as a concave surface, and a first beam splitting surface is arranged on the surface of either the first side or the second side of the curved mirror;

[0021] The image source is arranged on the first side of the curved mirror;

[0022] The reflector is arranged on the first side of the curved mirror, and the reflector is used to reflect the light emitted by the image source to the first side of the curved mirror; and,

[0023] The beam splitter is arranged on the second side of the curved mirror and is spaced from the curved mirror, and the beam splitter is used to reflect the imaging light transmitted through the curved mirror to the first beam splitting surface of the curved mirror. After the imaging light is reflected by the first beam splitting surface of the curved mirror again, it passes through the beam splitter and exits from the imaging optical system;

[0024] Wherein, 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.

[0025] The light emitted by the image source is incident from the first side of the curved mirror after being reflected by the reflector, passes through the curved mirror and exits from the second side of the curved mirror, and then is reflected when incident on the side of the beam splitter close to the curved mirror, is reflected to the second side of the curved mirror and reflected again, and is transmitted from the side of the beam splitter away from the curved mirror after being reflected to the beam splitter. A virtual image at a long distance can be observed at the observation position. The image source and the beam splitter are respectively arranged on both sides of the curved mirror. The above optical path forms a polarization folding optical path, and then the optical path between the curved mirror and the image source is folded by the reflector to form a back folding optical path. Thereby, the distance between the beam splitter and the curved mirror can be reduced, the distance between the curved mirror and the image source screen can be increased, the thickness of the folded optical path part can be controlled, and the overall shape is closer to that of a traditional display. Moreover, the angle of the light from the image source to the curved mirror can be controlled by the size of the reflector for optical path folding, so as to reduce the ghost image of the image source when viewed at a large angle.

[0026] Further, the curved mirror and the beam splitter extend along a first direction, the first side and the second side of the curved mirror are arranged opposite to each other in a second direction, the beam splitter is spaced from the curved mirror in the second direction, and the reflector and the image source are arranged opposite to each other in the first direction.

[0027] Both the curved mirror and the beam splitter extend along the first direction, and the beam splitter is not inclined relative to the curved mirror. While realizing virtual image imaging, the length of the curved mirror in the second direction is shortened, thereby reducing the thickness of the optical system.

[0028] Furthermore, the included angle formed between the extending direction of the mirror and the second direction is α, where α ≥ 45°.

[0029] By adjusting the angle of the mirror, the image source will not increase the overall thickness of the imaging optical system, and the length of the mirror in the thickness direction is small, further reducing the overall thickness.

[0030] Furthermore, the imaging optical system further includes at least one lens disposed between the image source and the mirror.

[0031] Thus, by adding lenses in the optical path, the field curvature and distortion of the real image can be optimized.

[0032] Furthermore, a flat glass and a plano-convex lens are arranged at intervals along the first direction between the image source and the mirror. The plano-convex lens is disposed between the flat glass and the mirror. The plane side of the plano-convex lens faces the flat glass, and the convex side of the plano-convex lens faces the mirror;

[0033] On the plane side of the plano-convex lens, a first reflective polarizer and a first quarter-wave plate are sequentially arranged in the direction close to the image source;

[0034] The flat glass has a first side and a second side that are oppositely arranged in the first direction. A second beam-splitting surface is provided on the surface of the first side or the second side of the flat glass.

[0035] Thus, by adding a polarization folding optical path, the volume and length of the back folding optical path are reduced, and the overall thickness of the imaging optical system is further reduced.

[0036] Furthermore, in order to match the polarization folding optical path of the subsequent stage, a second quarter-wave plate is provided between the plane side of the plano-convex lens and the first reflective polarizer.

[0037] Furthermore, the light-emitting end of the image source includes a first linear polarizer and a third quarter-wave plate that are sequentially arranged in the direction from the inside to the outside;

[0038] A first beam-splitting film is provided on the surface of the first side or the second side of the curved mirror to form the first beam-splitting surface;

[0039] On the side of the beam splitter facing the curved mirror, a second reflective polarizer and a fourth quarter-wave plate are sequentially arranged in the direction close to the curved mirror.

[0040] Thus, a polarization folding optical path can be formed to reduce the overall thickness of the imaging optical system.

[0041] Further, a second linear polarizer is disposed on a side of the second reflective polarizer facing away from the fourth quarter-wave plate.

[0042] Thereby, ghost images formed by light leakage during reflection of the first reflective polarizer can be reduced.

[0043] Further, to reduce reflection of ambient light by the beam splitter, a fifth quarter-wave plate and a third linear polarizer are sequentially disposed on a side of the beam splitter facing away from the curved mirror in a direction away from the curved mirror.

[0044] Further, to reduce ghost images reflected by the curved mirror, a sixth quarter-wave plate and a fourth linear polarizer are sequentially disposed on a side of the third linear polarizer facing away from the beam splitter in a direction away from the beam splitter.

[0045] In the technical solution of the present invention, light emitted from an image source is incident from a first side of the curved mirror through a reflector, passes through the curved mirror and exits from a second side of the curved mirror, and then is reflected on a side of the beam splitter close to the curved mirror, reflected to the second side of the curved mirror and reflected again, and then exits from a side of the beam splitter away from the curved mirror. A virtual image at a long distance can be observed at an observation position. The image source and the beam splitter are respectively disposed at two ends of the curved mirror. The curved mirror and the beam splitter both extend along a first direction. The beam splitter is not inclined relative to the curved mirror. While realizing virtual image imaging, the length of the curved mirror in a second direction is shortened, thereby reducing the thickness of the optical system; and the above optical path forms a polarization folding optical path, and then the optical path between the curved mirror and the image source is folded by a reflector to form a back folding optical path. Thereby, the distance between the beam splitter and the curved mirror can be reduced, the distance between the curved mirror and the image source screen can be increased, the thickness of the folded optical path part can be controlled, the overall shape is closer to a traditional display, and the light angle from the image source to the curved mirror can be controlled by the size of the reflector for optical path folding, thereby reducing image source ghost images during large-angle viewing. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for description in the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on the structures shown in these drawings without creative efforts.

[0047] Figure 1 is an imaging optical system in the related art;

[0048] Figure 2 is a schematic structural diagram of Embodiment 1 provided by the present invention;

[0049] Figure 3 Optical path schematic diagram of Embodiment 1 provided by the present invention;

[0050] Figure 4 is Figure 2 Schematic diagram of film material stacking;

[0051] Figure 5 Optical path grid distortion diagram of Embodiment 1 provided by the present invention;

[0052] Figure 6 Binocular parallax of the optical path of Embodiment 1 provided by the present invention;

[0053] Figure 7 Schematic diagram of film material stacking of the beam splitter of Embodiment 2 provided by the present invention;

[0054] Figure 8 Optical path schematic diagram of the reflected ghost image of the image source and the reflected ghost image of the curved mirror;

[0055] Figure 9 Schematic diagram of film material stacking of the beam splitter of Embodiment 3 provided by the present invention;

[0056] Figure 10 Optical path schematic diagram of the ghost image of the image source;

[0057] Figure 11 Schematic diagram of the relationship between the luminous brightness of the image source and the luminous angle of the pixel;

[0058] Figure 12 Schematic diagram of the structure of Embodiment 6 provided by the present invention;

[0059] Figure 13 Schematic diagram of angle adjustment of Embodiment 6 provided by the present invention;

[0060] Figure 14 Schematic diagram of the structure of Embodiment 7 provided by the present invention;

[0061] Figure 15 Schematic diagram of the structure of Embodiment 8 provided by the present invention;

[0062] Figure 16 Schematic diagram of the structure of the plano-convex lens and the image source of Embodiment 8 provided by the present invention;

[0063] Figure 17 Schematic diagram for comparing virtual imaging schemes of the prior art;

[0064] Figure 18 Schematic diagram of the propagation path of polarized light in the Pancake folding optical path.

[0065] Explanation of the reference numerals in the drawings:

[0066] 100. Imaging optical system; 1. Image source; 11. First linear polarizer; 12. Third quarter-wave plate; 13. First antireflection film; 2. Curved mirror; 21. First beam-splitting film; 3. Beam splitter; 31. Second antireflection film; 32. Fourth quarter-wave plate; 33. Second reflective polarizer; 34. Second linear polarizer; 35. Fifth quarter-wave plate; 36. Third linear polarizer; 37. Sixth quarter-wave plate; 38. Fourth linear polarizer; 39. Third antireflection film; 4. Reflecting mirror; 5. Lens; 6. Plano-convex lens; 7. Flat glass; 8. Observation position;

[0067] 200. Imaging optical system of related technology; 1'. Image source; 2'. Curved reflecting mirror; 3'. Beam splitter; 4'. Observation position.

[0068] The realization, functional features and advantages of the object of the present invention will be further described in conjunction with the embodiments and with reference to the accompanying drawings. Detailed implementation manners

[0069] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0070] It should be noted that if there are directional indications (such as up, down, left, right, front, back...) involved in the embodiments of the present invention, the directional indications are only used to explain the relative positional relationship and movement conditions between components in a certain specific posture. If this specific posture changes, the directional indications will also change accordingly.

[0071] 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 implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, if "and / or" or "and / or" appears throughout the text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or a solution where A and B are satisfied simultaneously. In addition, the technical solutions between the embodiments can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0072] To reduce the thickness of a desktop virtual image display device, the present invention proposes an imaging optical system 100.

[0073] Please refer to Figure 2 , in an 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, so as to have a first side and a second side that are oppositely arranged in a second direction, the first side of the curved mirror 2 is set as a convex surface, the second side of the curved mirror 2 is set as a concave surface, and a first beam splitting surface is provided on the surface of either the first side or the second side of the curved mirror 2; the image source 1 is arranged on the first side of the curved mirror 2, the light-emitting end of the image source 1 faces the first side of the curved mirror 2, and the imaging light rays emitted by it can pass through the curved mirror 2; the beam splitter 3 extends along the first direction and is arranged on the second side of the curved mirror 2, the beam splitter 3 and the curved mirror 2 are spaced apart in the second direction, and the beam splitter 3 is used to reflect the imaging light rays to the first beam splitting surface of the curved mirror 2, and after the imaging light rays are reflected again by the first beam splitting surface of the curved mirror 2, they pass through the beam splitter 3 and exit from the imaging optical system; wherein, the focal length of the curved mirror 2 is f, and the object distance between the image source 1 and the curved mirror 2 is s, and s < f.

[0074] In the technical solution of the present invention, the image source 1 and the beam splitter 3 are respectively arranged at both ends of the curved mirror 2, the curved mirror 2 and the beam splitter 3 both extend along the first direction, and the beam splitter is not inclined relative to the curved mirror. On the premise of satisfying virtual image imaging, the length of the beam splitter 3 in the second direction is shortened, thereby reducing the thickness of the optical system.

[0075] Among them, 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 twice the distance from the center of the curved mirror 2 to the center of the beam splitter 3.

[0076] The light rays emitted by the image source 1 pass through the curved mirror 2 and are incident on the beam splitter 3. Reflection occurs near the curved mirror 2 on the beam splitter 3, and the light rays are reflected to the curved mirror 2. Reflection occurs again on the first beam splitting surface of the curved mirror 2, and then the light rays are reflected to the beam splitter 3 and exit from the side of the beam splitter 3 far from the curved mirror 2 to reach the observation position 8. At the observation position 8, the observer can observe a distant virtual image.

[0077] Please refer to Figures 2 to 4 , in Embodiment 1 of the present invention, in order to achieve the above effect of optical path folding, the light-emitting end of the image source 1 includes a first linear polarizer 11 and a third quarter-wave plate 12 arranged in sequence in the direction from the inside to the outside; a first beam splitting film 21 is provided on the surface of either the first side or the second side ( Figure 4 not drawn in) of the curved mirror 2 to form a first beam splitting surface, and the opposite surface of the first beam splitting surface of the curved mirror 2 can be left untreated; on the side of the beam splitter 3 facing the curved mirror 2, a second reflective polarizer 33 and a fourth quarter-wave plate 32 are arranged in sequence in the direction close to the curved mirror 2.

[0078] 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 light reflection, a first anti-reflection film 13 is provided on the side of the first 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 second quarter-wave plate 32 away from the second reflective polarizer 32, and an anti-reflection film can be provided on the opposite surface of the first splitting surface of the curved mirror 2.

[0079] Along the direction of light propagation, after 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, it becomes linearly polarized light, and then becomes circularly polarized light after passing through the third quarter-wave plate 12. The imaging light reaches the curved mirror 2 after passing through the first anti-reflection film 13;

[0080] The circularly polarized light can pass through the first splitting film 21 on the curved mirror 2. Therefore, the imaging light reaches the beam splitter 3 after passing through the first splitting film 21;

[0081] When the imaging light is incident on the beam splitter 3, it becomes linearly polarized light after passing through the second anti-reflection film 31 and the fourth quarter-wave plate 32, and the linearly polarized light can be reflected by the second reflective polarizer 33. The imaging light propagates in the reverse direction after being reflected by the second reflective polarizer 33;

[0082] During the reverse propagation process, the imaging light reaches the curved mirror 2 after passing through the fourth quarter-wave plate 32 and the second anti-reflection film 31, and the linearly polarized light can be reflected by the first splitting film 21. Therefore, the imaging light is reflected by the first splitting film 21 on the curved mirror 2 and propagates in the forward direction again;

[0083] During the second forward propagation process, the imaging light passes through the second anti-reflection film 31 and the fourth quarter-wave plate 32 again and reaches the second reflective polarizer 33;

[0084] From the process where the imaging light starts to propagate in the reverse direction to the second forward propagation to the second reflective polarizer 33, it passes through the fourth quarter-wave plate 32 twice. The polarization direction of the imaging light is perpendicular to the polarization direction when it is reflected by the second reflective polarizer 33, so it can pass through the second reflective polarizer 33 and exit the optical system to reach the observation position 8.

[0085] Specifically, the angle between the light absorption axis direction of the first linear polarizer 11 and the slow axis direction of the third quarter-wave plate is set to 45°, and the angle between the slow axis direction of the fourth quarter-wave plate 32 and the reflection axis direction of the second reflective polarizer 33 is set to 45° or 90°.

[0086] Preferably, an anti-reflection film is provided on the second side surface of the curved mirror 2 to improve the transmittance of the light emitted from the image source 1 through the curved mirror 2.

[0087] Furthermore, during use, the beam splitter 3, the curved mirror 2, and the image source 1 can be moved in the second direction to adjust the position of the virtual image display.

[0088] Adopting the solution of Embodiment 1, when the virtual image distance is 2000 mm, the exit pupil distance is 200 mm, the horizontal field of view angle is approximately 34°, the vertical field of view angle is approximately 20°, and the diagonal field of view angle is approximately 39°, the corresponding optical thickness is approximately 65 mm.

[0089] Please refer to Figure 5 , the maximum value of the grid distortion corresponding to the system center eye point (the center position of the left eye point and the right eye point) in Embodiment 1 is approximately 3.1%.

[0090] 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 with the condition that the entrance pupil diameter is greater than the common pupil distance of 65 mm, the optimization goal is to minimize the RMS diameter of the imaging light spots in each field of view, thereby ensuring the binocular parallax index.

[0091] Please refer to Figure 6 , in Embodiment 1, the binocular parallax between the corresponding left eye point (X coordinate 32.5 mm) and the right eye point (X coordinate -32.5 mm) is as Figure 5 shown. Among them, Biocular Dipvergence represents the vertical binocular parallax, the abscissa is the field of view angle in the Y direction, the range is -10° to +10°, and each curve in the figure represents a different field of view angle in the X direction. BiocularConvergence represents the horizontal binocular parallax, and the offset value selected for the ordinate is 25 mrad.

[0092] Please refer to Figure 7 , in Embodiment 2, a second linear polarizer 34 is provided on the side of the second reflective polarizer 33 facing away from the fourth quarter-wave plate 32; on the side of the beam splitter 3 facing away from the curved mirror 2, a fifth quarter-wave plate 35 and a third linear polarizer 36 are sequentially provided in the direction away from the curved mirror 2.

[0093] Same as Embodiment 1, to enhance the light transmission effect of the imaging optical system 100 and reduce unnecessary light reflection, a third anti-reflection film 39 is provided in the direction of the third linear polarizer 36 away from the fifth quarter-wave plate 35.

[0094] In the technical solution of the present invention, a second linear polarizer 34 is provided on the side of the second reflective polarizer 33 facing away from the fourth quarter-wave plate 32 to reduce the ghost image formed by the light leakage during the reflection of the second reflective polarizer 33.

[0095] When the second reflective polarizer 33 reflects polarized light whose polarization direction is parallel to the reflection axis direction thereof, if the extinction ratio of the reflection axis of the second reflective polarizer 33 is insufficient, part of the light will be transmitted. To reduce this type of reflection, the absorption axis of the second linear polarizer 34 is arranged parallel to the reflection axis of the second reflective polarizer 33.

[0096] In the technical solution of the present invention, on the side of the beam splitter 3 away from the curved mirror 2, a fifth quarter-wave plate 35, a third linear polarizer 36, and a third anti-reflection film 39 are sequentially arranged in the direction away from the curved mirror 2 to reduce the reflection of the beam splitter 3 on ambient light.

[0097] During the process of ambient light incident on the beam splitter 3 and then reflected, the light passes through the third linear polarizer 36 and the fifth quarter-wave plate 35 in sequence and then reaches the surface of the beam splitter 3 for reflection. It passes through the fifth quarter-wave plate 35 and the third linear polarizer 36 again. The light that first passes through the third polarizer is linearly polarized light whose polarization direction is perpendicular to the absorption axis direction of the third polarizer. The linearly polarized light passes through the fifth 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 cannot pass through the third polarizer again, thereby reducing the reflection of the beam splitter 3 on ambient light.

[0098] Further, to ensure that the above solution will not affect the light emitted inside the optical system, the slow axis direction of the fifth quarter-wave plate 35 can be set at 45° or 135° with respect to the absorption axis direction of the second linear polarizer 34, and the absorption axis of the third linear polarizer 36 can be set at any angle with respect to the absorption axis of the second linear polarizer 34. When the internal light of the optical system is transmitted from the glass surface, it first passes through the fifth quarter-wave plate 35 to become circularly polarized light, and then passes through the third linear polarizer 36 and the third anti-reflection film 39 and is emitted outside the optical system to reach the observation position 8.

[0099] Please refer to Figure 8 , the light emitted by the image source 1 is not directly transmitted but reflected at the first beam splitting film 21, forming an image source reflection ghost image; the external ambient light is reflected by the curved mirror 2 after passing through the beam splitter 3 and then passes through the beam splitter 3 again for emission, forming a curved mirror 2 reflection ghost image.

[0100] In Embodiment 3, to reduce the image source reflection ghost image, based on Embodiment 2, an AG film is further provided at the light-emitting end of the image source 1. Preferably, the AG film is provided on the side of the first anti-reflection film 13 away from the third quarter-wave plate 12;

[0101] Please refer to Figure 9, in order to reduce the ghost image reflected by the curved mirror 2, on the side of the third linear polarizer 36 away from the beam splitter 3, a sixth quarter-wave plate 37 and a fourth linear polarizer 38 are sequentially arranged in the direction away from the beam splitter 3. Preferably, between the third linear polarizer 36 and the third antireflection film 39, a sixth quarter-wave plate 37 and a fourth linear polarizer 38 are sequentially arranged in the direction away from the beam splitter 3.

[0102] In the technical solution of the present invention, an AG film is added to the first antireflection film 13, so that the light rays starting from the image source and reflected by the curved mirror 2 once and falling on the screen of the image source 1 are scattered, the intensity is reduced, and strict imaging can no longer be achieved.

[0103] Furthermore, the higher the haze of the AG film, the better the effect of reducing the ghost image reflected by the image source. However, at the same time, the deterioration of the imaging clarity will be more serious. Therefore, an AG film with a haze greater than 3% is preferably used.

[0104] In the technical solution of the present invention, on the side of the beam splitter 3 in Embodiment 2 away from the curved mirror 2, a layer of circular polarizer, that is, a sixth quarter-wave plate 37 and a fourth linear polarizer 38, is added, which can effectively reduce the transmittance of the beam splitter 3 to ambient light and reduce the ghost image reflected by the curved mirror 2.

[0105] Please refer to Figure 10 , due to the dispersion of the third quarter-wave plate 12 and the fourth quarter-wave plate 32 themselves, and the phase delay of the third quarter-wave plate 12 and the fourth quarter-wave plate 32 for non-normal incident large-angle light deviating from the strict 1 / 4 wavelength phase difference, and the first linear polarizer 11 and the second linear polarizer 34 are not strictly orthogonal for non-normal incident large-angle light, it will cause large-angle light rays emitted from the image source screen to directly pass through the curved mirror 2 and the beam splitter 3, resulting in light leakage and thus the appearance of an image source ghost image.

[0106] In Embodiment 4, the transmittance of the first beam splitting film 21 is t, where t ≤ 50%.

[0107] In the technical solution of the present invention, when the transmittance t of the first beam splitting film 21 ≤ 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.

[0108] The transmittance of the first beam splitting film 21 is t, and the reflectance r is r = 1 - t. Then the imaging light brightness compared to the imaging light brightness of the solution with a transmittance of 50% is The brightness ratio of the image source ghost image becomes Then the contrast of the imaging light compared to the image source ghost image becomes 2×(1 - t) times the contrast of the solution with a transmittance of 50%. It can be seen that when the transmittance of the beam splitting film is lower than 50%, the contrast of the imaging light compared to the image source ghost image will be improved.

[0109] The transmittance of the preferred first beam-splitting film 21 is 10%. Compared with the first beam-splitting film 21 with a transmittance of 10%, the brightness of the ghost image of the image source is reduced to 1 / 5 of the original, and the brightness of the corresponding imaging light is reduced to The brightness contrast between the imaging light and the ghost image of the image source will become Therefore, the imaging light is much more prominent than the ghost image of the image source, and the ghost image of the image source is much less obvious than the imaging light.

[0110] The ghost image of the image source will become more obvious as the viewing angle increases. In Embodiment 5, in order to avoid the appearance of large-angle light, a collimating backlight film material is arranged between the first polarizing plate and the image source 1.

[0111] In the technical solution of the present invention, a collimating backlight film material is arranged between the first polarizing plate and the image source 1 to control the light-emitting angle of the image source 1, thereby avoiding the appearance of large-angle light and weakening the ghost image of the image source.

[0112] Please refer to Figure 11 , where the ordinate L is the light-emitting brightness of the image source 1, and the abscissa is the pixel light-emitting angle of the image source 1, where θ max represents the light-emitting angle at which the polarization film material in the optical path can achieve better elimination of the ghost image of the image source.

[0113] For LCD-type image source screens, the above effects can be achieved by adjusting the exit angle of the backlight. Common solutions include adding a collimating backlight film material such as 3M BEF (Brightness Enhancement Film) film, ALCF (Advanced Light Control Film) film, or using a collimating light guide plate with a micro-nano structure, or using a solution of a direct-lit backlight combined with a collimating lens 5; for uLED self-luminous image source screens, a solution of uLED combined with a matching collimating lens 5 array can be used.

[0114] In one embodiment, in order to further reduce the thickness of the optical system, the image source 1 extends along the first direction and is arranged at an interval and in parallel with the curved mirror 2 in the second direction.

[0115] When the window size of the desktop monitor becomes larger, the radius of curvature of the curved mirror 2 that can achieve good imaging will increase accordingly, and the object distance required for imaging will also increase accordingly, resulting in an increase in the distance from the beam splitter 3 to the image source screen, which appears thick in appearance and increases the limiting conditions in the actual structure layout.

[0116] Please refer to Figure 12, in Embodiment 6, to further reduce the thickness of the optical system, the image source 1 is extended along the second direction and is located on one side of the curved mirror 2 in the first direction; the imaging optical system 100 further includes a reflector 4 provided on the first side of the curved mirror 2. The reflector 4 is disposed opposite to the image source 1 in the second direction and is configured to reflect the light emitted from the image source 1 to the first side of the curved mirror 2.

[0117] 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. In an optical path system of the same volume, the optical path distance between the curved mirror 2 and the image source 1 is increased.

[0118] Further, 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 then the optical path between the curved mirror 2 and the image source 1 is folded by the reflector 4 to further reduce the thickness of the optical system.

[0119] The advantage of this solution is that the thickness of the folded optical path part is controllable in appearance, and the overall shape is closer to that of a traditional display. Another advantage is that the angle of the light from the image source 1 to the curved mirror 2 can be controlled by the size of the optical path folding reflector 4, thereby reducing the ghost image of the image source when viewed at a large angle.

[0120] After adding the folding reflector 4 in the optical path, the circular polarization of the circularly polarized light will change, and the polarization film material related to optical path isolation needs to be adjusted accordingly. Therefore, compared with Embodiment 1, the slow axis direction of the fourth quarter-wave plate 32 needs to be rotated by 90°.

[0121] Please refer to Figure 13 , in Embodiment 6, to enable the reflector 4 to effectively reduce the thickness of the optical system, the angle formed between the extending direction of the reflector 4 and the second direction is α, where α≥45°.

[0122] In the technical solution of the present invention, by adjusting the angle of the reflector 4, the overall volume of the imaging optical system 100 is smaller. 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 gradually decreases, further reducing the overall thickness. In this embodiment, α = 50°.

[0123] Since the degree of freedom for optimizing the use of a single curved mirror 2 for imaging is limited, especially currently limited by the processing technology 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 imaging may exceed the required specifications.

[0124] Please refer to Figure 14, in Embodiment 7, based on Embodiment 6, the imaging optical system 100 further includes at least one lens 5 disposed between the image source 1 and the mirror 4.

[0125] In the technical solution of the present invention, at least one lens 5 is disposed between the image source 1 and the mirror 4 to optimize the field curvature and distortion of the real image by increasing the number of lenses 5 in the optical path.

[0126] Please refer to Figure 15 and Figure 16 , in Embodiment 8, to reduce the distance between the image source 1 and the mirror 4, a flat glass 7 and a plano-convex lens 6 are disposed between the image source 1 and the mirror 4 at intervals along the first direction. The plano-convex lens 6 is disposed between the flat glass 7 and the mirror 4. The plane side of the plano-convex lens 6 faces the flat glass 7, and the convex side of the plano-convex lens 6 faces the mirror 4; on the plane side of the plano-convex lens 6, a first reflective polarizer 61 and a first quarter-wave plate 62 are sequentially disposed in the direction close to the image source 1, and a fourth anti-reflection film can be added to the surface of the first quarter-wave plate 62 to reduce unnecessary reflections; the flat glass 7 has a first side and a second side disposed oppositely in the first direction, and a second beam-splitting surface is disposed on the surface of the first side or the second side of the flat glass 7. Preferably, the second beam-splitting surface of the flat glass 7 is selected as a second beam-splitting film.

[0127] The light emitted from the image source 1 is reflected on the plane side of the plano-convex lens 6 after passing through the flat glass 7 and then propagates reversely; during the reverse propagation, it is reflected when reaching the second side of the flat glass 7, and the light propagates forward for the second time and then passes through the plano-convex lens 6 to reduce the thickness of the imaging optical system 100.

[0128] Meanwhile, in order to match the polarization folding optical path of the subsequent stage, preferably, a second quarter-wave plate 63 is added between the plane side of the plano-convex lens 6 and the first reflective polarizer so that the polarized light emitted from the plano-convex lens 6 is circularly polarized light matching the subsequent polarization folding optical path.

[0129] The above are only exemplary embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made under the technical concept of the present invention by using the content of the specification and drawings of the present invention, or any direct / indirect application 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 includes: A curved mirror (2) having a first side and a second side disposed opposite to each other. The first side of the curved mirror (2) is convex, and the second side of the curved mirror (2) is concave. A first beam-splitting surface is provided on the surface of either the first side or the second side of the curved mirror (2); An image source (1) disposed on the first side of the curved mirror (2); A reflecting mirror (4) disposed on the first side of the curved mirror (2), and the reflecting mirror (4) is configured to reflect the light emitted from the image source (1) to the first side of the curved mirror (2); and A beam splitter (3) disposed on the second side of the curved mirror (2) and spaced apart from the curved mirror (2). The beam splitter (3) is configured to reflect the imaging light passing through the curved mirror (2) to the first beam-splitting surface of the curved mirror (2). After the imaging light is reflected again by the first beam-splitting surface of the curved mirror (2), it passes through the beam splitter (3) and exits from the imaging optical system; Wherein, the focal length of the curved mirror (2) is f, and the object distance between the image source (1) and the curved mirror (2) is s, and s < f.

2. The imaging optical system according to claim 1, wherein The curved mirror (2) and the beam splitter (3) extend along a first direction. The first side and the second side of the curved mirror (2) are disposed opposite to each other in a second direction. The beam splitter (3) is spaced apart from the curved mirror (2) in the second direction. The reflecting mirror (4) and the image source (1) are disposed opposite to each other in the first direction.

3. The imaging optical system according to claim 2, wherein The included angle formed between the extending direction of the reflecting mirror (4) and the second direction is α, where α ≥ 45°.

4. The imaging optical system according to claim 2, characterized in that The imaging optical system further includes at least one lens (5) disposed between the image source (1) and the reflecting mirror (4).

5. The imaging optical system according to claim 2, wherein, A flat glass (7) and a plano-convex lens (6) are disposed between the image source (1) and the reflecting mirror (4) at intervals along the first direction. The plano-convex lens (6) is disposed between the flat glass (7) and the reflecting mirror (4). The planar side of the plano-convex lens (6) faces the flat glass (7), and the convex side of the plano-convex lens (6) faces the reflecting mirror (4); A first reflective polarizer (61) and a first quarter-wave plate (62) are sequentially disposed on the planar side of the plano-convex lens (6) in the direction close to the image source (1); The flat glass (7) has a first side and a second side disposed opposite to each other in the first direction. A second beam-splitting surface is provided on the surface of either the first side or the second side of the flat glass (7).

6. The imaging optical system according to claim 5, wherein A second quarter-wave plate (63) is disposed between the planar side of the plano-convex lens (6) and the first reflective polarizer (61).

7. The imaging optical system according to any one of claims 1 to 6, characterized in that, The light-emitting end of the image source (1) includes a first linear polarizer (11) and a third quarter-wave plate (12) sequentially disposed in the direction from the inside to the outside; A first beam-splitting film (21) is provided on the surface of either the first side or the second side of the curved mirror (2) to form the first beam-splitting surface; On one side of the beam splitter (3) facing the curved mirror (2), a second reflective polarizer (33) and a fourth quarter-wave plate (32) are sequentially arranged in the direction close to the curved mirror (2).

8. The imaging optical system according to claim 7, characterized in that, On one side of the second reflective polarizer (33) facing away from the fourth quarter-wave plate (32), a second linear polarizer (34) is arranged.

9. The imaging optical system according to claim 8, wherein: On one side of the beam splitter (3) facing away from the curved mirror (2), a fifth quarter-wave plate (35) and a third linear polarizer (36) are sequentially arranged in the direction away from the curved mirror (2).

10. The imaging optical system according to claim 9, wherein: On one side of the third linear polarizer (36) facing away from the beam splitter (3), a sixth quarter-wave plate (37) and a fourth linear polarizer (38) are sequentially arranged in the direction away from the beam splitter (3).

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