Imaging optical system

Abstract

The utility model discloses an imaging optical system, which relates to the technical field of desktop display and comprises 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 of 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 utility model, the thickness of the optical system can be effectively reduced while virtual image imaging is realized.

Description

Technical Field

[0001] This utility model relates to the field of desktop display technology, and in particular to an imaging optical system. Background Technology

[0002] To address the shortcomings of near-field eye-use products, desktop virtual image displays have been proposed. These displays employ an optical distance imaging scheme, magnifying a small, near-field image onto a large, distant virtual image within a small space on a desktop. This distance-based virtual image reduces the refractive power required for the eye to focus, thereby reducing eye strain and the risk of myopia.

[0003] In general optical imaging systems, including reflective imaging systems, the basic object-image relationship can be referenced to thin lens imaging. A thin lens is one whose thickness is negligible in imaging calculations. 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. (Vertical magnification) When the object is a real object, i.e., s>0, there are several possible imaging possibilities, as shown in Table 1.

[0004]

[0005]

[0006] Table 1 Thin Lens Imaging Analysis

[0007] VR optics, based on the imaging principle of the aforementioned thin-lens imaging system, has successively gone through three stages: aspherical lenses, Fresnel lenses, and pancake folded optical paths. (See also...) Figure 16 Fresnel lenses offer advantages in terms of low cost and controllable image quality. Their design principle involves eliminating the portion of light that travels in a straight line within the lens, retaining only the curved lens surface used to refract light. This significantly reduces lens thickness while preserving the optical characteristics of conventional lenses, achieving a lightweight design. However, because this approach requires placing the screen near the focal plane of the lens, the distance between the lens and the screen is relatively long, resulting in a larger overall optical module size. Furthermore, the single-layer lens design of Fresnel lenses inherently leads to issues such as blurred image edges, susceptibility to distortion, and the inability to adjust diopter.

[0008] Against this backdrop, the Pancake optical solution emerged and has gradually become the direction for the development and evolution of consumer-grade VR optics. Based on the principle of folded optical paths, this solution not only achieves ultra-short optical focusing and imaging, thereby greatly reducing lens thickness and headset size, but also overcomes the edge blurring and distortion phenomena of traditional Fresnel lens optical solutions, achieving a zero-distortion, full-field high-definition visual experience.

[0009] The core design concept of the Pancake optical solution is to fold the optical path through the reflection and refraction of polarized light. Also known as a folded optical path solution, the Pancake optical solution is a type of VR short-focal-length optical solution. The principle is that the image source emitted by the display screen enters a lens with semi-transparent and semi-reflective properties. The light then refracts multiple times between the lens, a quarter-phase retardation plate, and a reflective polarizer, finally exiting from the reflective polarizer and entering the human eye. Figure 17 As shown. In other words, this solution uses folded optical elements to allow light to travel the same distance in a narrower space, "folding" the original light path, thereby compressing the space between the optical lens and the display screen, and thus significantly reducing the size of the VR headset. Theoretically, this optical solution can reduce the size of the VR headset to 1 / 4 of that of the Fresnel lens solution.

[0010] The optical path principle of the desktop virtual image display device based on the above Pancake optical scheme is as follows: Figure 1 As shown, the specific polarized light emitted from the image source 1' (such as an LCD screen) is reflected by the beam splitter 3' and then shines on the curved mirror 2'. After being reflected by the curved mirror 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 against the light onto the virtual image surface and, based on the experience that light travels in a straight line, assumes that the light is emitted from the virtual image surface.

[0011] This technology is inspired by the mature Birdbath coaxial catadioptric optics solution in AR (Augmented Reality) displays. The project's product architecture can be considered an enlarged version of the Birdbath solution in AR glasses. Traditional AR glasses, as head-mounted products, prioritize small size for performance, hence the generally small size of the Birdbath curved mirrors. The curved mirrors used in AR glasses cannot meet the 10-inch to 20-inch aperture requirements of desktop designs. In recent years, the increasingly mature head-up display market has driven the industrialization of large-aperture curved mirrors to achieve a wider viewing angle. Currently, mass-produced freeform mirrors that meet imaging accuracy requirements have made desktop optical solutions with large viewing angles, large exit pupil distances, and large eyeboxes possible.

[0012] Desktop virtual image display devices employing the above technology have a longer image distance because the image source 1' is positioned within one focal length of the curved reflector 2' and close to the focal point. Consequently, the virtual image is also farther from the viewer's eye. Typical product designs have a virtual image distance greater than 5 meters, compared to approximately 30 centimeters for close-range reading. When viewing the display device, the accommodative effort required by the lens of the eye is significantly reduced, and the lens remains in a more relaxed state, thus reducing eye strain and the risk of myopia.

[0013] The distance from the observation position 8' to the beam splitter 3' is the exit pupil distance; the angle between the two lines connecting the observation position 8' as the vertex and the opposite edges of the light-emitting ends of the image source 1' from the observation position 8' 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 field of view angle increases, a larger beam splitter 3' is required to achieve the same display effect. However, the beam splitter 3' is tilted relative to the curved mirror 2', 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. Furthermore, the thickness of the optical design increases with the increase of the exit pupil distance and the field of view angle, thus limiting the use of desktop display devices. Therefore, how to reduce the thickness of desktop display systems is a problem that urgently needs to be solved by those skilled in the art. Utility Model Content

[0014] The main objective of this invention is to propose an imaging optical system to reduce the thickness of desktop display systems.

[0015] To achieve the above objectives, the imaging optical system proposed in this utility model 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, the second side of the curved mirror is configured as a concave surface, and a first beam splitter is provided on the surface of the first side or the second side of the curved mirror;

[0016] An image source, located on the first side of the curved mirror, emits imaging light that is circularly polarized and can pass through the first beam-splitting surface when it reaches the first beam-splitting surface; and,

[0017] A beam splitter is disposed on the second side of the curved mirror. A first quarter-wave plate and a first reflective polarizer are sequentially disposed on the side of the beam splitter facing the first beam splitter. The first quarter-wave plate converts the circularly polarized light from the first beam splitter into linearly polarized light. The first reflective polarizer reflects the linearly polarized light passing through the first quarter-wave plate back to the first beam splitter. The imaging light is reflected again by the first beam splitter and then passes through the first quarter-wave plate and the first reflective polarizer before exiting from the imaging optical system.

[0018] Wherein, the focal length of the curved mirror is f, and the object distance between the image source and the curved mirror is s, where s < f.

[0019] The light emitted from the image source passes through the first beam-splitting surface, where the imaging light is circularly polarized. It then becomes linearly polarized by a first quarter-wave plate inside the beam splitter, and is reflected back to the first beam-splitting surface by a first reflective polarizer inside the beam splitter. After being reflected again, it exits from the side of the beam splitter furthest 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, its polarization direction is perpendicular to its polarization direction when reflected by the first reflective polarizer, allowing it to pass through the first reflective polarizer). A virtual image at a distance can be observed at the viewing position. This overall polarization-folding optical path utilizes the polarization characteristics of light to achieve multiple folds and multiplexing of the optical path, compressing the beam propagation path without significantly increasing the number of optical elements, thereby effectively reducing the overall thickness of the optical system.

[0020] Furthermore, in order to convert the imaging light emitted by the image source into circularly polarized light, the light-emitting end of the image source includes a first linear polarizer and a second quarter-wave plate arranged sequentially from the inside to the outside.

[0021] According to one aspect of the present invention, in order to achieve the optical path folding effect, the angle between the light 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°.

[0022] According to one aspect of the present invention, in order to achieve the optical path folding effect, the beam splitter extends along a 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.

[0023] According to one aspect of this utility model, to achieve an optical path folding effect, the beam splitter extends along a 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... The angle between the reflection axis 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] Furthermore, in order to reduce the ghost image formed by light leakage during the reflection of the first reflective polarizer, a second linear polarizer is provided on the side of the first reflective polarizer away from the first quarter-wave plate.

[0025] Furthermore, to reduce the reflection of ambient light by the beam splitter, a third quarter-wave plate and a third linear polarizer are sequentially arranged on the side of the beam splitter away from the first beam splitter in a direction away from the first beam splitter.

[0026] Furthermore, in order to reduce the ghost image reflected from 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.

[0027] Preferably, a first beam-splitting film is provided on the first or second side surface of the curved mirror to form the first beam-splitting surface.

[0028] Furthermore, the transmittance of the first beam-splitting film is t, where t ≤ 50%. This improves the contrast of the imaging light compared to the ghost image, thereby reducing the impact of the ghost image on the display effect.

[0029] In this invention, the light emitted from the image source passes through the first beam-splitting surface, where the imaging light is circularly polarized. This circularly polarized light then passes through a first quarter-wave plate inside the beam splitter and is converted to linearly polarized light. The light is then reflected back to the first beam-splitting surface by a first reflective polarizer inside the beam splitter, where it is reflected again. After being reflected by the first reflective polarizer, the light is 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 virtual image at a distance can be observed at the observation position. This overall polarization-folded optical path utilizes the polarization characteristics of light to achieve multiple folds and multiplexing of the optical path, compressing the beam propagation path without significantly increasing the number of optical elements, thereby effectively reducing the overall thickness of the optical system. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0031] Figure 1 For imaging optical systems in related technologies;

[0032] Figure 2 A schematic diagram of the structure of Embodiment 1 provided by this utility model;

[0033] Figure 3 The optical path schematic diagram of Embodiment 1 provided by this utility model;

[0034] Figure 4 for Figure 2 A schematic diagram of membrane material stacking;

[0035] Figure 5 The optical path mesh distortion diagram of Embodiment 1 provided by this utility model;

[0036] Figure 6 The optical path binocular parallax provided in Embodiment 1 of this utility model;

[0037] Figure 7 A schematic diagram of the beam splitter film stacking in Embodiment 2 of this utility model;

[0038] Figure 8 A schematic diagram of the optical paths of the ghost image reflected from the image source and the ghost image reflected from the curved mirror;

[0039] Figure 9 A schematic diagram of the beam splitter film stacking in Embodiment 3 of this utility model;

[0040] Figure 10 This is a schematic diagram of the light path of the ghost image source;

[0041] Figure 11 This is a schematic diagram showing the relationship between the brightness of the image source and the emission angle of the pixels.

[0042] Figure 12 A schematic diagram of the structure of Embodiment 6 provided by this utility model;

[0043] Figure 13 A schematic diagram of angle adjustment for Embodiment 6 of this utility model;

[0044] Figure 14 A schematic diagram of the structure of Embodiment 7 provided by this utility model;

[0045] Figure 15 A schematic diagram of the structure of Embodiment 8 provided by this utility model;

[0046] Figure 16 This is a comparative diagram of existing virtual imaging solutions;

[0047] Figure 17 This is a schematic diagram of the propagation path of polarized light in a pancake fold.

[0048] Explanation of icon numbers:

[0049] 100. Imaging optical system; 1. Image source; 11. First linear polarizer; 12. Second quarter-wave plate; 13. First anti-reflection coating; 2. Curved mirror; 21. First beam splitter; 3. Beam splitter; 31. Second anti-reflection 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 anti-reflection coating; 4. Reflector; 5. Lens; 6. Plano-convex lens; 7. Flat glass; 8. Observation position;

[0050] 200. Imaging optical system of related technologies; 1'. Image source; 2'. Curved mirror; 3'. Beam splitter; 4'. Observation position.

[0051] The realization of the purpose, functional features and advantages of this utility model will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0052] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present utility model.

[0053] It should be noted that if the embodiments of this utility model involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0054] Furthermore, if the embodiments of this utility model involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this utility model.

[0055] To reduce the thickness of desktop virtual image display devices, this utility model proposes an imaging optical system 100.

[0056] Please see Figure 2 In one embodiment of this utility model, 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 and has 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 convex, the second side of the curved mirror 2 is concave, and a first beam splitting surface is provided on the surface of the first side or the second side of the curved mirror 2; the image source 1 is located 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 emitted by the image source 1 can pass through the curved mirror 2; the beam splitter 3 extends along the first direction and is located 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 splitting surface of the curved mirror 2, and the imaging light is reflected again by the first beam splitting surface of the curved mirror 2 and then exits 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.

[0057] In the technical solution of this utility model, the image source 1 and the beam splitter 3 are respectively arranged at both ends of the curved mirror 2. Both the curved mirror 2 and the beam splitter 3 extend along the first direction. The beam splitter is not tilted relative to the curved mirror. Under 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.

[0058] Among them, the object distance S is approximately equal to the sum of the distance from the center of image source 1 to the center of curved mirror 2 and the distance from the center of twice the curved mirror 2 to the center of beam splitter 3.

[0059] The light emitted from image source 1 passes through curved mirror 2 and is incident on beam splitter 3. It is reflected at the point where beam splitter 3 is close to curved mirror 2 and then reflected back to curved mirror 2. It is reflected again at the first beam splitting surface of curved mirror 2 and then reflected back to beam splitter 3. It then passes through the side of beam splitter 3 away from curved mirror 2 and reaches observation position 8. At observation position 8, the observer can observe a virtual image at a distance.

[0060] Please see Figures 2 to 4 In Embodiment 1 of this utility model, in order to achieve the above-mentioned optical path folding effect, the light-emitting end of the image source 1 includes a first linear polarizer 11 and a second quarter-wave plate 12 arranged sequentially from the inside to the outside; a curved mirror 2 ( Figure 4 The first or second side surface of the curved mirror 2 (not shown in the figure) is provided with a first beam splitting film 21 to form a first beam splitting surface. The opposite side surface of the first beam splitting surface of the curved mirror 2 may not be treated. The side of the beam splitter 3 facing the curved mirror 2 has a first reflective polarizer 33 and a first quarter-wave plate 32 arranged in sequence in the direction close to the curved mirror 2.

[0061] In the technical solution of this utility model, in order to enhance the light transmission effect of the imaging optical system 100 and reduce unnecessary reflection, 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. The anti-reflection film can also be provided on the side surface of the first beam splitter of the curved mirror 2.

[0062] Along the direction of light propagation, the imaging light emitted from the image source 1 becomes linearly polarized light after passing through the first linear polarizer 11 on the surface of the image source 1, and then becomes circularly polarized light after passing through the second quarter-wave plate 12. The imaging light then reaches the curved mirror 2 after passing through the first anti-reflection film 13.

[0063] Circularly polarized light can pass through the first beam splitter 21 on the curved mirror 2, so the imaging light reaches the beam splitter 3 after passing through the first beam splitter 21.

[0064] When the imaging light is incident on the beam splitter 3, it becomes linearly polarized light after passing through the second antireflection film 31 and the first quarter-wave plate 32. The linearly polarized light can be reflected by the first reflective polarizer 33, and the imaging light propagates in the opposite direction after being reflected by the first reflective polarizer 33.

[0065] During the reverse propagation process, 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 21. Therefore, the imaging light is reflected by the first beam splitter 21 on the curved mirror 2 and propagates again in the positive direction.

[0066] During the second forward propagation, the imaging light passes through the second antireflection film 31 and the first quarter-wave plate 32 again to reach the first reflective polarizer 33.

[0067] As the imaging light propagates backward and forward 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 the polarization direction when it is reflected by the first reflective polarizer 33, so it can pass through the first reflective polarizer 33 and exit outside the optical system to reach the observation position 8.

[0068] Specifically, the angle between the absorption axis of the first linear polarizer 11 and the slow axis of the second quarter-wave plate 12 is set to 45°, and the angle between the slow axis of the first quarter-wave plate 32 and the reflection axis of the first reflective polarizer 33 is set to 45° or 90°.

[0069] To achieve the optical path folding effect, alternatively, the angle between the absorption axis of the first linear polarizer 11 and the second direction can be θ; the slow axis direction of the second quarter-wave plate 12 can be θ±45°; the slow axis direction of the first quarter-wave plate 32 can be θ±90°; and the angle between the reflection axis direction of the first reflective polarizer 33 and the second direction can be θ. Alternatively, the slow axis direction of the first quarter-wave plate can be... The angle between the reflection axis direction of the first reflective polarizer and the second direction is θ.

[0070] Preferably, the second side surface of the curved mirror 2 is provided with an anti-reflection film to improve the transmittance of light emitted from the image source 1 in the curved mirror 2.

[0071] 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 position of the virtual image display.

[0072] Using the scheme of Example 1, when the virtual image distance is 2000mm, the exit pupil distance is 200mm, the horizontal field of view is about 34°, the vertical field of view is about 20°, and the diagonal field of view is about 39°, the corresponding optical thickness is about 65mm.

[0073] Please see Figure 5 In Example 1, the maximum mesh distortion value corresponding to the system center eye point (the center position between the left and right eye points) is approximately 3.1%.

[0074] During the optimization process, the front and rear surfaces of the curved mirror 2 are kept to have the same shape to ensure compatibility with the hot bending process of the flat glass 7. Furthermore, while keeping the entrance pupil diameter greater than the general interpupillary distance of 65mm, the optimization goal is to minimize the RMS diameter of the imaging spot in each field of view, thereby ensuring the binocular parallax index.

[0075] Please see Figure 6 In Example 1, the binocular parallax between the corresponding left eye point (X coordinate 32.5mm) and right eye point (X coordinate -32.5mm) is as follows: Figure 5 As shown in the figure. Biocular Dipvergence represents vertical binocular parallax, with the horizontal axis representing the field of view in the Y direction, ranging from -10° to +10°. Each line in the curve represents a different field of view in the X direction. Biocular Convergence represents horizontal binocular parallax, with the vertical axis using an offset of 25 mrad.

[0076] Please see Figure 7 In embodiment 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; on the side of the beam splitter 3 away from the curved mirror 2, a third quarter-wave plate 35 and a third linear polarizer 36 are sequentially provided in the direction away from the curved mirror 2.

[0077] Similar to Example 1, in order to enhance the light transmission effect of the imaging optical system 100 and reduce unnecessary reflections, a third anti-reflection film 39 is provided on the third linear polarizer 36 in a direction away from the third quarter-wave plate 35.

[0078] In the technical solution of this utility model, a second linear polarizer 34 is provided on the side of the first reflective polarizer 33 away from the first quarter-wave plate 32, so as to reduce the ghost image formed by light leakage when the first reflective polarizer 33 is reflected.

[0079] When the first reflective polarizer 33 reflects polarized light whose polarization direction is parallel to its reflection axis, the extinction ratio of the reflection axis of the first reflective polarizer 33 is insufficient, which will cause some light to be transmitted. In order 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.

[0080] In the technical solution of this utility model, 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 sequentially arranged in the direction away from the curved mirror 2 to reduce the reflection of ambient light by the beam splitter 3.

[0081] During the process of ambient light incident on beam splitter 3 and being reflected, the light passes sequentially through the third linear polarizer 36 and the third quarter-wave plate 35 before reaching the surface of beam splitter 3 and being reflected. It then 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 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 it cannot pass through the third polarizer again, thereby reducing the reflection of ambient light by beam splitter 3.

[0082] Furthermore, to ensure that the above scheme does not affect the emitted light from inside the optical system, the slow axis direction of the third quarter-wave plate 35 can be set at 45° or 135° to the absorption axis direction of the second linear polarizer 34, while the absorption axis of the third linear polarizer 36 can be set at any angle to the absorption axis of the second linear polarizer 34. When the light from inside the optical system is transmitted from the glass surface, it first passes through the third quarter-wave plate 35 to become circularly polarized light, and then passes through the third linear polarizer 36 and the third antireflection coating 39 before exiting the optical system and reaching the observation position 8.

[0083] Please see Figure 8The light emitted from image source 1 is not directly transmitted through the first beam splitter 21 but is reflected, forming a ghost image reflected from the image source; the ambient light is reflected by the curved mirror 2 after passing through the beam splitter 3 and then exits through the beam splitter 3, forming a ghost image reflected from the curved mirror 2.

[0084] In Embodiment 3, to reduce ghosting of the image source, 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 antireflection film 13 facing away from the second quarter-wave plate 12;

[0085] Please see Figure 9 To reduce ghosting in the reflection of the curved mirror 2, a fourth quarter-wave plate 37 and a fourth linear polarizer 38 are sequentially arranged 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 arranged between the third linear polarizer 36 and the third antireflection coating 39, in a direction away from the beam splitter 3.

[0086] In the technical solution of this utility model, an AG film is added to the first antireflection film 13, so that the light that falls on the screen of the image source 1 after being reflected once by the curved mirror 2 from the image source is scattered and its intensity is reduced, and it can no longer be strictly imaged.

[0087] Furthermore, the higher the haze of the AG film, the better it is at reducing ghosting of the image source, but at the same time, the more severe the degradation of image sharpness will be. Therefore, AG films with a haze greater than 3% are preferred.

[0088] In the technical solution of this utility model, on the side of the beam splitter 3 away from the curved mirror 2 in embodiment 2, a layer of circular polarizers, namely the fourth quarter-wave plate 37 and the 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.

[0089] Please see Figure 10 Due to the dispersion of the second quarter-wave plate 12 and the first quarter-wave plate 32, 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 deviating from the strict 1 / 4 wavelength phase difference, and the fact that the first linear polarizer 11 and the second linear polarizer 34 are not strictly orthogonal for non-normally incident large-angle light, 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 and thus image source ghosting.

[0090] In Example 4, the transmittance of the first spectral separator 21 is t, where t ≤ 50%.

[0091] In the technical solution of this utility model, when the transmittance t of the first beam splitter 21 is ≤ 50%, the contrast of the imaging light compared to the ghost image of the image source will be improved, thereby reducing the impact of the ghost image of the image source on the display effect.

[0092] The first beam splitter 21 has a transmittance of t and a reflectance of r = 1 - t. Therefore, the imaging brightness compared to the scheme with 50% transmittance is: The brightness ratio of the source ghost image becomes The contrast of the imaging light compared to the ghost image of the image source becomes 2×(1-t) of the contrast of the scheme with a transmittance of 50%. It can be seen that when the transmittance of the beam splitter is less than 50%, the contrast of the imaging light compared to the ghost image of the image source will be improved.

[0093] The preferred first beam splitter 21 has a transmittance of 10%. Compared to the first beam splitter 21 with a transmittance of 10%, the brightness of the ghost image source is reduced to 1 / 5 of its original value, while the corresponding brightness of the image is reduced to [a fraction of the original value]. The brightness contrast between the imaging light and the ghost image will become Therefore, the image light is more prominent than the image source ghost image, while the image source ghost image is less noticeable than the image light.

[0094] Image ghosting becomes more pronounced as the viewing angle increases. In embodiment 5, to avoid the appearance of large-angle light, a collimating backlight film is provided between the first polarizer and the image source 1.

[0095] In the technical solution of this utility model, a collimating backlight film is set between the first polarizer and the image source 1 to control the emission angle of the image source 1, thereby avoiding the occurrence of large-angle light and reducing image source ghosting.

[0096] Please see Figure 11 Where the vertical axis L represents the luminance of image source 1, and the horizontal axis represents the pixel emission angle of image source 1, where θ max This indicates that by using a polarizing film material in the optical path, a light emission angle that can effectively eliminate ghosting of the source image can be achieved.

[0097] For LCD image source screens, the above effect can be achieved by adjusting the backlight emission angle. Common solutions include adding collimating backlight materials such as 3M BEF (Brightness Enhancement Film) film or ALCF (Advanced Light Control Film), or using a micro-nano structured collimating light guide plate, or using a direct-lit backlight superimposed with a collimating lens 5, etc. For uLED self-emissive image source screens, a solution can be achieved by using uLEDs in conjunction with a matching collimating lens 5 array.

[0098] In one embodiment, to further reduce the thickness of the optical system, the image source 1 extends along a first direction and is spaced apart from and arranged in parallel with the curved mirror 2 in a second direction.

[0099] When the window size of the desktop monitor increases, the radius of curvature of the curved mirror 2, which can form a better image, will increase accordingly, and the object distance required for imaging will also increase accordingly. This will increase the distance between the beam splitter 3 and the image source screen, making it appear bulky and adding constraints to the actual structural placement.

[0100] Please see Figure 12 In embodiment 6, in order to further reduce the thickness of the optical system, the image source 1 extends along the second direction and is located on one side of the curved mirror 2 in the first direction; the imaging optical system 100 also includes a reflector 4 disposed on the first side of the curved mirror 2, the reflector 4 being disposed opposite to the image source 1 in the second direction, for reflecting the light emitted from the image source 1 to the first side of the curved mirror 2.

[0101] In the technical solution of this utility model, the optical path between the reflector 4 and 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.

[0102] 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 optical path between the curved mirror 2 and the image source 1 can be folded by the reflector 4 to further reduce the thickness of the optical system.

[0103] Please see Figure 13 In embodiment 6, in order 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°.

[0104] In the technical solution of this utility model, by adjusting the angle of the reflector 4, the overall volume of the imaging optical system 100 is made smaller. When α≥45°, the image source 1 will not increase the overall thickness of the imaging optical system 100. Moreover, 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°.

[0105] Since the degree of freedom to optimize a single curved mirror 2 for imaging is limited, especially given the current limitations in the manufacturing process of curved mirror 2, the surface shape of curved mirror 2 is mostly spherical, and the field curvature and distortion of the actual virtual image may exceed the required specifications.

[0106] Please see 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.

[0107] In the technical solution of this utility model, 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.

[0108] Please see Figure 15 In embodiment 8, to reduce the distance between the image source 1 and the reflector 4, a flat glass 7 and a planar convex lens 6 are arranged at intervals along a first direction between the image source 1 and the reflector 4. The planar convex lens 6 is positioned between the flat glass 7 and the reflector 4, with its planar side facing the flat glass 7 and its convex side facing the reflector 4. A second reflective polarizer and a fifth quarter-wave plate are sequentially arranged on the planar side of the planar convex lens 6 in the direction close to the image source 1. A fourth anti-reflection coating can be added to the surface of the fifth quarter-wave plate to reduce unnecessary reflection. The flat glass 7 has a first side and a second side arranged opposite to each other in the first direction, and a second beam-splitting surface is provided on the surface of either the first or 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.

[0109] The light emitted from image source 1 is reflected on the planar side of the plano-convex lens 6 after passing through the flat glass 7, thus propagating in the reverse direction. During the reverse propagation, the light reaches the second side of the flat glass 7 and is reflected again, and then propagates in the forward direction for the second time and passes through the plano-convex lens 6, thereby reducing the thickness of the imaging optical system 100.

[0110] Meanwhile, in order to match the polarization folding optical path of the next stage, it is preferable to add a sixth quarter-wave plate between the planar 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.

[0111] The above description is merely an exemplary embodiment of the present utility model and does not limit the patent scope of the present utility model. Any equivalent structural transformations made based on the technical concept of the present utility model and the contents of the present utility model specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present utility model.

Claims

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

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

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

4. The imaging optical system according to claim 2, characterized in that: 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, characterized in that: 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... 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.

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

7. The imaging optical system according to claim 1, characterized in that, The beam splitter (3) is located on the side opposite to the first beam splitting surface, and a third quarter-wave plate (35) and a third linear polarizer (36) are arranged sequentially in the direction away from the first beam splitting surface.

8. The imaging optical system according to claim 7, characterized in that, The third linear polarizer (36) is located on the side opposite to the beam splitter (3), and a fourth quarter-wave plate (37) and a fourth linear polarizer (38) are arranged sequentially in the direction away from the beam splitter (3).

9. The imaging optical system according to any one of claims 1 to 8, characterized in that: The first or second side surface of the curved mirror is provided with a first beam-splitting film to form the first beam-splitting surface.

10. The imaging optical system according to claim 9, characterized in that, The transmittance of the first spectrophotometer (21) is t, where t≤50%.

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