Optical system and head-mounted display device

Abstract

The embodiment of the invention discloses an optical system and head-mounted display equipment. In a specific implementation scheme, the optical system comprises an image source; the first prism is provided with a first surface, a second surface and a third surface, and the first surface of the first prism is close to the image source; a first lens located between the image source and the first prism; the second surface of the first prism is located on the side, away from the second prism, of the first prism, and the third surface of the first prism is located on the side, close to the second prism, of the first prism; the second lens is located on the side, away from the first prism, of the second prism, a first included angle between the first surface of the second prism and the optical axis of the second lens and a second included angle between the third surface of the first prism and the optical axis of the second lens are acute angles, and the first included angle is equal to the second included angle; the first film layer is located on the second surface of the first prism and can reflect light rays and transmit the light rays; and the second film layer is located on the first surface of the second lens and can reflect light.

Description

Technical Field

[0001] The present disclosure relates to the field of optical imaging technologies, and particularly to an optical system and a head-mounted display device. Background Art

[0002] At present, head-mounted display devices are increasingly widely used. For example, users can use head-mounted display devices for entertainment, office work, etc. The optical system is an important component of a head-mounted display device. Summary of the Invention

[0003] According to one aspect of the embodiments of the present disclosure, an optical system is provided, including: an image source; a first prism having a first surface, a second surface, and a third surface, with the first surface of the first prism being close to the image source; a first lens located between the image source and the first prism; a second prism, where the second surface of the first prism is on the side away from the second prism, and the third surface of the first prism is on the side close to the second prism, and the second prism has a first surface, with the first surface of the second prism being close to the third surface of the first prism; a second lens located on the side away from the first prism of the second prism, and both a first angle between the first surface of the second prism and the optical axis of the second lens and a second angle between the third surface of the first prism and the optical axis of the second lens are acute angles, and the first angle is equal to the second angle, and the second lens has a first surface, with the first surface of the second lens being on the side away from the second prism; a first film layer located on the second surface of the first prism, capable of reflecting light and transmitting light; a second film layer located on the first surface of the second lens, capable of reflecting light; where the light emitted by the image source passes through the first lens, enters the first prism, undergoes at least one total internal reflection in the first prism, is reflected by the first film layer, exits from the third surface of the first prism and enters the second prism from the first surface of the second prism, is reflected by the second film layer after passing through the second prism and the second lens, and the light reflected by the second film layer sequentially passes through the second lens, the first surface of the second prism, the third surface of the first prism, and the second surface of the first prism, and exits through the first film layer. The optical system satisfies: 1 ≤ (f1 × f2) / (f × f) ≤ 16, where f represents the focal length of the optical system, f1 represents the focal length of the first lens, and f2 represents the focal length of the second lens.

[0004] According to another aspect of the embodiments of the present disclosure, a head-mounted display device is provided, including: a frame structure; and the above optical system, with the optical system being installed on the frame structure. Description of the Drawings

[0005] The above and other objects, features, and advantages of the present disclosure will become more apparent by describing the embodiments of the present disclosure in more detail with reference to the accompanying drawings. The accompanying drawings are used to provide a further understanding of the embodiments of the present disclosure and constitute a part of the specification. Together with the embodiments of the present disclosure, they are used to explain the present disclosure and do not constitute a limitation to the present disclosure. In the drawings, the same reference numerals generally represent the same components or steps;

[0006] Figure 1 is a schematic structural diagram of an optical system provided by some exemplary embodiments of the present disclosure;

[0007] Figure 2 is a schematic structural diagram of an optical system provided by some other exemplary embodiments of the present disclosure;

[0008] Figure 3 is a schematic structural diagram of an optical system provided by some further exemplary embodiments of the present disclosure;

[0009] Figure 4 is a schematic structural diagram of an optical system provided by some other exemplary embodiments of the present disclosure;

[0010] Figure 5 is a schematic structural diagram of an optical system provided by some other exemplary embodiments of the present disclosure;

[0011] Figure 6 is a schematic structural diagram of an optical system provided by some other exemplary embodiments of the present disclosure;

[0012] Figure 7 is a schematic structural diagram of an optical system provided by some other exemplary embodiments of the present disclosure;

[0013] Figure 8 is a schematic diagram of the modulation transfer function curve of the optical system in some exemplary embodiments of the present disclosure;

[0014] Figure 9 is a schematic structural diagram of an optical system provided by some other exemplary embodiments of the present disclosure;

[0015] Figure 10 is a schematic diagram of the modulation transfer function curve of the optical system in some other exemplary embodiments of the present disclosure;

[0016] Figure 11-1 is a schematic structural diagram of an optical system provided by some other exemplary embodiments of the present disclosure;

[0017] Figure 11-2 is a schematic structural diagram of an optical system provided by some other exemplary embodiments of the present disclosure;

[0018] Figure 11-3 is a schematic structural diagram of an optical system provided by some other exemplary embodiments of the present disclosure;

[0019] Figure 12 is a schematic structural diagram of a head-mounted display device provided by some exemplary embodiments of the present disclosure.

[0020] In the figure, 18 is an image source; 20 is a first prism; 25 is a first lens; 30 is a second prism; 40 is a second lens; 45 is a first film layer; 50 is a second film layer; 201 is the first surface of the first prism; 203 is the second surface of the first prism; 205 is the third surface of the first prism; 207 is a groove; 100 is a human eye; 301 is the first surface of the second prism; 401 is the first surface of the second lens; 251 is the first surface of the first lens; 253 is the second surface of the first lens; 60 is a third prism; 601 is the first surface of the third prism; 603 is the second surface of the third prism; 70 is a third lens; 80 is an additional lens; Z is an axis; R1 is the angle between the first surface of the second prism and the optical axis of the second lens; R2 is the angle between the third surface of the first prism and the optical axis of the second lens; A is the angle between the second surface of the first prism and the target plane; B is the angle between the third surface of the first prism and the target plane; 90 is a frame structure. Detailed implementation manners

[0021] Next, exemplary embodiments according to the present disclosure will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments of the present disclosure. It should be understood that the present disclosure is not limited by the exemplary embodiments described herein.

[0022] In the description of the present disclosure, the orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", etc. is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the present disclosure and simplifying the description, rather than indicating or implying that the device referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present disclosure.

[0023] In the description of the present disclosure, unless otherwise clearly defined and limited, terms such as "mounted", "connected", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be directly connected, or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present disclosure can be understood according to specific circumstances.

[0024] Exemplary overview

[0025] A head-mounted display device can also be referred to as a Head-Mounted Display (HMD) or a headset. The head-mounted display device can be used to achieve augmented reality (AR) effects, virtual reality (VR) effects, mixed reality (MR) effects, etc. The head-mounted display device can be presented in the form of glasses, helmets, etc.

[0026] The optical system is an important component of the head-mounted display device. The optical system can also be called an optical engine. The optical system can be used to emit light and process the light so that the light enters the eyebox of the optical system. When the user wears the head-mounted display device, the user's eyes can be located in the eyebox, the light can be projected onto the user's eyes, and the user can see the display screen. Therefore, in order to ensure the user's experience, it is necessary to reasonably design the optical system.

[0027] Exemplary Structure

[0028] Some exemplary embodiments of the present disclosure provide an optical system. The optical system provided by the embodiments of the present disclosure may include an image source, a prism, and a lens. Each optical element in the embodiments of the present disclosure may be an element that is axisymmetric with respect to the optical axis of each optical element.

[0029] For example, as Figures 1 to 4 shown, the optical system provided by the embodiments of the present disclosure may include an image source 18, a first prism 20, a first lens 25, a second prism 30, and a second lens 40.

[0030] In some alternative embodiments of the present disclosure, the image source 18 can be used to emit the light of the display screen. The image source 18 may include, but is not limited to, an Organic Light Emitting Diode (OLED) image source, a Liquid Crystal image source, a Liquid Crystal on Silicon (LCOS) image source, a Micro Electro Mechanical System (MEMS) image source, a Digital Micromirror Device (DMD), etc. For example, the image source 18 can be an OLED display screen.

[0031] In some alternative embodiments of the present disclosure, the first prism 20 can be used to extend the optical path of the optical system. The first prism 20 can have a first surface 201, a second surface 203, and a third surface 205. For example, the first surface 201 and the second surface 203 of the first prism 20 can intersect, the first surface 201 and the third surface 205 can intersect, and the second surface 203 and the third surface 205 can intersect. As Figure 1 , Figure 3 shown, the first surface 201, the second surface 203, and the third surface 205 of the first prism 20 can all be planes. Alternatively, as Figure 2 , Figure 4 shown, the first surface 201 of the first prism 20 can include a curved portion, and the second surface 203 and the third surface 205 of the first prism 20 can both be planes.

[0032] It can be understood that the "intersection" or "included angle" described in the present disclosure can be the actual intersection of two elements and the actual included angle between the two elements. If two elements do not actually intersect, or no included angle is formed between the two elements, after the two elements are extended along their respective extension directions, the non-actual existing parts after extension can also intersect or form an included angle, meeting the relevant limitations in the embodiments of the present disclosure.

[0033] In some alternative embodiments of the present disclosure, the second surface 203 of the first prism 20 can be located on the side of the first prism 20 away from the second prism 30. The third surface 205 of the first prism 20 can be located on the side of the first prism 20 close to the second prism 30. The first surface 201 of the first prism 20 can be close to the image source 18. For example, the first surface 201 of the first prism 20 can be opposite to the image source 18. The first surface 201 and the second surface 203 of the first prism 20 can both be located on the side of the first prism 20 close to the eye box of the optical system. The second prism 30 can have a first surface 301. The first surface 301 of the second prism 30 can be close to the third surface 205 of the first prism 20. The first surface 301 of the second prism 30 can be a plane. The first surface 301 of the second prism 30 and the third surface 205 of the first prism 20 can be opposite and have an air gap therebetween.

[0034] It can be understood that the eye box of the optical system can be the area where the human eye (such as Figures 1 to 4 the human eye 100 in) can move. Within this area, the human eye 100 can see the display screen. The eye box of the optical system can also be referred to as Eye Box or EB. The size of the eye box of the optical system is an important design index in the optical system.

[0035] In some alternative embodiments of the present disclosure, the first lens 25 can be used to correct aberrations. The first lens 25 can be located between the image source 18 and the first prism 20. For example, as Figure 1 、 Figure 4 shown, the first lens 25 can be a positive lens. The surface of the positive lens close to the first surface 201 of the first prism 20 can be a convex surface protruding towards the first surface 201 of the first prism 20, and the surface of the positive lens away from the first prism 20 can be a flat surface. Optionally, for Figure 1 、 Figure 4 shown, the surface of the positive lens away from the first prism 20 can also not be set as a flat surface, but can be set as a convex surface protruding towards the image source 18. Again, for example, as Figure 2 、 Figure 3 shown, the first lens 25 can be a plano-convex lens. The surface of the plano-convex lens close to the first prism 20 can be a flat surface, and the surface of the plano-convex lens away from the first prism 20 can be a convex surface protruding towards the image source 18. Optionally, the first lens 25 and the first prism 20 can be an integral part. For example, reference can be made to Figure 2 . In the example where the first lens 25 and the first prism 20 are an integral part, it can be understood that the first surface 201 of the first prism 20 can include a curved surface portion, and this curved surface contributes to the focal length of the first lens 25. Or, the first lens 25 and the first prism 20 can be separately provided. For example, reference can be made to Figure 3 . If the first lens 25 and the first prism 20 are an integral part, the part constituting the first lens 25 and the part constituting the first prism 20 can be integrally injection-molded, with high production efficiency. If the first lens 25 and the first prism 20 are separately provided, the first lens 25 and the first prism 20 can be injection-molded separately and fixed by bonding or other means, which can facilitate the replacement, maintenance, etc. of the first lens 25 and the first prism 20.

[0036] In some alternative embodiments of the present disclosure, the second lens 40 can be used to bear the optical power and correct aberrations. The second lens 40 can be located on the side of the second prism 30 away from the first prism 20. The second lens 40 and the second prism 30 can be an integral part. For example, reference can be made to Figure 1 、 Figure 2 、 Figure 4 . Or, the second lens 40 and the second prism 30 can be separately provided. For example, reference can be made to Figure 3If the second lens 40 and the second prism 30 are integrally formed, the part forming the second lens 40 and the part forming the second prism 30 can be integrally injection-molded, with high production efficiency. If the second lens 40 and the second prism 30 are separately provided, the second lens 40 and the second prism 30 can be injection-molded separately and fixedly connected by means such as bonding, which facilitates the replacement, maintenance, etc. of the second lens 40 and the second prism 30. The second lens 40 may have a first surface 401. The first surface 401 of the second lens 40 may be located on the side of the second lens 40 away from the second prism 30. Optionally, the first surface 401 of the second lens 40 may be a curved surface. The "curved surface" in the embodiments of the present disclosure may include, but is not limited to, a spherical surface, an aspherical surface, a free-form surface, etc. In the example where the second lens 40 and the second prism 30 are integrally formed, the first surface 401 of the second lens 40 may also be understood as the surface of the second prism 30, and this surface contributes to the focal length as a curved surface.

[0037] In some alternative embodiments of the present disclosure, the optical system provided by the embodiments of the present disclosure may further include a film layer. The term "film layer" refers to a thin-layer structure, which may be an optical thin film or an optical sheet, for example, a semi-transmissive semi-reflective film, a polarizer, a polarization beam splitter film, a polarization beam splitter sheet, a wave plate, and the like. For example, as Figures 1 to 4 shown, the optical system provided by the embodiments of the present disclosure may further include a first film layer 45 and a second film layer 50. The first film layer 45 may be located on the second surface 203 of the first prism 20 and can reflect and transmit light. The first film layer 45 may be a semi-transmissive semi-reflective film without beam-splitting ability or a polarization beam splitter film. The first film layer 45 may be disposed on the second surface 203 of the first prism 20 by means such as bonding and coating. The second film layer 50 may be located on the first surface 401 of the second lens 40 and can reflect light. The second film layer 50 may be used to totally reflect or partially reflect light, so that the second film layer 50 may be a total reflection film or a semi-transmissive semi-reflective film. The second film layer 50 may be disposed on the first surface 401 of the second lens 40 by means such as bonding and coating.

[0038] It should be noted that the light emitted by the image source 18 passes through the first lens 25, enters the first prism 20, is totally reflected at least once in the first prism 20, is reflected by the first film layer 45, exits from the third surface 205 of the first prism 20 and enters the second prism 30 from the first surface 301 of the second prism 30, and is reflected by the second film layer 50 after passing through the second prism 30 and the second lens 40. The light reflected by the second film layer 50 passes through the second lens 40, the first surface 301 of the second prism 30, the third surface 205 of the first prism 20, and the second surface 203 of the first prism 20 in sequence, and exits through the first film layer 45. The light exiting from the first film layer 45 may enter the eyebox of the optical system.

[0039] In some alternative embodiments of the present disclosure, the light emitted from the image source 18 can enter the first lens 25 from one surface of the first lens 25. After passing through the first lens 25, the light enters the first prism 20 from the first surface 201 of the first prism 20. The light entering the first prism 20 can first undergo total internal reflection at the third surface 205 of the first prism 20, and then undergo a reflection (which can be reflected by the first film layer 45) at the second surface 203 of the first prism 20, and exits from the third surface 205 of the first prism 20 and enters the second prism 30 from the first surface 301 of the second prism 30. Of course, before the light exiting from the third surface 205 of the first prism 20, the number of times of total internal reflection experienced within the first prism 20 may not be limited to one, and the number of times of reflection within the first prism 20 may also not be limited to one. For example, after undergoing total internal reflection once at the third surface 205 of the first prism 20 and undergoing a reflection once at the second surface 203 of the first prism 20, it can undergo total internal reflection once again at the third surface 205 of the first prism 20 and undergo a reflection once again at the second surface 203 of the first prism 20, and then exit from the third surface 205 of the first prism 20.

[0040] The light exiting from the third surface 205 of the first prism 20 can enter the second prism 30 from the first surface 301 of the second prism 20. The light entering the second prism 30 can be propagated to the second film layer 50 after passing through the second prism 30 and the second lens 40 in sequence. The second film layer 50 can reflect the light to adjust the light propagation direction. For example, the second film layer 50 can adjust the propagation direction of the light from horizontal right to horizontal left. In this way, the light with the adjusted propagation direction can pass through the second lens 40, the first surface 301 of the second prism 30, the third surface 205 of the first prism 20, the second surface 203 of the first prism 20, and the first film layer 45 in sequence until it reaches the eyebox of the optical system.

[0041] In the optical system provided by the embodiments of the present disclosure, through the combined use of the image source 18, the first prism 20, the first lens 25, the second prism 30, the second lens 40, the first film layer 45, and the second film layer 50, the light emitted from the image source 18 can enter the eyebox of the optical system. In this way, the human eye 100 can see the display screen provided by the image source 18. Therefore, the head-mounted display device can display content normally to meet the user's usage requirements, such as meeting the user's movie-watching requirements.

[0042] In some alternative embodiments of the present disclosure, such as Figures 1 to 4As shown, the optical system provided by the embodiments of the present disclosure may further include a third prism 60. The third prism 60 may have a first surface 601 and a second surface 603. The first surface 601 of the third prism 60 may be located on the side of the third prism 60 away from the first prism 20. The second surface 603 of the third prism 60 may be located on the side of the third prism 60 close to the first prism 20. After the light reflected by the second film layer 50 passes through the first prism 20 again, it exits through the second surface 603 and the first surface 601 of the third prism 60. Optionally, the first film layer 45 is located between the first prism 20 and the third prism 60, and may be disposed on the second surface 603 of the third prism 60 by means of bonding, coating, etc., or adhered to both the first prism 20 and the third prism 60.

[0043] Optionally, the third prism 60 may be used as a compensating member to play the following two roles: (1) compensating for the deflection of light in the first prism 20; (2) compensating for the optical path and making up for the optical path difference generated after the light emitted from different light-emitting positions on the image source 18 propagates in the first prism 20, so that the optical paths of the light emitted from different light-emitting positions are basically the same.

[0044] Optionally, both the first surface 601 and the second surface 603 of the third prism 60 may be flat. Alternatively, the first surface 601 of the third prism 60 may be a curved surface, and the second surface 603 of the third prism 60 may be a flat surface. The first surface 601 and the second surface 603 of the third prism 60 may intersect. The first film layer 45 may be a polarization beam splitter film located between the second surface 603 of the third prism 60 and the second surface 203 of the first prism 20. A quarter-wave plate may be provided between the third surface 205 of the first prism 20 and the first surface 301 of the second prism 30. The polarization beam splitter film and the quarter-wave plate may be used in cooperation to enable the light emitted from the image source 18 to propagate along the following target path: the first lens 25 → the first prism 20 → the first film layer 45 → the first prism 20 → the second prism 30 → the second lens 40 → the second film layer 50 → the second lens 40 → the second prism 30 → the first prism 20 → the first film layer 45 → the third prism 60 → the eye box of the optical system.

[0045] In some alternative embodiments of the present disclosure, the second film layer 50 may be a semi-transmissive and semi-reflective film. As Figure 4 shown, the optical system provided by the embodiments of the present disclosure may further include an additional lens 80, and the additional lens 80 may be located on the side of the second film layer 50 away from the second lens 40.

[0046] Optionally, the additional lens 80 and the second film layer 50 may be adhered to each other. Alternatively, there may be a cavity gap between the additional lens 80 and the second film layer 50.

[0047] Here, the additional lens 80 can be used as a compensating lens for the second lens 40. Since the additional lens 80 is located on the side of the second film layer 50 away from the second lens 40, the light in the external environment (which can also be referred to as ambient light) can sequentially pass through the additional lens 80, the second film layer 50, the second lens 40, the second prism 30, the first prism 20, the third prism 60, and reach the exit pupil of the optical system. In this way, the ambient light can enter the human eye 100 without deflection, and when the user wears the head-mounted display device to observe the external environment, an undistorted environmental image can be seen.

[0048] In some alternative embodiments of the present disclosure, the first angle between the first surface 301 of the second prism 30 and the optical axis of the second lens 40 and the second angle between the third surface 205 of the first prism 20 and the optical axis of the second lens 40 can both be acute angles, and the first angle can be equal to the second angle. Here, the first angle can be equal to the second angle can be understood as that the two angles can be equal or substantially equal.

[0049] Optionally, the optical axis of the second lens 40 can be represented as Figures 1 to 4 the axis Z in. The optical axis of the second lens 40 can be parallel to the lower surface of the second prism 30. The first surface 301 of the second prism 30 can be inclined with respect to the optical axis of the second lens 40, that is, the first angle between the first surface 301 of the second prism 30 and the optical axis of the second lens 40 is an acute angle. The third surface 205 of the first prism 20 can be inclined with respect to the optical axis of the second lens 40, that is, the second angle between the third surface 205 of the first prism 20 and the optical axis of the second lens 40 is an acute angle. The inclination of the third surface 205 of the first prism 20 with respect to the optical axis of the second lens 40 can be consistent with the inclination of the first surface 301 of the second prism 30 with respect to the optical axis of the second lens 40. The inclination of the third surface 205 of the first prism 20 with respect to the optical axis of the second lens 40 can be characterized by the first angle between the third surface 205 of the first prism 20 and the optical axis of the second lens 40. The first angle can be referred to as, for example, Figure 4 R1 in. The inclination of the first surface 301 of the second prism 30 with respect to the optical axis of the second lens 40 can be characterized by the second angle between the first surface 301 of the second prism 30 and the optical axis of the second lens 40, and the second angle can be referred to as, for example, Figure 4 R2 in. Here, both R1 and R2 can be between 0 degrees and 90 degrees, and R1 and R2 can be equal.

[0050] Through research, it is found that making the third surface 205 of the first prism 20 and the first surface 301 of the second prism 30 both inclined with respect to the optical axis of the second lens 40, and making the inclination of the third surface 205 of the first prism 20 with respect to the optical axis of the second lens 40 consistent with the inclination of the first surface 301 of the second prism 30 with respect to the optical axis of the second lens 40 is beneficial to achieving a larger eyebox when the optical system has the same central thickness and the same field of view angle. In addition, it is also beneficial to achieving a smaller central thickness when the optical system has the same field of view angle and the same size of the eyebox, thus facilitating the miniaturization and lightweight of the optical system.

[0051] In some alternative embodiments of the present disclosure, the optical system may satisfy: 1 ≤ (f1 × f2) / (f × f) ≤ 16, where f represents the focal length of the optical system, f1 represents the focal length of the first lens 25, and f2 represents the focal length of the second lens 40. In other words, the ratio of the product of the focal lengths of the first lens 25 and the second lens 40 to the square of the system focal length may be limited within the range of [1, 16].

[0052] Optionally, for Figure 1 、 Figure 4 the optical system shown, the focal length of the first lens 25 may be the focal length of the surface of the first lens 25 close to the first prism 20. For Figure 2 、 Figure 3 the optical system shown, the focal length of the first lens 25 may be the focal length of the surface of the first lens 25 close to the image source 18. For Figures 1 to 4 the optical system shown, the focal length of the second lens 40 may be the focal length of the first surface 401 of the second lens 40.

[0053] Optionally, (f1 × f2) / (f × f) may be greater than or equal to 1 and less than or equal to 3, or greater than 3 and less than or equal to 10, or greater than 10 and less than or equal to 16. In other words, (f1 × f2) / (f × f) may be limited within the ranges of [1, 3], (3, 10], (10, 16]. For example, (f1 × f2) / (f × f) may be 1, 1.2, 2, 2.5, 3, or 3.5, 4, 5, 7, 8, 10, or 10.5, 11, 12, 14, 15, 16, etc., which will not be listed one by one here.

[0054] Through research, it is found that limiting (f1 × f2) / (f × f) within the range of [1, 16], such as within the ranges of [1, 3], (3, 10], (10, 16], can enable the first lens 25 and the second lens 40 to jointly play the role of improving the optical performance of the optical system and avoid excessive dependence on a single lens.

[0055] In some alternative embodiments of the present disclosure, the first surface 201 of the first prism 20 may include a curved surface portion with a focal length of f3 (e.g., Figure 4 as shown), and (f1×f2×f3) / (f×f×f) may be greater than or equal to 1 and less than or equal to 64. In other words, the ratio of the product of the focal lengths of the first lens 25, the second lens 40, and the first surface 201 of the first prism 20 to the cube of the system focal length may be limited within the range of [1, 64].

[0056] In some alternative embodiments of the present disclosure, as Figure 5 shown, the optical system provided by the embodiments of the present disclosure may include a third lens 70 located between the first lens 25 and the first surface 201 of the first prism 20. The third lens 70 may have a curved surface facing the image source 18. The focal length of the third lens 70 may be f3.

[0057] Optionally, (f1×f2×f3) / (f×f×f) may be greater than or equal to 1 and less than or equal to 10, or greater than 10 and less than or equal to 20, or greater than 20 and less than or equal to 40, or greater than 40 and less than or equal to 64. In other words, (f1×f2×f3) / (f×f×f) may be limited within the ranges of [1, 10], (10, 20], (20, 40], (40, 64]. For example, (f1×f2×f3) / (f×f×f) may be 1, 2, 4, 5, 7, 9, 10, or 11, 12, 14, 15, 17, 18, 20, or 21, 22, 25, 26, 29, 30, 35, 38, 39, 40, or 41, 44, 47, 50, 54, 57, 60, 61, 63, 64, etc., and will not be listed one by one here.

[0058] It is found through research that limiting (f1×f2×f3) / (f×f×f) within the range of [1, 64], such as within the ranges of [1, 10], (10, 20], (20, 40], (40, 64], the first lens 25, the second lens 40, and the first surface 201 of the first prism 20 can jointly play a role in improving the optical performance of the optical system. In addition, the optical performance of the optical system is relatively smooth without sudden changes.

[0059] Optionally, the third lens 70 may be a plano-convex lens. The plane of the plano-convex lens may face the first surface 201 of the first prism 20, and the curved surface (i.e., the convex surface) of the plano-convex lens may face the image source 18. Then the focal length of the third lens 70 may be the focal length of the curved surface of the plano-convex lens.

[0060] In some alternative embodiments of the present disclosure, as Figure 1 , Figure 4 , Figure 5As shown, the first lens 25 may have a first surface 251 and a second surface 253. The first surface 251 of the first lens 25 may be located on the side of the first lens 25 close to the first prism 20, and the second surface 253 of the first lens 25 may be located on the side of the first lens 25 close to the image source 18.

[0061] In some alternative embodiments of the present disclosure, the second surface 253 of the first lens 25 may be a curved surface or a flat surface, for example, it may be an aspherical surface.

[0062] Optionally, the radius of curvature of the best - fit spherical surface of the second surface 253 of the first lens 25 may be greater than or equal to 100 millimeters. In other words, the radius of curvature of the best - fit spherical surface of the second surface 253 of the first lens 25 may be limited within the range of [100 mm, +∞). For example, the radius of curvature of the best - fit spherical surface of the second surface 253 of the first lens 25 may be 100 mm, 180 mm, 500 mm, 1000 mm, etc., and will not be listed one by one here.

[0063] In the embodiments of the present disclosure, when limiting the second surface 253 of the first lens 25, what can be limited is the radius of curvature of the best - fit spherical surface of the second surface 253 of the first lens 25. It can be understood that the radius of curvature of the best - fit spherical surface means: using a spherical surface to replace the aspherical surface, making the vertices of the spherical surface and the aspherical surface coincide, and making the root - mean - square (RMS) of the vector height difference between the two in the effective aperture region the smallest, and obtaining the radius of the spherical surface, which is the radius of curvature of the best - fit spherical surface. In this way, the radius of curvature of the best - fit spherical surface of the second surface 253 of the first lens 25 can globally reflect the optical characteristics of the second surface 253 of the first lens 25. Through research, it is found that limiting the radius of curvature of the best - fit spherical surface of the second surface 253 of the first lens 25 within the range of [100 mm, +∞) is beneficial to ensuring the rationality of the parameters of the first lens 25, and thus beneficial to ensuring the imaging quality of the optical system.

[0064] Optionally, the paraxial radius of curvature of the second surface 253 of the first lens 25 may be greater than or equal to 50 millimeters. In other words, the paraxial radius of curvature of the second surface 253 of the first lens 25 may be limited within the range of [50 mm, +∞). For example, the paraxial radius of curvature of the second surface 253 of the first lens 25 may be 50 mm, 90 mm, 300 mm, 1200 mm, etc., and will not be listed one by one here.

[0065] In an embodiment of the present disclosure, when defining the second surface 253 of the first lens 25, the defined value can be the paraxial curvature radius of the second surface 253 of the first lens 25. It can be understood that the paraxial curvature radius of the second surface 253 of the first lens 25 can represent the curvature radius of the paraxial region (i.e., the region near the optical axis) of the second surface 253 of the first lens 25, and the light rays passing through the paraxial region have a greater impact on the imaging quality. Through research, it is found that restricting the paraxial curvature radius of the second surface 253 of the first lens 25 within the range of [50 mm, +∞) is beneficial to ensuring the rationality of the parameters of the first lens 25, and thus beneficial to ensuring the imaging quality of the optical system.

[0066] In some alternative embodiments of the present disclosure, the best-fit spherical curvature radius of the first surface 251 of the first lens 25 can be greater than or equal to 20 millimeters and less than or equal to 60 millimeters. In other words, the best-fit spherical curvature radius of the first surface 251 of the first lens 25 can be restricted within the range of [20 mm, 60 mm].

[0067] Optionally, the best-fit spherical curvature radius of the first surface 251 of the first lens 25 can be greater than or equal to 20 millimeters and less than or equal to 40 millimeters, or greater than 40 millimeters and less than or equal to 60 millimeters. In other words, the best-fit spherical curvature radius of the first surface 251 of the first lens 25 can be restricted within the ranges of [20 mm, 40 mm], (40 mm, 60 mm]. For example, the best-fit spherical curvature radius of the first surface 251 of the first lens 25 can be 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, or 42 mm, 45 mm, 50 mm, 55 mm, 60 mm, etc., and will not be listed one by one here.

[0068] The best-fit spherical curvature radius of a certain surface can globally reflect the optical characteristics of that surface. Restricting the best-fit spherical curvature radius of the first surface 251 of the first lens 25 within the range of [20 mm, 60 mm], for example, within the ranges of [20 mm, 40 mm], (40 mm, 60 mm], is beneficial to ensuring the rationality of the parameters of the first lens 25, and thus beneficial to ensuring the imaging quality of the optical system.

[0069] In some alternative embodiments of the present disclosure, the paraxial curvature radius of the first surface 251 of the first lens 25 can be greater than or equal to 5 millimeters and less than or equal to 200 millimeters. In other words, the paraxial curvature radius of the first surface 251 of the first lens 25 can be restricted within the range of [5 mm, 200 mm].

[0070] Optionally, the paraxial curvature radius of the first surface 251 of the first lens 25 may be greater than or equal to 5 mm and less than or equal to 20 mm, or greater than 20 mm and less than or equal to 60 mm, or greater than 60 mm and less than or equal to 200 mm. In other words, the paraxial curvature radius of the first surface 251 of the first lens 25 may be limited within the ranges of [5 mm, 20 mm], (20 mm, 60 mm], (60 mm, 200 mm]. For example, the paraxial curvature radius of the first surface 251 of the first lens 25 may be 5 mm, 8 mm, 15 mm, 18 mm, 20 mm, or 22 mm, 30 mm, 40 mm, 50 mm, 60 mm, or 65 mm, 80 mm, 90 mm, 120 mm, 150 mm, 180 mm, 200 mm, etc., which will not be listed one by one here.

[0071] The paraxial curvature radius of a certain surface can characterize the curvature radius of the paraxial region (i.e., the region near the optical axis) of that surface, and the light rays passing through the paraxial region are the light rays that have a greater impact on the imaging quality. Limiting the paraxial curvature radius of the first surface 251 of the first lens 25 within the range of [5 mm, 200 mm], for example, within the ranges of [5 mm, 20 mm], (20 mm, 60 mm], (60 mm, 200 mm], is beneficial to ensuring the rationality of the parameters of the first lens 25, and thus beneficial to ensuring the imaging quality of the optical system.

[0072] In some alternative embodiments of the present disclosure, if the sag heights at half-aperture x + △, at half-aperture x, and at half-aperture x - △ of the first surface 251 of the first lens 25 are respectively represented as sag(x + △), sag(x), and sag(x - △), then [sag(x + △) - sag(x)] / [sag(x) - sag(x - △)] > 1.

[0073] Optionally, [sag(x + △) - sag(x)] can be understood as the change in sag height caused by an increase in the half-aperture by △ based on the half-aperture x, and [sag(x) - sag(x - △)] can be understood as the change in sag height caused by a decrease in the half-aperture by △ based on the half-aperture x, and △ can be greater than zero. Since [sag(x + △) - sag(x)] / [sag(x) - sag(x - △)] > 1, this indicates that for the first surface 251 of the first lens 25, when the same △ change in the half-aperture is made at positions with a larger half-aperture and a smaller half-aperture, the change in sag height corresponding to the position with a larger half-aperture is greater. In other words, the rate of change of the sag height of the first surface 251 of the first lens 25 is accelerating.

[0074] Through research, it is found that making [sag(x + △) - sag(x)] / [sag(x) - sag(x - △)] greater than 1 can reduce the pupil shift distortion of the optical system and make the change of the resolving power after pupil shift smoother.

[0075] In some alternative embodiments of the present disclosure, in the optical axis direction of the first lens 25, the thickness of the first lens 25 is denoted as T1 (for example, see Figure 1 ), the refractive index of the first lens 25 is denoted as n1, and the target optical path length is denoted as d. The target optical path length is the optical path length that the light rays emitted from the image source 18 and propagating along the optical axis of the first lens 25 pass through from the moment they enter the first prism 20 through the first surface 201 of the first prism 20 until they first reach the second film layer 50. Then, T1 × n1 / d is greater than or equal to 0.05 and less than or equal to 0.15. In other words, T1 × n1 / d can be limited within the range of [0.05, 0.15].

[0076] Optionally, T1 × n1 / d is greater than or equal to 0.05 and less than or equal to 0.1, or greater than 0.1 and less than or equal to 0.15. In other words, T1 × n1 / d can be limited within the ranges of [(.05, 0.1], (0.1, 0.15]. For example, T1 × n1 / d can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or 0.11, 0.12, 0.13, 0.14, 0.15, etc., and will not be listed one by one here.

[0077] It should be noted that T1 × n1 can be understood as the optical path length that the light rays emitted from the image source 18 and propagating along the optical axis of the first lens 25 pass through in the first lens 25. Then, T1 × n1 / d can be understood as the optical path length (subsequently referred to as the first-stage optical path length) that the light rays emitted from the image source 18 and propagating along the optical axis of the first lens 25 pass through in the first lens 25 and the optical path length (subsequently referred to as the second-stage optical path length) that they pass through after the first lens 25 until they first reach the second film layer 50.

[0078] It should be noted that if T1×n1 / d is too small, it indicates that the optical path length in the first stage is too small, which will result in the first lens 25 being too thin and difficult to manufacture. If T1×n1 / d is too large, it indicates that the optical path length in the second stage is too small, then the overall sizes of the first prism 20 and the second prism 30 will be reduced, leading to a reduction in the eye box size of the optical system. Through research, it is found that restricting T1×n1 / d within the range of [0.05, 0.15], for example, within the ranges of [0.05, 0.1] or (0.1, 0.15], the distribution of the optical path length in the first stage and the second stage is relatively reasonable, which is beneficial to avoiding the first lens 25 being too thin and avoiding the reduction of the overall sizes of the first prism 20 and the second prism 30, thereby being able to reduce the manufacturing difficulty of the first lens 25 and achieve the largest possible eye box.

[0079] In some alternative embodiments of the present disclosure, the focal length of the optical system is greater than or equal to 5 millimeters and less than or equal to 50 millimeters. In other words, the focal length of the optical system can be restricted within the range of [5mm, 50mm].

[0080] Optionally, the focal length of the optical system can be greater than or equal to 5 millimeters and less than or equal to 15 millimeters, or greater than 15 millimeters and less than or equal to 30 millimeters, or greater than 30 millimeters and less than or equal to 50 millimeters. In other words, the focal length of the optical system can be restricted within the ranges of [5mm, 15mm], (15mm, 30mm], (30mm, 50mm]. For example, the focal length of the optical system can be 5mm, 7mm, 8mm, 10mm, 12mm, 14mm, 15mm, or 16mm, 18mm, 20mm, 25mm, 27mm, 28mm, 30mm, or 32mm, 35mm, 40mm, 42mm, 45mm, 50mm, etc., which will not be listed one by one here.

[0081] Through research, it is found that restricting the focal length of the optical system within the range of [5mm, 50mm], for example, within the ranges of [5mm, 15mm], (15mm, 30mm], (30mm, 50mm], is beneficial to ensuring the rationality of the parameters of the optical system, thereby being beneficial to ensuring the imaging quality of the optical system.

[0082] In some alternative embodiments of the present disclosure, the radius of curvature of the best-fit spherical surface of the first surface 201 of the first prism 20 can be greater than or equal to 30 millimeters. In other words, the radius of curvature of the best-fit spherical surface of the first surface 201 of the first prism 20 can be restricted within the range of [30mm, +∞].

[0083] Optionally, the best-fit spherical curvature radius of the first surface 201 of the first prism 20 may be greater than or equal to 30 mm and less than or equal to 50 mm, or greater than 50 mm and less than or equal to 100 mm. In other words, the best-fit spherical curvature radius of the first surface 201 of the first prism 20 may be limited to the ranges of [30 mm, 50 mm], (50 mm, 100 mm]. For example, the best-fit spherical curvature radius of the first surface 201 of the first prism 20 may be 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, or 55 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, etc., which will not be enumerated one by one here.

[0084] The best-fit spherical curvature radius of a certain surface can globally reflect the optical characteristics of the surface. Limiting the best-fit spherical curvature radius of the first surface 201 of the first prism 20 to the range of [30 mm, +∞), for example, limiting it to the ranges of [30 mm, 50 mm], (50 mm, 100 mm], is beneficial to ensuring the rationality of the parameters of the first prism 20, and thus beneficial to ensuring the imaging quality of the optical system.

[0085] In some alternative embodiments of the present disclosure, the paraxial curvature radius of the first surface 201 of the first prism 20 may be greater than or equal to 5 mm. In other words, the paraxial curvature radius of the first surface 201 of the first prism 20 may be limited to the range of [5 mm, +∞).

[0086] Optionally, the paraxial curvature radius of the first surface 201 of the first prism 20 may be greater than or equal to 5 mm and less than or equal to 20 mm, or greater than 20 mm and less than or equal to 100 mm, or greater than 100 mm and less than or equal to 200 mm. In other words, the paraxial curvature radius of the first surface 201 of the first prism 20 may be limited to the ranges of [5 mm, 20 mm], (20 mm, 100 mm], (100 mm, 200 mm]. For example, the paraxial curvature radius of the first surface 201 of the first prism 20 may be 5 mm, 8 mm, 10 mm, 15 mm, 18 mm, 20 mm, or 21 mm, 24 mm, 25 mm, 30 mm, 40 mm, 60 mm, 80 mm, 90 mm, 100 mm, or 110 mm, 120 mm, 140 mm, 150 mm, 160 mm, 180 mm, 200 mm, etc., which will not be enumerated one by one here.

[0087] The paraxial curvature radius of a certain surface can characterize the curvature radius of the paraxial region (i.e., the region near the optical axis) of the surface, and the light rays passing through the paraxial region are the light rays that have a greater impact on the imaging quality. Limiting the paraxial curvature radius of the first surface 201 of the first prism 20 within the range of [5 mm, +∞], for example, within the ranges of [5 mm, 20 mm], (20 mm, 100 mm], (100 mm, 200 mm], is beneficial to ensuring the rationality of the parameters of the first prism 20, and thus beneficial to ensuring the imaging quality of the optical system.

[0088] In some alternative embodiments of the present disclosure, the best-fit spherical curvature radius (or paraxial curvature radius) of the first surface 201 of the first prism 20 and the best-fit spherical curvature radius (or paraxial curvature radius) of the first surface 251 of the first lens 25 may be negatively correlated. Then, for the best-fit spherical curvature radius of the first surface 201 of the first prism 20 and the best-fit spherical curvature radius of the first surface 251 of the first lens 25, the larger one of them, the smaller the other one can be. In this way, if one of the first surface 201 of the first prism 20 and the first surface 251 of the first lens 25 is relatively flat, the other one will be more significantly convex, which is beneficial to correcting aberration to ensure the imaging quality of the optical system.

[0089] In some alternative embodiments of the present disclosure, the sag heights of the first surface 201 of the first prism 20 at a semi-aperture of x + △, at a semi-aperture of x, and at a semi-aperture of x - △ are successively represented as sag(x + △), sag(x), sag(x - △), then [sag(x + △) - sag(x)] / [sag(x) - sag(x - 1)] is greater than 1.

[0090] Here, making the first surface 201 of the first prism 20 satisfy [sag(x + △) - sag(x)] / [sag(x) - sag(x - 1)] greater than 1 can also reduce the pupil shift distortion of the optical system and make the change in the resolving power after pupil shift smoother.

[0091] In some alternative embodiments of the present disclosure, the best-fit spherical curvature radius of the first surface 401 of the second lens 40 may be greater than or equal to 40 millimeters and less than or equal to 80 millimeters. In other words, the best-fit spherical curvature radius of the first surface 401 of the second lens 40 can be limited within the range of [40 mm, 80 mm].

[0092] Optionally, the best-fit spherical curvature radius of the first surface 401 of the second lens 40 may be greater than or equal to 40 mm and less than or equal to 50 mm, or greater than 50 mm and less than or equal to 60 mm, or greater than 60 mm and less than or equal to 80 mm. In other words, the best-fit spherical curvature radius of the first surface 401 of the second lens 40 may be limited within the ranges of [40 mm, 50 mm], (50 mm, 60 mm], (60 mm, 80 mm]. For example, the best-fit spherical curvature radius of the first surface 401 of the second lens 40 may be 40 mm, 42 mm, 45 mm, 48 mm, 50 mm, or 51 mm, 52 mm, 55 mm, 56 mm, 58 mm, 60 mm, or 62 mm, 65 mm, 70 mm, 75 mm, 78 mm, 80 mm, etc., which will not be listed one by one here.

[0093] The best-fit spherical curvature radius of a certain surface can globally reflect the optical characteristics of the surface. Limiting the best-fit spherical curvature radius of the first surface 401 of the second lens 40 within the range of [40 mm, 80 mm], for example, within the ranges of [40 mm, 50 mm], (50 mm, 60 mm], (60 mm, 80 mm], is beneficial to ensuring the rationality of the parameters of the second lens 40, and thus beneficial to ensuring the imaging quality of the optical system.

[0094] In some alternative embodiments of the present disclosure, the paraxial curvature radius of the first surface 401 of the second lens 40 may be greater than or equal to 20 mm and less than or equal to 200 mm. In other words, the paraxial curvature radius of the first surface 401 of the second lens 40 may be limited within the range of [20 mm, 200 mm].

[0095] Optionally, the paraxial curvature radius of the first surface 401 of the second lens 40 may be greater than or equal to 20 mm and less than or equal to 40 mm, or greater than 40 mm and less than or equal to 100 mm, or greater than 100 mm and less than or equal to 200 mm. In other words, the paraxial curvature radius of the first surface 401 of the second lens 40 may be limited within the ranges of [40 mm, 100 mm], (100 mm, 200 mm]. For example, the paraxial curvature radius of the first surface 401 of the second lens 40 may be 40 mm, 60 mm, 70 mm, 80 mm, 90 mm, 100 mm, or 110 mm, 120 mm, 140 mm, 160 mm, 180 mm, 190 mm, 200 mm, etc., which will not be listed one by one here.

[0096] The paraxial curvature radius of a certain surface can characterize the curvature radius of the paraxial region (i.e., the region near the optical axis) of the surface, and the light rays passing through the paraxial region are the light rays that have a greater impact on the imaging quality. Limiting the paraxial curvature radius of the first surface 401 of the second lens 40 within the range of [20 mm, 200 mm], for example, within the ranges of [40 mm, 100 mm], (100 mm, 200 mm], is beneficial to ensuring the rationality of the parameters of the second lens 40, and thus beneficial to ensuring the imaging quality of the optical system.

[0097] In some alternative embodiments of the present disclosure, the sag heights of the first surface 401 of the second lens 40 at a semi-aperture of x + Δ, at a semi-aperture of x, and at a semi-aperture of x - Δ are respectively denoted as sag(x + Δ), sag(x), and sag(x - Δ), then [sag(x + Δ) - sag(x)] / [sag(x) - sag(x - 1)] is greater than 1.

[0098] Here, making the first surface 401 of the second lens 40 satisfy [sag(x + Δ) - sag(x)] / [sag(x) - sag(x - 1)] greater than 1 can also reduce the shift-pupil distortion of the optical system and make the change in the resolving power after the shift of the pupil smoother. In addition, it can also make the change in the field curvature and the resolving power of the entire picture of the optical system smoother.

[0099] In some alternative embodiments of the present disclosure, the focal length of the second lens 40 can be greater than or equal to 5 millimeters and less than or equal to 50 millimeters. In other words, the focal length of the second lens 40 can be limited within the range of [5 mm, 50 mm].

[0100] Optionally, the focal length of the second lens 40 can be greater than or equal to 5 millimeters and less than or equal to 15 millimeters, or greater than 15 millimeters and less than or equal to 30 millimeters, or greater than 30 millimeters and less than or equal to 50 millimeters. In other words, the focal length of the second lens 40 can be limited within the ranges of [5 mm, 15 mm], (15 mm, 30 mm], (30 mm, 50 mm]. For example, the focal length of the second lens 40 can be 5 mm, 8 mm, 10 mm, 12 mm, 15 mm, or 16 mm, 18 mm, 20 mm, 25 mm, 26 mm, 28 mm, 30 mm, or 35 mm, 42 mm, 45 mm, 50 mm, 52 mm, 55 mm, etc., and will not be listed one by one here.

[0101] Through research, it is found that limiting the focal length of the second lens 40 within the range of [5 mm, 50 mm], for example, within the ranges of [5 mm, 15 mm], (15 mm, 30 mm], (30 mm, 50 mm], is beneficial to ensuring the rationality of the parameters of the second lens 40, and thus beneficial to ensuring the imaging quality of the optical system.

[0102] In some optional embodiments of the present disclosure, such as Figure 6 As shown, the additional lens 80 may have a first surface 801. The first surface 801 of the additional lens 80 may be located on a side of the additional lens 80 close to the second lens 40. Optionally, the first surface 801 of the additional lens 80 may be a curved surface.

[0103] In some optional embodiments of the present disclosure, the best-fit spherical curvature radius of the first surface 801 of the additional lens 80 may be greater than or equal to 40 mm and less than or equal to 80 mm. In other words, the best-fit spherical curvature radius of the first surface 801 of the additional lens 80 may be limited to the range of [40 mm, 80 mm].

[0104] Optionally, the best-fit spherical curvature radius of the first surface 801 of the additional lens 80 may be greater than or equal to 40 mm and less than or equal to 50 mm, or greater than 50 mm and less than or equal to 60 mm, or greater than 60 mm and less than or equal to 80 mm. In other words, the best-fit spherical curvature radius of the first surface 801 of the additional lens 80 may be limited to the range of [40 mm, 50 mm], (50 mm, 60 mm], (60 mm, 80 mm]. For example, the best-fit spherical curvature radius of the first surface 801 of the additional lens 80 may be 40 mm, 42 mm, 45 mm, 46 mm, 48 mm, 50 mm, or 51 mm, 52 mm, 55 mm, 56 mm, 58 mm, 60 mm, or 62 mm, 65 mm, 68 mm, 70 mm, 72 mm, 75 mm, 78 mm, 80 mm, etc., which are not listed here one by one.

[0105] The best-fit spherical curvature radius of a surface can globally reflect the optical characteristics of that surface. Limiting the best-fit spherical curvature radius of the first surface 801 of the additional lens 80 to the range of [40 mm, 80 mm], for example, [40 mm, 50 mm], [50 mm, 60 mm], or [60 mm, 80 mm], helps ensure the rationality of the parameters of the additional lens 80, thereby improving the imaging quality of the optical system.

[0106] In some optional embodiments of the present disclosure, the paraxial radius of curvature of the first surface 801 of the additional lens 80 may be greater than or equal to 20 mm and less than or equal to 200 mm. In other words, the paraxial radius of curvature of the first surface 801 of the additional lens 80 may be limited to the range of [20 mm, 200 mm].

[0107] Optionally, the paraxial curvature radius of the first surface 801 of the additional lens 80 is greater than or equal to 20 mm and less than or equal to 40 mm, or greater than 40 mm and less than or equal to 100 mm, or greater than 100 mm and less than or equal to 200 mm. In other words, the paraxial curvature radius of the first surface 801 of the additional lens 80 can be limited within the ranges of [20 mm, 40 mm], (40 mm, 100 mm], (100 mm, 200 mm]. For example, the paraxial curvature radius of the first surface 801 of the additional lens 80 can be 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, or 45 mm, 50 mm, 60 mm, 80 mm, 90 mm, 100 mm, or 110 mm, 120 mm, 140 mm, 150 mm, 180 mm, 190 mm, 200 mm, etc., which will not be listed one by one here.

[0108] The paraxial curvature radius of a certain surface can characterize the curvature radius of the paraxial region (i.e., the region near the optical axis) of this surface, and the light rays passing through the paraxial region are the light rays that have a greater impact on the imaging quality. Limiting the paraxial curvature radius of the first surface 801 of the additional lens 80 within the range of [20 mm, 200 mm], for example, within the ranges of [20 mm, 40 mm], (40 mm, 100 mm], (100 mm, 200 mm], is beneficial to ensuring the rationality of the parameters of the additional lens 80, and thus beneficial to ensuring the imaging quality of the optical system.

[0109] In some alternative embodiments of the present disclosure, in the optical axis direction of the second lens 40, the thickness of the additional lens 80 is greater than or equal to 0.6 mm and less than or equal to 2 mm.

[0110] Optionally, the optical axis of the second lens 40 can be represented as Figure 6 the axis Z in, and in the optical axis direction of the second lens 40, the thickness of the additional lens 80 can be represented as Figure 6 D1 shown in. D1 can be limited within the range of [0.6 mm, 2 mm]. For example, D1 can be 0.6 mm, 0.8 mm, 1 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2 mm, etc., which will not be listed one by one here.

[0111] Through research, it is found that limiting D1 within the range of [0.6 mm, 2 mm] is beneficial to both ensuring the imaging quality of the optical system and ensuring the thinness and lightness of the second lens 40.

[0112] In some alternative embodiments of the present disclosure, in the optical axis direction of the second lens 40, the distance between the first surface 601 of the third prism 60 and the first surface 401 of the second lens 40 is greater than or equal to 8 mm and less than or equal to 11 mm.

[0113] Optionally, the optical axis of the second lens 40 can be represented as Figure 6 the axis Z in, and in the direction of the optical axis of the second lens 40, the distance between the first surface 601 of the third prism 60 and the first surface 401 of the second lens 40 can be represented as Figure 6 D2 shown. D2 can be restricted within the range of [8 mm, 11 mm]. For example, D2 can be 8 mm, 8.5 mm, 9 mm, 10 mm, 10.5 mm, 11 mm, etc., and will not be listed one by one here.

[0114] Through research, it is found that restricting D2 within the range of [8 mm, 11 mm] is beneficial to both ensuring the imaging quality of the optical system and ensuring the miniaturization and light weight of the optical system.

[0115] In some alternative embodiments of the present disclosure, the angle between the second surface 203 of the first prism 20 and the target plane can be greater than 20 degrees and less than 30 degrees, and the target plane can be a plane perpendicular to the optical axis of the second lens 40.

[0116] Optionally, the common edge of the second surface 203 and the third surface 205 of the first prism 20 can be referred to as the target common edge. The target plane can be a plane passing through the target common edge and perpendicular to the optical axis of the second lens 40. The angle between the second surface 203 of the first prism 20 and the target plane can be restricted within the range of (20°, 30°). For example, the angle between the second surface 203 of the first prism 20 and the target plane can be 21°, 23°, 24°, 25°, 27°, 28°, 29°, etc., and will not be listed one by one here.

[0117] Through research, it is found that restricting the angle between the second surface 203 of the first prism 20 and the target plane within the range of (20°, 30°) is beneficial to ensuring the rationality of the parameters of the first prism 20, and thus beneficial to ensuring the imaging quality of the optical system.

[0118] In some alternative embodiments of the present disclosure, the angle between the third surface 205 of the first prism 20 and the target plane can be greater than 3 degrees and less than 12 degrees, and the target plane can be a plane perpendicular to the optical axis of the second lens 40. In other words, the angle between the third surface 205 of the first prism 20 and the target plane can be restricted within the range of (3°, 12°). For example, the angle between the third surface 205 of the first prism 20 and the target plane can be 4°, 5°, 6°, 8°, 9°, 10°, 11°, etc., and will not be listed one by one here.

[0119] Through research, it is found that limiting the angle between the third surface 205 of the first prism 20 and the target plane to the range of (3°, 12°) is beneficial to ensuring the rationality of the parameters of the first prism 20, thereby ensuring the imaging quality of the optical system.

[0120] In some optional embodiments of the present disclosure, the structure of the optical system can be as follows: Figure 7 As shown, the light emitted by the image source 18 can pass through each surface in turn to form a virtual image 1. Each surface can be numbered in the direction opposite to the path of the light. Figure 7 1 to 14 are the numbers of these 14 surfaces. In an optional example, these 14 surfaces can satisfy the following Table 1 and Table 2:

[0121]

[0122] Table 1

[0123]

[0124]

[0125] Table 2

[0126] Among them, "S6" in Table 3 may refer to the surface with surface number 6, "S11" in Table 3 may refer to the surface with surface number 11, and "S12" in Table 3 may refer to the surface with surface number 12. The surface with surface number 6, the surface with surface number 11, and the surface with surface number 12 can all be aspherical surfaces.

[0127] In this example, the optical system can satisfy the following Table 3:

[0128]

[0129] Table 3

[0130] In addition, in this example, the angle between the second surface 203 of the first prism 20 and the target plane can be expressed as Figure 7 The angle between the third surface 205 of the first prism 20 and the target plane can be expressed as Figure 7 The angle between the normal line of the image source 18 and the optical axis of the second lens 40 may be 60°.

[0131] The Modulation Transfer Function (MTF) curve of the optical system can be obtained. It can be understood that the MTF curve is a curve that describes the performance of the optical system and can be used to judge the ability of the optical system to restore contrast. Optionally, the MTF curve of the optical system can be as follows:Figure 8 as shown Figure 8 In the figure, the horizontal axis can represent spatial frequency, the vertical axis can represent contrast, the solid line can represent the meridional direction, and the dashed line can represent the sagittal direction. As can be seen from Figure 8 the optical system has good resolution in different field-of-view directions and has a relatively high overall imaging quality.

[0132] In some alternative embodiments of the present disclosure, the structure of the optical system can be as shown in Figure 9 The light rays emitted by the image source 18 can form a virtual image 1 after passing through each surface in sequence. The surfaces can be numbered in the reverse direction of the path of the light rays. The numbers 1 to 16 shown in Figure 9 are the numbers of these 16 surfaces. In an alternative example, these 16 surfaces can satisfy Table 4 and Table 5 as follows:

[0133] Surface number Surface type Radius of curvature Thickness Refractive index Abbe number 1 Virtual image Infinity -5000 2 Diaphragm Infinity 15.00 3 Plane Infinity 7.00 1.544 56.00 4 Plane Infinity 0.10 5 Plane Infinity 1.00 1.544 56.00 6 Plane Infinity 1.80 1.694 53.20 7 Curved surface (reflection) -50.50 -1.80 1.694 8 Plane Infinity -1.00 1.544 56.00 9 Plane Infinity -0.10 10 Plane Infinity -3.50 1.544 56.00 11 Plane (reflection) Infinity 3.50 1.544 56.00 12 Plane (reflection) Infinity -7.2 1.544 56.00 13 Curved surface 51.16 -0.3 14 Curved surface -18.41 -2.00 1.544 56.00 15 Plane Infinity -0.3 16 Image plane

[0134] Table 4

[0135]

[0136] In this example, the optical system can satisfy Table 6 as follows:

[0137]

[0138] Table 6

[0139] In addition, in this example, the angle between the second surface 203 of the first prism 20 and the target plane can be represented as Figure 9 A in, and A can be 22°. The angle between the third surface 205 of the first prism 20 and the target plane can be represented as Figure 9 B in, and B can be 10°. The angle between the normal of the image source 18 and the optical axis of the second lens 40 can be 64°.

[0140] The MTF curve of the optical system can be obtained. Optionally, the MTF curve of the optical system can be as shown in Figure 10 as shown Figure 10 In the figure, the horizontal axis can represent spatial frequency, the vertical axis can represent contrast, the solid line can represent the meridional direction, and the dashed line can represent the sagittal direction. As can be seen from Figure 10 the optical system has good resolution in different field-of-view directions and has a relatively high overall imaging quality.

[0141] Optionally, in addition to being in the form of Figures 1 to 7 , and Figure 9 shown in, the optical system can also be in other structures. For example, the optical system can also be in the form of Figure 11-1The structure shown, i.e., the first surface 601 of the third prism 60 can be a curved surface, for example, a concave surface, to effectively compensate for the optical power of the second lens 40. In this case, it may not be necessary to additionally provide an additional lens 80 used as a compensating lens for the second lens 40. For another example, the optical system can also be in the form of Figure 11-2 or Figure 11-3 The structure shown, i.e., a partial region of the second surface 203 of the first prism 20 close to the image source 18 can have a groove 207, and the groove 207 can be recessed inward from this partial region into the first prism 20.

[0142] Some exemplary embodiments of the present disclosure also provide a head-mounted display device. The head-mounted display device can include Figure 12 The frame structure 90 shown and the optical system in any of the above embodiments. The optical system can be installed on the frame structure 90.

[0143] In some alternative embodiments of the present disclosure, the frame structure 90 can be a structure capable of supporting and accommodating the optical system. For example, the frame structure 90 can include, but is not limited to, a spectacle frame, a headband, etc.

[0144] In the embodiments of the present disclosure, through the setting of the frame structure 90, the installation of the optical system can be reliably achieved. Through the cooperation of the various optical elements in the optical system, the human eye 100 can see the display screen provided by the image source 18 to meet the user's usage requirements. In some embodiments, the human eye 100 can also see the external environment.

[0145] It should be noted that the various alternative embodiments and alternative implementation manners disclosed above can be flexibly selected and combined as needed to achieve the corresponding functions and effects, and the present disclosure does not list them one by one.

[0146] The basic principles of the present disclosure have been described above in conjunction with specific embodiments. However, it should be pointed out that the advantages, advantages, effects, etc. mentioned in the present disclosure are only examples and not limitations, and it cannot be considered that these advantages, advantages, effects, etc. are essential for each embodiment of the present disclosure. In addition, the above-disclosed specific details are only for the purpose of illustration and easy understanding, rather than limitations, and the above details do not limit the present disclosure to necessarily adopt the above specific details to implement.

[0147] Each embodiment in this specification is described in a progressive manner, and the key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0148] Those skilled in the art can make various changes and modifications to the present disclosure without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present disclosure and their equivalent technologies, the present disclosure also intends to include these changes and modifications.

Claims

1. An optical system, comprising: An image source; A first prism having a first surface, a second surface, and a third surface, with the first surface of the first prism being close to the image source; A first lens located between the image source and the first prism; A second prism, where the second surface of the first prism is on the side of the first prism away from the second prism, the third surface of the first prism is on the side of the first prism close to the second prism, the second prism has a first surface, and the first surface of the second prism is close to the third surface of the first prism; A second lens located on the side of the second prism away from the first prism. The first angle between the first surface of the second prism and the optical axis of the second lens and the second angle between the third surface of the first prism and the optical axis of the second lens are both acute angles, and the first angle is equal to the second angle. The second lens has a first surface, and the first surface of the second lens is on the side of the second lens away from the second prism; A first film layer located on the second surface of the first prism, capable of reflecting light and transmitting light; A second film layer located on the first surface of the second lens, capable of reflecting light; Wherein, the light emitted from the image source passes through the first lens and then enters the first prism. After at least one total reflection within the first prism, it is reflected by the first film layer, exits from the third surface of the first prism and enters the second prism from the first surface of the second prism. After passing through the second prism and the second lens, it is reflected by the second film layer. The light reflected by the second film layer sequentially passes through the second lens, the first surface of the second prism, the third surface of the first prism, and the second surface of the first prism, and exits through the first film layer. The optical system satisfies: 1 ≤ (f1 × f2) / (f × f) ≤ 16, where f represents the focal length of the optical system, f1 represents the focal length of the first lens, and f2 represents the focal length of the second lens.

2. The optical system according to claim 1, wherein, (f1 × f2) / (f × f) is greater than or equal to 1 and less than or equal to 3, or greater than 3 and less than or equal to 10, or greater than 10 and less than or equal to 16.

3. The optical system according to claim 1, wherein, The first surface of the first prism includes a curved surface portion with a focal length of f3, or the optical system further includes a third lens located between the first lens and the first surface of the first prism. The third lens has a curved surface facing the image source, and the focal length of the third lens is f3; The optical system satisfies: (f1 × f2 × f3) / (f × f × f) is greater than or equal to 1 and less than or equal to 64.

4. The optical system according to claim 3, wherein, (f1 × f2 × f3) / (f × f × f) is greater than or equal to 1 and less than or equal to 10, or greater than 10 and less than or equal to 20, or greater than 20 and less than or equal to 40, or greater than 40 and less than or equal to 64.

5. The optical system according to claim 1, wherein, The first lens has a first surface, the first surface of the first lens is located on the side of the first lens close to the first prism, and the best-fit spherical curvature radius of the first surface of the first lens is greater than or equal to 20 mm and less than or equal to 60 mm.

6. The optical system according to claim 5, wherein, The best-fit spherical curvature radius of the first surface of the first lens is greater than or equal to 20 mm and less than or equal to 40 mm, or greater than 40 mm and less than or equal to 60 mm.

7. The optical system according to claim 1, wherein, The first lens has a first surface, the first surface of the first lens is located on the side of the first lens close to the first prism, and the paraxial curvature radius of the first surface of the first lens is greater than or equal to 5 mm and less than or equal to 200 mm.

8. The optical system according to claim 7, wherein, The paraxial curvature radius of the first surface of the first lens is greater than or equal to 5 mm and less than or equal to 20 mm, or greater than 20 mm and less than or equal to 60 mm, or greater than 60 mm and less than or equal to 200 mm.

9. The optical system according to claim 1, wherein, The first lens has a first surface, the first surface of the first lens is located on the side of the first lens close to the first prism. The sag heights of the first surface of the first lens at a semi-aperture of x + △, at a semi-aperture of x, and at a semi-aperture of x - △ are represented as sag(x + △), sag(x), and sag(x - △) respectively. Then, [sag(x + △) - sag(x)] / [sag(x) - sag(x - △)] is greater than 1.

10. The optical system according to claim 1, wherein, In the optical axis direction of the first lens, the thickness of the first lens is represented as T1, the refractive index of the first lens is represented as n1, and the target optical path length is represented as d. The target optical path length is the optical path length that the light rays emitted from the image source and propagating along the optical axis of the first lens pass through from the incidence on the first surface of the first prism to the first arrival at the second film layer. Then, T1 × n1 / d is greater than or equal to 0.05 and less than or equal to 0.

15.

11. The optical system according to claim 10, wherein, T1 × n1 / d is greater than or equal to 0.05 and less than or equal to 0.1, or greater than 0.1 and less than or equal to 0.

15.

12. The optical system according to claim 1, wherein, The first lens has a second surface, the second surface of the first lens is located on the side of the first lens close to the light source, and the best-fit spherical curvature radius of the second surface of the first lens is greater than or equal to 100 mm.

13. The optical system according to claim 1, wherein, The first lens has a second surface, the second surface of the first lens is located on the side of the first lens close to the light source, and the paraxial curvature radius of the second surface of the first lens is greater than or equal to 50 mm.

14. The optical system according to claim 1, wherein, The focal length of the optical system is greater than or equal to 5 mm and less than or equal to 50 mm.

15. The optical system according to claim 14, wherein, The focal length of the optical system is greater than or equal to 5 mm and less than or equal to 15 mm, or greater than 15 mm and less than or equal to 30 mm, or greater than 30 mm and less than or equal to 50 mm.

16. The optical system according to any one of claims 1 and 3, wherein, The best-fit spherical curvature radius of the first surface of the first prism is greater than or equal to 30 mm.

17. The optical system according to claim 16, wherein, The best-fit spherical curvature radius of the first surface of the first prism is greater than or equal to 30 mm and less than or equal to 50 mm, or greater than 50 mm and less than or equal to 100 mm.

18. The optical system according to any one of claims 1 and 3, wherein, The paraxial curvature radius of the first surface of the first prism is greater than or equal to 5 mm.

19. The optical system according to claim 18, wherein, The paraxial curvature radius of the first surface of the first prism is greater than or equal to 5 mm and less than or equal to 20 mm, or greater than 20 mm and less than or equal to 100 mm, or greater than 100 mm and less than or equal to 200 mm.

20. The optical system according to claim 3, wherein, The first lens has a first surface, and the first surface of the first lens is located on the side of the first lens close to the first prism. The best-fit spherical curvature radius or the paraxial curvature radius of the first surface of the first prism is negatively correlated with the best-fit spherical curvature radius or the paraxial curvature radius of the first surface of the first lens.

21. The optical system according to any one of claims 1 and 3, wherein, The sag heights of the first surface of the first prism at semi-aperture x + △, at semi-aperture x, and at semi-aperture x - △ are successively represented as sag(x + △), sag(x), and sag(x - △), then [sag(x + △) - sag(x)] / [sag(x) - sag(x - 1)] is greater than 1.

22. The optical system according to claim 1, wherein, The best-fit spherical curvature radius of the first surface of the second lens is greater than or equal to 40 mm and less than or equal to 80 mm.

23. The optical system according to claim 22, wherein, The best-fit spherical curvature radius of the first surface of the second lens is greater than or equal to 40 mm and less than or equal to 50 mm, or greater than 50 mm and less than or equal to 60 mm, or greater than 60 mm and less than or equal to 80 mm.

24. The optical system according to claim 1, wherein, The paraxial curvature radius of the first surface of the second lens is greater than or equal to 20 mm and less than or equal to 200 mm.

25. The optical system according to claim 24, wherein, The paraxial curvature radius of the first surface of the second lens is greater than or equal to 20 mm and less than or equal to 40 mm, or greater than 40 mm and less than or equal to 100 mm, or greater than 100 mm and less than or equal to 200 mm.

26. The optical system according to claim 1, wherein, The sag heights of the first surface of the second lens at semi-aperture x + △, at semi-aperture x, and at semi-aperture x - △ are successively represented as sag(x + △), sag(x), and sag(x - △), then [sag(x + △) - sag(x)] / [sag(x) - sag(x - 1)] is greater than 1.

27. The optical system according to claim 1, wherein, The focal length of the second lens is greater than or equal to 5 mm and less than or equal to 50 mm.

28. The optical system according to claim 27, wherein, The focal length of the second lens is greater than or equal to 5 mm and less than or equal to 15 mm, or greater than 15 mm and less than or equal to 30 mm, or greater than 30 mm and less than or equal to 50 mm.

29. The optical system according to claim 1, wherein, The second film layer is a semi-transmissive and semi-reflective film, and the optical system further includes: An additional lens, and the additional lens is located on the side of the second film layer far from the second lens.

30. The optical system according to claim 29, wherein, The additional lens has a first surface, and the first surface of the additional lens is located on the side of the additional lens close to the second lens. The best-fit spherical curvature radius of the first surface of the additional lens is greater than or equal to 40 mm and less than or equal to 80 mm.

31. The optical system according to claim 30, wherein, The best-fit spherical curvature radius of the first surface of the additional lens is greater than or equal to 40 mm and less than or equal to 50 mm, or greater than 50 mm and less than or equal to 60 mm, or greater than 60 mm and less than or equal to 80 mm.

32. The optical system according to claim 29, wherein, The additional lens has a first surface, and the first surface of the additional lens is located on the side of the additional lens closer to the lens. The paraxial curvature radius of the first surface of the additional lens is greater than or equal to 20 mm and less than or equal to 200 mm.

33. The optical system according to claim 32, wherein, The paraxial curvature radius of the first surface of the additional lens is greater than or equal to 20 mm and less than or equal to 40 mm, or greater than 40 mm and less than or equal to 100 mm, or greater than 100 mm and less than or equal to 200 mm.

34. The optical system according to claim 29, wherein, In the optical axis direction of the second lens, the thickness of the additional lens is greater than or equal to 0.6 mm and less than or equal to 2 mm.

35. The optical system according to claim 1, further comprising: A third prism having a first surface and a second surface. The first surface of the third prism is located on the side of the third prism away from the first prism, and the second surface of the third prism is located on the side of the third prism closer to the first prism. After the light reflected by the second film layer passes through the first prism again, it exits through the second surface and the first surface of the third prism.

36. The optical system according to claim 35, wherein, In the optical axis direction of the second lens, the distance between the first surface of the third prism and the first surface of the second lens is greater than or equal to 8 mm and less than or equal to 11 mm.

37. The optical system according to claim 1, wherein, The angle between the second surface of the first prism and the target plane is greater than 20 degrees and less than 30 degrees, and the target plane is a plane perpendicular to the optical axis of the second lens.

38. The optical system according to claim 1, wherein The angle between the third surface of the first prism and the target plane is greater than 3 degrees and less than 12 degrees, and the target plane is a plane perpendicular to the optical axis of the second lens.

39. A head-mounted display device, comprising: A frame structure; The optical system according to any one of claims 1-38, and the optical system is mounted on the frame structure.

Images