Optical system and head-mounted display device

Abstract

The embodiment of the invention discloses an optical system and a head-mounted display device. The optical system comprises an image source, a first polarizing film, a first prism, a second phase delay film and a first lens. The first prism comprises a first surface, and a second surface and a third surface located at two sides of the first surface. Light emitted by the image source penetrates through the first polarizing film, then enters the first prism from the first surface, is reflected twice in the first prism, then exits from the second surface, then penetrates through the second phase delay film and is reflected in the first lens, and the reflected light is returned, sequentially penetrates through the second phase delay film and the first prism and then exits. According to the optical system, the design of extending the light path is adopted, a larger field angle can be achieved, stray light is effectively restrained by modulating the light polarization state through the polarization film, and the final imaging contrast ratio and definition are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical imaging, in particular to an optical system and a head-mounted display device. BACKGROUND

[0002] Augmented Reality (AR) technology generates virtual images through micro-displays and optically superimposes them with real scenes to increase users' perception of the real environment. The mainstream AR head-mounted display device uses a micro-display as an image source and projects images to the human eye using a transparent return optical system.

[0003] With the rapid development of virtual reality and augmented reality technology, the corresponding head-mounted display device has become a popular product in the display field. The head-mounted display device needs to meet the requirements of compact structure and light weight while achieving a larger field of view to increase the user's sense of immersion. However, due to the physical constraints of current display size and optical architecture, the development of the existing AR glasses in the field of view expansion is limited, and it is difficult to achieve a larger field of view. SUMMARY

[0004] Therefore, the purpose of the present application is to provide an optical system and a head-mounted display device, which has a compact structure and can achieve a larger field of view while ensuring high imaging quality.

[0005] In a first aspect, an optical system is provided, which comprises: an image source; a first polarizing film disposed on the light exit side of the image source, the light emitted by the image source being in a first polarization state after passing through the first polarizing film; a first prism comprising a first surface and a second surface and a third surface disposed on both sides of the first surface, the first surface being disposed opposite the light exit side of the image source, the first polarizing film being located between the image source and the first surface, the light in the first polarization state being incident on the first prism from the first surface and being emitted from the second surface after being reflected by the second surface and the third surface in turn; a second phase retardation film disposed outside the second surface of the first prism, the light emitted from the second surface passing through the second phase retardation film being in a second polarization state; a first lens disposed on the side of the second phase retardation film away from the first prism, the light in the second polarization state being reflected and returned by the first lens and being converted into a third polarization state after passing through the second phase retardation film again, the light in the third polarization state being emitted after passing through the second surface and the third surface in turn.

[0006] Optionally, a part of the second surface is provided with an enhanced reflection film.

[0007] Optionally, the enhanced reflective film is disposed extending from one end of the second surface closer to the image source to the other end, and the enhanced reflective film has a length of 2.5 mm.

[0008] Optionally, the enhanced reflective film is a metal reflective film or a dielectric multilayer total reflection film.

[0009] Optionally, the first polarizing film comprises a first phase retardation film and a first polarizer, the first phase retardation film is attached to the light-emitting side of the image source, and the first polarizer is disposed on the side of the first phase retardation film away from the image source.

[0010] Optionally, the optical system comprises a second polarizing film attached to the outside of the third surface, the second polarizing film reflects light in the first polarization state and transmits light in the third polarization state.

[0011] Optionally, the second polarizing film comprises a reflective polarizing film and a second polarizer, the reflective polarizing film is attached to the outside of the third surface, and the second polarizer is attached to the side of the reflective polarizing film away from the third surface.

[0012] Optionally, the optical system further comprises a second prism disposed on the side of the second polarizing film away from the first prism.

[0013] Optionally, the optical system further comprises a light splitting film disposed on the side of the first lens away from the second phase retardation film.

[0014] Optionally, the optical system further comprises a second lens disposed on the side of the light splitting film away from the first lens.

[0015] Optionally, the second phase retardation film is a quarter-wave plate.

[0016] Optionally, the side of the first lens closer to the first prism is a first plane, and the first plane has a first included angle with the second surface.

[0017] Optionally, the first included angle ranges from 0.01° to 0.1°.

[0018] Optionally, the normal line of the light-emitting surface of the image source has a second included angle with the second surface of the first prism.

[0019] Optionally, the second surface has a third included angle with the third surface.

[0020] Optionally, the second included angle is 38° and the third included angle is 29°.

[0021] In a second aspect, an embodiment of the present application provides a head-mounted display device, which comprises the optical system of the first aspect.

[0022] The optical system provided by the embodiment of the present application comprises an image source, a first polarizing film, a first prism, a second phase retardation film and a first lens. The first prism comprises a first surface and a second surface and a third surface located on both sides of the first surface. The light emitted by the image source is incident into the first prism from the first surface after passing through the first polarizing film, is reflected twice in the first prism and is emitted from the second surface, then is reflected in the first lens after passing through the second phase retardation film, and is emitted after passing through the second phase retardation film and the first prism in turn. The optical system adopts a design of prolonging the light path, which helps to realize a larger field of view, and at the same time, the modulation of the polarization state of the light by the polarizing film effectively suppresses stray light, and significantly improves the contrast and definition of the final image. BRIEF DESCRIPTION OF DRAWINGS

[0023] The above and other objects, features and advantages of the present application will become more apparent from the following description of the embodiments of the present application taken with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of the light path of the optical system of the embodiment of the present application; Figure 2 is a schematic diagram of the structure of the first polarizing film of the embodiment of the present application; Figure 3 is a schematic diagram of the structure of the second polarizing film of the embodiment of the present application; Figure 4 is a modulation transfer function diagram of the optical system of the embodiment of the present application; Figure 5 is a schematic diagram of the field curvature of the optical system of the embodiment of the present application; Figure 6 is a schematic diagram of the distortion of the optical system of the embodiment of the present application; Figure 7 is a schematic diagram of the grid distortion of the optical system of the embodiment of the present application.

[0024] Reference Signs: 10 - image source; 21 - first polarizing film; 211 - first phase retardation film; 212 - first polarizing plate; 22 - second phase retardation film; 23 - second polarizing film; 231 - reflective polarizing film; 232 - second polarizing plate; 31 - first prism; 311 - first surface; 312 - second surface; 313 - third surface; 32 - second prism; 41 - first lens; 411 - first plane; 412 - first convex surface; 42 - second lens; 43 - third lens; 51 - enhanced reflection film; 52 - light splitting film; a - first included angle; b - second included angle; c - third included angle. DETAILED DESCRIPTION

[0025] The present application is described in detail below based on examples, but the present application is not limited to only these examples. In the following detailed description of the present application, some specific details are described in detail. The present application can also be fully understood without the description of these details. In order to avoid confusion of the essence of the present application, the well-known methods, processes, procedures, elements and circuits are not described in detail.

[0026] In addition, those skilled in the art should understand that the drawings provided herein are for illustrative purposes only, and the drawings are not necessarily drawn to scale.

[0027] Unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be broadly understood, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0028] Unless the context clearly requires otherwise, the terms "including", "containing", and the like in the entire application should be interpreted as inclusive rather than exclusive or exhaustive; that is, as "including but not limited to".

[0029] In the description of the present application, it should be understood that the terms "first", "second" and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance. In addition, in the description of the present application, unless otherwise stated, the meaning of "multiple" is two or more.

[0030] Figure 1 is a structural schematic diagram of the optical system provided by the present embodiment. Referring to Figure 1 , the optical system includes an image source 10, a first polarizing film 21, a first prism 31, a second phase retardation film 22 and a first lens 41. The light rays emitted by the image source 10 are reflected into the human eye to form an image after passing through the first polarizing film 21, the first prism 31, the second phase retardation film 22 and the first lens 41 in turn.

[0031] Referring to Figure 1 , the first polarizing film 21 and the first prism 31 are arranged in turn along the light emitting direction of the image source 10. The first polarizing film 21 is arranged on the light emitting side of the image source 10, and the first prism 31 is arranged on the side of the first polarizing film 21 away from the image source 10. The first prism 31 includes a first surface 311, and a second surface 312 and a third surface 313 located on both sides of the first surface 311, respectively.

[0032] The first surface 311 is arranged opposite to the light exit side of the image source 10, that is, the first polarizing film 21 is located between the image source 10 and the first surface 311. The second phase retardation film 22 is arranged outside the second surface 312 of the first prism 31. The first lens 41 is arranged on the side of the second phase retardation film 22 away from the first prism 31, that is, the second phase retardation film 22 is located between the second surface 312 and the first lens 41.

[0033] Figure 1 is a schematic diagram of an optical path of the optical system of the embodiment. Referring to Figure 1 , the light rays emitted by the image source 10 pass through the first polarizing film 21 and then are incident on the first prism 31 from the first surface 311. After being reflected by the second surface 312 and the third surface 313 in the first prism 31, the light rays are emitted from the second surface 312. The light rays emitted from the second surface 312 pass through the second phase retardation film 22 and are incident on the first lens 41. The light rays are reflected in the first lens 41 and then pass through the first lens 41, the second phase retardation film 22, the second surface 312, and the third surface 313 in turn and are finally emitted into the human eye.

[0034] The two reflections of the light rays in the first prism 31 effectively lengthen the optical path, which helps to achieve a long focal length design in a limited space and lays a foundation for meeting the requirements of high resolution and a large field of view for the final imaging.

[0035] In addition, the optical system also effectively guides and controls the direction and path of the optical path by controlling the polarization state of the light rays.

[0036] In the embodiment, the light rays emitted by the image source 10 pass through the first polarizing film 21 and are in a first polarization state. The light rays in the first polarization state are incident on the first prism 31 from the first surface 311 and then are reflected by the second surface 312 and the third surface 313 in turn and are emitted from the second surface 312. The light rays emitted from the second surface 312 pass through the second phase retardation film 22 and are in a second polarization state. The light rays in the second polarization state are reflected in the first lens 41 and then pass through the second phase retardation film 22 again. The light rays in the second polarization state pass through the second phase retardation film 22 again and are in a third polarization state. The light rays in the third polarization state pass through the second surface 312 and the third surface 313 of the first prism 31 in turn and are emitted. The multiple polarization state transitions help to eliminate stray light and improve the contrast of the final imaging, thereby ensuring the quality of the final imaging.

[0037] Specifically, referring to Figure 2The first polarizing film 21 includes a first phase retardation film 211 and a first polarizer 212. The first phase retardation film 211 is attached to the light exit side of the image source 10, and the first polarizer 212 is arranged on the side of the first phase retardation film 211 away from the image source 10. The light rays emitted by the image source 10 pass through the first phase retardation film 211 and the first polarizer 212 in sequence, and finally have the first polarization state.

[0038] The first phase retardation film 211 is used to regulate the polarization state of the light rays. For example, linearly polarized light can be converted into circularly polarized light, or circularly polarized light can be converted into linearly polarized light. The first polarizer 212 can selectively transmit light waves with a polarization direction consistent with its transmission axis direction, and block light waves with other polarization directions, thereby converting the light rays passing through the first phase retardation film 211 into first linearly polarized light with a consistent polarization direction. Therefore, after the light rays emitted by the image source 10 pass through the first phase retardation film 211 and the first polarizer 212 in sequence, regardless of their initial polarization state, they are all finally converted and output as first linearly polarized light with a specific polarization direction, which corresponds to the light rays of the first polarization state here. The first polarizing film 21 ensures that the light signal received by the subsequent optical system has stable and consistent polarization characteristics, which is beneficial to improve the display effect of the final imaging.

[0039] Optionally, the first phase retardation film 211 can be a quarter-wave plate, a single-layer polymer stretched film, or a multi-layer optical film, and the first polarizer 212 can be a conventional linear polarizing film or a metal wire grid polarizer.

[0040] Referring to Figure 1 The optical system further includes a third lens 43 arranged on the side of the first polarizing film 21 away from the image source 10. The third lens 43 is a plano-convex lens, and the plane of the third lens 43 is arranged to face the image source 10. The light rays enter from the plane of the third lens 43 and exit from the convex surface. The convex surface of the third lens 43 can act as a converging element, more effectively collecting divergent light, and ensuring that all the light rays emitted by the image source 10 can enter the first prism 31. In addition, the third lens 43 is arranged in close contact with the first polarizing film 21, which can effectively improve the light coupling efficiency, reduce reflection loss, and reduce aberration, thereby helping to improve the clarity and brightness uniformity of the final imaging.

[0041] Optionally, the image source 10, the first polarizing film 21, and the third lens 43 are arranged in close contact through optical glue or precision pressing process.

[0042] Referring to Figure 1The first surface 311 of the first prism 31 is directed towards the image source 10, and the first surface 311 is spaced apart from the convex surface of the third lens 43. The first surface 311 is configured as a convex surface directed towards the image source 10, and the second surface 312 and the third surface 313 are both configured as flat surfaces. The light rays in the first polarization state are emitted from the third lens 43, and then enter the first prism 31 from the first surface 311 and propagate towards the second surface 312 on one side. Upon reaching the second surface 312, the light rays are totally internally reflected and reflected to the third surface 313 on the other side of the first prism 31. The convex first surface 311 can further focus the light rays and reduce the deviation and distortion of the final image.

[0043] With reference to Figure 1 The relative position and angle between the image source 10 and the first prism 31 are analyzed and designed by optical analysis, so as to ensure that the light rays emitted from the image source 10 can be totally internally reflected at the second surface 312 after entering the first prism 31 from the first surface 311. With reference to Figure 2 Part of the second surface 312 is further provided with a reinforced reflection film 51, so that part of the light rays that do not meet the total reflection condition can still be reflected to the third surface 313, thereby ensuring the integrity and clarity of the final image. The reinforced reflection film 51 is arranged on the side of the second surface 312 close to the image source 10 to reflect the edge light rays.

[0044] With reference to Figure 1 The normal line of the light emitting surface of the image source 10 and the second surface 312 of the first prism 31 form a second included angle b. In the embodiment, the second included angle b is 38°.

[0045] With reference to Figure 3 The reinforced reflection film 51 is arranged to extend from one end of the second surface 312 close to the image source 10 to the other end, and the length (as shown by h) of the extension of the reinforced reflection film 51 is 2.5 mm. Figure 3

[0046] Optionally, the reinforced reflection film 51 can be a metal reflection film or a dielectric multilayer total reflection film.

[0047] Further, the optical system can further adopt a larger size image source 10 to increase the field of view. The reinforced reflection film 51 of the second surface 312 can ensure that the light rays emitted from the image source 10 can be totally internally reflected at the second surface 312, complete the propagation path of the light rays, and further realize a larger field of view and a clear and stable final image.

[0048] With reference to Figure 1 and Figure 2 ​The optical system further comprises a second polarized film 23. The second polarized film 23 is attached to the outer side of the third surface 313, and is used to reflect light in the first polarization state and transmit light in the third polarization state. When the light in the first polarization state reaches the third surface 311, the second polarized film 23 can reflect the light again, and the light is reflected to the second surface 312 and exits from the second surface 312.

[0049] With reference to Figure 1 , the second surface 312 and the third surface 313 have a third included angle c. In this embodiment, the third included angle c is 29°.

[0050] With reference to Figure 3 , the second polarized film 23 comprises a reflective polarized film 231 and a second polarizer 232. The reflective polarized film 231 can selectively reflect light in a certain polarization direction and transmit light in a perpendicular direction. The second polarizer 232 has the same function as the first polarizer 212, which will not be described here. The reflective polarized film 231 is attached to the outer side of the third surface 313, and the second polarizer 232 is attached to the side of the reflective polarized film 231 away from the third surface 313. In this embodiment, the reflective polarized film 231 is used to reflect light in the first polarization state, so that the light can exit from the second surface 312, and the second polarizer 232 can effectively eliminate stray light.

[0051] Alternatively, the optical system can also be provided with a polarization beam splitter on the side of the third surface 313 to reflect light in the first polarization state.

[0052] With reference to Figure 1 , the second phase delay film 22 is attached to the first lens 41, and the second phase delay film 22 has a certain distance from the second surface 312. The light exiting from the second surface 312 passes through the second phase delay film 22 to convert into the third polarization state and is incident into the first lens 41. With reference to Figure 1 , the first lens 41 has a first flat surface 411 on the side close to the first prism 31, a first convex surface 412 on the side away from the first prism 31, and the second phase delay film 22 is attached to the first flat surface 411. The light in the second polarization state is incident from the first flat surface 411 and propagates to the first convex surface 412, is reflected when reaching the first convex surface 412, and then passes through the second phase delay film 22 again.

[0053] The second phase delay film 22 has the same function as the first phase delay film 211, which will not be described here. Therefore, the light passing through the second phase delay film 22 is converted from the first linearly polarized light (i.e., light in the first polarization state) to circularly polarized light (i.e., light in the second polarization state). The circularly polarized light is reflected after being incident into the first lens 41, passes through the second phase delay film 22 again to convert into light in the third polarization state.

[0054] In this embodiment, the second phase delay film 22 is a quarter-wave plate. Alternatively, the second phase delay film 22 can also be a single-layer polymer stretched film or a multi-layer optical film.

[0055] In this embodiment, the second phase delay film 22 is a quarter-wave plate. Alternatively, the second phase delay film 22 can also be a single-layer polymer stretched film or a multi-layer optical film.

[0056] With reference to Figure 1 , the first lens 41 is tilted relative to the eye viewing direction, thereby effectively eliminating the distortion deviation. In this embodiment, the first angle a is in the range of 0.01° to 0.1°.

[0057] Specifically, in this embodiment, the chief ray (i.e. Figure 1 , which is perpendicular to the eye viewing direction, has an offset from the center of the first convex surface 412 of the first lens 41. If the chief ray is incident on the first convex surface 412 at this offset position, the refraction angle will deviate from the ideal optical path, thereby causing the distortion deviation of the inconsistent up-down distortion. By setting the first angle a, the posture of the first lens 41 relative to the eye viewing direction can be adjusted, so that the relative position between the chief ray and the first convex surface 412 meets the optical symmetry requirement, thereby significantly reducing the asymmetric distortion caused by the offset, ensuring that the picture seen by the human eye has consistent up-down distortion, and improving the visual experience.

[0058] With reference to Figure 1 , the optical system further includes a light splitting film 52. The light splitting film 52 is arranged on the side of the first lens 41 away from the second phase delay film 22 and is attached to the first convex surface 412. The light splitting film 52 is used to reflect the light so that the light enters the human eye, while allowing the light from the external real environment to be transmitted, thereby forming a special visual effect of superimposing virtual images and reality.

[0059] With reference to Figure 1The optical system further comprises a second lens 42. The second lens 42 is arranged on the side of the light splitting film 52 away from the first lens 41 and closely abuts the light splitting film 52. The second lens 42 is a plano-concave lens, and the concave surface of the second lens 42 is shaped to match the first convex surface 412 of the first lens 41, so that the light splitting film 52 is sandwiched and closely abuts between the first lens 41 and the second lens 42. The second lens 42 is used to propagate the light of the real external environment, and the optical design can effectively compensate for the aberrations introduced by the light splitting film 52 and the first lens 41, the first prism 31 and other elements, so as to ensure that the user will not have obvious optical distortion when observing the real world through the device to which the optical system is applied.

[0060] Optionally, the first lens 41, the light splitting film 52 and the second lens 42 are arranged in close contact by optical glue or precise pressing process.

[0061] Reference Figure 1 The optical system further comprises a second prism 32 arranged on one side of the third surface 313 of the first prism 31. Specifically, the second prism 32 is arranged on the side of the second polarizing film 23 away from the first prism 31. The second prism 32 closely matches the surface close to the third surface 313 of the first prism 31, so that the second polarizing film 23 is closely arranged between the first prism 31 and the second prism 32.

[0062] After the light passes through the second phase delay film 22 for the second time, it enters the first prism 31 from the second surface 312 and reaches the second polarizing film 23. At this time, the light is in a third polarization state, which is a second linearly polarized light, and the polarization direction of the second linearly polarized light is perpendicular to that of the first linearly polarized light. As described above, the reflective polarizing film 231 in the second polarizing film 23 can selectively reflect light of a certain polarization direction while transmitting light of a perpendicular direction. Therefore, the light in the third polarization state can pass through the second polarizing film 23 and enter the second prism 32. The second prism 32 cooperates with the second polarizing film 23 to efficiently guide the light of a specific polarization state into the human eye, maintaining the stability and balance of the final imaging.

[0063] Figure 4 is a modulation transfer function (Modulation Transfer Function, MTF) curve of the optical system of the embodiment. The modulation transfer function reflects the relationship between the modulation degree and the logarithm of the line per millimeter in the image, and can be used to quantify the contrast transfer capability of the module at different spatial frequencies. It is an important indicator for evaluating the resolution and contrast of the optical module. By optimizing the MTF, the resolution and contrast of the module can be improved, thereby obtaining higher quality images. According to the diagram, the MTF values of the optical system of the embodiment in each field of view are all higher than 0.4, indicating that the system has excellent clarity and contrast performance. Figure 4 According to the diagram, the MTF values of the optical system of the embodiment in each field of view are all higher than 0.4, indicating that the system has excellent clarity and contrast performance.

[0064] Figure 5 is a field curvature diagram of the optical system of the embodiment, the horizontal coordinate represents the size of the aberration, i.e. the distance of the actual image plane from the ideal image plane. The closer the horizontal coordinate value is to 0, the flatter the image plane. The vertical coordinate represents the field angle. The straight line in the field curvature diagram represents the position of the ideal image plane. The field curvature diagram includes both the meridional field curvature and the sagittal field curvature. The higher the coincidence of the two, the smaller the astigmatism in different directions, and the more uniform the image quality. In addition, the farther the curve is from the middle straight line, the greater the field curvature, and the easier the edge of the final image is blurred. According to Figure 5 , it can be seen that the field curvature of the optical system of the embodiment is extremely small, which ensures clear imaging of the full field of view.

[0065] Figure 6 is a distortion diagram of the optical system of the embodiment, the horizontal coordinate represents the size of the distortion, i.e. the deformation ratio of the image. A positive percentage represents outward expansion of the line, and a negative percentage represents inward contraction of the line. The vertical coordinate represents the field angle. The straight line in the diagram represents the ideal distortion-free reference line, and the curve in the diagram is the distortion curve. The degree to which the distortion curve deviates from the reference line at the maximum value of the vertical coordinate is the maximum distortion. According to Figure 6 , it can be seen that the distortion of the optical system of the embodiment is consistent and smooth, and the maximum distortion is limited within a reasonable range.

[0066] Figure 7 is a grid distortion diagram of the optical system of the embodiment. Through the imaging deformation of the regular grid, the geometric distortion distribution of the optical system in actual imaging can be intuitively reflected, further assisting in evaluating the distortion correction effect of the optical system.

[0067] The optical system of the embodiment sets an enhanced reflection film to ensure that the light emitted by the image source can be completely reflected when a larger size image source is used. At the same time, the first prism in the optical system makes the light inside the prism undergo two reflections, effectively lengthening the optical path while keeping the volume compact, which helps to achieve a larger field of view. At the same time, the multiple polarization films arranged in the optical system can not only guide the propagation path of the light by converting the polarization state of the light multiple times, but also effectively suppress stray light by precisely controlling the polarization state of the light, thereby significantly improving the contrast and clarity of the final image.

[0068] In the embodiment, a head-mounted display device is also provided, which includes the optical system described in the above embodiments and can achieve the corresponding optical performance and imaging effect.

[0069] The above descriptions are only the preferred embodiment of the application, not intended to limit the application. The application can be variously changed and modified by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. An optical system, characterized in that, The optical system includes: Image source (10); A first polarizing film (21) is disposed on the light-emitting side of the image source (10), and the light emitted from the image source (10) is in a first polarization state after passing through the first polarizing film (21); The first prism (31) includes a first surface (311) and a second surface (312) and a third surface (313) respectively disposed on both sides of the first surface (311). The first surface (311) is disposed opposite to the light-emitting side of the image source (10). The first polarizing film (21) is located between the image source (10) and the first surface (311). Light in the first polarization state enters the first prism (31) from the first surface (311), and after being reflected by the second surface (312) and the third surface (313) in sequence, it exits from the second surface (312). The second phase retardation film (22) is disposed on the outside of the second surface (312) of the first prism (31). Light rays emitted from the second surface (312) are in the second polarization state after passing through the second phase retardation film (22). The first lens (41) is disposed on the side of the second phase retardation film (22) away from the first prism (31). The light in the second polarization state is reflected and folded back by the first lens (41), and after passing through the second phase retardation film (22) again, it is transformed into the third polarization state. The light in the third polarization state passes through the second surface (312) and the third surface (313) in sequence before being emitted.

2. The optical system according to claim 1, characterized in that, A portion of the second surface (312) is provided with an enhanced reflective film (51).

3. The optical system according to claim 2, characterized in that, The enhanced reflective film (51) extends from one end of the second surface (312) near the image source (10) to the other end, and the length of the enhanced reflective film (51) is 2.5 mm.

4. The optical system according to claim 2 or 3, characterized in that, The enhanced reflective film (51) is a metal reflective film or a dielectric multilayer total reflective film.

5. The optical system according to claim 1, characterized in that, The first polarizing film (21) includes a first phase retardation film (211) and a first polarizer (212). The first phase retardation film (211) is attached to the light-emitting side of the image source (10), and the first polarizer (212) is disposed on the side of the first phase retardation film (211) away from the image source (10).

6. The optical system according to claim 1, characterized in that, The optical system includes a second polarizing film (23) attached to the outside of the third surface (313), the second polarizing film (23) reflecting light in the first polarization state and transmitting light in the third polarization state.

7. The optical system according to claim 6, characterized in that, The second polarizing film (23) includes a reflective polarizing film (231) and a second polarizer (232). The reflective polarizing film (231) is attached to the outside of the third surface (313), and the second polarizer (232) is attached to the side of the reflective polarizing film (231) away from the third surface (313).

8. The optical system according to claim 6, characterized in that, The optical system also includes a second prism (32), which is disposed on the side of the second polarizing film (23) away from the first prism (31).

9. The optical system according to claim 1, characterized in that, The optical system further includes a beam splitter (52) disposed on the side of the first lens (41) away from the second phase retardation film (22).

10. The optical system according to claim 9, characterized in that, The optical system further includes a second lens (42), which is disposed on the side of the beam splitter (52) away from the first lens (41).

11. The optical system according to claim 1, characterized in that, The second phase delay film (22) is a quarter-wave plate.

12. The optical system according to claim 1, characterized in that, The side of the first lens (41) closest to the first prism (31) is a first plane (411), and the first plane (411) and the second surface (312) have a first included angle (a).

13. The optical system according to claim 12, characterized in that, The first included angle (a) ranges from 0.01° to 0.1°.

14. The optical system according to claim 1, characterized in that, The normal of the light-emitting surface of the image source (10) has a second included angle (b) with the second surface (312) of the first prism (31).

15. The optical system according to claim 14, characterized in that, The second surface (312) and the third surface (313) have a third included angle (c).

16. The optical system according to claim 15, characterized in that, The second included angle (b) is 38°, and the third included angle (c) is 29°.

17. A head-mounted display device, characterized in that, The head-mounted display device includes the optical system as described in any one of claims 1-16.

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