Polarization conversion mirror and LCOS projection system with same

Abstract

The utility model provides a polarization conversion mirror and a liquid crystal on silicon (LCOS) projection system with the same, the polarization conversion mirror comprises a first prism, a second prism, a third prism and a reflective quarter-wave plate which are connected in sequence, the connection surface of the first prism and the second prism and the connection surface of the second prism and the third prism are respectively provided with a polarization beam splitting film, the polarization beam splitting film can transmit P polarized light and reflect S polarized light, the reflective quarter-wave plate is provided with a reflective film, the polarization beam splitting film is used for reflecting the S polarized light to an LCOS screen of the LCOS projection system, and the surface, away from the second prism and the LCOS screen, of the first prism is a light incident surface of the polarization conversion mirror. The face, away from the first prism and the third prism, of the second prism is the light-emitting face of the polarization conversion mirror, and the light-emitting face and the LCOS screen are oppositely arranged so that non-polarized light entering the light-in face can be converted into P polarized light to be emitted out of the light-emitting face. According to the utility model, the problem of low light energy utilization rate of the LCOS projection system in the prior art is solved.

Description

Technical Field

[0001] The utility model relates to the technical field of AR optical projection devices, and more specifically, to a polarization conversion mirror and an LCOS projection system having the same. Background Art

[0002] With the development of the information age, Augmented Reality (AR) technology, a technology that combines the information of the virtual world and the real world, has gradually entered people's lives. Head-mounted AR devices have developed rapidly in recent years due to their portability and better visual experience. The LCOS (Liquid Crystal on Silicon) display engine is a commonly used projection system for waveguide AR glasses. It uses semiconductor silicon crystal technology to control liquid crystals and project a color image. Due to the polarization characteristics of the liquid crystal screen, polarized light illumination is required for the LCOS plane. Therefore, a polarization conversion system is needed in the LCOS projection system.

[0003] In traditional LCOS projection systems, a combination of a PBS (polarizing beam splitter prism) and a polarizer is used to convert natural light from a light source into polarized light and irradiate it onto the LCOS screen. Since the polarizer or PBS converts natural light into polarized light and attenuates half of the energy, at least half of the light energy is attenuated, and it is difficult to improve the light energy utilization rate.

[0004] That is to say, the existing LCOS projection system has the problem of low light energy utilization rate in the prior art. Summary of the Utility Model

[0005] The main purpose of the present utility model is to provide a polarization conversion mirror and an LCOS projection system having the same, so as to solve the problem of low light energy utilization rate of the LCOS projection system in the prior art.

[0006] To achieve the above object, according to one aspect of the present invention, a polarization conversion mirror is provided. The polarization conversion mirror is used in an LCOS projection system and includes a first prism, a second prism, a third prism, and a reflective quarter-wave plate connected in sequence. Polarization beam splitting films are provided on the connection surfaces between the first prism and the second prism, and between the second prism and the third prism. The polarization beam splitting film can transmit P-polarized light and reflect S-polarized light. A reflective film is provided on the surface of the reflective quarter-wave plate away from the third prism, so that the P-polarized light incident on the reflective quarter-wave plate is converted into S-polarized light. The polarization beam splitting film is used to reflect the S-polarized light to the LCOS screen of the LCOS projection system. The surface of the first prism away from the second prism and the LCOS screen is the light incident surface of the polarization conversion mirror, and the surface of the second prism away from the first prism and the third prism is the light exit surface of the polarization conversion mirror. The light exit surface is disposed opposite to the LCOS screen, so that the unpolarized light incident on the light incident surface is converted into P-polarized light and exits from the light exit surface.

[0007] Further, the connection surfaces between the first prism and the second prism, and between the second prism and the third prism are both flat surfaces, and the flat surfaces extend obliquely towards the center of the LCOS screen in the direction from away from the LCOS screen to towards the LCOS screen.

[0008] Further, the polarization beam splitting film is a metal wire grid polarization film, and the polarization beam splitting film is attached or plated on the flat surface.

[0009] Further, the light incident surface includes one of a flat surface, a spherical surface, an aspherical surface, and a free-form surface.

[0010] Further, a Fresnel lens is provided on the light incident surface; or the light incident surface is the object side surface of the Fresnel lens.

[0011] Further, the surface of the first prism facing the LCOS screen includes one of a flat surface, a spherical surface, an aspherical surface, and a free-form surface.

[0012] Further, the light exit surface includes one of a flat surface, a spherical surface, an aspherical surface, and a free-form surface.

[0013] Further, the surface of the third prism facing the LCOS screen includes one of a flat surface, a spherical surface, an aspherical surface, and a free-form surface.

[0014] Further, the included angle between the optical axis of the reflective quarter-wave plate and the P-polarized light incident on the reflective quarter-wave plate is an acute angle.

[0015] Further, the refractive index of the first prism is greater than 1 and less than 5; and / or the refractive index of the second prism is greater than 1 and less than 5; and / or the refractive index of the third prism is greater than 1 and less than 5.

[0016] According to another aspect of the present utility model, there is provided an LCOS projection system, including the above-mentioned polarization conversion mirror.

[0017] Applying the technical solution of the present utility model, the polarization conversion mirror is used in the LCOS projection system. The polarization conversion mirror includes a first prism, a second prism, a third prism, and a reflective quarter-wave plate that are sequentially connected. Polarization beam splitting films are provided on the connection surface between the first prism and the second prism and the connection surface between the second prism and the third prism. The polarization beam splitting film can transmit P-polarized light and reflect S-polarized light. A reflective film is provided on the surface of the reflective quarter-wave plate away from the third prism, so that the P-polarized light incident on the reflective quarter-wave plate is converted into S-polarized light. The polarization beam splitting film is used to reflect the S-polarized light to the LCOS screen of the LCOS projection system. The surface of the first prism away from the second prism and the LCOS screen is the light incident surface of the polarization conversion mirror. The surface of the second prism away from the first prism and the third prism is the light exit surface of the polarization conversion mirror. The light exit surface is disposed opposite to the LCOS screen, so that the unpolarized light incident on the light incident surface is converted into P-polarized light and exits from the light exit surface.

[0018] By providing a first prism, a second prism, a third prism, and a reflective quarter-wave plate that are sequentially connected, and using the polarization beam splitting films provided on the connection surface between the first prism and the second prism and the connection surface between the second prism and the third prism, the unpolarized light incident on the polarization conversion mirror from the light incident surface can be divided into P-polarized light and S-polarized light. The P-polarized light is transmitted by the polarization beam splitting film and thus can be incident on the reflective quarter-wave plate. After one polarization conversion by the reflective quarter-wave plate, it is reflected by the reflective film and then passes through one polarization conversion of the reflective quarter-wave plate again. Finally, the P-polarized light incident on the reflective quarter-wave plate is converted into S-polarized light. Therefore, there are two lights with different incident directions that are reflected by the polarization beam splitting film, and the reflected lights are both S-polarized light and irradiate the LCOS screen of the LCOS projection system to meet the polarization light irradiation conditions of the LCOS screen. In addition, since the LCOS screen can also perform polarization conversion and reflect the converted light back to the polarization conversion mirror, the P-polarized light converted by the LCOS screen then passes through the polarization beam splitting film in the polarization conversion mirror and exits from the light exit surface of the polarization conversion mirror for subsequent imaging use. In the above process, although the unpolarized light is divided into two polarized lights with different directions, both lights are utilized without being wasted, greatly improving the light energy utilization rate. Description of the Drawings

[0019] The specification drawings forming a part of this application are used to provide a further understanding of the present utility model. The schematic embodiments of the present utility model and their descriptions are used to explain the present utility model and do not constitute an improper limitation to the present utility model. In the drawings:

[0020] Figure 1Shows a schematic structural diagram of the LCOS projection system according to Embodiment 1 of the present utility model;

[0021] Figure 2 Shows Figure 1 a schematic structural diagram of the polarization conversion mirror in;

[0022] Figure 3 Shows Figure 1 an optical path diagram of the polarization conversion mirror cooperating with the LCOS screen in;

[0023] Figure 4 Shows a schematic structural diagram of the first prism of the polarization conversion mirror according to Embodiment 2 of the present utility model;

[0024] Figure 5 Shows a schematic structural diagram of the first prism of the polarization conversion mirror according to Embodiment 3 of the present utility model;

[0025] Figure 6 Shows a schematic structural diagram of the third prism of the polarization conversion mirror according to Embodiment 4 of the present utility model;

[0026] Figure 7 Shows an optical path diagram of the polarization conversion mirror cooperating with the LCOS screen according to Embodiment 5 of the present utility model;

[0027] Figure 8 Shows Figure 7 a connection diagram of the second prism and the polarization beam splitting film in;

[0028] Figure 9 Shows Figure 7 an optical path diagram of the metal wire grid type polarization beam splitting film in;

[0029] Figure 10 Shows Figure 7 a schematic structural diagram of the third prism of the polarization conversion mirror in;

[0030] Figure 11 Shows a comparison diagram of the projection spots of the polarization conversion mirrors according to Embodiment 5 and Embodiment 1 of the present utility model;

[0031] Figure 12 Shows a schematic structural diagram of the second prism of the polarization conversion mirror according to Embodiment 6 of the present utility model;

[0032] Figure 13 Shows a schematic diagram of a reflective quarter-wave plate according to an optional embodiment of the present utility model.

[0033] Among them, the above-mentioned drawings include the following reference numerals:

[0034] 101, Micro-LED light source; 102, Collimating lens group; 103, Polarization conversion mirror; 104, LCOS screen; 105, Projection imaging lens group; 106, AR optical waveguide; 201, First prism; 202, Second prism; 203, Third prism; 204, First polarization beam splitting film; 205, Second polarization beam splitting film; 206, Reflective quarter-wave plate; 301, Collimated beam; 302, First reflected S-polarized light; 303, First transmitted P-polarized light; 304, Second reflected S-polarized light; 305, Second transmitted P-polarized light; 401, First surface of the first prism; 402, Second surface of the first prism; 501, First surface of the second prism; 502, Second surface of the second prism; 503, Third surface of the second prism; 601, Natural light; 602, S-polarized light; 603, P-polarized light; 701, First surface of the third prism; 702, Second surface of the third prism; 703, Supplementary chamfer; 801, First light spot; 802, Second light spot; 901, Fast axis; 902, Slow axis; 903, Polarization state of the reflective quarter-wave plate. Detailed implementation manners

[0035] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments may be combined with each other. The present utility model will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0036] It should be pointed out that unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0037] In the present utility model, unless otherwise stated, the orientation terms such as "upper, lower, top, bottom" are generally in reference to the directions shown in the drawings, or in reference to the vertical, perpendicular or gravitational directions of the components themselves; similarly, for the convenience of understanding and description, "inner, outer" refer to the inner and outer of the contours of the respective components themselves, but the above orientation terms do not limit the present utility model.

[0038] In order to solve the problem of low light energy utilization rate in the existing LCOS projection system, the present utility model provides a polarization conversion mirror 103 and an LCOS projection system having the same.

[0039] As Figures 1 to 13As shown, the polarization conversion mirror 103 is used in the LCOS projection system. The polarization conversion mirror 103 includes a first prism 201, a second prism 202, a third prism 203, and a reflective quarter-wave plate 206 connected in sequence. Polarization beam splitting films are provided on the connection surface between the first prism 201 and the second prism 202 and on the connection surface between the second prism 202 and the third prism 203. The polarization beam splitting film can transmit P-polarized light and reflect S-polarized light. A reflective film is provided on the surface of the reflective quarter-wave plate 206 away from the third prism 203, so that the P-polarized light incident on the reflective quarter-wave plate 206 is converted into S-polarized light. The polarization beam splitting film is used to reflect the S-polarized light to the LCOS screen 104 of the LCOS projection system. The surface of the first prism 201 away from the second prism 202 and the LCOS screen 104 is the light incident surface of the polarization conversion mirror 103. The surface of the second prism 202 away from the first prism 201 and the third prism 203 is the light exit surface of the polarization conversion mirror 103. The light exit surface is disposed opposite to the LCOS screen 104, so that the unpolarized light incident on the light incident surface is converted into P-polarized light and exits from the light exit surface.

[0040] By providing the first prism 201, the second prism 202, the third prism 203, and the reflective quarter-wave plate 206 connected in sequence, and using the polarization beam splitting films provided on the connection surface between the first prism 201 and the second prism 202 and on the connection surface between the second prism 202 and the third prism 203, the unpolarized light incident on the polarization conversion mirror 103 from the light incident surface can be divided into P-polarized light and S-polarized light. The P-polarized light is transmitted by the polarization beam splitting film and thus can be incident on the reflective quarter-wave plate 206. After one polarization conversion by the reflective quarter-wave plate 206, it is reflected by the reflective film and then passes through one polarization conversion of the reflective quarter-wave plate 206 again. Finally, the P-polarized light incident on the reflective quarter-wave plate 206 is converted into S-polarized light. Therefore, there are two kinds of light with different incident directions that are reflected by the polarization beam splitting film. The reflected light is all S-polarized light and irradiates the LCOS screen 104 of the LCOS projection system to meet the polarization light irradiation conditions of the LCOS screen 104. In addition, since the LCOS screen 104 can also perform polarization conversion and reflect the converted light back to the polarization conversion mirror 103, the P-polarized light converted by the LCOS screen 104 is then transmitted by the polarization beam splitting film in the polarization conversion mirror 103 and exits from the light exit surface of the polarization conversion mirror 103 for subsequent imaging use. In the above process, although the unpolarized light is divided into two kinds of polarized light with different directions, both kinds of light rays are utilized without being wasted, greatly improving the light energy utilization rate.

[0041] Furthermore, the connecting surfaces of the first prism 201 and the second prism 202, and the connecting surfaces of the second prism 202 and the third prism 203 are both flat surfaces. Along the direction from away from the LCOS screen 104 to towards the LCOS screen 104, the flat surfaces extend obliquely towards the center of the LCOS screen 104. By setting the connecting surfaces of the first prism 201 and the second prism 202, and the second prism 202 and the third prism 203 as flat surfaces and extending them obliquely towards the center of the LCOS screen 104, the reflected S-polarized light can be irradiated towards the LCOS screen 104 by means of the tilt angle. At the same time, the setting of the flat surfaces facilitates the processing of the polarization beam splitting film and can also avoid the scattered irradiation of light to ensure the light energy utilization rate. At the same time, the two surfaces of the second prism 202 are respectively glued to the first prism 201 and the third prism 203, so that the three prisms form an integral body to ensure the compactness of the structure.

[0042] Optionally, the light incident surface includes one of a flat surface, a spherical surface, an aspherical surface, and a freeform surface. When the light incident surface is a flat surface, the light beam is directly incident on the polarization beam splitting film on the connecting surface of the first prism 201 and the second prism 202, and the divergence angle of the light beam remains unchanged. When the light incident surface is a spherical surface, an aspherical surface, a freeform surface or a Fresnel lens, the light beam from the light source can be shaped and collimated, and the divergence angle of the incident light beam can be changed, so as to change the spot size and the incident angle of the light beam on the polarization beam splitting film on the connecting surface of the first prism 201 and the second prism 202.

[0043] Of course, it is also possible to choose to set a Fresnel lens on the light incident surface, or the light incident surface is the object side surface of the Fresnel lens. Similarly, the light beam from the light source can be shaped and collimated, and the divergence angle of the incident light beam can be changed, so as to change the spot size and the incident angle of the light beam on the polarization beam splitting film on the connecting surface of the first prism 201 and the second prism 202.

[0044] Furthermore, one of a flat surface, a spherical surface, an aspherical surface, and a freeform surface is included in the surface of the first prism 201 facing the LCOS screen. The S-polarized light reflected by the polarization beam splitting film in the first prism 201 exits through the surface of the first prism 201 facing the LCOS screen and is transmitted towards the LCOS screen. By designing the surface shape of the exit surface and the law of refraction of light, the divergence angle and spot size of the exit light beam can be controlled, which can be adapted to LCOS screens 104 of different sizes, thus avoiding the waste of energy that cannot irradiate the LCOS screen 104 and improving the light source energy utilization rate.

[0045] Similarly, one of a flat surface, a spherical surface, an aspherical surface, and a freeform surface can be selected for the surface of the third prism 203 facing the LCOS screen 104.

[0046] Further, the light-emitting surface includes one of a plane surface, a spherical surface, an aspherical surface, and a free-form surface. By using the surface shape change of the light-emitting surface, the purpose of aberration correction can be further achieved in cooperation with the subsequent projection imaging lens group 105.

[0047] Further, the optical axis of the reflective quarter-wave plate 206 forms an acute angle with the P-polarized light incident on the reflective quarter-wave plate 206. The reflective quarter-wave plate 206 can convert the incident P-polarized light into S-polarized light, and combined with the polarization beam splitting film and the prism, the effect of polarization conversion can be achieved.

[0048] As Figure 13 shown, it is a schematic structural diagram of the reflective quarter-wave plate 206 according to an optional embodiment of the present application. The reflective quarter-wave plate 206 has a fast axis 901 and a slow axis 902, and the fast axis 901 and the slow axis 902 are perpendicular to each other. When the polarization state 903 incident on the reflective quarter-wave plate is not parallel to the fast axis 901 or the slow axis 902, the linearly polarized light will become elliptically polarized light after passing through the reflective quarter-wave plate 206. Specifically, when the relative angle between the fast axis 901 and the polarization state of the incident light beam is 45°, the emitted light is circularly polarized light. A reflective film is coated on the outer surface of the reflective quarter-wave plate 206, which can reflect the incident linearly polarized light back and rotate the polarization state by 90 degrees. For example, when P-polarized light enters the reflective quarter-wave plate 206, the emitted light is S-polarized light.

[0049] Optionally, the refractive index of the first prism 201 is greater than 1 and less than 5; optionally, the refractive index of the second prism 202 is greater than 1 and less than 5; optionally, the refractive index of the third prism 203 is greater than 1 and less than 5. The refractive indices of the first prism 201 to the third prism 203 are controlled within a certain range to ensure that the light is transmitted to the required surface.

[0050] Specifically, the materials of the first, second, and third prisms 203 can be selected from glass or optical resin, which can meet the mass production requirements of good processability and low cost.

[0051] In the polarization conversion mirror 103 of the present application, the surface shape of each prism satisfies the following formula:

[0052]

[0053]

[0054] Among them, k represents the conic coefficient, c represents the curvature, r is the radius of curvature, and x and y are the length and width of the prism. When c = 0, the surface shape is a plane; when c ≠ 0, c j = 0, k = 0, the surface shape is a spherical surface; when c ≠ 0, c j = 0, k ≠ 0, the surface shape is an aspherical surface; when c ≠ 0, c jWhen ≠0 and k≠0, the surface type is a free-form surface.

[0055] The present utility model also provides an LCOS projection system, which includes the above-mentioned polarization conversion mirror 103. The LCOS projection system can be applied to AR devices. In the LCOS projection system, the natural light coming out of the light source through the collimation system can be completely converted into polarized light with the required polarization state, thereby improving the light energy utilization rate of the LCOS projection system. In addition, the incident light spot can be enlarged by 2 times by reflecting the light with the upper and lower polarization beam splitting films of the polarization conversion mirror 103. The inclination angle of the polarization beam splitting film with respect to the incident light is θ (θ≠m*90°, m is an integer such as -1, 0, 1, 2), and the light beam turns to the direction where the LCOS screen 104 is located, and its turning angle is equal to 2θ.

[0056] Embodiment 1

[0057] As Figure 1 shown, the LCOS projection system of this embodiment applies the polarization conversion mirror 103 of the present application.

[0058] As Figure 1 shown, the LCOS projection system includes a micro LED light source 101, a collimating lens group 102, a polarization conversion mirror 103, an LCOS screen 104, a projection imaging lens group 105, and an AR optical waveguide 106. The divergent light beam emitted by the micro LED light source 101 becomes a collimated light beam after passing through the collimating lens group 102. The collimated light beam enters the polarization conversion mirror 103 and is converted into a polarized collimated light with S polarization state and the optical path turns by 90 degrees. After turning, the S polarized light irradiates on the LCOS screen 104. When the LCOS screen 104 is lit, the LCOS screen 104 converts the irradiated S polarized light into P polarized light and reflects it onto the polarization conversion mirror 103. The P polarized light directly passes through the polarization conversion mirror 103 and enters the projection imaging lens group 105, and then is coupled into the coupling port of the AR optical waveguide 106 by the projection imaging lens group 105.

[0059] As Figure 2 shown, the polarization conversion mirror 103 sequentially includes a first prism 201, a second prism 202, a third prism 203, and a reflective quarter-wave plate. A first polarization beam splitting film 204 is provided on the connection surface of the first prism 201 and the second prism 202, and a second polarization beam splitting film 205 is provided on the connection surface of the second prism 202 and the third prism 203. Both polarization beam splitting films are made by evaporation, and their thickness is less than 10μm. The first prism 201, the second prism 202, and the third prism 203 are all plane right-angle prisms, and the included angle between the right-angle surface and the inclined surface is 45 degrees.

[0060] As Figure 3The optical path diagram of the cooperation between the polarization conversion mirror 103 and the LCOS screen 104 is shown. The collimated beam 301 is natural light, which is transmitted through the first prism 201 to the first polarization beam splitting film 204 and is split into two polarized light by the first polarization beam splitting film 204. Among them, the S-polarized light is reflected as the first reflected S-polarized light 302, and the P-polarized light is transmitted as the first transmitted P-polarized light 303. After the first transmitted P-polarized light 303 is transmitted through the second prism 202, it is first incident on the second polarization beam splitting film 205. The P-polarized light will be directly transmitted through the second polarization beam splitting film 205 and transmitted to the reflective quarter-wave plate 206 through the third prism 203. In this embodiment, the optical axis of the reflective quarter-wave plate 206 is at 45 degrees with respect to the incident light polarization state. At this time, the reflective quarter-wave plate 206 first converts the incident P-polarized light into circularly polarized light, and then after being reflected by the lower surface of the reflective quarter-wave plate 206 and passing through the reflective quarter-wave plate 206 again, it is converted into the second reflected S-polarized light 304. The second reflected S-polarized light 304 is reflected after being incident on the second polarization beam splitting film 205, and the reflected light is the first reflected S-polarized light 302. After the first reflected S-polarized light 302 is incident on the lit LCOS screen 104, the polarization state is rotated 90 degrees by the LCOS screen 104, changing from the first reflected S-polarized light 302 to the second transmitted P-polarized light 305. The second transmitted P-polarized light 305 will directly pass through the polarization conversion mirror 103 and be transmitted to the rear projection imaging lens group 105.

[0061] Optionally, the polarization beam splitting film is a metal wire grid polarization film, and the polarization beam splitting film is formed by plating.

[0062] Embodiment 2

[0063] As Figure 4 shown, the difference from Embodiment 1 is that the surface shape of the first surface 401 of the first prism, which is also the light incident surface of the polarization conversion mirror 103, is different.

[0064] In this embodiment, the first surface 401 of the first prism is a spherical surface, and the refractive index n of the dielectric material of the first prism 201 satisfies 1 < n < 5. The first prism 201 with a spherical light incident surface forms a lens with a focal power, which can collimate the incident light with a divergence angle.

[0065] Embodiment 3

[0066] As Figure 5 shown, the difference from Embodiment 1 is that the surface shape of the first surface 401 of the first prism is different.

[0067] In this embodiment, the first surface 401 of the first prism is a Fresnel surface, and the refractive index n of the dielectric material of the first prism 201 satisfies 1 < n < 5. In this embodiment, a lens with a focal power is formed by using the Fresnel surface and the prism dielectric material, which can collimate the incident light with a divergence angle.

[0068] Example 4

[0069] As Figure 6 shown, the difference from Example 1 is that the surface shape of the second surface of the first prism 201 facing the LCOS screen 104 is different.

[0070] In this embodiment, the second surface 402 of the first prism is a spherical surface, and the refractive index n of the medium material of the first prism 201 satisfies 1 < n < 5. In this embodiment, a lens with a focal power is formed by the spherical surface and the prism medium material, which can realize changing the size and direction of the outgoing light spot of the first prism 201. The outgoing light spot can be effectively converged onto the LCOS screen 104, improving the utilization rate of the light beam.

[0071] Example 5

[0072] As Figures 7 to 11 shown, the difference from Example 4 is that the surface shape of the first surface of the third prism 203 facing the LCOS screen 104 is different, and the processing method of the polarization beam splitting film is also different.

[0073] In this embodiment, the first surface 701 of the third prism is also a spherical surface, and the polarization beam splitting film is attached to the bonding surface of the prism using optical glue. The polarization conversion mirror 103 realizes irradiating the primary reflected S-polarized light 302 onto the effective part of the LCOS screen 104, making full use of the beam energy and improving the light energy utilization rate of the LCOS projection system.

[0074] As Figure 8 shown, the polarization beam splitting film is attached to the first surface 501 and the second surface 502 of the second prism using optically transparent glue, and the film thickness t of the polarization beam splitting film satisfies: 70 μm < t < 120 μm, and the optical axes of the first polarization beam splitting film 204 and the second polarization beam splitting film 205 are parallel to each other.

[0075] Optionally, the type of the polarization beam splitting film is a metal wire grid or the PBS film 1000 of 3M Company.

[0076] As Figure 9 shown, it is the optical path diagram of the metal wire grid type polarization beam splitting film. Among them, natural light 601 is incident on the metal wire grid polarization film and is divided into two polarized light beams. The S-polarized light 602 is reflected, and the P-polarized light 603 is transmitted.

[0077] As Figure 10 shown, the second surface 702 of the third prism is attached with the second polarization beam splitting film 205, and the third prism 203 has a supplementary chamfer 703 to realize the coincidence of the second prism 202 and the third prism 203 when attaching the second polarization beam splitting film 205, avoiding the phenomenon of hollowing. The thickness of the supplementary chamfer 703 is equal to the thickness of the polarization beam splitting film.

[0078] As Figure 11 shown is a comparison diagram of the projected spot sizes of the polarization conversion mirror 103 in the first embodiment and this embodiment. Specifically, in the LCOS transmissive optical engine of the AR glasses, when the effective size of the LCOS screen 104 is greater than 2 mm, the polarization conversion mirror 103 as in the first embodiment can be directly used to obtain the first spot 801; when the effective size of the LCOS screen 104 is less than 2 mm, the polarization conversion mirror 103 shown in this embodiment can be used to obtain the second spot 802.

[0079] Embodiment Six

[0080] As Figure 12 shown, the difference from the first embodiment is that the surface shape of the third surface 503 of the second prism, which is also the light-emitting surface of the polarization conversion mirror 103, is different.

[0081] In this embodiment, the third surface 503 of the second prism is spherical, which is beneficial to achieving the purpose of aberration correction in cooperation with the projection imaging lens group 105.

[0082] Obviously, the above-described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0083] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0084] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0085] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A polarization conversion mirror, characterized in that, The polarization conversion mirror (103) is used in an LCOS projection system. The polarization conversion mirror (103) includes a first prism (201), a second prism (202), a third prism (203), and a reflective quarter-wave plate (206) connected in sequence. A polarization beam splitting film is provided on the connecting surface between the first prism (201) and the second prism (202) and on the connecting surface between the second prism (202) and the third prism (203). The polarization beam splitting film can transmit P-polarized light and reflect S-polarized light. A reflective film is provided on the surface of the reflective quarter-wave plate (206) away from the third prism (203) so that the P-polarized light incident on the reflective quarter-wave plate (206) is converted into S-polarized light. The polarization beam splitting film is used to reflect the S-polarized light to the LCOS screen (104) of the LCOS projection system. The surface of the first prism (201) away from the second prism (202) and the LCOS screen (104) is the light incident surface of the polarization conversion mirror (103). The surface of the second prism (202) away from the first prism (201) and the third prism (203) is the light exit surface of the polarization conversion mirror (103). The light exit surface is disposed opposite to the LCOS screen (104) so that the unpolarized light incident on the light incident surface is converted into P-polarized light and exits from the light exit surface.

2. The polarization conversion mirror according to claim 1, characterized in that, The connecting surface between the first prism (201) and the second prism (202) and the connecting surface between the second prism (202) and the third prism (203) are both planes. Along the direction from away from the LCOS screen (104) to close to the LCOS screen (104), the planes extend obliquely towards the center of the LCOS screen (104).

3. The polarization conversion mirror according to claim 2, wherein The polarization beam splitting film is a metal wire grid polarization film, and the polarization beam splitting film is attached or plated on the plane.

4. The polarization conversion mirror according to claim 1, wherein The light incident surface includes one of a plane, a spherical surface, an aspherical surface, and a free-form surface.

5. The polarization conversion mirror according to claim 1, wherein a Fresnel lens is provided on the light incident surface; or the light incident surface is the object side surface of a Fresnel lens.

6. The polarization conversion mirror according to claim 1, wherein, The surface of the first prism (201) facing the LCOS screen includes one of a plane, a spherical surface, an aspherical surface, and a free-form surface.

7. The polarization conversion mirror according to claim 1, wherein The light exit surface includes one of a plane, a spherical surface, an aspherical surface, and a free-form surface.

8. The polarization conversion mirror according to claim 1, wherein The surface of the third prism (203) facing the LCOS screen (104) includes one of a plane, a spherical surface, an aspherical surface, and a free-form surface.

9. The polarization conversion mirror according to claim 1, wherein The included angle between the optical axis of the reflective quarter-wave plate (206) and the P-polarized light incident on the reflective quarter-wave plate (206) is an acute angle.

10. The polarization conversion mirror according to any one of claims 1 to 9, wherein the refractive index of the first prism (201) is greater than 1 and less than 5; and / or the refractive index of the second prism (202) is greater than 1 and less than 5; and / or the refractive index of the third prism (203) is greater than 1 and less than 5.

11. An LCOS projection system, characterized in that, Comprising the polarization conversion mirror (103) according to any one of claims 1 to 10.

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