CN116009304A - Circular polarization beam splitting film, preparation method and VR display system - Google Patents

Abstract

The application belongs to the field of optics and provides a circular polarization beam splitting film, a preparation method and a VR display system, wherein the circular polarization beam splitting film comprises a nematic liquid crystal layer, and a spiral wire grid formed by rod-shaped chiral molecules is arranged in the nematic liquid crystal layer along the normal direction of a surface; pitch p of spiral wire grid, average refractive index n of nematic liquid crystal layer, center reflection wavelength lambda ₀ The following are satisfied: lambda (lambda) ₀ =np. In the working band, the reflectivity of circularly polarized light with the same handedness can reach about 50 percent, the transmissivity of light with the non-working band can reach more than 70 percent, when the incident angle is changed, the size of the reflection light bandwidth is not influenced, but the range of the reflection light bandwidth has certain deviation, and the doping period is used for homodromously mediatingThe mass layer can reduce this effect, achieving a large field angle. The method is applied to the VR display system to directly split circularly polarized light, so that the number and thickness of lenses can be effectively reduced, and the efficiency is improved. The preparation method of the circular polarization beam splitting film is simple and easy to realize batch preparation.

Description

Circular polarization beam splitting film, preparation method and VR display system

technical field

The application belongs to the field of optics, and in particular relates to a circular polarization beam splitting film.

Background technique

Polarizer refers to an optical film that selectively allows light in a specific vibration direction to pass through. It is mainly used to convert general unpolarized light into polarized light. Only one of the two orthogonal linear optical axes is allowed to pass through, so the polarizing element is selective to the polarization direction of light. The addition of polarizing beam splitter film in VR display technology is to use this characteristic to realize folding optical path and reduce the thickness of VR display system. The linear polarization beam splitter needs to be used in combination with the quarter-wave plate in the VR display system to process circularly polarized light. This structure will lead to problems such as poor optical efficiency and ghost images in the VR system.

Patent CN105404013A discloses a circularly polarized light beam splitter, which arranges spiral wire grids in an array on the substrate, each group of spiral wire grids includes 8 single spiral wire grids, and the direction of rotation of the 8 single spiral wire grids is the same, each group of spiral wire grids The initial rotation angle of the first single helix wire grid in the wire grid is 0 degrees, and the initial rotation angle of the latter single helix wire grid is 22.5 degrees larger than the initial rotation angle of the previous single helix wire grid. When circularly polarized light Vertically incident from one side of the spiral wire grid array, two beams of light are transmitted from the other side of the beam splitter, one of the transmitted beams is transmitted in the original direction, and the other beam of transmitted beams has a splitting angle with it, realizing circularly polarized light of splitting. In its preparation process, a photoresist deep ultraviolet coherent etching process is used to form a spiral air gap in the photoresist, and then an aluminum material is deposited in the air gap by an electrochemical deposition process to obtain a spiral wire grid. In this preparation method, the helical diameter of the helical air gap is at the nanometer level. When the electrochemical deposition process is used to prepare the aluminum material, the deposition efficiency of the material to the nanoscale air gap is low, and it is difficult to obtain a uniform and continuous helical wire grid structure, and the preparation process is cumbersome. Difficult to achieve batch preparation.

Contents of the invention

In order to solve the problems pointed out in the background technology, take the following technical solutions:

A circular polarization beam splitting film, comprising a nematic liquid crystal layer, a spiral wire grid composed of rod-shaped chiral molecules is arranged along the surface normal direction in the nematic liquid crystal layer; the pitch p of the spiral wire grid, the nematic liquid crystal The relationship between the average refractive index n of the layer and the central reflection wavelength λ ₀ satisfies: λ ₀ =np.

The length required for the rod-shaped chiral molecules in the circular polarization beam-splitting film to helix for one circle is the pitch, and the working wavelength of the circular polarization beam-splitting film is proportional to the size of the pitch. The handedness of the doped rod-shaped chiral molecules determines the working mode of the circular polarization beam splitting film. The circular polarizing beamsplitter reflects the circularly polarized light with the handedness of the chiral molecule and transmits the circularly polarized light with the opposite handedness.

Preferably, the spiral wire grid adopts a continuously variable pitch structure. The continuously variable pitch structure can broaden the working wavelength of the circular polarization beam splitting film, and its working band width can be extended to about 300nm by changing its material and exposure power.

Preferably, the circular polarization beam splitting film is formed by stacking circular polarization beam splitting films of different working wavelength bands. The stacking of the circular polarization beam splitting film structures with different working bands can make the working band of the circular polarizing beam splitting film after stacking be the superposition of the working bands of the stacked circular polarizing beam splitting films.

A multi-band circular polarization beam-splitting film is formed by laminating several layers of circular polarization beam-splitting films, wherein each layer of circular polarization beam-splitting film corresponds to a working band. Each layer of circular polarization beam splitting film corresponds to a working band, and selectively reflects circularly polarized light within its working band range without affecting other bands. The working bands of each layer of circular polarization beam splitting film do not cross and do not interfere with each other, and each layer works within its working range, which can realize multi-band circular polarization beam splitting film.

Preferably, the material of the nematic liquid crystal layer is E7 liquid crystal, and the rod-shaped chiral molecules are R5011 right-handed chiral molecules. The HTP value of R5011 ranges from about 100um ^-1 to 120um ^-1 , and the average refractive index of E7 is about 1.63; R5011 has a higher melting point and better environmental adaptability, and the HTP values of R5011 prepared in different ways are also different . When the mass ratio range of R5011 to E7 is about 2.07% to 2.48%, the working band is red, when it is 2.52% to 3.03%, the working band is green, and when it is 3.03% to 3.62%, the working band is blue. When there are other requirements for the helical pitch, the mass ratio of chiral molecules, and the hand direction, the chiral molecular material can be replaced, and the mass ratio of each band will also change accordingly.

A preferred visible light circular polarization beam-splitting film is formed by laminating three layers of circular polarization beam-splitting films, and the working bands of the three layers of circular polarization beam-splitting films are red light band, green light band and blue light band respectively. The material of the nematic liquid crystal layer is E7 liquid crystal, and the rod-shaped chiral molecules adopt R5011 right-handed chiral molecules; the mass ratios of R5011 and E7 in the top-down nematic liquid crystal layer are: 2.07%～2.48%, 2.52%～ 3.03%, 3.03% to 3.62%. This scheme can realize RGB three-band circular polarization beam splitting, and its three working bands are respectively in red light, green light and blue light, basically covering the visible light band, and can realize circular polarization beam splitting in the visible light band.

A VR display system based on a circular polarization beam-splitting film, including a display screen, a linear polarizer, a 1/4 wave plate, a semi-transparent and semi-reflective film, a visible light circular polarization beam-splitter film, and a human eye sensor; a display screen, a linear polarizer , 1/4 wave plate, semi-transparent and semi-reflective film, and visible light circular polarization beam splitting film are placed in parallel; The wavelength bands are red light band, green light band and blue light band; the light emitted by the display screen passes through the linear polarizer, the 1/4 wave plate, the semi-transparent and semi-reflective film and the visible light circular polarization beam-splitting film in sequence to obtain the rod-shaped chiral molecule The three-color circularly polarized light with opposite handedness is transmitted to the human eye sensor for display.

Wherein, the linear polarizer and the 1/4 wave plate together form a polarizing structure, and the light beam emitted by the display screen is polarized by the linear polarizer to obtain linearly polarized light with a specific polarization direction, and then the linearly polarized light passes through the 1/4 wave plate The phase retardation is carried out on it, so that the linearly polarized light is converted into circularly polarized light, and the obtained circularly polarized light is incident on the visible light circularly polarized beam splitting film through the semi-transparent and semi-reflective film, and the visible light circularly polarized beam splitting film will be rotated with the chiral molecule. Reflect to the same circularly polarized light, transmit the circularly polarized light with the opposite rotation, the reflected circularly polarized light is incident on the transflective film and then reflected again to reverse the circularly polarized light's rotation, and then incident to the visible circularly polarized light again The beam splitting film, due to the change of the hand direction, is opposite to the hand direction of the chiral molecule, so it can be transmitted out and enter the human eye sensor. The semi-transparent and semi-reflective film can transmit or reflect part of the light. The visible light circular polarization beam-splitting film is placed behind the transflective film, since this scheme uses the visible light circular polarization beam-splitting film to replace the circular polarization composed of 1/4 wave plate and linear polarization beam-splitting film in the traditional VR folding optical path scheme Devices that reduce the number of components used and reduce thickness while increasing optical efficiency.

Preferably, the semi-transparent and semi-reflective film is arranged on the concave surface of the plano-concave lens, or on the inner wall of the spherical shell lens. With the function of partial reflection and transmission, the circularly polarized light obtained by the polarizing structure can be transmitted through the structure, and then the light beam reflected to the structure will be reflected and its rotation direction will be changed.

The preparation method of circularly polarized beam splitting film in the present invention comprises the following steps:

S1. Cleaning the substrate; uniformly coating the photo-alignment agent on the surface of the substrate;

S2. Place the substrate on a hot stage and dry it at high temperature to obtain a photo-alignment layer on the substrate; fully volatilize the solvent of the photo-alignment agent, so that the solute molecules in the photo-alignment agent are closely arranged;

S3. Exposing the photo-alignment layer to linearly polarized ultraviolet light; making the molecular orientation in the photo-alignment layer complete;

S4. Evenly coating the mixture of nematic liquid crystal and rod-shaped chiral molecules on the surface of the photo-alignment layer; under the action of the photo-alignment layer, the rod-shaped chiral molecules form a spiral wire grid in the nematic liquid crystal;

S5. Carry out ultraviolet light curing, so that the helical wire grid formed by rod-shaped chiral molecules is cured in the nematic liquid crystal layer.

Description of drawings

Figure 1: A schematic diagram of a VR display system in this application;

Figure 2: Schematic diagram of the right-handed circular polarizing beam splitting film of this application;

Figure 3: Schematic diagram of the visible light circular polarization beam splitting film of this application;

Figure 4: Schematic diagram of continuous gradient pitch visible light circular polarization beam splitter film;

Figure 5: Schematic diagram of the structure of the multi-band circular polarization beam splitting film group;

Figure 6: Schematic diagram of a prior art VR display system;

Among them: 101 is the display screen, 102 is the first linear polarizer, 103 is the second 1/4 wave plate, 104 is the transflective film, 105 is the visible light circular polarization beam splitter film, 105a is the second 1/4 wave 105b is a linear polarizing beam-splitting film, 106 is a human eye sensor, 107 is a right-handed circular polarizing beam-splitting film, 108 is a multi-band circular polarizing beam-splitting film group, and 109 is a second linear polarizing plate.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the application is further described:

Embodiment one

A kind of circular polarizing beam splitting film as shown in Figure 2, it is right-handed circular polarizing beam splitting film 107, comprises nematic phase liquid crystal layer, in the nematic phase liquid crystal layer is arranged along the surface normal direction by rod-shaped chiral molecules A spiral wire grid is formed; the pitch p of the spiral wire grid, the average refractive index n of the nematic liquid crystal layer, and the central reflection wavelength λ ₀ satisfy: λ ₀ =np. When the right-handed circularly polarized light is incident on the surface of the circularly polarized beam splitter, the light is reflected because the right-handed circularly polarized light is in the same direction as the chiral molecule; but when the left-handedly polarized light is incident on the circularly polarized beam splitter film, because left-handed circularly polarized light is transmitted in the opposite direction to that of chiral molecules. In its working band, the reflectivity for circularly polarized light with the same handedness can reach about 50%, and the transmittance for light in the non-working band can reach more than 70%. At the same time, when the incident angle changes, the bandwidth of the reflected light will not be affected, but its range will be shifted to a certain extent. This effect can be reduced by doping the periodic isotropic dielectric layer to achieve a large viewing angle.

Taking a right-handed circularly polarizing beam-splitting film with a working wavelength in the red light range as an example, the preparation method of the circularly polarizing beam-splitting film includes the following steps:

Sa1. Clean the substrate; uniformly coat the SD1 photoalignment agent on the surface of the substrate; spin-coat at a speed of 3000 rpm for 30s;

Sa2. Place the substrate on a hot stage with a temperature of 120° and bake for 10 minutes; obtain a photo-alignment layer on the substrate; fully volatilize the solvent of the photo-alignment agent, so that the solute molecules in the photo-alignment agent are closely arranged;

Sa3. exposing the photo-alignment layer to linearly polarized ultraviolet light; making the orientation of SD1 molecules in the photo-alignment layer complete;

Sa4. Evenly coat the mixture of E7 liquid crystal and R5011 right-handed chiral molecules on the surface of the SD1 layer, and spin-coat at a speed of 3000 rpm for 30s; A spiral wire grid is formed in the mixture; the content of R5011 right-handed chiral molecules in the mixed solution is 2.27%;

Sa5. Carry out ultraviolet light curing, so that the helical wire grid formed by rod-shaped chiral molecules is cured in the nematic liquid crystal layer.

In this embodiment, the refractive index of ordinary light n _o = 1.54, the refractive index of extraordinary light _ne = 1.74, and the pitch p = 400nm can be obtained It can be obtained that λ ₀ =656nm. At the same time, according to the helical pitch p=[(HTP)×X _c ] ^-1 , HTP is the helical twist force constant of the chiral additive, and X _c is the content of the chiral additive in the liquid crystal composition; let its HTP value be 110um ^-1 , Furthermore, the content of chiral molecules is calculated to be 2.27%, and this concentration is in the red light band.

Through the above steps, the right-handed circular polarization beam-splitting film in the red band can be obtained, and the circularly polarized light can be directly split by using the right-handed circularly polarized beam-splitting film, because there is no need for much communication between circularly polarized light and linearly polarized light This conversion can avoid the ghost image problem existing in the VR display system of the linear polarization beam splitter film.

Embodiment two

Taking the RGB three-band multi-band circular polarization beam splitter film as shown in Figure 3 as an example, the preparation process of the visible light circular polarization beam splitter film is as follows:

Sb1. Evenly coat the photo-alignment agent SD1 on the cleaned substrate, and spin-coat at a speed of 3000 rpm for 30 seconds; Sb2. Put the substrate on a 120° hot table and bake for 10 minutes;

Sb3. Expose the substrate under linearly polarized ultraviolet light, so that the SD1 molecules are completely oriented;

Sb4. Evenly coat the mixture of E7 liquid crystal and R5011 right-handed chiral molecules on the surface of the SD1 layer, and spin-coat at a speed of 3000 rpm for 30s; A spiral wire grid is formed in the mixture; the content of R5011 right-handed chiral molecules in the mixed solution is 3.50%;

Sb5. Carrying out ultraviolet light curing, so that the helical wire grid formed by rod-shaped chiral molecules is cured in the nematic liquid crystal layer;

Sb6. Repeat step Sb4 once, the difference is that the content of R5011 right-handed chiral molecules in the mixed solution is 2.75%;

Sb7. Carry out ultraviolet light curing, make the helical wire grid formed by rod-shaped chiral molecules solidify in the nematic liquid crystal layer;

Sb8. Repeat step Sb4 once, the difference is that the content of R5011 right-handed chiral molecules in the mixed solution is 2.27%;

Sb9. Carry out ultraviolet light curing, so that the helical wire grid formed by rod-shaped chiral molecules is cured in the nematic liquid crystal layer.

According to the red light band, green light band and blue light band, the chiral molecule content of the R5011 right-handed chiral molecule content in the mixed solution was calculated respectively. The calculation basis is as follows: taking the ordinary light refractive index n _o = 1.54, the extraordinary light refractive index n _e = 1.74, and the pitch p = 400nm, we can get It can be obtained that λ ₀ =656nm. Reflection spectral band Δλ=pΔn, where Δn=( _ne −n _o ) is the birefringence. According to this formula, Δλ=80nm can be obtained, that is, the reflection waveband is from 576nm to 736nm, and the right-handed circularly polarized light in the red light waveband is reflected. Meanwhile, pitch p=[(HTP)×X _c ] ⁻¹ . HTP is the helical twist force constant of the chiral additive, and X _c is the content of the chiral additive in the liquid crystal composition. By increasing the content X _c of the chiral additive, the helical pitch p can be reduced, and the right-handed circular polarizing beam splitting film 107 in the green and blue bands can be obtained. Taking the helical pitch p as 330nm and 260nm respectively, the λ ₀ is 541nm and 426nm respectively, and the wave band Δλ is 66nm and 52nm. Assuming that the HTP value is 110um ^-1 , the calculated contents of the red, green and blue bands are 2.27%, 2.75%, and 3.50%, respectively.

Through the above steps, the RGB three-layer multi-band circular polarization beam splitting film can be obtained, and its three working bands are respectively in red light, green light and blue light, basically covering the visible light band, and can realize circular polarization beam splitting in the visible light band.

Embodiment Three

A circular polarization beam splitting film, as shown in Figure 4, the pitch of the spiral wire grid gradually increases from top to bottom. This makes its working band continuously increase from top to bottom, and can realize a wide band of working wavelengths. The pitch p gradually increases from top to bottom to form a gradient distribution. According to the formula of λ ₀ =np, since the pitch p presents a gradient change, the obtained central reflection wavelength will also change accordingly, so its working band can also be greatly broadened.

The preparation method of the circular polarization beam splitting film of the present embodiment comprises the following steps:

Sc1. Evenly coat the photo-alignment agent SD1 on the cleaned substrate, and spin-coat at a speed of 3000 rpm for 30s;

Sc2. Bake the substrate on a hot table at 120° for 10 minutes;

Sc3. Attach another clean glass to the spin-coated SD1 layer substrate, and use AB glue to bond the joint, where the SD1 layer

On the inside of the bonding, a liquid crystal cell is formed;

Sc4. Combining bifunctional liquid crystalline polymerizable monomers, monofunctional liquid crystalline polymerizable monomers, photoinitiators and ultraviolet light absorbing

The dye mixed solution is poured into the liquid crystal cell;

Sc5. Using ultraviolet light for asymmetric irradiation, the polymer concentration is high on the side close to the ultraviolet light source, and low on the side away from the ultraviolet light,

Further, a liquid crystal layer with a gradient pitch is obtained.

Through the above steps, a broadband circularly polarized beam splitting film can be produced. In this third embodiment, the working bandwidth can be extended from the maximum bandwidth of 80nm in the first embodiment to 220nm.

Compared with the lamination of several layers of circular polarization beam splitting film in embodiment two, the scheme of the third embodiment only uses a single layer structure to realize the circular polarization beam splitting film of wide band, which makes it compared with that of the second embodiment The laminated structure has thinner film thickness, and fewer transmissive film layers, resulting in higher optical efficiency.

Embodiment four

A multi-band circular polarization beam-splitting film group is formed by laminating several layers of multi-band circular polarization beam-splitting films. As shown in FIG. 5 , the multi-band circular polarizing beam splitting film set 108 is formed by stacking visible light circular polarizing beam splitting films 105 . The multi-band circular polarization beam-splitting film group is formed by laminating several layers of multi-band circular polarization beam-splitting films. Although the extinction ratio of a single-layer film for visible light circularly polarizing beam-splitting film can only reach about 10 at present, the liquid crystal can be coated with multiple layers to form a multi-layer film structure. After coating the three-layer film structure, the extinction ratio can reach about 1000, that is, about 30dB, which is basically close to the level of the metal wire grid polarizing beam splitting film with the extinction ratio of 35dB.

Compared with the metal wire grid polarizing beam splitting film system in this embodiment 4, the multi-band circular polarizing beam splitting film group can approach the extinction ratio that the metal wire grid polarizing beam splitting film can achieve, which can meet the basic application requirements; secondly , the metal wire grid polarizing beam-splitting film system needs to convert circularly polarized light into linearly polarized light through a 1/4 wave plate for reflection or transmission. Polarized light is split into beams, which can further avoid the 45° phase error problem between the linear polarization beam splitting film and the 1/4 wave plate, thereby eliminating dark field ghosts; moreover, the processing of the metal wire grid polarizing beam splitting film and The preparation requires a complex process and high technical requirements, but it is easier to prepare a circularly polarizing beam splitting film by using cholesteric liquid crystals in Example 4.

Embodiment five

A VR display system as shown in Figure 1, comprising a display screen 101, a first linear polarizer 102, a first 1/4 wave plate 103, a semi-transparent and semi-reflective film 104, a visible light circular polarizing beam splitting film 105, a human eye sensor 106. The display screen 101 , the first linear polarizer 102 , the first 1/4 wave plate 103 , the transflective film 104 , and the visible light circular polarization beam splitter film 105 are all placed in parallel. The light beam emitted by the display screen 101 is polarized by the first linear polarizer 107 into linearly polarized light, and then passed through the first 1/4 wave plate 103 at an angle of 45° to perform phase delay to convert the linearly polarized beam into circularly polarized light. The obtained circularly polarized light passes through the semi-transparent and semi-reflective film 104 and then enters the visible light circularly polarized beam splitting film, because the inside of the visible light circularly polarized beam splitting film 105 is a right-handed chiral molecule, which is consistent with the direction of the incident right-handed circularly polarized light, and then It is reflected by the visible light polarizing beam splitting film 105 back to the semi-transparent and semi-reflective film 104, and the semi-transparent and semi-reflective film reflects it back and changes its handedness to left-handed. Since the handedness becomes left-handed, the handedness of the chiral molecule opposite to that of the visible light circular polarization beam splitting film 105 can be transmitted to the human eye for imaging.

As a comparison with the VR display system in the prior art as shown in Figure 6, it consists of a display screen 101, a first linear polarizer 102, a first 1/4 wave plate 103, a semi-transparent and semi-reflective film 104, a second 1/4 A wave plate 105a, a linear polarization splitting film 105b, and a second linear polarizer 109. In this application, the visible light circular polarizing beam splitting film 105 is used to replace the second 1/4 wave plate 105a, the linear polarizing beam splitting film 105b, and the second linear polarizing plate 109 in the prior art, which reduces the use of optical elements , can reduce the thickness of the VR display system; secondly, using the visible light circular polarization beam splitter film 105 to directly operate on the circularly polarized light without multiple conversions between the circularly polarized light and the linearly polarized light, the optical efficiency of the system can be improved At the same time, the conversion between circularly polarized light and linearly polarized light requires a 45° angle between the second 1/4 wave plate 105a and the linearly polarized beam-splitting film 105b, and the VR display system based on the circularly polarized beam-splitting film directly Polarized light processing can avoid the angle error between the two optical elements and eliminate dark field ghosts.

Claims (10)

1. A circular polarization beam splitting film, comprising a nematic liquid crystal layer, is characterized in that: in the nematic liquid crystal layer, a helical wire grid composed of rod-shaped chiral molecules is set along the surface normal direction; the helical pitch of the helical wire grid p, the average refractive index n of the nematic liquid crystal layer, and the central reflection wavelength λ ₀ satisfy: λ ₀ =np. 2. The circular polarization beam splitting film according to claim 1, characterized in that: the spiral wire grid adopts a continuously variable pitch structure. 3. The circular polarization beam splitting film according to claim 1, wherein the material of the nematic liquid crystal layer is E7 liquid crystal, and the rod-shaped chiral molecules are R5011 right-handed chiral molecules. 4. A multi-band circular polarization beam-splitting film, characterized in that it is formed by laminating several layers of circular polarization beam-splitting films as claimed in claim 1 or 3, wherein each layer of circular polarization beam-splitting film corresponds to a working band. 5. A multi-band circular polarizing beam-splitting film set, characterized in that: it is formed by laminating several layers of the multi-band circular polarizing beam-splitting film as claimed in claim 4. 6. A visible light circular polarization beam-splitting film, characterized in that: it is formed by laminating three layers of circular polarization beam-splitting films as claimed in claim 1, and the working bands of the circular polarization beam-splitting films of the three layers are respectively red light bands , green band and blue band. 7. The visible light circular polarization beam splitting film according to claim 6, characterized in that: the material of the nematic liquid crystal layer is E7 liquid crystal, and the rod-shaped chiral molecules adopt R5011 right-handed chiral molecules; from top to bottom The mass ratios of R5011 and E7 in the nematic liquid crystal layer are respectively: 2.07%-2.48%, 2.52%-3.03%, and 3.03%-3.62%. 8. A VR display system, characterized in that: comprising a display screen, a linear polarizer, a 1/4 wave plate, a semi-transparent and semi-reflective film, a visible light circular polarization beam splitting film as claimed in claim 6, and a human eye sensor; The display screen, the linear polarizer, the 1/4 wave plate, the semi-transparent and semi-reflective film, and the visible light circular polarization beam splitting film are placed in parallel; the light emitted by the display screen passes through the linear polarizer and the 1/4 wave plate in turn , a semi-transparent and semi-reflective film and the visible light circular polarizing beam-splitting film to obtain three-color circularly polarized light opposite to the handedness of the rod-shaped chiral molecule and transmit it to the human eye sensor for display. 9 . The VR display system according to claim 8 , wherein the semi-transparent and semi-reflective film is arranged on the concave surface of the plano-concave lens, or on the inner wall of the spherical shell lens. 10. A method for preparing a circularly polarizing beam splitting film, comprising the steps of: S1. Cleaning the substrate; uniformly coating the photo-alignment agent on the surface of the substrate; S2. Place the substrate on a hot stage to dry at high temperature, and obtain a photo-alignment layer on the substrate; S3. exposing the photo-alignment layer to linearly polarized ultraviolet light; S4. Evenly coating the mixture of nematic liquid crystal and rod-shaped chiral molecules on the surface of the photo-alignment layer; under the action of the photo-alignment layer, the rod-shaped chiral molecules form a spiral wire grid in the nematic liquid crystal; S5. Carry out ultraviolet light curing, so that the helical wire grid formed by rod-shaped chiral molecules is cured in the nematic liquid crystal layer.

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