Flat-plate beam-splitting polarization film and preparation method thereof

Abstract

The invention belongs to the technical field of precision optics, and particularly relates to a flat plate beam splitting polarization film and a preparation method thereof. According to the method, film system design software is adopted to carry out film system design on the flat plate beam splitting polarization film, and a film system design result of the flat plate beam splitting polarization film is obtained; and respectively plating the two bottom surfaces of the substrate according to the film system design result, and respectively obtaining the flat beam splitting polarization films on the two bottom surfaces of the substrate. The flat plate beam splitting polarization film prepared by the invention has a high extinction ratio (ER = Tp: Ts) gt; gt; 10000: 1, a p component and an s component of incident light can be effectively separated; the actual adjustable wavelength range is wide (> = 13nm), and the technical problems of low extinction ratio and narrow actual adjustable wavelength range of an optical film are solved. Meanwhile, the reliability test results of the flat plate beam splitting polarization film prepared by the method are OK; and the preparation method is convenient for mass production maintenance and batch preparation.

Description

Technical Field

[0001] The present invention belongs to the field of precision optical technology, and particularly relates to a flat beam-splitting polarization thin film and a preparation method thereof. Background Art

[0002] With the continuous development of society, the development of optical thin films has advanced by leaps and bounds. At present, the application of optical thin films is not limited to simple anti-reflection, shell appearance color decoration, etc. In the field of precision optics, it is often necessary for optical thin film products to highly separate P-polarized light and S-polarized light to obtain a high extinction ratio. At the same time, optical thin film products need to meet various stringent environmental tests (i.e., reliability tests).

[0003] However, the optical thin films disclosed in the prior art have problems of low extinction ratio and relatively narrow actual adjustable wavelength range. Summary of the Invention

[0004] The purpose of the present invention is to provide a flat beam-splitting polarization thin film and a preparation method thereof. The flat beam-splitting polarization thin film prepared by the present invention has a high extinction ratio, and the extinction ratio (ER = Tp:Ts) >> 10000:1; and has a wide actual adjustable wavelength range, solving the technical problems of low extinction ratio and relatively narrow actual adjustable wavelength range existing in optical thin films.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions: The present invention provides a preparation method of a flat beam-splitting polarization thin film, including the following steps: Using film system design software to design the film system of the flat beam-splitting polarization thin film. The flat beam-splitting polarization thin film is formed by alternately laminating low-refractive-index materials and high-refractive-index materials to obtain the film system design result of the flat beam-splitting polarization thin film. The initial film stack used in the film system design is as shown in Formula 1: G0 / (0.5HL0.5H) S 0.5HLHL0.5H (0.5HL0.5H) S / AIR Formula 1; In Formula 1: G0 represents the substrate, AIR represents the incident medium, H represents the high-refractive-index material, L represents the low-refractive-index material, S represents the repetition frequency of the "(0.5HL0.5H)" unit, and S≥5; The film system design result includes the single-layer film thickness of the high-refractive-index material, the single-layer film thickness of the low-refractive-index material, the number of film layers of the high-refractive-index material, the number of film layers of the low-refractive-index material, the total number of layers, and the total thickness; Coating is respectively carried out on the two bottom surfaces of the substrate according to the film system design result, and the flat beam-splitting polarization thin films are respectively obtained on the two bottom surfaces of the substrate.

[0006] Preferably, the high refractive index material is titanium trioxide; the low refractive index material is silicon dioxide.

[0007] Preferably, the material of the substrate is ultraviolet fused silica; The thickness of the substrate is 0.6 - 6 mm.

[0008] Preferably, the film system design software includes TFCalc optical thin film design software or Essential Macleod optical thin film design software.

[0009] Preferably, the conditions for the film system design include: the incident angle is 45°; the incident medium is air; the exit medium is ultraviolet fused silica; the transmittance of p-polarized light in the target band of the flat beam splitting polarization film is set to 100%, and the transmittance of s-polarized light is set to 0.

[0010] Preferably, the conditions for plating include: the initial vacuum degree ≤ 3×10 -3 Pa; the substrate heating temperature is 150 - 200 °C; the film formation rate of the high refractive index material is 0.2 - 0.3 nm / s, and the film formation rate of the low refractive index material is 0.3 - 0.7 nm / s.

[0011] Preferably, before plating, it also includes ion source cleaning of the substrate. The vacuum degree of the ion source cleaning ≤ 3×10 -3 Pa, the time is 2 - 5 min, and the heating temperature of the substrate during ion source cleaning is 150 - 200 °C.

[0012] Preferably, the target band of the flat beam splitting polarization film is the visible light and near-infrared band.

[0013] Preferably, the visible light and near-infrared band is 400 - 2500 nm.

[0014] The present invention provides a flat beam splitting polarization film prepared by the preparation method described in the above technical solution. The extinction ratio of the flat beam splitting polarization film > 10000:1.

[0015] The present invention provides a preparation method of a flat beam splitting polarization film, including the following steps: using film system design software to perform film system design on the flat beam splitting polarization film. The flat beam splitting polarization film is formed by alternately laminating a low refractive index material and a high refractive index material to obtain the film system design result of the flat beam splitting polarization film. The initial film stack used in the film system design is as shown in Formula 1: G0 / (0.5HL0.5H) S 0.5HLHL0.5H (0.5HL0.5H) S / AIR Formula 1; in Formula 1: G0 represents the substrate, AIR represents the incident medium, H represents the high refractive index material, L represents the low refractive index material, S represents the repetition frequency of the "(0.5HL0.5H)" unit, and S ≥ 5; the film system design results include the single-layer film thickness of the high refractive index material, the single-layer film thickness of the low refractive index material, the number of film layers of the high refractive index material, the number of film layers of the low refractive index material, the total number of layers and the total thickness; plating is carried out on the two bottom surfaces of the substrate according to the film system design results respectively, and the flat beam-splitting polarization thin film is obtained on the two bottom surfaces of the substrate respectively. By reasonably setting the initial film stack formula, the present invention precisely optimizes the film system of the flat beam-splitting polarization thin film through film system design software, and then carries out plating according to the film system design results. Moreover, the present invention adopts a double-sided plating method on the substrate, and the obtained polarization beam-splitting thin film has excellent polarization beam-splitting effect. The flat beam-splitting polarization thin film prepared by the present invention has a high extinction ratio, and the extinction ratio (ER = Tp:Ts) >> 10000:1, which can effectively separate the p-component and s-component of the incident light; and the actual adjustable wavelength range is wide (≥ 13 nm), solving the technical problems of low extinction ratio and narrow actual adjustable wavelength range existing in optical thin films. At the same time, the reliability test results (including chemical stability, adhesion, friction test, low temperature test, high temperature test, boiling water, constant humidity and temperature gradient) of the flat beam-splitting polarization thin film prepared by the present invention are all OK; and the preparation method is convenient for mass production maintenance and batch preparation.

[0016] Further, in the present invention, the conditions for the film system design include: the incident angle is 45°. Different from traditional flat beam-splitting polarization thin films, the incident angle of the light of the flat beam-splitting polarization thin film prepared by the present invention is 45°, which is convenient for installation, debugging and use.

[0017] Further, in the present invention, the thickness of the substrate is 0.6 - 6 mm. By optimizing the thickness of the substrate, the present invention can obtain a flat beam-splitting polarization thin film with better performance. When the thickness of the substrate < 0.6 mm, the anti-extrusion ability of the substrate after coating decreases and the risk of being fragile increases. When the thickness of the substrate > 6 mm, the substrate is too thick and will affect the light transmission. Description of the Drawings

[0018] Figure 1 It is the design curve of the 532 nm flat beam-splitting polarization film in Example 1; Figure 2 It is the test curve of the 532 nm flat beam-splitting polarization film in Example 1; Figure 3 It is the design curve of the 1310 nm flat beam-splitting polarization film in Example 2; Figure 4 It is the test curve of the 1310 nm flat beam-splitting polarization film in Example 2. Detailed Embodiments

[0019] The present invention provides a method for preparing a flat beam-splitting polarization film, comprising the following steps: Using film system design software to design the film system of the flat beam-splitting polarization film, the flat beam-splitting polarization film is formed by alternately laminating low-refractive-index materials and high-refractive-index materials, obtaining the film system design result of the flat beam-splitting polarization film, and the initial film stack used in the film system design is as shown in Formula 1: G0 / (0.5HL0.5H) S 0.5HLHL0.5H (0.5HL0.5H) S / AIR Formula 1; In Formula 1: G0 represents the substrate, AIR represents the incident medium, H represents the high-refractive-index material, L represents the low-refractive-index material, S represents the repetition frequency of the "(0.5HL0.5H)" unit, and S≥5; The film system design result includes the single-layer film thickness of the high-refractive-index material, the single-layer film thickness of the low-refractive-index material, the number of film layers of the high-refractive-index material, the number of film layers of the low-refractive-index material, the total number of layers, and the total thickness; Coatings are respectively carried out on the two bottom surfaces of the substrate according to the film system design result, and the flat beam-splitting polarization films are respectively obtained on the two bottom surfaces of the substrate.

[0020] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well-known to those skilled in the art.

[0021] The present invention uses film system design software to design the film system of the flat beam-splitting polarization film, the flat beam-splitting polarization film is formed by alternately laminating low-refractive-index materials and high-refractive-index materials, obtaining the film system design result of the flat beam-splitting polarization film, and the initial film stack used in the film system design is as shown in Formula 1: G0 / (0.5HL0.5H) S 0.5HLHL0.5H (0.5HL0.5H) S / AIR Formula 1; In Formula 1: G0 represents the substrate, AIR represents the incident medium, H represents the high-refractive-index material, L represents the low-refractive-index material, S represents the repetition frequency of the "(0.5HL0.5H)" unit, and S≥5; The film system design result includes the single-layer film thickness of the high-refractive-index material, the single-layer film thickness of the low-refractive-index material, the number of film layers of the high-refractive-index material, the number of film layers of the low-refractive-index material, the total number of layers, and the total thickness.

[0022] In the present invention, the high-refractive-index material is preferably titanium pentoxide. The low-refractive-index material is preferably silicon dioxide. The titanium pentoxide and the silicon dioxide have the characteristics of high transmittance, low absorption, and high chemical stability.

[0023] In the present invention, it can be seen from the initial film stack formula 1 that a high refractive index material layer, a low refractive index material layer, a high refractive index material layer, a low refractive material layer, ..., a high refractive index material layer, and a low refractive material layer are sequentially arranged on the substrate.

[0024] In the present invention, the film system design software preferably includes TFCalc optical thin film design software or EssentialMacleod optical thin film design software, and in the embodiment, it can be TFCalc film system design software.

[0025] In the present invention, the conditions for the film system design preferably include: the incident angle is 45°; the incident medium is air; the output medium is ultraviolet fused quartz; the p-polarized light transmittance in the target band of the flat beam splitting polarization film is set to 100%, and the s-polarized light transmittance is set to 0.

[0026] In the present invention, the target wavelength of the flat beam splitting polarizing film is preferably visible light and near infrared wavelength. The visible light and near infrared wavelength is preferably 400-2500 nm, and in the embodiment, it can be 405 nm, 532 nm, 780 nm, 808 nm, 1030 nm, 1064 nm, 1310 nm or 1550 nm.

[0027] After obtaining the film system design result, the present invention performs coating on the two bottom surfaces of the substrate respectively according to the film system design result, and obtains the flat beam splitting polarization film on the two bottom surfaces of the substrate respectively.

[0028] In the present invention, the coating is preferably carried out by using an evaporation light-controlled coating machine, which may be an Aluga series evaporation coating machine in the embodiment. The evaporation light-controlled coating machine can accurately monitor the film thickness.

[0029] In the present invention, the material of the substrate is ultraviolet fused silica (UVFS). The thickness of the substrate is preferably 0.6-6 mm, more preferably 1-5 mm. The substrate is preferably a cylinder or a prism. The shape of the two bottom surfaces (i.e., the coating surface) of the substrate can be circular or square. In the embodiment, the substrate can be a cylindrical ultraviolet fused silica glass with a diameter of 25.4 mm.

[0030] In the present invention, before the plating, the present invention preferably further comprises cleaning the substrate with an ion source. The present invention preferably places the substrate in a collar, and places the collar with the substrate on a hollow umbrella of the machine; and then performs ion source cleaning. The vacuum degree of the ion source cleaning is preferably ≤3×10 -3Pa, the time is preferably 2~5min, and the heating temperature of the substrate during the ion source cleaning is preferably 150~200℃, and can be 180℃ in the embodiment. The present invention can reduce the ion absorption of the substrate during the ion source cleaning process by controlling the heating temperature of the substrate to 150~200℃ during the ion source cleaning. In the present invention, the voltage of the ion source cleaning is preferably 800~850V; the current is preferably 800~850mA. The gas used for the ion source cleaning is preferably oxygen and argon, and the flow ratio of the oxygen and argon is preferably 60:8. The flow rate of the oxygen is preferably 60sccm, and the argon includes a first argon and a second argon, the flow rate of the first argon (ion source argon) is preferably 0sccm, and the flow rate of the second argon (neutralizer argon) is preferably 8sccm.

[0031] In the present invention, the plating is performed after the ion source is cleaned. The plating preferably includes first plating a first flat beam splitting polarization film on one bottom surface (i.e., the first bottom surface) of the substrate; and then plating a second flat beam splitting polarization film on the other bottom surface (i.e., the second bottom surface) of the substrate. The film layer structure and composition of the first flat beam splitting polarization film and the second flat beam splitting polarization film are the same.

[0032] In the present invention, during the plating, the present invention preferably places the substrate in the ring, and places the ring with the substrate on the hollow umbrella of the machine. The plating conditions preferably include: the initial vacuum degree is preferably ≤3×10 -3 Pa; the substrate heating temperature is preferably 150-200° C., and in the embodiment, it can be 180° C. The film forming rate of the high refractive index material is preferably 0.2-0.3 nm / s, and the film forming rate of the low refractive index material is preferably 0.3-0.7 nm / s.

[0033] In the present invention, the ion source plated with a high refractive index material is preferably Ti 3 O 5 ; The voltage is preferably 800~850V; The current is preferably 800~850mA; The gases used are preferably oxygen and argon, and the flow ratio of oxygen to argon is preferably 75:16; The flow rate of oxygen is preferably 75sccm, and the argon includes a first argon gas and a second argon gas, the flow rate of the first argon gas (ion source argon gas) is preferably 8sccm, and the flow rate of the second argon gas (neutralizer argon gas) is preferably 8sccm.

[0034] In the present invention, the ion source plated with the low refractive index material is preferably SiO 2; The voltage is preferably 800 - 850V; the current is preferably 800 - 850mA; the gas used is preferably oxygen and argon, and the flow rate ratio of the oxygen and argon is preferably 60:8. The flow rate of the oxygen is preferably 60 sccm. The argon includes first argon and second argon. The flow rate of the first argon (ion source argon) is preferably 0 sccm, and the flow rate of the second argon (neutralizer argon) is preferably 8 sccm.

[0035] In the present invention, the coating preferably includes: sequentially coating a high refractive index material, a low refractive index material, a high refractive index material, a low refractive index material,..., a high refractive index material, and a low refractive index material on the surface of the substrate.

[0036] The present invention provides a flat beam splitting polarization film prepared by the preparation method described in the above technical solution, and the extinction ratio of the flat beam splitting polarization film > 10000:1.

[0037] In the present invention, the flat beam splitting polarization film includes a first flat beam splitting polarization film located on the first bottom surface of the substrate and a second flat beam splitting polarization film located on the second bottom surface of the substrate. The film layer structures and compositions of the first flat beam splitting polarization film and the second flat beam splitting polarization film are the same.

[0038] In the present invention, the extinction ratio (ER) of the first flat beam splitting polarization film or the second flat beam splitting polarization film is the ratio of the p-polarized light transmittance (Tp) to the s-polarized light transmittance (Ts).

[0039] The total extinction ratio of the first flat beam splitting polarization film and the second flat beam splitting polarization film is the product of the extinction ratio (ER1) of the first flat beam splitting polarization film and the extinction ratio (ER2) of the second flat beam splitting polarization film.

[0040] In the present invention, the actual adjustable wavelength range of the flat beam splitting polarization film is wide, and the actual adjustable wavelength range of the flat beam splitting polarization film ≥ 13 nm, which is convenient for mass production maintenance and batch preparation.

[0041] In the present invention, the flat beam splitting polarization film is a visible light and near-infrared single-point beam splitting film, and the wavelength band range of the flat beam splitting polarization film is 400 - 2500 nm. In the examples, it can be 405 nm, 532 nm, 780 nm, 808 nm, 1030 nm, 1064 nm, 1310 nm or 1550 nm.

[0042] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in conjunction with examples, but they cannot be understood as limiting the protection scope of the present invention.

[0043] Example 1 This embodiment provides a method for preparing a flat beam-splitting polarization thin film. The specification requirements of the flat beam-splitting polarization thin film prepared in this embodiment are as follows: single-point wavelength in the band is 532 nm, p-polarized light transmittance: Tp > 93%, s-polarized light transmittance Ts < 0.5%, and extinction ratio ER = Tp:Ts > 10000:1.

[0044] Specifically, it includes the following steps: 1. Common coating materials such as silicon dioxide (SiO 2 ) and titanium pentoxide (Ti 3 O 5 ) are selected because they have stable chemical properties in the visible light range. The substrate material is selected as ultraviolet fused silica (UVFS), whose transparent region ranges from about 185 to 2100 nm and has stable performance.

[0045] 2. Design using TFC film stack design software, set the incident angle to 45°, the incident medium is air (AIR), and both the substrate and the outgoing medium are set to use UVFS. Given the specification requirement limit conditions: a. For 525 - 550 nm, the p-polarized light transmittance Tp is set to 100%, b. For 525 - 550 nm, the s-polarized light transmittance Ts is set to 0. This setting has a wider wavelength range and stricter transmittance specifications than the required specifications. The purpose is to obtain a better design to ensure the stability of the thin film preparation scheme and sufficient wavelength margin is beneficial for mass production. The initial film stack is: G0 / (0.5HL0.5H) S 0.5HLHL0.5H (0.5HL0.5H) S / AIR, where G0 represents the substrate, AIR represents the incident medium is air, H represents the high refractive index material, in this embodiment H is titanium pentoxide (Ti 3 O 5 ), L represents the low refractive index material, in this embodiment L is silicon dioxide (SiO 2 ), S represents the repetition frequency of the "(0.5HL0.5H)" unit, S = 7. After optimization, the film layer structure is as shown in Table 1, with a total of 58 layers and a total thickness of about 4 μm. The first layer in contact with the substrate is titanium pentoxide, the second layer is silicon dioxide, the third layer is titanium pentoxide, the fourth layer is silicon dioxide,......, titanium pentoxide and silicon dioxide alternate repeatedly, and finally ends with the 58th layer: silicon dioxide. The design curve is as Figure 1 shown, Figure 1 the angle in it is 45.0°, and the relevant wavelength is 550.0 nm. Observing Figure 1 the shown design curve, Tp is about 99.95%, and Ts is about 3.7×10 -4(%), i.e., 0.00037%. Roughly calculated, ER = 270135, and this is only the single-sided ER, which is already far greater than 10000:1. Therefore, the design evaluation of this embodiment meets the requirements.

[0046] Table 1 Design film layer structure data of Example 1

[0047] 3. Use an Aluga vacuum and evaporation optoelectronic controlled coating machine to deposit the designed film system. First, place the cleaned substrate (here it is a cylindrical ultraviolet fused silica glass with a diameter of 25.4 mm and a height of 5 mm) in the pre-prepared collar, and place the collar on the hollow umbrella of the machine table to prepare for coating (in this embodiment, it is necessary to coat both bottom surfaces of the cylindrical substrate, and the side surfaces do not need to be coated). Close the chamber door and evacuate. When the vacuum reaches the set 3.0×10 -3 Pa, perform ion source cleaning for 3 minutes. The detailed ion source parameters are shown in Table 2. After the cleaning is completed, start film formation. The first layer in the design that contacts the substrate directly is titanium pentoxide (Ti 3 O 5 ); then deposit the second layer, i.e., silicon dioxide (SiO 2 ); then deposit the third layer, i.e., titanium pentoxide (Ti 3 O 5 ); then deposit the fourth layer, i.e., silicon dioxide (SiO 2 ); and so on, repeating and overlapping the deposition until the 58th layer of silicon dioxide is deposited, that is, the coating of the first bottom surface is completed, and a flat beam splitting polarization film is obtained on the first bottom surface.

[0048] 4. Next, complete the preparation of the film on the second bottom surface, that is, turn over the substrate that has been coated on the first bottom surface, close the chamber door and evacuate. When the vacuum reaches the set 3.0×10 -3 Pa, perform ion source cleaning. After the cleaning is completed, start film formation on the second surface. The film formation steps and parameters are the same as those for coating the first bottom surface until the end, that is, the preparation of the flat beam splitting polarization film on the second bottom surface is completed.

[0049] In the preparation process of the flat beam splitting polarization film in this embodiment, heating + full-process ion source assisted coating is adopted, where the heating temperature is 180°C, the film formation rate of SiO 2 is 0.4 nm / s, and the film formation rate of Ti 3 O 5 is 0.25 nm / s. The detailed coating parameters are shown in Table 3.

[0050] Table 2 Ion source cleaning parameter table in Example 1

[0051] Table 3 Coating Parameters in Example 1

[0052] The transmittances of p-polarized light and s-polarized light of the coated substrate were measured, and then the extinction ratio was calculated to detect whether it meets the specifications. Measured with a Hitachi UH4150 spectrophotometer, the transmission curves of the two surfaces were obtained as Figure 2 shown, where the p-polarized transmission of the first bottom surface is denoted as Tp-1 and Ts-1, and the p-polarized transmission of the second bottom surface is denoted as Tp-2 and Ts-2. The detailed extinction ratio data are shown in Table 4.

[0053] Table 4 Extinction Ratio Data in Example 1

[0054] It can be analyzed from Table 3 and Table 4 that the total extinction ratio of the flat beam-splitting polarization film prepared in this example at 532 nm on the first surface and the second surface of the substrate is far greater than 10000:1; in Table 4, Tp min = 94.7% > 93%, Ts max = 0.12% < 0.5%, that is, the reflectivity of s-polarized light (Rs) > 99.5%, meeting the specification requirements. Although the specification only requires a single point at 532 nm, this example actually meets the requirements from 527 to 540 nm, indicating that the controllable range of the film system prepared in this example is 13 nm, which can meet industrial production.

[0055] The flat beam-splitting polarization film product prepared in Example 1 was subjected to reliability tests, including adhesion, chemical stability, thermal shock, and high temperature and high humidity. The results were all OK, indicating that the preparation method of the flat beam-splitting polarization film provided in this example can withstand the environmental test. The test results are shown in Table 5. The standards for the test items in Table 5 are GBT 26332.3-2015 Optics and Photonics - Optical Thin Films - Part 3: Environmental Adaptability.

[0056] Table 5 Reliability Results of the Product in Example 1

[0057] Example 2 This example provides a method for preparing a flat beam-splitting polarization film. The specification requirements of the flat beam-splitting polarization film prepared in this example are: a single point at 1310 nm in the wavelength band, p-polarized light transmission: Tp > 96%, s-polarized light transmission Ts < 0.5%, and extinction ratio ER = Tp:Ts > 10000:1.

[0058] Specifically, it includes the following steps: 1. The coating materials selected are common silicon dioxide (SiO 2 ) and titanium pentoxide (Ti 3 O5 ) because it has stable chemical properties in the visible light range. The substrate material is selected as ultraviolet fused silica (UVFS), whose transparent range is about 185 - 2100 nm and the performance is stable.

[0059] 2. Design is carried out using TFC film system design software. The incident angle is set at 45°, the incident medium is air (AIR), and both the substrate and the outgoing medium are set to use UVFS. Given the specification requirements and limitations: a. For 1290 - 1330 nm, the transmittance Tp of p-polarized light is set to 100%, b. For 1290 - 1330 nm, the transmittance Ts of s-polarized light is set to 0. This setting has a wider wavelength range and stricter transmittance specifications than the required specifications. The purpose is to obtain a better design to ensure the stability of the thin film preparation scheme and sufficient wavelength margin is beneficial for mass production. The initial film stack is: G0 / (0.5HL0.5H) S 0.5HLHL0.5H (0.5HL0.5H) S / AIR, where G0 represents the substrate, AIR represents the incident medium as air, H represents the high refractive index material, and in this embodiment, H is titanium pentoxide (Ti 3 O 5 ) and L represents the low refractive index material. In this embodiment, L is silicon dioxide (SiO 2 ), S represents the repetition frequency of the "(0.5HL0.5H)" unit, and S = 7. After optimization, the film layer structure is as shown in Table 6, with a total of 52 layers and a total thickness of about 9 μm. The first layer in contact with the substrate is titanium pentoxide, the second layer is silicon dioxide, the third layer is titanium pentoxide, the fourth layer is silicon dioxide,... Titanium pentoxide and silicon dioxide alternate repeatedly, and finally end with the 52nd layer: silicon dioxide. The design curve is as Figure 3 shown, Figure 3 the angle in it is 45.0° and the relevant wavelength is 1220.nm. Observing Figure 3 the shown design curve, Tp is about 99.98% and Ts is about 0.00214%. Rough calculation shows that ER = 46719, and the single-sided ER is already far greater than 10000:1. Therefore, the design evaluation of this embodiment meets the requirements.

[0060] Table 6 Design film layer structure data of Example 2

[0061] 3. Use an Aluga vacuum evaporation optical control coating machine to deposit the designed film system, and the deposition parameters are the same as those in Example 1.

[0062] 4. Test the transmittance of p-polarized light and s-polarized light through the coated substrate, and then calculate the extinction ratio to detect whether it meets the specifications. Use a Hitachi UH4150 spectrophotometer for testing, and obtain the transmittance curves of the two surfaces as shown in Figure 4 . Among them, the polarized transmittance of the first bottom surface is expressed as Tp-1 and Ts-1, and the polarized transmittance of the second bottom surface is expressed as Tp-2 and Ts-2. The detailed extinction ratio data are shown in Table 7.

[0063] Table 7 Extinction ratio data table in Example 2

[0064] From Figure 4 and the analysis of Table 7, it can be seen that the total extinction ratio of the flat beam-splitting polarization film prepared in this example at the first surface and the second surface of the substrate at 1310 nm is much greater than 10000:1; in Table 7, Tp min = 97.52% > 96%, Ts max = 0.06335% < 0.5%, that is, the reflectivity of s-polarized light (Rs) > 99.5%, meeting the specification requirements. And the fluctuation range of the film system curve is about 15 nm, (1301~1316 nm), which can meet industrial production.

[0065] Perform reliability tests on the flat beam-splitting polarization film products prepared in Example 2. The items are the same as those in Example 1, and the results are all OK, indicating that the preparation method of the flat beam-splitting polarization film provided in Example 2 can withstand environmental tests. The test results are shown in Table 8. The standards for the test items in Table 8 are GBT 26332.3-2015 Optics and Photonics - Optical Thin Films - Part 3: Environmental Adaptability.

[0066] Table 8 Reliability results of the products in Example 2

[0067] From the above examples, it can be seen that the present invention accurately optimizes the film system of the flat beam-splitting polarization film through a film system design software by reasonably setting the initial film stack formula, and then performs coating according to the film system design results. Moreover, the present invention adopts a double-sided coating method on the substrate, and the obtained polarization beam-splitting film has excellent polarization beam-splitting effect. The flat beam-splitting polarization film prepared by the present invention has a high extinction ratio, and the extinction ratio (ER = Tp:Ts) >> 10000:1, which can effectively separate the p-component and s-component of the incident light; and the actual adjustable wavelength range is wide (≥13 nm), solving the technical problems of low extinction ratio and narrow actual adjustable wavelength range existing in optical thin films. At the same time, the reliability test results of the flat beam-splitting polarization film prepared by the present invention (including chemical stability, adhesion, friction test, low-temperature test, high-temperature test, boiling water test, constant humidity and heat, temperature gradient change) are all OK; and the preparation method is convenient for mass production maintenance and batch preparation.

[0068] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all of them. Other embodiments can also be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a flat beam splitting polarizing film, characterized in that: The following steps are involved: Film system design software is used to design a flat beam splitting polarization film. The flat beam splitting polarization film is formed by alternately stacking low refractive index materials and high refractive index materials. The film system design result of the flat beam splitting polarization film is obtained. The initial film stack used in the film system design is shown in Formula 1: G0 / (0.5HL0.5H) S 0.5HLHL0.5H (0.5HL0.5H) S / AIR Formula 1; In formula 1, G0 represents the substrate, AIR represents the incident medium, H represents the high refractive index material, L represents the low refractive index material, S represents the repetition frequency of the "(0.5HL0.5H)" unit, S≥5; The film system design results include the single-layer thickness of the high-refractive-index material, the single-layer thickness of the low-refractive-index material, the number of film layers of the high-refractive-index material, the number of film layers of the low-refractive-index material, the total number of layers and the total thickness; The two bottom surfaces of the substrate are respectively plated according to the film system design result, and the flat beam splitting polarization film is obtained on the two bottom surfaces of the substrate respectively.

2. The preparation method according to claim 1, characterized in that: The high refractive index material is titanium pentoxide; the low refractive index material is silicon dioxide.

3. The preparation method according to claim 1, characterized in that: The material of the substrate is ultraviolet fused quartz; The thickness of the substrate is 0.6-6 mm.

4. The preparation method according to claim 1, characterized in that: The film system design software includes TFCalc optical thin film design software or Essential Macleod optical thin film design software.

5. The preparation method according to any one of claims 1 to 4, characterized in that The film system design conditions include: the incident angle is 45°; the incident medium is air; the output medium is ultraviolet fused quartz; the p-polarized light transmittance of the flat beam splitting polarization film in the target band is set to 100%, and the s-polarized light transmittance is set to 0.

6. The preparation method according to claim 1, characterized in that: The plating conditions include: initial vacuum degree ≤ 3×10 -3 Pa; the substrate heating temperature is 150~200℃; the film forming rate of the high refractive index material is 0.2~0.3nm / s, and the film forming rate of the low refractive index material is 0.3~0.7nm / s.

7. The preparation method according to claim 1 or 6, characterized in that: Before the plating, the substrate is further subjected to ion source cleaning, wherein the vacuum degree of the ion source cleaning is ≤3×10 -3 Pa, the time is 2-5 min, and the heating temperature of the substrate during the ion source cleaning is 150-200°C.

8. The preparation method according to claim 1, characterized in that: The target waveband of the flat beam splitting polarization film is the visible light and near infrared waveband.

9. The preparation method according to claim 8, characterized in that: The visible light and near infrared bands are 400-2500nm.

10. The flat beam splitting polarizing film prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The extinction ratio of the flat beam splitting polarization film is greater than 10000:1.

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