A prism pbs beam splitting film with air gap in silicon substrate in mid-wave infrared

Abstract

The application discloses a prism PBS beam splitting film with an air gap in a middle wave infrared band of a silicon substrate, and has the structure of S / aLbHcLdHeLfHgLhHiA / S, wherein S represents the silicon substrate, A represents the air gap, H represents Ge, and L represents SiO; a-i represent the coefficients of the quarter reference wavelength optical thickness of the first layer to the eighth layer. The application provides the prism PBS beam splitting film with the air gap in the middle wave infrared band of the silicon substrate, adopts a glue-free gluing method, avoids the influence of the glue on the optical indicators in the light aperture, has good water resistance, and has durable, stable film layers and high transmittance.

Description

Technical Field

[0001] The invention relates to a prism PBS beam splitter film with an air gap in a silicon substrate mid-wave infrared band, belonging to the technical field of optical films. Background Art

[0002] A PBS polarizing beamsplitter prism is an optical component that can separate incident unpolarized light into two perpendicular linearly polarized beams. The P beam is fully transmitted, while the S beam is reflected. This component is constructed by gluing two right-angle prisms together, with a PBS beamsplitter coating applied to the prism's bevel.

[0003] PBS polarizing beam splitter prisms are almost still in the stage of foreign monopoly. The domestic technology is still immature, and they are generally glued with colloids. The refractive index of the colloid will affect the optical indicators, making the extinction ratio or transmittance unattainable; and the film layer is easy to absorb moisture, with poor durability and stability and low transmittance. Summary of the Invention

[0004] The present invention provides a silicon-based medium-wave infrared band air-gap prismatic PBS beam splitter film, which adopts a glue-free bonding method to avoid the influence of colloid on optical indicators within the light-clearing aperture; has good water resistance, a durable and stable film layer, and a high transmittance greater than 98.5%.

[0005] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0006] A prismatic PBS beam splitter film with a silicon substrate and a mid-wave infrared band and an air gap has a structure of: S / aLbHcLdHeLfHgLhHiA / S, wherein S represents the Si substrate, A represents the air gap, H represents Ge, and L represents SiO; a--i represent coefficients of a quarter reference wavelength optical thickness of the first to eighth layers.

[0007] After designing and optimizing different membrane systems, this application finally obtained a 9-layer membrane structure: Si substrate / SiO / Ge / SiO / Ge / SiO / Ge / SiO / Ge / Air(SiO2) / Si substrate, that is, the order from the first Si substrate to the second Si substrate: the first, third, fifth, and seventh layers are SiO layers, the second, fourth, sixth, and eighth layers are Ge layers, and the ninth layer is an Air gap layer (the supporting frame is made of SiO2, and the inner side of the supporting frame is an Air gap).

[0008] Research has found that if fluoride is used in combination with the film layer of the present application, the microstructure of the film layer is prone to porous columns, soft texture, and easy to absorb water vapor, resulting in poor durability of the components; by alternately plating SiO (low refractive index material) and Ge (high refractive index material), and at the same time using SiO2 to plate the support frame in the air gap, and using the air gap as an equivalent film layer, a film system structure with a small absorption coefficient and high transmittance in the mid-infrared range is obtained, thereby improving the optical performance and film stability.

[0009] In order to further take into account the optical and mechanical properties of the film, the reference wavelength is 4.5 μm, the value of a is 0.25~0.29, the value of b is 0.79~0.83, the value of c is 0.71~0.75, the value of d is 0.77~0.81, the value of e is 0.90~0.94, the value of f is 0.77~0.81, the value of g is 0.71~0.75, the value of h is 0.83~0.87, and the value of i is 0.1~0.15.

[0010] More preferably, the physical thickness of the aL layer is 170±20 nm, the physical thickness of the bH layer is 230±20 nm, the physical thickness of the cL layer is 460±30 nm, the physical thickness of the dH layer is 220±20 nm, the physical thickness of the eL layer is 580±50 nm, the physical thickness of the fH layer is 220±20 nm, the physical thickness of the gL layer is 460±30 nm, the physical thickness of the hH layer is 240±20 nm, and the physical thickness of the iA layer is 140±10 nm. The physical thickness of the aL layer refers to the physical thickness of the film layer at the position corresponding to aL, and the meanings of the remaining layers are similar.

[0011] The above-mentioned Si substrate has two pieces of identical structure, which are put together, and the beam splitting film is arranged between the two Si substrates. There is no colloidal layer in the thickness direction of the beam splitting film, which completely avoids the influence of the colloidal layer on the optical performance.

[0012] As one of the specific preferred implementation schemes, both Si substrates are right-angled triangular prism structures, the beam splitting film is arranged on the inclined surface of one of the right-angled triangular prism structures, and a supporting frame is arranged along the periphery of the inclined surface of the other right-angled triangular prism structure. The inclined surfaces of the two right-angled triangular prism structures are brought toward each other, and the supporting frame is bonded to the periphery of the beam splitting film to form a rectangular structure, and an air gap is formed inside the supporting frame; the supporting frame is made of SiO2, and the evaporation rate of SiO2 is controlled at 0.5-1nm / s.

[0013] The above-mentioned supporting frame and the inclined surface of another right-angled triangular prism structure are combined together by utilizing the attraction between film material molecules, without the need for optical glue, thus fundamentally avoiding the influence of colloid.

[0014] The aforementioned support frame is provided along either the ends or all four sides of the beam-splitting membrane. Specifically, the support frame is a square frame structure provided along all four sides of the beam-splitting membrane. Alternatively, the support frame is provided as support bars at both ends of the beam-splitting membrane, with the bars being parallel to each other and providing support. This provides isolation from the outside air, reducing air erosion on the membrane layer, while also forming an air gap to prevent the colloid from affecting optical performance. The thickness of the support frame is also the thickness of the air gap layer.

[0015] The coating method of the film layer will also affect the mechanical and optical properties of the film layer. After long-term research and development practice, it was found that the preferred coating process is: the above-mentioned aL layer, cL layer, eL layer and gL layer are coated with a barrier evaporation source; the bH layer, dH layer, fH layer and hH layer are coated with an electron gun evaporation source.

[0016] More preferably, the evaporation rate of SiO is controlled within 0.5-1 nm / s; and the evaporation rate of Ge is controlled within 0.3-0.5 nm / s.

[0017] The technologies not mentioned in this invention are all referred to the prior art.

[0018] The silicon-based medium-wave infrared air-gap glued prism PBS beam splitter film of the present invention uses silicon as a substrate and adopts a design structure of a film system with an air gap. By improving the film layer structure and adopting a glue-free bonding method between the film layers, the influence of the colloid on the optical indicators within the light aperture is avoided. By effectively selecting the coating material and reasonably controlling various process parameters, the air gap is used as the equivalent film layer, and a multi-layer thin film is plated on the substrate, so that the coating indicator extinction ratio reaches 2000:1. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the PBS beam splitter layer structure of a silicon-based mid-wave infrared band air gap cemented prism;

[0020] Figure 2 The cross-sectional view of a cemented prism with an air gap in the mid-wave infrared band on a silicon substrate;

[0021] Figure 3 : is the design curve of the PBS beam splitter layer of the silicon substrate mid-wave infrared band air gap cemented prism in the embodiment;

[0022] Figure 4 This is a test curve of the PBS beam splitter layer of the silicon substrate mid-wave infrared band air gap cemented prism in the embodiment;

[0023] In the figure, 1 is the film layer, 2 is the air gap, 3 is the Ge layer, 4 is the SiO layer, 5 is the supporting frame, and 6 is the Si substrate. DETAILED DESCRIPTION

[0024] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0025] like Figure 1-2 As shown, the structure of the cemented prism PBS beam splitter film with a silicon substrate mid-wave infrared and air gap is: S / aLbHcLdHeLfHgLhHiA / S, where S represents the Si substrate, A represents the air gap, H represents Ge, and L represents SiO. That is, in the order from the first Si substrate to the second Si substrate: the first, third, fifth, and seventh layers are SiO layers, the second, fourth, sixth, and eighth layers are Ge layers, and the ninth layer is an air gap; ai represents the coefficient of the optical thickness of one-quarter of the reference wavelength of the first to eighth layers; the reference wavelength is 4.5μm, and ai are 0.27, 0.81, 0.73, 0.79, 0.92, 0.79, 0.73, 0.85, and 0.12, respectively.

[0026] The physical thickness of the aL layer is 170nm, the physical thickness of the bH layer is 230nm, the physical thickness of the cL layer is 460nm, the physical thickness of the dH layer is 220nm, the physical thickness of the eL layer is 580nm, the physical thickness of the fH layer is 220nm, the physical thickness of the gL layer is 460nm, the physical thickness of the hH layer is 240nm, and the physical thickness of the iA layer is 140nm. The design curve is as follows Figure 3 .

[0027] like Figure 2 As shown, the two Si substrates are both right-angled triangular prism structures, the beam splitting film is arranged on the inclined surface of one of the right-angled triangular prism structures, and a support frame is arranged along the periphery of the inclined surface of the other right-angled triangular prism structure. The inclined surfaces of the two right-angled triangular prism structures are brought toward each other, and the support frame is bonded to the periphery of the beam splitting film. The overall shape (two right-angled triangular prisms spliced ​​together) forms a rectangular parallelepiped structure, and an air gap is formed inside the support frame. The support frame is made of SiO2, and the support frame and the inclined surface of the other right-angled triangular prism structure are tightly combined together by the attraction between the film material molecules. At the same time, the support frame can be formed on the side of the substrate (see Figure 2 The shadowed part in the middle is reinforced with colloid. There is no colloid in the thickness direction of the beam splitter film (working area). This ensures stability and avoids the influence of colloid on optical performance.

[0028] Preparation of membrane system:

[0029] The 1100 type coating machine of Chengdu Xingnan Technology was used, and the evaporation rate and film thickness of the film were monitored by the MXC-3B quartz crystal controller of Molin Technology, and the hollow cathode Hall ion source of Guangdong Zhongshan Boton Optoelectronics was used for assistance.

[0030] The first eight layers of this design were deposited on the inclined surface of the first Si prism using an electron gun and thermal evaporation, with an initial vacuum better than 1.0×10 -3 Pa, the baking temperature is 180℃. The ion source parameters are set as follows: discharge voltage 150-250V, discharge beam current 2-6A. Before evaporation, the substrate is bombarded with ions for 1 minute to clean the substrate and improve the adhesion of the film. During the film deposition process, the first layer (SiO) is deposited with the assistance of an ion source to improve the firmness of the film. The evaporation rate of SiO is controlled at 0.6nm / s, and the evaporation rate of Ge is controlled at 0.4nm / s. The first, third, fifth, and seventh layers are plated with SiO using a barrier evaporation source, and the second, fourth, sixth, and eighth layers are plated with Ge using an electron gun evaporation source.

[0031] In order to form an air gap, the ninth layer (support frame) of this design was deposited on both ends of the second Si prism slope by electron gun thermal evaporation. The initial vacuum degree was better than 1.0×10 -3 Pa, room temperature coating, no baking heating. Ion source parameters were set: discharge voltage 150-250V, discharge beam current 2-6A. Before evaporation, the substrate was bombarded with ions for 1 minute to clean the substrate and improve film adhesion. The SiO2 evaporation rate was controlled at 0.8nm / s. Finally, the two Si prism bevels were glued together without adhesive to complete the finished product.

[0032] Test results:

[0033] Optical performance test: The test was conducted using a Belarusian PHOTO RT spectrophotometer, and the obtained spectral curve met the design requirements, such as Figure 4 , transmittance is greater than 98.5%, and extinction ratio reaches 2000:1.

[0034] Environmental performance test: To ensure the reliability of optical components, the following environmental tests were conducted on the PBS beamsplitter film sample of the bonded prism in accordance with the requirements of GJB2485-95 General Specification for Optical Coatings:

[0035] (1) Abrasion resistance test: Wrap two layers of dry degreased gauze around the rubber friction head, rub the film along the same trajectory under a pressure of 9.8N for 100 times, and the film will not be damaged by scratches or other damage.

[0036] (2) Adhesion test: Use 1 cm wide 3M tape to stick firmly on the surface of the film layer. After quickly pulling the tape from the edge of the part toward the surface in a vertical direction, the film layer will not fall off or be damaged.

[0037] (3) Immersion test: The sample was completely immersed in distilled water or deionized water. After 24 hours, there was no abnormality in the film layer. Then, the wear resistance and adhesion tests were repeated in sequence according to the above method. There was no damage or shedding.

[0038] (4) High and low temperature test: -40℃ constant temperature for half an hour, quickly switch from -40℃ to 90℃ constant temperature for half an hour, then from 90℃ to -40℃ constant temperature for two hours, cycle five times, and the film layer has no abnormality. Then repeat the wear resistance, adhesion and immersion tests in accordance with the above method, and there is no damage, no shedding and no abnormality.

[0039] (5) Salt spray test: Temperature 35±2℃, concentration of 4.9%~5.1% NaCl solution, continuous spray for 24 hours, no abnormality in the film layer, then repeat the abrasion resistance, adhesion, immersion and high and low temperature tests in accordance with the above method, no damage, no shedding, no abnormality.

[0040] The experimental results above demonstrate that the Si-based prismatic PBS spectroscopic coating fabricated using this design achieves qualified spectral specifications, superior performance, and high reliability, meeting the requirements for optical systems operating in harsh environments. It exhibits a wide light transmission range and low absorption, stable mechanical and chemical properties, and strong adhesion and compatibility between the substrate and the coating, as well as between the coatings themselves.

[0041] Comparative Example 1

[0042] The difference from Example 1 is that no supporting frame and air gap are provided. Although the impact on mechanical performance is negligible, the impact on the optical performance of the component is significant, with the transmittance and extinction ratio both decreasing by more than 20%, thus affecting the use of the entire optical system.

Claims

1. A silicon-based mid-wave infrared prismatic PBS beam splitter with an air gap, characterized by: Its structure is: S / aLbHcLdHeLfHgLhHiA / S, where S represents the Si substrate, A represents the air gap, H represents Ge, and L represents SiO; ai represents the coefficient of the quarter reference wavelength optical thickness of the first to eighth layers; There are two Si substrates with the same structure, the two Si substrates are close together, and the beam splitter film is arranged between the two Si substrates, and there is no colloidal layer on the beam splitter film; The physical thickness of the aL layer is 170±20nm, the physical thickness of the bH layer is 230±20nm, the physical thickness of the cL layer is 460±30nm, the physical thickness of the dH layer is 220±20nm, the physical thickness of the eL layer is 580±50nm, the physical thickness of the fH layer is 220±20nm, the physical thickness of the gL layer is 460±30nm, the physical thickness of the hH layer is 240±20nm, and the physical thickness of the iA layer is 140±10nm.

2. The silicon-based mid-wave infrared band air-gap prismatic PBS beam splitter film according to claim 1, characterized in that: The reference wavelength is 4.5 μm, the value of a is 0.25~0.29, the value of b is 0.79~0.83, the value of c is 0.71~0.75, the value of d is 0.77~0.81, the value of e is 0.90~0.94, the value of f is 0.77~0.81, the value of g is 0.71~0.75, the value of h is 0.83~0.87, and the value of i is 0.1~0.

15.

3. The silicon-based mid-wave infrared band air-gap prismatic PBS beam splitter film according to claim 1 or 2, characterized in that: Both Si substrates are right-angled triangular prism structures. The beam splitting film is arranged on the inclined surface of one of the right-angled triangular prism structures. A supporting frame is arranged along the periphery of the inclined surface of the other right-angled triangular prism structure. The inclined surfaces of the two right-angled triangular prism structures are brought toward each other, and the supporting frame is bonded to the periphery of the beam splitting film to form a rectangular structure. An air gap is formed inside the supporting frame. The supporting frame is made of SiO2.

4. The silicon-based mid-wave infrared band air-gap prismatic PBS beam splitter film according to claim 3, characterized in that: When preparing the support frame, the evaporation rate of SiO2 is controlled at 0.5-1nm / s.

5. The silicon-based mid-wave infrared band air-gap prismatic PBS beam splitter film according to claim 1 or 2, characterized in that: The aL layer, cL layer, eL layer and gL layer are deposited by using a barrier evaporation source; the bH layer, dH layer, fH layer and hH layer are deposited by using an electron gun evaporation source.

6. The silicon-based mid-wave infrared band air-gap prismatic PBS beam splitter film according to claim 1 or 2, characterized in that: The evaporation rate of SiO is controlled at 0.5-1 nm / s.

7. The silicon-based mid-wave infrared band air-gap prismatic PBS beam splitter film according to claim 1 or 2, characterized in that: The evaporation rate of Ge is controlled at 0.3-0.5 nm / s.

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