Color separation film capable of reflecting visible light to short-wave infrared and transmitting wide-spectrum infrared and manufacturing method of color separation film

Abstract

The invention relates to a color separation sheet capable of reflecting visible light to short wave infrared and transmitting wide spectrum infrared and a manufacturing method thereof, the color separation sheet takes a germanium flat sheet as a substrate, a color separation film system adopts a film system structure of a long wave pass optical filter, and germanium, zinc sulfide and fluoride are used as high and low refractive index materials of different reflecting film stacks. A color separation film is designed on the front surface of the substrate, broadband high reflection is achieved through combination of different reflecting film stacks, and transmission passband ripples are reduced by optimizing a matching layer. A wide-spectrum antireflection film is designed on the rear surface of the substrate, high transmissivity of a transmission channel is obtained, residual reflection is reduced, and stray light is eliminated. In the preparation process of the color separation film, proper deposition rate, substrate temperature, local film layer ion auxiliary deposition and other processes are adopted, thin film absorption is reduced, and meanwhile the environmental reliability of the color separation film is improved. According to actually measured reflectivity and transmissivity curves, the color separation film is highly reflective in the wave band of 0.4-1.7 microns and highly transmissive in the short-wave infrared band of 2.1-2.4 microns and the medium-long wave infrared band of 3.5-14 microns, and is suitable for spectrum light splitting of a visible-to-infrared multi-channel remote sensing system.

Description

Technical Field

[0001] The invention relates to the technical field of optical films, in particular to a color separation film which reflects visible light to short-wave infrared and transmits wide-spectrum infrared and a manufacturing method thereof. Background Art

[0002] In multi-channel imagers for space remote sensing, by using wide-spectrum color separation sheets based on all-dielectric reflective film stacks for spectral color separation, light from the visible to short-wave infrared bands can be highly reflected, allowing it to enter the short-wave optical path and be received by the short-wave detector for imaging; at the same time, it can be highly transmitted to the mid- and long-wave infrared bands, allowing it to be received by a suitable infrared detector for imaging. Compared with the spectral color separation method of metal-induced transmission, the spectral color separation method based on all-dielectric reflective film stacks can improve the optical transmission efficiency of the visible to short-wave infrared channel, which is beneficial to improving the imaging quality of the visible to short-wave infrared channel for large field of view and long focal length systems; in addition, this color separation method is conducive to optimizing the optical path structure, eliminating the lens group of the rear optical path, reducing the optical transmission loss of the transmission optical path, and reducing the weight of the optical system. This type of color separation sheet can be used in a common aperture imaging system with visible-infrared dual detectors, and can play an important role in low-light night vision imaging, thermal infrared imaging, and all-weather rescue and security in severe weather such as rain, snow, fog and haze.

[0003] With the further development of space remote sensing ultra-wide spectrum imaging technology, the number of spectral channels that need to be covered is increasing, and the image quality requirements for the visible and near-infrared bands are getting higher and higher. The color separation method of the optical system using a long-wave filter structure has attracted much attention. At present, this color separation method still has the problem that the band coverage for efficient transmission is not wide enough, resulting in low utilization of the system's spectral channel resources; and because its film system structure is relatively complex and the number of film layers is as many as dozens, its spatial reliability needs to be improved. To this end, it is necessary to solve the above problems through the design of new color separation films and the improvement of the research and development process level. There has been no report on wide-spectrum color separation films with continuous high reflection in the reflection band of 0.4-1.7μm and continuous high transmission in the transmission band of 2.1-2.4μm short-wave infrared and 3.5-14μm medium- and long-wave infrared bands. Summary of the invention

[0004] The purpose of the present invention is to provide a color separation film which reflects visible light to short-wave infrared and transmits wide-spectrum infrared and a method for making the same, so as to solve the problem that the existing color separation method has insufficient coverage of the band for efficient transmission, resulting in low utilization rate of system spectral channel resources.

[0005] To achieve the above object, the technical solution of the present invention is:

[0006] A color separation film that reflects visible light to short-wave infrared and transmits wide-spectrum infrared comprises a substrate, a wide-spectrum color separation film and a wide-spectrum anti-reflection film, wherein the wide-spectrum color separation film is arranged on the upper surface of the substrate and the wide-spectrum anti-reflection film is arranged on the lower surface of the substrate; the wide-spectrum color separation film comprises a front matching layer, a reflection film stack and a rear matching layer, and its composition is as follows:

[0007] Base / A1(R1) a (R2) 6 (R3) b (R4) 7 A2 / Air

[0008] Among them, A1 is the front matching layer, R1, R2, R3, and R4 are four reflective film stacks, A2 is the rear matching layer, index a is the period number of the R1 reflective film stack, and index b is the period number of the R3 reflective film stack.

[0009] The substrate is composed of germanium; the R1 reflective film stack is composed of alternating dielectric layers of germanium and fluoride, and the three reflective film stacks R2, R3 and R4 are composed of alternating dielectric layers of zinc sulfide and fluoride.

[0010] The fluoride in the alternating medium layer is a low refractive index material with a refractive index of 1.41 to 1.57; the fluoride in the alternating medium layer is calcium fluoride or ytterbium fluoride or yttrium fluoride.

[0011] The alternating dielectric layer is a material with a low extinction coefficient in a wide band, and the extinction coefficient is lower than 0.002 in the visible and near-infrared bands, and lower than 0.018 in the long-wave infrared band.

[0012] The wide-spectrum anti-reflection film is composed of dielectric layers of germanium, zinc sulfide and fluoride. Germanium is a high-refractive-index material in the wide-spectrum anti-reflection film, zinc sulfide is a medium-refractive-index material in the wide-spectrum anti-reflection film, and fluoride is a low-refractive-index material in the wide-spectrum anti-reflection film.

[0013] The method for making a color separation film that reflects visible light to short-wave infrared and transmits wide-spectrum infrared includes the following steps: step 1, bombarding a substrate with an ion beam in a box-type vacuum coating device with a diffusion pump system; step 2, using electron beam evaporation to deposit alternating dielectric layers of germanium and fluoride to form an R1 reflective film stack; step 3, depositing alternating dielectric layers of zinc sulfide and fluoride to form three reflective film stacks of R2, R3 and R4.

[0014] The substrate is germanium or zinc selenide.

[0015] In step three, the zinc sulfide film layer is formed by resistance heating evaporation deposition.

[0016] The fluoride is ytterbium fluoride.

[0017] During production, the temperature of the substrate is controlled at 170°C to 200°C.

[0018] The advantages of the present invention are: 1. The color separation film system adopts the structure of a long-wave pass filter, and is designed to use four reflection film stacks to meet wide reflection requirements. According to the optical properties of different materials, different reflective film stacks are formed by selecting the best combination to extend the reflection band from the visible near-infrared band to the short-wave infrared band, obtain high reflectivity in the 0.4-1.7μm wide band, and add matching layers at both ends of the dichroic film reflective film stack. By optimizing the thickness of the matching layer, high transmittance in the short-wave infrared and medium- and long-wave bands is achieved; 2. The substrate temperature is controlled at 170℃~200℃ to avoid the increase of fluoride absorption in the long-wave infrared band, ensure the transmittance of the dichroic film in the 12-14μm band, and the film layer has good firmness, so a highly reliable dichroic film can be obtained; 3. The influence of zinc sulfide film on the reflection band waveform due to dispersion loss in the visible light 0.4-0.6μm band is reduced, and the absorption of fluoride film in the long-wave infrared 12-14μm band is reduced. High transmission efficiency is obtained in multiple continuous bands from visible light to long-wave infrared, with good reliability and stable product performance; BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the film structure of the color separation sheet of the present invention;

[0020] Figure 2 is the measured reflectance spectrum curve of the color separation sheet of the present invention;

[0021] Figure 3 is the measured transmittance spectrum curve of the color separation sheet of the present invention;

[0022] In the figure: 1-wide spectrum dichroic film; 2-substrate; 3-wide spectrum anti-reflection film; 4-incident light beam; 5-reflected light beam; 6-transmitted light beam. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the accompanying drawings, which are only used for exemplary description and cannot be understood as limiting the present invention.

[0024] In order to more concisely describe the present embodiment, some parts known to those skilled in the art but not related to the main content of the present invention are omitted in the drawings or descriptions. In addition, for the convenience of description, some parts in the drawings are omitted, enlarged or reduced, but they do not represent the size or entire structure of the actual product.

[0025] The present invention discloses a color separation film which reflects visible light to short-wave infrared and transmits wide-spectrum infrared. Figure 1 As shown, it includes a substrate 2, a wide spectrum dichroic film 1 and a wide spectrum anti-reflection film 3, the wide spectrum dichroic film 1 is arranged on the upper surface of the substrate 2, and the wide spectrum anti-reflection film 3 is arranged on the lower surface of the substrate 2; the wide spectrum dichroic film 1 includes a front matching layer, a reflective film stack and a rear matching layer, and its composition is:

[0026] Base / A1(R1) a (R2) 6 (R3) b (R4) 7 A2 / Air

[0027] Among them, A1 is the front matching layer, R1, R2, R3, and R4 are four reflective film stacks, A2 is the rear matching layer, index a is the period number of the R1 reflective film stack; index b is the period number of the R3 reflective film stack.

[0028] The substrate 2 is made of germanium, i.e., a germanium substrate; the R1 reflective film stack is made of alternating dielectric layers of germanium and fluoride; and the three reflective film stacks R2, R3 and R4 are made of alternating dielectric layers of zinc sulfide and fluoride.

[0029] The fluoride in the alternating dielectric layer is a low refractive index material with a refractive index of 1.41 to 1.57; the fluoride in the alternating dielectric layer is calcium fluoride or ytterbium fluoride or yttrium fluoride. Preferably, the fluoride is ytterbium fluoride.

[0030] The alternating dielectric layer is a material with a low extinction coefficient in a wide band, and the extinction coefficient is lower than 0.002 in the visible and near-infrared bands, and lower than 0.018 in the long-wave infrared band.

[0031] The wide-spectrum anti-reflection film 3 is composed of dielectric layers of germanium, zinc sulfide and fluoride. Germanium is a high-refractive-index material in the wide-spectrum anti-reflection film 3, zinc sulfide is a medium-refractive-index material in the wide-spectrum anti-reflection film 3, and fluoride is a low-refractive-index material in the wide-spectrum anti-reflection film 3.

[0032] Germanium, zinc sulfide and fluoride are used as high refractive index and low refractive index materials for different reflective film stacks, respectively. The reflection band is very wide, 0.4 to 1.7 μm. A single reflective film stack cannot meet the broadband reflection requirements. Four reflective film stacks are used in the wide-spectrum dichroic film 1, and matching layers are added at both ends of the reflective film stack to achieve reflection from the visible to short-wave infrared bands and transmit 2.1 to 2.4 μm and 3.5 to 14 μm infrared bands. A wide-spectrum anti-reflection film 3 is designed on the lower surface of the substrate 2, with germanium, zinc sulfide and fluoride as high refractive index materials, medium refractive index materials and low refractive index materials, respectively, and high transmittance is obtained in the 2.1 to 14 μm band by optimizing the film layer.

[0033] The realization of the color separation film of the present invention comprises the following steps:

[0034] First, the structure of the membrane system

[0035] According to the reflection band and the central wavelength, a reflection film stack R is constructed to expand the bandwidth of the reflection band. The film system structure of the wide spectrum dichroic film 1 is:

[0036] Base / A1(0.78H1.62L0.78H) a (0.56M0.92L0.56M) 6 (0.47M0.68L0.47M) b

[0037] (0.32M0.56L0.32M) 7 A2 / Air

[0038] Among them: A1 is the front matching layer, and the structure of A1 is k1Mk2Hk3Mk4Hk5Mk6H; A2 is the back matching layer, and the structure of A2 is t1Mt2Lt3Mt4Lt5Mt6Lt7M.

[0039] The film system of wide spectrum anti-reflection film is:

[0040] Base

[0041] / 0.283M3.55H0.787M3.265H1.527M2.381H2.477M1.438H3.823M0.531L2.735M1.08L3.24M2.382L1.48M6.476L0.21M / Air

[0042] Wherein: index a takes a value of 4 or 5; index b takes a value of 6 or 7; H represents a germanium film layer with an optical thickness of λ0 / 4, L represents a fluoride film layer with an optical thickness of λ0 / 4, M represents a zinc sulfide film layer with an optical thickness of λ0 / 4, λ0 is the center wavelength, k1, k2, k3, k4, k5, k6, t1, t2, t3, t4, t5, t6, t7 are proportional coefficients of the thickness of each film layer.

[0043] The method for manufacturing a color separation film that reflects visible light to short-wave infrared and transmits wide-spectrum infrared of the present invention comprises the following steps: step 1, bombarding a substrate 2 with an ion beam in a box-type vacuum coating device with a diffusion pump system; the substrate 2 is germanium or zinc selenide, preferably a germanium substrate. Step 2, electron beam evaporation is used to deposit alternating dielectric layers of germanium and fluoride to form an R1 reflective film stack; the fluoride is preferably ytterbium fluoride.

[0044] Step 3: Deposit alternating dielectric layers of zinc sulfide and fluoride to form three reflective film stacks R2, R3 and R4. The zinc sulfide film layer is made by resistance heating evaporation deposition.

[0045] Some film layers are deposited using ion beam assisted deposition, the ion source is MarkII, and the specific parameters are: anode voltage 130V~150V, anode current 3A~5A.

[0046] The analysis of the film material test results shows that when the substrate 2 temperature is higher than 200°C, zinc sulfide will have obvious reverse evaporation, which is not conducive to the deposition of the film on the substrate 2; and when the substrate 2 temperature is lower than 170°C, the absorption of fluoride in the long-wave infrared band will increase, which will affect the transmittance of the color separation film in the 12-14μm band. Therefore, by controlling the substrate 2 temperature at 170°C to 200°C, the film layer has good firmness and a highly reliable color separation film can be obtained.

[0047] Therefore, during the manufacturing process, the temperature of the substrate 2 is controlled at 170°C to 200°C.

[0048] Combined with Figure 1-3 The specific implementation modes of the present invention are further described in detail.

[0049] The material of the substrate 2 is a germanium sheet, and the fluoride of the low refractive index medium layer in this example is ytterbium fluoride.

[0050] According to the technical requirements, a technical solution is adopted in which a wide spectrum dichroic film 1 is prepared on the upper surface of a germanium substrate 2 and a wide spectrum anti-reflection film 3 is prepared on the lower surface of the substrate 2. The wide spectrum dichroic film 1 adopts the structure of a long-wave pass filter, and is designed to use four reflective film stacks to meet the wide reflection. According to the optical properties of different materials, different reflective film stacks are selected and combined to extend the reflection band from the visible near-infrared band to the short-wave infrared band, and high reflectivity is obtained in the 0.4-1.7μm wide band. Matching layers are added at both ends of the reflective film stack of the wide spectrum dichroic film 1. By optimizing the thickness of the matching layer, high transmittance in the short-wave infrared and medium-long wave bands is achieved. The stress matching between the film layers and the feasibility of process control are considered when designing the wide spectrum dichroic film 1. A wide spectrum anti-reflection film 3 is designed on the lower surface of the germanium substrate 2. When optimizing the film system, the thickness of individual key layers is controlled to reduce the reflectivity of the lower surface of the substrate 2 and improve the transmittance from the short-wave infrared to the long-wave infrared band.

[0051] Since germanium materials absorb in the near-infrared and short-wave infrared, the thicker the germanium film, the greater the absorption of the short-wave infrared channel and the lower the reflectivity. Also, since ytterbium fluoride materials have non-negligible absorption in the wavelength band greater than 12μm, the degree of absorption is directly related to the film thickness. Therefore, the number of layers and thickness of the overall film system must be considered comprehensively when designing the wide-spectrum color separation film 1.

[0052] The first one is when the number of membrane stack cycles a=4,b=7,

[0053] The film system is optimized by optical thin film design software, the thickness of very few key layers is controlled, and the film layer with a thickness ratio coefficient of zero is removed. The obtained film system is: substrate

[0054] / 0.71M3.225H1.141M2.638H2.045M1.127H(0.78H1.62L0.78H)4 (0.56M0.92L0.56M) 6 (0.47M0.68L0.47M) 7 (0.32M0.56L0.32M) 7 0.805L1.513M2.885L0.548M5.339L0.22M / air;

[0055] The design results achieve high reflectivity in the visible and near-infrared bands, and high transmittance in the short-wave infrared and mid- and long-wave infrared bands.

[0056] The second type, when the number of membrane stack cycles a = 4, b = 6,

[0057] The film system is optimized by software to control the thickness of very few key layers. The obtained film system is: substrate

[0058] / 0.804M2.937H1.332M2.502H2.398M0.997H(0.78H1.62L0.78H) 4 (0.56M0.92L0.56M) 6 (0.47M0.68L0.47M) 6 (0.32M0.56L0.32M) 7 2.203L1.298M0.397L0.275M6.021L0.228M / air;

[0059] The design results achieve high reflectivity in the visible and near-infrared bands, and high transmittance in the short-wave infrared and mid- and long-wave infrared bands.

[0060] The third type, when the number of membrane stack cycles a = 5, b = 6,

[0061] The film system is optimized by optical thin film design software, the thickness of very few key layers is controlled, and the film layer with a thickness ratio coefficient of zero is removed. The obtained film system is: substrate

[0062] / 0.683M3.978H1.203M2.275H1.926M1.491H(0.78H1.62L0.78H) 5 (0.56M0.92L0.56M) 6 (0.47M0.68L0.47M) 6 (0.32M0.56L0.32M) 7 1.594L0.2M1.811L0.55M4.023L0.183M / air;

[0063] The design results achieve high reflectivity in the visible and near-infrared bands, and high transmittance in the short-wave infrared and mid- and long-wave infrared bands.

[0064] The fourth type, when the number of membrane stack cycles a = 5, b = 7,

[0065] The film system is optimized by software, the thickness of very few key layers is controlled, and the film layer with a thickness ratio coefficient of zero is removed. The obtained film system is: substrate

[0066] / 1.179M2.448H1.619M1.409H(0.78H1.62L0.78H) 5 (0.56M0.92L0.56M) 6 (0.47M0.68L0.47M) 7 (0.32M0.56L0.32M) 7 1.388L0.4M3.304L0.2M / air;

[0067] The design results achieve high reflectivity in the visible and near-infrared bands, and high transmittance in the short-wave infrared and mid- and long-wave infrared bands.

[0068] Taking into account the absorption of germanium thin films in the near-infrared and short-wave infrared bands, the absorption of ytterbium fluoride in the long-wave infrared, and the reliability of the film system, the wide-spectrum color separation film 1 on the upper surface of the germanium substrate is actually made by selecting the film system of the third type mentioned above, combined with the wide-spectrum anti-reflection film 3 system on the lower surface of the germanium substrate. The final complete film system is:

[0069] S0 / 0.183M4.023L0.55M1.811L0.2M1.594L(0.32M0.56L0.32M) 7 (0.47M0.68L0.47M) 6 (0.56M0.92L0.56M) 6 (0.78H1.62L0.78H) 5 1.491H1.926M2.275H1.203M3.978H0.683M / S1 / 0.283M3.55H0.787M3.265H1.527M2 .381H2.477M1.438H3.823M0.531L2.735M1.08L3.24M2.382L1.48M6.476L0.21M / S0

[0070] Where: S1 is a germanium substrate, S0 is air, H represents a germanium film layer with an optical thickness of λ0 / 4, M represents a zinc sulfide film layer with an optical thickness of λ0 / 4, L represents an ytterbium fluoride film layer with an optical thickness of λ0 / 4, λ0 is the central wavelength, indices 4, 5, 6, and 7 are the period numbers of each reflective film stack, and the numbers before M, H, and L are the proportional coefficients of the thickness of each film layer.

[0071] In this embodiment, the substrate temperature of the color separation film is 180°C, and electron beam evaporation deposition is used to prepare germanium and ytterbium fluoride films. By adopting a pre-melting process and selecting a suitable deposition rate, the absorption of the germanium film in the short-wave infrared region and the absorption of the ytterbium fluoride film in the long-wave infrared 12-14 μm band are reduced. The zinc sulfide film is prepared by resistance evaporation deposition, and the local film layer is deposited by ion beam assisted deposition.

[0072] from Figure 2 It can be seen that this color separation film has high reflection in the 0.4-1.7μm band, and its average reflectivity is calculated to be 94%; Figure 3 It can be seen that the color separation film has high transmittance in the short-wave infrared band of 2.1-2.4 μm, and its average transmittance is calculated to be 91.5%. It has high transmittance in the medium- and long-wave infrared band of 3.5-14 μm, and its average transmittance is calculated to be 92%.

[0073] The color separation sheet of the invention has good reliability and stable optical and physical properties, and can be used for spectral color separation of space remote sensing imagers, and is also suitable for visible-infrared dual-detector common aperture imaging systems.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. That is, any equivalent changes and modifications made according to the content of the patent application scope of the present invention should be within the technical scope of the present invention.

Claims

1. A color separation film that reflects visible light to short-wave infrared and transmits wide-spectrum infrared, characterized in that: The invention comprises a substrate (2), a wide spectrum dichroic film (1) and a wide spectrum anti-reflection film (3), wherein the wide spectrum dichroic film (1) is arranged on the upper surface of the substrate (2), and the wide spectrum anti-reflection film (3) is arranged on the lower surface of the substrate (2); the wide spectrum dichroic film (1) comprises a front matching layer, a reflection film stack and a rear matching layer, and its composition is as follows: Base / A1(R1) a (R2) 6 (R3) b (R4) 7 A2 / Air Among them, A1 is the front matching layer, R1, R2, R3, and R4 are four reflective film stacks, A2 is the rear matching layer, index a is the period number of the R1 reflective film stack, and index b is the period number of the R3 reflective film stack.

2. The color separation film that reflects visible light to short-wave infrared and transmits wide-spectrum infrared according to claim 1, characterized in that: The substrate (2) is made of germanium; the R1 reflective film stack is made of alternating dielectric layers of germanium and fluoride; and the three reflective film stacks R2, R3 and R4 are made of alternating dielectric layers of zinc sulfide and fluoride.

3. The color separation sheet that reflects visible light to short-wave infrared and transmits wide-spectrum infrared according to claim 2, characterized in that: The fluoride in the alternating medium layer is a low refractive index material with a refractive index of 1.41 to 1.57; the fluoride in the alternating medium layer is calcium fluoride or ytterbium fluoride or yttrium fluoride.

4. The color separation film that reflects visible light to short-wave infrared and transmits wide-spectrum infrared according to claim 2, characterized in that: The alternating dielectric layer is a material with a low extinction coefficient in a wide band, and the extinction coefficient is lower than 0.002 in the visible and near-infrared bands, and lower than 0.018 in the long-wave infrared band.

5. The color separation film that reflects visible light to short-wave infrared and transmits wide-spectrum infrared according to claim 2, characterized in that: The wide-spectrum anti-reflection film (3) is composed of dielectric layers of germanium, zinc sulfide and fluoride, wherein germanium is a high-refractive-index material in the wide-spectrum anti-reflection film (3), zinc sulfide is a medium-refractive-index material in the wide-spectrum anti-reflection film (3), and fluoride is a low-refractive-index material in the wide-spectrum anti-reflection film (3).

6. The method for manufacturing a color separation film that reflects visible light to short-wave infrared and transmits wide-spectrum infrared according to any one of claims 2 to 5, characterized in that: Step 1: bombarding a substrate (2) with an ion beam in a box-type vacuum coating device with a diffusion pump system; Step 2: depositing germanium and fluoride alternating dielectric layers by electron beam evaporation to form an R1 reflective film stack; Step 3: depositing zinc sulfide and fluoride alternating dielectric layers to form three reflective film stacks R2, R3 and R4.

7. The method for manufacturing a color separation film that reflects visible light to short-wave infrared and transmits wide-spectrum infrared according to claim 6, characterized in that: The substrate (2) is germanium or zinc selenide.

8. The method for manufacturing a color separation film that reflects visible light to short-wave infrared and transmits wide-spectrum infrared according to claim 6, characterized in that: In step three, the zinc sulfide film layer is formed by resistance heating evaporation deposition.

9. The method for manufacturing a color separation film that reflects visible light to short-wave infrared and transmits wide-spectrum infrared according to claim 6, characterized in that: The fluoride is ytterbium fluoride.

10. The method for manufacturing a color separation film that reflects visible light to short-wave infrared and transmits wide-spectrum infrared according to claim 6, characterized in that: During the production, the temperature of the substrate (2) is controlled at 170°C to 200°C.

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