Wide-angle incidence color-insensitive mid-infrared window thin film

Abstract

The present application provides a wide-angle incident color-insensitive mid-infrared window film, which is structured from bottom to top as a base material G, a transition layer M1, a transition layer M2, a dielectric film system C, and an air layer A. The purpose of the present application is to achieve high transmittance of the infrared window in the mid-infrared spectral range under wide-angle incidence of 0-60°, while having the color-insensitive characteristic to visible light. The transition layer is composed of two oxides for improving the firmness of the film layer. The dielectric film system structure is composed of high and low refractive index materials deposited alternately, and the dielectric film system can ensure high transmittance of the infrared window in the mid-wave band range under wide-angle incidence, while having the color-insensitive characteristic to visible light. The wide-angle incident color-insensitive mid-infrared window film of the present application can be widely applied in the field of optical detection, imaging and other optical systems.

Description

Technical Field

[0001] This invention relates to the design and preparation method of a mid-infrared window film that is insensitive to color under wide-angle incident light, and in particular to a film that is insensitive to visible light color display and has high-efficiency mid-infrared transmittance under wide-angle incident light of 0 to 60°, belonging to the field of thin film optics technology. Background Technology

[0002] Mid-infrared windows play a crucial role in infrared detection, sensor technology, and optoelectronic display systems. Commonly used mid-infrared window substrates typically have high refractive indices, resulting in significant surface reflection. Therefore, an anti-reflection coating needs to be deposited on the surface to improve the overall transmittance of the window in the mid-infrared band.

[0003] Existing mid-infrared window film technologies often focus only on the high transmittance requirements of the mid-infrared band, neglecting the impact of visible light reflection on optical systems. At large incident angles, the window surface can exhibit color inhomogeneity due to varying visible light reflection, which can severely affect the practical application of precision optical components in optical systems. With the development of optical technology, optical systems place higher demands on the spectral performance of multi-band optical thin-film components, including short-wavelength, near-infrared, and infrared components. Furthermore, as a critical component connecting the internal and external environments of the system, the window is often used in harsh conditions, thus requiring higher durability and robustness of the window film. Therefore, on the one hand, we aim to achieve high transmittance in the mid-infrared band in mid-infrared windows while maintaining insensitivity to visible light color display; on the other hand, we desire excellent robustness in the mid-infrared window film. Summary of the Invention

[0004] The purpose of this invention is to provide a mid-infrared window film that is insensitive to wide-angle incident color. Through a specific film structure design, it achieves high transmittance in the target infrared band and has the characteristic of being insensitive to visible light color display.

[0005] The technical solution provided by this invention is as follows:

[0006] A wide-angle incident color-insensitive mid-infrared window film has a structure of G / M1M2 / C / A, where G represents the substrate material, M1 represents transition layer 1, M2 represents transition layer 2, C represents the dielectric film system, and A represents the incident medium air layer. The dielectric film system is formed by alternating deposition of low-refractive-index dielectric materials and high-refractive-index dielectric materials.

[0007] The initial structure expression of the thin film is G / M1M2(xHyL)^n / A, where G is the substrate material, M1 represents transition layer 1, M2 represents transition layer 2, H is a high refractive index material with an optical thickness of λ / 4, L is a low refractive index material with an optical thickness of λ / 4, n is the number of periods of the dielectric film system, x and y are the thickness coefficients of the high refractive index and low refractive index film layers, respectively, and A is the air layer.

[0008] The number of periods n of the dielectric film layer is selected from 1 to 10, the thickness coefficients x and y of the low refractive index and high refractive index film layers are between 0.1 and 5, and the ratio of the total thickness coefficient of the low refractive index film layer to the high refractive index film layer ∑y(L) / ∑x(H) after optimization is also between 0.1 and 5.

[0009] The substrate material is sapphire, zirconium oxide, yttrium oxide, calcium fluoride, zinc sulfide, or zinc selenide.

[0010] The materials of transition layer 1 and transition layer 2 are Al2O3 and Y2O3, respectively, and the thickness of both transition layer 1 and transition layer 2 is less than 50 nm.

[0011] The high refractive index medium material is TiO2, Ta2O5, ZrO2, HfO2 or ZnS.

[0012] The low-refractive-index dielectric material is SiO2, YF3, or YbF3.

[0013] Compared with the prior art, the technical effects of this invention are as follows:

[0014] 1. While ensuring high transmittance of the infrared window in the mid-infrared band, it achieves insensitivity to visible light color under wide incident angles of 0–60°.

[0015] 2. It has advantages such as thin film thickness and good mechanical stability. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a mid-infrared window thin film structure that is insensitive to wide-angle incident color according to the present invention.

[0017] Figure 2 This is the final membrane structure of Example 1.

[0018] Figure 3 The image shows the single-sided transmittance spectrum of the film system in Example 1 within the range of 0-60°.

[0019] Figure 4 (a) and (b) are the chromaticity and color patch diagrams of the film system in Example 1 within the range of 0-60°, respectively.

[0020] Figure 5 This is the final thin film structure of Comparative Example 1.

[0021] Figure 6 The transmittance spectrum of the window on one side in the range of 0-60° is shown for Comparative Example 1.

[0022] Figure 7 (a) and (b) are the chromaticity and color patch diagrams of the thin film in the range of 0-60°, respectively, of Comparative Example 1.

[0023] Figure 8 This is the final thin film structure of Comparative Example 2.

[0024] Figure 9 The transmittance spectrum of the window on one side in the range of 0-60° is shown for Comparative Example 2.

[0025] Figure 10 (a) and (b) are the chromaticity and color patch diagrams of the thin film in Comparative Example 2 in the range of 0-60°, respectively.

[0026] Figure 11 This is the final thin film structure of Example 2.

[0027] Figure 12 The transmittance spectrum of the window on one side in Example 2 is shown in the range of 0-60°.

[0028] Figure 13 (a) and (b) are the chromaticity and color patch diagrams of the film in Example 2 in the range of 0-60°, respectively. Detailed Implementation

[0029] The following detailed description of specific examples of the present invention is provided in conjunction with the accompanying drawings.

[0030] Figure 1 The present invention discloses a wide-angle incident color-insensitive mid-infrared window film with a structure of G / M1M2 / C / A, wherein G represents the substrate material, M1 represents transition layer 1, M2 represents transition layer 2, C represents the dielectric film system, and A represents the incident medium air layer. The dielectric film system is formed by alternating deposition of low-refractive-index dielectric materials and high-refractive-index dielectric materials.

[0031] The infrared window film design specifications required in Example 1 are: to achieve an average transmittance of >90% in the range of 3700nm to 4800nm ​​with an incident angle of 0-60° on the zirconia window, and to be insensitive to visible light color.

[0032] The design steps are as follows:

[0033] 1. Based on the spectral characteristics requirements of the target band, a wide-band, high-transmittance coating material was selected: Ta₂O₅ (high refractive index) and SiO₂ (low refractive index). The initial film structure was G / M₁M₂(0.5HL)⁴ / A, where H represents Ta₂O₅ with an optical thickness of one-quarter wavelength, L represents SiO₂ with an optical thickness of one-quarter wavelength, and M₁ and M₂ represent Al₂O₃ and Y₂O₃, respectively. The initial thickness of transition layer 1 and transition layer 2 was set to 30 nm. The refractive index parameters of the high-refractive-index material Ta₂O₅ and the low-refractive-index material SiO₂ were determined by the Sellmeier formula, as shown in Table 1.

[0034] Table 1: Refractive index parameters of high and low refractive index materials in Example 1

[0035] <![CDATA[A1]]> <![CDATA[B1]]> <![CDATA[A2]]> <![CDATA[B2 <!-- 2 -->]]> <![CDATA[Ta2O5]]> 3.26145 0.0295957 4.07352 202.585 <![CDATA[SiO2]]> 1.10828 0.0071807 2.08973 200.268

[0036] 2. The optimization targets were set as follows: transmittance greater than or equal to 99.5% in the mid-infrared band (3700-4800nm) and transmittance equal to 90% in the visible light band (400-780nm). Incident angles were set to 0°, 10°, 20°, 30°, 40°, 50°, and 60°, respectively. The initial membrane structure was optimized using the simplex and simulated annealing optimization algorithms in the membrane design software.

[0037] 3. The optimized membrane structure is: G / 0.05M10.12M20.25H0.21L0.16H1.92L0.14H0.91L0.2H0.65L / A. Figure 2 As shown, the total thickness is 752 nm, with 10 film layers. The thickness coefficient ratio of materials L and H, ∑y(L) / ∑x(H) = 4.95, and stress calculations indicate that the fracture factor of this thin film structure is 1.56. The single-sided transmittance spectrum of the infrared window within the 0-60° incident angle range is shown below. Figure 3 As shown. The chromaticity and color patch diagrams of this film system in the 0-60° incident angle range are shown below. Figure 4 As shown in (a) and (b).

[0038] Comparative Example 1: The difference between this comparative example and Example 1 is that the design optimization target is only a transmittance of ≥99.5% in the mid-infrared band of 3700-4800nm, without considering color sensitivity. The optimized film structure is: G / 0.32M10.35M20.42H1.52L2.2H2.89L2.98H2.17L0.42H2.89L / A, as shown. Figure 5As shown, the total thickness is 2462 nm, with 10 film layers. Stress calculations indicate that the fracture factor of this thin film structure is 14.9, suggesting a significant risk to the film's robustness. The single-sided transmittance spectrum within the 0-60° incident angle range is shown below. Figure 6 As shown, the chromaticity diagram and color patch diagram for the 0-60° incident angle range are respectively as follows: Figure 7 As shown in (a) and (b), the results indicate that the chromaticity diagram and color chart change significantly with the change of angle, meaning that they are sensitive to visible light color display and cannot meet the requirements.

[0039] Comparative Example 2: The difference between this comparative example and Example 1 is that the membrane structure lacks buffer layers M1 and M2. The optimized membrane structure is: G / 1.75H0.07L0.18H0.08L0.14H0.28L0.08H3.16L0.08H0.23L0.09H0.07L / A, as shown. Figure 8 As shown, the total thickness is 950 nm, and the film has 12 layers. Stress calculations indicate that the fracture factor of this thin film structure is 4.35. The single-sided transmittance spectrum within the 0-60° incident angle range is shown in the figure. Figure 9 As shown, the chromaticity diagram and color patch diagram for the 0-60° incident angle range are respectively as follows: Figure 10 As shown in (a) and (b), the results indicate that although the spectral performance in the 0-60° range meets the requirements, the fracture factor of the thin film structure is 4.35, which is three times that of the thin film structure in Example 1, indicating that there is a significant risk to the film's robustness.

[0040] The infrared window film design specifications required in Example 2 are: to achieve an average transmittance of >90% in the 3700nm to 4800nm ​​range, with an incident angle of 0-60°, and insensitivity to visible light color on the sapphire window.

[0041] The design steps are as follows:

[0042] 1. Based on the spectral characteristics requirements of the target band, a wide-band, high-transmittance coating material was selected: TiO2 (high refractive index) and SiO2 (low refractive index). The initial film structure was G / M1M2(0.5HL)^5 / A, where H represents TiO2 with an optical thickness of one-quarter wavelength, L represents SiO2 with an optical thickness of one-quarter wavelength, M1 and M2 represent Al2O3 and Y2O3, respectively, and the initial thickness of transition layer 1 and transition layer 2 was set to 30 nm. The refractive index parameters of the high-refractive-index material TiO2 and the low-refractive-index material SiO2 were determined by the Sellmeier formula, as shown in Table 2.

[0043] Table 2: Refractive index parameters of high and low refractive index materials in Example 2

[0044] <![CDATA[A1]]> <![CDATA[B1]]> <![CDATA[A2]]> <![CDATA[B2]]> <![CDATA[TiO2]]> 3.97674 0.0479993 2.31322 96.4369 <![CDATA[SiO2]]> 1.10828 0.0071807 2.08973 200.268

[0045] 2. The optimization targets were set as follows: transmittance greater than or equal to 99.5% in the mid-infrared band (3700-4800nm) and transmittance equal to 90% in the visible light band (400-780nm). Incident angles were set to 0°, 10°, 20°, 30°, 40°, 50°, and 60°, respectively. The initial membrane structure was optimized using the simplex and simulated annealing optimization algorithms in the membrane design software.

[0046] 3. The optimized membrane structure is: G / 0.11M10.12M20.26H0.15L0.32H0.17L0.2H1.67L0.1H2.19L0.15H0.59L / A. Figure 11 As shown, the total thickness is 970 nm, with 12 layers. The thickness coefficient ratio of materials L and H, ∑y(L) / ∑x(H) = 4.71, indicates that the fracture factor of this thin film structure is 1.71. The single-sided transmittance spectrum of the infrared window within the 0-60° incident angle range is shown below. Figure 12 As shown. The chromaticity and color patch diagrams of this film system in the 0-60° incident angle range are shown below. Figure 13 As shown in (a) and (b).

[0047] In addition, considering different window types and different combinations of film materials, other typical preferred embodiments are listed below, as shown in Table 3:

[0048] Table 3: Typical Preferred Embodiments

[0049]

[0050]

[0051] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A wide-angle incident color-insensitive mid-infrared window film, characterized in that, Its structure is G / M1M2 / C / A, where G represents the substrate material, M1 represents transition layer 1, M2 represents transition layer 2, C represents the dielectric film system, and A represents the incident medium air layer. The dielectric film system is formed by alternating deposition of low-refractive-index dielectric materials and high-refractive-index dielectric materials. The initial structure expression of the thin film is G / M1M2(xHyL)^n / A, where G is the substrate material, M1 represents transition layer 1, M2 represents transition layer 2, H is a high refractive index material with an optical thickness of λ / 4, L is a low refractive index material with an optical thickness of λ / 4, n is the number of periods of the dielectric film system, x and y are the thickness coefficients of the high refractive index and low refractive index film layers, respectively, A is the air layer, and λ is the reference wavelength. The number of dielectric film layers n is selected from 1 to 10, the thickness coefficients x and y of high refractive index and low refractive index film layers are between 0.1 and 5, and the ratio of the total thickness coefficient of low refractive index film layers to high refractive index film layers ∑y(L) / ∑x(H) after optimization is between 0.1 and 5. The materials of the transition layer 1 and the transition layer 2 are Al2O3 and Y2O3, respectively, and the thickness of both the transition layer 1 and the transition layer 2 is less than 50 nm. The film is insensitive to visible light color under a wide incident angle of 0–60°.

2. The wide-angle incident color-insensitive mid-infrared window film according to claim 1, characterized in that, The substrate material is sapphire, zirconium oxide, yttrium oxide, calcium fluoride, zinc sulfide, or zinc selenide.

3. The wide-angle incident color-insensitive mid-infrared window film according to claim 1, characterized in that, The high refractive index medium material is TiO2, Ta2O5, ZrO2, HfO2, or ZnS.

4. The wide-angle incident color-insensitive mid-infrared window film according to claim 1, characterized in that, The low-refractive-index dielectric material is SiO2, YF3, or YbF3.

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