Inclined incidence high-efficiency broadband long-wave light-splitting film

Abstract

The invention provides an oblique incidence high-efficiency broadband long-wave light splitting film, the working angle of the light splitting film is 45 degrees, an equivalent relation of double-sided design and single-sided design under oblique incidence is established through numerical calculation, 45-degree single-sided transmittance and reflectivity target values are set, and film system matching is performed by adopting a design method of alternating three refractive indexes. And then the same film system is plated on the two surfaces of the long-wave infrared substrate respectively, so that the preparation of the beam splitting film is realized. The objective of the invention is to realize high-efficiency light splitting of a long-wave infrared window in a transmittance / reflectivity ratio of 1: 1 in a wave band range of 7 [mu] m-12 [mu] m under 45-degree inclined incidence, and the light splitting film has the advantages of stable performance and small surface shape change, and is suitable for optical systems for imaging, detection and the like.

Description

Technical Field

[0001] The present invention belongs to the field of thin film optical technology, and particularly relates to an oblique incidence high-efficiency broadband long-wave splitting film technology, specifically a splitting film that can achieve high-efficiency splitting with a transmittance / reflectivity of 1:1 in the infrared window within the 7μm-12μm band under an incident angle of 45°. Background Art

[0002] Infrared optical systems play an important role in detection, remote sensing, laser applications and other fields. For multi-band composite optical test platforms, conventional single-wavelength spectroscopic films cannot meet the use requirements, and broadband spectroscopic solutions are required to reduce the complexity of the optical system, which puts higher requirements on the optical components in the optical system. Taking the surface shape change of optical components as an example, it will cause distortion of the transmission beam, which will seriously affect the practical application of precision optical components in optical systems. With the development of optical technology, optical systems have higher requirements for the performance of long-wave infrared spectroscopic films. We hope to have simple design and preparation, while meeting high performance requirements such as small surface shape changes, high efficiency and reliability.

[0003] The common design of existing spectroscopic films is one side for spectroscopic and the other side for broadband anti-reflection. It is necessary to design and optimize two film systems, and the structure of the spectroscopic film system and the broadband anti-reflection film system are relatively complex. At the same time, due to the large difference in the structure of the two film systems, the stress mismatch on both sides of the substrate can easily lead to large surface changes, which in turn can cause the transmission beam distortion in the laser system. In addition, the choice of substrate material will also have an important impact on the performance of the optical system. KBr is usually selected for the long-wave broadband spectroscopic film substrate, but this material is prone to moisture absorption and has poor environmental stability. In contrast, Ge and ZnSe substrates have good mechanical strength and stability.

[0004] In view of the above problems, the present invention is based on the low-absorption and high-transparency long-wave infrared window substrate Ge and ZnSe, establishes the equivalent relationship between the double-sided design and the single-sided design under oblique incidence through numerical calculation, sets the target values ​​of the single-sided transmittance and reflectance at 45°, adopts the design method of alternating three refractive indices of high, medium and low to match the film system, completes the film system structure design optimization, and then respectively plates the same film system on both sides of the infrared window substrate to realize the preparation of the spectroscopic film. The spectroscopic film has the advantages of simple design, stable performance, and small surface shape change. Summary of the invention

[0005] The purpose of the present invention is to provide an oblique-incidence high-efficiency broadband long-wave splitting film, in particular, a film that can achieve a high-efficiency splitting function of 1:1 transmittance / reflectivity of a long-wave infrared window in the 7μm-12μm band by optimizing a specific film system structure design under an incident angle of 45° and then coating the same film system on both sides of a substrate. The splitting film has the advantages of simple design, stable performance, and small surface shape change.

[0006] The technical solution provided by the present invention is as follows:

[0007] The invention discloses an oblique-incidence high-efficiency broadband long-wave splitting film, which is characterized in that based on the equivalent relationship between double-sided design and single-sided design under oblique incidence, target values ​​of transmittance and reflectance of the 45° single-sided design are set, a design method of alternating high, medium and low refractive indices is adopted to match the film system, and design optimization is completed on the basis of the initial film system structure to achieve 1:1 high-efficiency splitting of the transmittance / reflectance of the long-wave infrared window in the 7μm-12μm band under 45° oblique incidence; the initial film system structure expression is G / (a1Ha2Ma3L)^n a1H / A, G is a substrate, H, M, L are respectively three refractive index materials with high, medium and low optical thicknesses of λ / 4, n is the number of film layer periods, a1, a2, a3 are respectively film layer thickness coefficients of the three materials with high, medium and low refractive indexes, and A is an air layer.

[0008] The film layer period number n is selected in the range of 1 to 10, and the film layer thickness coefficients a1, a2, and a3 are between 0.1 and 5.

[0009] The long-wave infrared window substrate is Ge or ZnSe.

[0010] The high refractive index material is Ge or PbTe.

[0011] The medium refractive index material is ZnS or ZnSe.

[0012] The low refractive index material is YF3, YbF3 or SrF2.

[0013] Compared with the prior art, the technical effects of the present invention are:

[0014] 1. Compared with the existing common design of splitter film, which has one side for splitting and the other side for broadband anti-reflection, it is necessary to design and optimize two film systems, and the film system structure is relatively complex. The present invention establishes the equivalent relationship between the double-sided design and the single-sided design under oblique incidence through numerical calculation, sets the single-sided transmittance and reflectance target values, and only needs to design and optimize one film system structure.

[0015] 2. The conventional solution of splitting light on one side and broadband anti-reflection on the other side is prone to cause significant changes in the substrate surface shape due to the large difference in the film structure of the two sides. The present invention reduces the complexity of the design while reducing the change in the substrate surface shape, and has the advantages of simple design, stable performance, and small surface shape change. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a schematic diagram of the structure of an oblique-incidence high-efficiency broadband long-wavelength spectroscopic film.

[0017] Figure 2 This is a graph showing how the single-side transmittance and reflectance of Example 1 change with the incident angle.

[0018] Figure 3 This is the optimal film structure of Example 1.

[0019] Figure 4 It is the double-sided transmittance and reflectance spectral curve at an incident angle of 45° in Example 1.

[0020] Figure 5 This is a graph showing how the single-side transmittance and reflectance of Example 2 change with the incident angle.

[0021] Figure 6 This is the optimal film structure of Example 2.

[0022] Figure 7 It is the double-sided transmittance and reflectance spectral curve at an incident angle of 45° in Example 2. DETAILED DESCRIPTION

[0023] The specific examples of the present invention are described in detail below with reference to the accompanying drawings.

[0024] Figure 1 The invention discloses an oblique-incidence high-efficiency broadband long-wavelength spectroscopic film. The equivalent relationship between the double-sided design and the single-sided design under oblique incidence is established by numerical calculation, the single-sided transmittance and reflectance target values ​​at 45° are set, and the film system is matched by a design method of alternating high, medium and low refractive indices. The design optimization is completed on the basis of the initial film system structure, and then the same film system is plated on both sides of the ZnSe substrate to realize the preparation of the spectroscopic film. The initial film system structure expression is G / (a1Ha2Ma3L)^n a1H / A, G is the substrate, H, M, L are three refractive index materials with high, medium and low optical thicknesses of λ / 4, n is the number of periods, a1, a2, a3 are the film thickness coefficients of the three materials with high, medium and low refractive indexes, and A is the air layer.

[0025] Example 1

[0026] The design index of the infrared window film required by Example 1 is: to achieve a range of 7 μm-12 μm, an incident angle of 45°, and a splitting ratio T:R=1:1 on the ZnSe window.

[0027] The specific design steps are as follows:

[0028] 1. According to the spectral characteristics of the target band, select long-wave broadband high-transmittance coating materials, high refractive index material Ge, medium refractive index material ZnS, and low refractive index material YbF3. The initial film structure is G / (HML)^2H / A, where H represents Ge with an optical thickness of one quarter wavelength, M represents ZnS with an optical thickness of one quarter wavelength, and L represents YbF3 with an optical thickness of one quarter wavelength. The refractive index parameters of high refractive index material Ge, medium refractive index material ZnS, and low refractive index material YbF3 are all determined by the Sellmeier formula The specific parameters are shown in Table 1.

[0029] Table 1: Refractive index parameters of high, medium and low refractive index materials in Example 1

[0030] <![CDATA[A1]]> <![CDATA[B1]]> <![CDATA[A2]]> <![CDATA[B2]]> Ge 14.9647 0.291572 -0.0155259 203.543 ZnS 3.98348 0.0387852 40.955 15956.9 <![CDATA[YbF3]]> 1.39173 -0.000332655 98.1245 13801.9

[0031] 2. At oblique incidence, the relationship between single-sided transmittance and reflectivity without obvious absorption is T 单 =1-R 单 , the relationship between the double-sided transmittance and the single-sided transmittance is T 双 =|T 单 | 2 , and the double-sided reflectivity can be expressed as R 双 =1-T 双 . According to the indicator requirement of the splitting ratio T:R=1:1 under 45° inclined incidence, it can be known that the target values ​​of transmittance and reflectance after double-sided coating are 50%. Combined with the principle of multilayer film characteristics in reference materials such as "Modern Optical Films and Technologies", and through computer-assisted numerical calculations, the relationship between the single-sided transmittance, reflectance and oblique incident angle at different incident angles is obtained, as shown in Table 2, and the change graphs of single-sided transmittance and reflectance with the incident angle are plotted accordingly, as shown in Table 2. Figure 2 shown.

[0032] Table 2: Relationship between single-side transmittance, reflectivity and oblique incident angle in Example 1

[0033] 0° 15° 30° 45° 60° 75° <![CDATA[T 单 ]]> 66.66％ 66.68％ 66.48％ 65.53％ 62.45％ 56.21％ <![CDATA[R 单 ]]> 33.34％ 33.32％ 33.52％ 34.47％ 37.55％ 43.79％

[0034] 3. According to Table 2 or Figure 2The relationship between the single-side transmittance and reflectance and the incident angle was determined to determine that the transmittance target in the 7μm-12μm mid-infrared band was 65.53% or the reflectance was 34.47% when the incident angle was 45°. The simplex and simulated annealing parameters optimization algorithms in the film design software were used to optimize the initial film structure.

[0035] 4. The best design result is obtained by optimization, which is G / 0.56H1.72M0.54L2.30H0.60M0.39L1.33H / A. The optimal membrane structure is as follows Figure 3 As shown, the number of film layers is 7, and the total film thickness is 1320nm. At an incident angle of 45°, the double-sided transmittance / reflectance spectrum curve of the ZnSe window film is as follows Figure 4 shown.

[0036] Comparative Example 1

[0037] The difference between this comparative example and Example 1 is that the two film surfaces adopt 50% splitting and 100% high transmittance design schemes respectively. The best design result is obtained by optimization. The 50% splitting surface film system structure is specifically G / 0.66H0.62M1.65L1.25H2.19M1.46L1.55H0.74M0.43L3.76H / A, the number of film layers is 10, and the total film thickness is 2820nm. The 100% high transmittance surface film system structure is specifically G / 1.48H0.58M0.44L6.61H0.99M0.1L1.36H2.98M2.46L0.1H0.1M2.46L / A, the number of film layers is 12, and the total film thickness is 3946nm. Compared with Example 1, the film structures on both sides of this solution are more complex and have greater differences. The film thickness is 2 to 3 times the film thickness in Implementation 1, which can easily lead to larger surface shape changes and film quality problems.

[0038] Example 2

[0039] The design index of the infrared window film required by Example 2 is: to achieve a range of 7 μm-12 μm on the Ge window, an incident angle of 45°, and a splitting ratio T:R=1:1.

[0040] The specific steps are as follows:

[0041] 1. According to the requirements of the spectral characteristics of the target band, select long-wave broadband high-transmittance coating materials, high refractive index materials Ge, medium refractive index materials ZnS, and low refractive index materials YbF3. The initial film structure is G / (HML)^2H / A, where H represents Ge with an optical thickness of one quarter wavelength, M represents ZnS with an optical thickness of one quarter wavelength, and L represents YbF3 with an optical thickness of one quarter wavelength. The refractive index parameters of high refractive index materials Ge, medium refractive index materials ZnS, and low refractive index materials YbF3 all have Sellmeier formulas The specific parameters are shown in Table 3:

[0042] Table 3: Refractive index parameters of high, medium and low refractive index materials in Example 2

[0043] <![CDATA[A1]]> <![CDATA[B1]]> <![CDATA[A2]]> <![CDATA[B2]]> Ge 14.9647 0.291572 -0.0155259 203.543 ZnS 3.98348 0.0387852 40.955 15956.9 <![CDATA[YbF3]]> 1.39173 -0.000332655 98.1245 13801.9

[0044] 2. At oblique incidence, the relationship between single-sided transmittance and reflectivity without obvious absorption is T 单 =1-R 单 , the relationship between the double-sided transmittance and the single-sided transmittance is T 双 =|T 单 | 2 , and the double-sided reflectivity can be expressed as R 双 =1-T 双 . According to the indicator requirement of the splitting ratio T:R=1:1 under 45° inclined incidence, it can be known that the target values ​​of transmittance and reflectance after double-sided coating are 50%. Combined with the principle of multilayer film characteristics in reference materials such as "Modern Optical Films and Technologies", and through computer-assisted numerical calculations, the relationship between the single-sided transmittance, reflectance and oblique incident angle at different incident angles is obtained, as shown in Table 4, and the change graphs of single-sided transmittance and reflectance with the incident angle are plotted accordingly, as shown in Table 4. Figure 4 shown.

[0045] Table 4: Relationship between single-side transmittance, reflectivity and oblique incident angle in Example 2

[0046] 0° 15° 30° 45° 60° 75° <![CDATA[T 单 ]]> 67.96％ 67.94％ 67.79％ 66.87％ 63.80％ 61.39％ <![CDATA[R 单 ]]> 32.04％ 32.06％ 32.21％ 33.13％ 36.20％ 38.61％

[0047] 3. According to Table 2 or Figure 2 The relationship between the single-side transmittance and reflectance and the incident angle was determined to determine that the transmittance target in the 7μm-12μm mid-infrared band was 66.87% or the reflectance was 33.13% when the incident angle was 45°. The simplex and simulated annealing parameters optimization algorithms in the film design software were used to optimize the initial film structure.

[0048] 4. The best design result is obtained by optimization, which is G / 0.99H0.22M0.15L3.73H0.32M0.32L3.50H / A. The optimal membrane structure is as follows Figure 6 As shown, the number of film layers is 7. At an incident angle of 45°, the double-sided transmittance / reflectance spectrum curve of the Ge window film is as follows Figure 7 shown.

[0049] The above description is only a preferred example of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An oblique-incidence high-efficiency broadband long-wavelength spectroscopic film, characterized in that: Based on the equivalent relationship between double-sided design and single-sided design under oblique incidence, the target values ​​of transmittance and reflectance of the 45° single-sided design are set, and the film system is matched by a design method that alternates between high, medium and low refractive indices. The design optimization is completed based on the initial film system structure to achieve efficient spectral splitting with a transmittance / reflectance of 1:1 in the long-wave infrared window within the 7μm-12μm band under 45° oblique incidence. The initial film system structure expression is G / (a1Ha2Ma3L)^n a1H / A, where G is the substrate, H, M, and L are high, medium, and low refractive index materials with optical thickness of λ / 4, respectively, n is the number of film layer periods, a1, a2, and a3 are high, medium, and low material film layer thickness coefficients, respectively, and A is the air layer.

2. The oblique-incidence high-efficiency broadband long-wavelength spectroscopic film according to claim 1, characterized in that: The film layer period number n is selected in the range of 1 to 10, and the film layer thickness coefficients a1, a2, and a3 are between 0.1 and 5.

3. The oblique-incidence high-efficiency broadband long-wavelength spectroscopic film according to claim 1 or 2, characterized in that: The long-wave infrared window substrate is Ge or ZnSe.

4. The oblique-incidence high-efficiency broadband long-wavelength spectroscopic film according to claim 1 or 2, characterized in that: The high refractive index material is Ge or PbTe.

5. The oblique-incidence high-efficiency broadband long-wavelength spectroscopic film according to claim 1 or 2, characterized in that: The medium refractive index material is ZnS or ZnSe.

6. The oblique-incidence high-efficiency broadband long-wavelength spectroscopic film according to claim 1 or 2, characterized in that: The low refractive index material is YF3, YbF3 or SrF2.

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