A broadband optical glass anti-reflection structure

Abstract

This invention discloses a broadband optical glass antireflection structure, belonging to optical thin film technology, comprising an optical glass substrate, a first refractive layer, a second refractive layer, and a third refractive layer; the third refractive layer is disposed on the optical glass substrate, and the second and first refractive layers are sequentially disposed on the third refractive layer; the first and third refractive layers are made of TiO2, and the second refractive layer is made of MgF2. 2； The thickness of the first refractive layer is 4 nm; the thickness of the second refractive layer is 100 nm; and the thickness of the third refractive layer is 8 nm. Compared with the best existing three-layer anti-reflective film solution (average reflectivity 2.0%-2.2%), this invention reduces the average reflectivity of N-BK7 glass to 1.18%, reducing reflection loss by 41%-46%. Compared with uncoated N-BK7 glass, reflection loss is reduced by 72%, effectively improving the light transmission efficiency and imaging quality of the optical system.

Description

Technical Field

[0001] This invention relates to the field of optical thin film technology, and in particular to a broadband optical glass anti-reflection structure. Background Technology

[0002] Optical glass, as a core component in optoelectronic information, aerospace, and precision instruments, suffers from surface reflection that directly leads to light energy loss, reduced imaging contrast, and stray light interference, severely impacting the overall performance of optical systems. N-BK7 optical glass, due to its excellent optical uniformity, low dispersion characteristics, and superior processing performance, is widely used in key optical components such as lenses, prisms, and windows. In the visible light band (400-700nm), the refractive index of air is approximately 1.0, while that of N-BK7 optical glass is approximately 1.5168. According to Fresnel's law of reflection, the natural reflectivity of the air-glass interface is approximately 4.2%. In high-precision optical systems (such as camera lenses, laser rangefinders, and spectrometers), this reflection loss accumulates and amplifies, leading to decreased system transmittance and reduced imaging clarity. Therefore, it is crucial to reduce surface reflectivity through anti-reflective structural design. Existing anti-reflective film solutions typically employ the following methods: (1) Single-layer anti-reflective film solution; This was the earliest commercially available anti-reflection technology. Its core principle is to deposit a single-refractive-index optical thin film on the surface of N-BK7 glass, with a film thickness designed to be 1 / 4 of the center wavelength of visible light (approximately 550 nm). Commonly used single-layer thin film materials include magnesium difluoride (MgF2, refractive index n=1.38) and silicon dioxide (SiO2, refractive index n=1.46). The design logic is as follows: when the film refractive index satisfies n=√(n0×n_sub) (where n0 is the air refractive index and n_sub is the glass substrate refractive index), the reflected light amplitudes on the upper and lower surfaces of the film are equal. Combined with the phase difference introduced by the 1 / 4 wavelength thickness, destructive interference can be achieved. For N-BK7 glass (n_sub=1.52), the ideal refractive index of a single-layer thin film should be √(1.0×1.52)≈1.23. However, there are no commonly used materials with a perfectly matching refractive index. Therefore, the MgF2 (n=1.38) or SiO2 (n=1.46) used in practice are approximately matching materials. Their existence is due to the following reasons: limited reduction in reflectivity: due to the lack of thin film materials with ideal refractive indices, actual single-layer MgF2 or SiO2 films can only reduce the average reflectivity of N-BK7 glass from 4.2% to 2.5%-3.0%, which is insufficient to meet the requirements of high-precision optical systems for low reflectivity (e.g., below 2%); and insufficient stability: the adhesion between some single-layer films (such as SiO2) and the N-BK7 glass substrate is weak, and long-term use can easily lead to problems such as detachment and scratches.

[0003] (2) Double-layer anti-reflective film solution: To overcome the limited reflectivity reduction of single-layer antireflective films, a double-layer antireflective film scheme has been developed. This scheme involves depositing two thin films with different refractive indices (typically a high-refractive-index layer + a low-refractive-index layer or a low-refractive-index layer + a high-refractive-index layer). Utilizing the multiple interference effects of the two layers, the antireflective wavelength range is broadened, and reflectivity is further reduced. Common double-layer structure combinations include: titanium dioxide (TiO2, n=2.3-2.5) + magnesium difluoride (MgF2, n=1.38), and tantalum pentoxide (Ta2O5, n=2.1) + silicon dioxide (SiO2, n=1.46). For example, some schemes employ a structure of "high-refractive-index layer (TiO2, thickness approximately 30-50 nm) + low-refractive-index layer (MgF2, thickness approximately 80-120 nm)," optimizing the thickness of the two layers to further reduce the average reflectivity in the 400-700 nm wavelength band compared to single-layer schemes.

[0004] Its disadvantages are: there is still room for improvement in reflectivity: the average reflectivity of existing double-layer solutions is usually between 2.0% and 2.5%, which is difficult to break through the key threshold below 2.0%; the complexity of the process is increased: compared with the single-layer solution, the double-layer solution requires higher precision in film thickness control, resulting in reduced production efficiency and increased costs.

[0005] (3) Multi-layer (three or more layers) anti-reflective film solution; To meet the stringent requirements of high-precision optical systems, multilayer anti-reflective film solutions with three or more layers have emerged. These solutions further optimize refractive index gradient matching and interference phase adjustment by increasing the number of film layers, achieving anti-reflective effects with a wider wavelength range and lower reflectivity.

[0006] Existing multilayer designs often employ alternating refractive index structures of "high-low-high" or "low-high-low," with common material combinations including TiO2 (high), MgF2 (low), SiO2 (medium-low), and Ta2O5 (high). For example, some existing three-layer designs use structures such as "SiO2 (low, thickness 20-40nm) + TiO2 (high, thickness 50-70nm) + MgF2 (low, thickness 90-110nm)," or "TiO2 (high, thickness 30-40nm) + SiO2 (medium-low, thickness 60-80nm) + MgF2 (low, thickness 100-120nm)," aiming to achieve an average reflectivity of less than 2.5% in the visible light band.

[0007] Its drawbacks are: Unreasonable structural design: The material combination (e.g., "low-high-low") and thickness distribution (e.g., excessively thick high-refractive-index layer) of existing three-layer schemes result in insufficient superposition of interference effects, failing to fully utilize the phase adjustment effect of each layer; Limited reflectivity optimization: The average reflectivity of existing three-layer schemes is mostly between 2.0% and 2.2%, and performance needs improvement; High manufacturing difficulty: Increasing the number of layers significantly increases the difficulty of controlling the thickness uniformity and refractive index consistency of each thin film, and the compatibility of various high-refractive-index materials used in some schemes is poor, easily leading to problems such as interlayer diffusion and oxidation; High cost: The complex structural design and stringent process requirements result in high production costs for existing multilayer schemes, making large-scale application difficult. (4) Other auxiliary solutions; In addition to traditional thin film deposition methods, some studies have used the sol-gel method to prepare porous antireflective films and nanostructure array antireflective layers. However, these methods have problems such as poor process stability, low mechanical strength, and insufficient environmental resistance, and have not been widely used in industrial production. The mainstream commercial applications are still mainly based on vacuum deposition of multilayer thin films.

[0008] The disadvantages are: porous films prepared by the sol-gel method have problems such as difficulty in accurately controlling porosity, low mechanical strength, and poor resistance to humid and hot environments; while nanostructure array antireflective layers face problems such as complex preparation process, difficulty in large-scale production, and easy surface contamination, all of which cannot meet the stability and cost requirements of industrial applications. Summary of the Invention

[0009] The purpose of this invention is to provide a wide-band optical glass anti-reflection structure to solve the problems mentioned in the background art. By precisely designing the combination of thin film materials, refractive index gradient and the thickness of each layer, the average reflectivity of N-BK7 optical glass in the visible light band (400-700nm) is significantly reduced.

[0010] This invention is achieved through the following scheme: A broadband optical glass antireflection structure includes an optical glass substrate, a first refractive layer, a second refractive layer, and a third refractive layer; the third refractive layer is disposed on the optical glass substrate, and the second refractive layer and the first refractive layer are disposed sequentially on the third refractive layer; the first refractive layer and the third refractive layer are made of TiO2, and the second refractive layer is made of MgF2.

[0011] Based on the above-mentioned antireflective structure of a wide-band optical glass, the thickness of the first refractive layer is 4nm, and the optical thickness is 4nm×2.4=9.6nm.

[0012] Based on the above-mentioned antireflective structure of a wide-band optical glass, the thickness of the second refractive layer is 100nm, and the optical thickness is 100nm×1.38=138nm.

[0013] Based on the above-mentioned antireflective structure of a wide-band optical glass, the thickness of the third refractive layer is 8nm: the optical thickness is 8nm × 2.4 = 19.2nm.

[0014] Based on the above-mentioned anti-reflection structure of a wide-band optical glass, the optical glass substrate is an N-BK7 optical glass substrate; the refractive index of the N-BK7 optical glass substrate is 1.5168; the refractive index of TiO2 material is 2.4, the refractive index of MgF2 material is 1.38, and the refractive index of air is 1.0.

[0015] This solution also discloses a fabrication process for a broadband optical glass antireflection structure, including the following steps: Step S1: Substrate pretreatment: Clean the N-BK7 optical glass substrate to remove surface oil, dust and other impurities to ensure the cleanliness of the substrate surface; Step S2: Vacuum environment preparation: Place the pretreated glass substrate into the vacuum evaporation equipment and evacuate the vacuum to avoid the influence of gas on the film quality during the evaporation process; Step S3: Evaporation of refractive layers: Evaporation is performed on the first refractive layer, the second refractive layer, and the third refractive layer according to different refractive requirements; Step S4: Post-processing: After the vapor deposition is completed, the sample is kept warm in a vacuum environment, and then slowly cooled to room temperature before being taken out to ensure the adhesion and stability of the film layer to the substrate and between each film layer.

[0016] Step S3 specifically includes the following steps: S31: Third refractive layer evaporation: Electron beam evaporation is used with high-purity TiO2 as the evaporation source. A predetermined evaporation rate is adopted, and the film thickness is monitored in real time by a quartz crystal film thickness monitor. Evaporation is stopped when the thickness reaches 8nm. S32: Second refractive layer evaporation: Replace the evaporation source with high-purity MgF2, use the predetermined evaporation rate, continue to monitor the thickness through a quartz crystal film thickness monitor, and stop evaporation when it reaches 100nm; S33: First refractive layer evaporation: The TiO2 evaporation source was changed again, and the evaporation rate was precisely controlled to a thickness of 4nm before evaporation was stopped.

[0017] In step S31, the evaporation rate of TiO2 is 0.1-0.2 nm / s; In step S32, the evaporation rate of MgF2 is 0.2-0.3 nm / s; In step S33, the evaporation rate of TiO2 is 0.1 nm / s.

[0018] In step S1, the steps for cleaning the N-BK7 optical glass substrate are as follows: the N-BK7 optical glass substrate is cleaned by ultrasonic cleaning, wiped with alcohol, rinsed with deionized water, and dried in sequence.

[0019] In step S2: Evacuate to 1×10 -5 A high vacuum environment above Pa; in step S4, the sample is kept in a vacuum environment for 30 minutes.

[0020] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: (1) Significantly lower reflectivity: Compared with the best existing three-layer anti-reflective film solution (average reflectivity 2.0%-2.2%), the present invention reduces the average reflectivity of N-BK7 glass to 1.18%, and reduces reflection loss by 41%-46%; compared with uncoated N-BK7 glass, the reflection loss is reduced by 72%, effectively improving the light transmission efficiency and imaging quality of the optical system.

[0021] (2) Higher structural stability: The adhesion between TiO2 and N-BK7 glass substrate and MgF2 film is excellent. The chemical stability and mechanical strength of the three-layer structure are better than the existing multilayer schemes. The scratch resistance and damp heat resistance are more in line with the needs of industrial applications.

[0022] (3) Simpler and more controllable process: This invention uses only two commonly used optical materials (TiO2 and MgF2). Compared with the multiple material combinations used in the existing three-layer scheme, the process compatibility is better, the thickness control is easier, the production efficiency is higher, and the cost is more advantageous. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the three-layer anti-reflective film structure in this invention; Figure 2 This is a schematic diagram of the reflectivity of the N-BK7 glass + three-layer film structure in this invention; Figure 3 This is a schematic diagram of the preparation process in this invention. Detailed Implementation

[0024] All features disclosed in this specification, or steps in all methods or processes disclosed herein, may be combined in any way, except for mutually exclusive features and / or steps.

[0025] Any feature disclosed in this specification (including any appended claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0026] In the description of this invention, it should be understood that the terms "upper", "lower", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0027] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature.

[0028] Example 1 like Figures 1-2 As shown, the present invention provides a technical solution: A broadband optical glass antireflection structure includes an optical glass substrate, a first refractive layer, a second refractive layer, and a third refractive layer; the third refractive layer is disposed on the optical glass substrate, and the second refractive layer and the first refractive layer are disposed sequentially on the third refractive layer; the first refractive layer and the third refractive layer are made of TiO2, and the second refractive layer is made of MgF2. Based on the above structure, the TiO2 in this solution exhibits excellent adhesion to the N-BK7 glass substrate and the MgF2 film. The chemical stability and mechanical strength of the three-layer structure are superior to existing multilayer solutions, and its scratch resistance and damp heat resistance better meet the requirements of industrial applications. This invention uses only two commonly used optical materials (TiO2 and MgF2), which, compared to the multiple material combinations used in existing three-layer solutions, offers better process compatibility, easier thickness control, higher production efficiency, and greater cost advantages.

[0029] As an example, the thickness of the first refractive layer (TiO2) is 4nm, and the optical thickness is 4nm×2.4=9.6nm. This thickness design can enable effective destructive interference of reflected light in the short-wavelength region (400-500nm), making up for the defect of excessive short-wavelength reflectivity in traditional schemes. As an example, the second refractive layer (MgF2) has a thickness of 100nm, and an optical thickness of 100nm × 1.38 = 138nm, which is close to 1 / 4 of the center wavelength of visible light (550nm) (550nm / 4 = 137.5nm). It is the core layer for realizing destructive interference across the entire wavelength range and can effectively cancel the reflected light in the 500-600nm mid-wave region.

[0030] As an example, the thickness of the third refractive layer (TiO2) is 8nm: the optical thickness is 8nm × 2.4 = 19.2nm. This thickness design can form a phase complement with the first TiO2 film layer, accurately adjust the reflected light in the long-wavelength region (600-700nm), and ensure a uniform reduction in reflectivity across the entire wavelength range.

[0031] Based on the above structure, the synergistic design of the thickness of the three film layers in this scheme enables the reflected light of each wavelength in the 400-700nm band to generate superimposed destructive interference, ultimately achieving a significant reduction in average reflectivity, with an average reflectivity of 1.18% in the 400-700nm band.

[0032] As an example, the optical glass substrate is an N-BK7 optical glass substrate; the refractive index of the N-BK7 optical glass substrate is 1.5168 (average refractive index in the visible light band), and the average refractive index of each film material in the visible light band is: TiO2 (2.4), MgF2 (1.38), and the refractive index of air is 1.0; the anti-reflection structure of the present invention is deposited on the surface of the N-BK7 optical glass substrate, from the air side to the glass substrate side (i.e., the film deposition sequence is glass substrate → third refractive layer → second refractive layer → first refractive layer → air).

[0033] Material selection criteria: Titanium dioxide (TiO2): High-purity TiO2 is selected as a high-refractive-index material. Its refractive index (2.4) is much higher than that of N-BK7 glass substrate, which can effectively adjust the phase difference of reflected light. In addition, TiO2 has strong adhesion to N-BK7 glass substrate, good chemical stability, and excellent scratch resistance and damp heat resistance. Magnesium difluoride (MgF2): High-purity MgF2 is selected as a low refractive index material. Its refractive index (1.38) is close to the ideal low refractive index value. MgF2 has good optical transparency, chemical stability and film formation quality, and is a classic low refractive index material for anti-reflective films. Material combination logic: A three-layer structure of "high refractive index (TiO2) - low refractive index (MgF2) - high refractive index (TiO2)" is adopted to form a refractive index distribution of "air (1.0) → TiO2 (2.4) → MgF2 (1.38) → TiO2 (2.4) → N-BK7 glass (1.5168)". Through the "high-low-high" transition of refractive index, the gradient adaptation between air and glass substrate is achieved, reducing the abrupt change in interface reflection and enhancing the destructive interference effect.

[0034] Example 2 like Figure 3 As shown, the present invention provides a technical solution: A fabrication process for a broadband optical glass antireflection structure specifically includes the following steps: Step S1: Substrate pretreatment: The N-BK7 optical glass substrate is cleaned (sequentially ultrasonic cleaning, alcohol wiping, deionized water rinsing, and drying) to remove surface oil, dust and other impurities, ensuring the cleanliness of the substrate surface; Step S2: Vacuum Environment Preparation: Place the pretreated glass substrate into the vacuum evaporation equipment and evacuate to a vacuum level of 1×10⁻⁶. -5 A high vacuum environment above Pa is provided to avoid the impact of gas on the film quality during the vapor deposition process. Step S3: Refractive layer deposition: Deposition of the first, second, and third refractive layers by vapor deposition according to different refractive requirements; specifically including the following steps: S31: Third refractive layer (TiO2, 8nm) vapor deposition: Electron beam evaporation method is used, with high-purity TiO2 as the evaporation source, and the vapor deposition rate is controlled at 0.1-0.2nm / s. The film thickness is monitored in real time by a quartz crystal film thickness monitor, and the vapor deposition is stopped when the thickness reaches 8nm. S32: Second refractive layer (MgF2, 100nm) vapor deposition: Replace the evaporation source with high-purity MgF2, maintain the vapor deposition rate at 0.2-0.3nm / s, continue to monitor the thickness using a quartz crystal film thickness monitor, and stop vapor deposition when it reaches 100nm; S33: First refractive layer (TiO2, 4nm) vapor deposition: The TiO2 evaporation source was replaced again, the vapor deposition rate was controlled at 0.1nm / s, and the vapor deposition was stopped after the thickness was precisely controlled to 4nm. Step S4: Post-treatment: After the vapor deposition is completed, the sample is kept in a vacuum environment for 30 minutes, and then slowly cooled to room temperature before being taken out to ensure the adhesion and stability of the film layer to the substrate and between each film layer.

[0035] The preparation process is mature and reliable, and the parameter control precision of each step can be achieved with existing equipment, making it suitable for large-scale industrial production.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A broadband optical glass anti-reflection structure, characterized in that: It includes an optical glass substrate, a first refractive layer, a second refractive layer, and a third refractive layer; the third refractive layer is disposed on the optical glass substrate, and the second and first refractive layers are disposed on the third refractive layer in sequence; the materials of the first and third refractive layers are TiO2, and the material of the second refractive layer is MgF2; the thickness of the first refractive layer is 4nm, and the optical thickness is 4nm × 2.4 = 9.6nm; the thickness of the second refractive layer is 100nm, and the optical thickness is 100nm × 1.38 = 138nm; the thickness of the third refractive layer is 8nm, and the optical thickness is 8nm × 2.4 = 19.2nm; the optical glass substrate is an N-BK7 optical glass substrate; the refractive index of the N-BK7 optical glass substrate is 1.5168; the refractive index of TiO2 material is 2.4, the refractive index of MgF2 material is 1.38, and the refractive index of air is 1.

0.

2. The broadband optical glass anti-reflection structure as described in claim 1, characterized in that: This includes a fabrication process for a broadband optical glass antireflection structure, which comprises the following steps: Step S1: Substrate pretreatment: Clean the N-BK7 optical glass substrate to remove surface oil, dust and other impurities to ensure the cleanliness of the substrate surface; Step S2: Vacuum environment preparation: Place the pretreated glass substrate into the vacuum evaporation equipment and evacuate the vacuum to avoid the influence of gas on the film quality during the evaporation process; Step S3: Evaporation of refractive layers: Evaporation is performed on the first refractive layer, the second refractive layer, and the third refractive layer according to different refractive requirements; Step S4: Post-processing: After the vapor deposition is completed, the sample is kept warm in a vacuum environment, and then slowly cooled to room temperature before being taken out to ensure the adhesion and stability of the film layer to the substrate and between each film layer.

3. The broadband optical glass anti-reflection structure as described in claim 2, characterized in that: Step S3 specifically includes the following steps: S31: Third refractive layer evaporation: Electron beam evaporation is used with high-purity TiO2 as the evaporation source. A predetermined evaporation rate is adopted, and the film thickness is monitored in real time by a quartz crystal film thickness monitor. Evaporation is stopped when the thickness reaches 8nm. S32: Second refractive layer evaporation: Replace the evaporation source with high-purity MgF2, use the predetermined evaporation rate, continue to monitor the thickness through a quartz crystal film thickness monitor, and stop evaporation when it reaches 100nm; S33: First refractive layer evaporation: The TiO2 evaporation source was changed again, and the evaporation rate was precisely controlled to a thickness of 4nm before evaporation was stopped.

4. The broadband optical glass anti-reflection structure as described in claim 3, characterized in that: In step S31, the evaporation rate of TiO2 is 0.1-0.2 nm / s; In step S32, the evaporation rate of MgF2 is 0.2-0.3 nm / s; In step S33, the evaporation rate of TiO2 is 0.1 nm / s.

5. The broadband optical glass anti-reflection structure as described in claim 4, characterized in that: In step S1, the steps for cleaning the N-BK7 optical glass substrate are as follows: the N-BK7 optical glass substrate is cleaned by ultrasonic cleaning, wiped with alcohol, rinsed with deionized water, and dried in sequence.

6. The broadband optical glass anti-reflection structure as described in claim 5, characterized in that: In step S2: Evacuate to 1×10 -5 A high vacuum environment above Pa; in step S4, the sample is kept in a vacuum environment for 30 minutes.

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