Anti-reflection film, optical fiber, optical component, and method for manufacturing anti-reflection film

Abstract

To provide an anti-reflection coating which can be manufactured at low cost and which has a low refraction index in a wide band, irrespective of variation in optical film thickness and refractive index.SOLUTION: Provided is an anti-reflection coating 10, in which nine layers of optical thin-films (11-19) are laminated on a surface 2 of a substrate 1 the refractive index of which is 1.44 to 1.47 inclusive, the first layer which is in contact with the surface of the substrate and the third, fifth, seventh and ninth layers being composed of an SiO2 whose refractive index with respect to the design center wavelength is 1.45±0.01, the second, fourth, sixth and eighth layers being composed of a Ta2O5 whose refractive index is 2.10±0.10. The reflectance of the anti-reflection coating 10 in a wavelength band from 1260 nm to 1625 nm inclusive is 0.2% or less when the optical film thickness ndk of the k-th layer is 100nm≤nd1≤700nm, 100nm≤nd2≤165nm, 100nm≤nd3≤260nm, 100nm≤nd4≤700nm, 100nm≤nd5≤700nm, 100nm≤nd6≤700nm, 100nm≤nd7≤700nm, 100nm≤nd8≤700nm, and 100nm≤nd9≤700nm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an anti-reflection film, an optical fiber, an optical component, and a method for manufacturing an anti-reflection film. [Background technology]

[0002] A well-known anti-reflection coating made of a dielectric multilayer film is formed by alternately laminating two types of dielectric thin films (hereinafter sometimes referred to as "optical thin films") with different refractive indices on the surface of a substrate (such as an optical fiber or a glass substrate).

[0003] For example, in products using optical fibers (fiber assembly products: hereinafter referred to as FA products), anti-reflection coatings are provided on the end faces of optical fibers for the purposes of reducing insertion loss, preventing stray light, etc. A well-known anti-reflection coating formed on the end faces of optical fibers is one that, taking durability into consideration, is made by alternately laminating optical thin films made of SiO2, a low refractive index material, and Ta2O5, a high refractive index material.

[0004] Conventional antireflection coatings for optical fibers have an antireflection target wavelength band (hereinafter sometimes referred to as "antireflection band") of about 100 nm, and the number of layers in the dielectric multilayer coating is 4 to 5. However, in recent years, there has been a demand for antireflection coatings with a wider antireflection band, and Patent Document 1 below discloses an antireflection coating with 9 layers. Furthermore, Non-Patent Document 1 below provides an overview of a deposition apparatus (IAD) using ion beam assisted deposition technology related to the present invention. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3741692 [Non-patent literature]

[0006] [Non-Patent Document 1] Shincron Co., Ltd., "4. Various Physical Vapor Deposition (PVD) Film Forming Methods," [online], [Retrieved July 15, 2021], Internet<URL:https: / / www.shincron.co.jp / technical / device4-1.html> Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, antireflection films are required to have low reflectance (e.g., 0.2%) for light in a wide antireflection band (e.g., 1260 nm to 1625 nm). The antireflection film described in Patent Document 1 has such properties, but when considering mass production as an industrial product, the production costs are high and there is a possibility that the properties will vary.

[0008] Specifically, the optical properties of the optical thin films constituting each layer of the dielectric multilayer film that serves as an anti-reflection film are determined by the optical film thickness (also called optical film thickness, hereinafter referred to as "optical film thickness") nd, which is the product of the refractive index n of the film material and the physical film thickness d of the thin film. The optical thin films of each layer are formed using a film-forming device such as a sputtering device or a vapor deposition device.

[0009] Although sputtering devices are capable of forming uniform films and can control the film formation rate with high precision by adjusting the input power and film formation processing time, their film formation rate is slower than other film formation devices. Furthermore, sputtering devices are more expensive than vapor deposition devices and require strict target management. Therefore, when mass-producing industrial products such as optical fibers with anti-reflection coatings, it is desirable to use vapor deposition methods, which have low equipment costs, are suitable for mass production, and require low film formation temperatures.

[0010] On the other hand, evaporation equipment poses the challenge of unstable characteristics due to variations in the refractive index of the deposited optical thin film. This refractive index variation can occur in two ways. The first is a large variation dependent on the equipment, occurring between different evaporation equipment or depending on the position of the substrate within the vacuum chamber of the same evaporation equipment. For example, the refractive index of SiO2, a low-refractive-index material, can vary by up to 0.02, while the refractive index of Ta2O5, a high-refractive-index material, can vary by up to 0.2. While this type of variation stabilizes between batches, it is necessary to individually adjust the target thickness of the optical thin film for each evaporation equipment.

[0011] The second type of variation is small variations in refractive index that occur during the manufacturing process. This is due to contamination of the deposition equipment and the number of workpieces loaded (e.g., variations in the refractive index of the substrate). To address this type of variation, a film thickness control method is required in which the refractive index n and optical film thickness nd are measured using an optical film thickness meter and the film formation process is terminated when a set optical film thickness is reached. However, film thickness control methods using optical film thickness meters have the problem that the refractive index cannot be measured when the optical film thickness is 100 nm or less, making it difficult to correct for variations in refractive index. The anti-reflection coating described in Patent Document 1 includes a layer with an optical film thickness thinner than 100 nm.

[0012] Figure 1 shows the optical characteristics of the antireflection coating described in Patent Document 1, taking into account variations that occur during the manufacturing process. Figure 1 also shows the spectral reflectance characteristics of the antireflection coating described in Patent Document 1, obtained by simulation, which uses SiO2 and Ta2O5 as film materials (see Patent Document 1, Table 3). The figure shows the simulation results of the optical characteristics based on the design values ​​(R-Design) and the simulation results of the optical characteristics when there is variation in the refractive index, where the error from the design value is maximum (R-Max). As shown in Figure 1, the simulation results (R-Max) corresponding to the characteristics of the antireflection coating actually manufactured deviate from the design value characteristics (R-Design). In other words, even if the design specifications (in the figure, a reflectance of 0.2% or less in the wavelength band of 1260 nm to 1625 nm) are met, some of the antireflection coatings actually manufactured do not meet the specifications. Therefore, when antireflection coatings are manufactured using a vapor deposition system, the yield may be reduced. If the yield rate decreases, the manufacturing cost increases, and the benefit of cost reductions achieved by a vapor deposition apparatus that is suitable for mass production cannot be obtained.

[0013] Therefore, an object of the present invention is to provide an antireflection coating that can reduce manufacturing costs and has a low reflectance over a wide band even if there are variations in optical film thickness and refractive index during manufacturing, an optical fiber having such an antireflection coating formed on its end surface, an optical component including such an optical fiber, and a method for forming an antireflection coating. [Means for solving the problem]

[0014] One aspect of the present invention for achieving the above object is an antireflection coating comprising nine optical thin films laminated on the surface of a substrate having a refractive index of 1.44 to 1.47 relative to a medium having a refractive index of 1, The layer in contact with the surface of the substrate is designated as the first layer, and the SiO 2 layer has a refractive index of 1.45±0.01 for the design central wavelength. 2 and Ta having a refractive index of 2.10±0.10 for the design central wavelength. 2 O 5 The optical film thickness of the kth layer is nd. k Then, 100 nm ≦ nd 1 ≦150nm, 100nm≦nd 2 ≦165nm, 100nm≦nd 3 ≦260nm, 100nm≦nd 4 ≦500nm, 100nm≦nd 5 ≦400nm, 100nm≦nd 6 ≦260nm, 100nm≦nd 7 ≦260nm, 350nm≦nd 8 ≦650nm, 300nm≦nd 9 ≦400 nm, and the anti-reflection film has a reflectance of 0.2% or less in the wavelength band of 1260 nm or more and 1625 nm or less.

[0015] The scope of the present invention also includes an optical fiber having the above-mentioned antireflection film on its end face, and an optical component incorporating the optical fiber.

[0016] A method for manufacturing an antireflection film having a reflectance of 0.2% or less in a wavelength band of 1260 nm or more and 1625 nm or less, the method comprising: forming the antireflection film consisting of nine optical thin films on the surface of a substrate having a refractive index of 1.44 or more and 1.47 or less relative to a medium having a refractive index of 1, by a vapor deposition method; in the film formation step, the optical thin film in contact with the surface of the substrate is designated as a first layer; and forming first, third, fifth, seventh, and ninth layers made of SiO2 having a refractive index of 1.45±0.01 at a design central wavelength; and second, fourth, sixth, and eighth layers made of Ta2O5 having a refractive index of 2.10±0.10 at the design central wavelength, from the first layer to the ninth layer, in order based on the design values ​​of the optical thicknesses of the respective layers; and determining a design value nd of the optical thickness of the k-th layer, where k is a natural number from 1 to 9. k of, 100nm≦nd 1 ≦150nm, 100nm≦nd 2 ≦165nm, 100nm≦nd 3 ≦260nm, 100nm≦nd 4 ≦500nm, 100nm≦nd 5 ≦400nm, 100nm≦nd 6 ≦260nm, 100nm≦nd 7 ≦260nm, 350nm≦nd 8 ≦650nm, 300nm≦nd 9 ≦400nm, This is a method for manufacturing an anti-reflection film. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide an antireflection coating that can reduce manufacturing costs and has a low reflectance over a wide band even if there are variations in the optical film thickness and refractive index during manufacturing, an optical fiber having such an antireflection coating formed on its end face, an optical component including such an optical fiber, and a method for forming an antireflection coating. Other effects will be made clear in the following description. [Brief explanation of the drawings]

[0019] [Figure 1]FIG. 1 is a diagram showing the optical characteristics based on the design values ​​and the optical characteristics obtained by simulation when variations that occur in the manufacturing process are taken into consideration for the antireflection film described in Patent Document 1. [Figure 2] 1A and 1B are diagrams showing the structure of an anti-reflection film according to an example. [Figure 3] FIG. 10 is a diagram showing optical characteristics based on design values ​​and optical characteristics obtained by simulation when variations occurring in the manufacturing process are taken into consideration for the antireflection film according to the example. [Figure 4] FIG. 10 is a diagram showing measurement results of optical properties of an antireflection film according to an example. DETAILED DESCRIPTION OF THE INVENTION

[0020] An embodiment of the present invention will now be described with reference to the accompanying drawings.

[0021] ===Optical Simulation=== As is well known, the optical characteristics of an antireflection coating made of a dielectric multilayer film can be determined with high accuracy by simulation based on Fresnel's law, without actually measuring the fabricated antireflection coating. If each layer constituting the antireflection coating is fabricated according to the conditions (optical film thickness, refractive index, etc.) given in the simulation, the optical characteristics of the fabricated antireflection coating will reflect the optical characteristics obtained by the simulation.

[0022] However, as mentioned above, the above conditions vary during the manufacturing process of an anti-reflection film. This variation is particularly large when an optical thin film with an optical film thickness of less than 100 nm is manufactured using a deposition apparatus that controls the film thickness using an optical film thickness gauge. Therefore, if the variation in the conditions during the manufacturing process is not taken into consideration, the characteristics of the anti-reflection film actually manufactured will deviate from the characteristics obtained by simulation.

[0023] ===Example=== The antireflection coating according to the embodiment is formed on the surface of a substrate. Examples of the substrate include a glass substrate and an optical fiber. FIG. 2 shows a schematic structure of an antireflection coating 10 according to the embodiment. The antireflection coating 10 shown in FIG. 2 uses an optical fiber 1 as the substrate and is formed on the end surface 2 of the optical fiber 1, which is the surface of the substrate. The dielectric multilayer film constituting the antireflection coating 10 is formed from the first layer, which is in contact with the end surface 2 of the optical fiber 1, to the ninth layer, which is in contact with air. The first layer is an optical thin film 11 made of SiO2, the second layer is an optical thin film 12 made of Ta2O5, and optical thin films (13-19) made of SiO2 and Ta2O5 are alternately stacked toward the ninth optical thin film 19. In the figure, the optical thin films (11, 13, 15, 17, 19) made of SiO2 are indicated by dotted hatching, and the optical thin films (12, 14, 16, 18) made of Ta2O5 are indicated by diagonal hatching.

[0024] The antireflection coating 10 according to the embodiment satisfies the desired specifications even if there are variations in the various conditions that determine the optical characteristics during the manufacturing process. Here, the specification is set as "reflectance of 0.2% or less in the wavelength band of 1260 nm to 1625 nm." In order to satisfy the above specifications, the antireflection coating 10 according to the embodiment has appropriate optical film thicknesses set for predetermined layers of the first to ninth optical thin films (11 to 19) based on the optical simulation described above.

[0025] In the simulation, we assumed that an optical fiber was used as the substrate and that an antireflection coating 10 was fabricated on the end face of the optical fiber by vapor deposition, and set the lower limit of the optical film thickness of each optical thin film (11-19) to 100 nm or more. In addition, taking into account the refractive index of the core and cladding of the optical fiber in air (a medium with a refractive index of 1), we set the refractive index of the substrate to 1.44-1.47. Furthermore, because the refractive index of the optical thin film at the design center wavelength may vary depending on the deposition equipment or the position of the substrate within the vacuum chamber of the deposition equipment, in the simulation, the refractive index of SiO2 at the design center wavelength of 1450 nm was set to a range of 1.45 ± 0.01, the refractive index of Ta2O5 was set to a range of 2.10 ± 0.10, and four combinations of the refractive index n1 of SiO2 and the refractive index n2 of Ta2O5 were set: (n1, n2) = (1.44, 2.00), (1.44, 2.20), (1.46, 2.00), and (1.46, 2.20), where the refractive indexes were maximum and minimum. Then, under the settings related to the upper and lower limits of the optical thickness and the settings related to the variation in the refractive index, the optical thickness of each layer in the antireflection coating that satisfied the specifications for a reflectance of 0.2% or less in the antireflection band from 1260 nm to 1625 nm was determined by simulation. Table 1 below shows an example of a simulation result that satisfies the above specifications under the above settings.

[0026] [Table 1]

[0027] Table 1 shows the optical film thickness of each layer at a center wavelength λ=1450 nm when the refractive index of the substrate is 1.45. In order to make it easier to understand the tendency for the optical film thickness to increase or decrease in two specific adjacent layers, Table 1 also shows simulation results (samples a to h) when the optical film thickness of the second layer is set to 100 nm or 165 nm, while the optical film thickness of the first layer, which is first laminated on the substrate, is set to a uniform 125 nm, as well as simulation results (sample i) when the optical film thickness of the second layer is set to 170 nm.

[0028] As shown in Table 1, when comparing samples (ae, bf, cg, dh) with the same refractive index combination of SiO2 and Ta2O5, it is clear that as the optical thickness of one of the second and third layers increases, the other tends to decrease. Furthermore, in sample i, where the optical thickness of the second layer is 170 nm, which is larger than 165 nm, the optical thickness of the third layer is 103 nm, which is close to the lower limit (100 nm) desired for manufacturing, and the optical thickness of the sixth layer is also the lower limit of 100 nm. In other words, an antireflection coating designed with the optical thickness of each layer as in sample i may not meet the specifications when actually manufactured. In other words, it is easy to predict that an antireflection coating that meets the above specifications can be obtained as long as the optical thickness of each layer is within the numerical range of at least one of samples a to h. Therefore, to obtain an antireflection coating that meets the above specifications, the optical thickness of the second layer should be set to 100 nm or more and 165 nm or less, and the optical thickness of the third layer should be set to a lower limit of 100 nm and an upper limit of 260 nm based on sample c. The lower limit of the optical thickness of the other layers should be set to 100 nm. The upper limit of the optical thickness of the other layers cannot be increased arbitrarily, considering the possibility that high-power laser light incident on a thick layer could cause laser light absorption within the layer and damage the film material, the possibility of peeling off from the underlying layer, and the increased film deposition time. Therefore, the upper limit of the optical thickness of the other layers should be set to 700 nm based on the maximum optical thickness in Table 1 (sample g, layer 8, 635 nm). Of course, optical thin films with optical thicknesses of approximately 700 nm can be deposited reliably using a vapor deposition system.

[0029] Furthermore, to more reliably obtain an antireflection coating that satisfies the above specifications, the optical thicknesses of the second and third layers should be set within the above numerical ranges based on the simulation results in Table 1, and for example, the optical thickness of the first layer should be set to a uniform average thickness of 125 nm shown in Table 1 with a lower limit of 100 nm, and the optical thicknesses of the fourth to ninth layers should be set within the numerical ranges shown in Table 1. That is, when k is a natural number from 1 to 9, the optical thickness of the kth optical thin film layer should be set to nd kThen, the following may be satisfied: 100 nm≦nd1≦150 nm, 100 nm≦nd2≦165 nm, 100 nm≦nd3≦260 nm, 100 nm≦nd4≦500 nm, 100 nm≦nd5≦400 nm, 100 nm≦nd6≦260 nm, 100 nm≦nd7≦260 nm, 350 nm≦nd8≦650 nm, 300 nm≦nd9≦400 nm.

[0030] To verify the above simulation results, an antireflection coating was fabricated using an IAD (MIC-1350DSN, manufactured by Shincron Co., Ltd.) with an optical fiber as the substrate, a central wavelength λ of 1450 nm, and the optical thicknesses of the layers as designed shown in Table 2 below.

[0031] [Table 2]

[0032] FIG. 3 shows the results of a simulation of the optical characteristics of the antireflection coating shown in Table 2. FIG. 3 shows the simulation results (R-Design) of the optical characteristics of the antireflection coating based on the design values ​​shown in Table 2, and the simulation results (R-Max) of the optical characteristics of the antireflection coating when there is variation in the refractive index, where the error from the design value is maximum. In the simulation based on the design values, the refractive index of the substrate was set to 1.45, the refractive index of SiO2 was set to 1.45, and the refractive index of Ta2O5 was set to 2.10. According to the simulation results shown in FIG. 3, the antireflection coating according to the example satisfies the above specification (reflectance of 0.2% or less in the wavelength band of 1260 nm to 1625 nm) even if the refractive index varies from the design value during the manufacturing process.

[0033] Figure 4 shows the optical characteristics of antireflection coatings actually fabricated based on the design values ​​listed in Table 2. Figure 4 shows the results of measurements using a spectrophotometer (U-4100, Hitachi High-Tech Science Corporation) of the optical characteristics of antireflection coatings formed on substrates placed at three different heights in the vacuum chamber of the IAD. Figure 4 also shows the simulation results (R-Design) based on the design values ​​also shown in Figure 3, as well as the spectral reflectance characteristics of the antireflection coatings formed on the surfaces of substrates placed in the vacuum chamber: the antireflection coating formed at the top (R-UP), the antireflection coating formed at the bottom (R-Down), and the antireflection coating formed at an intermediate position between them (R-Center). As shown in Figure 4, it was confirmed that the antireflection coatings (R-UP, R-Down, R-Center) actually fabricated using the design values ​​listed in Table 2 for the IAD met the above specifications.

[0034] As described above, the antireflection coating according to the present invention can be fabricated by sequentially depositing the first to ninth layers using a vapor deposition apparatus such as an IAD. When depositing each layer, the vapor deposition apparatus can be set so that the optical thickness of each layer falls within the above-described numerical range. Even if the actual optical thickness deviates from the set value depending on the apparatus or the position of the substrate within the apparatus, the fabricated antireflection coating will meet the specifications, as shown in FIG. 4. In other words, the antireflection coating according to the present invention, fabricated so that the optical thickness of each layer falls within the above-described numerical range, will meet the specifications.

[0035] ===Other Examples=== The optical fiber having the anti-reflection coating according to the embodiment formed on its end surface can be used, for example, on the output side of various optical components (optical demultiplexers / multiplexers, wavelength selection filters, etc.) installed in optical communication networks, to output light incident on the optical component with extremely low loss. In addition, it can suppress the occurrence of return light reflected from the output side end surface of the optical fiber into the optical component, and can effectively suppress stray light that becomes noise in the optical component.

[0036] Of course, the anti-reflection film according to the embodiment is not limited to optical fibers, but can be applied to suitable devices such as infrared sensors and displays.

[0037] The anti-reflection films according to the above examples were produced using an IAD, but it goes without saying that they may also be produced using a deposition apparatus using a resistance heating method, a high-frequency induction heating method, or the like. [Explanation of symbols]

[0038] 1. Base material (optical fiber), 2. Surface of base material (end face of optical fiber), 10 Anti-reflection coating, 11,13,15,17,19 Optical thin film made of SiO2, 12,14,16,18 Optical thin films made of Ta2O5

Claims

1. An antireflection film consisting of nine optical thin films laminated on the surface of a substrate having a refractive index of 1.44 to 1.47 relative to a medium having a refractive index of 1, The layer in contact with the surface of the substrate is designated as the first layer, and the layer is made of SiO 2 having a refractive index of 1.45±0.01 for the design central wavelength. ２ and a Ta layer having a refractive index of 2.10±0.10 for the design center wavelength. ２ O ５ and second, fourth, sixth and eighth layers each consisting of k is a natural number from 1 to 9, and the optical thickness of the kth layer is nd ｋ Then, 100 nm≦nd 1 ≦150 nm, 100 nm≦nd2≦165 nm, 100 nm≦nd 3 ≦260 nm, 100 nm≦nd 4 ≦500 nm, 100 nm≦nd5≦400 nm, 100 nm≦nd6≦260 nm, 100 nm≦nd 7 ≦260 nm, 350 nm≦nd 8 ≦650 nm, 300 nm≦nd 9 ≦400 nm, and The reflectance is 0.2% or less in the wavelength band of 1260 nm or more and 1625 nm or less. Anti-reflective coating.

2. An optical fiber having the antireflection coating according to claim 1 on its end surface.

3. An optical component incorporating the optical fiber described in claim 2.

4. A method for manufacturing an anti-reflection film having a reflectance of 0.2% or less in a wavelength band of 1260 nm or more and 1625 nm or less, comprising: a deposition step of forming the antireflection film consisting of nine optical thin films on a surface of a substrate having a refractive index of 1.44 to 1.47 relative to a medium having a refractive index of 1 by a vapor deposition method; In the film-forming step, the optical thin film in contact with the surface of the base material is used as a first layer, and the optical thin film is made of SiO 2 having a refractive index of 1.45±0.01 for the design central wavelength. ２ and a Ta layer having a refractive index of 2.10±0.10 for the design center wavelength. ２ O ５ The second, fourth, sixth and eighth layers are sequentially formed from the first layer to the ninth layer based on the design values ​​of the optical thicknesses of the respective layers. The design value nd of the optical thickness of the kth layer when k is a natural number from 1 to 9 ｋ of, 100 nm≦nd 1 ≦150 nm, 100 nm≦nd2≦165 nm, 100 nm≦nd 3 ≦260 nm, 100 nm≦nd 4 ≦500 nm, 100 nm≦nd5≦400 nm, 100 nm≦nd6≦260 nm, 100 nm≦nd 7 ≦260 nm, 350 nm≦nd 8 ≦650 nm, 300 nm≦nd 9 ≦400 nm, Let's say, A method for manufacturing an anti-reflective coating.

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