Optical member, imaging device, and aerospace vehicle

Abstract

To solve the problem that in a low-reflection treatment, light absorption in a black porous layer is weakened in a region of wavelength of 700nm or more, so that reflectivity tends to increase as compared with a region of wavelength of 400 to 700 nm, therefore, when a sensor having sensitivity up to a wavelength region in a near infrared region is used, there is possibility that stray light is generated.SOLUTION: An optical member includes: a base material made of aluminum or an aluminum alloy; a first layer provided on the base material and made of black porous aluminum oxide; and a second layer provided on the first layer and made of aluminum oxide having a plurality of protrusions; and a third layer provided on the second layer and made of nickel or a nickel alloy.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an optical element, an optical member mounted in an imaging optical system such as an imaging device, a video camera, or a still camera, and to an imaging device and a spacecraft equipped with an optical member. [Background technology]

[0002] It has long been known that unwanted reflections inside a photographic lens can cause haloes or ghosts on the screen, degrading image quality. To prevent this, a light-absorbing black paint is applied to the inner surface of the lens barrel or the aperture blades.

[0003] However, when photographing a particularly bright object such as the sun, radial ghosts can appear around the object image, and light that hits the edges (corners) of the inner diameter ends of the aperture blades or light shielding plate can become stray light.

[0004] In Patent Document 1, an aluminum substrate is subjected to anodizing and etching processes to form a black porous aluminum oxide layer on the surface of the aluminum substrate, and an aluminum oxide layer having a plurality of protrusions on the black porous aluminum oxide layer, thereby reducing the reflectance of the substrate. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-56494 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the low-reflection treatment of Patent Document 1, the light absorption in the black porous layer is weakened in the wavelength range of 700 nm or more, so the reflectance tends to increase compared to the wavelength range of 400 to 700 nm. Therefore, when using a sensor that has sensitivity up to the near-infrared wavelength range, stray light may occur. [Means for solving the problem]

[0007] In order to solve the above problems, the optical element of the present invention is characterized by comprising: an aluminum or aluminum alloy substrate; a first layer of black porous aluminum oxide provided on the substrate; a second layer of aluminum oxide having a plurality of protrusions provided on the first layer; and a third layer of nickel or nickel alloy provided on the second layer. [Effects of the Invention]

[0008] According to the present invention, while maintaining the protrusions provided on the base material, the material of the light-reflective portions of the protrusion surface can be replaced with nickel, which has lower reflectivity than aluminum. This allows the reflectance to be sufficiently reduced even in wavelength ranges of 700 nm or more, and stray light can be suppressed even when using a sensor that is sensitive to wavelengths up to the near-infrared range. [Brief explanation of the drawings]

[0009] [Figure 1] Schematic diagram of a star sensor according to the present invention [Figure 2] Exploded view of a baffle according to the present invention [Figure 3] Schematic diagram of the oblique angle according to the present invention [Figure 4] 1 is a cross-sectional view of a vane according to the present invention; [Figure 5] Schematic diagram of a low-reflection structure according to the present invention. [Figure 6] An explanatory diagram of a method for fabricating a low-reflection structure according to the present invention. [Figure 7] Schematic diagram of a low-reflection structure in a comparative example [Figure 8] Reflection characteristics in Examples and Comparative Examples [Figure 9] A diagram illustrating an example of a spacecraft equipped with a star sensor DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0011] (star sensor) An example of a star sensor will be explained using the cross section of the star sensor shown in Figure 1. It consists of a star sensor 1, optical systems 2 and 3, of which baffle 2 and lens 3 are shown. It is an image sensor consisting of a CMOS sensor 5. To the right of the image sensor is a control unit 10, which serves as the subsequent circuitry. The image sensor receives light that has passed through the periphery of the opening of optical components such as baffle 2. The drive circuit communicates with the outside world via a connector 6, which has communication functions. When mounted on a satellite, this is where it connects and communicates with the host side, known as the satellite bus. These are the detection systems 5, 6, and 10.

[0012] Figure 2 shows an example of the baffle 30 and its internal configuration of vanes 7 and spacer ring 8. The vanes 7 are dropped in one direction from the opening of the baffle. The spacer ring 8 determines the position of the vanes 7 in the optical axis direction. Finally, it is fastened with a screw member 31 called a retaining ring.

[0013] Stars are assigned a magnitude based on their brightness, such as first magnitude stars (stars with the brightest magnitude), second magnitude stars, etc. There are 21 first magnitude stars, 68 second magnitude stars, 183 third magnitude stars, 585 fourth magnitude stars, 1,858 fifth magnitude stars, and 5,503 sixth magnitude stars in the entire sky. The number of stars required for attitude determination is determined by the star sensor's attitude detection process. The lens specifications (angle of view, focal length, F-number), image sensor selection, and image generation program are configured so that more than the required number of stars are included within the lens's field of view. In this first embodiment, a star sensor will be described that determines attitude using stars up to sixth magnitude.

[0014] When the star sensor photographs a star, the sun is in a close position. The ratio of the brightness of the sun to that of a sixth-magnitude star is approximately 10 to the 13th power, making it a strong light source. When sunlight is irradiated into the baffle 2, it contains reflected components from the surfaces of the vanes 7, the edges of the vanes (the end faces of the inner diameter), and the inner diameter of the spacing ring 8, and is input into the lens as stray light. If this light is irradiated within the effective area of ​​the image sensor 5 and is brighter than a sixth-magnitude star, it becomes stray light known as ghost or flare, causing errors in attitude determination.

[0015] For this reason, the inner surfaces of the baffle 2, i.e., the surfaces of the vanes 7 and the spacer ring 8, are surface treated to reduce the reflectivity of sunlight. This suppresses stray light entering the lens due to two or more reflections (diffuse reflection) on the inner surface of the baffle 2, making it possible to detect stars of the required magnitude. The angle from the optical axis at which the sun is closest and a star can be detected is generally called the solar intercept angle.

[0016] However, as shown in Figure 3, sunlight is reflected once at the inner diameter end surface of the vane 7, resulting in stray light entering the lens. In order to suppress the effect of stray light on the image sensor 5 caused by reflection at the inner diameter end surface of the vane, adjustments are made to the position of the vane 7, such as increasing the inner diameter, so that light is irradiated outside the effective range of the image sensor 5, but this is often difficult and poses a problem.

[0017] In the case of the star sensor of Example 1, when the lens half angle of view is 15 degrees, the solar intercept angle is 25 degrees. In other words, when the oblique angle is 65 degrees or less, sunlight is incident on the inner diameter end face of the vane 7, which affects star identification.

[0018] FIG. 4 shows a cross section of the inner diameter end face of the vane 7.

[0019] As a countermeasure against sunlight reflection, the vane 7 has an aluminum material as the base material, and is surface-treated to have a first layer 60 made of black porous aluminum oxide formed on the base material, and a second layer 61 made of aluminum oxide with multiple protrusions 62 formed on the first layer, thereby making it possible to keep reflection extremely low compared to conventional methods for incident light at an oblique angle of 60 degrees or more.

[0020] The vane 7 has a rounded or tapered surface 64 on its inner diameter. A knife edge 63 may be formed, and the corners of the knife edge end face may be rounded or tapered. As explained in FIGS. 1 and 2, the vane 7 is supported on its outer periphery. As explained in the low-reflection surface treatment for the vane, the inner diameter surface of the spacer ring 8 may also be similarly subjected to low-reflection treatment.

[0021] (Low reflective structure) Next, an embodiment of a low reflection structure will be described with reference to the drawings.

[0022] 5 is a schematic diagram of a low-reflection structure according to an embodiment. The low-reflection structure 200 according to this embodiment includes a base 204, a first layer 201, a second layer 202, and a third layer 203. The base 204 is made of aluminum or an aluminum alloy. The first layer 201 includes pores 301, which can be filled with dye to dye the base material, allowing it to be used as an exterior component. Furthermore, by selecting a dye that absorbs light, the reflectance of the base material can be reduced.

[0023] The first layer 201 in Fig. 5 has undergone a sealing treatment (not shown). The sealing treatment improves corrosion resistance by blocking pores, and when a dye is enclosed, it can prevent the dye from bleeding (fading) or deteriorating.

[0024] The second layer 202 in FIG. 5 is an aluminum oxide layer having a plurality of protrusions 205 .

[0025] 5 is a nickel or nickel alloy layer provided on the plurality of protrusions 205. By controlling the thickness of the third layer 205 to about 1 / 10 to 1 / 100 of the height of the plurality of protrusions 205, it is possible to replace the surface material from aluminum with nickel or a nickel alloy while maintaining the dimensions such as height and width and shape of the protrusions formed on the surface of the base material.

[0026] (Method of manufacturing low-reflection structure for optical components) Next, a method for manufacturing a low-reflection structure of an optical member will be described with reference to the drawings.

[0027] First, aluminum or an aluminum alloy is used as the substrate. If the substrate is formed by machining such as cutting, dirt and oil that has adhered during machining are removed. The substrate is degreased by immersing it in an organic solvent such as acetone and then ultrasonically cleaning it. Furthermore, dirt and natural oxide films that cannot be removed by ultrasonic cleaning are removed by degreasing using a commercially available aluminum degreasing solution. Furthermore, if scratches occur on the substrate during machining or subsequent handling, the scratches can be removed by etching the substrate with alkali or acid.

[0028] Next, the aluminum or aluminum alloy substrate is subjected to an anodizing treatment. When the anodizing treatment is performed, a first layer 201 of porous (also called porous structure) aluminum oxide coating having a plurality of pores 301 is generated on the surface of the base 204, which is the substrate itself, as shown in Figure 6.

[0029] Anodizing typically uses an electrolyte prepared by adding sulfuric acid and aluminum sulfate to pure water and adjusting the concentration. However, an electrolyte containing only sulfuric acid can also be used. Anodizing is performed by immersing an anode (substrate: aluminum or aluminum alloy) and a cathode in the electrolyte, connecting the cathode and anode to a power source, and applying current. The cathode can be made of any material that is low in reactivity with the electrolyte, such as carbon, platinum, titanium, or stainless steel. The temperature of the electrolyte is preferably controlled by a chiller. A voltage is applied between the electrodes, and anodizing is performed for 10 to 120 minutes, producing a first layer 201 of aluminum oxide coating with pores 301 near the surface of the substrate, as shown in Figure 6(a). The substrate is then removed from the treatment tank and the electrolyte is washed off with pure water.

[0030] Next, the pores 301 in the first layer 201 of the aluminum oxide coating formed by anodizing are filled with a solvent. The solvent preferably has good wettability with aluminum oxide. Examples of the solvent that can be used include acetone and isopropyl alcohol. The immersion time is, for example, 15 to 120 minutes. This immersion step may be omitted.

[0031] Next, the surface of the substrate with the pores formed is etched. An etching solution is prepared in a processing tank, and the substrate with the pores formed is immersed in it. The temperature of the etching solution is preferably 40 to 60°C, and the etching time is preferably 3 to 30 minutes. A liquid flow is preferably generated in the etching solution by stirring with a pump or air. By stirring the etching solution, temperature unevenness in the processing tank can be reduced and the etching rate can be controlled uniformly. The etching solution displaces the solvent filled into the pores while being compatible with the solvent, and penetrates deep into the pores. Thus, the surface of the substrate and the inner walls of the pores are simultaneously etched, forming a second layer 202 with aluminum oxide protrusions 205, as shown in Figure 6(b).

[0032] The thickness of the second layer (height of the protrusions) and the shape of the protrusions can be controlled by the etching rate, which can be controlled by the type of solvent, the immersion time in the solvent, and the type, temperature, concentration, and flow of the etching solution.

[0033] Next, the substrate is subjected to a dyeing process. A black dye is encapsulated in the pores 301 of the substrate formed by the anodizing process. The black dye can be encapsulated by immersing the substrate in a dyeing solution prepared by dissolving the dye in pure water and adjusting the concentration. To stabilize the dyeability of the substrate, the temperature of the dyeing solution is preferably 50 to 60°C, and the dyeing time is preferably 5 to 60 minutes. Furthermore, to reduce temperature variations in the dyeing tank, it is preferable to perform agitation using a pump or air agitation. To improve the dyeability of the pores in the substrate, a surface conditioning process may be performed on the substrate before the dyeing process. If appearance is not the goal and coloring is not required, this dyeing process may be omitted.

[0034] Next, the substrate is subjected to a sealing treatment. Generally, in anodizing of aluminum, the corrosion resistance can be improved by performing a sealing treatment to close the pores formed in the substrate. Furthermore, if a dye is encapsulated in the pores, performing the sealing treatment can prevent the dye from bleeding out or changes in appearance due to the dye's deterioration. The sealing treatment can be selected from hydration treatments such as pressurized steam treatment, boiling water treatment, chromate treatment / dichromate treatment, and nickel salt treatment.

[0035] Next, as shown in Fig. 6(c), a nickel or nickel alloy layer 203 is formed on the surface of the substrate. Any method can be selected that can form a nickel or nickel alloy layer on the surface of the protrusions without impairing the height, width, or shape of the protrusions. For example, wet plating such as electroless plating or electrolytic plating, or dry plating such as vapor deposition or sputtering can be used as appropriate.

[0036] Example 1 The method for manufacturing an optical element of the present invention is described below. An aluminum (A5052) plate with an outer diameter of 50 mm, an inner diameter of 20 mm, and a thickness of 0.5 mm was used as the substrate. To remove processing oil adhering to the substrate, the aluminum substrate was immersed in acetone and ultrasonically cleaned for 3 minutes. Subsequently, a degreasing treatment was performed for 5 minutes at 60°C using an aluminum degreasing solution (Top Alclean, manufactured by Okuno Pharmaceutical Industries). Furthermore, to remove scratches during substrate processing, an etching treatment was performed for 5 minutes at 55°C using an acid etching solution (Top Alsatin, manufactured by Okuno Pharmaceutical Industries). Subsequently, to remove smut generated by the etching treatment, a desmutting treatment was performed for 30 seconds at 25°C using a desmutting solution (nitric acid).

[0037] Next, an anodization process was performed using the substrate (aluminum) as the anode and a carbon plate as the cathode. The electrolyte was adjusted to 180 g / L of sulfuric acid. The temperature of the electrolyte was maintained at 20°C using a heater and chiller. An anodization process was then performed by applying a voltage to the anode and cathode using a power supply. The voltage was adjusted so that the current density was 3 A / dm2 relative to the area of ​​the part to be anodized. By applying the voltage for 45 minutes, an aluminum oxide layer with pores was formed, as shown in Figure 6(a).

[0038] Subsequently, the substrate with the pores formed therein was immersed in acetone for 60 minutes to allow the acetone to penetrate into the pores.

[0039] Next, the substrate surface was subjected to an etching treatment. Phosphoric acid with a concentration of 0.5 mol / L was prepared as an etching solution in a treatment tank, and the temperature of the phosphoric acid was maintained at 50°C. The substrate was immersed for 4.5 minutes while air was being agitated, thereby forming a second layer 202 of aluminum oxide having protrusions 205 as shown in FIG. 6(b) on the substrate surface. In this example, the thickness of the second layer 202 (height of the protrusions 205) was 5 μm to 10 μm. This thickness could be controlled by changing the etching conditions.

[0040] At this time, the aluminum oxide layer that remains unetched becomes the first layer 201 in the above-described embodiment. In this example, the thickness of the first layer is 20 μm. This thickness can be controlled by the anodization conditions, and is preferably controlled to 15 μm or more. In this example, the thickness of the second layer 202 is about 1 / 4 to 1 / 2 times the thickness of the first layer 201, but is not limited to this, and the thickness of the second layer is preferably 1 / 100 to 2 times the thickness of the first layer.

[0041] Next, a dyeing process was performed. In this example, we used the anodizing dye TAC BLACK manufactured by Okuno Chemical Industries, a chromium complex azo-based acid dye among metal azo salt dyes. The dyeing material is not limited to this, as long as it is black and light-absorbing. Secondary electrolytic coloring using inorganic dyes such as nickel or tin may also be performed. In this example, the dyeing solution was adjusted to a concentration of 10 g / L of TAC Black, and the substrate was immersed at 55°C for 30 minutes. The dye filled the pores 301 in the first layer 201 (Figure 6(b)), thereby dyeing the substrate. The dyeing material was fixed only to the outer walls of the porous structure, preventing the pores from being completely filled and the porous structure from disappearing. While the reflectance in the visible light region can be suppressed to approximately 0.1% without dyeing, the encapsulation of the dye can reduce the reflectance in the visible light region to 0.05% or less.

[0042] Next, a pore-sealing treatment was carried out. The pore-sealing treatment solution was prepared using Top Seal manufactured by Okuno Chemical Industries, Ltd., and diluted with pure water to a concentration of 40 ml / L. The pore-sealing treatment solution was heated to 90°C, and the substrate was immersed in the solution for 25 minutes while being agitated with air, thereby sealing the pores in the first layer 201 shown in Figure 6(b).

[0043] Next, a nickel or nickel alloy layer was formed. In this example, electroless plating was selected to form a nickel or nickel alloy layer on the substrate surface. To perform electroless plating, an electroless plating catalyst was first applied to the substrate surface. The electroless plating catalyst used was Activator manufactured by Okuno Pharmaceutical Industries, Ltd., diluted with pure water to a concentration of 50 ml / L. The activator solution was heated to 30°C and the substrate was immersed in the solution for 60 seconds to allow the electroless plating catalyst to adhere. The substrate was then immersed in an electroless nickel plating solution to form a nickel alloy layer on the substrate surface. Top Chemialloy manufactured by Okuno Pharmaceutical Industries, Ltd. was used as the electroless nickel plating solution. The electroless nickel plating solution was heated to 65°C and plated for 30 seconds with air agitation, forming a nickel-boron (less than 1% boron) alloy plating film on the substrate surface.

[0044] Example 2 The substrate was an aluminum (A5052) plate with an outer diameter of 50 mm, an inner diameter of 20 mm, and a thickness of 0.5 mm. The same process as in Example 1 was used, except that an electroless nickel alloy plating solution (SEK-797, electroless nickel plating solution manufactured by Nippon Kangen Co., Ltd.) was used to form the nickel or nickel alloy layer 203 on the outermost surface of the substrate, and a nickel-phosphorus alloy plating layer was formed. The electroless nickel plating solution was heated to 86°C, and the substrate was immersed for 30 seconds while being agitated by air, to form an electroless nickel-phosphorus alloy plating layer (1.5 to 2.0% phosphorus) on the outermost surface of the substrate.

[0045] Example 3 The substrate was an aluminum (A5052) plate having an outer diameter of 50 mm, an inner diameter of 20 mm, and a thickness of 0.5 mm. Treatment was carried out in the same manner as in Example 1, except that an electrolytic nickel plating solution was used to form a nickel or nickel alloy layer 203 on the outermost surface of the substrate.

[0046] An electrolytic plating process was carried out on the substrate having an electroless nickel-boron alloy layer formed on its surface in the process of Example 1. The electrolytic plating solution can be selected from a plating solution mainly containing nickel sulfate, a plating solution mainly containing nickel sulfamate, a plating solution mainly containing nickel chloride, etc., but in this case, a plating solution mainly containing nickel sulfate was prepared with the following composition and used to carry out the electrolytic plating process.

[0047] (Electroplating solution composition) Nickel sulfate 150g / L Boric acid 30g / L Sodium chloride 25g / L Sodium dodecyl sulfate 0.005g / L Sodium saccharin 0.05g / L A nickel plate (Sumitomo Electrolytic Nickel) was used as the anode, and was covered with an anode bag and immersed in the plating solution. A rectifier was connected to apply a current between the anode and the substrate. The plating solution was maintained at 50°C while circulating using a heater and a filtration pump. The substrate was then immersed in the plating solution, and the current density was increased to 1 A / dm 2 A current was applied so that the electrolytic plating treatment was carried out for 30 seconds.

[0048] (Comparative Example) The substrate was an aluminum (A5052) plate with an outer diameter of 50 mm, an inner diameter of 20 mm, and a thickness of 0.5 mm. As shown in Fig. 7, the substrate was treated in the same manner as in Example 1, except that the nickel or nickel alloy layer 203 on the outermost surface was not formed.

[0049] (evaluation) The optical properties of the flat portion of the substrate were evaluated. The optical properties were measured by measuring the reflectance in the visible light region at wavelengths of 350 nm to 850 nm. The reflectance was measured using a spectrophotometer U-4100 manufactured by Hitachi High-Tech Fielding. The regular reflectance was measured at light incident angles of 5° and 65°. The results are shown in Figure 8 (a), (b), (c), and (d). In Comparative Example 1, the reflectance increases from wavelengths around 700 nm, regardless of the light incident angle. On the other hand, it was confirmed that Example 1 maintained low reflectance even at wavelengths of 700 nm or more.

[0050] As described above, according to the present invention, even in an optical system using optical elements having corners, the occurrence of ghosts in images can be significantly reduced.

[0051] FIG. 9 is a diagram illustrating an example of a spacecraft equipped with a star sensor according to the present invention.

[0052] The star sensor 1 of the present invention is mounted on spacecraft such as, but not limited to, artificial satellites, lunar rovers, and Mars rovers. A spacecraft 80 shown in FIG. 9 has two star sensors, with star sensor 1 and star sensor 1a at a right angle. The spacecraft 80 (e.g., an artificial satellite) observes the Earth. An optical device (e.g., an imaging device) for capturing Earth images is housed inside a cylindrical opening 82 of the spacecraft 80. Therefore, the optical axis faces downward through the cylindrical opening 82. As shown in FIG. 9, when the Earth is illuminated by sunlight (i.e., it is daytime on Earth), the Sun is above the spacecraft 80 and the Earth is below the spacecraft 80. The smaller the solar intercept angle of star sensor 1 and star sensor 1a, the greater the range of attitude change of the spacecraft 80. This allows the spacecraft 80 to capture images of objects on Earth with high accuracy.

[0053] The optical member of the present invention can be applied to various other devices, such as the inside of a lens barrel or a shielding plate. [Explanation of symbols]

[0054] 1: Star sensor 5: Image sensor 7: Vane 9: Aperture 60: 1st layer 61: 2nd layer 62:Protrusion 63: Knife Edge 64: Tapered surface 200: Low reflection structure 201: 1st layer 202:Second layer 203:Third layer 204: Base 205:Protrusion

Claims

1. an aluminum or aluminum alloy substrate; a first layer of black porous aluminum oxide disposed on the substrate; a second layer of aluminum oxide disposed on the first layer and having a plurality of protrusions; and a third layer made of nickel or a nickel alloy and disposed on the second layer.

2. 2. The optical member according to claim 1, wherein the thickness of the third layer is smaller than the height of the protrusions of the second layer.

3. 3. The optical member according to claim 2, wherein the thickness of the third layer is set to be 1 / 100 to 1 / 10 of the height of the protrusions of the second layer.

4. The optical member according to claim 1 , an image pickup element that receives light that has passed through the optical member; An imaging device characterized by:

5. A spacecraft comprising the imaging device according to claim 4 as a star sensor.

Images