Optical member, imaging device, and aerospace vehicle

Abstract

To provide an optical member and an imaging device in which reflection at an end portion can be sufficiently suppressed even in the optical member, and ghosts can be reduced as the imaging device.SOLUTION: An optical member according to the present invention is an optical member including: 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, where the base material has an opening, an R-shape or a tapered shape is formed in a peripheral portion of the opening, and the first layer and the second layer are provided on the R-shape or the tapered shape.SELECTED DRAWING: Figure 4

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, the low-reflection treatment that utilizes aluminum anodization as in Patent Document 1 does not allow an aluminum oxide layer to be formed on the edges (corners) of the substrate. As a result, in optical components that have corners, reflection from the corners cannot be sufficiently suppressed, and light reflected from the corners may enter the sensor, causing ghost images. [Means for solving the problem]

[0007] In order to solve the above problems, the optical element of the present invention is an optical element comprising an aluminum or aluminum alloy substrate, a first layer of black porous aluminum oxide provided on the substrate, and a second layer of aluminum oxide provided on the first layer and having a plurality of protrusions, wherein the substrate has an opening, an R-shape or a tapered shape is formed around the periphery of the opening, and the first layer and the second layer are provided on the R-shape or the tapered shape. [Effects of the Invention]

[0008] According to the present invention, it is possible to significantly reduce the occurrence of reflection at the edge of an optical member. [Brief explanation of the drawings]

[0009] [Figure 1] Schematic diagram of a star sensor according to the present invention. [Figure 2] 1 is a development 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] Observation results of the edge corner of the optical member in Comparative Example 1 [Figure 6] Observation results of the edge corner of the optical member in Example 5 according to the present invention [Figure 7] Schematic diagram of a low-reflection structure according to the present invention. [Figure 8] An explanatory diagram of a method for fabricating a low-reflection structure according to the present invention. [Figure 9]1 is a cross-sectional view of a substrate of an optical member according to a first embodiment of the present invention; [Figure 10] Observation results of the edge corner of the optical member in Example 1 according to the present invention [Figure 11] 10 is a cross-sectional view of a substrate of an optical member according to a second embodiment of the present invention. [Figure 12] Observation results of the edge corner of the optical member in Example 2 according to the present invention [Figure 13] 10 is a cross-sectional view of a substrate of an optical member according to a third embodiment of the present invention. [Figure 14] Observation results of the edge corner of the optical member in Example 3 according to the present invention [Figure 15] 10 is a cross-sectional view of a substrate of an optical member according to a fourth embodiment of the present invention. [Figure 16] 10 is a cross-sectional view of a substrate of an optical member according to a fifth embodiment of the present invention. [Figure 17] 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] Figure 5 shows the results of observing the inner diameter end of a vane when low-reflection treatment was performed using a conventional method. Because the inner diameter end surface of the vane has a right-angled shape, no aluminum oxide layer is formed, and there are parts where the corners do not have a convex shape. Figure 6 shows the results of observing the inner diameter end surface of a vane when low-reflection treatment was performed using the method of the present invention. By providing R at the corners, an aluminum oxide layer can be formed at the corners as well, and a convex shape can be formed at the corners as well.

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

[0022] 7 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 203, a first layer 201, and a second layer 202. The base 203 is made of aluminum or an aluminum alloy. The first layer 201 includes pores 301, which can be filled with dye 401 to dye the substrate, allowing it to be used as an exterior component. Furthermore, by selecting a dye that absorbs light, reflection on the surface of the substrate can be reduced.

[0023] The first layer 201 in Fig. 7 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. 7 is an aluminum oxide layer having a plurality of protrusions 204 .

[0025] (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.

[0026] 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.

[0027] Next, the aluminum or aluminum alloy substrate is subjected to anodizing treatment, which results in the formation of a porous first layer 201 of aluminum oxide coating having a plurality of pores 301 on the surface of the base 203, which is the substrate itself, as shown in Figure 8(a).

[0028] 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 8(a). The substrate is then removed from the treatment bath and the electrolyte is washed off with pure water.

[0029] 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, 10 to 120 minutes. This immersion step may be omitted.

[0030] Next, the surface of the substrate with the pores formed therein is etched. An etching solution is prepared in a processing tank, and the substrate with the pores formed therein is immersed therein. 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 uniformly controlled. 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 204, as shown in Figure 8(b).

[0031] 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.

[0032] Next, the substrate is subjected to a dyeing treatment. A black dye is encapsulated in the pores 301 of the substrate formed by the anodizing treatment. 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 unevenness in the dyeing tank, it is preferable to perform stirring with a pump or air agitation. To improve the dyeability of the pores of the substrate, a surface conditioning treatment of the substrate may be performed before the dyeing process.

[0033] 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.

[0034] Example 1 The following describes a method for manufacturing an optical element of the present invention. 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. The inner diameter edge, which is the periphery of the opening of the substrate, had a rounded shape 401 (R 0.5 mm) machined on one side in the thickness direction of the substrate, as shown in Figure 9. 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 during the etching treatment, a desmutting treatment was performed for 30 seconds at 25°C using a desmutting solution (nitric acid).

[0035] Next, anodization 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. Anodization 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 8(a).

[0036] Subsequently, the substrate with the pores formed therein was immersed in acetone for 60 minutes to allow the acetone to penetrate into the pores.

[0037] 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 204 as shown in FIG. 8(b) on the substrate surface. In this example, the thickness of the second layer 202 (height of the protrusions 204) was 5 μm to 10 μm. This thickness could be controlled by changing the etching conditions.

[0038] 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.

[0039] Next, a dyeing process was performed. In this example, we used the anodized aluminum 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 sample was immersed at 55°C for 30 minutes to dye the first layer 201 shown in Figure 8(b). The dyeing material is fixed only to the outer walls of the porous material, so the pores are not completely filled and the porous material does not disappear. Even without the dyeing process, the reflectance in the visible light range can be suppressed to approximately 0.1%, but the reflectance in the visible light range can be further reduced by encapsulating a dye.

[0040] 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 by air, thereby sealing the pores in the first layer 201 shown in Figure 8(b).

[0041] (evaluation) When the inner diameter edge of the optical element fabricated using the above-described manufacturing method was examined, it was found that a fine shape could be formed even at the corner of the edge, as shown in Figure 10. Next, the optical properties of the flat portion were evaluated. The optical properties were measured by measuring the reflectance in the visible light range at wavelengths from 400 nm to 700 nm. The reflectance was measured using a Hitachi High-Tech Fielding U-4100 spectrophotometer. The regular reflectance was measured at light incident angles of 5°, 25°, 45°, and 65°, and it was confirmed that the reflectance was 0.1% or less at all angles.

[0042] 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 the inner diameter end was tapered stepwise (30° taper 402, 45° taper 403, and 30° taper 404) on one side of the substrate in the thickness direction, as shown in Figure 11. Observation of the inner diameter end of the fabricated optical element revealed a slight increase in cracks compared to Example 1, as shown in Figure 12, but a fine shape could be formed even in front of the inner diameter end. Evaluation of the optical properties of the flat portion of the fabricated optical element revealed that the specular reflectance (wavelength 400 to 700 nm) at incident angles of 5° to 65° was 0.05% or less, as in Example 1. Although a three-step taper was formed in Example 2, increasing the taper and adjusting the taper angle more finely to approximate an R shape could further reduce cracks.

[0043] Example 3 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 the inner diameter end was tapered (45° taper 405) from one side in the thickness direction of the substrate, as shown in Figure 13. As a result, as shown in Figure 14, although the crack width was slightly wider than in Example 2, a fine convex shape was successfully formed even at the corner of the inner diameter end of the substrate. The optical properties of the flat portion of the fabricated optical element were confirmed, and as with Example 1, the reflectance was 0.05% or less at all angles of incidence.

[0044] Example 4 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 substrate was processed using the same process as in Example 1, except that the inner diameter end was rounded (R0.25 mm) on both sides of the substrate thickness direction as shown in Figure 15. Observation of the inner diameter end of the fabricated optical element revealed that a convex shape could be formed even at the corner. Evaluation of the optical properties of the flat portion of the fabricated optical element revealed a reflectance of 0.05% or less at all angles of incidence, as in Example 1. In Example 1, a convex shape could not be formed at corners where no rounding was formed. Therefore, depending on the optical system, light reflected at corners on the non-rounded side may be a problem. However, by rounding both sides of the substrate thickness direction as in Example 3, the influence of light reflected at the corners of the substrate can be reduced.

[0045] Example 5 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 process was the same as in Example 1, except that the inner diameter end was tapered stepwise on both sides of the substrate in the thickness direction (30° taper 407, 45° taper 408, and 30° taper 409) as shown in Figure 16. Observation of the inner diameter end of the fabricated optical element revealed that a convex shape could be formed even at the corners. Evaluation of the optical properties of the flat portion of the fabricated optical element revealed a reflectance of 0.05% or less at all angles of incidence, similar to Example 1. In Example 2, a convex shape could not be formed at the corners on the non-tapered side. Therefore, depending on the optical system, light reflected at the corners on the non-tapered side may be a problem. However, by tapering stepwise on both sides of the substrate in the thickness direction, as in Example 4, the influence of light reflected at the corners of the substrate can be further reduced.

[0046] (Comparative Example 1) 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 inner diameter end was processed using the same process as in Example 1, without performing R processing or tapering. As a result, there were parts at the corners of the inner diameter end of the substrate where no convex shape was formed. When the optical properties of the flat part of the fabricated optical element were confirmed, the reflectance was 0.05% or less at all angles of incidence, as in Example 1.

[0047] 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.

[0048] FIG. 17 is a diagram illustrating an example of a spacecraft equipped with a star sensor according to the present invention.

[0049] 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. 17 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. 17, 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.

[0050] 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]

[0051] 1: Star sensor 7: Vane 60: 1st layer 61: 2nd layer 62:Protrusion 63 :R shape 64: Tapered surface 200: Low reflection structure 201: 1st layer 202:Second layer 203: Base material 204:Protrusion 301: pore 401: Black dye 501, 506: R shape 502, 504, 507, 509: 30° tapered shape at the inner diameter end of the base material 503, 505, 508: 45° tapered shape at the inner diameter end of the base material

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; An optical element comprising: the base material has an opening, and an R-shape or a tapered shape is formed on the periphery of the opening, The first layer and the second layer are provided on the R-shape or the tapered shape. An optical element characterized by:

2. The R shape or the tapered shape is The substrate is characterized in that it is formed on one side in the thickness direction. The optical member according to claim 1 .

3. The optical member according to claim 2 , wherein the peripheral edge of the opening is formed with only the R-shape, out of the R-shape and the tapered shape.

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