WO2020022295A1 - Optical element, optical system, and optical device - Google Patents

Abstract

An optical element (10) includes: a flange part (13) having an annular flat section extending in an outer diameter direction from a curved surface; and a light-absorbing layer (14) for reducing, in at least a portion of the flange part (13), the reflectance when light is made incident from inside the optical element (10), the light absorbing layer having a thickness of 2 μm or less. Alternatively, an optical element (10) includes a flange part (13) having an annular flat section extending in an outer diameter direction from a curved surface, the flange part (13) having the arithmetic average roughness of Ra 0.1 μm or less on the side surface thereof, and at least a portion of the flange part (13) having a light absorbing layer (14) containing a metal, a semiconductor, or a dielectric body.

Description

Optical element, optical system, and optical device

The present invention relates to an optical element capable of reducing stray light, an optical system having the optical element, and an optical device having the optical element.

す る と When unintended light such as light at a large incident angle enters the lens, stray light may be generated due to reflection inside the lens or an imaging system including the lens. Then, so-called ghosts and flares may occur due to stray light.

と し て As a method for preventing the generation of stray light, there is a method of centering the peripheral portion of the lens, and then applying black ink to the roughened peripheral portion (for example, see Patent Document 1). Further, Patent Literature 1 also discloses a method in which a peripheral portion of a lens is roughened and light is scattered by the roughened portion.

Japanese Patent Application Laid-Open No. 2016-206682

Taking a glass lens as an example, there is a problem that roughening the glass lowers the accuracy of the outer shape. When black ink is applied to glass that has not been roughened, there is a problem that the glass repels paint and does not have a desired coating. In addition, there is a problem that the outer shape of the glass lens and the flatness of the flat surface (flange surface) of the flange portion included in the glass lens are reduced due to the uneven thickness of the black ink.

(4) With the miniaturization of the imaging optical system and the like, there is an increasing demand for the shape accuracy of optical elements such as lens members. When a lens member is installed in a barrel of an imaging optical system, there are cases where the imaging optical system is assembled while adjusting the imaging optical system by contact with the inner surface of the barrel or a flange surface of an adjacent lens member. In such a case, higher accuracy is required for the flange surface and outer shape of the lens member. That is, in a miniaturized imaging optical system or the like, the problem due to the roughening of the glass and the problem of black coating become more prominent.

Therefore, it is an object of one embodiment of the present invention to provide an optical element capable of reducing stray light without significantly impairing the accuracy of a flange surface, an optical system having the optical element, and an optical device having the optical element.

An optical element according to one embodiment of the present invention is an optical element including a curved surface and a flange portion having an annular flat portion extending in the outer radial direction from the curved surface, and at least a part of the flange portion includes an optical element. A light absorbing layer for reducing the reflectance when light enters from the inside is provided, and the thickness of the light absorbing layer is 2 μm or less.

Further, an optical element according to one embodiment of the present invention is an optical element including a curved surface and a flange portion having an annular flat portion extending in the outer radial direction from the curved surface, wherein the side surface of the flange portion complies with JIS B0601. The arithmetic average roughness Ra is 0.1 μm or less, and at least a part of the flange portion has a light absorbing layer containing a metal, a semiconductor, or a dielectric.
An optical system according to one embodiment of the present invention includes the optical element.
An optical device according to one aspect of the present invention includes the optical element.

According to one aspect of the present invention, stray light can be reduced without significantly impairing the accuracy of the flange surface.

FIG. 1 is a cross-sectional view schematically illustrating a first embodiment of an optical element according to one aspect of the present invention. FIG. 4 is an explanatory diagram for describing stray light generated inside an optical element. It is sectional drawing which shows the mode at the time of forming a light absorption layer typically. 4 is a flowchart illustrating a method for forming a light absorbing layer. FIG. 4 is a cross-sectional view schematically illustrating a second embodiment of the optical element according to one aspect of the present invention. It is sectional drawing which shows the optical system assembled using the optical element typically. It is explanatory drawing which shows the refractive index and extinction coefficient of chromium oxide and chromium. FIG. 9 is an explanatory diagram showing calculation results of transmittance and reflectance when light is incident on the light absorption layer of the example. It is explanatory drawing which shows the reflectance at the time of light in the range of 5 degrees-85 degrees with respect to a light absorption layer in glass. It is explanatory drawing which shows the reflectance of light at the incident angle of 65 degrees when the film thickness of a light absorption layer is 70% and 50%.

Embodiment 1 FIG.
FIG. 1 is a sectional view schematically showing a first embodiment of an optical element 10 according to one aspect of the present invention. The optical element 10 has a first curved surface 11, a second curved surface 12, a flange 13, and a light absorbing layer 14 covering at least a part of a flat portion of the flange 13. The material of the optical element 10 is, for example, glass. As long as the optical element 10 is transparent in the wavelength band used, a material such as ceramics, plastic, or a mixed material of organic and inorganic materials may be used. FIG. 1 shows a cross section of the optical element 10. In the plan view, the flat portion of the flange portion 13 is annular, and the outer diameter of the optical element 10 extends from the outer periphery of the first curved surface 11. Direction.

In the example shown in FIG. 1, the first curved surface 11 is a convex surface, and the second curved surface 12 is a convex surface. However, the shape of the optical element 10 is not limited to such a shape. Each of the first curved surface 11 and the second curved surface 12 may be either a convex surface or a concave surface, or may be a flat surface. As an example, FIG. 2 illustrates a concave second curved surface 12. FIG. 3 illustrates a case where the second curved surface 12 is flat. The outer periphery of the flange portion 13 is not centered. The roughness of the outermost side surface of the flange portion 13 is Ra 0.1 μm or less. Note that Ra of 0.1 μm or less is an example, and the roughness may be smaller, such as 0.01 μm.

In addition, an antireflection layer may be provided on the optical surfaces of the first curved surface 11 and the second curved surface 12.

(4) The light absorbing layer 14 is formed on at least a part of the flat portion (the flange surface A on the front surface) or the side surface of the flange portion 13, or at least a part of the flange surface A and the side surface. The light absorption layer 14 is a thin film having a maximum thickness of 2 μm or less. Since the light absorbing layer 14 is a thin film, the flatness of the flange surface A and the accuracy of the outer shape can be prevented from deteriorating. The light absorption layer 14 is not limited to one layer. The light absorbing layer 14 may be an optical multilayer film in which two or more different materials are stacked.

(4) The light absorbing layer 14 partially includes a member having absorption in at least a part of the visible wavelength range. As such a material, various materials such as a metal, a semiconductor, and a dielectric can be used. For example, silicon, silicon compounds, carbon, carbon compounds, nickel compounds, zinc compounds, chromium compounds, phosphorus compounds, titanium compounds, molybdenum compounds, alloys thereof, organic materials, and the like can be used. In particular, since chromium oxide and silicon are widely used as materials for vacuum deposition and sputtering and have a large technical accumulation, these materials may be used.

FIG. 2 is an explanatory diagram for explaining stray light generated inside the optical element 10. As shown in FIG. 2, when light 21 enters the optical element 10 from an unintended direction, the light is reflected inside the optical element 10 and emitted from the optical element 10. If the light absorbing layer 14 does not exist, such light finally reaches an image sensor (not shown) as stray light, and generates flare and ghost. Light incident from an unintended direction corresponds to light incident on a portion outside the effective area (for example, the area of the first curved surface 11) of the optical element 10 (for example, the flange portion 13).

In the present embodiment, the light absorbing layer 14 is formed on at least a part of the flat portion and the side surface of the flange portion 13. In the path until the light 21 is emitted from the optical element 10, the intensity of the reflected light is reduced by the light absorbing layer 14.

Therefore, in order to sufficiently reduce stray light, it is preferable that the reflectance of the light absorbing layer 14 is sufficiently small when light enters from the glass side (the inside of the optical element 10). In particular, when the incident angle satisfies the condition of satisfying the total reflection, the light is guided inside the optical element 10 without being attenuated. Therefore, it is preferable that the reflectance is sufficiently small even at the incident angle at which the total reflection occurs.

Further, in the present embodiment, since the flange portion 13 is not roughened or black is not applied to the non-roughened flange portion 13, stray light can be generated without impairing the accuracy of the flange surface A. It becomes possible to reduce.

す る と Assuming that the refractive index of the glass is 1.52, the angle satisfying the total reflection condition is 41 °. That is, when light enters the incident surface (for example, the flange surface A) at an incident angle of 41 ° or more, the incident light is totally reflected on the incident surface. At an average incident angle of 65 ° between the angle satisfying the total reflection condition and the maximum incident angle of 90 °, the reflectance should be 50% or less in the visible light wavelength range (for example, a wavelength band of 400 to 700 nm). Is preferred. More preferably, the reflectance is 30% or less.

光 If the light absorbing layer 14 is also formed on the side surface of the flange portion 13 as shown in FIG. 2, the light 21 can be made to enter the light absorbing layer 14 twice. For example, even when the reflectance of the light absorption layer 14 is 30%, the reflectance after the second reflection can be 9%.

(4) The thickness of the light absorbing layer covering the side surface of the flange 13 may be reduced. In such a case, the reflectance spectrum generally shifts to the shorter wavelength side in the region where the film thickness is reduced. Therefore, it is preferable that the reflectance spectrum at an incident angle of 65 ° has a minimum value in a wavelength band of 500 to 900 nm. When the light absorption layer 14 is formed in such a manner, a sufficiently small reflectance can be obtained even when the film thickness is reduced and the reflectance spectrum is shifted by a short wavelength.

平均 Note that the average value of p-polarized light and s-polarized light can be used as the reflectance.

The light absorbing layer 14 can be formed by vacuum evaporation, sputtering, CVD (Chemical Vapor Deposition), or the like.

方法 A method of forming the light absorbing layer 14 (a film forming method) will be described with reference to FIGS. FIG. 3 is a cross-sectional view schematically showing a state when the light absorption layer 14 is formed. FIG. 4 is a flowchart showing a method for forming the light absorbing layer 14.

(4) When vacuum evaporation or sputtering is used, the evaporation material 30 comes to the optical element 10 from an evaporation source (not shown in FIG. 3). For this reason, for example, as shown in FIG. 3, the mask member 33 is installed in a vacuum evaporation apparatus or a sputtering apparatus so that the light absorption layer 14 is not formed on the functional surface of the optical element 10 (step S11). Next, the optical element 10 on which the light absorption layer 14 is not formed is mounted on a vacuum evaporation apparatus or a sputtering apparatus (Step S12). Then, vapor deposition or sputtering is performed (step S13). Note that the order of execution of the processing in step S11 and the processing in step S12 may be reversed. As shown in FIG. 3, when comparing the vapor deposition material 31 reaching the flat portion of the flange portion 13 and the vapor deposition material 32 reaching the side surface of the flange portion 13, the amount of the vapor deposition material 32 is generally equal to the amount of the vapor deposition material 31. Less. Generally, the flat portion of the flange portion 13 faces the vapor deposition source to install the optical element 10, and the flat portion has a larger solid angle at which the vapor deposition material 30 can fly.

In FIG. 3, the mask member 33 is not in contact with the optical element 10, but the mask member 33 may be in contact with the optical element 10, for example, by applying a resist agent or the like directly to the optical element 10. Further, the light absorbing layer 14 may be formed only on the side surface of the optical element 10 by increasing the size of the mask member 33. Further, by providing a notch or the like in the mask member 33, a marking function may be given to the light absorbing layer 14.

場合 If the flange 13 is small, it may be difficult to directly measure the optical characteristics of the light absorbing layer 14. In such a case, the optical element 10 may be cut, and the thickness of each layer may be measured with an electron microscope or the like, and the optical characteristics (reflectance R) may be evaluated based on equation (1).

In equation (1),

It is. Here, theta ₀ is the angle of incidence, n ₀ is the refractive index of the incident medium, n _r is the refractive index of each layer of the multilayer film, d _r is the respective layers of the multilayer film thickness, n _m represents the refractive index of the exit medium . When the material has absorption, a complex refractive index having an extinction coefficient as an imaginary part may be used as the refractive index.

Embodiment 2. FIG.
FIG. 5 is a sectional view schematically showing a second embodiment of the optical element 50 according to one aspect of the present invention. As shown in FIG. 5, in the second embodiment, the light absorbing layer 51 and the light absorbing layer 52 are formed over both surfaces of the flange portion 13 (the front flange surface A and the rear flange surface B). ing. With such a configuration, it is possible to increase the number of times that light incident on the optical element 10 is incident on the light absorbing layer in a path until the light is emitted from the optical element 10. Therefore, the intensity of stray light can be further reduced. FIG. 5 shows one cross section of the optical element 50, but in a plan view, the flat part of the flange portion 13 is annular, and the outer diameter of the optical element 50 extends from the outer periphery of the first curved surface 11. Direction. Further, as in the first embodiment, as long as the optical element 50 is transparent as long as it is transparent in the operating wavelength band, a material such as ceramics, plastic, or a mixed material of organic and inorganic materials may be used.

Also in the present embodiment, since the flange portion 13 is not roughened or black is not applied to the non-roughened flange portion 13, the accuracy of the flange surfaces A and B is not impaired. It becomes possible to reduce stray light.

The optical element 50 of the present embodiment can be molded in the same manner as the optical element 10 of the first embodiment (see FIGS. 3 and 4). That is, for example, a film can be formed by vacuum evaporation, sputtering, or a CVD (Chemical Vapor Deposition) method. However, in this embodiment, when vacuum evaporation or sputtering is used, after forming the light absorption layer 51 in the same manner as in the first embodiment, a mask member is provided between the evaporation source and the second curved surface 12. Then, the light absorption layer 52 is formed.

In the present embodiment, when vacuum deposition or sputtering is used, the number of molding steps is increased compared to the first embodiment. However, a method capable of forming the light absorbing layer 51 and the light absorbing layer 52 simultaneously is described. May be used.

Embodiment 3 FIG.
In the first and second embodiments, examples in which the flange portion is not roughened have been described. It is preferable that the flange portion not have a rough surface, but one embodiment of the present invention is not limited thereto, and does not exclude a case where the flange portion is roughened. When the flange portion is roughened, it is preferable that the flange portion be roughened so that the flatness of the flange portion is not impaired. The roughening that does not impair the flatness of the flange portion is preferably, for example, the following rough surface.
Two adjacent areas of 100 μm × 100 μm in the roughened flange portion are referred to as a first area and a second area, respectively. In the first region, the highest convex portion is defined as a first convex portion. In the second region, the highest convex portion is defined as a second convex portion. The difference in height between the first projection and the second projection is within 5 μm. The difference between the heights of the first convex portion and the second convex portion is preferably within 3 μm, more preferably within 2 μm, and further preferably within 1 μm.
Even when the flange portion is roughened, it is possible to prevent the accuracy of the flange surface from being significantly impaired by the roughened flange portion satisfying the above conditions. Further, by satisfying the above-mentioned range even when the flange portion is roughened, the inclination of the flat plate can be reduced when a flat plate is pressed against the flange portion. Therefore, when an optical system is assembled using the optical element of one embodiment of the present invention, the flange portion can be used as a reference for assembly. Further, by satisfying the above-mentioned range even in the case of a roughened flange portion, it is possible to prevent the flat plate from being pressed against the flange portion to prevent deformation and play, thereby causing tilt.
The configuration other than the roughened flange portion may be similar to the configuration of the first and second embodiments, and therefore, detailed description is omitted.

FIG. 6 is a cross-sectional view schematically showing an optical system 60 assembled using the optical element 10. In an optical system 60 illustrated in FIG. 6, an optical element 10, a lens member 20, and a spacer 63 are arranged inside a lens barrel 61. FIG. 6 illustrates the optical element 10 of the first embodiment, but the optical element 50 of the second embodiment may be used.

As described above, in the first embodiment (the same applies to the second embodiment and the third embodiment), the precision of the flange surface A (or the flange surfaces A and B) of the optical element 10 is not impaired. Therefore, the clearance between the optical element 10 and the lens barrel 61 can be made sufficiently small. Therefore, the center of the opening of the lens barrel 61 and the axis of the optical element 10 can be accurately adjusted. In addition, since the flange surface A (or the flange surfaces A and B) of the optical element 10 is sufficiently flat, the optical element 10 is not tilted with the surface of the lens barrel 61 that receives the flange portion 13, and the optical element 10 is not tilted. 61 can be assembled.
The optical element of one embodiment of the present invention (the optical element described in the first to third embodiments) can be applied (for example, incorporated) to various optical systems and optical devices. That is, one embodiment of the present invention can provide an optical system including the optical element of one embodiment of the present invention. The optical system of one embodiment of the present invention can include, in addition to the optical element, a lens that cooperates with the optical element, an optical filter such as an antireflection film or a bandpass filter, a cover glass, and an aperture. However, these are merely examples, and the application target of the optical element of one embodiment of the present invention is not limited to these optical systems.
One embodiment of the present invention can provide an optical device including the optical element of one embodiment of the present invention. The optical device of one embodiment of the present invention may be an imaging device including an imaging element or an optical device not including an imaging element. Examples of the imaging device include a camera and the like.

Next, an example in which the optical element 10 of the first embodiment shown in FIG. 1 is used will be described. Glass having a refractive index of 1.52 is subjected to glass preform processing and molded into a lens shape (the optical element 10 in a state where the light absorbing layer 14 is not formed) by molding. The end surface of the optical element 10 is a glass molding surface. The roughness of the side surface of the flange portion 13 is Ra 0.1 μm or less.

With the mask member 33 installed on such an optical element 10, chromium oxide (Cr ₂ O ₃ ) and chromium (Cr) are deposited as the light absorbing layer 14 to a thickness of 60 nm and 10 nm, respectively, by sputtering. Therefore, the thickness of the light absorption layer 14 thus formed is 2 μm or less.

FIG. 7 is an explanatory diagram showing the refractive index and the extinction coefficient of chromium oxide and chromium used in this example. FIG. 7A shows the refractive index (Refractive @ Index) and the extinction coefficient (Extinction @ coefficient) of chromium oxide. FIG. 7B shows the refractive index and extinction coefficient of chromium. In FIG. 7, n (dashed line) indicates the refractive index, and k (solid line) indicates the extinction coefficient.

FIG. 8 is an explanatory diagram showing calculation results of the transmittance (Transmittance) and the reflectance (Reflectance) when light is vertically incident on the light absorbing layer 14 in the glass in the present embodiment. The values of the transmittance and the reflectance are average values of the p-polarized light and the s-polarized light.

FIG. 9A shows the reflectance when light is incident on the light absorbing layer 14 in the glass 90 within a range of 5 ° to 85 °. FIG. 9B shows a structure assumed when calculating the transmittance and the reflectance. A chromium oxide (Cr ₂ O ₃ ) of 60 nm is formed on the glass 90, and the chromium (Cr) is formed. ) Is illustrated as having a thickness of 10 nm. As shown in FIG. 9A, even at an incident angle of 65 °, that is, an angle of 65 ° with respect to the vertical direction of the light absorbing layer, the reflectance becomes 30% or less in a wavelength band of 400 to 700 nm. I have. The minimum value of the reflectance at the incident angle of 65 ° is about 560 nm.

FIG. 10 shows that the thickness of the light absorbing layer 14 made of chromium oxide and chromium is 70% (chromium oxide 酸化 42 nm, chromium 7 nm) and 50% (relative to the light absorbing layer 14 shown in FIG. 9B). In the case where chromium oxide (30 nm, chromium 5 nm), the reflectance of light at an incident angle of 65 ° is shown. The minimum value of the reflectance shifts to the shorter wavelength side as the film thickness decreases, but the reflectance is 30% or less at each thickness.

From the above, in the optical element 10 of the present embodiment, the refractive index of glass is set to 1.52 at the average incident angle 65 ° of the angle 41 ° satisfying the total reflection condition and the maximum incident angle 90 °. .), It can be said that the reflectance is sufficiently small. That is, stray light is reduced.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention.

This application is based on Japanese Patent Application (No. 2018-139972) filed on July 26, 2018, the contents of which are incorporated herein by reference.

According to the present invention, stray light can be reduced without greatly impairing the accuracy of the flange surface. The present invention having this effect is useful for an optical element, an optical system, and an imaging optical device.

10, 50 optical element 11 first curved surface 12 second curved surface 13 flange portion 14, 51, 52 light absorption layer 20 lens member 30, 31, 32 vapor deposition material 33 mask member 60 optical system 61 lens barrel 63 spacer

Claims (10)

1. An optical element including a curved surface and a flange portion having an annular flat portion extending in an outer radial direction from the curved surface,
   At least a portion of the flange portion has a light absorbing layer for reducing the reflectance when light is incident from inside the optical element,
   An optical element, wherein the thickness of the light absorbing layer is 2 μm or less.
2. The optical element according to claim 1, wherein the optical element is formed of glass.
3. The optical element according to claim 1, further comprising the light absorbing layer on a side surface that is an outermost surface of the flange portion.
4. The reflectance of light incident from the interior of the optical element to the light absorbing layer at an angle of 65 ° with respect to the vertical direction of the light absorbing layer in a wavelength band of 400 nm to 700 nm is 50% or less. Item 4. The optical element according to any one of Items 1 to 3.
5. The reflectance of light incident from the inside of the optical element to the light absorbing layer at an angle of 65 ° with respect to the vertical direction of the light absorbing layer in a wavelength band of 400 nm to 700 nm is 30% or less. Item 5. The optical element according to item 4,
6. A curved surface, an optical element including a flange portion having an annular flat portion extending in the outer radial direction from the curved surface,
   The arithmetic mean roughness of the side surface of the flange portion is Ra 0.1 μm or less,
   An optical element comprising a light absorbing layer containing a metal, a semiconductor, or a dielectric in at least a part of the flange portion.
7. The optical element according to claim 6, wherein the optical element is formed of glass.
8. The optical element according to claim 6, wherein an arithmetic average roughness of the side surface that is the outermost surface of the flange portion is Ra 0.01 μm or less.
9. An optical system having the optical element according to any one of claims 1 to 8.
10. An optical device comprising the optical element according to any one of claims 1 to 8 and an image sensor.

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