JP2012159720A - Optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical system which suppresses occurrence of a ghost.SOLUTION: In an optical system having a plurality of optical surfaces, at least two surfaces includes antireflection structures having fine uneven structure whose average pitch is equal to or less than 400 nm. An average height of the fine uneven structure is different between an antireflection structure A formed on one surface and an antireflection structure B formed on the other surface.

Description

  The present invention relates to an optical system, and more particularly to an optical system that suppresses the generation of ghosts.

  Conventionally, lenses using a transparent medium (transparent member) such as glass or plastic have been subjected to surface treatment such as providing an antireflection film on the light incident / exit surface in order to reduce the loss of transmitted light. Yes. For example, as an antireflection film for visible light, a multilayer film (multicoat) in which a plurality of dielectric thin films are stacked is known. This multilayer film is formed by depositing a metal oxide on a transparent substrate surface by vacuum deposition or the like.

  In recent years, optical systems such as lenses for digital cameras are required to have high optical performance and to be small and light as a whole. In response to this, a lens having a large aperture or a lens having a surface with a small radius of curvature has been increasingly used.

  When such a lens is used in an optical system, light rays are incident at a large angle around the lens. For this reason, an antireflection film in which a dielectric thin film is laminated in a single layer or multiple layers has a wide angle of incidence, so that reflection cannot be sufficiently suppressed, causing harmful light such as ghosts and flares. .

  In view of such a situation, Patent Document 1 discloses an optical system in which two or more reflective boundary surfaces that cause a ghost are provided with antireflection coatings having reflective properties that are complementary to each other.

JP-A-5-323226

  In Patent Document 1, generation of ghosts is suppressed by applying antireflection coatings having reflection characteristics complementary to each other to two or more reflection boundary surfaces that cause ghosts. In particular, when the refractive index of the medium at the reflection boundary surface of two or more surfaces that cause ghost is n and the incident angle of light is θ, the surface with the smaller n · sin θ is longer than the short wavelength region. It is preferable to apply an antireflection coating having excellent antireflection properties.

  However, at a specific incident angle where a ghost is generated at the two reflection boundary surfaces, the product of the reflectance is small and the ghost is effectively suppressed, but at other incident angles (for example, 0 °) This is at the expense of reflectivity. When such an anti-reflection film is used in an optical system with a large number of lenses (for example, a high-power zoom lens), even if ghosts can be suppressed, the loss of the amount of imaged light increases and the transmittance performance decreases. There was a problem.

  An antireflection structure consisting of a fine concavo-convex structure whose average pitch is less than or equal to the working wavelength, especially in a shape where the space occupancy of the structure is continuously changing, there are an infinite number of films whose refractive index changes gradually. Is substantially equivalent to At this time, an infinite number of reflected lights with small amplitudes are generated from each part (film). If this occurs with a phase shift exceeding a certain level (for example, 360 ° or more), the amplitude of the interfered wave is very small. As a result, high antireflection performance can be obtained.

  Therefore, the interference condition that cancels the reflected light is maintained even for incident light that is different from the design wavelength and the design incident angle, so that an antireflection structure excellent in wavelength band characteristics and incident angle characteristics can be obtained. .

  The present invention is an optical system having a plurality of optical surfaces, and has an antireflection structure having a fine concavo-convex structure with an average pitch of 400 nm or less on at least two surfaces. Then, the above problem is solved by making the average height of the fine concavo-convex structure different between the antireflection structure A formed on one surface and the antireflection structure B formed on the other surface. Yes.

  Furthermore, as another method, the above problem is solved by making the reflectance characteristics different between the antireflection structure A formed on one surface and the antireflection structure B formed on the other surface. is doing.

  According to the present invention, it is possible to obtain an optical system that suppresses the generation of ghost light due to multiple reflections on the optical surface inside the optical system and that reduces the loss of light quantity of imaging light.

Sectional drawing of the principal part of the optical system of Example 1 of this invention Schematic cross-sectional view of antireflection structure A1 having a fine concavo-convex structure whose average pitch is equal to or less than the operating wavelength Explanatory drawing of average pitch ((a) In case of periodic arrangement, (b) In case of non-periodic arrangement) Reflectivity characteristics of the antireflection structure A1 ((a) incident angle: 0 °, (b) incident angle: 60 °) Schematic cross-sectional view of antireflection structure B1 having a fine concavo-convex structure with an average pitch equal to or less than the operating wavelength Reflectivity characteristics of the antireflection structure B1 ((a) incident angle: 0 °, (b) incident angle: 60 °) Product of reflectance of antireflection structure A1 and reflectance of antireflection structure B1 ((a) incident angle: 0 °, (b) incident angle: 60 °) Sectional drawing of the principal part of the optical system of Example 2 of this invention Schematic cross-sectional view of antireflection structure A2 having a fine concavo-convex structure whose average pitch is equal to or less than the operating wavelength Reflectivity characteristics of the antireflection structure A2 ((a) incident angle: 0 °, (b) incident angle: 60 °) Schematic cross-sectional view of antireflection structure B2 having a fine concavo-convex structure whose average pitch is equal to or less than the operating wavelength Reflectivity characteristics of the antireflection structure B2 ((a) incident angle: 0 °, (b) incident angle: 60 °) Product of reflectance of antireflection structure A2 and reflectance of antireflection structure B2 ((a) incident angle: 0 °, (b) incident angle: 60 °)

  Hereinafter, the optical system of the present invention will be described with reference to the drawings. The optical system of the present invention is configured to have an antireflection structure having a fine concavo-convex structure in which at least two of the optical surfaces have different average heights and an average pitch of 400 nm or less.

  The antireflection structure having a fine concavo-convex structure with an average pitch of 400 nm or less according to the present invention may be produced by any method.

  For example, a method can be used in which a film is formed by applying a solution containing aluminum on the lens surface, and a fine uneven structure is formed by performing hot water treatment on the film. Also, a method may be used in which pores formed when anodizing aluminum or an aluminum alloy are formed on the mold surface, and the pores are transferred to the lens surface by a replica method or a molding method. If these methods are used, it is possible to form a fine concavo-convex structure having an average pitch equal to or less than the operating wavelength on a lens surface having a large area at low cost.

  In addition, it may be formed by using a photolithography method, an interference exposure method, an etching method, an array pattern of fine particles, or the like.

  FIG. 2 shows a schematic cross-sectional view of the antireflection structure A1 used in Example 1 of the present invention. A fine concavo-convex structure 23 made of a material containing aluminum oxide on a substrate (lens) 22 having a refractive index (nd) of 1.696680 and a refractive index dispersion (νd) of 55.5 and having an average pitch of 400 nm or less. Was formed to have an average height of 270 nm.

  If the used wavelength is not a single wavelength but covers a certain range, the average pitch may be set to be equal to or shorter than the shortest wavelength in the used wavelength range. Here, the case of the visible range is applied, and the average pitch is set to 400 nm or less.

  This is because, if an average pitch larger than the shortest wavelength used is used, harmful light due to diffraction is generated.

  Here, the average pitch and the average height will be described with reference to FIG. 3 (a) and 3 (b) are views of the fine concavo-convex structure having a wavelength shorter than the use wavelength as viewed from above. The fine irregular shape is typically round.

  FIG. 3A shows an example in which fine irregularities are periodically arranged in a triangular lattice pattern. In this case, the average pitch is equal to the interval between one fine unevenness and the adjacent fine unevenness.

  FIG. 3B shows an example in which fine irregularities are arranged aperiodically. In such a case, the average pitch is: (1) Select six fine irregularities in order from one fine irregularity, calculate the average value of the intervals, (2) Calculate (1) for all fine irregularities And calculating the average value. However, since it is practically difficult to measure all the fine concavo-convex structures provided on the optical surface, one or several points on the optical surface are observed with a scanning electron microscope and the values calculated within a certain area are used. You may substitute.

  For the average height, the height in the surface normal direction of the provided surface may be measured for all fine irregularities and the average value calculated.

  The reflectance RA1 (0 °) at an incident angle of 0 ° and the reflectance RA1 (60 °) at an incident angle of 60 ° of the substrate (lens) 21 on which the antireflection structure A1 is formed are shown in FIGS. Shown in b). The anti-reflection structure consisting of a fine concavo-convex structure with an average pitch equal to or less than the working wavelength has excellent incident angle characteristics. Therefore, when the incident angle is 0 °, the reflectance is 0.3% or less over the entire visible range, and even when the incident angle is 60 °. The reflectivity is almost 2.0% or less over the entire region.

  FIG. 5 shows a schematic cross-sectional view of the antireflection structure B1 used in Example 1 of the present invention. Reference numeral 53 denotes a substrate (lens) having a refractive index (nd) of 1.60311 and a refractive index dispersion (νd) of 60.7. A fine concavo-convex structure 53 made of a material containing aluminum oxide and having an average pitch of 400 nm or less is formed on the substrate 53 through a thin film 54 made of a material containing silica so as to have an average height of 280 nm. did.

  The reflection rate RB1 (0 °) at an incident angle of 0 ° and the reflectance RB1 (60 °) at an incident angle of 60 ° of the substrate (lens) 51 on which the antireflection structure B1 is formed are shown in FIGS. Shown in b). Since the antireflection structure having a fine concavo-convex structure with an average pitch of not more than the working wavelength has excellent incident angle characteristics, the reflectance is 0.3% or less at an incident angle of 0 ° over the entire wavelength range from 450 nm to 650 nm. Even at 60 °, the reflectance is 1.5% or less.

FIG. 7A shows the product of the reflectance RA1 (0 °) at an incident angle of 0 ° of the antireflection structure A1 and the reflectance RB1 (0 °) at an incident angle of 0 ° of the antireflection structure B1. RA1 (0 °) × RB1 (0 °) is very small because the characteristics of RA1 (0 °) and RB1 (0 °) are different, and is 3.0 over the entire wavelength region from 450 nm to 650 nm. × 10 ^-4 % or less.

Furthermore, the product of the reflectance RA1 (60 °) at an incident angle of 60 ° of the antireflection structure A1 and the reflectance RB1 (60 °) at an incident angle of 60 ° of the antireflection structure B1 is shown in FIG. Show. RA1 (60 °) × RB1 (60 °) is a value of 3.0 × 10 ⁻² % or less over the entire wavelength region from 450 nm to 650 nm.

  This is because the antireflection structure A1 made of a fine concavo-convex structure having an average pitch equal to or less than the use wavelength and the antireflection structure B1 made of a fine concavo-convex structure having an average height different from that of the antireflection structure A1 are used. This is the performance that can be achieved. In addition, it is difficult to achieve with an antireflection film in which a dielectric thin film is laminated in a single layer or multiple layers.

  FIG. 1 is a cross-sectional view of an essential part of the optical system according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 1 denotes an optical system, which is a wide-angle lens for a camera having a focal length of 14 mm. In this optical system, an antireflection structure A1 having a fine concavo-convex structure with an average pitch of 400 nm or less is formed on the r02 surface. Similarly, an antireflection structure B1 having a fine uneven structure with an average pitch of 400 nm or less is formed on the r03 surface. As a result, the reflectivity of the double reflection is extremely low at both an incident angle of 0 ° and an incident angle of 60 °, so that high-performance optics that suppresses the occurrence of ghosts well and reduces the loss of the amount of imaging light (transmitted light). The system is realized.

  FIG. 9 shows a schematic cross-sectional view of the antireflection structure A2 used in Example 2 of the present invention. On a substrate (lens) 92 having a refractive index (nd) of 1.696680 and a refractive index dispersion (νd) of 55.5, a fine uneven structure 93 made of the same material and having a pitch of 400 nm or less has an average height. It formed so that it might become 315 nm.

  The reflectance RA2 (0 °) at an incident angle of 0 ° and the reflectance RA2 (60 °) at an incident angle of 60 ° of the substrate (lens) 91 on which the antireflection structure A2 is formed are shown in FIGS. Shown in b). The anti-reflection structure consisting of a fine concavo-convex structure with a pitch less than the working wavelength has excellent incident angle characteristics. Therefore, the reflectance is 0.3% or less over the entire visible region at an incident angle of 0 °, and the visible region even at an incident angle of 60 °. Reflectance of 1.5% or less is achieved in the entire area.

  FIG. 11 is a schematic cross-sectional view of the antireflection structure B2 used in Embodiment 2 of the present invention. A fine concavo-convex structure 113 made of a material containing aluminum oxide on a substrate (lens) 112 having a refractive index (nd) of 1.67790 and a refractive index dispersion (νd) of 55.3 and having a pitch of 400 nm or less. It was formed to have an average height of 750 nm.

  The reflectance RB2 (0 °) at an incident angle of 0 ° and the reflectance RB2 (60 °) at an incident angle of 60 ° of the substrate (lens) 111 on which the antireflection structure B2 is formed are shown in FIGS. Shown in b). The anti-reflection structure consisting of a fine concavo-convex structure with a pitch less than the working wavelength has excellent incident angle characteristics. Therefore, the reflectance is 0.3% or less over the entire visible region at an incident angle of 0 °, and the visible region even at an incident angle of 60 °. Reflectance of 1.5% or less is achieved in the entire area.

FIG. 13A shows the product of the reflectance RA2 (0 °) at an incident angle of 0 ° of the antireflection structure A2 and the reflectance RB2 (0 °) at an incident angle of 0 ° of the antireflection structure B2. RA2 (0 °) × RB2 (0 °) is very small because the characteristics of RA2 (0 °) and RB2 (0 °) are different, and is 2.0 × 10 ⁻⁴ over the entire visible range. % Or less.

Furthermore, the product of the reflectance RA2 (60 °) at an incident angle of 60 ° of the antireflection structure A2 and the reflectance RB2 (60 °) at an incident angle of 60 ° of the antireflection structure B2 is shown in FIG. Show. RA2 (60 °) × RB2 (60 °) is a value of 2.0 × 10 ⁻² % or less over the entire visible range.

  This is because the antireflection structure A2 made of a fine concavo-convex structure having an average pitch equal to or less than the use wavelength and the antireflection structure B2 made of a fine concavo-convex structure having an average height different from that of the antireflection structure A2 are used. This is the performance that can be achieved. In addition, it is difficult to achieve with an antireflection film in which a dielectric thin film is laminated in a single layer or multiple layers.

  FIG. 8 is a sectional view of an essential part of the optical system according to the second embodiment of the present invention. In FIG. 8, reference numeral 1 denotes an optical system, which is a camera wide-angle lens having a focal length of 24 mm. In this optical system, an antireflection structure A2 having a fine concavo-convex structure with an average pitch equal to or less than the use wavelength is formed on the r04 surface, and an antireflection structure B2 having a fine concavo-convex structure with an average pitch equal to or less than the use wavelength is formed on the r05 surface. did. As a result, the reflectivity of the double reflection is extremely low at both an incident angle of 0 ° and an incident angle of 60 °, so that a high-performance optical system that suppresses the occurrence of ghosts well and reduces the loss of the amount of imaging light (transmitted light). Is realized.

  As described above, an antireflection structure having a fine uneven structure with an average pitch equal to or less than the use wavelength and having a different average height is used for at least two or more surfaces in an optical system having a plurality of optical surfaces. Then, since the reflectance is very small not only at an incident angle of 0 ° but also at an incident angle of 60 °, it is possible to effectively suppress a ghost generated by twice reflection of a light beam having a large incident angle, and to obtain imaging light (transmission). It is possible to realize a high-performance optical system with little light loss.

  In this embodiment, the optical system is a wide-angle lens for a camera lens. However, the present invention is not limited to this, and a telephoto lens having a long focal length may be used. Furthermore, an observation optical system such as binoculars or a scanning optical system may be used. It may be used in the system.

A1, A2: Antireflection structure A
B1, B2: Antireflection structure B
1: Optical system 2: Diaphragm 3: Imaging element or film 21, 51, 91, 111: Substrate (lens) on which antireflection structure A or B is formed
22, 52, 92, 112: Substrate (lens)
23, 53, 93, 113: Fine concavo-convex structure with an average pitch equal to or smaller than the operating wavelength 54: A thin film made of a material containing silica

Claims (18)

  An optical system having a plurality of optical surfaces, wherein at least two of the optical surfaces have an antireflection structure A having a fine concavo-convex structure with an average pitch of 400 nm or less, and the antireflection structure A is fine. An optical system comprising an antireflection structure B having a fine concavo-convex structure in which the average height of the concavo-convex structure is different and an average pitch is 400 nm or less. The average height of the fine concavo-convex structure of the antireflection structure A is defined as HAave,
The average height of the fine concavo-convex structure of the antireflection structure B is defined as HBave
When
5 (mm) ≦ | HAave−HBave | ≦ 500 (mm)
The optical system according to claim 1, wherein the following relational expression is satisfied.   An optical system having a plurality of optical surfaces, wherein at least two of the optical surfaces have an antireflection structure A having a fine concavo-convex structure with an average pitch of 400 nm or less, and the antireflection structure A has a reflectance. An optical system characterized in that an antireflection structure B having a fine uneven structure with different characteristics and an average pitch of 400 nm or less is formed. The reflectance of light incident at an incident angle of 0 ° on the optical surface on which the antireflection structure A is formed is RA (0 °),
When the reflectance of light incident on the optical surface on which the antireflection structure B is formed at an incident angle of 0 ° is RB (0 °),
RA (0 °) × RB (0 °) ≦ 1 × 10 ⁻³ (%)
The optical system according to claim 3, wherein the following relational expression is satisfied over the entire wavelength region ranging from a wavelength of 450 nm to 650 nm. The reflectance of light incident at an incident angle of 60 ° on the optical surface on which the antireflection structure A is formed is RA (60 °),
When the reflectance of a light beam incident on the optical surface on which the antireflection structure B is formed at an incident angle of 60 ° is RB (60 °),
RA (60 °) × RB (60 °) ≦ 1 × 10 ⁻¹ (%)
The optical system according to claim 3, wherein the following relational expression is satisfied over the entire wavelength region ranging from a wavelength of 450 nm to 650 nm. On the optical surface on which the antireflection structure A is formed, the reflectance of light incident at an incident angle of 0 ° is RA (0 °), the reflectance of light incident at an incident angle of 60 ° is RA (60 °),
The reflectance of light incident on the optical surface on which the antireflection structure B is formed at an incident angle of 0 ° is RB (0 °), and the reflectance of the light incident at an incident angle of 60 ° is RB (60 °). When
RA (0 °) × RB (0 °) ≦ 1 × 10 ⁻³ (%)
And RA (60 °) × RB (60 °) ≦ 1 × 10 ⁻¹ (%)
The optical system according to claim 3, wherein the following two relational expressions are satisfied over the entire wavelength region ranging from a wavelength of 450 nm to 650 nm. The reflectance of light incident at an incident angle of 0 ° on the optical surface on which the antireflection structure A is formed is RA (0 °),
When the reflectance of light incident on the optical surface on which the antireflection structure B is formed at an incident angle of 0 ° is RB (0 °),
| RA (0 °) -RB (0 °) | ≧ 0.05 (%)
The optical system according to claim 3, wherein the following relational expression is satisfied in at least a part of a wavelength region ranging from a wavelength of 400 nm to 700 nm. The reflectance of light incident at an incident angle of 60 ° on the optical surface on which the antireflection structure A is formed is RA (60 °),
When the reflectance of a light beam incident on the optical surface on which the antireflection structure B is formed at an incident angle of 60 ° is RB (60 °),
| RA (60 °) −RB (60 °) | ≧ 0.2 (%)
The optical system according to claim 3, wherein the following relational expression is satisfied in at least a part of a wavelength region ranging from a wavelength of 400 nm to 700 nm. On the optical surface on which the antireflection structure A is formed, the reflectance of light incident at an incident angle of 0 ° is RA (0 °), the reflectance of light incident at an incident angle of 60 ° is RA (60 °),
The reflectance of light incident on the optical surface on which the antireflection structure B is formed at an incident angle of 0 ° is RB (0 °), and the reflectance of the light incident at an incident angle of 60 ° is RB (60 °). When
| RA (0 °) -RB (60 °) | ≧ 0.05 (%)
And | RA (60 °) −RB (60 °) | ≧ 0.2 (%)
The optical system according to claim 3, wherein the two relational expressions are satisfied in at least a part of a wavelength region ranging from a wavelength of 400 nm to 700 nm.   Either one or both of the antireflection structure A and the antireflection structure B are made of the same material as the substrate on which the structure is formed. An optical system according to claim 1.   One or both of the antireflection structure A and the antireflection structure B are made of a material containing aluminum or aluminum oxide. The optical system described.   One of the antireflection structure A and the antireflection structure B is made of the same material as the substrate on which the structure is formed, and the other is made of a material containing aluminum or aluminum oxide. The optical system according to claim 1, wherein the optical system is an optical system.   Of the antireflection structure A and the antireflection structure B, one or both of the fine concavo-convex structure body made of a material containing aluminum or aluminum oxide, the fine concavo-convex structure body, and the concavo-convex structure body The optical system according to any one of claims 1 to 9, wherein the optical system comprises a laminated structure of a thin film made of a material containing silica provided between the optical surface.   14. The antireflection structure A and the antireflection structure B have one or both pitches that are non-periodic, and an average pitch of 30 nm or more and 400 nm or less. The optical system according to any one of the above.   The optical system according to claim 1, wherein the optical system is an imaging optical system.   The optical system according to claim 1, wherein the optical system is an observation optical system.   The optical system according to claim 1, wherein the optical system is a scanning optical system.   An optical apparatus comprising one or more optical systems according to any one of claims 15 to 17.