JP2007298918A - Optical element and optical system including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical element having a high-performance antireflection structure without increasing difficulty level in production such as molding, in an optical element which ensures antireflection property by minute parts, and to obtain an optical system using the same. <P>SOLUTION: The optical element includes a substrate and a plurality of minute parts having projected parts or recessed parts disposed on the surface of the substrate and has antireflection property, wherein the plurality of minute parts are arranged with a cycle of 1/4 to 1 time as long as the arbitrary wavelength of light used, and first minute parts among the plurality of minute parts are shifted in the thickness direction of the substrate with respect to second minute parts among the plurality of minute parts. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical element and an optical system having the optical element, and for example, relates to an optical element in which a plurality of fine portions having antireflection properties are provided on the surface (light incident / exit surface) of an optical member to effectively prevent reflection. is there.

  Conventionally, in an optical element using a translucent medium such as glass or plastic, surface treatment such as providing an antireflection film on a light incident / exit surface is performed to reduce light due to surface reflection. For example, as an antireflection film for visible light, a multilayer film in which a plurality of thin dielectric films are stacked is known. This multilayer film is formed by forming a thin film of metal oxide or the like on the surface of a light-transmitting substrate by vacuum deposition or the like.

  Further, as an antireflection structure used for an optical element, a structure in which a region (fine concavo-convex region) 13 having a plurality of fine portions (fine concavo-convex shape) 15 is formed on a substrate 14 as shown in FIG. 9 is known. (Refer nonpatent literature 1).

  FIG. 10A shows an enlarged sectional view of the optical element 11 shown in FIG. 9 cut along the yz section.

  In general, when a plurality of fine portions 15 having a periodic structure as shown in FIG. 10A are formed on the surface of an optical element, light incident on the surface is diffracted. In this case, the diffraction direction is obtained by the following formula.

n2 · sin θ2−n1 · sin θ1 = mλ / P (1)
Here, n1 is the refractive index of the incident medium 12, n2 is the refractive index of the exit medium 14, θ1 is the incident angle, θ2 is the exit angle (diffraction angle), m is the diffraction order, λ is the wavelength of the light used, and P is the grating Period (period).

  The fine part 15 in a state where only the 0th-order diffracted light is generated due to the narrowing of the period (interval) P acts like a thin film having a specific refractive index.

  For example, when the fine portion (rectangular lattice) 15 shown in FIG. 9 is formed at a volume ratio of 50% of the medium and air at the interface between the medium refractive index n2 = 1.5 and air (refractive index n1 = 1), The part 15 behaves like a thin film having a refractive index neff = 1.25 between the medium and air. If the height d of the fine portion 15 is set so that neff × d is 1/4 of the operating wavelength λ, the fine portion 15 functions as an antireflection film.

  FIG. 10B shows an equivalent refractive index n in the thickness direction (depth direction) of the substrate 14 of the fine portion 15 in FIG. In FIG. 10B, the horizontal axis indicates the refractive index n in each region, and the vertical axis indicates the depth d from the substrate 14. This is the same structure as a single-layer antireflection film.

  Further, by making the shape of the fine portion 15 into a cone shape as shown in FIGS. 11 and 12, the same effect as a film in which the refractive index n continuously changes on the surface of the optical element is obtained (see Patent Document 1). .

  As a method of manufacturing an optical element having such a fine portion 15 on the surface, a method is known in which the fine portion 15 is formed on the surface of a molding die, and a plastic resin or the like is molded with the die (Patent Document 2). reference).

  In addition, a method has been proposed in which after forming a fine uneven resist pattern on the surface of a mold, anisotropic etching such as reactive ion etching is performed to remove the resist pattern to produce a fine portion. (See Patent Document 1).

  Alternatively, a method of forming a pseudo-conical shape into a mold by repeating anodized porous alumina and etching is also known (see Patent Document 3).

  In addition, as a reflection preventing structure having a random shape instead of the periodic structure as described above, a manufacturing method in which a fine part is formed by spraying nanoparticles on a mold has been proposed (see Patent Document 4).

  In addition, in view of the molding situation, proposals have been made to regulate the deviation of the molded shape from the ideal shape to make full use as an optical element (see Patent Documents 5 and 6).

  13A is an enlarged cross-sectional view of the optical element 11 having the antireflection structure disclosed in Patent Document 5, and FIG. 13B is an equivalent refractive index in the thickness direction of the fine portion 15 in FIG. 13A. It is explanatory drawing which shows. In Patent Document 5, by setting the transfer rate at the time of molding to 70% or more, deterioration of optical performance from the antireflection performance obtained with an ideal cone shape is reduced.

  14A is an enlarged cross-sectional view of the optical element 11 having an antireflection structure disclosed in Patent Document 6, and FIG. 14B is an equivalent refractive index in the thickness direction of the fine portion 15 in FIG. It is explanatory drawing which shows. In Patent Document 6, the filling property (transferability) of the resin into the fine concave portion of the mold is improved by changing the shape from an ideal cone shape to a shape with a missing tip.

  Since the optical element 11 in FIG. 14A has a shape in which the tip of the fine portion 15 is missing, a discontinuous portion of the refractive index is formed at the interface with air, and Fresnel reflection occurs.

As described above, in Patent Documents 5 and 6 described above, a shape in which optical performance is not relatively deteriorated in a situation where an ideal cone shape cannot be obtained due to difficulty in molding is specified.
JP 2001-272505 A JP-A-62-96902 JP 2005-156695 A JP 2002-286906 A JP 2004-287238 A JP 2005-173457 A Applied Optics, Vol. 25, no. 24, pp 4562-4567, (1986)

  In order to obtain a high-performance antireflection characteristic by forming a plurality of fine parts having a fine concavo-convex structure on a substrate, it is important to appropriately set the shape of the fine parts and the arrangement conditions on the substrate. .

  Further, it is important that the shape of the fine portion is easy to mold. If the structure of the fine portion is not appropriate, Fresnel reflection increases or unnecessary diffracted light is generated, and the reflection characteristics deteriorate. In addition, it is difficult to manufacture the fine portion, and if the shape of the fine portion deviates from the design shape, a good antireflection effect cannot be obtained.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical element having high performance antireflection without increasing the manufacturing difficulty such as molding. It is another object of the present invention to provide an optical system having good optical performance that does not generate unnecessary diffracted light or flare light by using the optical element of the present invention in the optical system.

The optical element of the invention of claim 1 comprises:
An optical element having a substrate and a plurality of fine portions having convex portions or concave portions provided on the substrate surface and having antireflection properties,
The period in which the plurality of fine portions are arranged is a period that is not less than 1/4 times and not more than 1 time of an arbitrary wavelength of the used light,
The first fine portion among the plurality of fine portions is shifted in the thickness direction of the substrate with respect to the second fine portion among the plurality of fine portions.

The invention of claim 2 is the invention of claim 1,
The fine portion is formed by forming a shape having an inverted concavo-convex shape on a mold, and molding and transferring using the mold.

The invention of claim 3 is the invention of claim 1,
The height of the fine portion is characterized by being 1/5 or more of an arbitrary wavelength of light used.

The invention of claim 4 is the invention of claim 1,
The range in which the first fine portion is shifted in the thickness direction of the substrate is a range of 1/10 to 1/2 of the height of the fine portion.

The invention of claim 5 is the invention of claim 1,
The range in which the first fine portion is shifted in the thickness direction of the substrate is a range from 1/40 to 1/8 of an arbitrary wavelength of light to be used.

The invention of claim 6 is the invention of claim 1,
The period Pa of the first fine part shifted in the thickness direction of the substrate of the fine part is larger than the period P of the fine part in the in-plane direction of the substrate on which the fine part is formed. It is a feature.

The invention of claim 7 is the invention of claim 6,
The period Pa of the first fine part shifted in the thickness direction of the substrate of the fine part is equal to or less than an arbitrary wavelength of the wavelength of light used in the in-plane direction of the substrate on which the fine part is formed. It is characterized by being.

The invention of claim 8 is the invention of claim 1,
The plurality of fine portions have a ratio da / Pa of a shift amount da to a cycle Pa that shifts some of the fine portions in the thickness direction of the substrate as compared with a ratio d / P of a height d to the cycle P. It is small.

The invention of claim 9 is the invention of claim 1, 3 or 5,
The light to be used is visible light.

The optical system of the invention of claim 10 is
The optical element according to claim 1 is used.

  According to the present invention, an optical element having high performance antireflection properties can be achieved without increasing the difficulty in manufacturing such as molding. Furthermore, according to the present invention, by using the optical element in the optical system, it is possible to achieve an optical system having good optical performance that does not generate unnecessary diffracted light or flare light.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a perspective view of an essential part of an optical element having antireflection properties (antireflection structure) according to Example 1 of the present invention.

  In the figure, reference numeral 1 denotes an optical element, which is made of a plastic resin or an ultraviolet curable resin, and has a plurality of fine portions (fine concavo-convex shape) 5 formed of convex portions or concave portions on the surface (light incident / exit surface) on the substrate 4. The provided region (fine uneven region) 3 is formed.

  When the period (interval) P of the fine portion 5 is shorter than the wavelength λ of incident light, ± 1st-order or higher-order reflected diffracted light is not generated at normal incidence, and only 0th-order reflected diffracted light is generated. Since the optical element 1 of this embodiment generally uses transmitted light, it is desirable that diffraction does not occur in the transmitted light. In that case, if the period P of the fine portion 5 is 1 / (n2) or less of the wavelength λ of the incident light, the vertically incident transmitted light is only the 0th-order transmitted diffracted light.

  Furthermore, not only vertically incident light but also light is incident on optical elements such as lenses at various incident angles. In this case, the period P of the fine portion 5 may be determined so that transmitted and reflected diffracted light is not generated from the above-described equation (1).

  For example, when visible light having a wavelength of 400 to 700 nm is used, the period P of the fine portion 5 when the above-described diffracted light is not generated needs to be 400 nm or less. Furthermore, in order to prevent generation of diffracted light with respect to transmitted diffracted light or light incident at a specific incident angle, the period P is preferably 200 nm or less.

  In the present embodiment, the plurality of fine portions 5 are provided in the range of 1/4 to 1 times the arbitrary wavelength λ of the wavelength of light used by the period P of adjacent convex portions or concave portions, and the incident light is transmitted therethrough. In addition, the period P is determined so that diffracted light other than the 0th order is not generated during reflection. The wavelength of light used (hereinafter referred to as “use wavelength”) λ is a wavelength within the range of visible light wavelength 400 to 700 nm.

  In addition, some fine portions (first fine portions) among the plurality of fine portions 50 in the present embodiment are in the thickness direction (depth direction) of the substrate 4 with respect to other fine portions (second fine portions). ) In the range of the width da. The height d of the convex portion or concave portion of the fine portion 5 from the substrate 4 is formed to be 1/5 or more of the operating wavelength λ.

  Here, each of the first and second fine portions is composed of a single or a plurality of fine portions 5.

  The concavo-convex shape of the fine portion 5 (the shape of the convex portion or the concave portion) is a cone shape or a bell shape, and has a structure in which a pattern of the shape is periodically arranged in the xy direction in FIG.

  In this embodiment, Fresnel reflection is thereby greatly reduced, and an antireflection effect superior to that of a normal thin film can be obtained. A higher height d of the fine portion 5 is preferable because the refractive index n changes gently, and is preferably 1/5 or more of the wavelength λ of the light to be used, and functions as an antireflection.

  The shape of the fine part 5 is preferably a cone shape or a bell shape, unlike the one-dimensional lattice shape shown in FIG. 9, so that the polarization dependence of the equivalent refractive index can be reduced, which is preferable for applications such as antireflection. In this case, the period P of the fine portion 5 may be an expression obtained by extending the above-described expression (1) to a two-dimensional grating, and the grating period P is set so that light incident on the two-dimensional grating is not generated except for the 0th-order diffracted light. Can be determined.

  In addition, the fine portion 5 is formed and transferred using a mold having a shape in which the uneven shape is reversed formed on a mold.

  The fine part 5 may be made of the same material as the substrate 4.

  In this manufacturing method, an antireflection structure can be formed simultaneously with the molding of the optical element 1, so that unlike an ordinary thin antireflection film, there is no additional process for applying an antireflection treatment, and the manufacture is facilitated.

  The uneven shape of the fine portion 5 is not limited to the bell shape. For example, in the case of the one-dimensional periodic structure shown in FIG. 9, it may be triangular, trapezoidal, rectangular or the like. In the case of a two-dimensional periodic structure, a conical shape, a truncated cone shape, a quadrangular pyramid shape, a cylindrical shape, or the like may be used.

  Furthermore, in the case of a two-dimensional periodic structure, the arrangement of the plurality of fine portions 5 may be an arrangement such as a triangular arrangement in addition to the arrangement having a period in the xy direction shown in FIG. Further, the period need not be the same in the xy directions as shown in FIG. For example, when used as an optical element with an antireflection function added to the surface (curved surface or flat surface) of a transmissive optical element such as a lens or a plane-parallel plate, You may set with a separate period in xy direction.

  Next, the characteristics of the optical element 1 of the present embodiment will be described with reference to FIGS.

  FIG. 2A is a schematic diagram (enlarged sectional view) showing a sectional shape of the optical element in FIG. 1 on the yz plane. FIG. 2B is an explanatory diagram showing the equivalent refractive index in the thickness direction of the cross-sectional shape shown in FIG.

  In this embodiment, as shown in FIG. 2A, a plurality of fine portions 5 having a structure of period P and height (depth) d are shifted in the thickness direction with width (shift amount) da and period Pa. ing. As a result, the width of the region where the equivalent refractive index changes becomes D as shown in FIG. When the fine portion 5 is not shifted, the width of the region where the equivalent refractive index changes is the height d of the fine portion 5, and in this embodiment, the width D of the region where the equivalent refractive index changes is widened. ing. That is, the equivalent refractive index changes more gently. The antireflection effect is improved as the width of change of the refractive index increases. Further, the effect of this embodiment is equivalent to increasing the height d of the fine portion 5 to D when the width of change in the refractive index is to be achieved only by the fine portion 5. Increasing the height of the fine part means that the fine shape becomes sharp. For this reason, when an optical element is obtained by producing a fine uneven shape on the mold as described above and molding a plastic resin or the like, transferability and releasability are difficult. Since this embodiment can increase the width of change in refractive index without changing the shape of the fine portion, it is suitable for obtaining high-performance antireflection performance. Further, in order to obtain a high-performance antireflection characteristic, it is desirable that the refractive index change of the region (fine uneven region) 3 linearly changes in the thickness direction as shown in FIGS. 2 (a) and 2 (b). .

  Next, a method of shifting the first fine part, which is a feature of the present embodiment, will be described.

  FIG. 2 shows a period Pa in the case where the first fine portion is composed of a plurality of fine portions 5. The first fine part may be composed of a single fine part 5.

  First, the shift amount da in the thickness direction of the first fine portion will be described. FIG. 3 is a graph showing the antireflection performance (relationship between the width D and the reflectance) when the width D of the region where the equivalent refractive index changes is changed. In FIG. 3, the horizontal axis represents the wavelength in the visible range, and the vertical axis represents the reflectance of the optical element.

  In this embodiment, it is assumed that light is incident perpendicularly to the optical element surface, and the medium n1 on the incident side is air, and the medium n2 on the emission side is PMMA (polymethyl methacrylate). The grating period P is sufficiently small so that the equivalent refractive index is established, and the equivalent refractive index of the width D of the region where the equivalent refractive index changes is linearly changed in the thickness direction as shown in FIG. . The graph in FIG. 3 represents the reflectance with respect to the wavelength when the width D of the region where the equivalent refractive index changes is set to a depth of 0, 100, 150, 200, and 250 nm. The width D of the region where the equivalent refractive index changes is 0 nm when there is no fine portion 5 and Fresnel reflection occurs on the surface. It can be seen from FIG. 3 that if the width D of the region where the equivalent refractive index changes is 100 nm or more, sufficient antireflection characteristics are obtained. It can also be seen that the reflectance is reduced by more than 1/2 when the width D of the region where the equivalent refractive index changes increases from 100 nm to 150 nm and from 150 nm to 200 nm.

  FIG. 4 is a graph in which the horizontal axis is the width D of the region where the equivalent refractive index changes in the same optical element configuration as in FIG. The reflectance at wavelengths 400, 550, and 700 nm in the visible range is shown. The reflectance decreases as the width D of the region where the equivalent refractive index changes while the minimum value and the maximum value are repeated at any wavelength. In particular, when the width D of the region where the equivalent refractive index changes is 100 nm to 200 nm, the reduction of the reflectance is remarkable. In this range, the antireflection characteristic is reduced by about 0.5 to 0.7% just by increasing the width D of the region where the equivalent refractive index changes by only 20 nm. For example, if the height d of the fine portion 5 is 100 nm and the shift amount da is 20 nm, the refractive index n changes within the range of 120 nm as the width D of the region where the equivalent refractive index changes. Become. Various combinations of the height d of the fine portion 5 and the shift amount da can be considered.

  In order to improve the antireflection characteristic without deteriorating the manufacturing difficulty, the shift amount (range in which the first fine portion is shifted in the thickness direction) da is reduced to 1/10 of the height d of the fine portion 5. It is desirable to be in the range of 1/2 or less.

  If the shift amount da is 1/10 or less with respect to the height d of the fine portion 5, the effect of improving the antireflection characteristic is small, which is not preferable. Further, if the shift amount da is ½ or more, the influence of the shape to be shifted on the manufacturing becomes large, which is not preferable. Also, as will be described later, depending on the period Pa for shifting the first fine portion, the adverse effect on the optical performance other than the antireflection characteristic is increased, for example, the intensity of unnecessary diffracted light other than the 0th order diffracted light becomes strong.

  Next, the period Pa (see FIG. 2) for shifting the first fine portion in the thickness direction will be described.

  First, the ratio d / P between the period P of the fine part 5 and the height d is defined as the aspect ratio Rd. For this aspect ratio Rd, the ratio da / Pa between the period Pa for shifting the first fine portion in the thickness direction and the shift amount da is defined as the aspect ratio RD.

  In this embodiment, an optical element having a high-performance antireflection structure is realized without increasing the manufacturing difficulty such as molding caused by the fine portion 5. Therefore, it is necessary to determine the period Pa and the shift amount da to be shifted so that Rd ≧ RD. Otherwise, it is necessary to form a structure having an aspect ratio higher than that of the fine part 5 due to the shift, and the difficulty in manufacturing increases.

  In this embodiment, as shown in FIG. 2A, the value of the period Pa for shifting the first fine portion in the thickness direction is set in the in-plane direction of the element surface on which the fine portion 5 is formed. It is set to be larger than the period P of 5. Here, characteristics when the period Pa is larger than the period P will be described.

  As described in the background art section, the period P of the fine portion 5 is determined so that the 0th-order diffracted light is not generated. That is, the period P is set to be shorter than the wavelength of incident light. On the other hand, when the value of the period Pa to be shifted is larger than the used wavelength, diffracted light other than the 0th-order diffracted light is generated depending on conditions such as the incident angle. That is, when the period Pa to be shifted becomes larger than the use wavelength, higher-order diffracted light is generated. Therefore, as an optical element having antireflection characteristics, the period Pa of the first fine portion to be shifted is preferably equal to or less than the use wavelength in the in-plane direction of the element surface on which the fine portion 5 is formed.

  As described above, increasing the shift amount da is preferable for obtaining high-performance antireflection characteristics. However, if the shift amount da is too large, the intensity of diffracted light increases, which is not preferable as an optical element.

  Note that the shift period Pa of the first fine part may be periodic or random in the in-plane direction of the element surface on which the fine part 5 is formed.

  FIG. 5 shows the 0th-order transmittance in a period in which transmitted diffracted light other than the 0th-order diffracted light is generated. In FIG. 5, the horizontal axis represents the wavelength, and the vertical axis represents the zeroth-order transmittance, and shows the relationship between the shift amount da of the fine portion 5 and the zeroth-order transmitted light. The 0th-order transmittance is the ratio of the 0th-order transmitted light in the total transmitted light amount. The shift amount da of the first fine portion is shifted in a sine wave shape as shown in FIG. 5, and the amplitude (shift amount) da is changed to 10, 20, 50, and 75 nm. It can be seen that the 0th-order transmittance decreases as the shift amount da increases.

  From FIG. 5, the shift amount da is preferably 50 nm or less. More precisely, since the decrease on the short wavelength side is significant, the shift amount da is preferably in the range of 1/8 or less of the wavelength on the short wavelength side. Desirably, the range of 1/40 to 1/8 of the wavelength used is good.

  In practice, the behavior of diffracted light other than the 0th order when the optical element of this embodiment is used in the optical system may be examined to determine the allowable amount of diffracted light other than the 0th order.

  FIG. 6 is a graph similar to FIG. 5, in which the first fine portion is shifted in a rectangular shape as shown in FIG. 6. Also in this case, it can be seen that the zero-order transmittance decreases as the shift amount da increases. 5 and 6, it can be seen that the degree of decrease in the 0th-order transmittance varies depending on how the first fine portion is shifted.

  As shown in FIGS. 5 and 6, when the first fine portion is periodically shifted in the in-plane direction, the decrease in the 0th-order diffracted light becomes diffracted light of another order. Depending on the configuration of the optical system, it is conceivable that light of a specific diffraction order forms strong flare light, for example, forms an image on the evaluation surface of the optical system, and deteriorates optical performance. In such a case, it is preferable that the first fine portion is randomly shifted in the in-plane direction (thickness direction) without having a periodic structure, so that concentration to a specific diffraction order can be suppressed.

  In this embodiment, as described above, the first fine portion is shifted in a specific range in the thickness direction. Therefore, the method of shifting in the in-plane direction may be periodic, random or intermediate, and is not particularly limited.

  As described above, in this embodiment, the actual change region can be increased with respect to the change region of the equivalent refractive index obtained only by the fine portion 5 as described above, thereby obtaining a wider change region of the equivalent refractive index. Can do. This is equivalent to increasing the depth of the fine part alone, and high-performance antireflection characteristics can be obtained.

  On the other hand, since each fine part 5 is only shifted in the thickness direction, the difficulty in manufacturing such as molding caused by the fine part 5 does not deteriorate.

  So far, the shift amount of the first fine portion and the periodic distribution in the in-plane direction have been described specifically, the shift amount da and the shift cycle Pa.

  Here, the shape (such as the sine wave or rectangular wave shown in FIGS. 5 and 6) for shifting the first fine portion will be described.

  The shape to be shifted may be determined so that the degree of change in the equivalent refractive index when the first fine portion is shifted within a specific range has desired optical characteristics. Ideally, the shape of the first fine portion and the shift shape may be determined so that the equivalent refractive index changes linearly in the thickness direction as shown in FIG. This can be determined by obtaining an equivalent refractive index based on the volume ratio of the medium n1 and the medium n2 within the period of the larger value of the period P of the fine part 5 or the period Pa to be shifted. If the shape to be shifted is a random shape, a similar equivalent refractive index distribution may be obtained in a sufficiently random region.

  For the created optical element, the equivalent refractive index of the evaluation region that can be regarded as sufficiently uniform may be analyzed by, for example, spectroscopic ellipsometry.

  Next, an example of the manufacturing method of the metal mold | die for producing the optical element which has the reflection preventing structure of this invention is demonstrated.

  First, the die is cut with a diamond tool to create the surface shape of the optical element. Specifically, in the case of an optical element having a lens surface shape, curved processing of the lens surface is performed. At this time, the roughness of the surface is reduced so that a normal optical element becomes a mirror surface.

  In the present embodiment, the roughness corresponding to the shift amount described above is left on the mold surface by changing the cutting conditions. Thereafter, the shape of the optical element of the present example in which the fine part is shifted within a specific range can be realized by applying a process for forming the fine part to the mold. A method such as anodized porous alumina can be used to form the fine portion. Or in the manufacturing method which produces a fine part using a resist and etching, it can achieve easily by changing the conditions of etching and roughening the surface to the extent corresponding to the shift amount.

  In addition, when the shape to which the first fine portion is shifted has a period, this embodiment can be configured by forming the shifted shape and the fine portion twice in succession by using the same manufacturing method as the processing for creating the fine portion 5. The structure can be realized.

  Further, as a method of forming an optical element using this mold, there are 2P molding, hot press molding, resin injection molding, etc., using generally known UV curable resins.

  A method of obtaining an optical element by manufacturing a mold having a fine concavo-convex structure and molding a plastic resin or the like is preferable because a high-performance antireflection effect can be easily obtained.

  In order to obtain higher-performance antireflection characteristics, considering the application with visible light, the period P of the fine portion is 200 nm or less so that diffracted light other than the 0th order is not generated up to a specific incident angle in transmission reflection. It is desirable to be finer.

  On the other hand, the height d of the fine portion is preferably as high as 1/5 or more of the wavelength λ of the light used as described above, since the higher the refractive index n regarded as equivalent, the higher the performance.

  7 and 8 show examples in which the optical element having antireflection properties of the present invention is applied to an optical system.

  FIG. 7 is a schematic diagram in which the optical element having antireflection properties of the present invention is used in an imaging optical system (photographing lens) of a camera. In FIG. 7, reference numeral 6 denotes a taking lens unit, which has an aperture 8 and the above-described optical element 1 of the present invention. In FIG. 7, an antireflection structure is formed on the first surface (light incident surface) of the optical element (final lens) closest to the imaging surface 7. The image plane 7 is a film or a CCD. The optical element 1 is an optical element having a lens function in FIG. 7 and suppresses reflection of the lens surface to reduce generation of flare light.

  In FIG. 7, the anti-reflection optical element 1 is provided in the final lens of the photographing lens unit 6. However, the present invention is not limited to this, and it may be used for other lenses or a plurality of lenses may be used. May be.

  Further, in the present embodiment, the case of the photographing lens of the camera having the fine portion described above is shown, but the present invention is not limited to this. For example, even when the optical element of the present invention is used in an imaging optical system used in a wide wavelength range such as a video camera photographing lens, an office machine image scanner, or a digital copying machine reader lens, the same as in the above-described embodiments. An antireflection effect is obtained.

  FIG. 8 is a schematic diagram in which the optical element having antireflection properties of the present invention is used in an observation optical system such as binoculars. In FIG. 8, 9 is an objective lens unit, and 10 is a prism for establishing an image, which is shown expanded. Reference numeral 7 denotes an aperture, and reference numeral 11 denotes an eyepiece. The optical element 1 of the present invention described above is included therein. Reference numeral 12 denotes an evaluation surface (pupil surface).

  In FIG. 8, one optical element 1 having antireflection properties is provided in the eyepiece 11, but the present invention is not limited to this, and a plurality of optical elements 1 may be provided.

  8 shows the case where the optical element 1 of the present invention is used for the eyepiece unit 11 in the observation optical system. However, the present invention is not limited to this. For example, the surface of the prism 10 or a lens in the objective lens unit 9 is used. In this case, the same effect as in the above-described embodiment can be obtained.

  In the present embodiment, binoculars are shown, but the present invention is not limited to this. The optical element of the present invention can be applied to observation optical systems such as a terrestrial telescope and an astronomical observation telescope, and the same effect can be obtained. Further, even when applied to an optical viewfinder such as a lens shutter camera or a video camera, the same effect as the above-described embodiment can be obtained.

1 is an enlarged perspective view of an optical element having an antireflection structure according to Embodiment 1 of the present invention. FIG. 1 is an enlarged sectional view of the optical element in FIG. 1 and a diagram showing an equivalent refractive index. 2 is a graph showing the relationship between the width of the region where the equivalent refractive index changes in FIG. 2 and the reflectance. 2 is a graph showing the relationship between the width of the region where the equivalent refractive index changes in FIG. 2 and the reflectance. FIG. 1 is a graph showing the relationship between the shift amount and the zero-order transmitted light in FIG. FIG. 1 is a graph showing the relationship between the shift amount and the zero-order transmitted light in FIG. Schematic diagram using an optical element having an antireflection structure of the present invention in an imaging optical system Schematic diagram using an optical element having an antireflection structure of the present invention in an observation optical system Enlarged perspective view of an optical element having a conventional antireflection structure FIG. 9 is an enlarged sectional view of the optical element in FIG. 9 and a diagram showing an equivalent refractive index. Enlarged perspective view of an optical element having a conventional antireflection structure 11 is an enlarged cross-sectional view of the optical element in FIG. 11 and a diagram showing an equivalent refractive index. An enlarged sectional view of another conventional optical element and a diagram showing an equivalent refractive index An enlarged sectional view of another conventional optical element and a diagram showing an equivalent refractive index

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical element 2 Incident medium 3 Area | region (fine uneven | corrugated area | region)
4 Injection medium 5 Fine part (fine uneven shape)
6 Imaging optical system 7 Imaging surface 8 Aperture 9 Objective lens unit 10 Prism 11 Eyepiece unit 12 Evaluation surface (pupil surface)

Claims (10)

An optical element having a substrate and a plurality of fine portions having convex portions or concave portions provided on the substrate surface and having antireflection properties,
The period in which the plurality of fine portions are arranged is a period that is not less than 1/4 times and not more than 1 time of an arbitrary wavelength of the used light,
An optical element, wherein a first fine portion of the plurality of fine portions is shifted in a thickness direction of the substrate with respect to a second fine portion of the plurality of fine portions.   2. The optical element according to claim 1, wherein the fine portion is formed by forming a shape having an inverted concavo-convex shape on a mold, and molding and transferring using the mold.   2. The optical element according to claim 1, wherein the height of the fine portion is 1/5 or more of an arbitrary wavelength of light used.   2. The optical device according to claim 1, wherein a range in which the first fine portion is shifted in the thickness direction of the substrate is in a range of 1/10 to 1/2 of the height of the fine portion. element.   The range in which the first fine portion is shifted in the thickness direction of the substrate is a range from 1/40 to 1/8 of an arbitrary wavelength of light to be used. Optical elements.   The period Pa of the first fine part shifted in the thickness direction of the substrate of the fine part is larger than the period P of the fine part in the in-plane direction of the substrate on which the fine part is formed. The optical element according to claim 1.   The period Pa of the first fine part shifted in the thickness direction of the substrate of the fine part is equal to or less than an arbitrary wavelength of the wavelength of light used in the in-plane direction of the substrate on which the fine part is formed. The optical element according to claim 6.   The plurality of fine portions have a ratio da / Pa of a shift amount da to a cycle Pa that shifts some of the fine portions in the thickness direction of the substrate as compared with a ratio d / P of a height d to the cycle P. The optical element according to claim 1, wherein the optical element is small.   The optical element according to claim 1, wherein the light to be used is visible light.   An optical system comprising the optical element according to claim 1.