JP2012208257A - Anti-reflection structure and optical member - Google Patents

Abstract

Provided is an antireflection structure which can obtain a low reflectance with respect to light of different wavelengths and obliquely incident light, is easy to manufacture, and has high mechanical strength.
An antireflection structure is formed by a medium 1 and a medium 3, and when an effective refractive index of the antireflection structure is N _eff ,
N _eff = r _A N _A + r _C N _C
Where r _A , r _C : volume ratio of the first medium and the third medium
N _A , N _C : two layers (layer A and layer B) having different effective refractive indexes represented by the refractive indexes of the first medium and the third medium, and the layer A is the minimum wavelength in the antireflection wavelength region The following convex microstructures 4 are arranged.
[Selection] Figure 1

Description

  The present invention relates to an antireflection structure having a fine two-dimensional uneven structure and an optical member having the antireflection structure on the surface.

  In various products using light, such as lighting equipment, display devices, information equipment, and photography equipment, optical members having translucency made of glass or plastic are often used. These optical members have functions such as condensing light by controlling the direction of light and protecting the inside of the product from dirt and impacts. However, on the other hand, the reflected light generated at the interface when light enters or exits the optical member lowers the efficiency of the lighting device, reduces the visibility of the display device, and causes noise in the information device. This also contributes to a decrease in performance, such as lowering the image quality of the image taken by the device.

  That is, the reflected light generated at the interface of these optical members is generated due to the difference between the refractive index of the surrounding medium such as air and the refractive index of the optical member. This is because when light enters a medium having a different refractive index, a component returning to the incident side is generated due to the continuity of the wave at the interface.

  For example, in a lighting device, reflected light generated on the surface of the optical member returns to the light source side and is absorbed without being emitted from the emission surface, which causes a reduction in illumination efficiency. In addition, in an image display device provided with a display device, a part of the external light is reflected on the panel surface of the display device and reaches the observer, so that the ratio of light originally emitted from the panel surface is reduced, It becomes a factor that the contrast is lowered.

  For this reason, conventionally, a method of coating a thin film on the surface of the optical member is generally used in order to reduce reflection at the interface of the optical member, which causes the above-described performance degradation. By coating the surface of the optical member with a thin film, reflected light generated at the interfaces of the surrounding medium, thin film, and optical member can interfere with each other, and the amplitude of the light returning to the incident side can be reduced.

  By the way, in recent years, in order to obtain a better antireflection effect, as a technique that is completely different from the structure in which a thin film is coated on the surface of the optical member as described above to prevent the reflection, A technique for obtaining an antireflection effect by forming a concavo-convex structure, a so-called “moth eye structure” has been proposed (see, for example, Patent Documents 1 and 2).

  In the technology described in Patent Document 1, by combining the effect of changing the refractive index stepwise and the light interference effect by controlling the shape of the structure smaller than the wavelength of the light called the “moth eye structure”, Low reflectivity is achieved.

  Further, in the technique described in Patent Document 2, by controlling the shape of a structure called “moth eye structure” smaller than the wavelength of light, the refractive index is changed stepwise to suppress the generation of reflected light, Low reflectivity is achieved.

Japanese Patent No. 4398507 Special table 2008-508553

  By the way, with the technique of the said patent document 1, there exists a problem that a reflectance raises with respect to the light of a different wavelength, or the light of diagonal incidence by utilizing an interference effect. Further, since it is necessary to precisely control the shape of the structure smaller than the wavelength in the height direction, mass production is difficult and productivity is low.

  In addition, although the technique of Patent Document 2 can realize a very low reflectance in principle, it is necessary to control the shape of the structure smaller than the wavelength in the height direction, which makes mass production difficult. Productivity is low. In addition, since the tip has a very sharp structure, the strength of the structure is low when another member, a fingertip or the like comes into contact with the structure, or the structure may be damaged.

  Accordingly, the present invention provides an antireflection structure capable of obtaining a low reflectance with respect to light of different wavelengths and obliquely incident light, is easy to manufacture, and has high mechanical strength, and the antireflection structure. It aims at providing the optical member which has on the surface.

In order to achieve the above object, an invention according to claim 1 is an antireflection structure provided at a boundary between a first medium and a second medium, and the antireflection structure is formed on the first medium. And the third medium, and when the effective refractive index of the antireflection structure is N _eff ,
N _eff = r _A N _A + r _C N _C
Where r _A , r _C : volume ratio of the first medium and the third medium
N _A , N _C : two layers having different effective refractive indexes represented by the refractive indexes of the first medium and the third medium, and at least one of the two layers is the minimum wavelength in the antireflection wavelength region It has the following two-dimensional uneven structure.

  The invention according to claim 2 is characterized in that the antireflection structure has a two-stage two-dimensional uneven structure in which the volume ratio of the third medium is different in the height direction.

According to a third aspect of the present invention, when the refractive index of the first medium is N _A , the refractive index of the second medium is N _B , and the refractive index of the third medium is N _C , _A <N _C <N _B.

According to a fourth aspect of the present invention, when the refractive index of the first medium is N _A , the refractive index of the second medium is N _B , and the refractive index of the third medium is N _C , N _A <N _C = N _B.

  The invention according to claim 5 is characterized in that the second medium and the third medium are the same substance.

According to a sixth aspect of the present invention, of the two layers having different effective refractive indexes, the first medium side layer is a first layer, the second medium side layer is a second layer, and reflection is performed. When an arbitrary wavelength in the prevention wavelength range is λ, the effective refractive index of the first layer is N _{eff_1} , the thickness is d ₁ , the effective refractive index of the second layer is N _{eff_2} , and the thickness is d _2. ,
d ₁ = λ / 4N _{eff_1}
d ₂ = λ / 4N _{eff_2}
It is characterized by being.

According to a seventh aspect of the present invention, of the two layers having different effective refractive indexes, the first medium side layer is a first layer, the second medium side layer is a second layer, and The effective refractive index of the first layer is N _{eff_1} , the thickness is d ₁ , the effective refractive index of the second layer is N _{eff_2} , the thickness is d ₂ , and arbitrary wavelengths in the antireflection wavelength region are λ, λ ₁ , λ ₂ , when satisfying the relationship of λ ₁ <λ <λ ₂ or λ ₂ <λ <λ ₁ ,
d ₁ = λ ₁ / 4N _{eff_1}
d ₂ = λ ₂ / 4N _{eff_2}
0.02λ <| λ ₁ −λ ₂ | <0.08λ
It is characterized by being.

  In the invention according to claim 8, the two-dimensional uneven structure projects the structure of the first layer and the structure of the second layer onto a plane parallel to the boundary between the first medium and the second medium. In this case, the ratio of the area occupied by the third medium is 10 to 90%.

  The optical member according to claim 9 has the antireflection structure according to any one of claims 1 to 8 on the translucent substrate of the optical member.

  The antireflection structure according to the present invention provides an antireflection structure that can obtain low reflectivity even for light of different wavelengths and obliquely incident light, is easy to manufacture, and has high mechanical strength. can do.

  Moreover, according to the optical member which concerns on this invention, since it has the reflection preventing structure which concerns on this invention on the translucent base material of an optical member, the optical member which can acquire a high reflection preventing effect is provided. be able to.

  Next, before describing the antireflection structure according to the present invention, for example, as shown in FIG. 35, the principle that the reflected light can be reduced in the antireflection structure when the medium 3 is provided between the medium 1 and the medium 2. This will be described below.

As shown in FIG. 35, when light enters the medium 2 from the medium 1 side through the medium 3 having a thickness equivalent to the wavelength of the light, the interface between the medium 1 and the medium 3, the medium 3 and the medium 2 Components I ₁ and I ₂ returning to the incident side are generated at the interface. When the amplitudes of the waves I ₁ and I ₂ are the same and the phases are reversed, the two components I ₁ and I ₂ cancel each other, and the synthesized reflected light is reduced.

  In order to reduce the reflected light by interference, it is necessary that the components returning to the incident side at the respective interfaces have amplitudes that cancel each other by the interference. Since this amplitude is determined by the refractive index of the medium forming the interface, a material capable of obtaining the desired amplitude may be used, but it is often difficult to obtain a material having a low refractive index.

  By using the medium 1 and the medium 3 and providing a structure having a wavelength equal to or smaller than the minimum wavelength in the antireflection wavelength region, it is possible to obtain an effective antireflective index that cannot be realized with a normal substance. In a structure below the wavelength, light cannot recognize the structure, and behaves as if there is an average medium for each medium forming the structure.

At this time, the average refractive index of the medium can be obtained by the following equation, where N _eff is the effective refractive index.
N _eff = r _A N _A + r _C N _C
r _A , r _C : Volume ratio of media 1 and 3
N _A , N _C : Refractive index of media 1 and 3

  The effect of interference can be explained using a vector diagram. The component returning to the incident side at each interface can be represented by a vector as shown in FIG. 36, for example. In this vector, the inclination of the X axis from the positive direction represents the wave phase, the length represents the amplitude, and the wave superposition is represented by the sum of the vectors. Therefore, the component returning to the incident side at each interface is represented by a vector, and the sum of the components can be considered to determine the wave amplitude of the reflected light.

FIG. 37A shows a vector in the case of the antireflection structure shown in FIG. As shown in this figure, since I ₁ and I ₂ have the same amplitude and opposite phases, the reflected light becomes zero. Here, the amplitudes of I ₁ and I ₂ are half that of “1” when there is no antireflection structure.

On the other hand, for example, the diagram shown in FIG. 37 (b) represents a vector when the wavelength is different from the anti-reflection condition such as incidence from an oblique direction. As shown in this figure, the light and having different wavelengths, such as when the obliquely incident, the phase of the I ₂ is displaced with respect to I _1, and thus the synthesized wave I ₁ + I ₂ occurs. When the phase shift is φ, I ₁ + I ₂ is 1/2 × sinφ (≈φ / 2 when φ is sufficiently small). For example, for a wavelength 20% longer than the wavelength shown in FIG. 37 (a), φ = 0.52 rad (= 30 °) and the amplitude is 0.50 / 2 (= 0.25). The rate is 6%, which is the square of the amplitude, compared to the case where no antireflection structure is provided.

  As shown in FIG. 37B, since the phases are different at different wavelengths, cancellation due to interference becomes insufficient. In addition, the phase is different even when the passing distance viewed from the light is different, such as incidence from an oblique direction, and the effect of reducing reflection becomes insufficient.

  On the other hand, as shown in FIG. 38, the antireflection structure (medium 3 + medium 1) provided between the medium 1 and the medium 2 has two interfaces (layer A and layer B) having different effective refractive indexes, and has three interfaces. By providing and canceling each other by interference of three waves, a low reflectance can be realized even in a wide wavelength range and a wide incident angle.

As shown in FIG. 38, the interface 1 that is the boundary between the medium 1 and the antireflection structure (medium 3 + medium 1), the interface 2 that is a boundary having a different effective refractive index in the antireflection structure, the antireflection structure and the medium 2 The components I ₁ , I ₂ , and I ₃ returning to the incident side are generated at the three interfaces of the interface 3 that is the boundary of For example, the antireflection structure is controlled so that I ₁ and I ₃ have the same phase and amplitude at a certain wavelength, and I ₂ has a phase opposite to I ₁ and a double amplitude. At this time, at this wavelength, the sum of I ₁ and I ₃ cancels with I _2, and a low reflectance can be realized.

  Hereinafter, the antireflection structure of the present invention will be described with reference to the vector diagrams shown in FIGS. 39 to 41, to explain that low reflectance can be realized even with respect to obliquely incident light and different wavelengths.

FIG. 39 (a) is a diagram showing a vector when the light is incident on the antireflection structure of the present invention at a target wavelength and angle. As shown in FIG. 39 (a), a wave I ₂ at the interface 2 in Figure 38 as a phase reference, the waves at the interface 1 and interface 3 in FIG. 38, I ₁ and I ₃ are opposite in phase, I ₂ The length of the vector is twice I ₁ and I ₃ , and the sum of the three waves is zero. Here, I ₂ is 1/2, and I ₁ and I ₃ are 1/4.

On the other hand, when it deviates from the target wavelength or angle, the phases of I ₁ and I ₃ are deviated with reference to I ₂ , resulting in a relationship like the vector shown in FIG. At this time, the sum of the waves of I ₁ and I ₃ is smaller than I ₂ by (1−cos φ) and becomes 1/2 × (1−cos φ) (approximate (φ / 2) when φ is sufficiently small. ² ) A reflection with an amplitude proportional to ² ) occurs.

However, in many cases, the absolute value of φ / 2 is smaller than 1, so that the reflected light can be kept low. For example, for a wavelength 20% longer than the wavelength in the case of FIG. 39A, φ = 0.52 rad, and the amplitude of I ₁ + I ₂ + I ₃ is 0.13 / 2 (≈ (0.52 / 2) ² ) = 0.066, and the reflectance can be suppressed to 0.4% in the case where the antireflection structure is not provided.

  In addition, in the case of an antireflection structure called a “moth eye structure” whose refractive index changes stepwise, it can be represented by a vector diagram as shown in FIG. By changing the refractive index stepwise, short-length vectors are continuously connected in each phase, but here, 10 vectors are represented. In this case, the length is 1/10.

  And when a phase shifts from Drawing 40 (a), it becomes a relation as shown in Drawing 40 (b). At this time, the amplitude of the reflected wave is generated by the area of the excess and deficiency of the continuously connected vectors. This area is proportional to φ / (2π). For example, for a wavelength 20% longer than the wavelength of FIG. 40A, φ = 0.52 rad, and the amplitude of the synthesized wave is 0.52 / (2π). = 0.083, and the reflectance is 0.7% when the antireflection structure is not provided, which is larger than the antireflection structure of the present invention.

  In addition, the antireflection structure of the present invention can realize a low reflectance as compared with, for example, an antireflection film formed of the well-known two-layer thin films a and b on the medium 2 as shown in FIG. . This is because when the components returning to the incident side in each of the layers a and b are small and have different wavelengths and angles, the synthesized amplitude can be kept low.

  The antireflection structure of the present invention according to claim 1 is formed by two layers having different effective refractive indexes determined only by volume ratios of the first medium and the third medium, and at least one layer has an antireflection wavelength. The structure has a two-dimensional concavo-convex structure with a wavelength less than the minimum wavelength.

  With such a configuration, since it is not necessary to use a special different material, mass production is easy and productivity is high. Moreover, since precise control of the structure below the wavelength is not required and a structure having a sharp tip is not required, mass production is easy and the strength of the structure is high.

  According to the invention described in claim 2, it is possible to arbitrarily select an effective refractive index of the antireflection structure by using a two-stage two-dimensional uneven structure in which the volume ratio of the third medium is different. Lower reflectivity can be achieved in the desired antireflection area. In addition, the antireflection structure can be manufactured only by forming a two-dimensional uneven structure in a lump, so that precise film thickness control is not required and productivity is high.

  According to the third aspect of the present invention, the refractive index of the third medium forming the antireflection structure is set between the refractive index of the first medium and the third medium, so that the incident light at each interface is incident. It is possible to reduce the amplitude of the component returning to the side. Therefore, the reflectance can be lowered with respect to a wide wavelength range and a wide incident angle. Further, in the antireflection structure formed by the first medium and the third medium, the volume ratio of the third medium can be increased, and an antireflection structure having higher strength and less scratches can be obtained. It is done.

  Furthermore, a base material layer made of the third medium can be integrally formed on the back side of the two-dimensional concavo-convex structure formed by the first medium and the third medium and having a wavelength equal to or less than the minimum wavelength of the antireflection area. . By providing such a base material layer, the strength of the antireflection structure can be further increased.

  According to the fourth aspect of the present invention, the third medium and the second medium can be made the same by making the refractive index of the third medium forming the antireflection structure the same as the refractive index of the second medium. The reflected light at the interface can be eliminated, and a smaller reflectance can be realized.

  According to the fifth aspect of the present invention, the third medium constituting the antireflection structure is made of the same material as that of the second medium, so that the antireflection structure can be easily and inexpensively transferred to an optical member. Can be formed.

  According to the sixth aspect of the present invention, the phase between the interfaces 1 and 3 and the interface 2 shown in FIG. 38 is inverted at the target wavelength by setting the wavelength to 1/4 of the wavelength in the layer. The reflectance can be reduced.

  According to the seventh aspect of the present invention, by providing a layer having a thickness that cancels the phase shift of the component returning to the incident side at each interface at different wavelengths and angles, the reflectivity can be obtained over a wide range of wavelengths and angles. Can be reduced.

  According to the eighth aspect of the present invention, the effective refractive index necessary for reducing the reflectivity can be obtained by setting the ratio of the third medium in this range. Further, the strength can be increased, such as being hard to be damaged.

  According to the optical member of the ninth aspect, since the antireflection structure of the present invention is provided on the translucent base material, the reflection on the surface can be suppressed to a small level, and illumination, display elements, information equipment, etc. High efficiency, high quality, and low noise can be realized.

  Here, examples of the optical member include a protective member for protecting the interior of the illumination, and a diffusion plate and a light guide plate for emitting light uniformly. Moreover, the lens etc. which are used for information equipment, such as a protection member for protecting the screen of a display, a touch panel, a camera, are mentioned. Moreover, the film which has the reflection preventing structure of this invention is pointed out. By sticking this film, it is possible to easily realize the antireflection of the target member.

1 is a schematic perspective view showing an optical element having an antireflection structure according to Embodiment 1 of the present invention. Sectional drawing which shows the optical element which has the reflection preventing structure which concerns on Embodiment 1 of this invention. The schematic perspective view which shows the optical element which has the reflection preventing structure which concerns on the modification of Embodiment 1 of this invention. The schematic perspective view which shows the optical element which has the reflection preventing structure which concerns on Embodiment 2 of this invention. The schematic perspective view which shows the optical element which has the reflection preventing structure which concerns on the modification of Embodiment 2 of this invention. The schematic perspective view which shows the optical element which has the reflection preventing structure which concerns on the modification of Embodiment 2 of this invention. The schematic perspective view which shows the optical element which has the reflection preventing structure which concerns on the modification of Embodiment 2 of this invention. 1 is a schematic perspective view showing an antireflection structure according to Embodiment 1 of the present invention. The schematic perspective view which shows the reflection preventing structure which concerns on Example 2, 11 of this invention. The schematic perspective view which shows the reflection preventing structure which concerns on Example 3 of this invention. The schematic perspective view which shows the anti-reflective structure which concerns on Examples 4-10 of this invention. The schematic perspective view which shows the reflection preventing structure which concerns on the comparative example 1 of this invention. The schematic perspective view which shows the reflection preventing structure which concerns on the comparative example 2 of this invention. The schematic perspective view which shows the reflection preventing structure which concerns on the comparative example 3 of this invention. The schematic perspective view which shows the reflection preventing structure which concerns on the comparative example 4 of this invention. The schematic perspective view which shows the reflection preventing structure which concerns on the comparative example 5 of this invention. The schematic perspective view which shows the reflection preventing structure which concerns on the comparative example 6 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on Example 1 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on Example 2 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on Example 3 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on Example 4 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on Example 5 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on Example 6 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on Example 7 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on Example 8 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on Example 9 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on Example 10 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on Example 11 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on the comparative example 1 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on the comparative example 2 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on the comparative example 3 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on the comparative example 4 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on the comparative example 5 of this invention. The figure which shows the calculation result of the reflectance by the reflection preventing structure which concerns on the comparative example 6 of this invention. The figure for demonstrating the reflection preventing structure of this invention. The figure for demonstrating the reflection preventing structure of this invention. The figure for demonstrating the reflection preventing structure of this invention. The figure for demonstrating the reflection preventing structure of this invention. The figure for demonstrating the reflection preventing structure of this invention. The figure for demonstrating the reflection preventing structure of this invention. The figure for demonstrating the conventional antireflection structure.

  Hereinafter, the present invention will be described based on the illustrated embodiments.

<Embodiment 1>
FIG. 1 is a schematic perspective view showing an optical element having an antireflection structure according to Embodiment 1 of the present invention, and FIG. 2 is a side view thereof.

As shown in FIGS. 1 and 2, the antireflection structure according to the present embodiment includes a medium 1 and a medium 3 provided at the boundary between the medium 1 and the medium 2 as a light-transmitting substrate of the optical element. When the effective refractive index of this antireflection structure is N _eff ,
N _eff = r _A N _A + r _C N _C
Where r _A : volume ratio of medium 1
r _C : Volume ratio of medium 3
N _A : Refractive index of medium 1
N _C : Two layers (layer A and layer B) having different effective refractive indexes represented by the refractive index of the medium 3 are provided. The layer A is formed on the flat layer B, and is composed of the convex microstructures 4 arranged two-dimensionally and a medium 1 such as air between them.

  The medium 1 is, for example, air or water, and a medium around the usage environment can be selected.

  The medium 2 is a translucent base material constituting the optical element, and a material of a member whose reflectance is desired to be reduced can be selected. Examples of the material of the medium 2 include glass, inorganic materials such as Si and sapphire, and resins.

  The layer B and the convex microstructure 4 arranged in two dimensions of the layer A are formed by the medium 3. In FIG. 1, layer A has a cylindrical convex microstructure 4.

  Further, as shown in FIG. 3, the layer A may be configured to have a cylindrical concave microstructure 4 a made of the medium 3, which is two-dimensionally arranged on the layer B. By adopting such a concave structure, the connected flat surfaces come to the boundary, so that the strength can be further increased. Further, in addition to the cylindrical convex microstructure 4 and the concave microstructure 4a, for example, a quadrangular prism-shaped convex microstructure or a quadrangular prism-shaped concave microstructure may be used. Thus, the layer A of the medium 3 has a concavo-convex structure arranged two-dimensionally.

The concavo-convex structure of the layer A made of the medium 3 (cylindrical convex fine structure 4 in FIG. 1) can be formed, for example, by etching or the like using glass, an inorganic substance, or the like. When a low refractive index material such as MgF ₂ is selected, the volume ratio of the concavo-convex structure of the layer A can be increased to increase the strength.

  As a manufacturing method of the concavo-convex structure of the layer A made of the medium 3 (cylindrical convex fine structure 4 in FIG. 1), for example, after exposure of the resist by photolithography, etching is performed using the resist as a mask. Further, after exposure of the resist by electron beam lithography, etching using the resist as a mask is performed. Further, the etching is performed by arranging the particles and using the particles as a mask. By these manufacturing methods, a concavo-convex structure (columnar convex fine structure 4 in FIG. 1) having a wavelength equal to or smaller than the minimum wavelength in the antireflection wavelength region can be formed.

  Further, the concavo-convex structure of the layer A of the medium 3 (cylindrical convex fine structure 4 in FIG. 1) is formed by transferring from a mold using a photocurable resin, a thermosetting resin, a thermoplastic resin, or the like. You can also In this case, it is possible to transfer the shape of the medium 2 (the translucent base material constituting the optical element) and the medium 3 at once, so that the productivity can be improved and the cost can be reduced.

  The size of the concavo-convex structure of the layer A (in FIG. 1, the interval between the convex portions of the cylindrical convex microstructure 4 and in FIG. 3, the interval between the concave portions of the concave microstructure 4a) is set to be equal to or less than the minimum wavelength of the antireflection wavelength region. Has been. When the size of the concavo-convex structure of the layer A is larger than the minimum wavelength or less, diffracted light is generated, which causes an increase in reflectance and coloring.

  The concavo-convex structure of the layer A (in FIG. 1, the interval between the convex portions of the cylindrical convex microstructure 4 and in FIG. 3 the interval between the concave portions of the concave microstructure 4a) is an appropriate interval according to the productivity and the strength of the structure. For example, for visible light having a wavelength of 380 nm to 780 nm, the minimum wavelength is 380 nm or less, desirably 300 nm or less, and more desirably 250 nm or less.

  When the concavo-convex structure of the layer A (in FIG. 1, the interval between the convex portions of the cylindrical convex microstructure 4 and in FIG. 3 the interval between the concave portions of the concave microstructure 4 a) is 300 nm or less, the incident light is obliquely incident. On the other hand, no diffracted light is generated, and in the case of a size of 250 nm or less, no diffracted light is generated for a wide incident angle even with a periodic structure.

  In addition, regarding the periodicity of the concavo-convex structure (the cylindrical convex fine structure 4 in FIG. 1 and the concave fine structure 4a in FIG. 3) arranged two-dimensionally in the layer A, for example, photolithography or electron beam lithography In the case of the production by, it is easy to produce a regular structure.

In the antireflection structure of the present embodiment, when the refractive index of the medium 1 is N _A , the refractive index of the medium 2 is N _B , and the refractive index of the medium 3 is N _C , N _A <N _C <N _B is satisfied. As described above, the refractive indexes N _A , N _B , and N _C of the media 1, 2, and 3 are set. Thereby, at each interface, the amplitude of the component returning to the incident side is small, and the reflectance can be further reduced.

Furthermore, an effective refractive rate of the layer _A N eff_1, when the effective refractive rate of the layer B was _{N eff_2, N A <N eff_1} <N eff_2 < it is desirable that N _B. Thereby, the amplitude of the component returning to the incident side can be further reduced at each interface.

Furthermore, an effective refractive rate N _{Eff_2} effective refractive rate N _{Eff_1} and Layer B of the layer A, it is preferable to set so as to satisfy the following condition.

((N _A ³ N _B ) ^1/4 −1) × 0.5 + 1 <N _{eff_1} <((N _A ³ N _B ) ^1/4 −1) × 1.5 + 1
((N _A N _B ³ ) ^1/4 −1) × 0.5 + 1 <N _{eff_2} <((N _A N _B ³ ) ^1/4 −1) × 1.5 + 1

More preferably, the effective refractive rate N _{Eff_2} effective refractive rate N _{Eff_1} and Layer B of the layer A, is set to satisfy the following condition.
((N _A ³ N _B ) ^1/4 −1) × 0.8 + 1 <N _{eff_1} <((N _A ³ N _B ) ^1/4 −1) × 1.3 + 1
((N _A N _B ³ ) ^1/4 −1) × 0.8 + 1 <N _{eff_2} <((N _A N _B ³ ) ^1/4 −1) × 1.3 + 1

And most desirably, the effective refractive rate N _{Eff_2} effective refractive rate N _{Eff_1} and Layer B of the layer A, is set to satisfy the following condition.
((N _A ³ N _B ) ^1/4 −1) × 0.9 + 1 <N _{eff_1} <((N _A ³ N _B ) ^1/4 −1) × 1.1 + 1
((N _A N _B ³ ) ^1/4 −1) × 0.9 + 1 <N _{eff_2} <((N _A N _B ³ ) ^1/4 −1) × 1.1 + 1

Thus, by setting the effective refractive rate N _{Eff_2} effective refractive rate N _{Eff_1} and Layer B of the layer A to the most desirable conditions, as shown in FIG. 38, returns to the incident side of the interface 1 and interface 3 The amplitude of the component is almost equal, and the amplitude of the component returning to the incident side at the interface 2 is double that of the interface 1. In this case, the combined wave of the interface 1 and the interface 3 can be canceled with the interface 2, and a low reflectance can be realized.

As another condition, the effective refraction rate N _{Eff_2} effective refractive rate N _{Eff_1} and Layer B of the most desired layer A, is to satisfy the following relation.
((N _A ³ N _B ) ^1/4 −1) × 1.01 + 1 <N _eff — 1 <((N _A ³ N _B ) ^1/4 −1) × 1.3 + 1
N _{eff_2} = N _A N _B / N _{eff_1}

  In this case, the amplitude of the component returning to the incident side at the interface 1 and the interface 3 is substantially equal, and is slightly larger than ½ of the amplitude of the component returning to the incident side at the interface 2. As a result, the combined wave of the interface 1 and the interface 3 can be canceled with the interface 2 for obliquely incident light and different wavelengths, and a low reflectance can be realized for a wide range of wavelengths and angles. .

  Furthermore, it is possible to increase the volume ratio of the medium 3, and it is possible to obtain an antireflection structure with higher strength and less scratching.

In the antireflection structure in the present embodiment, the effective refractive index of layer A is N _{eff_1} , the thickness is d ₁ , the effective refractive index of layer B is N _{eff_2} , the thickness is d ₂ , and an arbitrary wavelength in the antireflection wavelength region is set. In the case of λ, d ₁ and d ₂ were set so as to satisfy the following conditions.
d ₁ = λ / 4N _{eff_1}
d ₂ = λ / 4N _{eff_2}
Thus, in this case, the thicknesses d ₁ and d ₂ of the layers A and B are antireflection structures corresponding to 1/4 of the wavelength in the medium. By setting the thicknesses of the layer A and the layer B to 1/4 of the wavelength, as shown in FIG. 38, the phases of the interface 1, the interface 3 and the interface 2 can be reversed at the target wavelength. It is possible to reduce the reflectance.

Further, in the antireflection structure in the present embodiment, the effective refractive index of layer A is N _{eff_1} , the thickness is d ₁ , the effective refractive index of layer B is N _{eff_2} , the thickness is d ₂ , and an arbitrary wavelength in the antireflection wavelength region is set. When λ ₁ <λ <λ ₂ or λ ₂ <λ <λ ₁ as λ, λ ₁ , and λ ₂ , the ranges of d ₁ , d ₂ , and wavelength λ satisfy the following conditions: did.

d ₁ = λ ₁ / 4N _{eff_1}
d ₂ = λ ₂ / 4N _{eff_2}
0.02λ <| λ ₁ −λ ₂ | <0.08λ
Thus, in this case, the thicknesses d ₁ and d ₂ of the layer A and the layer B are antireflection structures in which the wavelength λ in the medium is shifted in the range of 0.02λ to 0.08λ, respectively. By providing a layer having a thickness that cancels the phase shift of the component returning to the incident side at each interface at different wavelengths and angles, it is possible to reduce the reflectance in a wide range of wavelengths and angles.

  Further, in the antireflection structure in the present embodiment, when the structure of the layer A and the structure of the layer B are projected on a plane parallel to the boundary between the medium 1 and the medium 2, the ratio of the area occupied by the medium 3 is respectively It sets so that it may become 10 to 90%.

  If the ratio of the area occupied by the medium 3 in the layers A and B is smaller than 10% and larger than 90%, a difference in refractive index necessary for preventing reflection cannot be obtained. Desirably, the ratio of the area occupied by the medium 3 in the layers A and B is in the range of 20 to 70% for the layer A and 40 to 80% for the layer B, so that a high antireflection effect is obtained. It is done. More desirably, the ratio of the area occupied by the medium 3 in the layers A and B is in the range of 20 to 50% for the layer A and 50 to 80% for the layer B, thereby obtaining a higher antireflection effect. It is done.

  Thus, by making the ratio of the area occupied by the medium 3 in the layer A and the layer B within the above range, it is possible to obtain an effective refractive index necessary for reducing the reflectance. Further, it is possible to increase the strength such as being hard to be damaged.

<Embodiment 2>
In the antireflection structure according to Embodiment 2 of the present invention, the layer A and the layer B have a concavo-convex structure in which the layers A and B are two-dimensionally arranged, and the volume ratios are different in the height direction of the medium 3. Other configurations are the same as those of the first embodiment, and redundant description is omitted.

  FIG. 4 is a schematic perspective view showing an optical element having an antireflection structure according to Embodiment 2 of the present invention. In the antireflection structure of Embodiment 2 shown in FIG. 4, the layer A and the layer B have the convex microstructures 4 made of the medium 3 and arranged in two dimensions. The convex microstructure 4 is a cylinder having a different width (diameter) between the layer A and the layer B. Thereby, the volume ratio of the medium 3 is different between the layer A and the layer B, and the effective refractive index can be changed. Note that the convex microstructures formed in the layers A and B may be quadrangular columns.

  In addition, as shown in FIG. 5, the layer A and the layer B are two-dimensional cylindrical concave microstructures 4a made of the medium 3 and having different widths (diameters) in the height (depth) direction. You may arrange in. Note that the layer A and the layer B may have a rectangular concave microstructure with different widths (diameters) in the height direction.

  Further, in the antireflection structure shown in FIG. 6, the layer A and the layer B have a convex microstructure 4 made of the medium 3 and arranged in a two-dimensional manner, and the convex microstructure 4 is a cylinder having a different height. Are arranged. Note that the layer A and the layer B may have a convex fine structure in which square pillars having different heights are arranged.

  Further, as shown in FIG. 7, the layer A and the layer B may be two-dimensionally arranged with cylindrical concave microstructures 4 a made of the medium 3 and having different depths.

  The concavo-convex structure of the layer A of Embodiment 2 shown in FIGS. 4 to 7 is formed, for example, by changing the resist exposure amount by photolithography or changing the resist exposure amount by electron beam lithography. can do.

  As described above, according to the antireflection structures of the first and second embodiments, low reflectance can be obtained even for light of different wavelengths and obliquely incident light, and manufacturing is easy, and mechanical strength is improved. Can provide a high antireflection structure.

  Moreover, according to the optical member which has the antireflection structure of the said Embodiment 1, 2, the optical member which can acquire a high antireflection effect can be provided.

  Next, in order to evaluate the effect of reducing the reflectance by the antireflection structure of the present invention, the antireflection structures of Examples 1 to 11 and Comparative Examples 1 to 6 shown below were prepared.

  In order to evaluate the effect of reducing the reflectance, the reflectance was calculated using the electromagnetic wave analysis simulation software Diffract MOD (R-Soft) by the RCWA (strict coupling wave analysis) method. The setting conditions of Examples 1 to 11 and Comparative Examples 1 to 6 and the calculation results of the reflectance are as described in Table 1 below.

The conditions in this reflectance calculation were set as follows.
Antireflection wavelength range: 380 to 780 nm (visible range)
Medium 1: Refractive index 1 (air)
Medium 2: Refractive index 1.5 (glass or resin)
Light was incident at 0 deg, 40 deg, and 60 deg from the normal line of the interface, and the average value of reflectance in the wavelength range of 380 to 780 nm was calculated.

<Example 1>
As shown in FIG. 8, the concavo-convex structure of the layer B is a structure in which square columnar convex microstructures 4 are two-dimensionally arranged, and the following conditions are set.

Refractive index N _{C of} medium 3: 1.38
Layer A: formed of a convex structure having a period of 200 nm, a height of 110 nm, a width of 125 nm and air (medium 1) formed of the medium 3 (effective refractive index N _{eff —} 1.15)
Layer B: Height: Structure made of medium 3 having a thickness of 100 nm (effective refractive index N _{eff —2} : 1.38)

  FIG. 18 is a diagram illustrating a calculation result of the reflectance in the first embodiment.

<Example 2>
As shown in FIG. 9, the concavo-convex structure of the layer A and the layer B made of the medium 3 is a structure in which square columnar convex microstructures 4 stacked in two steps are two-dimensionally arranged, and the following conditions Set to.

Refractive index N _{C of} medium 3: 1.46
Layer A: formed of a convex structure having a period of 200 nm, a height of 110 nm, and a width of 114 nm formed from the medium 3 and air (effective refractive index N _{eff —} 1.15)
Layer B: formed of a convex structure formed of the medium 3 and having a period of 200 nm, a height of 110 nm, and a width of 174 nm and air (effective refractive index N _{eff_2} : 1.35)

  FIG. 19 is a diagram illustrating a calculation result of the reflectance in the second embodiment.

<Example 3>
As shown in FIG. 10, the concave and convex structure of the layer A and the layer B made of the medium 2 (= medium 3) is a structure in which quadrangular prism-like convex microstructures 4 stacked in two steps are two-dimensionally arranged. The following conditions were set.

Medium 3 was formed of the same medium as medium 2. Refractive index N _C : 1.50
Layer A: formed of a convex structure having a period of 200 nm, a height of 110 nm, and a width of 110 nm formed from the medium 2 and air (effective refractive index N _{eff —} 1.15)
Layer B: formed of a convex structure having a period of 200 nm, a height of 100 nm, and a width of 167 nm, formed of the medium 2, and air (effective refractive index N _{eff_2} : 1.35)

  FIG. 20 is a diagram illustrating a calculation result of the reflectance in the third embodiment.

<Example 4>
As shown in FIG. 11, as the concavo-convex structure of layer A and layer B made of medium 2 (= medium 3), a structure in which square pillar holes (concave microstructure 4a) overlapped in two steps are two-dimensionally arranged. Therefore, the following conditions were set.

Medium 3 was formed of the same medium as medium 2. Refractive index N _C : 1.50
Layer A: formed of a concave structure formed of the medium 2 and having a period of 200 nm, a height of 120 nm, and a width of 179 nm and air (effective refractive index N _{eff —} 1.10)
Layer B: formed of medium 2 with a concave structure of period: 200 nm, height: 100 nm, width: 110 nm and effective refractive index _{Neff_2} : 1.35

  FIG. 21 is a diagram illustrating a calculation result of the reflectance in the fourth embodiment.

<Example 5>
As shown in FIG. 11, as the concavo-convex structure of layer A and layer B made of medium 2 (= medium 3), a structure in which square pillar holes (concave microstructure 4a) overlapped in two steps are two-dimensionally arranged. Therefore, the following conditions were set.

Medium 3 was formed of the same medium as medium 2. Refractive index N _C : 1.50
Layer A: formed of a concave structure formed of medium 2 and having a period of 200 nm, a height of 110 nm, and a width of 155 nm and air (effective refractive index _{Neff_1} : 1.20)
Layer B: formed of a concave structure formed of the medium 2 and having a period of 200 nm, a height of 90 nm, and a width of 110 nm and air (effective refractive index _{Neff_2} : 1.35)

  FIG. 22 is a diagram illustrating a calculation result of the reflectance in the fifth embodiment.

<Example 6>
As shown in FIG. 11, as the concavo-convex structure of layer A and layer B made of medium 2 (= medium 3), a structure in which square pillar holes (concave microstructure 4a) overlapped in two steps are two-dimensionally arranged. Therefore, the following conditions were set.

Medium 3 was formed of the same medium as medium 2. Refractive index N _C : 1.50
Layer A: formed of a concave structure formed of medium 2 and having a period of 200 nm, a height of 120 nm, and a width of 167 nm and air (effective refractive index N _{eff —} 1.15)
Layer B: formed with a concave structure formed of medium 2 and having a period: 200 nm, height: 100 nm, width: 89 nm and air (effective refractive index N _{eff —2} : 1.40)

  FIG. 23 is a diagram illustrating the calculation result of the reflectance in the sixth embodiment.

<Example 7>
As shown in FIG. 11, as the concavo-convex structure of layer A and layer B made of medium 2 (= medium 3), a structure in which square pillar holes (concave microstructure 4a) overlapped in two steps are two-dimensionally arranged. Therefore, the following conditions were set.

Medium 3 was formed of the same medium as medium 2. Refractive index N _C : 1.50
Layer A: formed of a concave structure formed of the medium 2 and having a period of 200 nm, a height of 124 nm, and a width of 177 nm and air (effective refractive index N _{eff_1} : 1.11)
Layer B: formed of a concave structure formed of the medium 2 and having a period of 200 nm, a height of 101 nm, and a width of 106 nm and air (effective refractive index _{Neff_2} : 1.36)

In this embodiment, the wavelength λ is set to 550 nm, and d ₁ = λ / 4N _eff — ₁ and d ₂ = λ / 4N _eff — ₂ are controlled.

  FIG. 24 is a diagram illustrating the calculation result of the reflectance in the seventh embodiment.

<Example 8>
As shown in FIG. 11, as the concavo-convex structure of layer A and layer B made of medium 2 (= medium 3), a structure in which square pillar holes (concave microstructure 4a) overlapped in two steps are two-dimensionally arranged. Therefore, the following conditions were set.

Medium 3 was formed of the same medium as medium 2. Refractive index N _C : 1.50
Layer A: formed of a concave structure formed of medium 2 and having a period of 200 nm, a height of ₁₂₂ nm, and a width of 172 nm and air (effective refractive index N _{eff —} 1.13)
Layer B: formed of a concave structure formed of medium 2 and having a period of 200 nm, a height of 103 nm, and a width of 117 nm and air (effective refractive index N _{eff_2} : 1.33)

In this embodiment, the wavelength λ is set to 550 nm, and d ₁ = λ / 4N _eff — ₁ and d ₂ = λ / 4N _eff — ₂ are controlled.

  FIG. 25 is a diagram illustrating a calculation result of reflectance in Example 8.

<Example 9>
As shown in FIG. 11, as the concavo-convex structure of layer A and layer B made of medium 2 (= medium 3), a structure in which square pillar holes (concave microstructure 4a) overlapped in two steps are two-dimensionally arranged. Therefore, the following conditions were set.

Medium 3 was formed of the same medium as medium 2. Refractive index N _C : 1.50
Layer A: formed of a concave structure formed of medium 2 and having a period of 200 nm, a height of 119 nm, and a width of 177 nm and air (effective refractive index N _{eff — 1} : 1.11)
Layer B: formed of a concave structure formed of medium 2 and having a period of 200 nm, a height of 105 nm, and a width of 106 nm and air (effective refractive index N _{eff — =} 1.36)

In this embodiment, the wavelength λ is set to 550 nm, and λ ₁ = 528 nm, λ ₂ = 571 nm, and | λ ₁ −λ ₂ | = 0.078λ.

  FIG. 26 is a diagram illustrating a calculation result of the reflectance in the ninth embodiment.

<Example 10>
As shown in FIG. 11, as the concavo-convex structure of layer A and layer B made of medium 2 (= medium 3), a structure in which square pillar holes (concave microstructure 4a) overlapped in two steps are two-dimensionally arranged. Therefore, the following conditions were set.

Medium 3 was formed of the same medium as medium 2. Refractive index N _C : 1.50
Layer A: formed of a concave structure formed of medium 2 and having a period of 200 nm, a height of 117 nm, and a width of 172 nm and air (effective refractive index N _{eff —} 1.13)
Layer B: formed of a concave structure formed of medium 2 and having a period of 200 nm, a height of 107 nm, and a width of 117 nm and air (effective refractive index N _{eff_2} : 1.33)

In this embodiment, the wavelength λ is set to 550 nm, and λ ₁ = 529 nm, λ ₂ = 569 nm, and | λ ₁ −λ ₂ | = 0.073λ.

  FIG. 27 is a diagram illustrating the calculation result of the reflectance in the tenth embodiment.

<Example 11>
As shown in FIG. 10, the concave and convex structure of the layer A and the layer B made of the medium 2 is a structure in which quadrangular columnar convex microstructures 4 stacked in two steps are two-dimensionally arranged, and the following conditions Set to.

Medium 3 was formed of the same medium as medium 2. Refractive index N _C : 1.46
Layer A: formed of a convex structure having a period of 200 nm, a height of 100 nm, and a width of 132 nm, formed of the medium 2, and air (effective refractive index N _{eff —} 1.20)
Layer B: formed of a convex structure having a period of 200 nm, a height of 80 nm, and a width of 162 nm formed of the medium 2 and air (effective refractive index N _{eff_2} : 1.33)

  FIG. 28 is a diagram illustrating a calculation result of reflectance in Example 11.

The antireflection structure of the comparative example for each of the above-described Examples 1 to 11 was set as follows.
<Comparative example 1>
As shown in FIG. 12, the comparative example 1 has no antireflection structure, and light is incident on the medium 2 having a refractive index of 1.5 from the medium 1 having a refractive index of 1 (air).

  FIG. 29 is a diagram showing a calculation result of reflectance in Comparative Example 1.

<Comparative example 2>
As shown in FIG. 13, in Comparative Example 2, a thin film (LR film) 10 having a refractive index of 1.38 and a thickness of 100 nm was formed on the surface of the medium 2.

  FIG. 30 is a diagram showing a calculation result of reflectance in Comparative Example 2.

<Comparative Example 3>
As shown in FIG. 14, Comparative Example 3 has a configuration in which an AR film (three layers) is formed on the surface of the medium 2, and the first thin film having a refractive index of 1.64 and a thickness of 83.8 nm in order from the bottom. 11, a second thin film 12 having a refractive index of 2.0 and a thickness of 137.5 nm, and a third thin film 13 having a refractive index of 1.38 and a thickness of 99.6 nm are formed.

FIG. 31 is a diagram showing the calculation result of the reflectance in Comparative Example 3.
<Comparative example 4>
As shown in FIG. 15, the comparative example 4 is a structure in which the quadrangular columnar convex microstructures 4 are two-dimensionally arranged as the concave and convex microstructures of the layer A made of the medium 2, and the following conditions are set. did.

Layer A (medium 3) was formed from the same medium as medium 2. Refractive index N _C : 1.50
Layer A: formed of a convex structure formed of the medium 2 and having a period of 200 nm, a height of 112 nm, and a width of 174 nm and air (effective refractive index N _{eff — 1} : 1.22)

FIG. 32 is a diagram showing a calculation result of reflectance in Comparative Example 4.
<Comparative Example 5>
As shown in FIG. 16, in Comparative Example 5, a square pyramid-shaped moth-eye structure 14 having a height of 300 nm was formed on the medium 2 using the same medium.

The moth eye structure 14 was formed from the same medium as the medium 2. Refractive index N _C : 1.50

FIG. 33 is a diagram showing a calculation result of reflectance in Comparative Example 5.
<Comparative Example 6>
As shown in FIG. 17, in Comparative Example 6, the conical moth-eye structure 15 with the tip of a 225 nm height projecting like a bullet in the same medium was formed on the medium 2.

The moth eye structure 15 was formed of the same medium as the medium 2. Refractive index N _C : 1.50

  FIG. 34 is a diagram showing a calculation result of reflectance in Comparative Example 6.

  As described above, according to the antireflection structures of Examples 1 to 11, a lower reflectance than that of Comparative Examples 1 to 6 can be realized in the entire wavelength range of 380 to 780 nm. In addition, a low reflectance can be maintained even for light incident with an inclination from the normal line of the interface.

  Further, in the antireflection structures of Examples 3 to 11, the antireflection performance can be realized only by the structure of the medium 2, and it is not necessary to use materials having different refractive indexes, so that the cost is low and the productivity is high. .

  Further, for example, the antireflection structure shown in Example 11 can be formed on transparent substrates having different refractive indexes such as a refractive index of 1.5. As long as the medium 2 portion has such a thickness that optical coherence disappears, it is not necessary to consider interference caused by reflected light between the medium 2 and the transparent substrate. This thickness is about 1 μm, and the medium 2 only needs to have a thickness greater than this. In addition, when the refractive index of the transparent substrate is 1.5, the incident angle is sufficiently small at 0.01% when incident at 0 deg from the normal direction and 0.15% when incident at 60 deg from the normal direction of the interface. . Therefore, the reflectance can be easily reduced by transferring the structure with a thickness of 1 μm or more on the transparent substrate.

1 medium (first medium)
2 Medium (second medium)
3 Medium (3rd medium)
4 Convex microstructure (two-dimensional concavo-convex structure)
4a Concave microstructure (two-dimensional uneven structure)

Claims (9)

An antireflection structure provided at a boundary between the first medium and the second medium,
The antireflection structure is formed by the first medium and the third medium, and when the effective refractive index of the antireflection structure is N _eff ,
N _eff = r _A N _A + r _C N _C
Where r _A , r _C : volume ratio of the first medium and the third medium
N _A , N _C : two layers having different effective refractive indexes represented by the refractive indexes of the first medium and the third medium,
At least one of the two layers has a two-dimensional concavo-convex structure having a wavelength equal to or less than the minimum wavelength of the antireflection wavelength region.   The antireflection structure according to claim 1, wherein the antireflection structure has a two-stage two-dimensional uneven structure in which a volume ratio of the third medium is different in a height direction. When the refractive index of the first medium is N _A , the refractive index of the second medium is N _B , and the refractive index of the third medium is N _C ,
N _A <N _C <N _B
The antireflection structure according to claim 1 or 2, wherein When the refractive index of the first medium is N _A , the refractive index of the second medium is N _B , and the refractive index of the third medium is N _C ,
N _A <N _C = N _B
The antireflection structure according to claim 2, wherein   The antireflection structure according to claim 4, wherein the second medium and the third medium are made of the same material. Of the two layers having different effective refractive indexes, the first medium side layer is the first layer, and the second medium side layer is the second layer,
When an arbitrary wavelength in the antireflection wavelength region is λ, the effective refractive index of the first layer is N _{eff_1} , the thickness is d ₁ , the effective refractive index of the second layer is N _{eff_2} , and the thickness is d ₂ In addition,
d ₁ = λ / 4N _{eff_1}
d ₂ = λ / 4N _{eff_2}
The antireflection structure according to any one of claims 1 to 5, wherein the antireflection structure is provided. Of the two layers having different effective refractive indexes, the first medium side layer is the first layer, and the second medium side layer is the second layer,
The effective refractive index of the first layer is N _{eff_1} , the thickness is d ₁ ,
The effective refractive index of the second layer is N _{eff_2} , the thickness is d ₂ ,
Arbitrary wavelengths in the antireflection wavelength region are λ, λ ₁ , and λ ₂ ,
When satisfying the relationship of λ ₁ <λ <λ ₂ or λ ₂ <λ <λ ₁ ,
d ₁ = λ ₁ / 4N _{eff_1}
d ₂ = λ ₂ / 4N _{eff_2}
0.02λ <| λ ₁ −λ ₂ | <0.08λ
The antireflection structure according to any one of claims 1 to 5, wherein the antireflection structure is provided.   When the two-dimensional concavo-convex structure projects the structure of the first layer and the structure of the second layer onto a plane parallel to the boundary between the first medium and the second medium, the structure of the third medium The ratio of the area to occupy is 10 to 90%, respectively, The antireflection structure as described in any one of Claims 1 thru | or 7 characterized by the above-mentioned.   An optical member comprising the antireflection structure according to any one of claims 1 to 8 on a light-transmitting substrate of the optical member.