JP2011017781A - Optical device and optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical device, for example, having a curved surface, where a fine antireflection structure to the visual light is formed at least a part thereof; and to provide an optical system that uses the optical device.SOLUTION: In the optical element 1 having the curved surface 2a partially having the fine antireflection structure 3 with respect to the visual light, the fine antireflection structure 3 is formed from a plurality of projecting parts or a plurality of recessed part formed, in a period shorter than the wavelength of the visual light on the curved surface 2a, wherein the formation direction of at least a part of the projecting part among the plurality of the projecting parts or the forming direction of at least a part of the recessed part among the plurality of the recessed parts is oblique with respect to the normal line of the curved surface in the forming position of each of projecting part or the recessed part.

Description

  The present invention relates to an optical element and an optical system. For example, the present invention relates to an optical element having a curved surface in which a fine antireflection structure for visible light is formed at least in part and an optical system using the same.

Conventionally, in order to reduce reflected return light on the surface of an optical element such as a lens, it has been known to provide an antireflection structure having a fine uneven structure called Sub-Wavelength-Structure (SWS) on the surface of the optical element. Yes.
In the optical element having such a fine antireflection structure, a convex or concave shape of the fine structure is formed along the normal direction at each position on the optical element surface, and the light incident on the normal direction at each position is formed. On the other hand, it is characterized by a high antireflection effect. As optical elements having such a conventional fine antireflection structure, for example, those described in Patent Documents 1 to 3 below have been proposed.

JP 2003-43203 A JP 2005-316393 A JP 2006-171219 A

However, the following problems remain in the conventional optical element.
That is, in the above optical element, the convex shape or the concave shape is oriented in the normal direction at each position. Therefore, depending on the curvature of the optical element, reflection in the vicinity of the optical axis of the optical element with respect to incident light in the same direction. The difference between the reflectance and the reflectance of the peripheral portion of the optical element becomes large.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical element capable of making the reflectance distribution on the optical element surface suitable even when light is incident from various directions. To do.

In order to achieve the above object, the present invention provides the following means.
The optical element of the present invention is an optical element having a curved surface in which a fine antireflection structure for visible light is formed at least in part, and the fine antireflection structure is formed on the curved surface with respect to the wavelength of the visible light. Formed by a plurality of convex portions or a plurality of concave portions formed with a short period, and at least a portion of the plurality of concave portions, or at least a portion of the plurality of concave portions. The optical element is formed so as to be inclined with respect to the normal direction of the curved surface at the position where each convex portion or concave portion is formed.
In the optical element according to the present invention, the fine antireflection structure by the convex part or the concave part is formed in at least a part on the curved surface of the optical element with a period shorter than the wavelength of visible light. At this time, the formation direction of the convex portion or the concave portion of the fine antireflection structure does not coincide with the normal direction of the curved surface of the optical element at each formation position, and is formed to be inclined with respect to this normal direction. By appropriately setting the formation direction of the convex portion or the concave portion, the reflectance with respect to incident light from a direction different from the normal direction at the formation position is reduced.

In the optical element of the present invention, it is preferable that the forming direction of the convex portion or the concave portion is inclined by 5 ° or more with respect to the normal direction of the curved surface.
In this case, since the formation direction of the convex portion or the concave portion is inclined by 5 ° or more with respect to the normal direction of the curved surface, even if the optical element has a small radius of curvature, the variation in the reflectance with respect to the incident light. Is reduced.

In the optical element of the present invention, it is preferable that the formation direction of the convex portion or the concave portion is inclined toward the optical axis side of the curved surface with respect to the normal direction of the curved surface.
In this case, since the forming direction of the convex portion or the concave portion is inclined toward the optical axis side with respect to the normal direction of the curved surface, variation in reflectance with respect to incident light from the optical axis direction is reduced over the entire curved surface of the optical element. In addition, the reflectance with respect to incident light incident at a greatly inclined angle with respect to the optical axis, which is likely to cause flare or the like, is reduced.

In the optical element of the present invention, it is preferable that at least one of the inclination direction and the inclination angle is randomly formed with respect to the normal direction of the curved surface in the formation direction of the convex portions or concave portions.
In this case, since at least one of the inclination direction and the inclination angle with respect to the normal direction of the curved surface in the formation direction of the plurality of convex portions or concave portions formed on the curved surface of the optical element is randomly formed, Thus, the reflectance with respect to incident light incident at an angle inclined in various directions is reduced substantially uniformly.

The optical system of the present invention provides an optical system comprising the optical element of the present invention.
In the optical system according to the present invention, flare light and ghost light that can be generated by surface reflection of the optical element are reduced.

  According to the optical element and the optical system of the present invention, the convex portion or the concave portion of the fine antireflection structure is formed to be inclined with respect to the normal direction of the curved surface of the optical element, so that light is incident from various directions. Even in this case, the effect that the light reflectance distribution on the optical element surface can be made suitable is obtained.

These are the schematic block diagrams seen from the side of the optical element shown as 1st Embodiment of this invention. Is an enlarged sectional view of part A in FIG. These are the schematic diagrams which expanded a part of cross section of an example of a fine antireflection structure. These are the schematic block diagrams seen from the side of the optical element shown as 2nd Embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
(First embodiment)
A first embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a schematic configuration diagram viewed from the side of an optical element 1 having a fine antireflection structure, and FIG. 2 is a schematic diagram enlarging a cross section at a portion A of the lens in FIG.

As shown in FIG. 1, the optical element 1 of the present embodiment has an outer diameter D0, an effective diameter D1 (where D1 <D0), a first surface (curved surface) 2a is a convex surface, and a second surface 2b is It is a plano-convex lens made of a flat surface, and a fine antireflection structure 3 for reducing the reflectance of visible light is formed in the effective diameter range S of the first surface 2a.
If necessary, a fine antireflection structure may be provided on the second surface 2b.

As schematically shown in FIG. 2, the fine antireflection structure 3 is a transparent convex having a substantially circular cross-sectional shape gradually reduced in diameter from the base end toward the tip end on the spherical first surface 2 a. A plurality of portions (substantially bullet-shaped) 4 are formed with a period W shorter than the wavelength of visible light.
The period W of the plurality of convex portions 4 is formed with the same period W in a range shorter than 400 nm, for example, in the range of 100 nm to less than 400 nm, when the used light is visible light having a wavelength of 400 nm or more.
Note that the height of each convex portion 4 is sufficiently smaller than the radius of curvature of the curved surface, and does not affect the refractive power determined by the radius of curvature of the first surface 2a.

The formation direction 6 of each convex part 4 constituting the fine antireflection structure 3 is directed to the optical axis 9 side or the top 8 side with respect to the normal direction 7 at the formation position of each convex part 4 on the first surface 2a. It is formed so as to be inclined.
The inclination in the forming direction 6 of the convex part 4 is determined by an inclination angle between an average center line (center axis of the convex part 4) formed by connecting the centers of the cross-sectional outlines of the convex part 4 and the normal line.
In particular, the formation direction 6 of the convex portion 4 at a location away from the surface top 8 is formed so as to be inclined in the direction of the optical axis 9 with an inclination θ of 5 ° or more with respect to the normal direction 7 of the first surface 2a. Yes.

Next, a method for forming the fine antireflection structure 3 in the optical element 1 of the first embodiment will be described.
As a method of forming the fine antireflection structure 3, any method may be used. For example, an optical element using a mold having a shape opposite to that of the fine antireflection structure 3 to be formed is used. A method of forming the fine antireflection structure 3 on the first surface 2a of the optical element 1 at the same time that 1 is molded with glass or resin can be mentioned.
Further, for example, after applying a curable material such as an ultraviolet curing agent or a curable resin to the first surface 2a of the optical element 1, a mold having a shape opposite to that of the fine antireflection structure 3 to be formed is used. Examples thereof include a method of transferring a shape to a curable material and curing the curable material.
Moreover, for example, a method of drawing an electron beam directly on the first surface 2a of the optical element 1 can be mentioned.

In addition, any method may be used as a method for manufacturing a mold having a shape opposite to that of the fine antireflection structure 3 to be formed. For example, electron beam drawing in a semiconductor process is used. Can do.
In addition, for example, a method of manufacturing a mold having a shape opposite to that of the fine antireflection structure 3 to be formed on the mold base using a lithography technique such as ion etching can be used.
Further, for example, after forming the fine antireflection structure 3 to be formed on the mold base, a method of producing an inverted mold by electroforming using a metal such as nickel (Ni) can be used.

According to such an optical element 1, since the formation direction 6 of the convex part 4 is formed so as to be inclined toward the surface top 8 side with respect to the respective normal directions 7 of the first surface 2a, the optical axis 9 Variation in reflectance within the effective diameter range S in which the fine antireflection structure 3 is formed with respect to light incident from a direction or light incident on a shallow angle with respect to the optical axis 9, for example, an effective half angle of view. The reflectance can be reduced in a state in which the above is suppressed. In addition, reflection of light within the effective diameter range S is suppressed for light incident at a deep angle with respect to the direction of the optical axis 9, for example, an angle larger than the effective half field angle.
This makes it difficult for light incident at a deep angle with respect to the optical axis 9 that is likely to cause flare and ghost to enter the optical element 1, thereby reducing flare and ghost.
Further, flare and ghost can be removed more efficiently by gradually increasing the inclination angle of the convex portion 4 from the optical axis 9 of the optical element 1 toward the peripheral portion of the optical element 1.
Further, by forming the fine antireflection structure 3 only in a range where the antireflection effect is necessary, the time and cost for producing the fine antireflection structure 3 can be minimized.

  In addition, each of the plurality of fine antireflection structures 3 may be provided with at least one of an inclination angle and an inclination direction at random with respect to the normal direction 7 of the first surface 2a. In this case, an optical element capable of reducing the reflectance in the optical element plane more uniformly, particularly with respect to incidence of light from various directions.

  The optical element of this embodiment may constitute part or all of an optical system including a plurality of optical elements. Such an optical system can reduce surface reflection in various directions between the optical elements, so that good optical performance can be obtained. In particular, when the optical element of the present invention is used for the outermost optical element on the incident side, the incident light quantity of external light can be suitably controlled, and flare caused by external light can be effectively reduced. That is, by arranging the optical element of the present invention at a position where light from various directions is incident, an antireflection effect with a small reflectance distribution in the optical element surface can be obtained. A system can be obtained.

  Further, in the optical element 1, the entire convex portion 4 of the fine antireflection structure 3 is inclined toward the optical axis direction 9 side of the optical element 1, and the formation direction 6 is inclined toward the top 8 side with respect to the normal direction 7. However, the convex portion 4 may be formed so as to be inclined with respect to the normal line only in a portion where the uniform antireflection effect of the optical element 1 is required.

In the optical element 1, the central axis of the convex portion 4 is provided with an angle θ between the normal line so as to be inclined toward the surface apex 8, and therefore the convex portion 4 farther from the surface apex 8 is closer to the formation direction 6. The angle θ formed by the normal direction 7 increases, and the angle θ decreases as the surface apex 8 is approached.
FIG. 3 is a schematic diagram in which a part of a cross section of an example of the fine antireflection structure 3 is enlarged. In a place where the antireflection effect is to be efficiently exhibited, the angle θ may be a constant angle or may be random as shown in FIG. 3, for example.

  In the optical element 1, the convex portions 4 are formed with the same period W, but the period W may be randomly formed as long as the antireflection effect is maintained within a wavelength range.

In the optical element 1, the fine antireflection structure 3 is formed by the convex portion 4, but it may be configured by a concave portion having a concave shape opposite to the convex portion 4 recessed from the first surface 2 a.
In addition, as the shape of the convex portion and the concave portion, various tapered shapes such as a cone shape such as a cone and a bell shape can be adopted as long as the antireflection effect is maintained.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIG. Regarding the second embodiment, items described in the first embodiment are omitted, and only differences from the first embodiment will be described. Moreover, in 2nd Embodiment, the same code | symbol is attached | subjected about the structure similar to 1st Embodiment.
FIG. 4 is a schematic configuration diagram viewed from the side of the optical element 21 having a fine antireflection structure.
In FIG. 4, the optical element 21 is a plano-convex lens having an outer diameter of D0 and an effective diameter of D1, the first surface 2a is a convex surface, and the second surface 2b is a flat surface. In the optical element 21 of the second embodiment, the fine antireflection structure 23 is formed on the entire curved surface including the outside of the effective diameter of the first surface 2a.
If necessary, a fine antireflection structure may be provided on the second surface 2b.

The second embodiment differs from the first embodiment in the formation range of the fine antireflection structure 3.
In the first embodiment, the fine antireflection structure 3 is formed only within the effective diameter range S, but in the second embodiment, the fine antireflection structure 23 is formed even on a curved surface outside the effective diameter. Similarly to the first embodiment, the second embodiment is formed such that the formation direction 6 of each convex portion 4 is inclined to the optical axis 9 side with respect to the normal direction 7, so that the fine antireflection structure 23 is effective. The convex part 4 outside the diameter has an angle of 5 ° or more between the forming direction 6 and the normal direction 7 and acts to efficiently suppress the reflectance of light outside the effective diameter D1.

  According to the optical element 21, since the formation direction 6 of the convex portion 4 within the effective diameter range S of the optical element 21 is formed to be inclined toward the surface top 8 side with respect to the normal direction 7, the optical axis direction 9 The variation in reflectance can be reduced in the entire fine antireflection structure 23 with respect to the light incident from. Thereby, even in the optical element 21 having a curved surface with a small radius of curvature, a good antireflection effect can be obtained within the effective diameter range S, and a fine antireflection structure is provided on the curved surface outside the effective diameter of the optical element. Since it is formed, reflection of incident light can be more effectively suppressed.

Needless to say, the present invention is not limited to the configuration exemplified in the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
In the present embodiment, the case where the fine antireflection structure has a convex shape has been described, but a concave shape may be employed.
Moreover, although the central axis of the convex part 4 forms the substantially straight line in the optical element 1, it does not need to be a straight line, such as making it curve.

1, 21 Optical element 2a First surface (curved surface)
3, 23 Fine antireflection structure 4 Convex part 6 Formation direction 7 Normal direction 8 Top surface 9 Optical axis W Period θ Inclination angle

Claims (5)

An optical element having a curved surface in which a fine antireflection structure for visible light is formed at least in part,
The fine antireflection structure is formed on the curved surface by a plurality of convex portions or a plurality of concave portions formed with a period shorter than the wavelength of the visible light,
The formation direction of at least some of the plurality of projections or the formation direction of at least some of the plurality of depressions is the normal line of the curved surface at the position where each projection or depression is formed. An optical element formed by being inclined with respect to a direction.   The optical element according to claim 1, wherein a direction in which the convex portion or the concave portion is formed is inclined by 5 ° or more with respect to a normal direction of the curved surface.   The optical element according to claim 1, wherein a direction in which the convex portion or the concave portion is formed is inclined toward the optical axis side of the curved surface with respect to a normal direction of the curved surface.   4. The method according to claim 1, wherein at least one of an inclination direction and an inclination angle is randomly formed with respect to a normal line direction of the curved surface as a forming direction of the convex portion or the concave portion. The optical element described.   An optical system comprising the optical element according to claim 1.

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