Optical element and imaging apparatus including the same

A lens includes a first optical surface including an optical axis X, and a first cut end surface at an outer circumference of the first optical surface. The first optical surface has a first SWS configured to reduce reflection of light. The first cut end surface has a second SWS configured to reduce reflection of light. A reflectance of the second SWS with respect to light having a predetermined wavelength is higher than the reflectance of the first SWS with respect to the light having the predetermined wavelength.

BACKGROUND

A technique disclosed herein relates to optical elements including surfaces having antireflection structures configured to reduce reflection of incident light.

In recent years, various optical elements including surfaces having antireflection structures for reducing reflection of light have been proposed.

A technique has been proposed in which fine structural units (e.g., fine structures made of linear recessed portions or linear raised portions, or fine structures made of conical or columnar recessed portions or raised portions) as antireflection structures are formed on a surface of an optical member with a pitch smaller than or equal to the wavelength of incident light.

For example, in Japanese Patent Publication No. 2008-276059, an antireflection structure is formed not only on an optical functional surface of a lens but also on a non-optical functional surface of a cut end portion, or the like, and an opaque film is further formed on the antireflection structure of the non-optical functional surface. In this way, reflection at the entire surface of the lens is reduced.

SUMMARY

When a lens is attached to a lens frame or a barrel, a tilt of the lens may be adjusted. The tilt of the lens is adjusted by irradiating the lens with a laser beam, and observing reflected light of the laser beam.

However, when the reflectance of the entire lens is low, the reflected light cannot be observed, and the tilt of the lens cannot be adjusted. Normally, in many cases, a cut end surface is irradiated with a laser beam to adjust the tilt of the lens. However, when the antireflection structure is provided also on the cut end surface as in Japanese Patent Publication No. 2008-276059, it becomes more difficult to adjust the tilt of the lens. That is, it is difficult to achieve both reduction of the reflection of portions other than optical functional surface and adjustment of the tile of the lens.

A technique disclosed herein was devised in view of the foregoing, and is directed to achieve both the reduction of the reflection of portions other than optical functional surface and the adjustment of the tile of the lens.

An optical element disclosed herein includes: an optical functional surface including an optical axis; and a cut end surface at an outer circumference of the optical functional surface, wherein the optical functional surface has a first antireflection structure configured to reduce reflection of light, the cut end surface has a second antireflection structure configured to reduce reflection of light, and a reflectance of the second antireflection structure with respect to light having a predetermined wavelength is higher than a reflectance of the first antireflection structure with respect to the light having the predetermined wavelength.

An imaging apparatus disclosed herein includes the optical element.

According to the optical element, it is possible to achieve both the reduction of the reflection of portions other than optical functional surface and the adjustment of the tile of the lens.

According to the imaging apparatus, it is possible to achieve both the reduction of the reflection of portions other than optical functional surface and the adjustment of the tile of the lens.

DETAILED DESCRIPTION

Embodiments are described in detail below with reference to the attached drawings. However, unnecessarily detailed description may be omitted. For example, detailed description of well known techniques or description of the substantially same elements may be omitted. Such omission is intended to prevent the following description from being unnecessarily redundant and to help those skilled in the art easily understand it. Inventors provide the following description and the attached drawings to enable those skilled in the art to fully understand the present disclosure. Thus, the description and the drawings are not intended to limit the scope of the subject matter defined in the claims.

Example embodiments will be described in detail below with reference to the drawings.

FIG. 1is a sectional view illustrating a lens10.

The lens10includes an optical portion11including an optical axis X and a cut end portion12provided at an outer periphery of the optical portion11. The optical portion11and the cut end portion12constitute an element body. The lens10is a biconvex lens. The lens10is a resin molded product produced by injection molding. The lens10is an example of an optical element.

The optical portion11includes a first optical surface14and a second optical surface15. The first and second optical surfaces14and15are optical functional surfaces (also referred to as optical effective surfaces).

The cut end portion12includes a first cut end surface12aon the same side as the first optical surface14, a second cut end surface12bon the same side as the second optical surface15, and an outer circumferential surface12c. A plane including the first cut end surface12aintersects the optical axis X, specifically, is orthogonal to the optical axis X. Likewise, a plane including the second cut end surface12bintersects the optical axis X, specifically, is orthogonal to the optical axis X. Note that it is not necessary for the first cut end surface12aand the second cut end surface12bto be orthogonal to the optical axis X. The first cut end surface12aand the second cut end surface12bare examples of a peripheral surface.

The first optical surface14, the second optical surface15, the first cut end surface12a, and the second cut end surface12beach have a sub-wavelength structure (SWS)13. The SWS13is an example of an antireflection structure. The SWS13includes a plurality of fine structural units arranged with a pitch smaller than or equal to a predetermined pitch (period), and can reduce reflection of light having a wavelength longer than or equal to the predetermined pitch. Structural units of the SWS13of the present embodiment are raised portions16. The raised portions16each have a conical shape.

Specifically, the SWSs13are first SWSs13aprovided on the first optical surface14and the second optical surface15, and second SWSs13bprovided on the first cut end surface12aand the second cut end surface12b. Each first SWS13aincludes first raised portions16a. Each second SWS13bincludes second raised portions16b. When a distinction is not made between the first SWSs13aand the second SWSs13b, the first SWSs13aand the second SWSs13bare hereinafter simply referred to as SWS(s)13. Moreover, when a distinction is not made between the first raised portions16aand the second raised portions16b, the first raised portions16aand the second raised portions16bare hereinafter simply referred to as raised portion(s)16.

The plurality of raised portions16are arranged in the SWS13, so that a plurality of recessed portions are each formed by being surrounded by the raised portions16. A virtual surface formed by connecting bottoms (the lowest portions) of the recessed portions is referred to as base surfaces L. The base surface L includes first base surfaces L1which are the first optical surface14and the second optical surface15, and the second base surfaces L2which are the first cut end surface12aand the second cut end surface12b. The first base surfaces L1are formed to have a shape necessary for obtaining optical properties required for the lens10. The first base surfaces L1are curved surfaces. For example, the first base surfaces L1may be spheric surfaces, aspheric surfaces, or free-form surfaces. Note that the first base surfaces L1may be flat surfaces. The second base surfaces L2are flat surfaces orthogonal to the optical axis X. Note that, the second base surfaces L2do not have to be orthogonal to the optical axis X, or be flat. When a distinction is not made between the first base surfaces L1and the second base surfaces L2, the first base surfaces L1and the second base surfaces L2are hereinafter simply referred to as base surface(s) L.

Here, the pitch of the raised portions16is a distance between vertices of adjacent ones of the raised portions16in a direction parallel to a plane orthogonal to the optical axis X. Moreover, the height of each raised portion16in the optical axis direction is a distance from the vertex of the raised portion16to the base surface L in the optical axis direction.FIG. 2is an enlarged sectional view illustrating the lens10. As illustrated inFIG. 2, the vertex of the raised portion16is denoted by A, and an intersection of a line segment extending from the vertex A in the optical axis direction and the base surface L is an intersection B. The height H of each raised portion16in the optical axis direction is defined by a distance from the vertex A to the intersection B. Specifically, the height H1of the first raised portion16ais a distance from the vertex A to the intersection B at the first base surface L1. The height H2of the second raised portion16bis a distance from the vertex A to the intersection B at the second base surface L2. Note that the tip of the raised portion16actually formed may have a small curvature. In this case, the topmost portion of the raised portion16is the vertex A. The “height of the raised portion(s),” unless otherwise specified, hereinafter means the height in the optical axis direction.

The SWS13can reduce reflection of light having at least a wavelength longer than or equal to the pitch of the raised portions16. When the lens10is used in an imaging optical system, light whose reflection is to be reduced is visible light. In this case, since a target wavelength is 400 nm-700 nm, the pitch of the raised portions16is preferably less than or equal to 400 nm.

Moreover, in order to enhance the effect of antireflection, the height of the raised portions16is preferably 0.4 or more times as large as the target wavelength. When the target wavelength is that of visible light, the height of the raised portions16is preferably greater than or equal to 280 nm.

Moreover, in order to prevent light from being diffracted at the SWS13, the pitch of the raised portions16is preferably less than or equal to a solution obtained by dividing the target wavelength by the refractive index of the lens10. When the target wavelength is that of visible light, and the refractive index of the lens10is 1.5, the pitch of the raised portions16is less than or equal to 266 nm.

Note that the optical functional surface of the lens10preferably has a relatively low reflectance and a relatively high transmittance. For example, when the pitch of the raised portions16is 230 nm, and the height of the raised portions16is 350 nm, the reflectance in the entire range of visible light can be lower than or equal to 0.1-0.2%, so that it is possible to obtain a satisfactory effect of antireflection.

Here, the reflectance of the first SWS13awith respect to visible light is lower than or equal to about 1%. For example, the height H1of the first raised portion16ais, as previously described, greater than or equal to 280 nm. In a preferable example, the height H1of the first raised portion16ais 350 nm.

The reflectance of the second SWS13bwith respect to infrared light (wavelength 700 nm-1000 nm) is higher than the reflectance of the first SWS13awith respect to the infrared light. Specifically, the height H2of the second raised portion16bis smaller than the height H1of the first raised portion16a. The second SWS13bis used for adjusting a tilt of the lens10. Thus, the reflectance of the second SWS13bwith respect to infrared light may be at a level at which the tilt can be adjusted, and may be, for example, about 1% or higher.

Moreover, with respect to infrared light in the entire infrared range, the reflectance of the second SWS13bdoes not have to be higher than that of the first SWS13a, but with respect to light having at least one wavelength included in the infrared range, the reflectance of the second SWS13bmay be higher than that of the first SWS13a. By using the light having the one wavelength, the tilt of the lens10can be adjusted as described later.

Note that when with respect to infrared light in the entire infrared range, the reflectance of the second SWS13bis higher than that of the first SWS13a, it is possible to expand the selection range of infrared light used for adjusting the tilt of the lens10in the entire infrared range.

For example, the height H1of the first raised portion16ais about 350 nm, and the height H2of the second raised portion16bis about 280 nm. With this configuration, the first SWS13acan exhibit an enhanced effect of antireflection with respect to visible light, and the second SWS13bcan reflect infrared light.

The wavelength of infrared light is longer than that of visible light. Thus, even when the height of the second raised portion16bis small to allow the second SWS13bto reflect infrared light, it is possible to reduce reflection of visible light at the second SWS13b.

[2. Adjustment of Tilt of Lens]

When the lens10is attached to a lens frame, or the like, a tilt of the optical axis X is adjusted.FIG. 3shows a layout of the lens10and an adjustment device50in adjusting the tilt.FIG. 4shows a monitored image of the adjustment device50.

The lens10is attached to a lens frame19. At that time, the lens10is fixed to the lens frame19via an adhesive such as UV curing resin.

The adjustment device50includes a laser light source51and a light receiving portion52. The laser light source51outputs a laser beam (e.g., an infrared laser beam having a wavelength of 850 nm). The light receiving portion52receives the laser beam reflected from the lens10.

In adjusting the tilt, the lens10is first attached to the lens frame19. At this point, the adhesive is not cured. Next, the cut end portion12of the lens10is irradiated with a laser beam from the laser light source51. The light receiving portion52receives light reflected from the cut end portion12. The adjustment device50displays a spot image53of the reflected and received light on a monitor as shown inFIG. 4.

Subsequently, the tilt and the position of the lens10relative to the lens frame19are adjusted so that the spot image53is displayed on a predetermined position on a screen of the monitor (the center of the screen of the monitor in the example ofFIG. 4). After completion of the adjustment, the adhesive is irradiated with UV light to fix the lens10to the lens frame19.

[3. Production of Lens]

The lens10is produced by injection molding.FIGS. 5A-5Fare views illustrating steps for forming a molding die used in the injection molding. The molding die includes a molding die for molding the first optical surface14, and a molding die for molding the second optical surface15. Here, steps for forming one of the molding dies will be described, but the other of the molding dies can be formed in similar steps.

First, a molding die base material41is prepared. Then, as illustrated inFIG. 5A, an inverted shape of the lens10is formed in the molding die base material41by mechanical processing. The inverted shape of the lens10at this point means the inverted shape of the lens10with the raised portions16being omitted from the optical surface and the cut end surface, and corresponds to the first base surface L1and the second base surface L2of the lens10. The molding die base material41may be a material which has a high strength and in which a fine pattern can be easily formed by etching. For example, as the molding die base material41, SiO2(quartz), Si (silicon), GC (glassy carbon), SiC (silicon carbide), WC (cemented), or the like may be used.

Next, as illustrated inFIG. 5B, a metal mask42is formed on a surface of the molding die base material41. The metal mask42may be formed by sputtering or vapor deposition. As a material of the metal mask42, Cr, Ta, WSi, Ni, W, or the like may be used.

Subsequently, as illustrated inFIG. 5C, a resist mask43is formed on the metal mask42. The resist mask43may be formed by spin coating, spray coating, or the like.

After that, as illustrated inFIG. 5D, a resist dot pattern44corresponding to the SWS13is formed from the resist mask43. The resist dot pattern44may be formed by electron beam lithography, interference exposure (hologram exposure), or the like. The resist dot pattern44is formed not only on a portion corresponding to the optical surface, but also on a portion corresponding to the cut end surface. That is, the resist dot pattern44includes a first resist dot pattern44ain a portion corresponding to the optical surface, and a second resist dot pattern44bin a portion corresponding to the cut end surface.

Next, as illustrated inFIG. 5E, the resist dot pattern44is transferred to the metal mask42by dry etching. Thus, a metal mask dot pattern45is formed. Alternatively, the metal mask dot pattern45may be formed by wet etching. In the same manner as the resist dot pattern44, the metal mask dot pattern45is formed not only a portion corresponding to the optical surface but also a portion corresponding to the cut end surface. That is, the metal mask dot pattern45includes a first metal mask dot pattern45ain a portion corresponding to the optical surface, and a second metal mask dot pattern45bin a portion corresponding to the cut end surface.

Subsequently, as illustrated inFIG. 5F, the metal mask dot pattern45is transferred to the molding die base material41by dry etching. Thus, recessed portions35having an inverted shape of the raised portions16are formed on the surface of the molding die base material41. In the same manner as the metal mask dot pattern45, the recessed portions35are formed not only on a portion corresponding to the optical surface but also on a portion corresponding to the cut end surface. That is, the recessed portions35include first recessed portions35ain a portion corresponding to the optical surface and second recessed portions35bin a portion corresponding to the cut end surface.

Thus, a molding die31is formed. The other molding die is also formed in a similar manner.

Here, the first recessed portions35aare deeper than the second recessed portions35b. For example, when the hole size of the first resist dot pattern44ais larger than the hole size of the second resist dot pattern44b, the first recessed portions35acan be deeper than the second recessed portions35b. The first resist dot pattern44ais formed to have a hole size different from the hole size of the second resist dot pattern44b, which results in different etching depths. The hole sizes of the first resist dot pattern44aand the second resist dot pattern44bcan be adjusted by varying the exposure amount when the resist is exposed to light.

Alternatively, the first recessed portions35acan be formed to be deeper than the second recessed portions35bby adjusting the etching depth in etching. In general, plasma (ions) generated in a dry etching device is likely to concentrate on a projection or a pointed portion of the object being processed. In the process, when the molding die base material41is subjected to a dry etching process, plasma concentrates on a circumferential portion of the molding die base material41corresponding to the cut end surface. As a result, the etching rate is higher in the circumferential portion than in the center portion of the molding die base material41. Even when the hole size of the first resist dot pattern44ais equal to the hole size of the second resist dot pattern44b, the second resist dot pattern44band the second metal mask dot pattern45bcorresponding to the cut end surface are removed earlier than the first resist dot pattern44aand the first metal mask dot pattern45acorresponding to the optical surface. Therefore, when etching is performed until a portion of the mask corresponding to the optical surface is removed, the circumferential portion of the molding die base material41corresponding to the cut end surface is continued to be etched after the mask has been removed, which results in overetching. As a result, the recessed portions35in the circumferential portion of the molding die base material41are shallow.

By using the thus formed molding die, the lens10is molded, so that the lens10can have the second raised portions16bwhich are lower than the first raised portions16a. Examples of a method for molding a lens include reheat press molding in the case of the material of the lens10being glass, injection molding, UV curing resin molding, and thermosetting resin molding in the case of the material of the lens10being resin, etc.

Moreover, the molding surface of the molding die is preferably subjected to a release treatment before the molding. In the case of glass molding, a thin film made of, for example, an alloy containing at least one or more metals of carbon (C), boron nitride (BN), diamond-like carbon (DLC), noble metal film (platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), osmium (Os), ruthenium (Ru), rhenium (Re), tungsten (W), and tantalum (Ta) may be formed on the molding surface. In the case of the resin molding, a fluorine-based release agent may be applied to the molding surface. Performing such a release treatment can increase the releasability of a molded product.

Note that even in the case of using a molding die in which the depth of the first recessed portions35ais equal to the depth of the second recessed portions35b, it is possible to manufacture a lens10in which the second raised portions16bare lower than the first raised portions16a. For example, the second raised portions16bcan be lower than the first raised portions16aby adjusting molding conditions in the injection molding or the reheat press molding. Since the cut end portion12is thinner than the optical portion11, the cut end portion12is cured earlier than the optical portion11. Thus, it is difficult for a molding material to flow into the second recessed portions35b. In order to overcome this problem, in general, the temperature of the pressure the molding material is increased. However, in manufacturing a lens10in which the second raised portions16bare lower than the first raised portion16a, any measures to allow the molding material to easily flow into the second recessed portions35bare not taken. As a result, the filling rate of the molding material is lower in the second recessed portions35bthan in the first recessed portions35a, and thus the lens10in which the second raised portions16bare lower than the first raised portions16acan be manufactured.

Next, a camera100including the lens10will be described.FIG. 6is a schematic view illustrating the camera100.

The camera100includes a camera body110, and an interchangeable lens120attached to the camera body110. The camera100is an example of an imaging apparatus.

The camera body110includes an imaging element130.

The interchangeable lens120is configured to be detachable from the camera body110. The interchangeable lens120is, for example, a telephoto zoom lens. The interchangeable lens120includes an imaging optical system140for focusing a light bundle on the imaging element130of the camera body110. The imaging optical system140includes the lens10and refracting lenses150and160. The lens10serves as a lens element.

Thus, the lens10includes the first optical surface14including the optical axis X, and the first cut end surface12aprovided at an outer circumference of the first optical surface14, wherein the first optical surface14has the first SWS13aconfigured to reduce reflection of light, the first cut end surface12ahas the second SWS13bconfigured to reduce reflection of light, and the reflectance of the second SWS13bwith respect to light having a predetermined wavelength is higher than the reflectance of the first SWS13awith respect to the light having the predetermined wavelength.

With the above configuration, the first SWS13ais provided on the first optical surface14, and the second SWS13bis provided on the first cut end surface12a, so that the reflection at the entirety of the lens10can be reduced. Additionally, the reflectance of the second SWS13bwith respect to light having a predetermined wavelength is higher than the reflectance of the first SWS13awith respect to the light having the predetermined wavelength, so that the tilt of the lens10can be adjusted by irradiating the second SWS13bwith the light having the predetermined wavelength. That is, it is possible to achieve both the reduction of the reflection of portions other than optical functional surface and the adjustment of the tile of the lens.

The predetermined wavelength is a wavelength out of the visible light range.

With this configuration, the predetermined wavelength is a wavelength out of the visible light range, so that when light having the predetermined wavelength is reflected at the second SWS13b, people cannot visually identify the reflected light. That is, when the lens10and an apparatus including the same are directed to people, it is possible to reduce adverse effects caused by reflection of light at the second SWS13b.

Moreover, the reflectance of the first SWS13awith respect to visible light is lower than or equal to 1%.

With this configuration, it is possible to significantly reduce reflection of visible light at the first optical surface.

Moreover, the predetermined wavelength is a wavelength in the infrared range.

With this configuration, the tilt of the lens10can be easily adjusted. That is, when the lens10has the above-described configuration, the tilt of the lens10can be adjusted by using light having the predetermined wavelength. In general, a general-purpose light source other than visible light is a light source of infrared light. Thus, the general-purpose light source can be used to adjust the tilt of the lens10by increasing the reflectance of the second SWS13bwith respect to the infrared light.

Moreover, the first SWS13aincludes the first raised portions16a, the second SWS13bincludes the second raised portions16b, and the height of the second raised portions16bin the optical axis X is smaller than the height of the first raised portions16ain the optical axis X.

The antireflection effect of the SWS13depends on the height of the raised portions. The higher the raised portions are, the more the antireflection effect is enhanced. Thus, when the height of the second raised portions16bis smaller than the height of the first raised portions16a, the reflectance of the second raised portions16bcan be higher than the reflectance of the first raised portion16a.

Moreover, when the raised portions are low, the reflectance of light having a relatively long wavelength increases. Thus, when the height of the second raised portions16bis smaller than the height of the first raised portions16a, the reflectance of light having a relatively long wavelength can be increased while the reflectance of light having a relatively short wavelength is reduced. For example, as previously described, when the wavelength of light to be reflected is longer than the wavelength of light whose reflection is to be reduced, it is effective to reduce the height of the second raised portions16b. For example, when light to be reflected is infrared light, and light whose reflection is to be reduced is visible light, it is effective to reduce the height of the second raised portions16b. That is, by reducing the height of the second raised portions16b, it is possible both to enhance reflection of light to be reflected and to reduce reflection of light whose reflection is to be reduced.

The camera100includes the lens10.

With this configuration, reflection at the entire lens10of the camera100can be reduced, and the optical axis X of the lens10can precisely match the optical axis of the lens barrel.

Next, lenses according to variations will be described.

The configuration of a second SWS213bof a lens210in a variation is different from that of the second SWS13bof the lens10. Thus, like reference numerals as those used for the lens10are used to represent equivalent elements of the lens210, and the explanation thereof will be omitted. The difference from the lens10will be mainly described below.FIG. 7is an enlarged sectional view illustrating the lens210according to the variation.

The lens210includes first SWSs13aprovided on a first optical surface14and a second optical surface15, and second SWSs213bprovided on a first cut end surface12aand a second cut end surface12b.

In the same manner as in the lens10, each first SWS13aincludes first raised portions16aand is configured to reduce reflection of visible light.

Each second SWS213bincludes second raised portions216b. A first flat surface216cis formed at a top portion of each second raised portion216b. That is, each second raised portion216bhas a shape of circular truncated cone. Moreover, in the second SWS213b, each of recessed portions216dis formed by being surrounded by the second raised portions216b. A second flat surface216eis formed at a bottom of each recessed portion216d. The flat surface216cand the flat surface216eare both orthogonal to an optical axis X. Note that the first flat surface216cand the second flat surface216edo not have to be strictly flat.

The distance between the first flat surface216cand the second flat surface216ein an optical axis direction is set to approximately a half of a predetermined wavelength. For example, the distance is set to approximately a half of the wavelength of infrared light (e.g., 850 nm). In this configuration, light having a predetermined wavelength and reflected at the first flat surfaces216cand light having the predetermined wavelength and reflected at the second flat surfaces216einterfere with each other, and thus are enhanced. Consequently, the reflectance of light having the predetermined wavelength at the second SWS213bincreases. The wavelength of light having a high reflectance can be adjusted by accordingly setting the distance between the first flat surface216cand the second flat surface216ein the optical axis direction.

Thus, each second SWS213bof the lens210according to the variation includes the plurality of second raised portions216b, the first flat surface216cis formed on the top portion of each second raised portion216b, each recessed portion216dis formed by being surrounded by the second raised portions216b, the second flat surfaces216eis formed at the bottom of each recessed portion216d, and the distance between the first flat surface216cof the second raised portion216band the second flat surface216eof the recessed portion216din the optical axis X is a half of the predetermined wavelength.

In this configuration, light having a predetermined wavelength and reflected at the first flat surfaces216cand light having the predetermined wavelength and reflected at the second flat surfaces216einterfere with each other, and thus are enhanced. Consequently, the reflectance of light having the predetermined wavelength can be increased.

Note that the distance between the first flat surface216cand the second flat surface216ein the optical axis direction does not have to be strictly a half of the predetermined wavelength, but may be substantially a half of the predetermined wavelength. That is, substantially a half means that light reflected at the first flat surfaces216cand light reflected at the second flat surface216ehave such a relationship that they are enhanced through interference.

Other Embodiments

As described above, the embodiments have been described as example techniques disclosed in the present application. However, the techniques according to the present disclosure are not limited to these embodiments, but are also applicable to those where modifications, substitutions, additions, and omissions are made. In addition, elements described in the embodiments may be combined to provide a different embodiment. As such, elements illustrated in the attached drawings or the detailed description may include not only essential elements for solving the problem, but also non-essential elements for solving the problem in order to illustrate such techniques. Thus, the mere fact that those non-essential elements are shown in the attached drawings or the detailed description should not be interpreted as requiring that such elements be essential.

Embodiments of the present disclosure may have the following configurations.

It is not necessary that the SWSs13are provided on the first optical surface14and the second optical surface15, but the SWS13may be provided either one of the surfaces. Alternatively, it is not necessary that the SWSs13are provided on the first cut end surface12aand the second cut end surface12b, but the SWS13may be provided either one of the surfaces. The SWS13may be provided on the outer circumferential surface12c.

The second SWSs13b,213bare provided on the first cut end surface12aand the second cut end surface12b, but the second SWS13b,213bmay be provided on any one of the first cut end surface12aor the second cut end surface12b.

Moreover, the second SWS13b,213bmay be provided not on the entirety but on part of the first cut end surface12aor the second cut end surface12b. That is, the second SWS13b,213bmay be provided on part of the first cut end surface12aor the second cut end surface12b, and the first SWS13amay be provided on the rest of the first cut end surface12aor the second cut end surface12b.

Note that the shape and numerical values of the first raised portions16aand the second raised portions16bare mere examples. The reflectance of the SWS13varies depending on the material or the shape of the SWS13. The material, height, and pitch of the raised portions can be varied to adjust the reflectance of the SWS13. In the embodiment, since the raised portions16are made of the same material and have the same pitch in the first SWS13aand in the second SWS13b, the first raised portions16aare formed to have a height different from the height of the second raised portions16bso that the first SWS13ahas a reflectance different from the reflectance of the second SWS13b. Alternatively, for example, the first raised portions16amay be formed to have a pitch different from the pitch of the second raised portions16b. That is, the pitch and height of the first raised portions16aand the pitch and height of the second raised portion16bmay be adjusted to increase the reflectance of the second SWS13bwith respect to infrared light compared to the reflectance of the first SWS13awith respect to the infrared light.

The antireflection structure is not limited to the SWS. The antireflection structure may be an AR coating or an AR sheet including one or more thin films. The AR coating and the AR sheet can be those reducing reflection by light interference. The AR coating is applied to a surface of the optical portion11. The AR sheet is attached to the surface of the optical portion11. Alternatively, the antireflection structure may have fine gaps in a layer provided on an optical surface. Even in such antireflection structures, the reflectance of the antireflection structure provided on the cut end surface with respect to light having a predetermined wavelength (e.g., infrared light) is higher than the reflectance of the antireflection structure provided on the optical surface with respect to the light having the predetermined wavelength (e.g., infrared light). As a result, it is possible to reduce reflection not only at the optical functional surface but also at the cut end surface, and additionally, the tilt of the lens can be adjusted.

The SWS13reduces reflection of visible light, but light whose reflection is reduced by the first SWS13ais not necessarily visible light. Light for which the first SWS13ais provided can accordingly be determined depending on use conditions of the lens10. The pitch, the height, etc. of the first raised portions16aof the first SWS13acan be varied to change the wavelength of light whose reflection is reduced by the first SWS13a. Likewise, the second SWS13b,213breflects infrared light, but light reflected at the second SWS13b,213bis not necessarily infrared light. Note that when the optical element is directed to use by people, light for which the second SWS13b,213bis provided is preferably invisible light such as ultraviolet light, infrared light, etc. That is, when light is reflected at the second SWS13b,213b, the reflected light is invisible light, so that people cannot visually identify the reflected light.

The structural unit of the SWS13has a conical shape (seeFIG. 8A), but the shape of the structural units is not limited to this shape. Alternatively, as illustrated inFIG. 8B, the structural unit may be in the shape of a pyramid such as a hexagonal pyramid, a quadrangular pyramid, etc. The structural unit may be in the shape of a column as illustrated inFIG. 8C, or a prism as illustrated inFIG. 8D. Alternatively, the structural unit may be in the shape of a column or a prism whose top portion is rounded as illustrated inFIG. 8EorFIG. 8F. The structural unit may be in the shape of a truncated cone or a truncated pyramid as illustrated inFIG. 8GorFIG. 8H.

Moreover, the structural units may be raised portions formed by forming a plurality of recessed portions, the raised portions each formed by being surrounded by the recessed portions. That is, the raised portions have a relative relationship with respect to the recessed portions. In the SWS, the recessed portions are each formed among the plurality of raised portions, whereas the raised portions are each formed among the plurality of recessed portions. That is, it is possible to say that a plurality of raised portions are arranged in the SWS or that a plurality of recessed portions are arranged in the SWS.

It is not necessary that the structural unit has a geometrically exact shape. The structural units may have a raised shape allowing the structural units to be arranged with a pitch smaller than the wavelength of light whose reflection is to be reduced.

The lens10has, but not limited to, a biconvex shape. Alternatively, the lens10may have a biconcave shape, a convex meniscus shape, or a concave meniscus shape. Alternatively, it is not necessary that the lens10serves as a lens element.

The method for forming the molding die is not limited to the above-described forming method. In the above-described forming method, when the resist dot pattern44is formed from the resist mask43, electron beam lithography is used. However, interference exposure (hologram exposure) or lithography such as X-ray lithography may be used. The mask may be formed by nanoimprinting or a particle array.

As described above, the technique disclosed herein is useful for optical elements having antireflection structures configured to reduce reflection of incident light. For example, by using the optical element disclosed herein, it is possible to obtain various optical systems such as high-quality imaging optical systems, objective optical systems, scanning optical systems, and pickup optical systems, various optical units such as barrel units, optical pickup units, and imaging units, imaging apparatuses, optical pickup devices, optical scanning devices, etc.

Various embodiments have been described above as example techniques of the present disclosure, in which the attached drawings and the detailed description are provided. Since the embodiments described above are intended to illustrate the techniques in the present disclosure, it is intended by the following claims to claim any and all modifications, substitutions, additions, and omissions that fall within the proper scope of the claims appropriately interpreted in accordance with the doctrine of equivalents and other applicable judicial doctrines.