JP2018136529A - Diffraction optical element and optical device - Google Patents

Diffraction optical element and optical device Download PDF

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JP2018136529A
JP2018136529A JP2018010318A JP2018010318A JP2018136529A JP 2018136529 A JP2018136529 A JP 2018136529A JP 2018010318 A JP2018010318 A JP 2018010318A JP 2018010318 A JP2018010318 A JP 2018010318A JP 2018136529 A JP2018136529 A JP 2018136529A
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resin layer
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研逸 岩田
Kenichi Iwata
研逸 岩田
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Canon Inc
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Abstract

PROBLEM TO BE SOLVED: To provide a diffraction optical element having a wall surface formed with a waveguide layer capable of preventing degradation of optical characteristic due to separation of a high refraction index layer from a grating layer by suppressing the separation on the interface therebetween.SOLUTION: The diffraction optical element has a first resin layer 2 which has steps on a surface and a second resin layer 3 adhered and integrated with the first resin layer 2. The diffraction optical element further has a high refraction index layer 5, the refraction index of which is higher than the refraction index of the first resin layer 2 and the second resin layer 3, between the wall surface 2b of the first resin layer 2 and the wall surface 3b of the second resin layer 3. The high refraction index layer 5 is continuously formed extending from the boundary of the wall surface 2b and a neighboring inclined plane 2a up to a part of the inclined plane 2a.SELECTED DRAWING: Figure 1

Description

本発明は、カメラやビデオカメラ、顕微鏡、内視鏡等の光学機器に使用される回折光学素子に関するものである。   The present invention relates to a diffractive optical element used in optical equipment such as a camera, a video camera, a microscope, and an endoscope.

回折光学素子の一つであるレリーフ型回折格子は、同心円状の複数の段差（レリーフパターン）を有しており、係る段差を形成する複数の壁面と、該壁面によって区画される複数の斜面とからなる。斜面は、光学素子として作用するいわゆる光学有効面であり、入射光を所望の位置に結像させる領域である。一方、壁面は光学素子としては作用しない領域である。壁面に入射した光は、該壁面で反射や屈折することにより、所望の結像位置からずれた位置に到達し、その結果、画像上にはフレアと呼ばれる現象が現れ、画質を大きく低下させてしまう。そのため、係るフレアを抑制するための方法が種々提案されている。
例えば、特許文献１には、壁面に、格子を形成している樹脂層よりも屈折率が高い材料からなる導波路層を形成することで回折効率を向上させた構成が開示されている。係る構成の回折光学素子に入射した光は、壁面での反射や屈折を起こすことなく導波路層内に入射し、該導波路内で全反射を繰り返しながら壁面に平行な方向に進んで導波路層先端から出力される。よって、原理上、フレアを低減することが可能である。 A relief type diffraction grating, which is one of the diffractive optical elements, has a plurality of concentric steps (relief patterns), a plurality of wall surfaces forming the steps, and a plurality of inclined surfaces partitioned by the wall surfaces. Consists of. The inclined surface is a so-called optically effective surface that acts as an optical element, and is a region where incident light is imaged at a desired position. On the other hand, the wall surface is a region that does not act as an optical element. The light incident on the wall surface is reflected or refracted by the wall surface and reaches a position deviated from a desired imaging position. As a result, a phenomenon called flare appears on the image, which greatly reduces the image quality. End up. Therefore, various methods for suppressing such flare have been proposed.
For example, Patent Document 1 discloses a configuration in which diffraction efficiency is improved by forming a waveguide layer made of a material having a refractive index higher than that of a resin layer forming a grating on a wall surface. The light incident on the diffractive optical element having such a structure is incident on the waveguide layer without causing reflection or refraction on the wall surface, and proceeds in a direction parallel to the wall surface while repeating total reflection in the waveguide. Output from the top of the layer . Therefore, in principle, flare can be reduced.

国際公開第２０１１／９９５５０号パンフレットInternational Publication No. 2011/99550 Pamphlet

特許文献１に開示された構成では、フレアを低減することは可能であるが、係る構成を密着二層型の回折格子に適用した場合には、導波路層を設けたことによる以下のような問題が発生する。
密着二層型の回折格子では、レリーフパターンが形成された格子界面を介して、第１の格子層と第２の格子層とを、密着させて一体化している。よって、係るレリーフパターンの壁面に上記導波路層を形成した場合には、係る壁面においては、第１の格子層と導波路層と第２の格子層と、の３種類の材料が互いに接した状態となる。透過型の回折格子の場合、第１の格子層及び第２の格子層はガラスや光学樹脂で構成されているが、少なくとも一方は光学樹脂が使用されている場合が多い。一方、導波路層には、第１の格子層や第２の格子層よりも高い屈折率が要求されている点、及び薄い膜厚で均一に形成する点から、無機材料が用いられる。
よって、密着二層型の回折格子に特許文献１の導波路層を設けた場合には、壁面において、有機材料と無機材料とが混在していることになる。有機材料と無機材料とでは、線膨張係数が大きく異なり、例えば、光学材料として一般的に使用されるアクリル樹脂では５×１０-5／℃であるのに対して、アルミナなどの無機材料では７×１０-6／℃と、一桁低い値となる。
密着二層型の回折格子を製造する際、一般的には、第１の格子層をレプリカ法などで成形し、その後、導波路層を壁面に形成してから、最後に第２の格子層を第１の格子層と密着する形で成形する手順を踏むと考えられる。第２の格子層は、第１の格子層に密着させた状態で樹脂を硬化させて形成するが、一般的な樹脂であれば硬化前後で５乃至１０％程度の体積変化を生じる。そのため、双方の材料の粘弾性特性にもよるが、第２の格子層の樹脂の硬化反応は、既に成形されている第１の格子層へも影響を及ぼすことになる。つまり、第２の格子層の成形時に第１の格子層が変形することになるが、壁面は形状的に応力が生じ易いため、該壁面において変形が大きくなり、格子層と導波路層との界面で剥離が生じ、格子層と導波路層との間に空気層が発生してしまう。格子層と導波路層との界面に空気層が存在すると、格子層と導波路層との界面での屈折率が設計値とは異なる値となってしまう。そのため、導波路層内に入射した光が導波路層内で全反射を行わずに、途中で格子層側に抜けてしまい、設計通りに導波路層端部から出力せず、フレアの低減効果が得られなくなってしまうおそれがある。
また、格子層と導波路層との界面で剥離が生じる現象は、高温や低温、高温高湿といった環境によっても引き起こされやすい。よって、初期には光学性能を満足していても、経時的に変化してしまうおそれもある。
本発明の課題は、壁面に導波路層を設けた密着二層型の回折光学素子において、導波路層と格子層との界面における剥離を抑制し、フレアの発生を初期から長期にわたって低減することにある。 In the configuration disclosed in Patent Document 1, flare can be reduced. However, when such a configuration is applied to a close-contact double-layer diffraction grating, the following is provided by providing a waveguide layer. A problem occurs.
In the close-contact type diffraction grating, the first grating layer and the second grating layer are brought into close contact with each other via a grating interface on which a relief pattern is formed. Therefore, when the waveguide layer is formed on the wall surface of the relief pattern, the three types of materials of the first grating layer, the waveguide layer, and the second grating layer are in contact with each other on the wall surface. It becomes a state. In the case of a transmission type diffraction grating, the first grating layer and the second grating layer are made of glass or optical resin, but at least one of them is often made of optical resin. On the other hand, an inorganic material is used for the waveguide layer because it has a higher refractive index than the first and second grating layers and is uniformly formed with a thin film thickness.
Therefore, when the waveguide layer of Patent Document 1 is provided in the two-layered diffraction grating, the organic material and the inorganic material are mixed on the wall surface. The organic material and the inorganic material have greatly different linear expansion coefficients, for example, 5 × 10 −5 / ° C. for an acrylic resin generally used as an optical material, whereas 7 for an inorganic material such as alumina. × 10 -6 / ° C, an order of magnitude lower value.
When manufacturing a close-contact two-layer type diffraction grating, generally, the first grating layer is formed by a replica method or the like, and then the waveguide layer is formed on the wall surface, and finally the second grating layer. It is thought that the procedure for forming the film in a form in close contact with the first lattice layer is taken. The second lattice layer is formed by curing a resin in a state of being in close contact with the first lattice layer. However, in the case of a general resin, a volume change of about 5 to 10% occurs before and after curing. Therefore, although depending on the viscoelastic characteristics of both materials, the curing reaction of the resin of the second lattice layer also affects the already formed first lattice layer. In other words, the first lattice layer is deformed when the second lattice layer is formed, but the wall surface is prone to be stressed in shape. Therefore, the deformation is large on the wall surface, and the lattice layer and the waveguide layer are deformed. Separation occurs at the interface, and an air layer is generated between the lattice layer and the waveguide layer. If an air layer exists at the interface between the grating layer and the waveguide layer, the refractive index at the interface between the grating layer and the waveguide layer becomes a value different from the design value. Therefore, the light incident on the waveguide layer does not undergo total reflection in the waveguide layer , but escapes to the grating layer side in the middle, and is not output from the end of the waveguide layer as designed, thereby reducing flare. May not be obtained.
In addition, the phenomenon in which peeling occurs at the interface between the grating layer and the waveguide layer is likely to be caused by an environment such as high temperature, low temperature, and high temperature and high humidity. Therefore, even if the optical performance is initially satisfied, there is a possibility that it may change over time.
An object of the present invention is to suppress peeling at the interface between a waveguide layer and a grating layer and to reduce the occurrence of flare over a long period from the beginning in a two-layer diffractive optical element having a waveguide layer on a wall surface. It is in.

本発明の第一は、一方の表面が、複数の段差を有する複数の壁面と、前記壁面によって区画される複数の斜面と、を有する第１の樹脂層と、
前記第１の樹脂層の、前記一方の表面側に配置され、前記第１の樹脂層側の表面が、前記第１の樹脂層の前記段差に対応する段差を有する第２の樹脂層と、
前記第１の樹脂層の壁面と前記第２の樹脂層の壁面との間に、前記第１の樹脂層及び前記第２の樹脂層よりも屈折率が高い高屈折率層を有する回折光学素子であって、
前記高屈折率層は、前記壁面から前記斜面の一部にまで設けられていることを特徴とする。
本発明の第二は、上記本発明の回折光学素子を、色収差を補正するためのレンズとして用いることを特徴とする光学機器である。 In the first aspect of the present invention, a first resin layer having one surface having a plurality of wall surfaces having a plurality of steps and a plurality of slopes partitioned by the wall surfaces,
A second resin layer disposed on the one surface side of the first resin layer, the surface on the first resin layer side having a step corresponding to the step of the first resin layer;
A diffractive optical element having a high refractive index layer having a higher refractive index than the first resin layer and the second resin layer between the wall surface of the first resin layer and the wall surface of the second resin layer. Because
The high refractive index layer is provided from the wall surface to a part of the slope.
A second aspect of the present invention is an optical apparatus characterized in that the diffractive optical element of the present invention is used as a lens for correcting chromatic aberration.

本発明においては、壁面に高屈折率層を設けたことにより、導波路効果によって、該壁面に起因するフレアを低減することができる。さらに、本発明においては、高屈折率層を斜面と壁面との境界から斜面内にまで延設していることから、高屈折率層と第１の樹脂層及び第２の樹脂層との界面での剥離を抑制することができる。よって、本発明によれば、製造直後から長期にわたってフレアが低減された回折光学素子が提供され、該回折光学素子を用いて、優れた光学性能を長期にわたって得られる光学機器が得られる。   In the present invention, by providing the high refractive index layer on the wall surface, flare caused by the wall surface can be reduced by the waveguide effect. Furthermore, in the present invention, since the high refractive index layer extends from the boundary between the slope and the wall surface into the slope, the interface between the high refractive index layer and the first resin layer and the second resin layer. Can be prevented from peeling. Therefore, according to the present invention, a diffractive optical element with reduced flare is provided for a long period of time immediately after manufacture, and an optical apparatus capable of obtaining excellent optical performance over a long period of time is obtained using the diffractive optical element.

本発明の回折光学素子の構成を模式的に示す図であり、（ａ）は厚さ方向の断面の全体図、（ｂ）は厚さ方向の断面の部分拡大図、（ｃ）は入射光側から見た平面図である。It is a figure which shows typically the structure of the diffractive optical element of this invention, (a) is the whole figure of the cross section of thickness direction, (b) is the elements on larger scale of the cross section of thickness direction, (c) is incident light. It is the top view seen from the side. 図１の回折光学素子の壁面近傍の拡大図である。It is an enlarged view of the wall surface vicinity of the diffractive optical element of FIG. 図１の回折光学素子の製造方法を示す工程図である。It is process drawing which shows the manufacturing method of the diffractive optical element of FIG. 図１の回折光学素子の製造方法を示す工程図である。It is process drawing which shows the manufacturing method of the diffractive optical element of FIG. 図１の回折光学素子の製造方法を示す工程図である。It is process drawing which shows the manufacturing method of the diffractive optical element of FIG. 本発明の一実施形態に係る光学機器を示す概略図である。It is the schematic which shows the optical instrument which concerns on one Embodiment of this invention.

本発明について、適宜図面を参照しながら実施形態について詳細に説明するが、本発明は以下に説明する実施形態に限定されるものではない。また以下の説明において特段説明されていない部分や、図面において特段図示されなかった部分に関しては、当該技術分野の周知或いは公知の技術を適用することができる。   The present invention will be described in detail with reference to the drawings as appropriate, but the present invention is not limited to the embodiments described below. In addition, a well-known or publicly known technique in the technical field can be applied to a part not specifically described in the following description or a part not specifically illustrated in the drawings.

図１は、本発明の回折光学素子の一実施形態の構成を模式的に示すであり、図１（ａ）は厚さ方向の断面の全体図であり、図１（ｂ）はその部分拡大図である。また、図１（ｃ）は入射光側から見た平面図である。図１（ａ）及び（ｂ）は、図１（ｃ）のＡ−Ａ’部分で切断した時の回折光学素子の断面を示した図であり、Ａ−Ａ’部分は回折光学素子の中心にある光軸を通る。即ち、厚さ方向断面とは、回折光学素子を上面（入射光側）から見た時の中心を通るように切断した時の、回折光学素子の断面のことである。図１に示すように、本発明の回折光学素子は、第１の樹脂層２と、第２の樹脂層３とを有する密着二層型である。第１の樹脂層（ブレーズド回折格子）２は、一方の表面側に、厚さ方向の断面が鋸歯状となる複数の段差が、光の入射方向から見た場合に同心円状となるように形成されている。また、係る段差は、壁面２ｂによって形成され、第１の樹脂層２の一方の表面は、係る壁面２ｂと、該壁面２ｂによって区画された斜面２ａとを、それぞれ複数備えている。即ち、壁面２ｂと斜面２ａとで、レリーフパターンが形成されている。第２の樹脂層３は、第１の樹脂層２と密着して配置されているため、第１の樹脂層側の表面に、第１の樹脂層２の段差に対応する段差を有している。そして、第１の樹脂層２の壁面２ｂと第２の樹脂層３の壁面３ｂとの間には、高屈折率層５が設けられている。
尚、本例においては、第１の樹脂層２に高屈折率層５を形成し、次いで、第１の樹脂層２及び高屈折率層５に対して密着するように樹脂を硬化させて第２の樹脂層３を形成したものとする。 FIG. 1 schematically shows a configuration of an embodiment of the diffractive optical element of the present invention. FIG. 1A is an overall view of a cross section in the thickness direction, and FIG. FIG. FIG. 1C is a plan view seen from the incident light side. FIGS. 1A and 1B are views showing a cross section of the diffractive optical element when cut at the AA ′ portion in FIG. 1C, where the AA ′ portion is the center of the diffractive optical element. It passes through the optical axis. That is, the cross section in the thickness direction is a cross section of the diffractive optical element when the diffractive optical element is cut so as to pass through the center when viewed from the upper surface (incident light side). As shown in FIG. 1, the diffractive optical element of the present invention is a close-contact two-layer type having a first resin layer 2 and a second resin layer 3. The first resin layer (blazed diffraction grating) 2 is formed on one surface side such that a plurality of steps having a sawtooth cross section in the thickness direction are concentric when viewed from the light incident direction. Has been. The step is formed by the wall surface 2b, and one surface of the first resin layer 2 includes a plurality of the wall surface 2b and a plurality of slopes 2a partitioned by the wall surface 2b. That is, a relief pattern is formed by the wall surface 2b and the slope 2a. Since the second resin layer 3 is disposed in close contact with the first resin layer 2, the second resin layer 3 has a step corresponding to the step of the first resin layer 2 on the surface of the first resin layer 2. Yes. A high refractive index layer 5 is provided between the wall surface 2 b of the first resin layer 2 and the wall surface 3 b of the second resin layer 3.
In this example, the high refractive index layer 5 is formed on the first resin layer 2, and then the resin is cured so as to be in close contact with the first resin layer 2 and the high refractive index layer 5. 2 resin layer 3 is formed.

図１の実施形態では、第１の樹脂層２の他方の表面側に第１のベース基板１が、第２の樹脂層３の第１の樹脂層２とは反対側の表面に第２のベース基板４が、それぞれ設けられている。これらベース基板１，４としては、透明性等、所望の光学特性を満足するものであれば、ガラス材料、光学樹脂材料のいずれでも用いることができるが、特性変動がしにくい（信頼性）という観点からはガラス材料の方が好適である。具体的には、ランタン系の高屈折率低分散ガラスである「Ｓ−ＬＡＨ５５」（（株）オハラ製）や超低分散ガラスである「Ｓ−ＦＰＬ５１」（（株）オハラ製）等が挙げられる。尚、第２のベース基板４はあってもなくても構わない。回折格子として得られる光学性能に大きな差が生じないためである。   In the embodiment of FIG. 1, the first base substrate 1 is on the other surface side of the first resin layer 2, and the second resin layer 3 has a second surface on the surface opposite to the first resin layer 2. A base substrate 4 is provided. As these base substrates 1 and 4, any glass material and optical resin material can be used as long as they satisfy desired optical characteristics such as transparency, but the characteristics are hardly changed (reliability). From the viewpoint, a glass material is more preferable. Specifically, “S-LAH55” (manufactured by OHARA INC.) Which is a lanthanum-based high refractive index low dispersion glass, “S-FPL51” (manufactured by OHARA INC.) Which is an ultra-low dispersion glass, and the like. It is done. Note that the second base substrate 4 may or may not be present. This is because there is no significant difference in optical performance obtained as a diffraction grating.

第１の樹脂層２及び第２の樹脂層３は、それぞれ回折格子であり、これらを形成する樹脂材料としては、光学特性、信頼性を満足する光学樹脂材料であれば特に制限は無く、製造が容易であることから、感光性樹脂材料が好ましい。具体的には、アクリレート系樹脂、ポリカーボネート樹脂、などが好適に使用される。この光学樹脂材料には要求される光学性能を達成するために、状況に応じて無機微粒子を内添させることも可能である。無機微粒子は要求される光学特性により選択される。具体的には、酸化ジルコニア、酸化チタン、酸化亜鉛、酸化インジウム、酸化錫、酸化アンチモン、インジウム錫酸化物（ＩＴＯ）、アンチモンをドープした酸化スズ（ＡＴＯ）、亜鉛をドープした酸化インジウム（ＩＺＯ）等が挙げられる。   The first resin layer 2 and the second resin layer 3 are each a diffraction grating, and the resin material forming these is not particularly limited as long as it is an optical resin material that satisfies optical characteristics and reliability. Is preferable, a photosensitive resin material is preferable. Specifically, acrylate resins, polycarbonate resins, and the like are preferably used. In order to achieve the required optical performance, this optical resin material can be internally added with inorganic fine particles depending on the situation. The inorganic fine particles are selected according to the required optical properties. Specifically, zirconia oxide, titanium oxide, zinc oxide, indium oxide, tin oxide, antimony oxide, indium tin oxide (ITO), antimony-doped tin oxide (ATO), zinc-doped indium oxide (IZO) Etc.

図１（ｂ）は、図１（ａ）の一部分を拡大したものである。図１（ｂ）に示すように、本発明においては、高屈折率層５は、第１の樹脂層２の壁面２ｂと第２の樹脂層３の壁面３ｂとの間に設けられているが、係る高屈折率層５は、それぞれの斜面２ａ、３ａにまで延設されている。より具体的には、第１の樹脂層２に着目して説明すると、壁面２ｂに形成された高屈折率層５は、該壁面２ｂと斜面２ａとの境界から斜面２ａの一部にまで連続して形成されている。本発明では、このように、高屈折率層５が、壁面２ｂのみならず、斜面２ａにまで延設されていることにより、高屈折率層５と第１の樹脂層２及び第２の樹脂層３との界面における剥離が抑制される。   FIG. 1B is an enlarged view of a part of FIG. As shown in FIG. 1B, in the present invention, the high refractive index layer 5 is provided between the wall surface 2 b of the first resin layer 2 and the wall surface 3 b of the second resin layer 3. The high refractive index layer 5 is extended to the slopes 2a and 3a. More specifically, the description will be made by paying attention to the first resin layer 2. The high refractive index layer 5 formed on the wall surface 2b is continuous from the boundary between the wall surface 2b and the inclined surface 2a to a part of the inclined surface 2a. Is formed. In the present invention, the high refractive index layer 5 extends not only to the wall surface 2b but also to the inclined surface 2a in this way, so that the high refractive index layer 5, the first resin layer 2 and the second resin are extended. Peeling at the interface with the layer 3 is suppressed.

しかしながら、斜面２ａにまで高屈折率層５を延設すると、斜面２ａの実質的な面積が低減してしまい、本来、回折光学素子に要求されている光学特性が低下してしまうことになる。よって、本発明においては、剥離による光学特性の低下を抑制し得る範囲で、本来の光学特性が大きく低下しないように、高屈折率層５の斜面２ａに占める割合を設定することが望ましい。以下に、具体的に説明する。   However, when the high refractive index layer 5 is extended to the inclined surface 2a, the substantial area of the inclined surface 2a is reduced, and the optical characteristics originally required for the diffractive optical element are deteriorated. Therefore, in the present invention, it is desirable to set the ratio of the high refractive index layer 5 to the inclined surface 2a so that the original optical characteristics are not greatly reduced within a range in which the deterioration of the optical characteristics due to peeling can be suppressed. This will be specifically described below.

図１（ｂ）において、壁面２ｂの頂部を第１の樹脂層２の格子山部２ｃ、壁面２ｂの底部を第１の樹脂層２の格子谷部２ｄと称する。格子山部２ｃ及び格子谷部２ｄはいずれも、斜面２ａと壁面２ｂとの境界である。また、Ｌ２は、回折光学素子の厚さ方向断面において、格子山部２ｃに隣接する斜面２ａに占める高屈折率層５の長さを示しており、Ｌ３は、格子谷部２ｄに隣接する斜面２ａに占める高屈折率層５の長さから厚さＬ４を除いた長さである。尚、以下の説明では、第１の樹脂層２の斜面２ａに占める高屈折率層５の長さについて説明するが、第２の樹脂層３についても、同様である。   In FIG. 1B, the top of the wall surface 2 b is referred to as a lattice peak 2 c of the first resin layer 2, and the bottom of the wall surface 2 b is referred to as a lattice valley 2 d of the first resin layer 2. Each of the lattice peak portion 2c and the lattice valley portion 2d is a boundary between the slope 2a and the wall surface 2b. L2 indicates the length of the high refractive index layer 5 in the slope 2a adjacent to the grating peak 2c in the cross section in the thickness direction of the diffractive optical element, and L3 indicates the slope adjacent to the grating valley 2d. This is the length obtained by removing the thickness L4 from the length of the high refractive index layer 5 occupying 2a. In the following description, the length of the high refractive index layer 5 occupying the inclined surface 2a of the first resin layer 2 will be described, but the same applies to the second resin layer 3.

上記したように、斜面２ａに占める高屈折率層５の長さＬ２及びＬ３は、回折光学素子として要求される光学性能と、剥離の低減とを同時に達成しうる範囲に調整される。回折光学素子として要求される光学性能の中で最も重要なものは回折効率である。回折効率は、設計回折次数の回折光が入射した光に対してどの程度の割合で所望の位置に出射しているかを示すものであり、斜面２ａに入射した光の全てが有効光線となる設計をしている。設計にもよるが、一般的には斜面２ａには格子界面を構成する二種類の材料のみが存在するのが前提で、異物は効率を低下させる要因となる。斜面２ａに界面を構成する材料よりも高屈折率の材料が存在した場合には、光学屈折系としては、光は設計とは異なる屈折角で進行していくことになり、結果的には所望の位置に光が集光しなくなってしまう。一方、回折光学系としては設計とは異なる屈折率間での回折現象となるので、所望の回折次数が得られなくなる。いずれにしても、本来の設計とは異なる現象が発現されて、回折効率及び画質を低下させることになってしまう。このため、光学性能の観点からは、斜面２ａに占める高屈折率層５の割合は極力少ない方が良い。   As described above, the lengths L2 and L3 of the high refractive index layer 5 occupying the inclined surface 2a are adjusted to a range in which the optical performance required for the diffractive optical element and reduction of peeling can be achieved at the same time. The most important optical performance required as a diffractive optical element is diffraction efficiency. The diffraction efficiency indicates how much the diffracted light of the designed diffraction order is emitted to a desired position with respect to the incident light, and the design is such that all of the light incident on the inclined surface 2a becomes an effective light beam. I am doing. Although it depends on the design, it is generally assumed that there are only two kinds of materials constituting the lattice interface on the inclined surface 2a, and the foreign matter becomes a factor of reducing the efficiency. When a material having a higher refractive index than the material constituting the interface is present on the inclined surface 2a, the optical refraction system causes light to travel at a refraction angle different from the design, resulting in a desired result. The light will not be collected at the position of. On the other hand, a diffractive optical system has a diffraction phenomenon between refractive indexes different from that of the design, so that a desired diffraction order cannot be obtained. In any case, a phenomenon different from the original design is developed, and the diffraction efficiency and the image quality are lowered. For this reason, from the viewpoint of optical performance, the proportion of the high refractive index layer 5 in the inclined surface 2a is preferably as small as possible.

一般に、レリーフパターンを有する回折光学素子は、光軸中心から円の外周に近づくに従って格子ピッチを徐々に小さくすることにより、レンズ作用（光の収斂作用や発散作用）を有するように構成されている。斜面２ａを無効にするものが、ある一定距離で形成されている場合、その影響の大きさは斜面２ａの長さに比例する。斜面２ａが長い、つまり格子ピッチの大きい場合は影響が小さく、逆に斜面２ａが短い、つまり格子ピッチの小さい場合は影響が大きくなる。   In general, a diffractive optical element having a relief pattern is configured to have a lens action (a light converging action or a diverging action) by gradually decreasing the grating pitch from the center of the optical axis toward the outer periphery of the circle. . When what makes the slope 2a invalid is formed at a certain distance, the magnitude of the influence is proportional to the length of the slope 2a. When the slope 2a is long, that is, when the grating pitch is large, the influence is small. Conversely, when the slope 2a is short, that is, when the grating pitch is small, the influence is large.

上記の高屈折率層５の場合で考えると、一般のレリーフパターンを有する回折光学素子では、光軸中心に近いほど高屈折率層５の影響が小さく、円の外周に近づくに従って高屈折率層５が画質を劣化させる影響は大きくなっていく。このため、高屈折率層５が斜面２ａに占める長さは、理想的にはピッチに比例して変化していることが望ましい。つまり、光軸中心から円の外周に近づくに従って斜面２ａに形成される距離が短くなっていくことが、理想である。   Considering the case of the high refractive index layer 5 described above, in a diffractive optical element having a general relief pattern, the influence of the high refractive index layer 5 is smaller as it is closer to the center of the optical axis. 5 has a greater effect of degrading the image quality. For this reason, the length that the high refractive index layer 5 occupies in the inclined surface 2a is ideally changed in proportion to the pitch. In other words, it is ideal that the distance formed on the slope 2a becomes shorter from the center of the optical axis toward the outer periphery of the circle.

しかしながら、高屈折率層５を壁面２ｂに形成する方法にもよるが、通常想定される方法によれば斜面２ａに形成される長さは略一定になると推定される。その場合には、図１（ｂ）に示した上記Ｌ２が０．１μｍ以上、上記Ｌ３が０．２μｍ以上であることが好ましい。また、Ｌ２が０．１μｍ以上、Ｌ３が０．２μｍ以上で、且つ、Ｌ２＜Ｌ３が好ましい。 However, although it depends on the method of forming the high refractive index layer 5 on the wall surface 2b, it is estimated that the length formed on the inclined surface 2a is substantially constant according to a generally assumed method. In that case, the L2 shown in FIG. 1B is preferably 0.1 μm or more, and the L3 is preferably 0.2 μm or more. Moreover, it is preferable that L2 is 0.1 μm or more, L3 is 0.2 μm or more, and L2 <L3.

そして、回折光学素子全体で、Ｌ２及びＬ３の合計の、斜面２ａの長さＬ１の合計に対する割合が、５％以下であることが好ましい。即ち、高屈折率層５によって阻害された斜面２ａの影響を５％以下にする、つまり設計値に対して９５％以上の回折効率を確保することを意味している。上記割合が５％を超えると、回折効率が低下して回折格子が本来要求されている色収差補正効果も小さくなり、結果的に撮影した画像は全体的にぼやけた感じになり、フレアの抑制効果も小さくなってしまう。   In the entire diffractive optical element, the ratio of the total of L2 and L3 to the total of the length L1 of the inclined surface 2a is preferably 5% or less. That is, it means that the influence of the inclined surface 2a obstructed by the high refractive index layer 5 is 5% or less, that is, a diffraction efficiency of 95% or more with respect to the design value is secured. If the above ratio exceeds 5%, the diffraction efficiency is lowered and the chromatic aberration correction effect originally required for the diffraction grating is reduced. As a result, the photographed image becomes totally blurred and the flare is suppressed. Will also get smaller.

一方で、第１の樹脂層２又は第２の樹脂層３と高屈折率層５との界面での剥離を抑制するためには、斜面２ａに占める高屈折率層５の長さＬ２，Ｌ３が長い方が好ましい。係る剥離は、例えば、温度や湿度といった環境変化による第１の樹脂層２及び第２の樹脂層３の伸縮、及び、第２の樹脂層３を形成する際の樹脂の硬化収縮による第１の樹脂層２の変形が要因となって発生する。よって、これを抑制するには、第１の樹脂層２及び第２の樹脂層３の伸縮を低減することが重要である。本発明において、第１の樹脂層２の格子山部２ｃ及び格子谷部２ｄが高屈折率層５で覆われていることで、係る伸縮が制限され、結果として、これら樹脂層２，３と高屈折率層５の界面における剥離を抑制することが可能となる。   On the other hand, in order to suppress peeling at the interface between the first resin layer 2 or the second resin layer 3 and the high refractive index layer 5, the lengths L2 and L3 of the high refractive index layer 5 occupying the inclined surface 2a. Is longer. Such peeling is, for example, the first expansion and contraction of the first resin layer 2 and the second resin layer 3 due to an environmental change such as temperature and humidity, and the first curing and shrinkage of the resin when the second resin layer 3 is formed. The deformation is caused by the deformation of the resin layer 2. Therefore, in order to suppress this, it is important to reduce the expansion and contraction of the first resin layer 2 and the second resin layer 3. In the present invention, the lattice peaks 2c and the lattice valleys 2d of the first resin layer 2 are covered with the high refractive index layer 5, so that the expansion and contraction is limited. As a result, the resin layers 2, 3 and It is possible to suppress peeling at the interface of the high refractive index layer 5.

図２は、図１の壁面２ｂ、３ｂ近傍を拡大した図であり、図中のαは、厚さ方向断面において、第１の樹脂層２の格子山部２ｃのなす角度、βは第１の樹脂層２の格子谷部２ｄのなす角度を示している。また、ｈ１は、第１の樹脂層２の格子山部２ｃから第２のベース基板４までの距離（格子山部２ｃにおける第２の樹脂層３の厚さ）、ｈ２は第１の樹脂層２の格子谷部２ｄから第２のベース基板４までの距離（格子谷部２ｄにおける第２の樹脂層３の厚さ）である。尚、図２において、高屈折率層５は便宜上、省略した。 FIG. 2 is an enlarged view of the vicinity of the wall surfaces 2b and 3b of FIG. 1, in which α is the angle formed by the lattice peak 2c of the first resin layer 2 in the thickness direction cross section, and β is the first The angle formed by the lattice valley portions 2d of the resin layer 2 is shown. H1 is the distance from the lattice peak 2c of the first resin layer 2 to the second base substrate 4 (the thickness of the second resin layer 3 at the lattice peak 2c), and h2 is the first resin layer. 2 is the distance (the thickness of the second resin layer 3 in the lattice valley portion 2d) from the two lattice valley portions 2d to the second base substrate 4. In FIG. 2, the high refractive index layer 5 is omitted for convenience.

本例のように、レリーフパターンが入射した光を所望の位置に結像させる斜面２ａと、光学素子としては作用しない壁面２ｂとで構成されている回折格子の場合、（０＜）α≦１２０°、（２１０＜）β≦２７０°の範囲になることが一般的である。この様な形状の回折格子においては、格子谷部２ｄでは広角での収縮が１点に集中しており、格子山部２ｃに比較して大きな応力が発生する傾向にある。更にｈ１＜ｈ２の関係より、第２の樹脂層３を形成する際の樹脂材料の硬化収縮量の影響は、格子山部２ｃよりも格子谷部２ｄの方が大きくなる。つまり、格子山部２ｃに比較して格子谷部２ｄでは、応力が大きくなる傾向があり、第１の樹脂層２と高屈折率層５との界面での剥離が発生し易くなる。よって、斜面２ａにまで連続的に形成される高屈折率層５は、格子山部２ｃよりも格子谷部２ｄの方を長くすることが好ましく、具体的にはＬ２≧０．１μｍ、Ｌ３≧０．２μｍとすることで、層間での剥離を効果的に抑制し得ることが判った。   As in this example, in the case of a diffraction grating composed of a slope 2a that forms an image of light incident on a relief pattern at a desired position and a wall surface 2b that does not act as an optical element, (0 <) α ≦ 120 In general, it is in the range of (210 <) β ≦ 270 °. In the diffraction grating having such a shape, the wide-angle contraction is concentrated at one point in the lattice valley portion 2d, and a large stress tends to be generated as compared with the lattice peak portion 2c. Furthermore, from the relationship of h1 <h2, the influence of the curing shrinkage amount of the resin material when forming the second resin layer 3 is larger in the lattice valley portion 2d than in the lattice mountain portion 2c. That is, in the lattice valley portion 2d as compared with the lattice peak portion 2c, the stress tends to increase, and peeling at the interface between the first resin layer 2 and the high refractive index layer 5 is likely to occur. Therefore, in the high refractive index layer 5 continuously formed up to the inclined surface 2a, it is preferable to make the lattice valley portion 2d longer than the lattice peak portion 2c. Specifically, L2 ≧ 0.1 μm, L3 ≧ It was found that by setting the thickness to 0.2 μm, peeling between layers can be effectively suppressed.

高屈折率層５の材料としては、樹脂層２，３を構成する材料にもよるが、これらの樹脂材料よりも高い屈折率を有していることと低い線膨張係数を有していることが重要である。高屈折率層５はその屈折率にもよるが膜厚は最大でも数百ｎｍの薄膜であり、設計からの形状ズレに関しても数十ｎｍレベルである。更に、設計によるが材料屈折率の許容ズレも０．０５以下程度であることを考慮すると、高屈折率層の形成には真空成膜プロセスが想定される。しかしながら、レンズなどの曲面に成膜する場合には、入射する角度によって屈折率が大きく変化してしまい、所望の効果が得られなくなる懸念がある。屈折率の成膜角依存は材料としての特性もあるが、狙い屈折率にも依存する。正対入射で成膜した時は、材料本来が持つ密度、屈折率になるが、入射角度が浅くなるにつれて密度が小さくなり、結果的に屈折率も小さくなる。正対入射時に高い屈折率を有する材料ほど、その変化が大きくなるので、安定的に製造する観点からは正対入射時の屈折率は高くない方が良い。樹脂で形成された回折格子間で導波路の効果を持ち、製造安定性も得られる屈折率範囲としては、正対入射時に１．６以上２．１以下程度までの無機材料が好適に使用される。無機材料として具体的にはＡｌ2Ｏ3、ＨｆＯ2、ＺｒＯ2、Ｌａ2Ｏ3、などのガラス材料成分が挙げられ、更にその二種以上の混合物なども好適に使用される。 The material of the high refractive index layer 5 depends on the material constituting the resin layers 2 and 3, but has a higher refractive index and a lower linear expansion coefficient than these resin materials. is important. Although depending on the refractive index, the high refractive index layer 5 is a thin film having a thickness of several hundred nm at the maximum, and the shape deviation from the design is on the order of several tens of nm. Furthermore, considering that the allowable deviation of the refractive index of the material is about 0.05 or less depending on the design, a vacuum film forming process is assumed to form the high refractive index layer. However, when a film is formed on a curved surface such as a lens, the refractive index changes greatly depending on the incident angle, and there is a concern that a desired effect cannot be obtained. Although the dependence of the refractive index on the film formation angle has characteristics as a material, it also depends on the target refractive index. When the film is formed with normal incidence, the density and refractive index inherent to the material are obtained. However, as the incident angle becomes shallower, the density becomes smaller and consequently the refractive index becomes smaller. A material having a higher refractive index at the time of front-facing incidence has a larger change, so that the refractive index at the time of front-facing incidence should not be high from the viewpoint of stable production. As a refractive index range that has the effect of a waveguide between diffraction gratings made of resin and that also provides manufacturing stability, an inorganic material of 1.6 to 2.1 is preferably used at the time of normal incidence. The Specific examples of the inorganic material include glass material components such as Al 2 O 3 , HfO 2 , ZrO 2 , La 2 O 3 , and a mixture of two or more thereof is also preferably used.

ここで、図１に例示した回折光学素子の製造方法の一例について図３乃至図５を用いて説明するが、本発明の回折光学素子は、その性能を満足するものであれば、係る製造方法には限定されない。
第１のベース基板１上に第１の樹脂層２をレプリカ法で成形する。具体的には、第１の樹脂材料１１を滴下したベース基板１（図３（ａ））を所望の形状を有する金型１２の上に配置して樹脂材料１１をベース基板１と金型１２の間に充填させる（図３（ｂ））。次いで、紫外線光源１３によってベース基板１を通して第１の樹脂材料１１を硬化させて（図３（ｃ））、所望の形状を有する第１の樹脂層２をベース基板１の上に形成する。ベース基板１と一体化した第１の樹脂層２を金型１２から外し（図４（ｄ））、更に、オーブン中で加熱処理することにより、樹脂を完全に硬化させる。 Here, an example of a method for manufacturing the diffractive optical element illustrated in FIG. 1 will be described with reference to FIGS. 3 to 5. If the diffractive optical element of the present invention satisfies the performance, such a manufacturing method will be described. It is not limited to.
The first resin layer 2 is formed on the first base substrate 1 by a replica method. Specifically, the base substrate 1 onto which the first resin material 11 is dropped (FIG. 3A) is placed on a mold 12 having a desired shape, and the resin material 11 is placed on the base substrate 1 and the mold 12. (FIG. 3B). Next, the first resin material 11 is cured through the base substrate 1 by the ultraviolet light source 13 (FIG. 3C), and the first resin layer 2 having a desired shape is formed on the base substrate 1. The first resin layer 2 integrated with the base substrate 1 is removed from the mold 12 (FIG. 4 (d)), and further heat-treated in an oven to completely cure the resin.

次に、第１の樹脂層２の壁面に高屈折率層５を形成する。第１の樹脂層２の全面にリフトオフ用のネガ型レジストを塗布し、壁面に水平な方向（レンズ光軸方向）から紫外線を照射した後、炭酸ナトリウム溶液中で現像を行う。壁面では、壁面に水平な方向での膜厚が厚いため、十分な照射量が得られず、また格子谷部では壁面の影響を受けて十分な照射量が得られないため、レジストは現像されてしまう。また、格子山部では十分な照射は得られるが、形状的に現像液の置換効率が高くなるため、他の場所に比べてエッチングレートが大きくなる。よって、紫外線照射量と現像時間を最適化することでレジスト１４の残膜率を調整し、壁面及び格子山部、格子谷部ではレジストが現像されて残存していない状態にする（図４（ｅ））。レジストパターニングが完了した第１の樹脂層２を蒸着装置に入れ、壁面に正対する方向から高屈折率層材料１５を成膜した（図４（ｆ））後、強アルカリ溶液中でレジスト１４を剥離する。これにより、第１の樹脂層２の壁面及び斜面の一部にまで連続的に形成された高屈折率層５が得られる（図５（ｇ））。   Next, the high refractive index layer 5 is formed on the wall surface of the first resin layer 2. A negative resist for lift-off is applied to the entire surface of the first resin layer 2, and ultraviolet light is irradiated on the wall surface from the horizontal direction (lens optical axis direction), followed by development in a sodium carbonate solution. On the wall surface, the film thickness in the direction parallel to the wall surface is thick, so a sufficient dose cannot be obtained, and in the lattice valleys, a sufficient dose cannot be obtained due to the influence of the wall surface. End up. In addition, although sufficient irradiation can be obtained at the lattice peaks, since the replacement efficiency of the developer is high in shape, the etching rate is higher than in other places. Therefore, the residual film ratio of the resist 14 is adjusted by optimizing the ultraviolet irradiation amount and the development time, so that the resist is developed and does not remain on the wall surfaces, lattice peaks, and lattice valleys (FIG. 4 ( e)). The first resin layer 2 having undergone resist patterning is placed in a vapor deposition apparatus, and a high refractive index layer material 15 is formed from the direction facing the wall surface (FIG. 4 (f)), and then the resist 14 is formed in a strong alkaline solution. Peel off. Thereby, the high refractive index layer 5 continuously formed to the wall surface of the 1st resin layer 2 and a part of slope is obtained (FIG.5 (g)).

最後に、上記の第１の樹脂層２と第２のベース基板４との間に第２の樹脂材料１６を充填し、第２のベース基板４を通して紫外線光源１３より紫外線を照射し（図５（ｈ））、樹脂材料１６を硬化させることで第２の樹脂層３を得ることができる。これにより、密着二層型の回折光学素子が得られる。
本発明の回折光学素子は、種々の光学機器に用いられ、具体的には、静止画像を撮影するカメラや動画を撮影するビデオカメラ、顕微鏡、内視鏡が挙げられる。 Finally, the second resin material 16 is filled between the first resin layer 2 and the second base substrate 4, and ultraviolet rays are irradiated from the ultraviolet light source 13 through the second base substrate 4 (FIG. 5). (H)) The second resin layer 3 can be obtained by curing the resin material 16. Thereby, a close-contact two-layer type diffractive optical element is obtained.
The diffractive optical element of the present invention is used in various optical instruments, and specifically includes a camera that captures still images, a video camera that captures moving images, a microscope, and an endoscope.

図６は、本発明の光学機器の好適な実施形態の一例である一眼レフカメラの交換レンズ鏡筒の光学系の断面図である。レンズ鏡筒３０は筐体３１とその内部に光学系を有する。光学系は、レンズ２１乃至２９及び回折光学素子２０が光軸Ｏに対して垂直に配列されている。ここでレンズ２１側が光学系の入射光側であり、レンズ２９側がカメラとの着脱マウント側である。本発明の回折光学素子２０を光学系の適切な位置に配置させることにより、色収差を低減した小型かつ軽量のレンズ鏡筒を提供することができる。また、図６のように回折光学素子２０をレンズ２１の内側に設けることにより、回折光学素子２０に外光が直接当たることを防止できるため、フレアの発生を抑制することができる。 FIG. 6 is a cross-sectional view of an optical system of an interchangeable lens barrel of a single-lens reflex camera that is an example of a preferred embodiment of the optical apparatus of the present invention. The lens barrel 30 has a housing 31 and an optical system therein. In the optical system, lenses 21 to 29 and a diffractive optical element 20 are arranged perpendicular to the optical axis O. Here, the lens 21 side is the incident light side of the optical system, and the lens 29 side is the detachable mount side with respect to the camera. By disposing the diffractive optical element 20 of the present invention at an appropriate position in the optical system, a small and lightweight lens barrel with reduced chromatic aberration can be provided. Further, by providing the diffractive optical element 20 inside the lens 21 as shown in FIG. 6, it is possible to prevent external light from directly hitting the diffractive optical element 20, so that the occurrence of flare can be suppressed.

（実施例１、比較例１）
図１に例示した密着二層型の回折光学素子を、図３乃至図５に示した工程で作製した。凸形状を有する第１のベース基板１と凹形状を有する第２のベース基板４は、いずれもホウ素とシリコンを含有した光学ガラス（（株）オハラ製「Ｓ−ＢＳＬ７」）レンズであり、大きさはベース基板１がφ５８ｍｍ、ベース基板４がφ６１ｍｍのものを準備した。 (Example 1, Comparative Example 1)
The close-contact two-layered diffractive optical element illustrated in FIG. 1 was produced by the steps shown in FIGS. The first base substrate 1 having a convex shape and the second base substrate 4 having a concave shape are both optical glass (“S-BSL7” manufactured by OHARA INC.) Lenses containing boron and silicon. A base substrate 1 having a diameter of 58 mm and a base substrate 4 having a diameter of 61 mm was prepared.

第１のベース基板１と第２のベース基板４の間には、第１のベース基板１側から第１の樹脂層２、第２の樹脂層３が形成されている。第１の樹脂層２は、不飽和官能基を有するウレタン変性ポリエステルアクリレートとジシクロペンテニルオキシエチルメタクリレートを主成分とする紫外線硬化型アクリル樹脂に酸化インジウム錫微粒子を分散させた紫外線硬化型樹脂で形成した。第２の樹脂層３は、不飽和官能基を有するウレタン変性ポリエステルアクリレートとジシクロペンテニルオキシエチルメタクリレートを主成分とする紫外線硬化型アクリル樹脂に酸化ジルコニア微粒子を分散させて用いた。第１の樹脂層２、第２の樹脂層３の屈折率は、ｄ線基準でそれぞれ１．５７と１．６２であった。第１の樹脂層２の格子高さは１０μｍであり、隣接する格子の間隔は光軸中心から円の外周に近づくに従って３．０ｍｍから０．１ｍｍまで徐々に小さくなっており、壁面の数は全部で８０である。   A first resin layer 2 and a second resin layer 3 are formed between the first base substrate 1 and the second base substrate 4 from the first base substrate 1 side. The first resin layer 2 is formed of an ultraviolet curable resin in which indium tin oxide fine particles are dispersed in an ultraviolet curable acrylic resin mainly composed of urethane-modified polyester acrylate having an unsaturated functional group and dicyclopentenyloxyethyl methacrylate. did. The second resin layer 3 was used by dispersing zirconia oxide fine particles in an ultraviolet curable acrylic resin mainly composed of urethane-modified polyester acrylate having an unsaturated functional group and dicyclopentenyloxyethyl methacrylate. The refractive indexes of the first resin layer 2 and the second resin layer 3 were 1.57 and 1.62 on the d-line basis, respectively. The grid height of the first resin layer 2 is 10 μm, and the interval between adjacent grids gradually decreases from 3.0 mm to 0.1 mm as it approaches the outer circumference of the circle from the center of the optical axis, and the number of wall surfaces is 80 in total.

本実施例の高屈折率層５は、Ａｌ2Ｏ3とＺｒＯ2の混合酸化物であり、ｄ線基準での屈折率が１．７０で、厚さは１７０ｎｍとした。高屈折率層５が斜面２ａに占める長さは、第１の樹脂層２の格子山部２ｃに隣接した面内ではＬ２＝０．２５μｍであり、格子谷部２ｄに隣接した面内ではＬ３＝０．３５μｍであった。この時の、Ｌ２及びＬ３の合計が、斜面２ａの長さＬ１の合計に対する割合は０．２８％であった。 The high refractive index layer 5 of this example is a mixed oxide of Al 2 O 3 and ZrO 2 , the refractive index on the d-line basis is 1.70, and the thickness is 170 nm. The length of the high refractive index layer 5 occupying the inclined surface 2a is L2 = 0.25 μm in the plane adjacent to the lattice peak 2c of the first resin layer 2, and L3 in the plane adjacent to the lattice valley 2d. = 0.35 μm. At this time, the ratio of the total of L2 and L3 to the total of the length L1 of the slope 2a was 0.28%.

本実施例の回折光学素子をフレア測定用に改造を施した撮像光学系（キヤノン（株）製 ＥＦレンズ鏡筒）に組み込んで、壁面によるフレアの測定を行った。壁面によるフレアの測定は、光軸中心から数えて１０番目の輪帯の格子部分にのみ赤（６３５ｎｍ）、緑（５３２ｎｍ）、青（４７３ｎｍ）のレーザー光線を入射させ、得られる回折光をＣＣＤで捉えて、入射した光に対する不要回折光の割合として算出した。レーザー光線は、昭和オプトロニクス（株）製のレーザー「ＪＵＮＯ−Ｃｏｍｐａｃｔ」を用いて照射した。本実施例の回折光学素子では、＋１次回折光を使用する設計なので、それ以外の回折光は設計想定外の不要光であるが、有効画素内で結像してしまうのは０、＋２次光、−１、＋３次光の位置に現れる回折光であるため、その不要回折光量を測定することとした。具体的には、ＣＣＤセンサーの直前に０、＋２次光、−１、＋３次光のみを透過させるスリットを配することで、ＣＣＤセンサーに入射する光は所望の回折光のみである状態を作った。尚、測定の精度を保証するため、測定は温度が２３±０．５℃、湿度が５０±１０％の環境下で実施し、更に外部の光の影響を無くすために、実験系は遮光幕の中に設定した。測定の結果、本実施例の回折光学素子の壁面によるフレアは０．００２％であった。 The diffractive optical element of this example was incorporated into an imaging optical system (an EF lens barrel manufactured by Canon Inc.) modified for flare measurement, and flare measurement was performed on the wall surface. The flare is measured by the wall surface by making red (635 nm), green (532 nm), and blue (473 nm) laser beams incident only on the lattice portion of the tenth ring zone counted from the center of the optical axis. And calculated as a ratio of unnecessary diffracted light to incident light. The laser beam was irradiated using a laser “JUNO-Compact” manufactured by Showa Optronics. Since the diffractive optical element of this embodiment is designed to use + 1st order diffracted light, the other diffracted light is unnecessary light that is not designed, but it is 0, + second order light that forms an image within the effective pixel. Since the diffracted light appears at the positions of −1, + 3rd order light, the amount of unnecessary diffracted light is measured. Specifically, by providing a slit that transmits only the 0, + second order light, −1, +3 order light immediately before the CCD sensor, the light incident on the CCD sensor is only the desired diffracted light. It was. In order to guarantee the accuracy of the measurement, the measurement is performed in an environment where the temperature is 23 ± 0.5 ° C. and the humidity is 50 ± 10%. Further, in order to eliminate the influence of external light, the experimental system is a light-shielding curtain. Set in. As a result of the measurement, the flare due to the wall surface of the diffractive optical element of this example was 0.002%.

また、回折光学素子の回折効率を測定した。具体的には、格子間隔が１００μｍとなる領域に光軸方向から回折光学素子に光を入射させて、回折光の出射側に設計次数の回折光のみを通過させるスリットを配して、分光光度計で回折光量を計測し、回折光量の入射光に対する比率として回折効率とした。分光光度計としては、（株）日立ハイテクノロジーズ製の分光光度計「Ｕ−４０００」を用いた。測定の結果、本実施例における回折効率は９８．７％以上となった。   Further, the diffraction efficiency of the diffractive optical element was measured. Specifically, light is incident on the diffractive optical element from the direction of the optical axis in a region where the grating interval is 100 μm, and a slit that allows only the diffracted light of the designed order to pass is disposed on the diffracted light emission side, and the spectrophotometer The diffracted light quantity was measured with a meter, and the diffraction efficiency was defined as the ratio of the diffracted light quantity to the incident light. A spectrophotometer “U-4000” manufactured by Hitachi High-Technologies Corporation was used as the spectrophotometer. As a result of the measurement, the diffraction efficiency in this example was 98.7% or more.

比較例１として、壁面に高屈折率層５が形成されていないこと以外は、上記と全く同様の回折光学素子を準備し、上記と同様のフレア測定と回折効率測定を行ったところ、壁面によるフレアは０．０１８％であり、回折効率は９９．０％以上であった。
よって、本実施例では、高屈折率層５の形成により、回折効率の低下を抑えながら、壁面によるフレアを１／９にまで減少させることができた。 As Comparative Example 1, a diffractive optical element exactly the same as described above was prepared except that the high refractive index layer 5 was not formed on the wall surface, and flare measurement and diffraction efficiency measurement were performed as described above. The flare was 0.018%, and the diffraction efficiency was 99.0% or more.
Therefore, in this example, the formation of the high refractive index layer 5 was able to reduce the flare caused by the wall surface to 1/9 while suppressing a decrease in diffraction efficiency.

本実施例の回折光学素子に対して、耐久試験として熱衝撃試験（−４０℃と４０℃にそれぞれ２０分維持を３０サイクル）を実施した後に上記と同様のフレア測定と回折効率測定を行った。その結果、壁面によるフレアは０．００２％であり、回折効率は９８．８％以上となり、熱衝撃試験前後での光学特性に変化は認められなかった。また、外観上も特に変化は認められなかった。
回折光学素子の形状は成形段階で干渉計（Ｚｙｇｏ社製 ３次元光学プロファイラ「Ｎｅｗ−Ｖｉｅｗ」）を使用して計測したものであり、高屈折率層５の形状に関しては、熱衝撃試験完了後に切断して断面をＳＥＭ（Ｓｃａｎｎｎｉｎｇ Ｅｌｅｃｔｒｏｎ Ｍｉｃｒｏｓｃｏｐｅ）によって観察、測定した結果である。 For the diffractive optical element of this example, a thermal shock test (30 cycles of 20 minutes at -40 ° C. and 40 ° C., respectively) was performed as a durability test, and then the same flare measurement and diffraction efficiency measurement were performed. . As a result, the flare caused by the wall surface was 0.002%, the diffraction efficiency was 98.8% or more, and no change was observed in the optical characteristics before and after the thermal shock test. Also, no particular change was observed in appearance.
The shape of the diffractive optical element was measured by using an interferometer (three-dimensional optical profiler “New-View” manufactured by Zygo) at the molding stage, and the shape of the high refractive index layer 5 was measured after completion of the thermal shock test. It is the result of cutting and observing and measuring the cross section with SEM (Scanning Electron Microscope).

（実施例２、比較例２）
第１のベース基板１がφ３４ｍｍ、第２のベース基板４がφ３８ｍｍのものを用い、実施例１と同様にして第１の樹脂層２及び第２の樹脂層３を形成して密着二層型の回折光学素子を作製した。第１の樹脂層２及び第２の樹脂層３の屈折率は、ｄ線基準でそれぞれ１．５７と１．６２であった。第１の樹脂層２の格子高さは１０μｍであり、隣接する格子の間隔は光軸中心から円の外周に近づくに従って３．９ｍｍから０．２ｍｍまで徐々に小さくなっており、壁面の数は全部で６５である。 (Example 2, comparative example 2)
A first base substrate 1 having a diameter of 34 mm and a second base substrate 4 having a diameter of 38 mm is used, and the first resin layer 2 and the second resin layer 3 are formed in the same manner as in Example 1 to form a close-contact two-layer type. The diffractive optical element was manufactured. The refractive indexes of the first resin layer 2 and the second resin layer 3 were 1.57 and 1.62 on the d-line basis, respectively. The grid height of the first resin layer 2 is 10 μm, and the interval between adjacent grids gradually decreases from 3.9 mm to 0.2 mm from the center of the optical axis toward the outer periphery of the circle, and the number of wall surfaces is A total of 65.

本実施例の高屈折率層５は、Ａｌ2Ｏ3とＬａ2Ｏ3の混合酸化物であり、ｄ線基準での屈折率が１．６８で、厚さは１４０ｎｍとした。高屈折率層５が斜面２ａに占める長さは、第１の樹脂層２の格子山部２ｃに隣接した面内ではＬ２＝６．５μｍであり、格子谷部２ｄに隣接した面内ではＬ３＝９．０μｍであった。この時の、Ｌ２及びＬ３の合計が、斜面２ａの長さＬ１の合計に対する割合は４．９７％であった。
実施例１と同様にして、本実施例の回折光学素子を撮像光学系に組み込んで、壁面によるフレアの測定及び回折効率の測定を行った。その結果、本実施例の回折光学素子の壁面によるフレアは０．００３％、回折効率は９５．０％以上となった。 The high refractive index layer 5 of this example is a mixed oxide of Al 2 O 3 and La 2 O 3 , the refractive index on the d-line basis is 1.68, and the thickness is 140 nm. The length of the high refractive index layer 5 in the inclined surface 2a is L2 = 6.5 μm in the plane adjacent to the lattice peak 2c of the first resin layer 2, and L3 in the plane adjacent to the lattice valley 2d. = 9.0 μm. At this time, the ratio of the total of L2 and L3 to the total of the length L1 of the slope 2a was 4.97%.
In the same manner as in Example 1, the diffractive optical element of this example was incorporated in the imaging optical system, and flare measurement and diffraction efficiency measurement by the wall surface were performed. As a result, the flare due to the wall surface of the diffractive optical element of this example was 0.003%, and the diffraction efficiency was 95.0% or more.

比較例２として、壁面に高屈折率層５が形成されていないこと以外は、上記と全く同様の回折光学素子を準備し、上記と同様のフレア測定と回折効率測定を行ったところ、壁面によるフレアは０．０３０％であり、回折効率は９９．０％以上であった。
よって、本実施例では、高屈折率層５の形成により、回折効率の低下を５％以内に抑えながら、壁面によるフレアは１／１０にまで減少させることができた。 As Comparative Example 2, a diffractive optical element exactly the same as described above was prepared except that the high refractive index layer 5 was not formed on the wall surface, and flare measurement and diffraction efficiency measurement were performed as described above. The flare was 0.030%, and the diffraction efficiency was 99.0% or more.
Therefore, in this example, the formation of the high refractive index layer 5 allowed the flare caused by the wall surface to be reduced to 1/10 while suppressing the reduction in diffraction efficiency to within 5%.

本実施例の回折光学素子に対して実施例１と同様の熱衝撃試験を実施した後に、上記と同様のフレア測定と回折効率測定を行った。その結果、壁面によるフレアは０．００３％であり、回折効率は９５．０％以上となり、熱衝撃試験前後での光学特性に変化は認められなかった。また、外観上も特に変化は認められなかった。   The same thermal shock test as in Example 1 was performed on the diffractive optical element of this example, and then the flare measurement and diffraction efficiency measurement were performed in the same manner as described above. As a result, the flare due to the wall surface was 0.003%, the diffraction efficiency was 95.0% or more, and no change was observed in the optical characteristics before and after the thermal shock test. Also, no particular change was observed in appearance.

（実施例３）
斜面に占める高屈折率層５の長さを、Ｌ２＝１０μｍ、Ｌ３＝１５μｍとした以外は実施例２と同様にして密着二層型の回折光学素子を作製した。本実施例の回折光学素子において、Ｌ２及びＬ３の合計が、斜面２ａの長さＬ１の合計に対する割合は８．０２％であった。
実施例１と同様にして、本実施例の回折光学素子を撮像光学系に組み込んで、壁面によるフレアの測定及び回折効率の測定を行った。その結果、本実施例の回折光学素子の壁面によるフレアは０．００３％、回折効率は９１．８％以上となった。 (Example 3)
A close-contact two-layer diffractive optical element was produced in the same manner as in Example 2 except that the length of the high refractive index layer 5 occupying the slope was set to L2 = 10 μm and L3 = 15 μm. In the diffractive optical element of this example, the ratio of the total of L2 and L3 to the total of the length L1 of the inclined surface 2a was 8.02%.
In the same manner as in Example 1, the diffractive optical element of this example was incorporated in the imaging optical system, and flare measurement and diffraction efficiency measurement by the wall surface were performed. As a result, the flare due to the wall surface of the diffractive optical element of this example was 0.003%, and the diffraction efficiency was 91.8% or more.

比較例２（フレア：０．０３０％、回折効率：９９．０％）と比較すると、本実施例の回折光学素子は、高屈折率層５の形成により、壁面によるフレアを１／１０にまで減少させることができた。しかしながら、回折効率は斜面への成膜の影響もあり８％程度減少していた。尚、回折光学素子を使用していないレンズと比較すると、色収差が改善されており、回折光学素子として十分な性能を発揮していることが確認された。   Compared with Comparative Example 2 (flare: 0.030%, diffraction efficiency: 99.0%), the diffractive optical element of this example has a flare caused by the wall surface to 1/10 due to the formation of the high refractive index layer 5. It was possible to decrease. However, the diffraction efficiency was reduced by about 8% due to the influence of film formation on the slope. In addition, chromatic aberration was improved as compared with a lens not using a diffractive optical element, and it was confirmed that a sufficient performance as a diffractive optical element was exhibited.

本実施例の回折光学素子に対して実施例１と同様の熱衝撃試験を実施した後に上記と同様のフレア測定と回折効率測定を行った。その結果、壁面によるフレアは０．００３％であり、回折効率は９１．８％以上となり、熱衝撃試験前後での光学特性に変化は認められなかった。また、外観上も特に変化は認められなかった。   After performing the same thermal shock test as in Example 1 on the diffractive optical element of this example, the same flare measurement and diffraction efficiency measurement as described above were performed. As a result, the flare caused by the wall surface was 0.003%, the diffraction efficiency was 91.8% or more, and no change was observed in the optical characteristics before and after the thermal shock test. Also, no particular change was observed in appearance.

（比較例３）
高屈折率層５を壁面にのみ形成し、斜面に延設していない、即ちＬ２＝Ｌ３＝０とした以外は、実施例１と同様にして密着二層型の回折光学素子を作製した。
実施例１と同様にして、本比較例の回折光学素子を撮像光学系に組み込んで、壁面によるフレアの測定及び回折効率の測定を行った。その結果、本実施例の回折光学素子の壁面によるフレアは０．００２％、回折効率は９９．０％以上となった。
比較例１（フレア：０．０１８％、回折効率：９９．０％）と比較すると、高屈折率層５の形成により、回折効率の低下を抑えながら、壁面によるフレアを１／９にまで減少させることができた。 (Comparative Example 3)
A close-contact two-layer type diffractive optical element was produced in the same manner as in Example 1 except that the high refractive index layer 5 was formed only on the wall surface and was not extended on the slope, that is, L2 = L3 = 0.
In the same manner as in Example 1, the diffractive optical element of this comparative example was incorporated in an imaging optical system, and flare measurement and diffraction efficiency measurement using a wall surface were performed. As a result, the flare due to the wall surface of the diffractive optical element of this example was 0.002%, and the diffraction efficiency was 99.0% or more.
Compared with Comparative Example 1 (flare: 0.018%, diffraction efficiency: 99.0%), the formation of the high refractive index layer 5 reduces the flare caused by the wall surface to 1/9 while suppressing the decrease in diffraction efficiency. I was able to.

本比較例の回折光学素子に対して実施例１と同様の熱衝撃試験を実施した後に上記と同様のフレア測定と回折効率測定を行ったところ、回折効率は９８．９％以上となり、熱衝撃試験前後での変化は認められなかった。一方、壁面によるフレアは０．０１０％となり、フレア抑制の効果が１／２にまで低減してしまった。また、外観確認用のＬＥＤ光源を回折光学素子に照射して外観を確認したところ、耐久前には見られなかった輝線が格子の輪帯に沿って発生しているのが確認された。   When the same flare measurement and diffraction efficiency measurement as those described above were performed on the diffractive optical element of this comparative example after performing the same thermal shock test as in Example 1, the diffraction efficiency was 98.9% or more. There was no change before and after the test. On the other hand, the flare caused by the wall surface was 0.010%, and the effect of suppressing flare was reduced to ½. Further, when the appearance was confirmed by irradiating the diffractive optical element with an LED light source for appearance confirmation, it was confirmed that bright lines that were not seen before the endurance were generated along the ring zones of the lattice.

熱衝撃試験で光学性能及び外観の変化した回折光学素子を切断して、断面をＳＥＭ観察したところ、壁面で第１の樹脂層２又は第２の樹脂層３と、高屈折率層５との間での剥離が確認された。以下の表１に、上記実施例及び比較例の結果をまとめて示す。   When the diffractive optical element whose optical performance and appearance changed in the thermal shock test was cut and the cross section was observed by SEM, the first resin layer 2 or the second resin layer 3 and the high refractive index layer 5 were formed on the wall surface. Separation was confirmed. Table 1 below summarizes the results of the above examples and comparative examples.

Figure 2018136529
Figure 2018136529

１，４：ベース基板、２：第１の樹脂層、２ａ，３ａ：斜面、２ｂ，３ｂ：壁面、３：第２の樹脂層、５：高屈折率層   DESCRIPTION OF SYMBOLS 1,4: Base substrate, 2: First resin layer, 2a, 3a: Slope, 2b, 3b: Wall surface, 3: Second resin layer, 5: High refractive index layer

Claims (10)

一方の表面が、複数の段差を有する複数の壁面と、前記壁面によって区画される複数の斜面と、を有する第１の樹脂層と、
前記第１の樹脂層の、前記一方の表面側に配置され、前記第１の樹脂層側の表面が、前記第１の樹脂層の前記段差に対応する段差を有する第２の樹脂層と、
前記第１の樹脂層の壁面と前記第２の樹脂層の壁面との間に、前記第１の樹脂層及び前記第２の樹脂層よりも屈折率が高い高屈折率層を有する回折光学素子であって、
前記高屈折率層は、前記壁面から前記斜面の一部にまで設けられていることを特徴とする回折光学素子。 A first resin layer having one surface having a plurality of wall surfaces having a plurality of steps and a plurality of slopes defined by the wall surfaces;
A second resin layer disposed on the one surface side of the first resin layer, the surface on the first resin layer side having a step corresponding to the step of the first resin layer;
A diffractive optical element having a high refractive index layer having a higher refractive index than the first resin layer and the second resin layer between the wall surface of the first resin layer and the wall surface of the second resin layer. Because
The diffractive optical element, wherein the high refractive index layer is provided from the wall surface to a part of the slope. 厚さ方向断面において、前記第１の樹脂層の格子山部において、前記斜面に占める前記高屈折率層の長さが０．１μｍ以上であり、前記第１の樹脂層の格子谷部において、前記斜面に占める前記高屈折率層の長さより前記壁面に設けられた前記高屈折率層の厚さを除いた長さが０．２μｍ以上であることを特徴とする請求項１に記載の回折光学素子。   In the cross section in the thickness direction, in the lattice peak portion of the first resin layer, the length of the high refractive index layer occupying the slope is 0.1 μm or more, and in the lattice valley portion of the first resin layer, 2. The diffraction according to claim 1, wherein a length obtained by removing a thickness of the high refractive index layer provided on the wall surface from a length of the high refractive index layer occupying the slope is 0.2 μm or more. Optical element. 前記第１の樹脂層の格子山部における前記斜面に占める前記高屈折率層の長さより、前記第１の樹脂層の格子谷部における前記斜面に占める前記高屈折率層の長さより前記壁面に設けられた前記高屈折率層の厚さを除いた長さが長いことを特徴とする請求項２に記載の回折光学素子。   From the length of the high refractive index layer occupying the slope in the lattice peak portion of the first resin layer, to the wall surface from the length of the high refractive index layer occupying the slope in the lattice valley portion of the first resin layer. The diffractive optical element according to claim 2, wherein a length excluding a thickness of the high refractive index layer provided is long. 厚さ方向断面において、前記斜面に占める前記高屈折率層の長さより前記壁面に形成された前記高屈折率層の厚さを除いた長さの合計が、前記斜面の長さの合計の５％以下であることを特徴とする請求項１乃至３のいずれか１項に記載の回折光学素子。   In the cross section in the thickness direction, the total length excluding the thickness of the high refractive index layer formed on the wall surface from the length of the high refractive index layer occupying the slope is 5 times the total length of the slope. The diffractive optical element according to any one of claims 1 to 3, wherein the diffractive optical element is not more than%. 前記段差は、同心円状に設けられていることを特徴とする請求項１乃至４のいずれか１項に記載の回折光学素子。 The step, the diffraction optical element according to any one of claims 1 to 4, characterized in that provided concentrically. 前記第１の樹脂層の他方の表面側に第１のベース基板を有することを特徴とする請求項１乃至５のいずれか１項に記載の回折光学素子。   The diffractive optical element according to claim 1, further comprising a first base substrate on the other surface side of the first resin layer. 前記第２の樹脂層の前記第１の樹脂層とは反対側の表面側に第２のベース基板を有していることを特徴とする請求項６に記載の回折光学素子。   The diffractive optical element according to claim 6, further comprising a second base substrate on a surface side of the second resin layer opposite to the first resin layer. 前記高屈折率層が、無機材料からなることを特徴とする請求項１乃至７のいずれか１項に記載の回折光学素子。   The diffractive optical element according to claim 1, wherein the high refractive index layer is made of an inorganic material. 前記無機材料が、Ａｌ2Ｏ3、ＨｆＯ2、ＺｒＯ2、Ｌａ2Ｏ3のうちの一種或いは二種以上の混合物であることを特徴とする請求項８に記載の回折光学素子。 The diffractive optical element according to claim 8 , wherein the inorganic material is one or a mixture of two or more of Al 2 O 3 , HfO 2 , ZrO 2 , and La 2 O 3 . 請求項１乃至９のいずれか１項に記載の回折光学素子を、色収差を補正するためのレンズとして用いることを特徴とする光学機器。   10. An optical apparatus using the diffractive optical element according to claim 1 as a lens for correcting chromatic aberration.
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