JP4393252B2 - Diffractive optical element and optical system having the same - Google Patents
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Description
本発明は、回折光学素子及びそれを有する光学系に関し、例えば複数の波長、あるいは帯域光で使用するデジタルカメラ、ビデオカメラ、フィルム用カメラ、望遠鏡、双眼鏡等の各種の光学機器に好適なものである。 The present invention relates to a diffractive optical element and an optical system having the diffractive optical element, and is suitable for various optical devices such as a digital camera, a video camera, a film camera, a telescope, and binoculars used with a plurality of wavelengths or band lights. is there.
従来より、分散の異なる複数の硝材の組み合わせにより光学系の色収差を減じる方法に対して、レンズ面やあるいは光学系の１部に回折作用を有する回折光学素子（以下回折格子とも言う）を設けることで、色収差を減じる方法が知られている（非特許文献１、特許文献１〜３）。これは、光学系中の屈折面と回折面とでは、ある基準波長の光線に対する色収差の出方が逆方向に発現するという物理現象を利用したものである。 Conventionally, a diffractive optical element (hereinafter also referred to as a diffraction grating) having a diffractive action is provided on a lens surface or a part of an optical system, in contrast to a method of reducing chromatic aberration of an optical system by combining a plurality of glass materials having different dispersions. Thus, a method of reducing chromatic aberration is known (Non-patent Document 1, Patent Documents 1 to 3). This utilizes a physical phenomenon in which chromatic aberration with respect to a light beam having a certain reference wavelength appears in the opposite direction between the refracting surface and the diffractive surface in the optical system.
さらに、このような回折光学素子は、その周期的構造の周期を変化させることで非球面レンズ的な効果をも持たせることができ収差の低減に大きな効果がある。 Furthermore, such a diffractive optical element can have an aspherical lens effect by changing the period of the periodic structure, and has a great effect on reducing aberrations.
ここで、屈折においては、１本の光線は屈折後も１本の光線であるのに対し、回折においては１本の光線が、各次数の複数の光に分かれてしまう。そこで、レンズ系の一要素として回折光学素子を用いる場合には、使用波長領域の光束が１つの特定次数（以後設計次数とも言う）に集中するように格子構造を決定する必要がある。 Here, in refraction, one light beam is still one light after refraction, but in diffraction, one light beam is divided into a plurality of lights of each order. Therefore, when a diffractive optical element is used as one element of the lens system, it is necessary to determine the grating structure so that the luminous flux in the used wavelength region is concentrated in one specific order (hereinafter also referred to as a design order).
そこで、一般的に図２５に示すように、レンズと同様に用いられる回折光学素子（回折レンズ）１は、格子面４と、格子側面５から構成されるブレーズ構造より成っている。このような、ブレーズ構造の回折光学素子１は、特定の回折次数と、特定の波長に対して、高い効率で光を回折できる。しかしながらその一方で、格子側面５に入射した光束は、格子側面５で反射、屈折など格子面４と異なる振る舞いをするため、回折レンズとしては、不要な光となり好ましくない。 Therefore, as shown in FIG. 25, a diffractive optical element (diffractive lens) 1 generally used in the same manner as a lens has a blazed structure including a grating surface 4 and a grating side surface 5. Such a blazed diffractive optical element 1 can diffract light with high efficiency for a specific diffraction order and a specific wavelength. However, on the other hand, the light beam incident on the grating side surface 5 behaves differently from the grating surface 4 such as reflection and refraction at the grating side surface 5, so that it becomes unnecessary light as a diffractive lens.
そこで、この格子側面５での不要光を抑制するようにした回折光学素子が知られている（特許文献４〜６）。 Therefore, diffractive optical elements are known that suppress unnecessary light on the grating side surface 5 (Patent Documents 4 to 6).
図２６はＵＳＰ５８０１８８９で提案されている回折光学素子を有した光学系の要部概略図である。図２６においては、光学系に回折光学素子を配置する際に、格子側面５に入射光束が当たりにくいように、格子溝を連ねた包絡面７の曲率と格子側面５の角度を最適化している。尚、図２６において、４０は絞り、４１は像面である。図２６では、特定の入射角に対して最適な側面形状を与える方法として、入射角に概平行となるように格子側面５を形成している。 FIG. 26 is a schematic view of the essential part of an optical system having a diffractive optical element proposed in US Pat. No. 5,801,889. In FIG. 26, when the diffractive optical element is arranged in the optical system, the curvature of the envelope surface 7 with the grating grooves and the angle of the grating side surface 5 are optimized so that the incident light beam does not easily hit the grating side surface 5. . In FIG. 26, 40 is a stop, and 41 is an image plane. In FIG. 26, as a method of giving an optimum side shape for a specific incident angle, the grating side surface 5 is formed so as to be approximately parallel to the incident angle.
また、特開平１０−２６８１１５号公報や、特開平２００３−２９４９２４号公報でも、同様に入射光または、射出角が格子側面で、ケラレないように配置する構成であるため、本質的に格子側面で発生する不要光を低減する考え方は同じである。 Also, in Japanese Patent Laid-Open No. 10-268115 and Japanese Patent Laid-Open No. 2003-294924, the configuration is such that the incident light or the emission angle is arranged on the grating side surface so that there is no vignetting. The idea of reducing the unnecessary light generated is the same.
上記、従来例のように、格子側面を、入射光の方向に概平行に形成されるのは、格子側面での不要光を抑制する手段として好ましいが、様々な形状の回折格子を含む回折光学素子を考えた場合、入射角と概平行方向に格子側面を形成できない場合が発生する。以下、順をおって説明する。 As described above, it is preferable to form the grating side surface substantially parallel to the direction of the incident light as in the conventional example as a means for suppressing unnecessary light on the grating side surface, but the diffractive optics including diffraction gratings of various shapes. Considering the element, there are cases where the grating side face cannot be formed in a direction substantially parallel to the incident angle. Hereinafter, it will be described in order.
回折光学素子の製法としては、型を作成し、型から複製を行なうことで回折光学素子を製造するのが、量産性、コストの観点から一般的である。このような製法を前提とした場合、型から回折光学素子を良好に形状を転写しながら離型できる形状には制約がある。今図２５に示すような、同心円形状の回折格子部より成る回折光学素子を、型から離型する場合、図３１（Ａ）で示したように、成形用型８を用い、外周の１箇所を起点Ｓとし、反対側の外周を離型の終点Ｅとする。そうすると、格子形状にもよるが、回折面４と格子側面５には特定の方向に図３２に示すような変形が発生し、光学性能上問題となる。図３０に示す回折格子の格子形状では、回折光学素子の中心から離型終点方向の格子形状に変形が発生しやすい。そこで、格子形状の変形を発生しないためには、図３１（Ｂ）で示したように、外周部全域を離型起点Ｓとし、中心部が離型終点Ｅとなるように、離型を行なっていくことが必要となってくる。このような離型方法では、微小領域では、回折光学素子が面法線方向に離型されていると見なすことができる。 As a manufacturing method of a diffractive optical element, it is common from the viewpoint of mass productivity and cost to manufacture a diffractive optical element by creating a mold and replicating from the mold. When such a manufacturing method is assumed, there is a limitation on the shape in which the diffractive optical element can be released while the shape is transferred from the mold. When the diffractive optical element composed of the concentric diffraction grating part as shown in FIG. 25 is released from the mold, as shown in FIG. Is the starting point S and the outer periphery on the opposite side is the releasing end point E. Then, although depending on the grating shape, the diffractive surface 4 and the grating side surface 5 are deformed as shown in FIG. 32 in a specific direction, which causes a problem in optical performance. In the grating shape of the diffraction grating shown in FIG. 30, deformation tends to occur in the grating shape from the center of the diffractive optical element toward the release end point. Therefore, in order to prevent the deformation of the lattice shape, as shown in FIG. 31 (B), the mold is released so that the entire outer peripheral portion is the release start point S and the center is the release end point E. It is necessary to continue. In such a mold release method, it can be considered that the diffractive optical element is released in the surface normal direction in a minute region.
このような、比較的一般に用いられている回折光学素子の製法では、図３０に示すような凸面に正のパワー（焦点距離の逆数）の回折格子部３を付加したような形状で、格子側面５が光軸Ｏに平行な方向となるような回折光学素子１は格子形状の変形という観点から製造上かなり困難な形状である。従って、凸面に正のパワーの回折格子部を付加したような形状では、図２３に示すように格子側面５は凸面の面法線６ａ方向に概平行となる構成となる。このような形状にすることで、図３１（Ｂ）に示した離型方法で、格子変形は大幅に改善される。 In such a relatively commonly used method for manufacturing a diffractive optical element, the side surface of the grating is shaped like a diffraction surface 3 having a positive power (reciprocal of focal length) added to the convex surface as shown in FIG. The diffractive optical element 1 in which 5 is in a direction parallel to the optical axis O has a considerably difficult shape in manufacturing from the viewpoint of deformation of the grating shape. Therefore, in a shape in which a positive power diffraction grating portion is added to the convex surface, the grating side surface 5 is substantially parallel to the surface normal 6a direction of the convex surface as shown in FIG. By adopting such a shape, the lattice deformation is greatly improved by the mold release method shown in FIG.
図３４はこのときの成形型８と回折光学素子１の成形における離型方法を示す概略図である。
図３３に示す形状の回折光学素子は、図から明らかのように、回折光学素子１に、光軸Ｏに近い方向（図中ａ）から光束が入射すると、格子側面５で不要光が発生し、これを抑制することが難しい。回折光学素子の製作に問題がなく、従来の構成が適用できるのは、図３３中の光軸Ｏに離れた側から光軸Ｏ側に進むｂの方向から光が入射する場合であるが、ｂの方向からの光束が通常、結像に寄与することは稀である。 As is clear from the drawing, the diffractive optical element having the shape shown in FIG. 33 generates unnecessary light on the grating side surface 5 when a light beam enters the diffractive optical element 1 from a direction close to the optical axis O (a in the figure). It is difficult to suppress this. There is no problem in the production of the diffractive optical element, and the conventional configuration can be applied when light is incident from the direction b traveling from the side away from the optical axis O to the optical axis O side in FIG. The light flux from the direction b usually rarely contributes to image formation.
また、この不要光の発生は、上述した１種類の回折格子から構成される回折光学素子だけでなく、積層構造の回折光学素子にも当てはまる。積層構造の回折光学素子は、回折格子の数も増え、回折格子の格子高さも高くなる傾向にあるので、不要光の発生はより多くなってくる。 The generation of unnecessary light applies not only to the above-described diffractive optical element composed of one type of diffraction grating, but also to a diffractive optical element having a laminated structure. In a diffractive optical element having a laminated structure, the number of diffraction gratings increases and the grating height of the diffraction grating tends to increase, so that unnecessary light is generated more.
本発明は、格子側面に入射光が到達するような場合であっても、格子側面で生ずる不要光が、像性能を低下させにくい回折光学素子及びそれを有する光学系の提供を目的とする。 An object of the present invention is to provide a diffractive optical element and an optical system having the diffractive optical element in which unnecessary light generated on a grating side face hardly deteriorates image performance even when incident light reaches the grating side face.
さらに、製造上からも型での成形など量産性の良い製造方式を使用できるような回折光学素子の提供を目的としている。 Furthermore, another object of the present invention is to provide a diffractive optical element that can be used for manufacturing because of its high mass productivity such as molding with a mold.
請求項１の発明の回折光学素子は、格子面と格子側面を含み、使用波長領域全域で特定次数に回折するブレーズ型の回折格子を同心円状の周期構造とした回折格子部を有する回折光学素子に於いて、
前記回折格子部は、２種類の異なる材料の境界に回折格子が形成されており、
該格子側面の回折格子の格子先端を連ねた包絡面の面法線に対する傾き角度θｋは、該回折格子部の中心では実質的に０であり、該回折格子部の中心領域から周辺領域に向かって、該格子側面が該回折格子の格子先端を連ねた包絡面の各格子先端位置における面法線と格子面がなす角度に対してより鈍角となる方向に変化し、
且つ隣接する回折格子間の傾き角度が連続してほぼ０の第１の領域を前記回折格子部の中心を含む領域に有し、前記第１の領域よりも周辺に前記変化量Δθｋが０．２より大きい第２の領域を有することを特徴としている。
The diffractive optical element of the invention of claim 1 includes a diffraction grating portion including a grating surface and a grating side surface, and a blazed diffraction grating that diffracts to a specific order over the entire wavelength region to be used has a concentric periodic structure. In
The diffraction grating portion has a diffraction grating formed at the boundary between two different materials,
The inclination angle θk with respect to the surface normal of the envelope surface connecting the grating tips on the side surface of the grating is substantially 0 at the center of the diffraction grating portion, and extends from the central region of the diffraction grating portion to the peripheral region . Then, the grating side surface changes in a direction that becomes more obtuse than the angle formed by the surface normal and the grating surface at each grating tip position of the envelope surface connecting the grating tips of the diffraction grating ,
In addition, a first region in which the tilt angles between adjacent diffraction gratings are continuously zero is provided in a region including the center of the diffraction grating portion, and the variation Δθk is about 0.1 mm in the periphery of the first region. It has the 2nd area | region larger than 2, It is characterized by the above-mentioned.
請求項２の発明の回折光学素子は、分散の異なる材料からなる回折格子を２つ以上近接させて重ね合わされた積層格子構造の回折光学部を持ち、使用波長領域で、設計波長を２つ以上有する回折光学素子に於いて、
該回折格子部は、格子面と格子側面を含むブレーズ型の回折格子が同心円状の周期構造より成り、
前記回折格子部は、２種類の異なる材料の境界に回折格子が形成されており、
該格子側面の回折格子の格子先端を連ねた包絡面の面法線に対する傾き角度θｋは、該回折格子部の中心では実質的に０であり、該回折格子部の中心領域から周辺領域に向かって、該格子側面が該回折格子の格子先端を連ねた包絡面の各格子先端位置における面法線と格子面がなす角度に対してより鈍角となる方向に変化し、
且つ隣接する回折格子間の傾き角度が連続してほぼ０の第１の領域を前記回折格子部の中心を含む領域に有し、前記第１の領域よりも周辺に前記変化量Δθｋが０．２より大きい第２の領域を有する
ことを特徴としている。
The diffractive optical element of the invention of claim 2 has a diffractive optical part of a laminated grating structure in which two or more diffraction gratings made of materials having different dispersions are stacked close to each other, and has two or more design wavelengths in the used wavelength region. In a diffractive optical element having
The diffraction grating portion has a periodic structure in which a blazed diffraction grating including a grating surface and a grating side surface is concentric,
The diffraction grating portion has a diffraction grating formed at the boundary between two different materials,
The inclination angle θk with respect to the surface normal of the envelope surface connecting the grating tips on the side surface of the grating is substantially 0 at the center of the diffraction grating portion, and extends from the central region of the diffraction grating portion to the peripheral region. Then, the grating side surface changes in a direction that becomes more obtuse than the angle formed by the surface normal and the grating surface at each grating tip position of the envelope surface connecting the grating tips of the diffraction grating,
In addition, a first region in which the tilt angles between adjacent diffraction gratings are continuously zero is provided in a region including the center of the diffraction grating portion, and the variation Δθk is about 0.1 mm in the periphery of the first region. Characterized by having a second region greater than two .
本発明によれば、格子側面に入射光が到達するような場合であっても、格子側面で生ずる不要光が、像性能を低下させにくい回折光学素子及びそれを有する光学系を達成することができる。 According to the present invention, it is possible to achieve a diffractive optical element and an optical system having the diffractive optical element in which unnecessary light generated on the grating side face hardly deteriorates the image performance even when incident light reaches the grating side face. it can.
この他本発明によれば、製造上からも型での成形など量産性の良い製造方式を使用できるような回折光学素子を得ることができる。 In addition, according to the present invention, it is possible to obtain a diffractive optical element capable of using a manufacturing method with good mass productivity such as molding with a mold.
以下、本発明の各実施例を各図を用いて説明する。 Embodiments of the present invention will be described below with reference to the drawings.
図１は本発明の実施例１の回折光学素子の正面図及び側面図である。回折光学素子１は平板又はレンズより成る基板２の片側又は両方の面に回折格子部３を設けて形成されている。そして、本実施例では、回折格子部３が形成されている基板２の面は、曲面（図では凸面）となっている。回折格子部３は光軸Ｏを中心とした同心円状の回折格子形状からなり、レンズ作用を有している。 1A and 1B are a front view and a side view of a diffractive optical element according to Example 1 of the present invention. The diffractive optical element 1 is formed by providing a diffraction grating portion 3 on one or both surfaces of a substrate 2 made of a flat plate or a lens. In this embodiment, the surface of the substrate 2 on which the diffraction grating portion 3 is formed is a curved surface (convex surface in the figure). The diffraction grating portion 3 has a concentric diffraction grating shape with the optical axis O as the center, and has a lens action.
図２は図１の回折光学素子１を図中Ａ−Ａ′断面で切断した断面形状の一部の拡大図である。図２は格子深さ方向にかなりデフォルメされた図となっている。また、構成を分かりやすくするために格子数も実際よりは少なく描かれている。 FIG. 2 is an enlarged view of a part of the sectional shape of the diffractive optical element 1 of FIG. FIG. 2 is a view that is considerably deformed in the lattice depth direction. Also, in order to make the configuration easy to understand, the number of grids is drawn smaller than the actual number.
回折格子部３は、格子面４と格子側面５から構成されるブレーズ構造の回折格子３ａからなり、光軸Ｏから外周部にいくに従って格子ピッチｐＬ（Ｌ＝１，２…）を徐々に変化させることで、レンズ作用（光の収斂作用や発散作用）を有するようにしている。また、ブレーズ構造にすることで、回折光学素子１に入射した入射光は、回折格子３ａで回折せずに透過する０次回折方向に対し、特定の回折次数（図では１次）方向に集中して回折する。また、回折格子部３の格子先端部（格子先端）３ｂを連ねた包絡面６は曲面からなり、基板２の格子形成側の面２ａの曲率半径とほぼ等しい曲率半径の曲面である。 The diffraction grating unit 3 is composed of a blazed diffraction grating 3a composed of a grating surface 4 and a grating side surface 5, and gradually changes the grating pitch pL (L = 1, 2,...) From the optical axis O to the outer periphery. By doing so, it has a lens action (light convergence action or diverging action). Further, by using the blazed structure, incident light incident on the diffractive optical element 1 is concentrated in a specific diffraction order (first order in the figure) direction with respect to the 0th order diffraction direction that is transmitted without being diffracted by the diffraction grating 3a. And diffract. In addition, the envelope surface 6 connecting the grating tip portions (grating tip) 3b of the diffraction grating portion 3 is a curved surface, and is a curved surface having a curvature radius substantially equal to the curvature radius of the surface 2a on the grating forming side of the substrate 2.
厳密には、基板２の曲率中心と包絡面６の曲率中心が一致する曲率半径となっている。一方、格子溝部３ｃを連ねた包絡面７は、後述するが、中心から数えてｋ番目の格子高さｄ（ｋ）が、回折格子３ａ毎に変化しているので、非球面の曲面となっている。 Strictly speaking, the radius of curvature coincides with the center of curvature of the substrate 2 and the center of curvature of the envelope surface 6. On the other hand, the envelope surface 7 in which the grating grooves 3c are connected, as will be described later, is an aspherical curved surface because the k-th grating height d (k) from the center changes for each diffraction grating 3a. ing.
そして、本実施例において、格子側面５は、格子先端部３ｂを連ねた包絡面６と中心から数えてｋ番目の格子先端部３ｂとの交点での包絡面６の面法線６ａに対して、特定の角度θｋを有しており、その格子側面５の傾き角θｋが、格子毎に変化している。さらに、格子側面５の傾き角θｋの隣り合う回折格子３ａ間の差分Δθｋを
Δθｋ＝θｋ+1−θｋ （１）
としたとき、Δθｋが連続して０でない領域を少なくとも１箇所以上有している。
In this embodiment, the lattice side surface 5 is relative to the surface normal 6a of the envelope surface 6 at the intersection of the envelope surface 6 connecting the lattice tip portions 3b and the kth lattice tip portion 3b counting from the center. And a specific angle θk, and the inclination angle θk of the lattice side surface 5 varies for each lattice. Further, the difference Δθk between the adjacent diffraction gratings 3a having the inclination angle θk of the grating side surface 5 is set to Δθk = θk + 1−θk (1)
In this case, there are at least one region where Δθk is not continuously zero.
又、格子側面は円錐面の一部から成るようにしている。 Further, the lattice side surface is formed of a part of a conical surface.
以下、図を用いて説明する。 This will be described below with reference to the drawings.
説明をわかりやすくするために、図３に示すように、基板２の回折格子部３が形成される面を平面とする。このとき、回折格子部３の格子先端部３ｂを連ねた包絡面６は、光軸Ｏに垂直な平面となる。さらに、前述の格子先端部３ｂとの交点での包絡面６の面法線６ａは、全て、光軸Ｏと平行な方向になる。 For easy understanding, as shown in FIG. 3, the surface of the substrate 2 on which the diffraction grating portion 3 is formed is a plane. At this time, the envelope surface 6 connecting the grating tip portions 3b of the diffraction grating portion 3 is a plane perpendicular to the optical axis O. Furthermore, all of the surface normals 6a of the envelope surface 6 at the intersections with the lattice tip 3b described above are in a direction parallel to the optical axis O.
また、包絡面６の面法線６ａと格子側面５がなす傾き角θｋの符号は、図３で各格子側面が傾いている方向を正とする。つまり、格子面４と包絡面６の面法線６ａがなす角度Ｓ１に対し、格子面４と格子側面５がなす角度Ｓ２がより鈍角となる方向を、格子側面５の傾き角θｋが正とする。格子側面５の傾き角θｋが正となる形状は、型から回折光学素子を離型するときに、格子変形が発生しない形状である。 The sign of the inclination angle θk formed by the surface normal 6a of the envelope surface 6 and the lattice side surface 5 is positive in the direction in which each lattice side surface is inclined in FIG. That is, with respect to the angle S1 formed by the surface normal 6a between the lattice surface 4 and the envelope surface 6, the angle S2 formed by the lattice surface 4 and the lattice side surface 5 is a more obtuse angle, and the inclination angle θk of the lattice side surface 5 is positive. To do. The shape in which the inclination angle θk of the grating side surface 5 is positive is a shape in which no grating deformation occurs when the diffractive optical element is released from the mold.
次に、回折格子３ａの格子高さｄ（ｋ）について説明する。一番簡単な例として、図３の回折光学素子１に、包絡面６に垂直な方向、つまり光軸０と平行な方向から波長λの光束が入射する場合を考える。入射側の媒質を空気とし、回折格子部３の材料の屈折率をｎ１（λ）としたとき、波長λの光束が、ｍ次回折光で最大の回折光を得るためには、以下の式を満足するように格子高さｄを決定すれば良い。 Next, the grating height d (k) of the diffraction grating 3a will be described. As the simplest example, let us consider a case where a light flux having a wavelength λ is incident on the diffractive optical element 1 in FIG. 3 from a direction perpendicular to the envelope surface 6, that is, a direction parallel to the optical axis 0. In order to obtain the maximum diffracted light by the m-order diffracted light when the medium on the incident side is air and the refractive index of the material of the diffraction grating part 3 is n1 (λ), the following formula is obtained. What is necessary is just to determine the lattice height d so that it may be satisfied.
｛ｎ１（λ）−１｝ｄ＝ｍλ （２）
格子高さ以外は、既知の値であるので、格子高さは一意的に決定することができる。
{N1 (λ) −1} d = mλ (2)
Since the values other than the lattice height are known values, the lattice height can be uniquely determined.
図４に、実際の格子高さｄ（ｋ）の決定方法を示す。図４（ａ）は、格子側面５の傾き角θａ＝０のときの格子形状を示している。この場合の格子高さｄａは、（２）式で求められたｄとすれば良い（ｄａ＝ｄ）。一般的に、回折格子３ａの格子高さは、図２、図３で示す格子先端３ｂの包絡面６の法線方向６ａに測った高さで定義される。図４（ｂ）は、格子側面５の傾き角θｂ＞０のときの格子形状を示している。 FIG. 4 shows a method for determining the actual grid height d (k). FIG. 4A shows the lattice shape when the inclination angle θa = 0 of the lattice side surface 5. The lattice height da in this case may be d obtained by the equation (2) (da = d). In general, the grating height of the diffraction grating 3a is defined by the height measured in the normal direction 6a of the envelope surface 6 of the grating tip 3b shown in FIGS. FIG. 4B shows the lattice shape when the inclination angle θb> 0 of the lattice side surface 5.
ここで、格子面４は、図４（ａ）で、決定された形状と同じである。同形状にすることで、格子面４を通過する光束は、最適な回折光が得られるように伝播される。格子側面５のほうは、格子先端３ｂを基準にして、傾き角θｂだけ傾くように形成する。図４からも明らかなように、傾き角θｂが正の値をとるときは、格子面４と格子側面５の溝側の交点Ｂは、先端３ｂよりにずれるため、格子高さｄｂは、格子高さｄａに比べて小さくなる。 Here, the lattice plane 4 has the same shape as that determined in FIG. By adopting the same shape, the light beam passing through the grating surface 4 is propagated so as to obtain optimum diffracted light. The grating side surface 5 is formed so as to be inclined by the inclination angle θb with respect to the grating tip 3b. As is clear from FIG. 4, when the inclination angle θb takes a positive value, the intersection B on the groove side of the lattice plane 4 and the lattice side surface 5 is shifted from the tip 3b. It becomes smaller than the height da.
以上説明したように、格子側面５の傾き角θｋによって、格子高さｄ（ｋ）が変わるので、図２、図３の格子溝３ｃを連ねた包絡面７は、球面や平面にはならず、非球面形状となる。 As described above, since the lattice height d (k) changes depending on the inclination angle θk of the lattice side surface 5, the envelope surface 7 connecting the lattice grooves 3c in FIGS. 2 and 3 does not become a spherical surface or a flat surface. It becomes an aspherical shape.
次に、図２に示したように、包絡面６が曲面となる回折格子部３に任意の入射角αで入射した光束を考える。ｍ次回折光で最大の回折光を得るためには、（２）式は、
｛ｎ１（λ）ｃｏｓα′ｍ−ｃｏｓα｝ｄ＝ｍλ （３）
となる。ここで、α′ｍは、ｍ次回折光の回折角である。なお、このときの、入射角、回折角の角度は、格子先端３ｂを連ねた包絡面６の面法線６ａと、入射光、回折光のなす角度である。
Next, as shown in FIG. 2, a light beam that is incident on the diffraction grating portion 3 having an envelope surface 6 having a curved surface at an arbitrary incident angle α will be considered. In order to obtain the maximum diffracted light with m-order diffracted light, the equation (2) is
{N1 (λ) cos α′m−cos α} d = mλ (3)
It becomes. Here, α′m is the diffraction angle of the m-th order diffracted light. At this time, the incident angle and the diffraction angle are angles formed by the surface normal 6a of the envelope surface 6 connecting the grating tips 3b and the incident light and diffracted light.
この場合も、前述のように、各格子面４を最適な回折光が得られるように決定し、その後、格子側面５の傾き角θｋを最適化し、格子高さｄ（ｋ）を決めていく手順を取ればよい。 Also in this case, as described above, each grating surface 4 is determined so that optimum diffracted light can be obtained, and thereafter the inclination angle θk of the grating side surface 5 is optimized to determine the grating height d (k). Just follow the steps.
最後に、格子側面５の傾き角θｋについて説明する。図５は、実施例１における各回折格子での傾き角θｋのグラフである。横軸は、輪帯番号ｋであり、中心（光軸Ｏ）側が第１輪帯、最外周部が第５０輪帯となるようにした回折光学素子の例である（尚、輪帯の数は仕様により任意である）。縦軸は、格子側面５の傾き角θｋの値である。図５で、第１輪帯から第１５輪帯までの第１の領域における傾き角θｋは、連続してほぼ０の値であり、第１６輪帯から第４０輪帯まで、徐々に増加している。そして、第４１輪帯から第５０輪帯で、傾き角は約１４°となる。 Finally, the inclination angle θk of the grating side surface 5 will be described. FIG. 5 is a graph of the tilt angle θk at each diffraction grating in the first embodiment. The horizontal axis is an example of a diffractive optical element in which the ring number is k, the center (optical axis O) side is the first ring zone, and the outermost periphery is the 50th ring zone (note that the number of ring zones) Is optional depending on the specification). The vertical axis represents the value of the inclination angle θk of the lattice side surface 5. In FIG. 5, the inclination angle θk in the first region from the first annular zone to the fifteenth annular zone has a value of substantially 0 continuously , and gradually increases from the 16th annular zone to the 40th annular zone. ing. The inclination angle is about 14 ° from the 41st to 50th zones.
実施例１の特徴は、第１６輪帯から第４０輪帯の領域のように、傾き角が急激に変化する領域を有することである。即ち傾き角の変化量が連続して０でない領域を１以上有することである。図６は、（１）式で表わした差分Δθｋを、図５の傾き角θｋに対して計算したグラフである。差分Δθｋが０とならず、増加している領域と、減少している領域があることが、グラフから見て取れる。図６における実施例１の特徴は、差分Δθｋが０でない値が複数の回折格子に連続してあることである。 The characteristic of Example 1 is that it has the area | region where an inclination angle changes rapidly like the area | region of the 16th ring zone to the 40th ring zone. That is, it has one or more regions where the change amount of the inclination angle is not continuously zero. FIG. 6 is a graph in which the difference Δθk expressed by the equation (1) is calculated with respect to the inclination angle θk of FIG. It can be seen from the graph that the difference Δθk does not become 0 but there are an increasing area and a decreasing area. The feature of the first embodiment in FIG. 6 is that a value of the difference Δθk that is not 0 is continuously present in a plurality of diffraction gratings.
従来例との、格子側面の形状との違いを明らかにするため、従来例の回折光学素子について、同様のグラフを図３５、図３６に示す。図３５、図３６は、格子側面５が、包絡面６の法線方向６ａと一致する図３３の回折光学素子１のグラフである。法線方向６ａと一致しているため、傾き角θｋは全域で０となり、差分Δθｋも全域で０となる。 In order to clarify the difference between the shape of the grating side surface and the conventional example, similar graphs are shown in FIGS. 35 and 36 for the diffractive optical element of the conventional example. 35 and 36 are graphs of the diffractive optical element 1 in FIG. 33 in which the grating side surface 5 coincides with the normal direction 6 a of the envelope surface 6. Since it coincides with the normal direction 6a, the inclination angle θk is 0 in the entire region, and the difference Δθk is also 0 in the entire region.
図２７は、従来例である特開平１０−２６８１１５号公報に提案されている回折光学素子１の説明図である。この回折光学素子１は、中央領域で、格子側面５が法線６ａ方向と一致し、周辺領域は、特定の傾き角ｒを有する構成である。 FIG. 27 is an explanatory diagram of the diffractive optical element 1 proposed in Japanese Patent Laid-Open No. 10-268115, which is a conventional example. This diffractive optical element 1 has a configuration in which the grating side surface 5 coincides with the direction of the normal 6a in the central region, and the peripheral region has a specific inclination angle r.
図２８、図２９は、図２７の従来例に対応するグラフである。図２８からわかるように、傾き角θｋが離散的に変化しているので、差分Δθｋは、離散的に変化している境界の１輪帯でだけ、大きな変化量を有することになる。このように、グラフの上からも、実施例１である格子側面５の傾き角θｋは、従来例と異なっていることが明らかである。また、傾き角θｋの最大値は、図２中の格子側面５の格子ピッチ方向（図２中のｙ方向）の射影長さ（格子先端部３ｂと溝部３ｃとの光軸Ｏの垂直方向の長さ）ΔｐＬが、
０＜ΔｐＬ／ｐＬ＜０．０５ （４）
を満足する範囲で、変化させるのが好ましい。この範囲とすることで、格子面４を通過する使用光束の回折効率を大幅に低下させることなく、格子側面５の不要光を抑制できる。
28 and 29 are graphs corresponding to the conventional example of FIG. As can be seen from FIG. 28, since the inclination angle θk changes discretely, the difference Δθk has a large amount of change only in one ring zone of the boundary changing discretely. Thus, also from the top of the graph, it is clear that the inclination angle θk of the grating side surface 5 which is Example 1 is different from the conventional example. Further, the maximum value of the inclination angle θk is the projection length in the grating pitch direction (y direction in FIG. 2) of the grating side surface 5 in FIG. 2 (in the direction perpendicular to the optical axis O between the grating tip 3b and the groove 3c). Length) ΔpL is
0 <ΔpL / pL <0.05 (4)
It is preferable to change within a range that satisfies the above. By setting it as this range, the unnecessary light of the grating side surface 5 can be suppressed without significantly reducing the diffraction efficiency of the used light beam passing through the grating surface 4.
続いて、実施例１の格子側面５の形状による、不要光の発生を抑制する考え方について説明を行う。 Next, the concept of suppressing the generation of unnecessary light by the shape of the grating side surface 5 of Example 1 will be described.
実施例１では、格子側面５を透過する光束が、不要光として振る舞う場合を対象としている。さらに、実施例１により、不要光の発生を抑制するのに特に効果があるのは、図７に示すように、入射角ω０より透過屈折角ω１が大きくなるな関係で、格子側面５に光束が入射する場合である。ここで、入射角、透過屈折角は、格子側面５の面法線５ａと、入射光、透過光のなす角ω０、ω１である。 The first embodiment is intended for the case where the light beam transmitted through the grating side surface 5 behaves as unnecessary light. Furthermore, the embodiment 1 is particularly effective in suppressing the generation of unnecessary light because the transmission refraction angle ω1 is larger than the incident angle ω0 as shown in FIG. Is incident. Here, the incident angle and the transmission refraction angle are angles ω0 and ω1 formed by the surface normal 5a of the grating side surface 5 and the incident light and transmitted light.
格子面４を形成する入射側の媒質の波長λでの屈折率をｎ１（λ）、射出側の媒質の波長λでの屈折率をｎ２（λ）とすると、上記関係は入射側の媒質の屈折率が射出側に比べて高いｎ１（λ）＞ｎ２（λ）であるときに成立する。 When the refractive index at the wavelength λ of the incident side medium forming the grating plane 4 is n1 (λ), and the refractive index at the wavelength λ of the emission side medium is n2 (λ), the above relationship is as follows. This holds when n1 (λ)> n2 (λ) is higher than the refractive index on the exit side.
このとき、入射光、透過光の関係は、スネルの法則で考えて差し障りがない。図８、図９に２つの格子形状における入射角ω０と透過屈折角ω１の関係を示す。図８は、入射側に空気以外の媒質があり、射出側が空気である構成である。図８は入射側の材料に大日本インキ化学工業（株）製の紫外線硬化樹脂ＲＣ−Ｃ００１（ｎｄ＝１．５２４、νｄ＝５０．８）を用いたときのグラフであり、実線がｄ線の波長における関係、点線がｇ線の波長における関係を表わしている。入射光が臨界角を超えて入射するまで透過光は存在し、透過屈折角ω１は０°から９０°の全範囲に存在可能である。ただし、ｄ線とｇ線の波長における透過屈折光の振る舞いに大きな差はない。 At this time, the relationship between the incident light and the transmitted light can be considered by Snell's law. 8 and 9 show the relationship between the incident angle ω0 and the transmission refraction angle ω1 in the two grating shapes. FIG. 8 shows a configuration in which a medium other than air is present on the incident side and air is present on the emission side. FIG. 8 is a graph when using UV-curable resin RC-C001 (nd = 1.524, νd = 50.8) manufactured by Dainippon Ink & Chemicals, Inc. as the incident side material, and the solid line is the d line. The dotted line represents the relationship in the wavelength of the g-line. The transmitted light exists until the incident light enters beyond the critical angle, and the transmission refraction angle ω1 can exist in the entire range from 0 ° to 90 °. However, there is no significant difference in the behavior of transmitted refracted light at the wavelengths of d-line and g-line.
図９は、入射側と射出側が分散の異なる媒質（材料）の境界に格子面（回折格子）が形成されている構成である。図９は、入射側の材料の屈折率が出射側の材料の屈折率に比べて高い場合であり、入射側の材料に紫外線硬化樹脂（ｎｄ＝１．６３６、νｄ＝２２．８）、射出側の材料に大日本インキ化学工業（株）製の紫外線硬化樹脂ＲＣ−Ｃ００１（ｎｄ＝１．５２４、νｄ＝５０．８）を用いたときのグラフであり、図８と同様に実線がｄ線の波長における関係、点線がｇ線の波長における関係を表わしている。 FIG. 9 shows a configuration in which a grating surface (diffraction grating) is formed at the boundary of a medium (material) having different dispersions on the incident side and the emission side. FIG. 9 shows a case where the refractive index of the material on the incident side is higher than the refractive index of the material on the outgoing side. As the material on the incident side, ultraviolet curable resin (nd = 1.636, νd = 22.8), FIG. 9 is a graph when using UV-curable resin RC-C001 (nd = 1.524, νd = 50.8) manufactured by Dainippon Ink & Chemicals, Inc. as the material on the side, and the solid line is d as in FIG. The relationship in the wavelength of the line, and the dotted line represents the relationship in the wavelength of the g-line.
この場合、図８の構成に比べて格子面を構成する材料の屈折率差が小さいので、入射角ω０が０°から７０°とかなり広い範囲で透過屈折光が発生する。また、ｄ線とｇ線の臨界角がそれぞれ、６８．７４°、６６．５６°と約２°異なっている。従って、６７°の入射角で入射した光束は、ｄ線の波長は透過し、ｇ線の波長は全反射するので、透過屈折光は、色づいた光束となる。 In this case, since the difference in refractive index of the material constituting the lattice plane is smaller than that in the configuration of FIG. 8, transmitted refracted light is generated in a considerably wide range of the incident angle ω 0 from 0 ° to 70 °. Further, the critical angles of the d-line and the g-line are different from each other by 68.74 ° and 66.56 °, respectively. Accordingly, since the light beam incident at an incident angle of 67 ° transmits the wavelength of the d-line and totally reflects the wavelength of the g-line, the transmitted refracted light becomes a colored light beam.
以上のように本実施例では、回折光学素子として、２種類の異なる材料の境界に回折光学素子部が形成されている構成を用いることにより、格子側面に光束が入射する場合でも、不要光が像性能を低下させるのを少なくし、又光学系に組み込んだ場合でも、フレア等を有効に抑制している。 As described above, in this embodiment, by using a configuration in which the diffractive optical element portion is formed at the boundary between two different materials as the diffractive optical element, unnecessary light is generated even when the light beam is incident on the grating side surface. It reduces the degradation of image performance and effectively suppresses flare and the like even when incorporated in an optical system.
以下、実施例１の効果を説明するのに、従来例との差が顕著となるように、図１０に媒質の境界に回折格子面を有する回折格子部をもつ回折光学素子を用いた光学系を例に説明を行う。 Hereinafter, in order to explain the effects of the first embodiment, an optical system using a diffractive optical element having a diffraction grating portion having a diffraction grating surface at the boundary of the medium is shown in FIG. 10 so that the difference from the conventional example becomes significant. An example will be described.
図１０は、上記回折光学素子２１の概略図である。回折光学素子２１は第１の回折光学素子２２と第２の回折光学素子（第２の素子部）２３が近接した構成よりなっている。そして、近接した境界面に回折格子部が形成されている。 FIG. 10 is a schematic view of the diffractive optical element 21. The diffractive optical element 21 has a configuration in which a first diffractive optical element 22 and a second diffractive optical element (second element part) 23 are close to each other. A diffraction grating portion is formed on the adjacent boundary surface.
図１０中Ａ−Ａ′線で切断した断面形状の概略を図１１に示す。基板２４の曲面（図では凹面）２４ａ上に形成され、正のパワーの回折レンズとして作用する第１の回折格子部２６を有する第１の素子部２２と、基板２５の曲面（図では凸面）上に形成され、負のパワーの回折レンズとして作用する第２の回折格子部２７を有する第２の素子部２３が、空気層２８を介して近接した構成となっている。ここでパワーとは焦点距離の逆数である。 FIG. 11 shows an outline of a cross-sectional shape cut along the line AA ′ in FIG. A first element portion 22 having a first diffraction grating portion 26 formed on a curved surface (concave surface in the figure) 24a of the substrate 24 and acting as a positive power diffraction lens, and a curved surface (convex surface in the figure) of the substrate 25. The second element part 23 having the second diffraction grating part 27 formed above and acting as a diffractive lens having a negative power has a configuration in which the second element part 23 is in close proximity via the air layer 28. Here, power is the reciprocal of the focal length.
第２の回折格子部２７は、基板２５の表面側に正の光学パワーの回折レンズとして作用する回折格子２９と、その上に負の光学パワーの回折レンズとして作用する回折格子３０が、格子面３２で貼り合わされた構成であり、全体として負のパワーを有している。回折格子３０の格子面３２と反対の面３３は回折格子が形成されていない曲面３３で、基板２５の回折格子を形成する側の曲面２５ａと実効的に等しい曲率を有している。 The second diffraction grating portion 27 includes a diffraction grating 29 that acts as a diffraction lens with a positive optical power on the surface side of the substrate 25 and a diffraction grating 30 that acts as a diffraction lens with a negative optical power on the grating surface. 32, and has a negative power as a whole. A surface 33 opposite to the grating surface 32 of the diffraction grating 30 is a curved surface 33 on which no diffraction grating is formed, and has a curvature that is effectively equal to the curved surface 25a of the substrate 25 on the side where the diffraction grating is formed.
３６、３７、３８、３９は各々第１の回折格子部２６の格子溝部、格子先端部、第２の回折格子部２７の格子先端部、格子溝部を連ねた包絡面である。 Reference numerals 36, 37, 38, and 39 denote envelope surfaces in which the grating groove portion and the grating tip portion of the first diffraction grating portion 26, the grating tip portion and the grating groove portion of the second diffraction grating portion 27 are connected.
上記、第２の回折格子部２７が、前述の図９で示した特性を有する回折格子部である。そしてこれらの第１、第２の回折格子部２６、２７を合成して、一つの回折光学素子２１として作用するようにしている。 The second diffraction grating portion 27 is a diffraction grating portion having the characteristics shown in FIG. These first and second diffraction grating portions 26 and 27 are combined so as to act as one diffractive optical element 21.
上記回折光学素子２１に、光束が入射したときの、各格子側面３４、３５での不要光の振る舞いについて説明する。 The behavior of unnecessary light on the grating side surfaces 34 and 35 when a light beam enters the diffractive optical element 21 will be described.
図１２に回折格子部２６、２７を拡大した模式図を示す。微小領域の回折格子部２６、２７は、微少領域における包絡面３６にδだけ傾いた回折格子で構成されていると考えられる。まず、図中Ａで示した第１の回折格子部２６の格子側面３４へ入射する光束の振る舞いを調べる。 FIG. 12 shows an enlarged schematic diagram of the diffraction grating portions 26 and 27. It is considered that the diffraction grating portions 26 and 27 in the minute region are constituted by diffraction gratings inclined by δ with respect to the envelope surface 36 in the minute region. First, the behavior of the light beam incident on the grating side surface 34 of the first diffraction grating portion 26 indicated by A in the figure is examined.
第１の回折格子部２６は、材質の屈折率ｎ１（λ）と空気により形成されている。図中左の方向から側面に到達する光束Ａは、一旦格子面３１を射出した後に、格子側面３４に到達する。そのため、空気から媒質への透過となり、図に示したように、光軸に対して大きな角度を有して射出されるため、一般的な光学系では問題とならない。 The first diffraction grating portion 26 is formed of a material refractive index n1 (λ) and air. The light beam A that reaches the side surface from the left direction in the drawing reaches the grating side surface 34 after exiting the grating surface 31 once. Therefore, the air is transmitted from the medium to the medium, and is emitted with a large angle with respect to the optical axis as shown in the figure, so that there is no problem in a general optical system.
次に、図中Ｂで示した第２の回折格子部２７の格子側面３５へ入射する光束の振る舞いを説明する。 Next, the behavior of the light beam incident on the grating side surface 35 of the second diffraction grating portion 27 shown by B in the figure will be described.
図中Ｂの光束は、第１の回折格子部２６を通過後、曲面３３で屈折し、格子側面３５へ入射する。回折格子３０内を伝播する光束の光軸とのなす角度をωｉとする。格子側面３４へ入射する入射角ω０は、以下のようになる。 The light beam B in the drawing passes through the first diffraction grating portion 26, is refracted by the curved surface 33, and enters the grating side surface 35. The angle formed by the optical axis of the light beam propagating through the diffraction grating 30 is assumed to be ωi. The incident angle ω 0 incident on the grating side surface 34 is as follows.
ω０（度）＝９０−ωｉ−δ−θｋ （５）
格子側面３５を透過屈折した光Ｂの屈折角をω１としたとき、この光束が、光軸となす角度ωｅは、
ωｅ（度）＝９０−ω１−δ−θｋ （６）
となる。角度ω０と角度ω１の関係は、スネルの法則により計算されるので、入射角ωｉと、ωｅの関係は、各格子側面で一意的に決定できる。
ω0 (degrees) = 90−ωi−δ−θk (5)
When the refraction angle of the light B transmitted and refracted through the grating side surface 35 is ω1, the angle ωe formed by this light beam and the optical axis is
ωe (degrees) = 90−ω1−δ−θk (6)
It becomes. Since the relationship between the angle ω0 and the angle ω1 is calculated according to Snell's law, the relationship between the incident angle ωi and ωe can be uniquely determined on each grating side surface.
図１３、図１４に入射光ωｉと透過屈折角ωｅの関係を表わす。第２の回折格子部２７を形成する材質は、図９と同じとし、包絡面３６の傾き角を図１３はδ＝５°図１４はδ＝１５°とする。また、各グラフ中実線と点線は、波長ｄ線の光束に対して、格子側面３５の傾き角θｋが１４°と０°を表わしている。 13 and 14 show the relationship between the incident light ωi and the transmission refraction angle ωe. The material for forming the second diffraction grating portion 27 is the same as in FIG. 9, and the inclination angle of the envelope surface 36 is δ = 5 ° in FIG. 13 and δ = 15 ° in FIG. In each graph, the solid line and the dotted line represent the inclination angle θk of the grating side surface 35 of 14 ° and 0 ° with respect to the light flux of wavelength d line.
グラフの符号は、図１２の入射光束の向きが正、透過屈折光の向きが負となる。傾き角θｋ＝０°のグラフ（図中実線）を見ると、δ＝５°の構成では、殆どの入射角で臨界角を越えた入射となるため、透過屈折光は存在していない。δ＝１５°では、入射角が約６°以下は、臨界角を越えた入射となるため、透過屈折光は存在していないが、入射角６〜１１°付近で透過屈折角ωｅが負となっていることがわかる。 The sign of the graph is that the direction of the incident light beam in FIG. 12 is positive and the direction of the transmitted refracted light is negative. Looking at the graph of the inclination angle θk = 0 ° (solid line in the figure), in the configuration where δ = 5 °, the incident angle exceeds the critical angle at almost all incident angles, so there is no transmitted refracted light. At δ = 15 °, when the incident angle is about 6 ° or less, the incident angle exceeds the critical angle. Therefore, there is no transmitted refracted light, but the transmitted refracting angle ωe is negative near the incident angle of 6 to 11 °. You can see that
それに対し傾き角θｋ＝１４°のグラフ（図中点線）は、δ＝５°の構成では、入射角が約２°以下の時に、透過屈折光が存在しない領域があるものの、δ＝１５°では、入射角が２０°までの範囲では、全入射角度で透過屈折光が存在していることがわかる。また、傾き角θｋ＝１４°では、屈折角ωｅが負となる入射角ωｉがθｋ＝０°に比べ、低入射角側へシフトしていることがわかる。 On the other hand, the graph of the inclination angle θk = 14 ° (dotted line in the figure) shows that in the configuration where δ = 5 °, there is a region where transmitted refracted light does not exist when the incident angle is about 2 ° or less, but δ = 15 °. Then, it can be seen that transmitted refracted light exists at all incident angles in the range of incident angles up to 20 °. It can also be seen that at the inclination angle θk = 14 °, the incident angle ωi at which the refraction angle ωe is negative is shifted to the low incident angle side compared to θk = 0 °.
続いて、実際の光学系へ、上記回折光学素子を適用した場合の不要光について説明する。 Next, unnecessary light when the diffractive optical element is applied to an actual optical system will be described.
最初に、傾き角θｋ＝０°の回折光学素子を適用した場合の、不要光について簡単に説明し、その後、本実施例の回折光学素子２１についての説明を行う。 First, unnecessary light when a diffractive optical element having an inclination angle θk = 0 ° is applied will be briefly described, and then the diffractive optical element 21 of the present embodiment will be described.
図３７は回折光学素子での不要光の模式図である。図３８に、回折光学素子２１を用いた結像光学系の概念図を示す。図１１、図１２、図３７、図３８において、光軸Ｏに対して入射角ωで入射した光束は、回折光学素子２１の前側に配置された屈折レンズ（図示せず）を通過し、第１の回折光学素子２２の基板２４および格子面３１を通過後、回折格子３０の格子面３２と反対の曲面３３で屈折し、格子側面３５に角度ωｉで入射する。 FIG. 37 is a schematic view of unnecessary light in the diffractive optical element. FIG. 38 shows a conceptual diagram of an imaging optical system using the diffractive optical element 21. In FIG. 11, FIG. 12, FIG. 37, and FIG. 38, a light beam incident at an incident angle ω with respect to the optical axis O passes through a refractive lens (not shown) disposed on the front side of the diffractive optical element 21, and After passing through the substrate 24 and the grating surface 31 of the first diffractive optical element 22, the light is refracted by a curved surface 33 opposite to the grating surface 32 of the diffraction grating 30 and is incident on the grating side surface 35 at an angle ωi.
格子側面３５で透過屈折した光束は、屈折角ωｅで射出し、第２の回折光学素子２３の基板２５を通過後、絞り４０の前後に配置された屈折レンズ（図示せず）を介して、結像面４１に到達する。 The light beam transmitted and refracted by the grating side surface 35 exits at a refraction angle ωe, passes through the substrate 25 of the second diffractive optical element 23, and then passes through a refractive lens (not shown) disposed before and after the stop 40. It reaches the imaging plane 41.
図３８中にｍ番目とｎ番目の２箇所の格子側面から透過屈折した不要光を示す。図からわかるように、不要光が、絞り４０を通過し、結像面４１に到達するのは、屈折角ωｅが負となる方向である。また、外周部の回折格子ほど、負の値が大きくならないと不要光として結像面４１には到達しないことが図から見て取れる。 FIG. 38 shows unnecessary light that has been transmitted and refracted from the grating side surfaces of the m-th and n-th two locations. As can be seen from the figure, the unnecessary light passes through the diaphragm 40 and reaches the image plane 41 in the direction in which the refraction angle ωe is negative. Further, it can be seen from the drawing that the diffraction grating at the outer peripheral portion does not reach the imaging plane 41 as unnecessary light unless the negative value is increased.
さらに、図９で説明したように、格子側面を透過する光は波長により屈折角が異なり、短波長ほど屈折角が大きくなるので、ひとつの格子側面からの不要光は、波長毎に結像面上での到達位置が異なる。図３８では、下線側が短波長となる。つまり、ｍ番目の格子側面からの不要光は、上線の波長λｍ，２より、下線の波長λｍ，１のほうが短波長となる。 Furthermore, as described with reference to FIG. 9, the light transmitted through the grating side surface has a refraction angle different depending on the wavelength, and the shorter the shorter wavelength, the larger the refraction angle. The arrival position on the top is different. In FIG. 38, the underline is the short wavelength. In other words, the unnecessary light from the mth grating side surface is shorter in the underline wavelength λm, 1 than in the overline wavelength λm, 2.
図１５に、本実施例の不要光について説明する。従来例に比べて、外周部では格子側面の傾き角θｋが大きくなっている。従って、図１３に示したように、同じ入射角では、射出する屈折角ωｅは正の方向にシフトしている。そのため、外周部の格子側面を透過屈折した光は、図示したように絞り４０で斜光され、結像面には到達しない。 FIG. 15 illustrates unnecessary light in this embodiment. Compared to the conventional example, the inclination angle θk of the lattice side surface is larger in the outer peripheral portion. Therefore, as shown in FIG. 13, at the same incident angle, the exiting refraction angle ωe is shifted in the positive direction. Therefore, the light that has been transmitted and refracted on the grating side surface of the outer peripheral portion is obliquely illuminated by the diaphragm 40 as shown, and does not reach the imaging surface.
一方、光軸付近の格子側面は、従来例と、実施例１ともに、概０°としてある。光軸付近の不要光は、図１３で説明した包絡面３６の傾き角が小さな構成に対応するので、傾き角θｋ＝０°で格子側面３５を透過する光束は存在しなくなる構成である。比較として、図３９に、全域の格子側面３５の傾き角をθｋ＝１４°としたときの不要光の振る舞いを示す。 On the other hand, the grating side surface in the vicinity of the optical axis is approximately 0 ° in both the conventional example and the first embodiment. The unnecessary light in the vicinity of the optical axis corresponds to the configuration in which the inclination angle of the envelope surface 36 described with reference to FIG. 13 is small, so that there is no light beam transmitted through the grating side surface 35 at the inclination angle θk = 0 °. For comparison, FIG. 39 shows the behavior of unnecessary light when the inclination angle of the grating side surface 35 in the entire region is θk = 14 °.
外周付近の格子側面を通過する不要光束は、本発明の実施例１と同じく低減されるが、逆に、光軸付近の不要光が、図１３の点線で示したように、透過屈折してしまうため、従来例に比べて、悪化してしまう。 The unnecessary light flux passing through the grating side surface near the outer periphery is reduced as in the first embodiment of the present invention, but conversely, the unnecessary light near the optical axis is transmitted and refracted as shown by the dotted line in FIG. Therefore, it is worse than the conventional example.
以上のことを鑑みて、本発明の実施例１では、図５に示したように、光軸付近は傾き角θｋを約０°とし、外周付近は傾き角θｋを約１４°とし、その間の回折格子部を、傾き角θｋが徐々に変化するように構成している。 In view of the above, in the first embodiment of the present invention, as shown in FIG. 5, the inclination angle θk is set to about 0 ° near the optical axis, and the inclination angle θk is set to about 14 ° near the outer periphery. The diffraction grating portion is configured such that the inclination angle θk changes gradually.
これにより、光軸０付近の回折格子部は、臨界角を越えた入射角で、格子側面３５に入射させることで、不要光の発生をなくし、外周部付近の回折格子部は、格子側面を屈折した光束の屈折角を調整し、結像面４１へ到達しないようにしている。そして、中間の回折格子部は、急激に傾き角θｋを変えることで、透過屈折角ωｅが大きく負となる領域を低減させている。図６に示した傾き角の差分Δθｋは、最大で０．６以上変化している。格子ピッチｐＬや、全輪帯数に依存するため、変化量は特定できないが、差分Δθｋが０．２（Δθｋ＞０．２）以上の領域（第２の領域）を有することが、透過屈折角ωｅが大きく負となる領域を低減させるためには好ましい。 As a result, the diffraction grating portion near the optical axis 0 is made incident on the grating side surface 35 with an incident angle exceeding the critical angle, thereby eliminating unnecessary light generation. The refraction angle of the refracted light beam is adjusted so as not to reach the image plane 41. In the intermediate diffraction grating portion, the region in which the transmission refraction angle ωe is largely negative is reduced by changing the inclination angle θk abruptly. The difference Δθk in inclination angle shown in FIG. 6 changes by a maximum of 0.6 or more. Although the amount of change cannot be specified because it depends on the lattice pitch pL and the number of all zones, it is necessary to have a region (second region) in which the difference Δθk is 0.2 (Δθk> 0.2) or more. This is preferable for reducing a region where the angle ωe is largely negative.
図１６に、特定の光学系へ、本発明の実施例１の回折光学素子を適用した場合の、結像面４１へ不要光が到達する回折格子番号を数えた表を示す。回折格子形状は図５に示した形状で、総輪帯数は５０である。格子側面を通過する光束には、一般のスネルの法則を適用し、それ以外の面には、通常屈折面、回折面に用いられる光線追跡の手法を適用した。 FIG. 16 shows a table in which the diffraction grating numbers at which unnecessary light reaches the imaging plane 41 when the diffractive optical element according to the first embodiment of the present invention is applied to a specific optical system are shown. The diffraction grating has the shape shown in FIG. The general Snell's law was applied to the light flux passing through the grating side surface, and the ray tracing method normally used for the refractive and diffractive surfaces was applied to the other surfaces.
光学系へ一様な入射角度ωをもつ光束が入射した場合を計算し、格子側面へ入射した光束が、光学系を介して結像面へ到達した場合を到達側面と数え、全格子側面に対して計算を行なった。計算波長は、可視域の４００ｎｍから７００ｎｍの波長であり、いずれかの波長の光束が、結像面へ到達した場合を、到達側面として数えている。 Calculate the case where a light beam with a uniform incident angle ω is incident on the optical system, and count the case where the light beam incident on the grating side surface reaches the imaging surface via the optical system as the arrival side surface. Calculations were performed on the results. The calculated wavelength is a wavelength of 400 nm to 700 nm in the visible range, and the case where a light beam having any wavelength reaches the imaging surface is counted as a reaching side surface.
例えば、実施例１の入射角ω＝７．５°の光束では、第１９輪帯目の格子側面から第３０輪帯までの格子側面の光束が、結像面へ到達していることを表わし、到達側面の数は３０−１８＝１２より１２である。本実施例において好ましくは回折格子間の傾き角度の変化量が０でない領域は１０輪帯以上であるのが良い。特に全輪帯数の１／３以上が良い。図１６に示す表から明らかであるが、いずれの入射角でも実施例１の回折光学素子２１を用いた光学系のほうが、従来例に比べて不要光が結像面へ到達する格子側面の数は大幅に低減されていることがわかる。 For example, in the light beam with the incident angle ω = 7.5 ° in the first embodiment, the light beam on the grating side surface from the grating side surface of the 19th annular zone to the 30th annular zone reaches the imaging plane. The number of reaching side faces is 12 from 30-18 = 12. In the present embodiment, it is preferable that the region where the change amount of the tilt angle between the diffraction gratings is not 0 is 10 or more zones. In particular, 1/3 or more of the total number of rings is good. As is apparent from the table shown in FIG. 16, the optical system using the diffractive optical element 21 of Example 1 at any incident angle has a greater number of grating side surfaces where unnecessary light reaches the imaging plane than the conventional example. It can be seen that is significantly reduced.
上述した本発明の実施例１の回折光学素子は、格子面４へ入射する光束が、包絡面６の法線６ａ方向から一方向に偏っているとき、つまり格子側面５に面と平行でない方向から光束が入射する光学系で、効果が顕著となる。そのため、光学系へ回折光学素子を適用する際、最適な面を選定する必要がある。 In the diffractive optical element according to Example 1 of the present invention described above, when the light beam incident on the grating surface 4 is deviated in one direction from the normal 6a direction of the envelope surface 6, that is, in a direction not parallel to the surface of the grating side surface 5. The effect becomes remarkable in the optical system in which the luminous flux enters from the center. Therefore, when applying a diffractive optical element to an optical system, it is necessary to select an optimal surface.
例えば、包絡面の曲率半径が適用する光学系の焦点距離の１／２以下の曲率半径を持った面などへ回折光学素子が形成される場合に本発明の構成を適用すると効果的で好ましい。 For example, it is effective and preferable to apply the configuration of the present invention when the diffractive optical element is formed on a surface having a radius of curvature of 1/2 or less of the focal length of the optical system to which the radius of curvature of the envelope surface is applied.
以上の説明は、基準曲面が球面となる回折光学素子について行ったが、基準曲面が非球面や、シリンドリカル面、トーリック面など任意の面も同様に適用することができる。 The above description has been given for a diffractive optical element whose reference curved surface is a spherical surface, but any surface such as an aspherical surface, a cylindrical surface, or a toric surface can be applied in the same manner.
以上説明したように、本実施例によれば、格子面と格子側面を含む回折格子部を、使用波長領域全域で特定次数（設計次数）に回折するブレーズ型の回折格子を、レンズ作用をするように同心円状の周期構造とし、格子側面が、回折格子の格子先端を連ねた包絡面の各格子先端位置における面法線と格子側面がなす傾き角度が、格子中心領域から周辺領域で変化し、且つ隣接する回折格子間の傾き角度の変化量が連続して０でない領域を少なくとも１箇所以上有することで、格子側面に光束が比較的大きな角度で入射するような光学系に適用しても、不要光の発生を抑制することができる。 As described above, according to the present embodiment, the blazed diffraction grating that diffracts the diffraction grating portion including the grating surface and the grating side surface to the specific order (design order) over the entire wavelength range to be used has a lens effect. In this way, the angle of inclination between the surface normal and the grating side surface at each grating tip position of the envelope surface connecting the grating tips of the diffraction grating varies from the grating center region to the peripheral region. In addition, the present invention can be applied to an optical system in which a light flux is incident on a side surface of a grating at a relatively large angle by having at least one region where the amount of change in tilt angle between adjacent diffraction gratings is not continuously zero. Generation of unnecessary light can be suppressed.
また、基板と回折格子部を形成する材料を同一とし、基板と回折格子部を一体で作成することにより、基板外径と格子中心の位置精度や、基板がレンズの場合は、基板レンズの芯と格子中心を精度良く合せられるので、偏心による結像性能の劣化は大幅に低減することができ、性能の良い光学系が得られる。 Also, by making the substrate and the diffraction grating part the same material, and making the substrate and the diffraction grating part integrally, the substrate outer diameter and the position accuracy of the grating center, and if the substrate is a lens, the core of the substrate lens And the center of the grating can be aligned with high accuracy, so that the degradation of imaging performance due to decentration can be greatly reduced, and an optical system with good performance can be obtained.
次に本発明の実施例２について説明する。 Next, a second embodiment of the present invention will be described.
図１７は、傾き角θｋの値を各格子側面で図５の実施例１の半分にした回折光学素子に対し、図１６と同様の計算を行なった表である。この場合、格子側面の結像面への到達数は、図１６に比べて増加しているが、従来例に比べると、約２／３と十分減少している。この回折光学素子では、最大の傾き角が半分の７°になっているので、図２におけるΔｐ（格子先端部と溝部との光軸と垂直方向の長さ）は、全輪帯で減少し、実施例１に比べて、使用光束における回折効率の低下が改善されることになる。以上のように、使用光の回折効率と、格子側面の不要光の抑制を考慮し、最適な傾き角を設定すればよい。ただし、不要光の抑制効果を得るためには、最大の傾き角は最低でも５°以上であることが好ましい。 FIG. 17 is a table in which the same calculation as in FIG. 16 is performed on a diffractive optical element in which the value of the inclination angle θk is halved on each grating side surface as in Example 1 of FIG. In this case, the number of lattice side surfaces reaching the imaging surface is increased as compared with FIG. 16, but is sufficiently reduced to about 2/3 as compared with the conventional example. In this diffractive optical element, since the maximum inclination angle is 7 °, which is half, Δp in FIG. 2 (the length in the direction perpendicular to the optical axis of the grating tip and the groove) decreases in all the annular zones. Compared with Example 1, the reduction in diffraction efficiency in the used light beam is improved. As described above, the optimum tilt angle may be set in consideration of the diffraction efficiency of the used light and the suppression of unnecessary light on the side surfaces of the grating. However, in order to obtain the effect of suppressing unnecessary light, the maximum inclination angle is preferably at least 5 ° or more.
次に本発明の実施例３について説明する。 Next, a third embodiment of the present invention will be described.
実施例３は、図１８、図１９に示すように、実施例１とは異なり、傾き角θｋを滑らかに変化させないで段階的に変化させる構成をとることも可能である。このような構成にすれば、型を加工する際に、領域に分けて格子側面の値を参照するようにすれば良く、また傾き角θｋも直線近似で精度良く算出できるため、加工は比較的簡単に行なうことができる。 As shown in FIGS. 18 and 19, the third embodiment can be configured to change the inclination angle θk stepwise without changing smoothly, unlike the first embodiment. With such a configuration, when the mold is machined, it is only necessary to divide into regions and refer to the values of the lattice side surfaces, and the inclination angle θk can be calculated accurately by linear approximation. It can be done easily.
次に本発明の実施例４について説明する。 Next, a fourth embodiment of the present invention will be described.
実施例４では、図２０に示すように、基板２４の曲面（図では凹面）２４ａ上に形成され、負のパワーの回折レンズとして作用する第１の回折格子部２６を有する第１の回折光学素子２２と、基板２５の曲面（図では凸面）２５ａ上に形成され、正のパワーの回折レンズとして作用する第２の回折格子部２７を有する第２の回折光学素子２３が、空気層２８を介して近接した構成となる積層構造の回折光学素子２１より成っている。 In the fourth embodiment, as shown in FIG. 20, the first diffractive optical element having the first diffraction grating portion 26 formed on the curved surface (concave surface in the figure) 24a of the substrate 24 and acting as a negative power diffractive lens. The second diffractive optical element 23 having the element 22 and the second diffraction grating portion 27 formed on the curved surface (convex surface in the figure) 25a of the substrate 25 and acting as a positive power diffractive lens has the air layer 28. It is composed of a diffractive optical element 21 having a laminated structure having a configuration close to each other.
この構成では、第１、第２回折格子部２６、２７の両方の回折格子部２６、２７に対して格子側面３４、３５を変化させることが可能である。この構成では、第１の回折格子部２６と、第２の回折格子部２７で、不要光が発生する入射角度の方向が異なっている。そのため、各々の回折格子部２６、２７で不要光が抑制できるように、独立に格子側面３４、３５の傾き角θｋを最適化しても良いし、どちらか、一方だけに本発明を実施しても良い。 In this configuration, it is possible to change the grating side surfaces 34 and 35 with respect to both the diffraction grating portions 26 and 27 of the first and second diffraction grating portions 26 and 27. In this configuration, the first diffraction grating portion 26 and the second diffraction grating portion 27 have different incident angles at which unnecessary light is generated. For this reason, the inclination angle θk of the grating side surfaces 34 and 35 may be optimized independently so that unnecessary light can be suppressed in each of the diffraction grating portions 26 and 27, or the present invention is carried out on only one of them. Also good.
尚、第１、第２の回折格子部２６、２７の材料は互いに分散が異なった材料より成っている。使用波長領域で設計波長（積層格子での光学光路長差が波長の整数倍となる波長）を２つ以上有している。 The first and second diffraction grating portions 26 and 27 are made of materials having different dispersions. Two or more design wavelengths (wavelengths at which the optical optical path length difference in the laminated grating is an integral multiple of the wavelength) are used in the used wavelength region.
次に本発明の実施例５について説明する。 Next, a fifth embodiment of the present invention will be described.
前述の実施例で説明した回折光学素子は、格子側面の傾き角が、光軸付近で約０°、外周付近で、特定の角度をもち、光軸から周辺部に向けて徐々に傾き角が変化する構成である。しかしながら、本発明の回折光学素子は、このような構成に限定されるものではない。光学系へ回折光学素子を適用し、不要光の発生状況によって、図２１や図２２で示すように一定の傾き角（０°を含む）を有する領域と、傾き角が徐々に変化する領域を、少なくとも１つの領域有していれば良い。 In the diffractive optical element described in the above-described embodiments, the inclination angle of the grating side surface is approximately 0 ° near the optical axis, has a specific angle near the outer periphery, and gradually increases from the optical axis toward the peripheral portion. It is a configuration that changes. However, the diffractive optical element of the present invention is not limited to such a configuration. A diffractive optical element is applied to the optical system, and an area having a constant inclination angle (including 0 °) and an area where the inclination angle gradually changes as shown in FIGS. It suffices to have at least one region.
次に本発明の実施例６について説明する。 Next, a sixth embodiment of the present invention will be described.
本発明の回折光学素子は基板と回折格子部を形成する材料が異なっていたがこれに限定するものではなく、回折格子部を形成する材料を基板と同じ材料で構成し基板と一体で製造してもよい。このような構成にすることで、基板外径と回折格子中心の位置が精度良くあわせられる。或いは基板がレンズ形状を有する場合は、基板レンズの芯と回折格子中心を良好に合せることが可能になる。 In the diffractive optical element of the present invention, the material forming the diffraction grating portion is different from that of the substrate. However, the invention is not limited to this. The material forming the diffraction grating portion is made of the same material as the substrate and is manufactured integrally with the substrate. May be. With such a configuration, the outer diameter of the substrate and the position of the diffraction grating center can be matched with high accuracy. Alternatively, when the substrate has a lens shape, the core of the substrate lens and the center of the diffraction grating can be well matched.
従って、本発明の回折光学素子を他のレンズ系に組込む際の光軸合せ精度が向上し、回折光学素子が偏心することによって生じる結像性能等の収差の劣化は大幅に低減することができる。 Therefore, the optical axis alignment accuracy when the diffractive optical element of the present invention is incorporated into another lens system is improved, and the deterioration of aberration such as imaging performance caused by the diffractive optical element being decentered can be greatly reduced. .
次に本発明の実施例７について説明する。 Next, a seventh embodiment of the present invention will be described.
本発明の実施例７の概略図２３に示す。図２３はカメラ等の撮影光学系の断面を示したものであり、同図中、１０１は撮影レンズで、内部に絞り４０と本発明の前述した各実施例の回折光学素子２１を有している。４１は結像面であるフィルムまたはＣＣＤが配置されている。 A schematic diagram 23 of Example 7 of the present invention is shown in FIG. FIG. 23 shows a cross section of a photographic optical system such as a camera. In FIG. 23, reference numeral 101 denotes a photographic lens having an aperture 40 and the diffractive optical element 21 of each of the above-described embodiments of the present invention. Yes. Reference numeral 41 denotes a film or CCD which is an imaging plane.
特に回折光学素子の各回折格子部に入射する光束の入射角の分布の重心（図形の重心と同じ）が包絡面の回折格子の中心での面法線に対し、回折格子部の中心よりに分布するようにしている。 In particular, the center of gravity of the incident angle distribution of the light beam incident on each diffraction grating portion of the diffractive optical element (same as the center of gravity of the figure) is closer to the surface normal at the center of the envelope diffraction grating than the center of the diffraction grating portion. To be distributed.
本発明の回折光学素子を適用すれば、格子側面に光束が入射した場合でも、不要光の発生が大幅に改善されているので、フレアが少なく解像力も高い高性能な撮影レンズが得られる。また本発明の回折光学素子は、簡単な製法で作成できるので、撮影光学系としては量産性に優れた安価な光学系を提供できる。 When the diffractive optical element of the present invention is applied, even when a light beam is incident on the side surface of the grating, the generation of unnecessary light is greatly improved, so that a high-performance photographic lens with little flare and high resolving power can be obtained. Further, since the diffractive optical element of the present invention can be produced by a simple manufacturing method, an inexpensive optical system excellent in mass productivity can be provided as a photographing optical system.
図２３では前玉のレンズの貼り合せ面に回折光学素子２１を設けたが、これに限定するものではなく、レンズ表面に設けても良いし、撮影レンズ内に複数、回折光学素子を使用しても良い。 In FIG. 23, the diffractive optical element 21 is provided on the lens surface of the front lens. However, the present invention is not limited to this, and the diffractive optical element 21 may be provided on the lens surface. May be.
また、本実施例では、カメラの撮影レンズの場合を示したが、これに限定するものではなく、ビデオカメラの撮影レンズ、事務機のイメージスキャナーや、デジタル複写機のリーダーレンズなど広波長域で使用される結像光学系に使用しても同様の効果が得られる。 In this embodiment, the case of a camera taking lens is shown. However, the present invention is not limited to this. In a wide wavelength range, such as a video camera taking lens, an office machine image scanner, or a digital copier reader lens. The same effect can be obtained even when used for the imaging optical system used.
次に本実施例の実施例８について説明する。 Next, an eighth embodiment of the present embodiment will be described.
本発明の実施例８を概略を図２４に示す。図２４は、双眼鏡等の観察光学系の断面を示したものであり、同図中２１は回折光学素子である対物レンズ、１０４は像を正立させるための像反転手段としてのプリズム、１０５は接眼レンズ、１０６は評価面（瞳面）である。回折光学素子２１は対物レンズの結像面４１での色収差等を補正する目的で使用されている。 FIG. 24 schematically shows Example 8 of the present invention. FIG. 24 shows a cross section of an observation optical system such as binoculars. In FIG. 24, 21 is an objective lens which is a diffractive optical element, 104 is a prism as an image inverting means for erecting an image, and 105 is An eyepiece 106 is an evaluation surface (pupil surface). The diffractive optical element 21 is used for the purpose of correcting chromatic aberration and the like on the imaging surface 41 of the objective lens.
本発明の回折光学素子を適用すれば、格子側面に光束が入射した場合でも、不要光の発生が大幅に改善されているので、フレアが少なく解像力も高い高性能な対物レンズが得られる。また本発明の回折光学素子は、簡単な製法で作成できるので、観察光学系としては量産性に優れた安価な光学系を提供できる。 When the diffractive optical element according to the present invention is applied, the generation of unnecessary light is greatly improved even when a light beam is incident on the side surface of the grating, so that a high-performance objective lens with little flare and high resolving power can be obtained. Further, since the diffractive optical element of the present invention can be produced by a simple manufacturing method, an inexpensive optical system excellent in mass productivity can be provided as an observation optical system.
本実施例では、対物レンズ２１に回折光学素子を形成した場合を示したが、これに限定するものではなく、プリズム表面や接眼レンズ内の位置であっても同様の効果が得られる。結像面より物体側に設けると、対物レンズのみでの色収差低減効果があるため、肉眼の観察系の場合すくなくとも対物レンズ側に設けることが望ましい。 In the present embodiment, the case where the diffractive optical element is formed on the objective lens 21 is shown, but the present invention is not limited to this, and the same effect can be obtained even at the prism surface or the position in the eyepiece. If it is provided on the object side from the imaging surface, it has the effect of reducing chromatic aberration only by the objective lens. Therefore, in the case of the naked eye observation system, it is desirable to provide it at least on the objective lens side.
また本実施例では、双眼鏡の場合を示したが、これに限定するものではなく地上望遠鏡や天体観測用望遠鏡などであってもよく、またレンズシャッターカメラやビデオカメラなどの光学式のファインダーであっても同様の効果が得られる。 In the present embodiment, binoculars are shown, but the present invention is not limited to this, and may be a terrestrial telescope, an astronomical observation telescope, or the like, or an optical finder such as a lens shutter camera or a video camera. However, the same effect can be obtained.
１、２１、回折光学素子 ２、２４、２５、基板 ３、回折格子部 ４、格子面
５、３４、３５、格子側面 ６、格子先端の包絡面 ７、格子溝の包絡面
８、成形用型 ２２、第１の回折光学素子 ２３、第２の回折光学素子
２６、第１の回折格子部 ２７、第２の回折格子部 ２８、空気層
２９、３０、回折格子 ３１、第１の回折格子面 ３２、第２の回折格子面
３３、曲面 ３６、第１の格子溝の包絡面 ３７、第１の格子先端の包絡面
３８、第２の格子先端の包絡面 ３９、第２の格子溝の包絡面
４０、１０２、絞り ４１、１０３、結像面 １０１、撮影レンズ
１０４、プリズム １０５、接眼レンズ １０６、評価面（瞳面）
1, 21, diffractive optical elements 2, 24, 25, substrate 3, diffraction grating portion 4, grating surfaces 5, 34, 35, grating side surface 6, grating tip envelope surface 7, grating groove envelope surface 8, molding die 22, first diffractive optical element 23, second diffractive optical element 26, first diffractive grating part 27, second diffractive grating part 28, air layers 29 and 30, diffractive grating 31, first diffractive grating surface 32, second diffraction grating surface 33, curved surface 36, first grating groove envelope 37, first grating tip envelope 38, second grating tip envelope 39, second grating groove envelope Surfaces 40 and 102, apertures 41 and 103, imaging surface 101, photographing lens 104, prism 105, eyepiece lens 106, evaluation surface (pupil surface)
Claims (14)
前記回折格子部は、２種類の異なる材料の境界に回折格子が形成されており、
該格子側面の回折格子の格子先端を連ねた包絡面の面法線に対する傾き角度θｋは、該回折格子部の中心では実質的に０であり、該回折格子部の中心領域から周辺領域に向かって、該格子側面が該回折格子の格子先端を連ねた包絡面の各格子先端位置における面法線と格子面がなす角度に対してより鈍角となる方向に変化し、
且つ隣接する回折格子間の傾き角度が連続してほぼ０の第１の領域を前記回折格子部の中心を含む領域に有し、前記第１の領域よりも周辺に前記変化量Δθｋが０．２より大きい第２の領域を有することを特徴とする回折光学素子。 In a diffractive optical element having a diffraction grating portion including a grating surface and a grating side surface, and having a blazed diffraction grating that diffracts to a specific order over the entire wavelength region to be used as a concentric periodic structure,
The diffraction grating portion has a diffraction grating formed at the boundary between two different materials,
The inclination angle θk with respect to the surface normal of the envelope surface connecting the grating tips on the side surface of the grating is substantially 0 at the center of the diffraction grating portion, and extends from the central region of the diffraction grating portion to the peripheral region . Then, the grating side surface changes in a direction that becomes more obtuse than the angle formed by the surface normal and the grating surface at each grating tip position of the envelope surface connecting the grating tips of the diffraction grating ,
In addition, a first region in which the tilt angles between adjacent diffraction gratings are continuously zero is provided in a region including the center of the diffraction grating portion, and the variation Δθk is about 0.1 mm in the periphery of the first region. A diffractive optical element having a second region greater than two .
該回折格子部は、格子面と格子側面を含むブレーズ型の回折格子が同心円状の周期構造より成り、
前記回折格子部は、２種類の異なる材料の境界に回折格子が形成されており、
該格子側面の回折格子の格子先端を連ねた包絡面の面法線に対する傾き角度θｋは、該回折格子部の中心では実質的に０であり、該回折格子部の中心領域から周辺領域に向かって、該格子側面が該回折格子の格子先端を連ねた包絡面の各格子先端位置における面法線と格子面がなす角度に対してより鈍角となる方向に変化し、
且つ隣接する回折格子間の傾き角度が連続してほぼ０の第１の領域を前記回折格子部の中心を含む領域に有し、前記第１の領域よりも周辺に前記変化量Δθｋが０．２より大きい第２の領域を有する
ことを特徴とする回折光学素子。 In a diffractive optical element having a diffractive optical part having a laminated grating structure in which two or more diffraction gratings made of materials having different dispersions are stacked close to each other, and having two or more design wavelengths in a used wavelength region,
The diffraction grating portion has a periodic structure in which a blazed diffraction grating including a grating surface and a grating side surface is concentric,
The diffraction grating portion has a diffraction grating formed at the boundary between two different materials,
The inclination angle θk with respect to the surface normal of the envelope surface connecting the grating tips on the side surface of the grating is substantially 0 at the center of the diffraction grating portion, and extends from the central region of the diffraction grating portion to the peripheral region. Then, the grating side surface changes in a direction that becomes more obtuse than the angle formed by the surface normal and the grating surface at each grating tip position of the envelope surface connecting the grating tips of the diffraction grating,
In addition, a first region in which the tilt angles between adjacent diffraction gratings are continuously zero is provided in a region including the center of the diffraction grating portion, and the variation Δθk is about 0.1 mm in the periphery of the first region. A diffractive optical element having a second region greater than two .
０≦ΔｐＬ／ｐＬ≦０．０５
を満たすことを特徴とする請求項１乃至８のいずれか１項の回折光学素子。 When the projected length of the grating side surface in the grating pitch direction is ΔpL and the grating pitch of each diffraction grating is pL,
0 ≦ ΔpL / pL ≦ 0.05
The diffractive optical element of any one of claims 1 to 8, characterized in that meet.
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