JP2011170028A - Diffractive optical element and imaging optical system having the same - Google Patents

Diffractive optical element and imaging optical system having the same Download PDF

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JP2011170028A
JP2011170028A JP2010032413A JP2010032413A JP2011170028A JP 2011170028 A JP2011170028 A JP 2011170028A JP 2010032413 A JP2010032413 A JP 2010032413A JP 2010032413 A JP2010032413 A JP 2010032413A JP 2011170028 A JP2011170028 A JP 2011170028A
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grating
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diffractive optical
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Hidemi Takayama
英美 高山
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Canon Inc
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffractive optical element capable of obtaining an excellent image by reducing flare generated from the grating wall surface of a diffraction grating, when the diffractive optical element is used to reduce the chromatic aberration of an imaging optical system and to provide the imaging optical system having the diffractive optical element. <P>SOLUTION: The diffractive optical element is provided in the optical path of the imaging optical system. The diffractive optical element has a diffraction surface including a grating surface and the grating wall surface arranged at a predetermined grating pitch in at least a part of the boundary between a first material and a second material different from each other in dispersion and refractive index. When the side of the first material is set as a light incident side, the refractive index of the first material is smaller than the refractive index of the second material; and when a position where the grating wall surface is in parallel with the center axis of the diffractive optical element is set as the reference position of the grating wall surface, the grating wall surface is inclined in a direction where a vertex angle of grating formed by the grating wall surface and the grating surface is smaller than that in the reference position in at least a part of the range of the diffraction surface. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

本発明は回折光学素子及びそれを用いた撮像光学系に関し、特に回折光学素子を形成する回折格子から生ずるフレア光を軽減し、良好なる光学性能が得られるデジタルカメラ、ビデオカメラ、TVカメラ、監視用カメラ等に好適なものである。   The present invention relates to a diffractive optical element and an imaging optical system using the diffractive optical element, and more particularly to a digital camera, a video camera, a TV camera, and a monitor capable of reducing flare light generated from a diffraction grating forming the diffractive optical element and obtaining good optical performance. It is suitable for a camera.

従来、撮像光学系の色収差を減じる方法として撮像光学系の1部に回折作用を有する回折光学素子を設ける方法が知られている(非特許文献1)。回折光学素子を撮像光学系中に用いるときには使用波長域全域において設計次数の光線の回折効率が十分高いことが必要になる。回折効率が低いと、即ち設計次数以外の回折次数をもった光線が多く存在すると、これらの光線は、設計次数の光線とは別な所に結像するため結像に悪影響を与えるフレア光となる。   Conventionally, as a method of reducing chromatic aberration of an imaging optical system, a method of providing a diffractive optical element having a diffractive action in a part of the imaging optical system is known (Non-Patent Document 1). When the diffractive optical element is used in the imaging optical system, it is necessary that the diffraction efficiency of the light beam of the designed order is sufficiently high over the entire use wavelength range. When the diffraction efficiency is low, that is, when there are many light beams having diffraction orders other than the design order, these light beams are imaged at a place different from the light of the design order, and flare light that adversely affects the image formation. Become.

回折効率の低下を防止するためには、回折格子を構成する格子面を格子壁面より成る回折面の格子ピッチを適切に設定することが重要である。この他、回折効率が低くなる要因として、回折格子の回折作用に寄与しない格子壁面で反射又は透過する光が多くなることがある。回折光学素子を撮像光学系に用いるとき、回折格子のうち回折作用に寄与しない格子壁面で光が反射又は透過した光が像面に到達するとフレア光となる。このため格子壁面で反射又は透過した光は像面に到達しないようにすることが重要である。   In order to prevent a reduction in diffraction efficiency, it is important to appropriately set the grating pitch of the diffraction surface composed of the grating wall surface as the grating surface constituting the diffraction grating. In addition, as a factor that lowers the diffraction efficiency, there is a large amount of light reflected or transmitted by the grating wall surface that does not contribute to the diffraction action of the diffraction grating. When a diffractive optical element is used in an imaging optical system, flare light is generated when light reflected or transmitted by a grating wall surface that does not contribute to the diffractive action of the diffraction grating reaches the image plane. For this reason, it is important that the light reflected or transmitted by the grating wall surface does not reach the image plane.

回折格子の回折効率を高めるために回折格子の格子壁面の角度を適切に設定することで、格子壁面でのケラレを少なくし、有効画角内の光束に対して最適化した回折光学素子が知られている(特許文献1、2)。また、格子壁面の角度を格子頂角が、より鈍角方向となるように傾けることで、格子壁面からの反射フレアが像面に到達するのを軽減するといった回折光学素子が知られている(特許文献3)。また、複数の回折格子を密着した回折光学素子において格子壁面に遮光手段を設けた回折光学素子が知られている(特許文献4)。   A diffractive optical element optimized for the luminous flux within the effective angle of view is known by reducing the vignetting on the grating wall surface by appropriately setting the grating wall angle to increase the diffraction efficiency of the diffraction grating. (Patent Documents 1 and 2). Further, there is known a diffractive optical element that reduces the reflection flare from the grating wall surface to reach the image plane by tilting the grating wall angle so that the vertex angle of the grating becomes an obtuse angle direction (patent) Reference 3). Further, there is known a diffractive optical element in which a light shielding means is provided on a grating wall surface in a diffractive optical element in which a plurality of diffraction gratings are closely attached (Patent Document 4).

特開2003−294924号公報JP 2003-294924 A 特開10−186118号公報JP 10-186118 A 特開2005−292571号公報JP 2005-292571 A 特開2004−126394号公報JP 2004-126394 A SPIE Vol.1354 International Lens Design Conference (1990)SPIE Vol.1354 International Lens Design Conference (1990)

回折光学素子を撮像光学系に用いたとき、回折格子より生ずるフレア光を軽減するのに有効画面内の光の回折効率を高める方法は、有効画面内の光に対する格子壁面から生ずるフレア光の抑制には有効である。しかしながら、有効画面外に太陽光等の強い輝度の物体があるような逆光シーンの実写においてはフレア光が増大してくる。   When a diffractive optical element is used in an imaging optical system, a method for increasing the diffraction efficiency of light within the effective screen to reduce flare light generated from the diffraction grating is to suppress flare light generated from the grating wall surface with respect to the light within the effective screen. Is effective. However, flare light increases in a real scene of a backlight scene in which an object with strong brightness such as sunlight is outside the effective screen.

一般に、回折格子に入射する光線の入射角度が格子壁面の角度からずれた場合には、格子壁面により反射され像面に到達した光はフレアとして画像に悪影響を及ぼす。この対策として、格子壁面の角度を格子頂角が、より鈍角方向となるように傾ければ、反射フレアが像面に到達するのを軽減することができる。しかしながら、格子壁面を格子頂角が鈍角方向となるように傾けることで透過光の位置を変えても不要光の影響を大きく減らすことが難しいということが本発明者の最近の検討で判明した。これは、不要光の発生の状況は幾何光学的な振る舞いだけでは無く、回折現象を起こすことで幾何光学的な光線の追跡では到達し得ない位置に光が到達することによる。また、回折格子の格子壁面に遮光手段を設ける方法は、加工が困難である。   In general, when the incident angle of a light beam incident on the diffraction grating deviates from the angle of the grating wall surface, the light reflected by the grating wall surface and reaching the image plane has a bad influence on the image as flare. As a countermeasure, if the angle of the grating wall surface is tilted so that the grating apex angle becomes a more obtuse angle, it is possible to reduce the reflection flare from reaching the image plane. However, the inventors have recently found that it is difficult to greatly reduce the influence of unnecessary light even if the position of transmitted light is changed by tilting the grating wall surface so that the grating apex angle becomes an obtuse angle direction. This is because the generation of unnecessary light is not only the geometrical optical behavior but also the fact that the light reaches a position that cannot be reached by the geometrical optical ray tracing by causing a diffraction phenomenon. Also, the method of providing the light shielding means on the grating wall surface of the diffraction grating is difficult to process.

撮像光学系の光路中に回折光学素子を使用する場合には、多くの場合回折光学素子に、画像形成に使用される有効画角内の光束以外の有効画角外からの光が入射する。特に撮像光学系の絞りより物体側に回折光学素子を使用して色収差の補正を行う場合には、有効画角外からの光が回折光学素子に入射し易くなりフレアが多く発生する原因となる。特に、有効画面内のうち最大画角の外側の30度以下の比較的低い角度から入射する太陽光のような強い光が、回折光学素子に直接入射すると、回折光学素子を2次光源としたフレアが多く発生する原因となる。   When a diffractive optical element is used in the optical path of the imaging optical system, in many cases, light from outside the effective field angle other than the light beam within the effective field angle used for image formation is incident on the diffractive optical element. In particular, when correcting chromatic aberration by using a diffractive optical element closer to the object side than the stop of the imaging optical system, light from outside the effective angle of view easily enters the diffractive optical element and causes a lot of flare. . In particular, when strong light such as sunlight that is incident from a relatively low angle of 30 degrees or less outside the maximum angle of view within the effective screen is directly incident on the diffractive optical element, the diffractive optical element is used as a secondary light source. It causes a lot of flare.

本発明は、撮像光学系の色収差を軽減するために回折光学素子を用いたとき回折格子の格子壁面から生ずるフレアを軽減し、良好なる画像が得られる回折光学素子及びそれを有する撮像光学系の提供を目的とする。   The present invention reduces a flare generated from the grating wall surface of a diffraction grating when a diffractive optical element is used to reduce chromatic aberration of the imaging optical system, and a diffractive optical element capable of obtaining a good image and an imaging optical system having the diffractive optical element. For the purpose of provision.

本発明の回折光学素子は、撮像光学系の光路中に設けられる回折光学素子であって、該回折光学素子は互いに分散と屈折率が異なる第1の材料と第2の材料の境界の少なくとも一部に所定の格子ピッチで配列された格子面と格子壁面を含む回折面を有し、該第1の材料側を光の入射側としたとき、該第1の材料の屈折率は該第2の材料の屈折率よりも小さく、該格子壁面が該回折光学素子の中心軸に対して平行となる位置を該格子壁面の基準位置とするとき、該格子壁面は該回折面の少なくとも一部の範囲内で該格子壁面と格子面とのなす格子頂角が基準位置の時に比べて小さくなる方向に傾いていることを特徴としている。   The diffractive optical element of the present invention is a diffractive optical element provided in the optical path of the imaging optical system, and the diffractive optical element is at least one of the boundaries between the first material and the second material having different dispersion and refractive index. When the first material side is a light incident side, the refractive index of the first material is the second refractive index when the portion has a diffraction surface including a grating surface and a grating wall surface arranged at a predetermined grating pitch. When the position where the grating wall surface is parallel to the central axis of the diffractive optical element is the reference position of the grating wall surface, the grating wall surface is at least part of the diffraction surface. Within the range, the lattice apex angle formed by the lattice wall surface and the lattice surface is inclined in a direction to be smaller than that at the reference position.

この他本発明の回折光学素子は、撮像光学系の光路中に設けられる回折光学素子であって、該回折光学素子は互いに分散と屈折率が異なる第1の材料と第2の材料の境界の少なくとも一部に所定の格子ピッチで配列された格子面と格子壁面を含む回折面を有し、該第1の材料側を光の入射側としたとき、該第1の材料の屈折率は該第2の材料の屈折率よりも大きく、該格子壁面が該回折光学素子の中心軸に対して平行となる位置を該格子壁面の基準位置とするとき、該格子壁面は該回折面の少なくとも一部の範囲内で該格子壁面と格子面とのなす格子頂角が基準位置の時に比べて大きくなる方向に傾いていることを特徴としている。   In addition, the diffractive optical element of the present invention is a diffractive optical element provided in the optical path of the imaging optical system, and the diffractive optical element has a boundary between the first material and the second material having different dispersion and refractive index. When a diffraction surface including a grating surface and a grating wall surface arranged at a predetermined grating pitch at least in part and the first material side is a light incident side, the refractive index of the first material is When the position of the grating wall surface that is larger than the refractive index of the second material and is parallel to the central axis of the diffractive optical element is a reference position of the grating wall surface, the grating wall surface is at least one of the diffraction surfaces. It is characterized in that the lattice apex angle formed by the lattice wall surface and the lattice plane is inclined in a direction larger than that at the reference position within the range of the portion.

本発明によれば、撮像光学系の色収差を軽減するために回折光学素子を用いたとき回折格子の格子壁面から生ずるフレアを軽減し、良好なる画像が得られる回折光学素子及びそれを有する撮像光学系が得られる。   According to the present invention, when a diffractive optical element is used to reduce chromatic aberration of an image pickup optical system, flare generated from the grating wall surface of the diffraction grating is reduced, and a diffractive optical element capable of obtaining a good image and an image pickup optical having the same A system is obtained.

本発明の実施例1の撮像光学系の説明図Explanatory drawing of the imaging optical system of Example 1 of this invention 本発明の実施例1の回折光学素子の断面図Sectional drawing of the diffractive optical element of Example 1 of this invention 本発明の実施例1を実施しなかった場合の回折格子の壁面角度の説明図Explanatory drawing of the wall surface angle of the diffraction grating at the time of not implementing Example 1 of this invention 本発明の実施例1の回折格子の格子壁面の角度の説明図Explanatory drawing of the angle of the grating | lattice wall surface of the diffraction grating of Example 1 of this invention 回折光学素子への光線入射角度の説明図Explanatory drawing of light incident angle to diffractive optical element 本発明の実施例1を実施しない場合のフレア発生状況の説明図Explanatory drawing of the flare occurrence situation when not implementing Example 1 of the present invention 本発明の実施例1の格子壁面の傾けの効果の説明図Explanatory drawing of the effect of the inclination of the lattice wall surface of Example 1 of this invention 本発明の回折光学素子の下側に入射した光線のフレア説明図Flare explanatory diagram of light incident on the lower side of the diffractive optical element of the present invention 本発明の回折光学素子の下側に入射した光線のフレア発生状況説明図Explanatory diagram of the occurrence of flare of light incident on the lower side of the diffractive optical element of the present invention 本発明の実施例2の回折光学素子の説明図Explanatory drawing of the diffractive optical element of Example 2 of this invention 本発明の実施例2を実施しない場合の回折光学素子の拡大図Enlarged view of the diffractive optical element when the second embodiment of the present invention is not carried out 本発明の実施例2を実施した場合の回折光学素子の拡大図Enlarged view of a diffractive optical element when Example 2 of the present invention is implemented 本発明の実施例2を実施しない場合のフレア発生状況の説明図Explanatory drawing of the flare occurrence situation when not implementing Example 2 of the present invention 本発明の実施例2の回折光学素子の下側に入射した光線のフレア説明図Flare explanatory drawing of a light ray incident on the lower side of the diffractive optical element of Example 2 of the present invention 本発明の実施例2の回折光学素子の下側に入射した光線のフレア発生状況の説明図Explanatory drawing of the flare generation | occurrence | production state of the light ray which injected into the lower side of the diffractive optical element of Example 2 of this invention 回折光学素子に入射した角度に対する回折効率変化の説明図Explanatory drawing of diffraction efficiency change with respect to the angle incident on the diffractive optical element 本発明の実施例3の回折光学素子の説明図Explanatory drawing of the diffractive optical element of Example 3 of this invention 本発明の実施例4の回折光学素子の説明図Explanatory drawing of the diffractive optical element of Example 4 of this invention

本発明の回折光学素子1は、デジタルカメラ、ビデオカメラ等の撮像装置の撮像光学系の光路中に設けられる。回折光学素子1は互いに分散と屈折率が異なる第1の材料31と第2の材料32の境界の少なくとも一部に所定の格子ピッチで配列された格子面46と格子壁面44を含む回折面を有している。第1の材料31と第2の材料32はレンズ部材のレンズ面上に積層して形成されている。第1の材料41側を光の入射側としたとき、第1の材料41の屈折率は第2の材料42の屈折率よりも小さい。格子壁面44が回折光学素子1の中心軸(光軸)21に対して平行となる位置を格子壁面44の基準位置とする。このとき、格子壁面44は回折面の少なくとも一部の範囲内で格子壁面44と格子面46とのなす格子頂角40が基準位置の時に比べて小さくなる方向に傾いている。また第1の材料41の屈折率が第2の材料42の屈折率よりも大きいときは、格子頂角が基準位置のときに比べて大きくなる方向に傾いている。そして格子壁面44が基準位置に比べて、傾いている回折面の少なくとも一部は回折光学素子1の中心軸21を含む範囲内又は中心軸21を含まない範囲内である。また格子壁面44が傾いていない範囲における格子壁面の傾きは基準位置と同じである。   The diffractive optical element 1 of the present invention is provided in an optical path of an imaging optical system of an imaging apparatus such as a digital camera or a video camera. The diffractive optical element 1 has a diffractive surface including a grating surface 46 and a grating wall surface 44 arranged at a predetermined grating pitch on at least a part of the boundary between the first material 31 and the second material 32 having different dispersion and refractive index. Have. The first material 31 and the second material 32 are laminated on the lens surface of the lens member. When the first material 41 side is the light incident side, the refractive index of the first material 41 is smaller than the refractive index of the second material 42. A position where the grating wall surface 44 is parallel to the central axis (optical axis) 21 of the diffractive optical element 1 is set as a reference position of the grating wall surface 44. At this time, the grating wall surface 44 is inclined in a direction where the grating apex angle 40 formed by the grating wall surface 44 and the grating surface 46 is smaller than that at the reference position within at least a part of the diffraction surface. Further, when the refractive index of the first material 41 is larger than the refractive index of the second material 42, the lattice apex angle is inclined in a direction larger than that at the reference position. Then, at least a part of the diffraction surface on which the grating wall surface 44 is inclined relative to the reference position is in a range including the central axis 21 of the diffractive optical element 1 or in a range not including the central axis 21. Further, the inclination of the grating wall surface in the range where the grating wall surface 44 is not inclined is the same as the reference position.

図1は本発明の実施例1の回折光学素子を焦点距離400mmの望遠レンズ(撮像光学系)に適用したときのレンズ断面図である。図1において、1は回折光学素子、2は開口絞り、3aはCCD等の撮像素子3が配置される像面である。4は最大画角の光束、5は撮像光学系1の光軸、6は有効画角の外側(有効画角外)からの太陽光等の平行の有効画角外光の一部である。回折光学素子1は、正のパワーを有するように格子中央から外側かけて格子ピッチを狭くした回折格子をレンズ面に付加している。これにより撮像光学系の色収差を改善している。   FIG. 1 is a lens cross-sectional view when the diffractive optical element according to Example 1 of the present invention is applied to a telephoto lens (imaging optical system) having a focal length of 400 mm. In FIG. 1, 1 is a diffractive optical element, 2 is an aperture stop, 3a is an image plane on which an image pickup device 3 such as a CCD is disposed. Reference numeral 4 denotes a light beam having the maximum field angle, 5 denotes an optical axis of the imaging optical system 1, and 6 denotes a part of parallel outside effective field angle light such as sunlight from outside the effective field angle (outside the effective field angle). In the diffractive optical element 1, a diffraction grating having a grating pitch narrowed from the center of the grating to the outside so as to have a positive power is added to the lens surface. This improves the chromatic aberration of the imaging optical system.

本実施例においては回折光学素子1は開口絞り2よりも物体側で第1レンズG1と第2レンズG2とその間に設けた回折光学部(回折格子)より成っている。このため、太陽光等の入射光は殆ど鏡筒で遮光されることなく、回折光学素子1に入射する。図1においては説明のため有効画角の外側からの有効画角外光6第1面の全面に入射している有効画角外の5度の入射光において、波長550nmの光が−30次の方向に回折する光を示している。実際の撮像光学系に入射する光は可視の波長域の光が、広い次数範囲に渡って回折光学素子1の回折格子で回折する。従って、像面3aに配置したCCD3上に形成される画像はこれらの光の積分により形成される。たとえば、図1の有効画角外光6は波長が異なると回折角度及び回折光の強度が変化するため、CCD3に到達する光束の幅及び位置及び強度が変化する。また、回折次数によって光の強度及び回折角度が変化し、CCD3に到達する光束の幅及び位置及び強度が変化する。   In this embodiment, the diffractive optical element 1 includes a first lens G1 and a second lens G2 on the object side of the aperture stop 2, and a diffractive optical part (diffraction grating) provided therebetween. For this reason, incident light such as sunlight enters the diffractive optical element 1 almost without being shielded by the lens barrel. In FIG. 1, for the sake of explanation, light having a wavelength of 550 nm is -30th-order in incident light at 5 degrees outside the effective angle of view that is incident on the entire first surface of the first surface 6 from outside the effective angle of view. The light diffracted in the direction is shown. The light incident on the actual imaging optical system is diffracted by the diffraction grating of the diffractive optical element 1 over a wide order range. Therefore, an image formed on the CCD 3 arranged on the image plane 3a is formed by integrating these lights. For example, since the diffraction angle and the intensity of the diffracted light change when the wavelength of the light 6 outside the effective angle of view in FIG. 1 is different, the width, position, and intensity of the light beam reaching the CCD 3 change. Further, the intensity and angle of light change depending on the diffraction order, and the width, position and intensity of the light beam reaching the CCD 3 change.

図2は図1で用いている回折光学素子1の説明図である。図2において21は光軸(中心軸)、22は第1レンズ、23は第2レンズ、24は低屈折率高分散の第1の材料、25は高屈折率低分散の第2の材料である。第1の材料は第2の材料より低屈折率材料より成っている。24a、25aは回折格子である。このように低屈折率高分散の第1材料24と高屈折率低分散の第2の材料25を組み合わせて広い波長域で高い回折効率を得ている。ここで第1の材料側が光入射側である。また、26は光軸(中心軸)21より上側の回折格子24a、25aの輪帯の格子壁面24b1に入射する有効画面外(有効画角外)の光線、27は光軸(中心軸)21より下側の回折格子の輪帯の格子壁面24b2に入射する有効画面外の光線を示している。光線26と光線27は平行光束の一部を示している。光線が上から入射して回折光学素子1の上側に入射する場合と光線が上から入射して光軸21を超えて回折光学素子1の下側に入射する光では光線が格子壁面24b1、24b2に入射して反射する状況が異なっている。   FIG. 2 is an explanatory diagram of the diffractive optical element 1 used in FIG. In FIG. 2, 21 is an optical axis (center axis), 22 is a first lens, 23 is a second lens, 24 is a first material with low refractive index and high dispersion, and 25 is a second material with high refractive index and low dispersion. is there. The first material is made of a material having a lower refractive index than the second material. Reference numerals 24a and 25a denote diffraction gratings. In this way, high diffraction efficiency is obtained in a wide wavelength region by combining the first material 24 with low refractive index and high dispersion and the second material 25 with high refractive index and low dispersion. Here, the first material side is the light incident side. Reference numeral 26 denotes a light beam outside the effective screen (outside the effective field angle) that enters the annular grating wall surface 24b1 of the diffraction gratings 24a and 25a above the optical axis (center axis) 21, and 27 denotes the optical axis (center axis) 21. Light rays outside the effective screen incident on the grating wall surface 24b2 of the annular zone of the lower diffraction grating are shown. A light beam 26 and a light beam 27 indicate a part of the parallel light flux. In the case where the light beam is incident from above and incident on the upper side of the diffractive optical element 1 and in the light beam incident from above and incident on the lower side of the diffractive optical element 1 beyond the optical axis 21, the light beams are grating wall surfaces 24 b 1 and 24 b 2. The situation where the light enters and reflects is different.

図3は従来の回折光学素子の回折格子の格子壁面34の角度の説明図である。図4は本実施例に係る回折格子の格子壁面44の角度の説明図である。図3、図4において31、41は低屈折率高分散の第1の材料(第1の回折格子)、32、42は高屈折率低分散の第2の材料(第2の回折格子)である。33、43は画像を形成する光線の有効画角内(有効画面内)の最大角度の光線39、49と最小角度光線38、48の平均角度を示した補助線(中心角度光線)である。35、45は有効画角の外(有効画角外)から回折格子の格子壁面34、44に入射する光線(有効画角外光)を示している。36、46は格子面である。   FIG. 3 is an explanatory diagram of the angle of the grating wall surface 34 of the diffraction grating of the conventional diffractive optical element. FIG. 4 is an explanatory diagram of the angle of the grating wall surface 44 of the diffraction grating according to the present embodiment. 3 and 4, reference numerals 31 and 41 denote a first material (first diffraction grating) with a low refractive index and high dispersion, and reference numerals 32 and 42 denote a second material (second diffraction grating) with a high refractive index and low dispersion. is there. Reference numerals 33 and 43 denote auxiliary lines (center angle light beams) indicating the average angles of the maximum light rays 39 and 49 and the minimum angle light beams 38 and 48 within the effective field angle (effective screen) of the light rays forming the image. Reference numerals 35 and 45 denote light rays (outside the effective field angle) that are incident on the grating wall surfaces 34 and 44 of the diffraction grating from outside the effective field angle (outside the effective field angle). Reference numerals 36 and 46 denote lattice planes.

上記の平均角度の決定方法としては、図5に示すように回折光学素子1に入射する光線角度を求めた上で決定する。図5は回折光学素子1の形成されている面(図2の面28)に対する入射角度を、横軸に回折光学素子1の中心(光軸)を0とした時の光線入射高さ、縦軸に光線角度を示している。51は有効画角内の最大角度の光線39、49である。52は有効画角内の最小角度の光線38、48である。53は平均角度の光線33、43を示している。有効画角内の光線の平均角度に対して回折効率を最も高くするためには、この平均角度の光線33と一致させた方向に回折格子31の格子壁面34を傾けた方が良い。図3はこの時の状態を示した説明図である。   As a method for determining the average angle, the angle of light incident on the diffractive optical element 1 is determined as shown in FIG. 5 shows the incident angle with respect to the surface on which the diffractive optical element 1 is formed (surface 28 in FIG. 2). The horizontal axis represents the incident light height when the center (optical axis) of the diffractive optical element 1 is 0, and The ray angle is shown on the axis. Reference numeral 51 denotes light rays 39 and 49 having the maximum angle within the effective angle of view. Reference numeral 52 denotes the light rays 38 and 48 having the minimum angle within the effective angle of view. Reference numeral 53 denotes light rays 33 and 43 having an average angle. In order to maximize the diffraction efficiency with respect to the average angle of light rays within the effective angle of view, it is better to incline the grating wall surface 34 of the diffraction grating 31 in the direction that coincides with the light rays 33 having this average angle. FIG. 3 is an explanatory view showing the state at this time.

図3における格子壁面34の方向は回折格子31への入射光の有効画角内の最大角度の光線39と最小角度の光線38の平均値である補助線(平均角度の光線)33の方向に平行にしている。この時、回折光学素子1に入射した有効画角外光線35は低屈折率の第1の材料31を通過した後、高屈折率の第2の材料32に入射し、図3に示したように低い角度で回折格子に入射した時は格子壁面34において全反射する。この時のフレア発生状況を回折光学素子1への入射角度が10°の場合について、横軸に回折角度、縦軸に全光量を100%とした時の光量分布を図6に示す。また、計算に使用した回折格子は1次の回折効率が最も高くなるように最適化した回折格子として計算している。グラフの横軸の角度は回折光学素子1の面法線に対する角度であり図3に示したように+側を取る。   The direction of the grating wall surface 34 in FIG. 3 is in the direction of an auxiliary line (light ray of average angle) 33 that is the average value of the light beam 39 having the maximum angle and the light beam 38 having the minimum angle within the effective field angle of the incident light on the diffraction grating 31. They are parallel. At this time, the light beam 35 outside the effective angle of view incident on the diffractive optical element 1 passes through the first material 31 having a low refractive index and then enters the second material 32 having a high refractive index, as shown in FIG. When the light enters the diffraction grating at a low angle, it is totally reflected at the grating wall surface 34. FIG. 6 shows a light amount distribution when the flare generation state at this time is when the incident angle to the diffractive optical element 1 is 10 ° and the horizontal axis indicates the diffraction angle and the vertical axis indicates the total light amount as 100%. The diffraction grating used in the calculation is calculated as an optimized diffraction grating so that the first-order diffraction efficiency is the highest. The angle of the horizontal axis of the graph is an angle with respect to the surface normal of the diffractive optical element 1 and takes the + side as shown in FIG.

図6において、10度付近に飽和しているピークを有しているが、これが1次の回折光の発生位置である。また、−10度付近に光量ピークがあるがこれが格子壁面の全反射光により発生しているフレアである。このピークを中心に回折によるフレアが発生していることが分かる。また、図6において像面に光が到達する角度は0度±1度〜0度±2度付近のフレアであり、-10度付近の全反射ピークは像面に到達していない。また、全反射光からの回折光は0度付近まで裾を引いた形状となっている。これを防止する方法として本実施例は図4に示すようにしている。回折格子の格子壁面44を有効画面内の光線のうち回折光学素子1への最大角度の光線49と最小角度の光線48の平均値の方向(中心角度の光線)43に対して鋭角方向に傾けている。即ち図3の格子頂角30が小さくなる方向に格子壁面44を傾けて図4の格子頂角40となるようにしている。   In FIG. 6, there is a saturated peak around 10 degrees, which is the position where the first-order diffracted light is generated. Moreover, although there is a light amount peak in the vicinity of −10 degrees, this is a flare generated by the total reflected light on the grating wall surface. It can be seen that flare due to diffraction occurs around this peak. In FIG. 6, the angle at which the light reaches the image plane is flare around 0 ° ± 1 ° to 0 ° ± 2 °, and the total reflection peak near −10 ° does not reach the image plane. In addition, the diffracted light from the totally reflected light has a shape with a skirt extending to around 0 degrees. As a method for preventing this, the present embodiment is configured as shown in FIG. The grating wall surface 44 of the diffraction grating is tilted in an acute angle direction with respect to the average value direction 43 (the central angle light beam) 43 of the maximum light beam 49 and the minimum light beam 48 to the diffractive optical element 1 among the light beams in the effective screen. ing. That is, the lattice wall surface 44 is inclined in the direction in which the lattice apex angle 30 in FIG. 3 becomes smaller so that the lattice apex angle 40 in FIG. 4 is obtained.

図7は格子壁面44の傾け角度に対するフレア光量の変化を示した説明図である。図7において横軸は回折角、縦軸はフレア光量である。図7において、格子壁面44の壁面角度を方向43に対して−10度まで鋭角方向に変化させた時のフレア発生状況を示している。グラフから0度入射の時に−10度付近にあったフレアピークが0度から遠ざかり裾の部分によるフレアも減少している事が分かる。また、その効果は傾け角度を大きくすることでよりフレアにとっては良い方向となるが、傾け角度を大きくすると回折効率が劣化するという問題が発生する。   FIG. 7 is an explanatory diagram showing changes in the amount of flare with respect to the inclination angle of the grating wall surface 44. In FIG. 7, the horizontal axis represents the diffraction angle, and the vertical axis represents the flare light quantity. In FIG. 7, the flare generation | occurrence | production situation when the wall surface angle of the lattice wall surface 44 is changed to an acute angle direction to -10 degree | times with respect to the direction 43 is shown. From the graph, it can be seen that the flare peak near -10 degrees when incident at 0 degrees is away from 0 degrees, and the flare caused by the skirt portion also decreases. Further, the effect is better for flare by increasing the tilt angle. However, if the tilt angle is increased, the problem arises that the diffraction efficiency deteriorates.

回折効率の劣化量については格子のピッチや傾け角度に依存する。この劣化のメカニズムは回折格子の壁面に入射する光束が壁面で蹴られることにより、回折格子に入射する光束の入射角度が変化した場合と発生のメカニズムは同じである。従って、格子のピッチが大きくなると蹴られる比率が小さくなるため、同じ格子壁面の傾け角度であっても回折効率の劣化は少なくなる。図16にこの回折格子への入射角度に対する回折効率の劣化の状況を示したグラフを示した。図16に示したように回折光学素子への入射角度が大きくなった時の回折効率はピッチが50μm、100μm、350μmと広くなるに従って大幅に改善していく事が分かる。   The amount of degradation in diffraction efficiency depends on the pitch and tilt angle of the grating. The mechanism of this deterioration is the same as the mechanism of occurrence when the incident angle of the light beam incident on the diffraction grating changes because the light beam incident on the wall surface of the diffraction grating is kicked by the wall surface. Accordingly, the ratio of kicking decreases as the grating pitch increases, so that the degradation of diffraction efficiency is reduced even at the same inclination angle of the grating wall surface. FIG. 16 shows a graph showing the state of deterioration of diffraction efficiency with respect to the incident angle to the diffraction grating. As shown in FIG. 16, it can be seen that the diffraction efficiency when the incident angle to the diffractive optical element is increased is greatly improved as the pitch is increased to 50 μm, 100 μm, and 350 μm.

一般に撮像光学系に使用する回折光学素子に用いられる回折格子は100μm以上のピッチを有しており、本実施例においては格子ピッチを200μm以上で構成している。さらに内側(光軸側)の輪帯に行くに従って格子ピッチはミリ単位まで大きくなる。したがって、格子壁面を10度程度傾けても回折効率の劣化は2%以下であり、十分許容範囲である。以上の説明については、有効画角外からの太陽光等の強い光(有効画角外光)が回折光学素子の上側に当たった図2の光線26についての説明であった。図2において光軸21を超えて回折光学素子1の下側の輪帯に入射した場合について以下に説明する。   In general, a diffraction grating used for a diffractive optical element used in an imaging optical system has a pitch of 100 μm or more, and in this embodiment, the grating pitch is 200 μm or more. Further, the grating pitch increases to the millimeter unit as it goes to the inner (optical axis side) ring zone. Therefore, even if the grating wall surface is tilted by about 10 degrees, the deterioration of the diffraction efficiency is 2% or less, which is sufficiently acceptable. The above description is about the light ray 26 in FIG. 2 in which strong light such as sunlight from outside the effective angle of view (light outside the effective angle of view) hits the upper side of the diffractive optical element. The case where the light enters the lower annular zone of the diffractive optical element 1 beyond the optical axis 21 in FIG. 2 will be described below.

図8は図2において回折光学素子1の下側に入射した光線86が格子壁面89に入射した時の状況を示した説明図である。図8において81は低屈折率高分散の第1の材料(第1の回折格子)、82は高屈折率低分散の第2の材料(第2の回折格子)である。83は画像を形成する光線の有効画角内の最大角度の光線と最小角度の光線の平均角度を示した補助線である。86は有効画角の外から回折格子の格子壁面89に入射する光線を示している。図8に示したように低屈折率の第1の材料81を通過した光線86は高屈折率の第2の材料82との境界において、フレネル反射及び透過することで2つの光線87、88に分離する。可視域の光に対して回折効率を高めた密着タイプの回折光学素子においては、第1の材料81と第2の材料82との屈折率差は0.1以下となるのが普通であり、従って殆どの光については透過光となる。   FIG. 8 is an explanatory diagram showing a situation when the light beam 86 incident on the lower side of the diffractive optical element 1 in FIG. In FIG. 8, 81 is a first material (first diffraction grating) having a low refractive index and high dispersion, and 82 is a second material (second diffraction grating) having a high refractive index and low dispersion. Reference numeral 83 denotes an auxiliary line indicating the average angle between the maximum angle ray and the minimum angle ray within the effective field angle of the light rays forming the image. Reference numeral 86 denotes light rays that enter the grating wall surface 89 of the diffraction grating from outside the effective angle of view. As shown in FIG. 8, the light ray 86 that has passed through the first material 81 having the low refractive index is reflected and transmitted at the boundary with the second material 82 having the high refractive index, so that two light rays 87 and 88 are formed. To separate. In the close contact type diffractive optical element with improved diffraction efficiency for visible light, the difference in refractive index between the first material 81 and the second material 82 is usually 0.1 or less, Therefore, most of the light is transmitted light.

例えば格子壁面89の法線方向に対して80度で回折格子の格子壁面89に入射した場合に約94%は透過光であり、6%が反射光である。実際にCCD面に到達するフレア光は反射光の方向に進むフレアであり、また、この反射光自体ではなく、この反射光の周辺に発生する回折光である。従って光軸を横切って回折光学素子の下側に入射した光によるフレアの発生は非常に少なく画像の劣化に対しては問題を発生させないレベルである。   For example, when incident on the grating wall surface 89 of the diffraction grating at 80 degrees with respect to the normal direction of the grating wall surface 89, about 94% is transmitted light and 6% is reflected light. The flare light that actually reaches the CCD surface is flare that travels in the direction of the reflected light, and is not the reflected light itself but the diffracted light generated around the reflected light. Accordingly, the occurrence of flare due to the light incident on the lower side of the diffractive optical element across the optical axis is very small and does not cause a problem with respect to image degradation.

図9はこの時の様子を回折光学素子への入射角度が10°の場合について、横軸に回折角度、縦軸に全光量を100%とした時の光量分布である。また、計算に使用した回折格子は1次の回折効率が最も高くなるように最適化した回折格子として計算している。グラフの横軸の角度は回折光学素子の面法線に対する角度であり図8に示したように+側を取る。   FIG. 9 shows the light quantity distribution when the incident angle to the diffractive optical element is 10 ° at this time and the horizontal axis represents the diffraction angle and the vertical axis represents the total light quantity as 100%. The diffraction grating used in the calculation is calculated as an optimized diffraction grating so that the first-order diffraction efficiency is the highest. The angle of the horizontal axis of the graph is an angle with respect to the surface normal of the diffractive optical element, and takes the + side as shown in FIG.

図9において、−10度付近に飽和しているピークを有しているが、これが1次の回折光の発生位置である。また、+10度付近に光量ピークがあるがこれが格子壁面のフレネル反射光により発生しているフレアである。このピークを中心に回折によるフレアが発生しているが、いずれにしてもフレアの量としては微弱な光である。また、図9において像面に光が到達する角度は0度±1度〜0度±2度付近の光であり、フレアの量としては微弱で画像を劣化させるレベルではない。従って、本実施例において説明したように、有効画角外からの光の入射側即ち、本実施例においては回折光学素子の上側に入射する光線に対して、対策を行うことでフレアを十分抑制することができる。   In FIG. 9, there is a saturated peak around −10 degrees, which is the position where the first-order diffracted light is generated. Further, there is a light amount peak near +10 degrees, which is a flare generated by Fresnel reflected light on the grating wall surface. Flares due to diffraction occur around this peak, but in any case, the amount of flare is weak light. Further, in FIG. 9, the angle at which the light reaches the image plane is light in the vicinity of 0 ° ± 1 ° to 0 ° ± 2 °, and the amount of flare is so weak that it does not deteriorate the image. Therefore, as described in the present embodiment, flare is sufficiently suppressed by taking measures against the incident side of light from outside the effective angle of view, that is, the upper side of the diffractive optical element in this embodiment. can do.

図10は本発明の実施例2の回折光学素子の説明図である。図10において101は光軸(中心軸)、102は第1レンズ、103は第2レンズ、106は高屈折率低分散の第1の材料、107は低屈折率高分散の第2の材料である。第1の材料は第2の材料より高屈折率材料より構成されている。このように低屈折率高分散の第2の材料107と高屈折率低分散の第1の材料106を組み合わせて広い波長域で高い回折効率を得ている。また、108は光軸101より上側の回折格子の輪帯の格子壁面106b1に入射する有効画面外の光線、109は光軸101より下側の回折格子の輪帯の格子壁面106b2に入射する有効画面外の光線を示している。光線108と光線109は平行光束の一部を示している。光線が上から入射して回折光学素子1の上側に当たる場合と光線が上から入射して光軸101を超えて回折光学素子1の下側に入射する光では光線が格子壁面106b1、106b2に入射して反射する状況が異なっている。   FIG. 10 is an explanatory diagram of a diffractive optical element according to Example 2 of the present invention. In FIG. 10, 101 is an optical axis (center axis), 102 is a first lens, 103 is a second lens, 106 is a first material having a high refractive index and low dispersion, and 107 is a second material having a low refractive index and high dispersion. is there. The first material is made of a material having a higher refractive index than that of the second material. In this way, a high diffraction efficiency is obtained in a wide wavelength range by combining the second material 107 having a low refractive index and a high dispersion and the first material 106 having a high refractive index and a low dispersion. In addition, 108 is a light beam outside the effective screen incident on the annular grating wall surface 106b1 of the diffraction grating above the optical axis 101, and 109 is effective incident on the grating wall surface 106b2 of the annular ring below the optical axis 101. Shows off-screen rays. A light beam 108 and a light beam 109 indicate a part of the parallel light flux. In the case where the light beam is incident from above and hits the upper side of the diffractive optical element 1 and in the light beam incident from above and incident on the lower side of the diffractive optical element 1 beyond the optical axis 101, the light beam is incident on the grating wall surfaces 106b1 and 106b2. And the situation of reflection is different.

図11は従来の回折光学素子の回折格子の格子壁面101b1の角度の説明図である。図12は本実施例に係る回折格子の格子壁面101b1の角度の説明図である。図11、図12において111、121は高屈折率低分散の第1の材料、112、122は低屈折率高分散の第2の材料である。113、123は画像を形成する光線の有効画角内の最大角度の光線116、126と最小角度の光線117、127の平均角度を示した補助線(中心角度の光線)である。115、125は有効画角の外(有効画角外)から回折格子の格子壁面101b1に入射する光線(有効画角外光線)を示している。   FIG. 11 is an explanatory diagram of the angle of the grating wall surface 101b1 of the diffraction grating of the conventional diffractive optical element. FIG. 12 is an explanatory diagram of the angle of the grating wall surface 101b1 of the diffraction grating according to the present embodiment. 11 and 12, reference numerals 111 and 121 denote a first material having a high refractive index and a low dispersion, and reference numerals 112 and 122 denote a second material having a low refractive index and a high dispersion. Reference numerals 113 and 123 denote auxiliary lines (light beams having a central angle) indicating the average angles of the light beams 116 and 126 having the maximum angle and the light beams 117 and 127 having the minimum angle within the effective field angle of the light beam forming the image. Reference numerals 115 and 125 denote light rays (outside the effective angle of view) that enter the grating wall surface 101b1 of the diffraction grating from outside the effective angle of view (outside the effective angle of view).

図11において、有効画面外の光線115は高屈折率の第1の材料111を通過し、高屈折率の第2の材料111と低屈折率の第1の材料112の回折格子の格子壁面101b1において全反射する。全反射のためこの時のフレアの光量は強い光となるが、角度的にCCD面には到達しない。この時の様子を回折光学素子1への入射角度が10°の場合について、横軸に回折角度、縦軸に全光量を100%とした時の光量としたグラフを図13に示す。また、計算に使用した回折格子は1次の回折効率が最も高くなるように最適化した回折格子として計算している。グラフの横軸の角度は回折光学素子1の面法線に対する角度であり図11に示したように+側を取る。   In FIG. 11, the light beam 115 outside the effective screen passes through the first material 111 having a high refractive index, and the grating wall surface 101b1 of the diffraction grating of the second material 111 having a high refractive index and the first material 112 having a low refractive index. Totally reflected. Due to total reflection, the amount of flare at this time is strong, but it does not reach the CCD surface in terms of angle. FIG. 13 is a graph showing the state at this time, where the incident angle to the diffractive optical element 1 is 10 °, and the horizontal axis represents the diffraction angle and the vertical axis represents the total light amount as 100%. The diffraction grating used in the calculation is calculated as an optimized diffraction grating so that the first-order diffraction efficiency is the highest. The angle on the horizontal axis of the graph is the angle with respect to the surface normal of the diffractive optical element 1, and is on the + side as shown in FIG.

図13において、−10度付近に飽和しているピークを有しているが、これが1次の回折光の発生位置である。また、+10度付近に光量ピークがあるがこれが格子壁面の全反射光により発生しているフレアである。このピークを中心に回折によるフレアが発生していることが分かる。また、図13のグラフにおいて像面に光が到達する角度は0度±1度〜0度±2度付近のフレアであり、+10度付近の全反射ピークは像面に到達していない。また、全反射光からの回折光は0度付近まで裾を引いた形状となっている。これを防止する方法として本実施例は回折格子の格子壁面を有効画面内の光線の回折光学素子1への最大角度の光線116、126と最小角度の光線117、127の平均値の方向113、123に対して鈍角方向に傾けている。   In FIG. 13, there is a saturated peak in the vicinity of −10 degrees, which is the generation position of the first-order diffracted light. In addition, there is a light amount peak near +10 degrees, which is a flare generated by the total reflected light on the grating wall surface. It can be seen that flare due to diffraction occurs around this peak. In the graph of FIG. 13, the angle at which light reaches the image plane is a flare near 0 ° ± 1 ° to 0 ° ± 2 °, and the total reflection peak near + 10 ° does not reach the image plane. Further, the diffracted light from the totally reflected light has a shape with a skirt extending to near 0 degrees. As a method for preventing this, in the present embodiment, the grating wall surface of the diffraction grating is formed on the effective screen with the average angle direction 113 of the maximum angle rays 116 and 126 and the minimum angle rays 117 and 127 to the diffractive optical element 1. It is inclined in an obtuse angle direction with respect to 123.

即ち、格子頂角110が大きくなる方向に格子壁面101b1を傾けている。図12はこの格子頂角120が鈍角方向に傾けた回折格子の状態を示した説明図である。図12に示したように鈍角方向に回折格子の格子壁面101b1を傾けることで、光線125の格子壁面101b1で反射後の全反射光は図13の0度から遠ざかる方向に移動し、これに伴い発生する0度付近のフレア光も減少する。   That is, the lattice wall surface 101b1 is inclined in the direction in which the lattice apex angle 110 increases. FIG. 12 is an explanatory view showing a state of a diffraction grating in which the grating apex angle 120 is inclined in an obtuse angle direction. As shown in FIG. 12, by tilting the grating wall surface 101b1 of the diffraction grating in the obtuse angle direction, the total reflected light reflected by the grating wall surface 101b1 of the light beam 125 moves in a direction away from 0 degrees in FIG. The generated flare light near 0 degrees is also reduced.

図14は図10において、回折光学素子1の下側に入射した光線が格子壁面106b2に入射した時の状況を示した説明図である。図14において141は高屈折率低分散の第1の材料、142は低屈折率高分散の第2の材料である。143は画像を形成する光線の有効画角内の最大角度の光線と最小角度の光線の平均角度を示した補助線である。145は有効画角の外から回折格子の格子壁面106b2に入射する光線を示している。図14に示したように高屈折率の第1の材料141を通過した光線は低屈折率の第2の材料142との境界を通過する。その後、再び高屈折率の第1の材料141との境界の回折格子の格子壁面106b2において、フレネル反射及び透過することで2つの光線146、147に分離する。   FIG. 14 is an explanatory diagram showing a situation when the light beam incident on the lower side of the diffractive optical element 1 in FIG. 10 enters the grating wall surface 106b2. In FIG. 14, 141 is a first material having a high refractive index and low dispersion, and 142 is a second material having a low refractive index and high dispersion. Reference numeral 143 denotes an auxiliary line indicating the average angle between the maximum angle ray and the minimum angle ray within the effective field angle of the light ray forming the image. Reference numeral 145 denotes light rays that enter the grating wall surface 106b2 of the diffraction grating from outside the effective angle of view. As shown in FIG. 14, the light beam that has passed through the first material 141 having a high refractive index passes through the boundary with the second material 142 having a low refractive index. Thereafter, the light beam is separated into two light beams 146 and 147 by Fresnel reflection and transmission on the grating wall surface 106b2 of the diffraction grating at the boundary with the first material 141 having a high refractive index.

可視域の光に対して回折効率を高めた密着タイプの回折光学素子においては、第1の材料141と第2の材料142との屈折率差は0.1以下となるのが普通であり、従って殆どの光については透過光となる。例えば格子壁面106b2の法線方向に対して80度で回折格子の格子壁面106b2に入射した場合に約94%は透過光であり、6%が反射光である。実際にCCD面に到達するフレア光は反射光の方向に進むフレアであり、また、この反射光自体ではなく、この反射光の周辺に発生する回折光である。従って光軸を横切って回折光学素子の下側に入射した光によるフレアの発生は非常に少なく画像の劣化に対しては問題を発生させないレベルである。   In the close contact type diffractive optical element with enhanced diffraction efficiency with respect to light in the visible range, the refractive index difference between the first material 141 and the second material 142 is usually 0.1 or less, Therefore, most of the light is transmitted light. For example, when light is incident on the grating wall surface 106b2 of the diffraction grating at 80 degrees with respect to the normal direction of the grating wall surface 106b2, about 94% is transmitted light and 6% is reflected light. The flare light that actually reaches the CCD surface is flare that travels in the direction of the reflected light, and is not the reflected light itself but the diffracted light generated around the reflected light. Accordingly, the occurrence of flare due to the light incident on the lower side of the diffractive optical element across the optical axis is very small and does not cause a problem with respect to image degradation.

図15はこの時の様子を回折光学素子への入射角度が10°の場合について、横軸に回折角度、縦軸に全光量を100%とした時の光量分布である。また、計算に使用した回折格子は1次の回折効率が最も高くなるように最適化した回折格子として計算している。グラフの横軸の角度は回折光学素子の面法線に対する角度であり図15に示したように−側を取る。図15において、+10度付近に飽和しているピークを有しているが、これが1次の回折光の発生位置である。また、−10度付近に光量ピークがあるがこれが格子壁面のフレネル反射光により発生しているフレアである。このピークを中心に回折によるフレアが発生しているが、いずれにしてもフレアの量としては微弱な光である。また、図15において像面に光が到達する角度は0度±1度〜0度±2度付近の光であり、フレアの量としては微弱で画像を劣化させるレベルではない。従って、本実施例において説明したように、有効画角外からの光の入射側即ち、本実施例においては回折光学素子の上側に入射する光線に対して、対策を行うことでフレアを抑制することができる。   FIG. 15 is a light amount distribution when the incident angle to the diffractive optical element is 10 ° at this time, with the diffraction angle on the horizontal axis and the total light amount on the vertical axis as 100%. The diffraction grating used in the calculation is calculated as an optimized diffraction grating so that the first-order diffraction efficiency is the highest. The angle on the horizontal axis of the graph is the angle with respect to the surface normal of the diffractive optical element, and is negative as shown in FIG. In FIG. 15, there is a saturated peak around +10 degrees, which is the position where the first-order diffracted light is generated. Further, although there is a light amount peak near -10 degrees, this is flare generated by Fresnel reflected light on the grating wall surface. Flares due to diffraction occur around this peak, but in any case, the amount of flare is weak light. Further, in FIG. 15, the angle at which the light reaches the image plane is light in the vicinity of 0 ° ± 1 ° to 0 ° ± 2 °, and the amount of flare is so weak that it does not deteriorate the image. Therefore, as described in the present embodiment, flare is suppressed by taking measures against the light incident side from outside the effective angle of view, that is, the light beam incident on the upper side of the diffractive optical element in this embodiment. be able to.

図17は本発明の実施例3の回折光学素子の説明図である。図17は回折格子を正面から見た説明図である。図17において171は回折格子の格子壁面を画像を形成する光線の有効画角内の最大角度の光線と最小角度の光線の平均角度に対して傾けた範囲である。172は回折格子の格子壁面の角度を画像を形成する光線の有効画角内の最大角度の光線と最小角度の光線の平均角度とした範囲を示している。   FIG. 17 is an explanatory diagram of a diffractive optical element according to Example 3 of the present invention. FIG. 17 is an explanatory view of the diffraction grating as viewed from the front. In FIG. 17, reference numeral 171 denotes a range in which the grating wall surface is tilted with respect to the average angle of the maximum and minimum angle rays within the effective field angle of the light rays forming the image. Reference numeral 172 denotes a range in which the angle of the grating wall surface of the diffraction grating is the average angle of the maximum and minimum angles within the effective field angle of the light rays forming the image.

範囲171においては、回折格子の格子ピッチが大きいため比較的に大きな角度傾けても有効画角内の光に対して回折効率は殆ど悪化しない。一方、範囲172については比較的、回折格子の格子ピッチが小さく、大きく傾けると回折効率の劣化が懸念される。一方、範囲172は有効画角外の光が回折光学素子に入射する場合に光学鏡筒に蹴られて回折光学素子に光が入射しない領域が多く存在する。このため第1レンズよりCCD側にレンズを配置した場合、画面外の光が当たりにくくなりフレアの発生事態が少なくなる。従って、回折光学素子の光軸付近のみ回折格子の格子壁面を傾けることで、フレアの抑制した上で高い回折効率を維持することができる。   In the range 171, since the grating pitch of the diffraction grating is large, the diffraction efficiency is hardly deteriorated with respect to the light within the effective angle of view even if the grating is inclined at a relatively large angle. On the other hand, in the range 172, if the grating pitch of the diffraction grating is relatively small and tilted greatly, there is a concern that the diffraction efficiency will deteriorate. On the other hand, in the range 172, there are many regions where light outside the effective angle of view is kicked by the optical barrel when no light enters the diffractive optical element and no light enters the diffractive optical element. For this reason, when the lens is arranged on the CCD side from the first lens, it is difficult for light outside the screen to hit and the occurrence of flare is reduced. Therefore, by tilting the grating wall surface only in the vicinity of the optical axis of the diffractive optical element, high diffraction efficiency can be maintained while suppressing flare.

図18は本発明の実施例4の回折光学素子の説明図である。図18において、181は回折格子の格子壁面の角度を画像を形成する光線の有効画角内の最大角度の光線と最小角度の光線の平均角度に対して傾けた範囲である。182は回折格子の格子壁面の角度を画像を形成する光線の有効画角内の最大角度の光線と最小角度の光線の平均角度から回折格子の格子壁面を傾けフレアを抑制する範囲である。また、範囲183については回折格子の格子壁面の角度を画像を形成する光線の有効画角内の最大角度の光線と最小角度の光線の平均角度として構成する。図17の回折光学素子と異なる部分は中央付近の回折格子の格子壁面の角度である。これは範囲181の回折格子のフレアは回折格子の格子ピッチが大きいことと、範囲182と比較して像面に到達するフレア光の次数が高次となるためフレアの発生は非常に少なく、回折効率の維持を優先させたためである。   FIG. 18 is an explanatory diagram of a diffractive optical element according to Example 4 of the present invention. In FIG. 18, reference numeral 181 denotes a range in which the angle of the grating wall surface of the diffraction grating is tilted with respect to the average angle of the maximum light ray and the minimum light ray within the effective field angle of the light ray forming the image. Reference numeral 182 denotes a range in which the grating wall surface of the diffraction grating is tilted from the average angle of the light beam having the maximum angle and the light beam having the minimum angle within the effective field angle of the light beam forming the image to suppress flare. In the range 183, the angle of the grating wall surface of the diffraction grating is configured as the average angle of the maximum light ray and the minimum light ray within the effective field angle of the light ray forming the image. The difference from the diffractive optical element in FIG. 17 is the angle of the grating wall surface of the diffraction grating near the center. This is because the flare of the diffraction grating in the range 181 has a large grating pitch and the order of the flare light reaching the image plane is higher than that in the range 182 so that the generation of flare is very small. This is because priority is given to maintaining efficiency.

以上のように本発明の各実施例によれば、撮像光学系に回折光学素子を使用した場合に、最大画角に対して更に外側から入射する光束による回折格子の壁面に到達する光の像面への到達を防ぎカブリの少ない良好な撮影画像を得る事が出来る。   As described above, according to each embodiment of the present invention, when a diffractive optical element is used in the imaging optical system, an image of light reaching the wall surface of the diffraction grating by a light beam incident from the outside with respect to the maximum field angle. A good photographed image with little fogging can be obtained by preventing the surface from reaching the surface.

1 回折光学素子、2 絞り、3 CCD等の像面、4 最大画角の光束、5 撮像光学系の光軸、6 有効画角の外側からの太陽光等の平行光の一部、21 光軸、22 第1レンズ、23 第2レンズ、24 低屈折率高分散の第1の材料、25 高屈折率低分散の第2の材料、31、41 低屈折率高分散の第1の材料、32、42 高屈折率低分散の第2の材料、33、43 画像を形成する光線の有効画角内の最大角度と最小角度の平均角度を示した補助線、35、45 有効画角の外から回折格子壁面に入射する光線、31、41 低屈折率高分散の第1の材料、32、42 高屈折率低分散の第2の材料、33、43 画像を形成する光線の有効画角内の最大角度と最小角度の平均角度を示した補助線、35、45 有効画角の外から回折格子壁面に入射する光線、51 有効画角内の最大角度、52 有効画角内の最小角度、53 平均角度 DESCRIPTION OF SYMBOLS 1 Diffractive optical element, 2 Diaphragm, 3 CCD image surface, 4 Light flux of maximum field angle, 5 Optical axis of imaging optical system, 6 Part of parallel light, such as sunlight from outside effective field angle, 21 light Axis 22 First lens 23 Second lens 24 Low refractive index high dispersion first material 25 High refractive index low dispersion second material 31, 41 Low refractive index high dispersion first material, 32, 42 Second material with high refractive index and low dispersion, 33, 43 Auxiliary line showing average angle between maximum angle and minimum angle within effective field angle of ray forming image, 35, 45 Outside effective field angle Rays incident on the diffraction grating wall surface, 31, 41 First material with low refractive index and high dispersion, 32, 42 Second material with high refractive index and low dispersion, 33, 43 Within the effective angle of view of rays forming an image Auxiliary line showing average angle of maximum and minimum angles, 35, 45 Diffracted from outside effective field angle Ray incident on child wall 51 maximum angle of the effective angle of view, 52 minimum angle of the effective angle of view, 53 average angle

Claims (10)

撮像光学系の光路中に設けられる回折光学素子であって、該回折光学素子は互いに分散と屈折率が異なる第1の材料と第2の材料の境界の少なくとも一部に所定の格子ピッチで配列された格子面と格子壁面を含む回折面を有し、該第1の材料側を光の入射側としたとき、該第1の材料の屈折率は該第2の材料の屈折率よりも小さく、該格子壁面が該回折光学素子の中心軸に対して平行となる位置を該格子壁面の基準位置とするとき、該格子壁面は該回折面の少なくとも一部の範囲内で該格子壁面と格子面とのなす格子頂角が基準位置の時に比べて小さくなる方向に傾いていることを特徴とする回折光学素子。   A diffractive optical element provided in an optical path of an imaging optical system, the diffractive optical element being arranged at a predetermined grating pitch on at least a part of a boundary between a first material and a second material having different dispersion and refractive index When the first material side is the light incident side, the refractive index of the first material is smaller than the refractive index of the second material. When the position where the grating wall surface is parallel to the central axis of the diffractive optical element is a reference position of the grating wall surface, the grating wall surface is separated from the grating wall surface and the grating within at least a part of the diffraction surface. A diffractive optical element, wherein a lattice apex angle formed with a surface is inclined in a direction smaller than that at a reference position. 撮像光学系の光路中に設けられる回折光学素子であって、該回折光学素子は互いに分散と屈折率が異なる第1の材料と第2の材料の境界の少なくとも一部に所定の格子ピッチで配列された格子面と格子壁面を含む回折面を有し、該第1の材料側を光の入射側としたとき、該第1の材料の屈折率は該第2の材料の屈折率よりも大きく、該格子壁面が該回折光学素子の中心軸に対して平行となる位置を該格子壁面の基準位置とするとき、該格子壁面は該回折面の少なくとも一部の範囲内で該格子壁面と格子面とのなす格子頂角が基準位置の時に比べて大きくなる方向に傾いていることを特徴とする回折光学素子。   A diffractive optical element provided in an optical path of an imaging optical system, the diffractive optical element being arranged at a predetermined grating pitch on at least a part of a boundary between a first material and a second material having different dispersion and refractive index When the first material side is a light incident side, the refractive index of the first material is larger than the refractive index of the second material. When the position where the grating wall surface is parallel to the central axis of the diffractive optical element is a reference position of the grating wall surface, the grating wall surface is separated from the grating wall surface and the grating within at least a part of the diffraction surface. A diffractive optical element characterized in that a lattice apex angle formed with a surface is inclined in a direction larger than that at a reference position. 前記格子壁面が基準位置に比べて、傾いている回折面の少なくとも一部は該回折光学素子の中心軸を含む範囲内であることを特徴とする請求項1又は2の回折光学素子。   3. The diffractive optical element according to claim 1, wherein at least a part of the diffractive surface on which the grating wall surface is inclined relative to a reference position is within a range including a central axis of the diffractive optical element. 前記格子壁面が基準位置に比べて、傾いている回折面の少なくとも一部は該回折光学素子の中心軸を含まない範囲内であることを特徴とする請求項1又は2の回折光学素子。   3. The diffractive optical element according to claim 1, wherein at least a part of the diffractive surface on which the grating wall surface is inclined relative to a reference position is within a range not including the central axis of the diffractive optical element. 前記第1の材料と前記第2の材料はレンズ部材のレンズ面上に積層して形成さ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項の回折光学素子。   5. The diffractive optical element according to claim 1, wherein the first material and the second material are laminated on a lens surface of a lens member. 前記回折面のうち前記格子壁面が基準位置に比べて傾いていない範囲における該格子壁面の傾きは基準位置と同じであることを特徴とする請求項1乃至5のいずれか1項の回折光学素子。   6. The diffractive optical element according to claim 1, wherein an inclination of the grating wall surface in a range where the grating wall surface is not inclined relative to a reference position in the diffraction surface is the same as the reference position. . 請求項1乃至6のいずれか1項の回折光学素子を有することを特徴とする撮像光学系。   An imaging optical system comprising the diffractive optical element according to any one of claims 1 to 6. 前記回折光学素子は開口絞りよりも物体側に配置されていることを特徴とする請求項7の撮像光学系。   8. The imaging optical system according to claim 7, wherein the diffractive optical element is disposed on the object side of the aperture stop. 互いに分散と屈折率の異なる第1の材料と第2の材料の境界に回折格子を設けた回折光学素子を光路中に有する撮像装置において、第1の材料は第2の材料より低屈折率材料にて構成され、該回折光学素子は画像を形成する光束の入射する格子面と格子壁面を有し、画像を形成する光線の有効画角内の最大角度と最小角度の平均である中心角度の光線に対して、格子壁面の角度を格子面と格子壁面で構成される格子頂角が小さくなる方向に傾けられていることを特徴とする撮像装置。   In an imaging apparatus having a diffractive optical element in the optical path having a diffraction grating at the boundary between a first material and a second material having different dispersion and refractive index, the first material is a lower refractive index material than the second material The diffractive optical element has a grating surface on which a light beam forming an image is incident and a grating wall surface, and has a central angle that is an average of the maximum angle and the minimum angle within the effective field angle of the light beam forming the image. An imaging apparatus, wherein an angle of a grating wall surface is inclined with respect to a light beam in a direction in which a grating apex angle formed by the grating surface and the grating wall surface is reduced. 互いに分散と屈折率の異なる第1の材料と第2の材料の境界に回折格子を設けた回折光学素子を光路中に有する撮像装置において、第1の材料は第2の材料より高屈折率材料にて構成され、該回折光学素子は画像を形成する光束の入射する格子面と格子壁面を有し、画像を形成する光線の有効画角内の最大角度と最小角度の平均である中心角度の光線に対して、格子壁面の角度を格子面と格子壁面で構成される格子頂角が大きくなる方向に傾けられていることを特徴とする撮像装置。   In an imaging apparatus having a diffractive optical element in the optical path having a diffraction grating at the boundary between a first material and a second material having different dispersion and refractive index, the first material is a material having a higher refractive index than the second material. The diffractive optical element has a grating surface on which a light beam forming an image is incident and a grating wall surface, and has a central angle that is an average of the maximum angle and the minimum angle within the effective field angle of the light beam forming the image. An imaging apparatus, wherein an angle of a grating wall surface is inclined with respect to a light beam in a direction in which a grating apex angle formed by the grating surface and the grating wall surface is increased.
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013114959A1 (en) 2012-02-03 2013-08-08 オムロン株式会社 Confocal measurement device
CN111781715A (en) * 2020-08-10 2020-10-16 厦门力鼎光电股份有限公司 Wide-angle low-distortion optical imaging lens
US11249321B2 (en) 2016-10-31 2022-02-15 Canon Kabushiki Kaisha Diffractive optical element, optical system having the same, and imaging apparatus

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2013114959A1 (en) 2012-02-03 2013-08-08 オムロン株式会社 Confocal measurement device
JP2013160628A (en) * 2012-02-03 2013-08-19 Omron Corp Confocal measurement device
US11249321B2 (en) 2016-10-31 2022-02-15 Canon Kabushiki Kaisha Diffractive optical element, optical system having the same, and imaging apparatus
CN111781715A (en) * 2020-08-10 2020-10-16 厦门力鼎光电股份有限公司 Wide-angle low-distortion optical imaging lens

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