JP2014145871A - Imaging optical system using diffraction optical element - Google Patents

Imaging optical system using diffraction optical element Download PDF

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JP2014145871A
JP2014145871A JP2013013883A JP2013013883A JP2014145871A JP 2014145871 A JP2014145871 A JP 2014145871A JP 2013013883 A JP2013013883 A JP 2013013883A JP 2013013883 A JP2013013883 A JP 2013013883A JP 2014145871 A JP2014145871 A JP 2014145871A
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optical element
diffractive optical
refractive index
diffraction grating
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Hidemi Takayama
英美 高山
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Canon Inc
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Abstract

PROBLEM TO BE SOLVED: To provide a compact imaging optical system that has a sufficient chromatic aberration using an aberration correction effect of a diffraction optical element, by suppressing unnecessary diffracted light occurring when light from a high-luminance light source or sunlight enters the diffraction optical element.SOLUTION: In the diffraction optical element, the diffraction efficiency is increased in a wide wavelength region by tightly bonding a projecting lattice to a recessed lattice. When the diffraction optical element is disposed on an imaging surface side of a diaphragm, all lattices or some lattices in a range from the optical axis of the diffraction optical element to the periphery are set to have positive power. While, when the diffraction optical element is disposed on the front side of the diaphragm, the code of the power in the range from the optical axis of the diffraction optical element to the periphery is inverted.

Description

本発明は、広い波長域において回折効率を高めた回折光学素子およびそれを用いた撮像光学系に関するものである。   The present invention relates to a diffractive optical element with improved diffraction efficiency in a wide wavelength range and an imaging optical system using the same.

従来、光学系の色収差を減じる方法として光学系の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）。   Conventionally, as a method of reducing chromatic aberration of an optical system, a method of providing a diffractive optical element having a diffractive action in a part of the optical system is known (Non-Patent Document 1).

また、回折光学素子の形状としてはベースの形状に光路差関数で定義される位相項を付加した形状となっている。まず、ベースの形状としてはレンズの表面の形状であり、球面形状や非球面形状、平面形状であったりする。また、回折レンズ構造による光路長の付加量は、光軸からの高さｈ、ｎ次(偶数次)の光路差関数係数Cn、波長λを用いて、
φ(ｈ)＝(C1ｈ2＋C2ｈ4＋C3ｈ6＋…)×2π/λ
により定義される光路差関数φ(ｈ)により表す。一例として曲率がRのレンズ表面に上記の光路差関数φ（ｈ）にて格子形状を付加する場合、光軸方向の位置をX、ｋを中心から数えた輪帯番号、ｄを格子高さとした時 The shape of the diffractive optical element is a shape obtained by adding a phase term defined by an optical path difference function to the shape of the base. First, the shape of the base is the shape of the surface of the lens, and may be a spherical shape, an aspherical shape, or a planar shape. Further, the additional amount of the optical path length by the diffractive lens structure is obtained by using the height h from the optical axis, the optical path difference function coefficient Cn of the nth order (even order), and the wavelength λ.
φ (h) = (C1h 2 + C2h 4 + C3h 6 + ...) × 2π / λ
It is represented by an optical path difference function φ (h) defined by As an example, when a grating shape is added to the lens surface having the curvature R by the above optical path difference function φ (h), the position in the optical axis direction is X, the ring number is counted from the center, and d is the grating height. When

で表される形状とすることで、回折作用を付加した回折レンズを作成することが可能である。即ち上記の式においては最初の2項はベース形状を示しており、第3項は光路差関数で位相項を付加した形状を示している。また、第2項については輪帯番号が変わる部分でｘの位置が不連続となっており、これにより格子形状が生じる。 It is possible to create a diffractive lens to which a diffraction effect is added. That is, in the above formula, the first two terms represent the base shape, and the third term represents the shape with the phase term added by the optical path difference function. For the second term, the position of x is discontinuous at the part where the zone number changes, and this causes a lattice shape.

回折光学素子を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。   When a diffractive optical element is used in an optical system, it is necessary that the diffraction efficiency of the light beam of the designed order is sufficiently high over the entire wavelength range used.

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フレア光となる。   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 form flare light because they are imaged at different locations from the light beams of the design order.

図１８、図１９は従来の回折光学素子の説明図である。図１８において、１９２は回折格子の輪帯であり、格子の間隔（ピッチ）を変えることで光学的なパワーを与えることが出来る。また、図１９は第1の回折格子２０５と第2の回折格子２０６を空気を挟んで配置しており、この構成を取る事により広い波長域に対して高い回折効率を得る事が可能となっている。   18 and 19 are explanatory views of a conventional diffractive optical element. In FIG. 18, reference numeral 192 denotes a ring zone of the diffraction grating, and optical power can be given by changing the interval (pitch) of the grating. In FIG. 19, the first diffraction grating 205 and the second diffraction grating 206 are arranged with air sandwiched therebetween, and this configuration makes it possible to obtain high diffraction efficiency over a wide wavelength range. ing.

図２０は積層型回折格子の説明図である２１１は第1の回折格子、２１２は第2の回折格子、２１３は空気層である。第1の回折格子２１１と第2回折格子２１２は分散の異なる材質からなり、本実施例の回折格子においては、第1の回折格子２１１に紫外線硬化樹脂１（nd=1.635,νd=23.0）、第2の回折格子２１２に紫外線硬化樹脂２(nd=1.524,νd=50.8)を用い、第1の回折格子２１１の格子高さｄ１は7.8μｍ、第2の回折格子２１２の格子高さｄ２は10.7μｍ、2つの格子間の空気層の厚みｄ３は1.0μｍである。又、格子ピッチは140μｍ、設計次数は１次である。   FIG. 20 is an explanatory diagram of a laminated diffraction grating. 211 is a first diffraction grating, 212 is a second diffraction grating, and 213 is an air layer. The first diffraction grating 211 and the second diffraction grating 212 are made of materials having different dispersions. In the diffraction grating of this embodiment, the first diffraction grating 211 includes the ultraviolet curable resin 1 (nd = 1.635, νd = 23.0), An ultraviolet curable resin 2 (nd = 1.524, νd = 50.8) is used for the second diffraction grating 212, the grating height d1 of the first diffraction grating 211 is 7.8 μm, and the grating height d2 of the second diffraction grating 212 is The thickness d3 of the air layer between the two lattices is 10.7 μm and 1.0 μm. The lattice pitch is 140 μm, and the design order is primary.

このタイプの回折光学素子において、９８％以上の高い回折効率を可視の波長域全域にて確保するためには、低屈折率材料について部分分散比θgFを通常の材料より小さな値（リニア異常分散性）とする必要がある。   In this type of diffractive optical element, in order to ensure a high diffraction efficiency of 98% or more in the entire visible wavelength range, the partial dispersion ratio θgF of a low refractive index material is smaller than that of a normal material (linear anomalous dispersion) ) Is necessary.

回折効率を高めることは回折光学素子を使用した撮影光学系において高輝度点光源の撮影時に発生する輪帯状の不要回折光の低減に効果がある。一方、太陽光のような強い光が回折光学素子に直接入射することで発生するフレアについても様々な対策が提案されている。   Increasing the diffraction efficiency is effective in reducing the ring-shaped unnecessary diffracted light generated when photographing with a high brightness point light source in a photographing optical system using a diffractive optical element. On the other hand, various countermeasures have been proposed for flare generated when strong light such as sunlight is directly incident on the diffractive optical element.

例えば特許文献１では回折光学素子に高輝度光源の光や太陽光が入射した場合には不要回折光が発生し、この対策として光軸近傍のパワーの絶対値を最小とするように構成する方法が提案されている。具体的には回折光学素子のパワーを軸上から周辺に向けてパワーが反転しないように単調に変化させている。   For example, in Patent Document 1, unnecessary diffracted light is generated when light from a high-intensity light source or sunlight is incident on a diffractive optical element, and as a countermeasure against this, a method of minimizing the absolute value of power near the optical axis is used. Has been proposed. Specifically, the power of the diffractive optical element is monotonously changed so that the power does not reverse from the axial direction toward the periphery.

また、特許文献２では壁面の角度をより鈍角方向に傾けることで、反射フレアーを像面に到達させないようにしている。   In Patent Document 2, the reflection flare is prevented from reaching the image plane by inclining the angle of the wall surface in an obtuse angle direction.

また、特許文献３では密着タイプの回折光学素子の格子壁面に遮光手段を設けて、フレアーの発生を防止している。   In Patent Document 3, light shielding means is provided on the grating wall surface of the close-contact type diffractive optical element to prevent flare.

また、特許文献４の請求項３では硝子と樹脂の境界に回折格子を設けた正の回折光学素子を光学系の絞り又は瞳より像側に配置した場合に、硝子、回折格子、樹脂の順に回折光学素子を構成することで回折効率を高めている。   Further, in claim 3 of Patent Document 4, when a positive diffractive optical element provided with a diffraction grating at the boundary between glass and resin is arranged on the image side from the stop or pupil of the optical system, glass, diffraction grating, and resin are arranged in this order. The diffraction efficiency is increased by configuring the diffractive optical element.

特開２００２−１５６５８２号公報JP 2002-156582 A 特開２００５−２９２５７１号公報JP 2005-292571 A 特開２００４−１２６３９４号公報JP 2004-126394 A 特開平１１−２７１５１４号公報Japanese Patent Laid-Open No. 11-271514

SPIE Vol.1354 International Lens Design Conference (1990)SPIE Vol.1354 International Lens Design Conference (1990)

しかしながら特許文献１の方法は回折格子の格子間隔を広げることで、高輝度光源による不要回折光の低減には一定の効果があるものの、画面外から入射している強い光束については、効果は限定的である。これは、高輝度光源による不要回折光は回折効率の劣化に主に起因して発生しているのに対して画面外からの光によるフレアは主に回折格子の壁面による反射回折光で発生しているためである。   However, although the method of Patent Document 1 has a certain effect in reducing unwanted diffracted light by a high-intensity light source by widening the grating interval of the diffraction grating, the effect is limited for a strong light beam incident from the outside of the screen. Is. This is because unwanted diffracted light from a high-intensity light source is mainly caused by deterioration in diffraction efficiency, whereas flare from light from the outside of the screen is mainly caused by reflected diffracted light from the wall surface of the diffraction grating. This is because.

また、特許文献２の壁面の角度をより鈍角方向に傾けることで、反射フレアーを像面に到達させないようにするといった対策は幾何光学的には正しい方法に思える。しかしながら、鈍角に傾けることで透過光の位置を変えることは不要光を減らすことにある程度の効果はあるが、不要回折光のかなりの部分が残ることが最近行った詳細な検討で判明した。これは、回折光学素子の不要光の解析においては幾何光学的計算では不十分な評価であり、光を波として取り扱える厳密な電磁場解析が必要となるからである。実際に厳密結合波解析(RCWA)を行ったところ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し、壁面を傾けることだけでは不十分であることが分かってきた。   Further, the countermeasure of preventing the reflection flare from reaching the image plane by tilting the wall surface angle in Patent Document 2 in an obtuse angle direction seems to be a correct method in terms of geometric optics. However, a recent detailed study revealed that changing the position of transmitted light by tilting it at an obtuse angle has a certain effect on reducing unnecessary light, but a considerable part of unnecessary diffracted light remains. This is because geometrical optical calculation is insufficient for analysis of unnecessary light of the diffractive optical element, and strict electromagnetic field analysis that can handle light as a wave is required. Actually, rigorous coupled wave analysis (RCWA) has been carried out, and it has been found that the light reaches a position that cannot be reached by geometric optical ray tracing, and it is not sufficient to tilt the wall.

また、特許文献３のように密着タイプの回折光学素子の格子壁面に遮光手段を設けるといった方法については壁面に遮光部材を設けるためには、加工上の課題も多く、大幅なコスト上昇を招く可能性が強い。   Further, as for the method of providing the light shielding means on the grating wall surface of the close-contact type diffractive optical element as in Patent Document 3, there are many problems in processing because the light shielding member is provided on the wall surface, which may cause a significant cost increase. Strong nature.

通常の光源の光量が低い場合にはフレアの発生は限定的であり大きな問題となることは少ない。これに対して日中の撮影における太陽光は照度が最大で１０万lxに達するため、注意が必要である。特に逆光時の撮影においては、遮光用のフードを取り付けるといった対策を行うことが多いが、太陽光の撮像光学系への入射角度によっては、フレア発生を引き起こしてしまう。   When the amount of light from a normal light source is low, the occurrence of flare is limited and is not a major problem. On the other hand, since sunlight in daytime shooting reaches 100,000 lx at the maximum, attention is required. In particular, when taking a picture during backlighting, measures such as attaching a light shielding hood are often taken, but flare may be caused depending on the incident angle of sunlight to the imaging optical system.

特に、撮像光学系の前側に回折光学素子を配置した場合には最大画角の外側の２０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は、回折光学素子に直接光が当たりやすく、回折光学素子を２次光源としたフレアが発生する。このフレア光が像面へ到達することで、画像のカブリやゴーストといった問題が発生する。   In particular, when a diffractive optical element is disposed on the front side of the imaging optical system, strong light such as sunlight entering from a relatively low angle of 20 degrees or less outside the maximum field angle is directly applied to the diffractive optical element. It is easy to hit, and flare using a diffractive optical element as a secondary light source occurs. When the flare light reaches the image plane, problems such as image fogging and ghosting occur.

また、特許文献４は回折効率を高める観点での特許であるが、本発明の構成となっている絞りと回折格子の関係についての記載がある。しかしながら、フレアーの抑制の観点での考慮は特に行われていないため、回折格子壁面の方向については記載が無い。また、特許の内容も格子の高さが一定であることを前提としており、入射角度によって格子の高さを変えることで、回折効率の入射角度特性が改善することについては考慮されていない。   Moreover, although patent document 4 is a patent from a viewpoint of improving diffraction efficiency, there exists description about the relationship between the aperture_diaphragm | restriction and diffraction grating which are the structures of this invention. However, there is no description about the direction of the wall surface of the diffraction grating because no consideration is given to the suppression of flare. Further, the content of the patent also assumes that the height of the grating is constant, and no consideration is given to improving the incident angle characteristic of diffraction efficiency by changing the height of the grating according to the incident angle.

本発明は撮像光学系の撮影画面外にある太陽光のような強い光源からの光が回折光学素子に入射する時に発生するフレアを防止し、高い回折効率でかつ回折光学素子の収差補正能力を活用することで良好な画像が得られる撮像光学系を提供する。   The present invention prevents flare generated when light from a strong light source such as sunlight outside the imaging screen of the imaging optical system enters the diffractive optical element, and has high diffraction efficiency and aberration correction capability of the diffractive optical element. Provided is an imaging optical system that can be used to obtain a good image.

本発明は上記の課題に対して、相対的に高屈折率で低分散の第1材料と低屈折率で高分散の第２材料の境界面に回折格子を形成した回折光学素子において、該第１の材料の使用波長の中心波長における屈折率をnd1、該第２の材料の使用波長の中心波長における屈折率をnd2、該回折格子の最も回折効率を高めた回折次数をMとした時、該回折光学素子を撮像光学系の絞りより後ろ側に配置し、該第１の材料を光線入射側に配置し、該回折光学素子の中心から周辺部にかけて全て又は一部の回折光学素子が正のパワーを有し、回折格子は光束の殆どの光透過する位相付加面と位相付加面を繋ぐ格子壁面を有し、該格子壁面の角度は撮像光学系の格子壁面を通過する光束の主光線の方向と光軸方向の間の角度とし、
6.8 < |M/(nd1-nd2)| < 51.1 〜(1)
|nd1-nd2| ≦ 0.1 〜(2)
を満たした回折光学素子としたことを特徴とする。 The present invention is directed to a diffractive optical element in which a diffraction grating is formed on the interface between a first material having a relatively high refractive index and low dispersion and a second material having low refractive index and high dispersion. When the refractive index at the center wavelength of the used wavelength of the material 1 is nd1, the refractive index at the center wavelength of the used wavelength of the second material is nd2, and the diffraction order with the highest diffraction efficiency of the diffraction grating is M, The diffractive optical element is disposed behind the stop of the imaging optical system, the first material is disposed on the light incident side, and all or some of the diffractive optical elements are positive from the center to the periphery of the diffractive optical element. The diffraction grating has a phase addition surface that transmits most of the light beam of the light beam and a grating wall surface that connects the phase addition surface, and the angle of the grating wall surface is the principal ray of the light beam that passes through the grating wall surface of the imaging optical system And the angle between the direction of the optical axis and
6.8 <| M / (nd1-nd2) | <51.1-(1)
| nd1-nd2 | ≤ 0.1 to (2)
The diffractive optical element satisfies the above.

本発明の他の発明は相対的に高屈折率で低分散の第1材料と低屈折率で高分散の第２材料の境界面に回折格子を形成した回折光学素子において、該回折格子は相対的に低屈折率で高分散の第1材料と高屈折率で低分散の第２材料を密着させて構成し、該第１の材料の使用波長の中心波長における屈折率をnd1、該第２の材料の使用波長の中心波長における屈折率をnd2、該回折格子の最も回折効率を高めた回折次数をMとした時、該回折光学素子を撮像光学系の絞りより後ろ側に配置し、該第１の材料を光線入射側に配置し、回折光学素子の中心から周辺部にかけて回折光学素子のパワーの符号が反転し、該回折光学素子の中心から周辺部にかけて全て又は一部の回折光学素子が正のパワーを有し、回折格子は光束の殆どの光透過する位相付加面と位相付加面を繋ぐ格子壁面を有し、該格子壁面の角度は撮像光学系の格子壁面を通過する光束の主光線の方向と光軸方向の間の角度とし、
6.8 < |M/(nd1-nd2)| < 51.1 〜(1)
|nd1-nd2| ≦ 0.1 〜(2)
を満たした回折光学素子としたことを特徴とする。 Another invention of the present invention is a diffractive optical element in which a diffraction grating is formed at the interface between a first material having a relatively high refractive index and low dispersion and a second material having a low refractive index and high dispersion. In particular, a first material having a low refractive index and a high dispersion is adhered to a second material having a high refractive index and a low dispersion, and the refractive index at the center wavelength of the used wavelength of the first material is nd1, the second When the refractive index at the center wavelength of the used wavelength of the material is nd2, and the diffraction order with the highest diffraction efficiency of the diffraction grating is M, the diffractive optical element is arranged behind the stop of the imaging optical system, The first material is arranged on the light incident side, the sign of the power of the diffractive optical element is inverted from the center to the peripheral part of the diffractive optical element, and all or part of the diffractive optical element from the center to the peripheral part of the diffractive optical element Has a positive power, and the diffraction grating is aligned with the phase addition surface that transmits most of the light beam. Has a lattice wall that connects the addition surface, the angle of the grating wall surface and the angle between the direction and the optical axis direction of the principal ray of the light flux passing through the grating wall surface of the imaging optical system,
6.8 <| M / (nd1-nd2) | <51.1-(1)
| nd1-nd2 | ≤ 0.1 to (2)
The diffractive optical element satisfies the above.

また、本発明の他の発明は 相対的に高屈折率で低分散の第1材料と低屈折率で高分散の第２材料の境界面に回折格子を形成した回折光学素子において、該回折格子は相対的に低屈折率で高分散の第1材料と高屈折率で低分散の第２材料を密着させて構成し、該第１の材料の使用波長の中心波長における屈折率をnd1、該第２の材料の使用波長の中心波長における屈折率をnd2、該回折格子の最も回折効率を高めた回折次数をMとした時、該回折光学素子を撮像光学系の絞りより前側に配置し、該第１の材料を光線入射側に配置し、回折光学素子の中心から周辺部にかけて回折光学素子のパワーの符号が反転し、
6.8 < |M/(nd1-nd2)| < 51.1 〜(1)
|nd1-nd2| ≦ 0.1 〜(2)
を満たした回折光学素子としたことを特徴とする。 According to another aspect of the present invention, there is provided a diffractive optical element in which a diffraction grating is formed on a boundary surface between a relatively high refractive index and low dispersion first material and a low refractive index and high dispersion second material. Is composed of a first material having a relatively low refractive index and a high dispersion and a second material having a high refractive index and a low dispersion, and the refractive index at the center wavelength of the used wavelength of the first material is nd1, When the refractive index at the center wavelength of the wavelength used for the second material is nd2, and the diffraction order that maximizes the diffraction efficiency of the diffraction grating is M, the diffractive optical element is arranged in front of the stop of the imaging optical system, The first material is disposed on the light incident side, and the sign of the power of the diffractive optical element is reversed from the center to the periphery of the diffractive optical element,
6.8 <| M / (nd1-nd2) | <51.1-(1)
| nd1-nd2 | ≤ 0.1 to (2)
The diffractive optical element satisfies the above.

本発明によれば、回折光学素子に高輝度光源の光や太陽光が入射した場合に発生する不要回折光を抑制することで、回折光学素子の収差補正効果を生かしたコンパクトで色収差が良好な撮像光学系の提供が可能となる。   According to the present invention, the diffractive optical element is compact and has good chromatic aberration by taking advantage of the aberration correction effect of the diffractive optical element by suppressing unnecessary diffracted light generated when light of high-intensity light source or sunlight enters the diffractive optical element. An imaging optical system can be provided.

本発明の第１の実施例の光学系の説明図Explanatory drawing of the optical system of 1st Example of this invention 本発明の第１の実施例の素子断面図Device sectional view of the first embodiment of the present invention 本発明の第１の実施例の１次光の回折効率のグラフGraph of the diffraction efficiency of the primary light of the first embodiment of the present invention 本発明の第１の実施例の０次光と２次光の回折効率のグラフGraph of diffraction efficiency of zero-order light and second-order light of the first embodiment of the present invention 第１の実施例の回折光学素子の格子付近の説明図Explanatory drawing of the vicinity of the grating of the diffractive optical element of the first embodiment 本発明を実施しなかった場合の格子付近の説明図Explanatory drawing of the vicinity of the lattice when the present invention is not carried out フレネル反射率の説明図Illustration of Fresnel reflectivity 本発明を実施した時不要回折光の説明図Explanatory drawing of unnecessary diffracted light when the present invention is implemented 本発明を実施しなかった場合の不要回折光の説明図Explanatory drawing of unnecessary diffracted light when not carrying out the present invention 本発明の第２実施例の光学系説明図Optical system explanatory drawing of 2nd Example of this invention 本発明の第２実施例の回折格子による位相関数説明図Phase function explanatory diagram of the diffraction grating of the second embodiment of the present invention 本発明の第２実施例の回折格子の格子形状説明図Illustration of grating shape of diffraction grating of second embodiment of the present invention 本発明の第２実施例の回折光学素子のパワーの説明図Explanatory drawing of the power of the diffractive optical element of the second embodiment of the present invention 回折格子の格子成形の説明図Illustration of grating forming of diffraction grating 本発明の第３実施例の光学系の説明図Explanatory drawing of the optical system of 3rd Example of this invention 本発明の第３実施例の回折光学素子の説明図Explanatory drawing of the diffractive optical element of 3rd Example of this invention 本発明の第３実施例の回折格子の格子形状説明図Illustration of grating shape of diffraction grating of third embodiment of the present invention 従来の回折光学素子の上面図Top view of a conventional diffractive optical element 従来の回折光学素子の断面図Sectional view of a conventional diffractive optical element 従来の回折光学素子の拡大図Enlarged view of a conventional diffractive optical element

「実施例１」
図１は本発明の第1の実施例をレトロフォーカスタイプの広角撮像光学系に適用した場合の光学系の断面図である。 "Example 1"
FIG. 1 is a sectional view of an optical system when the first embodiment of the present invention is applied to a retrofocus type wide-angle imaging optical system.

図において、撮像光学系は物体側から像側に順に負の屈折力を有する第1レンズ群１、正の屈折力を有する第2レンズ群２を有する単一焦点距離の光学系である。   In the figure, the imaging optical system is a single focal length optical system having a first lens group 1 having a negative refractive power and a second lens group 2 having a positive refractive power in order from the object side to the image side.

第2レンズ群2のレンズ間には開口絞り３が設けられている。開口絞３よりも像側に配置され、CCD等の像面４に最も近い接合レンズ５の接合面は正のパワーの回折光学素子６が設けられている。この回折光学素子により色収差を良好に補正している。   An aperture stop 3 is provided between the lenses of the second lens group 2. A diffractive optical element 6 having a positive power is provided on the cemented surface of the cemented lens 5 which is disposed on the image side of the aperture stop 3 and closest to the image surface 4 such as a CCD. This diffractive optical element corrects chromatic aberration satisfactorily.

図２は本発明の回折光学素子を示した説明図である。図において２１は光軸、２２は回折光学素子を第2面側に成形する第1のレンズ、２３は回折光学素子を第1面側に成形する成形する第2のレンズ、２４は回折光学素子の第1の回折格子であり、第１の材料により構成されており、屈折率はnd1であり、アッベ数はνd1である。また、２５は第2の回折格子で屈折率はnd2であり、アッベ数はνd2である。２６は回折光学素子の格子面に入射する軸外光の主光線、２７は回折光学素子の壁面を透過した透過光、２８は回折光学素子の壁面により反射された反射光を示している。   FIG. 2 is an explanatory view showing a diffractive optical element of the present invention. In the figure, 21 is an optical axis, 22 is a first lens for shaping the diffractive optical element on the second surface side, 23 is a second lens for shaping the diffractive optical element on the first surface side, and 24 is a diffractive optical element. The first diffraction grating is made of the first material, has a refractive index of nd1, and an Abbe number of νd1. Reference numeral 25 denotes a second diffraction grating having a refractive index of nd2 and an Abbe number of νd2. Reference numeral 26 denotes a principal ray of off-axis light incident on the grating surface of the diffractive optical element, 27 denotes transmitted light transmitted through the wall surface of the diffractive optical element, and 28 denotes reflected light reflected by the wall surface of the diffractive optical element.

本発明においては、回折光学素子のパワーは正のパワーであり、第１の回折格子の材料に高屈折率低分散材料、第2の回折格子の材料に低屈折率高分散材料を使用する。すなわち
nd1 > nd2
νd1 > νd2
としている。 In the present invention, the power of the diffractive optical element is positive, and a high refractive index and low dispersion material is used as the material of the first diffraction grating, and a low refractive index and high dispersion material is used as the material of the second diffraction grating. Ie
nd1> nd2
νd1> νd2
It is said.

具体的な材料としては高屈折率低分散材料としてはアクリル系の紫外線硬化樹脂(nd=1.52、νd=51)に対してZrO2微粒子を19.9vol%混ぜた材料を使用した。微粒子分散後の高屈折率低分散材料の屈折率はnd=1.608,νd=48.7である。また、低屈折率高分散材料としては同じ紫外線硬化樹脂に対してITOの微粒子分散濃度を12.5vol%とした樹脂を使用した。また、高屈折率低分散材料としては同じ紫外線硬化樹脂に対してZrO2微粒子を19.9vol%混ぜた材料を使用した。この結果、微粒子分散後の低屈折率高分散材料の屈折率はnd=1.565,νd=22.7である。ITO微粒子の混合比率を高めることで、材料としては波長に対して線形の異常分散性を有する（リニア）の異常分散性を有した低アッベ数の材料を提供することが出来る。これにより格子の厚みは13.7μmと比較的に低い格子厚にすることが可能となる。この時の１次光の回折効率を図3に示す。また、設計次数の回折光に隣接する不要回折光(０２次光)の回折効率を図4に示す。１次の回折光が撮像光学系の結像に使用している回折光であり、良好な回折効率を全波長域において維持していることがわかる。また、高輝度光源の周辺に同心円状に発生する不要回折光の原因となる０次光と２次光共に全波長域で小さい値となっていることが分かる。   As a specific material, a material having 19.9 vol% of ZrO2 fine particles mixed with an acrylic ultraviolet curable resin (nd = 1.52, νd = 51) was used as a high refractive index and low dispersion material. The refractive indexes of the high refractive index and low dispersion material after dispersion of the fine particles are nd = 1.608 and νd = 48.7. Further, as the low refractive index and high dispersion material, a resin in which the fine particle dispersion concentration of ITO is 12.5 vol% with respect to the same ultraviolet curable resin was used. As the high refractive index and low dispersion material, a material in which 19.9 vol% of ZrO2 fine particles were mixed with the same ultraviolet curable resin was used. As a result, the refractive index of the low refractive index and high dispersion material after dispersion of the fine particles is nd = 1.565 and νd = 22.7. By increasing the mixing ratio of the ITO fine particles, it is possible to provide a material having a low Abbe number having a linear anomalous dispersion with respect to the wavelength (linear). As a result, the grating thickness can be reduced to a relatively low grating thickness of 13.7 μm. The diffraction efficiency of the primary light at this time is shown in FIG. FIG. 4 shows the diffraction efficiency of unnecessary diffracted light (02th order light) adjacent to the diffracted light of the designed order. It can be seen that the first-order diffracted light is the diffracted light used for imaging of the imaging optical system, and that good diffraction efficiency is maintained in the entire wavelength region. It can also be seen that both the 0th order light and the 2nd order light, which cause unnecessary diffracted light concentrically generated around the high brightness light source, have small values in the entire wavelength region.

請求項の（１）式は密着タイプの回折光学素子において、M次光の回折光を高めた回折格子の格子高さd線の波長に対して何倍とするかを示している。この（１）式の上限値を超えると壁面反射が増加してフレアが増加して問題となる。また（１）式の下限値以下については格子壁面起因のフレアの観点からは望ましいが、可視域の全波長範囲で高い回折効率を維持することが困難となり、結果として不要回折光が増加して問題となる。   The expression (1) in the claims shows how many times the wavelength of the grating height d line of the diffraction grating in which the diffracted light of the M-th order light is increased in the contact type diffractive optical element. If the upper limit of the equation (1) is exceeded, wall surface reflection increases and flare increases, which causes a problem. Further, the lower limit of the expression (1) is desirable from the viewpoint of flare caused by the grating wall surface, but it becomes difficult to maintain high diffraction efficiency in the entire wavelength range in the visible range, resulting in an increase in unnecessary diffracted light. It becomes a problem.

図１および図２からわかるように絞りより後ろ側に配置した回折光学素子に対する軸外からの光線の入射角度は、素子の上側に入射する光線は下から上に向かう方向に入射する。また、撮像光学系の絞りを絞った時には光束はより細くなり、主光線を中心とした狭い光束となる。一方、回折格子の壁面からのフレア光の画像に対する影響は絞りを絞ったときに顕著に表れるようになる。これは、絞りを絞ると素子に入射する光の入射角度のフレ幅が小さくなり、壁面からのフレアもより指向性を強く有する。このため、狭い範囲にフレアが集まり易くなるためである。従って、絞りを絞った時のフレアの発生を優先して抑制するべきである。このときの素子付近の状況を説明した説明図が図５である。   As can be seen from FIGS. 1 and 2, the incident angle of the light beam from the off-axis with respect to the diffractive optical element disposed behind the stop is such that the light beam incident on the upper side of the element is incident in the direction from bottom to top. Further, when the stop of the imaging optical system is reduced, the light beam becomes narrower and becomes a narrow light beam centered on the principal ray. On the other hand, the influence of the flare light from the wall surface of the diffraction grating on the image becomes noticeable when the aperture is stopped. This is because, when the stop is stopped, the flare width of the incident angle of the light incident on the element is reduced, and the flare from the wall surface has higher directivity. For this reason, flare tends to gather in a narrow range. Therefore, the generation of flare when the aperture is reduced should be suppressed with priority. FIG. 5 is an explanatory diagram for explaining the situation near the element at this time.

図において、５１は高屈折率低分散材料にて作成されが第1の回折格子、５２は低屈折率高分散材料で作成された第2の回折格子である。５３は回折格子壁面の方向をしめした補助線、５４は入射角度の負の方向を示した矢印、５５は回折光学素子に入射する入射光線であり、５６は格子壁面による反射光、５７は透過光、５８は回折格子の壁面を示している。なお、実際には反射光、透過光ともに回折の効果により広がりを有しているが、説明のために幾何光学的な光により説明を行う。また、回折格子の壁面５８が起因して不要回折光が発生するため、壁面５８付近の光のみを示して説明を行う。   In the figure, 51 is a first diffraction grating made of a high refractive index and low dispersion material, and 52 is a second diffraction grating made of a low refractive index and high dispersion material. 53 is an auxiliary line indicating the direction of the diffraction grating wall surface, 54 is an arrow indicating the negative direction of the incident angle, 55 is an incident light beam incident on the diffractive optical element, 56 is reflected light by the grating wall surface, and 57 is transmitted. The light 58 indicates the wall surface of the diffraction grating. Actually, both reflected light and transmitted light have a spread due to the effect of diffraction, but for the sake of explanation, description will be made with geometric optical light. Further, since unnecessary diffraction light is generated due to the wall surface 58 of the diffraction grating, only the light near the wall surface 58 will be described.

本発明を実施した場合にはまず入射光は第1の回折格子５１を通過後に第2の回折格子５２に入射し、回折格子の壁面５８に到達する。この時第1の回折格子を構成する材料の屈折率よりも第2の回折格子を構成する材料の方が屈折率が低いために、壁面５８に入射した光はフレネルの法則により反射光と透過光に分離する。   In the case of implementing the present invention, the incident light first passes through the first diffraction grating 51 and then enters the second diffraction grating 52 and reaches the wall surface 58 of the diffraction grating. At this time, since the refractive index of the material constituting the second diffraction grating is lower than the refractive index of the material constituting the first diffraction grating, the light incident on the wall 58 is reflected and transmitted by Fresnel's law. Separate into light.

このときの反射光と透過光の割合は第1の材料と第2の材料の屈折率が近いほど透過光の割合が増加する。図７は屈折率とフレネル反射の反射率を示したグラフである。図において、第1の材料の屈折率と第2の材料の屈折率の差Δｎにより反射率がどのように変化するかを示している。実際の回折光学素子の壁面５８の方向は入射光線の方向と平行となるように構成する方が壁面５８による反射光が減るために入射光線に出来るだけ平行となるように構成する。従って、壁面入射角度は大きな値となっており、材料の屈折率差Δｎが大きくなると反射光が大きくなるが、屈折率差Δｎが０．１以下であれば反射光が少なくなり、壁面５８に起因する不要回折光は撮像光学系では殆ど問題のないレベルまで減少する。   At this time, the ratio of the reflected light and the transmitted light increases as the refractive index of the first material and the second material is closer. FIG. 7 is a graph showing the refractive index and the reflectivity of Fresnel reflection. In the figure, it is shown how the reflectance changes depending on the difference Δn between the refractive index of the first material and the refractive index of the second material. When the direction of the wall surface 58 of the actual diffractive optical element is configured to be parallel to the direction of the incident light beam, the reflected light from the wall surface 58 is reduced so that it is as parallel as possible to the incident light beam. Therefore, the wall surface incident angle is a large value, and the reflected light increases as the refractive index difference Δn of the material increases. However, if the refractive index difference Δn is 0.1 or less, the reflected light decreases, and the wall surface 58 The unnecessary diffracted light resulting from the reduction is reduced to a level causing almost no problem in the imaging optical system.

図５の格子壁面は図２の光軸にほぼ平行の場合の格子壁面を示している。また、入射光５５は図２の２６の光の主光線を示している。この時の壁面付近の光線の振る舞いは上記に示した通りである。一方、仮に格子壁面５８の方向が図の５４の方向に主光線の角度を超えて傾いた場合には、高屈折率の第1の格子から壁面５８に入射し、壁面の界面においては高屈折率材料から低屈折率材料の方向に入射するため、全反射が発生し強いフレアが発生することになって問題である。従って本実施例のように壁面の角度を主光線の角度より光軸側の角度とする必要がある。また、光軸を超えて回折格子壁面５８を傾けると、回折格子を成形により作成する場合に型と素子が噛んでしまう方向であり離型が難しくなり素子の作成が困難となる。また、壁面８により光線を遮る幅が広くなり、フレアの発生、回折効率の劣化と言った問題が発生する。   The lattice wall surface in FIG. 5 shows the lattice wall surface in the case of being substantially parallel to the optical axis in FIG. Further, the incident light 55 indicates the chief ray of the light 26 in FIG. The behavior of the light beam near the wall at this time is as described above. On the other hand, if the direction of the grating wall surface 58 is inclined beyond the angle of the principal ray in the direction 54 in the figure, it enters the wall surface 58 from the first grating having a high refractive index and is highly refracted at the interface of the wall surface. Since the light is incident in the direction from the refractive index material to the low refractive index material, total reflection occurs and a strong flare is generated. Therefore, as in the present embodiment, the angle of the wall surface needs to be an angle closer to the optical axis than the angle of the principal ray. In addition, if the diffraction grating wall surface 58 is tilted beyond the optical axis, it is a direction in which the mold and the element bite when the diffraction grating is formed by molding, making it difficult to release and making the element difficult. In addition, the width of the light blocking the light by the wall surface 8 becomes wide, and problems such as generation of flare and deterioration of diffraction efficiency occur.

図８はこのときの不要回折光の状況をRCWAにて計算した結果である。図において、回折角を横軸、縦軸に回折効率を示している。グラフにおいては回折格子の素子入射角度を−１０度にて計算しているため、回折角10度に一次光の回折ピークが存在する。像面に到達する回折光は０度付近の回折光であり、不要回折光は殆ど像面に到達していないことが分かる。グラフに示したように、回折角に対して左右非対称のフレアが顕著に表れているのは密着タイプの回折光学素子の特徴である。   FIG. 8 shows the result of calculation of unnecessary diffracted light at this time by RCWA. In the figure, the diffraction angle is shown on the horizontal axis, and the diffraction efficiency is shown on the vertical axis. In the graph, since the element incident angle of the diffraction grating is calculated at −10 degrees, a diffraction peak of primary light exists at a diffraction angle of 10 degrees. It can be seen that the diffracted light reaching the image plane is diffracted light near 0 degrees, and almost no unnecessary diffracted light reaches the image plane. As shown in the graph, it is a feature of the contact type diffractive optical element that the asymmetric flare appears remarkably with respect to the diffraction angle.

図６は本発明と異なった構成の回折光学素子の格子付近の説明図である。図において６１は低屈折率高分散材料にて作成されが第1の回折格子、６２は高屈折率低分散材料で作成された第2の回折格子である。６３は回折格子壁面の方向をしめした補助線、６４は入射角度の負の方向を示した矢印、６５は回折光学素子に入射する入射光線であり、６６は格子壁面による反射光を示している。   FIG. 6 is an explanatory view of the vicinity of the grating of a diffractive optical element having a configuration different from that of the present invention. In the figure, 61 is a first diffraction grating made of a low refractive index and high dispersion material, and 62 is a second diffraction grating made of a high refractive index and low dispersion material. 63 is an auxiliary line indicating the direction of the diffraction grating wall surface, 64 is an arrow indicating the negative direction of the incident angle, 65 is an incident light beam incident on the diffractive optical element, and 66 is reflected light by the grating wall surface. .

まず入射光は第1の回折格子６１を通過後に第2の回折格子６２に入射し、回折格子の壁面に到達する。この時第1の回折格子を構成する材料の屈折率よりも第2の回折格子を構成する材料の方が屈折率が高いために、壁面に入射した光の殆どは全反射により強い反射光となって回折光学素子から出射する。   First, incident light passes through the first diffraction grating 61 and then enters the second diffraction grating 62 and reaches the wall surface of the diffraction grating. At this time, since the refractive index of the material constituting the second diffraction grating is higher than the refractive index of the material constituting the first diffraction grating, most of the light incident on the wall surface is reflected by strong reflection due to total reflection. And exits from the diffractive optical element.

図９はこのときの不要回折光の状況をRCWAにて計算した結果である。図において、回折角を横軸、縦軸に回折効率を示している。グラフにおいては回折格子の素子入射角度を−１０度にて計算しているため、回折角１０度に一次光の回折ピークが存在する。像面に到達する回折光は０度付近の回折光であるが、不要回折光が存在していることがわかる。このときの不要回折光のピークは10度付近にあり、これが反射のピークとなっており、回折によって裾を引いて０度付近に到達していると理解できる。   FIG. 9 shows the result of calculation of the state of unnecessary diffracted light at this time by RCWA. In the figure, the diffraction angle is shown on the horizontal axis, and the diffraction efficiency is shown on the vertical axis. In the graph, since the element incident angle of the diffraction grating is calculated at −10 degrees, a diffraction peak of primary light exists at a diffraction angle of 10 degrees. Although the diffracted light that reaches the image plane is diffracted light near 0 degrees, it can be seen that unnecessary diffracted light exists. At this time, the peak of unnecessary diffracted light is around 10 degrees, which is a reflection peak, and it can be understood that it reaches the vicinity of 0 degrees with a tail by diffraction.

また、フレアの発生は壁面による反射回折光であるために、壁面自体の数を減らすことが有効な対策となる。具体的には壁面の数を減らすためには回折格子の、格子の間隔であるピッチを広げる必要があり、最小ピッチを300μm以上とすることが有効な手法である。   Further, since flare is reflected and diffracted by the wall surface, reducing the number of wall surfaces is an effective measure. Specifically, in order to reduce the number of wall surfaces, it is necessary to increase the pitch of the diffraction grating, which is the interval between the gratings, and it is an effective technique to set the minimum pitch to 300 μm or more.

「実施例２」
図１０は本発明の第2の実施例の説明図である。図において、１０１はマスターレンズ、１０２はリアアタッチメントレンズ、１０３は回折光学素子、１０４は絞り、１０５はＣＣＤ等の像面、１０６は軸上の光束、１０７は最も軸外の光束を示している。リアアタッチメントレンズの倍率は2倍であり、マスターレンズの収差を倍率分増幅するため設計においてはマスターレンズを取り付けた状態にて設計を行う必要がある。特に倍率色収差については、画像の色滲みとなり問題となる。このため、色収差補正に効果がある回折光学素子の中心付近では負のパワーを有し、フレアに影響の大きい周辺は正のパワーを有した回折光学素子１０３を光学系に導入することで良好に色収差を補正した上にフレアの発生を抑制することが可能となる。 "Example 2"
FIG. 10 is an explanatory diagram of the second embodiment of the present invention. In the figure, 101 is a master lens, 102 is a rear attachment lens, 103 is a diffractive optical element, 104 is a stop, 105 is an image plane such as a CCD, 106 is an axial light beam, and 107 is the most off-axis light beam. . The magnification of the rear attachment lens is double, and in order to amplify the aberration of the master lens by the magnification, it is necessary to design with the master lens attached. In particular, the chromatic aberration of magnification causes a color blur in the image and causes a problem. For this reason, a diffractive optical element 103 having a negative power near the center of the diffractive optical element effective in correcting chromatic aberration and having a positive influence on the flare is favorably introduced into the optical system. It is possible to suppress the occurrence of flare while correcting chromatic aberration.

図１２は本発明の回折格子の形状を説明した説明図である。図において１２１が光軸、１２２が有効径の最周辺、１２３が負のパワーを有した回折格子、１２４が正のパワーを有した回折格子を示している。また、１２５は第1の回折格子、１２６は第2の回折格子を示している。図に示したように回折格子は密着しており、第1の回折格子は低屈折率高分散材料、第2の回折格子には高屈折率低分散材料を使用する。図に示したように回折格子の形状が正のパワー部分と負のパワー部分では異なった形状となっており、回折格子を成形するためには格子の形状に注意が必要である。   FIG. 12 is an explanatory view for explaining the shape of the diffraction grating of the present invention. In the figure, 121 is the optical axis, 122 is the outermost periphery of the effective diameter, 123 is a diffraction grating having negative power, and 124 is a diffraction grating having positive power. Reference numeral 125 denotes a first diffraction grating, and 126 denotes a second diffraction grating. As shown in the figure, the diffraction gratings are in close contact, and the first diffraction grating uses a low refractive index and high dispersion material, and the second diffraction grating uses a high refractive index and low dispersion material. As shown in the figure, the shape of the diffraction grating is different between the positive power portion and the negative power portion, and attention must be paid to the shape of the grating in order to form the diffraction grating.

第1実施例に示したように絞りの後ろ側に配置した回折光学素子は正のパワーを有した方がフレア上有利である。しかしながら、収差補正上は負の回折光学素子を入れる方が有利である。本発明においては、倍率色収差補正に対して主要な効果を発揮する光軸を中心とした有効径3/4のエリアについては負のパワーの回折格子とし、周辺部分を正のパワーの回折格子とする。この対策により、通常回折格子のピッチが細かくなる周辺部の回折格子において、フレアの発生を抑制することが可能となる。   As shown in the first embodiment, it is advantageous in terms of flare that the diffractive optical element disposed behind the stop has a positive power. However, it is more advantageous to insert a negative diffractive optical element for aberration correction. In the present invention, an area with an effective diameter of 3/4 centered on the optical axis that exerts a main effect on correcting chromatic aberration of magnification is a negative power diffraction grating, and a peripheral part is a positive power diffraction grating. To do. By taking this measure, it is possible to suppress the occurrence of flare in the peripheral diffraction grating where the pitch of the diffraction grating is usually fine.

図１１は本発明の第2実施例の回折光学素子の位相関数を示している。横軸が径方向の高さであり、縦軸が位相の付加量である。図にしめしたように、光軸からの高さが9.4mm付近で位相が減少に転じている。この時の回折格子による回折角を図１３に示した。図において、光軸方向に回折するときを負としている。図より、光軸から9.4mm付近までは正の値となっており、回折格子のパワーとしては負のパワーとなっていることが分かる。また、9.4mm付近から回折格子の周辺部にかけては正のパワーとなっていることが分かる。   FIG. 11 shows the phase function of the diffractive optical element according to the second embodiment of the present invention. The horizontal axis is the height in the radial direction, and the vertical axis is the added amount of phase. As shown in the figure, the phase starts to decrease when the height from the optical axis is around 9.4 mm. The diffraction angle by the diffraction grating at this time is shown in FIG. In the figure, the time of diffraction in the optical axis direction is negative. From the figure, it can be seen that the value up to 9.4 mm from the optical axis is a positive value, and the power of the diffraction grating is a negative power. It can also be seen that the power is positive from around 9.4 mm to the periphery of the diffraction grating.

図１２において１２７は負のパワーを有した回折光学素子に入射している光線を示している。既に説明したように軸外の光束の主光線は矢印１２７の方向に入射し、回折格子の壁面に対して高屈折率低分散材料側から入射して、低屈折率高分散材料との境界である壁面により全反射する。これにより反射回折光となる。一方、正のパワー部分の回折格子１２４の部分に入射した光は回折格子の壁面付近で低屈折率高分散材料から高屈折率低分散材料側に入射するためフレネル反射は起こるが殆どの光は透過する。フレネル反射については、高屈折率低分散材料と低屈折率高分散材料の屈折率差を0.1以下にしておくことで大幅に抑制することが出来る。一方、負のパワーの回折格子はピッチの広い領域であるためフレアの発生は少なく問題無いレベルに抑えることが出来る。従って、画像に有害な全反射光起因の反射光は回折格子の負の回折格子部分で発生することになり、発生エリアの面積が減少することと、ピッチの小さくなる周辺部分においては正のパワーの回折格子で発生を抑制できるため大幅なフレア改善が可能となる。   In FIG. 12, reference numeral 127 denotes a light beam incident on the diffractive optical element having a negative power. As described above, the principal ray of the off-axis light beam enters in the direction of the arrow 127, enters the wall surface of the diffraction grating from the high refractive index / low dispersion material side, and at the boundary with the low refractive index / high dispersion material. Total reflection by a wall. Thereby, it becomes reflected diffracted light. On the other hand, the light incident on the diffraction grating 124 of the positive power portion enters the high refractive index / low dispersion material side from the low refractive index / high dispersion material in the vicinity of the wall surface of the diffraction grating. To Penetrate. Fresnel reflection can be significantly suppressed by setting the refractive index difference between the high refractive index and low dispersion material and the low refractive index and high dispersion material to 0.1 or less. On the other hand, since the negative power diffraction grating is a wide pitch region, the occurrence of flare is small and it can be suppressed to a level with no problem. Therefore, the reflected light caused by the total reflection light harmful to the image is generated in the negative diffraction grating portion of the diffraction grating, the area of the generation area is reduced, and the positive power is generated in the peripheral portion where the pitch is reduced. The generation of the diffraction grating can suppress generation of flare.

図１４は回折格子を成形する場合の型と回折格子の関係を示した説明図である。図において１４１は型により成形される回折格子、１４８は回折格子を成形するための型である。図において、回折格子は樹脂の液体状態で型に充填され、紫外線硬化等により硬化され型から離型させることで格子形状を作成する。この時樹脂を反らせながら離型をさせることになるが、回折格子の格子形状が回折格子の成形面の面法線方向よりも格子壁面が開いた方向に傾いている方が成形される回折格子の壁面が型の回折格子の壁面と干渉しにくい方向に傾くことになり望ましい。   FIG. 14 is an explanatory diagram showing the relationship between the mold and the diffraction grating when the diffraction grating is formed. In the figure, reference numeral 141 denotes a diffraction grating formed by a mold, and 148 denotes a mold for forming the diffraction grating. In the figure, a diffraction grating is filled in a mold in a resin liquid state, cured by ultraviolet curing or the like, and released from the mold to create a grating shape. At this time, the mold is released while warping the resin, but the diffraction grating is shaped when the grating shape of the diffraction grating is inclined in the direction in which the grating wall surface is opened rather than the surface normal direction of the molding surface of the diffraction grating. It is desirable that the wall surface of the metal plate be inclined in a direction in which it does not easily interfere with the wall surface of the type diffraction grating.

一方、格子の壁面の方向は光線の通過方向と一致させておく方が望ましい。これは壁面による光線のケラレによる光の損失（シャドー損失）を抑制するためには有利となるためである。これらを考え合わせて、壁面の方向を設定する。既に説明したように撮像光学系において絞りより後ろに回折光学素子を配置した場合には画角の付いた軸外からの光線は素子に対して入射側から出射側に向かって光軸から離れる方向に通過する。このため回折光学素子の壁面の角度は図２にしめしたように光軸から離れる方向に傾けることになる。更に負のパワーの回折格子とするためには入射側の回折格子に低屈折率材料、出射側の回折格子に高屈折率材料を使用した構成としないと、上記の離型性を確保することが出来ない。   On the other hand, it is desirable to make the direction of the wall surface of the lattice coincide with the light passing direction. This is because it is advantageous for suppressing light loss (shadow loss) due to vignetting of light rays on the wall surface. Considering these, the direction of the wall surface is set. When the diffractive optical element is disposed behind the stop in the imaging optical system as described above, the off-axis light beam with a field angle is away from the optical axis from the incident side to the output side with respect to the element. To pass through. For this reason, the angle of the wall surface of the diffractive optical element is inclined in a direction away from the optical axis as shown in FIG. In addition, in order to obtain a negative power diffraction grating, the above-mentioned mold releasability is ensured unless a structure using a low refractive index material for the incident side diffraction grating and a high refractive index material for the output side diffraction grating is used. I can't.

これに対して、回折格子の周辺部において、回折格子のパワーの符号を変える場合には格子の周辺部において離型が困難な方向となる。このため周辺部においては離型に有利な形とする必要があり、周辺部の格子壁面形状を面法線方向に合わせる方向に変更する必要がある。逆に面法線方向より更に大きく格子壁面を鈍角方向に傾けると壁面によるシャドー損失が増加して回折効率が劣化する。従って、バランスを考えると格子壁面を面法線付近にすることがベストとなる。   On the other hand, when the sign of the power of the diffraction grating is changed in the peripheral part of the diffraction grating, the mold release is difficult in the peripheral part of the grating. For this reason, it is necessary to make it a shape advantageous for mold release in the peripheral portion, and it is necessary to change the shape of the lattice wall surface in the peripheral portion to a direction that matches the surface normal direction. Conversely, if the grating wall surface is tilted in an obtuse angle direction larger than the surface normal direction, the shadow loss due to the wall surface increases and the diffraction efficiency deteriorates. Therefore, considering the balance, it is best to make the lattice wall surface near the surface normal.

「実施例３」
図１５は本発明の第三の実施例の説明図である。図において１５１は回折光学素子、１５２は絞り、１５３はＣＣＤ等の像面、１５４は画角が付いた光束の最軸外の光束、１５５は軸上の光束を示している。図に示したように超望遠レンズ等のポジティブリードの光学系においては回折光学素子は絞りより前側に回折光学素子を配置した方が収差補正上は有利である。これにより最軸外の光束の主光線については回折光学素子を図の上から下、すなわち入射側から出射側に向かって光軸に近づく方向に進むことになる。 "Example 3"
FIG. 15 is an explanatory diagram of the third embodiment of the present invention. In the figure, 151 is a diffractive optical element, 152 is a stop, 153 is an image plane of a CCD or the like, 154 is an off-axis light beam with a field angle, and 155 is an axial light beam. As shown in the figure, in a positive lead optical system such as a super telephoto lens, it is more advantageous in terms of aberration correction to dispose the diffractive optical element in front of the stop. As a result, the principal ray of the most off-axis light beam advances the diffractive optical element from the top to the bottom of the drawing, that is, in the direction approaching the optical axis from the incident side toward the emission side.

正のパワーの回折光学素子を構成したときは、図１６の構成の回折光学素子が壁面によるシャドー損失を抑制した上に離型性を確保するためには有利となる。図１６において、１６１は光軸、１６２は第１のレンズ１６３は第２のレンズ、１６４は第１の回折格子、１６５は第２の回折格子である。第１の回折格子１６４は低屈折率高分散材料であり、第２の回折格子は高屈折率低分散材料である。   When a diffractive optical element having a positive power is configured, the diffractive optical element having the configuration shown in FIG. 16 is advantageous for ensuring releasability while suppressing shadow loss due to the wall surface. In FIG. 16, 161 is an optical axis, 162 is a first lens 163 is a second lens, 164 is a first diffraction grating, and 165 is a second diffraction grating. The first diffraction grating 164 is a low refractive index and high dispersion material, and the second diffraction grating is a high refractive index and low dispersion material.

図において、画面外から入射した光線１６６は高屈折率材料と低屈折率材料の境界において全反射をする。この光束が像面に到達すると画像の劣化が発生する。一方、回折光学素子の下側に入射した光線１６７は低屈折率材料と高屈折率材料の界面で全反射はしないがフレネル反射をする。このとき、屈折率差が０．１以下であれば大きな画像の劣化が無く許容範囲内である。具体的な材料としては高屈折率低分散材料としてはアクリル系の紫外線硬化樹脂(nd=1.52、νd=51)に対してZrO2微粒子を19.9vol%混ぜた材料を使用した。微粒子分散後の高屈折率低分散材料の屈折率はnd=1.608,νd=48.7である。この結果、微粒子分散後の低屈折率高分散材料の屈折率はnd=1.565,νd=22.7である。ITO微粒の混合比率を高めることで、材料としてはリニアの異常分散性を有した低アッベ数の材料を提供することが出来る。これにより格子の厚みは13.7μmと比較的に低い格子高さにすることが可能となる。   In the figure, a light ray 166 incident from the outside of the screen is totally reflected at the boundary between the high refractive index material and the low refractive index material. When this light beam reaches the image plane, image degradation occurs. On the other hand, the light beam 167 incident on the lower side of the diffractive optical element does not undergo total reflection at the interface between the low refractive index material and the high refractive index material, but does Fresnel reflection. At this time, if the refractive index difference is 0.1 or less, there is no significant image deterioration and it is within the allowable range. As a specific material, a material having 19.9 vol% of ZrO2 fine particles mixed with an acrylic ultraviolet curable resin (nd = 1.52, νd = 51) was used as a high refractive index and low dispersion material. The refractive indexes of the high refractive index and low dispersion material after dispersion of the fine particles are nd = 1.608 and νd = 48.7. As a result, the refractive index of the low refractive index and high dispersion material after dispersion of the fine particles is nd = 1.565 and νd = 22.7. By increasing the mixing ratio of the ITO fine particles, a low Abbe number material having linear anomalous dispersion can be provided. As a result, the grating thickness can be reduced to a relatively low grating height of 13.7 μm.

本発明においては、回折光学素子の光軸からはなれた周辺部において、負のパワーを有した回折光学素子とすることでフレアの発生を抑制する。既に説明したように光線１６６は全反射により画像を劣化させるが、回折光学素子の周辺部を負のパワーとすることで、低屈折率材料から高屈折率材料に入射することになり全反射を抑制することが出来る。更に第１の回折格子の材料と第２の回折格子の材料の屈折率差を0.1以下とすることで、フレネル反射も抑制されるために、フレアの発生を抑制することが可能となる。   In the present invention, the occurrence of flare is suppressed by using a diffractive optical element having a negative power in the peripheral part away from the optical axis of the diffractive optical element. As described above, the light beam 166 deteriorates the image by total reflection. However, by making the peripheral portion of the diffractive optical element have a negative power, the light is incident on the high refractive index material from the low refractive index material, and thus totally reflected. Can be suppressed. Furthermore, since the difference in refractive index between the material of the first diffraction grating and the material of the second diffraction grating is 0.1 or less, Fresnel reflection is also suppressed, so that the occurrence of flare can be suppressed.

図１７は本発明の回折格子の形状を説明した説明図である。図において径方向高さ０が光軸、１７３が正のパワーを有した回折格子、１７４が負のパワーを有した回折格子を示している。また、１７５は第1の回折格子、１７６は第2の回折格子を示している。図に示したように回折格子は密着しており、第1の回折格子１７５は低屈折率高分散材料、第2の回折格子１７６には高屈折率低分散材料を使用する。   FIG. 17 is an explanatory view for explaining the shape of the diffraction grating of the present invention. In the figure, a radial height 0 is the optical axis, 173 is a diffraction grating having a positive power, and 174 is a diffraction grating having a negative power. Reference numeral 175 denotes a first diffraction grating, and 176 denotes a second diffraction grating. As shown in the figure, the diffraction gratings are in close contact, and the first diffraction grating 175 uses a low refractive index and high dispersion material, and the second diffraction grating 176 uses a high refractive index and low dispersion material.

図に示したように回折格子の形状が正のパワー部分と負のパワー部分では異なった形状となっており、回折格子を成形するためには格子の形状は第2実施例と同様の注意が必要である。   As shown in the figure, the shape of the diffraction grating is different between the positive power portion and the negative power portion, and in order to mold the diffraction grating, the shape of the grating should be the same as in the second embodiment. is necessary.

１７７は正のパワーを有した回折光学素子に入射している光線を示している。既に説明したように軸外の光束の主光線は矢印１７７の方向に入射し、高屈折率低分散材料側から入射して、低屈折率高分散材料との境界である壁面により全反射する。これにより反射回折光となる。一方、負のパワー部分の回折格子１７４の部分に入射した光は回折格子の壁面付近で低屈折率高分散材料から高屈折率低分散材料側に入射するためフレネル反射は起こるが殆どの光は透過する。フレネル反射については、高屈折率低分散材料と低屈折率高分散材料の屈折率差を0.1以下にしておくことで大幅意に抑制することが出来る。従って、画像に有害な全反射光起因の反射光は回折格子の正の回折格子部分で発生することになり、発生エリアの面積が減少することで抑制される。また、本発明の光学系のように回折光学素子で正のパワーをつける場合には位相の付加量は光軸から離れるに従って大きくする必要がある。このため、回折光学素子のピッチは光軸から離れるに従って小さくなる。一方、ピッチが小さい部分は壁面の数が多くフレアを発生させ易い。本発明においては、ピッチの小さくなる周辺部分においては負のパワーの回折格子で発生を抑制できるため、通常の回折光学素子と比較すると大幅なフレア改善が可能となる。   Reference numeral 177 denotes a light beam incident on a diffractive optical element having a positive power. As described above, the principal ray of the off-axis light beam is incident in the direction of the arrow 177, is incident from the high refractive index / low dispersion material side, and is totally reflected by the wall surface that is the boundary with the low refractive index / high dispersion material. Thereby, it becomes reflected diffracted light. On the other hand, the light incident on the diffraction grating 174 in the negative power portion is incident on the side of the diffraction grating from the low refractive index high dispersion material to the high refractive index low dispersion material side. To Penetrate. Fresnel reflection can be significantly suppressed by setting the difference in refractive index between the high refractive index low dispersion material and the low refractive index high dispersion material to 0.1 or less. Therefore, the reflected light caused by the total reflection light harmful to the image is generated in the positive diffraction grating portion of the diffraction grating, and is suppressed by reducing the area of the generation area. In addition, when a positive power is applied by a diffractive optical element as in the optical system of the present invention, the amount of added phase needs to increase as the distance from the optical axis increases. For this reason, the pitch of the diffractive optical element decreases as the distance from the optical axis increases. On the other hand, the portion where the pitch is small has a large number of wall surfaces and easily generates flare. In the present invention, since the generation can be suppressed by the diffraction grating having a negative power in the peripheral portion where the pitch is reduced, the flare can be greatly improved as compared with a normal diffractive optical element.

以上、本発明の好ましい実施形態について説明したが、本発明はこれらの実施形態に限定されず、その要旨の範囲内で種々の変形および変更が可能である。   As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

本発明は、広い波長域において回折効率を高めた回折光学素子およびそれを用いた撮像光学系に関するものである。   The present invention relates to a diffractive optical element with improved diffraction efficiency in a wide wavelength range and an imaging optical system using the same.

１〜負の屈折力の第１レンズ群
２〜正の屈折力の第２レンズ群
３〜絞り
４〜ＣＣＤ等の像面
５〜回折光学素子を接合面に有すレンズ
６〜回折光学素子 1. First lens group having negative refractive power 2. Second lens group having positive refractive power 3. Diaphragm 4. Image surface 5 such as CCD 5. Lens 6 having diffractive optical element at junction surface. Diffractive optical element.

Claims (8)

相対的に高屈折率で低分散の第1材料と低屈折率で高分散の第２材料の境界面に回折格子を形成した回折光学素子において、該第１の材料の使用波長の中心波長における屈折率をnd1、該第２の材料の使用波長の中心波長における屈折率をnd2、該回折格子の最も回折効率を高めた回折次数をMとした時、該回折光学素子を撮像光学系の絞りより後ろ側に配置し、該第１の材料を光線入射側に配置し、該回折光学素子の中心から周辺部にかけて全て又は一部の回折光学素子が正のパワーを有し、回折格子は光束の殆どの光透過する位相付加面と位相付加面を繋ぐ格子壁面を有し、該格子壁面の角度は撮像光学系の格子壁面を通過する光束の主光線の方向と光軸方向の間の角度とし、
6.8 < |M/(nd1-nd2)| < 51.1 〜(1)
|nd1-nd2| ≦ 0.1 〜(2)
を満たしたことを特徴とする回折光学素子。 In a diffractive optical element in which a diffraction grating is formed at an interface between a first material having a relatively high refractive index and a low dispersion and a second material having a low refractive index and a high dispersion, the first material is used at the center wavelength. When the refractive index is nd1, the refractive index at the center wavelength of the second material used is nd2, and the diffraction order with the highest diffraction efficiency of the diffraction grating is M, the diffractive optical element is the aperture of the imaging optical system. The first material is arranged on the light incident side, all or some of the diffractive optical elements have a positive power from the center to the peripheral part of the diffractive optical element, and the diffraction grating has a luminous flux A phase addition surface that transmits most of the light and a grating wall surface that connects the phase addition surface, and the angle of the grating wall surface is an angle between the principal ray direction of the light beam passing through the grating wall surface of the imaging optical system and the optical axis direction. age,
6.8 <| M / (nd1-nd2) | <51.1-(1)
| nd1-nd2 | ≤ 0.1 to (2)
A diffractive optical element characterized by satisfying 相対的に高屈折率で低分散の第1材料と低屈折率で高分散の第２材料の境界面に回折格子を形成した回折光学素子において、該回折格子は相対的に低屈折率で高分散の第1材料と高屈折率で低分散の第２材料を密着させて構成し、該第１の材料の使用波長の中心波長における屈折率をnd1、該第２の材料の使用波長の中心波長における屈折率をnd2、該回折格子の最も回折効率を高めた回折次数をMとした時、該回折光学素子を撮像光学系の絞りより後ろ側に配置し、該第１の材料を光線入射側に配置し、回折光学素子の中心から周辺部にかけて回折光学素子のパワーの符号が反転し、該回折光学素子の中心から周辺部にかけて全て又は一部の回折光学素子が正のパワーを有し、回折格子は光束の殆どの光透過する位相付加面と位相付加面を繋ぐ格子壁面を有し、該格子壁面の角度は撮像光学系の格子壁面を通過する光束の主光線の方向と光軸方向の間の角度とし、
6.8 < |M/(nd1-nd2)| < 51.1 〜(1)
|nd1-nd2| ≦ 0.1 〜(2)
を満たしたことを特徴とする回折光学素子。 In a diffractive optical element in which a diffraction grating is formed at the interface between a first material having a relatively high refractive index and a low dispersion and a second material having a low refractive index and a high dispersion, the diffraction grating has a relatively low refractive index and a high value. The first material of dispersion is in close contact with the second material of high refractive index and low dispersion, and the refractive index at the center wavelength of the wavelength used of the first material is nd1, and the center of the wavelength of the second material used When the refractive index at the wavelength is nd2 and the diffraction order with the highest diffraction efficiency of the diffraction grating is M, the diffractive optical element is arranged behind the stop of the imaging optical system, and the first material is incident on the light beam. The sign of the power of the diffractive optical element is inverted from the center to the peripheral part of the diffractive optical element, and all or some of the diffractive optical elements have positive power from the center to the peripheral part of the diffractive optical element. The diffraction grating is a grating that connects the phase addition surface and the phase addition surface that transmit most of the light beam. Having a surface, the angle of the grating wall surface and the angle between the direction and the optical axis direction of the principal ray of the light flux passing through the grating wall surface of the imaging optical system,
6.8 <| M / (nd1-nd2) | <51.1-(1)
| nd1-nd2 | ≤ 0.1 to (2)
A diffractive optical element characterized by satisfying 回折光学素子は光軸付近は負のパワーを有し、周辺部分は正のパワーを有したことを特徴とする請求項２に記載の回折光学素子。   The diffractive optical element according to claim 2, wherein the diffractive optical element has a negative power near the optical axis and a peripheral part has a positive power. 相対的に高屈折率で低分散の第1材料と低屈折率で高分散の第２材料の境界面に回折格子を形成した回折光学素子において、該回折格子は相対的に低屈折率で高分散の第1材料と高屈折率で低分散の第２材料を密着させて構成し、該第１の材料の使用波長の中心波長における屈折率をnd1、該第２の材料の使用波長の中心波長における屈折率をnd2、該回折格子の最も回折効率を高めた回折次数をMとした時、該回折光学素子を撮像光学系の絞りより前側に配置し、該第１の材料を光線入射側に配置し、回折光学素子の中心から周辺部にかけて回折光学素子のパワーの符号が反転し、
6.8 < |M/(nd1-nd2)| < 51.1 〜(1)
|nd1-nd2| ≦ 0.1 〜(2)
を満たしたことを特徴とする回折光学素子。 In a diffractive optical element in which a diffraction grating is formed at the interface between a first material having a relatively high refractive index and a low dispersion and a second material having a low refractive index and a high dispersion, the diffraction grating has a relatively low refractive index and a high value. The first material of dispersion is in close contact with the second material of high refractive index and low dispersion, and the refractive index at the center wavelength of the wavelength used of the first material is nd1, and the center of the wavelength of the second material used When the refractive index at the wavelength is nd2 and the diffraction order of the diffraction grating with the highest diffraction efficiency is M, the diffractive optical element is arranged in front of the stop of the imaging optical system, and the first material is placed on the light incident side. And the sign of the power of the diffractive optical element is reversed from the center to the periphery of the diffractive optical element,
6.8 <| M / (nd1-nd2) | <51.1-(1)
| nd1-nd2 | ≤ 0.1 to (2)
A diffractive optical element characterized by satisfying 光軸付近は正のパワーを有し、周辺部分は負のパワーを有した回折光学素子としたことを特徴とする請求項４に記載の回折光学素子。   5. The diffractive optical element according to claim 4, wherein the diffractive optical element has a positive power in the vicinity of the optical axis and a negative power in the peripheral part. 回折光学素子の格子と格子の間隔の最小間隔は300μm以上であることを特徴とする請求項１乃至請求項５のいずれか１項に記載の回折光学素子。   6. The diffractive optical element according to claim 1, wherein a minimum gap between the gratings of the diffractive optical element is 300 μm or more. 回折光学素子のパワーの反転する付近の格子壁面のテーパ角度は回折光学素子が配置される光学面の面線方向に対して5度以内にあることを特徴とする請求項１乃至請求項６のいずれか１項に記載の回折光学素子。   7. The taper angle of the grating wall surface near the power reversal of the diffractive optical element is within 5 degrees with respect to the plane direction of the optical surface on which the diffractive optical element is disposed. The diffractive optical element according to any one of the above. 回折光学素子は撮像光学系のリアアタッチメントレンズに使用したことを特徴とする請求項乃至請求項３のいずれか１項に記載の回折光学素子。   The diffractive optical element according to any one of claims 1 to 3, wherein the diffractive optical element is used in a rear attachment lens of an imaging optical system.
JP2013013883A 2013-01-29 2013-01-29 Imaging optical system using diffraction optical element Pending JP2014145871A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2020134373A1 (en) * 2018-12-28 2020-07-02 瑞声通讯科技(常州)有限公司 Camera optical lens
CN111367048A (en) * 2020-03-31 2020-07-03 玉晶光电(厦门)有限公司 Optical imaging lens

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2020134373A1 (en) * 2018-12-28 2020-07-02 瑞声通讯科技(常州)有限公司 Camera optical lens
CN111367048A (en) * 2020-03-31 2020-07-03 玉晶光电(厦门)有限公司 Optical imaging lens

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