JP2005164773A - Diffraction optical element and lens for projection using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection lens of a coaxial system suitable to, specially, a projection type display device etc., such as a liquid crystal projector by using a diffraction optical element which has high diffraction efficiency in the whole use wavelength range (light in visible region) and can reduce incidence angle dependency of light incident on the diffraction optical element. <P>SOLUTION: The projection lens of the coaxial system can be realized by introducing a stack type diffraction optical element at a position where the absolute value of the height from the optical axis of a pupil paraxial light beam passing through each lens is large and the center of a circle or ellipse forming the diffraction optical element is shifted from the optical axis of an introduced lens substrate according to a distribution of light beams incident on a surface of the diffraction optical element. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a diffractive optical element and an optical system using the diffractive optical element, and in particular, can reduce the reduction in diffraction efficiency due to the incident angle dependence of the diffractive optical element in the used wavelength region (visible light region), and More particularly, the present invention relates to a coaxial projection lens suitable for a liquid crystal projector apparatus that enlarges and projects an image displayed on a light valve using an element on a screen.

  In contrast to the conventional method of reducing chromatic aberration by combining glass materials, a technology that reduces chromatic aberration by providing a diffractive optical element having a diffractive action on the lens surface or part of the optical system is the SPIE vol.1354 International Lens Design Conference ( 1990), JP-A-4-213421, JP-A-6-324262, USP5,044,706, and the like. These are based on the physical phenomenon that refracting surfaces and diffractive surfaces in an optical system exhibit chromatic aberration in a reverse direction with respect to a light beam having a certain reference wavelength. This means that the normal optical glass has a positive dispersion characteristic, whereas the diffractive optical element has a negative dispersion characteristic (νd = −3.453). In addition, the diffractive optical element has a strong anomalous dispersion (θg, F = 0.2956) and, in addition, has a characteristic that it can have an aspherical effect by changing the periodic structure of the diffractive optical element. ing. From the above, the diffractive optical element can use two effects of correcting the chromatic aberration using the negative dispersion characteristic and the strong anomalous dispersion and the aspheric effect, and the optical performance can be greatly improved. Furthermore, since the diffractive optical element has a fine shape, the space occupancy can be made very low, and the optical system can be easily reduced in weight and size.

  On the other hand, projection-type display devices such as liquid crystal projectors for enlarging and projecting display images such as liquid crystal panels have been improved in performance in recent years and have been used in various places. Further improvement is demanded in terms of brightness, size reduction, weight reduction, and the like.

  A so-called “three-plate type liquid crystal projector” is known as a liquid crystal projector that is currently mainstream, in which liquid crystal panels are arranged for red, blue, and green wavelength regions, respectively. This “three-plate liquid crystal projector” uses a color synthesizing optical system such as a dichroic prism on the optical path in order to display the images displayed on the three liquid crystal panels on the screen as a color image. In order to prevent unevenness in the color of the projected image caused by the angle dependence of the dichroic film in this dichroic prism, and the decrease in contrast caused by the viewing direction of the liquid crystal panel, the projection optical system has an image plane on the reduction conjugate side. Telecentricity is required. Further, in order to reduce the color shift of the enlarged images of the three liquid crystal panels, the projection lens is required to reduce the chromatic aberration of magnification. Further, in recent years, microlenses have been adopted for liquid crystal panels so that images can be observed even in a relatively bright room. For this reason, the solid angle of the light emitted from the liquid crystal panel is increased, and in order to effectively use this light, a brighter projection lens is required.

  When the diffractive optical element is used in a projection optical system, the diffraction efficiency must be taken into consideration. In the case of a refracting optical system, one light beam incident on a certain refracting surface is one light beam after refraction, but in diffraction, light is separated into a plurality of diffraction orders. Therefore, when a diffractive optical element is used as the lens system, it is necessary to determine the grating structure so that the light flux in the used wavelength region is concentrated in one specific order (hereinafter referred to as the design order). When light is concentrated at the design order, the light intensity of the other diffracted light is low, and when the intensity is 0, the diffracted light does not exist. When there is a light beam having a diffraction order other than the design order, an image is formed at a position different from the light beam of the design order, so that the flare light has a blur on the designed image plane. Therefore, in an optical system using the diffraction effect, it is important to sufficiently consider not only the spectral distribution of diffraction efficiency at the design order but also the behavior of light rays other than the design order. For this reason, in order to effectively use the chromatic aberration correction effect of the diffractive optical element, which is the feature described above, it is necessary that the diffraction efficiency of the light of the designed order is sufficiently high in the entire use wavelength range.

  FIG. 11 shows an example of the diffraction efficiency (FIG. 11 (b)) of a single-layer diffractive optical element (FIG. 11 (a)) formed of a certain material. FIG. 11 (a) shows a simplified diagram of a single-layer diffractive optical element, in which d1 is the grating height, Pitch is the grating pitch, and (nd1, νd1) is the ultraviolet curing used for the grating. The refractive index and Abbe number at the d-line of the resin are respectively shown. FIG. 11B shows the wavelength dependence characteristics of the diffraction efficiency of FIG. At this time, in FIG. 11 (a), the calculation result with d1 = 1.0 [μm], Pitch = 1000 [μm], (nd1, νd1) = (1.513, 51.0) is shown in FIG. 11 (b). is there. In FIG. 11B, the wavelength dependence characteristics of the diffraction efficiency of the first order light, which is the designed order, and the other orders, the zero order light and the second order light, are also shown. In FIG. 11B, the horizontal axis represents wavelength [μm] and the vertical axis represents diffraction efficiency [%]. From FIG. 11 (b), it can be seen that the diffraction efficiency of the primary light is high at a specific wavelength, but the diffraction efficiency at wavelengths away from the specific wavelength is greatly reduced. In the wavelength region where the diffraction efficiency is lowered, the diffraction efficiency of the zero-order light and the second-order light other than the designed order is high, which causes image degradation such as flare.

  Japanese Patent Laid-Open No. 10-133149 and Japanese Patent Laid-Open No. 10-39639 disclose such a configuration that reduces the wavelength dependency of diffraction efficiency. The technology such as Japanese Patent Application Laid-Open No. 10-133149 is based on the wavelength dependence of diffraction efficiency as seen in a single-layer diffraction grating by forming a diffraction grating with two materials with different dispersion and reducing the phase difference due to wavelength. Deterioration is reduced. FIG. 12 is an example of the diffraction efficiency of a diffractive optical element as found in the technique of Japanese Patent Laid-Open No. 10-133149. In Japanese Patent Laid-Open No. 10-133149, the two materials are in close contact with each other, but FIG. 12 (a) shows a configuration in which the materials are separated with an air layer interposed therebetween. Here, d1 and d2 are the grating height, Pitch is the grating pitch, nd1 and nd2 are the refractive indices at the d-line of the ultraviolet curable resins 1 and 2 used in the grating, and νd1 and νd2 are the ultraviolet curable resin 1 and 2 represents the Abbe number on the d line. FIG. 12B shows the wavelength dependence characteristics of the diffraction efficiency of FIG. 12A. In FIG. 12A, d1 = 6.9 [μm], d2 = 9.5 [μm], Pitch = The calculation results are shown with 1000 [μm], (nd1, νd1) = (1.636, 22.8), (nd2, νd2) = (1.513, 51.0). From FIG. 12 (b), it can be seen that the diffraction efficiency of the primary light shows high diffraction efficiency over a wide wavelength range. At this time, the diffraction efficiencies of the zero-order light and the second-order light other than the designed order are low. Thus, by sandwiching the air layer, the selectivity of the two materials is expanded, and the optical performance can be improved. Hereinafter, the shape of a diffractive element constituted by this technique is referred to as a laminated diffractive optical element as opposed to a single-layered diffractive optical element.

  Examples of using the diffractive optical element in a projection optical system (coaxial system) such as a projector apparatus include Japanese Patent Application Laid-Open Nos. 2000-019400 and 2001-066499. In the optical systems proposed in the above-mentioned JP-A-2000-019400 and JP-A-2001-066499, since the F value of the projection optical system is relatively small, the incident angle of the marginal ray on the diffractive optical element becomes large. As a result, the diffraction efficiency tends to decrease greatly. In order to solve this problem, the Japanese Patent Application Laid-Open No. 2000-019400 has been mainly aimed at correcting various aberrations, particularly lateral chromatic aberration, and therefore does not mention the diffraction efficiency of the diffractive optical element, particularly the deterioration of diffraction efficiency with respect to oblique incidence. It was. On the other hand, in Japanese Patent Application Laid-Open No. 2001-066499, a lens having a positive refractive power is disposed between the optical path between the diffractive optical element and the reduced image plane, the refractive power of the diffractive optical element is appropriately conditioned, By adjusting the curvature of the base surface on which the diffractive optical element is formed, fluctuations in the incident angle of light rays incident on the diffractive optical element have been alleviated to some extent. However, the current mainstream projection lens for LCD projectors (coaxial system) is required to be brighter (the F value of the optical system is smaller) and wider than that of the published patent. Further, it is considered that oblique incidence of light on the diffractive optical element becomes a problem more than ever, and there has been a problem that the degradation of diffraction efficiency cannot be alleviated only by the above measures.

  By the way, especially the projection lens of the coaxial system for the current liquid crystal projector, when projecting an image on the screen, the projection range on the screen is only half on one side from the optical axis of the projection lens of the coaxial system. Mainly used. At this time, the light beam passing through the lens is biased at a position away from the aperture of the projection lens (a position where the absolute value of the height of the paraxial light beam passing through each lens from the optical axis is high). . Utilizing this, the diffractive optical element is introduced to a position where the absolute value of the height of the paraxial light beam passing through each lens from the optical axis is high, and the center position of the diffractive optical element is determined according to the light distribution. The Applicant has attempted to consider in this patent whether it can be displaced.

  Examples of proposals for shifting the center position of the diffractive optical element as countermeasures against the deterioration of diffraction efficiency with respect to the oblique incidence of the diffractive optical element include Japanese Patent Nos. 2532729 and 25670703. In the patent, the diffraction efficiency deterioration due to oblique incidence is caused by making the pattern shape of the diffraction grating an ellipse, and gradually shifting the position of the center of the ellipse in the outer peripheral direction according to the incident angle of the light beam. The deterioration was mitigated. However, the above-mentioned patent is only a countermeasure against the oblique incidence deterioration of the diffraction efficiency in a single wavelength (He-Ne laser), and it cannot be said that a high diffraction efficiency is obtained.

  In the present invention, the above conventional problems are solved, the optical system is bright and compact, various aberrations, in particular, chromatic aberration can be corrected well, and the incident angle dependence of the diffractive optical element in the entire operating wavelength range (visible light range). It is an object of the present invention to provide a diffractive optical element suitable for projection type display devices such as a liquid crystal projector, and a coaxial projection lens using the same.

  In order to solve the above problems, a diffractive optical element of the present invention and a projection lens using the diffractive optical element have the following configurations.

  (1) The diffractive optical element of the present invention is a diffractive optical element used in a wide wavelength range, and the diffractive optical element has a diffraction grating formed on a lens substrate, and the pattern shape of the diffraction grating is circular. Or it is elliptical, The center position of the said circle | round | yen or an ellipse has shifted | deviated with respect to the optical axis of the said lens board | substrate.

  (2) In the diffractive optical element of the present invention, the shift direction of the center position of the circular or elliptical shape of the diffractive optical element is shifted in a direction in which a light passing region incident on the diffractive optical element is biased. It is characterized by.

  (3) In the diffractive optical element of the present invention, the direction of deviation of the center position of the circular or elliptical shape of the diffractive optical element is one diameter perpendicular to the optical axis of the lens substrate in the case of the circular shape. In the case of the ellipse, the direction is shifted in one major axis or minor axis direction perpendicular to the optical axis of the lens substrate.

  (4) The diffractive optical element of the present invention is characterized in that the center position of the circular or elliptical shape of the diffraction grating becomes smaller as the grating pitch decreases toward the periphery of the diffraction grating. .

  (5) The diffractive optical element of the present invention is characterized in that the used wavelength region is a visible light region.

  (6) The diffractive optical element according to the present invention is mainly used in a coaxial projection lens.

  (7) In the diffractive optical element of the present invention and a projection lens using the diffractive optical element, the diffractive optical element is positioned at a position where the height from the optical axis of the paraxial ray passing through each lens satisfies the following conditional expression: It is characterized by being introduced.

ここで、

here,

は回折光学素子を導入するレンズ面の瞳近軸光線の光軸からの高さを、R_DOEは回折光学素子を導入するレンズ面における光線有効半径を各々表している。

Denotes the height of the lens paraxial ray from the optical axis of the lens surface where the diffractive optical element is introduced, and R _DOE denotes the effective ray radius at the lens surface where the diffractive optical element is introduced.

  (8) In the diffractive optical element of the present invention and the projection lens using the diffractive optical element, the deviation amount of the center position of the circular or elliptical shape of the diffractive optical element satisfies the following conditional expression.

0.0 <| Yshift / R _DOE | <0.3 ……… (2)
Here, Yshift is the amount of deviation of the center position of the circular or elliptical shape of the diffractive optical element in the direction perpendicular to the optical axis of the lens surface for introducing the diffractive optical element in the projection lens, and R _DOE is the diffractive optical Each of the effective ray radii on the lens surface where the element is introduced is shown.

  (9) In the diffractive optical element of the present invention and a projection lens using the diffractive optical element, the diffractive optical element has a diffraction grating formed on a lens substrate, and the pattern shape of the diffraction grating is circular or elliptical. The multilayer diffractive optical element is formed by laminating a plurality of layers formed in (1).

  (10) In the diffractive optical element of the present invention and the projection lens using the diffractive optical element, the diffractive optical element has a configuration in which two layers of the diffraction grating composed of two materials having different dispersions are arranged close to each other. It is a feature.

  (11) The projector device according to the present invention is characterized in that the projection image original image is projected on the screen surface using the projection lens according to any one of (6) to (10).

  According to the present invention, as described above, in the coaxial projection zoom lens, the diffractive optical element is introduced at a position where the absolute value of the height from the optical axis of the paraxial light beam passing through each lens is high. This can be realized by shifting the circular or elliptical center forming the diffractive optical element with respect to the optical axis of the lens substrate in accordance with the distribution of light rays incident on the diffractive optical element surface. Furthermore, by appropriately setting the shift position of the introduction position of the diffractive optical element and the center of the circle or ellipse forming the diffractive optical element, various aberrations, in particular chromatic aberration, are further corrected, and the diffraction efficiency is inclined. It is possible to realize an optical system in which incident deterioration is mitigated.

  1 to 4 and FIGS. 14 and 15 are respectively (a) at the wide-angle end of Numerical Examples 1 to 4 of the present invention and Conventional Examples 1 and 2 to be compared with the present Example. Each lens sectional view (optical path diagram) is shown. In each figure, the enlargement conjugate side corresponds to the screen side, and the reduction conjugate side corresponds to the liquid crystal panel side. Further, L1 to L6 in the drawings represent the lens groups of the first lens group to the sixth lens group. SP is a stop, which exists between the third lens unit L3 and the fourth lens unit L4 in each of the examples and the comparative conventional examples. The diffractive optical element is shown in Numerical Example 1 of FIG. 1, Numerical Example 2 of FIG. 2 and Comparative Conventional Example 1 of FIG. 14 on the cemented surface of the sixth lens unit L6, and Numerical Example 3 of FIG. In Numerical Example 4 of FIG. 4 and Comparative Example 2 of FIG. 15, each is introduced to the cemented surface of the first lens unit L1. GB is a glass block such as a color synthesis prism. The arrows indicate the movement trajectory of each lens group when zooming from the wide-angle end to the telephoto end. The coordinate system of the optical system (relationship between X, Y, and Z axes) is as shown in each drawing.

  In this proposal, in each optical system of each example and each comparative conventional example, the first lens unit L1 having a negative refractive power, the second lens unit L2 having a positive refractive power, the first lens unit having a positive refractive power in order from the magnification conjugate side. Coaxial projection zoom lens with 6 lens groups: 3 lens unit L3, 4th lens unit L4 with negative refractive power, 5th lens unit L5 with positive refractive power, 6th lens unit L6 with positive refractive power It is. When zooming from the wide-angle end to the telephoto end, the first lens unit L1 and the sixth lens unit L6 are fixed, and the second lens unit L2 and the third lens in each example and each comparative conventional example. The zooming is performed by moving the group L3 and the fifth lens unit L5 from the reduction conjugate side to the enlargement conjugate side. In each of the optical systems of the examples and comparative conventional examples, focusing is performed by moving the first lens unit L1.

  1 to 4, 14, and 15, (b) and (c) are numerical examples 1 to 4 of the present invention (each (a) of FIGS. 1 to 4) and a comparison of the present invention. XY sectional drawing and YZ sectional drawing of the diffraction optical element used for the optical system of the prior art examples 1 and 2 (each (a) of FIG. 14, 15) are each represented. Here, the coordinate system of each cross-sectional view coincides with the coordinate system of the optical system of each figure (a). In each figure, the number of diffraction gratings (the number of circumferences) in (b) is simplified, and the depth of the diffraction grating in (c) is a deformed figure.

  Next, each numerical example of the present invention will be described with reference to each drawing.

  Prior to the description of the embodiments of the present invention, the diffractive optical element of the present invention and the optical system and the diffractive optical element to be compared with the optical system using the same were also examined. .

14 (a) to 14 (c) shows a comparative example 1 in the coaxial zoom projection zoom lens having the 6-group configuration shown in FIG. 14 (a), on the cemented surface of the sixth lens group L6. 14 shows a conventional example to be compared with the present invention, in which a rotationally symmetric laminated diffractive optical element as shown in FIGS. 14 (b) and (c) is introduced. Specifically, a laminated diffractive optical element is formed on the 24th surface r24 and the 25th surface r25. (In this numerical data, the phase function is shown on the 24th surface r24, but in reality, the diffractive optical elements are formed on the two surfaces, so that the diffractive optics are formed on the 24th surface r24 and the 25th surface r25. Forming an element.)
In describing the diffractive optical element, a phase function represented by the following equation was used.

上記(A)式において、λは設計波長(550nm)、Ciは位相係数、x及びyは投射光学系のXY座標系における光軸からの位置(x,y)を各々表している。尚、本比較従来例及び後述の各実施例においては、設計次数を1次としているため、位相差が2πとなるように格子のピッチが決定される。本比較従来例１においては、回転対称な回折光学素子を用いていることより、C3、C5、C10、C12、C14の位相係数を使用し最適化を行った。(他の位相係数の値は0である。)
次に、異なる２種類の材料により成る積層型回折光学素子において、回折格子の格子形状を決定するための方法について説明する。

In the above formula (A), λ represents the design wavelength (550 nm), Ci represents the phase coefficient, and x and y represent the position (x, y) from the optical axis in the XY coordinate system of the projection optical system. In this comparative conventional example and each of the examples described later, the design order is the first order, and therefore the pitch of the grating is determined so that the phase difference is 2π. In this comparative conventional example 1, since a rotationally symmetric diffractive optical element was used, optimization was performed using phase coefficients of C3, C5, C10, C12, and C14. (The other phase coefficient values are 0.)
Next, a method for determining the grating shape of the diffraction grating in the laminated diffractive optical element made of two different materials will be described.

  In this comparative conventional example 1, UV curable resin 1 (nd = 1.636, νd = 22.8) is formed on the first layer between the 23rd surface r23 and the 24th surface r24, and the first layer between the 25th surface r25 and the 26th surface r26. An example is shown in which two layers are made of ultraviolet curable resin 2 (nd = 1.513, νd = 51.0). At this time, if the grid heights of the ultraviolet curable resins 1 and 2 are d1 and d2, respectively, the grid heights d1 and d2 satisfying the following conditional expressions are determined.

ここで、n1(λ)、n2(λ)は波長λにおける前記紫外線硬化樹脂１及び２の屈折率を、nair(=1)は空気の屈折率を、mは設計次数（ここでは１次）を各々表している。上記(i)式から、本比較従来例及び後述の各実施例では、前記紫外線硬化樹脂1及び2の格子高さd1、d2を各々6.9μm、9.5μmとした。また、両樹脂より構成される格子間に空気層（1.0μm）を設けている。本比較従来例の数値データ中において、前記紫外線硬化樹脂の各厚みを0.05mmとしているが、これは回折光学素子の格子部の厚み(格子高さ)のみを表しているのではなく、前記回折光学素子を構成する樹脂のベース部分の厚みも考慮して示している。しかしながら、回折光学素子の構成についてはこれに限定するものではない。

Here, n1 (λ) and n2 (λ) are the refractive indexes of the ultraviolet curable resins 1 and 2 at the wavelength λ, nair (= 1) is the refractive index of air, and m is the design order (here, the first order). Respectively. From the above formula (i), in this comparative conventional example and each example described later, the grating heights d1 and d2 of the ultraviolet curable resins 1 and 2 were set to 6.9 μm and 9.5 μm, respectively. In addition, an air layer (1.0 μm) is provided between the lattices made of both resins. In the numerical data of this comparative conventional example, each thickness of the ultraviolet curable resin is set to 0.05 mm, but this does not represent only the thickness (grating height) of the grating portion of the diffractive optical element, but the diffraction The thickness of the base portion of the resin constituting the optical element is also taken into consideration. However, the configuration of the diffractive optical element is not limited to this.

  Next, the oblique incidence dependence of the first-order diffraction efficiency with respect to the comparative example 1 is shown in FIG. Before describing the details of FIG. 6A, a method for calculating the oblique incidence diffraction efficiency will be briefly described.

  As shown in FIG. 13, the relationship of the optical optical path length difference when entering the grating 1 of the resin layer 1 of the laminated diffractive optical element at the incident angle θ1 is expressed by the following equation.

ここで、θ1は格子1への入射角を、θairは格子1からの射出角（格子2への入射角）を、θ2は格子2からの射出角を各々表しており、残りの屈折率、格子厚、設計次数等は上記(i)式の場合と同じである。ここで、各角度は面法線を基準にして、反時計回りを正、時計回りを負としている。上記関係式が成り立つ時のm次の回折効率η(λ)は、以下の式で求められる。

Here, θ1 represents the incident angle to the grating 1, θair represents the exit angle from the grating 1 (incident angle to the grating 2), θ2 represents the exit angle from the grating 2, and the remaining refractive index, The lattice thickness, the design order, etc. are the same as those in the above formula (i). Here, with respect to each angle, the counterclockwise direction is positive and the clockwise direction is negative with respect to the surface normal. The m-th order diffraction efficiency η (λ) when the above relational expression is satisfied is obtained by the following expression.

ここで、Ψ(λ)は以下の式で表される。

Here, Ψ (λ) is expressed by the following equation.

上記(iii)、(iv)式で算出された1次の回折効率の入射角θ1による依存特性を図6(a)に示した。また図６(a)を算出する際、以下のことを考慮した。図５(a)は、図１４(b)のY軸上（Y≧0）における位置yと格子ピッチp及び入射角度θ1の分布との関係を示している。図５(a)中において、横軸が輪帯半径r[mm]（Y軸上の位置y[mm]）を、縦軸が格子ピッチp[μm]及び入射角度θ1[deg.]を各々表している。ここで、この図の見方は、格子ピッチpは◆で表してあり、左のY軸の値を読み、入射角θ1はその値の最大値をθ1maxとして塗りつぶし□で表し、その値の最小値をθ1minとして塗りつぶし△で表し、右のY軸の値を読むようにする。つまり、前記θ1maxとθ1minの間の範囲が、回折光学素子に入射する入射角度θ1の範囲に相当する。この図５(a)より、格子ピッチpは輪帯半径r（位置y）が大きくなる（周辺部に向かう）につれて小さくなり（格子ピッチが細かくなり）、一方入射角度θ1の分布は、輪帯半径r（位置y）が大きくなる（周辺部に向かう）につれて分布幅が狭まっていることが分かる。この図５(a)から、図６(a)の1次の回折効率の入射角θ1による依存特性を評価する位置yを、格子ピッチpの値がある程度細かく、且つ入射角度θ1の分布幅もある程度広いy=12.0[mm]位置で行うこととした。

FIG. 6 (a) shows the dependency of the first-order diffraction efficiency calculated by the above equations (iii) and (iv) on the incident angle θ1. In calculating FIG. 6A, the following was taken into consideration. FIG. 5A shows the relationship between the position y on the Y axis (Y ≧ 0) of FIG. 14B and the distribution of the grating pitch p and the incident angle θ1. In FIG. 5 (a), the horizontal axis represents the zone radius r [mm] (position y [mm] on the Y axis), and the vertical axis represents the grating pitch p [μm] and the incident angle θ1 [deg.]. Represents. In this figure, the grid pitch p is represented by ◆, the value on the left Y axis is read, the incident angle θ1 is represented by a solid square □ with the maximum value of θ1max, and the minimum value of the value Is represented by a solid Δ as θ1min, and the value on the right Y-axis is read. That is, the range between θ1max and θ1min corresponds to the range of the incident angle θ1 incident on the diffractive optical element. From FIG. 5 (a), the grating pitch p decreases as the annular radius r (position y) increases (towards the periphery) (the grating pitch becomes finer), while the distribution of the incident angle θ1 is It can be seen that the distribution width narrows as the radius r (position y) increases (towards the periphery). From FIG. 5 (a), the position y at which the dependence characteristic of the first-order diffraction efficiency on the incident angle θ1 in FIG. 6 (a) is evaluated has a fine value of the grating pitch p and the distribution width of the incident angle θ1. It was decided to carry out at a somewhat wide y = 12.0 [mm] position.

  Based on FIG. 5A, in FIG. 6A, the position (x, y) = (0, 12.0) [mm from the optical axis of the XY coordinate system of the projection optical system on the diffractive optical element introduction surface. The incident angle distribution θ1 = −6 ° to 6 ° is taken every 3 ° intervals, and the result of the first-order diffraction efficiency for each angle θ1 is shown. At this time, the horizontal axis represents wavelength [μm] and the vertical axis represents diffraction efficiency [%]. The lattice pitch p at this time is 93.8 [μm]. From FIG. 6 (a), it can be seen that the value of the diffraction efficiency decreases near the wavelength of 0.48 [μm] as the value of the incident angle θ1 increases in the positive direction. In particular, it can be seen that when θ1 = + 6 °, the diffraction efficiency drops by about 6% with respect to θ1 = 0 °. This reduction means that the diffraction efficiency of other unnecessary orders of diffracted light is increased, which may cause flare light (noise light) and cause image degradation. On the other hand, when the value of θ1 is negative, the diffraction efficiency is somewhat lowered at the wavelengths at both ends of the visible region of 0.40 [μm] and 0.70 [μm], but the value that is almost the same as when θ1 = 0 ° is maintained. From the above results, it was found that the decrease in diffraction efficiency when the incident angle θ1 is positive is a problem in the optical system of Comparative Example 1 of the present comparative example.

In view of the problem in the comparative example 1, the first example of the present invention is shown in FIGS. Example 1 in FIGS. 1 (a) to 1 (c) is similar to the optical system in FIG. 14 (a) in the six-group coaxial zoom zoom lens system shown in FIG. 1 (a). An example in which a laminated diffractive optical element in which the center of the circular pattern shape of the diffraction grating is shifted in the Y-axis direction as shown in FIGS. 1B and 1C is introduced to the cemented surface of the sixth lens unit L6. It is. Specifically, this is an example in which the center of the circular pattern shape is shifted by Yshift = + 2 [mm] in the Y-axis direction, and the other parts (such as places where the diffractive optical element is introduced) are in the case of Comparative Example 1 described above. It is the same. The reason for shifting the center of the circular pattern shape in the Y-axis direction as in Example 1 is that the sixth lens in which a diffractive optical element is introduced in the optical path diagram of FIG. This is because the cemented surface of the group L6 is at a position where the height of the paraxial light beam passing through the optical axis is high, so that the light beam passing through the diffraction surface is biased. (In FIG. 1 (a), the positive direction of the Y-axis) Further, the coaxial projection lens as used in the present embodiment has a projection range on the screen when an image is projected on the screen. Is mainly used on one half of the optical axis of the coaxial projection lens, so even if the center of the circular pattern shape of the diffraction grating is shifted in the (positive) direction of the Y-axis, This is because it is determined that there is not much problem in efficiency performance. (This means that even if the diffraction efficiency of the part that is not used for projection (the part where the light beam does not pass) deteriorates, there is not much influence on the projection.)
In the first embodiment, a diffractive optical element having a configuration in which the center of the circular pattern shape is shifted in the positive direction of the Y axis is used, so that C2, C3, C5, C7, C9, Optimization was performed using each phase coefficient of C10, C12, and C14. (The other phase coefficient values are 0.)
Further, the ultraviolet curable resins 1 and 2 and the lattice heights d1 and d2 used in Example 1 are the same as those in Comparative Example 1.

  The oblique incidence dependence of the first-order diffraction efficiency for Example 1 at this time is shown in FIG. Similarly to the case of the comparative example 1, the relationship between the position y on the Y axis (Y ≧ 0) in FIG. 1B and the distribution of the grating pitch p and the incident angle θ1 is shown in FIG. 5B. Indicated. In FIG. 5 (b), the grating pitch p becomes smaller (the grating pitch becomes finer) as the ring zone radius r (position y) becomes larger (towards the periphery), but in the case of Comparative Example 1 (FIG. 5). It can be seen that the decrease is moderate compared to 5 (a)). On the other hand, the distribution of the incident angle θ1 becomes narrower as the ring zone radius r (position y) increases (towards the periphery), which is almost the same as in the case of the comparative example 1 (FIG. 5A). It can be seen that they have the same angular distribution. In FIG. 6B, the position y for evaluating the dependency characteristic of the first-order diffraction efficiency depending on the incident angle θ1 is set at the position y = 12.0 [mm] as in the comparative example 1.

  In FIG. 6B, similar to the comparative example 1, the incident angle distribution θ1 = − at the position (x, y) = (0, 12.0) [mm] from the optical axis of the XY coordinate system of the projection optical system. 6 ° to 6 ° is taken every 3 ° intervals, and the results of the first-order diffraction efficiency for each angle θ1 are shown. The lattice pitch p at this time is 166.15 [μm]. From the result of FIG. 6 (b), the value of the diffraction efficiency near the wavelength of 0.48 [μm] as the value of the incident angle θ1 increases in the positive direction, which is a problem in the comparative example 1 described above. Although this is a decrease, the diffraction efficiency in Example 1 is about 3% higher (improved) compared to the case of Comparative Conventional Example 1 when θ1 = + 6 °. I understand. As a result, the value of the diffraction efficiency near the wavelength of 0.48 [μm] when θ1 = + 6 ° is improved to about 3% with respect to θ1 = 0 °. On the other hand, when the value of θ1 is negative, good diffraction efficiency is obtained over the entire visible light range, and a value almost unchanged from the diffraction efficiency when θ1 = 0 ° is maintained. As described above, by using the diffractive optical element having the configuration in which the center of the circular pattern shape of the diffraction grating is shifted in the Y-axis direction, the oblique incidence deterioration of the diffraction efficiency can be alleviated.

  Example 2 in FIGS. 2A to 2C is an example in which the amount of deviation of the center of the circular pattern shape of the diffraction grating from the Y axis of Example 1 is further increased. Specifically, in the six-group coaxial projection zoom lens shown in FIG. 2 (a), the cemented surface of the sixth lens group L6 is shown in FIGS. 2 (b) and 2 (c). This is an example in which a laminated diffractive optical element in which the center of the circular pattern shape of the diffraction grating is shifted in the Y-axis direction as shown is shifted by Yshift = + 5 [mm]. Other portions (such as a place where the diffractive optical element is introduced) are the same as those in the first embodiment. In addition, the phase coefficient used in the second embodiment is the same as that in the first embodiment, and optimization was performed using each phase coefficient.

  FIG. 5 (c) shows the relationship between the position y on the Y axis (Y ≧ 0) and the distribution of the grating pitch p and the incident angle θ1, as in FIGS. 5 (a) and 5 (b). In FIG. 5 (c), the grating pitch p becomes smaller (the grating pitch becomes finer) as the annular radius r (position y) becomes larger (towards the periphery), but in the case of Example 1 (FIG. 5 (c)). Compared with b)), it can be seen that the degree of decrease is even slower. On the other hand, it can be seen that the distribution of the incident angle θ1 is substantially the same as that in the comparative conventional example 1 and the example 1 (FIGS. 5A and 5B). It should be noted that the position y at which the dependence characteristic of the first-order diffraction efficiency on the incident angle θ1 is evaluated is determined at the position y = 12.0 [mm] as in the comparative example 1 and example 1.

  In FIG. 6 (c), the incident angle at the position (x, y) = (0, 12.0) [mm] from the optical axis of the XY coordinate system of the projection optical system, as in Comparative Example 1 and Example 1. The distribution θ1 = −6 ° to 6 ° is taken every 3 ° interval, and the result of the first-order diffraction efficiency for each angle θ1 is shown. The lattice pitch p at this time is 580.0 [μm]. From the result of FIG. 6 (c), there is almost no decrease in diffraction efficiency near the wavelength of 0.48 [μm] when the value of the incident angle θ1 is positive, which was a problem in the comparative conventional example 1. In Example 2, it can be seen that the value of the diffraction efficiency, which was the minimum when θ1 = + 6 °, is about 2% higher (improved) than in Example 1. As a result, the diffraction efficiency value near the wavelength of 0.48 [μm] when θ1 = + 6 ° is almost the same as the value when θ1 = 0 °, and the dependence on the incident angle θ1 is almost eliminated. . As described above, by further increasing the amount by which the center of the circular pattern shape of the diffraction grating is shifted in the Y-axis direction, the oblique incidence deterioration of the diffraction efficiency can be further mitigated as compared with the case of Example 1.

  Next, Comparative Example 2 shown in FIGS. 15A to 15C is formed on the cemented surface of the first lens unit L1 in the six-group coaxial projection zoom lens shown in FIG. This is an example to be compared with the present invention (described later), in which a rotationally symmetric laminated diffractive optical element as shown in FIGS. 15B and 15C is introduced. Specifically, in this comparative conventional example 2, a laminated diffractive optical element is formed on the third surface r3 and the fourth surface r4 (in this numerical data, a phase function is applied to the third surface r3). Although shown, in practice, a diffractive optical element is formed on the third surface r3 and the fourth surface r4 in order to form the diffractive optical element on two surfaces.

  In this comparative conventional example 2, similar to the comparative conventional example 1, since a rotationally symmetric diffractive optical element is used, optimization was performed using phase coefficients of C3, C5, C10, C12, and C14. (The other phase coefficient values are 0.)

  Further, the material, the grating height, etc. constituting the laminated diffractive optical element are all the same as those in Comparative Example 1 and Examples 1 and 2.

  FIG. 7A shows the position y on the Y-axis (Y ≦ 0) in FIG. 15B in the same manner as FIGS. 5A to 5C in the comparative example 1 and Examples 1 and 2. And the distribution of the grating pitch p and the incident angle θ1. From FIG. 7 (a), the grating pitch p becomes smaller as the annular radius r (position y) becomes smaller (towards the periphery) (the grating pitch becomes finer), while the distribution of the incident angle θ1 is It can be seen that the distribution width becomes narrower as the radius r (position y) becomes smaller (towards the periphery). From FIG. 7 (a), the position y for evaluating the dependency of the first-order diffraction efficiency on the incident angle θ1 in FIG. 8 (a) has a fine grating pitch p value and the distribution width of the incident angle θ1. It was decided to perform at a somewhat wide y = −12.0 [mm] position.

  Based on FIG. 7 (a), in FIG. 8 (a), the position (x, y) = (0, −12.0) [from the optical axis of the XY coordinate system of the projection optical system on the diffractive optical element introduction surface. The incident angle distribution θ1 = −2 ° to 8 ° in mm] is taken in the order of θ1 = −2 °, 0 °, 3 °, 5 °, 8 °, and the results of the first-order diffraction efficiency for each angle θ1 are shown. Yes. At this time, the lattice pitch p is 109.34 [μm]. FIG. 8 (a) shows that the value of the diffraction efficiency decreases near the wavelength of 0.48 [μm] as the value of the incident angle θ1 increases in the positive direction. In particular, it can be seen that when θ1 = + 8 °, the diffraction efficiency drops by about 9% with respect to θ1 = 0 °. This reduction means that the diffraction efficiency of other unnecessary orders of diffracted light is increased, which may cause flare light (noise light) and cause image degradation. On the other hand, when the value of θ1 is negative, the diffraction efficiency is somewhat lowered at the wavelengths at both ends of the visible region of 0.40 [μm] and 0.70 [μm], but the value that is almost the same as when θ1 = 0 ° is maintained. From the above results, it was found that, as in the case of the comparative conventional example 1, this comparative conventional example 2 also has a problem that the diffraction efficiency is lowered when the incident angle θ1 is positive.

In view of the problem in the comparative example 2, the same examination as in the case of the examples 1 and 2 was also attempted in the example 3 of the present invention. Example 3 in FIGS. 3 (a) to 3 (c) is similar to the optical system in FIG. 15 (a) in the six-group coaxial projection zoom lens shown in FIG. 3 (a). An example in which a laminated diffractive optical element in which the center of the circular pattern of the diffraction grating is shifted in the Y-axis direction as shown in FIGS. 3B and 3C is introduced to the cementing surface of the first lens unit L1. It is. Specifically, this is an example in which the center of the circular pattern shape is shifted by Yshift = −2 [mm] in the Y-axis direction, and the other parts (such as places where the diffractive optical element is introduced) are the same as those in Comparative Example 2 described above. Same as the case. The reason for shifting the center of the circular pattern shape in the Y-axis direction as in the third embodiment is that the first lens in which the diffractive optical element is introduced in the optical path diagram of FIG. This is because the cemented surface of the group L1 is at a position where the absolute value of the height of the paraxial light beam passing through the optical axis is high, so that the light beam passing through the diffraction surface is biased. (The negative direction of the Y-axis in FIG. 3A) Further, the coaxial projection lens as used in the present embodiment has a projection range on the screen when an image is projected onto the screen. Is mainly used on one half of the optical axis of the projection lens of the coaxial system, so even if the center of the circular pattern shape of the diffraction grating is shifted in the (negative) direction of the Y-axis, diffraction is performed. This is because it is determined that there is not much problem in efficiency performance. (This means that even if the diffraction efficiency of the part that is not used for projection (the part where the light beam does not pass) deteriorates, there is not much influence on the projection.)
In Example 3, a diffractive optical element having a configuration in which the center of the circular pattern shape is shifted in the negative direction of the Y axis is used, so that C2, C3, C5, C7, C9, Optimization was performed using each phase coefficient of C10, C12, and C14. (The other phase coefficient values are 0.)
Further, the ultraviolet curable resins 1 and 2 and the lattice heights d1 and d2 used in Example 3 are the same as those in Comparative Example 2.

  The oblique incidence dependence of the first-order diffraction efficiency for Example 3 at this time is shown in FIG. As in the case of the comparative example 2, the relationship between the position y on the Y axis (Y ≦ 0) in FIG. 3B and the distribution of the grating pitch p and the incident angle θ1 is shown in FIG. 7B. Indicated. In FIG. 7B, the grating pitch p decreases as the zone radius r (position y) decreases (towards the periphery) (the grating pitch becomes finer), but in the case of the comparative example 2 (FIG. It can be seen that the degree of decrease is moderate compared to 7 (a)). On the other hand, the distribution of the incident angle θ1 narrows as the ring zone radius r (position y) decreases (towards the periphery), which is almost the same as in the case of the comparative example 2 (FIG. 7A). It can be seen that they have the same angular distribution. In FIG. 8B, the position y for evaluating the dependence characteristic of the first-order diffraction efficiency depending on the incident angle θ1 is set at the position y = −12.0 [mm] as in the comparative example 2.

  In FIG. 8 (b), as in Comparative Example 2, the incident angle distribution θ1 = at the position (x, y) = (0, −12.0) [mm] from the optical axis of the XY coordinate system of the projection optical system. -2 ° to 8 ° are taken in the order of θ1 = −2 °, 0 °, 3 °, 5 °, and 8 °, and the result of the first-order diffraction efficiency for each angle θ1 is shown. At this time, the lattice pitch p is 199.20 [μm]. From the result of FIG. 8 (b), the value of the diffraction efficiency in the vicinity of the wavelength of 0.48 [μm] decreases as the value of the incident angle θ1 increases in the positive direction, which is a problem in the comparative conventional example 2. However, the value of the diffraction efficiency, which was the minimum when θ1 = + 8 °, in Example 3 is about 5% higher (improved) than in the case of Comparative Example 2 described above. I understand. As a result, the value of the diffraction efficiency in the vicinity of the wavelength of 0.48 [μm] when θ1 = + 8 ° is improved to about 5% with respect to θ1 = 0 °. On the other hand, when the value of θ1 is negative, good diffraction efficiency is obtained over the entire visible region, and a value that is almost the same as the diffraction efficiency when θ1 = 0 ° is maintained. As described above, by using the diffractive optical element having the configuration in which the center of the circular pattern shape of the diffraction grating is shifted in the Y-axis direction, the oblique incidence deterioration of the diffraction efficiency can be alleviated.

  Example 4 of FIGS. 4A to 4C is an example in which the amount of deviation of the center of the circular pattern shape of the diffraction grating from the Y axis of Example 3 is further increased. Specifically, in the same manner as in the third embodiment, in the coaxial projection zoom lens having the six-group configuration as shown in FIG. 4A, the joint surface of the first lens unit L1 is shown in FIG. This is an example in which a laminated diffractive optical element in which the center of a circular pattern shape of a diffraction grating of Yshift = −5 [mm] is shifted in the Y axis direction as shown in (b) and (c) is introduced. Other parts (such as the place where the diffractive optical element is introduced) are the same as in the third embodiment. Further, the phase coefficient used in the fourth embodiment was also optimized using the same coefficient as in the third embodiment.

  FIG. 7 (c) shows the relationship between the position y on the Y axis (Y ≦ 0) and the distribution of the grating pitch p and the incident angle θ1, as in FIGS. 7 (a) and 7 (b). In FIG. 7C, the grating pitch p becomes smaller (the grating pitch becomes finer) as the zone radius r (position y) becomes smaller (towards the periphery), but in the case of the third embodiment (FIG. 7 (c)). Compared with b)), it can be seen that the degree of decrease is even slower. On the other hand, it can be seen that the distribution of the incident angle θ1 is substantially the same as that of the comparative prior art example 2 and the example 2 (FIGS. 7A and 7B). It should be noted that the position y at which the dependence characteristic of the first-order diffraction efficiency on the incident angle θ1 is evaluated is the y = −12.0 [mm] position as in the comparative example 2 and the example 3.

  In FIG. 8 (c), as in Comparative Example 2 and Example 3, incidence at the position (x, y) = (0, −12.0) [mm] from the optical axis of the XY coordinate system of the projection optical system. The angle distribution θ1 = −2 ° to 8 ° is taken in the order of θ1 = −2 °, 0 °, 3 °, 5 °, and 8 °, and the result of the first-order diffraction efficiency for each angle θ1 is shown. The lattice pitch p at this time is 600.00 [μm]. From the result of FIG. 8 (c), there is almost no decrease in diffraction efficiency near the wavelength of 0.48 [μm] when the incident angle θ1 is positive, which was a problem in the comparative example 2 described above. It can be seen that the value of diffraction efficiency in Example 4 which is the minimum when θ1 = + 8 ° is increased (improved) by about 3% compared to the case of Example 3. As a result, the value of diffraction efficiency near the wavelength of 0.48 [μm] when θ1 = + 8 ° is improved to about 3% when θ1 = 0 °, and the dependence on the incident angle θ1 is almost eliminated. I understand that. As described above, by further increasing the amount by which the center of the circular pattern shape of the diffraction grating is shifted in the Y-axis direction, the oblique incidence deterioration of the diffraction efficiency can be further reduced as compared with the case of Example 3.

  Furthermore, in the first to fourth embodiments, the diffraction grating pattern shape in the diffractive optical element is an elliptical pattern shape as shown in FIGS. 9 (a) and 9 (b) and FIGS. 10 (a) and 10 (b). It has been found that even a configuration in which the center is shifted is established (however, the diffractive optical element in FIGS. 11 and 12 is shown as an example corresponding to the optical system in the first and second embodiments. FIGS. 9A and 9B show the case where the major axis of the ellipse is in the Y-axis direction, while FIGS. 10A and 10B show the case where the major axis of the ellipse is in the X-axis direction. Yes.)

  By taking the diffractive optical element having the above-described configuration and the lens configuration described in the present embodiment using the diffractive optical element, the problems listed in the present invention can be achieved.

  Further, in order to achieve an optical system in which various aberrations are sufficiently corrected and the diffraction efficiency deterioration with respect to oblique incidence is alleviated, it is desirable to satisfy the following conditional expression.

  In the diffractive optical element of the present invention and a coaxial projection zoom lens using the same,

を回折光学素子が導入されるレンズ面の瞳近軸光線の光軸からの高さとし、R_DOEを回折光学素子を導入するレンズ面における光線有効半径とした際、以下の条件式を満足することである。

Is the height from the optical axis of the paraxial light beam on the lens surface where the diffractive optical element is introduced, and R _DOE is the effective ray radius at the lens surface where the diffractive optical element is introduced, the following conditional expression must be satisfied: It is.

条件式（１）は、光学系と回折光学素子の導入箇所との関係に関するものである。条件式（１）の範囲外の箇所に前記回折光学素子を導入すると、その導入箇所における光線分布に偏りが生じなくなるので好ましくない。

Conditional expression (1) relates to the relationship between the optical system and the place where the diffractive optical element is introduced. If the diffractive optical element is introduced at a location outside the range of the conditional expression (1), the light distribution at the introduced location will not be biased, which is not preferable.

  After satisfying the conditional expression (1), the following conditional expression (2) must be satisfied.

In the diffractive optical element of the present invention and a coaxial projection zoom lens using the diffractive optical element, Yshift is the center position of the circular or elliptical shape of the diffractive optical element, and the lens surface that introduces the diffractive optical element in the projection lens When the amount of deviation in the direction perpendicular to the optical axis is used and R _DOE is the effective ray radius on the lens surface where the diffractive optical element is introduced, the following conditional expression is satisfied.
0.0 <| Yshift / R _DOE | <0.3 ……… (2)
Conditional expression (2) relates to the movement amount of the diffractive optical element in the coaxial projection zoom lens using the diffractive optical element. If the value is outside the range of the conditional expression (2), it is not preferable for correcting aberrations of the optical system.

  The diffractive optical element according to the present invention and a coaxial projection zoom lens using the diffractive optical element can obtain better optical performance over the entire zooming range by satisfying the above conditional expressions. In addition, it is possible to achieve an optical system in which the oblique incidence deterioration of the diffractive optical element is reduced.

  The numerical examples of the present invention will be described below. In numerical examples, ri is the radius of curvature of the i-th lens surface in order from the magnification conjugate side, di is the i-th lens thickness and air spacing in order from the magnification conjugate side, and ni and vi are respectively in order from the magnification conjugate side. It represents the glass refractive index and Abbe number at the d-line of the i-th lens.

また、以下に各数値実施例の条件式の値を示す。

Moreover, the value of the conditional expression of each numerical example is shown below.

上記の表の各値は、前記条件式（１）及び（２）の範囲を満足しており、以上の構成をとることにより、諸収差、特に色収差の補正が十分になされ、且つ斜入射に対する回折効率劣化の緩和がなれた光学系を達成することができた。

Each value in the above table satisfies the range of the conditional expressions (1) and (2). By adopting the above configuration, various aberrations, in particular, chromatic aberration are sufficiently corrected, and against oblique incidence. It was possible to achieve an optical system in which the degradation of diffraction efficiency was alleviated.

FIG. 2 is a lens cross-sectional view (optical path diagram) ((a)) and a cross-sectional view of a diffractive optical element ((b), (c)) at a wide angle end according to Numerical Example 1 of the present invention. FIG. 5 is a lens cross-sectional view (optical path diagram) ((a)) and a cross-sectional view of a diffractive optical element ((b), (c)) at a wide angle end according to Numerical Example 2 of the present invention. FIG. 6 is a lens cross-sectional view (optical path diagram) ((a)) and a cross-sectional view of a diffractive optical element ((b), (c)) at a wide angle end according to Numerical Example 3 of the present invention. FIG. 6 is a lens cross-sectional view (optical path diagram) ((a)) and a cross-sectional view of a diffractive optical element ((b), (c)) at a wide angle end according to Numerical Example 4 of the present invention. (a) The relationship figure of the ring zone radius, grating | lattice pitch, and incident angle in the comparative example 1 with respect to this invention. (b) The relationship figure of the ring zone radius, a grating | lattice pitch, and an incident angle in Example 1 of this invention. (c) Relationship diagram between ring zone radius, grating pitch and incident angle in Embodiment 2 of the present invention. (a) The figure of the incident angle dependence characteristic of the 1st-order diffraction efficiency in the comparative example 1 with respect to this invention. (b) The incident angle dependence characteristic of the 1st-order diffraction efficiency in Example 1 of this invention. (c) The incident angle dependence characteristic of the 1st-order diffraction efficiency in Example 2 of this invention. (a) Comparison diagram of annular zone radius, grating pitch and incident angle in Comparative Example 2 for the present invention. (b) Relationship diagram of annular zone radius, grating pitch and incident angle in Example 3 of the present invention. (c) Relationship diagram between ring zone radius, grating pitch, and incident angle in Example 4 of the present invention. (a) The figure of the incident angle dependence characteristic of the 1st-order diffraction efficiency in the comparative prior art example 2 with respect to this invention. (b) The figure of the incident angle dependence characteristic of the 1st-order diffraction efficiency in Example 3 of this invention. (c) The incident angle dependence characteristic of the 1st-order diffraction efficiency in Example 4 of this invention. Sectional drawing ((a), (b)) of the diffractive optical element which concerns on this invention. Sectional drawing ((a), (b)) of the diffractive optical element which concerns on this invention. (a) Explanatory drawing of the single layer diffractive optical element which concerns on this invention. (b) Explanatory drawing of the diffraction efficiency wavelength dependence characteristic of the diffractive optical element of said (a). (a) Explanatory drawing of the laminated diffractive optical element which concerns on this invention. (b) Explanatory drawing of the diffraction efficiency wavelength dependence characteristic of the diffractive optical element of said (a). Explanatory drawing of the definition of the incident angle to the laminated | stacked diffractive optical element which concerns on this invention. FIG. 2 is a lens cross-sectional view (optical path diagram) ((a)) and a cross-sectional view of a diffractive optical element ((b), (c)) at the wide-angle end of Comparative Example 1 for the present invention. Sectional view (optical path diagram) ((a)) and sectional views ((b), (c)) of the diffractive optical element at the wide angle end of Comparative Example 2 for the present invention.

Claims (11)

  A diffractive optical element used in a broad wavelength region, the diffractive optical element having a diffraction grating formed on a lens substrate, the pattern shape of the diffraction grating being circular or elliptical, the circular or elliptical The center position of the diffractive optical element is shifted with respect to the optical axis of the lens substrate.   2. The diffractive optical element according to claim 1, wherein a shift direction of the center position of the circular or elliptical shape of the diffractive optical element is shifted in a direction in which a passing region of light incident on the diffractive optical element is biased. Optical element.   The circular or elliptical center position of the diffractive optical element is shifted in one radial direction perpendicular to the optical axis of the lens substrate in the case of the circular shape, and in the case of the elliptical shape, the lens. 3. The diffractive optical element according to claim 2, wherein the diffractive optical element is shifted in one major axis or minor axis direction perpendicular to the optical axis of the substrate.   4. The diffractive optical element has a shape in which a center position of the circular or elliptical shape of the diffraction grating becomes smaller as a grating pitch becomes smaller toward a peripheral portion of the diffraction grating. The diffractive optical element according to 1.   5. The diffractive optical element according to claim 1, wherein the use wavelength region is a visible light region.   6. The diffractive optical element according to claim 1, wherein the diffractive optical element is mainly used in a coaxial projection lens, and the projection lens using the diffractive optical element. In the projection lens using the diffractive optical element, the diffractive optical element is introduced at a position where the height from the optical axis of the paraxial ray passing through each lens satisfies the following conditional expression: 7. The diffractive optical element according to claim 6, and a projection lens using the diffractive optical element.

here,

: The height from the optical axis of the paraxial ray on the lens surface where the diffractive optical element is introduced.
R _DOE : Effective ray radius at the lens surface where the diffractive optical element is introduced.
Respectively. 8. The diffractive optical element according to claim 7, and a projection lens using the diffractive optical element according to claim 7, wherein a deviation amount of the center position of the circular or elliptical shape of the diffractive optical element satisfies the following conditional expression: .
0.0 <| Yshift / R _DOE | <0.3
here,
Yshift: A shift amount of the center position of the circular or elliptical shape of the diffractive optical element in the direction perpendicular to the optical axis of the lens surface where the diffractive optical element is introduced in the projection lens.
R _DOE : Effective ray radius at the lens surface where the diffractive optical element is introduced.
Respectively.   The diffractive optical element has a diffraction grating formed on a lens substrate, and a laminated diffractive optical element configured by laminating a plurality of layers in which the pattern shape of the diffraction grating is circular or elliptical. The diffractive optical element according to claim 1, and a projection lens using the diffractive optical element.   The diffractive optical element according to claim 9, wherein the diffractive optical element has a configuration in which two layers of the diffraction grating formed of two materials having different dispersions are arranged close to each other. The projection lens used. 11. A projection apparatus that projects a projected image original image on a screen surface using the projection lens according to claim 6.

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