JP5137432B2 - Adherent two-layer type diffractive optical element and optical system and optical apparatus using the same - Google Patents

Description

  The present invention relates to a diffractive optical element used in an optical system or an optical apparatus, and more particularly to a diffractive optical element in which diffraction gratings formed of two materials are in contact with each other.

  In contrast to the method of reducing chromatic aberration by combining glass materials, a method of reducing chromatic aberration by providing a diffractive optical element (hereinafter also referred to as a diffraction grating) having a diffractive action on a lens surface or a part of an optical system is disclosed in Non-Patent Document 1. And Patent Documents 1 to 3. This utilizes the physical phenomenon that chromatic aberration appears in the opposite direction with respect to a light beam having a certain reference wavelength at the refracting surface and the diffractive surface in the optical system.

  Furthermore, such a diffractive optical element can have an effect similar to that of an aspheric lens by changing the period of the periodic structure, which has a great effect on reducing aberrations.

  In an optical system having a diffractive optical element, light in the wavelength range of use (incident light to the diffractive optical element) is concentrated on diffracted light of a specific one order (hereinafter also referred to as design order), otherwise The intensity of the diffracted light of the diffraction order is low. For example, when the intensity is 0, the diffracted light does not exist. However, when there is diffracted light other than the designed order and it has a certain intensity, it forms an image at a position different from the diffracted light of the designed order, so that it becomes flare light in the optical system.

  Therefore, in order to utilize the chromatic aberration reducing action of the diffractive optical element, it is necessary that the diffraction efficiency of the diffracted light of the designed order is sufficiently high in the entire use wavelength region. For this reason, it is important to sufficiently consider the spectral distribution of diffraction efficiency at this design order and the behavior of diffracted light other than the design order.

  Here, the diffraction efficiency of a certain order of diffracted light is the ratio (also referred to as transmittance) of the light amount of the diffracted light of that order to the light amount of the total luminous flux transmitted through the diffractive optical element.

  FIG. 13 shows a diffractive optical element (hereinafter referred to as a single-layer DOE) including a substrate 109 and a diffraction grating 108 formed on the substrate 109. D 1 is the grating thickness of the diffraction grating 108. FIG. 14 shows the characteristics of diffraction efficiency with respect to a specific order when this single-layer DOE is formed on a certain surface.

  In FIG. 14, the horizontal axis indicates the wavelength of incident light, and the vertical axis indicates the diffraction efficiency. As described above, the value of the diffraction efficiency represents the ratio of the light amount of the diffracted light at each order to the light amount of the total transmitted light beam. Here, in order to simplify the explanation, the reflected light at the lattice boundary surface is not considered.

  As shown in FIG. 14, the single-layer DOE shown in FIG. 13 is designed so that the diffraction efficiency (the thick solid line in the figure) of the first order diffraction order, which is the designed order, is highest in the wavelength range of use. ing. At this design order, the diffraction efficiency is highest at a certain wavelength (hereinafter, this wavelength is referred to as a design wavelength), and gradually decreases at other wavelengths. The light corresponding to the amount of decrease in diffraction efficiency at this design order becomes diffracted light of other orders and becomes flare light. FIG. 14 also shows diffraction efficiency of orders (0th order and 2nd order) in the vicinity of the design order as other orders.

  Various configurations for reducing the influence of flare light generated in this way have been proposed.

  As shown in FIG. 15, the diffractive optical element disclosed in Patent Document 4 optimally selects three kinds of different grating materials 110 to 112 and two kinds of different grating thicknesses d1 and d2, and selects a plurality of diffraction gratings. Closely arranged with equal pitch distribution. As a result, as shown in FIG. 16, high diffraction efficiency at the design order is realized over the entire visible wavelength range.

  Further, the diffractive optical element 113 disclosed in Patent Document 5 shown in FIG. 17 has a structure in which element portions 114 and 115 each including a diffraction grating are brought close to each other via an air layer 116. Hereinafter, the diffractive optical element having such a configuration is referred to as a stacked DOE. By optimizing the refractive index, dispersion characteristics, and grating thickness of each layer constituting each diffraction grating, as shown in FIG. 18A, high diffraction efficiency at the design order is realized over the entire visible wavelength range. In addition, as shown in FIG. 18B, the diffraction efficiency of unnecessary diffracted light that is zero-order diffracted light and second-order diffracted light is generally suppressed.

Further, the diffractive optical element disclosed in Patent Document 6 is the same stacked DOE as the diffractive optical element disclosed in Patent Document 5. However, by optimizing the grating thickness of each layer using a material in which a fine particle material and a resin material are mixed, higher diffraction efficiency is realized than the diffractive optical element of Patent Document 5, as shown in FIG. 19A. . Further, as shown in FIG. 19B, the diffraction efficiency of unnecessary diffraction order light that is 0th order diffracted light and second order diffracted light is also sufficiently suppressed.

Furthermore, the diffractive optical element 119 disclosed in Patent Document 7 shown in FIG. 20 has a configuration in which diffraction gratings 117 and 118 formed of two different types of resin materials are in close contact with each other on their grating surfaces. Hereinafter, the diffractive optical element having such a configuration is referred to as a contact two-layer DOE. With such a configuration, a diffractive optical element that is easy to manufacture and inexpensive can be realized.
SPIE Vol.1354 International Lens Design Conference (1990) JP-A-4-213421 JP-A-6-324262 US Pat. No. 5,044,706 JP-A-9-127322 JP 2000-98118 A JP 2004-78166 A JP 2005-107298 A

  In the multilayer DOE disclosed in Patent Documents 4 and 5, the diffraction efficiency of the designed order is greatly improved as compared with the single-layer DOE so that it is 94% or more in the entire use wavelength region. In addition, unnecessary diffracted light that becomes flare light is also suppressed to approximately 2% or less.

  However, in an optical system mounted on an optical device such as a still camera or a video camera, there is a concern that slightly remaining flare light may be a problem when a high-luminance light source exists as a subject.

  In the multilayer DOE using the material obtained by mixing the fine particle material and the resin material disclosed in Patent Document 6, the diffraction efficiency of the designed order is 99.5% or more in the entire use wavelength region, and the unnecessary diffracted light is 0.05%. In the following, higher performance than the stacked DOEs of Patent Documents 4 and 5 is realized. As a result, the flare light is also expected to be inconspicuous.

  However, a diffractive optical element that is easier to manufacture than the multilayer DOE including an air layer disclosed in Patent Document 6 is desired.

On the other hand, the contact 2-layer DOE disclosed in Japanese Patent Document 7, the performance of the diffractive optical element itself, especially the diffraction efficiency of first order diffracted light that is the designed order is sufficiently and about 95 to 97% by using a wavelength region entire It is not very expensive. That is, there is a concern that flare caused by unnecessary diffracted light becomes a problem. Further, since the grating thickness is as thick as about 20 μm or more, degradation of diffraction efficiency due to vignetting with respect to obliquely incident light becomes a problem.

  The present invention provides a diffractive optical element that can obtain high diffraction efficiency with respect to diffracted light of a specific order (design order) in a wide wavelength region, can sufficiently suppress unnecessary diffracted light, and is easy to manufacture.

The diffractive optical element according to one aspect of the present invention has a configuration in which diffraction gratings formed of the first and second materials are in contact with each other on the grating surfaces. The second material is a material in which a first fine particle material that satisfies all of the following conditions is mixed with a resin material, and the first and second materials satisfy all of the following conditions: .

1.5218 ≦ nd1 ≦ 1.6110 … (1)
45.4 ≤ νd1 ≤ 57.9 (2)
0.54 ≦ θg, F1 ≦ 0.57 … (3)
1.23 ≦ θg, d1 ≦ 1.27 (4)
1.4688 ≦ nd2 ≦ 1.5673 … (5)
12.1 ≦ νd2 ≦ 21.7 (6)
0.36 ≦ θg, F2 ≦ 0.42 (7)
0.97 ≦ θg, d2 ≦ 1.07 … (8)
0.04 ≦ nd1-nd2 ≦ 0.10 … (9)
1.77 ≦ ndb2 ≦ 1.93 (10)
6.8 ≦ νdb2 ≦ 7.7 … (11)
6.0 ≦ d ≦ 13.9 (15)
Where ng1, nF1, nd1, and nC1 are the refractive indices of the first material for g-line, F-line, d-line, and C-line,
ng2, nF2, nd2, and nC2 are the refractive indices of the second material for g-line, F-line, d-line, and C-line,
nFb2, ndb2, and nCb2 are the refractive indices of the first particulate material for the F-line, d-line, and C-line,
νd1 = (nd1-1) / (nF1-nC1)
νd2 = (nd2-1) / (nF2-nC2)
θg, F1 = (ng1-nF1) / (nF1-nC1)
θg, d1 = (ng1-nd1) / (nF1-nC1)
θg, F2 = (ng2-nF2) / (nF2-nC2)
θg, d2 = (ng2-nd2) / (nF2-nC2)
νdb2 = (ndb2-1) / (nFb2-nCb2)
d is the grating thickness of the diffraction grating,
It is.

  Note that the optical system and the optical apparatus having the diffractive optical element constitute another aspect of the present invention.

  According to the present invention, it is possible to realize a diffractive optical element that can obtain high diffraction efficiency with respect to diffracted light of a specific order (design order) in a wide wavelength region and can sufficiently suppress unnecessary diffracted light. Furthermore, since it is a close-contact two-layer DOE, it can be easily manufactured. If the diffractive optical element is used, it is possible to realize an optical system and an optical apparatus having good optical performance with less flare light.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a front view (left view) and a side view (right view) of a diffractive optical element that is Embodiment 1 of the present invention. O in FIG. 1 indicates the central axis of the diffractive optical element. FIG. 2 shows an enlarged part of a cross-sectional shape when the diffractive optical element shown in FIG. 1 is cut along the line AA ′. However, FIG. 2 shows a configuration that is considerably deformed in the lattice depth direction.

  As shown in these drawings, the diffractive optical element 10 has a first element portion 12 and a second element portion 13. The first element portion 12 includes a first transparent substrate 14, a grating base portion 16 provided on the first transparent substrate 14, and a first diffraction grating 18 formed integrally with the grating base portion 16. And a first lattice forming layer configured. The second element portion 13 includes a second transparent substrate 15, a grating base portion 17 provided on the second transparent substrate 15, and a second diffraction grating formed integrally with the grating base portion 17. 19 and a second lattice forming layer.

  The first and second diffraction gratings 18 and 19 have the same grating shape (periodic structure), that is, the same grating thickness d and the same grating pitch p distribution. In other words, they have lattice shapes with the same pattern. The lattice shape is a shape in which convex portions (hereinafter referred to as peaks) and concave portions (hereinafter referred to as valleys) appear alternately.

  The first and second element parts 12 and 13 are configured so that the grating surfaces (surfaces corresponding to the inclined surfaces of the gratings) 18a and 19a and the grating wall surfaces 18b and 19b of the first and second diffraction gratings 18 and 19 are not spaced from each other. It has the structure which contact | connected, ie, contact | adhered without passing through an air layer. The first and second element portions 12 and 13 function as one diffractive optical element as a whole.

  The first and second diffraction gratings 18 and 19 have concentric grating shapes, and have a lens function by changing the grating pitch in the radial direction.

In this embodiment, the wavelength region of light incident on the diffractive optical element 10, that is, the used wavelength region is a visible wavelength region. Material and the grating thickness constituting the first and second diffraction gratings 18 and 19 is selected such that the diffraction efficiency of first order diffracted light that is the designed order in the visible wavelength region entire increases.

  Next, the diffraction efficiency of the diffractive optical element 10 of the present embodiment will be described. In the conventional single-layer DOE shown in FIG. 13, the conditions under which the diffraction efficiency of a certain order of diffracted light is maximized when the design wavelength is λ 0 are as follows.

  That is, when the light beam enters perpendicularly to the base surface of the diffraction grating (the surface indicated by the dotted line in FIG. 13), the difference between the optical path lengths of the peaks and valleys of the diffraction grating (that is, the peaks and valleys pass through each). On the condition that the difference in the optical path length between the light rays to be an integral multiple of the wavelength. This is expressed as follows.

(n01-1) xd = mxλ0 (20)
Here, n01 is the refractive index of the material that forms the diffraction grating for light of wavelength λ0, d is the grating thickness, and m is the diffraction order.

  Since the equation (20) includes a term of wavelength, an equal sign is established only at the design wavelength at the same order, and the diffraction efficiency is reduced from the maximum value at wavelengths other than the design wavelength.

  Further, the diffraction efficiency η (λ) at an arbitrary wavelength λ can be expressed as the following equation (21).

η (λ) = sinc ² [π × {m− (n1 (λ) −1) × d / λ}] (21)
Here, m is the diffraction order, and n1 (λ) is the refractive index of the material forming the diffraction grating for light of wavelength λ. Also, sinc ² ( a ) is a function represented by {sin ( a ) / a } ² .

  As in this embodiment, the basics are the same for a diffractive optical element having a laminated structure of two or more layers. In order to act as one diffractive optical element through all layers, the following is performed. The optical path length difference between the peaks and valleys of the diffraction grating formed at the boundary of the material constituting each layer is obtained, and this optical path length difference is added over the entire diffraction grating. Then, the dimension of the grating shape is determined so that the added optical path length difference is an integral multiple of the wavelength.

  Accordingly, in the diffractive optical element 10 shown in FIG. 2, when the design wavelength is λ 0, the conditions under which the diffraction efficiency of m-th order diffracted light is maximized are as follows.

± (n01-n02) xd = mxλ0 (22)
Here, n01 is the refractive index of the material forming the first diffraction grating 18 in the first element unit 12 with respect to light of wavelength λ 0, and n02 forms the second diffraction grating 19 in the second element unit 13. It is a refractive index with respect to light of wavelength λ0 of the material to be processed. D is the common grating thickness of the diffraction gratings 18 and 19.

The diffraction order of the light diffracted obliquely downward with respect to the 0th-order diffracted light in FIG. 2 is defined as a positive diffraction order, and the diffraction order of light diffracted obliquely upward with respect to the 0th-order diffracted light is defined as a negative diffraction order. In this case, the sign of addition / subtraction in the equation (22) is as follows. In the figure, a diffraction grating having a grating shape with a grating thickness increasing from the top to the bottom is positive, and conversely, a diffraction grating having a grating shape with a grating thickness decreasing from the top to the bottom is negative.

  In the configuration shown in FIG. 2, the diffraction efficiency η (λ) at a wavelength λ other than the design order λ0 can be expressed by the following equation.

η (λ) = sinc ² (π × [m− {± (n1 (λ) −n2 (λ)) × d / λ}])
= Sinc ² (π × (m−φ (λ) / λ)) (23)
φ (λ) = ± (n1 (λ) −n2 (λ)) × d (24)
Here, m is the diffraction order, n1 (λ) is the refractive index at the wavelength λ of the material forming the first diffraction grating 18, and n2 (λ) is the wavelength λ of the material forming the second diffraction grating 19. Is the refractive index. D is a common grating thickness of the first and second diffraction gratings 18 and 19. Moreover, it is a function represented by sinc ² ( a ) = {sin ( a ) / a } ² .

  Next, conditions for obtaining high diffraction efficiency in the diffractive optical element 10 of the present embodiment will be described.

  In order to obtain high diffraction efficiency over the entire use wavelength region, the value η (λ) expressed by the equation (23) should be close to 1 for all use wavelengths. In other words, in order to increase the diffraction efficiency at the design order m, φ (λ) / λ in the above equation (23) should be close to m. For example, when the design order m is primary, φ (λ) / λ may be close to 1.

  Furthermore, the optical optical path length difference φ (λ) obtained from the grating shape changes linearly in proportion to the wavelength λ from the above relationship, that is, the right side term of the equation (24) needs to have linearity. . That is, the change in the refractive index due to the wavelength of the material forming the second diffraction grating 19 with respect to the change in the refractive index due to the wavelength of the material forming the first diffraction grating 18 is a constant ratio throughout the wavelength region used. is necessary.

  A more specific embodiment will be described as a configuration satisfying the relationship shown above.

In the diffractive optical element 10 shown in FIG. 2, the first diffraction grating 18 has a material (nd = 1.542, νd = 53) in which Al ₂ O ₃ fine particles ( second fine particle material) are mixed with acrylic resin. .2) is used. The second diffraction grating 19 is made of a material (nd = 1.491, νd = 19.8) in which ITO fine particles ( first fine particle material) are mixed with fluorine resin. At this time, the common grating thickness d of the first and second diffraction gratings 18 and 19 is 11.4 μm.

  FIG. 3A shows the diffraction efficiency of the first-order diffracted light of the diffractive optical element 10 of this embodiment. The design order of the diffractive optical element 10 is first order. FIG. 3B shows the diffraction efficiency of the diffracted light of the designed order ± 1st order (0th order and 2nd order).

  As can be seen from these drawings, the diffractive optical element 10 of the present example has a diffraction efficiency of the first-order diffracted light that is the designed order diffracted light as compared with the diffractive optical elements disclosed in Patent Documents 4, 5, and 7. It has improved. In addition, in the diffractive optical element 10 of this embodiment, the diffraction efficiencies of the zero-order diffracted light and the second-order diffracted light that are unnecessary diffraction orders are further reduced, and flare light is less likely to be generated.

  In addition, the diffractive optical element 10 of the present example has a total grating thickness (the sum of the thicknesses of two diffraction grating layers and an air layer in the stacked DOE) as compared with the diffractive optical element disclosed in Patent Document 6. Is small. However, the same or better performance is achieved with respect to the designed order diffracted light (first order diffracted light) and unnecessary diffraction order light (0th order diffracted light and second order diffracted light). Furthermore, in the diffractive optical element 10 of this embodiment, the diffraction efficiency of the first-order diffracted light is 99.9% or more in the entire visible wavelength region, and the diffraction efficiency of unnecessary diffraction order light (0th-order diffracted light and second-order diffracted light) is also improved. It is sufficiently suppressed to 0.02% or less.

  Here, the diffraction efficiency of unnecessary-order diffracted light is targeted only for the design order ± first-order 0th-order diffracted light and second-order diffracted light, but this has a smaller proportion of contribution to flare as the diffraction order is farther from the design order. Because. That is, if flare light that is 0th-order and second-order diffracted light is reduced, flare light by other diffracted order light can be similarly reduced. This is because, in a diffractive optical element designed so that the diffracted light of the designed order is mainly diffracted, the diffraction efficiency of the diffracted light far from the designed order decreases, and the diffracted light of the order far from the designed order This is due to the fact that the formed image is greatly blurred on the imaging surface and is not noticeable as a flare.

Next, a material (material 1) obtained by mixing the material disclosed in Patent Document 5 and the acrylic resin used in this embodiment with Al ₂ O ₃ fine particles (material 1) and a material obtained by mixing ITO fine particles with a fluororesin (material) The refractive index characteristic in the visible wavelength region of 2) is shown in FIG. The materials disclosed in Patent Document 5 are acrylic resin 1 (nd = 1.523, νd = 51.1) and acrylic resin 2 (nd = 1.636, νd = 23.0).

  In FIG. 4, the refractive index characteristic graphs of the material 1 and the material 2 of this example seem to have different slopes, but the change in the refractive index with respect to the change in wavelength is almost constant. On the other hand, in the acrylic resins 1 and 2 of Patent Document 5, the change in the refractive index with respect to the change in the wavelength is almost constant in the acrylic resin 2, whereas in the acrylic resin 1, the degree of change on the short wavelength side is large. It is a characteristic.

  In Patent Document 5, only νd = (nd-1) / (nF-nC) is mentioned with respect to the characteristics of the material, where the refractive indexes for the F-line, d-line, and C-line are nF, nd, and nC. This is because νd is only a value defining an average inclination of the refractive index change near the d line. This νd characteristic is an evaluation characteristic suitable for improving the diffraction efficiency as compared with a single-layer DOE while keeping the grating thickness thin in a diffractive optical element having a laminated structure.

  However, the present embodiment aims to further improve the diffraction efficiency as compared with the diffractive optical element of Patent Document 5. For this purpose, it is not sufficient to use the νd characteristic representing the average refractive index change as an evaluation scale.

  Therefore, the partial dispersion ratio θg, F for the g line and the F line and the partial dispersion ratio θg, d for the g line and the d line are used as new evaluation measures. Partial dispersion ratio θg, F is expressed as θg, F = (ng-nF) / (nF-nC), where nF, nC, and ng are the refractive indices for F-line, C-line, and g-line, respectively. . Partial dispersion ratio θg, d is θg, d = (ng-nd) / (nF-nC, where nF, nd, nC, ng is the refractive index for F-line, d-line, C-line, and g-line, respectively. ). Each expression represents a ratio between a change in refractive index on the short wavelength side and a change in refractive index on the long wavelength side.

  The material 1 of this example is θg, F = 0.55, θg, d = 1.25, and the material 2 has θg, F = 0.41, θg, d = 1.04, which are small θg, F and θg, d, respectively. On the other hand, the acrylic resin 1 of Patent Document 5 is θg, F = 0.58, θg, d = 1.28, and the acrylic resin 2 is θg, F = 0.68, θg, d = 1.40. Θg, F and θg, d of the acrylic resin 1 are not significantly different from the material 1 of this embodiment, but θg, F and θg, d of the acrylic resin 2 are compared with the material 2 of this embodiment. It is a big value. Therefore, it can be said that the present embodiment is a combination of materials in which the change in refractive index with respect to the change in the wavelength of each material is kept constant and the higher diffraction efficiency is obtained in the entire use wavelength region.

  Also, in this embodiment, unlike Patent Documents 4 to 7, by using the above materials 1 and 2, the first and second diffraction gratings 18 and 19 have the same grating pattern while maintaining high diffraction efficiency. It can be realized as a close-contact two-layer DOE in contact with a lattice plane having As a result, it is not necessary to align the first and second diffraction gratings 18 and 19 with high accuracy, and manufacturing is facilitated.

  In the present embodiment described above, the diffractive optical element in which the diffraction gratings 18 and 19 are provided on the transparent substrates 14 and 15 as flat plates has been described as shown in FIGS. However, even if a lens is used instead of the flat transparent substrate and a diffraction grating is provided on a curved surface such as a convex surface or a concave surface of the lens, the same effect as in this embodiment can be obtained.

  Further, in the present embodiment, the diffractive optical element whose design order is the first order has been described, but the design order is not limited to 1. Even if the diffracted light has a different order from the first order, such as the second order or the third order, the composite value of the optical optical path length difference in each diffraction grating is set so that the desired design wavelength is obtained at the desired design order. The same effects as in this embodiment can be obtained.

  A second embodiment of the present invention will be described. The diffractive optical element of the present embodiment is basically the same as the first embodiment in shape. That is, it has the element configuration shown in FIGS. For this reason, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof will be omitted, and only different portions will be described in detail.

In the diffractive optical element 10 of the present embodiment, a material (nd = 1.611, νd = 45.5) in which ZrO ₂ fine particles are mixed with an acrylic resin is used for the first diffraction grating 18 shown in FIG. . For the second diffraction grating 19, a material (nd = 1.567, νd = 21.7) in which ITO fine particles are mixed with acrylic resin is used. The common grating thickness d of the first and second diffraction gratings 18 and 19 is 13.3 μm.

  FIG. 5A shows the diffraction efficiency of the first-order diffracted light in the diffractive optical element 10 of the present embodiment. The design order is first order. FIG. 5B shows the diffraction efficiency of the designed order ± first order diffracted light (0th order diffracted light and second order diffracted light). Similar to the diffractive optical element 10 of the first embodiment, the diffractive optical element 10 of the present embodiment is improved in the diffraction efficiency of the first-order diffracted light that is the designed order diffracted light, and the zero-order that is unnecessary diffracted light. The diffraction efficiency of the folded light and second-order diffracted light is also reduced, and flare light is less likely to be generated.

  Specifically, the diffraction efficiency of the first-order diffracted light is 99.8% or more in the entire visible wavelength region, and the diffraction efficiency of unnecessary diffraction order light (0th-order diffracted light and second-order diffracted light) is 0.04% or less. It is suppressed.

  A third embodiment of the present invention will be described. The diffractive optical element of the present embodiment is basically the same as the first embodiment in shape. That is, it has the element configuration shown in FIGS. For this reason, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed descriptions thereof are omitted, and only different portions will be described in detail.

In the diffractive optical element 10 of the present embodiment, a material (nd = 1.594, νd = 58.0) in which Al ₂ O ₃ fine particles are mixed in an acrylic resin is used for the first diffraction grating 18 shown in FIG. use. The second diffraction grating 19 is made of a material (nd = 1.519, νd = 16.5) in which ITO fine particles are mixed with fluorine resin. The common grating thickness d of the first and second diffraction gratings 18 and 19 is 7.8 μm.

  FIG. 6A shows the diffraction efficiency of the first-order diffracted light in the diffractive optical element 10 of this embodiment. The design order is first order. FIG. 6B shows the diffraction efficiency of the designed order ± first order diffracted light (0th order diffracted light and second order diffracted light). Similar to the diffractive optical elements 10 of the first and second embodiments, the diffractive optical element 10 of the present embodiment is improved in the diffraction efficiency of the first-order diffracted light that is the designed order diffracted light and is unnecessary diffracted light. The diffraction efficiency of the 0th order diffracted light and the 2nd order diffracted light is also reduced, and flare light is less likely to be generated.

  Specifically, the diffraction efficiency of the first-order diffracted light is 99.8% or more in the entire visible wavelength region, and the diffraction efficiency of unnecessary diffraction order light (0th-order diffracted light and second-order diffracted light) is 0.04% or less. It is suppressed.

  Embodiment 4 of the present invention will be described. The diffractive optical element of the present embodiment is basically the same as the first embodiment in shape. That is, it has the element configuration shown in FIGS. For this reason, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed descriptions thereof are omitted, and only different portions will be described in detail.

In the diffractive optical element 10 of this embodiment, the first diffraction grating 18 shown in FIG. 2 is made of a material (nd = 1.566, νd = 55.4) in which Al ₂ O ₃ fine particles are mixed with acrylic resin. use. For the second diffraction grating 19, a material (nd = 1.469, νd = 12.1) in which ITO fine particles are mixed with an optical material is used. The common grating thickness d of the first and second diffraction gratings 18 and 19 is 6.0 μm.

  FIG. 7A shows the diffraction efficiency of the first-order diffracted light in the diffractive optical element 10 of the present embodiment. The design order is first order. FIG. 7B shows the diffraction efficiency of the designed order ± first order diffracted light (0th order diffracted light and second order diffracted light). The diffractive optical element 10 of the present embodiment is an unnecessary diffracted light as well as the diffraction efficiency of the first-order diffracted light that is the designed order diffracted light is improved as in the diffractive optical elements 10 of the first to third embodiments. The diffraction efficiency of the 0th order diffracted light and the 2nd order diffracted light is also reduced, and flare light is less likely to be generated.

  Specifically, the diffraction efficiency of the first-order diffracted light is 99.9% or more in the entire visible wavelength region, and the diffraction efficiency of unnecessary diffraction order light (0th-order diffracted light and second-order diffracted light) is 0.02% or less. It is suppressed.

  A fifth embodiment of the present invention will be described. The diffractive optical element of the present embodiment is basically the same as the first embodiment in shape. That is, it has the element configuration shown in FIGS. For this reason, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof will be omitted, and only different portions will be described in detail.

In the diffractive optical element 10 of this embodiment, an acrylic resin material (nd = 1.522, νd = 51.3) is used for the first diffraction grating 18 shown in FIG. Here, unlike the first to fourth embodiments, the material of the first diffraction grating 18 of the present embodiment is simply a material made of an acrylic resin that is not mixed with a fine particle material. On the other hand, the second diffraction grating 19 is made of a material (nd = 1.480, νd = 21.3) in which ITO fine particles are mixed with fluorine resin. The common grating thickness d of the first and second diffraction gratings 18 and 19 is 13.9 μm.

  FIG. 8A shows the diffraction efficiency of the first-order diffracted light in the diffractive optical element 10 of the present embodiment. The design order is first order. FIG. 8B shows the diffraction efficiency of the designed order ± first order diffracted light (0th order diffracted light and second order diffracted light). The diffractive optical element 10 of the present embodiment is an unnecessary diffracted light as well as the diffraction efficiency of the first-order diffracted light that is the designed order diffracted light is improved as in the diffractive optical elements 10 of the first to fourth embodiments. The diffraction efficiency of the 0th order diffracted light and the 2nd order diffracted light is also reduced, and flare light is less likely to be generated.

  Specifically, the diffraction efficiency of the first-order diffracted light is 99.9% or more in the entire visible wavelength region, and the diffraction efficiency of unnecessary diffraction order light (0th-order diffracted light and second-order diffracted light) is 0.02% or less. It is suppressed.

  Next, conditions to be satisfied by the first and second diffraction gratings 18 and 19 in each of the above embodiments will be described.

  In the diffractive optical element 10 of Examples 1 to 5, the first material and the second material (hereinafter referred to as the material 1 and the material 2, respectively) forming the first and second diffraction gratings are as follows. Satisfied. The material 2 is a material in which a fine particle material satisfying the following conditions is mixed with a resin material.

ng1, nF1, nd1, and nC1 are refractive indexes of the first material with respect to g-line, F-line, d-line, and C-line, respectively. ng2, nF2, nd2, and nC2 are refractive indexes of the second material with respect to g-line, F-line, d-line, and C-line, respectively. NFb2, ndb2, and nCb2 are refractive indexes of the fine particle material with respect to the F-line, d-line, and C-line, respectively. “Eb” represents “× 10 ^−b ”.

further,
νd1 = (nd1-1) / (nF1-nC1)
νd2 = (nd2-1) / (nF2-nC2)
θg, F1 = (ng1-nF1) / (nF1-nC1)
θg, d1 = (ng1-nd1) / (nF1-nC1)
θg, F2 = (ng2-nF2) / (nF2-nC2)
θg, d2 = (ng2-nd2) / (nF2-nC2)
νdb2 = (ndb2-1) / (nFb2-nCb2)
It is.

Material 1:
nd1 ≧ 1.5 (1)
νd1 ≧ 40 (2)
(-1.665E-07 × νd1 ³ + 5.213E-05xνd1 ² ‐5.656E-03xνd1 + 0.675) ≦ θg, F1
≦ (‐1.665E-07xνd1 ³ + 5.213E-05xνd1 ² ‐5.656E-03xνd1 + 0.825)
… (3)
(‐1.687E-07xνd1 ³ + 5.702E-05xνd1 ² ‐6.603E-03xνd1 + 1.400) ≦ θg, d1
≦ (‐1.687E-07xνd1 ³ + 5.702E-05xνd1 ² ‐6.603E-03xνd1 + 1.580)
…(Four)

Material 2:
nd2 ≦ 1.6 (5)
νd2 ≦ 30 (6)
θg, F2 ≦ (-1.665E-07xνd2 ³ + 5.213E-05xνd2 ² ‐5.656E-03xνd2 + 0.675)… (7)
θg, d2 ≦ (-1.687E-07xνd2 ³ + 5.702E-05xνd2 ² ‐6.603E-03xνd2 + 1.400)… (8)

Material 1 and Material 2:
nd1-nd2> 0 ... (9)

Particulate material:
ndb2 ≧ 1.70… (10)
νdb2 ≦ 20 (11)

  Conditional expressions (1) to (4) define the characteristics of the material 1. Further, the material 1 needs to satisfy all the conditional expressions (1) to (4). Here, in order to make it easy to imagine the relationship between the conditions, a description will be given with reference to FIGS. 10 shows the relationship between nd and νd, FIG. 11 shows the relationship between θg, F and νd, and FIG. 12 shows the relationship between θg, d and νd. In these figures, the vertical axis represents nd, θg, F, θg, d, respectively, and the horizontal axis represents νd. 10 to 12, the conditional expression numbers are indicated by encircled numerals.

  Conditional expressions (1) and (2) define the range of nd and νd of the material 1 for realizing the diffractive optical element of the embodiment, as shown in FIG. If the lower limit of conditional expressions (1) and (2) is not reached, material 2 that can realize the configuration of the diffractive optical element of the embodiment (adherent two-layer type), that is, conditional expressions ((5) to (8)) is satisfied. There is no material 2 to do.

  Conditional expression (3) defines the range of θg, F and νd of the material 1 for forming the diffractive optical element of the embodiment, as shown in FIG. As described above, this conditional expression must be satisfied after conditional expressions (1) and (2) are satisfied. If the lower limit of conditional expression (3) is not reached, the grating thickness of the diffractive optical element of the embodiment becomes thick, leading to deterioration of diffraction efficiency with respect to light incident on the diffractive optical element obliquely (hereinafter referred to as oblique incident light). . If the upper limit of conditional expression (3) is exceeded, material 2 for obtaining high diffraction efficiency with the configuration of the diffractive optical element of the embodiment (adherent two-layer type), that is, conditional expressions ((5) to (8) There is no material 2 that satisfies (2).

  Conditional expression (4) defines the range of θg, d and νd of the material 1 for realizing the diffractive optical element of the embodiment, as shown in FIG. This relationship must also be satisfied after conditional expressions (1) to (3) are satisfied. If the lower limit of conditional expression (4) is not reached, the grating thickness of the diffractive optical element of the embodiment becomes thick, leading to deterioration of diffraction efficiency for obliquely incident light. If the upper limit of conditional expression (4) is exceeded, material 2 for obtaining high diffraction efficiency with the configuration of the diffractive optical element of the embodiment (adherent two-layer type), that is, conditional expressions ((5) to (8) There is no material 2 that satisfies (2).

  In order to make the grating thickness thinner while realizing higher diffraction efficiency, the material 1 preferably satisfies the following conditional expression in relation to the existence condition of the material 2. The a attached to the number of the following conditional expression indicates that the conditional expression is preferably satisfied more than the original conditional expression. “b” indicates that it is preferable to satisfy the conditional expression with “a”. The same applies to other conditional expressions described later.

1.50 ≦ nd1 ≦ 1.75… (1a)
1.50 ≦ nd1 ≦ 1.70… (1b)
40 ≦ νd1 ≦ 80 (2a)
40 ≦ νd1 ≦ 70… (2b)
(-1.665E-07xνd1 ³ + 5.213E-05xνd1 ² -5.656E-03xνd1 + 0.700) ≦ θg, F1
≦ (−1.665E-07xνd1 ³ + 5.213E-05xνd1 ² −5.656E-03xνd1 + 0.662)
… (3a)
(-1.687E-07xνd1 ³ + 5.702E-05xνd1 ² -6.603E-03xνd1 + 1.425) ≦ θg, d1
≦ (-1.687E-07xνd1 ³ + 5.702E-05xνd1 ² -6.603E-03xνd1 + 1.513)
… (4a)

  Conditional expressions (5) to (8) define the characteristics of the material 2. The material 2 needs to satisfy all of the conditional expressions (5) to (8) after the material 1 satisfies all of the conditional expressions (1) to (4). Here, in order to make it easy to imagine the relationship between the conditions, description will be made with reference to FIGS.

  Conditional expressions (5) and (6) define the range of nd and νd of the material 2 for forming the diffractive optical element of the embodiment, as shown in FIG. If the upper limit value of conditional expressions (5) and (6) is exceeded, material 1 that can realize the configuration of the diffractive optical element of the embodiment (adherent two-layer type), that is, conditional expressions ((1) to (4)) are satisfied. There is no material 1 to perform.

  Conditional expression (7) defines the range of θg, F and νd of the material 2 for forming the diffractive optical element of the embodiment, as shown in FIG. As described above, this conditional expression must be satisfied after conditional expressions (5) and (6) are satisfied. If the upper limit of conditional expression (7) is exceeded, the material 1 for obtaining high diffraction efficiency in the configuration of the diffractive optical element of the embodiment (adherent two-layer type), that is, conditional expressions ((1) to (4)) There is no satisfactory material 1 present.

  Conditional expression (8) defines the range of θg, d and νd of the material 2 for forming the diffractive optical element of the embodiment, as shown in FIG. This relationship must also be satisfied after conditional expressions (1) to (4) are satisfied. If the upper limit of conditional expression (8) is exceeded, the material 1 for obtaining high diffraction efficiency with the configuration of the diffractive optical element of the embodiment (adherent two-layer type), that is, conditional expressions ((1) to (4)) There is no satisfactory material 1 present.

  The material 2 preferably satisfies the following conditional expression in relation to the existence condition of the material 1 in order to make the grating thickness thinner while realizing higher diffraction efficiency.

1.4 ≦ nd2 ≦ 1.6 (5a)
νd2 ≦ 25 (6a)
θg, F2 ≦ −1.665E-07xνd2 ³ + 5.213E-05xνd2 ² −5.656E-03xνd2 +0.600)
… (7a)
θg, d2≤ (-1.687E-07xνd2 ³ + 5.702E-05xνd2 ² -6.603E-03xνd2 ++ 1.300)
… (8a)

  Conditional expression (9) shows the magnitude relationship between the refractive indexes of the material 1 and the material 2 in the diffractive optical element of the example. If this conditional expression is not satisfied, the desired diffraction efficiency cannot be obtained.

  Conditional expressions (10) and (11) define the range of material characteristics of the particulate material used for the material 2 to satisfy the conditional expressions (5) to (8) in the diffractive optical element of the embodiment. Examples of the fine particle material satisfying the conditional expressions (10) and (11) include any inorganic fine particle material of ITO, Ti, Nr, Cr and oxides, composites, and mixtures thereof. In the examples, ITO (ndb2 = 1.77, νd = 6.8) was used as an example. If the lower limit value of conditional expression (10) is exceeded or the upper limit value of conditional expression (11) is exceeded, the material 2 cannot satisfy the conditional expressions (5) to (8).

  Here, the fine particle material is not limited to the one used in the above example as long as it satisfies the conditional expressions (10) and (11).

  Moreover, it is preferable that the particulate material further satisfies the following conditions.

ndb2 ≧ 1.75… (10a)
νdb2 ≦ 18 (11a)

  In addition to the conditional expressions (1) to (11), it is more preferable that the diffractive optical element 10 of the example satisfies the following conditions. λF, λd, and λC are the wavelengths of the F-line, d-line, and C-line, respectively. m (λF), m (λd), and m (λC) are the optical optical paths at the convex and concave parts of each diffraction grating for the m-th order (design order) diffracted light at the wavelengths of F-line, d-line, and C-line, respectively. It is a value obtained by dividing the difference in length by the wavelength. d is the grating thickness of the diffraction grating.

m (λF) = {dx (nF1-nF2)} / λF (12)
m (λd) = {dx (nd1-nd2)} / λd (13)
m (λC) = {dx (nC1-nC2)} / λC (14)
d ≦ 20 (15)
0.92 ≦ {m (λF) + m (λd) + m (λC)} / 3 ≦ 1.08 (16)

  These conditional expressions (12) to (16) define the diffraction efficiency of the contact two-layer DOE of the embodiment formed by the material 1 and the material 2. If the upper limit value of conditional expression (15) is exceeded, there is a possibility that the degradation of diffraction efficiency for obliquely incident light will increase. Further, if the conditional expression (16) is outside the range, there is a possibility that a desired diffraction efficiency cannot be obtained.

  In order to achieve higher diffraction efficiency, it is better to satisfy the following conditional expression. “C” attached to the number of the following conditional expression indicates that the conditional expression is more preferably satisfied than the conditional expression attached with “b”.

d ≦ 15 (15a)
0.93 ≦ {m (λF) + m (λd) + m (λC)} / 3 ≦ 1.07 (16a)
0.94 ≦ {m (λF) + m (λd) + m (λC)} / 3 ≦ 1.06 (16b)
0.96 ≦ {m (λF) + m (λd) + m (λC)} / 3 ≦ 1.04 (16c)

  In Examples 1 to 4 in which the material 1 is mixed with the particulate material, the particulate material preferably satisfies all the following conditions. nFb1, ndb1, and nCb1 are refractive indexes of the particle material with respect to the F-line, d-line, and C-line, respectively. Further, νdb1 = (ndb1-1) / (nFb1-nCb1).

ndb1 ≧ 1.65… (17)
νdb1 ≧ 35 (18)
Conditional expressions (17) and (18) define the characteristics of the particulate material mixed with the material 1. Examples of the fine particle material satisfying the conditional expressions (17) and (18) include inorganic fine particle materials of any one of Al, Zr, Y and oxides, composites, and mixtures thereof. In this example, Al ₂ O ₃ (ndb1 = 1.71, νd = 68.0) and ZrO ₂ (ndb1 = 1.87, νd = 39.4) were used as examples. If the lower limit value of conditional expressions (17) and (18) is exceeded, the material 1 that satisfies the conditional expressions (1) to (4) may not be realized.

  Here, the fine particle material is not limited to that used in the above example as long as it satisfies the conditional expressions (17) and (18).

  Further, a general ultraviolet curable resin or the like may be used without necessarily using a material in which fine particles are mixed. However, as described in Examples 1 to 4, the use of a material in which fine particles are mixed (dispersed) in both the material 1 and the material 2 can reduce the grating thickness. Is preferred.

  The fine particle material may further satisfy the following conditions.

ndb1 ≧ 1.70… (17a)
νdb1 ≧ 38 (18a)

  Moreover, it is preferable that the average particle diameter of particulate material is 1/4 or less of the wavelength (use wavelength or design wavelength) of the incident light to a diffractive optical element. When the particle diameter is larger than this, there is a possibility that light scattering will increase when the fine particle material is mixed with the resin material.

  The resin material to which the fine particle material is mixed is an ultraviolet curable resin, and examples thereof include acrylic, fluorine, vinyl, and epoxy organic resins. In this example, acrylic resin and fluorine resin were used as examples.

  As the last condition, the diffractive optical element of the embodiment preferably satisfies the following conditional expression when the grating pitch of the diffraction grating shown in FIG. 2 is P and the grating thickness is d.

   d / P <1/7… (19)

  Conditional expression (19) defines the shape (grating pitch and grating thickness) of the diffraction grating constituting the diffractive optical element. If the upper limit value of conditional expression (19) is exceeded, the grating pitch becomes too fine, which may lead to a decrease in diffraction efficiency for obliquely incident light. Further, satisfying conditional expression (19) has an advantage that the grating shape can be easily machined with respect to a mold for manufacturing (resin molding) a diffractive optical element.

  Table 1 shows numerical values of conditional expressions (1) to (19) of the diffractive optical elements described in Examples 1 to 5.

  As described above, in each of the above embodiments, the material 1 and the material 2 in which the partial dispersion ratio θg, F for the g line and the F line and the partial dispersion ratio θg, d for the g line and the d line are appropriately set are used. A close-contact two-layer type diffractive optical element is formed. This makes it possible to sufficiently suppress unwanted diffracted light that can be flare light, while increasing the diffraction efficiency for diffracted light of a specific order (design order) throughout the wavelength (use wavelength) region of incident light. An optical element can be realized. Further, by using a close-contact two-layer type diffractive optical element, it is easy to manufacture and can be manufactured at a relatively low cost.

  Note that the shape of the diffractive optical element shown in FIGS. 1 and 2, particularly the shape of the grating portion, is merely an example, and other shapes can be employed.

  The diffractive optical elements described in Examples 1 to 5 can be used for the following applications.

  FIG. 9A shows a configuration of an optical system that includes the diffractive optical elements of Embodiments 1 to 5 and that is used as an imaging optical system in an imaging apparatus (optical apparatus) 200 such as a still camera or a video camera.

  In FIG. 9A, reference numeral 101 denotes an imaging optical system mainly composed of refractive optical elements (for example, ordinary lens elements). In the imaging optical system 101, an aperture stop 102 and the diffractive optical element 10 described in Examples 1 to 5 are provided. Reference numeral 103 denotes a photosensitive member such as a film or an imaging element disposed on the imaging surface of the imaging optical system 101. As the image sensor, a photoelectric conversion element such as a CCD sensor or a CMOS sensor is used.

  The diffractive optical element 10 is an element having a lens function as described above, and plays a role of correcting chromatic aberration generated by the refractive optical element in the imaging optical system 101. And as demonstrated in Examples 1-5, the diffraction efficiency characteristic of the diffractive optical element 10 is greatly improved compared with the conventional one. For this reason, an imaging optical system and an imaging apparatus having good optical performance with less flare light and high resolving power at low frequencies are realized.

  Moreover, since the diffractive optical element 10 described in Examples 1 to 5 is a close-contact two-layer DOE that does not have an air layer, it is easy to manufacture and effective in increasing the mass productivity of the imaging optical system. is there.

  Although FIG. 9A shows an example in which the diffractive optical element 10 is provided on a flat glass surface arranged in the vicinity of the stop 102, the arrangement form of the diffractive optical element 10 is not limited to this. As described above, the diffractive optical element 10 may be provided on the concave or convex surface of the lens element. A plurality of diffractive optical elements 10 may be arranged in the imaging optical system.

  In FIG. 9A, the case where the diffractive optical element 10 of Examples 1 to 5 is used in the imaging optical system of the imaging apparatus has been described. However, the diffractive optical element 10 may be used in an imaging optical system that is used in a wide wavelength region, such as an image scanner that is an office machine (optical device) or a reader lens of a digital copying machine. Also in this case, it is possible to realize an imaging optical system and an office machine that have good optical performance with little flare light and high resolving power at low frequencies.

  FIG. 9B shows a configuration of an observation optical system that includes the diffractive optical elements described in Examples 1 to 5 and is mounted on an observation apparatus (optical apparatus) 300 such as binoculars.

  In FIG. 9B, reference numeral 104 denotes an objective lens, and 105 denotes a prism for erecting an inverted image formed by the objective lens 104. Reference numeral 106 denotes an eyepiece lens. By placing an eye on the evaluation surface 107 (pupil surface), the observer can observe the object through the eyepiece lens 106.

  The objective lens 104 includes the diffractive optical element 10 described in the first to fifth embodiments. The diffractive optical element 10 is provided for the purpose of correcting chromatic aberration and other aberrations on the imaging surface 103 of the objective lens 104.

  As described in Examples 1 to 5, the diffractive optical element 10 has greatly improved diffraction efficiency characteristics compared to the conventional one. For this reason, an observation optical system and an observation apparatus having good optical performance with little flare light and high resolving power at a low frequency are realized.

  Moreover, since the diffractive optical element 10 described in Examples 1 to 5 is a close-contact two-layer DOE that does not have an air layer, it is easy to manufacture and effective in increasing the mass productivity of the imaging optical system. It is.

  Although FIG. 9B shows an example in which the diffractive optical element 10 is provided on a flat glass surface arranged near the lens element constituting the objective lens 104, the arrangement form of the diffractive optical element 10 is not limited to this. As described above, the diffractive optical element 10 may be provided on the concave or convex surface of the lens element. A plurality of diffractive optical elements 10 may be arranged in the imaging optical system.

  9B shows the case where the diffractive optical element 10 is provided in the objective lens 104, it can also be provided in the optical surface of the prism 105 or in the eyepiece lens 106. In this case as well, as described above. The effect is obtained.

  However, providing the diffractive optical element 10 closer to the object side than the imaging surface 103 has an effect of reducing chromatic aberration generated in the objective lens 104. Therefore, in the case of a naked eye observation system, the diffractive optical element 10 is provided at least in the objective lens 104. Is desirable.

  Furthermore, in addition to the binocular viewing optical system shown in FIG. 9B, the diffractive optical element 10 described in the first to fifth embodiments can be provided in an observation optical system such as a telescope or a camera optical finder. In this case, the same effect as described above can be obtained.

The front view and side view of the diffractive optical element which are Examples 1-5 of this invention. FIG. 6 is a partial cross-sectional view of the diffractive optical elements of Examples 1 to 5. FIG. 3 is a graph showing diffraction efficiency characteristics at the design order of the diffractive optical element of Example 1. FIG. 3 is a graph showing diffraction efficiency characteristics in the design order ± first order of the diffractive optical element of Example 1. FIG. 3 is a graph showing the refractive index characteristic (n-λ characteristic) of the material constituting the diffractive optical element of Example 1. FIG. 6 is a graph showing diffraction efficiency characteristics at the design order of the diffractive optical element of Example 2. FIG. 6 is a graph showing diffraction efficiency characteristics in the design order ± 1st order of the diffractive optical element of Example 2. FIG. 6 is a graph showing diffraction efficiency characteristics at the design order of the diffractive optical element of Example 3. FIG. 6 is a graph showing diffraction efficiency characteristics at the design order ± 1st order of the diffractive optical element of Example 3. FIG. 6 is a graph showing diffraction efficiency characteristics at the design order of the diffractive optical element of Example 4. FIG. 10 is a graph showing diffraction efficiency characteristics in the design order ± first order of the diffractive optical element of Example 4. FIG. 9 is a graph showing diffraction efficiency characteristics at the design order of the diffractive optical element of Example 5. FIG. 6 is a graph showing diffraction efficiency characteristics in the design order ± first order of the diffractive optical element of Example 5. FIG. 6 is a diagram illustrating a configuration of a photographing optical system using the diffractive optical elements of Examples 1 to 5 and an imaging apparatus including the photographing optical system. The figure which shows the structure of the observation optical system using the diffractive optical element of Examples 1-5, and an observation apparatus provided with the same. The graph which shows the refractive index characteristic (nd-νd characteristic) of the material which comprises the diffractive optical element of Examples 1-5. The graph which shows the refractive index characteristic ((theta) g, F- (nu) d characteristic) of the material which comprises the diffractive optical element of Examples 1-5. The graph which shows the refractive index characteristic ((theta) g, d- (nu) d characteristic) of the material which comprises the diffractive optical element of Examples 1-5. The fragmentary sectional view of the conventional single layer type diffractive optical element. The graph which shows the design efficiency of the conventional single layer type | mold diffractive optical element, and the diffraction efficiency characteristic of a design order +/- 1st order. The fragmentary sectional view of the conventional laminated type diffractive optical element. The graph which shows the diffraction efficiency characteristic in the design order of the conventional lamination type diffractive optical element. The fragmentary sectional view of the conventional laminated type diffractive optical element. The graph which shows the diffraction efficiency characteristic in the design order of the conventional lamination type diffractive optical element. The graph which shows the diffraction efficiency characteristic in the design order +/- 1st order of the conventional lamination type diffractive optical element. The graph which shows the diffraction efficiency characteristic in the design order of the conventional lamination type diffractive optical element. The graph which shows the diffraction efficiency characteristic in the design order +/- 1st order of the conventional lamination type diffractive optical element. The fragmentary sectional view of the conventional adhesion two-layer type diffractive optical element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Diffractive optical element 12 1st element part 13 2nd element part 14 1st transparent substrate 15 2nd transparent substrate 16 1st grating | lattice base part 17 2nd grating | lattice base part 18 1st diffraction grating 19 1st Two diffraction gratings 101 Imaging optical system 104 Observation optical system

Claims (8)

A diffractive optical element having a configuration in which diffraction gratings respectively formed of a first material and a second material are in contact with each other on a grating surface,
The second material is a material in which a first fine particle material that satisfies all of the following conditions is mixed with a resin material,
The diffractive optical element according to claim 1, wherein each of the first and second materials satisfies all of the following conditions.
1.5218 ≤ nd1 ≤ 1.6110
45.4 ≦ νd1 ≦ 57.9
0.54 ≤ θg, F1 ≤ 0.57
1.23 ≤ θg, d1 ≤ 1.27
1.4688 ≦ nd2 ≦ 1.5673
12.1 ≦ νd2 ≦ 21.7
0.36 ≦ θg, F2 ≦ 0.42
0.97 ≦ θg, d2 ≦ 1.07
0.04 ≦ nd1-nd2 ≦ 0.10
1.77 ≦ ndb2 ≦ 1.93
6.8 ≦ νdb2 ≦ 7.7
6.0 ≦ d ≦ 13.9
Where ng1, nF1, nd1, and nC1 are the refractive indices of the first material for the g-line, F-line, d-line, and C-line,
ng2, nF2, nd2, and nC2 are the refractive indices of the second material for g-line, F-line, d-line, and C-line,
nFb2, ndb2, and nCb2 are refractive indexes of the first fine particle material with respect to F-line, d-line, and C-line,
νd1 = (nd1-1) / (nF1-nC1)
νd2 = (nd2-1) / (nF2-nC2)
θg, F1 = (ng1-nF1) / (nF1-nC1)
θg, d1 = (ng1-nd1) / (nF1-nC1)
θg, F2 = (ng2-nF2) / (nF2-nC2)
θg, d2 = (ng2-nd2) / (nF2-nC2)
νdb2 = (ndb2-1) / (nFb2-nCb2)
d is the grating thickness of the diffraction grating,
It is. The diffractive optical element according to claim 1, wherein the first and second materials further satisfy all of the following conditions.
m (λF) = {dx (nF1-nF2)} / λF
m (λd) = {dx (nd1-nd2)} / λd
m (λC) = {dx (nC1-nC2)} / λC
0.998 ≦ {m (λF) + m (λd) + m (λC)} / 3 ≦ 1.001
Where λF, λd and λC are the wavelengths of the F-line, d-line and C-line
m (λF), m (λd), and m (λC) are optical values at the convex and concave portions of the diffraction gratings with respect to the mth-order diffracted light, which is the designed order at the wavelengths of the F-line, d-line, and C-line, respectively. The value obtained by dividing the difference in optical path length by the wavelength,
It is. 2. The diffractive optical element according to claim 1, wherein the first material is a material in which a second fine particle material that satisfies all of the following conditions is mixed with a resin material.
1.71 ≤ ndb1 ≤ 1.87
39.4 ≦ νdb1 ≦ 68.0
Where nFb1, ndb1, and nCb1 are the refractive indices of the second fine particle material with respect to the F-line, d-line, and C-line,
νdb1 = (ndb1-1) / (nFb1-nCb1)
It is.   4. The diffractive optical element according to claim 3, wherein an average particle diameter of the first and second fine particle materials is ¼ or less of a wavelength of incident light to the diffractive optical element.   The diffractive optical element according to claim 1, wherein the first material is a resin material in which a particulate material is not mixed. The diffractive optical element according to claim 1, further satisfying the following condition.
0.03 ≤ d / P ≤ 0.07
Here, P and d are the grating pitch and grating thickness of the diffraction grating, respectively.   An optical system comprising the diffractive optical element according to claim 1.   An optical apparatus comprising the optical system according to claim 7.