JP5676927B2 - Diffractive optical element, optical system, and optical instrument - Google Patents

Description

  The present invention relates to a diffractive optical element configured to suppress generation of unnecessary light.

  In a diffractive optical element used for a lens of an optical system, two diffraction gratings are arranged in close contact, and the material and the grating height that constitute each diffraction grating are set appropriately to obtain high diffraction efficiency in a wide wavelength band. Are known. The light beam incident on the grating wall surface of the diffractive optical element having the grating surface and the grating wall surface is reflected or refracted by the grating wall surface, thereby generating unnecessary light (flare). Therefore, Patent Documents 1 and 2 disclose a diffractive optical element configured to suppress unnecessary light generated on a grating wall surface. In the diffractive optical element disclosed in Patent Document 1, a light shielding portion such as an absorption film or a reflection film is provided on the incident side or the emission side from the diffraction grating. By this light shielding portion, the light beam incident on the grating wall surface or the light beam emitted from the grating wall surface is shielded, and unnecessary light generated on the grating wall surface is suppressed. In the diffractive optical element disclosed in Patent Document 2, a light absorbing portion is provided on the grating surface, and the light beam incident on the grating wall surface is generated on the grating wall surface by absorbing the light beam emitted from the grating wall surface by Fresnel reflection. To suppress unnecessary light. Moreover, the manufacturing cost is reduced by providing the light absorbing portion on the lattice plane. Patent Document 3 discloses calculation of diffraction efficiency using a rigorous coupled wave analysis (RCWA: Regulated Coupled Wave Analysis).

JP 2002-48906 A JP 2006-162822 A JP 2009-217139 A

  However, when the diffractive optical element disclosed in Patent Documents 1 and 2 is applied to an optical system such as a photographing lens, it is highly refracted by a light beam incident at an oblique incident angle (off-screen light incident angle) different from that of the photographing light beam. Unwanted light is generated due to total reflection occurring at the interface between the refractive index medium and the low refractive index medium. A part of the unnecessary light reaches the imaging surface, and there is a possibility that the image performance is deteriorated.

  Therefore, the present invention provides a diffractive optical element that suppresses degradation of image performance.

The diffractive optical element according to one aspect of the present invention has a different refractive index from each other, the diffractive optical element comprising a first 及 beauty second diffraction grating which are arranged in contact each of the grating surface and the grating wall surface of each other A plurality of light shielding members provided for each of the grating wall surfaces, and in a cross section including an optical axis, an extension line of the grating wall surface and an end portion of the light shielding member closer to the optical axis. distance wL, the distance between the other end of the extension line and the shielding member of the grating wall surface wH, said first and second grating pitch of the diffraction grating P, and the minimum wavelength in the used wavelength band .lambda.0, And when
wH> wL ≧ 0
0 <(wH + wL) / P <0.05
0 <λ0 <wH
It satisfies the following condition .

  Other objects and features of the present invention are illustrated in the following examples.

  ADVANTAGE OF THE INVENTION According to this invention, the diffractive optical element which suppresses degradation of image performance can be provided.

It is a principal part schematic of the diffractive optical element in a present Example. It is a conceptual diagram which shows the unnecessary light in the optical system which has a diffractive optical element. 2 is an enlarged cross-sectional view of a diffractive optical element in Example 1. FIG. 3 is an enlarged cross-sectional view of a diffraction grating part in Example 1. FIG. 3 is a graph of diffraction efficiency with respect to a design incident light beam of the diffractive optical element in Example 1. 6 is a graph of diffraction efficiency for a light beam with an off-screen incidence of +10 degrees of the diffractive optical element according to Example 1. 4 is a graph of diffraction efficiency with respect to a light beam of -10 degrees off-screen incidence of the diffractive optical element in Example 1; FIG. 6 is an enlarged cross-sectional view of another form of the diffractive optical element in Example 1. 7 is a graph of diffraction efficiency with respect to a design incident light beam of a diffractive optical element in Example 2. 6 is a graph of diffraction efficiency with respect to a light beam having an off-screen incidence of +10 degrees and a diffractive optical element in Example 2. 6 is a graph of diffraction efficiency with respect to a light beam of -10 degrees off-screen incidence of the diffractive optical element in Example 2. 6 is an enlarged cross-sectional view of a diffraction grating portion in Example 3. FIG. 12 is a graph of diffraction efficiency with respect to an incident light beam of a diffractive optical element in Example 3. 6 is an enlarged cross-sectional view of a diffraction grating part in Example 4. FIG. 10 is a graph of diffraction efficiency with respect to an incident light beam of a diffractive optical element in Example 4. 10 is a graph of diffraction efficiency with respect to an incident light beam of a diffractive optical element in Example 5. 10 is an enlarged cross-sectional view of a diffraction grating portion in Example 6. FIG. 10 is a graph of diffraction efficiency with respect to an incident light beam of a diffractive optical element in Example 6. 10 is an enlarged cross-sectional view of a diffraction grating portion in Example 6. FIG. FIG. 10 is a schematic cross-sectional view of a photographic optical system in Example 7. 5 is a graph of diffraction efficiency with respect to a design incident light beam of a diffractive optical element in Comparative Example 1. It is a schematic diagram which shows the mode of propagation of the unnecessary light with respect to the design incident light beam of the diffractive optical element in a comparative example. 6 is a graph of diffraction efficiency for a light beam with an off-screen incidence of +10 degrees of the diffractive optical element in Comparative Example 1. It is a schematic diagram which shows the mode of propagation of the unnecessary light with respect to the light beam of off-screen incidence +10 degree | times of the diffraction optical element in a comparative example. 6 is a graph of diffraction efficiency with respect to a light beam of -10 degrees off-screen incidence of the diffractive optical element in Comparative Example 1. It is a schematic diagram which shows the mode of propagation of the unnecessary light with respect to the light beam of -10 degree | times incident off-screen of the diffraction optical element in a comparative example. It is a schematic diagram which shows the relationship between the structure of the diffractive optical element in a comparative example, and an off-screen incident light beam. 6 is a graph of diffraction efficiency with respect to an incident light beam of a diffractive optical element in Comparative Example 2.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same members are denoted by the same reference numerals, and redundant description is omitted.

  First, the diffractive optical element in Example 1 of the present invention will be described. The diffractive optical element of this embodiment is suitably used for an optical system lens. FIG. 1 is a schematic view (front view and side view) of the diffractive optical element 1. The diffractive optical element 1 includes a diffraction grating portion 10 sandwiched between substrates 2 and 3 made of flat plates or lenses. In the present embodiment, the surfaces of the substrates 2 and 3 on which the diffraction grating portion 10 is provided are curved surfaces. The diffraction grating portion 10 has a concentric diffraction grating shape centered on the optical axis O and has a lens action.

  FIG. 3 is an enlarged cross-sectional view of the diffractive optical element 1 obtained by cutting and enlarging the A-A ′ plane of FIG. 1. In order to make the lattice shape easy to understand, FIG. 3 is a diagram deformed in the lattice depth direction. The number of grids is also drawn less than actual. The same applies to the cross-sectional views described below. As shown in FIG. 3, the diffraction grating portion 10 of the diffractive optical element 1 includes a first diffraction grating 11, a second diffraction grating 12, and a light shielding member 20. The first diffraction grating 11 includes a grating surface 11a (first grating surface) and a grating wall surface 11b (first grating wall surface) formed concentrically with a predetermined grating pitch P around the optical axis O of the lens. A plurality. The second diffraction grating 12 includes a grating surface 12a (second grating surface) and a grating wall surface 12b (second grating wall surface) formed concentrically with a grating pitch P around the optical axis O. The first diffraction grating 11 and the second diffraction grating 12 have different refractive indexes (n11, n22) and constitute a high refractive index region and a low refractive index region. The grating surface 11 a of the first diffraction grating 11 is in contact with (in close contact with) the grating surface 12 a of the second diffraction grating 12. Similarly, the grating wall surface 11 b of the first diffraction grating 11 is in contact with the grating wall surface 12 b of the second diffraction grating 12.

  A plurality of light shielding members 20 are formed concentrically around the optical axis O at a lattice pitch P. The light shielding member 20 is disposed inside the first diffraction grating 11 and has a film shape structure. However, the present invention is not limited to this, and as will be described later, the light shielding member 20 may have other shapes, and the inside of the second diffraction grating 12 or of these diffraction gratings. You may arrange | position in other positions, such as a boundary. The light shielding member 20 reduces total reflected light generated at the boundary between the first diffraction grating 11 and the second diffraction grating 12.

  As shown in FIGS. 1 and 3, the first diffraction grating 11 and the second diffraction grating 12 are concentric blazed diffraction gratings composed of grating surfaces 11a and 12a and grating wall surfaces 11b and 12b, respectively. It is. Then, by gradually changing the grating pitch from the optical axis O toward the outer circumference of the circle, it is configured to have a lens action (light convergence action or diverging action). In addition, the grating surfaces 11a and 12a and the grating wall surfaces 11b and 12b are in contact with each other without a gap, and the first diffraction grating 11 and the second diffraction grating 12 function as one diffraction grating portion 10 as a whole. Further, by making the diffraction grating portion 10 a blazed structure, light (incident light) incident on the diffractive optical element 1 has a specific diffraction order with respect to the 0th-order diffraction direction that is transmitted without being diffracted by the diffraction grating portion 10. Diffraction is concentrated in the direction (+ 1st order in this embodiment).

  Moreover, the use wavelength range of the diffractive optical element 1 of the present embodiment is the visible range. For this reason, the material and the grating height d constituting the first diffraction grating 11 and the second diffraction grating 12 are selected so that the diffraction efficiency of the diffracted light of the designed order is high in the entire visible region. That is, the maximum optical path length difference of light passing through the plurality of diffraction gratings (the first diffraction grating 11 and the second diffraction grating 12) (the maximum optical optical path length difference between the peaks and valleys of the diffraction part) is within the use wavelength range. Thus, the material of each diffraction grating and the grating height d are determined so as to be close to an integral multiple of the wavelength. Thus, by appropriately setting the material and shape of the diffraction grating, high diffraction efficiency can be obtained over the entire wavelength range.

  Inside the first diffraction grating 11 (on the incident side of the first grating surface 11a, the second grating surface 12a, the first grating wall surface 11b, and the second grating wall surface 12b), the light shielding member 20 is provided. Is provided. By appropriately setting the material and shape of the light shielding member 20, it is possible to suppress unnecessary light generated by the obliquely incident (off-screen incident) light beam. In addition, although the light shielding member 20 is provided in the inside (incident side) of the 1st diffraction grating 11, a present Example is not limited to this. The light shielding member 20 may be provided in another area on the incident side or on the emission side. For example, it may be formed inside the second diffraction grating 12, on the substrate 2 or the substrate 3, inside the substrate 2 or the substrate 3, or on the first diffraction grating 11 or the second diffraction grating 12.

  Next, the configuration of the diffractive optical element 1 and unnecessary light in this embodiment will be described. FIG. 4A is an enlarged cross-sectional view of the diffraction grating portion 10 in the present embodiment. In FIG. 4A, the number of lattices is drawn less than the actual number, and only the light shielding members for the m lattice and the m ′ lattice are shown for easy understanding. FIG. 4B is a cross-sectional view in which the diffraction grating portion 10 is further enlarged. As a material for the first diffraction grating 11, a resin (nd = 1.482, νd = 20.7, θgF = 0.404, n550 = 1.383) in which ITO fine particles are mixed with a fluorine acrylic ultraviolet curable resin. Used. As the material of the second diffraction grating 12, an acrylic ultraviolet curable resin (nd = 1.524, νd = 51.6, θgF = 0.539, n550 = 1.524) is used. In this embodiment, the grating height d of each diffraction grating is 13.51 μm, and the design order is + 1st order.

  The light shielding member 20 is incident on the grating surface (first grating surface 11a, second grating surface 12a) and grating wall surfaces (first grating wall surface 11b, second grating wall surface 12b) of each diffraction grating. It is provided in the vicinity of the lattice wall (left side in the figure). A plurality of light shielding members 20 are provided for each grating wall surface of the first diffraction grating 11 and the second diffraction grating 12. Each light shielding member 20 is divided into two regions in the cross section of the lens including the optical axis O by a grating wall surface (first grating wall surface 11b, second grating wall surface 12b) and an extension line E of the grating wall surface. One region is a high refractive index region (second diffraction grating 12) when the position of the grating wall surface is used as a reference, and the other region is a low refractive index when the position of the grating wall surface is used as a reference. This is a region (first diffraction grating 11). In this embodiment, the width wH of the light shielding member 20 arranged on the high refractive index region side is larger than the width wL of the light shielding member 20 arranged on the low refractive index region side. Note that the directions of the widths wH and wL in the curved diffraction grating portion 10 are defined as a direction perpendicular to the grating wall surface and the extension line E of the grating wall surface (tangential direction of the curved surface) in FIG.

  According to such a configuration, a light beam (b in FIG. 4B, B in FIG. 4A) incident at a downward oblique incident angle (off-screen incident angle) in the figure is totally reflected on the grating wall surface. The flare which arises by this can be suppressed. Further, since the width wL is smaller than the width wH, the amount of reduction in diffraction efficiency due to the design incident angle is also small. In the light shielding member 20 of the present embodiment, the width wH is 2.0 μm, the width wL is 0.5 μm, the thickness d1 of the light shielding member 20 is 0.2 μm, the light shielding member 20 and each diffraction grating (first diffraction grating 11, The distance d2 from the second diffraction grating 12) is 1.0 μm. The light shielding member 20 is made of a metal material, and specifically, is made of Al (n550 = 0.958, k550 = 6.69).

  FIG. 5 is a calculation result of a rigorous coupled wave analysis (RCWA) at an incident angle of 0 degrees (a in FIG. 4B), a grating pitch of 100 μm, and a wavelength of 550 nm, which is a designed incident angle of the diffractive optical element. . FIG. 5A shows the diffraction efficiency in the vicinity of the + 1st order diffracted light that is the designed order. The horizontal axis is the diffraction order, and the vertical axis is the diffraction efficiency. FIG. 5B is a result of enlarging the low diffraction efficiency portion of the vertical axis in FIG. 5A and showing the high diffraction angle range with the horizontal axis as the diffraction order to the diffraction angle. The diffraction angle has a downward direction in FIG. 4B as a positive direction. In FIG. 5 (a), the diffraction efficiency of the + 1st order diffracted light, which is the designed order, is 96.88% (diffraction angle +0.21 degree). The remaining light becomes unnecessary light and propagates as a plurality of small peaks as shown in FIG. This is because the incident-side light shielding member shields a component of the incident light beam that enters the vicinity of the grating wall surface before reaching the grating wall surface. On the other hand, the light shielding member 20 originally shields a part of the light beam diffracted into the + 1st order light by each diffraction grating, resulting in phase mismatch. As a result, the diffraction efficiency of the order of relatively low order (approximately ± 25th order, diffraction angle ± 5 degrees) increases, and the diffraction efficiency of the + 1st order diffracted light that is the designed order decreases. The grating pitch assumed in this embodiment is 100 μm as one reference. As shown in FIG. 1, the lattice pitch increases as the ring zone is closer to the optical axis, and the adverse effects of the grating wall surface and the light shielding member are reduced. For this reason, the diffraction efficiency of the designed order is high, and the diffraction efficiency of unnecessary light is low.

  Next, a light beam (b in FIG. 4B and B in FIG. 4A) that enters the diffractive optical element at an oblique incident angle (off-screen light incident angle) downward from the designed incident angle is assumed. FIG. 6 shows RCWA calculation results at an incident angle of +10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm. With respect to the incident angle, the downward direction in FIG. FIG. 6A shows the diffraction efficiency in the vicinity of the + 1st order diffracted light that is the designed order. The horizontal axis is the diffraction order, and the vertical axis is the diffraction efficiency. FIG. 6B is a result of enlarging the low diffraction efficiency portion of the vertical axis in FIG. 6A and showing the high diffraction angle range with the horizontal axis as the diffraction order to the diffraction angle. The diffraction angle has a downward direction in FIG. 4B as a positive direction. In FIG. 6A, the diffraction efficiency of the + 1st order diffracted light, which is the designed order, is concentrated, but the diffraction efficiency is 96.57% (diffraction order + 1, diffraction angle + 9.94 degrees), and the designed incident angle is 0. It is decreasing because it is tilted from the degree. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining light becomes unnecessary light and propagates as a plurality of small peaks without a peak in a specific angular direction, as shown in FIG. 6B. This is because the component incident on the vicinity of the grating wall surface of the incident light beam is shielded before reaching the grating wall surface by the width wH of the incident-side light shielding member. As shown in FIGS. 2 and 15, when the diffractive optical element 1 is applied to the optical system, diffraction of unnecessary light by off-screen light that substantially matches the diffraction angle +0.21 degree at which the design diffraction order at the design incident angle propagates. Light reaches at least the image plane. The diffraction efficiency in the vicinity of the diffraction angle +0.21 degrees in FIG. 6 indicates that the diffraction efficiency at the diffraction order −45 (diffraction angle +0.38 degrees) is 0.00074% and the diffraction order −46 (diffraction angle +0. 17 degrees) is 0.0010%, and the diffraction efficiency is greatly reduced.

  Next, a light beam (c in FIG. 4B, B ′ in FIG. 4A) that enters the diffractive optical element at an oblique incident angle (off-screen light incident angle) upward from the designed incident angle is assumed. FIG. 7 shows RCWA calculation results at an incident angle of −10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm. With respect to the incident angle, the downward direction in FIG. 4B is a positive direction (in the m ′ lattice in FIG. 4A, the upward direction is a positive direction). FIG. 7A shows the diffraction efficiency in the vicinity of the + 1st order diffracted light that is the designed order. The horizontal axis is the diffraction order, and the vertical axis is the diffraction efficiency. FIG. 7B is a result of enlarging the low diffraction efficiency portion of the vertical axis in FIG. 7A and showing the high diffraction angle range with the horizontal axis as the diffraction order to the diffraction angle. The diffraction angle has a downward direction in FIG. 4B as a positive direction (upward is a positive direction in the m ′ grating in FIG. 4A). In FIG. 7A, the diffraction efficiency of the + 1st order diffracted light, which is the designed order, is concentrated, but the diffraction efficiency is 93.15% (diffraction order + 1, diffraction angle−9.52 degrees), which is the designed incident angle. Since it is tilted from 0 degree, it is lowered. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining unnecessary light propagates as unnecessary light having a peak in a specific angular direction, as shown in FIG. This unnecessary light has a peak in a direction of approximately −16 degrees. The propagation direction of the peak in the direction of about -16 degrees is substantially equal to the emission direction of transmitted light of the light beam having an off-screen incident angle of -10 degrees incident on the grating wall surface -16.6 degrees. Compared to the case where no light shielding member is provided, the diffraction efficiency is slightly reduced. This is because a part of the incident light flux that is incident on the vicinity of the grating wall surface is shielded by the portion of the incident-side light shielding member having the width wL before reaching the grating wall surface. As shown in FIGS. 2 and 15, when the diffractive optical element 1 is applied to the optical system, diffraction of unnecessary light by off-screen light that substantially matches the diffraction angle +0.21 degree at which the design diffraction order at the design incident angle propagates. Light reaches at least the image plane. The diffraction efficiency in the vicinity of the diffraction angle +0.21 degree in FIG. 7 is 0.0050% for the diffraction order +48 (diffraction angle +0.24 degree) and the diffraction order +47 (diffraction angle +0.08 degree) from the RCWA calculation result. ) Is 0.0050%.

As described above, when the off-screen light beam is incident on the optical system to which the diffractive optical element 1 of the present embodiment is applied, the unnecessary light can be reduced by providing the light shielding member 20. As a result, unnecessary light that reaches the imaging surface is reduced, so that deterioration in image performance can be suppressed. Further, by reducing the width wL on the low refractive index region side (first diffraction grating 11 side) than the width wH on the high refractive index region side (second diffraction grating 12 side), the diffraction efficiency of the designed order can be reduced. Reduction can be suppressed to an extent that does not affect image performance.
Here, the lattice pitch is 100 μm. Further, since the contribution of the wall surface is small in an annular zone with a wide grating pitch, the diffraction efficiency of the designed order is high and the diffraction efficiency of unnecessary light is low. Although not shown, the propagation direction of the unnecessary light does not depend on the grating pitch, and the propagation direction is the same. Therefore, the diffraction efficiency with a grating pitch of 100 μm is shown as one reference.

  Further, here, it is assumed that the incident angles of the off-screen light beams B and B ′ are +10 degrees outside the screen (the incident angle ω is +13.16 degrees with respect to the optical axis direction). At angles smaller than this incident angle, ghosts due to lens surface and image plane reflection, scattering inside the lens, and surface irregularities are large, and therefore unnecessary light of the diffractive optical element is relatively inconspicuous. At an angle larger than this incident angle, the influence of unnecessary light of the diffractive optical element is relatively small due to reflection of the front lens surface and light shielding by the lens barrel. For this reason, the off-screen incident light flux has the greatest influence on the unnecessary light of the diffractive optical element in the vicinity of +10 degrees. Here, the incident angle of the off-screen light flux is assumed to be approximately +10 degrees.

  In this embodiment, as shown in FIGS. 2 and 4A, the peak of unnecessary light is shielded by the diaphragm 40 (Bm− and B′m− in FIG. 2), but is not limited thereto. It is not a thing. The unnecessary light can also be suppressed by guiding the unnecessary light peak to the lens barrel and blocking it, or by reflecting it at an angle that does not reach the image plane by the rear lens. The light shielding member is not limited to a rectangular structure as shown in FIG. 4B for the purpose of shielding the light beam totally reflected by the grating wall surface. In the case of a light shielding member other than a rectangular structure, the width wH and the width wL are divided by dividing the light shielding member having a grating cross section with one period by an extension line of the grating wall surface, and extending the light in the surface normal direction of the diffraction grating with that period. The maximum distance of the member. In this embodiment, the design order is + 1st order, but the design order may be other than + 1st order. Moreover, it is also possible to control for each ring zone by changing the width and shape of the light shielding member 20 for each ring zone of the diffractive optical element 1. As a result, unnecessary light reaching the imaging plane can be effectively suppressed.

  In the present embodiment, the manufacturing method of the light shielding member 20 is not particularly limited. For example, the second diffraction grating 12 is manufactured, and the first diffraction grating 11 and the base part (part d2 in FIG. 4B) are manufactured. Thereafter, the light shielding member 20 is selectively formed. Specifically, after the material constituting the light shielding member 20 is formed into a thin film shape by a vacuum deposition method or the like, patterning is performed using a lithography method or a nanoimprint method, and the material is selectively formed by an etching method or the like. Alternatively, a method of selectively forming by a vapor deposition method using a mask pattern, a method of directly forming only on a lattice wall surface using an inkjet process, or the like can be used. Thereafter, the same material as that of the first diffraction grating 11 is formed again, whereby the diffractive optical element 1 can be manufactured. At this time, it is not necessary to use the same material as that of the first diffraction grating 11, and a different material may be used. Moreover, the 2nd diffraction grating 12 can be manufactured, and the grating | lattice part of the 1st diffraction grating 11, a base part, and the light shielding member 20 can be shape | molded simultaneously using another type | mold. Thereafter, the material constituting the light shielding member 20 is selectively formed by the above-described method or the like, and then the same material as that of the first diffraction grating 11 is formed again to manufacture the diffractive optical element. At this time, it is not necessary to use the same material as that of the first diffraction grating 11, and a different material may be used. In addition, the first diffraction grating 11 and the second diffraction grating 12 can be manufactured after the light shielding member 20 is formed using the above-described method or the like. The light shielding member 20 may be directly formed on the substrate 2 (shown in FIG. 3) on the incident side, for example.

  In the above description, the relationship between the refractive index n11 of the first diffraction grating 11 and the refractive index n22 of the second diffraction grating 12 is n11 <n22. However, the present embodiment is not limited to this. Absent. The present invention is also applicable when the refractive index relationship is n11> n22. Hereinafter, this case will be described. FIG. 8 is an enlarged cross-sectional view of the diffractive optical element 1 when the relationship between the refractive index n11 of the first diffraction grating 11 and the refractive index n22 of the second diffraction grating 12 is n11> n22. In FIG. 8, the component of the light beam having an off-screen incident angle of 10 degrees incident on the grating wall surface 1b of the m grating is from the high refractive index material side (first diffraction grating 11 side) to the low refractive index material side (second diffraction). Since it is incident on the grating 12 side) at a critical angle of 76.7 degrees or more and +80 degrees, total reflection occurs. For this reason, unnecessary light spreads and propagates around the total reflection emission direction on the grating wall surface 1b. On the other hand, the component of the light beam having an off-screen incident angle of 10 degrees incident on the grating wall surface 1b ′ of the m ′ grating is diffracted into + 1st order light on the grating surface and then incident on the high refractive index material interface side from the low refractive index material side. To do. At this time, unnecessary light spreads and propagates on the grating wall surface 1b 'centering on the transmitted light emission direction and the reflected light emission direction, but the unnecessary light in the transmitted light emission direction is large. As described above, regarding the unnecessary light due to the grating wall surface, the relationship of the refractive index of each diffraction grating can be applied regardless of whether n11 <n22 or n11> n22.

  Next, a diffractive optical element according to Example 2 of the present invention will be described. In the diffractive optical element of this embodiment, the material and grating height of each diffraction grating are different from those of the first embodiment. Since other structures such as the structure of the light shielding member are the same as those in the first embodiment, the description thereof is omitted. In the present embodiment, the material of the first diffraction grating 11 is a resin (nd = 1.504, νd = 16.3, θgF = 0.390, n550 = a mixture of fluorine acrylic ultraviolet resin and ITO fine particles. 1.511) is used. The material of the second diffraction grating 12 is a resin in which ZrO2 fine particles are mixed with an acrylic ultraviolet curable resin (nd = 1.567, νd = 47.0, θgF = 0.568, n550 = 1.570. ) Is used. The grating height d is 9.29 μm, and the design order is + 1st order.

  FIG. 9 shows RCWA calculation results at an incident angle of 0 degree, which is a designed incident angle of the diffractive optical element, a grating pitch of 100 μm, and a wavelength of 550 nm. In FIG. 9A, the diffraction efficiency of the + 1st order diffracted light, which is the designed order, is 97.16% (diffraction angle + 0.20 degree). The remaining light becomes unnecessary light and propagates as a plurality of small peaks as shown in FIG. This is because a component incident on the vicinity of the grating wall surface of the incident light beam is shielded by the incident-side light shielding member before reaching the grating wall surface. On the other hand, a part of the light beam that is originally diffracted into + 1st order light by each diffraction grating is also shielded by the light shielding member, and phase mismatch occurs.

  Next, a light beam incident on the diffractive optical element at an oblique incident angle (off-screen light incident angle) downward from the designed incident angle is assumed. FIG. 10 shows RCWA calculation results at an incident angle of +10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm. In FIG. 10A, the diffraction efficiency of the + 1st order diffracted light, which is the designed order, is concentrated, but the diffraction efficiency is 97.66% (diffraction order + 1, diffraction angle + 9.82 degrees). Since it is inclined from a certain 0 degree, it is lowered. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining light becomes unnecessary light and propagates as a plurality of small peaks as shown in FIG. This is because the component incident on the vicinity of the grating wall surface of the incident light beam is shielded by the portion of the light shielding member 20 arranged on the incident side before reaching the grating wall surface. As shown in FIG. 2 and FIG. 4A, when a diffractive optical element is applied to the optical system, it is unnecessary due to off-screen light substantially matching the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle. The diffracted light of light reaches at least the image plane. The diffraction efficiency in the vicinity of the diffraction angle +0.20 degree in FIG. 10 is 0.0035% at the diffraction order −46 and 0.0038% at the diffraction order −47 from the RCWA calculation result, compared to the case where there is no light shielding member. Decrease.

  Next, a light beam incident on the diffractive optical element at an oblique incident angle (off-screen light incident angle) upward from the designed incident angle is assumed. FIG. 11 shows RCWA calculation results at an incident angle of −10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm. In FIG. 11A, the diffraction efficiency of the + 1st order diffracted light that is the designed order is concentrated, but the diffraction efficiency is 94.86%, which is lowered because it is tilted from 0 degree that is the designed incident angle. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining light becomes unnecessary light and propagates as a plurality of peaks as shown in FIG. This is because a part of the component incident near the grating wall surface is shielded by the portion of the light shielding member 20 arranged on the incident side with the width wL before reaching the grating wall surface. As shown in FIG. 2 and FIG. 4A, when a diffractive optical element is applied to the optical system, it is unnecessary due to off-screen light substantially matching the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle. The diffracted light of light reaches at least the image plane. From the RCWA calculation results, the diffraction efficiency of diffraction order +49 is 0.0065%, and the diffraction efficiency of diffraction order +48 is 0.0063%, as shown in FIG.

  As described above, according to the diffractive optical element of the present embodiment, it is possible to reduce unnecessary light reaching the imaging surface of the optical system and suppress deterioration in image performance. Further, by reducing the width wL on the low refractive index region side than the width wH on the high refractive index region side, it is possible to suppress the reduction in the diffraction efficiency of the design order to the extent that the image performance is not affected.

  In the present embodiment, a material formed by dispersing fine particles in a resin material is used as the material of the diffractive optical element, but the present invention is not limited to this. For example, an organic material such as a resin material, a glass material, an optical crystal material, a ceramic material, or the like may be used. In addition, as the fine particle material for dispersing the fine particles, an inorganic fine particle material of oxide, metal, ceramics, composite, or mixture is used, and is not limited to the fine particle material. 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 Rayleigh scattering becomes large when the fine particle material is mixed with the resin material. In addition, as the resin material to be mixed with the fine particle material, for example, an ultraviolet curable resin, which is an organic resin of acrylic type, fluorine type, vinyl type, or epoxy type is used.

  Next, a diffractive optical element according to Example 3 of the present invention will be described. The present embodiment is different from Embodiments 1 and 2 arranged on the incident side in that the light shielding member is arranged on the emission side. FIG. 12A is an enlarged cross-sectional view of the diffraction grating portion of the present embodiment. FIG. 12B is a cross-sectional view in which the diffraction grating portion is further enlarged. The material of each diffraction grating, the grating height d, and the design order are the same as in the second embodiment.

  Similarly to the first and second embodiments, in this embodiment, the width wH of the light shielding member 20 disposed on the high refractive index region side is larger than the width wL of the light shielding member 20 disposed on the low refractive index region side. . By such a light shielding member 20, a light beam (b in FIG. 12B and B in FIG. 12A) incident on the diffractive optical element at a downward oblique incident angle (off-screen incident angle) is totally reflected on the grating wall surface. The flare produced by doing so can be suppressed. Further, since the width wL is smaller than the width wH, the amount of reduction in diffraction efficiency due to the design incident angle is also small. The widths wH and wL, the thickness d1, the distance d2 and the materials related to the light shielding member 20 are the same as those in the first and second embodiments.

  FIG. 13A shows an RCWA calculation result at an incident angle of 0 degree, which is a designed incident angle of the diffractive optical element, a grating pitch of 100 μm, and a wavelength of 550 nm. The diffraction efficiency of the + 1st order diffracted light, which is the designed order, is 97.06% (diffraction angle + 0.20 degrees), which is lower than when no light shielding member is provided. The remaining light becomes unnecessary light and propagates as a plurality of small peaks as shown in FIG. This is because a component incident on the vicinity of the grating wall surface of the incident light flux is emitted from the grating wall surface and then shielded by the light shielding member by the light shielding member on the emission side. On the other hand, a part of the light beam that is originally diffracted into the + 1st order light by each diffraction grating is shielded by the light shielding member, and phase mismatch occurs. As a result, the diffraction efficiency of the relatively low order increases, and the diffraction efficiency of the + 1st order diffracted light, which is the designed order, decreases. The lattice pitch assumed here is 100 μm as one reference. As shown in FIG. 1, the ring pitch closer to the optical axis increases as the grating pitch increases, and the adverse effects of the grating wall surface and the light shielding member are reduced. Therefore, the diffraction efficiency of the design order is high and the diffraction efficiency of unnecessary light is low.

  Next, a light beam incident on the diffractive optical element at an oblique incident angle (off-screen light incident angle) downward from the designed incident angle is assumed. FIG. 13B shows the RCWA calculation result at an incident angle of +10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm. The diffraction efficiency of the + 1st order diffracted light, which is the designed order, is 96.32%, which is lowered because it is tilted from 0 degrees, which is the designed incident angle. Since the + 1st order diffracted light having the off-screen light incident angle does not reach the image plane, the influence is small. The remaining light becomes unnecessary light and propagates as a plurality of small peaks as shown in FIG. This is because the component of the incident light beam that is incident on the vicinity of the grating wall surface is totally reflected by the grating wall surface and emitted by the light shielding member 20 by the width wH portion of the light shielding member 20 arranged on the exit side. It is. As shown in FIGS. 2 and 12A, when a diffractive optical element is applied to the optical system, it is unnecessary due to off-screen light that substantially matches the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle. The diffracted light of light reaches at least the image plane. The diffraction efficiency in the vicinity of the diffraction angle +0.20 degree in FIG. 13B is 0.0037% at the diffraction order −46 and 0.0033% at the diffraction order −47 from the RCWA calculation result, and there is no light shielding member. Decrease more.

Next, a light beam incident on the diffractive optical element at an oblique incident angle (off-screen light incident angle) upward from the designed incident angle is assumed. FIG. 13C shows the RCWA calculation result at an incident angle of −10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm. The diffraction efficiency of the + 1st order diffracted light, which is the designed order, is 96.45% (diffraction order + 1, the diffraction angle is −9.42 degrees), which is lowered because it is tilted from the designed incident angle of 0 degrees. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining light becomes unnecessary light and propagates as a plurality of peaks in a specific angular direction, as shown in FIG. This is because a part of the incident light flux that is incident on the vicinity of the grating wall surface is shielded by the portion of the light shielding member 20 having the width wL before reaching the grating wall surface. As shown in FIGS. 2 and 12A, when a diffractive optical element is applied to the optical system, it is unnecessary due to off-screen light that substantially matches the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle. The diffracted light of light reaches at least the image plane. The diffraction efficiency in the vicinity of the diffraction angle +0.20 degree in FIG. 13C is 0.0012% at the diffraction order +49 and 0.0010% at the diffraction order +48 from the RCWA calculation result, which is more than that without the light shielding member. Decrease.
According to the configuration of the present embodiment, it is possible to suppress a decrease in image performance. Further, by reducing the width wL on the low refractive index region side than the width wH on the high refractive index region side, it is possible to suppress the reduction in the diffraction efficiency of the design order to the extent that the image performance is not affected.

  Next, a diffractive optical element according to Example 4 of the present invention will be described. The present embodiment is different from the third embodiment in that the width wL of the light shielding member is substantially zero. FIG. 14A is an enlarged cross-sectional view of the diffraction grating portion in the present embodiment. FIG. 14B is a cross-sectional view in which the diffraction grating portion is further enlarged. The material of each diffraction grating, the grating height d, the design order, and the point that the light shielding member is arranged on the exit side are the same as in the third embodiment.

  In the present embodiment, the width wL of the light shielding member 20 is substantially zero. That is, the light shielding member 20 has a grating wall surface in the region divided by the grating wall surface (first grating wall surface 11b, second grating wall surface 12b) and the extension line of the grating wall surface in the cross section of the lens including the optical axis O. When the position is used as a reference, it is arranged only on the high refractive index region side. By such a light shielding member 20, a light beam (b in FIG. 14B and B in FIG. 14A) incident downward with an oblique incident angle (off-screen incident angle) is generated by total reflected light generated on the grating wall surface. Flares can be suppressed. Furthermore, since the width wL is substantially 0, the amount of reduction in diffraction efficiency due to the design incident angle is small. The material of the light shielding member 20, the width wH, the thickness d1, and the distance d2 between the light shielding member 20 and each diffraction grating are the same as in the third embodiment.

  FIG. 15A shows an RCWA calculation result at an incident angle of 0 degrees (a in FIG. 14B), which is a designed incident angle of the diffractive optical element, a grating pitch of 100 μm, and a wavelength of 550 nm. The diffraction efficiency of the + 1st order diffracted light, which is the designed order, is 97.44% (diffraction angle +0.20 degrees), which is lower than the case where there is no light shielding member, but in the case of Examples 1 to 3 where the width wL exists. High compared. The remaining light becomes unnecessary light and propagates as a plurality of small peaks as shown in FIG. This is because a component incident on the vicinity of the grating wall surface of the incident light flux is emitted from the grating wall surface and then shielded by the light shielding member by the light shielding member on the emission side. On the other hand, a part of the light beam that is originally diffracted into the + 1st order light by each diffraction grating is shielded by the light shielding member, and phase mismatch occurs. As a result, the diffraction efficiency of the order of relatively low order (approximately ± 25th order, diffraction angle ± 5 degrees) increases, and the diffraction efficiency of the + 1st order diffracted light that is the designed order decreases. However, the diffraction efficiency of relatively low-order light is low compared to the cases of Examples 1 to 3 where the width wL portion exists, and the diffraction efficiency of + 1st-order diffracted light, which is the designed order, is increased.

  Next, it is assumed that the light beam is incident downward from the designed incident angle of the diffractive optical element at an oblique incident angle (off-screen light incident angle). FIG. 15B shows the RCWA calculation result at an incident angle of +10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm. The diffraction efficiency of the + 1st order diffracted light, which is the designed order, is 96.39% (diffraction order + 1, diffraction angle + 9.82 degrees), which is lowered because it is inclined from the designed incident angle of 0 degrees. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining light becomes unnecessary light and propagates as a plurality of small peaks as shown in FIG. This is because the component of the incident light beam that is incident on the vicinity of the grating wall surface is totally reflected by the grating wall surface and then emitted by the light shielding member due to the width wH of the light shielding member on the exit side. As shown in FIG. 2 and FIG. 14A, when a diffractive optical element is applied to the optical system, it is unnecessary due to off-screen light that substantially matches the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle. The diffracted light of light reaches at least the image plane. The diffraction efficiency in the vicinity of the diffraction angle +0.20 degree in FIG. 13B is 0.0025% at the diffraction order −46 and 0.0021% at the diffraction order −47 from the RCWA calculation result, and there is no light shielding member. Decrease more.

  Next, a light beam incident upward from an oblique incident angle (off-screen light incident angle) with respect to the designed incident angle of the diffractive optical element is assumed. FIG. 15C shows the RCWA calculation result at an incident angle of −10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm. The diffraction efficiency of the + 1st order diffracted light that is the designed order is 95.94%, which is lowered because it is tilted from 0 degrees that is the designed incident angle. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining light becomes unnecessary light and propagates with a plurality of peaks in a specific angular direction, as shown in FIG. This is because a portion of the incident light flux that is incident on the vicinity of the grating wall surface is shielded after being emitted from the grating wall surface by the width wH portion of the light shielding member. As shown in FIG. 2 and FIG. 14A, when a diffractive optical element is applied to the optical system, it is unnecessary due to off-screen light that substantially matches the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle. The diffracted light of light reaches at least the image plane. From the RCWA calculation result, the diffraction efficiency of diffraction order +49 is 0.0049% and the diffraction efficiency of diffraction order +48 is 0.0050%, as shown in FIG.

  According to the configuration of the present embodiment, unnecessary light reaching the imaging surface of the optical system can be reduced, so that deterioration in image performance can be suppressed. As in this embodiment, the reduction in the diffraction efficiency of the designed order can be further reduced by making the width wL of the light blocking member on the low refractive index region side substantially zero.

  Next, a diffractive optical element according to Example 5 of the present invention will be described. This embodiment has the same configuration as that of the fourth embodiment except that the width wH of the light shielding member 20 arranged on the emission side is different from that of the fourth embodiment. In this embodiment, the width wH of the light shielding member 20 is 1.0 μm.

  FIG. 16A shows an RCWA calculation result at an incident angle of 0 degree, which is a designed incident angle of the diffractive optical element, a grating pitch of 100 μm, and a wavelength of 550 nm. The diffraction efficiency of the + 1st order diffracted light, which is the designed order, is 97.88% (diffraction angle +0.20 degrees), which is lower than that when no light shielding member is provided, but from the case of Examples 1 to 3 having the width wL. high. The remaining light becomes unnecessary light and propagates as a plurality of small peaks as shown in FIG. This is because a part of the component incident on the vicinity of the grating wall surface of the incident light beam is shielded by the light shielding member after exiting from the grating wall surface by the light shielding member on the emission side. On the other hand, a part of the light beam that is originally diffracted into the + 1st order light by each diffraction grating is shielded by the light shielding member, and phase mismatch occurs. As a result, the diffraction efficiency of the relatively low order increases, and the diffraction efficiency of the + 1st order diffracted light, which is the designed order, decreases. However, compared with Examples 1 to 4, the diffraction efficiency of relatively low-order light is low, and the diffraction efficiency of + 1st-order diffracted light, which is the designed order, is increased.

  Next, a light beam incident on the diffractive optical element at an oblique incident angle (off-screen light incident angle) downward from the designed incident angle is assumed. FIG. 16B shows the RCWA calculation result at an incident angle of +10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm. The diffraction efficiency of the + 1st order diffracted light, which is the designed order, is 96.90% (diffraction order + 1, diffraction angle + 9.82 degrees), which is lowered because it is inclined from the designed incident angle of 0 degrees. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining light becomes unnecessary light and propagates as a plurality of small peaks as shown in FIG. This is because a part of the incident light beam that is incident on the vicinity of the grating wall surface is totally reflected by the grating wall surface and then emitted by the light shielding member due to the width wH of the light shielding member on the exit side. As shown in FIG. 2 and FIG. 14A, when a diffractive optical element is applied to the optical system, it is unnecessary due to off-screen light that substantially matches the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle. The diffracted light of light reaches at least the image plane. From the RCWA calculation result, the diffraction efficiency of diffraction order −46 is 0.00046% and the diffraction efficiency of diffraction order −47 is 0.00064%. . Since the valley portion of the ripple of unnecessary light is in the 0 degree direction, the diffraction efficiency is reduced as compared with the case where no light shielding member is provided.

  Next, a light beam incident on the diffractive optical element at an oblique incident angle (off-screen light incident angle) upward from the designed incident angle is assumed. FIG. 16C shows an RCWA calculation result at an incident angle of −10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm. The diffraction efficiency of the + 1st order diffracted light that is the designed order is 96.64%, which is lowered because it is tilted from the designed incident angle of 0 degrees. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining light becomes unnecessary light and propagates with a peak in a specific angular direction as shown in FIG. This is because a part of the incident light flux near the grating wall surface is not shielded after being emitted from the grating wall surface by the width wH of the light shielding member on the emission side. As shown in FIG. 2 and FIG. 14A, when a diffractive optical element is applied to the optical system, it is unnecessary due to off-screen light that substantially matches the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle. The diffracted light of light reaches at least the image plane. From the RCWA calculation result, the diffraction efficiency of diffraction order +49 is 0.0029% and the diffraction efficiency of diffraction order +48 is 0.0030%, as shown in FIG.

  According to the optical system to which the diffractive optical element of the present embodiment is applied, it is possible to reduce unnecessary light reaching the imaging plane, and thus it is possible to suppress deterioration in image performance.

  Next, a diffractive optical element according to Example 6 of the present invention will be described. This embodiment is different from the first to fifth embodiments in that the light shielding member 20 is provided on the grating surface of the diffraction grating. That is, the light shielding member 20 of this embodiment is disposed at the boundary between the first diffraction grating 11 and the second diffraction grating 12 so as to be in contact with the first grating surface 11a and the first grating wall surface 11b. .

  FIG. 17A is an enlarged cross-sectional view of the diffractive optical element in the present embodiment. FIG. 17B is a cross-sectional view further enlarging the diffraction grating. The material of each diffraction grating, the grating height d, and the design order are the same as those in Examples 2 to 5. The light shielding member 20 is provided on the high refractive index region side (second diffraction grating 12 side), that is, on the tip of the second diffraction grating 12 (contact region between the grating surface and the grating wall surface). By such a light shielding member 20, a light beam (b in FIG. 17B and B in FIG. 17A) incident downward with an oblique incident angle (off-screen incident angle) is generated by the total reflected light generated on the grating wall surface. Flares can be suppressed. Furthermore, since the width wL is substantially 0 as in the fourth and fifth embodiments, the amount of reduction in diffraction efficiency due to the design incident angle is small. In the present embodiment, the width wH of the light shielding member 20 is 2.0 μm.

  FIG. 18A shows the RCWA calculation result at an incident angle of 0 degree, which is the designed incident angle of the diffractive optical element, a grating pitch of 100 μm, and a wavelength of 550 nm. The diffraction efficiency of the + 1st order diffracted light, which is the designed order, is 97.39% (diffraction angle +0.20 degrees), which is lower than when no light shielding member is provided, but in the case of Examples 1 to 3 having a width wL. High compared. The remaining light becomes unnecessary light and propagates as a plurality of small peaks as shown in FIG. This is because a part of the component incident on the grating wall surface of the incident light beam is emitted from the grating wall surface and then shielded by the light shielding member by the light shielding member 20 on the emission side. On the other hand, a part of the light beam that is originally diffracted into the + 1st order light by each diffraction grating is shielded by the light shielding member, and phase mismatch occurs. As a result, the diffraction efficiency of the relatively low order increases, and the diffraction efficiency of the + 1st order diffracted light, which is the designed order, decreases. However, the diffraction efficiency of low-order light is lower than that of Examples 1 to 3, and the diffraction efficiency of + 1st-order diffracted light, which is the designed order, is increased.

  Next, a light beam incident on the diffractive optical element at an oblique incident angle (off-screen light incident angle) downward from the designed incident angle is assumed. FIG. 18B shows the RCWA calculation result at an incident angle of +10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm. The diffraction efficiency of the + 1st order diffracted light, which is the designed order, is 98.46% (diffraction order + 1, diffraction angle + 9.82 degrees), which is lowered because it is tilted from the designed incident angle of 0 degrees. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining light becomes unnecessary light and propagates as a plurality of small peaks as shown in FIG. This is because a component incident on the vicinity of the grating wall surface of the incident light beam is shielded by the portion of the light shielding member 20 having the width wH before reaching the grating wall surface. As shown in FIGS. 2 and 17A, when a diffractive optical element is applied to the optical system, it is unnecessary due to off-screen light that substantially matches the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle. The diffracted light of light reaches at least the image plane. From the RCWA calculation result, the diffraction efficiency of diffraction order −46 is 0.00065%, and the diffraction efficiency of diffraction order −47 is 0.00078%. . This is significantly less than when no light shielding member is provided.

  Next, a light beam incident on the diffractive optical element at an oblique incident angle (off-screen light incident angle) upward from the designed incident angle is assumed. FIG. 18C shows an RCWA calculation result at an incident angle of −10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm. The diffraction efficiency of the + 1st order diffracted light that is the designed order is 94.78%, which is lowered because it is tilted from 0 degrees that is the designed incident angle. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining light becomes unnecessary light and propagates as a peak in a specific angular direction as shown in FIG. This is because the component incident on the vicinity of the grating wall surface of the incident light flux is not shielded by the width wH portion of the light shielding member. As shown in FIGS. 2 and 17A, when a diffractive optical element is applied to the optical system, it is unnecessary due to off-screen light that substantially matches the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle. The diffracted light of light reaches at least the image plane. With respect to the diffraction efficiency in the vicinity of the diffraction angle +0.20 degree in FIG. 18C, from the RCWA calculation result, the diffraction efficiency of diffraction order +49 is 0.0021%, and the diffraction efficiency of diffraction order +48 is 0.0019%.

  If the flare resulting from total reflection can be shielded as in this embodiment, the position of the light shielding member is not limited, and the light shielding member may be provided on the lattice plane. According to the optical system to which the diffractive optical element of the present embodiment is applied, it is possible to reduce unnecessary light reaching the imaging plane, and thus it is possible to suppress deterioration in image performance.

  By providing the light shielding member on the lattice surface as in this embodiment, the manufacturing becomes simpler. Although the manufacturing method of the light shielding member 20 is not particularly limited, as an example, the light shielding member 20 is selectively formed after the first diffraction grating 11 is manufactured. Specifically, after the material of the light shielding member 20 is formed into a thin film shape by a vacuum deposition method or the like, it can be selectively formed by an etching method or the like by patterning by a lithography method or a nanoimprint method or the like. Alternatively, a method of selectively forming by a vapor deposition method or the like using a mask pattern, a method of directly forming only on a lattice wall surface using an ink jet process, or the like may be used. After that, the diffractive optical element can be manufactured by forming the second diffraction grating 12. Thus, it can manufacture more simply compared with Example 1 thru | or 5, and it is possible to manufacture at low cost and low energy.

  In the present embodiment, the relationship between the refractive index n11 of the first diffraction grating 11 and the refractive index n22 of the second diffraction grating 12 is n11 <n22. Therefore, the light shielding member 20 is provided on the incident side. On the other hand, when the relationship between these refractive indexes is n11> n22, the light shielding member 20 is provided on the exit side. FIGS. 19A and 19B are enlarged cross-sectional views of the diffraction grating portion when the refractive index relationship is n11> n22. A light beam (b in FIG. 19 (b), B in FIG. 19 (a) incident on the m grating in FIG. 19 (a), which has a large influence of unnecessary light, downwardly incident at an oblique incident angle (off-screen light incident angle). The unnecessary light is shielded by the light shielding member after being totally reflected by the grating wall surface and emitted. Thus, even in the configuration in which the light shielding member 20 is provided on the lattice plane, the light shielding member 20 can be applied to both the incident side and the emission side.

  Next, Examples 1 to 6 will be described with reference to Table 1. Table 1 shows the material of the first diffraction grating used in the diffractive optical elements of Examples 1 to 6, the refractive index nd1 at the d-line, the Abbe number vd1, the partial dispersion ratio θgF1, and the refractive index n1_550 having a wavelength of 550 nm. Show. In addition, the material of the second diffraction grating, the refractive index nd2 at the d-line, the Abbe number vd2, and the refractive index n2_550 having a wavelength of 550 nm are shown. Also, the grating height d, the position of the light shielding member, the material of the light shielding member, the width wH on the high refractive index region side, the width wL on the low refractive index region side, the thickness d1 of the light shielding member, and the distance between the light shielding member and the diffraction grating d2 is shown.

  As shown in Examples 1 to 6, in order to suppress unnecessary light having a large influence on image performance, the width wH on the high refractive index region side of the region divided by the grating wall surface and the extension line of the grating wall surface is The width wL on the low refractive index region side preferably satisfies the following formula (1).

wH> wL ≧ 0 (1)
When the expression (1) is not satisfied, it is difficult to suppress unnecessary light by suppressing a decrease in the diffraction efficiency of the design order.

  Further, when the sum of the widths of the light shielding members (wH + wL) is increased, the phase mismatch region is enlarged, and the diffraction efficiency of the design order is lowered. As a result, there is a possibility that the image performance is deteriorated so that it cannot be ignored. For this reason, it is preferable that the sum (wH + wL) of the width | variety of the light shielding member in a design incident angle satisfy | fills the following formula | equation (2).

0 <(wH + wL) / P <0.05 (2)
In Formula (2), P is a lattice pitch. In each of the above-described embodiments, the diffraction grating having the grating pitch P of 100 μm has been described. However, regarding the diffraction efficiency of the design order, the relationship between the sum of the widths of the light shielding members (wH + wL) and the grating pitch P has a linear relationship. The diffraction efficiency of the design order of the diffraction grating with the sum of the width of the light shielding member (wH + wL) and the grating pitch P and the design order of the diffraction grating with the width of the light shielding member (wH + wL) × 2 and the grating pitch P × 2. It is almost the same. For example, the diffraction efficiency of the designed orders of the diffraction grating having the grating pitch of 100 μm and the light shielding member width of 2.5 μm and the diffraction pitch of 200 μm and the light shielding member width of 5.0 μm shown in the first embodiment are almost the same. It is. For this reason, the formula (2) of the sum (wH + wL) of the grating pitch P and the width of the light shielding member is obtained. Furthermore, in order to obtain a diffractive optical element that does not affect image performance, it is more preferable to satisfy the following expression (3).

0 <(wH + wL) / P <0.03 (3)
As described in the first to sixth embodiments, the width wH of the light shielding member is particularly important. When the width wH is reduced, the effect of suppressing unnecessary light is also reduced. In order to obtain a sufficient suppression effect of unnecessary light, it is preferable to satisfy the following expression (4).

0 <λ0 <wH (4)
In equation (4), λ0 is the minimum wavelength in the used wavelength band. In each of the above embodiments, the wavelength band used by the diffractive optical element is the visible range, so λ0 is 400 nm. In order to further enhance the effect of the light shielding member for reducing unnecessary light, it is more preferable to satisfy the following expression (5).

0 <2 × λ0 <wH (5)
The light shielding member in the present embodiment is particularly configured to satisfy both the expression (2) for suppressing the decrease in the diffraction efficiency of the design order and the expression (4) necessary for suppressing unnecessary light. It is preferable. The width wL is particularly insensitive to unnecessary light suppression due to total reflection. For this reason, it is preferable that the width wL is substantially 0 in order to suppress the reduction amount of the diffraction efficiency of the designed order. On the other hand, since manufacturing variations at the time of manufacturing occur, the width wL may be designed and manufactured with emphasis on the width wH without regard to the width wL. Thereby, the choice of a manufacturing method spreads, and since it can manufacture at low cost and low energy, it becomes a manufacturing advantage.

  In addition, the light shielding members of Examples 1 to 6 are formed using Al which is a metal material, but are not limited thereto, and an absorbing material for absorbing unnecessary light can be used. As the absorbent material, for example, a material in which carbon-based fine particles such as black carbon, metal compound fine particles such as metal oxides, metal sulfides, and metal carbonates, pigments, dyes, and the like are dispersed in a resin is used. It can also be realized by a structure having a similar effect by a fine structure, a carbon nanotube, or the like. In addition, it is more preferable to configure the material in accordance with the refractive index and extinction coefficient of each diffraction grating. For this reason, the thickness d1 of the light shielding member varies depending on the material constituting the light shielding member. As in Examples 1 to 6, the light shielding member made of a metal material functions sufficiently with a thickness of about several hundreds of nanometers. However, when other absorbing materials are used, the light shielding member is compared with the metal material. It needs to be thick.

  The distance d2 between the light shielding member and the diffraction grating is not particularly limited as long as unnecessary light can be shielded. However, since the width of the light shielding member increases as the distance d2 increases, it is preferable that the width is set to satisfy an expression (2) or an expression (3) for suppressing a decrease in the diffraction efficiency of the design order. In Examples 1 to 6, the two-layer DOE is used as the diffractive optical element. However, the present invention is not limited to this, and can be applied to a laminated DOE in which diffraction gratings are further laminated. Further, an optimum diffractive optical element can be configured by changing the light shielding member from the central region to the peripheral region. Moreover, it is not necessary to provide a light shielding member in all the annular zones, and they may be provided in a part of the annular zones. At this time, it is effective to provide a reflecting member in a part including the minimum lattice pitch. This is because a diffraction grating with a small grating pitch has a large diffraction efficiency of unnecessary light, and the contribution of unnecessary light generated in the entire diffractive optical element is large.

In each of the above embodiments, attention is paid to providing a light shielding member on the grating wall surface, but the design order is an order other than the + 1st order, reflecting means is provided on the grating wall surface, the grating wall angle is shifted, It can also be combined with unnecessary light control means, for example, by making the lattice wall surface into a staircase shape.
(Comparative Example 1)
Hereinafter, a diffractive optical element as a comparative example with respect to Example 1 will be described. The diffractive optical element as Comparative Example 1 is the case where the material of the diffraction grating and the grating height are the same as in Example 1, and no unnecessary light suppression means is provided on the grating wall surface.

  FIG. 21 shows RCWA calculation results at an incident angle of 0 degree, which is a designed incident angle of the diffractive optical element, a grating pitch of 100 μm, and a wavelength of 550 nm. FIG. 21A shows the diffraction efficiency in the vicinity of the + 1st order diffracted light that is the designed order. FIG. 21B is a result of enlarging the low diffraction efficiency portion of the vertical axis in FIG. 21A and displaying the high diffraction angle range with the horizontal axis as the diffraction order to the diffraction angle. FIG. 21A shows that the diffraction efficiency is concentrated on the + 1st order diffracted light that is the designed order, but the diffraction efficiency is 98.49%, not 100%. The remaining light is unnecessary light and propagates as unnecessary light having a peak in a specific angle direction as shown in FIG. Regarding this phenomenon, as shown in FIG. 22, it is considered that the component a ′ incident on the grating wall surface of the incident light beam is circulated so as to be reflected to the high refractive index material side on the grating wall surface. Since it is rare to directly photograph a high-intensity light source such as the sun during the day at this designed incident angle (photographing light incident angle), this unnecessary light has little effect and does not pose a problem as a result.

  Next, assuming a light beam incident at an oblique incident angle (off-screen light incident angle) downward from the designed incident angle of the diffractive optical element, RCWA calculation results at an incident angle of +10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm are shown in FIG. Shown in FIG. 23A shows the diffraction efficiency in the vicinity of the + 1st order diffracted light that is the designed order. FIG. 23B is a result of enlarging the low diffraction efficiency portion of the vertical axis in FIG. 23A and displaying the high diffraction angle range with the horizontal axis as the diffraction order to the diffraction angle. As shown in FIG. 23A, the diffraction efficiency of the + 1st order diffracted light, which is the designed order, is concentrated, but the diffraction efficiency is 95.62%, which is 100% because it is tilted from 0 degrees, which is the designed incident angle. It is lower. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining unnecessary light propagates as unnecessary light having a peak in a specific angle direction as shown in FIG. This unnecessary light has a peak in a direction of approximately −10 degrees, and this propagation direction is substantially equal to the exit direction in which the component of the off-screen incident angle +10 degrees light beam incident on the grating wall surface is propagated with total reflection and −10 degrees. The grating wall surface is incident at +80.6 degrees with a critical angle of 76.7 degrees or more from the high refractive index material side to the low refractive index material side, so that total reflection occurs. Further, the unnecessary light spreads from a peak in a direction of about −10 degrees to a high angle range. As shown in FIG. 24, the component b ′ incident on the grating wall surface of the incident light beam is totally reflected on the grating wall surface and propagates in the −10 degree direction, and the unnecessary light spreads in the center of the total reflection emission direction. It is thought that it is propagating.

  When a diffractive optical element is applied to the optical system, diffracted light of unnecessary light caused by off-screen light that substantially matches the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle reaches at least the image plane. With respect to the diffraction efficiency in the vicinity of the diffraction angle +0.20 degree in FIG. 24B, the diffraction efficiency at the diffraction order −45 (diffraction angle +0.38 degree) is 0.021% and the diffraction order −46 (times) from the RCWA calculation result. The diffraction efficiency at the folding angle +0.17 degrees is 0.021%.

Next, assuming a light beam incident at an oblique incident angle (off-screen light incident angle) upward from the designed incident angle of the diffractive optical element, RCWA calculation results at an incident angle of −10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm are shown in FIG. 25. FIG. 25A shows the diffraction efficiency in the vicinity of the + 1st order diffracted light that is the designed order. FIG. 25B is a result of enlarging the low diffraction efficiency portion of the vertical axis of FIG. 25A and displaying the high diffraction angle range with the horizontal axis as the diffraction order to the diffraction angle. As shown in FIG. 25 (a), the diffraction efficiency of the + 1st order diffracted light that is the designed order is concentrated, and the diffraction efficiency is 95.48%, which is inclined from 0 degree that is the designed incident angle. ing. The remaining unnecessary light is propagated as unnecessary light having a peak in a specific angle direction, as shown in FIG. This unnecessary light has small peaks in the direction of about −15 degrees and the direction of about +10 degrees, and the propagation direction is the off-screen incident angle incident on the grating wall surface −the emission direction of the transmitted light of the light flux of −10 degrees. It is approximately equal to 6 degrees and the emission direction of reflected light +9.5 degrees. Further, since the grating wall surface is incident at +80 degrees from the low refractive index material side to the high refractive index material side, the transmittance of the transmitted light is 94% and the reflected light of the reflected light is 6%. This corresponds to a large peak in the direction of 15 degrees and a small peak in the direction of approximately +10 degrees. Further, this unnecessary light spreads from the peak to a high angle range. As shown in FIG. 26, the component c ′ incident on the grating wall surface of the incident light beam propagates separately on the grating wall surface into transmitted light and reflected light, and further propagates spreading around each peak. it is conceivable that.
When a diffractive optical element is applied to the optical system, diffracted light of unnecessary light caused by off-screen light that substantially matches the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle reaches at least the image plane. With respect to the diffraction efficiency in the vicinity of the diffraction angle +0.20 degree in FIG. 25B, the diffraction efficiency of the diffraction order +48 (diffraction angle +0.24 degree) is 0.0015% and the diffraction order +47 (diffraction angle +0). (.03 degree) diffraction efficiency is 0.0015%.

  As described above, in the optical system to which the diffractive optical element as the comparative example 1 is applied, when a light beam having an off-screen incident angle of approximately 10 degrees is incident, the diffraction angle by the m grating shown in FIGS. The unnecessary light emitted is large, and the unnecessary light emitted near the diffraction angle of 0 ° by the m ′ grating is small. For this reason, the contribution of the m-lattice is large for the decrease in image performance. When a diffractive optical element and an optical system were actually created and photographed, unnecessary light reached the image plane, and it was confirmed that image performance was degraded.

In the conventional method, a light beam incident on the grating wall surface is treated as a geometrical optical phenomenon. In this case, light incident on the grating wall surface is emitted and propagated only in a specific direction according to Snell's law. When a diffractive optical element is applied to the optical system as shown in FIGS. 2 and 27 and a light beam with an off-screen incident angle of approximately 10 degrees is incident, only total reflection is achieved with the m grating, and 94% transmitted light and 6 with the m ′ grating. % Of reflected light is generated. However, in either case, since the light is shielded by the diaphragm 40, it does not reach the image plane 41. As described above, the conventional method is insufficient for suppressing unnecessary light, and the unnecessary light to be suppressed has not been sufficiently considered.
(Comparative Example 2)
Hereinafter, a diffractive optical element as a comparative example for Examples 2 to 6 will be described. The diffractive optical element as Comparative Example 2 is the case where the material of the diffraction grating and the grating height are the same as those in Examples 2 to 6, and no unnecessary light suppression means is provided on the grating wall surface.

  FIG. 28A shows an RCWA calculation result at an incident angle of 0 degree, which is a designed incident angle of the diffractive optical element, a grating pitch of 100 μm, and a wavelength of 550 nm. Similar to Comparative Example 1, the diffraction efficiency is concentrated on the + 1st order diffracted light that is the designed order, and the diffraction efficiency is 98.76%, not 100%. However, since it is rare to directly photograph a high-intensity light source such as the sun during the day at this designed incident angle (photographing light incident angle), this unnecessary light has little influence and does not cause a problem as a result.

  Next, assuming a light beam incident at an oblique incident angle (off-screen light incident angle) downward from the designed incident angle of the diffractive optical element, RCWA calculation results at an incident angle of +10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm are shown in FIG. Shown in (b). The diffraction efficiency of the + 1st order diffracted light that is the designed order is concentrated, but the diffraction efficiency is 97.15%, which is lower than 100% because it is tilted from 0 degree that is the designed incident angle. Since the + 1st-order diffracted light with this off-screen light incident angle never reaches the image plane, its influence is small. The remaining unnecessary light has a peak in the direction of about −10 degrees as in Comparative Example 1. This propagation direction is substantially the same as the emission direction minus 10 degrees direction in which the off-screen incident angle incident on the grating wall surface +10 degrees of the luminous flux component is totally reflected and propagated. The grating wall surface is incident at +80.6 degrees with a critical angle of 74.2 degrees or more from the high refractive index material side to the low refractive index material side, and thus total reflection occurs. Further, the unnecessary light spreads from a peak in a direction of about −10 degrees to a high angle range. When a diffractive optical element is applied to the optical system, diffracted light of unnecessary light caused by off-screen light that substantially matches the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle reaches at least the image plane. As for the diffraction efficiency in the vicinity of the diffraction angle +0.20 degree in FIG. 28B, the diffraction efficiency at the diffraction order −46 (diffraction angle +0.34 degree) is 0.014% and the diffraction order −47 (times) from the RCWA calculation result. The diffraction efficiency (fold angle +0.14 degrees) is 0.014%.

  Next, assuming a light beam incident at an oblique incident angle (off-screen light incident angle) upward from the designed incident angle of the diffractive optical element, RCWA calculation results at an incident angle of −10 degrees, a grating pitch of 100 μm, and a wavelength of 550 nm are shown in FIG. It is shown in 28 (c). The diffraction efficiency of the + 1st order diffracted light that is the designed order is concentrated, and the diffraction efficiency is 97.00%, which is tilted from 0 degree that is the designed incident angle, and is lower than 100%. The remaining unnecessary light has a peak in the direction of about −17 degrees and the direction of about +10 degrees as in Comparative Example 1, and this propagation direction is the off-screen incident angle incident on the grating wall surface of the light beam of −10 degrees. The emission direction is −18.6 degrees and is substantially equal to the reflected light emission direction +9.5 degrees. As shown in FIG. 26, the component c ′ incident on the grating wall surface of the incident light beam propagates separately on the grating wall surface into transmitted light and reflected light, and further propagates spreading around each peak. it is conceivable that. When a diffractive optical element is applied to the optical system, diffracted light of unnecessary light caused by off-screen light that substantially matches the diffraction angle +0.20 degrees at which the designed diffraction order propagates at the designed incident angle reaches at least the image plane. As for the diffraction efficiency in the vicinity of the diffraction angle +0.20 degree in FIG. 28C, the diffraction efficiency of the diffraction order +49 (diffraction angle +0.26 degree) is 0.0022% and the diffraction order +48 (diffraction angle +0) from the RCWA calculation result. .06 degrees) is 0.0022%.

  As described above, in the optical system to which the diffractive optical element as Comparative Example 2 is applied, when a light beam having an off-screen incident angle of approximately 10 degrees is incident, the diffraction angle by the m grating shown in FIGS. The unnecessary light emitted is large, and the unnecessary light emitted near the diffraction angle of 0 ° by the m ′ grating is small. For this reason, the contribution of the m-lattice is large for the decrease in image performance. When a diffractive optical element and an optical system were actually created and photographed, unnecessary light reached the image plane, and it was confirmed that image performance was degraded.

  Next, a seventh embodiment of the present invention will be described. FIG. 20 is a schematic cross-sectional view of the photographing optical system (optical system). In FIG. 20, reference numeral 101 denotes a photographic lens, which includes the diffractive optical element 1 of each of the embodiments described above, a diaphragm 40 disposed on the rear side of the diffractive optical element 1, and a refractive optical unit 42. Reference numeral 41 denotes an image forming surface such as a film or a CCD as an image forming surface. In particular, the center of the diffraction grating portion is centered on the surface normal at the center of the envelope diffraction grating where the center of gravity of the incident angle distribution of the light beam incident on each diffraction grating portion of the diffractive optical element 1 is the same as the center of gravity of the envelope. More distributed. If the diffractive optical element of this embodiment is applied to such an optical system, the generation of unnecessary light is greatly improved even when a light beam is incident on the grating wall surface, so that high performance and high resolving power are achieved. A photographic lens is obtained. In addition, since the diffractive optical element of each example can be easily manufactured, an inexpensive optical system excellent in mass productivity can be provided.

  In FIG. 20, the diffractive optical element 1 is provided on the surface of the lens of the front lens. However, the present invention is not limited to this. The diffractive optical element 1 may be provided on the lens surface, and a plurality of diffractive optical elements are provided in the photographing lens. It may be used. In the present embodiment, the case of a photographing lens of a camera as an optical device has been shown, but the present invention is not limited to this. The optical system of the present embodiment can also be applied to imaging optical systems (optical devices) used in a wide wavelength region such as a video camera photographing lens, an office image scanner, and a digital copying machine reader lens.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

1: diffractive optical element 2, 3: substrate 10: diffraction grating portion 11: first diffraction grating 12: second diffraction grating 11a, 12a, 1a: grating surfaces 11b, 12b, 1b: grating wall surface 20, 50: light shielding Element

Claims (9)

Have different refractive indices, a diffractive optical element comprising a first 及 beauty second diffraction grating which are arranged in contact each of the grating surface and the grating wall surface of each other,
A plurality of light shielding members provided for each of the lattice wall surfaces;
In the cross section including an optical axis, wL a distance between an end of the closer to the optical axis extension line and the shielding member of the grid wall, and the other end portion of said light blocking member and an extension of the grating wall surface when the distance of wH, said first and second grating pitch of the diffraction grating P, and the minimum wavelength in the used wavelength band .lambda.0, that,
wH> wL ≧ 0
0 <(wH + wL) / P <0.05
0 <λ0 <wH
A diffractive optical element characterized by satisfying the following condition.   The diffractive optical element according to claim 1, wherein the light shielding member reduces total reflected light generated at a boundary between the first diffraction grating and the second diffraction grating.   3. The diffractive optical element according to claim 1, wherein each of the grating surface, the grating wall surface, and the light shielding member is disposed concentrically around the optical axis. 4. The diffractive optical element according to claim 1, wherein the light shielding member is disposed inside the first or second diffraction grating. 5.   The said light-shielding member is arrange | positioned in the boundary of a said 1st diffraction grating and a said 2nd diffraction grating so that the said grating surface and the said grating | lattice wall surface may be touched. 2. A diffractive optical element according to item 1. wL = 0
The diffractive optical element according to claim 1, wherein: Optical system, wherein the diffractive optical element, a refractive optical unit, that has a according to any one of claims 1 to 6. A diffractive optical element according to any one of claims 1 to 6, the optical system characterized by having a a diaphragm which is disposed on the rear side of the diffractive optical element. An optical apparatus comprising the optical system according to claim 7 or 8 .