Diffractive optical element, optical system, imaging device, and display device

Abstract

To provide a diffraction optical element that has high optical performance, is small-sized, and has excellent moldability.SOLUTION: A diffraction optical element has an orbicular zone area in which a plurality of concentrically arranged orbicular zones are formed. At least one of the plurality of orbicular zones is an orbicular zone, the whole circumference of which is partially cut off. When the shortest distance from the center of the plurality of orbicular zones to the outer periphery of the orbicular zone area is defined as Rdc (mm), the radius of an orbicular zone most distant from the center of the plurality of orbicular zones as Re (mm), and the minimum value of an arrangement pitch of the diffraction optical element as Pmin (μm), a conditional expression of 6<Pmin×Rdc / Re<65 is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a diffractive optical element, an optical system, an imaging device, and a display device. [Background technology]

[0002] Patent Document 1 discloses a diffractive optical element having high diffraction efficiency across the entire visible spectrum by stacking diffraction gratings made of two different materials. Patent Document 2 discloses a diffractive optical element with improved diffraction efficiency by closely forming a diffraction grating made of another material on a diffraction grating made of an injection-molded material. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2009-217139 [Patent Document 2] International Publication No. 2010 / 032347 [Overview of the project] [Problems that the invention aims to solve]

[0004] The diffractive optical element disclosed in Patent Document 1 is costly because it requires multiple molding steps to form a diffraction grating on a substrate using a mold. The diffractive optical element disclosed in Patent Document 2 can be formed at low cost, but if a so-called D-cut shape is adopted, in which a portion of the lens is cut off for miniaturization, defects during molding are more likely to occur.

[0005] Therefore, the present invention aims to provide a diffractive optical element that has high optical performance, is compact, and has excellent moldability. [Means for solving the problem]

[0006] One aspect of the present invention is a diffractive optical element having a diffraction region including a plurality of annular bands arranged concentrically, wherein at least one of the plurality of annular bands isA ring with a portion missing from its entire circumference. where the shortest distance from the center of the plurality of annular bands to the outer periphery of the diffraction region is Rdc (mm), the radius of the annular band farthest from the center among the plurality of annular bands is Re (mm), and the minimum value of the arrangement pitch of the plurality of annular bands is Pmin (μm). The radius of the ring band among the plurality of ring bands whose arrangement pitch is the minimum value Pmin is RPm (mm). When 6 < Pmin × Rdc / Re < 65 0.70 <Rdc / RPm<1.50 the conditional expression is satisfied.

[0007] Other objects and features of the present invention will be described in the following examples.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a diffractive optical element having high optical performance, being small-sized, and having excellent formability.

Brief Description of the Drawings

[0009] [Figure 1] Front views and side views of the diffractive optical elements in Examples 1 to 4. [Figure 2] Partial cross-sectional views of the diffractive optical elements in Examples 1 to 4. [Figure 3] A diagram showing the relationship between the diffraction efficiency and wavelength in Example 1. [Figure 4] A schematic diagram of the outer shape of the diffractive optical element in Example 1. [Figure 5] [[ID=4D]]A diagram showing the outer shape of the diffractive optical element in Example 1. [Figure 6] An explanatory diagram of the phase shape of the diffractive optical element in Example 1.<000009D> [Figure 7] A diagram showing the relationship between the diffraction efficiency and wavelength in Example 2. [Figure 8] A diagram showing the outer shape of the diffractive optical element in Example 2. [Figure 9] An explanatory diagram of the phase shape of the diffractive optical element in Example 2. [Figure 10] A diagram showing the relationship between the diffraction efficiency and wavelength in Example 3. [Figure 11] This figure shows the external shape of the diffractive optical element in Example 3. [Figure 12] This is an explanatory diagram of the phase shape of the diffractive optical element in Example 3. [Figure 13] This figure shows the relationship between diffraction efficiency and wavelength in Example 4. [Figure 14] This figure shows the external shape of the diffractive optical element in Example 4. [Figure 15] This is an explanatory diagram regarding the phase shape of the diffractive optical element in Example 4. [Figure 16] This is a diagram showing the configuration of an optical system equipped with a diffractive optical element in each embodiment. [Figure 17] These are schematic diagrams of imaging devices equipped with diffractive optical elements in each embodiment. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Examples]

[0011] First, the diffractive optical element 1 in Embodiment 1 of the present invention will be described with reference to Figures 1(a), (b) and 2. Figure 1(a) is a front view of the diffractive optical element 1. Figure 1(b) is a side view of the diffractive optical element 1. Figure 2 is a partial cross-sectional view of the diffractive optical element 1 when it is cut along the line A-A' in Figure 1. However, Figure 2 is a distorted view in the direction of the lattice depth.

[0012] The diffractive optical element 1 has a second element portion 3 that has sufficient thickness and optical power on the optical axis O and a first element portion 2 that is thin, which are arranged in close contact with each other, and a diffraction grating is formed between the first element portion 2 and the second element portion 3. The diffractive optical element 1 has a first diffraction grating 8 made of a first material and a second diffraction grating 9 made of a second material different from the first material. The first diffraction grating 8 and the second diffraction grating 9 are stacked in close contact with each other via grating surfaces (grating slopes and grating walls).

[0013] As shown in Figure 2, the first element portion 2 has a first lattice forming layer consisting of a lattice base portion 6 and a first diffraction grating 8 integrally formed with the lattice base portion 6. The second element portion 3, similar to the first element portion 2, has a second lattice forming layer consisting of a lattice base portion 7 and a second diffraction grating 9 integrally formed with the lattice base portion 7. The first diffraction grating 8 and the second diffraction grating 9 are stacked with the lattice slope (diffraction slope) 8a of the first diffraction grating 8 and the lattice slope (diffraction slope) 9a of the second diffraction grating 9 in close contact, and the lattice wall surface 8b of the first diffraction grating 8 and the lattice wall surface 9b of the second diffraction grating 9 in close contact. In this embodiment, the first element portion 2 and the second element portion as a whole function as one diffractive optical element 1.

[0014] The first diffraction grating 8 and the second diffraction grating 9 each have a concentric (rotationally symmetric) grating shape, and the lens effect is achieved by changing the arrangement pitch in the radial direction. That is, the diffractive optical element 1 has multiple annular regions with different arrangement pitches in the radial direction. Also, as shown in Figure 1(a), in the diffractive optical element 1 of this embodiment, the annular region (Diffraction region) This includes rings that are not missing from the entire circumference (circular) and rings that are missing from the entire circumference (part of a circle). (Non-circular) It has ring bands and an outer diameter shape that is a so-called D-cut shape. In this embodiment, concentricity includes the case where, with respect to the ring band that is missing a portion of its circumference, the center of the circle formed by its extension coincides with the center of the other ring band that is not missing. Furthermore, rotational symmetry includes the case where, with respect to the ring band that is missing a portion of its circumference, the circle formed by its extension is rotationally symmetrical.

[0015] Furthermore, the diffractive optical element 1 has an outer peripheral region 11 where no diffraction grating is formed outside the region with a radius Re from the optical axis O (center of the annulus). The outer peripheral region 11 is integrally molded when the second diffraction grating 9 is formed. In this embodiment, the wavelength range of light incident on the diffractive optical element 1, i.e., the usable wavelength range, is the visible region, and the materials and grating thicknesses constituting the first diffraction grating 8 and the second diffraction grating 9 are selected to maximize the diffraction efficiency of the first-order diffracted light throughout the entire visible region.

[0016] Next, the specific configuration of the diffractive optical element 1 will be described. In the diffractive optical element 1 of this embodiment, the first material forming the first diffraction grating 8 is an episulfide resin (Nd=1.6731, νd=36.4, θgF=0.584). The second material forming the second diffraction grating 9 is a polycarbonate thermoplastic resin (Nd=1.6160, νd=25.8, θgF=0.623).

[0017] In this embodiment, the definitions of the Abbe number νd and the partial dispersion ratio θgF with respect to the d line are the same as those generally used. When the refractive indices for the Fraunhofer lines g, F, d, and C are Ng, NF, Nd, and NC, respectively, the Abbe number νd and the partial dispersion ratio θgF are expressed by the following equations (a) and (b).

[0018] νd=(Nd-1) / (NF-NC) ···(a) θgF=(Ng-NF) / (NF-NC) ···(b) The 2 Element part (lens part) 3 The thickness on the optical axis O is 3.5 mm, and the outer diameter is 43 mm. 1 Element part (lens part) 2 The thickness on the optical axis O is 0.15 mm. 1 Element part (lens part) 2 The interface with the first element portion (lens portion 2) and the central radius of curvature of the air-facing surface of the second element portion 3 are approximately the same.

[0019] The phase shape P of each diffraction surface of the diffracting optical element in each numerical example is expressed by the following equation (c).

[0020] P(h) = (2π / mλ0)(C2h) 2 +C4h 4 +C6h 6 …) ···(c) Here, h is the height perpendicular to the optical axis O. m: diffraction order of diffracted light λ0: Design wavelength Ci: Phase coefficient (i=2,4,6…) That is the case.

[0021] Similarly, the optical path difference function Ψ of the diffraction plane is expressed by the following equation (d).

[0022] Ψ(h)=C2h 2 +C4h 4 +C6h 6 … ···(d) Furthermore, the power φd at the grating plane of a diffraction grating for any wavelength λ and any diffraction order m can be expressed by the following equation (e) using the lowest-order phase coefficient C2. φd = -2C2mλ / λ0···(e) Furthermore, the focal length fd at the grating plane of the diffraction grating is expressed by the following equation (f).

[0023] fd = 1 / φd ···(f) In each numerical example, the diffraction order m of each diffraction grating constituting the diffractive optical element is 1, and the design wavelength λ0 is the wavelength of the d line (587.56 nm) in all cases.

[0024] The phase coefficients of the diffractive optical element 1 in this embodiment are C2=-9.271E-04, C4=1.051E-06, and C6=-1.382E-09. The focal length fd at the diffraction plane is 539 mm, and the radius Re of the outermost annulus is 19.40 mm. Here, the notation "E±Z" is "10 ±Z It means "...".

[0025] The diffractive optical element 1 of this embodiment aims to have a configuration that can be manufactured at low cost. Therefore, it is preferable to form the second element portion 3, which has a second diffraction grating 9 with a large wall thickness, by integral molding using a mold. Specifically, by using a thermoplastic material to form the second diffraction grating 9 and forming the second element portion 3 using an injection mold, the lens shape of the second diffraction grating 9 and the second element portion 3 can be obtained with high precision. After forming the second element portion 3 having a diffraction slope 9a, a diffractive optical element 1 can be obtained by applying another resin material onto the diffraction slope 9a and curing it, thereby closely laminating the first element portion 2 having a first diffraction grating 8. In this case, by using an ultraviolet-curing resin or the like as the material to form the first diffraction grating 8, it becomes easier to obtain a diffractive optical element whose shape after curing is a desired grating shape.

[0026] Next, referring to Figure 2, the relationship between the phase difference and diffraction efficiency of the diffractive optical element 1 in this embodiment will be described. In the diffractive optical element 1, for a wavelength λ, the condition for maximizing the diffraction efficiency of diffracted light of diffraction order m is that the optical path length difference Φ(λ) satisfies the following equation (g).

[0027] Φ(λ)=―(n02-n01)×d1=mλ ···(g) Here, in equation (g), n02 is the refractive index of the material forming the second diffraction grating 9 for light of wavelength λ, and similarly, n01 is the refractive index of the material forming the first diffraction grating 8 for light of wavelength λ. d1 is the grating height (grating thickness) of the first diffraction grating 8 and the second diffraction grating 9.

[0028] In Figure 2, the diffraction order of light diffracted downward from the zero-order diffracted light is denoted as the negative diffraction order, and the diffraction order of light diffracted upward from the zero-order diffracted light is denoted as the positive diffraction order. In this case, for a diffraction grating with a grating shape in which the grating thickness of the incident first diffraction grating 8 increases from bottom to top in Figure 3, as shown in Figure 2, the sign of the grating height d1 in equation (g) is positive.

[0029] Furthermore, the diffraction efficiency η(λ) at any wavelength λ is expressed by the following equation (h).

[0030] η(λ)=sinc 2 [π{m-Φ(λ) / λ}] ···(h) In equation (h), m is the order of the diffracted light to be evaluated, and Φ(λ) is the optical path length difference in one unit cell of the diffractive optical element for light of wavelength λ. Also, sinc(x) is a function expressed as {sin(x) / x}. Furthermore, the design wavelength λd of the diffractive optical element 1 in this embodiment is 587.56 nm. The same applies to the following embodiments. Here, the design wavelength is a value near the average value of the wavelengths used by the diffractive optical element, and specifically, when the average value of the wavelengths used is λave(nm), it is the wavelength range expressed by the following equation (1).

[0031] 0.9 < λd / λave < 1.1 ... (1) The diffractive optical element 1 in this embodiment is used in the visible range, with wavelengths of 400 nm to 700 nm and a λave of 550 nm. In the diffractive optical element 1 shown in Figure 2, the diffraction efficiency is highest in the visible wavelength range when the minimum array pitch Pmin = 100 μm and the lattice height d1 = 10.01 μm.

[0032] The grating wall 8b of the first diffraction grating 8 does not need to be perpendicular to the envelope formed by connecting the vertices of the first diffraction grating 8, and can be angled according to the angle of incidence of the light ray. As shown in Figure 2, when the grating wall 8b is angled with respect to the envelope formed by connecting the vertices of the first diffraction grating 8, the distance between the envelope formed by connecting the vertices of the first diffraction grating 8 and the grating vertices is d1t.

[0033] In this embodiment, the first diffraction grating 8 and the second diffraction grating 9 are formed from different materials. For example, the second diffraction grating 9 is made of a low refractive index, high dispersion material, and the first diffraction grating 8 is made of a high refractive index, low dispersion material having a higher refractive index. Preferably, a high diffraction efficiency can be obtained by satisfying the following condition (2).

[0034] 1.0<(N1-N2) / (1 / ν2-1 / ν1)<20.0 ···(2) However, the refractive indices of the materials constituting the first diffraction grating 8 and the second diffraction grating 9 in the d-line are N1 and N2, respectively, and the Abbe numbers of the materials constituting diffraction gratings 8 and 9 with respect to the d-line are ν1 and ν2.

[0035] More preferably, the numerical range of condition (2) is set as shown in condition (2a) below.

[0036] 1.2<(N1-N2) / (1 / ν2-1 / ν1)<18.0 (2a) More preferably, the numerical range of condition (2) is set as shown in condition (2b) below.

[0037] 1.5<(N1-N2) / (1 / ν2-1 / ν1)<15.0 (2b) Figure 3 shows the diffraction efficiency of the diffractive optical element 1 of this embodiment in an annular band with a minimum array pitch of 21.0 μm and a lattice height d1 = 10.42 μm. In Figure 3, the horizontal axis represents wavelength (nm), and the vertical axis represents diffraction efficiency (%). At this time, the angle of the envelope formed by connecting the vertices of the diffraction grating on the lattice wall surface with respect to the perpendicular is 5.4 degrees, and d1t = 9.96 μm. As shown in Figure 3, by adopting a configuration that satisfies equation (2), high diffraction efficiency is obtained over a wide wavelength range in the visible region.

[0038] Next, we will describe the D-cut shape adopted in the diffractive optical element 1 of this embodiment. For example, when using the diffractive optical element 1 in a binocular optical system (observation optical system), widening the field of view of the optical system increases the outer diameter of the lens. However, in the case of a binocular observation optical system, the interpupillary distance must be kept constant, so the space between the binocular lenses becomes smaller. Since components such as nose pads must also be placed between the binocular lenses, it is necessary to secure space by cutting a part of the lens.

[0039] However, when a concentric diffraction grating like the diffractive optical element 1 in this embodiment is formed, if a shape like that of a lens with a part cut out is adopted, the annular structure of the diffraction grating will be interrupted midway. In this embodiment, even if the annular structure is interrupted midway by a D-cut shape or the like, it is defined as an annular structure if it has a concentric circular structure.

[0040] As mentioned above, in order to achieve a low-cost configuration, the diffractive optical element 1 of this embodiment is manufactured by injection molding using a large-volume second diffraction grating 9. In this process, in the annular band where a portion of the entire circumference is missing (the part where the annular band is interrupted midway (D-cut section)), the continuity of the grating shape is interrupted, making it difficult to form the desired shape due to stress concentration during molding.

[0041] Furthermore, when forming the second diffraction grating 9 by injection molding, it is important for molding to create a structure that facilitates demolding by having an outer region without a diffraction grating outside the region with annular bands. In this case, the mold structure can be simplified by creating a step between the D-cut portion and the region outside it, but if there is a step in the D-cut portion, resin stagnation and other issues may occur during molding, making it easier for stress concentration to occur during molding. In particular, a narrower arrangement pitch makes molding more difficult, which is undesirable.

[0042] In this embodiment, the diffractive optical element 1 is formed by coating and curing a first diffraction grating 8 on a second diffraction grating 9. Therefore, if the spacing between adjacent annular bands in the D-cut portion becomes narrow, stress concentration increases near the annular bands, making delamination between the first diffraction grating 8 and the second diffraction grating 9 more likely.

[0043] Figures 4(a) and 4(b) are schematic diagrams showing variations in the width of the D-cut portion from the center of the annular band (optical axis O). The diffractive optical element in Figure 4(b) has a shorter shortest distance Rdc from the center to the outer circumference of the annular region than the diffractive optical element in Figure 4(a). In configurations with a shorter shortest distance Rdc, the distance Pout between the annular band ends at the point where the annular band is interrupted (D-cut portion) is narrower in the configuration of Figure 4(b) than in the configuration of Figure 4(a). As a result, stress concentration is more likely to occur during molding, making the moldability difficult.

[0044] Figure 5(a) shows the range of the outer shape of the region having an annular band in this embodiment. Figure 5(b) shows the distance (radius R) from the center of the outer shape in Figure 5(a) as a function of the angle θ with respect to the optical axis. In Figure 5(b), the horizontal axis represents the angle θ (deg) and the vertical axis represents the radius R (mm). As shown in Figures 5(a) and 5(b), the diffractive optical element of this embodiment achieves miniaturization of the optical system by shortening the distance from the center of the annular band to the outer shape near θ=0 degrees. Specifically, the shortest distance Rdc is set to 17.0 mm.

[0045] Based on the above, the diffractive optical element of this embodiment has an annular region in which multiple rotationally symmetric (concentric) annular bands are formed. The diffractive optical element also has an annular region that includes annular bands that are not missing around their entire circumference and annular bands that are missing around their entire circumference, and has an outer diameter shape of a so-called D-cut portion. When the shortest distance from the center of the annular band to the outer circumference of the annular region is Rdc (mm), the radius of the annular band furthest from the center among the multiple annular bands is Re (mm), and the minimum value of the array pitch of the diffractive optical element 1 is Pmin (μm), the following condition (3) is satisfied.

[0046] 6 <Pmin×Rdc / Re<65 ···(3) Here, the shortest distance Rdc refers to the distance between the envelope formed by connecting the annular ends where the annular band is interrupted in the non-rotationally symmetric outer shape, and the center (the rotation center of the annular band). In other words, the shortest distance Rdc is the distance from the center to the annular band that is furthest from the center among multiple annular bands that do not have any missing parts around their entire circumference. By appropriately setting the minimum value of the array pitch Pmin and the distance from the center of the annular band in the D-cut section so as to satisfy condition (3), a high chromatic aberration correction effect can be obtained by widening the spacing Pout between the annular band ends to maintain moldability while having an appropriate diffraction pitch.

[0047] If the value falls below the lower limit of condition (3), the spacing Pout between the annular ends in the D-cut section becomes narrower, resulting in reduced moldability. On the other hand, if the value exceeds the upper limit of condition (3), the width of the distance Rdc becomes larger, making it difficult to miniaturize the optical system, or the diffraction pitch (minimum value of the array pitch) becomes larger, resulting in insufficient chromatic aberration correction effect of the optical system.

[0048] More preferably, the numerical range of condition (3) is set as shown in condition (3a) below.

[0049] 9 <Pmin×Rdc / Re<55 ···(3a) More preferably, the numerical range of condition (3) is set as shown in condition (3b) below.

[0050] 11 <Pmin×Rdc / Re<45 ···(3b) Furthermore, in this embodiment, it is preferable that the following condition (4) is satisfied.

[0051] 0.50 <Rdc / Re<0.95 ···(4) If the value falls below the lower limit of condition (4), the spacing Pout between the annular ends in the D-cut section becomes narrower, which reduces moldability and is therefore undesirable. On the other hand, if the value exceeds the upper limit of condition (4), the width of the distance Rdc becomes larger, which makes it difficult to miniaturize the optical system and is therefore undesirable.

[0052] More preferably, the numerical range of the conditional expression (4) is set as in the following conditional expression (4a).

[0053] 0.70 < Rdc / Re < 0.92 ···(4a) Even more preferably, the numerical range of the conditional expression (4) is set as in the following conditional expression (4b).

[0054] 0.60 < Rdc / Re < 0.90 ···(4b) In the diffractive optical element 1, a configuration in which the array pitch decreases from the central portion of the optical axis toward the peripheral portion is common. Therefore, by relatively weakening the power of the peripheral portion compared to the power of the central portion of the optical axis, the interval Pout between the annular ends in the D-cut portion can be widened. Here, when the radius of the first annular zone counted from the optical axis O (center of the annular zone) is R1 (mm) and the radius of the second annular zone counted from the optical axis O is R2 (mm), it is preferable to satisfy the following conditional expression (5).

[0055] 0.8 < 1000×(R2 2 -R1 2 ) / (Re×Pmin) < 2.4 ···(5) In the conditional expression (5), (R2 2 -R1 2 ) / (2×Re) indicates the minimum value (mm) of the array pitch in the peripheral portion when the power of the central portion of the optical axis (paraxial power) is extended. That is, the conditional expression (5) indicates the ratio between the minimum value of the array pitch in the peripheral portion when the power of the optical axis O (center) is extended and the actual minimum value of the array pitch. If the upper limit value of the conditional expression (5) is exceeded, the minimum value of the array pitch in the peripheral portion becomes small, and the formability in the D-cut portion deteriorates, which is not preferable. On the other hand, if the lower limit value of the conditional expression (5) is not reached, the minimum value of the array pitch becomes wide, and a sufficient chromatic aberration correction effect cannot be obtained as an optical system, which is not preferable.

[0056] More preferably, the numerical range of the conditional expression (5) is set as in the following conditional expression (5a). 1.1 < 1000×(R2 2 -R1 2) / (Re×Pmin)<2.3 ···(5a) More preferably, the numerical range of condition (5) is set as shown in condition (5b) below. 1.3 < 1000 × (R2 2 -R1 2 ) / (Re×Pmin)<2.2 ···(5b) Furthermore, when the design wavelength of the diffractive optical element 1 is λ0 (μm) and the focal length at the diffraction plane is fd (mm), it is preferable that the following condition (6) is satisfied. By satisfying condition (6), the same effect as described in condition (5) can be obtained.

[0057] 0.40 <fd×λ0 / (Re×Pmin)<1.20 ···(6) If the upper limit of condition (6) is exceeded, the minimum value of the array pitch in the peripheral area becomes smaller, and the moldability of the D-cut portion decreases, which is undesirable. On the other hand, if the lower limit of condition (6) is exceeded, the minimum value of the array pitch becomes wider, and a sufficient chromatic aberration correction effect cannot be obtained as an optical system, which is also undesirable.

[0058] More preferably, the numerical range of condition (6) is set as shown in condition (6a) below.

[0059] 0.55 <fd×λ0 / (Re×Pmin)<1.15 ···(6a) More preferably, the numerical range of condition (6) is set as shown in condition (6b) below.

[0060] 0.65 <fd×λ0 / (Re×Pmin)<1.10 ···(6b) Furthermore, in the diffractive optical element of this embodiment, the distance perpendicular to the optical axis O is h (mm), and the second derivative of the optical path difference function Ψ of the diffracted surface with respect to distance h, as shown in equation (d) above, is Ψ²(h). In this case, by having a region that satisfies the following condition (7), the minimum value of the array pitch can be controlled even more effectively.

[0061] -5.0<(Ψ2(h)-2 ×C2) / C2<-0.5 ···(7) Here, C2 is the second-order phase coefficient. (Ψ2(h)-2) is the h of the second derivative of the optical path difference function Ψ(h). 4 This refers to the higher-order components mentioned above. Note that Ψ2(h) is given by the following equation.

[0062] Ψ²(h)=2 ×C 2 + 12 × C4h 2 +30×C6h 4 … ···(i) As shown in equation (i) and conditional equation (7), there are no higher-order phase coefficients C4, C6··, and paraxial h 2 In the case of a diffractive optical element composed only of a phase coefficient C2, the value of condition (7) is fixed at 0. If the value of condition (7) is negative, it means that the power is reduced in the peripheral region of the diffractive optical element 1 compared to the paraxial region, i.e., the pitch is widened.

[0063] Figure 6 is an explanatory diagram of the phase shape of the diffractive optical element in this embodiment, and shows the value of conditional equation (7) for the distance h perpendicular to the optical axis O. In Figure 6, the horizontal axis is the distance h (mm), and the vertical axis is (Ψ2(h)-2×C 2 ) / C The two values ​​are shown below. As shown in Figure 6, the pitch width in the D-cut section can be appropriately adjusted by having a region that satisfies the value of condition (7).

[0064] More preferably, the numerical range of condition (7) is set as shown in condition (7a) below.

[0065] -4.5<(Ψ2(h)-2 ×C 2) / C2<-0.6 ···(7a) More preferably, the numerical range of condition (7) is set as shown in condition (7b) below.

[0066] -4.0<(Ψ2(h)-2 ×C 2) / C2<-0.7 ···(7b) As described above, the diffractive optical element of this embodiment achieves high diffraction efficiency across the entire visible spectrum by stacking diffraction gratings made of two different materials. However, in the case of a diffractive optical element using two different materials, the grating height becomes several times higher than that of a single-layer diffraction grating, resulting in a configuration that is disadvantageous in terms of molding and demolding.

[0067] Therefore, in order to improve the moldability in the D-cut section, it is necessary to appropriately set the relationship between the grating height and pitch of the diffraction grating. When the minimum value of the array pitch of the diffractive optical elements is Pmin (μm) and the grating height in the annulus having the minimum value Pmin is Dm (μm), it is preferable to satisfy the following condition (8).

[0068] 0.05 <Dm / Pmin<1.00 ···(8) In condition (8), the grating height Dm corresponds to the distance d1t between the envelope of the vertices of the diffraction grating and the grating vertices, as shown in Figure 2, when the grating wall is angled with respect to the envelope of the vertices of the diffraction grating. Exceeding the upper limit of condition (8) is undesirable because the ratio of grating height to pitch becomes high, making moldability difficult. On the other hand, falling below the lower limit of condition (8) is undesirable because the minimum value of the array pitch becomes wide, making it impossible to obtain sufficient chromatic aberration correction effect as an optical system, or the grating height becomes low, making it difficult to obtain good diffraction efficiency.

[0069] More preferably, the numerical range of condition (8) is set as shown in condition (8a) below.

[0070] 0.07 <Dm / Pmin<0.80 ···(8a) More preferably, the numerical range of condition (8) is set as shown in condition (8b) below.

[0071] 0.10 <Dm / Pmin<0.70 ···(8b) Furthermore, by bringing the shortest distance Rdc (mm) from the center of the ring strip closer to the radius RPm (mm) of the ring strip having the minimum array pitch, the spacing Pout at the ends of the ring strips in the D-cut section can be widened. In this case, it is preferable that the following condition (9) is satisfied.

[0072] 0.70 <Rdc / RPm<1.50 ···(9) More preferably, the numerical range of condition (9) is set as shown in condition (9a) below.

[0073] 0.72 <Rdc / RPm<1.40 ···(9a) More preferably, the numerical range of condition expression (9) is set as shown in condition expression (9b) below.

[0074] 0.75 <Rdc / RPm<1.30 ···(9b) In the diffractive optical element of this embodiment, the minimum distance Poutm between the annular ends in the D-cut portion is 84.2 μm. That is, by appropriately setting the shape of the D-cut portion and the pitch of the diffractive optical element 1, the minimum distance Poutm between the annular ends in the D-cut portion can be increased, resulting in a configuration with excellent moldability.

[0075] In the diffractive optical element of this embodiment, when the distance between the ends of adjacent annular bands in which a portion of the entire circumference is missing is Pout (μm), and the minimum distance of the distance Pout is Poutm (μm), it is preferable that the following condition (10) is satisfied.

[0076] 1.5 <Poutm / Pmin<6.0 ···(10) To satisfy condition (10), it is preferable to connect the D-cut section and the outermost ring band with a gentle curve. By satisfying condition (10), the distance Pout between the ring band ends in the D-cut section can be relatively widened, thereby improving moldability.

[0077] More preferably, the numerical range of condition expression (10) is set as shown in condition expression (10a) below.

[0078] 1.7 <Poutm / Pmin<5.5 ···(10a) More preferably, the numerical range of condition expression (10) is set as shown in condition expression (10b) below.

[0079] 2.0 <Poutm / Pmin<5.0 ···(10b) In the diffractive optical element of this embodiment, the outermost annulus is an annulus in which a part of the entire circumference is missing, and when the length of the arc in the outermost annulus is Lae (mm), it is preferable that the following condition (11) is satisfied.

[0080] 3.0 <Lae / Re<6.0 ···(11) If the upper limit of condition (11) is exceeded, the distance Rdc from the center of the annulus to the D-cut portion (annulus with a portion missing from the entire circumference) becomes large, making it difficult to miniaturize the optical system or diffractive optical element, which is undesirable. On the other hand, if the lower limit of condition (11) is exceeded, the distance Rdc from the center of the annulus to the D-cut portion becomes small, the minimum spacing Poutm between the annulus ends becomes small, and the moldability decreases. Alternatively, the region where the annulus is interrupted becomes larger, increasing the difficulty of processing the mold, which is also undesirable.

[0081] More preferably, the numerical range of condition expression (11) is set as shown in condition expression (11a) below.

[0082] 4.0 <Lae / Re<5.5 ···(11a) More preferably, the numerical range of conditional expression (11) is set as shown in conditional expression (11b) below.

[0083] 4.2 <Lae / Re<5.2 ···(11b) When the number of annular bands in the diffractive optical element of this embodiment is denoted by NR, it is preferable that the following condition (12) is satisfied.

[0084] 150 <NR<800 ···(12) If the value falls below the lower limit of condition (12), the chromatic aberration correction effect of the diffractive optical element decreases, making it difficult to correct various aberrations in the optical system. On the other hand, if the value exceeds the upper limit of condition (12), the pitch becomes smaller, reducing the moldability of the D-cut section and making it difficult to create the diffraction grating type.

[0085] More preferably, the numerical range of condition expression (12) is set as shown in condition expression (12a) below.

[0086] 170 <NR<670 ···(12a) More preferably, the numerical range of condition expression (12) is set as shown in condition expression (12b) below.

[0087] 200 <NR<550 ···(12b) When Ndc is the number of annular bands in a diffractive optical element that are greater than distance Rdc and have a radius smaller than radius Re, it is preferable that the following condition (13) is satisfied.

[0088] 20 <Ndc<300 ···(13) If the value falls below the lower limit of condition (13), the external dimensions become larger, making it difficult to miniaturize the optical system, which is undesirable. On the other hand, if the value exceeds the upper limit of condition (13), the spacing Pout between the annular ends in the D-cut section becomes narrower, which is also undesirable.

[0089] More preferably, the numerical range of conditional expression (13) is set as shown in conditional expression (13a) below.

[0090] twenty five <Ndc<250 ···(13a) More preferably, the numerical range of conditional expression (13) is set as shown in conditional expression (13b) below.

[0091] 30 <Ndc<200 ···(13b) In this embodiment, the diffractive optical element is formed by injection molding a second diffraction grating 9 with a large volume. In this case, it is preferable that the direction of the gate portion and the direction of the D-cut portion are opposite to each other. That is, within the annular region, it is preferable that the direction of the shortest length from the center of the annular region and the direction of the gate portion are opposite to each other with respect to the annular rotation center.

[0092] As mentioned above, in areas where the ring band is interrupted midway, such as the D-cut section, and where there is a step difference with the outer shape, the fluidity of the resin decreases in that area during molding. Therefore, if a section where the ring band is interrupted is placed near the resin inlet (gate), the resin will not properly fill the vertices and valleys of the grid at the interrupted section, and the desired grid shape cannot be obtained.

[0093] In this embodiment, the diffractive optical element has a gate shape positioned at an angle θ with respect to the optical axis O, as shown in Figure 5(b), near 180 degrees. The same applies to subsequent embodiments. As a result, the fluidity of the resin in the D-cut portion is high, and a diffractive optical element with the desired lattice shape is obtained. [Examples]

[0094] Next, Embodiment 2 of the present invention will be described. The diffractive optical element of this embodiment differs from Embodiment 1 in that the material or grid shape forming each lens has been changed. The basic configuration of the diffractive optical element of this embodiment is the same as that of Embodiment 1, as shown in Figures 1(a), (b) and 2.

[0095] In this embodiment, the first material forming the first diffraction grating 8 is an episulfide resin (Nd=1.6630, νd=36.8, θgF=0.583). The second material forming the second diffraction grating 9 is a polycarbonate thermoplastic resin (Nd=1.5880, νd=28.3, θgF=0.619). In this embodiment, the phase coefficients shown in equation (c) are C2=-4.673E-04, C4=-5.980E-07, C6=2.100E-09, the focal length fd at the diffraction plane is 1070 mm, and the radius Re of the outermost annulus is 18.38 mm.

[0096] Similar to Example 1, the diffractive optical element in this embodiment has a D-cut shape in a portion of its annular band, resulting in a structure where the annular band is interrupted midway. Within the annular band region of the diffractive optical element in this embodiment, the shortest distance from the center of the annular band, Rdc, is 16.0 mm.

[0097] Figure 7 shows the diffraction efficiency in an annular band of the diffractive optical element of this embodiment, with a minimum array pitch of Pmin = 45.6 μm and a lattice height d1 = 7.46 μm. In Figure 7, the horizontal axis represents wavelength (nm), and the vertical axis represents diffraction efficiency (%). At this time, the angle of the envelope formed by connecting the vertices of the diffraction grating on the lattice wall surface with respect to the perpendicular is 8.9 degrees, and d1t = 7.27 μm. As shown in Figure 7, by adopting a configuration that satisfies condition (2), high diffraction efficiency can be obtained over a wide wavelength range in the visible region.

[0098] Figure 8 shows the distance (radius R) from the center of the annular shape of the diffractive optical element in this embodiment as a function of the angle θ with respect to the optical axis O. In Figure 8, the horizontal axis represents the angle θ (deg) and the vertical axis represents the radius R (mm). As shown in Figure 8, miniaturization of the optical system is achieved in the diffractive optical element of this embodiment by shortening the outer diameter shape near θ = 0 degrees.

[0099] Figure 9 shows the second derivative Ψ²(h) of the higher-order optical path difference function of condition (7) with respect to the distance h perpendicular to the optical axis O in the diffractive optical element of this embodiment. In Figure 9, the horizontal axis is h (mm), and the vertical axis is (Ψ2(h)-2×C 2 ) / C Figure 2 shows the respective values. As shown in Figure 9, the diffractive optical element of this embodiment has a configuration in which the power due to diffraction in the peripheral area is appropriately controlled. In the diffractive optical element of this embodiment, the minimum distance Poutm between the annular ends in the D-cut portion is a large value of 211.9 μm, resulting in a configuration with excellent moldability. [Examples]

[0100] Next, Embodiment 3 of the present invention will be described. The diffractive optical element of this embodiment differs from Embodiment 1 in that the material or grid shape forming each lens has been changed. The basic configuration of the diffractive optical element of this embodiment is the same as that of Embodiment 1, as shown in Figures 1(a), (b) and 2.

[0101] In this embodiment, the first material forming the first diffraction grating 8 is an enthiol-based resin (Nd=1.6430, νd=36, θgF=0.584). The second material forming the second diffraction grating 9 is a polycarbonate-based thermoplastic resin (Nd=1.5880, νd=28.3, θgF=0.619). In this embodiment, the phase coefficients shown in equation (c) are C2=-4.875E-04, C4=-7.967E-07, C6=1.890E-09, the focal length fd at the diffraction plane is 1026 mm, and the radius Re of the outermost annulus is 19.78 mm.

[0102] Similar to Example 1, the diffractive optical element in this embodiment has a D-cut shape in a portion of its annular band, resulting in a structure where the annular band is interrupted midway. Within the annular band region of the diffractive optical element in this embodiment, the shortest distance Rdc from the center of the annular band is 17.0 mm.

[0103] Figure 10 shows the diffraction efficiency in an annular band of the diffractive optical element of this embodiment, with a minimum array pitch of Pmin = 33.9 μm and a lattice height d1 = 10.57 μm. In Figure 10, the horizontal axis represents wavelength (nm), and the vertical axis represents diffraction efficiency (%). At this time, the angle of the envelope formed by connecting the vertices of the diffraction grating on the lattice wall surface with respect to the perpendicular is 12.1 degrees, and d1t = 9.90 μm. As shown in Figure 10, by adopting a configuration that satisfies condition (2), high diffraction efficiency can be obtained over a wide wavelength range in the visible region.

[0104] Figure 11 shows the distance (radius R) from the center of the annular shape of the diffractive optical element in this embodiment as a function of the angle θ with respect to the optical axis O. In Figure 11, the horizontal axis represents the angle θ (deg) and the vertical axis represents the radius R (mm). As shown in Figure 11, the diffractive optical element in this embodiment achieves miniaturization of the optical system by shortening the outer diameter shape near θ = 0 degrees.

[0105] Figure 12 shows the second derivative Ψ²(h) of the higher-order optical path difference function of condition (7) with respect to the distance h perpendicular to the optical axis O in the diffractive optical element of this embodiment. In Figure 12, the horizontal axis is h (mm), and the vertical axis is (Ψ2(h)-2×C 2 ) / C Figure 2 shows the respective aspects. As shown in Figure 12, the diffractive optical element of this embodiment has a configuration in which the power due to diffraction in the peripheral area is appropriately controlled. In the diffractive optical element of this embodiment, the minimum distance Poutm between the annular ends in the D-cut portion is a large value of 110.1 μm, resulting in a configuration with excellent moldability. [Examples]

[0106] Next, Embodiment 4 of the present invention will be described. The diffractive optical element of this embodiment differs from that of Embodiment 1 in that the material or grid shape forming each lens has been changed. The basic configuration of the diffractive optical element of this embodiment is the same as that of Embodiment 1, as shown in Figures 1(a), (b) and 2.

[0107] In this embodiment, the first material forming the first diffraction grating 8 is an episulfide resin (Nd=1.6630, νd=36.8, θgF=0.583). The second material forming the second diffraction grating 9 is a polycarbonate thermoplastic resin (Nd=1.616, νd=25.8, θgF=0.623). In this embodiment, the phase coefficients shown in equation (c) are C2=-8.753E-04, C4=1.186E-06, C6=-2.150E-09, the focal length fd at the diffraction plane is 571 mm, and the radius Re of the outermost annulus is 18.52 mm.

[0108] Similar to Example 1, the diffractive optical element in this embodiment has a D-cut shape in a portion of its annular band, resulting in a structure where the annular band is interrupted midway. Within the annular band region of the diffractive optical element in this embodiment, the shortest distance Rdc from the center of the annular band is 15.0 mm.

[0109] Figure 13 shows the diffraction efficiency in an annular band of the diffractive optical element of this embodiment, with a minimum array pitch of Pmin = 19.4 μm and a lattice height d1 = 12.96 μm. In Figure 13, the horizontal axis represents wavelength (nm), and the vertical axis represents diffraction efficiency (%). At this time, the angle of the envelope formed by connecting the vertices of the diffraction grating on the lattice wall surface with respect to the perpendicular is 5.4 degrees, and d1t = 12.18 μm. As shown in Figure 13, by adopting a configuration that satisfies condition (2), high diffraction efficiency can be obtained over a wide wavelength range in the visible region.

[0110] Figure 14 shows the distance (radius R) from the center of the annular shape of the diffractive optical element in this embodiment as a function of the angle θ with respect to the optical axis O. In Figure 14, the horizontal axis represents the angle θ (deg) and the vertical axis represents the radius R (mm). As shown in Figure 14, the diffractive optical element in this embodiment achieves miniaturization of the optical system by shortening the outer diameter shape near θ = 0 degrees.

[0111] Figure 15 shows the second derivative Ψ²(h) of the higher-order optical path difference function of condition (7) with respect to the distance h perpendicular to the optical axis O in the diffractive optical element of this embodiment. In Figure 15, the horizontal axis is h (mm), and the vertical axis is (Ψ2(h)-2×C 2 ) / C Figure 2 shows the respective values. As shown in Figure 15, the diffractive optical element of this embodiment has a configuration in which the power due to diffraction in the peripheral area is appropriately controlled. In the diffractive optical element of this embodiment, the minimum distance Poutm between the annular ends in the D-cut portion is a large value of 46.6 μm, resulting in a configuration with excellent moldability.

[0112] Table 1 shows the numerical values ​​corresponding to each of the conditions for each of Examples 1 to 4.

[0113] [Table 1] [Examples]

[0114] Next, with reference to Figure 16, the optical system (observation optical system) 100 in Embodiment 5 of the present invention will be described. Figure 16 is a configuration diagram of the optical system 100. In Figure 16, 101 is a display panel such as an LCD, 102 is an optical path branching means, 103 is a corrective lens, and 105 is the pupil plane. 104 is a diffractive optical element of any of Embodiments 1 to 4, and is provided to correct chromatic aberration, etc., of the corrective lens 103.

[0115] As described in the embodiments above, the optical system 100 has high diffraction efficiency and is easy to manufacture and low cost. The optical system 100 can be applied to observation optical systems such as terrestrial telescopes or astronomical telescopes, observation optical systems such as head-mounted displays (HMDs), or optical viewfinders such as lens shutter cameras or video cameras, and the same effects as described above can be obtained. In this embodiment, one diffractive optical element is arranged in the optical system 100, but it is not limited to this, and multiple diffractive optical elements may be arranged in the photographic lens. [Examples]

[0116] Next, with reference to Figure 17, the imaging device (video camera) 200 in Embodiment 6 of the present invention will be described. Figure 17 is a schematic diagram of the imaging device 200. In Figure 17, 201 is the video camera body, 202 is the imaging optical system that forms a subject image on an image sensor (not shown), and 203 is a sound-collecting microphone. 204 is an observation device (electronic viewfinder, display device) for observing the subject image (image) displayed on a display element (not shown) via an observation optical system (for example, the optical system 100 of Embodiment 5). The observation device guides light from the display element that displays the image. The display element is made up of a liquid crystal panel or the like, and the subject image formed by the imaging optical system 202 is displayed on the display element.

[0117] Thus, the optical system 100 of Example 5 can be applied to an imaging device 200 such as a video camera. This makes it possible to obtain an imaging device 200 having an eyepiece optical system (observation optical system) that satisfies a wide field of view and can adequately correct various aberrations such as field curvature and astigmatism, while securing sufficient space for arranging optical path branching means in the optical system 100. Note that the eyepiece optical system of this embodiment is not limited to video cameras as shown in Figure 17, but can also be applied to, for example, interchangeable lens mirrorless cameras or HMDs.

[0118] Each embodiment provides a diffractive optical element that has high optical performance, is compact, and has excellent moldability. Furthermore, by using the diffractive optical elements of each embodiment in an optical system, it is possible to provide an optical system, imaging device, and display device in which various aberrations such as chromatic aberration and flare are well reduced.

[0119] Each embodiment disclosed includes the following configuration:

[0120] (Composition 1) A diffractive optical element having an annular region in which multiple annular bands are formed in a concentric arrangement, At least one of the aforementioned multiple rings is a ring in which a portion of the entire circumference is missing, When Rdc (mm) is the shortest distance from the center of the plurality of annular bands to the outer circumference of the annular band region, Re (mm) is the radius of the annular band furthest from the center among the plurality of annular bands, and Pmin (μm) is the minimum value of the array pitch of the diffractive optical elements, 6 <Pmin×Rdc / Re<65 A diffractive optical element characterized by satisfying the following condition. (Configuration 2) 0.50 <Rdc / Re<0.95 The diffractive optical element according to configuration 1, characterized in that it satisfies the following condition. (Composition 3) When the radius of the first ring from the center is R1 (mm) and the radius of the second ring from the center is R2 (mm), 0.8 < 1000 × (R2 2 -R12 ) / (Re×Pmin)<2.4 A diffractive optical element according to configuration 1 or 2, characterized by satisfying the following conditional expression. (Composition 4) When the design wavelength of the diffractive optical element is λ0 (μm) and the focal length at the diffraction plane is fd (mm), 0.40 <fd×λ0 / (Re×Pmin)<1.20 A diffractive optical element according to any one of configurations 1 to 3, characterized in that it satisfies the following conditional expression. (Composition 5) When the lattice height in the annulus with the minimum value Pmin is Dm (μm), 0.05 <Dm / Pmin<1.00 A diffractive optical element according to any one of configurations 1 to 4, characterized in that it satisfies the following conditional expression. (Composition 6) When the radius of the ring having the minimum value Pmin is denoted as RPm (mm), 0.70 <Rdc / RPm<1.50 A diffractive optical element according to any one of configurations 1 to 5, characterized in that it satisfies the following conditional expression. (Composition 7) When the distance between the ends of adjacent rings in the aforementioned rings, where a portion of the entire circumference is missing, is Pout(μm), and the minimum distance of the distance Pout is Poutm(μm), 1.5 <Poutm / Pmin<6.0 A diffractive optical element according to any one of configurations 1 to 6, characterized in that it satisfies the following conditional expression. (Composition 8) In the aforementioned diffractive optical element, the outermost ring is missing a portion of the entire circumference, and the length of the arc in the outermost ring is Lae (mm). 3.0 <Lae / Re<6.0 A diffractive optical element according to any one of configurations 1 to 7, characterized in that it satisfies the following conditional expression. (Composition 9) When the number of the aforementioned multiple rings is NR 150 <NR<800 A diffractive optical element according to any one of configurations 1 to 8, characterized by satisfying the following conditional expression. (Composition 10) When Ndc is the number of rings among the aforementioned multiple rings that have a radius greater than distance Rdc and a radius smaller than radius Re, 20 <Ndc<300 A diffractive optical element according to any one of configurations 1 to 9, characterized in that it satisfies the following conditional expression. (Composition 11) The diffractive optical element according to any one of configurations 1 to 10, characterized in that the optical material forming the diffractive optical element includes a thermoplastic resin. (Composition 12) The diffractive optical element is characterized in that it is constructed by stacking a first diffraction grating made of a first material and a second diffraction grating made of a second material different from the first material, as described in any one of configurations 1 to 11. (Composition 13) A diffractive optical element according to any one of configurations 1 to 12, characterized in that it has an outer peripheral region where a diffraction grating is not formed outside an annular band having radius Re. (Composition 14) In the diffractive optical element, the distance perpendicular to the optical axis is h (mm), and the optical path difference function Ψ of the diffracted surface is Ψ(h)=C2h 2 +C4h 4 +C6h 6 ... year, When the second derivative of the optical path difference function Ψ with respect to h is denoted as Ψ²(h), -5.0 < (Ψ2(h)-2) / C2 < -0.5 (C i :Phase coefficient (i=2,4,6…)) A diffractive optical element according to any one of configurations 1 to 13, characterized in that it satisfies the following conditional expression. (Composition 15) The diffractive optical element has a gate portion, A diffractive optical element according to any one of configurations 1 to 14, characterized in that, in the annular region, the direction of the shortest length from the center of the annular region and the direction of the gate portion are opposite to each other with respect to the annular rotation center. (Composition 16) An optical system characterized by having a diffractive optical element as described in any of configurations 1 to 15. (Composition 17) An imaging device characterized by having an optical system as described in configuration 16 and an image sensor that receives an image formed by the optical system. (Composition 18) An imaging device characterized by having the optical system described in configuration 16 and a display element.

[0121] Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of its essence. [Explanation of symbols]

[0122] 1. Diffractive optical element

Claims

1. A diffractive optical element having a diffraction region including multiple annular bands arranged in concentric circles, At least one of the aforementioned multiple rings is a ring in which a portion of the entire circumference is missing. When the shortest distance from the center of the plurality of annular bands to the outer circumference of the diffraction region is Rdc (mm), the radius of the annular band furthest from the center among the plurality of annular bands is Re (mm), the minimum value of the arrangement pitch of the plurality of annular bands is Pmin (μm), and the radius of the annular band whose arrangement pitch is the minimum value Pmin among the plurality of annular bands is RPm (mm), 6<Pmin×Rdc / Re<65 0.70<Rdc / RPm<1.50 A diffractive optical element characterized by satisfying the following condition.

2. 0.50<Rdc / Re<0.95 The diffractive optical element according to claim 1, characterized in that it satisfies the following condition.

3. When, among the plurality of rings, the radius of the first ring counting from the center is R1 (mm), and the radius of the second ring counting from the center is R2 (mm), 0.8<1000×(R2) ２ -R1 ２ ) / (Rｲe×ｰｯes)<2.4 The diffractive optical element according to claim 1, characterized in that it satisfies the following condition.

4. When the design wavelength is λ0 (μm) and the focal length in the diffraction region is fd (mm), 0.40 < fd × λ0 / (Re × Pmin) < 1.20 The diffractive optical element according to claim 1, characterized in that it satisfies the following condition.

5. When the grid height in the ring where the array pitch is the minimum value Pmin among the plurality of rings is Dm (μm), 0.05<Dm / Pmin<1.00 The diffractive optical element according to claim 1, characterized in that it satisfies the following condition.

6. When the distance between the ends of adjacent rings in the aforementioned rings with a portion of their circumference missing is Pott (μm), and the minimum distance of the distance Pott is Pottm (μm), 1.5<Poutm / Pmin<6.0 The diffractive optical element according to claim 1, characterized in that it satisfies the following condition.

7. A diffractive optical element having a diffraction region including a plurality of annular bands arranged in a concentric circle, At least one of the aforementioned multiple rings is a ring in which a portion of the entire circumference is missing. When the shortest distance from the center of the plurality of annular bands to the outer circumference of the diffraction region is Rdc (mm), the radius of the annular band furthest from the center among the plurality of annular bands is Re (mm), the minimum value of the arrangement pitch of the plurality of annular bands is Pmin (μm), the distance between the ends of adjacent annular bands among the annular bands with a portion missing from the entire circumference is Put (μm), and the minimum distance of the distance Put is Putm (μm), 6<Pmin×Rdc / Re<65 1.5<Poutm / Pmin<6.0 A diffractive optical element characterized by satisfying the following condition.

8. The ring furthest from the center is a ring with a portion missing from its entire circumference, and the length of the arc in this outermost ring is Lae (mm). 3.0<Lae / Re<6.0 The diffractive optical element according to claim 1, characterized in that it satisfies the following condition.

9. When the number of the aforementioned multiple rings is NR 150<NR<800 The diffractive optical element according to claim 1, characterized in that it satisfies the following condition.

10. A diffractive optical element having a diffraction region including a plurality of annular bands arranged in a concentric circle, At least one of the aforementioned multiple rings is a ring in which a portion of the entire circumference is missing. When the shortest distance from the center of the plurality of annular bands to the outer circumference of the diffraction region is Rdc (mm), the radius of the annular band furthest from the center among the plurality of annular bands is Re (mm), the minimum arrangement pitch of the plurality of annular bands is Pmin (μm), and the number of the plurality of annular bands is NR, 6<Pmin×Rdc / Re<65 150<NR<800 A diffractive optical element characterized by satisfying the following condition.

11. When Ndc is the number of rings among the aforementioned plurality of rings that have a radius greater than distance Rdc and a radius smaller than radius Re, 20<Ndc<300 The diffractive optical element according to claim 1, characterized in that it satisfies the following condition.

12. The diffractive optical element according to claim 1, characterized in that the diffractive optical element includes a thermoplastic resin.

13. The diffractive optical element according to claim 1, characterized in that the diffractive optical element includes a first diffraction grating made of a first material and a second diffraction grating made of a second material different from the first material.

14. The diffractive optical element according to claim 1, characterized in that it has a non-diffractive region located on the outer edge of the annular band furthest from the center.

15. Let h (mm) be the distance from the optical axis in a direction perpendicular to the optical axis, and let Ψ be the optical path difference function of the diffraction region. Ψ(h)=C ２ h ２ +C ４ h ４ +C ６ h ６ … year, When the second derivative of the optical path difference function Ψ with respect to h is denoted as Ψ²(h), -5.0<(Ψ2(h)-2×C 2) / C ２ <-0.5 (C) ｉ : Phase coefficient (i=2, 4, 6...)) The diffractive optical element according to claim 1, characterized in that it satisfies the following condition.

16. A diffractive optical element having a diffraction region including a plurality of annular bands arranged in a concentric circle, At least one of the aforementioned multiple rings is a ring in which a portion of the entire circumference is missing. Let Rdc (mm) be the shortest distance from the center of the plurality of annular bands to the outer circumference of the diffraction region, Re (mm) be the radius of the annular band furthest from the center among the plurality of annular bands, Pmin (μm) be the minimum value of the arrangement pitch of the plurality of annular bands, and h (mm) be the distance from the optical axis in a direction perpendicular to the optical axis, and let Ψ be the optical path difference function of the diffraction region. Ψ(h)=C2h2+C4h4+C6h6... year, When the second derivative of the optical path difference function Ψ with respect to h is denoted as Ψ²(h), 6<Pmin×Rdc / Re<65 -5.0<(Ψ2(h)-2×C 2 ) / C 2 <-0.5 (C i: Phase coefficient (i = 2, 4, 6...)) A diffractive optical element characterized by satisfying the following condition.

17. Having a gate section, The diffractive optical element according to claim 1, characterized in that, in the diffraction region, the direction toward the outer periphery closest to the center and the direction toward which the gate portion protrudes are opposite to each other with respect to the center.

18. A diffraction region comprising a plurality of rings arranged in a concentric circle, A diffractive optical element having a gate portion, At least one of the aforementioned multiple rings is a ring in which a portion of the entire circumference is missing. In the diffraction region, the direction toward the outer circumference closest to the center of the plurality of annular bands and the direction toward which the gate portion protrudes are opposite to each other with respect to the center. When the shortest distance from the center to the outer periphery of the diffraction region is Rdc (mm), the radius of the annular band furthest from the center among the plurality of annular bands is Re (mm), and the minimum value of the arrangement pitch of the plurality of annular bands is Pmin (μm), 6<Pmin×Rdc / Re<65 A diffractive optical element characterized by satisfying the following condition.

19. An optical system characterized by having a diffractive optical element according to any one of claims 1 to 18.

20. An imaging device characterized by having an optical system according to claim 19 and an image sensor that receives an image formed by the optical system.

21. A display device comprising a display element for displaying an image and an optical system according to claim 19 for guiding light from the display element.

Images