JP2011123317A - Diffraction optical element, optical system and optical apparatus - Google Patents

Diffraction optical element, optical system and optical apparatus Download PDF

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JP2011123317A
JP2011123317A JP2009281242A JP2009281242A JP2011123317A JP 2011123317 A JP2011123317 A JP 2011123317A JP 2009281242 A JP2009281242 A JP 2009281242A JP 2009281242 A JP2009281242 A JP 2009281242A JP 2011123317 A JP2011123317 A JP 2011123317A
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optical
diffractive optical
diffractive
diffraction
light
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Kenzaburo Suzuki
憲三郎 鈴木
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Nikon Corp
株式会社ニコン
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffraction optical element which can increase diffraction efficiency and in which coloring can be felt closely to natural light (white) even in the generation of flare light. <P>SOLUTION: The diffraction optical element (100) is composed of two sheets of optical members (11, 12) in which diffraction optical surfaces each having a lattice structure in which a diffraction face (13) and an end face (14) are continuous at a prescribed pitch (P), are made to face each other and stick to each other to be laminated. Then, the diffraction optical element (100) has steps including a first plane (141) in which the end face (14) extends in the pitch direction, and a second plane (142) which intersects with the first plane (141). When a reference wavelength is a d-line (587.6 nm) and the refractive index difference of the d-line of the two sheets of optical members (11, 12) is ΔNd, the diffraction optical element (100) satisfies the following condition of 0.02<ΔNd<0.45. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a diffractive optical element having a grating structure and an optical system or optical apparatus using the diffractive optical element.

  Conventionally, a diffractive optical element is an element that diffracts transmitted light / reflected light with a fine periodic structure and performs operations such as spectroscopy, branching, and coupling of incident light. In addition, the diffractive optical apparatus can realize operations such as condensing, divergence, and imaging by modulating the periodic structure of the diffractive optical element into various shapes.

The diffractive optical element disclosed in Patent Document 1 is provided with a step at the edge of the diffractive optical element in order to obtain a diffractive optical element having high diffraction efficiency in a wide wavelength range and less flare and an optical system having the flared optical element. A stepped shape was provided. Thereby, even when incorporated in an optical system, it is possible to provide an optical system that can maintain high diffraction efficiency and can effectively suppress flare and the like.
JP 2002-71925 A

  However, as shown in Patent Document 1, in the separation type diffractive optical element having a space between a pair of elements, the amount of a part of incident light reflected by the surface of the separation type diffractive optical element increases. There are disadvantages. For this reason, there arises a disadvantage that the energy of transmitted diffracted light to be used is reduced. Furthermore, although the separation type diffractive optical element disclosed in Patent Document 1 can suppress the generation of flare light, it has low diffraction efficiency, so that it feels flare light colored in red, for example, not white. Become.

  The present invention has been made in view of the above problems, and proposes a diffractive optical element that makes it possible to feel the hue close to natural light (white) even when flare light is generated.

The diffractive optical element of the first aspect is composed of two optical members in which diffractive optical surfaces having a grating structure in which a diffractive surface and an end surface are continuous at a predetermined pitch are faced to each other and closely stacked. The diffractive optical element has a staircase including a first plane whose end face extends in the pitch direction and a second plane intersecting the first plane, and a reference wavelength is d-line (587.6 nm). If the refractive index difference of the d-line of the optical member is ΔNd, the following condition is satisfied.
0.02 <ΔNd <0.45

  The optical system of the second aspect has a plurality of optical elements and guides light and acts on the light. In the optical system, at least one of the optical elements is the diffractive optical element of the first aspect.

  The optical device according to the third aspect includes the diffractive optical element according to the first aspect.

  The diffractive optical element of the present invention can increase the reflection efficiency and can obtain white light even if flare occurs.

FIG. 2A is a cross-sectional view of the diffraction grating 11 constituting the diffractive optical element 100. FIG. FIG. 2B is a cross-sectional view of the diffraction grating 12 constituting the diffractive optical element 100. FIG. 2C is a cross-sectional view of the diffractive optical element 100 constituted by the diffraction gratings 11 and 12. (D) is an enlarged view of a portion surrounded by a dotted line E in (c). (A) is sectional drawing of 100 A of 1st diffractive optical elements. (B) is an enlarged view of a portion surrounded by a dotted line A in (a). 4 is a graph showing the flare amount calculated in Table 3. (A) is sectional drawing of the 2nd diffractive optical element 100B. (B) is an enlarged view of a portion surrounded by a dotted line B in (a). 7 is a graph showing the flare amount calculated in Table 6. It is the elements on larger scale of 3rd diffractive optical element 100C of 3rd Embodiment. It is the elements on larger scale of 4th diffractive optical element 100D of 4th Embodiment. It is sectional drawing for demonstrating the structure of the 5th diffractive optical element 100E. (A) is the schematic of the optical system 200 with which the diffractive optical element 100 is arrange | positioned. FIG. 2B is a schematic diagram of an optical system 210 in which the diffractive optical element 100 is disposed.

<Configuration of Diffractive Optical Element 100>
The configuration of the diffractive optical element 100 will be described with reference to FIG. FIG. 1 is a diagram for explaining the configuration of the diffractive optical element 100. FIG. 1A is a sectional view of the diffraction grating 11 constituting the diffractive optical element 100. FIG. 1B is a cross-sectional view of the diffraction grating 12 constituting the diffractive optical element 100. FIG. 1C is a cross-sectional view of the diffractive optical element 100 constituted by the diffraction gratings 11 and 12. FIG.1 (d) is an enlarged view of the part enclosed by the dotted line E of (c). As shown in FIG. 1C, the side surface of the diffractive optical element 100 is rectangular, the direction in which the long side extends is the X-axis direction, the direction in which the short side extends is the Z-axis, and the XZ plane A direction perpendicular to the Y axis direction will be described.

  The first diffraction grating 11 shown in FIG. 1A has a sawtooth shape in which the linear diffraction surface 13 and the stepped end surface 14 are continuous in the X-axis direction with a predetermined pitch on the −Z side. An optical member having a lattice structure. Similarly, the second diffraction grating 12 shown in FIG. 1 (b) has the same shape as the first diffraction grating 11, and the linear diffraction surface 13 and the stepped end surface 14 have a predetermined pitch P on the + Z side. It is an optical member having a sawtooth lattice structure that is continuous in the X-axis direction. Here, the refractive index N1 of the first diffraction grating 11 and the refractive index N2 of the second diffraction grating 12 may be made of an ultraviolet curable resin and may be different from each other.

  The height of the end face 14 in the Z-axis direction is H, and the width in the X-axis direction is ΔP. Accordingly, the height of the diffractive surface 13 in the Z-axis direction is H, and the width in the X-axis direction is (P−ΔP).

  As shown in FIG. 1 (c), the diffractive optical element 100 is a multi-layer type diffraction in which the first diffraction grating 11 and the second diffraction grating 12 are closely contacted with each other in the Z-axis direction so as to face the grating structure. It is an optical element. That is, the corresponding diffraction surface 13 of the first diffraction grating 11 and the diffraction surface 13 of the second diffraction grating 12 are in close contact with each other, and the corresponding end surface 14 of the first diffraction grating 11 and the end surface 14 of the second diffraction grating 12 are in close contact with each other. Has been. That is, the bonded diffractive optical element 100 is formed in a rectangular shape. For this reason, the diffractive surface 13 and the end surface 14 of the diffractive optical element 100 are formed in a sawtooth shape with a predetermined pitch P. Here, the diffractive optical element 100 improves the flare characteristic by forming the end face 14 which is a phase mismatch region into a stepped shape.

  As shown in FIG. 1D, the end face 14 of the diffractive optical element 100 has, for example, a step shape of 8 steps, and a portion surrounded by a dotted line F is one step. Each step has a first surface 141 extending along the X-axis direction and a second surface 142 extending along the + Z-axis direction from the + X side end of the first surface 141. Therefore, the first surface 141 and the second surface 142 are perpendicular. Further, when the diffractive optical element 100 is manufactured using a mold, the corner portion to which the first surface 141 and the second surface 142 are connected is rounded.

  In FIG. 1D, the width in the X-axis direction of the first surface 141 in each step is w, the height in the Z-axis direction of the second surface 142 is h, and the rounded radius is R.

  In addition, the diffractive optical element 100 is preferably manufactured by a method in which the diffraction gratings 11 and 12 are formed by UV resin shaping using a mold. The optical diffraction gratings 11 and 12 constituting the diffractive optical element 100 have the viscosity (uncured) of the material constituting the diffraction grating 11 (or the diffraction grating 12) in order to maintain good moldability and ensure excellent mass productivity. The product viscosity is preferably at least 40 or more. If the viscosity is 40 or less, the resin tends to flow during molding, and it becomes difficult to mold a precise shape. The viscosity of the material constituting the diffraction grating 12 (or the diffraction grating 11) is preferably at least 2000 or more.

  Furthermore, it is preferable in production that both the optical diffraction gratings 11 and 12 constituting the diffractive optical element 100 are made of UV curable resin. This is because production efficiency is increased and costs are reduced.

  In order to reduce the size and weight of the diffractive optical element 100, it is preferable to use a resin material having a specific gravity of 2.0 or less as the optical material constituting the diffractive optical element 100. Since the specific gravity of resin is smaller than that of glass, it is effective for reducing the weight of the diffractive optical element 100. Furthermore, in order to fully exhibit the effect of weight reduction, it is preferable that specific gravity is 1.6 or less.

<Outline of Diffractive Optical Element 100>
In order to increase the reflection efficiency and make flare light close to the wavelength characteristic of natural light, the diffractive optical element 100 preferably satisfies the following conditions.

  Formula 1 defines the refractive index difference ΔNd between the refractive index N1 of the first diffraction grating 11 and the refractive index N2 of the second diffraction grating 12.

0.02 <ΔNd <0.45 (1)
Here, ΔNd represents the difference in refractive index between the refractive index N1 of the first diffraction grating 11 and the refractive index N2 of the second diffraction grating 12 at the d-line (587.6 nm) which is the reference wavelength. The refractive index N1 of the first diffraction grating 11 may be larger than the refractive index N2 of the second diffraction grating 12, and conversely, the refractive index N2 of the second diffraction grating 12 is larger than the refractive index N2 of the first diffraction grating 11. May be. That is, the refractive index N1 of the first diffraction grating 11 and the refractive index N2 of the second diffraction grating 12 may be different. Further, the first diffraction grating 11 may be on the object side, and the second diffraction grating 12 may be on the object side.

However, it is preferable to make the refractive index difference ΔNd smaller than 0.45 in order to reduce the manufacturing error sensitivity. Further, since the Fresnel reflection can be obtained by {ΔNd / (N1 + N2)} 2 , the smaller the refractive index difference ΔNd, the smaller the reflection loss of the light amount at the interface between the first diffraction grating 11 and the second diffraction grating 12. . For this reason, it is more preferable to make the refractive index difference ΔNd smaller than 0.2. Furthermore, the upper limit may be set to 0.1 in order to fully exhibit the effect.

  On the other hand, if the lower limit of Expression (1) is not reached, the refractive index difference ΔNd becomes too small, and the height H of the end face 14 of the diffractive optical element 100 must be increased in order to generate the necessary diffraction. . For this reason, if it falls below the lower limit of Equation (1), the first diffraction grating 11 and the second diffraction grating 12 are disadvantageous in manufacturing, and the end face 14 causes a shadow on the incident light. Further, flare light due to scattering and reflection due to incident light incident on the end face 14 becomes large. In addition, in order to fully demonstrate the effect of Numerical formula (1), it is more preferable to set a lower limit to 0.15.

  Formula 2 defines the relationship h / w between the width w in the X-axis direction of the first surface 141 and the height h in the Z-axis direction of the second surface 142 at each step of the staircase.

1.0 <h / w <20.0 (2)

  When the diffractive optical element 100 satisfies Expression (2), the scattering is sufficiently increased at the interface between the first diffraction grating 11 and the second diffraction grating 12. In particular, the condition of Equation 2 can make flare light generated at the end face 14 close to the wavelength characteristic of natural light. Further, the upper limit may be set to 10.0 in order to fully exhibit the effect. Note that it is preferable to set the upper limit to 10.0 because ΔP decreases, the width of the diffraction surface 13 in the X-axis direction (P−ΔP) increases, and the diffraction efficiency of regular imaging light increases. When the relationship h / w is 1.0 or less, the width (P−ΔP) of the diffraction surface 13 in the X-axis direction is narrowed, which is not preferable because the diffraction efficiency of regular imaging light decreases.

Formula 3 defines the relationship w / P between the width w in the X-axis direction of the first surface 141 of each step of the staircase and the pitch P of the diffractive optical element 100.
0.003 <w / P <0.5 (3)
In Expression (3), when the relationship w / P exceeds the upper limit value, the end face 14 of the diffractive optical element 100 is not formed in a stepped shape. On the other hand, if the upper limit value exceeds 0.5, w becomes too large compared to P, and the phase mismatch region (the width ΔP of the end surface 14 in the X-axis direction) increases, resulting in a zeroth order. The inconvenience of increasing flare due to light tends to occur. Moreover, in order to fully exhibit an effect, it is preferable to make an upper limit into 0.25. This reduces the phase mismatch region ΔP, which is preferable because flare caused by zero-order light is reduced. When the lower limit is 0.003 or less, the width w in the X-axis direction of the first surface 141 becomes relatively small, which tends to cause inconvenience that it is difficult to process.

Equation 4 defines the number of steps n of the stepped end face 14.
2 ≦ n <16 (4)
In Expression (4), when the upper limit is exceeded, the degree of scattering is weakened in a partial wavelength region, and the whitening effect is diminished. Further, when the number of steps is increased, it becomes difficult to perform precise shape processing with a normal processing machine, and a highly accurate and expensive processing machine or process is required, resulting in an increase in cost. Below the lower limit, the end face 14 of the diffractive optical element 100 is not formed stepwise.

Formula 5 defines the radius R of the roundness when the corner of each step on the stepped end face 14 is rounded.
R <5.0 μm (5)

In the formula (5), when the upper limit exceeds 5.0 μm, the occurrence of flare light in the diffractive optical element 100 is increased, which tends to cause inconvenience of lowering the image quality. When the pitch P of the diffractive optical element 100 is 100 μm, the intensity of flare light is estimated to be 1− (1−5 / 100) 2 = 0.0975 = about 10% at the maximum. Furthermore, when the upper limit is set to 2.0 μm, flare light generated in the phase mismatch region can be suppressed, which is more preferable. This is because when the pitch of the diffractive optical element 100 is 100 μm, the intensity of flare light is estimated to be about 4% at the maximum, which is a level that can be used for general imaging equipment.

Equation 6 defines the relationship H / P between the height H in the Z-axis direction on the diffractive surface 13 and the end surface 14 and the pitch P of the diffractive optical element 100.
0.01 <H / P <5.0 (6)

  Formula (6) is a formula indicating an appropriate ratio of the height H of the diffractive surface 13 and the end surface 14 in the Z-axis direction and the pitch P of the diffractive optical element 100, that is, an aspect ratio. In Expression (6), if the upper limit is exceeded, the maximum height of the end face 14 becomes too large, which causes a disadvantage that it is difficult to manufacture. In addition, the aspect ratio becomes large, and there is a disadvantage that the environmental resistance and durability are lowered. If the lower limit is not reached, there is an inconvenience that the whitening function declines, and the angular characteristics of the end face 14 deteriorate. Therefore, flare light is likely to occur. Furthermore, in order to fully exhibit the effect, the upper limit may be set to 3.0 and the lower limit may be set to 0.015.

Equation 7 defines an appropriate range of the balance of diffraction efficiency when the wavelength of light is broadened.
(EC + Eg) / 2> 0.9 × Ed (7)

  In Equation (7), Ed represents the diffraction efficiency design value of the d line (587.6 nm), Eg represents the diffraction efficiency design value of the g line (435.8 nm), and EC represents the C line (656.3 nm). The diffraction efficiency design value is shown. In Formula (7), if the left side is less than the right side, the diffraction efficiency is lowered at either the short wavelength or the long wavelength, flare light is generated, and the image quality is impaired. Furthermore, in order to exhibit the effect sufficiently, it is preferable to set the upper limit of the right-hand side value to 0.95 and the lower limit to 0.8.

Equation 8 defines the appropriate refractive index and dispersion distribution of the first diffraction grating 11 and the second diffraction grating.
−20.0 <ΔNd / Δ (NF−NC) <− 2.0 (8)

  In Expression (8), NF indicates the refractive index of the F line (486.1 nm), and NC indicates the refractive index of the C line (656.3 nm). Equation (8) is an essential condition for obtaining a sufficiently high diffraction efficiency over a wide band of wavelengths. Therefore, when the inequality sign is reversed, a sufficiently high diffraction efficiency cannot be obtained. Furthermore, in order to exhibit the effect sufficiently, the upper limit may be set to -3.0 and the lower limit may be set to -10.0.

  Further, in the diffractive optical element 100 shown in FIG. 1, since the end face 14 is formed in a stepped shape, a predetermined angle θ (tan θ = ΔP / H = w / h) from the axis Ax extending in the Z-axis direction. It is formed with an inclination. Further, when the light LL passing through the diffractive optical element 100 is incident on the diffractive optical element 100 with a predetermined angle θ from the Z axis, the end face 14 and the incident light LL are parallel to each other. The projected area for is zero. Therefore, flare light is less likely to occur at the end face 14. Optical performance can be improved.

(First embodiment)
The configuration of the first diffractive optical element 100A of the first embodiment will be described with reference to FIG. FIG. 2 is a diagram for explaining the configuration of the first diffractive optical element 100A of the first embodiment. FIG. 2A is a cross-sectional view of the first diffractive optical element 100A. FIG. 2B is an enlarged view of a portion surrounded by a dotted line A in FIG.

  As shown in FIG. 2A, the first diffractive optical element 100A is formed by laminating a first diffraction grating 11A and a second diffraction grating 12A having the same shape in close contact in the Z-axis direction. The first diffraction grating 11A is an optical member having a sawtooth grating structure in which a linear diffraction surface 13A and a stepped end surface 14A are continuous in the X-axis direction with a predetermined pitch P1 on the −Z side. Similarly, the second diffraction grating 12A is an optical member having a sawtooth-like grating structure in which a linear diffraction surface 13A and a stepped end surface 14A are continuous in the X-axis direction with a predetermined pitch P1 on the + Z side. . Here, the first diffraction grating 11A and the second diffraction grating 12A in the first embodiment are in close contact with each other so as to face the grating structure. Furthermore, the refractive index N1 of the first diffraction grating 11A and the refractive index N2 of the second diffraction grating 12A may be different from each other.

  As shown in FIG. 2B, the end face 14A has a step shape of 8 steps, and a portion surrounded by a dotted line G is defined as one step. Each step has a first surface 141A extending along the X-axis direction and a second surface 142A extending along the + Z-axis direction from the + X side end of the first surface 141A. Therefore, the first surface 141A and the second surface 142A are vertical. Further, when the first diffractive optical element 100A is manufactured with a mold, the corner portion to which the first surface 141A and the second surface 142A are connected is rounded.

In FIG. 2, the height of the end surface 14A in the Z-axis direction is H1, the width of the first surface 141A of each step in the X-axis direction is w1, the height of the second surface 142A in the Z-axis direction is h1, and rounded. The radius of the shape is R1. The specific balamers of the first diffractive optical element 100A are as shown in Table 1.
Here, the unit of length is μm.

When formulas (1) to (8) are calculated based on the numerical values in Table 1, the results are as shown in Table 2.

  As shown in Table 2, the first diffractive optical element 100A of the first embodiment satisfies Expressions (1) to (8).

Table 3 shows that when the measurement wavelength range of light is 404.7 (h line) nm to 706.5 nm (r line), the first diffractive optical element 100A that is a multilayer type and the diffractive optical that is a single layer type. It is the calculation result of the flare amount in the end surface with an element. Here, a d-line blazed grating composed of a high refractive index medium is used as the single-layer diffractive optical element, and has an 8-step stepped end face. Further, since it is difficult to measure the flare amount in an actual diffractive optical element, in Table 3, calculation is performed using the diffraction efficiency value of the first-order diffracted light at the end face as an estimated value of the flare amount (hereinafter referred to as flare amount). ). Of course, the smaller the flare amount shown in Table 3, the better the performance of the diffractive optical element.

  FIG. 3 is a graph showing the flare amount calculated in Table 3. In FIG. 3, the solid line indicates the flare amount of the multilayer first diffractive optical element 100A, and the dotted line indicates the flare amount of the single-layer d-line blazed grating. In FIG. 3, the energy of light incident on one grating is normalized as 1.0 = 100%.

  As can be readily seen in FIG. 3, in the multilayered first diffractive optical element 100A indicated by the solid line, the flare amount hardly changes from purple to red in the visible light, and is about 0.16. However, in the single-layer d-line blazed grating indicated by the dotted line, the amount of flare changes greatly from purple to red in visible light, and changes from about 0.06 to about 0.16. In particular, the flare amount in the wavelength region of 404.7 nm to 546.1 nm is smaller than the flare amount in the wavelength region of 546.1 nm to 706.5 nm. That is, in the single-layer d-line blazed grating, the intensity of red flare light is higher than that of purple flare light. For this reason, flare light is generally felt reddish in a single-layer d-line blazed grating.

  According to Table 2, Table 3, and FIG. 3, since the first diffractive optical element 100A is a multi-layer type in which the end face 14A is formed in a stepped shape of 8 steps, light of each wavelength uniformly generates flare light generated on the end face 14A. And flare light is entirely whitened.

  In the first embodiment, white light is obtained by forming the end faces 14A of the diffraction gratings 11A and 12A of the first diffractive optical element 100A having a wide use wavelength region in a step shape.

(Second Embodiment)
The configuration of the second diffractive optical element 100B of the second embodiment will be described with reference to FIG. FIG. 4 is a diagram for explaining the configuration of the second diffractive optical element 100B of the second embodiment. FIG. 4A is a cross-sectional view of the second diffractive optical element 100B. FIG. 4B is an enlarged view of a portion surrounded by a dotted line B in FIG.

  In the second diffractive optical element 100B, as shown in FIG. 4A, the first diffraction grating 11B and the second diffraction grating 12B having the same shape are stacked in close contact in the Z-axis direction. The first diffraction grating 11B is an optical member having a sawtooth grating structure in which a linear diffraction surface 13B and a stepped end surface 14B are continuous in the X-axis direction with a predetermined pitch P2 on the −Z side. Similarly, the second diffraction grating 12B is an optical member having a sawtooth grating structure in which a linear diffraction surface 13B and a stepped end surface 14B are continuous in the X-axis direction with a predetermined pitch P2 on the + Z side. . Here, the first diffraction grating 11B and the second diffraction grating 12B in the second embodiment are in close contact with each other so as to face the grating structure. Furthermore, the refractive index N1 of the first diffraction grating 11B and the refractive index N2 of the second diffraction grating 12B may be different from each other.

  As shown in FIG. 4B, the end face 14B has a four-step staircase shape, and a portion surrounded by a dotted line J is defined as one step. Each step has a first surface 141B extending along the X-axis direction and a second surface 142B extending along the + Z-axis direction from the + X side end of the first surface 141B. Therefore, the first surface 141B and the second surface 142B are vertical. Further, when the second diffractive optical element 100B is manufactured using a mold, the corner portion to which the first surface 141B and the second surface 142B are connected is rounded.

In FIG. 4, the height of the end surface 14B in the Z-axis direction is H2, the width of the first surface 141B in the X-axis direction of each step is w2, and the height of the second surface 142B in the Z-axis direction is h2, which is rounded. The radius of the shape is R2. Specific parameterers of the second diffractive optical element 100B are as shown in Table 4.
Here, the unit of length is μm.

When formulas (1) to (8) are calculated based on the numerical values in Table 4, the results are as shown in Table 5.

  As shown in Table 5, the second diffractive optical element 100B of the second embodiment satisfies Expressions (1) to (8).

Table 6 shows that when the measurement wavelength range is 404.7 (h line) nm to 706.5 nm (r line), the second diffractive optical element 100B which is a multilayer type and the diffractive optical element which is a single layer type are shown. It is a calculation result of the amount of flare in the end face of. Here, as the single-layer type diffractive optical element, a d-line blazed grating composed of a high refractive index medium is used and has a stepped end face of four steps. In addition, since it is difficult to measure the flare amount in an actual diffractive optical element, Table 6 uses the diffraction efficiency value of the first-order diffracted light at the end face as an estimated value of the flare amount (hereinafter referred to as flare amount). ). Of course, the smaller the flare amount shown in Table 6, the better the performance of the diffractive optical element.

  FIG. 5 is a graph showing the flare amount calculated in Table 6. In FIG. 5, the solid line indicates the flare amount of the multilayer type second diffractive optical element 100 </ b> B, and the dotted line indicates the flare amount of the single layer type d-line blazed grating. In FIG. 5, the energy of light incident on one grating is normalized as 1.0 = 100%.

  As can be readily seen in FIG. 5, in the multilayered second diffractive optical element 100B indicated by the solid line, the flare amount hardly changes from purple to red in visible light, and is about 0.05. However, in the single-layer d-line blazed grating indicated by the dotted line, the amount of flare changes greatly from purple to red in visible light, and changes from about 0.018 to about 0.05. In particular, the flare amount in the wavelength region of 404.7 nm to 546.1 nm is smaller than the flare amount in the wavelength region of 546.1 nm to 706.5 nm. That is, in the single-layer d-line blazed grating, the intensity of red flare light is higher than that of purple flare light. For this reason, flare light is generally felt reddish in a single-layer d-line blazed grating.

  According to Table 5, Table 6, and FIG. 5, since the second diffractive optical element 100B is a multi-layer type in which the end face 14B is formed in a four-step staircase shape, light of each wavelength uniformly generates flare light generated on the end face 14B. And flare light is entirely whitened.

  In the second embodiment, white light can be obtained by forming the end faces 14B of the diffraction gratings 11B and 12B of the second diffractive optical element 100B having a wide usable wavelength region in a step shape.

(Third embodiment)
The configuration of the third diffractive optical element 100C of the third embodiment will be described with reference to FIG. FIG. 6 is a partially enlarged view showing the end face 14C of the third diffractive optical element 100C of the third embodiment.

  As shown in FIG. 6, the third diffractive optical element 100 </ b> C of the third embodiment is configured such that the first diffraction grating 11 </ b> C and the second diffraction grating 12 </ b> C having the same shape are closely stacked in the Z-axis direction. . The third diffractive optical element 100C has the same configuration as that described in the first embodiment except for the end face 14C. For example, the diffractive surface 13C is the same as the diffractive surface A described in the first embodiment, and a description thereof will be omitted.

  The end face 14C has a step shape of 8 steps, and a portion surrounded by a dotted line K is defined as one step. Each step has a first surface 141C extending along the X-axis direction and a second surface 142C extending along the + Z-axis direction from the + X side end of the first surface 141C. Therefore, the first surface 141A and the second surface 142A are connected vertically.

  Here, since the third diffractive optical element 100 </ b> C of the third embodiment is not manufactured with a mold, it is necessary to cut and form each step.

  The multi-layered third diffractive optical element 100C has the end face 14C formed in an eight-step staircase shape, so that the flare light generated at the end face 14C by the light of each wavelength can be made uniform. Whitened.

  In the third embodiment, white light can be obtained by forming the end faces 14C of the diffraction gratings 11C and 12C of the third diffractive optical element 100C having a wide usable wavelength region in a step shape.

(Fourth embodiment)
The configuration of the fourth diffractive optical element 100D of the fourth embodiment will be described with reference to FIG. FIG. 7 is a partially enlarged view showing the end face 14D of the fourth diffractive optical element 100D of the fourth embodiment.

  As shown in FIG. 7, the fourth diffractive optical element 100D of the fourth embodiment is a first diffractive grating 11D and a second diffractive grating 12D having the same shape, which are stacked in close contact in the Z-axis direction. . Further, in the fourth diffractive optical element 100D, the other parts excluding the end face 14D are the same as those described in the second embodiment. For example, the diffractive surface 13D is the same as the diffractive surface B described in the second embodiment, and a description thereof will be omitted.

  The end face 14D has a four-step staircase shape, and a portion surrounded by a dotted line L is defined as one step. Each step has a first surface 141D extending along the X-axis direction and a second surface 142D extending along the + Z-axis direction from the + X side end of the first surface 141D. Therefore, the first surface 141D and the second surface 142D are connected vertically.

  Here, since the fourth diffractive optical element 100D of the fourth embodiment is not manufactured by a mold, it is necessary to form each step by cutting.

  The multi-layered fourth diffractive optical element 100D has the end face 14D formed in a four-step staircase shape, so that the flare light generated by the light of each wavelength on the end face 14D can be made uniform. Whitened.

  In the fourth embodiment, by forming the end faces 14D of the diffraction gratings 11D and 12D of the fourth diffractive optical element 100D having a wide usable wavelength region in a step shape, the reflection efficiency can be increased and white light can be obtained. It is done.

(Fifth embodiment)
The configuration of the fifth diffractive optical element 100E of the fifth embodiment will be described with reference to FIG. FIG. 8 is a cross-sectional view for explaining the configuration of the fifth diffractive optical element 100E of the fifth embodiment. In FIG. 8, although the optical member 20 is drawn, it does not actually belong to the fifth diffractive optical element 100E.

  Here, as shown in FIG. 8, the fifth diffractive optical element 100 </ b> E includes a first diffractive grating 11 </ b> E and a second diffractive grating 12 </ b> E, and is bonded to the flat optical member 20.

  The fifth diffractive optical element 100E has a saw-toothed grating structure that is continuous in the X-axis direction. More specifically, in the first diffraction grating 11E or the second diffraction grating 12E, a diffractive surface 13E that is a convexly curved curved surface and a stepped end surface 14E are formed with a pitch P5. The fifth diffractive optical element 100E is line symmetric with respect to the Z axis. Further, since the pitch P5 is gradually narrowed from the center of the XZ plane toward the periphery, the fifth diffractive optical element 100E has the same positive power as that of a general convex lens in the + Z-axis direction. Moreover, the height of the diffractive surface 13E and the end surface 14E in the Z-axis direction is H5.

  In the fifth embodiment, the end face 14E of the fifth diffractive optical element 100E has a four-step staircase shape. Each step may be formed to have round corners as described in the first embodiment and the second embodiment, or at right angles as described in the third embodiment and the fourth embodiment. May be formed.

  The multi-layered fifth diffractive optical element 100E has the end face 14E formed in a staircase shape, so that the flare light generated by the light of each wavelength on the end face 14E can be made uniform, and the flare light is entirely whitened. The

  In the fifth embodiment, by forming the end faces 14E of the diffraction gratings 11E and 12E of the fifth diffractive optical element 100E having a wide usable wavelength region in a step shape, the reflection efficiency can be increased and white light can be obtained. It is done.

In the fifth embodiment, the end face 14E has a four-step step shape, but may be an eight-step step shape as described in the first and third embodiments.
In the fifth embodiment, the fifth diffractive optical element 100E is bonded to the flat optical member 20, but may be bonded to a convex lens having a convex surface in the Z-axis direction.

<Optical System 200, 210 Using Diffraction Optical Element 100>
FIG. 9 is a conceptual cross-sectional view of the optical system 200 or the optical system 210 that uses the diffractive optical element 100. FIG. 9A shows an optical system 200 in which the diffractive optical element 100 is disposed on the image plane side from the stop DP. FIG. 9B shows an optical system 210 in which the diffractive optical element 100 is disposed on the object side of the stop DP.

  In the optical system 200 shown in FIG. 9A, the left side of FIG. 9A is an object (not shown) and the right side is an imaging plane IP. The optical system 200 includes an imaging lens 211, a diaphragm DP (pupil plane), and a diffractive optical element 100 in order from the left side. The optical system 200 is used as a photographing lens of a camera, for example.

  In the diffractive optical element 100, the end face 14 is formed in a stepped shape as shown in FIG. 1, so that the flare light generated by the light of each wavelength on the end face 14E can be made uniform. Whitened. Further, the end faces 14 of the diffraction gratings 11 and 12 of the diffractive optical element 100 having a wide-band operating wavelength region and having a lens function used at a specific wavelength, a plurality of wavelengths, or all wavelengths are formed in a staircase shape. Thus, the reflection efficiency can be increased and white light can be obtained.

  In the optical system 210 shown in FIG. 9B, the left side of FIG. 9B is an object (not shown) and the right side is an imaging plane IP. The optical system 210 includes an imaging lens 212, a diffractive optical element 100, a diaphragm DP (pupil plane), and an imaging lens 213 in order from the left side. The optical system 210 is also used as a camera taking lens.

  In the diffractive optical element 100, the end face 14 is formed in a stepped shape as shown in FIG. 1, so that the flare light generated by the light of each wavelength on the end face 14E can be made uniform. Whitened. Further, the end faces 14 of the diffraction gratings 11 and 12 of the diffractive optical element 100 having a wide-band operating wavelength region and having a lens function used at a specific wavelength, a plurality of wavelengths, or all wavelengths are formed in a staircase shape. Thus, the reflection efficiency can be increased and white light can be obtained.

  In FIG. 9B, the imaging lens 212 and the diffractive optical element 100 are separate bodies. However, the present invention is not limited to this, and the diffractive optical element 100 may be provided in the imaging lens 212.

  The optical system 200 or the optical system 210 shown in FIG. 9 can uniformize the flare light generated by the light of each wavelength on the end surface 14E by forming the end surface 14 of the diffractive optical element 100 in a step shape. The flare light is entirely whitened.

  Further, although the optical system 200 or the optical system 210 is shown as a camera taking lens, the present invention is not limited to this, but a video camera taking lens, an office image scanner, a digital copier reader lens, binoculars, a microscope, etc. The same effect can be obtained even when used in an imaging optical system such as an optical system of an observation apparatus.

  In FIG. 9, the diffractive optical element 100 described in FIG. 1 is used as the diffractive optical element, but the diffractive optical elements of the first to fifth embodiments may be used.

The optimum embodiment of the present invention has been described above, but as will be apparent to those skilled in the art, the present invention can be implemented with various modifications within the technical scope thereof.
For example, a sub-wavelength surface (SWS: Sub-Wavelength Structured) that can prevent reflection in a diffractive optical element.
Surface) may be provided.
In addition, as an optimal embodiment, the broadband visible light has been described. However, the present invention can also be applied to a diffractive optical element, a diffractive optical member, and an optical system in which narrow-band visible light, narrow-band or broadband infrared light or ultraviolet light is incident. Further, the present invention can be applied not only to a transmission type but also to a reflection type optical system.

11, 11A, 11B, 11C, 11D, 11E ... 1st diffraction grating 12, 12A, 12B, 12C, 12D, 12E ... 2nd diffraction grating 13, 13A, 13B, 13C, 13D, 13E ... Diffraction surface 14, 14A, 14B, 14C, 14D, 14E ... End face 141, 141A, 141B, 141C, 141D ... First face 142, 142A, 142B, 142C, 142D ... Second face 100, 100A, 100B, 100C, 100D, 100E ... Diffractive optical element 200, 210 ... Optical system 211, 212, 213 ... Imaging lens DP ... Diaphragm h, h1, h2 ... Height of second surface in Z-axis direction H, H1, H2, H5 ... Z-axis direction of diffraction surface and end surface Height IP ... Imaging plane P, P1, P2, P5 ... Pitch R, R1, R2 ... Corner rounding radius w, w1 w2 ... width in the X-axis direction of the first surface

Claims (12)

  1. A diffractive optical element comprising two optical members in which a diffractive optical surface having a grating structure in which a diffractive surface and an end surface are continuous at a predetermined pitch is faced to each other and laminated,
    A step including a first plane in which the end surface extends in the pitch direction and a second plane intersecting the first plane;
    A diffractive optical element that satisfies the following conditions, where the reference wavelength is d-line (587.6 nm) and the difference in refractive index between the two optical members is dN.
    0.02 <ΔNd <0.45 (1)
  2. When the width of the first plane is w and the height of the second plane is h,
    The diffractive optical element according to claim 1, wherein the width w and the height h satisfy the following conditional expression.
    1.0 <h / w <20.0 (2)
  3. The diffractive optical element according to claim 2, wherein a minimum pitch among the predetermined pitches of the grating structure is P, and the following condition is satisfied.
    0.003 <w / P <0.5 (3)
  4. The diffractive optical element according to claim 3, wherein the number of steps of the staircase is n, and the following condition is satisfied.
    2 ≦ n <16 (4)
  5. 5. The diffractive optical element according to claim 1, wherein the following condition is satisfied, where R is a roundness of a corner portion where the first plane intersects the second plane.
    R <5.0 μm (5)
  6. 6. The diffractive optical element according to claim 1, wherein the height of the end face is H, and the following condition is satisfied.
    0.01 <H / P <5.0 (6)
  7. The diffraction efficiency design value of d line (587.6 nm) is set to Ed, the diffraction efficiency design value of g line (435.8 nm) is set to Eg, the diffraction efficiency design value of C line (656.3 nm) is set to EC, and the following The diffractive optical element according to claim 1, wherein the conditional expression is satisfied.
    (EC + Eg) / 2> 0.9 × Ed (7)
  8. The following conditional expression is satisfied, where Δ (NF−Nc) is a difference in main dispersion (NF−Nc) between the two optical members. The diffractive optical element described.
    -20.0 <[Delta] Nd / [Delta] (NF-NC) <-2.0 (8)
  9.   The diffractive optical element according to any one of claims 1 to 8, wherein the end face is parallel to an optical axis of light transmitted through the diffractive optical element.
  10.   The diffractive optical element according to any one of claims 1 to 9, wherein a material of the two optical members is an ultraviolet curable resin.
  11. An optical system having a plurality of optical elements, guiding light and acting on the light,
    An optical system in which at least one of the optical elements is a diffractive optical element according to any one of claims 1 to 10.
  12.   An optical apparatus comprising the diffractive optical element according to any one of claims 1 to 10.
JP2009281242A 2009-12-11 2009-12-11 Diffraction optical element, optical system and optical apparatus Pending JP2011123317A (en)

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JP2004271583A (en) * 2003-03-05 2004-09-30 Nikon Corp Method for manufacturing optical element, optical element manufactured by same manufacturing method, and optical system equipped with same optical element
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JPH10186118A (en) * 1996-12-24 1998-07-14 Canon Inc Diffraction optical element and optical equipment having the same
JP2004157404A (en) * 2002-11-07 2004-06-03 Nikon Corp Diffraction optical element and method for manufacturing diffraction optical element, and optical system using diffraction optical element
JP2004271583A (en) * 2003-03-05 2004-09-30 Nikon Corp Method for manufacturing optical element, optical element manufactured by same manufacturing method, and optical system equipped with same optical element
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