JP2019012209A - Diffractive optical element and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a phase shift of a transmitted wavefront of light transmitted through a diffractive optical element by irradiating light having an intensity distribution in a molding step of a second layer of the diffractive optical element. A method of manufacturing a diffractive optical element in which a first layer having a diffraction grating shape and a second layer in close contact with the first layer are sequentially formed on a substrate, the thickness of the second layer being The second layer is formed by applying light energy and curing the second layer. The intensity distribution of the light energy is b (mm) from the optical axis of the diffractive optical element to the trough of the mth (m is an integer) grating, and the m + 1th grating from the trough of the mth grating. When the distance to the valley is p (mm) and the distance from the optical axis to the position where the light intensity in the second layer is maximum is I (r) max (mm), b ≦ I (r) A method for manufacturing a diffractive optical element, wherein max ≦ b + 0.4p is satisfied. [Selection] Figure 1

Description

  The present invention relates to a diffractive optical element used in an optical apparatus such as a camera or a video, and a manufacturing method thereof. The present invention also relates to an optical apparatus using a diffractive optical element.

  Composite optical elements obtained by molding a photocurable resin or thermosetting resin on a base material (substrate) are widely used in cameras, videos, and other optical equipment optical systems. Specific examples include an aspherical lens, a pickup lens, and a diffractive optical element. Among them, various manufacturing methods have been proposed for diffractive optical elements. In the method of manufacturing a diffractive optical element disclosed in Patent Document 1, first, a first material is provided between a first mold having a predetermined shape and a substrate, and light energy is applied to cure the first material. The step and the step of releasing the first material from the first mold and forming the first layer on the substrate are sequentially performed. Thereafter, a step of providing a second material between the second mold and the first layer, a step of applying light energy to cure the second material, and releasing the second material from the second mold Then, it is disclosed that the step of forming the second layer on the first layer is sequentially performed.

JP 2012-218394 A

  However, in the method for manufacturing a diffractive optical element described in Patent Document 1, light having a uniform intensity is irradiated onto the second layer. Therefore, in the step of curing and forming the second layer, the surface of the second layer formed on the first layer is not in contact with the first layer (flat surface), and the first layer has a lattice shape. Caused deformation (swell, dent) occurs. That is, a flat surface that should be flat and smooth is deformed into an uneven shape. As a result, the transmitted wavefront of the light transmitted through the diffractive optical element reaches the imaging surface of the optical system while causing a phase shift, and is concentric with the blurred image of the captured image (an image outside the focal range of the lens). There was a problem that a striped pattern was generated.

  The present invention has been made to address the above-described problems, and an object of the present invention is to provide a diffractive optical element that reduces a phase shift of a transmitted wavefront of light transmitted through the diffractive optical element, and a method for manufacturing the same.

  A method of manufacturing a diffractive optical element for solving the above-described problem is a first material including a photocurable resin or a thermosetting resin between a first mold having a shape obtained by inverting a diffraction grating shape and a substrate. A step of applying heat or light energy to cure the first material to form a first layer on the substrate, and releasing the first layer from the first mold. Providing a second material containing a photocurable resin between the second mold and the first layer, applying light energy to cure the second material, and Forming a second layer having a thickness of 0.5 μm or more and 100 μm or less in close contact with the first layer on the layer, and releasing the second layer from the second mold. A method of manufacturing a diffractive optical element, wherein the light energy is diffracted in the step of forming the second layer. The distance from the optical axis of the optical element to the valley of the mth (m is an integer) lattice is b (mm), and the distance from the valley of the mth lattice to the valley of the (m + 1) th lattice is p (mm). ), Where b ≦ I (r) max ≦ b + 0.4p is satisfied, where I (r) max (mm) is the distance from the optical axis to the position where the light intensity in the second layer is maximum. It is characterized by.

  A diffractive optical element for solving the above problem is a diffractive optical element in which a first layer having a diffraction grating shape on a base material and a second layer in close contact with the first layer are provided. The thickness of the second layer is not less than 0.5 μm and not more than 100 μm, and the distance from the optical axis of the diffractive optical element to the valley of the mth (m is an integer) grating is b (mm), The distance from the valley of the m-th grating to the valley of the m + 1-th grating is p (mm), the radial distance of the diffractive optical element from the optical axis is r (mm), and r is b ≦ r ≦ b + 0. When the refractive index of the second layer when satisfying 4p is Ka and the refractive index of the second layer when r satisfies b + 0.4p <r <b + p is Kb, Ka / Kb is from 1.0001. It is characterized by being in the range up to 1.0006.

  According to the present invention, it is possible to provide a diffractive optical element excellent in optical performance and a method for manufacturing the same, in which the deformation of the second layer is suppressed and the phase shift of the transmitted wavefront of light transmitted through the diffractive optical element is reduced. .

It is process drawing which shows one Embodiment of the manufacturing method of the diffractive optical element of this invention. It is the schematic which shows one Embodiment of the process of hardening the 2nd material of the manufacturing method of the diffractive optical element of this invention, and forming a 2nd layer. FIG. 2 is a top view and a cross-sectional view of an embodiment of a diffractive optical element of the present invention. It is a partial expanded sectional view of a diffractive optical element. It is the schematic which shows one Embodiment of the process of hardening the 2nd material of the manufacturing method of the diffractive optical element of this invention, and forming a 2nd layer. It is the schematic which shows one Embodiment of the optical instrument of this invention.

(Diffraction optical element manufacturing method)
The method for producing the diffractive optical element of the present invention will be described below.

  FIGS. 1A to 1F are process diagrams showing an embodiment of a method for producing a diffractive optical element of the present invention.

  As shown in FIG. 1, the method for manufacturing a diffractive optical element of the present invention uses a photocurable resin or a thermosetting resin between a first mold 3 having a shape obtained by inverting a diffraction grating shape and a substrate 1. A step (a) of providing the first material 2a to be included. Also, the step (b) of applying the heat or light energy to cure the first material 2a to form the first layer 2 on the substrate, and releasing the first layer 2 from the first mold 3 (C). Moreover, it has the process (d) which provides the 2nd material 4a containing a photocurable resin between the 2nd type | mold 5 and the 1st layer 2. FIG. Furthermore, the process of applying light energy to cure the second material 4a and forming the second layer 4 having a thickness of 0.5 μm or more and 100 μm or less in close contact with the first layer 2 on the first layer 2 (E) and a step (f) of releasing the second layer 4 from the second mold 5.

(Process a)
The first mold 3 has a shape obtained by inverting the diffraction grating shape. As the material of the first mold 3, a known material such as metal or resin can be used. For example, what was manufactured by forming a plating layer of NiP, Cu or the like on a metal base material, and cutting or polishing the plating layer may be used.

  As a method of providing the first material 2 a between the first mold 3 and the base material 1, the first material 2 a is applied to the base material 1 or the first mold 3 or both the base material 1 and the first mold 3. There is a method in which one material 2 a is dropped and the material 2 a is spread between the substrate 1 and the first mold 3. As a method of spreading the first material 2a, a method in which the base material 1 and the first mold 3 are brought closer to each other, and a direction in which the base material 1 and the first mold 3 are brought closer to each other. A known method such as a method of applying a load to can be used. Here, FIG. 1A shows a method of applying a load to the first mold 3 in the direction of the arrow. In addition, a method of filling the substrate 1 or the first mold 3 with its own weight, a method of filling the first material 2a by heating and lowering the viscosity, or the like can be used.

  Here, the first material 2a is spread until the desired thickness is reached and the lattice shape in the optically effective portion is covered. The first material 2a includes a photocurable resin or a thermosetting resin. The first material 2a is preferably a resin material having a low refractive index and high dispersion. Specifically, a fluorine-based epoxy resin, a sulfur-containing acrylic resin, titanium oxide, indium tin oxide, zirconium oxide, or the like can be used.

(Process b)
In order to cure the first material 2a, it is necessary to apply heat or light energy necessary for curing to the first material 2a. FIG. 1B shows a method for applying light energy to the material 2 a by the light source 12 from the substrate 1 side. As the light energy, for example, ultraviolet light or visible light can be used. Here, the 1st layer 2 can be formed on the base material 1 by hardening the 1st material 2a. Moreover, light energy and heat energy may be applied simultaneously, or both may be used stepwise.

(Process c)
As a method of releasing the first layer 2 from the first mold 3, a method of applying a load in the direction of releasing from the first mold 3 to the end of the substrate 1, the first mold A known method such as a method of applying a load to the mold 3 in the direction of releasing from the substrate 1 can be used. Here, the diffraction grating 7 having a height of z is transferred to the first layer 2 by the first mold 3.

(Process d)
As a method of providing the second material 4 a between the second mold 5 and the first layer 2, the first layer 2 or the second mold 5, or the first layer 2 and the second layer 2 can be used. There is a method in which the second material 4 a is dropped on both of the molds 5 and the second material 4 a is spread between the first layer 2 and the second mold 5. As a method of spreading the second material, a method of bringing the base material 1 and the second mold 5 close to each other or a direction of approaching the base material 1 and the second mold 5 to each other. A known method such as a method of applying a load can be used. Moreover, the method of filling with the self-weight of the base material 1 or the 2nd type | mold 5, the method of filling by heating the 2nd material 4a and reducing a viscosity, etc. can be used. Here, FIG. 1D shows a method of applying a load in the direction of the arrow to the second mold 5.

  Here, the second material 4a is spread so that the thickness of the second layer 4 is not less than 0.5 μm and not more than 100 μm, and covers the lattice shape in the optically effective portion. The second material 4a includes a photocurable resin. The second material 4a is preferably a resin material having a high refractive index and low dispersion. Specifically, a fluorine-based epoxy resin, a sulfur-containing acrylic resin, titanium oxide, indium tin oxide, zirconium oxide, or the like can be used. Further, the first material 2a and the second material 4a are preferably different materials.

(Process e)
In order to cure the second material 4a, it is necessary to impart light energy necessary for curing to the second material 4a. FIG. 1E shows a method of applying light energy to the material 4a by the light source 12 from the second mold 5 side. As the light energy, for example, ultraviolet light, visible light, or the like can be given to the second material 4a. By curing the second material 4a, the second layer 4 adhered to the first layer 2 can be formed. The light energy for curing the second material 4a has an intensity distribution. Specifically, the distance from the optical axis of the diffractive optical element to the valley of the mth (m is an integer) grating is b (mm), and from the valley of the mth grating to the valley of the m + 1st grating. Is the distance p (mm). Further, when the distance from the optical axis to the position where the light intensity in the second layer 4 is maximum is I (r) max (mm), the relational expression b ≦ I (r) max ≦ b + 0. An intensity distribution satisfying 4p is provided. Preferably b <I (r) max ≦ b + 0.2p, more preferably b <I (r) max ≦ b + 0.1p.

  Alternatively, the height of the diffraction grating of the first layer 2 is z (mm), and the radial distance of the diffractive optical element from the optical axis is r (mm). At that time, an intensity distribution is set such that the light intensity in the second layer 4 at the position of r = b + z is higher than the light intensity in the second layer 4 at the position of r = b + p−z. .

  FIG. 5 is a diagram showing an example of a technique for giving an intensity distribution to the light energy applied to the second layer 4. As shown in FIG. 5, for example, a gray mask 10 is disposed between a light source 12 such as an ultraviolet irradiation lamp that gives light energy 11 and the second mold 5, and light is irradiated through the gray mask 10 to obtain intensity. Distribution can be given. Alternatively, the gray mask 10 may be disposed between the light source 12 and the substrate 1 so that light is irradiated from the substrate 1 side.

  FIG. 2 is a schematic view showing one embodiment of a step of curing the second material of the method for producing a diffractive optical element of the present invention. In FIG. 2, a light intensity I (r) having an intensity distribution in the r direction indicating a radial distance from the optical axis 8 of the diffractive optical element is provided on the first layer 2 on the substrate 1. The second material 4a is irradiated. For convenience of explanation, the second mold 5 is omitted in FIG. Here, the distance b from the optical axis 8 of the diffractive optical element to the valley 13 of the mth grating, the distance p from the mth grating to the m + 1st grating, the second layer from the optical axis 8 of the diffractive optical element. The distance I (r) max to the position where the light intensity in 4 is maximum is defined as shown in FIG.

  In the second layer 4 formed by curing the second material 4a, the portion irradiated with strong light (for example, the position of r = I (r) max) is compressed by curing shrinkage or expansion of reaction heat. Stress is generated. On the other hand, a tensile stress is relatively generated in the portion of the second layer 4 irradiated with light with low intensity. In the subsequent step of releasing the second layer 4 from the second mold 5, the second mold 5, which restrains the stress on the flat surface 6, is removed, so that the stress in the second layer 4 is somewhat increased. Opened. Since the portion where the compressive stress is generated in the second layer 4 expands due to the release of stress after release, the flat surface 6 moves toward the convex shape. On the contrary, the portion where the tensile stress is generated in the second layer 4 is contracted by releasing the stress after the mold release, so that the flat surface 6 moves toward the concave shape.

  When the second layer 4 is released by irradiating the second layer 4 with light of uniform intensity as in the prior art, the flat surface 6 is waved following the lattice shape of the first layer 2 as shown in FIG. Shape occurs. In the present specification, the swell thickness refers to the length indicated by U in the figure. The interval of the wavy shape in the lens radial direction follows the interval of the lattice shape of the first layer 2, but the waviness thickness in the normal direction of the lens surface is the distance r from the optical axis, the thickness of the second layer 4 and the thickness of the second layer 4. 1 depends on the lattice height z of the lattice shape of the layer 2. The waviness thickness increases as the distance from the optical axis of the second layer 4 becomes shorter. In particular, the waviness thickness is remarkably increased in the second layer 4 at a distance within 20% of the lens radius centered on the optical axis. The waviness thickness increases as the thickness of the second layer 4 decreases. In particular, when the thickness of the second layer 4 is 100 μm or less, the waviness thickness is significantly increased. The waviness thickness increases as the lattice height of the lattice shape increases. Here, the preferable thickness of the second layer 4 is 20 μm or more.

  Such a phenomenon is caused by curing shrinkage of the photocurable resin constituting the second layer 4. Since the stress due to the curing shrinkage of the second layer 4 increases as it approaches the optical axis of the lens, the undulation thickness also increases as it approaches the optical axis of the lens. Further, since the same stress is dispersed in the layer as the thickness of the second layer 4 is increased, the undulation thickness is also reduced as the thickness of the second layer 4 is increased. Moreover, since the shear component of the stress increases as the lattice height z increases, the undulation thickness also increases as the lattice height z increases.

  Hereinafter, the waviness shape and the generation mechanism thereof will be described in more detail.

  FIG. 4 is a partially enlarged cross-sectional view of a diffractive optical element in which a first layer and a second layer in close contact with the first layer are sequentially provided on the substrate 1. Here, the close contact means that there is no gap or air layer. As shown in FIG. 4, the thickness of the second layer 4 is thin at the lattice tip of the lower layer and thick at the lattice valley. When the second material 4a is uniformly cured and shrunk, the amount of cure shrinkage in the thickness direction of the second layer 4 is increased by the thickness of the lattice valley portion being thicker than the lattice tip portion. Further, the position of the wavy concave portion in the lens radial direction depends on the lattice height of the lattice shape of the first layer 2. The wavy concave portion is generated on the thick side of the second layer 4 in the vicinity of the lattice wall surface. When the lattice height of the lattice shape is X μm, the undulating concave portion is generated at a position of about X μm from the lattice wall surface in the lens radial direction. In the present invention, a compressive stress is generated in the portion where a relatively strong light is irradiated to the portion in which the undulating concave portion is originally generated. By utilizing this compressive stress, the flat surface 6 can be formed more flat and smooth by conversely expanding the wavy concave portion. On the other hand, the undulating convex portion is generated on the side where the thickness of the second layer 4 in the vicinity of the lattice wall surface is thin. A tensile stress is generated by irradiating relatively weak intensity light to the portion where the undulating convex portion is generated. By using this tensile stress, the flat surface 6 can be formed more flat and smooth by contracting the undulating convex portion. That is, the light energy for curing the second material 4a has an intensity distribution satisfying the relational expression b ≦ I (r) max ≦ b + 0.4p, thereby achieving flat and smooth (small waviness thickness). Surface 6 can be obtained.

  Here, when I (r) max is larger than b + 0.4p, a compressive stress is applied to the second layer 4 at a position different from the generation position of the undulating concave portion, and thus the undulating shape cannot be sufficiently suppressed. . As a result, the phase shift of the transmitted wavefront of the light transmitted through the diffractive optical element cannot be sufficiently reduced.

  The ratio of the maximum value of the light intensity to the minimum value of the light intensity in the second layer at a position of radius r from the optical axis (where b ≦ r <b + p) is 1.2. It is preferable that it is 10 or less. This is because in this range, compressive stress and tensile stress suitable for reducing the waviness shape are generated in the second layer 4. As a result, the phase shift of the transmitted wavefront of the light transmitted through the diffractive optical element can be further reduced.

Furthermore, the maximum value of the light intensity is preferably 10 mW / cm ² or more and 50 mW / cm ² or less. This is because in this range, a compressive stress more suitable for reducing the waviness shape is generated in the second layer 4. As a result, the phase shift of the transmitted wavefront of the light transmitted through the diffractive optical element can be further reduced. Here, the value of the light intensity can be measured using, for example, an ultraviolet integrated light meter.

(Process f)
Finally, the second layer 4 is released from the second mold 5 to obtain a diffractive optical element.

(Diffraction optical element)
FIG. 3 is a top view and a sectional view of the diffractive optical element of the present invention. In the diffractive optical element of the present invention, a first layer 2 having a diffraction grating shape and a second layer 4 are provided on the substrate 1 in close contact with each other in the optical axis direction. Structure. The second layer 4 has a thickness of 0.5 μm or more and 100 μm or less and a flat surface 6. Here, the thickness of the second layer 4 is the thickness of the second layer 4 in a direction substantially perpendicular to the flat surface 6, and does not include the height of the step of the diffraction grating 7. That is, the thickness is indicated by T in FIG.

  By setting the thickness of the second layer 4 to 100 μm or less, the distribution of stress due to curing shrinkage generated in the second layer 4 in the step of curing the second material 4a can be made remarkable. When the thickness of the second layer 4 exceeds 100 μm, the stress generated by the hardening shrinkage of the second layer 4 is dispersed in the thick second layer 4, so that the stress distribution is not remarkable. On the other hand, when the thickness of the second layer 4 is less than 0.5 μm, strong compressive stress or tensile stress in the second layer 4 due to irradiation with light having an intensity distribution is a sink (a dent caused by hardening shrinkage of the material). , The dent). In particular, sink marks are likely to occur at the interface close to the lattice tip of the lower layer of the second layer 4. When sink marks occur, the appearance of the diffractive optical element deteriorates, and sufficient optical performance cannot be obtained. A preferable thickness of the second layer 4 is 20 μm or more.

  In the diffractive optical element of the present invention, the distance from the optical axis of the diffractive optical element to the valley of the mth (m is an integer) grating is b (mm), and the m + 1th from the valley of the mth grating. The distance to the valley of the grating is p (mm), and the radial distance from the optical axis to the diffractive optical element is r (mm). At that time, the refractive index of the second layer when r satisfies b ≦ r ≦ b + 0.4p is defined as Ka. The refractive index of the second layer when r satisfies b + 0.4p <r <b + p is Kb. At that time, Ka / Kb is in the range of 1.0001 to 1.0006. When this range is satisfied, good optical performance can be obtained.

  When Ka / Kb is less than 1.0001, the generation of compressive stress and tensile stress in the second layer is reduced, and the swell thickness is increased. On the other hand, when Ka / Kb exceeds 1.0006, the generation of compressive stress and tensile stress in the second layer increases, and sink marks are likely to occur.

  Here, the refractive index can be measured using, for example, a microspectrophotometer.

  Furthermore, in the diffractive optical element of the present invention, the undulation thickness in the second layer is preferably 80 nm or less. If the undulation thickness exceeds 80 nm, the transmitted wavefront of the light transmitted through the diffractive optical element reaches the imaging surface of the optical system while causing a phase shift, and there is a possibility that a concentric striped pattern is generated in the captured image. .

  In the diffractive optical element of the present invention, it is preferable that the curing reaction rate of the portion irradiated with the strong light in the second layer 4 is higher than the curing reaction rate of the portion irradiated with the weak light. Here, the portion irradiated with the intense light is a portion where r satisfies b ≦ r ≦ b + 0.4p. The portion irradiated with light having a low intensity is a portion where r satisfies b + 0.4p <r <b + p. This is because when the curing reaction rate satisfies the above condition, the Ka / Kb can be easily set in the range of 1.0001 to 1.0006. The curing reaction rate can be determined from the residual rate of the carbon double bond spectrum using, for example, microscopic Fourier transform infrared spectroscopy. Here, the state in which the carbon double bond spectrum is not detected is defined as a curing reaction rate of 100%. In addition, the cure shrinkage rate of a general photocurable resin is about 5 to 10%.

(Evaluation of diffractive optical element)
The phase shift of the transmitted wavefront of the diffractive optical element can be measured by an optical interferometer, but can also be evaluated more simply by a photograph taken using the diffractive optical element. Specifically, it can be evaluated by the relationship between the undulation thickness of the flat surface and the luminance difference in the bright and dark stripes in the blurred image of the photograph. This is because the phase shift of the transmitted wavefront appears as a concentric bright and dark stripe pattern in the blurred image of the photographed photograph, but the brightness difference and contrast value of the light and dark are equal to the degree of phase shift of the transmitted wavefront. The brightness difference between bright and dark stripes in a photographic blurred image can be analyzed using general image processing software. If the brightness difference of the striped pattern in the photographic blurred image is about 60, the striped pattern is not very thin and noticeable, so the appearance of the photographed image does not deteriorate. If the brightness difference of the striped pattern in the photographic blurred image exceeds 150, the striped pattern becomes dark and conspicuous, so that the photographed image is deteriorated in appearance.

  As described above, by suppressing the deformation of the second layer 4 that occurs in the step of forming the second layer 4 and reducing the phase shift of the transmitted wavefront of the light transmitted through the diffractive optical element, the optical performance is improved. It is possible to provide a diffractive optical element excellent in the above.

(Optical equipment)
Next, the optical apparatus of the present invention will be described. An optical apparatus according to the present invention is characterized in that the diffractive optical element and a lens are arranged.

  FIG. 6 is a cross-sectional view of an optical system of an interchangeable lens barrel of a single-lens reflex camera that is an example of a preferred embodiment of the optical apparatus of the present invention. In the optical system of the lens barrel 30, the lenses 21 to 28 and the diffractive optical element 20 are arranged perpendicular to the optical axis O. Here, the lens 21 side is the surface of the lens barrel, and the lens 28 side is the detachable mount side with the camera.

  By disposing the diffractive optical element 20 of the present invention at an appropriate position in the optical system, it is possible to provide a small and lightweight lens barrel with reduced blur images and reduced chromatic aberration. In addition, by providing the diffractive optical element 20 inside the lens 21 as shown in FIG. 6, it is possible to prevent external light from directly hitting the diffractive optical element 20, so that flare can be suppressed.

  Examples The diffractive optical element of the present invention and the method for producing the same will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples.

Example 1
(Manufacture of diffractive optical elements)
A method for manufacturing the diffractive optical element of this embodiment will be described with reference to FIG.

  As the substrate 1, glass having a radius of 30 mm and a thickness of 3 mm made of glass (manufactured by OHARA INC., Product name: S-FPL) was used. A colorless and transparent photocurable fluorine-based epoxy resin was used for the first material 2a, and a colorless and transparent photocurable sulfur-containing acrylic resin was used for the second material 4a.

  First, the surface of the substrate 1 on which the first layer 2 is formed was subjected to a silane coupling treatment in order to strengthen the adhesion with the fluorine-based epoxy resin.

  Next, the silane coupling treatment surface of the base material 1 was disposed toward the first mold 3 side. The first die 3 is a stainless steel base plated with NiP, and was manufactured by cutting so that the diffraction grating shape was inverted.

  Next, 600 mg of a fluorine-based epoxy resin was dropped in the vicinity of the center of the first mold 3 with a dispenser (not shown) (FIG. 1A). In addition, you may dripped a fluorine-type epoxy resin to the center vicinity of the silane coupling process surface of the base material 1. FIG.

  Next, the first mold 3 was pressed with a force of 3 kgf for 10 seconds to spread and fill the fluorine-based epoxy resin between the base material 1 and the first mold 3 (FIG. 1B). At this time, the fluorinated epoxy resin was spread out until the thickness between the substrate 1 and the first mold 3 became 200 μm, and covered the lattice shape in the optically effective portion. Here, in order to fill the fluorinated epoxy resin concentrically between the substrate 1 and the first mold 3, a step of rotating the substrate 1 or the first mold 3 around the optical axis may be added. .

Next, the fluorine-based epoxy resin was cured using an ultraviolet irradiation lamp (manufactured by HOYA CANDEO OPTRONICS Co., Ltd., product name: UL750). The fluorine-based epoxy resin was irradiated with ultraviolet light having a light intensity of 10 mW / cm ² through the substrate 1 for 10 minutes. Here, the light intensity was measured using an ultraviolet integrated light meter (manufactured by USHIO INC., Product name: UIT-250).

  Next, the first layer 2 integrated with the substrate 1 was released from the first mold 3 to form the first layer 2 on the substrate 1. The diffraction grating 7 was transferred to the first layer 2 by the first mold 3 (FIG. 1C).

  Next, the base material 1 was disposed with the first layer 2 facing the second mold 5 side. The second mold 5 is made of a quartz material that transmits ultraviolet rays, and is manufactured by polishing.

  Next, 150 mg of sulfur-containing acrylic resin was dropped in the vicinity of the center of the second mold 5 with a dispenser (not shown) (FIG. 1 (d)). Note that the sulfur-containing acrylic resin may be dropped near the center of the first layer 2 on the substrate 1.

  Next, the base material 1 was pressed with a force of 10 kgf for 15 seconds, and the sulfur-containing acrylic resin was spread and filled between the first layer 2 and the second mold 5 on the base material 1 (FIG. 1 ( e)). At this time, the sulfur-containing acrylic resin was spread until the thickness between the first layer 2 and the second mold 5 reached 50 μm and covered the lattice shape in the optically effective portion. Here, in order to fill the sulfur-containing acrylic resin concentrically between the first layer 2 and the second mold 5, a step of rotating the substrate 1 or the second mold 5 around the optical axis is added. Also good.

  Next, using an ultraviolet irradiation lamp as the light source 12, the sulfur-containing acrylic resin was irradiated with ultraviolet light through the second mold 5 for 15 minutes to be cured. In this embodiment, the intensity distribution of ultraviolet light is provided by arranging a gray mask between the ultraviolet irradiation lamp and the second mold 5 and irradiating light through this gray mask (see FIG. 5). Note that a gray mask may be disposed between the ultraviolet irradiation lamp and the substrate 1 to irradiate light from the substrate 1 side. Light irradiation through the gray mask is performed only on the second grating from the optical axis of the diffractive optical element, and other gratings are directly irradiated with light from the ultraviolet irradiation lamp without using the gray mask. did.

At this time, maximum and minimum values of the light intensity in the second layer 4 are each 10 mW / cm ² and 2 mW / cm ^2, the ratio of the maximum value to the minimum value was 5. The light intensity was measured using an ultraviolet integrated light meter (manufactured by USHIO INC., Product name: UIT-250). The distance p of the first grating (m = 1, b = 0 mm) close to the optical axis of the diffractive optical element was 3 mm (b + 0.4p = 1.2 mm). Further, the positions of the maximum value and the minimum value of the light intensity in the second layer of the same lattice were the distance on the optical axis (I (r) max = 0 mm) and 2.98 mm from the optical axis, respectively. The distance p of the second grating (m = 2, b = 3 mm) from the optical axis of the diffractive optical element was 1.6 mm (b + 0.4p = 3.64 mm). The positions of the maximum value and the minimum value of the average light intensity in the second layer of the lattice are 3.02 mm (I (r) max = 3.02 mm) and 4.58 mm from the optical axis, respectively. there were.

  Finally, the second layer 4 integrated with the substrate 1 and the first layer 2 was released from the second mold 5 to obtain the diffractive optical element of the present invention (FIG. 1 (f)). .

  The obtained diffraction grating is a blazed diffraction grating that is axially symmetric with respect to the optical axis, the grating height is 20 μm, and the distance of the grating in the lens radial direction is distributed in the range of 0.2 to 3 mm. . (See Figure 3)

  The flat surface 6 was transferred to the second layer 4 by the second mold 5, and the waviness thickness on the flat surface 6 was 50 nm.

(Evaluation of diffractive optical element)
Subsequently, the obtained diffractive optical element was evaluated.

  In the diffractive optical element of this example, the waviness thickness of 50 nm on the flat surface corresponds to a luminance difference of 60 in the bright and dark stripe pattern in the blurred image of the photograph.

  In this example, the second layer 4 was irradiated with light having an intensity distribution using a gray mask. In the portion of the second layer 4 irradiated with strong light, compressive stress is generated due to curing shrinkage and reaction heat expansion. On the contrary, a tensile stress is relatively generated in the portion of the second layer 4 irradiated with light with low intensity.

  Since the grating height of the grating shape of this embodiment is 20 μm, if light having no intensity distribution is irradiated, a wavy concave portion is generated at a position of about 20 μm from the grating wall surface in the lens radial direction. In this example, a compressive stress was generated in the part by irradiating light with a relatively strong intensity with respect to the part where the undulating concave part was originally generated. By utilizing this compressive stress, the undulating concave portion was expanded in reverse to form the flat surface 6 more flat and smooth. On the other hand, as shown in FIG. 4, the undulation-shaped convex portion is generated on the side where the thickness of the second layer 4 near the lattice wall surface is thin. A tensile stress was generated by irradiating relatively weak light to the portion where the undulating convex portion was generated. By using this tensile stress, the undulating convex portion was contracted in reverse to form the flat surface 6 more flat and smooth.

  Further, in this embodiment, the entire surface of the flat surface 6 is irradiated by irradiating light having an intensity distribution to the second layer 4 of the second lattice from the optical axis where a particularly large waviness shape occurs. It was formed flat and smooth.

  The refractive index in the second layer 4 of the diffractive optical element of this example was measured using a microspectrophotometer. As a result, the refractive index Ka of the second layer 4 when the distance r in the radial direction of the diffractive optical element from the optical axis satisfies b ≦ r ≦ b + 0.4p was 1.5559. The refractive index Kb of the second layer 4 when r satisfies b + 0.4p <r <b + p was 1.5554. That is, Ka / Kb was 1.0003.

  In addition, the curing reaction rate in the second layer 4 of the diffractive optical element in this example was measured using microscopic Fourier transform infrared spectroscopy. As a result, the curing reaction rate of the portion where the radial distance r of the diffractive optical element from the optical axis satisfies b ≦ r ≦ b + 0.4p was 87%. Moreover, the curing reaction rate of the part where r satisfies b + 0.4p <r <b + p was 76%.

  According to the method for manufacturing a diffractive optical element of this embodiment, deformation of the second layer 4 that occurs in the step of forming the second layer 4 can be suppressed. As a result, the undulation thickness of the flat surface 6 can be suppressed and the phase shift of the transmitted wavefront of the light transmitted through the diffractive optical element can be reduced, so that a diffractive optical element having excellent optical performance can be manufactured.

(Comparative Example 1)
In Comparative Example 1, only the thickness of the second layer 4 is different from that in Example 1, and the other conditions are the same. The thickness of the second layer 4 of Comparative Example 1 was 105 μm, which was thicker than that of Example 1.

  In Comparative Example 1, since the thickness of the second layer 4 was large, the compressive stress and the tensile stress in the second layer 4 due to irradiation with light having an intensity distribution did not remarkably occur. Since the flattening of the wavy shape is insufficient due to the release of stress after release, the phase shift of the transmitted wavefront of the light transmitted through the diffractive optical element cannot be reduced sufficiently.

(Comparative Example 2)
In Comparative Example 2, only the thickness of the second layer 4 is different from that in Example 1, and the other conditions are the same. The thickness of the second layer 4 of Comparative Example 2 was 0.4 μm, which was thinner than that of Example 1.

  In Comparative Example 2, since the thickness of the second layer 4 was thin, sink marks were generated due to strong compressive stress and tensile stress in the second layer 4 by irradiation with light having an intensity distribution. In particular, sink marks occurred at the interface close to the lattice tip of the lower layer of the second layer 4. Since sink marks were generated, the appearance of the diffractive optical element was deteriorated, and sufficient optical performance could not be obtained.

(Example 2)
The manufacturing method of the diffractive optical element of this example is different from that of Example 1 only in the maximum and minimum values of the light intensity and the irradiation range in the step of irradiating the second layer 4 with light having an intensity distribution. The other conditions are the same.

Maximum value and a minimum value of the light intensity in the second layer 4 of the present embodiment are each 5 mW / cm ² and 0.5 mW / cm ^2, the ratio of the maximum value to the minimum value was 10.

  Furthermore, in Example 1, the light having the intensity distribution was applied to the second grating from the optical axis of the diffractive optical element, but in this example, the entire surface of the second layer 4 was applied.

Since the lattice height of the lattice shape of the present example is 15 μm, the undulating concave portion is generated at a position of about 15 μm from the lattice wall surface to the thick side of the second layer. The portion where the undulating concave portion is generated was irradiated with light having a maximum value of light intensity of 5 mW / cm ² .

  The configuration of the obtained diffractive optical element was the same as that of Example 1 except that the shapes of the second layer 4 and the diffraction grating 7 were different from those of Example 1. The thickness of the second layer 4 was 20 μm, and the undulation thickness of the flat surface 6 was 80 nm. The height of the diffraction grating 7 was 15 μm. (See Figure 3)

  In the diffractive optical element of this example, the undulation thickness of 80 nm on the flat surface 6 corresponds to a luminance difference of 100 in the bright and dark stripe pattern in the photographic blurred image.

  When the refractive index in the second layer 4 of the diffractive optical element of this example was measured using a microspectrophotometer, Ka was 1.5553 and Kb was 1.5545. That is, Ka / Kb was 1.0005.

  Moreover, the curing reaction rate in the 2nd layer 4 of the diffractive optical element of a present Example was measured. As a result, the curing reaction rate of the portion where the distance r in the radial direction of the diffractive optical element from the optical axis satisfies b ≦ r ≦ b + 0.4p was 82%. Moreover, the curing reaction rate of the part where r satisfies b + 0.4p <r <b + p was 68%.

  In this way, in this embodiment, the deformation of the second layer 4 that occurs in the step of forming the second layer 4 is suppressed, and the phase shift of the transmitted wavefront of the light transmitted through the diffractive optical element is reduced. A diffractive optical element having excellent optical performance can be provided. In particular, even when the thickness of the second layer 4 becomes thinner, by increasing the ratio of the maximum value to the minimum value of the light intensity in the second layer 4, a good flat surface in which the waviness shape is suppressed 6 can be formed. Furthermore, by irradiating the entire surface of the second layer 4 with light having an intensity distribution, a good flat surface with a suppressed waviness shape can be formed on the entire surface of the second layer 4.

(Comparative Example 3)
Comparative Example 3 is the same in other configurations except that the position of the maximum value of the light intensity in the second layer is different from that in Example 2.

  The position of the maximum value of the light intensity in Comparative Example 3 is 45% from the grating wall surface to the thicker side of the second layer with respect to the distance of each grating (I (r) max = b + 0.45p). It was. Specifically, with respect to a grating having a distance p of 1 mm, the position of the maximum value of the light intensity was 0.45 mm from the grating wall surface to the thicker side of the second layer.

  In Comparative Example 3, since the compressive stress was applied to the second layer 4 at a position different from the position where the undulating concave portion was generated, the undulating shape could not be sufficiently suppressed. Therefore, the phase shift of the transmitted wavefront of the light transmitted through the diffractive optical element cannot be reduced sufficiently.

(Example 3)
The manufacturing method of the diffractive optical element of this example uses a photocurable resin in which ITO fine particles are dispersed in the first material 2a, and uses a photocurable acrylic resin in which ZrO2 fine particles are dispersed in the _second material 4a. Used differently. Further, the maximum value and minimum value of the average light intensity in the step of irradiating the second layer 4 with light having an intensity distribution, and the light irradiation direction are also different from those in the first embodiment. Same as 1.

Average between the maximum value and the minimum value of the light intensity in the second layer 4 of the present embodiment are each 12 mW / cm ² and 10 mW / cm ^2, the ratio of the maximum value to the minimum value was 1.2. Further, in Example 1, light having an intensity distribution was irradiated from the second mold 5 side that transmits ultraviolet rays through the gray mask, but in this example, the intensity was applied from the substrate 1 side through the gray mask. Irradiated with light having a distribution. At this time, the light intensity to be irradiated was set in consideration of the attenuation rate of ultraviolet rays by the first layer 2.

Since the lattice height of the lattice shape of the present embodiment is 30 μm, the undulating concave portion is generated at a position of about 30 μm from the lattice wall surface to the thick side of the second layer. The portion where the undulating concave portion is generated was irradiated with light having a maximum light intensity of 12 mW / cm ² .

  The structure of the obtained diffractive optical element is the same as that of Example 1 except for the materials of the first layer 2 and the second layer 4 and the shapes of the second layer 4 and the diffraction grating 7. It is. The thickness of the second layer 4 was 100 μm, and the undulation thickness of the flat surface 6 was 20 nm. The grating height of the diffraction grating 7 was 30 μm. (See Figure 3)

  In the diffractive optical element of this example, the waviness thickness of 20 nm on the flat surface 6 corresponds to a luminance difference of 30 in the bright and dark stripe pattern in the photographic blurred image.

  When the refractive index in the second layer 4 of the diffractive optical element in this example was measured using a microspectrophotometer, Ka was 1.6208 and Kb was 1.6205. That is, Ka / Kb was 1.0002.

  Moreover, the curing reaction rate in the 2nd layer 4 of the diffractive optical element of a present Example was measured. As a result, the curing reaction rate at the portion where the distance r in the radial direction of the diffractive optical element from the optical axis satisfies b ≦ r ≦ b + 0.4p was 88%. Moreover, the curing reaction rate of the part where r satisfies b + 0.4p <r <b + p was 81%.

  In this way, in this embodiment, the deformation of the second layer 4 that occurs in the step of forming the second layer 4 is suppressed, and the phase shift of the transmitted wavefront of the light transmitted through the diffractive optical element is reduced. A diffractive optical element having excellent optical performance can be provided. In particular, when the thickness of the second layer 4 is thicker, by reducing the ratio of the maximum value to the minimum value of the light intensity in the second layer 4, a good flat surface in which the waviness shape is suppressed 6 can be formed. Furthermore, since the light which has intensity distribution can be irradiated from the base material 1 side, the 2nd type | mold 5 can be manufactured with the arbitrary materials which considered the specification and cost.

DESCRIPTION OF SYMBOLS 1 Base material 2 1st layer 2a 1st material 3 1st type | mold 4 2nd layer 4a 2nd material 5 2nd type | mold 6 Flat surface 7 Diffraction grating 8 Optical axis 9 Lattice wall surface 10 Gray mask 11 Light Intensity of energy 12 Light source 13 Valley of m-th grating 20 Diffractive optical element 21 Lens 22 Lens 23 Lens 24 Lens 25 Lens 26 Lens 27 Lens 28 Lens 30 Lens barrel

Claims (7)

Providing a first material containing a photocurable resin or a thermosetting resin between the first mold having a shape obtained by inverting the diffraction grating shape and the substrate;
Applying heat or light energy to cure the first material to form a first layer on the substrate;
Releasing the first layer from the first mold;
Providing a second material containing a photocurable resin between a second mold and the first layer;
Applying the light energy to cure the second material, and forming a second layer having a thickness of 0.5 μm or more and 100 μm or less in close contact with the first layer on the first layer;
Demolding the second layer from the second mold;
A diffractive optical element manufacturing method comprising:
In the step of forming the second layer, the distance from the optical axis of the diffractive optical element to the m-th (m is an integer) valley of the grating is b (mm), and m + 1 from the m-th grating. When the distance to the second grating is p (mm) and the distance from the optical axis to the position where the light intensity in the second layer is maximum is I (r) max (mm),
b ≦ I (r) max ≦ b + 0.4p
The manufacturing method of the diffractive optical element characterized by satisfy | filling.   The ratio of the maximum value of the light intensity to the minimum value of the light intensity in the second layer at the position of the distance r in the radial direction of the diffractive optical element from the optical axis (where b ≦ r <b + p). The method for producing a diffractive optical element according to claim 1, wherein is 1.2 or more and 10 or less. The method for producing a diffractive optical element according to claim 2, wherein the maximum value of the light intensity is 10 mW / cm ² or more and 50 mW / cm ² or less. Providing a first material containing a photocurable resin or a thermosetting resin between the first mold having a shape obtained by inverting the diffraction grating shape and the substrate;
Applying heat or light energy to cure the first material to form a first layer having a diffraction grating shape with a height of z (mm) on the substrate;
Releasing the first layer from the first mold;
Providing a second material containing a photocurable resin between a second mold and the first layer;
Applying the light energy to cure the second material, and forming a second layer having a thickness of 0.5 μm or more and 100 μm or less in close contact with the first layer on the first layer;
Demolding the second layer from the second mold;
A diffractive optical element manufacturing method comprising:
In the step of forming the second layer, the distance from the optical axis of the diffractive optical element to the m-th (m is an integer) valley of the grating is b (mm), and m + 1 from the m-th grating. When the distance to the second grating is p (mm) and the radial distance of the diffractive optical element from the optical axis is r (mm), the light intensity in the second layer at the position of r = b + z is , R = b + p−z The light intensity in the second layer at the position is higher than that of the diffractive optical element. A diffractive optical element in which a first layer having a diffraction grating shape on a substrate and a second layer are provided in close contact with each other on the first layer,
The thickness of the second layer is not less than 0.5 μm and not more than 100 μm,
The distance from the optical axis of the diffractive optical element to the valley of the mth (m is an integer) grating is b (mm), and the distance from the valley of the mth grating to the valley of the m + 1st grating is p ( mm), the radial distance of the diffractive optical element from the optical axis is r (mm), the refractive index of the second layer when r satisfies b ≦ r ≦ b + 0.4p, and Ka is r + b + 0.4p < A diffractive optical element, wherein Ka / Kb is in a range of 1.0001 to 1.0006, where Kb is a refractive index of the second layer when r <b + p is satisfied.   The diffractive optical element according to claim 5, wherein the waviness thickness in the second layer is 80 nm or less.   An optical apparatus comprising the diffractive optical element according to claim 5 and a lens.

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