JPH1123820A - Method for manufacturing diffractive optical element and optical apparatus having the diffractive optical element - Google Patents

Abstract

(57) [Problem] To provide a diffractive optical element constituted by overlapping a plurality of different materials. SOLUTION: A first step of injecting an ultraviolet curable resin 5 having a volume not less than the volume of a concave portion into a surface of a first layer diffraction grating 2 and a flat plate 6 while pressing a curved flat plate 6 relatively to the first layer diffraction grating 2. Of the first layer diffraction grating 2 and a third step of curing the ultraviolet curable resin 5 to manufacture a diffractive optical element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a diffractive optical element, and more particularly to a method for manufacturing a diffractive optical element in which a plurality of different materials are superposed.

[0002]

2. Description of the Related Art Conventionally, in an optical system composed only of a refraction system, chromatic aberration is reduced by combining glass materials having different dispersion characteristics. For example, in an objective lens such as a telescope, a glass material having a small dispersion is a positive lens, and a glass material having a large dispersion is a negative lens. By using these in combination, chromatic aberration appearing on the axis is corrected. For this reason, when the number of constituent lenses is limited, or when the usable glass material is limited, the chromatic aberration cannot be sufficiently corrected in some cases.

A method for correcting chromatic aberration by combining glass materials is described in SPIE Vol.1354 International Lens Des.
Documents such as Ign Conference (1990) disclose a method of reducing chromatic aberration by providing a diffractive optical element having a diffractive action in a part of an optical system. This method utilizes the physical phenomenon that dispersion occurs in opposite directions between the refractive optical element and the diffractive optical element as shown in FIG.

As the diffractive optical element, for example, a kinoform type which can concentrate the amount of light on the diffracted light of a predetermined order or a phase type diffractive optical element having a binary lattice cross-sectional shape approximating the kinoform type in a stepwise manner is known. Have been. In such a diffractive optical element, by changing the concentric grating period from the center of the element toward the periphery, the same converging function and diverging function as the refractive optical element can be provided.

In a kinoform-type or binary-type diffractive optical element, when the refractive index of the element is n, the grating height d is set as follows: d = mλ / (n−1) (1) The diffraction efficiency of the m-th order diffracted light at the wavelength λ can be maximized. Here, the diffraction efficiency is a ratio of the amount of light distributed to diffracted light of a specific order, and is expressed by a ratio of the amount of light of the entire incident light to the amount of diffracted light of a specific order.

Incidentally, the diffraction efficiency of the diffracted light of a specific order of the phase type diffractive optical element has a characteristic as shown in FIG. 6, for example. In FIG. 6, the horizontal axis represents wavelength, and the vertical axis represents diffraction efficiency. As shown in FIG. 6, this diffractive optical element is designed so that the diffraction efficiency of the diffracted light of a specific order is the highest at a specific wavelength λD (λL ≦ λD ≦ λU). The efficiency is relatively lower than the diffraction efficiency at the wavelength λD. This is the grid height d
Is optimized using the equation (1) at the wavelength λD, so that the optimal value is not obtained at other wavelengths. The wavelength used to determine the grating height d such as λD will be referred to as a design wavelength, and the order of the target diffracted light will be referred to as a design order.

For example, when the design wavelength is 550 nm, the design order is 1st, and the diffractive optical element is formed by an annular stepped structure of eight steps, the diffraction efficiency at the design wavelength becomes about 95%, and the wavelength at the wavelength of 650 nm. The diffraction efficiency of the first-order diffracted light is about 88%, and the diffraction efficiency of the first-order diffracted light at a wavelength of 440 nm is about 80%. If the diffraction efficiency is less than 100%, the light becomes a diffracted light other than the designed order.

[0008] Of these, diffracted light of orders distant from the design order is significantly displaced from the imaging position of the diffracted light of the design order, and therefore does not contribute to image formation, and the entire surface remains in a flare-like state. Will be added. On the other hand, the diffracted light of the order near the design order (specifically, the design order ± 1st order) does not resolve in the spatial frequency region where the imaging performance is evaluated, but is not completely blurred and has a low space. An image is formed in the frequency domain. For this reason,
If the diffraction efficiency of the diffracted light of this order is high, the spot becomes a spot having a considerably large side lobe around the diffracted light of the design order, and there is a problem that the optical performance is deteriorated.

That is, in order to obtain good optical performance by using the diffractive optical element in an optical system, the diffraction efficiency of the diffracted light of the design order is kept high over the entire wavelength band used, and particularly, the diffraction efficiency near the design order is high. It was necessary to keep the diffraction efficiency of the diffracted light low.

[0010]

In order to keep the diffraction efficiency of diffracted light of the order near the design order low and to maintain the diffraction efficiency of the diffracted light of the design order high over a wide wavelength band, a plurality of optical materials having different dispersions are stacked. The combined diffractive optical element
JP-A-9-127321 and JP-A-9-12732.
No. 2 discloses this.

However, in the above-mentioned publication, although the material of the optical material constituting the diffractive optical element is disclosed, no specific manufacturing method using the material is disclosed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to provide a method of manufacturing a diffractive optical element constituted by overlapping a plurality of different materials.

[0013]

In order to achieve the above object, a method of manufacturing a diffractive optical element according to the present invention comprises a step of injecting a resin before curing into a surface of a substrate on which an uneven portion is formed, the resin having a volume not less than the volume of the concave portion. 1 step, loosening the curvature of the elastic member while relatively pressing the curved elastic member against the substrate surface,
The method includes a second step of removing an excess portion of the resin before curing from the surface of the substrate, and a third step of curing the resin.

An optical apparatus according to the present invention is characterized by having a diffractive optical element manufactured by the manufacturing method according to the present invention.

[0015]

FIG. 1 is an enlarged sectional view of a two-layer diffractive optical element manufactured by the manufacturing method of the present invention. For example, in the optical system of an optical device such as a camera, a diffractive optical element used for achromatism in combination with a refractive lens,
Usually, an annular grating whose pitch decreases as the distance from the optical axis increases is reduced. However, in the present embodiment, for simplification, the grating is illustrated as a grating having a constant pitch.

In FIG. 1, reference numeral 1 denotes an optical base on which a first-layer diffraction grating is formed. Reference numeral 2 denotes a first-layer diffraction grating formed on the surface of the optical substrate 1 with an ultraviolet curable resin. In the present embodiment, the optical substrate 1 and the first-layer diffraction grating 2 are substrates of the present invention. Is equivalent to The cross-sectional shape of the first-layer diffraction grating 2 is a shape obtained by approximating a blazed kinoform shape or a sawtooth shape by eight steps. In this embodiment, an eight-step shape is formed. Reference numeral 3 denotes a second-layer diffraction grating formed on the first-layer diffraction grating 2 with an ultraviolet curable resin. The second-layer diffraction grating 3 is formed using a material having a higher dispersion than the first-layer diffraction grating 2. The two-layer diffractive optical element 4 is formed by the optical substrate 1, the first-layer diffraction grating 2, and the second-layer diffraction grating 3.
Is configured.

Next, a method of manufacturing the two-layer diffractive optical element 4 will be described with reference to FIGS.

First, in the step shown in FIG.
On a well-cleaned and smooth flat surface of an optical substrate 1 made of optical glass having a refractive index of 1.52 and an Abbe number of 64, a first grating having an eight-step stair structure with one grating formed by a known replica molding method.
The layer diffraction grating 2 is formed.

As the UV curable resin material of the first layer diffraction grating 2, a refractive index of 1.5 close to the optical characteristics of the optical substrate 1 is used.
2. A urethane-modified polyester acrylate having an Abbe number of 50 was used as a main component.

Next, in the step shown in FIG.
The refractive index after curing is 1.5 in the concave portion of the first layer diffraction grating 2.
9. An uncured UV-curable resin 5 containing a modified epoxy acrylate having an Abbe number of 28 as a main component is dropped so as not to entrap bubbles. At this time, the ultraviolet curing resin 5
Is dropped in an amount larger than the volume occupied by the concave portion, and fills the concave portion with a sufficient amount.

Next, in the step shown in FIG.
The flat plate 6 made of nickel coated with a release material thinly is curved so that the diffractive optical element side is convex, and the center of the diffractive optical element is brought into contact with the convex vertex of the flat plate 6 at a point or a minute surface. The flat plate 6 corresponds to the elastic member of the present invention.

Next, in the step shown in FIG.
While pressing the curved flat plate 6 against the first layer diffraction grating 2,
The warpage of the flat plate 6 is gradually loosened, and the surplus portion of the ultraviolet curable resin 5 is pushed out of the diffractive optical element.

Next, in the step shown in FIG.
The curved flat plate 6 is pressed against the entire protruding portion of the first-layer diffraction grating 2, and in this state, ultraviolet rays are irradiated from the optical substrate 1 side to cure the ultraviolet curing resin 5.

Next, in the step shown in FIG.
The flat plate 6 is peeled off.

Through the above steps, a two-layer diffractive optical element 4 is obtained.

When the surface of the diffractive optical element is smooth as in this embodiment, dust does not enter the uneven portion when used in an optical device such as a camera, and the dust can be easily removed.
Further, there is an advantage that an optical thin film such as an antireflection film can be easily formed.

Also, since the resin is hardened in a state where the resin is made uniform from the center to the periphery of the diffractive optical element, a high-quality two-layer diffractive optical element can be easily manufactured.

In this embodiment, the flat plate 6 is used.
Is made of nickel, but a metal such as aluminum, copper, chromium, or a mixture thereof may be used.

In addition to the metal, a transparent glass material which can be elastically deformed to some extent may be used. In this case, FIG.
In the step shown in (e), the ultraviolet curing resin 5 can be cured by irradiating ultraviolet rays not from the optical substrate 1 side but from the flat plate 6 side.

Further, the material of the flat plate 6 may be rubber.

That is, the material used for the flat plate 6 is a material that can be elastically deformed to some extent when a load is applied, and can recover to the shape before the load is applied when the load is removed. If so, various things can be used.

When a two-layer diffractive optical element 10 formed on a curved surface as shown in FIG. 3 is manufactured, an elastic member 11 having a curved surface instead of a flat plate is used. The steps shown may be performed. That is, the elastic member that is not curved needs to have a shape that matches the surface shape of the second-layer diffraction grating, and is not necessarily a flat plate.

In the present embodiment, the cross-sectional shape of the diffraction grating is eight steps, but may be any other number of steps, a kinoform shape, or a sawtooth shape. Furthermore, if the grating pitch has a constant period extending in one direction, an optical low-pass filter having no wavelength dependence can be realized.

FIG. 4 is a schematic structural view of a camera having a two-layer diffractive optical element manufactured by the manufacturing method of the present invention. In the figure, reference numeral 20 denotes a camera body, 21 denotes a photographing optical system, and 22 denotes a finder optical system. The two-layer diffractive optical element of the present invention can be provided at an arbitrary position in the photographing optical system 21 or the finder optical system 22. By using the two-layer diffractive optical element of the present invention in the optical system of an optical device such as a camera, the optical performance of the optical device can be improved.

[0035]

As described above, according to the manufacturing method of the present invention, it is possible to manufacture a diffractive optical element constituted by overlapping a plurality of different materials.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a two-layer diffractive optical element manufactured by a manufacturing method of the present invention.

FIG. 2 is a diagram for explaining a manufacturing process of a manufacturing method of the present invention.

FIG. 3 is a diagram showing one embodiment of the manufacturing method of the present invention.

FIG. 4 is a schematic view of a camera having a two-layer diffractive optical element.

FIG. 5 is a diagram illustrating how a dispersion occurs between a refractive optical element and a diffractive optical element.

FIG. 6 is a diagram showing the wavelength dependence of the diffraction efficiency of a phase-type diffractive optical element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical base material 2 First-layer diffraction grating 3 Second-layer diffraction grating 4 Two-layer diffraction optical element 5 Ultraviolet-curable resin 6 Curved flat plate

Claims (9)

[Claims] A first step of injecting an uncured resin having a volume equal to or greater than the volume of the concave portion into the surface of the substrate on which the concave and convex portions are formed, and the elastic member while relatively pressing the curved elastic member against the substrate surface; A method for manufacturing a diffractive optical element, comprising: a second step of loosening the curvature of the resin and removing an excess portion of the resin before curing from the surface of the substrate, and a third step of curing the resin. 2. The method of manufacturing a diffractive optical element according to claim 1, wherein, in the first step, when the resin is injected into the substrate surface, the resin is dropped on the substrate surface. 3. The diffractive optic according to claim 1, wherein said resin is an active energy ray-curable resin, and said resin is cured by irradiating with an active energy ray in said third step. Device manufacturing method. 4. The method according to claim 1, wherein the elastic member is made of metal. 5. The method according to claim 1, wherein the elastic member is glass. 6. The method according to claim 1, wherein the elastic member is a rubber. 7. The method for manufacturing a diffractive optical element according to claim 1, wherein the elastic member is a flat plate. 8. The method of manufacturing a diffractive optical element according to claim 1, wherein the uneven portion is an annular grating having a blazed cross-sectional shape for concentrating energy on diffracted light of a predetermined order. Method. 9. An optical apparatus having a diffractive optical element manufactured by the manufacturing method according to claim 1.