JP2003227913A - Diffraction optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffraction optical element in which the angular characteristic is improved to be better than heretofore and the productivity of a diffraction grating is improved. <P>SOLUTION: In the diffraction element 20 a first diffraction element 10 and a second diffraction element 20 which are made of materials different from each other are tightly joined and a diffraction grating groove 30 having a prescribed figure is formed on the joined plane of the diffraction grating elements 10 and 20. The material of one of the diffraction grating elements 10 and 20 is glass for glass mold and the material of the other is an ultraviolet curing resin, and the relation 7.0 μm≤h≤18.0 μm is satisfied where the height of the diffraction grating groove 30 is given by h. Further, the pitch p of the diffraction grating groove 30 is 70 μm or larger. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffractive optical element, and more particularly to a multi-layer diffractive optical element composed of a plurality of diffractive element elements.

[0002]

2. Description of the Related Art Diffractive optical elements have a minute interval (about 1 mm).
It is an optical element made with a slit-like or groove-like lattice structure with a few evenly spaced slits or grooves, and when light is incident, the pitch (spacing) of the slits or grooves and the wavelength of the light will change. It has a property of generating a diffracted light beam in a fixed direction. Such a diffractive optical element is used in various optical systems, and for example, one that collects diffracted light of a specific order at one point and uses it as a lens is known.

In recent years, such diffractive optical elements have been used.
A diffractive optical element called a multi-layer type has been proposed.
This type of diffractive optical element is formed by stacking a plurality of diffractive element elements having sawtooth-shaped surfaces,
It has a characteristic that a high diffraction efficiency is maintained in almost all of a desired wide wavelength region (for example, a visible light region), that is, wavelength characteristics are good.

Generally, in the structure of the multi-layer type diffractive optical element, as shown in FIG. 3, for example, the first diffractive element 110 made of the first material and the first material have different refractive indexes and Abbe numbers. The second diffractive element element 120 made of the second material and the sawtooth-shaped surfaces of the respective diffractive element elements facing each other are arranged in a state of being separated with the air 130 interposed therebetween. . Here, the first diffractive element 1 is designed to satisfy the achromatic condition for two specific wavelengths.
The height d1 of 10 is set to a predetermined value, and the height d2 of the second diffractive element 120 is set to another predetermined value. As a result, the diffraction efficiency becomes 1.0 for two specific wavelengths, and a considerably high diffraction efficiency can be obtained for other wavelengths. In the present specification, the diffraction efficiency in the transmission type diffractive optical element, the ratio of the amplitude value I ₁ between the amplitude value I ₀ of incident light first-order diffracted light eta (= I ₁ / I ₀
X 100%).

[0005]

However, in the multi-layer type diffractive optical element having such a structure, depending on the height of the diffraction grating groove, the angle characteristic, that is, the degree of decrease of the diffraction efficiency with respect to the change of the incident angle of the incident light beam. There is a problem that may be worse. Further, there is a problem that it is difficult to form the diffraction grating groove depending on the size of the pitch of the diffraction grating groove.

Further, in the conventional multilayer diffractive optical element shown in FIG. 3, the height d1 of the diffraction grating groove in the first diffraction element element 110 and the height d2 of the diffraction grating groove in the second diffraction element element 120. Is different from that of the diffractive element 11
0 and 120 must be manufactured separately by the same procedure, and finally, both diffractive element elements 110 and 12 must be manufactured.
Since it is necessary to accurately align 0, it is very difficult to make.

The present invention has been made in view of such a problem, and provides a diffractive optical element capable of improving the angle characteristic as compared with the conventional one and improving the productivity of the diffraction grating. It is intended to be provided.

[0008]

In order to achieve such an object, in the diffractive optical element according to claim 1, the first diffractive element element and the second diffractive element element made of different materials are in close contact with each other. A diffractive optical element that is bonded and has a diffraction grating groove of a predetermined shape formed on the bonding surface of both diffractive element elements,
One material of both diffractive element is glass for glass mold and the other material is ultraviolet curable resin,
Assuming that the height of the diffraction grating groove is h, the formula 7.0 μm ≦ h ≦
It is characterized in that 18.0 μm is satisfied.

A diffractive optical element according to a second aspect is
A diffractive optical element in which a first diffractive element element and a second diffractive element element, which are made of different materials, are closely bonded and a diffractive grating groove having a predetermined shape is formed on a bonding surface of both diffractive element elements. One of the materials of the diffractive element is glass for glass molding, the other material is an ultraviolet curable resin, and the pitch of the diffraction grating grooves is 70 μm or more.

A diffractive optical element according to a third aspect is
In the diffractive optical element according to claim 1 or 2, the glass for glass molding has a refractive index of ndG at d line,
When the Abbe number is νdG, the formula 1.55 ≦ ndG ≦
1.65 and 55 ≦ νdG ≦ 65 are satisfied, and the above-mentioned ultraviolet curable resin has the formula 1.50 ≦ ndR ≦ 1.6, where the refractive index at d-line is ndR and the Abbe number is νdR.
It is characterized by satisfying 0 and νdR ≦ 40.

Further, the diffractive optical element according to claim 4 is
In the diffractive optical element according to claim 1 or 2, the glass for glass molding has a refractive index of ndG at d line,
When the Abbe number is νdG, the expression 1.63 ≦ ndG ≦
1.73 and 50 ≦ νdG ≦ 60 are satisfied, and the above ultraviolet curable resin has a refractive index at the d-line of ndR and an Abbe's number of νdR, the formula 1.58 ≦ ndR ≦ 1.6.
8 and νdR ≦ 35 are satisfied.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the concept of a diffractive optical element according to the present invention, and is a schematic cross-sectional view of a multi-layer diffractive optical element composed of two layers in close contact, that is, a contact multi-layer diffractive optical element. In the diffractive optical element 1 according to the present embodiment, the first diffractive element element 10 and the second diffractive element element 20 made of different materials are in close contact with each other, and the diffractive optical element 1 and the diffractive element elements 10 and 20 have a predetermined boundary. A diffraction grating groove 30 having a shape is formed. In the present embodiment, the diffraction grating groove 30 has a sawtooth shape as shown in the figure, but the present invention is not limited to this.

In the diffractive optical element 1 of the present invention, one of the materials forming the first and second diffractive element elements 10 and 20 is made of glass for glass molding, and the other is made of an ultraviolet curable resin. In the present embodiment, the first diffractive element element 10 is described as being made of glass for glass molding, and the second diffractive element element 20 is made of an ultraviolet curable resin. Good. In the present invention, by using glass for glass molding, injection molding is possible and mass productivity is improved. Further, in the present invention, an ultraviolet curable resin is used instead of the thermoplastic resin. Since the thermoplastic resin has a large shrinkage factor during molding, it has a drawback that it has poor adhesion to glass and cannot be easily bonded. Moreover, the molding apparatus for the thermoplastic resin is large-scale, and is not so good in terms of mass productivity. On the other hand, the ultraviolet curable resin has an advantage that it has good adhesion to glass and can be molded by a small-scale apparatus. Further, in the present invention, since the contact multilayer diffractive optical element as shown in FIG. 1 is used, the height of the groove of the diffraction grating can be made lower than that of the conventional multilayer diffractive optical element shown in FIG. It is possible.
Thereby, the angle characteristic can be improved.

In the diffractive optical element 1 of the present invention, the diffraction grating groove 3
When the height of 0 is h, the following expression (1) is satisfied.

[0015]

[Equation 1] 7.0 μm ≦ h ≦ 18.0 μm (1)

The above equation (1) is a condition relating to the angle characteristic (the degree of decrease in the diffraction efficiency with respect to the change of the incident angle of the incident light beam). By satisfying this condition, the conventional contact multi-layer diffractive optical system The angle characteristic can be improved as compared with the element. That is, the height h of the diffraction grating groove 30
By lowering the height of the diffraction grating groove 30 to be equal to or less than the upper limit value (18.0 μm) of Expression (1), it is possible to reduce loss during light transmission and improve the angle characteristic. However, if the value of the height h is reduced infinitely, it may not be possible to satisfy the strict manufacturing accuracy.
In, the height h has a lower limit value. Here, when the lower limit value of the conditional expression (1) is set to 8.0 μm and the upper limit value is set to 16.5 μm, even better results are obtained.

Further, in the diffractive optical element 1 of the present invention, the pitch (minimum pitch) p (see FIG. 1) of the diffraction grating groove 30 is set to 7
By increasing it to 0 μm or more, the apex angle θ (see FIG. 1) of the diffraction grating groove 30 can be made gentle. If the apex angle θ of the diffraction grating groove 30 is made gentle in this way, as described later, when the first diffraction element element 10 is molded using the mold (first mold 50), The shape can be accurately transferred, and the ultraviolet curable resin dropped on the diffraction grating groove 30 thus transfer-molded is formed (transferred) on the first diffraction element element 10. Since it will be fully spread over the depression of 30,
It is possible to easily form the diffraction grating groove 30 having a predetermined shape, and thus it is possible to improve the productivity of the present diffractive optical element 1. If the pitch (minimum pitch) p of the diffraction grating groove 30 is further increased to about 100 μm or more, the apex angle θ of the diffraction grating groove 30 becomes gentler, so that the formation of the diffraction grating groove 30 becomes easier. . Also, if the pitch is increased, the angle characteristic is improved. According to the simulation, good results could be obtained at approximately 70 μm or more.

In the diffractive optical element 1 of the present invention, the glass for the glass mold forming the first diffractive element 10 has a refractive index of ndG at d line and an Abbe number of νd.
When G is set, the following two equations (2) and (3) are satisfied, and the ultraviolet curable resin that constitutes the second diffractive optical element 20 has a refractive index at d line of ndR and an Abbe number of When νdR is set, it is preferable to satisfy the following two expressions (4) and (5).

[0019]

[Equation 2] 1.55 ≦ ndG ≦ 1.65 (2) 55 ≦ νdG ≦ 65 (3) 1.50 ≦ ndR ≦ 1.60 (4) νdR ≦ 40 (5)

Alternatively, the glass for the glass mold may satisfy both of the following expressions (6) and (7), and the ultraviolet curable resin may satisfy both of the following expressions (8) and (9). .

[0021]

[Equation 3] 1.63 ≦ ndG ≦ 1.73 (6) 50 ≦ νdG ≦ 60 (7) 1.58 ≦ ndR ≦ 1.68 (8) νdR ≦ 35 (9)

The above formulas (2) and (3), or both formulas (6) and (7) indicate the region having a good compatibility with the ultraviolet curable resin, among the many glasses for glass molding. There is. Outside the area specified by these equations,
First diffractive element 10 (glass for glass mold)
It becomes difficult to obtain the present multi-layer type diffractive optical element in which the second diffractive element element 20 (UV curable resin) and the second diffractive element element 20 are in contact with each other in the common diffraction grating groove 30. Here, if the lower limit of Expression (2) is set to 1.57 and the upper limit is set to 1.63, and the lower limit of Expression (3) is set to 57 and the upper limit is set to 63, even better results are obtained. Similarly, if the lower limit of the formula (6) is 1.65 and the upper limit is 1.70, and the lower limit of the formula (7) is 52 and the upper limit is 58, a better result can be obtained.

The above expressions (4) and (5) or both expressions (8) and (9) are conditions for keeping various performances of the obtained diffractive optical element 1. If these conditions are not satisfied, even if the first diffraction element element 10 (glass for glass molding) and the second diffraction element element 20 (ultraviolet curing resin) are in contact with each other at the common diffraction grating groove 30. As a result, the height h of the diffraction grating groove 30 becomes high and the angle characteristics deteriorate, or the diffraction efficiency for various wavelengths decreases. Here, if the lower limit of formula (4) is set to 1.52 and the upper limit is set to 1.58, and the upper limit of formula (5) is set to 25, even better results are obtained. Similarly, if the upper limit of the equation (8) is set to 1.65 and the lower limit of the equation (9) is set to 20 and the upper limit is set to 30, an even better result is obtained.

Next, a procedure for manufacturing the diffractive optical element 1 according to the present invention will be described. For this purpose, first, a first mold 50 in which a diffraction grating groove having a predetermined shape is formed in advance and a second mold 60 in which a predetermined surface is formed in advance are prepared. Further, a glass 10 'for a glass mold, which is formed into a predetermined shape (disc-shaped in the present embodiment) and is heated to a glass transition point or higher, is prepared (see FIG. 2A). As the glass 10 'for the glass mold, those shown in Examples described later may be used.

Next, the glass 10 ′ for glass molding heated above the glass transition point is embossed by the first mold 50 and the second mold 60, and then gradually cooled,
Solidify (see FIG. 2 (B)). Then, the solidified glass 10 'for glass mold is taken out from the first and second molds 50, 60 (see FIG. 2C). As a result, the shape of the diffraction grating groove formed in the first mold 50 is transferred to the glass mold glass 10 ′ to form the first diffractive optical element 10.

Subsequently, an appropriate amount of liquid ultraviolet curable resin 20 'is dropped on the surface of the first diffractive optical element 10 thus manufactured on which the diffraction grating groove 30 is formed (FIG. 2).
(D)). As the ultraviolet curable resin 20 ', those shown in Examples described later may be used. The third metal mold 70 for surface formation is pressed against the surface of the liquid ultraviolet curable resin 20 'opposite to the surface on which the diffraction grating groove 30 is formed (see FIG. 2E). Further, the liquid ultraviolet curable resin 20 ′ is cured by irradiating the liquid ultraviolet curable resin 20 ′ with the ultraviolet rays 80 (see FIG. 2F). As a result, the second diffractive element element 20 that is in close contact with the first diffractive element element 10 is formed. Finally, if the third metal mold 70 for surface formation is removed, the first diffractive element 10 is formed.
(Glass for glass mold) and second diffractive element 2
The contact multilayer diffractive optical element 1 according to the present invention, which is composed of 0 (ultraviolet curable resin), is completed.

When the diffractive optical element 1 of the present invention is manufactured by the above procedure, the number of the molds for which the diffraction grating groove 30 must be formed in advance is one (the first mold 5 in this case).
0) is sufficient and the manufacturing cost can be reduced.
Further, the work of aligning both diffraction grating grooves 30 formed in the first and second diffraction element elements 10 and 20 is also unnecessary.

[0028]

EXAMPLE (First Example) In this example, a glass mold glass 10 'was VC78 (n) manufactured by Sumita Optical Glass Co., Ltd.
dG = 1.66910, νdG = 55.4), and the ultraviolet curable resin 20 'was HV16 (ndR = 1.5980, νdR = 28.0) manufactured by Adele Co., and the height h of the diffraction grating groove 30 was 8.1 μm. With this configuration, in the wavelength range from g-line to C-line,
A high diffraction efficiency of 0.97 or more could be obtained.

(Second Embodiment) In this embodiment, the glass 10 'for glass molding is a low transition point glass A (ndG = 1.677).
90, νdG = 55.3), the ultraviolet curable resin 20 'was the ultraviolet curable resin a (ndR = 1.6350, νdR = 23.0), and the height h of the diffraction grating groove 30 was 15.0 µm. With such a configuration, a high diffraction efficiency of 0.97 or more could be obtained in the wavelength range from the g-line to the C-line.

(Third Embodiment) In this embodiment, glass 10 'for glass molding is HV79 manufactured by Sumita Optical Glass Co., Ltd.
(ndG = 1.60970, νdG = 57.8), UV curable resin 2
0'is UV curable resin b (ndR = 1.5440, νdR = 29.3)
And the height h of the diffraction grating groove 30 was set to 8.8 μm. With this configuration, in the wavelength range from g-line to C-line,
A high diffraction efficiency of 0.98 or more could be obtained.

(Fourth Embodiment) In this embodiment, the glass 10 'for glass molding is a low transition point glass C (ndG = 1.598).
13, νdG = 61.1), the ultraviolet curable resin 20 'was the ultraviolet curable resin c (ndR = 1.5539, νdR = 38.1), and the height h of the diffraction grating groove 30 was 16.4 μm. With such a structure, a high diffraction efficiency of 0.98 or more could be obtained in the wavelength region from the g-line to the C-line.

From the above embodiment, the height h of the diffraction grating groove 30 is
It can be confirmed that a high diffraction efficiency of 0.97 or more can be obtained in the wavelength range from the g-line to the C-line, and that the angle characteristics are good, when is a value that satisfies the above formula (1). It was

[0033]

As described above, according to the diffractive optical element of the present invention, the angle characteristic can be improved as compared with the conventional one, and the productivity can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a multi-layer diffractive optical element composed of two layers in close contact, showing an embodiment of a diffractive optical element according to the present invention.

FIG. 2 is a diagram showing manufacturing steps of the diffractive optical element of the present invention in the order of (A) to (G).

FIG. 3 is a schematic cross-sectional view showing the configuration of a conventional diffractive optical element.

[Explanation of symbols]

1 Diffractive optical element 10 First diffractive element element Glass for 10 'glass mold 20 Second diffractive element element 20 'UV curable resin 30 diffraction grating groove 50 First mold 60 Second mold 70 Third mold 80 UV

Claims (4)

[Claims] 1. A diffraction device in which a first diffractive element element and a second diffractive element element, which are made of different materials, are closely bonded to each other, and a diffraction grating groove having a predetermined shape is formed on a bonding surface of both diffractive element elements. An optical element, one material of both of the diffractive element elements is glass for glass molding and the other material is an ultraviolet curable resin, and when the height of the diffraction grating groove is h, an equation of 7.0 μm is obtained. A diffractive optical element, wherein ≦ h ≦ 18.0 μm is satisfied. 2. A diffractive element in which a first diffractive element element and a second diffractive element element, which are made of different materials, are closely bonded to each other, and a diffraction grating groove having a predetermined shape is formed on a bonding surface of the both diffractive element elements. An optical element, wherein one material of the both diffraction element elements is glass for glass molding and the other material is an ultraviolet curable resin, and the pitch of the diffraction grating grooves is 70 μm or more. Optical element. 3. The glass for a glass mold satisfies both equations 1.55 ≦ ndG ≦ 1.65 55 ≦ νdG ≦ 65, where dG is a refractive index of ndG and Abbe's number is νdG. Further, the ultraviolet curable resin satisfies both equations 1.50 ≦ ndR ≦ 1.60 νdR ≦ 40 when the refractive index at the d-line is ndR and the Abbe number is νdR. Item 3. The diffractive optical element according to item 1 or 2. 4. The glass for a glass mold satisfies both equations 1.63 ≦ ndG ≦ 1.73 50 ≦ νdG ≦ 60 when the refractive index at d-line is ndG and the Abbe number is νdG. Further, the ultraviolet curable resin satisfies both equations 1.58 ≦ ndR ≦ 1.68 νdR ≦ 35 when the refractive index at d-line is ndR and the Abbe number is νdR. Item 3. The diffractive optical element according to item 1 or 2.