Patent Application
20220413195
The present invention relates to a diffractive optical element and a method of manufacturing a diffractive optical element.
JP2007-041542A discloses a technique of preventing the shape of a stepped surface and its vicinity from collapsing and maintaining high diffraction efficiency in a case where a scanning lens having a diffractive lens structure is manufactured by injection molding.
JP2019-032518A discloses a method of reducing deformation of a lens surface due to cure shrinkage of a resin in a case where the diffractive optical element is produced by curing the resin.
JP2015-011293A discloses a technique of reducing a phase shift of transmitted wavefront of light transmitted through a diffractive optical element.
In a case where a diffractive optical element is manufactured by cementing two materials, it is difficult to bring the optical characteristics into a desired state due to the shrinkage stress during curing of the materials. In JP2019-032518A and JP2015-011293A, the manufacturing process is complicated. JP2007-041542A manufactures a diffractive lens structure by injection molding, and does not relate to a technique of manufacturing a diffractive optical element by cementing two materials.
An object of the present invention is to provide a diffractive optical element capable of easily obtaining desired optical characteristics and a method of manufacturing the same.
According to an aspect of the present invention, there is provided a diffractive optical element comprising: a first material layer that has a diffractive grating shape; and a second material layer that is laminated on the first material layer, the diffractive grating shape forming a plurality of concentric annular ring zones in a plan view from a lamination direction of the first material layer and the second material layer. A radius of an innermost first ring zone among the plurality of ring zones is less than any one of distances between the ring zones.
According to an aspect of the present invention, there is provided a diffractive optical element comprising: a first material layer that has a diffractive grating shape; and a second material layer that is laminated on the first material layer, the diffractive grating shape forming a plurality of concentric annular ring zones in a plan view from a lamination direction of the first material layer and the second material layer. In a case where, assuming that a reference wavelength is λ, a difference in refractive index between the first material layer and the second material layer is Δn, a radius of each ring zone is r, an even-order phase difference function at the radius as a variable is φ(r), a start phase of the phase difference function is C, and a remainder obtained by dividing the added value of φ(r) and C by 2π is MOD(r), and a shape of a structure forming each ring zone is defined by Expression obtained by dividing MOD(r)×λ by 2π×Δn, C is greater than 0 and less than 2π.
According to an aspect of the present invention, there is provided a method of manufacturing a diffractive optical element having a first material layer that has a diffractive grating shape and a second material layer that is laminated on the first material layer, the diffractive grating shape forming a plurality of concentric annular ring zones in a plan view from a lamination direction of the first material layer and the second material layer. The method comprises forming a radius of an innermost first ring zone among the plurality of ring zones to be less than any one of distances between the adjacent ring zones.
According to an aspect of the present invention, there is provided a method of manufacturing a diffractive optical element having a first material layer that has a diffractive grating shape and a second material layer that is laminated on the first material layer, the diffractive grating shape forming a plurality of concentric annular ring zones in a plan view from a lamination direction of the first material layer and the second material layer. In a case where, assuming that a reference wavelength is λ, a difference in refractive index between the first material layer and the second material layer is Δn, a radius of each ring zone is r, an even-order phase difference function at the radius as a variable is φ(r), a start phase of the phase difference function is C, and a remainder obtained by dividing the added value of φ(r) and C by 2π is MOD(r), and a shape of a structure forming each ring zone is defined by Expression obtained by dividing MOD(r)×λ by 2π×Δn, the structure is designed in a state where C is greater than 0 and less than 2π, and the diffractive grating shape is formed in accordance with the design.
According to the present invention, desired optical characteristics can be easily obtained.
Hereinafter, an embodiment of the present invention will be described, with reference to the drawings.
The diffractive optical element 100 comprises a glass lens 10, a first material layer 11 that has a refractive index N1 and is laminated on a surface of one side of a direction A which is a direction of an optical axis K of the glass lens 10, a second material layer 12 that has a refractive index N2 and is laminated on the first material layer 11, and a glass lens 13 that is laminated on the second material layer 12. The first material layer 11 and the second material layer 12 are layers including a resin, respectively. The resin used for the first material layer 11 and the second material layer 12 is selected so as to satisfy a diffraction condition Δnd=λ. Here, λ, is a wavelength of light, Δn is a difference in refractive index between the first material layer 11 and the second material layer 12 with respect to the light having the wavelength λ, and d is a height of a diffractive grating. In order to obtain high diffraction efficiency in a wide wavelength band, it is preferable that a resin having a high refractive index and low dispersion is used for one of the first material layer 11 and the second material layer 12 and a resin having a low refractive index and high dispersion is used for the other thereof. For the first material layer 11 and the second material layer 12, for example, it is possible to use an ultraviolet curable resin. Examples of the ultraviolet curable resin include an acrylate-based resin and an epoxy-based resin. As the ultraviolet curable resin, an acrylate-based resin is particularly preferable. The first material layer 11 and the second material layer 12 may each include metal or metal oxide particles. Examples of the particles, which are included in the first material layer 11 and the second material layer 12, include titanium oxide, zirconium oxide, indium tin oxide, antimony oxide, and the like. For example, the refractive index N1 is lower than the refractive index N2. The lamination direction of the glass lens 10, the first material layer 11, the second material layer 12, and the glass lens 13 coincides with the direction A in which the optical axis K extends. A direction orthogonal to the direction A is described as a direction B. A direction from the glass lens 13 to the glass lens 10 in the direction A is referred to as the direction D.
In
The diffractive optical element 100 is manufactured by providing a glass lens 10 having the first material layer 11 formed on the surface thereof by a mold or the like and a glass lens 13 having a resin coated on the surface, cementing the first material layer 11 side of the glass lens 10 and the resin side of the glass lens 13, and curing the resin on the glass lens 13 side. For example, it is possible to employ a method of forming the shape of the first material layer 11 into a mold by cutting or the like and transferring the shape to the resin by a molding process such as ultraviolet curing, thermosetting, or injection molding.
The first material layer 11 has a plurality of projected structures Sn (n is 1 to 10) on the surface opposite to the glass lens 10 side (10 in the examples of
As shown in
As shown in
The outer peripheral edges of the structures Sn form a diffractive grating shape of the first material layer 11. Specifically, as shown in
In the following description, a distance between the ring zone Rn and the ring zone Rn+1 in a case where an upper limit value of n is 9 will be described as a distance Pn. The distance Pn corresponds to a width of a recessed portion Dn+1 in the direction B. That is, a distance P1 corresponds to a width of a recessed portion D2 in the direction B, a distance P2 corresponds to a width of a recessed portion D3 in the direction B, a distance P3 corresponds to a width of a recessed portion D4 in the direction B, a distance P4 corresponds to a width of a recessed portion D5 in the direction B, a distance P5 corresponds to a width of a recessed portion D6 in direction B, a distance P6 corresponds to a width of a recessed portion D7 in direction B, a distance P7 corresponds to a width of a recessed portion D8 in direction B, a distance P8 corresponds to a width of a recessed portion D9 in the direction B, and a distance P9 corresponds to a width of a recessed portion D10 in the direction B.
Some diffractive optical elements do not have a structure in the vicinity of the optical axis. For example, a configuration in which the structure S1 in the diffractive optical element 100 of
In this reference configuration, the width of the recessed portion in the direction B of the innermost structure S2 is large. Therefore, a shrinkage stress of the resin in a case where the second material layer 12 is cured acts strongly on the recessed portions. As a result, the glass lens 13 tends to be recessed in the vicinity of the optical axis thereof, and it is difficult to obtain desired optical characteristics.
On the other hand, in the diffractive optical element 100, the structure S1 is provided in the vicinity of the optical axis. Therefore, as compared with the reference configuration, the structure S1 is able to reduce a volume of the recessed portion existing in the vicinity of the optical axis. Therefore, the shrinkage of the resin in a case where the second material layer 12 is cured in the vicinity of the optical axis can be suppressed by the structure S1. As a result, the glass lens 13 is prevented from being recessed in the vicinity of the optical axis, and it is possible to obtain desired optical characteristics.
The effect of such a structure S1 can obtained by preventing the diameter of the innermost ring zone R1 (that is, the width of the recessed portion D1) from being the maximum among the widths of all the recessed portions Dn. In other words, the above effect can be obtained in a case where the diameter of the ring zone R1 is less than any one of the distances P1 to P9 corresponding to the widths of the other recessed portions Dk. Further, in other words, the above effect can be obtained in a case where the diameter of the ring zone R1 is less than the maximum value among the distances P1 to P9 corresponding to the widths of the other recessed portions Dk.
The above effect can be obtained even in a case where a depth of the recessed portion D1 is equal to depths of the other recessed portions Dk. However, like the diffractive optical element 100, it is preferable that the depth of the recessed portion D1 is less than the depths of the other recessed portions Dk. With such a configuration, the volume of the recessed portion D1 can be reduced, and the shrinkage stress can be more strongly relaxed. Further, it is possible to improve the optical characteristics such as the diffraction efficiency of the diffractive optical element 100.
Further, in the diffractive optical element 100, the distance P1 is greater than a radius of the ring zone R1. With such a configuration, in a case where the diffractive optical element 100 is applied to a lens disposed on the subject side in a lens device such as a camera, desired optical characteristics can be satisfied.
Further, in the diffractive optical element 100, the distance P1 is the maximum among all the distances Pk. With such a configuration, in a case where the diffractive optical element 100 is applied to a lens disposed on the subject side in the above lens device, desired optical characteristics can be satisfied.
The distance P1, (however, the upper limit of n is 9) may be reduced as a value of n increases. In such a manner, the desired optical characteristics can be satisfied.
In the example of
For example, it is assumed that the diffractive optical element 100 has an error of a projection of 35 nm on the transmitted wavefront. In such a case, the required correction amount ΔW (=−35 nm) of the transmitted wavefront is expressed by Expression (F0), where Δd is the adjustment amount of the height of the outer peripheral edge of the structure S1.
ΔW=(N2−N1)×Δd (F0)
In a case where the refractive index N1 of the first material layer 11 is less than the refractive index N2 of the second material layer 12, an adjustment amount Δd is a negative value. That is, as shown in
In the example of
The shape D(Sn) of the structure Sn of the first material layer 11 can be defined in Expression (F1) obtained by dividing MOD(rn)×λ by 2π×Δn. Here, λ is a reference wavelength determined by the application of the diffractive optical element 100 and the like, Δn is a difference (=N1−N2) in refractive index between the first material layer 11 and the second material layer 12, φ(rn) is an even-order phase difference function at the radius (hereinafter referred to as “rn”) of the ring zone Rn as a variable, C is a start phase of the phase difference function, and MOD(rn) is a remainder obtained by dividing the added value of φ(rn) and C by 2π. The shape of the structure Sn can be designed in accordance with this expression D(Sn), and the first material layer 11 can be formed on the glass lens 10 by a mold or the like on the basis of the design result.
D(Sn)={MOD(rn)×λ}/{2π×Δn} (F1)
The phase difference function φ(rn) is expressed by Expression (F2) as an example. The C2, C4, C6, C8, and C10 in Expression (F2) are predetermined coefficients, respectively. As the phase difference function used for designing the shape of the structure Sn, it is desirable to use one having no extreme value in the optical effective diameter range of the diffractive optical element 100, as exemplified by Expression (F2). In such a manner, chromatic aberration can be corrected. In a case of a special use as the diffractive optical element 100 such as an ultra-low profile lens such as a small imaging module used in a mobile phone or an in-vehicle device or an ultra-wide-angle lens used in a projector, it should be noted that the phase difference function may have extreme values.
φ(rn)=C2rn2+C4rn4+C6rn6+C8rn8+C10rn10 (F2)
In the example of
Hereinafter, results of inspection of the diffractive optical element 100 will be described with reference to
By setting Δd to 0.06 and changing the start phase C between 0 and 2π, the shape of the structure Sn is designed.
In order to satisfy the condition in which the radius of the ring zone R1 is less than the distance P1, as shown in
In the first inspection example, a material of the glass lens 10 and the glass lens 13 is BSC7 (manufactured by HOYA Corporation). In this case, results of manufacturing the diffractive optical element 100 with the start phase C as 1.8π will be described as Example 1. The shape error from the design value at the optical axis position of the diffractive optical element 100 of Example 1 was a recess of 20 nm, and the error from the design value at the transmitted wavefront at this optical axis position was 10 nm or less.
In the first inspection example, the material of the glass lens 10 and the glass lens 13 is BSC7, and the start phase C is 0π. In this case, results of manufacturing the diffractive optical element 100 will be described as Reference Example 1a. The shape error from the design value at the optical axis position of the diffractive optical element 100 of Reference Example 1a was a recess of 60 nm, and the error from the design value at the transmitted wavefront at this optical axis position was a projection of 30 nm.
In the second inspection example, the material of the glass lens 10 is S-LAH55V (manufactured by OHARA Corporation), the material of the glass lens 13 is S-FPL51 (manufactured by OHARA Corporation), and the start phase C is 1.8π. In this a case, the results of manufacturing the diffractive optical element 100 will be described as Example 2. The shape error from the design value at the optical axis position of the diffractive optical element 100 of Example 2 was a recess of 40 nm, and the error from the design value at the transmitted wavefront at this optical axis position was a projection of 35 nm.
In the second inspection example, the material of the glass lens 10 is S-LAH55V, the material of the glass lens 13 is S-FPL51, and the start phase C is 0π. In this case, the results of manufacturing the diffractive optical element 100 will be described as Reference Example 2a. The shape error from the design value at the optical axis position of the diffractive optical element 100 of Reference Example 2a was a recess of 100 nm, and the error from the design value at the transmitted wavefront at this optical axis position was a projection of 80 nm.
In the second inspection example, the material of the glass lens 10 is S-LAH55V, the material of the glass lens 13 is S-FPL51, the start phase C is 1.8π, and the height of the structure S1 is higher than the design value. In this case, the results of manufacturing the diffractive optical element 100 by achieving reduction in size by 58.4 nm will be described as Example 3. The shape error from the design value at the optical axis position of the diffractive optical element 100 of Example 3 was 10 nm or less, and the error from the design value at the transmitted wavefront at this optical axis position was 10 nm or less.
The results of summarizing each of the above examples are shown in
In the description hitherto given, the shape of the ring zone Rn has been described as a circular shape, but the circular shape in the present specification is a concept including not only a perfect circle but also a tolerance. The radius of the ring zone Rn in a case where the shape of the ring zone Rn is not a perfect circle is a half of a linear distance between an optional point on the ring zone Rn and a point on the ring zone Rn farthest from the one point as viewed in a plan view. The diameter of the ring zone Rn in a case where the shape of the ring zone Rn is not a perfect circle is a linear distance between an optional point on the ring zone Rn and a point on the ring zone Rn farthest from the one point as viewed in a plan view.
In a similar manner, the plurality of concentric annular ring zones Rn is a concept in which the shape of each ring zone Rn includes not only a perfect circle but also a tolerance. The centers of the concentrically disposed ring zones Rn are at not exactly the same position and may include tolerances.
The shape of the ring zone Rn may be, for example, an ellipse. The radius in a case where the shape of the ring zone Rn is an ellipse is a half of the linear distance between an optional point on the ring zone Rn and a point where an extension of a straight line connecting the point and the center of the ellipse intersects the ellipse as viewed in a plan view. The diameter in a case where the shape of the ring zone Rn is an ellipse is a linear distance between an optional point on the ring zone Rn and a point where an extension of a straight line connecting the one point and the center of the ellipse intersects the ellipse as viewed in a plan view.
The diffractive optical element 100 may be cut and applied to the product as necessary. For example, a part outside the ring zone R5 may be cut to make a final product.
As described above, the present description discloses the following items. The constituent elements and the like corresponding to the above-mentioned embodiments are shown in parentheses, but the present invention is not limited thereto.
(1)
In a diffractive optical element (diffractive optical element 100) including: a first material layer (first material layer 11) that has a diffractive grating shape; and a second material layer (second material layer 12) that is laminated on the first material layer, the diffractive grating shape forming a plurality of concentric annular ring zones (ring zone Rn) in a plan view from a lamination direction (direction D) of the first material layer and the second material layer,
a radius of an innermost first ring zone (ring zone R1) among the plurality of ring zones is less than any one of distances between the ring zones.
(2)
In the diffractive optical element according to (1),
a diameter of the first ring zone is less than any one of the distances between the ring zones.
(3)
In the diffractive optical element according to (1),
a radius of the first ring zone is less than a maximum value of the distances between the ring zones.
(4)
In the diffractive optical element according to any one of (1) to (3),
a first distance (distance P1) between the first ring zone and the second ring zone (ring zone R2) adjacent to the first ring zone is greater than the radius of the first ring zone.
(5)
In the diffractive optical element according to (4),
the first distance is the maximum among the distances between the ring zones.
(6)
In the diffractive optical element according to any one of (1) to (5),
a depth of a recessed portion (recessed portion D1) inside the first ring zone in a structure (structure S1) forming the first ring zone is less than a depth of a recessed portion between structures forming the respective ring zones.
(7)
In the diffractive optical element according to any one of (1) to (6),
in a case where, assuming that
(8)
In the diffractive optical element according to any one of (1) to (7),
a height of a structure forming the first ring zone is different from a height of a structure forming each ring zone other than the first ring zone.
(9)
In the diffractive optical element according to (8),
a refractive index of the first material layer is less than a refractive index of the second material layer, and
the height of the structure forming the first ring zone is less than the height of the structure forming each ring zone other than the first ring zone.
(10)
In the diffractive optical element according to (8),
a refractive index of the first material layer is greater than a refractive index of the second material layer, and
the height of the structure forming the first ring zone is greater than the height of the structure forming each ring zone other than the first ring zone.
(11)
In the diffractive optical element according to any one of (1) to (10),
a distance between the ring zones is narrower at a position closer to an outside thereof than a center thereof.
(12)
A diffractive optical element comprising: a first material layer that has a diffractive grating shape; and a second material layer that is laminated on the first material layer, the diffractive grating shape forming a plurality of concentric annular ring zones in a plan view from a lamination direction of the first material layer and the second material layer,
in a case where, assuming that
(13)
In the diffractive optical element according to (12),
C is greater than a value of C at which a radius of an innermost first ring zone among the plurality of ring zones and a distance between the first ring zone and a second ring zone adjacent to the first ring zone are equal.
(14)
In the diffractive optical element according to (12) or (13), the phase difference function has no extreme value in an optical effective diameter range.
(15)
A method of manufacturing a diffractive optical element having a first material layer that has a diffractive grating shape and a second material layer that is laminated on the first material layer, the diffractive grating shape forming a plurality of concentric annular ring zones in a plan view from a lamination direction of the first material layer and the second material layer, the method comprising
forming a radius of an innermost first ring zone among the plurality of ring zones to be less than any one of distances between the adjacent ring zones.
(16)
A method of manufacturing a diffractive optical element having a first material layer that has a diffractive grating shape and a second material layer that is laminated on the first material layer, the diffractive grating shape forming a plurality of concentric annular ring zones in a plan view from a lamination direction of the first material layer and the second material layer, the method comprising
in a case where, assuming that
designing the structure in a state where C is greater than 0 and less than 2π, and
forming the diffractive grating shape in accordance with the design.
(17)
In the method of manufacturing a diffractive optical element according to (16),
C is greater than a value of C at which a radius of a first ring zone having a smallest diameter among the plurality of ring zones and a distance between the first ring zone and a second ring zone adjacent to the first ring zone are equal.
Although various embodiments have been described above with reference to the drawings, it is needless to say that the present invention is not limited to such examples. It is apparent to those skilled in the art that various variations or modifications can be made within the scope of the claims, and it should be understood that such variations or modifications belong to the technical scope of the invention. Further, each constituent element in the above-mentioned embodiment may be arbitrarily combined without departing from the spirit of the invention.
This application is on the basis of a Japanese patent application filed on Mar. 31, 2020 (Japanese Patent Application No. 2020-063803), the contents of which are incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-063803 | Mar 2020 | JP | national |
This is a continuation of International Application No. PCT/JP2021/005119 filed on Feb. 10, 2021, and claims priority from Japanese Patent Application No. 2020-063803 filed on Mar. 31, 2020, the entire disclosures of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2021/005119 | Feb 2021 | US |
| Child | 17902892 | US |
