KR102059945B1 - Diffraction optical element and optical device including the same - Google Patents

Abstract

The present invention is a diffractive optical element having a diffraction pattern formed on at least one surface, the height of the diffraction pattern is changed from the center of the one surface to the edge, the height of the first diffraction pattern formed in the center and the second diffraction pattern formed on the edge Discloses diffractive optical elements having different heights and optical devices including the same.

Description

Diffraction optical element and optical device including the same {DIFFRACTION OPTICAL ELEMENT AND OPTICAL DEVICE INCLUDING THE SAME}

The present invention relates to a diffractive optical element having a uniform diffraction efficiency according to the wavelength and the incident angle.

Diffractive optical elements (DOEs) have the opposite method of chromatic aberration as compared to refractive optical systems having the same power. This is because of the physical phenomenon in which chromatic aberration with respect to the light of the reference wavelength is expressed in the reverse direction on the refractive surface and the diffraction surface in the optical system.

Diffraction optical elements are easier to correct aberrations than conventional refractive optics, so that the height of the lens assembly can be lowered, which makes it possible to miniaturize and reduce the price of the product according to the reduction in the number of lenses.

However, the diffraction optical element has a problem in that the diffraction efficiency difference occurs according to the wavelength range of the incident light and the incident angle of the lens, and as a result, a color phenomena occurs, thereby degrading the performance of the image.

In order to solve this problem, technologies for improving diffraction efficiency by stacking a plurality of diffractive optical devices have been developed. However, a single diffraction optical device alone does not improve the diffraction efficiency difference according to the wavelength and the incident angle.

The present invention provides a diffractive optical element having a similar diffraction efficiency according to wavelength and incident angle.

The present invention is designed as a single diffraction optical element to provide a diffraction optical element that is a thin film.

In the diffraction optical element according to the embodiment of the present invention, a diffraction pattern is formed on at least one surface, and the height of the diffraction pattern is changed from the center of the one surface to the edge, and the height of the first diffraction pattern formed on the center and the The height of the second diffraction pattern formed at the edge is formed differently.

In the diffractive optical device according to the embodiment of the present invention, the difference between the height of the first diffraction pattern and the height of the second diffraction pattern is 600 nm to 1400 nm.

In the diffractive optical device according to the embodiment of the present invention, the height of the first diffraction pattern is formed higher than the height of the second diffraction pattern.

In the diffractive optical device according to the embodiment of the present invention, the height of the first diffraction pattern is 1500 nm to 1900 nm, and the height of the second diffraction pattern is 500 nm to 900 nm.

In a diffractive optical element according to an embodiment of the present invention, the height h _o of the first diffraction pattern satisfies Equation 1 below, and the height h ₁ of the second diffraction pattern is expressed by Equation 2 below. Satisfies.

[Equation 1]

[Equation 2]

(Where n _d is the refractive index of the diffractive optical element, and is 750 nm ≦ λ ₁ ≦ 950 nm and 250 nm ≦ λ ₂ ≦ 450 nm).

In the diffractive optical device according to the embodiment of the present invention, the height h _r of the diffraction pattern that changes from the center of the one surface to the edge satisfies Equation 3 below.

[Equation 3]

Where h _o is the height of the first diffraction pattern, h ₁ is the height of the second diffraction pattern, r _eff is the radius of the effective diameter, r is the radius of the diffraction pattern, and γ is 0.1≤γ≤3 .)

A diffraction optical element according to another embodiment of the present invention is a diffraction optical element having a diffraction pattern formed on at least one surface thereof, and the height of the diffraction pattern changes from the center of the one surface toward the edge and passes through the center of the red light (R1). ), The primary light diffraction efficiency of the green light (G1), blue light (B1) satisfies the following equation 1, the primary light diffraction efficiency of the red light (R2), green light (G2), blue light (B2) passing through the edge is Satisfies relation 2.

[Relationship 1]

R1 ＞ G1 ＞ B1

[Relationship 2]

R2 <G2 <B2

According to the present invention, the diffraction efficiency according to the wavelength and the angle of incidence can be similarly controlled only by the diffraction optical element of a single medium.

In addition, uniform color light (white light) can be implemented for all areas by reducing color difference (color deviation) for each field caused by the diffraction efficiency difference in the DOE optical system.

1 is a side view of a diffractive optical element according to an embodiment of the present invention,
FIG. 2 is a graph showing a slope in which a diffraction pattern height changes according to a change in the constant γ of Equation 3;
3 is a view for explaining the wavelength dependence of the diffractive optical element according to an embodiment of the present invention,
4 is a view for explaining wavelength dependence of a diffraction optical element having the same height of a diffraction pattern,
5 is a side view and a plan view of a diffractive optical element according to another embodiment of the present invention;
6 is a view showing the synthesized shape of the aspherical lens in the diffraction optical element of the present invention,
7 is a graph showing the primary light efficiency of the diffractive optical element shown in FIG.
8 is a graph showing the primary light efficiency of the diffractive optical device according to the embodiment of the present invention,
FIG. 9 is an image image photographed by an optical apparatus including the diffractive optical element shown in FIG. 4.
10 is an image taken by an optical device including a diffractive optical element according to an embodiment of the present invention,
11 is a video image photographed using an existing optical device.

As the invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description.

Terms including ordinal numbers such as first and second may be used to describe various components, but the components are not limited by the terms.

The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the second component may be referred to as the first component, and similarly, the first component may also be referred to as the second component.

When a component is referred to as being "connected" or "connected" to another component, it may be directly connected or connected to that other component, but it may be understood that other components may be present in between. Should be.

On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that there is no other component in between.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

In the present invention, the terms "comprises" or "having" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, and one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, components, or a combination thereof.

In addition, it is to be understood that the accompanying drawings in the present invention are shown enlarged or reduced for convenience of description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the drawings. Like reference numerals designate like elements throughout, and duplicate descriptions thereof will be omitted.

1 is a side view of a diffractive optical device according to an exemplary embodiment of the present invention, and FIG. 2 is a graph showing a slope in which a diffraction pattern height changes according to a change in Equation (3).

Referring to FIG. 1, the optical diffraction element 10 according to the exemplary embodiment of the present invention has a plurality of diffraction patterns 100 formed on at least one surface thereof. The diffraction pattern 100 may have a sawtooth shape (Fresnel DOE shape), and diffracts incident light L1 into zero order light L2, primary light L3, and secondary light. Primary light is similar to the refractive optical system. Therefore, the diffraction efficiency is described below as the diffraction efficiency of the primary light.

The height of the diffraction pattern 100 changes continuously or discontinuously from the center C of the diffractive optical element to the edge E. FIG. In this case, the height of the diffraction pattern 100 may be designed to be lower from the center to the edge, or conversely, may be designed to be higher from the center to the edge. Hereinafter, the height of the diffraction pattern 100 will be described as being designed to be lowered from the center to the edge, and the height of the diffraction pattern is defined as the distance between the peak d2 and the valley d1 of the sawtooth pattern.

The height h _o of the diffraction pattern (hereinafter referred to as first diffraction pattern 101) at the center portion is formed higher than the height of the diffraction pattern (hereinafter referred to as second diffraction pattern h ₁ ) at the edge. Further, the diffraction patterns 102 and 103 between the first diffraction pattern 101 and the second diffraction pattern 104 continuously decrease in height. The height h _o of the first diffraction pattern satisfies Equation 1 below, and the height h ₁ of the second diffraction pattern satisfies Equation 2 below.

[Equation 1]

[Equation 2]

Where n _d is the refractive index of the diffractive optical element (1.5 to 1.6), and is 750 nm ≦ λ ₁ ≦ 950 nm and 250 nm ≦ λ ₂ ≦ 450 nm. In this case, when the range of λ ₁ and λ ₂ is satisfied, the diffraction efficiency may be approximately adjusted in the entire visible light region. The ranges of λ ₁ and λ ₂ were derived through repeated experiments.

At this time, the range of lambda _{1 and} the range of lambda ₂ are designed such that the primary light diffraction efficiency of the incident light becomes 0.5 or more. Accordingly, when the refractive index n _d of the diffractive optical element is 1.5, the height h _o of the first diffraction pattern may be 1500 nm to 1900 nm, and the height h ₁ of the second diffraction pattern may be 500 nm to 900 nm. The difference between the height h _o of the first diffraction pattern and the height h ₁ of the second diffraction pattern may be 600 nm to 1400 nm.

Therefore, the long wavelength light has a high diffraction efficiency at the center of the diffractive optical element and a low diffraction efficiency at the edge of the diffractive optical element. On the contrary, light having a short wavelength has high diffraction efficiency at the edge of the diffractive optical element and low diffraction efficiency at the center of the diffractive optical element. As a result, the total diffraction efficiency of the long wavelength and the short wavelength passing through the diffractive optical element can be controlled to be similar to each other.

The heights h _r of the diffraction patterns 102 and 103, which change from the center of the diffractive optical element toward the edges, are designed to satisfy the following equation (3).

[Equation 3]

Here, h _o is the height of the first diffraction pattern 101, h ₁ is the height of the second diffraction pattern 104, r _eff is the radius of the effective diameter, r is the radius of the diffraction pattern, γ is 0.1 ≤ γ ≤ 3.

Therefore, the plurality of diffraction patterns 102 and 103 disposed between the first diffraction pattern 101 and the second diffraction pattern 104 have a height defined by Equation (3).

In general, a diffractive optical element has an effective radius (r _eff ) having a diffraction effect, and the outside thereof is defined as a machining diameter for pattern processing. Therefore, the second diffraction pattern 104 is defined as a diffraction pattern disposed at the end of the effective mirror (outermost).

In Equation 3, γ is a slope constant, and the slope of the height of the diffraction pattern is determined according to the size of γ. Table 1 below shows the height of the diffraction pattern that changes according to the change of γ when the height h _o of the first diffraction pattern is 1500 nm and the height h ₁ of the second diffraction pattern is 400 nm.

γ Ring 1 Ring 2 Ring 3 Ring 4 Ring 5 One 1500 1053 855 696 553 0.9 1500 1001 820 671 539 0.8 1500 963 783 644 524 0.7 1500 913 743 617 509 0.6 1500 858 702 589 494 0.5 1500 797 548 560 479

Referring to FIG. 2 and Table 1, when the value of γ is 0.5, the height of the pattern decreases rapidly toward the outer ring, but when the value of γ is 1, the height of the pattern decreases smoothly with a nearly straight slope. . That is, Equation 3 may be defined as the slope h _{r of the} height of the diffraction pattern.

At this time, the range of gamma satisfies 0.1≤γ≤3. If γ is less than 0.1 or more than 3, the height of the diffraction pattern is drastically reduced, which makes it difficult to process the diffraction pattern.

3 is a view for explaining the wavelength dependence of the diffractive optical device according to an embodiment of the present invention, Figure 4 is a view for explaining the wavelength dependency of the diffraction optical device having the same height of the diffraction pattern.

Referring to FIG. 3, in the diffractive optical element according to the exemplary embodiment of the present invention, the height of the diffraction pattern decreases from the center portion C to the edge portion E. FIG. In addition, as described above, the diffraction efficiency of the long wavelength is relatively increased at the center portion, and the diffraction efficiency of the short wavelength is relatively increased at the edge portion.

Therefore, the efficiency of 600-700 nm red light (R1), 500-600 nm green light (G1) and 400-500 nm blue light (B1) passing through the center satisfy the following equation 1.

[Relationship 1]

R1 ＞ G1 ＞ B1

That is, the primary light diffraction efficiency of the red light is the best and the primary light diffraction efficiency of the blue light is the lowest in the center portion. However, on the contrary, the efficiency of the red light R2 of 600-700 nm, the green light G2 of 500-600 nm, and the blue light B2 of 400-500 nm that pass through the edges satisfy the following Equation 2.

[Relationship 2]

R2 <G2 <B2

Therefore, the total diffraction efficiency of the red light, the green light, and the blue light passing through the diffractive optical element can be adjusted almost similarly.

However, when the height h ₂ of the diffraction pattern is formed to be the same as shown in FIG. 4, the light of the wavelength band corresponding to the design wavelength has the maximum efficiency, but the light of the other wavelength bands has very low diffraction efficiency. there is a problem.

If the design wavelength is 546nm green light, only the efficiency of green light at the center or at the edge is good (G3 »R3 = B3, G4» R4 = B4). The diffraction optical device has a flare phenomenon due to the difference in diffraction efficiency according to the wavelength.

Referring back to FIG. 3, the diffraction optical element according to the present invention becomes less dependent on the incident angle. For example, assuming the first light incident at the first angle and the second light incident at the second angle, when the first light has a high diffraction efficiency at the center, the diffraction efficiency is near the edge where the height of the diffraction pattern is different. If the second light has low efficiency at the center, the height of the diffraction pattern is increased at the other edge. Therefore, the primary light diffraction efficiency according to the incident angle is controlled almost similarly.

In other words, when the wavelength is changed and the incident angle is changed, the high or low efficiency is compensated in the other region (edge) by the change of the height of the diffraction pattern to pass through the diffraction optical element. The total diffraction efficiency of the light can be similarly controlled.

5 is a side view and a plan view of a diffractive optical device according to still another embodiment of the present invention, and FIG. 6 is a view showing a synthesized shape of an aspherical lens of the diffractive optical device of the present invention.

Referring to FIG. 5, the diffractive optical element according to another exemplary embodiment of the present invention is designed such that the peak of the diffraction pattern is lowered from the center to the edge, and the height thereof becomes gradually lower. This is the same as the height of the pattern is reduced by changing the valley d1 of the diffraction pattern in FIG. 1. At this time, each diffraction pattern is formed in a ring shape (r ₁ , r ₂ ).

Referring to FIG. 6, the diffractive optical element 10 may be formed on one surface of the aspherical lens 20. The aspherical lens 20 may be a convex lens or a concave lens. Therefore, the chromatic aberration generated in the refractive optical system can be effectively corrected by the diffractive optical element 10.

FIG. 7 is a graph showing the primary light efficiency of the diffractive optical device shown in FIG. 4, and FIG. 8 is a graph showing the primary light efficiency of the diffractive optical device according to an embodiment of the present invention.

At this time, the primary light diffraction efficiency η of FIG. 8 is a result of simulating the result calculated by Equation 4 below.

[Equation 4]

Is the wavelength of incident light, n ₁ is the refractive index of the diffractive optical element, n ₂ is the refractive index of air, θ ₂ is the incident angle of light, m is the diffraction order.

Referring to FIG. 7, a diffractive optical element (see FIG. 4) having a constant height of a diffraction pattern has a maximum efficiency at a design wavelength (eg, 546 nm, G), but is less than 0.6 at a wavelength band B other than the design wavelength. You can see this fall sharply.

In addition, it can be seen that the sharp change according to the incident angle. The efficiency difference according to the wavelength band and the incident angle causes color blur problem. At this time, the dotted lines Bn, Gn, and Rn are light other than the primary light and act as noise in the actual image.

On the contrary, as shown in FIG. 8, the diffraction optical element according to the exemplary embodiment of the present invention has almost similar primary light diffraction efficiency for each wavelength band.

Specifically, the primary light diffraction efficiency of the light having the red wavelength (R), the green wavelength (G), and the blue wavelength (B) is all uniformly located between 0.6 and 0.8, and the red wavelength (R), the green wavelength (G), It can be seen that the diffraction efficiency difference between the blue wavelengths B is also 0.2 or less.

The angle of light incident on the diffraction element may be perpendicular to the diffraction element (0 degrees), or may have a predetermined angle. However, according to the exemplary embodiment of the present invention, it can be seen that there is almost no change in efficiency at an angle of view of 0 degrees to 40 degrees.

Therefore, since the diffraction efficiency is 0.6 or more in the entire visible light region and the diffraction efficiency difference of each wavelength band is 0.2 or less, the wavelength dependence and the incident angle dependence of the diffractive optical element are alleviated, so that the color bleeding problem can be effectively solved.

Furthermore, the diffractive optical element according to the present invention is designed as a single layer structure, rather than a stacked element in which a plurality of diffraction patterns are stacked, so that the diffraction optical element can be designed in a thin film. Therefore, a compact optical system including the same can be realized.

In addition, the diffractive optical element may be applied to various optical devices such as a camera module for a communication terminal, a digital still camera, and a camcorder.

FIG. 9 is an image image photographed by the optical apparatus including the diffractive optical element shown in FIG. 4, and FIG. 10 is an image image photographed by the optical apparatus including the diffractive optical element according to an embodiment of the present invention. 11 is a video image taken using the existing optical device.

Referring to FIG. 9, purple color bleeding was observed in an image image photographed using an optical device (eg, a camera module) equipped with a diffraction optical element having the same height of a diffraction pattern, and an outer color (0.7). In F), blue color bleeding was observed. This can be seen that the color blur is very large when compared with the image of FIG. 11 using the refractive optical system.

On the contrary, as shown in FIG. 10, the image image photographed using the optical device equipped with the diffractive optical element according to the exemplary embodiment does not have a large color difference in the center field (0.1F) and the outer (0.7F). It can be seen. It can be seen that the color bleeding problem is greatly alleviated when compared with the image of FIG. 11 using the refractive optical system.

Claims (14)

A diffractive optical element having a diffraction pattern formed on at least one surface,
The height of the diffraction pattern is changed from the center of the one surface toward the edge, the height of the dome-shaped first diffraction pattern formed in the center and the height of the second diffraction pattern formed on the edge is different,
The height of the first diffraction pattern of the dome shape is higher than the height of the neighboring diffraction pattern,
The height h _o of the first diffraction pattern satisfies Equation 1 below, and the height h ₁ of the second diffraction pattern satisfies Equation 2 below.
[Equation 1]

[Equation 2]

(Where n _d is the refractive index of the diffractive optical element, and is 750 nm ≦ λ ₁ ≦ 950 nm and 250 nm ≦ λ ₂ ≦ 450 nm).
The method of claim 1,
Diffraction optical element that is a single layer.
The method of claim 1,
The difference between the height of the first diffraction pattern and the height of the second diffraction pattern is 600nm to 1400nm.
The method of claim 1,
The height of the first diffraction pattern is higher than the height of the second diffraction pattern.
The method of claim 4, wherein
The height of the first diffraction pattern is 1500nm to 1900nm, the height of the second diffraction pattern is 500nm to 900nm.
delete The method of claim 1,
The height (h _r ) of the diffraction pattern that changes from the center of the one surface to the edge satisfies the following equation (3).
[Equation 3]

Where h _o is the height of the first diffraction pattern, h ₁ is the height of the second diffraction pattern, r _eff is the radius of the effective diameter, r is the radius of the diffraction pattern, and γ is 0.1≤γ≤3 .)
The method of claim 1,
The primary light diffraction efficiency of the red light (R1), green light (G1), blue light (B1) passing through the center satisfies the following relation 1,
The first optical diffraction efficiency of the red light (R2), green light (G2), blue light (B2) passing through the edge satisfies the following equation (2).
[Relationship 1]
R1 ＞ G1 ＞ B1
[Relationship 2]
R2 <G2 <B2
The method of claim 8,
The height of the first diffraction pattern formed in the center is higher than the height of the second diffraction pattern formed on the edge.
delete The method of claim 9,
The height (h _r ) of the diffraction pattern that changes from the center of the one surface to the edge satisfies the following equation (3).
[Equation 3]

Where h _o is the height of the first diffraction pattern, h ₁ is the height of the second diffraction pattern, r _eff is the radius of the effective diameter, r is the radius of the diffraction pattern, and γ is 0.1≤γ≤3 .)
The method of claim 8,
The red light is a light of 600 ~ 700nm wavelength band, the green light is a light of 500 ~ 600nm, the blue light is a light of the wavelength band 400 ~ 500nm.
An optical system comprising the diffractive optical element according to any one of claims 1 to 5, 7 to 9, 11 and 12.
An optical device comprising the diffractive optical element according to any one of claims 1 to 5, 7 to 9, 11 and 12.

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