Diffractive optical elements and devices

Abstract

The present disclosure provides a diffractive optical element and a device. A diffractive optical element includes a diffractive layer having a plurality of optical axes along an in-plane direction, wherein the diffractive layer includes an anisotropic material satisfying one of equations 1A to 3A, wherein equation 1AΔn 1 (450nm)<Δn 1 (550nm)≤Δn 1 (650nm) Relationship 2AΔn 1 (450nm)≤Δn 1 (550nm)<Δn 1 (650nm) Relationship 3AΔn 1 (450nm) = Δn 1 (550nm) = Δn 1 (650nm) where, in equations 1A to 3A, Δn 1 (450nm) is the birefringence of the anisotropic material at a wavelength of 450 nanometers, Δn 1 (550nm) is the birefringence of the anisotropic material at a wavelength of 550 nanometers, and Δn 1 (650nm) is the birefringence of the anisotropic material at a wavelength of 650 nanometers.

Description

Technical Field

[0001] Disclosed are a diffractive optical element and a device comprising the diffractive optical element. Background Art

[0002] In the development of highly integrated optical devices, research has been conducted to develop optical devices with small size and thin thickness. Among these, it is expected to develop a diffractive optical element using the light diffraction phenomenon and apply the diffractive optical element to an optical system such as a lens or a prism. Summary of the invention

[0003] One embodiment provides a diffractive optical element having excellent diffraction efficiency and a wide bandwidth.

[0004] Another embodiment provides a device including the diffractive optical element.

[0005] According to one embodiment, a diffractive optical element includes a diffractive layer including a plurality of optical axes along an in-plane direction, wherein the diffractive layer includes an anisotropic material satisfying one of Relationships 1A to 3A.

[0006] Relation 1A

[0007] Δn 1 (450 nanometers (nm)) < Δn 1 (550nm)≤Δn 1 (650nm)

[0008] Relation 2A

[0009] Δn 1 (450nm)≤Δn 1 (550nm)<Δn 1 (650nm)

[0010] Relation 3A

[0011] Δn 1 (450nm) = Δn 1 (550nm) = Δn 1 (650nm)

[0012] In equations 1A to 3A,

[0013] Δn 1 (450nm) is the birefringence of the anisotropic material at a wavelength of 450 nanometers (nm),

[0014] Δn 1 (550nm) is the birefringence of the anisotropic material at a wavelength of 550nm, and

[0015] Δn1 (650nm) is the birefringence of the anisotropic material at a wavelength of 650nm.

[0016] The optical axis of the diffraction layer may be configured to change periodically along the in-plane direction.

[0017] The diffraction layer may include at least one grating pitch, each grating pitch including the plurality of optical axes, and the grating pitch may be about 0.8 micrometers (μm) to about 10 μm.

[0018] The anisotropic material may include liquid crystal, the diffraction layer may include a plurality of liquid crystals disposed in a thickness direction, and the plurality of liquid crystals disposed in the thickness direction may not be twisted in an in-plane direction of the diffraction layer.

[0019] Anisotropic materials have a birefringence dispersion that satisfies relations 4A and 5A.

[0020] Relation 4A

[0021] 0.70≤Δn 1 (450nm) / Δn 1 (550nm)≤1.00

[0022] Relation 5A

[0023] 1.00≤Δn 1 (650nm) / Δn 1 (550nm)≤1.25

[0024] In equations 4A and 5A,

[0025] Δn 1 (450nm) is the birefringence of the anisotropic material at a wavelength of 450nm,

[0026] Δn 1 (550nm) is the birefringence of the anisotropic material at a wavelength of 550nm, and

[0027] Δn 1 (650nm) is the birefringence of the anisotropic material at a wavelength of 650nm.

[0028] The anisotropic material may have a birefringence index of about 0.1 to about 0.5 at a wavelength of 550 nm.

[0029] The diffraction angle of the diffraction layer at a wavelength of 450 nm, the diffraction angle at a wavelength of 550 nm, and the diffraction angle at a wavelength of 650 nm may be the same or different and may be within about 1 degree (°) to about 50 degrees.

[0030] The diffraction efficiency of the diffractive optical element at a wavelength of 450 nm, at a wavelength of 550 nm, and at a wavelength of 650 nm may be independently about 70% to about 100%.

[0031] A difference between a maximum diffraction efficiency and a minimum diffraction efficiency among diffraction efficiencies of the diffraction optical element at a wavelength of 450 nanometers, a wavelength of 550 nanometers, and a wavelength of 650 nanometers may be less than about 20%.

[0032] The diffractive optical element can be a lens or a prism.

[0033] The diffractive optical element may be a planar diffractive optical element having a constant thickness and a constant curvature.

[0034] According to another embodiment, a diffractive optical element includes multiple optical axes along an in-plane direction, wherein the birefringence of the diffractive optical element for light having a wavelength of 550 nanometers to 650 nanometers is greater than or equal to the birefringence of the diffractive optical element for light having a wavelength of 450 nanometers to less than 550 nanometers, and the diffraction efficiency of the diffractive optical element at a wavelength of 450 nm, a wavelength of 550 nm, and a wavelength of 650 nm is each independently greater than or equal to about 70% to about 100%.

[0035] The diffractive optical element may have a birefringence dispersion satisfying one of Relationships 1B to 3B.

[0036] Relation 1B

[0037] Δn 2 (450nm)<Δn 2 (550nm)≤Δn 2 (650nm)

[0038] Relation 2B

[0039] Δn 2 (450nm)≤Δn 2 (550nm)<Δn 2 (650nm)

[0040] Relation 3B

[0041] Δn 2 (450nm) = Δn 2 (550nm) = Δn 2 (650nm)

[0042] In equations 1B to 3B,

[0043] Δn 2 (450nm) is the birefringence of the diffractive optical element at a wavelength of 450nm,

[0044] Δn 2 (550nm) is the birefringence of the diffractive optical element at a wavelength of 550nm, and

[0045] Δn 2 (650nm) is the birefringence of the diffractive optical element at a wavelength of 650nm.

[0046] A difference between a maximum diffraction efficiency and a minimum diffraction efficiency among diffraction efficiencies at a wavelength of 450 nanometers, a wavelength of 550 nanometers, and a wavelength of 650 nanometers may be less than about 20%.

[0047] According to another embodiment, a stacked diffractive optical element includes a plurality of the diffractive optical elements stacked together.

[0048] The stacked diffractive optical elements may include a blue diffractive optical element exhibiting a maximum diffraction efficiency in a wavelength region of about 400nm to about 500nm, a green diffractive optical element exhibiting a maximum diffraction efficiency in a wavelength region of about 500nm to about 600nm, and a red diffractive optical element exhibiting a maximum diffraction efficiency in a wavelength region of about 600nm to about 700nm.

[0049] The stacked diffractive optical element may further comprise at least one wavelength selective filter.

[0050] According to another embodiment, a device comprises the diffractive optical element or the stacked diffractive optical element.

[0051] High diffraction efficiency and wide bandwidth can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1A is a top view of a cross section of an embodiment of a diffractive optical element,

[0053] Figure 1B is a side view of a cross section of an embodiment of a diffractive optical element,

[0054] Figure 2 is a top view showing an embodiment of the arrangement of multiple optical axes of a diffractive layer in a diffractive optical element,

[0055] Figure 3 is a top view showing another embodiment of the arrangement of multiple optical axes of the diffractive layer in the diffractive optical element,

[0056] Figure 4 is a schematic diagram showing the principle of a polarization grating of one embodiment of a diffraction layer in a diffractive optical element,

[0057] Figure 5is a schematic diagram of an embodiment of a stacked diffractive optical element,

[0058] Fig. 6A , Figure 6B and Figure 6C Includes blue ( Fig. 6A ),green( Figure 6B ) or red ( Figure 6C ) is a schematic diagram of an embodiment of a stacked diffractive optical element for selecting optical filters, and

[0059] Figure 7 is a graph of birefringence (Δn, nm) versus wavelength (λ, nm), showing the wavelength dependence of birefringence of anisotropic materials in simulations.

[0060] Figures 8 to 10 Each of is a graph of diffraction efficiency (n, %) versus wavelength (nm), which shows the diffraction efficiency of the diffractive optical elements according to the examples and comparative examples depending on the wavelength. DETAILED DESCRIPTION

[0061] Hereinafter, exemplary embodiments of the present invention will be described in detail so that those skilled in the art will understand the exemplary embodiments. However, the present disclosure may be embodied in many different forms and is not to be construed as limited to the exemplary embodiments set forth herein.

[0062] In the accompanying drawings, the thickness of layers, films, panels, regions, etc., is exaggerated for clarity. Throughout the specification, the same reference numerals represent the same elements. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element, or there can be intervening elements. Conversely, when an element is referred to as being "directly on" another element, there are no intervening elements.

[0063] The terms used here are only for the purpose of describing specific embodiments and are not intended to be limited. As used herein, "one", "the", "at least one" do not represent quantitative limitations, and are intended to cover both the singular and the plural, unless the context clearly indicates otherwise. For example, unless the context clearly indicates otherwise, "an element" has the same meaning as "at least one element". "Or" means "and / or". As used herein, the term "and / or" includes any and all combinations of one or more related listed items. It will also be understood that the terms "comprising" and / or "comprising ... " or "including" and / or "including ... ", when used in this specification, specify the presence of the features, regions, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, parts and / or their groups.

[0064] In addition, relational terms such as "below" or "bottom" and "above" or "top" may be used herein to describe the relationship of one element to another element as shown in the accompanying drawings. It will be understood that, in addition to the orientations depicted in the accompanying drawings, the relational terms are intended to cover different orientations of the device. For example, if the device in one of the accompanying drawings is turned over, the element described as being on the "lower" side of the other element will be oriented on the "upper" side of the other element. Depending on the specific orientation of the accompanying drawings, the exemplary term "below" can therefore cover both "lower" and "upper" orientations. Similarly, if the device in one of the accompanying drawings is turned over, the element described as being "below" or "below" the other element will be oriented "above" the other element. Therefore, the exemplary term "below" or "below" can cover both above and below orientations.

[0065] As used herein, "about" or "approximately" is inclusive of the stated value and means within an acceptable range of deviation for a particular value determined by one of ordinary skill in the art, taking into account the measurement in question and the errors associated with the measurement of the particular quantity (i.e., the limitations of the measurement system). For example, "about" can mean within one or more standard deviations, or within ±30%, 20%, 10%, or 5% of the stated value.

[0066] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present disclosure belongs. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted as an idealized or overly formalized meaning, unless explicitly defined as such herein.

[0067] Hereinafter, a diffractive optical element according to an embodiment is described.

[0068] Figure 1A is a top view of a cross section of a diffractive optical element according to one embodiment, Figure 1B is a side view of a cross section of a diffractive optical element according to one embodiment, Figure 2 is a top view showing an embodiment of the arrangement of multiple optical axes of a diffractive layer in a diffractive optical element, Figure 3 is a top view showing another embodiment of the arrangement of multiple optical axes of the diffractive layer in the diffractive optical element, Figure 4 FIG. 1 is a schematic diagram schematically illustrating the principle of a polarization grating of a diffraction layer in a diffractive optical element according to an embodiment.

[0069] Reference Figure 1A and Figure 1B According to one embodiment, a diffractive optical element 10 includes a substrate 11 , an alignment layer 12 , and a diffractive layer 13 .

[0070] The substrate 11 may include, for example, an inorganic material or an organic material. The inorganic material may include glass, silicon, or a combination thereof. For example, the substrate 11 may be a silicon wafer. The organic material may include polycarbonate, polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyvinyl alcohol, triacetyl cellulose, polyimide, polyamide, polyether sulfone (PES), copolymers thereof, derivatives thereof, or a combination thereof. The substrate 11 may be omitted.

[0071] The alignment layer 12 can control the orientation of the anisotropic material as further described below, and can include, for example, polyvinyl alcohol, polyolefin, polyamic acid, polyimide, or a combination thereof. When a physical treatment such as friction or a light treatment such as photo-orientation is applied, the surface of the alignment layer 12 can impart a predetermined orientation (e.g., pre-tilt) capability to the anisotropic material. The alignment layer 12 can be omitted.

[0072] The diffraction layer 13 may be an anisotropic diffraction layer including an anisotropic material capable of changing the direction of the wavelength of light, thereby exhibiting an additional phase delay in addition to the phase delay from the anisotropic layer. The diffraction layer 13 may effectively function as a polarization grating, and may be configured to diffract incident light into two circularly polarized lights (e.g., left polarized light and right polarized light) that are circularly polarized in opposite directions to each other. The diffraction layer 13 may be a half-wave plate.

[0073] The diffraction layer 13 may have a plurality of optical axes in the in-plane direction. The plurality of optical axes may be arranged, for example, in a radial shape or in a shape that changes in a clockwise direction or a counterclockwise direction. The orientation angles between adjacent optical axes may be constant, uniformly changing, or non-uniformly changing. A combination of a constant orientation angle and a changing orientation angle may also be used.

[0074] The multiple optical axes may be changed periodically so that the optical axis of the diffraction layer changes in a periodic manner along the in-plane direction of the diffraction layer. For example, the diffraction layer 13 may include at least one grating pitch (Λ) each including the multiple optical axes, and the grating pitch (Λ) may be constant or may be changed in a periodic manner.

[0075] For example, refer to Figure 2 , the diffraction layer 13 may include a plurality of grating pitches (Λ) each including the plurality of optical axes, and the plurality of grating pitches (Λ) may be constant. For example, the plurality of grating pitches (Λ) may be constant in a first direction (e.g., y direction) and may be arranged in a repeated pattern in a second direction (e.g., x direction).

[0076] For example, refer to Figure 3The diffraction layer 13 may include a plurality of grating pitches (Λ) each including the plurality of optical axes, and the grating pitches (Λ) may be different from each other. For example, the plurality of grating pitches (Λ) may be arranged in a non-repeating pattern.

[0077] The diffraction angle (θ) may vary according to the grating pitch (Λ) and may be expressed by Relationship 1.

[0078] Relation 1

[0079]

[0080] In equation 1,

[0081] m is the diffraction order,

[0082] θ m is the mth diffraction angle,

[0083] θ in is the angle of incidence of the incident light,

[0084] Λ is the grating pitch, and

[0085] λ is the wavelength of the incident light.

[0086] For example, in equation 1, when the diffraction order (m) is 1 and the incident angle (θ in ) is 0, the diffraction angle (θ) can be expressed by equation A.

[0087] Relation A

[0088]

[0089] In the relation A

[0090] θ is the diffraction angle,

[0091] Λ is the grating pitch, and

[0092] λ is the wavelength of the incident light.

[0093] For example, the grating pitch (Λ) of the diffraction layer 13 can be greater than the wavelength of the incident light. In one aspect, a plurality of grating pitches can be provided, and at least one grating pitch (Λ) of the plurality of grating pitches can be independently greater than or equal to about 0.8 micrometers (μm). Within this range, at least one grating pitch (Λ) can be independently greater than or equal to about 0.9 μm, within this range, greater than or equal to about 1.0 μm, greater than or equal to about 1.1 μm, greater than or equal to about 1.2 μm, greater than or equal to about 1.5 μm, greater than or equal to about 1.8 μm, or greater than or equal to about 2.0 μm, and within this range, about 0.8 μm to about 10 μm, about 1.0 μm to about 1.0 μm, about 1.1 μm to about 10 μm, about 1.2 μm to about 10 μm, about 1.5 μm to about 10 μm, about 1.8 μm to about 10 μm, or about 2.0 μm to about 10 μm.

[0094] For example, the diffraction angle (θ) of the diffraction layer 13 can be the same or different at wavelengths of 450nm, 550nm, and 650nm, and they can be respectively within about 1 degree to about 50 degrees. Within this range, the diffraction angle (θ) of the diffraction layer 13 at wavelengths of 450nm, 550nm, and 650nm can be within about 2 degrees to 50 degrees, 5 degrees to 50 degrees, 10 degrees to about 50 degrees, about 15 degrees to about 50 degrees, about 20 degrees to about 50 degrees, about 5 degrees to about 40 degrees, about 10 degrees to about 40 degrees, about 15 degrees to about 40 degrees, or about 20 degrees to about 40 degrees.

[0095] For example, the diffraction layer may have a diffraction angle (θ) at a wavelength of 450 nm that is smaller than the diffraction angle (θ) at a wavelength of 550 nm and a wavelength of 650 nm, and the diffraction angle (θ) at a wavelength of 550 nm may be smaller than the diffraction angle (θ) at a wavelength of 650 nm. For example, the difference between the diffraction angle (θ) of the diffraction layer 13 at a wavelength of 450 nm and the diffraction angle at a wavelength of 550 nm may be less than or equal to about 20 degrees, or within the range of about 1 degree to about 20 degrees, about 1 degree to about 15 degrees, or about 1 degree to about 10 degrees. The difference between the diffraction angle (θ) of the diffraction layer 13 at a wavelength of 550 nm and a wavelength of 650 nm may be less than or equal to about 20 degrees, within the range of about 1 degree to about 20 degrees, about 1 degree to about 15 degrees, or about 1 degree to about 10 degrees.

[0096] The diffraction layer 13 includes an anisotropic material 13a. The anisotropic material 13a may be, for example, a liquid crystal, and for example, the liquid crystal may be a rod-shaped liquid crystal, a disc-shaped liquid crystal, or a combination thereof. The diffraction layer may include a plurality of liquid crystals. The liquid crystal may include a monomer, an oligomer, a polymer, or a combination thereof. For example, the liquid crystal may include at least one mesogenic moiety and at least one polymerizable functional group, a cured product thereof, or a combination thereof.

[0097] Reference Figure 1A and Figure 1B , the diffraction layer 13 includes a plurality of anisotropic materials 13a aligned in the thickness direction, and the plurality of anisotropic materials 13a aligned in the thickness direction may form a region A having the same optical axis. The plurality of anisotropic materials 13a in a region A are not twisted relative to the in-plane direction of the diffraction layer 13, but may be substantially horizontally aligned. For example, the plurality of anisotropic materials 13a in a region A may be substantially horizontally aligned from the lower surface of the diffraction layer 13 to its upper surface. As used herein, the term "substantially horizontally aligned" means that at least 95%, or at least 97%, or at least 99% of the plurality of anisotropic materials of the diffraction layer are horizontally aligned. In one aspect, 100% of the plurality of anisotropic materials are horizontally aligned.

[0098] The birefringence of the anisotropic material 13a is the difference between the maximum refractive index and the minimum refractive index of the anisotropic material 13a at a selected wavelength of light. For example, the anisotropic material can have a birefringence of less than or equal to about 0.5, less than or equal to about 0.4, or less than or equal to about 0.3, and within this range, about 0.1 to about 0.5, about 0.1 to about 0.4, about 0.1 to about 0.3, or about 0.2 to about 0.4.

[0099] The birefringence of the anisotropic material may be the same or different depending on the wavelength of light, and when the birefringence is different depending on the wavelength, the anisotropic material may have a birefringence dispersion in which the birefringence increases as the wavelength of light increases. For example, the birefringence dispersion of the anisotropic material may be compared by determining the birefringence of the anisotropic material at a plurality of wavelengths in the visible light wavelength region (e.g., at a wavelength of 450 nm, a wavelength of 550 nm, and a wavelength of 650 nm).

[0100] For example, the birefringence dispersion of the anisotropic material at wavelengths of 450 nm, 550 nm, and 650 nm may satisfy one of Relationships 1A to 3A.

[0101] Relation 1A

[0102] Δn 1 (450nm)<Δn 1 (550nm)≤Δn 1 (650nm)

[0103] Relation 2A

[0104] Δn 1 (450nm)≤Δn 1 (550nm)<Δn 1 (650nm)

[0105] Relation 3A

[0106] Δn 1 (450nm) = Δn 1 (550nm) = Δn 1 (650nm)

[0107] In equations 1A to 3A,

[0108] Δn 1 (450nm) is the birefringence of the anisotropic material at a wavelength of 450nm,

[0109] Δn 1 (550nm) is the birefringence of the anisotropic material at a wavelength of 550nm, and

[0110] Δn 1 (650nm) is the birefringence of the anisotropic material at a wavelength of 650nm.

[0111] The birefringence dispersion of the anisotropic material 13a in the short wavelength region can be expressed as a ratio of the birefringence at a wavelength of 450 nm to the birefringence at a wavelength of 550 nm, and the birefringence dispersion of the anisotropic material 13a in the short wavelength region can satisfy Relationship 4A.

[0112] Relation 4A

[0113] 0.70≤Δn 1 (450nm) / Δn 1 (550nm)≤1.00

[0114] For example, the birefringence dispersion of the anisotropic material 13a in the short wavelength region may satisfy Relational Expression 4A-1.

[0115] Relation 4A-1

[0116] 0.72≤Δn 1 (450nm) / Δn 1 (550nm)≤0.95

[0117] For example, the birefringence dispersion of the anisotropic material 13a in the short wavelength region may satisfy Relational Expression 4A-2.

[0118] Relation 4A-2

[0119] 0.75≤Δn 1 (450nm) / Δn 1 (550nm)≤0.95

[0120] For example, the birefringence dispersion of the anisotropic material 13a in the short wavelength region may satisfy Relational Expression 4A-3.

[0121] Relation 4A-3

[0122] 0.80≤Δn 1 (450nm) / Δn 1 (550nm)≤0.92

[0123] The birefringence dispersion of the anisotropic material 13a in the long wavelength region can be expressed as a ratio of the birefringence at a wavelength of 550 nm to the birefringence at a wavelength of 650 nm, and the birefringence dispersion of the anisotropic material 13a in the long wavelength region can satisfy Relationship 5A.

[0124] Relation 5A

[0125] 1.00≤Δn 1 (650nm) / Δn 1 (550nm)≤1.25

[0126] For example, the birefringence dispersion of the anisotropic material 13a in the long wavelength region may satisfy Relational Expression 5A-1.

[0127] Relation 5A-1

[0128] 1.05≤Δn 1 (650nm) / Δn 1 (550nm)≤1.25

[0129] For example, the birefringence dispersion of the anisotropic material 13a in the long wavelength region may satisfy Relational Expression 5A-2.

[0130] Relation 5A-2

[0131] 1.07≤Δn 1 (650nm) / Δn 1 (550nm)≤1.20

[0132] For example, the birefringence dispersion of the anisotropic material 13a in the long wavelength region may satisfy Relational Expression 5A-3.

[0133] Relation 5A-3

[0134] 1.08≤Δn 1 (650nm) / Δn 1 (550nm)≤1.19

[0135] The birefringence of the diffractive optical element 10 may be the same as the birefringence of the diffractive layer 13, and the birefringence of the diffractive layer 13 may be expressed as the difference between the refractive index at the optical axis with the maximum in-plane refractive index of the diffractive layer 13 and the refractive index at the optical axis with the minimum in-plane refractive index of the diffractive layer 13. For example, the birefringence of the diffractive optical element 10 (or the birefringence of the diffractive layer 13) may be less than or equal to about 0.5, less than or equal to about 0.4, or less than or equal to about 0.3, within the range of about 0.1 to about 0.5, about 0.1 to about 0.4, about 0.1 to about 0.3, or about 0.2 to about 0.4.

[0136] The birefringence of the diffractive optical element 10 (or the birefringence of the diffractive layer 13) may be the same or different depending on the wavelength of light. If the birefringence varies depending on the wavelength of light, it may have a birefringence dispersion in which the birefringence increases as the wavelength increases. For example, the birefringence of the diffractive optical element 10 (or the birefringence of the diffractive layer 13) may be determined by comparing the birefringence measured at a plurality of wavelengths in the visible light wavelength region (e.g., the birefringence at wavelengths of 450 nm, 550 nm, and 650 nm).

[0137] For example, the birefringence dispersion of the diffractive optical element 10 (or the diffractive layer 13) at wavelengths of 450 nm, 550 nm, and 650 nm may satisfy one of Relationships 1B to 3B.

[0138] Relation 1B

[0139] Δn 2 (450nm)<Δn 2 (550nm)≤Δn 2 (650nm)

[0140] Relation 2B

[0141] Δn 2 (450nm)≤Δn 2 (550nm)<Δn 2 (650nm)

[0142] Relation 3B

[0143] Δn 2 (450nm) = Δn 2 (550nm) = Δn 2 (650nm)

[0144] In equations 1B to 3B,

[0145] Δn 2 (450nm) is the birefringence of the diffractive optical element (or diffractive layer) at a wavelength of 450nm,

[0146] Δn 2 (550nm) is the birefringence of the diffractive optical element (or diffractive layer) at a wavelength of 550nm, and

[0147] Δn 2 (650 nm) is the birefringence of the diffractive optical element (or diffractive layer) at a wavelength of 650 nm.

[0148] The birefringence dispersion of the diffractive optical element 10 (or the diffractive layer 13) in the short wavelength region can be expressed as the ratio of the birefringence at wavelengths of 450nm and 550nm, and the birefringence dispersion of the diffractive optical element 10 (or the diffractive layer 13) in the short wavelength region can satisfy equation 4B.

[0149] Relation 4B

[0150] 0.70≤Δn 2 (450nm) / Δn 2 (550nm)≤1.00

[0151] For example, the birefringence dispersion of the diffractive optical element 10 (or the diffractive layer 13) in the short wavelength region may satisfy the relational expression 4B-1.

[0152] Relation 4B-1

[0153] 0.72≤Δn 2 (450nm) / Δn 2 (550nm)≤0.95

[0154] For example, the birefringence dispersion of the diffractive optical element 10 (or the diffractive layer 13) in the short wavelength region may satisfy the relational expression 4B-2.

[0155] Relation 4B-2

[0156] 0.75≤Δn 2 (450nm) / Δn 2 (550nm)≤0.95

[0157] For example, the birefringence dispersion of the diffractive optical element 10 (or the diffractive layer 13) in the short wavelength region may satisfy the relational expression 4B-3.

[0158] Relation 4B-3

[0159] 0.80≤Δn 2 (450nm) / Δn 2 (550nm)≤0.92

[0160] The birefringence dispersion of the diffractive optical element 10 (or the diffractive layer 13) in the long wavelength region can be expressed as the ratio of the birefringence at wavelengths of 550nm and 650nm, and the birefringence dispersion of the diffractive optical element 10 (or the diffractive layer 13) in the long wavelength region can satisfy equation 5B.

[0161] Relation 5B

[0162] 1.00≤Δn 2 (650nm) / Δn 2 (550nm)≤1.25

[0163] For example, the birefringence dispersion of the optical element 10 (or the diffraction layer 13) in the long wavelength region may satisfy the relational expression 5B-1.

[0164] Relation 5B-1

[0165] 1.05≤Δn 2 (650nm) / Δn 2 (550nm)≤1.25

[0166] For example, the birefringence dispersion of the optical element 10 (or the diffraction layer 13) in the long wavelength region may satisfy the relational expression 5B-2.

[0167] Relation 5B-2

[0168] 1.07≤Δn 2 (650nm) / Δn 2 (550nm)≤1.20

[0169] For example, the birefringence dispersion of the optical element 10 (or the diffraction layer 13) in the long wavelength region may satisfy the relational expression 5B-3.

[0170] Relation 5B-3

[0171] 1.08≤Δn 2 (650nm) / Δn 2 (550nm)≤1.19

[0172] By including the anisotropic material 13a and / or the diffractive layer 13 satisfying the above-mentioned birefringence dispersion characteristics, the diffraction efficiency of the diffractive optical element 10 in the visible light wavelength region can be improved.

[0173] The diffraction efficiency can be expressed as, for example, relation 2.

[0174] Relation 2

[0175]

[0176] In equation 2,

[0177] η ±1 is the diffraction efficiency of the diffractive optical element in left and right polarization,

[0178] λ is the wavelength of the incident light,

[0179] Δn is the birefringence of the anisotropic material at wavelength λ,

[0180] d is the thickness of the diffractive layer, and

[0181] S 3 ' is the normalized Stokes parameter and can be +1 (left polarization) or -1 (right polarization).

[0182] For example, the diffraction efficiency of the diffractive optical element at a wavelength of 450nm may be a first diffraction efficiency, the diffraction efficiency of the diffractive optical element at a wavelength of 550nm may be a second diffraction efficiency, and the diffraction efficiency of the diffractive optical element at a wavelength of 650nm may be a third diffraction efficiency. Each of the first diffraction efficiency, the second diffraction efficiency, and the third diffraction efficiency may be independently greater than or equal to about 70%. Within this range, each of the first diffraction efficiency, the second diffraction efficiency, and the third diffraction efficiency may be greater than or equal to about 75%, greater than or equal to about 80%, greater than or equal to about 85%, greater than or equal to about 90%, or greater than or equal to about 95%, respectively. In an embodiment, each of the first diffraction efficiency, the second diffraction efficiency, and the third diffraction efficiency may be from about 70% to about 100%, or from about 75% to about 100%, or from about 85% to about 100%, or from about 95% to about 100%, or from about 98% to about 100%.

[0183] For example, the difference between the maximum diffraction efficiency and the minimum diffraction efficiency among the first diffraction efficiency, the second diffraction efficiency and the third diffraction efficiency may be less than about 20%, within this range, less than or equal to about 18%, less than or equal to about 16%, less than or equal to about 15%, less than or equal to about 12%, less than or equal to about 10%, less than or equal to about 8%, less than or equal to about 5%, less than or equal to about 3%, less than or equal to about 2%, or less than or equal to about 1%. For example, the difference between the maximum diffraction efficiency and the minimum diffraction efficiency among the first diffraction efficiency, the second diffraction efficiency and the third diffraction efficiency may be between 0 and about 20%, between about 0.01% and about 20%, between about 0.05% and about 20%, between about 0.1% and about 20%, between about 0.2% and about 20%, between about 0.3% and about 20%, between about 0.4% and about 20%, or between about 0.5% and about 20%, or between about 0.5% and about 15%, or between about 0.5% and about 10%.

[0184] In addition, the diffractive optical element can increase the bandwidth of the diffractive optical element in the visible light wavelength region by including an anisotropic material that satisfies the above-mentioned birefringence dispersion. The bandwidth can be the width of the light wavelength region that satisfies a predetermined diffraction efficiency, such as the width of the light wavelength region that satisfies the predetermined diffraction efficiency in the visible wavelength region.

[0185] For example, the bandwidth of the diffractive optical element 10 satisfying a diffraction efficiency of greater than or equal to about 70% in a wavelength region of about 400 nm to about 700 nm may be greater than or equal to about 180 nm. Within this range, the bandwidth of the diffractive optical element 10 satisfying a diffraction efficiency of greater than or equal to about 70% in a wavelength region of about 400 nm to about 700 nm may be greater than or equal to about 190 nm, greater than or equal to about 200 nm, greater than or equal to about 210 nm, or greater than or equal to about 220 nm, within this range, about 180 nm to about 300 nm, about 190 nm to about 300 nm, about 200 nm to about 300 nm, about 210 nm to about 300 nm, or about 220 nm to about 300 nm.

[0186] For example, the bandwidth of the diffractive optical element 10 satisfying a diffraction efficiency of greater than or equal to about 80% in a wavelength region of about 400 nm to about 700 nm may be greater than or equal to about 180 nm. Within this range, the bandwidth of the diffractive optical element 10 satisfying a diffraction efficiency of greater than or equal to about 80% in a wavelength region of about 400 nm to about 700 nm may be greater than or equal to about 190 nm, greater than or equal to about 200 nm, greater than or equal to about 210 nm, or greater than or equal to about 220 nm, within this range, about 180 nm to about 300 nm, about 190 nm to about 300 nm, about 200 nm to about 300 nm, about 210 nm to about 300 nm, or about 220 nm to about 300 nm.

[0187] For example, the bandwidth of the diffractive optical element 10 satisfying a diffraction efficiency of greater than or equal to about 90% in a wavelength region of about 400 nm to about 700 nm may be greater than or equal to about 180 nm. Within this range, the bandwidth of the diffractive optical element 10 satisfying a diffraction efficiency of greater than or equal to about 90% in a wavelength region of about 400 nm to about 700 nm may be greater than or equal to about 190 nm, greater than or equal to about 200 nm, greater than or equal to about 210 nm, or greater than or equal to about 220 nm, within this range, about 180 nm to about 300 nm, about 190 nm to about 300 nm, about 200 nm to about 300 nm, about 210 nm to about 300 nm, or about 220 nm to about 300 nm.

[0188] As described above, the diffractive optical element 10 according to the embodiment can realize a high-performance diffractive optical element by having excellent diffraction efficiency and a wide bandwidth. In addition, in the embodiment, by forming the diffraction layer 13 using an anisotropic material such as liquid crystal, the diffractive optical element 10 can be easily designed to have a grating pitch and thickness, and thus can be effectively applied to a large-area diffractive optical element.

[0189] The diffractive optical element according to the embodiment may be, for example, a lens or a prism. The diffractive optical element according to the embodiment may be a plane diffractive optical element such as a plane lens or a plane prism having a constant thickness and a constant curvature, and may perform the functions of a concave lens and a convex lens having various focal lengths without changing the shape and / or curvature of the diffractive optical element, but by adjusting the above-mentioned grating pitch and diffraction angle of the diffraction layer.

[0190] The above-described diffractive optical element may be used as a stacked diffractive optical element including a plurality of diffractive optical elements configured to selectively diffract light of different wavelengths.

[0191] The stacked diffractive optical element can be manufactured by stacking a plurality of diffractive optical elements, each of which includes a diffractive layer including a plurality of optical axes along the in-plane direction. The diffractive layer of each diffractive optical element independently includes an anisotropic material satisfying one of the above-mentioned relations 1A to 3A.

[0192] Figure 5 and Figure 6A-6C is a schematic diagram of a stacked diffractive optical element according to an embodiment.

[0193] For example, the stacked diffractive optical element 100 may include a blue diffractive optical element 100B exhibiting a maximum diffraction efficiency in a wavelength region of greater than or equal to about 400 nm and less than about 500 nm, a green diffractive optical element 100G exhibiting a maximum diffraction efficiency in a wavelength region of about 500 nm to about 600 nm, and a red diffractive optical element 100R exhibiting a maximum diffraction efficiency in a wavelength region of greater than about 600 nm and less than or equal to about 700 nm. The blue diffractive optical element 100B may include at least one of the above-mentioned diffractive optical elements 10, the green diffractive optical element 100G may include at least one of the above-mentioned diffractive optical elements 10, and the red diffractive optical element 100R may include at least one of the above-mentioned diffractive optical elements 10.

[0194] For example, the stacked diffractive optical element 100 can have a diffraction angle (θ) at wavelengths of 450 nm, 550 nm, and 650 nm that can be between about 1 degree and 50 degrees, within the range of about 2 degrees to about 50 degrees, about 5 degrees to about 50 degrees, about 10 degrees to about 50 degrees, about 15 degrees to about 50 degrees, about 20 degrees to about 50 degrees, or about 20 degrees to about 40 degrees.

[0195] For example, the grating pitches (Λ) of the stacked diffractive optical element 100 at wavelengths of 450nm, 550nm, and 650nm may be different from each other. For example, the grating pitch (Λ) at a wavelength of 450nm may be smaller than the grating pitch (Λ) at a wavelength of 550nm, and the grating pitch (Λ) at a wavelength of 550nm may be smaller than the grating pitch (Λ) at a wavelength of 650nm.

[0196] For example, the blue diffractive optical element 100B, the green diffractive optical element 100G, and the red diffractive optical element 100R may include two of the above-described diffractive optical elements 10 and the wavelength selective filters 20B, 20G, 20R respectively disposed therebetween.

[0197] Reference Fig. 6A , the blue diffractive optical element 100B may include two diffractive optical elements 10B and a blue wavelength selective filter 20B disposed therebetween. Figure 6B , the green diffractive optical element 100G may include two diffractive optical elements 10G and a green wavelength selective filter 20G disposed therebetween. Figure 6C , the red diffractive optical element 100R may include two diffractive optical elements 10R and a red wavelength selective filter 20R disposed therebetween. The blue wavelength selective filter 20B included in the blue diffractive optical element 100B may exhibit a half-wave plate characteristic in a blue wavelength region such as a wavelength of about 450 nm; the green wavelength selective filter 20G included in the green diffractive optical element 10G may exhibit a half-wave plate characteristic in a green wavelength region such as a wavelength of about 550 nm; and the red wavelength selective filter 20R included in the red diffractive optical element 10R may exhibit a half-wave plate characteristic in a red wavelength region such as a wavelength of about 650 nm.

[0198] By combining a plurality of diffractive optical elements suitable for each wavelength region, the diffraction efficiency and bandwidth of the stacked diffractive optical elements can be further improved.

[0199] The aforementioned diffractive optical elements and stacked diffractive optical elements may be included in various devices that benefit from improved diffraction properties, such as optical devices, augmented reality (AR) devices, virtual reality (VR) devices, or holographic devices.

[0200] Hereinafter, the embodiments will be described in more detail with reference to examples. However, these examples are exemplary, and the present scope is not limited thereto.

[0201] Example

[0202] Design of Diffractive Optical Element I

[0203] (1) Design of anisotropic materials

[0204] Based on Table 1 and Figure 7 The properties of the anisotropic material (liquid crystal) shown in FIG. 1 are used to set a diffractive optical element having the configuration shown in FIG. 1 .

[0205] Figure 7 is a graph showing the birefringence according to wavelength of an anisotropic material used for simulation.

[0206] Table 1

[0207]

[0208] (2) Other design aspects

[0209] The average refractive index of the anisotropic material and the birefringence of the diffraction layer, the diffraction angle and the grating pitch are designed within the following ranges.

[0210] - Average refractive index: 1.58

[0211] - Birefringence: 0.1 to 0.4

[0212] -Diffraction angle (θ): 5 degrees to 40 degrees

[0213] - Grating pitch (Λ): Calculate the grating pitch (0.86 μm to 6.31 μm) of the diffraction angle that satisfies equation 1

[0214] -Thickness: The thickness is set to that of a λ / 2 wave plate at a wavelength of 550nm

[0215] Simulation I

[0216] The diffractive optical element designed under the above conditions was optically simulated using FDTD software (Finite Difference Time Domain, Lumerical Inc.).

[0217] The results are shown in Tables 2 to 7.

[0218] Table 2

[0219]

[0220]

[0221] Table 3

[0222]

[0223] Table 4

[0224]

[0225]

[0226] Table 5

[0227]

[0228] Table 6

[0229]

[0230]

[0231] Table 7

[0232]

[0233] Referring to Tables 2 to 7 above, the diffractive optical elements according to the examples (Tables 2 to 6) show improved diffraction efficiency under the same conditions, compared with the diffractive optical element according to the comparative example (Table 7).

[0234] Figures 8 to 10 : is a graph showing the diffraction efficiency according to the wavelength of the diffractive optical elements according to the example and the comparative example.

[0235] Reference Figures 8 to 10 , confirming that: compared with the diffractive optical element according to the comparative example (anisotropic material F), the diffractive optical element according to the example (anisotropic material AE) has smaller diffraction efficiency variation at various wavelengths under the same conditions, for example, the diffraction efficiency of the diffractive optical element according to the example is greater than or equal to about 70%, greater than or equal to about 80%, or greater than or equal to about 90%.

[0236] Design of Diffractive Optical Element II

[0237] Based on Table 1 and Figure 7 The properties of the anisotropic material (liquid crystal) shown are assumed to have Figure 5 FIG6 is a stacked diffractive optical element configured as shown in FIG6 .

[0238] The stacked diffractive optical element consists of a blue diffractive optical element (B), a green diffractive optical element (G), and a red diffractive optical element (R), and the properties of each diffractive optical element are shown in Table 8.

[0239] Table 8

[0240]

[0241] Simulation II

[0242] Optical simulations were performed using FDTD software on a stacked diffractive optical element designed to satisfy the above conditions.

[0243] The results are shown in Table 9.

[0244] Table 9

[0245] Birefringence Diffraction efficiency (B / G / R,%) Example 68 0.2 95.9 / 94.9 / 91.3 Example 69 0.3 97.5 / 96.3 / 94.6 Example 70 0.4 99.8 / 99.4 / 96.4 Comparative Example 17 0.2 52.9 / 60.2 / 53.0

[0246] Referring to Table 9, the stacked diffractive optical element according to the example has a much greater diffraction efficiency than the stacked diffractive optical element according to the comparative example.

[0247] While the present disclosure has been described in conjunction with what are presently considered to be practical example embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0248] This application claims priority to and the benefit of Korean Patent Application No. 10-2019-0082044 filed in the Korean Intellectual Property Office on July 8, 2019, the contents of which are incorporated herein by reference in their entirety.

Claims

1. A diffractive optical element, include: A diffractive layer including a plurality of optical axes along an in-plane direction, The diffraction layer comprises an anisotropic material satisfying one of the relations 1A to 3A: Relation 1A Δn 1 (450nm)<Δn 1 (550nm)≤Δn 1 (650nm) Relation 2A Δn 1 (450nm)≤Δn 1 (550nm)<Δn 1 (650nm) Relation 3A Δn 1 (450nm)=Δn 1 (550nm)=Δn 1 (650nm) Wherein, in equations 1A to 3A, Δn 1 (450nm) is the birefringence of the anisotropic material at a wavelength of 450 nanometers, Δn 1 (550 nm) is the birefringence of the anisotropic material at a wavelength of 550 nanometers, and Δn 1 (650nm) is the birefringence of the anisotropic material at a wavelength of 650 nanometers, The anisotropic material further has a birefringence dispersion satisfying equations 4A and 5A: Relation 4A 0.70≤Δn 1 (450nm) / Δn 1 (550nm)≤1.00 Relation 5A 1.00≤Δn 1 (650nm) / Δn 1 (550nm)≤1.25。 2 . The diffractive optical element according to claim 1 , wherein the plurality of optical axes of the diffractive layer are configured to change periodically along the in-plane direction.

3. The diffractive optical element according to claim 1, wherein The diffractive layer comprises at least one grating pitch, each grating pitch comprises the plurality of optical axes, and The grating pitch is 0.8 microns to 10 microns.

4. The diffractive optical element according to claim 1, wherein The anisotropic material is liquid crystal, The diffraction layer includes a plurality of liquid crystals arranged in a thickness direction of the diffraction layer, and The plurality of liquid crystals arranged in the thickness direction are not twisted in the in-plane direction of the diffraction layer. 5 . The diffractive optical element according to claim 1 , wherein the birefringence of the anisotropic material at a wavelength of 550 nanometers is 0.01 to 0.

5.

6. The diffractive optical element according to claim 1, wherein a diffraction angle of the diffraction layer at a wavelength of 450 nanometers, a diffraction angle of the diffraction layer at a wavelength of 550 nanometers, and a diffraction angle of the diffraction layer at a wavelength of 650 nanometers are the same or different and are within 1 degree to 50 degrees. 7 . The diffractive optical element according to claim 1 , wherein the diffraction efficiency of the diffractive optical element at a wavelength of 450 nanometers, the diffraction efficiency at a wavelength of 550 nanometers, and the diffraction efficiency at a wavelength of 650 nanometers are each independently 70% to 100%.

8. The diffractive optical element according to claim 7, wherein The difference between the maximum diffraction efficiency and the minimum diffraction efficiency of the diffraction optical element among the diffraction efficiency at a wavelength of 450 nanometers, the diffraction efficiency at a wavelength of 550 nanometers, and the diffraction efficiency at a wavelength of 650 nanometers is less than 20%. 9 . The diffractive optical element according to claim 1 , wherein the diffractive optical element is a lens or a prism. 10 . The diffractive optical element according to claim 1 , wherein the diffractive optical element is a planar diffractive optical element having a constant thickness and a constant curvature.

11. A diffractive optical element comprising a plurality of optical axes along an in-plane direction, wherein the birefringence of the diffractive optical element for light having a wavelength of 550 nanometers to 650 nanometers is greater than or equal to the birefringence of the diffractive optical element for light having a wavelength of 450 nanometers to less than 550 nanometers, and The diffraction efficiency of the diffractive optical element at a wavelength of 450 nanometers, the diffraction efficiency at a wavelength of 550 nanometers, and the diffraction efficiency at a wavelength of 650 nanometers are each independently 70% to 100%, The birefringence dispersion of the diffractive optical element satisfies equations 4B and 5B: Relation 4B 0.70≤Δn 2 (450nm) / Δn 2 (550nm)≤1.00 Relation 5B 1.00≤Δn 2 (650nm) / Δn 2 (550nm)≤1.25 in, In equations 4B and 5B, Δn 2 (450nm) is the birefringence of the diffractive optical element at a wavelength of 450 nanometers, Δn 2 (550 nm) is the birefringence of the diffractive optical element at a wavelength of 550 nanometers, and Δn 2 (650nm) is the birefringence of the diffractive optical element at a wavelength of 650 nanometers.

12. The diffractive optical element according to claim 11, wherein the diffractive optical element has a birefringence dispersion satisfying one of relations 1B to 3B: Relation 1B Δn 2 (450nm)<Δn 2 (550nm)≤Δn 2 (650nm) Relation 2B Δn 2 (450nm)≤Δn 2 (550nm)<Δn 2 (650nm) Relation 3B Δn 2 (450nm)=Δn 2 (550nm)=Δn 2 (650nm)。 13. The diffractive optical element according to claim 11, wherein The difference between the maximum diffraction efficiency and the minimum diffraction efficiency of the diffraction optical element at a wavelength of 450 nanometers, a wavelength of 550 nanometers, and a wavelength of 650 nanometers is less than 20%.

14. A stacked diffractive optical element, comprising a plurality of diffractive optical elements according to claim 1 stacked together.

15. The stacked diffractive optical element according to claim 14, include: The blue diffractive optical element exhibits the maximum diffraction efficiency in the wavelength region of 400 nm to 500 nm. A green diffractive optical element that exhibits maximum diffraction efficiency in the wavelength region of 500 nanometers to 600 nanometers, and The red diffractive optical element exhibits maximum diffraction efficiency in the wavelength region of 600nm to 700nm.

16. The stacked diffractive optical element of claim 14, further comprising at least one wavelength selective filter. 17 . An optical device comprising the diffractive optical element according to claim 1 , the diffractive optical element according to claim 11 , or the stacked diffractive optical element according to claim 14 .

18. An augmented reality device, comprising the diffractive optical element according to claim 1, the diffractive optical element according to claim 11, or the stacked diffractive optical element according to claim 14.

19. A virtual reality device, comprising the diffractive optical element according to claim 1, the diffractive optical element according to claim 11, or the stacked diffractive optical element according to claim 14.

20. A holographic device comprising the diffractive optical element according to claim 1, the diffractive optical element according to claim 11, or the stacked diffractive optical element according to claim 14.

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