KR102767847B1 - Grating device and method of manufacturing the same and optical apparatus including grating device - Google Patents

Abstract

Disclosed are a diffraction grating element, a method for manufacturing the same, and an optical device including the diffraction grating element. According to one embodiment, the diffraction grating element includes a diffraction grating arranged on a light reflecting substrate. The diffraction grating includes a plurality of diffraction elements, and each of the plurality of diffraction elements has a height at which light reflected from its upper surface and light reflected from its lower surface destructively interfere with each other for light incident at an incident angle of 45° or more. According to one embodiment, the optical device includes a light source, a first diffraction grating element, and a second diffraction grating element. According to one embodiment, the method for manufacturing the diffraction grating element includes forming a dielectric layer on a light reflecting substrate, and then patterning the dielectric layer to form a plurality of diffraction elements forming a diffraction grating on the substrate. The refractive index of the dielectric layer is 2.0 or less.

Description

{Grating device and method of manufacturing the same and optical apparatus including grating device}

The present disclosure relates to a diffractive element, and more specifically, to a diffractive grating element, a method for manufacturing the same, and an optical device including the diffractive grating element.

A diffraction grating can be viewed as an optical device that gives periodic changes to the amplitude and phase of light. A diffraction grating acts like a prism to disperse light. Therefore, a diffraction grating can be used to obtain a spectrum of light.

A diffraction grating is a structure that provides periodic changes to the amplitude and phase of light. For example, it can have a structure that is periodically engraved with diffraction holes, obstacles, or parallel thin lines on a flat or concave glass plate or metal plate.

Diffraction gratings can be classified into transmission gratings and reflection gratings. Transmission gratings have a structure in which a large number of slits are arranged at regular intervals on a transparent substrate. Reflection gratings have a structure in which a large number of lines are engraved at regular intervals on an opaque substrate, such as a reflective mirror.

In the present disclosure, a diffraction grating element capable of increasing diffraction efficiency for a high incident angle is provided.

In the present disclosure, a diffraction grating element capable of securing a wide field of view and minimizing the volume is provided.

The present disclosure provides an optical device capable of reducing chromatic dispersion including such a diffraction grating element.

The present disclosure provides a method for manufacturing a diffraction grating element, which can easily implement a large-area diffraction grating element while reducing production costs.

In one embodiment of the present disclosure, a diffraction grating element includes a diffraction grating arranged on a light reflecting substrate. The diffraction grating includes a plurality of diffraction elements, and each of the plurality of diffraction elements has a height at which light reflected from its upper surface and light reflected from its lower surface cause destructive interference with each other for light incident at an incident angle of 75° or greater.

In one embodiment, a dielectric layer may exist as a spacer layer between the substrate and the diffraction grating, and the thickness of the dielectric layer is n times (n=1,2,3, etc.) the wavelength of incident light. The substrate may be a Bragg reflector including dielectrics having different refractive indices. The refractive index of the diffraction grating may be 2.0 or less. For example, the refractive index of the diffraction grating may be 1.3 to 2.0.

In one embodiment, the plurality of diffractive elements may each include a main diffractive element and an auxiliary diffractive element. The width of the main diffractive element may be greater than the width of the auxiliary diffractive element. The auxiliary diffractive element may include a plurality of auxiliary diffractive elements spaced apart from each other, and the widths of the plurality of auxiliary diffractive elements may be the same as or different from each other. The plurality of diffractive elements may each include a main diffractive element and a plurality of auxiliary diffractive elements, and the plurality of auxiliary diffractive elements may be arranged such that as the number of the plurality of auxiliary diffractive elements increases, a negative diffraction angle range capable of obtaining high diffraction efficiency increases.

In one embodiment, the plurality of diffractive elements may be arranged so as to exhibit the same diffraction characteristics.

In other embodiments, the plurality of diffractive elements may be arranged to exhibit different diffraction characteristics.

The dielectric layer may be a single layer. In another embodiment, the dielectric layer comprises laminated first and second dielectric layers, and the refractive indices of the first and second dielectric layers may be different from each other.

In one embodiment, the substrate may be a metallic substrate or a reflective wire gird polarizer (WGP).

In one embodiment, the plurality of diffractive elements may be arranged so as to exhibit either positive or negative diffraction characteristics. The pitch between the plurality of diffractive elements may be the same.

In another example, the plurality of diffraction elements may include diffraction elements exhibiting positive diffraction characteristics and diffraction elements exhibiting negative diffraction characteristics.

The refractive index of the above dielectric layer may be equal to or greater than the refractive index of the above diffraction grating.

In one embodiment, the refractive index of the dielectric layer in direct contact with the diffractive element among the first and second dielectric layers may be greater than the refractive index of the diffractive element, and the refractive index of the dielectric layer in direct contact with the diffractive element among the first and second dielectric layers may be greater than the refractive index of the dielectric layer provided directly underneath it.

In one embodiment, the diffraction elements exhibiting the positive diffraction characteristic may be arranged so that the degree of the positive diffraction characteristic is different from each other. The pitches of the diffraction elements exhibiting the positive diffraction characteristic may be different from each other.

In one embodiment, the diffraction elements exhibiting the negative diffraction characteristic may be arranged so that the degree of the negative diffraction characteristic is different from each other. The pitches of the diffraction elements exhibiting the negative diffraction characteristic may be different from each other.

In one embodiment of the present disclosure, an optical device includes a first diffraction grating element that diffracts light incident from a light source. The first diffraction grating element is a diffraction grating element that includes any one of the characteristics of the diffraction grating element according to one embodiment of the present disclosure described above.

According to one embodiment, the light source unit may include a light source that directly emits light and a second diffraction grating element that diffracts light incident from the light source and provides incident light to the first diffraction grating element.

According to one embodiment, the first diffraction grating element and the second diffraction grating element may be diffraction grating elements exhibiting identical diffraction characteristics.

According to another embodiment, the first diffraction grating element and the second diffraction grating element may be diffraction grating elements exhibiting different diffraction characteristics.

According to another embodiment, the light source unit may include a light source that directly emits light, a second diffraction grating element that diffracts light incident from the light source in a given direction, and a transmission element that transmits the diffracted light of the second diffraction grating element to the first diffraction grating element.

According to one embodiment, the remaining elements may be arranged at an angle less than 45° with respect to a normal line perpendicular to the diffraction plane of one of the first diffraction grating elements and the second diffraction grating elements.

In one embodiment, the first and second diffraction grating elements may be diffraction grating elements that act as beam expanders.

In another embodiment, the first diffraction grating element may be a diffraction grating element that acts as a lens, and the second diffraction grating element may be a diffraction grating element that acts as a beam expander.

In one embodiment, the transmitting element may be a light reflector.

In one embodiment of the present disclosure, a method for manufacturing a diffraction grating element comprises forming a dielectric layer on a light reflecting substrate, and then patterning the dielectric layer to form a plurality of diffraction elements forming a diffraction grating on the substrate. Here, the refractive index of the dielectric layer is 2.0 or less.

According to one embodiment, the process of patterning the dielectric layer includes aligning a template having a diffractive element pattern corresponding to the plurality of diffractive elements engraved on one side thereof on the dielectric layer, imprinting the template onto the dielectric layer in an aligned state, and then removing the template.

According to one embodiment, for light incident at an angle of incidence of 75° or greater, each of the plurality of diffractive elements may have a height at which light reflected from its upper surface and light reflected from its lower surface cause destructive interference with each other.

In another embodiment, a spacer layer may be further formed between the substrate and the dielectric layer.

In one embodiment, each of the plurality of diffractive elements may include a primary diffractive element and an auxiliary diffractive element. The auxiliary diffractive element may include a plurality of auxiliary diffractive elements. The plurality of diffractive elements may all be formed to have the same pitch or different pitches. The plurality of auxiliary diffractive elements may be arranged so that as the number of the plurality of auxiliary diffractive elements increases, the negative diffraction angle range for which high diffraction efficiency can be obtained increases.

In other embodiments, some of the plurality of diffractive elements may include a main diffractive element and an auxiliary diffractive element, while others may include only a main diffractive element.

In the diffraction grating element according to the disclosed embodiment, the diffraction elements have a height capable of canceling out the 0th-order diffracted light for incident light obliquely incident at an incident angle of 75° or more. In addition, for the diffraction elements causing negative diffracted light, auxiliary diffraction elements are appropriately arranged together with the main diffraction elements to remove the 2nd-order or higher diffracted light. Accordingly, a high diffraction efficiency close to 1 can be obtained for the 1st-order diffracted light. In the disclosed diffraction grating element, the configuration and specifications (height, pitch, etc.) of the diffraction elements are optimized for the diffraction of incident light having a high incident angle close to the horizontal, so that the overall volume of the diffraction grating element becomes very thin. Therefore, when the disclosed diffraction grating element is applied to another device, the volume of the device can be reduced compared to the existing one.

In addition, since the output angle of the diffraction light can be controlled by adjusting the pitch of the diffraction elements or the number of auxiliary diffraction elements, a wide range of output angles can be secured. This suggests that the disclosed diffraction grating element can contribute to expanding the viewing angle in a display.

In addition, in the case of the disclosed diffraction grating elements, by optically combining two of them, color dispersion that may appear in diffracted light when only one is used can be reduced or eliminated.

In addition, in the disclosed diffraction grating element, the diffraction elements are formed of a material (e.g., a polymer) having a refractive index of 2.0 or less. Accordingly, the disclosed diffraction grating element can be formed using a nanoimprint manufacturing method, so that not only can a large-diameter diffraction grating element be easily formed, but also the production cost can be reduced.

Fig. 1 is a cross-sectional view showing a diffraction grating element according to one embodiment.
Fig. 2 is a cross-sectional view showing a diffraction grating element according to another embodiment.
Fig. 3 is a cross-sectional view showing a diffraction grating element according to another embodiment.
Figure 4 is a three-dimensional diagram of the diffraction grating element of Figure 2.
Fig. 5 is a cross-sectional view of a diffraction grating element according to another embodiment.
Fig. 6 is a cross-sectional view of a diffraction grating element according to another embodiment.
Fig. 7 is a cross-sectional view of a diffraction grating element according to another embodiment.
Figures 8 to 11 are graphs showing the results of simulations conducted to determine the diffraction efficiency according to the diffraction element shape of the diffraction grating element according to the previously described example.
FIGS. 12A to 12C are cross-sectional views showing a case where a diffraction grating element according to one embodiment is used as a beam expander.
Fig. 13 is a cross-sectional view showing a case where a diffraction grating element according to one embodiment is used as a lens.
Fig. 14 is a cross-sectional view showing a case where a diffraction grating element according to one embodiment is used as a component of a display device.
Fig. 15 is a cross-sectional view showing an optical device including a diffraction grating element according to one embodiment.
FIG. 16 is a cross-sectional view showing another optical device including a diffraction grating element according to one embodiment.
FIG. 17 is a cross-sectional view showing another optical device including a diffraction grating element according to one embodiment.
Figures 18 and 19 are cross-sectional views taken along the 18-18' direction of Figure 17.
FIGS. 20 to 24 are cross-sectional views showing step-by-step the process of manufacturing a template used to imprint a diffraction grating in a method for manufacturing a diffraction grating element according to one embodiment.
FIGS. 25 to 29 are cross-sectional views showing a method of forming a diffraction grating element according to one embodiment using the template formed in FIGS. 20 to 24.

Hereinafter, a diffraction grating element and a method for manufacturing the same and an optical device including the diffraction grating element according to one embodiment will be described in detail with reference to the attached drawings. In this process, the thicknesses of layers or regions illustrated in the drawings are exaggerated for the clarity of the specification.

Figure 1 shows a diffraction grating element according to one embodiment.

Referring to FIG. 1, a diffraction grating element (5) according to one embodiment includes a substrate (10) and a plurality of diffraction elements (20) provided on the substrate (10). The substrate (10) may be a material layer capable of reflecting incident light. In other words, the substrate (10) may be a light reflecting substrate that reflects incident light. For example, the substrate (10) may be a metallic mirror or a substrate or metal substrate that exhibits light reflection characteristics, including a metal. In another example, a reflective wire grid polarizer (WGP) may be used as the substrate (10). The entirety of the plurality of diffraction elements (20) may be collectively referred to as a diffraction grating. The diffraction elements (20) may be arranged on one surface of the substrate (10). For example, the diffraction elements (20) may be arranged on an upper surface of the substrate (10). The plurality of diffraction elements (20) are spaced apart from each other. The diffractive elements (20) may be distributed on the substrate (10) to have a given pitch (P1). The diffractive elements (20) have a given height (H1) and a given width (W1). If these specifications of the diffractive elements (20) change, the diffraction characteristics by the diffractive elements (20) may also change. The refractive index of the diffractive elements (20) may be 2.0 or less. For example, for high-efficiency operation and small aspect ratio, the refractive index of the diffractive elements (20) may be about 1.35 to 2.0. The diffractive elements (20) may be formed by including a low-loss dielectric material such as a polymer or SiO2. Here, ‘low loss’ means that the absorption loss of incident light is low. That is, the absorption loss of incident light by the diffractive elements (20) is low. The height (H1) of the diffractive elements (20) may be determined in connection with the wavelength of the incident light. By doing so, the zeroth order light of the diffraction can be removed through destructive interference. For example, a path difference occurs between the light (L1) reflected from the upper surface of the diffractive elements (20) and the light (L2) reflected from the bottom of the diffractive elements (20), and the height (H1) of the diffractive elements (20) can be set to a height that satisfies the condition that destructive interference occurs between the light (L1) reflected from the upper surface and the light (L2) reflected from the bottom. This height characteristic can be one cause of increasing the diffraction efficiency. A plurality of diffractive elements (20) can also be provided to have a given fill factor. The fill factor is defined as the diffraction grating coverage on one period (P1). In one example, the fill factor of the plurality of diffractive elements (20) may be set so that the percentage of light reflected from the upper surface of each diffractive element (20) and the percentage of light reflected from the bottom surface of each diffractive element (20) are the same for the incident light. At this time, the light absorption loss is excluded. This fill factor may vary depending on the incident light, the light absorption rate, the refractive index of the diffractive element (20), etc. The lower the refractive index of the plurality of diffractive elements (20), the larger the fill factor may be required.

The diffraction characteristics of the diffraction grating element (5) may vary depending on the pitch (P1) of the plurality of diffraction elements (20). Depending on the pitch (P1) of the plurality of diffraction elements (20), the diffraction grating element (5) may exhibit positive or negative diffraction characteristics. When the incident light (L0) is diffracted in the diffraction element (20) toward the light source that emits the incident light (L0), it can be said that the diffraction grating element (5) exhibits or has positive diffraction characteristics. In this case, the diffracted light (L3) has a positive output angle. In other words, when the incident light (L0) incident on the diffraction element (20) in FIG. 1 appears as diffracted light (L3) that is diffracted to the left of the reference line (10L) that is perpendicular to the upper surface of the substrate (10), it can be said that the diffraction grating element (5) has a positive diffraction characteristic or the diffraction element (20) has a positive diffraction characteristic. Conversely, when the incident light (L0) is diffracted in the opposite direction to the side where the light source is, that is, when the incident light (L0) appears as diffracted light (L4) that is diffracted to the right of the reference line (10L), it can be said that the diffraction grating element (5) exhibits or has a negative diffraction characteristic, and it can also be said that the diffraction element (20) exhibits or has a negative diffraction characteristic. In this case, the diffracted light (L4) has a negative output angle. When multiple diffraction elements (20) arranged on a substrate (10) are all geometrically identical and the pitch (P1) between the diffraction elements (20) is the same, the diffraction grating element (5) may have positive or negative diffraction characteristics overall depending on the pitch (P1).

Meanwhile, as will be described later, when the pitches of some of the diffraction elements (20) are different from the remaining diffraction elements, the diffraction grating element (5) may exhibit different diffraction characteristics depending on the region. For example, among the diffraction elements (20) on the left, the two diffraction elements may be arranged to have pitches exhibiting negative diffraction characteristics, and the two diffraction elements on the right may be arranged to have pitches exhibiting positive diffraction characteristics. As a result, the diffraction grating element (5) may be used as various optical elements (e.g., optical expanders, lenses, etc.) depending on the diffraction characteristics of the diffraction elements (20). This will be described later.

The incident angle (θ1) of the incident light (L0) incident on the diffraction element (20) in the diffraction grating element (5) may be 45° or more. For example, the range of the incident angle (θ1) may be 75°≤θ1<90°. Since the incident angle (θ1) is relatively large at 45° or more and a relatively wide range of diffraction light can be obtained, an ultra-small diffraction grating element can be implemented.

In another embodiment, the diffraction element (20) of the diffraction grating element (5) may be replaced with the second diffraction element (30) illustrated in FIG. 2 or the third diffraction element (40) illustrated in FIG. 3. All of the plurality of diffraction elements (20) may be replaced with the second diffraction element (30) illustrated in FIG. 2 or the third diffraction element (40) illustrated in FIG. 3. In another embodiment, only some of the plurality of diffraction elements (20) may be replaced with the diffraction element (30) illustrated in FIG. 2 or the diffraction element (40) illustrated in FIG. 3. In this case, the diffraction grating element (5) may exhibit two diffraction characteristics simultaneously.

Referring to FIG. 2, the second diffractive element (30) formed on the substrate (10) includes a main diffractive element (30A) and an auxiliary diffractive element (30B). The main diffractive element (30A) and the auxiliary diffractive element (30B) are spaced apart from each other and do not contact each other. The height of the main diffractive element (30A) and the height of the auxiliary diffractive element (30B) may be the same. The width (W2) of the main diffractive element (30A) is wider than the width (W3) of the auxiliary diffractive element (30B). The second diffractive element (30) may be provided to have a pitch exhibiting a negative diffraction characteristic. Accordingly, light (L30) incident on the second diffractive element (30) is diffracted to the right of the reference line (10L). One way to increase diffraction efficiency is to remove high-order components (e.g., diffracted light of the second or higher order) from the diffracted light, and an auxiliary diffraction element (30B) is provided for this purpose. Due to the presence of the auxiliary diffraction element (30B), a diffraction component that can cause phase cancellation interference with the high-order diffraction component is generated. Accordingly, undesired high-order diffraction components included in the diffracted light can be removed. Taking this into account, the width (W3) of the auxiliary diffraction element (30B), the interval between the main diffraction element (30A) and the auxiliary diffraction element (30B), etc. can be set. By including the auxiliary diffraction element (30B), a diffraction efficiency close to 1 can be obtained.

Multiple auxiliary diffraction elements can be provided for one main diffraction element, and Fig. 3 shows an example of this.

Referring to FIG. 3, the third diffraction element (40) formed on the substrate (10) includes a main diffraction element (40A) and first to third auxiliary diffraction elements (40B, 40C, 40D). Two or three or more auxiliary diffraction elements may be provided. By providing these auxiliary diffraction elements, a wide diffraction angle can be obtained even at a large lateral angle of incidence, and the diffraction efficiency can also be increased. In addition, the range of diffraction angles at which high diffraction efficiency can be obtained can be widened in proportion to the number of auxiliary diffraction elements.

The height of the main diffractive element (40A) may be the same as the heights of the first to third auxiliary diffractive elements (40B, 40C, 40D). The heights of the first to third auxiliary diffractive elements (40B, 40C, 40D) may be the same. The width (W4) of the main diffractive element (40A) is wider than the widths of each of the first to third auxiliary diffractive elements (40B, 40C, 40D). The main diffractive element (40A) and the first to third auxiliary diffractive elements (40B, 40C, 40D) are spaced apart from each other and do not contact each other. The first to third auxiliary diffractive elements (40B, 40C, 40D) are spaced apart from each other and do not contact each other. The spacing (D1) between the main diffractive element (40A) and the first auxiliary diffractive element (40B) and the spacings (D2, D3) between the first to third auxiliary diffractive elements (40B, 40C, 40D) may be the same or different.

When the spacing (D1, D2, D3) is different, the spacing (D1) between the main diffractive element (40A) and the first auxiliary diffractive element (40B) may be wider or narrower than the spacing (D2, D3) between the first to third auxiliary diffractive elements (40B, 40C, 40D), and the spacing (D2, D3) between the first to third auxiliary diffractive elements (40B, 40C, 40D) may become wider or narrower as the distance from the main diffractive element (40A) increases.

For convenience, the widths of the first to third auxiliary diffractive elements (40B, 40C, 40D) are all illustrated as being the same, but the widths of the first to third auxiliary diffractive elements (40B, 40C, 40D) may be different from each other. For example, the first to third auxiliary diffractive elements (40B, 40C, 40D) may be arranged in a direction in which the widths become wider or narrower as they move away from the main diffractive element (40A).

The specifications (height, width, spacing, etc.) of the main diffractive element (40A) and the first to third auxiliary diffractive elements (40B, 40C, 40D) can be adjusted during the manufacturing stage according to the characteristics of the required diffracted light. As the number of auxiliary diffractive elements increases, the destructive interference effect on the higher-order diffraction components (LD1, LD2) of the diffracted light can also increase. Ultimately, due to the presence of the auxiliary diffractive elements, a diffraction efficiency close to 1 can be obtained. That is, among the components included in the diffracted light, only light of a specific component (order), for example, the first-order diffracted light, can be displayed. The diffraction grating element of the present disclosure can be applied to various devices due to such diffraction characteristics. For example, it can be applied to a beam expander, or can be used as an optical combiner for augmented reality, virtual reality, or a light field display system.

Figure 4 shows a three-dimensional view of a diffraction grating element having the second diffraction element (30) illustrated in Figure 2.

Referring to FIG. 4, the second diffraction elements (30) are arranged in parallel with each other in a spaced state on the substrate (10). In addition, the main diffraction element (30A) and the auxiliary diffraction element (30B) are also arranged in parallel with each other in a spaced state. The diffraction elements (20) of FIG. 1 and the third diffraction elements (40) of FIG. 3 may also be arranged on the substrate (10) like the second diffraction elements (30).

In Fig. 4, reference numeral 4L1 represents light reflected from the upper surface of the main diffractive element (30A), and reference numeral 4L2 represents light reflected from the bottom surface of the main diffractive element (30A). The reflected lights (4L1, 4L2) correspond to 0th-order diffraction light. Since the height (H1) of the main diffractive element (30A) has a height such that the path difference between the reflected lights (4L1, 4L2) becomes ½ of the wavelength of the incident light, the reflected lights (4L1, 4L2) cancel each other out and disappear. That is, due to this height condition of the main diffractive element (30A), the 0th-order diffraction light can be removed through destructive interference.

Fig. 5 shows a diffraction grating element (55) according to another embodiment.

Referring to FIG. 5, the diffraction grating element (55) includes a substrate (10), a first spacer or space material layer (50), a plurality of diffraction elements (20), etc. Instead of the plurality of diffraction elements (20), the second diffraction element (30) of FIG. 2 or the third diffraction element (40) of FIG. 3 may be arranged. The first spacer (50) may be arranged between the diffraction elements (20) and the substrate (10). The first spacer (50) may be arranged on one surface of the substrate (10), for example, may be provided on the upper surface of the substrate (10). The first spacer (50) may cover the entire upper surface of the substrate (10). The first spacer (50) may have a thickness (T1) corresponding to an integer multiple of the wavelength of incident light. The thickness (T1) of the first spacer (50) can be determined by considering the incident angle of light, the diffraction angle, the refractive index of the first spacer (50), the refractive index of the diffractive element (20), etc. The first spacer (50) can be a material layer formed of a low-loss material having a low light absorption rate for incident light, for example, a dielectric layer having a lower refractive index than the diffractive element (20). Therefore, when light is incident on the diffraction grating element (55), the light absorption loss due to the first spacer (50) can be ignored. The diffraction grating elements disclosed herein can be manufactured by various methods, one of which is a nano-imprint method. This will be described later. Considering this manufacturing method, the first spacer (50) can be a material layer of the same material as the diffraction element (20). The first spacer (50) can be a single layer. A plurality of diffractive elements (20) are arranged spaced apart from each other on the first spacer (50). The plurality of diffractive elements (20) may be arranged at a constant pitch on the upper surface of the first spacer layer (50). In another example, the pitch of some of the plurality of diffractive elements (20) may be different from the pitch of the remaining ones. In other words, the plurality of diffractive elements (20) may be arranged to exhibit positive diffraction characteristics, may be arranged to exhibit negative diffraction characteristics, or may be arranged to exhibit both positive and negative diffraction characteristics. A residual material layer (52) may exist on the first spacer (50) between the plurality of diffractive elements (20). The residual material layer (52) is located below the diffractive elements (20) and may cover the entire upper surface of the first spacer (50). The residual material layer (52) is a layer remaining below the diffraction elements (20) during the process of manufacturing the diffraction grating element (55), and its thickness does not exceed 30 nm, and may be, for example, 20 nm or less. The thickness of the residual material layer (52) may be reduced to 20 nm or less or may not be formed depending on the process conditions during the manufacturing process. Since the thickness of the residual material layer (52) is very thin, the influence of the residual material layer (52) on diffraction can be ignored. The residual material layer (52) is a layer of the same material as the diffraction elements (20).

Fig. 6 shows a diffraction grating element according to another embodiment. The diffraction grating element illustrated in Fig. 6 has a similar part in terms of configuration to the diffraction grating element (55) illustrated in Fig. 5. Therefore, only the parts different from Fig. 5 will be described with respect to Fig. 6.

Referring to FIG. 6, a second spacer (60) exists between a substrate (10) and a plurality of diffractive elements (20). The second spacer (60) can be in direct contact with the substrate (10) and the diffractive elements (20). The second spacer (60) is formed on one surface of the substrate (10), for example, an upper surface, and can cover the entire upper surface. The plurality of diffractive elements (20) are positioned on the second spacer (60). The second spacer (60) includes a first dielectric layer (60a) and a second dielectric layer (60b) that are sequentially laminated. The first dielectric layer (60a) is formed on the upper surface of the substrate (10). The second dielectric layer (60b) is formed on the first dielectric layer (60a). The diffractive elements (20) are positioned on the second dielectric layer (60b) and are in direct contact with the second dielectric layer (60b). In the second spacer (60), at least the refractive index of the second dielectric layer (60b) may be greater than the refractive index of the plurality of diffractive elements (20). In addition, the refractive index of the second dielectric layer (60b) may be greater than the refractive index of the first dielectric layer (60a). In this way, since the refractive indices of the first and second dielectric layers (60a, 60b) are different from each other, the second spacer (60) may function as a Bragg Reflector. The second spacer (60) may include more dielectric layers in addition to the first and second dielectric layers (60a, 60b). For example, the second spacer (60) may have a layer structure in which a plurality of unit layers are sequentially laminated using the first and second dielectric layers (60a, 60b) as unit layers. The thickness (T2) of the second spacer (60) may be an integer multiple of the wavelength of light (6L1) incident obliquely at a large incident angle on the diffraction grating element (55). While satisfying this condition, the thickness of the first dielectric layer (60a) and the thickness of the second dielectric layer (60b) included in the second spacer (60) may be the same as or different from each other. When the light reflection loss due to the substrate (10) is not negligible or a small output angle is required, the first spacer (50) of FIG. 5 or the second spacer (60) of FIG. 6 may be helpful in improving the diffraction efficiency. A residual material layer (62) may exist on the second spacer (60) between the plurality of diffraction elements (20). The residual material layer (62) may be the same as the residual material layer (52) of FIG. 5.

Meanwhile, when the second spacer (60) is used as a Bragg reflection layer, the substrate (10) may be omitted or replaced with a transparent substrate such as glass. Thus, the diffraction grating element (65) may be transparent.

Fig. 7 shows a diffraction grating element according to another embodiment.

Figure 7 shows a case where multiple diffraction elements (70, 72, 74) with different diffraction characteristics are distributed on the same substrate (10).

Referring to FIG. 7, a first diffraction element (70), a second diffraction element (72), and a third diffraction element (74) are provided on a substrate (10). The first diffraction element (70) may be a diffraction element having a negative diffraction characteristic that diffracts incident light (7L1) at a given diffraction angle (-θ1) to the right of a reference line (10L). The first diffraction element (70) may be the second diffraction element (30) illustrated in FIG. 2 or the third diffraction element (40) illustrated in FIG. 3. The second diffraction element (72) may be a diffraction element having a positive diffraction characteristic that diffracts incident light (7L1) in a direction parallel to the reference line (10L1), that is, in a direction perpendicular to the upper surface of the substrate (10). The second diffraction element (72) may be the diffraction element (20) of FIG. 1 that does not have an auxiliary diffraction element. The third diffraction element (74) may be a diffraction element having a positive diffraction characteristic that diffracts incident light to the left of the reference line (10L1) at a given diffraction angle (+θ1). The third diffraction element (74) may be the diffraction element (20) of FIG. 1. Since the diffraction characteristics of the first to third diffraction elements (70, 72, 74) are different from each other, the pitches of the first to third diffraction elements (70, 72, 74) may be different from each other. Due to these diffraction characteristics of the first to third diffraction elements (70, 72, 74), the incident light (7L1) is converged to a given position after diffraction. As a result, the diffraction grating element (75) of FIG. 7 may function as a lens or mirror that converges the incident light to a focus. By changing the diffraction characteristics of the first and third diffraction elements (70, 74) in the opposite direction, the diffraction grating element (75) of FIG. 7 can function as a lens or mirror that causes incident light to diverge. In this way, by arranging diffraction elements having various diffraction characteristics on the substrate (10) with an appropriate pitch, the diffraction grating element (75) can also be used as an optical element like a lens or a mirror. In FIG. 7, a plurality of diffraction elements can be further arranged between the first to third diffraction elements (70, 72, 74), and the diffraction direction characteristics of the diffraction elements further arranged can be different from each other and also different from the diffraction characteristics of the first to third diffraction elements (70, 72, 74). For example, in the case of diffraction elements further arranged between the first and second diffraction elements (70, 72), the pitch between the diffraction elements may be adjusted so that the negative diffraction characteristic gradually decreases from the first diffraction element (70) to the second diffraction element (72), that is, the negative output angle gradually decreases. In the case of diffraction elements further arranged between the first and second diffraction elements (70, 72), the number of auxiliary diffraction elements may also be different. In the case of diffraction elements further arranged between the second diffraction element (72) and the third diffraction element (74), the pitch may be adjusted so that the positive diffraction characteristic gradually decreases from the third diffraction element (74) to the second diffraction element (72), that is, the positive output angle gradually decreases.

Figures 8 to 11 show the results of simulations conducted to determine diffraction efficiency according to the shape of the diffraction element. In the simulation, the maximum value of the aspect ratio of the main diffraction element was set to 3. In each figure, the horizontal axis represents the output angle, and the vertical axis represents the diffraction efficiency.

Figure 8 shows the diffraction efficiency when the diffraction element includes only the main diffraction element without auxiliary diffraction elements.

Referring to Figure 8, it can be seen that when the diffraction elements include only the main diffraction elements, the diffraction efficiency is higher at a positive output angle than at a negative output angle.

Figure 9 shows the diffraction efficiency when the diffraction element includes only the main diffraction element (G1) and when the diffraction element includes the main diffraction element and one auxiliary diffraction element (G2).

Referring to Fig. 9, when a diffractive element includes a main diffractive element and one auxiliary diffractive element, it shows equivalent diffraction efficiency at positive and negative output angles. This suggests that when a diffractive element including a main diffractive element and one auxiliary diffractive element is used, positive diffraction light and negative diffraction light can be equally generated. However, compared to the case where the diffractive element includes only a main diffractive element (G1), it can be seen that at a positive output angle, the diffraction efficiency of the diffractive element including only a main diffractive element is higher than the diffraction efficiency of the diffractive element including a main diffractive element and one auxiliary diffractive element. Conversely, at a negative output angle, it can be seen that the diffraction efficiency of the diffractive element including a main diffractive element and one auxiliary diffractive element is higher than the diffraction efficiency of the diffractive element including only a main diffractive element. Therefore, in order to generate diffracted light having a negative output angle, i.e., negative direction diffracted light, it may be more advantageous to use a diffractive element including a main diffractive element and one auxiliary diffractive element.

Figure 10 shows the diffraction efficiency when the diffraction element includes a main diffraction element and two auxiliary diffraction elements.

Referring to FIG. 10, the first graph (G1) shows the diffraction efficiency of a diffractive element including only a main diffractive element. The second graph (G2) shows the diffraction efficiency of a diffractive element including a main diffractive element and one auxiliary diffractive element. The third graph (G3) shows the diffraction efficiency of a diffractive element including a main diffractive element and two auxiliary diffractive elements.

Comparing the second graph (G2) and the third graph (G3), as the number of auxiliary diffractive elements increases, the diffraction efficiency at the positive output angle decreases, whereas the diffraction efficiency at the negative output angle, especially at the relatively large negative output angle, increases. These results suggest that when diffractive elements including the main diffractive element and the auxiliary diffractive element are used, the diffraction efficiency of the negative diffracted light can also increase as the number of auxiliary diffractive elements increases. This suggestion becomes clearer from the results of Fig. 11.

Figure 11 shows the diffraction efficiency (G1) when the diffraction element includes only a primary diffraction element, the diffraction efficiency (G2) when the diffraction element includes a primary diffraction element and one auxiliary diffraction element, the diffraction efficiency (G3) when the diffraction element includes a primary diffraction element and two auxiliary diffraction elements, and the diffraction efficiency (G4) when the diffraction element includes a primary diffraction element and three auxiliary diffraction elements.

Comparing the first to fourth graphs (G1-G4) of Fig. 11, the diffraction efficiency (G4) increases in the order of diffraction elements including one auxiliary diffraction element to diffraction elements including three auxiliary diffraction elements in the region where the negative output angle is large. This result suggests that when diffraction elements including a main diffraction element and an auxiliary diffraction element are used, the diffraction efficiency of negative diffraction light increases as the number of auxiliary diffraction elements increases, and such a phenomenon is evident in a region where the negative output angle is relatively large (for example, a region including -40°).

From the results in Fig. 11, it can be seen that in order to increase the diffraction efficiency of diffracted light having a positive output angle, a diffraction element including only a main diffraction element is advantageous, and in order to increase the diffraction efficiency of diffracted light having a negative output angle, a diffraction element including a main diffraction element and an auxiliary diffraction element is advantageous.

Next, various application examples of the diffraction grating element according to one embodiment are described. The diffraction grating element according to one embodiment can be applied to various devices even without the application exceptions described below.

Figures 12a to 12c show a case where a diffraction grating element according to one embodiment is used as a beam expander.

Referring to FIG. 12A, light is incident on the diffraction grating element (92) from the light source (90). At this time, the incident angle of the light with respect to the reference line (13L) may be greater than 45°. Since the incident light is incident at a large incident angle with respect to the reference line (13L) in this way, the incident light is incident obliquely on the upper surface of the diffraction grating element (92), and the inclination angle becomes smaller than 45°. Here, the inclination angle refers to the angle between the light emitted from the light source (90) and the upper surface of the diffraction grating element (92). Since the light emitted from the light source (90) is obliquely incident on the upper surface of the diffraction grating element (92) in this way, even a light source with a small light emission aperture can illuminate a wide area of the upper surface of the diffraction grating element (92). If the aperture of the light source (90) is fixed, the angle of inclination between the light emitted from the light source (90), that is, the light incident on the diffraction grating element (92), and the upper surface of the diffraction grating element (92) can be adjusted so that the light emitted from the light source (90) reaches the entire upper surface of the diffraction grating element (92). Accordingly, diffracted light can be generated from the entire upper surface of the diffraction grating element (92). If all the diffraction elements arranged on the upper surface of the diffraction grating element (92) have the same diffraction characteristics, as illustrated in FIGS. 12a to 12c, parallel diffracted light (94, 94a, 94b), that is, parallel light, directed in a given direction can be emitted from the entire upper surface of the diffraction grating element (92).

The diffraction grating element (92) may be the diffraction grating element (5) of FIG. 1. At this time, the plurality of diffraction elements (20) may all have the same diffraction characteristic. For example, if the plurality of diffraction elements (20) have positive diffraction characteristics and are diffraction elements that generate diffracted light having an output angle of 0° with respect to the reference line (10L1), light incident on the upper surface of the diffraction grating element (92) is diffracted by the diffraction element (20). As a result, as illustrated in FIG. 12A, parallel diffracted light (94) that propagates in a direction perpendicular to the upper surface of the diffraction grating element (92) is generated. In other words, light parallel to the reference line (13L) is generated on the entire upper surface of the diffraction grating element (92).

When a plurality of diffraction elements (20) have positive diffraction characteristics and are diffraction elements that generate diffracted light having a positive output angle greater than 0, light incident on the upper surface of the diffraction grating element (92) is diffracted by the diffraction elements (20). As a result, as shown in Fig. 12b, parallel diffracted light (94a) that travels to the left of the reference line (13L), that is, in a direction having a positive output angle, is generated. In other words, parallel light (94a) that travels to the left of the reference line (13L) on the entire upper surface of the diffraction grating element (92) and has the same angle with respect to the reference line (13L) is generated.

In the case where a plurality of diffraction elements (20) have negative diffraction characteristics and are diffraction elements (main diffraction element + auxiliary diffraction element) that generate diffracted light having a negative output angle, light incident on the upper surface of the diffraction grating element (92) is diffracted by the diffraction elements (20). As a result, as shown in Fig. 12c, parallel diffracted light (94b) that travels to the right of the reference line (13L), that is, in the direction having a negative output angle, is generated. In other words, parallel light (94b) that travels to the right of the reference line (13L) on the entire upper surface of the diffraction grating element (92) and has the same angle with respect to the reference line (13L) is generated.

In the case of the big expanders according to the embodiments described above, since the incident light is obliquely incident on the diffraction grating element (92) at an incident angle greater than 45°, for example, at an incident angle greater than 80°, the overall volume of the device can be made thin and the device can be miniaturized.

Fig. 13 shows a case where a diffraction grating element according to one embodiment is used as a lens. Since the diffraction grating element (102) in Fig. 13 has been described above, its detailed configuration is omitted.

Referring to Fig. 13, the diffraction grating element (102) used as a lens includes diffraction elements having different diffraction characteristics as described above on the upper surface. These diffraction elements may include diffraction elements having positive diffraction characteristics and diffraction elements having negative diffraction characteristics as described in Figs. 1 to 3 and Fig. 7, etc.

For example, diffraction elements having negative diffraction characteristics may be arranged in a first region (102A) of an upper surface of a diffraction grating element (102), and diffraction elements having positive diffraction characteristics may be arranged in a second region (102B). In the case of the diffraction elements arranged in the first region (102A), all have negative diffraction characteristics, but they may be arranged so that their output angles are different from each other so that the diffraction grating element (102) exhibits lens characteristics. To this end, the pitches of the diffraction elements arranged in the first region (102) may be different from each other. For example, the pitches of the diffraction elements may gradually increase or decrease from the edge to the center of the diffraction grating element (102). Here, the pitch means the pitch between main diffraction elements.

The diffraction characteristics of the diffraction elements arranged in the second region (102B) are different from the diffraction characteristics of the diffraction elements arranged in the first region (102A). The diffraction characteristics of the diffraction elements arranged in the second region (102B) may be opposite to the diffraction characteristics of the diffraction elements arranged in the first region (102A). All of the diffraction elements arranged in the second region (102B) include diffraction elements having positive diffraction characteristics. All of the diffraction elements arranged in the second region (102B) have positive diffraction characteristics, but the pitches between the diffraction elements may be different. For example, in the case of the diffraction elements arranged in the second region (102B), the pitch between the diffraction elements may increase or decrease from the edge to the center of the diffraction grating element (102). There may be a center diffraction element at the center of the upper surface of the diffraction grating element (102) that diffracts incident light vertically. The above-mentioned central diffraction element may have a positive diffraction characteristic. In one example, among the diffraction elements arranged in the second region (102B), the one arranged at the center of the upper surface of the diffraction grating element (102) or the diffraction element arranged closest to the first region (102A) may serve as the central diffraction element.

Light incident on the first region (102A) from the light source (90) to the diffraction grating element (102) is diffracted and becomes light having a negative output angle, that is, light traveling toward the right side of the reference line (14L). As described above, the diffraction elements arranged in the first region (102A) can be arranged with different pitches sequentially from the edge to the center of the diffraction grating element (102), and in the case of FIG. 14, the pitch of the diffraction elements in the first region (102A) is set so that the output angle of the diffracted light (102C) decreases from the edge to the center of the diffraction grating element (102), so that the negative output angle of the light diffracted in the first region (102A) also decreases sequentially from the edge to the center of the diffraction grating element (102). As a result, the diffracted light (102C) generated in the first region (102A) is directed toward one location (point) on the reference line (14L).

In contrast, light incident on the second region (102B) from the light source (90) is diffracted and becomes light having a positive output angle, that is, light traveling toward the left side of the reference line (14L). Similar to the diffractive elements arranged in the first region (102A), the pitch of the diffractive elements arranged in the second region (102B) also sequentially increases or decreases from the edge to the center of the diffraction grating element (102). In the case of FIG. 14, the pitch of the diffractive elements arranged in the second region (102B) is set so that the output angle of the diffracted light (102D) decreases from the edge to the center of the diffraction grating element (102), and thus the positive output angle of the light diffracted in the second region (102B) also gradually decreases from the edge to the center of the diffraction grating element (102). As a result, the diffracted light (102D) generated in the second region (102B) also faces the above position on the reference line (14L).

Ultimately, the diffraction grating element (102) diffracts light incident from a light source (90) and focuses it at a certain location. In other words, the diffraction grating element (102) plays a role equivalent to a convex lens or a concave mirror.

Meanwhile, if the diffraction elements arranged in the first region (102A) and the diffraction elements arranged in the second region (102B) have diffraction characteristics that are opposite to each other, for example, if the diffraction elements arranged in the first region (102A) have positive diffraction characteristics and the diffraction elements arranged in the second region (102B) have negative diffraction characteristics, the diffraction grating element (102) can serve as an optical element that emits light incident from a light source (90).

In this way, the diffraction grating element according to one embodiment can be used as a variety of optical elements, and can be applied to various optical devices, such as AR devices, VR devices, and light field display diffraction optical elements.

Figure 14 shows a case where a diffraction grating element according to one embodiment is used as a component of a display device.

Referring to FIG. 14, the display device (150) includes a light source (110), a spatial light modulator (SLM) (112), and a diffractive optical element (116). The light source (110) may be a light source that emits parallel light. The light source (110) may also include a device that provides an image. The spatial light modulator (112) is arranged between the light source (110) and the diffractive optical element (116). The spatial light modulator (112) modulates the intensity and phase of light or an image incident from the light source (110) according to a given signal and transmits the modulated light or an image to the diffractive optical element (116). The diffractive optical element (116) provides the light or an image incident from the spatial light modulator (112) to the viewer (118). The diffractive optical element (116) may be a diffractive grating element according to one embodiment, and may be a diffractive grating element that acts as a lens. The diffractive optical element (116) may include a plurality of diffractive elements formed on a surface (116S) on which light is incident from the spatial light modulator (112). These diffractive elements may be arranged to act as lenses as described in FIG. 14.

Fig. 15 shows an optical device (160) including a diffraction grating element according to one embodiment. The diffraction grating elements introduced in Fig. 15 correspond to the diffraction grating elements described above, and the diffraction elements arranged on the light incident surface are not shown.

Referring to FIG. 15, an optical device (160) including a diffraction grating element according to one embodiment includes a first diffraction grating element (130), a second diffraction grating element (132), and a light source (134). The light source (134) may be a light source that emits parabolic light, for example, a light source that emits a laser or a light source including a light-emitting diode. The second diffraction grating element (132) is arranged between the light source (134) and the first diffraction grating element (130). The arrangement relationship between the light source (134) and the second diffraction grating element (132) may follow the arrangement relationship between the light source and the diffraction grating element of any one of the diffraction grating elements according to the embodiments described above, for example, the arrangement relationship between the light source (90) and the diffraction grating element (92) illustrated in any one of FIGS. 12A to 12C. Therefore, the light (134L) emitted from the light source (134) is obliquely incident at an angle of less than 45° with respect to the light incident surface of the second diffraction grating element (132). The second diffraction grating element (132) diffracts the light incident from the light source (134) and transmits it to the first diffraction grating element (130). The diffraction characteristics of the first and second diffraction grating elements (130, 132) may be the same or different. For example, the first and second diffraction grating elements (130, 132) may be diffraction grating elements that generate parallel diffracted light, like in the case of a beam expander. In another example, the second diffraction grating element (132) may be a diffraction grating element that generates parallel diffracted light, like a beam expander, and the first diffraction grating element (130) may be a diffraction grating element that generates parallel diffracted light or non-parallel diffracted light. Here, the non-parallel diffracted light may include light that converges at a given position after diffraction or light that diverges after diffraction. The first diffraction grating element (130) may be a diffraction grating element that functions as a beam expander (e.g., the diffraction grating element of any one of FIGS. 12A to 12C) or a diffraction grating element that functions as a lens as described above (e.g., the diffraction grating element of FIG. 13). The second diffraction grating element (132) may be a diffraction grating element that functions as a beam expander as described above. The second diffraction grating element (132) provides light parallel to the first diffraction grating element (130) as incident light. In this respect, the second diffraction grating element (132) may function as a light source for the first diffraction grating element (130). Therefore, the combination of the light source (134) and the second diffraction grating element (132) may be considered as a light source device or light source unit that provides incident light to the first diffraction grating element (130). This technical idea may also be applied to other examples including two diffraction grating elements described below.

Looking at the operation of the optical device (160), light (134L) incident on the second diffraction grating element (132) from the light source (134) is diffracted by the second diffraction grating element (132). The second diffraction grating element (132) can act as a beam expander. Therefore, parallel diffracted light (132L) is generated from the second diffraction grating element (132). The diffracted light (132L) generated from the second diffraction grating element (132) is incident obliquely with respect to the upper surface of the first diffraction grating element (130). At this time, the inclination angle (θ2) can be less than 45°, for example, 30° or less. The arrangement relationship between the second diffraction grating element (132) and the first diffraction grating element (130) may follow the arrangement relationship between the light source (90) and the diffraction grating element (92) illustrated in FIGS. 12A to 12C. When the first diffraction grating element (130) is a beam expander, light (132L) incident on the first diffraction grating element (130) is diffracted in a direction perpendicular to the upper surface of the first diffraction grating element (130) as illustrated, and the diffracted light (130L) becomes parallel light.

Meanwhile, the light (134L) emitted from the light source (134) is monochromatic light, but is not perfectly monochromatic light. That is, the light source (134) is a light source that emits light of a set single wavelength, but it may be realistically difficult to perfectly emit only light of a set single wavelength. As a result, the light (134L) emitted from the light source (134) includes the set single wavelength as a center wavelength, and also includes a wavelength (hereinafter, noise wavelength) close to the center wavelength. At this time, the intensity of the light of the noise wavelength is extremely small compared to the intensity of the light of the center wavelength. However, in the process in which the light (134L) emitted from the light source (134) is diffracted by the second diffraction grating element (132), the light corresponding to the noise wavelength is also diffracted. Accordingly, chromatic dispersion may appear in the diffracted light (132L) generated from the second diffraction grating element (132). Soon, the diffraction light (132l) includes main diffraction light resulting from diffraction of light corresponding to the central wavelength, and further includes noise diffraction light resulting from diffraction of light corresponding to the noise wavelength, the color of which is different from the propagation direction of the main diffraction light. The influence of the noise diffraction light does not appear or is minimal in a short-distance beam expansion or beam focusing process, but may appear in a long-distance beam expansion or beam focusing process. The noise diffraction light can be removed when the diffraction light (132L) is diffracted again by the first diffraction grating element (130). To this end, the pitch of the diffraction elements included in the first diffraction grating element (130) may be the same as the pitch of the diffraction elements included in the second diffraction grating element (132). The diffraction light (130L) generated from the first diffraction grating element (130) does not include noise diffraction light.

Fig. 16 shows another optical device (170) including a diffraction grating element according to one embodiment. The diffraction grating elements introduced in Fig. 16 correspond to the diffraction grating elements described above, and the diffraction elements arranged on the light incident surface are not shown.

Referring to FIG. 16, the optical device (170) includes a light source (146), a first diffraction grating element (140), a second diffraction grating element (142), and a reflector (144). On the optical path from the light source (146) to the first diffraction grating element (140), the second diffraction grating element (142) is disposed between the light source (146) and the reflector (144). And the reflector (144) is disposed between the first diffraction grating element (140) and the second diffraction grating element (142). The light source (146) is for providing incident light to the second diffraction grating element (142). The light source (146) may be the same as the light source (134) of FIG. 15 in terms of configuration and role. Therefore, the light source (134) of FIG. 15 may also be used as the light source (146). The first and second diffraction grating elements (140, 142) may be one of the diffraction grating elements described above. For example, the first diffraction grating element may be a diffraction grating element that functions as a beam expander or a diffraction grating element that functions as a lens. The second diffraction grating element (142) may be a diffraction grating element that diffracts light incident from a light source (146) to provide parallel light to a reflector (144). The second diffraction grating element (142) may be a diffraction grating element that functions as a beam expander. The arrangement relationship between the light source (146) and the second diffraction grating element (142) may follow the arrangement relationship between the light source (134) and the second diffraction grating element (132) of FIG. 15. The reflector (144) reflects light incident from the second diffraction grating element (142) through one surface to the diffraction surface (e.g., the upper surface) of the first diffraction grating element (140). That is, the reflector (144) may be one of the light transmission elements that transmits the diffracted light of the second diffraction grating element (142) to the first diffraction grating element (140). The reflector (144) may be a prism or a reflection device including a prism. In addition to a prism, other reflection devices or devices such as a mirror may be used as the reflector (144). The reflector (144) reflects light incident from the second diffraction grating element (142) and causes it to be obliquely incident on the diffraction surface of the first diffraction grating element (140) at a given inclination angle (θ3). The inclination angle (θ3) may be 45° or less, and for example, 30° or less. The arrangement relationship between the reflector (144) and the first diffraction grating element (140) considering the incident angle incident on the first diffraction grating element (140) may follow the arrangement relationship of the first diffraction grating element (130) and the second diffraction grating element (132) of Fig. 15. That is, the reflector (144) may be arranged between the first diffraction grating element (140) and the second diffraction grating element (142) such that the above light incidence condition for the first diffraction grating element (140) is maintained.

The diffracted light generated from the second diffraction grating element (142) is parallel light. Therefore, the light incident from the reflector (144) to the first diffraction grating element (140) is also parallel light. The light reflected from the reflector (144) can be incident simultaneously on the entire diffraction surface of the first diffraction grating element (140). When the first diffraction grating element (140) is a diffraction grating element that functions as a beam expander, the diffracted light generated from the first diffraction grating element (140) can be parallel light, as illustrated in FIG. 16. The dotted arrows indicate the propagation direction of the parallel diffracted light when all diffraction elements formed on the diffraction surface of the first diffraction grating element (140) have positive diffraction characteristics (left arrow) or when they have negative diffraction characteristics (right arrow).

Fig. 17 shows another optical device (180) including a diffraction grating element according to one embodiment.

Referring to FIG. 17, the optical device (180) includes a light source (186), a first diffraction grating element (182), and a second diffraction grating element (184). The second diffraction grating element (184) is disposed between the light source (186) and the first diffraction grating element (182) on an optical path starting from the light source (186). The light source (186) may be a light source that emits parallel light. For example, the light source (186) may be a light source that emits a laser or a light source including an LED. The first and second diffraction gratings (182, 184) may be any one of the diffraction grating elements according to the embodiments described above. The first diffraction grating element (182) may be a diffraction grating element that generates parallel light on the entire diffraction plane on which light is incident, as illustrated in FIGS. 12A to 12C. The first diffraction grating element (182) may also be a diffraction grating element that generates convergent light that is gathered at a predetermined position in front of the first diffraction grating element (182). In this case, the first diffraction grating element (182) may be a diffraction grating element that acts as a lens of FIG. 13. The second diffraction grating element (184) diffracts light incident from a light source (186) to provide incident light (184L) to the first diffraction grating element (182). The incident light (184L) may be parallel light. The second diffraction grating element (184) may be, for example, the diffraction grating element illustrated in FIG. 12A.

The light source (186), the first diffraction grating element (182), and the second diffraction grating element (184) can be arranged in consideration of the incident angle of incident light.

Specifically, the light source (186) and the second diffraction grating element (184) may be arranged so that light emitted from the light source (186) is incident on the first diffraction grating element (182) at a given incident angle. At this time, the measurement of the angle is based on a reference line (normal line) (184V of FIG. 18) perpendicular to the diffraction plane (184S) of the second diffraction grating element (184). The incident angle at which the light emitted from the light source (186) is incident on the diffraction plane (184S) of the first diffraction grating element (182) may be greater than 45°, and in one example may be 75° or more. When the incident angle is measured based on the diffraction plane (184S), the incident angle may be less than 45°, and in one example may be less than 30°.

The diffraction surface (184S) of the second diffraction grating element (184) may be rectangular. The light source (186) and the second diffraction grating element (184) may be arranged on the same plane. The light source (186) is arranged on a side surface of the second diffraction grating element (184) and irradiates light to the diffraction surface (184S) in the longitudinal direction of the second diffraction grating element (184). The diffraction light generated from the diffraction surface (184S) of the second diffraction grating element (184) is parallel light emitted perpendicularly to the diffraction surface (184S). The diffraction light (184L) generated from the diffraction surface (184S) of the second diffraction grating element (184) is incident on the entire area of the diffraction surface (upper surface) (182S) of the first diffraction grating element (182).

In this situation, the relationship of the light incidence angle between the light source (186) and the second diffraction grating element (184) must also be satisfied between the first diffraction grating element (182) and the second diffraction grating element (184). Considering this, the first and second diffraction grating elements (182, 184) can be arranged as shown in FIGS. 18 and 19.

Figures 18 and 19 are examples of cross-sections taken along the 18-18’ direction of Figure 17.

Referring to FIG. 18, the second diffraction grating element (184) is arranged vertically, and the first diffraction grating element (182) is arranged obliquely with respect to the second diffraction grating element (184). The first diffraction grating element (182) is arranged to have a given angle (θ4) with respect to a reference line (normal line) (184V) perpendicular to the diffraction plane (184S) of the second diffraction grating element (184). The given angle (θ4) may be less than 45°, in one example, the given angle (θ4) may be 30° or less, and in another example, may be 15° or less. Diffracted light (184L) that is perpendicular to and parallel to the diffraction plane (184S) is emitted from the diffraction plane (184S) of the second diffraction grating element (184). As described above, the first diffraction grating element (182) is inclined at a given angle (θ4) with respect to the second diffraction grating element (184), and the propagation direction of the diffracted light (184L) emitted from the second diffraction grating element (184) is perpendicular to the diffraction plane (184S) of the second diffraction grating element (184). Therefore, the incident angle (θ5) when the diffracted light (184L) emitted from the diffraction plane (184S) of the second diffraction grating element (184) is incident on the first diffraction grating element (182) becomes the same as the inclination angle (θ4) of the first diffraction grating element (182). The inclination angle (θ4) and the incident angle (θ4) may follow the incident angle condition when the light emitted from the light source (186) is incident on the second diffraction grating element (184).

Depending on the diffraction characteristics of the diffraction elements arranged on the diffraction plane (182S) of the first diffraction grating element (182), diffracted light (182L2) parallel to a reference line (180L) perpendicular to the diffraction plane (182S) may be emitted from the first diffraction grating element (182), or diffracted light (182L1) directed toward the right side of the reference line (180L) may be emitted. In addition, although not illustrated, diffracted light directed toward the left side of the reference line (182L1) may be emitted, or diffracted light converging on a position in front of the first diffraction grating element (182) may be emitted.

Fig. 19 shows a case opposite to Fig. 18. That is, the first diffraction grating element (182) is arranged horizontally, and the second diffraction grating element (184) is arranged at an angle (θ6) with respect to the first diffraction grating element (182). Specifically, the second diffraction grating element (184) is arranged at an angle (θ6) with respect to a reference line (normal line) (182V) perpendicular to the upper surface of the first diffraction grating element (182). This angle (θ6) may be the same as the angle (θ4) of the first diffraction grating element (182) of Fig. 18. Since the diffracted light (184L) emitted from the second diffraction grating element (184) is perpendicular to the diffraction plane of the second diffraction grating element (184), the angle at which the diffracted light (184L) is incident on the first diffraction grating element (182) and the diffraction result appearing from the first diffraction grating element (182) according to the incidence of the diffracted light (184L) may be the same as described in FIG. 18.

Next, a method for manufacturing a diffraction grating element according to an embodiment will be described in detail with reference to FIGS. 20 to 29.

FIGS. 20 to 24 show a process for manufacturing a template used to print a diffraction grating in a method for manufacturing a diffraction grating element according to one embodiment.

Referring to FIG. 20, a plurality of mask patterns (21M) are formed on a parent substrate (210) to be processed as a template. The plurality of mask patterns (21M) are spaced apart from each other. Therefore, the upper surface of the parent substrate (210) between the mask patterns (21M) is exposed. The spacing between the mask patterns (21M) or the size of the mask patterns (21M) can be set in consideration of the pitch of the diffraction elements of the diffraction grating element to be finally formed. After the mask patterns (21M) are formed, the exposed area of the upper surface of the parent substrate (210) is etched using electron beam lithography (220). The etching stops before reaching the bottom surface of the parent substrate (210).

As shown in Fig. 21, a plurality of protrusions (210A) and a plurality of grooves (210B) are formed on the substrate (210) by the above etching. The plurality of grooves (210B) are spaced apart from each other, and protrusions (210A) exist between the plurality of grooves (210B). The plurality of grooves (210B) can be formed with a given pitch (22P). Accordingly, the diffraction elements of the diffraction grating element that is finally formed can also be formed with the same pitch. The depth (D1) of the plurality of grooves (210B) can correspond to the height of the diffraction elements that are finally formed.

After the above etching, the mask pattern (21M) is removed. Fig. 22 shows a completed template (230) from which the mask pattern (21M) has been removed.

Figures 23 and 24 show a process for manufacturing different templates in a method for manufacturing a diffraction grating element according to one embodiment.

Referring to FIG. 23, a mask (24M) is formed on a substrate (210) to cover a part of the substrate (210) and expose the rest. The mask (24M) may be formed on an upper surface of the substrate (210). The mask (24M) includes a plurality of spaced apart unit patterns (P11). The unit patterns (P11) include a main pattern (24M1) and an auxiliary pattern (24M2). The width of the main pattern (24M1) is wider than the width of the auxiliary pattern (24M2). The main pattern (24M1) and the auxiliary pattern (24M2) are spaced apart from each other. The spacing between the main pattern (24M1) and the auxiliary pattern (24M2) is smaller than the spacing between the unit patterns (P11). The width (W11) of the main pattern (24M1) can determine the spacing of diffraction elements including auxiliary diffraction elements of a diffraction grating element to be finally formed. Additionally, the width (W22) of the auxiliary pattern (24M2) can determine the spacing between the main diffraction element and the auxiliary diffraction element in the diffraction element including the auxiliary diffraction element of the diffraction grating element that is finally formed.

After forming the mask (24M), the exposed portion of the upper surface of the mother substrate (210) is etched. This etching may be etching using an electron beam lithography method. The etching may be performed until a groove of a predetermined depth is formed in the mother substrate (210). The depth of the groove is smaller than the thickness of the mother substrate (210). As a result of the etching, as shown in FIG. 24, a plurality of grooves (210G1, 210G2) and a plurality of protrusions (210P1, 210P2) are formed in the mother substrate (210). The plurality of protrusions (210P1, 210P2) are regions of the substrate (210) located under the main pattern (24M1) and the auxiliary pattern (24M2) of the mask (24M). Among the plurality of grooves (210G1, 210G2), the first groove (210G1) having a relatively wide width determines the specifications (width, height, etc.) of the primary diffraction element of the diffraction element of the diffraction grating element to be finally formed. The second groove (210G2) adjacent to the first groove (210G1) and having a narrower width than the first groove (210G1) determines the specifications of the secondary diffraction element of the diffraction element of the diffraction grating element to be finally formed. The specifications (width, height, interval, etc.) of the first groove (210G1) and the second groove (210G2) can determine the specifications of the diffraction elements including the primary diffraction element and the secondary diffraction element of the diffraction grating element to be finally formed. The pitch between the first grooves (210G1) determines the pitch of the diffraction elements including the secondary diffraction elements of the diffraction grating element to be finally formed. When forming the mask (24M) of Fig. 23, the specifications of the main pattern (24M1) and the auxiliary pattern (24M2) can be determined by considering these factors.

Figures 25 to 29 show a method of forming a diffraction grating element according to one embodiment using a previously formed template.

Referring to FIG. 25, a low refractive index dielectric layer (264) is formed on a substrate (260). The material of the substrate (260) may be the same as the material of the substrate (10) described in FIG. 1. The dielectric layer (264) is a material layer that is ultimately used as a diffractive element. The dielectric layer (264) may be the same material as the material used as the diffractive element (20) described in FIG. 1. The template (210) of FIG. 22 is aligned on the dielectric layer (264). The template (210) is aligned so that the surface on which the protrusions (210A) and grooves (210B) are formed faces the entire upper surface of the dielectric layer (264). After the alignment of the template (210) is completed, the aligned template (210) is lowered as it is and pressed into the dielectric layer (264) as if stamping a seal. After imprinting, the template (210) is separated from the dielectric layer (264). Accordingly, the pattern formed on the back surface of the template (210), that is, the pattern composed of the protrusions (210A) and the grooves (210B), is transferred to the dielectric layer (264). As a result, a plurality of dielectric layer patterns (264A) spaced apart from each other are formed on the substrate (260) as illustrated in FIG. 26. The dielectric layer patterns (264A) are used as diffraction elements and correspond to the diffraction elements (20) of FIG. 1. During this imprinting process, a residual layer of the dielectric layer (264) (e.g., 52 of FIG. 5 or 62 of FIG. 6) may remain on the substrate (260) between the dielectric layer patterns (264A), but its thickness does not exceed 30 nm. The processes of FIGS. 25 and 26 can be equally applied to form a diffraction grating element having a different type of diffraction element when the pattern of the diffraction element to be formed on the back surface of the template (210) is changed to correspond to the pattern of the diffraction element to be formed. FIGS. 27 and 28 show examples of this.

Description of the parts described in Figures 25 and 26 is omitted.

Referring to FIG. 27, the template (280) formed in FIG. 24 is aligned on the dielectric layer (264). The template (280) is aligned so that the protrusions (210P1, 210P2) and grooves (210G1, 210G2) formed on the back surface thereof face the upper surface of the dielectric layer (264). In this aligned state, the template (280) is lowered to imprint the template (28) on the dielectric layer (264) as if stamping a seal, and then separated from the dielectric layer (264). As a result, the protrusion and groove patterns formed on the back surface of the template (280) are transferred to the dielectric layer (264), and as illustrated in FIG. 28, a plurality of dielectric layer patterns using the main pattern (264B) and the auxiliary pattern (264C) as one unit are formed on the substrate (260). The main pattern (264B) corresponds to the main diffraction element (30A) described in FIG. 2, FIG. 3, etc., and the auxiliary pattern (264C) corresponds to the auxiliary diffraction element (30B).

Meanwhile, as illustrated in FIG. 29, a space layer (300) may be formed between the substrate (260) and the dielectric layer (264). The space layer (300) may have the same layer configuration as the spacer (50) of FIG. 5 or the spacer (60) of FIG. 6. After the dielectric layer (264) is formed, a template (310) may be aligned thereon, and then, as illustrated in FIG. 25 or FIG. 27, an imprint process may be performed to transfer a pattern formed on the back surface of the template (310) to the dielectric layer (264). The template (310) may be the template illustrated in FIG. 25 or FIG. 27.

Although many things are specifically described in the above description, they should be construed as examples of preferred embodiments rather than as limiting the scope of the invention. Therefore, the scope of the present invention should not be determined by the described embodiments, but by the technical ideas described in the patent claims.

4L1: Light reflected from the upper surface of the main diffractive element (30A)
4L2: Light reflected from the bottom of the main diffractive element (30A)
5: Diffraction grating element 6L1: Light incident at a large angle of incidence
10: Board 10L: Reference line
13L, 14L: Baseline 20: 2nd diffraction element
21M: Mask pattern 22P: Groove pitch
24M: Mask 24M1: Main Pattern
24M2: Auxiliary pattern 30: 3rd diffraction element
30A: Main diffractive element 30B: Auxiliary diffractive element
40: 3rd diffractive element 40A: Main diffractive element
40B: 1st auxiliary diffractive element 40C: 2nd auxiliary diffractive element
40D: 3rd auxiliary diffractive element 50: 1st spacer
52: Residual material layer 55: Diffraction grating element
60:2nd spacer 60a:1st dielectric layer
60b:Second dielectric layer 62:Residual material layer
65: Diffraction grating element 70: First diffraction element
72: 2nd diffraction element 74: 3rd diffraction element
75: Diffraction grating element 7L1: Incident light
90: Light source 102: Diffraction grating element
102A: Area 1 102B: Area 2
102C: Light diffracted in the first region 102D: Light diffracted in the second region
110: Light source 112: Spatial light modulator
116: Diffractive optical element 116S: Light incident surface of diffractive optical element
118:Viewer 130:First grating element
130L: Diffracted light generated from the first diffraction grating element
132:Second diffraction grating element
132L: Diffracted light generated from the second diffraction grating element
134: Light source 134L: Light emitted from the light source
140: First diffraction grating element 142: Second diffraction grating element
146:Light source 144:Transmitting element (reflector)
150: Display device 160, 170, 180: Optical device
180L: Reference line (normal line) perpendicular to the upper surface of the first diffraction grating element
182: First diffraction grating element
182S: Diffraction plane of the first diffraction grating element
184:Second diffraction grating element
184L: Diffracted light emitted from the second diffraction grating element
184S: Diffraction plane of the second diffraction grating element
186:Light source
182L1: Diffracted light emitted to the right of the baseline
182L2: Diffracted light emitted perpendicular to the diffraction plane of the first diffraction grating element
210:Mosquito plate 210A:Protrusion
210B: Groove 220: Electron Beam Lithography
230:Template 210G1:1st groove
210G2: 2nd groove 210P1, 210P2: Multiple protrusions
260:Substrate 264:Dielectric layer
264A: Genetic layer pattern 264B: Main pattern
264C:Auxiliary pattern 280:Template
300:Space layer 310:Template
D1: Spacing between the main diffractive element (40A) and the first auxiliary diffractive element (40B)
D2, D3: Spacing between the first to third auxiliary diffractive elements (40B, 40C, 40D)
D5: Depth of groove (210B) H1: Height
L0: Incident light L1: Light reflected from the upper surface of the diffraction element (20)
L2: Light reflected from the bottom of the diffraction element (20)
L3: Diffracted light diffracted to the left of the reference line (10L)
L30: Light incident on the second diffraction element (30)
L4: Diffracted light diffracted to the right of the reference line (10L)
LD1, LD2: Higher order diffraction components of diffracted light
P1: Pitch P11: Unit Pattern
T1: Thickness of the first spacer (50) T2: Thickness of the second spacer (60)
W1: width W2: width of main diffractive element
W11: Width of the main pattern (24M1) W22: Width of the auxiliary pattern (24M2)
W3: Width of auxiliary diffraction element (30B)

Claims (42)

optical reflective substrate;
a diffraction grating arranged on the substrate; and
A dielectric layer provided between the substrate and the diffraction grating;
The thickness of the above dielectric layer is n times the wavelength of the incident light (n=1,2,3..).
The above diffraction grating comprises a plurality of diffraction elements,
A diffraction grating element in which each of the plurality of diffraction elements has a height at which light reflected from its upper surface and light reflected from its lower surface cause destructive interference with respect to light incident at an angle of incidence of 45° or greater. delete In paragraph 1,
The above substrate is a diffraction grating element which is a Bragg reflector containing dielectrics having different refractive indices. In paragraph 1,
A diffraction grating element having a refractive index of 1.3 to 2.0. In paragraph 1,
The above plurality of diffractive elements are diffractive grating elements each including a main diffractive element and an auxiliary diffractive element. In paragraph 1,
A diffraction grating element in which all of the above diffraction elements are arranged so as to exhibit the same diffraction characteristics. In paragraph 1,
The above plurality of diffraction elements are diffraction grating elements arranged so as to exhibit different diffraction characteristics. In paragraph 1,
The above multiple diffractive elements each include a main diffractive element and multiple auxiliary diffractive elements,
The above-mentioned plurality of auxiliary diffraction elements are arranged so that the negative diffraction angle range for obtaining high diffraction efficiency increases as the number of auxiliary diffraction elements increases. In paragraph 1,
The above dielectric layer is a single-layer diffraction grating element. In paragraph 1,
The dielectric layer comprises laminated first and second dielectric layers, and the first and second dielectric layers have different refractive indices and are diffraction grating elements. In paragraph 1,
The above substrate is a diffraction grating element which is a metallic substrate. In paragraph 1,
The above substrate is a diffraction grating element which is a reflective WGP. In paragraph 5,
A diffraction grating element in which the width of the main diffraction element is greater than the width of the auxiliary diffraction element. In paragraph 5,
The above auxiliary diffraction element is a diffraction grating element including a plurality of auxiliary diffraction elements spaced apart from each other, and the widths of the plurality of auxiliary diffraction elements are the same or different from each other. In paragraph 6,
A diffraction grating element in which all of the above diffraction elements are arranged so as to exhibit positive diffraction characteristics. In paragraph 6,
A diffraction grating element in which all of the above diffraction elements are arranged so as to exhibit negative diffraction characteristics. In paragraph 6,
The pitch between the above plurality of diffraction elements is the same diffraction grating element. In paragraph 7,
A diffraction grating element wherein the above plurality of diffraction elements include diffraction elements exhibiting positive diffraction characteristics and diffraction elements exhibiting negative diffraction characteristics. In Article 9,
A diffraction grating element having a refractive index of the dielectric layer equal to or greater than the refractive index of the diffraction grating. In Article 10,
A diffraction grating element wherein the refractive index of the dielectric layer in direct contact with the diffractive element among the first and second dielectric layers is greater than the refractive index of the diffractive element, and the refractive index of the dielectric layer in direct contact with the diffractive element among the first and second dielectric layers is greater than the refractive index of the dielectric layer provided directly underneath. In Article 18,
A diffraction grating element in which the diffraction elements exhibiting the above positive diffraction characteristics are arranged so that the degrees of the positive diffraction characteristics are different from each other. In Article 18,
A diffraction grating element in which the diffraction elements exhibiting the above negative diffraction characteristics are arranged so that the degree of the negative diffraction characteristics is different from each other. In Article 21,
The pitches of the diffraction elements exhibiting the above positive diffraction characteristics are different diffraction grating elements. In paragraph 22,
The pitches of the diffraction elements exhibiting the above negative diffraction characteristics are different in the diffraction grating element. light source;
It includes a first diffraction grating element that diffracts light incident from the light source;
An optical device wherein the first diffraction grating element is a diffraction grating element according to any one of claims 1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, and 24. In Article 25,
The above light source part,
A light source that directly emits light; and
An optical device including a second diffraction grating element that diffracts light incident from the light source and provides incident light to the first diffraction grating element. In Article 26,
An optical device wherein the first diffraction grating element and the second diffraction grating element are diffraction grating elements exhibiting identical diffraction characteristics. In Article 26,
An optical device in which the first diffraction grating element and the second diffraction grating element are diffraction grating elements exhibiting different diffraction characteristics. In Article 25,
The above light source part,
A light source that directly emits light; and
A second diffraction grating element that diffracts light incident from the light source in a given direction; and
An optical device including a transmission element that transmits the diffracted light of the second diffraction grating element to the first diffraction grating element. In Article 26,
An optical device in which the remaining elements are arranged at an angle less than 45° with respect to the normal line perpendicular to the diffraction plane of one of the first diffraction grating elements and the second diffraction grating elements. In Article 27,
An optical device wherein the first and second diffraction grating elements are diffraction grating elements that act as beam expanders. In paragraph 28,
An optical device in which the first diffraction grating element is a diffraction grating element that acts as a lens, and the second diffraction grating element is a diffraction grating element that acts as a beam expander. In Article 29,
The above transmitting element is an optical device which is a light reflector. delete delete delete delete delete delete delete delete delete

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