CN113325503A - Diffractive optical element and optical apparatus - Google Patents
Diffractive optical element and optical apparatus Download PDFInfo
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- CN113325503A CN113325503A CN202110604615.5A CN202110604615A CN113325503A CN 113325503 A CN113325503 A CN 113325503A CN 202110604615 A CN202110604615 A CN 202110604615A CN 113325503 A CN113325503 A CN 113325503A
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/18—Diffraction gratings
- G02B5/1861—Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
- G02B27/4205—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
- G02B27/4233—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive element [DOE] contributing to a non-imaging application
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Abstract
The invention discloses a diffractive optical element and an optical apparatus, the diffractive optical element includes: a first structural layer, a second structural layer, and a third structural layer. The first structure layer has a first refractive index, the second structure layer is arranged on the first structure layer, the second structure layer has a second refractive index, the second refractive index is larger than the first refractive index, the second structure layer is provided with a first diffraction part, the third structure layer has a third refractive index, the third refractive index is smaller than the second refractive index, and the third structure layer is arranged on one side of the second structure layer, which is deviated from the first structure layer. According to the diffractive optical element, the first structure layer, the second structure layer and the third structure layer are arranged, the second refractive index of the second structure layer is larger than the first refractive index of the first structure layer and the third refractive index of the third structure layer, so that a Fabry-Perot resonance effect can be generated in the second structure layer when light rays pass through the diffractive optical element, and the diffractive efficiency of the diffractive optical element is high.
Description
Technical Field
The present invention relates to the field of diffractive optical elements, and in particular, to a diffractive optical element and an optical device.
Background
In the three-dimensional ranging or three-dimensional imaging technology, a light source needs to be diffracted by a Diffractive Optical Element (DOE) to obtain a required light intensity distribution, so that the distance of a target surface in a different region is determined by detecting reflected light of the region, thereby realizing three-dimensional ranging or three-dimensional imaging. In the process of diffracting the light source by the diffractive optical element, the higher the diffraction efficiency of the diffractive optical element, the larger the amount of light diffracted to the target area after passing through the diffractive optical element, the less stray light is generated, and the higher the quality of three-dimensional distance measurement or three-dimensional imaging is. Therefore, how to improve the diffraction efficiency of the diffractive optical element is a problem that needs to be solved urgently in the industry.
Disclosure of Invention
The invention discloses a diffractive optical element and an optical apparatus, the diffractive optical element having high diffraction efficiency.
In order to achieve the above object, in a first aspect, the present invention discloses a diffractive optical element comprising:
a first structural layer having a first refractive index;
the second structure layer is arranged on the first structure layer, has a second refractive index, and is greater than the first refractive index, and is provided with a first diffraction part; and
and the third structural layer is provided with a third refractive index which is smaller than the second refractive index, and the third structural layer is arranged on one side of the second structural layer, which deviates from the first structural layer.
By arranging the first structure layer, the second structure layer and the third structure layer and enabling the second refractive index of the second structure layer to be larger than the first refractive index of the first structure layer and the third refractive index of the third structure layer, the interface between the first structure layer and the second structure layer and the interface between the second structure layer and the third structure layer have higher reflection performance, so that the light can generate a Fabry-Perot resonance effect in the second structure layer in the process that the light passes through the diffractive optical element, and the diffractive efficiency of the diffractive optical element is high.
As an optional implementation manner, in an embodiment of the first aspect of the present application, the first diffractive part is formed on a side of the second structural layer facing the third structural layer, and a second diffractive part is formed on a side of the third structural layer facing the second structural layer, and the second diffractive part and the first diffractive part are matched with each other; and/or
The first diffraction part is formed on one side, facing the first structural layer, of the second structural layer, the third diffraction part is formed on one side, facing the second structural layer, of the first structural layer, and the third diffraction part and the first diffraction part are matched with each other, so that different diffraction functions of the diffraction optical element can be realized through different distributions of the first diffraction part, and the diffraction optical element is suitable for more extensive use requirements.
As an optional implementation manner, in an embodiment of the first aspect of the present application, the first diffractive part includes a plurality of first protrusions arranged at intervals, the second diffractive part includes a plurality of second protrusions arranged at intervals, and each of the second protrusions is respectively attached to each of the adjacent first protrusions; and/or
The first diffraction part comprises a plurality of third bulges which are arranged at intervals, the third diffraction part comprises a plurality of fourth bulges which are arranged at intervals, and each fourth bulge is respectively attached and connected to each adjacent third bulge.
As an optional implementation manner, in an embodiment of the first aspect of the present application, in order to simplify a manufacturing process of the diffractive optical element, a thickness of each structural layer should not be too thin, and in order to improve a precision of the diffractive optical element, the thickness of each structural layer should not be too thick, based on which, in a direction from the first structural layer to the third structural layer, a thickness d1 of the first structural layer is 250um to 400um, a thickness d2 of the second structural layer is 2.0um to 4.3um, and a thickness d3 of the third structural layer is 2.0um to 4.2um, and in order to realize a function of the first diffractive portion for generating diffraction of light, the first diffractive portion should have a certain thickness, and meanwhile, in order to improve the precision of the diffractive optical element, the thickness of the first diffractive portion should not be too thick, based on which, a thickness d4 of the first diffractive portion is 1.3um to 1.5 um.
As an alternative implementation manner, in the embodiment of the first aspect of the present application, in order to achieve the effect of increasing the diffraction efficiency of the diffractive optical element, the first refractive index is 1.4 to 1.5, the second refractive index is 1.6 to 1.75, and the third refractive index is 1.3 to 1.55.
As an optional implementation manner, in an embodiment of the first aspect of the present application, the second structure layer includes a plurality of sub-structure layers, the second refractive index includes a plurality of sub-refractive indices, the plurality of sub-structure layers are sequentially stacked in a direction from the first structure layer to the third structure layer, the sub-structure layers have the sub-refractive indices, and the sub-refractive indices of two adjacent sub-structure layers are different from each other in size.
As an optional implementation manner, in an embodiment of the first aspect of the present application, in two adjacent sub-structure layers, each of the two adjacent sub-structure layers is provided with the first diffraction portion, and the first diffraction portions on the two adjacent sub-structure layers are mutually matched and connected, so that the first diffraction portion can be formed inside the second structure layer.
As an alternative implementation manner, in the embodiment of the first aspect of the present application, in an ideal case, when the distribution of the second refractive index of the second structure layer is a gradient refractive index distribution with a high middle and low two sides along the up-down direction, the fabry-perot resonance generated when the light passes through the diffractive optical element is the best, and the diffraction efficiency of the diffractive optical element is the highest, based on which the distribution of the sub-refractive indices of the plurality of sub-structure layers is a gradient refractive index distribution along the direction from the first structure layer to the third structure layer.
As an optional implementation manner, in an embodiment of the first aspect of the present application, the sub-structure layer located in the middle is an intermediate layer, and the sub-refractive indices of the sub-structure layers are gradually decreased along the direction from the intermediate layer to the first structure layer and along the direction from the intermediate layer to the third structure layer, so that the distribution of the sub-refractive indices of the sub-structure layers can be close to a gradient refractive index distribution with a high middle and low two sides from the bottom to the top, and the diffraction efficiency of the diffractive optical element is close to that in an ideal case, so as to further improve the diffraction efficiency of the diffractive optical element.
As an optional implementation manner, in an embodiment of the first aspect of the present application, a functional layer is disposed between the second structure layer and the first structure layer, and/or between the second structure layer and the third structure layer, and the functional layer is configured to increase a light reflectivity of an interface between the second structure layer and the first structure layer toward a side of the second structure layer, or an interface between the second structure layer and the third structure layer toward a side of the second structure layer, so as to adjust the light reflectivity of the interface between the second structure layer and the first structure layer, or the interface between the second structure layer and the third structure layer toward the side of the second structure layer, so that more light rays can generate fabry-perot resonance in the second structure layer, and further increase a diffraction efficiency of the diffractive optical element.
As an optional implementation manner, in an embodiment of the first aspect of the present application, the first diffraction unit forms an amplitude grating or a phase grating, so that light can be diffracted when passing through the first diffraction unit, so as to realize a function of the diffractive optical element for diffracting light.
In a second aspect, the present application further discloses an optical device, including the diffractive optical element according to the first aspect, where the diffractive optical element has a high diffraction efficiency, so that the precision of the optical device can be improved, and the usability of the optical device can be improved.
Compared with the prior art, the invention has the beneficial effects that:
according to the diffractive optical element and the optical device provided by the invention, the first structural layer, the second structural layer and the third structural layer are arranged, and the second refractive index of the second structural layer is greater than the first refractive index of the first structural layer and the third refractive index of the third structural layer, so that the interface between the first structural layer and the second structural layer and the interface between the second structural layer and the third structural layer have higher reflection performance, so that the light can generate Fabry-Perot resonance in the second structural layer in the process of passing through the diffractive optical element, and the diffraction efficiency of the diffractive optical element is high.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 is a first structural schematic diagram of a diffractive optical element disclosed in an embodiment of the present application;
FIG. 2 is a schematic diagram of a second structure of a diffractive optical element disclosed in an embodiment of the present application;
FIG. 3 is a schematic view of a third structure of a diffractive optical element disclosed in an embodiment of the present application;
fig. 4 is a first structural schematic diagram of a diffractive optical element (first diffraction part is omitted) disclosed in an embodiment of the present application;
fig. 5 is a schematic view of a second structure of a diffractive optical element (omitting a first diffractive part) disclosed in an embodiment of the present application;
fig. 6 is a schematic view of a first structure of a diffractive optical element (a second structural layer is a plurality of layers) disclosed in an embodiment of the present application;
fig. 7 is a schematic diagram of a second structure of the diffractive optical element (the second structural layer is a plurality of layers) disclosed in the embodiment of the present application;
fig. 8 is a schematic view of a third structure of the diffractive optical element (the second structural layer is a plurality of layers) disclosed in the embodiment of the present application;
fig. 9 is a schematic diagram showing a fourth structure of the diffractive optical element (the second structural layer is a plurality of layers) disclosed in the embodiment of the present application;
fig. 10 is a schematic diagram of a fifth structure of a diffractive optical element (a second structural layer is a plurality of layers) disclosed in an embodiment of the present application;
fig. 11 is a schematic view of a sixth structure of the diffractive optical element (the second structural layer is a plurality of layers) disclosed in the embodiments of the present application;
fig. 12 is a schematic view of a seventh structure of a diffractive optical element (a second structural layer is a plurality of layers) disclosed in an embodiment of the present application;
fig. 13 is a schematic view of an eighth structure of the diffractive optical element (the second structural layer is a plurality of layers) disclosed in the embodiment of the present application;
fig. 14 is a schematic view of a ninth structure of the diffractive optical element (the second structural layer is a plurality of layers) disclosed in the embodiment of the present application;
fig. 15 is a schematic structural diagram of an optical device disclosed in an embodiment of the present application.
Icon: 1. a diffractive optical element; 11. a first structural layer; 110. a third diffraction unit; 110a, a fourth protrusion; 12. a second structural layer; 120. a first diffraction unit; 120a, a first protrusion; 120b, a third protrusion; 121. a sub-structure layer; 121a, a first substructure layer; 121b, a second substructure layer; 121c, a third substructure layer; 121d, a fourth substructure layer; 121e, a fifth sub-structure layer; 122. an intermediate layer; 13. a third structural layer; 130. a second diffraction unit; 130a, a second protrusion; 2. an optical device; 20. a light emitting member.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the present invention, the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "center", "vertical", "horizontal", "lateral", "longitudinal", and the like indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings. These terms are used primarily to better describe the invention and its embodiments and are not intended to limit the indicated devices, elements or components to a particular orientation or to be constructed and operated in a particular orientation.
Moreover, some of the above terms may be used to indicate other meanings besides the orientation or positional relationship, for example, the term "on" may also be used to indicate some kind of attachment or connection relationship in some cases. The specific meanings of these terms in the present invention can be understood by those skilled in the art as appropriate.
Furthermore, the terms "mounted," "disposed," "provided," "connected," and "connected" are to be construed broadly. For example, it may be a fixed connection, a removable connection, or a unitary construction; can be a mechanical connection, or an electrical connection; may be directly connected, or indirectly connected through intervening media, or may be in internal communication between two devices, elements or components. The specific meanings of the above terms in the present invention can be understood by those of ordinary skill in the art according to specific situations.
Furthermore, the terms "first," "second," and the like, are used primarily to distinguish one device, element, or component from another (the specific nature and configuration may be the same or different), and are not used to indicate or imply the relative importance or number of the indicated devices, elements, or components. "plurality" means two or more unless otherwise specified.
The technical solution of the present invention will be further described with reference to the following embodiments and the accompanying drawings.
Referring to fig. 1, a first aspect of the embodiments of the present application discloses a diffractive optical element 1, including: a first structural layer 11, a second structural layer 12 and a third structural layer 13. The first structure layer 11 has a first refractive index, the second structure layer 12 is disposed on the first structure layer 11, the second structure layer 12 has a second refractive index, the second refractive index is greater than the first refractive index, the second structure layer 12 is formed with the first diffraction portion 120, the third structure layer 13 has a third refractive index, the third refractive index is less than the second refractive index, and the third structure layer 13 is disposed on a side of the second structure layer 12 away from the first structure layer 11.
It should be noted that, because the second structure layer 12 and the first structure layer 11 are two different structures, an interface between the second structure layer 12 and the first structure layer 11 forms a reflective surface with a certain reflective performance, and similarly, because the second structure layer 12 and the third structure layer 13 are two different structures, an interface between the second structure layer 12 and the third structure layer 13 forms a reflective surface with a certain reflective performance, and when light passes through the diffractive optical element 1, under the action of the two interfaces, a fabry perot resonance occurs inside the second structure layer 12. Specifically, taking the case where light exits the diffractive optical element 1 in the direction from the third structural layer 13 to the first structural layer 11 as an example, when a light beam is emitted to the interface between the second structural layer 12 and the first structural layer 11, a part of the light beam will pass through the interface and be emitted into the first structural layer 11 and to the outside of the diffractive optical element 1, and another part of the light beam will be reflected by the interface to the third structural layer 13 and be reflected by another interface formed between the third structural layer 13 and the second structural layer 12 to be emitted again to the interface between the second structural layer 12 and the first structural layer 11, so that the light intensity emitted from the diffractive optical element 1 can finally float up and down in a certain regular manner by oscillating motion, wherein when the emitted light intensity is at the highest peak, the diffraction efficiency of the diffractive optical element 1 reaches the highest value.
By adopting the diffractive optical element 1 of the embodiment of the present application, the first structure layer 11, the second structure layer 12, and the third structure layer 13 are arranged, and the second refractive index of the second structure layer 12 is greater than the first refractive index of the first structure layer 11 and the third refractive index of the third structure layer 13, so that the interface between the first structure layer 11 and the second structure layer 12 and the interface between the second structure layer 12 and the third structure layer 13 have a certain reflective performance, and thus, in the process of passing through the diffractive optical element 1, the light can generate the fabry-perot resonance effect in the second structure layer 12, and the diffractive efficiency of the diffractive optical element 1 is high.
The interface refers to a surface formed at the intersection of two structural layers, that is, a connection surface where the two structural layers are connected, for example, the interface between the first structural layer 11 and the second structural layer 12 refers to a connection surface where the first structural layer 11 is connected to the second structural layer 12, and the interface between the second structural layer 12 and the third structural layer 13 refers to a connection surface where the second structural layer 12 is connected to the third structural layer 13.
Alternatively, the first structural layer 11 may be made of glass or a polymer material (e.g., plastic or resin), so that the diffractive optical element 1 can obtain good optical performance. Similarly, the second structural layer 12 can be a plate-shaped body made of glass or polymer material (such as plastic or resin), the third structural layer 13 can also be a plate-shaped body made of glass or polymer material (such as plastic or resin),
it is understood that the first refractive index, the second refractive index and the third refractive index of the first structural layer 11, the second structural layer 12 and the third structural layer 13 respectively can be adjusted according to the material and the molding temperature, which is not limited in this embodiment.
Optionally, according to the usage requirement, any two of the first structural layer 11, the second structural layer 12 and the third structural layer 13 may be made of the same type or different types of materials, that is, the materials of the first structural layer 11 and the second structural layer 12 may be the same type or different types, the materials of the first structural layer 11 and the third structural layer 13 may be the same type or different types, and the materials of the second structural layer 12 and the third structural layer 13 may be the same type or different types. For example, the first structural layer 11 and the second structural layer 12 may be both made of plastic, or the first structural layer 11 may be made of glass, and the second structural layer 12 may be made of plastic.
It can be understood that, between two adjacent structural layers, for example, between the first structural layer 11 and the second structural layer 12, and between the second structural layer 12 and the third structural layer 13, the two adjacent structural layers can be bonded together by optical adhesives such as UV (Ultraviolet ray glue) or OCA (optical Clear Adhesive), so as to stabilize the connection between the two adjacent structural layers, avoid the two adjacent structural layers from being separated, and simultaneously, avoid an air layer being formed between the two adjacent structural layers, thereby avoiding the air layer from affecting the diffraction efficiency of the diffractive optical element 1.
For convenience of explanation, the direction from the first structural layer 11 to the third structural layer 13 is defined as an upward direction, and the direction from the third structural layer 13 to the first structural layer 11 is defined as a downward direction, as shown in fig. 1, and the upward and downward directions are shown by arrows in fig. 1.
Alternatively, in the up-down direction, in order to make the diffractive optical element 1 less prone to deformation or damage due to external force, the overall diffractive optical element 1 should have a certain thickness, and at the same time, in order to improve the diffraction accuracy of the diffractive optical element 1, the thicknesses of the respective structural layers should not be set too thick. In the setting, considering that the second structural layer 12 is disposed above the first structural layer 11, and the third structural layer 13 is disposed above the second structural layer 12, that is, the first structural layer 11 serves as a support reference for the second structural layer 12 and the third structural layer 13, the thickness of the first structural layer 11 may be set to be larger than the thicknesses of the second structural layer 12 and the third structural layer 13. For example, with the thickness of the first structural layer 11 being d1, the thickness of the second structural layer 12 being d2, and the thickness of the third structural layer 13 being d3, i.e., d1 > d2, d1 > d3, the thickness d2 of the second structural layer 12 may be the same as or different from the thickness d3 of the third structural layer 13, e.g., d2 ═ d3, d2 > d3, or d2 < d 3.
Further, in order to simplify the manufacturing process of the diffractive optical element 1, the thickness of each structural layer should not be too thin, and therefore, the thickness d1 of the first structural layer 11 may be 250um-400um, for example, the thickness d1 of the first structural layer 11 may be 250um, 300um, 350um or 400um, etc., the thickness d2 of the second structural layer 12 may be 2.0um-4.3um, for example, the thickness d2 of the second structural layer 12 may be 2.0um, 2.4um, 2.8um, 3.2um, 3.6um, 4.0um or 4.3um, etc., the thickness d3 of the third structural layer 13 may be 2.0um-4.2um, for example, the thickness d3 of the third structural layer 13 may be 2.0um, 2.3um, 2.5um, 2.7um, 2.9um, 3.1um, 3.3um, 3.5um, 3.7um, 3.9um, 4.1um, or 4um, etc.
It should be noted that, because the first diffraction part 120 is disposed on the second structure layer 12, along the up-down direction, in order to implement the function of the first diffraction part 120 for diffracting light, the first diffraction part 120 should have a certain thickness, and meanwhile, in order to improve the precision of the diffractive optical element 1, the thickness of the first diffraction part 120 should not be too thick, based on which, the thickness d4 of the first diffraction part 120 may be 1.3um-1.5um, for example, the thickness d4 of the first diffraction part 120 may be 1.3um, 1.35um, 1.4um, 1.45um or 1.5um, etc.
In some embodiments, in order to achieve the effect of increasing the diffraction efficiency of the diffractive optical element 1, the first refractive index may be 1.4-1.5, for example, the first refractive index may be 1.4, 1.42, 1.44, 1.46, 1.48, 1.5, or the like; the magnitude of the second refractive index may be 1.6-1.75, e.g., the magnitude of the second refractive index may be 1.6, 1.63, 1.66, 1.69, 1.72, 1.75, etc.; the third refractive index may be 1.3-1.55, for example the third refractive index may be 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, etc.
It is understood that when the thicknesses of the structural layers and the diffraction layer are different, the optimal refractive indexes of the structural layers are also different, and for example, when the thickness d1 of the first structural layer 11 is 400um, the thickness d2 of the second structural layer 12 is 1.0um, and the thickness d3 of the third structural layer 13 is 1.0um, the thickness d4 of the first diffraction part 120 is 1.4um, at this time, the first refractive index is preferably 1.5, the second refractive index is 1.703, and the third refractive index is 1.390. It will be appreciated that the diffraction efficiency of the diffractive optical element 1 is related to the light passing through the diffractive optical element 1, i.e. the diffraction efficiencies are different when different light is diffracted by the same diffractive optical element 1. Taking the diffractive optical element 1 for diffracting light with a wavelength of 940nm as an example, in the related art, the diffraction efficiency of the diffractive optical element 1 without using the anti-reflection film is about 70%, and the diffraction efficiency of the diffractive optical element 1 provided in the preferred example is about 75.25%, which is greatly improved.
As can be seen from the foregoing, under the reflection action of the interface between the second structure layer 12 and the first structure layer 11 and the interface between the second structure layer 12 and the third structure layer 13, the fabry-perot resonance can occur in the second structure layer 12 during the light passing through the diffractive optical element 1. It is understood that when the thicknesses of the structural layers and the diffraction layer are different, the optimal values of the reflectivities of the interface between the second structural layer 12 and the first structural layer 11 and the interface between the second structural layer 12 and the third structural layer 13 are also different.
In view of this, in some embodiments, in order to further adjust the reflectivity of the interface between the second structure layer 12 and the first structure layer 11 or the interface between the second structure layer 12 and the third structure layer 13, so as to make the reflectivity of the interface between the second structure layer 12 and the first structure layer 11 or the interface between the second structure layer 12 and the third structure layer 13 closer to an ideal value, so as to enable more light rays to generate fabry-perot resonance in the second structure layer 12, thereby further improving the diffraction efficiency of the diffractive optical element 1, a functional layer (not shown) may be disposed between the second structure layer 12 and the first structure layer 11, and/or between the second structure layer 12 and the third structure layer 13, and is configured to improve the light reflectivity of the interface between the second structure layer 12 and the first structure layer 11 or the interface between the second structure layer 12 and the third structure layer 13 toward the side of the second structure layer 12, without affecting the light transmittance from the first structural layer 11 to the second structural layer 12, or from the third structural layer 13 to the second structural layer 12. Specifically, a functional layer may be disposed between the second structural layer 12 and the first structural layer 11, or between the second structural layer 12 and the third structural layer 13, or between the second structural layer 12 and the first structural layer 11, and between the second structural layer 12 and the third structural layer 13. It is understood that when the functional layers are disposed between the second structure layer 12 and the first structure layer 11, and between the second structure layer 12 and the third structure layer 13, the maximum light can generate the fabry perot resonance in the second structure layer 12 during passing through the second structure layer 12, so as to improve the diffraction efficiency of the diffractive optical element 1 to the maximum extent.
It can be understood that the functional layer is only arranged to increase the light reflectivity of the interface between the second structural layer 12 and the first structural layer 11 or the interface between the second structural layer 12 and the third structural layer 13 toward the second structural layer 12 side, so as to adjust the light reflectivity of the interface between the second structural layer 12 and the first structural layer 11 or the interface between the second structural layer 12 and the third structural layer 13 toward the second structural layer 12 side to be close to or to reach an optimal value, therefore, the arrangement of the functional layer does not make the interface between the second structural layer 12 and the first structural layer 11 or the interface between the second structural layer 12 and the third structural layer 13 form a reflective surface with total reflection, in other words, when the functional layer is arranged on the interface between the second structural layer 12 and the first structural layer 11 or the interface between the second structural layer 12 and the third structural layer 13, the light can still pass through the interface between the second structural layer 12 and the first structural layer 11 or the interface between the second structural layer 12 and the third structural layer 13 The interfaces between the layers 13 are structured to pass through the diffractive optical element 1.
Alternatively, in actual operation, the functional layer may be a metal reflective film or a dielectric reflective film that covers the upper side surface of the first structural layer 11, the upper side or lower side surface of the second structural layer 12, or the lower side surface of the third structural layer 13.
In some embodiments, the third structural layer 13 may be provided with a second diffraction part 130 for cooperating with the first diffraction part 120, and/or the first structural layer 11 may be provided with a third diffraction part 110 for cooperating with the first diffraction part 120, so that the diffractive optical element 1 can realize different diffraction functions through different distributions of the first diffraction part 120 to meet more extensive use requirements.
In addition, the first diffraction part 120 and the second diffraction part 130 are matched, which means that the first diffraction part 120 and the second diffraction part 130 are connected and no air layer exists between the first diffraction part 120 and the second diffraction part 130. Similarly, the matching of the third diffraction part 110 and the second diffraction part 130 means that the third diffraction part 110 and the second diffraction part 130 are closely connected and no air layer exists between the third diffraction part 110 and the second diffraction part 130.
In an alternative embodiment, as shown in fig. 1, a second diffraction part 130 for matching with the first diffraction part 120 may be disposed on the third structure layer 13, and at this time, the first diffraction part 120 may be formed on the side of the second structure layer 12 facing the third structure layer 13, that is, the first diffraction part 120 may be formed on the upper side of the second structure layer 12. Thus, when light is emitted from the third structural layer 13 to the diffractive optical element 1, the light may be diffracted when passing through the first and second diffractive parts 120 and 130, then fabry-perot resonance may be generated in the second structural layer 12 to enhance the light intensity of each diffracted light beam, and finally, each light beam may pass through the first structural layer 11 and be emitted. The diffraction efficiency of the diffractive optical element 1 can be effectively improved by a method of enhancing the intensity of light rays through the Fabry-Perot resonance effect after light rays are diffracted.
In another alternative embodiment, as shown in fig. 2, a third diffraction part 110 for matching with the first diffraction part 120 may be provided on the first structure layer 11, and at this time, the first diffraction part 120 may be formed on the side of the second structure layer 12 facing the first structure layer 11, that is, the first diffraction part 120 may be formed on the lower side of the second structure layer 12. Thus, when light is emitted from the first structural layer 11 to the diffractive optical element 1, the light may be diffracted when passing through the first diffractive part 120 and the third diffractive part 110, then a fabry-perot resonance may be generated in the second structural layer 12 to enhance the light intensity of each diffracted light beam, and finally, each light beam may pass through the third structural layer 13 and be emitted. The diffraction efficiency of the diffractive optical element 1 can be effectively improved by a method of enhancing the intensity of light rays through the Fabry-Perot resonance effect after light rays are diffracted.
In still another alternative embodiment, as shown in fig. 3, a second diffraction part 130 for matching with the first diffraction part 120 may be provided on the third structure layer 13, and a third diffraction part 110 for matching with the first diffraction part 120 may be provided on the first structure layer 11, and then, the first diffraction part 120 may be formed on the side of the second structure layer 12 facing the third structure layer 13 and the side facing the first structure layer 11, that is, the first diffraction part 120 may be formed on both upper and lower sides of the second structure layer 12.
It is understood that when the first diffraction part 120 is formed on the upper side of the second structure layer 12, the second diffraction part 130 is formed on the lower side of the third structure layer 13, the thickness d5 of the second diffraction part is equal to the thickness d4 of the first diffraction part 120, the first diffraction part 120 is formed on the lower side of the second structure layer 12, and the thickness d6 of the third diffraction part 110 is equal to the thickness d4 of the first diffraction part 120 when the third diffraction part 110 is formed on the upper side of the first structure layer 11.
Referring to fig. 3, taking the first diffraction part 120 formed on the upper side of the second structure layer 12 as an example, the second diffraction part 130 is formed on the lower side of the third structure layer 13, so that the second diffraction part 130 and the first diffraction part 120 are matched with each other, and the third structure layer 13 and the second structure layer 12 can be tightly connected, thereby preventing an air layer from being formed between the second structure layer 12 and the third structure layer 13, and preventing the air layer from affecting the diffraction efficiency of the diffractive optical element 1. As described above, the second diffractive part 130 and the first diffractive part 120 can be connected by an optical adhesive (such as OCA adhesive or UV adhesive), so that the connection between the second diffractive part 130 and the first diffractive part 120 is stable, and the second diffractive part 130 is prevented from being separated from the first diffractive part 120. It is understood that when the first diffraction part 120 is formed on the lower side of the second structure layer 12, the connection relationship between the third diffraction part 110 and the first diffraction part 120 can refer to the relationship between the second diffraction part 130 and the first diffraction part 120, and will not be described herein again.
In some embodiments, the first diffraction part 120 may form an amplitude grating or a phase grating, so that light can be diffracted when passing through the first diffraction part 120 to realize the function of the diffractive optical element 1 for light diffraction. Alternatively, the first diffraction part 120 may form a dammann grating, which is a binary phase grating having a specific aperture function, and can diffract light to form a pattern with uniform light intensity, so as to control and accurately measure the diffracted light. For example, the first diffraction part 120 may form a speckle dammann grating, a dot-matrix dammann grating, a square dammann grating, or a ring-shaped dammann grating, etc., according to design requirements.
It can be understood that, when the first diffraction part 120 is formed on the upper side of the second structure layer 12, the first diffraction part 120 is connected with the second diffraction part 130 in a matching manner, and the interface between the first diffraction part 120 and the second diffraction part 130 forms a grating structure for allowing light to be diffracted when the light is emitted from the first diffraction part 120 to the second diffraction part 130 or from the second diffraction part 130 to the first diffraction part 120.
Alternatively, when the first diffraction part 120 is formed on the upper and lower sides of the second structure layer 12, the structure of the first diffraction part 120 located on the upper side of the second structure layer 12 may be the same as or different from the structure of the first diffraction part 120 located on the lower side of the second structure layer 12. For example, the first diffraction part 120 located at the upper side of the second structure layer 12 may be formed as a speckle dammann grating, and the first diffraction part 120 located at the lower side of the second structure layer 12 may be formed as a lattice dammann grating. Alternatively, the first diffraction part 120 located on the upper side of the second structure layer 12 and the first diffraction part located on the lower side of the second structure layer 12 may be formed as a speckle dammann grating.
In some embodiments, the first diffraction part 120 may be a protrusion or a recess, and similarly, the second diffraction part 130 may be a protrusion or a recess, and the third diffraction part 110 may also be a protrusion or a recess, so that a grating capable of being used for diffracting light can be formed by a simple arrangement of structures.
Referring to fig. 1 and fig. 3, taking the first diffraction part 120, the second diffraction part 130 and the third diffraction part 110 as an example, specifically, the first diffraction part 120 may include a plurality of first protrusions 120a arranged at intervals, the second diffraction part 130 includes a plurality of second protrusions 130a arranged at intervals, and each second protrusion 130a is respectively attached to each adjacent first protrusion 120a, so that the second diffraction part 130 is connected to the first diffraction part 120 in a matching manner.
Wherein, the second protrusion 130a attached to the first protrusion 120a means: the surface of the second protrusion 130a is fitted to the surface of the adjacent one of the first protrusions 120a, so that the second protrusion 130a is tightly coupled to the adjacent two of the first protrusions 120 a.
Referring to fig. 2 and 3, similarly, when the first diffraction part 120 is formed at the lower side of the second structure layer 12, the third diffraction part 110 is formed at the upper side of the first structure layer 11, so that the third diffraction part 110 and the first diffraction part 120 are matched with each other, the first structure layer 11 and the second structure layer 12 can be tightly connected, an air layer is prevented from being formed between the first structure layer 11 and the second structure layer 12, and the air layer is prevented from affecting the diffraction efficiency of the diffractive optical element 1. Specifically, the first diffraction part 120 may include a plurality of third protrusions 120b arranged at intervals, the third diffraction part 110 includes a plurality of fourth protrusions 110a arranged at intervals, and each fourth protrusion 110a is attached to each adjacent third protrusion 120b, so that the third diffraction part 110 is connected to the first diffraction part 120 in a matching manner.
The fitting of the fourth protrusion 110a to the third protrusion 120b means: the surface of the fourth protrusion 110a is conformed to the surface of the adjacent third protrusion 120b, so that the fourth protrusion 110a is closely coupled to the adjacent two third protrusions 120 b.
It is understood that the shape and distribution of the protrusions may be designed according to actual use requirements, and the shape and distribution of the first protrusion 120a, the second protrusion 130a, the third protrusion 120b, and the fourth protrusion 110a shown in fig. 3 are only an example and do not constitute a limitation on the shape and distribution of the protrusions.
Alternatively, the second structural layer 12 may be a single-layer structure or a multi-layer structure according to design requirements. In an alternative embodiment, the second structure layer 12 is a single-layer structure, so that the diffractive optical element 1 can be configured in the simplest manner, and the effect of improving the diffraction efficiency of the diffractive optical element 1 can be achieved.
In another alternative embodiment, the second structural layer 12 is a multi-layer structure. Specifically, the second structure layer 12 includes a plurality of sub-structure layers 121, the second refractive index includes a plurality of sub-refractive indexes, the plurality of sub-structure layers 121 are sequentially stacked in a direction from the first structure layer 11 to the third structure layer 13, the sub-structure layers 121 have sub-refractive indexes, the sub-refractive indexes of two adjacent sub-structure layers 121 are different, and by providing the plurality of sub-structure layers 121, when light passes through the diffractive optical element 1, the effect of the fabry-perot resonance effect generated in the second structure layer 12 can be achieved by adjusting the refractive index of each sub-structure layer 121, so that the diffraction efficiency of the diffractive optical element 1 is improved.
It is understood that when the second structure layer 12 includes a multi-layer structure, the second structure layer 12 has a second refractive index that is a refractive index range including sub-refractive indices of the plurality of sub-structure layers 121 included in the second structure layer 12. For example, the refractive index of the second refractive index is in a range of 1.6 to 1.75, so that the sub-refractive indexes of the plurality of sub-structure layers 121 included in the second structure layer 12 are within a range of 1.6 to 1.75, which is not particularly limited in this embodiment. It is understood that the connection between the sub-structure layers 121 may refer to the connection between the structure layers described above, and will not be described herein again. Alternatively, the sub-structure layer 121 may be two, three, four, five, six or more, according to design requirements. Illustratively, as shown in fig. 4, fig. 4 shows that there are two sub-structure layers 121, and the two sub-structure layers 121 have different sub-refractive index magnitudes.
Referring to fig. 5, optionally, in an ideal case, when the second structure layer 12 has a gradient refractive index distribution with a high middle and low two sides along the up-down direction, the fabry-perot resonance generated when light passes through the diffractive optical element 1 is the best, and the diffraction efficiency of the diffractive optical element 1 is the highest. Therefore, it is preferable that the distribution of the sub-refractive indices of the plurality of sub-structure layers 121 is substantially a gradient refractive index distribution in the up-down direction, in other words, by making the second layer structure 12 include the plurality of sub-structure layers 121, the sub-refractive indices of the sub-structure layers 121 are adjusted so that the distribution of the sub-refractive indices of the sub-structure layers 121 is fitted to the gradient refractive index distribution in the up-down direction, so that the diffraction efficiency of the diffractive optical element 1 can be obtained close to the ideal case, and the diffraction efficiency of the diffractive optical element 1 can be further improved.
It should be noted that the gradient refractive index profile that can enable the second structure layer 12 to achieve the optimal fabry-perot resonance effect can be calculated according to actual design requirements, and the gradient refractive index profile shown in fig. 5 is only an example and is not a limitation on the shape of the gradient refractive index profile.
It is understood that the larger the number of layers of the sub-structure layer 121, the higher the degree of fitting of the distribution of the sub-refractive indices of each sub-structure layer 121 to the gradient refractive index distribution, and thus the closer the diffraction efficiency of the diffractive optical element 1 can be made to the diffraction efficiency in the ideal case, the higher the diffraction efficiency of the diffractive optical element 1.
In some embodiments, the intermediate sub-structure layer 121 is the intermediate layer 122, and the sub-refractive index of each sub-structure layer 121 gradually decreases along the direction from the intermediate layer 122 to the first structure layer 11 and along the direction from the intermediate layer 122 to the third structure layer 13, so that the distribution of the sub-refractive index of each sub-structure layer 121 can be close to the gradient refractive index distribution with a high middle and low two sides from the bottom to the top, and the diffraction efficiency of the diffractive optical element 1 is close to the ideal condition, thereby further improving the diffraction efficiency of the diffractive optical element 1.
It should be noted that the middle sub-structure layer 121 refers to the middle sub-structure layer 121 located in position in the up-down direction, and is not the middle sub-structure layer 121 in number. It can be understood that, as shown in fig. 6, when the number of the sub-structure layers 121 is an odd number, and the thicknesses h of the sub-structure layers 121 in the up-down direction are all substantially the same, the sub-structure layer 121 in the middle of the position in the up-down direction is also the sub-structure layer 121 in the middle of the number. Fig. 6 shows that the number of the sub-structure layers 121 is five, the thicknesses h of the five sub-structure layers 121 in the vertical direction are substantially the same, and the five sub-structure layers 121 from the bottom to the top are defined as a first sub-structure layer 121a, a second sub-structure layer 121b, a third sub-structure layer 121c, a fourth sub-structure layer 121d and a fifth sub-structure layer 121e in sequence, and then in the vertical direction, the third sub-structure layer 121c is located in the middle of the five sub-structure layers 121, so that the third sub-structure layer 121c is an intermediate layer 122, the intermediate layer 122 (i.e., the third sub-structure layer 121c) has the largest sub-refractive index, the second sub-structure layer 121b has a sub-refractive index larger than that of the first sub-structure layer 121a, and the fourth sub-structure layer 121d has a sub-refractive index larger than that of the fifth sub-structure layer 121 e.
As can be seen from the foregoing, the first diffraction part 120 may be formed on the upper side and/or the lower side of the second structure layer 12, and when the second structure layer 12 includes a plurality of sub-structure layers 121, the first diffraction part 120 may be formed inside the second structure layer 12. For example, in two adjacent sub-structure layers 121, each sub-structure layer 121 is provided with a first diffraction part 120, and the first diffraction parts 120 on the two adjacent sub-structure layers 121 are connected in a matching manner, in other words, the first diffraction part 120 may be formed between all two adjacent sub-structure layers 121, or the first diffraction part 120 may be formed between two partial adjacent sub-structure layers 121, so as to form different grating structures. It is understood that the number and the position of the first diffraction part 120 in the second structure layer 12 can be adjusted according to the actual use requirement, and the embodiment is not particularly limited.
It is understood that when the first diffraction part 120 is formed between two adjacent sub-structure layers 121, at the same time, the first diffraction part 120 may not be formed on the surface of the second structure layer 12 connected to the first structure layer 11 and the surface of the second structure layer 12 connected to the third structure layer 13, so that the light reflection performance of the surface of the second structure layer 12 connected to the first structure layer 11 and the surface of the second structure layer 12 connected to the third structure layer 13 may be enhanced, so that more light can generate fabry-perot resonance inside the plurality of sub-structure layers 121 of the second structure layer 12, and the diffraction efficiency of the diffractive optical element 1 is better. It is understood that, in other embodiments, in the case that the first diffraction part 120 is formed inside the second structure layer 12, the first diffraction part 120 may also be formed on the side of the second structure layer 12 facing the first structure layer 11 and/or the side facing the second structure layer 12, that is, the first diffraction part 120 may be formed inside the second structure layer 12 and on the upper surface, or the first diffraction part 120 may be formed inside the second structure layer 12 and on the lower surface, or the first diffraction part 120 may be formed inside the second structure layer 12, on the upper surface and on the lower surface.
Next, taking the example that the first diffraction part 120 is formed inside the second structure layer 12, and the first diffraction part 120 is not formed on the upper side and/or the lower side surface of the second structure layer 12, several distributions of the first diffraction part 120 in the second structure layer 12 will be described in detail with reference to the drawings.
In an alternative embodiment, as shown in fig. 4, there are two sub-structure layers 121, the two sub-structure layers 121 are stacked from bottom to top, and the first diffraction part 120 is formed between the two sub-structure layers 121.
In another alternative embodiment, as shown in fig. 7, there are three sub-structure layers 121, the three sub-structure layers 121 are stacked in sequence from bottom to top, and the three sub-structure layers 121 are defined as a first sub-structure layer 121a, a second sub-structure layer 121b, and a third sub-structure layer 121c in sequence from bottom to top. For example, the first diffraction part 120 may be formed between the first and second sub-structure layers 121a and 121b (as shown in fig. 7), or the first diffraction part 120 may be formed between the third and second sub-structure layers 121c and 121b (as shown in fig. 8), or the first diffraction part 120 may be formed between the first and second sub-structure layers 121a and 121b, and between the third and second sub-structure layers 121c and 121b (as shown in fig. 9).
In another alternative embodiment, as shown in fig. 10, the number of the sub-structure layers 121 is four, the four sub-structure layers 121 are sequentially stacked from bottom to top, and the four sub-structure layers 121 are defined as a first sub-structure layer 121a, a second sub-structure layer 121b, a third sub-structure layer 121c, and a fourth sub-structure layer 121d from bottom to top.
In this embodiment, as an example, the first diffraction part 120 is formed between the second and third sub-structure layers 121b and 121 c. As another example, as shown in fig. 11, the first diffraction part 120 is formed between the first and second sub-structure layers 121a and 121b, and between the second and third sub-structure layers 121b and 121 c. As still another example, as shown in fig. 12, the first diffraction part 120 is formed between the first and second sub-structure layers 121a and 121b, and between the third and fourth sub-structure layers 121c and 121 d. It is understood that, in other examples, the first diffraction part 120 may also be formed between each two adjacent sub-structure layers 121.
In another alternative embodiment, as shown in fig. 13, five sub-structure layers 121 are stacked in sequence from bottom to top, and the five sub-structure layers 121 are defined as a first sub-structure layer 121a, a second sub-structure layer 121b, a third sub-structure layer 121c, a fourth sub-structure layer 121d, and a fifth sub-structure layer 121e in sequence from bottom to top. For example, the first diffraction part 120 may be formed between the first and second sub-structure layers 121a and 121b, and between the third and fourth sub-structure layers 121c and 121d (as shown in fig. 13), or the first diffraction part 120 may be formed between the first and second sub-structure layers 121a and 121b, between the third and fourth sub-structure layers 121c and 121d, and between the fourth and fifth sub-structure layers 121d and 121e (as shown in fig. 14). It is understood that, in other examples, the first diffraction part 120 may also be formed between each two adjacent sub-structure layers 121.
In a second aspect, referring to fig. 15, the present application further discloses an optical device comprising a diffractive optical element 1 as described above in relation to the first aspect. Specifically, the optical device 2 may include, but is not limited to, a diffractive optical lens, an optical sensor, a 3D (three-dimensional) distance measuring device, a 3D imaging device, a watch, a mobile phone, an automobile, a machine tool, and the like, which have a 3D distance measuring function or a 3D imaging function. Further, in practical operation, the optical device 2 may implement a 3D ranging function or a 3D imaging function by diffracted light rays through a time of flight (TOF) method.
Optionally, the optical device 2 may further include a light emitting member 20, so that light rays for passing through the diffractive optical element 1 to be diffracted can be generated by the light emitting member 20 to implement various functions of the optical device 2, such as a 3D ranging function or a 3D imaging function, using the light rays.
Since light having a wavelength of 940nm is absorbed in a large amount during the sunlight passes through the atmosphere, light having a wavelength of 940nm is very little between the landmark table of the earth and the atmosphere, and thus, the light emitting member 20 may emit light having a wavelength of 940nm in order to avoid interference of the sunlight.
According to the optical device 2 disclosed in the second aspect of the embodiment of the present application, by providing the diffractive optical element 1 provided in the first aspect of the embodiment, the accuracy of the optical device 2 can be improved and the usability of the optical device 2 can be improved due to the high diffraction efficiency of the diffractive optical element 1.
The diffractive optical element and the optical device disclosed in the embodiments of the present invention are described in detail above, and the principles and embodiments of the present invention are explained herein by applying specific examples, and the above description of the embodiments is only used to help understanding the diffractive optical element and the optical device of the present invention and the core concept thereof; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.
Claims (12)
1. A diffractive optical element, characterized in that it comprises:
a first structural layer having a first refractive index;
the second structure layer is arranged on the first structure layer, has a second refractive index, and is greater than the first refractive index, and is provided with a first diffraction part; and
and the third structural layer is provided with a third refractive index which is smaller than the second refractive index, and the third structural layer is arranged on one side of the second structural layer, which deviates from the first structural layer.
2. The diffractive optical element according to claim 1, wherein the first diffractive part is formed on a side of the second structural layer facing the third structural layer, and a second diffractive part is formed on a side of the third structural layer facing the second structural layer, the second diffractive part cooperating with the first diffractive part; and/or
The first diffraction part is formed on one side of the second structure layer facing the first structure layer, and a third diffraction part is formed on one side of the first structure layer facing the second structure layer and matched with the first diffraction part.
3. The diffractive optical element according to claim 2, wherein the first diffractive part includes a plurality of first protrusions arranged at intervals, and the second diffractive part includes a plurality of second protrusions arranged at intervals, and each of the second protrusions is attached to each of the adjacent first protrusions; and/or
The first diffraction part comprises a plurality of third bulges which are arranged at intervals, the third diffraction part comprises a plurality of fourth bulges which are arranged at intervals, and each fourth bulge is respectively attached to each adjacent third bulge.
4. A diffractive optical element according to one of claims 1 to 3, characterized in that, in the direction of the first structural layer to the third structural layer, the thickness d1 of the first structural layer is 250um to 400um, the thickness d2 of the second structural layer is 2.0um to 4.3um, the thickness d3 of the third structural layer is 2.0um to 4.2um, and the thickness d4 of the first diffractive part is 1.3um to 1.5 um.
5. The diffractive optical element according to one of claims 1 to 3, characterized in that the first refractive index is 1.4 to 1.5, the second refractive index is 1.6 to 1.75 and the third refractive index is 1.3 to 1.55.
6. The diffractive optical element according to any one of claims 1 to 3, wherein the second structural layer comprises a plurality of sub-structural layers, the second refractive index comprises a plurality of sub-refractive indices, the plurality of sub-structural layers are stacked in sequence along the first structural layer toward the third structural layer, the sub-structural layers have the sub-refractive indices, and two adjacent sub-structural layers have different sub-refractive indices.
7. The diffractive optical element according to claim 6, wherein in two adjacent sub-structure layers, each of the sub-structure layers is provided with the first diffractive portion, and the first diffractive portions on the two adjacent sub-structure layers are mutually matched.
8. The diffractive optical element according to claim 6, wherein the plurality of sub-structural layers have a distribution of the sub-refractive indices in a gradient refractive index distribution in a direction from the first structural layer toward the third structural layer.
9. The diffractive optical element according to claim 6, wherein the intermediate sub-structure layers are intermediate layers, and the sub-refractive indices of the respective sub-structure layers gradually decrease in a direction from the intermediate layers to the first structure layer and in a direction from the intermediate layers to the third structure layer.
10. The diffractive optical element according to any one of claims 1 to 3, wherein a functional layer is disposed between the second structural layer and the first structural layer, and/or between the second structural layer and the third structural layer, and the functional layer is configured to increase the optical reflectivity of the interface between the second structural layer and the first structural layer toward the second structural layer side, or the interface between the second structural layer and the third structural layer toward the second structural layer side.
11. The diffractive optical element according to any one of claims 1 to 3, wherein the first diffractive part forms an amplitude grating or a phase grating.
12. An optical device comprising a diffractive optical element according to any one of claims 1 to 11.
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