Superlens structure parameter determination method, superlens and optical imaging system

Abstract

The invention provides a super lens structure parameter determination method, a super lens and an optical imaging system. The super lens comprises at least one nano fin; the method comprises the steps that the sizes of the nano-fins included in the super-lens are determined according to the target focal length of the super-lens, the sizes of the same nano-fin in different directions are different, therefore, polarization-dependent wavefront control can be achieved on incident light in different directions, multi-focus imaging of the super-lens is achieved, the structure is simple, and the integration degree is high.

Description

Technical Field

[0001] The present application relates to the field of micro-nano optical technology, and in particular to a method for determining structural parameters of a superlens, a superlens, and an optical imaging system. Background Art

[0002] In the visible light band, lenses that can focus and achieve zoom functions are important basic optical components in optical imaging systems.

[0003] In geometric optics, conventional zoom solutions usually use a cascade of multiple geometric lenses to achieve zoom by adjusting the geometric parameters and distances of the geometric lenses in the lens group.

[0004] However, since the working principle of the lens is to achieve focusing by changing the phase and polarization of the incident light, it is limited by the refractive index of traditional geometric optical materials. If the size of the optoelectronic device needs to be reduced to the millimeter scale, a single geometric lens will find it difficult to accumulate enough focusing distance to achieve the purpose of focusing. It is usually necessary to achieve focusing by increasing the thickness or the number of lenses, which makes the zoom system in the imaging system larger and less integrated. Summary of the invention

[0005] The present application provides a method for determining the structural parameters of a metalens, a metalens, and an optical imaging system, which are used to solve the problem in the related art that a cascade of geometric lenses is used to achieve zooming by adjusting the geometric parameters and distances of the geometric lenses in the lens group, resulting in a large size of the zoom system and a low degree of integration.

[0006] In a first aspect, the present application provides a method for determining structural parameters of a superlens, wherein the superlens includes at least one nanofin; comprising:

[0007] The size of the nanofins included in the superlens is determined according to the target focal length of the superlens, wherein the size of the same nanofin in different directions is different.

[0008] In a possible implementation, determining the size of the nanofins included in the superlens according to the target focal length of the superlens includes:

[0009] Determining a target phase distribution of the metalens in multiple directions according to the target focal lengths of the metalens in multiple directions;

[0010] The sizes of the nanofins included in the superlens in multiple directions are determined according to the target phase distribution of the superlens in multiple directions.

[0011] In a possible implementation, determining the sizes of the nanofins included in the superlens in multiple directions according to the target phase distribution of the superlens in multiple directions includes:

[0012] Constructing a mapping relationship between nanofin size and phase, wherein the mapping relationship is used to represent phases corresponding to different preset sizes in multiple directions among at least two preset sizes;

[0013] According to the target phase distribution of the superlens in multiple directions and the mapping relationship, the sizes of the nanofins included in the superlens in multiple directions are determined.

[0014] In a possible implementation, the multiple directions include a first direction and a second direction; and determining the sizes of the nanofins included in the superlens in the multiple directions according to the target phase distribution of the superlens in the multiple directions and the mapping relationship includes:

[0015] The sizes of the nanofins included in the superlens in the first direction and the second direction are determined according to the first target phase distribution of the superlens in the first direction, the second target phase distribution in the second direction, and the mapping relationship.

[0016] In a possible implementation, determining the sizes of the nanofins included in the superlens in the first direction and the second direction according to the first target phase distribution of the superlens in the first direction, the second target phase distribution in the second direction, and the mapping relationship includes:

[0017] For any nanofin, a first target phase corresponding to the position of the nanofin is determined according to the first target phase distribution, a second target phase corresponding to the position of the nanofin is determined according to the second target phase distribution, and sizes of the nanofin in the first direction and the second direction are determined according to the first target phase, the second target phase and the mapping relationship.

[0018] In a possible implementation, the mapping relationship includes a first phase corresponding to different preset sizes in the first direction and a second phase corresponding to the second direction in at least two preset sizes; and determining the size of the nanofin in the first direction and the second direction according to the first target phase, the second target phase and the mapping relationship includes:

[0019] For each preset size, calculating a phase difference corresponding to the preset size, wherein the phase difference is used to characterize a difference between the first target phase and the first phase and a difference between the second target phase and the second phase;

[0020] According to the phase difference corresponding to each preset size, a size matching the first target phase and the second target phase is determined from a plurality of preset sizes.

[0021] In a possible implementation, for each preset size, calculating the phase difference corresponding to the preset size includes:

[0022] For each preset size, determining a first difference between a first phase corresponding to the preset size in the first direction and the first target phase, and a second difference between a second phase corresponding to the preset size in the second direction and the second target phase;

[0023] The phase difference is determined according to the first difference and the second difference.

[0024] In a possible implementation, constructing a mapping relationship between the nanofin size and the phase includes:

[0025] For any direction, determining the phase and transmittance corresponding to a plurality of preset sizes;

[0026] According to the transmittance, the at least two preset sizes that meet the preset requirement are determined from a plurality of preset sizes; wherein the preset requirement is: the transmittance is greater than a transmittance threshold.

[0027] In a possible implementation manner, determining phases and transmittances corresponding to a plurality of preset sizes includes:

[0028] Scanning is performed sequentially according to the preset step length to obtain phases and transmittances corresponding to multiple preset sizes within the preset size range.

[0029] In a possible implementation, the multiple directions include a first direction and a second direction; and determining the target phase distribution of the metalens in the multiple directions according to the target focal lengths of the metalens in the multiple directions includes:

[0030] Based on a phase wavefront formula of the metalens in the first direction, determining a first target phase distribution corresponding to the metalens in the first direction according to a first incident wavelength and a first target focal length of the metalens in the first direction;

[0031] Based on the phase wavefront formula of the metalens in the second direction, according to the first incident wavelength and the second target focal length of the metalens in the second direction, a second target phase distribution corresponding to the metalens in the second direction is determined.

[0032] In a second aspect, the present application provides a superlens, the superlens comprising:

[0033] substrate;

[0034] At least one nanofin is disposed on the substrate, wherein the same nanofin has different sizes in different directions, and the metalens has multiple focal lengths.

[0035] In a possible implementation manner, the transmittance of the nanofin is greater than a transmittance threshold.

[0036] In a possible implementation manner, the heights of the plurality of nanofins are the same, and a ratio of the heights to the first incident wavelength is less than a first threshold.

[0037] In a possible implementation, the cross-section of the nanofin is elliptical or rectangular.

[0038] In a possible implementation, the size of the nanofin is determined by:

[0039] The size of the nanofins included in the superlens is determined according to the target focal length of the superlens.

[0040] In a third aspect, the present application provides an optical imaging system, comprising the metalens described in any one of the second aspects.

[0041] In a fourth aspect, the present application provides a device for determining metalens structure parameters, comprising: a processor and a memory, wherein the memory stores code, and the processor runs the code stored in the memory to execute the method as described in any one of the first aspects.

[0042] In a fifth aspect, the present application provides a computer-readable storage medium, in which computer-executable instructions are stored. When the computer-executable instructions are executed by a processor, they are used to implement any method as in the first aspect.

[0043] In a sixth aspect, the present application provides a computer program product, comprising a computer program, which implements any method in the first aspect when executed by a processor.

[0044] The present application provides a method for determining the structural parameters of a superlens, a superlens, and an optical imaging system. The superlens includes at least one nanofin. The method includes: determining the size of the nanofin included in the superlens according to the target focal length of the superlens, wherein the size of the same nanofin in different directions is different. Since the size of the same nanofin in different directions is different, polarization-dependent wavefront manipulation of the incident light in different directions can be achieved, and the function of multi-focus imaging of the superlens can be achieved. Compared with focusing imaging using traditional geometric optical lenses, the superlens of the present application has a simple structure, a small volume, and a high degree of integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0046] Figure 1It is a schematic diagram of the structure of a traditional optical lens;

[0047] Figure 2 A flow chart of a method for determining the structural parameters of a metalens provided in an embodiment of the present application;

[0048] Figure 3 A schematic diagram of a first target phase distribution provided in an embodiment of the present application;

[0049] Figure 4 A schematic diagram of a second target phase distribution provided in an embodiment of the present application;

[0050] Figure 5 A flow chart of a method for determining the size of a nanofin provided in an embodiment of the present application;

[0051] Figure 6 A schematic diagram of phase distribution corresponding to multiple preset sizes provided in an embodiment of the present application;

[0052] Figure 7 A schematic diagram of transmittance distribution corresponding to a plurality of preset sizes provided in an embodiment of the present application;

[0053] Figure 8 A schematic diagram of the distribution of elliptical nanofins on a dual-focus metalens provided in an embodiment of the present application;

[0054] Fig. 9 A schematic diagram of the corresponding electric field distribution when the polarization direction of the incident light is a first direction provided in an embodiment of the present application;

[0055] Fig.10 A schematic diagram of the corresponding electric field distribution when the polarization direction of the incident light is the second direction provided in an embodiment of the present application;

[0056] Fig.11 A schematic diagram of a first phase distribution of a metalens in a first direction provided in an embodiment of the present application;

[0057] Fig.12 A schematic diagram of a second phase distribution of a metalens in a second direction provided in an embodiment of the present application;

[0058] Fig.13 A schematic diagram of the structure of a metalens provided in an embodiment of the present application;

[0059] Fig.14 A schematic diagram of a device for determining the structural parameters of a metalens provided in an embodiment of the present application;

[0060] Fig.15 A schematic diagram of a device for determining the structural parameters of a superlens provided in an embodiment of the present application.

[0061] The above drawings have shown clear embodiments of the present application, which will be described in more detail later. These drawings and text descriptions are not intended to limit the scope of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0062] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0063] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with the relevant laws, regulations and standards of the relevant countries and regions, and provide corresponding operation entrances for users to choose to authorize or refuse.

[0064] In the visible light band, a lens that can focus and achieve zoom function is a very important basic optical element in the optical imaging system. In geometric optics, the conventional zoom solution usually adopts a cascade of multiple geometric lenses to achieve the purpose of zoom by adjusting the geometric parameters and distance of the traditional lens group.

[0065] Since the working principle of traditional lenses is to achieve focusing by changing the phase and polarization of incident light, and is limited by the refractive index of traditional geometric optical materials, if the size of optoelectronic devices needs to be reduced to the millimeter scale, a single geometric refractive lens will find it difficult to accumulate enough focusing distance to achieve the purpose of focusing. Focusing is usually achieved by increasing the thickness or the number of lenses, which makes the zoom system in the imaging system relatively large and complex in structure, with low integration, and a limited achievable zoom range. It is often impossible to simultaneously image at different focal points, which restricts its applicability and acceptance in portable and wearable devices.

[0066] Taking smartphones as an example, due to the large size and low integration of the zoom system, the camera in smartphones usually protrudes in order to have a sufficient focusing and imaging distance, which not only destroys the overall aesthetics of the smartphone, but also increases the processing and manufacturing cost of the product.

[0067] Figure 1is a schematic diagram of the structure of a traditional optical lens, refer to Figure 1 As shown, the lens group of the optical lens includes: a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, a fifth lens L5 and a sixth lens L6, which are arranged in sequence from the object side to the image side along the optical axis of the optical lens, i.e., the main optical axis.

[0068] The optical lens can be used for focusing, and the lenses in the lens group are easy to process, but their size is in the order of centimeters, their volume is large, and their integration is low.

[0069] In order to overcome the limitations of the above-mentioned traditional optical devices, the concept of superlens came into being. Superlens is an optical metasurface similar to a geometric optical lens that can realize lens imaging. Although the concept of superlens is novel, its function is similar to that of a traditional geometric optical lens. In terms of structure, unlike traditional geometric optical lenses that use changes in the distribution of refractive index surfaces to manipulate incident light, superlenses are often based on sub-wavelength artificial structural units to regulate parameters such as the phase and amplitude of the incident light, thereby realizing various functions similar to focusing imaging of geometric optical lenses.

[0070] Since the superlens uses artificial micro-nanostructures to precisely control light waves, it has an ultra-light and ultra-thin planar structure, which facilitates the realization of a highly compact and integrated imaging system within a limited volume. It is expected to replace the large and bulky geometric optical lens groups in traditional optical systems. Therefore, highly integrated and variable-focus superlenses are very important.

[0071] Based on this, the present application proposes a method for determining the structural parameters of a superlens, a superlens, and an optical imaging system. The superlens includes at least one nanofin, and the structural parameters of the superlens include the size of the nanofin. The size of the nanofin included in the superlens can be determined according to the preset target focal length. Among them, the same nanofin has different sizes in different directions to achieve polarization-dependent wavefront manipulation of the incident light in different directions, thereby realizing the multi-focus imaging function of the superlens. Compared with traditional geometric optical lenses, the superlens of the present application has a simple structure, a small size, and a high degree of integration.

[0072] The technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems are described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0073] Figure 2A flow chart of a method for determining a metalens structure parameter provided in an embodiment of the present application, wherein the metalens includes at least one nanofin. The method of this embodiment can be executed by a device for determining a metalens structure parameter, and can be implemented by hardware, software, or a combination of hardware and software. Figure 2 As shown, the method may include:

[0074] S201: Determine the size of the nanofins included in the superlens according to the target focal length of the superlens, wherein the size of the same nanofin in different directions is different.

[0075] In one implementation scenario, the target focal length of the metalens can be multiple, and the target focal lengths in different directions can be different.

[0076] The number of target focal lengths is the number of metalens focal points, and the number and size of the target focal lengths can be set according to actual needs.

[0077] In some embodiments, determining the size of the nanofins included in the superlens according to the target focal length of the superlens includes:

[0078] Determining a target phase distribution of the metalens in multiple directions according to the target focal lengths of the metalens in multiple directions;

[0079] The sizes of the nanofins included in the superlens in multiple directions are determined according to the target phase distribution of the superlens in multiple directions.

[0080] The multiple directions may be planes perpendicular to the transmission direction of the incident light and directions parallel to the planes.

[0081] The metalens has a corresponding target focal length in each direction. For any direction, the target phase distribution corresponding to the direction can be determined according to the target focal length in the direction until the target phase distribution of the metalens in multiple directions is obtained. The target phase distribution is used to characterize the target phase corresponding to different positions of the metalens.

[0082] In some embodiments, the multiple directions include a first direction and a second direction; and determining the target phase distribution of the metalens in the multiple directions according to the target focal length of the metalens in the multiple directions includes:

[0083] Based on a phase wavefront formula of the metalens in the first direction, determining a first target phase distribution corresponding to the metalens in the first direction according to a first incident wavelength and a first target focal length of the metalens in the first direction;

[0084] Based on the phase wavefront formula of the metalens in the second direction, according to the first incident wavelength and the second target focal length of the metalens in the second direction, a second target phase distribution corresponding to the metalens in the second direction is determined.

[0085] The first incident wavelength is the wavelength of the incident light. The phase wavefront formula of the metalens in the first direction can be referred to as follows:

[0086]

[0087] In the above formula (1), represents the first target phase distribution of the metalens in the first direction, f x represents the first target focal length, λ represents the first incident wavelength, and x and y are used to represent a certain position on the metalens.

[0088] The first incident wavelength may be the wavelength of the light emitted by the helium-neon laser, such as 633 nm, the first target focal length may be 100 μm, and the second target focal length may be 150 μm. Based on the above formula (1), the first target phase distribution of the superlens in the first direction may be obtained. For details, please refer to Figure 3 As shown, Figure 3 A schematic diagram of a first target phase distribution provided in an embodiment of the present application, Figure 3 The target phasex in is used to represent the first target phase distribution.

[0089] Similarly, the phase wavefront formula of the metalens in the second direction can be referred to as follows:

[0090]

[0091] In the above formula (2), represents the second target phase distribution of the metalens in the second direction, f y represents the first target focal length, λ represents the first incident wavelength, and x and y are used to represent a certain position on the metalens.

[0092] Based on the above formula (2), the second target phase distribution of the metalens in the second direction can be obtained. For details, please refer to Figure 4 As shown, Figure 4 A schematic diagram of a second target phase distribution provided in an embodiment of the present application, Figure 4 The targetphasey in is used to represent the second target phase distribution.

[0093] It can be seen from the above that the two phase wavefront formulas are independent of each other, so the target phase distribution in the two directions can be achieved through different refractive index distributions of the nanofins in the first direction and the second direction.

[0094] It should be noted that the above is only an exemplary description of the first target phase distribution in the first direction and the second target phase distribution in the second direction of the metalens determined by taking multiple directions including the first direction and the second direction as examples. If the multiple directions also include other directions, the target phase distribution corresponding to the other directions can be determined by referring to the above process of determining the first target phase distribution and the second target phase distribution, and the principles are basically the same, which will not be described in detail here.

[0095] In one implementation scenario, when determining the sizes of the nanofins included in the superlens in multiple directions based on the target phase distribution of the superlens in multiple directions, since different sizes have corresponding actual phase distributions, usually, the actual phase distribution will deviate from the target phase distribution to a certain extent. Therefore, the actual phase distribution with the smallest deviation from the target phase distribution can be determined, and the size corresponding to the actual phase distribution can be used as the size of the nanofin.

[0096] Since the sizes of the same nanofin in different directions are different, that is, the geometric structures of the nanofins in different directions are not isotropic, therefore, in each period of the superlens, the sizes of the nanofins in various directions can be precisely designed to achieve an asymmetric equivalent refractive index distribution of the superlens in the horizontal plane, so that the superlens can achieve different phase wavefront operations for different polarization states of the incident light, achieving a performance effect similar to that of crystal birefringence spectroscopy, that is, different phase offsets are introduced in multiple directions, that is, the nanofins introduce different phase offsets in multiple directions.

[0097] Still taking multiple directions including the first direction and the second direction as an example for explanation, the Jones matrix J(x, y) corresponding to the super lens can be written as:

[0098]

[0099] in, It is used to represent the phase shift introduced by the nanofin in the first direction. It is used to indicate the phase shift introduced by the nanofin in the second direction.

[0100] When the phase shift introduced by the nanofin in the first direction and the second direction can cover (0, 2π), polarization-dependent wavefront manipulation can be achieved in the first direction and the second direction, thereby achieving dual-focus focusing at two different positions of the metalens.

[0101] In one implementation scenario, when the first direction and the second direction are perpendicular to each other, the cross-section of the nanofin can be an ellipse or a rectangle. Taking an ellipse as an example, the first direction can represent the direction corresponding to the long axis of the ellipse, and the second direction can represent the direction corresponding to the short axis of the ellipse.

[0102] In one implementation scenario, in addition to the sizes of the nanofins in multiple directions, the structural parameters of the metalens may also include the height and period of the nanofins, etc. Among them, the height of the nanofin is related to the first incident wavelength. In order to effectively operate the incident light corresponding to the first incident wavelength, the height of the nanofin needs to be controlled to be within a roughly comparable range with the first incident wavelength.

[0103] The period of the nanofins is used to represent the distance between the centers of two adjacent nanofins in multiple directions. The period of the nanofins is also related to the first incident wavelength. Usually, the period is slightly smaller than the first incident wavelength.

[0104] The embodiment of the present application provides a method for determining the structural parameters of a superlens, wherein the superlens includes at least one nanofin. According to the target focal length of the superlens, the size of the nanofin included in the superlens is determined, wherein the size of the same nanofin is different in different directions. Since the size of the same nanofin is different in different directions, different equivalent refractive index distributions will be produced in different directions, so that polarization-dependent wavefront manipulation of the incident light in different directions can be achieved, realizing the function of multi-focal imaging of the superlens. Compared with focusing imaging using traditional geometric optical lenses, the structure is simple, the volume is small, and the integration is high.

[0105] Figure 5 A flow chart of a method for determining the size of a nanofin provided in an embodiment of the present application, refer to Figure 5 As shown, in some embodiments, determining the sizes of the nanofins included in the superlens in multiple directions according to the target phase distribution of the superlens in multiple directions includes:

[0106] S501: constructing a mapping relationship between nanofin size and phase, wherein the mapping relationship is used to represent phases corresponding to different preset sizes in multiple directions among at least two preset sizes.

[0107] Each preset size includes sizes in multiple directions. Different preset sizes have corresponding phases. The phase is the actual phase that can be achieved after the incident light is incident on the nanofin of the corresponding preset size, which can also be called the phase offset.

[0108] In some embodiments, constructing a mapping relationship between nanofin size and phase includes:

[0109] For any direction, determining the phase and transmittance corresponding to a plurality of preset sizes;

[0110] According to the transmittance, the at least two preset sizes that meet the preset requirement are determined from a plurality of preset sizes; wherein the preset requirement is: the transmittance is greater than a transmittance threshold.

[0111] In one implementation scenario, since there will be certain differences in the transmittance corresponding to different preset sizes, in order to reduce absorption loss and enhance the nanofin's binding of electromagnetic waves, the nanofin has a higher transmittance requirement. Therefore, when constructing a mapping relationship between nanofin size and phase, the transmittance corresponding to multiple preset sizes can be obtained, so as to optimize the multiple preset sizes according to the transmittance, remove one or more preset sizes with a transmittance less than a transmittance threshold, and obtain at least two preset sizes with a transmittance greater than the transmittance threshold.

[0112] In one implementation scenario, determining the phases and transmittances corresponding to a plurality of preset sizes includes:

[0113] Scanning is performed sequentially according to the preset step length to obtain phases and transmittances corresponding to multiple preset sizes within the preset size range.

[0114] In order to provide enough nanofins so that the phase they cover can satisfy the phase wavefront formula of the superlens in multiple directions, it is necessary to scan the nanofins in multiple directions to obtain the phases and transmittances corresponding to multiple preset sizes within the preset size range.

[0115] The nanofin has a corresponding preset size range in each direction, and the preset size ranges in different directions can be the same or different, and can be set according to actual needs. The preset compensation and the preset size range can also be set according to actual needs.

[0116] In one implementation scenario, the shape of the cross section of the nanofin is an ellipse, and when the wavelength of the incident light, i.e., the first incident wavelength, is 633 nm, the polarization direction of the incident light is parallel to the first direction, and the preset size ranges in the first direction and the second direction are both (0.05 μm, 0.25 μm), the obtained phase distribution and transmittance distribution can be respectively referred to Figure 6 and Figure 7 shown.

[0117] in, Figure 6 A schematic diagram of phase distribution corresponding to multiple preset sizes provided in an embodiment of the present application, Figure 7 A schematic diagram of transmittance distribution corresponding to multiple preset sizes provided in an embodiment of the present application.

[0118] Since the ellipse is symmetrical along the major axis and the minor axis, when the polarization direction of the incident light is parallel to the second direction, it is only necessary to Figure 6 The phase distribution shown is mirrored with a 45-degree oblique symmetry axis to obtain the phase distribution corresponding to the polarization direction parallel to the second direction. Figure 7The transmittance distribution shown is mirrored with a 45-degree oblique symmetry axis to obtain a transmittance distribution corresponding to when the polarization direction is parallel to the second direction.

[0119] Therefore, it can be seen that in the first direction and the second direction, except for a few resonance valleys, the transmittance corresponding to the other preset sizes is generally maintained above 0.4 within the preset size range, and within the preset size range, the phases corresponding to the two directions cover (-π, π). Therefore, under the premise of a single wavelength, there are enough nanofins within the preset size range to design a metalens that satisfies arbitrary wavefront phases in the first direction and the second direction.

[0120] S502: Determine the sizes of the nanofins included in the superlens in multiple directions according to the target phase distribution of the superlens in multiple directions and the mapping relationship.

[0121] The target phase distribution is used to characterize the target phase corresponding to different positions of the metalens. For any position, the target phase corresponding to the position can be determined according to the target phase distribution. At the same time, since the mapping relationship is used to represent the phases corresponding to different preset sizes in multiple directions in at least two preset sizes, the phase matching the target phase in the mapping relationship can be determined, and then the size corresponding to the phase can be determined according to the mapping relationship. The determined size is the size of the nanofin at the position, and this process is repeated until the size of each nanofin in the metalens is obtained.

[0122] After determining the size of each nanofin in multiple directions, the structural distribution of the superlens can be obtained. Still taking the multiple directions including the first direction and the second direction as an example, the cross-sectional shape of the nanofin is an ellipse. At this time, the superlens has two focal points, and the two focal lengths can be 150μm and 100μm respectively. At this time, the diameter of the superlens can be 640μm. After determining the size of each nanofin in the first direction and the second direction, the structural distribution of the superlens can be obtained. For details, please refer to Figure 8 As shown, Figure 8 A schematic diagram of the distribution of elliptical nanofins on a dual-focus metalens provided in an embodiment of the present application.

[0123] Polarized light with the first polarization direction and the second polarization direction is used as the incident light, and the electric field distribution of the incident light passing through the double focus of the metalens is obtained. For details, please refer to Fig. 9 and Fig.10 .

[0124] in, Fig. 9 A schematic diagram of the corresponding electric field distribution when the polarization direction of the incident light is the first direction provided in an embodiment of the present application is as follows: Fig. 9 It can be seen that when the polarization direction of the incident light is the first direction and is incident on the superlens, there will be a focusing effect at about 100 μm, and the focal length f1 is 100 μm.

[0125] Fig.10 A schematic diagram of the corresponding electric field distribution when the polarization direction of the incident light is the second direction provided in an embodiment of the present application is as follows: Fig.10 It can be seen that when the polarization direction of the incident light is the second direction and is incident on the superlens, there will be a focusing effect at about 150 μm, and the focal length f2 is 150 μm.

[0126] As can be seen from the above, by adjusting the polarization direction of the incident light, the focus energy ratio between the two focal points can be adjusted, and focal energy redistribution can be achieved at different focal lengths. In one implementation scenario, the incident light is linearly polarized light.

[0127] In summary, a mapping relationship between the size of the nanofin and the phase is constructed, and the size of the nanofins included in the superlens in multiple directions is determined according to the target phase distribution of the superlens in multiple directions and the mapping relationship, so as to obtain a superlens with multiple focal points. At the same time, when constructing the mapping relationship, at least two preset sizes with a transmittance greater than a transmittance threshold are determined from multiple preset sizes according to the transmittance, so as to meet the high transmittance requirements of the nanofin, reduce absorption losses, and enhance the binding of the nanofin to electromagnetic waves.

[0128] In one or more embodiments of the present application, the multiple directions include a first direction and a second direction; and determining the sizes of the nanofins included in the superlens in the multiple directions according to the target phase distribution of the superlens in the multiple directions and the mapping relationship includes:

[0129] The sizes of the nanofins included in the superlens in the first direction and the second direction are determined according to the first target phase distribution of the superlens in the first direction, the second target phase distribution in the second direction, and the mapping relationship.

[0130] When the multiple directions include a first direction and a second direction, correspondingly, the target phase distribution of the metalens in the multiple directions includes a first target phase distribution in the first direction and a second target phase distribution in the second direction.

[0131] The first target phase distribution represents the first target phases corresponding to different positions in the first direction, and the second target phase distribution is used to represent the second target phases corresponding to different positions in the second direction.

[0132] At this time, the mapping relationship includes phases corresponding to different preset sizes in the first direction and phases corresponding to different preset sizes in the second direction among at least two preset sizes.

[0133] In some embodiments, determining the sizes of the nanofins included in the metalens in the first direction and the second direction according to the first target phase distribution of the metalens in the first direction, the second target phase distribution in the second direction, and the mapping relationship comprises:

[0134] For any nanofin, a first target phase corresponding to the position of the nanofin is determined according to the first target phase distribution, a second target phase corresponding to the position of the nanofin is determined according to the second target phase distribution, and sizes of the nanofin in the first direction and the second direction are determined according to the first target phase, the second target phase and the mapping relationship.

[0135] Since the superlens includes multiple nanofins, and the multiple nanofins are located at different positions of the superlens, the first target phase distribution is used to characterize the first target phases corresponding to different positions in the first direction. Therefore, for any nanofin, once the position is determined, the first target phase corresponding to the position can be determined in the first target phase distribution.

[0136] Similarly, the second target phase distribution is used to characterize the second target phases corresponding to different positions in the second direction. Therefore, when a position is determined, the second target phase corresponding to the position can also be determined in the second target phase distribution.

[0137] In one implementation scenario, the mapping relationship includes at least two preset sizes, where different preset sizes correspond to a first phase in the first direction and a second phase in the second direction; and determining the size of the nanofin in the first direction and the second direction according to the first target phase, the second target phase and the mapping relationship includes:

[0138] For each preset size, calculating a phase difference corresponding to the preset size, wherein the phase difference is used to characterize a difference between the first target phase and the first phase and a difference between the second target phase and the second phase;

[0139] According to the phase difference corresponding to each preset size, a size matching the first target phase and the second target phase is determined from a plurality of preset sizes.

[0140] In one implementation scenario, for each preset size, calculating the phase difference corresponding to the preset size includes:

[0141] For each preset size, determining a first difference between a first phase corresponding to the preset size in the first direction and the first target phase, and a second difference between a second phase corresponding to the preset size in the second direction and the second target phase;

[0142] The phase difference is determined according to the first difference and the second difference.

[0143] In one implementation scenario, the degree of difference between the first target phase and the first phase can be characterized by a difference between the two, i.e., a first difference. When the first difference is smaller, it indicates that the degree of difference between the first target phase and the first phase is smaller; when the first difference is larger, it indicates that the degree of difference between the first target phase and the first phase is larger.

[0144] Similarly, the degree of difference between the second target phase and the second phase may also be represented by a difference between the two, that is, a second difference. In this case, the phase difference may be the sum of the first difference and the second difference.

[0145] In another implementation scenario, the degree of difference between the first target phase and the first phase can be characterized by a ratio of the first difference value to the first reference value. The first reference value can be the first target phase, the first phase, or the average value of the first target phase and the first phase, etc., which is not limited in this application.

[0146] Similarly, the difference between the second target phase and the second phase can be characterized by the ratio of the second difference to the second reference value. The second reference value can be the second target phase, the second phase, or the average value of the second target phase and the second phase, etc., which is not limited in this application.

[0147] At this time, the phase difference may be the sum of the ratio of the first difference value to the first reference value and the ratio of the second difference value to the second reference value.

[0148] In another implementation scenario, the difference between the first target phase and the first phase may also be represented by the square of the first difference, and the difference between the second target phase and the second phase may also be represented by the square of the second difference.

[0149] The above only exemplarily illustrates three methods for calculating the phase difference. The phase difference may also be calculated by other methods, which are not limited in the present application.

[0150] In one implementation scenario, after determining the phase difference corresponding to each preset size, when determining the size that matches the first target phase and the second target phase, among multiple preset sizes, the first phase and the second phase corresponding to the smallest deviation from the first target phase and the second target phase, that is, the first phase and the second phase when the phase difference is the smallest, can be used as the phase that matches the first target phase and the second target phase, and then the preset sizes corresponding to the first phase and the second phase can be used as the sizes of the nanofins at that position.

[0151] The above is explained with a nanofin in a superlens. For each nanofin, it is necessary to obtain the first phase and the second phase that match the first target phase and the second target phase corresponding to the position of the nanofin, which can be obtained as follows: Fig.11 and Fig.12 The actual phase distribution shown is based on the preset size corresponding to each phase and the second phase as the size of the nanofin at that position.

[0152] in, Fig.11 A schematic diagram of a first phase distribution of a metalens in a first direction provided in an embodiment of the present application, Fig.11 The real phasex in is used to represent the first phase distribution; Fig.12 A schematic diagram of a second phase distribution of a metalens in a second direction provided in an embodiment of the present application, Fig.12 The real phasey in is used to represent the second phase distribution.

[0153] It should be noted that the first phase and the second phase are both actual phases corresponding to the incident light after it enters the nanofin.

[0154] In summary, when the multiple directions include a first direction and a second direction, the sizes of each nanofin in the first direction and the second direction can be determined according to the first target phase distribution of the superlens in the first direction, the second target phase distribution in the second direction, and the mapping relationship to obtain a superlens with dual focal points.

[0155] Fig.13 A schematic diagram of the structure of a metalens provided in an embodiment of the present application, referring to Fig.13 As shown, the metalens includes:

[0156] Substrate 10;

[0157] At least one nanofin 20 is disposed on the substrate 10 , wherein the same nanofin 20 has different sizes in different directions, and the superlens has multiple focal lengths.

[0158] In one implementation scenario, in order to reduce energy loss caused by reflection when incident light enters the substrate 10, silicon dioxide with a lower refractive index may be selected for the substrate 10. The refractive index of silicon dioxide is 1.46.

[0159] In some embodiments, the structure of the substrate 10 may be a cubic structure.

[0160] In some embodiments, the transmittance of the nanofin 20 is greater than a transmittance threshold.

[0161] In one implementation scenario, in order to reduce absorption loss, confine electromagnetic waves in the nanofin 20 waveguide, and reduce the coupling of electromagnetic fields between nanowaveguides, the material of the nanofin 20 can be titanium dioxide with a high refractive index, and the refractive index of titanium dioxide is 2.49.

[0162] In another implementation scenario, in addition to titanium dioxide, the material of the nano-fin 20 may also be silicon nitride with a high refractive index.

[0163] Since the substrate 10 and the nano-fins 20 in the superlens are made of all-dielectric materials such as silicon dioxide and titanium dioxide, the processing difficulty is reduced.

[0164] In some embodiments, the heights of the plurality of nanofins 20 are the same, and a ratio of the heights to the first incident wavelength is less than a first threshold.

[0165] The first incident wavelength is the wavelength of the incident light incident to the metalens. The ratio of the height of the nanofin 20 to the first incident wavelength is less than the first threshold, that is, the height of the nanofin 20 and the first incident wavelength are within a roughly comparable range, so as to effectively regulate the incident light corresponding to the first incident wavelength.

[0166] The height of the nanofin 20 is Fig.13 The specific height of H shown in can be set according to actual needs. In one implementation scenario, the first incident wavelength is 633 nm visible light emitted by a helium-neon laser, and the height of the nanofin 20 can be set to 1 μm.

[0167] Since the structure of the metalens of the present application is a single-layer structure, the structure is simple, and the dual-focus function that the traditional geometric optical lens needs to have a thickness of centimeters can be realized with a thickness of micrometers. In most imaging systems, the thickness of micrometers is almost negligible. Therefore, the metalens of the present application can be applied to highly integrated focal imaging systems due to its advantages such as compact size and ultra-thinness. At the same time, the metalens of the present application has a small processing volume, is easy to manipulate, and is not easily disturbed.

[0168] In some embodiments, the cross-section of the nanofin 20 is elliptical or rectangular.

[0169] Fig.13 It is exemplarily shown that the cross-section of the nanofin 20 is in the shape of an ellipse, Dx is used to represent the major axis of the ellipse, and Dy is used to represent the minor axis of the ellipse. In this case, the structure of the nanofin 20 is an elliptical column. Fig.13 Px and Py are also shown, where Px is used to represent the period in the long axis direction, that is, the distance between the centers of two adjacent nanofins 20 in the long axis direction, and Py is used to represent the period in the short axis direction, that is, the distance between the centers of two adjacent nanofins 20 in the short axis direction.

[0170] In one implementation scenario, when the cross-sectional shape of the nanofin 20 is elliptical, the same nanofin 20 has different sizes in multiple directions. At this time, the multiple directions may include the major axis direction and the minor axis direction of the ellipse, that is, the sizes of the major axis and the minor axis are different. At this time, the major axis direction and the minor axis direction will produce different equivalent refractive index distributions, so that polarization-dependent wavefront manipulation of the incident light can be achieved in two directions, realizing the dual-focus imaging function of the superlens, and the superlens has two focal lengths.

[0171] In another implementation scenario, when the cross-section of the nanofin 20 is a rectangle, the multiple directions include two directions corresponding to the length and width of the rectangle. Since the length and width of the rectangle are different, the polarization-dependent wavefront manipulation of the incident light can also be achieved in the two directions corresponding to the length and width, thereby realizing the dual-focus imaging function of the superlens. At this time, the superlens has two focal lengths.

[0172] In some embodiments, the size of the nanofin can be determined as follows:

[0173] The size of the nanofins included in the superlens is determined according to the target focal length of the superlens.

[0174] The specific process of determining the size of each nanofin in multiple directions may refer to the above embodiment, and its implementation principle and technical effect are similar, which will not be described in detail here.

[0175] The embodiment of the present application provides a superlens, including a substrate 10 and at least one nanofin 20, wherein the nanofin 20 is located on the substrate 10. The same nanofin 20 has different sizes in multiple directions, and the superlens has multiple focal lengths. Compared with using a geometric optical lens to achieve multi-focal imaging, the superlens of the present application has a simple structure, is easy to adjust, and has a high degree of integration.

[0176] An embodiment of the present application provides an optical imaging system, comprising the metalens described in any of the above embodiments.

[0177] Fig.14 A schematic diagram of a device for determining structural parameters of a superlens provided in an embodiment of the present application, wherein the superlens includes at least one nanofin. Fig.14 As shown, an embodiment of the present application provides a device 1400 for determining a metalens structure parameter, which may include a determination module 1401.

[0178] The determination module 1401 is used to determine the size of the nanofins included in the superlens according to the target focal length of the superlens, wherein the size of the same nanofin in different directions is different.

[0179] The device of this embodiment can be used to execute the method embodiment shown above. Its implementation principle and technical effects are similar and will not be described in detail here.

[0180] Fig.15 A schematic diagram of a device for determining the structural parameters of a metalens provided in an embodiment of the present application. Fig.15 As shown, an embodiment of the present application provides a device 1500 for determining a metalens structure parameter, including a processor 1501 and a memory 1502 , wherein the processor 1501 and the memory 1502 are connected via a bus 1503 .

[0181] In the specific implementation process, the memory 1502 stores codes, and the processor 1501 runs the codes stored in the memory 1502 to execute the method of the above method embodiment.

[0182] The specific implementation process of the processor 1501 can be found in the above method embodiment, and its implementation principle and technical effect are similar, so this embodiment will not be repeated here.

[0183] In the above Fig.15 In the illustrated embodiment, it should be understood that the processor 1501 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), etc. A general-purpose processor may be a microprocessor or any conventional processor. The steps of the method disclosed in the invention may be directly implemented as being executed by a hardware processor, or may be executed by a combination of hardware and software modules in the processor.

[0184] The memory 1502 may include a high-speed RAM memory, and may also include a non-volatile storage NVM, such as at least one disk storage.

[0185] The bus 1503 may be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. The bus may be divided into an address bus, a data bus, a control bus, etc. For ease of representation, the bus in the drawings of the present application is not limited to only one bus or one type of bus.

[0186] An embodiment of the present application provides a computer-readable storage medium, in which computer-executable instructions are stored. When the computer-executable instructions are executed by a processor, they are used to implement the method of the above method embodiment.

[0187] The computer-readable storage medium mentioned above can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic disk or optical disk. The readable storage medium can be any available medium that can be accessed by a general or special-purpose computer.

[0188] An exemplary readable storage medium is coupled to a processor so that the processor can read information from the readable storage medium and write information to the readable storage medium. Of course, the readable storage medium can also be a component of the processor. The processor and the readable storage medium can be located in an application specific integrated circuit (Application Specific Integrated Circuits, referred to as: ASIC). Of course, the processor and the readable storage medium can also exist in the device as discrete components.

[0189] An embodiment of the present application provides a computer program product, including a computer program. When the computer program is executed by a processor, the method provided in any embodiment of the present application is implemented.

[0190] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the invention disclosed herein. The present application is intended to cover any modification, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary techniques in the art that are not disclosed in the present application. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present application are indicated by the following claims.

[0191] It should be understood that the present application is not limited to the precise structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A method for determining the structural parameters of a metalens, characterized in that: The metalens comprises at least one nanofin; the method comprises: The size of the nanofins included in the superlens is determined according to the target focal length of the superlens, wherein the size of the same nanofin in different directions is different.

2. The method according to claim 1, characterized in that Determining the size of the nanofins included in the superlens according to the target focal length of the superlens includes: Determining a target phase distribution of the metalens in multiple directions according to the target focal lengths of the metalens in multiple directions; The sizes of the nanofins included in the superlens in multiple directions are determined according to the target phase distribution of the superlens in multiple directions.

3. The method according to claim 2, characterized in that The step of determining the sizes of the nanofins included in the superlens in multiple directions according to the target phase distribution of the superlens in multiple directions comprises: Constructing a mapping relationship between nanofin size and phase, wherein the mapping relationship is used to represent phases corresponding to different preset sizes in multiple directions among at least two preset sizes; According to the target phase distribution of the superlens in multiple directions and the mapping relationship, the sizes of the nanofins included in the superlens in multiple directions are determined.

4. The method according to claim 3, characterized in that The multiple directions include a first direction and a second direction; and determining the sizes of the nanofins included in the superlens in the multiple directions according to the target phase distribution of the superlens in the multiple directions and the mapping relationship, including: The sizes of the nanofins included in the superlens in the first direction and the second direction are determined according to the first target phase distribution of the superlens in the first direction, the second target phase distribution in the second direction, and the mapping relationship.

5. The method according to claim 4, characterized in that The determining, according to the first target phase distribution of the metalens in the first direction, the second target phase distribution in the second direction, and the mapping relationship, the sizes of the nanofins included in the metalens in the first direction and the second direction, comprises: For any nanofin, a first target phase corresponding to the position of the nanofin is determined according to the first target phase distribution, a second target phase corresponding to the position of the nanofin is determined according to the second target phase distribution, and sizes of the nanofin in the first direction and the second direction are determined according to the first target phase, the second target phase and the mapping relationship.

6. The method according to claim 5, characterized in that The mapping relationship includes, among at least two preset sizes, a first phase corresponding to different preset sizes in the first direction and a second phase corresponding to different preset sizes in the second direction; The determining the size of the nanofin in the first direction and the second direction according to the first target phase, the second target phase and the mapping relationship comprises: For each preset size, calculating a phase difference corresponding to the preset size, wherein the phase difference is used to characterize a difference between the first target phase and the first phase and a difference between the second target phase and the second phase; According to the phase difference corresponding to each preset size, a size matching the first target phase and the second target phase is determined from a plurality of preset sizes.

7. The method according to claim 6, characterized in that For each preset size, calculating the phase difference corresponding to the preset size includes: For each preset size, determining a first difference between a first phase corresponding to the preset size in the first direction and the first target phase, and a second difference between a second phase corresponding to the preset size in the second direction and the second target phase; The phase difference is determined according to the first difference and the second difference.

8. The method according to claim 3, characterized in that The step of constructing a mapping relationship between the nanofin size and the phase includes: For any direction, determining the phase and transmittance corresponding to a plurality of preset sizes; According to the transmittance, the at least two preset sizes that meet the preset requirement are determined from a plurality of preset sizes; wherein the preset requirement is: the transmittance is greater than a transmittance threshold.

9. The method according to claim 8, characterized in that The determining of phases and transmittances corresponding to a plurality of preset sizes includes: Scanning is performed sequentially according to the preset step length to obtain phases and transmittances corresponding to multiple preset sizes within the preset size range.

10. The method according to claim 2, characterized in that The multiple directions include a first direction and a second direction; and determining the target phase distribution of the metalens in the multiple directions according to the target focal lengths of the metalens in the multiple directions includes: Based on a phase wavefront formula of the metalens in the first direction, determining a first target phase distribution corresponding to the metalens in the first direction according to a first incident wavelength and a first target focal length of the metalens in the first direction; Based on the phase wavefront formula of the metalens in the second direction, according to the first incident wavelength and the second target focal length of the metalens in the second direction, a second target phase distribution corresponding to the metalens in the second direction is determined.

11. A superlens, characterized in that: The metalens comprises: substrate; At least one nanofin is disposed on the substrate, wherein the same nanofin has different sizes in different directions, and the metalens has multiple focal lengths.

12. The metalens according to claim 11, characterized in that The transmittance of the nanofin is greater than a transmittance threshold.

13. The metalens according to claim 11, characterized in that The heights of the plurality of nanofins are the same, and a ratio of the heights to the first incident wavelength is less than a first threshold.

14. The metalens according to claim 11, characterized in that The cross section of the nano-fin is in an elliptical or rectangular shape.

15. The metalens according to any one of claims 11 to 14, characterized in that: The size of the nanofin is determined as follows: The size of the nanofins included in the superlens is determined according to the target focal length of the superlens.

16. An optical imaging system, characterized in that: The metalens comprising the metalens according to any one of claims 11 to 15.

17. A device for determining the structural parameters of a metalens, comprising: A processor and a memory, wherein codes are stored in the memory, and wherein the processor runs the codes stored in the memory to execute the method according to any one of claims 1 to 10.

18. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer-executable instructions, which are used to implement the method according to any one of claims 1 to 10 when executed by a processor.

19. A computer program product, comprising a computer program, wherein when the computer program is executed by a processor, the method according to any one of claims 1 to 10 is implemented.

Images