An imaging method and an imaging system

Abstract

The present invention provides an imaging method, the method comprising the following steps: providing a metalens, including an illumination modulation region in the middle of the metalens and a detection modulation region surrounding the illumination modulation region; in the illumination optical path, guiding an illumination beam to the illumination modulation region of the metalens via an optical fiber, so as to focus on the object to be measured through the illumination modulation region, in the detection optical path, receiving, through the detection modulation region of the metalens, a beam reflected from the object to be measured and containing information of the object to be measured, and guiding the beam containing information of the object to be measured to a detector via an optical fiber, and then performing imaging. The present invention also relates to a corresponding imaging system. Through the method and system of the present invention, the diffraction limit can be broken through to achieve super-resolution imaging.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging, and in particular, to an imaging method and system. Background Art

[0002] Common resolution improvement techniques, such as Stimulated Emission Depletion (STED) super-resolution imaging technology, utilize the stimulated emission effect. The fluorescence molecules are excited by the excitation light, and then the depletion light is used to cause some electrons in the periphery of the excitation spot to return to the ground state by stimulated emission, and the remaining excited electrons in the center of the excitation spot return to the ground state by spontaneous fluorescence. The photons received by the detector are generated by the fluorescence sample in the central part of the excitation spot through spontaneous fluorescence, reducing the fluorescence emission area and improving the system resolution.

[0003] For the above-mentioned existing resolution improvement techniques, two irradiation lights are required to reduce the excitation sample area, and at least two light sources are needed. In addition, strict timing control of the emission time difference between the excitation light and the depletion light is required. Therefore, there is a need to maintain or even improve the accuracy of super-resolution imaging while simplifying the system. Summary of the Invention

[0004] To solve the above problems, the purpose of the embodiments of the present invention is to provide an imaging method and an imaging system.

[0005] In the first aspect of the present invention, an imaging method is provided, including:

[0006] Providing a metalens, the metalens including an illumination modulation region in the middle of the metalens and a detection modulation region surrounding the illumination modulation region;

[0007] In the illumination optical path, guiding the illumination beam to the illumination modulation region of the metalens via an optical fiber, so as to be focused on the object to be measured through the illumination modulation region,

[0008] In the detection optical path, receiving the beam reflected from the object to be measured and containing the information of the object to be measured through the detection modulation region of the metalens,

[0009] Guiding the beam containing the information of the object to be measured to the detector via an optical fiber, and then performing imaging,

[0010] wherein the phase distributions of the illumination modulation region and the detection modulation region of the metalens are designed such that the point spread function in the illumination optical path is modulated by the point spread function in the detection optical path, so as to be able to adjust the full width at half maximum of the overall point spread function formed by the detection modulation region and the illumination modulation region.

[0011] In an embodiment of the imaging method of the present invention, the illumination beam is a non-diffracting beam.

[0012] In an embodiment of the imaging method of the present invention, the illumination beam is a Bessel beam.

[0013] In an embodiment of the imaging method of the present invention, the point spread function in the illumination optical path is modulated by the point spread function of the detection optical path, so that the full width at half maximum of the overall point spread function formed by the detection modulation region and the illumination modulation region is lower than the full width at half maximum of the point spread function of the illumination modulation region.

[0014] In an embodiment of the imaging method of the present invention, the phase distribution of the illumination modulation region satisfies:

[0015]

[0016] NA = sin(θ)

[0017] where x and y are the coordinate positions on the surface of the metalens, θ is the deflection angle of the metalens for the parallel incident beam, and λ is the wavelength of the illumination beam.

[0018] In an embodiment of the imaging method of the present invention, the phase distribution of the detection modulation region satisfies:

[0019]

[0020] where

[0021]

[0022]

[0023] where n represents the order, and φ is the azimuth angle, which is used to characterize the vortex phase of the outgoing light in the detection modulation region.

[0024] In an embodiment of the imaging method of the present invention, the phase distribution of the detection modulation region satisfies:

[0025]

[0026] where

[0027]

[0028]

[0029] where n represents the order, and φ is the azimuth angle, which is used to characterize the vortex phase of the outgoing light in the detection modulation region.

[0030] In an embodiment of the imaging method of the present invention, n = 1, 2, or 3.

[0031] In an embodiment of the imaging method of the present invention, the method further includes setting constraint conditions through deep learning to design the phase distribution of the detection modulation region of the superlens.

[0032] In a second aspect of the present invention, an imaging system is provided, which is used to implement the imaging method according to the present invention, and the system includes:

[0033] A light source, a superlens, an incident optical fiber, a receiving optical fiber, and a detector;

[0034] The superlens includes an illumination modulation region and a detection modulation region surrounding the illumination modulation region;

[0035] The incident optical fiber connects the light source to the superlens,

[0036] The receiving optical fiber connects the superlens to the detector.

[0037] In an embodiment of the imaging system of the present invention, the superlens is an adjustable superlens, and the adjustable superlens can change the phase distribution of the illumination modulation region and / or the detection modulation region by applying an external excitation.

[0038] In an embodiment of the imaging system of the present invention, the external excitation includes electrical excitation, thermal excitation, optical excitation, and mechanical excitation.

[0039] In the present invention, due to the design of the imaging method and imaging system of the present invention, the superlens is used to adjust the full width at half maximum of the total point spread function, so that super-resolution imaging can be achieved with only a single light source, while significantly reducing the complexity, volume, weight, and cost of the system.

[0040] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following specific preferred embodiments are given, and in conjunction with the accompanying drawings, the detailed description is as follows. Description of the Drawings

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will explain the embodiments of the present invention in detail with reference to the accompanying drawings. Obviously, the drawings in the following description are only some embodiments of the present invention, and the present invention is not limited to the embodiments shown. For those of ordinary skill in the art, other implementation schemes can be obtained according to the attached drawings without creative efforts.

[0042] Figure 1 A schematic flowchart of an embodiment of an imaging method provided by the present invention is shown;

[0043] Figure 2Shows a schematic diagram of the overall structure of an embodiment of an imaging system provided by the present invention;

[0044] Figure 3 Shows a top view of the metalens 10 provided by the embodiment of the present invention;

[0045] Figure 4 Shows a point spread function diagram (zeroth-order Bessel function) of the illumination modulation region of an embodiment of an imaging method provided by the present invention;

[0046] Figure 5 Shows a point spread function diagram (sum of zeroth-order Bessel function and second-order Bessel function) of the detection modulation region of an embodiment of an imaging method provided by the present invention;

[0047] Figure 6 Shows a total point spread function diagram of an embodiment of an imaging method provided by the present invention (the illumination modulation region is a zeroth-order Bessel function, and the detection modulation region is the sum of a zeroth-order Bessel function and a second-order Bessel function);

[0048] Figure 7 Shows a point spread function diagram (sum of zeroth-order Bessel function and third-order Bessel function) of the detection modulation region of an embodiment of another imaging method provided by the present invention;

[0049] Figure 8 Shows a total point spread function diagram of an embodiment of an imaging method provided by the present invention (the illumination modulation region is a zeroth-order Bessel function, and the detection modulation region is the sum of a zeroth-order Bessel function and a third-order Bessel function);

[0050] Figure 9 Shows a point spread function diagram (difference between zeroth-order Bessel function and first-order Bessel function) of the detection modulation region of an embodiment of another imaging method provided by the present invention;

[0051] Figure 10 Shows a total point spread function diagram of an embodiment of an imaging method provided by the present invention (the illumination modulation region is a zeroth-order Bessel function, and the detection modulation region is the difference between a zeroth-order Bessel function and a first-order Bessel function);

[0052] Figure 11 Shows a schematic diagram of the arrangement of the meta-units of the metalens 10 provided by the embodiment of the present invention;

[0053] Figure 12 Shows a structural diagram of the nanostructures in the metalens 10 provided by the embodiment of the present invention;

[0054] Figure 13 Shows a structural diagram of an embodiment of the tunable metalens provided by the embodiment of the present invention.

[0055] List of reference numerals:

[0056] 10 - Superlens, 11 - Irradiation modulation region, 12 - Detection modulation region, 111 - First electrode, 112 - Second electrode, 113 - Connection layer, 114 - Nanostructure, 115 - First insulating layer, 116 - Second insulating layer, 117 - Filler, 211 - Substrate, 20 - Incident optical fiber, 30 - Receiving optical fiber, 40 - Detector, 50 - Light source. Detailed implementation manners

[0057] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0058] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0059] In the present invention, unless otherwise clearly specified and defined, the terms "mounted", "connected", "connected with", "fixed" and other terms should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0060] Traditional resolution improvement techniques, for example, in Stimulated Emission Depletion (STED) microscopy, multiple light sources are required. At the same time, the emission time difference between the excitation light and the depletion light needs to be strictly controlled. Therefore, the system composition structure and the adjustment method are complex.

[0061] In view of this, the present application proposes an imaging method.

[0062] As Figure 1As shown, the present invention proposes an imaging method, which includes:

[0063] Providing a metalens 10, the metalens 10 includes an illumination modulation region 11 in the middle of the metalens 10 and a detection modulation region 12 surrounding the illumination modulation region 11;

[0064] In the illumination optical path, guiding the illumination beam to the illumination modulation region 11 of the metalens 10 via an optical fiber, so as to be focused on the object to be measured through the illumination modulation region 11,

[0065] In the detection optical path, receiving, through the detection modulation region 12 of the metalens 10, the beam reflected from the object to be measured and containing the information of the object to be measured,

[0066] Guiding the beam containing the information of the object to be measured to a detector via an optical fiber, and then performing super-resolution imaging,

[0067] Wherein the phase distributions of the illumination modulation region 11 and the detection modulation region 12 of the metalens 10 are designed such that the point spread function in the illumination optical path is modulated by the point spread function in the detection optical path, so as to be able to adjust the full width at half maximum of the overall point spread function formed by the detection modulation region 12 and the illumination modulation region 11.

[0068] In the method of the present invention, the core idea is: using the metalens 10 to achieve zoned illumination and detection, and by designing the phase distributions of the illumination modulation region 11 and the detection modulation region 12, it is possible to specifically adjust the full width at half maximum of the overall point spread function formed by the detection modulation region 12 and the illumination modulation region 11, so as to achieve super-resolution imaging and at the same time improve the lateral resolution.

[0069] In a preferred embodiment of the present application, the illumination beam is a non-diffracting beam, preferably a Bessel beam, where the physical meaning of the non-diffracting beam is a beam with a small central spot diameter and does not change with the propagation distance.

[0070] Here, a Bessel beam can be understood as a wave whose amplitude is described by the Bessel function of the first kind. It is characterized by no diffraction, the ability to self-recover after passing through an obstacle, and a large diffraction distance. An ideal Bessel beam shows that the transverse distribution of the light intensity remains unchanged, and its longitudinal distribution also remains unchanged. Among them, the light intensity distribution of an ideal zero-order Bessel beam shows a central spot and multiple concentric rings on the cross-section perpendicular to the propagation direction. An ideal Bessel beam with an infinite cross-sectional area requires infinite energy to achieve, which is physically infeasible today. Therefore, the ideal Bessel beam only has theoretical significance to a large extent. In practical applications, only an approximate Bessel beam can be obtained, and its non-diffraction characteristic is manifested as the light intensity and size of the central spot of the beam remaining basically unchanged within a certain finite propagation distance range. Therefore, for an approximate Bessel beam, only when the transverse dimension of the obstacle is smaller than the beam width can it recover to the original transverse light intensity distribution. The reason why the approximate Bessel beam exhibits such characteristics is that compared with the ideal Bessel beam, the finite beam width of the approximate Bessel beam limits the energy. The fact that the central spot of the Bessel beam maintains a constant intensity and size is the result of the diffraction superposition of the surrounding annular lobes. The more side lobes the Bessel beam has, the greater the diffraction propagation distance.

[0071] It can be seen from this that although the Bessel beam has self-healing properties, due to its own characteristics, it has relatively strong side lobes, which will excite signals in non-focal planes, reduce the image contrast and signal-to-noise ratio, and degrade the image quality.

[0072] Therefore, through the phase design of the superlens of the present application, the point spread function in the illumination optical path is modulated by the point spread function of the detection optical path, so as to be able to adjust the full width at half maximum of the overall point spread function formed by the detection modulation region 12 and the illumination modulation region 11. Preferably, the full width at half maximum of the overall point spread function formed by the detection modulation region 12 and the illumination modulation region 11 is lower than the full width at half maximum of the point spread function of the illumination modulation region 11. Thus, the side lobes of the Bessel beam can be suppressed, and then super-resolution of the image can be achieved.

[0073] Here, it is first necessary to explain that: in the embodiments of the present application and each alternative embodiment, the provided metalens is a metasurface, and the metasurface is a sub-wavelength artificial nanostructured film, which can modulate the amplitude, phase, and polarization of incident light through the nanostructure units provided thereon. It should be noted that the nanostructure can be understood as a sub-wavelength structure containing all-dielectric or plasmonic that can cause phase mutations, and the nanostructure unit is a structural unit centered on each nanostructure obtained by dividing the metalens. In the metalens, the nanostructures are periodically arranged on the substrate, and the nanostructures in each period form a superstructure unit. The superstructure unit is a closely packed pattern, such as a regular quadrilateral, a regular hexagon, etc. Each period contains a group of nanostructures, and nanostructures can be provided at the vertices and / or centers of the superstructure unit. In the case where the superstructure unit is a regular hexagon, at least one nanostructure is provided at each vertex and center position of the regular hexagon. Or, in the case where it is a square, at least one nanostructure is provided at each vertex and center position of the square. Ideally, the superstructure unit should be the nanostructures arranged at the vertices and centers of a hexagon, or the nanostructures arranged at the vertices and centers of a square. It should be understood that in actual products, due to the limitation of the shape of the metalens, there may be a lack of nanostructures at the edge of the metalens, making it not satisfy a complete hexagon / square. Specifically, as Figure 11 shown, the superstructure unit is formed by arranging nanostructures according to a rule, and several superstructure units are arranged in an array to form a metasurface structure.

[0074] As Figure 11 (1) shows an embodiment, the superstructure unit includes a central nanostructure and 6 peripheral nanostructures that are equidistant from it. Each peripheral nanostructure is evenly distributed along the circumference, forming a regular hexagon, and can also be understood as the combination of multiple regular triangles composed of nanostructures.

[0075] As Figure 11 (2) shows an embodiment, the superstructure unit includes a central nanostructure and 4 peripheral nanostructures that are equidistant from it, forming a square.

[0076] The superstructure unit and its closely packed / array form can also be a fan-shaped arrangement in a circle, as Figure 11 (3) shows, including a fan shape with two arc edges, or it can also be a fan shape with one arc edge, as Figure 11 the lower left corner area in (3). Nanostructures are provided at the intersection points of each side and the center of the fan shape.

[0077] Exemplarily, the nanostructures provided in the embodiments of the present application may be polarization-independent structures, and such structures impose a propagation phase on the incident light. According to the embodiments of the present application, the nanostructures may be positive structures or negative structures. For example, the shapes of the nanostructures include cylinders, hollow cylinders, square prisms, hollow square prisms, etc. Figure 12 The left side shows a schematic structural diagram of a nanostructure unit when the nanostructure is a cylinder.

[0078] Exemplarily, the nanostructures may be polarization-dependent structures, and such structures impose a geometric phase on the incident light. The nanostructures may be positive structures or negative structures. For example, the nanostructures may be structures such as elliptical cylinders and nanoscale fins. Figure 12 The right side shows a schematic structural diagram of a nanostructure unit when the nanostructure is a nanoscale fin. According to the embodiments of the present application, the characteristic size of the nanostructure is greater than or equal to 0.2λ c and less than or equal to 0.8λ c ; λ c is the central wavelength of the incident radiation.

[0079] In the specific design of the superlens, first, the target phase of the superlens is determined according to the required function. Then, according to the designed phase, for each coordinate on the superlens, the nanostructure closest to the target phase of that coordinate is found respectively. Finally, the selected nanostructures are arranged according to the target phase.

[0080] The phases of the illumination modulation region 11 and the detection modulation region 12 of the superlens 10 of the present application are designed according to the correlation between the illumination modulation region 11, the detection modulation region 12, and the overall point spread function. Here, the point spread function of the illumination modulation region 11 is PSF ill , the point spread function formed by the detection modulation region 12 is PSF det , and the overall point spread function of the superlens 10 is PSF sys , and the following relationship is satisfied among the three:

[0081] PSF sys = PSF ill * PSF det .

[0082] Among them, PSF sys is the point spread function of the final image, PSF ill is the point spread function formed by the illumination modulation region 11, and PSF det is the point spread function formed by the detection modulation region 12.

[0083] Therefore, in the case of using a Bessel beam, for the irradiation modulation region 11 of the metalens 10, the phase distribution of the metalens 10 that generates the Bessel beam satisfies the following relational expression, and a zero-order Bessel beam can be generated:

[0084]

[0085] NA = sin(θ)

[0086] where λ is the wavelength of the irradiation beam, x and y are the coordinate positions on the surface of the metalens 10, and θ is the deflection angle of the metalens 10 for the parallel incident beam. The image plane distribution of this zero-order Bessel function is as Figure 4 shown, where the ordinate is the normalized intensity and the abscissa is the distance of any nanostructure in the metasurface from the center of the optical axis.

[0087] The phase distribution required for generating a high-order Bessel beam satisfies the following relational expression:

[0088]

[0089]

[0090] n represents the order, and φ is the azimuth angle, which is used to characterize the vortex phase of the outgoing light.

[0091] For the above formula, in the preferred embodiment of the present application, n = 1, 2, or 3. Of course, n can also take other integer values.

[0092] At this time, the phase distribution of the detection modulation region 12 of the metalens 10 needs to satisfy:

[0093]

[0094] According to the above formula, when n = 2, the point spread function generated by the detection modulation region 12 is the sum of the zero-order Bessel function and the second-order Bessel function. Thus, the total point spread function is obtained by multiplying the point spread function of the detection modulation region 12 and the point spread function of the irradiation modulation region 11. Regarding this, the image plane distribution diagrams of the point spread function of the detection modulation region 12 and the total point spread function are respectively shown in Figure 5 and Figure 6 respectively.

[0095] From the Figure 4 and Figure 6 comparison, it can be clearly obtained that: the metalens 10 designed according to the above design method excellently suppresses the sidelobes of the Bessel beam, thereby significantly improving the imaging quality of the imaging method of the present application.

[0096] In addition, in another embodiment, as Figure 7As shown, the point spread function generated by the detection modulation region 12 can also be the sum of a zero-order Bessel function and a third-order Bessel function. At this time, refer to Figure 8 , in Figure 8 , the image plane distribution diagram of the total point spread function is shown. Therefore, it can be seen that: this embodiment also suppresses the side lobes of the irradiation beam well.

[0097] It is also conceivable that the phase distribution of the detection modulation region 12 satisfies:

[0098]

[0099] That is, the point spread function of the detection modulation region 12 is the difference between a zero-order Bessel function and an n-order Bessel function.

[0100] For the above formula, in the preferred embodiment of the present application, n = 1, 2 or 3. Of course, n can also take other integer values.

[0101] Therefore, in an exemplary embodiment, as Figure 9 shown, the point spread function generated by the detection modulation region 12 is the difference between a zero-order Bessel function and a first-order Bessel function; at this time, refer to Figure 10 , in Figure 10 , the image plane distribution diagram of the total point spread function is shown. Therefore, it can be seen that: this embodiment also suppresses the side lobes of the irradiation beam well.

[0102] In addition, it is also conceivable that: other orders and calculation methods can also be used to design the phase distribution of the detection modulation region 12.

[0103] Above, only the imaging method according to the present application is described exemplarily by means of Bessel beams, and the present invention is not limited to the use of Bessel beams. It is also conceivable that the present invention can of course also consider other non-diffracting beams, such as Mathieu beams, Airy beams, etc., to achieve super-resolution imaging.

[0104] Therefore, in a step of the imaging method of the present application, by deep learning to set constraint conditions, the phase distribution of the detection modulation region 12 of the superlens 10 is designed. For example, the corresponding phase distribution design can be carried out for different non-diffracting beams and / or different orders of beams. Thereby, super-resolution imaging that meets different requirements can be achieved for different requirements.

[0105] In another aspect of the present invention, an imaging system is further provided. The imaging system is preferably configured to execute the imaging method according to the present application. For the structure of the imaging system, refer to Figure 2 , the imaging system includes: a light source 50, a superlens 10, an incident optical fiber 20, a receiving optical fiber 30, and a detector 40; wherein,

[0106] The metalens 10 includes an illumination modulation region 11 and a detection modulation region 12;

[0107] The incident optical fiber 20 connects the light source 50 to the metalens 10,

[0108] and the receiving optical fiber 30 connects the metalens 10 to the detector 40.

[0109] As Figure 3 shown, the metalens 10 is circular, where the illumination modulation region 11 is also circular, and the detection modulation region 12 is a closed circular ring. However, the shape of the metalens 10 of the present invention is not limited thereto, and other shapes such as a square, a regular hexagon, etc. can also be adopted, and the detection modulation region does not necessarily have to be a closed ring, and a non-closed surrounding shape can also be adopted as long as its phase distribution meets the design requirements.

[0110] In addition, the number of light sources 50 is preferably one.

[0111] Through the metalens designed in blocks and the use of non-diffracting beams, compared with the prior art, the sidelobes are well suppressed, thereby improving the lateral resolution and imaging effect. In addition, through the above imaging system, compared with the prior art, while achieving high-quality super-resolution imaging, the number of components is reduced, such as the number of light sources, and the use of the metalens also simplifies the structure of the entire system, making the system more compact, lighter in weight, and more convenient to use.

[0112] For example, in order to generate the Bessel beam defined in this application, the nanostructure of the metalens 10 is preferably polarization-dependent, which acts as a half-wave plate for the designed wavelength here and can modulate the incident circularly polarized light into its orthogonal polarization state to generate a Bessel beam. The polarization-dependent nanostructure is as Figure 12 shown on the right.

[0113] In a preferred embodiment of the present application, the metalens 10 is an adjustable metalens, and this adjustable metalens can change the phase distribution of the illumination modulation region 11 and / or the detection modulation region 12 by applying an external excitation. As an embodiment, the external excitation can include electrical excitation, thermal excitation, optical excitation, and mechanical excitation.

[0114] There are various possible implementation methods for the adjustable metalens of the present application. For example, a phase change material can be added to the metalens 10 to form a phase change material layer, and by applying an external excitation, the phase state of the phase change material is changed, thereby changing the phase of the metalens 10; another example is that at least part of the nanostructure of the metalens 10 is composed of a phase change material, and by applying an external excitation, the phase state of the phase change material is changed, thereby changing the phase of the metalens 10.

[0115] When the phase change material in the above embodiments is an electro - induced phase change material, the applied external excitation is an electrical excitation. For example, the phase change state of the electro - induced phase change material can be changed by changing the voltage applied to the electro - induced phase change material, so as to change the phase of the superlens 10.

[0116] When the phase change material in the above embodiments is a thermosensitive phase change material, the applied external excitation is a thermal excitation. For example, the phase change state of the thermosensitive phase change material can be changed by changing the temperature applied to the thermosensitive phase change material, so as to change the phase of the superlens 10.

[0117] When the phase change material in the above embodiments is a photosensitive phase change material, the applied external excitation is a light excitation. For example, by changing the light intensity of the light beam irradiating the photosensitive phase change material, the temperature of the photosensitive phase change material can be changed, thereby changing the phase change state of the photosensitive phase change material, so as to change the phase of the superlens 10.

[0118] Hereinafter, taking the electrical excitation as an example, the implementation scheme of the tunable superlens of the present application will be specifically described. A control voltage is set on the tunable superlens. The nanostructure unit of the tunable superlens uses a phase change material. The phase change material can greatly change the dielectric constant by changing the lattice inside the substance under an external excitation (such as heat, laser, applied voltage).

[0119] Ge x Sb y Te z (abbreviation GST) As a commonly used phase change material, it is composed of three elements: germanium (Ge), antimony (Sb), and tellurium (Te), and is widely used in rewritable optical disc technology. Solid - state GST has two phase states: crystalline state and amorphous state, and there is a large difference in the dielectric constants of the two states.

[0120] When the temperature of amorphous GST exceeds the crystallization temperature (mostly 160 °C), the amorphous state will first transform into a metastable face - centered cubic crystal structure, similar to NaCl. If the temperature continues to rise, the metastable crystal structure will change into a stable hexagonal structure. The phase change process from amorphous to crystalline can be achieved by heating GST on a heating plate, irradiating with laser pulses, applying an external voltage, and other means.

[0121] Conversely, heating crystalline GST above its melting point (mostly 640 °C) and liquefying it, and then rapidly cooling it can form amorphous GST. The entire cooling and solidification process needs to be completed rapidly within 10 ns. If the solidification time is too long, the liquid GST has enough time to reorganize into a crystalline structure. In the case of applying a laser, the phase change of GST from crystalline to amorphous often requires a short - pulse (pulse width < 10 ns) laser with a large power.

[0122] Once the phase change process of GST from crystalline to amorphous or vice versa is completed, GST can maintain the post-phase change crystalline or amorphous state for a long time even after removing the external excitation and returning to room temperature. The crystallization ratio of GST can be obtained by controlling the physical parameters of the crystallization process. For example, when heating amorphous GST, the crystallization ratio can be adjusted by changing the heating temperature or heating time to obtain different refractive indices.

[0123] In Figure 13 , (1) and (2) show a schematic diagram of a nanostructure of the tunable superlens of the present application, namely, the phase change unit. Here, the phase change unit is a transmissive phase change unit. Conductivity and heating can be directly achieved using the phase change element. As Figure 13 shown in (1) of , the first electrode 111 is electrically connected to the lower side of the nanostructure 114, and the second electrode 112 is electrically connected to the upper side of the nanostructure 114. Under the action of the two electrodes, the nanostructure 114 made of the phase change material directly conducts electricity and generates heat to realize the change of the phase state. Here, the materials of the first electrode 111 and the second electrode 112 are transparent in the working wavelength band to avoid reducing the light transmittance.

[0124] Here, the first electrode 111 can be directly electrically connected to the nanostructure 114; or, as Figure 13 shown in (1) of , the phase change unit further includes: a connection layer 113, and the connection layer 113 is transparent in the working wavelength band. The connection layer is located on the side of the nanostructure 114 away from the first electrode 111 and is electrically connected to the nanostructure 114; the second electrode 112 is located between the first electrode 111 and the connection layer 113 and is electrically connected to the connection layer 113. In this embodiment, the layered first electrode 111 and the connection layer 113 are both made of conductive and transparent materials. For example, ITO can be used.

[0125] For example, in order to avoid leakage between the first electrode 111 and the second electrode 112 arranged at intervals, as Figure 13 shown in (1) of , the phase change unit further includes: a first insulating layer 115; the first insulating layer 115 is located between the first electrode 111 and the second electrode 112 and abuts against the first electrode 111 and the second electrode 112. Optionally, the phase change unit may further include a second insulating layer 116 arranged in parallel with the nanostructure 114, and insulation can also be achieved when it can support part of the electrodes. In addition, the second insulating layer 116 can also play a role in supporting the connection layer.

[0126] See Figure 13As shown in (2) therein, the phase change unit may also include: a filler 117 that is transparent in the working band; the filler is filled between the nanostructures 114. In the embodiment of the present invention, a transparent material, that is, the filler 117, is filled around the nanostructures; the filler has a high transmittance in the working band, and the difference between the refractive index of the filler 117 and the refractive index of the phase change material is not less than 0.5 to ensure the modulation effect of the nanostructures 114.

[0127] In the present application, as Figure 13 shown in (1) and (2) therein, the phase change unit is a transmissive type, where light A is incident on the phase change unit, the phase change unit performs phase modulation on light A, and the modulated light B is emitted, and the light B is a transmitted light.

[0128] Taking the external excitation as light excitation as an example below, the implementation scheme of the tunable superlens of the present application will be illustrated. For example, the nanostructures of the superlens 10 are made of a photosensitive phase change material. By changing the optical signals applied to the nanostructures of the superlens 10, the temperature of the nanostructures in the light signal irradiation area is regulated, so as to change the refractive index of the nanostructures in the light signal irradiation area, and further regulate the phase distributions of the irradiation modulation area 11 and the detection modulation area 12 in the superlens 10 to reach the required values.

[0129] Taking the external excitation as mechanical excitation as an example below, the implementation scheme of the tunable superlens of the present application will be illustrated. For example, a flexible substrate is selected as the substrate of the superlens 10, and the period of the nanostructure units of the superlens 10 is changed by mechanical stretching to regulate the phase distribution of the superlens 10. Specifically, the superlens 10 can be configured as follows: the substrate is made of a stretchable material, the nanostructures are fixed on the substrate, and by stretching or compressing the substrate with an external mechanical device, the spacing between the nanostructures on the superlens 10 is changed, so as to change the period of the nanostructure units passing through the superlens 10, and further adjust the phases of the irradiation modulation area 11 and the detection modulation area 12 in the superlens 10.

[0130] Since different diffracted light beams have different application scenarios, by using the tunable superlens, the imaging method and imaging system of the present application can be used more flexibly. It is possible to achieve super-resolution imaging for different non-diffracting light beams with a single superlens, and it is possible to switch between different application scenarios.

[0131] It should be noted that: all the technical features and technical effects described in the imaging method according to the present invention can be transferred to the imaging system of the present invention, and vice versa.

[0132] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technical solution that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. An imaging method, characterized in that, Comprising: Providing a metalens (10), the metalens (10) including an illumination modulation region (11) in the middle of the metalens (10) and a detection modulation region (12) surrounding the illumination modulation region (11); In the illumination optical path, guiding an illumination beam to the illumination modulation region (11) of the metalens (10) via an incident optical fiber, so as to be focused on the object to be measured through the illumination modulation region (11); In the detection optical path, receiving, through the detection modulation region (12) of the metalens (10), a beam reflected from the object to be measured and containing information of the object to be measured; Guiding the beam containing the information of the object to be measured to a detector via a receiving optical fiber, and then performing imaging; Wherein, the phase distributions of the illumination modulation region (11) and the detection modulation region (12) of the metalens (10) are designed such that the point spread function in the illumination optical path is modulated by the point spread function of the detection optical path, so that the full width at half maximum of the overall point spread function formed by the detection modulation region (12) and the illumination modulation region (11) can be adjusted.

2. The imaging method according to claim 1, characterized in that, The illumination beam is a non-diffracting beam.

3. The imaging method according to claim 2, characterized in that, The illumination beam is a Bessel beam.

4. The imaging method according to claim 1, characterized in that, Modulating the point spread function in the illumination optical path by the point spread function of the detection optical path, so that the full width at half maximum of the overall point spread function formed by the detection modulation region (12) and the illumination modulation region (11) is lower than the full width at half maximum of the point spread function of the illumination modulation region (11).

5. The imaging method according to claim 3, characterized in that, The phase distribution of the illumination modulation region (11) satisfies: NA = sin(θ) Wherein, x and y are the surface coordinate positions of the metalens (10), θ is the deflection angle of the metalens (10) for a parallel incident beam, and λ is the wavelength of the illumination beam.

6. The imaging method according to claim 5, characterized in that, The phase distribution of the detection modulation region (12) satisfies: Wherein Wherein, n represents the order, and φ is the azimuth angle, which is used to characterize the vortex phase of the outgoing light of the detection modulation region (12).

7. The imaging method according to claim 5, characterized in that, The phase distribution of the detection modulation region (12) satisfies: Wherein Wherein, n represents the order, and φ is the azimuth angle, which is used to characterize the vortex phase of the outgoing light of the detection modulation region (12).

8. The imaging method according to claim 6 or 7, characterized in that, n = 1, 2 or 3.

9. The imaging method according to claim 1, characterized in that, This method further includes designing the phase distribution of the detection modulation region (12) of the metalens (10) by setting constraint conditions through deep learning.

10. An imaging system for implementing the imaging method according to any one of claims 1 to 9, wherein the system comprises: A light source (50), a metalens (10), an incident optical fiber (20), a receiving optical fiber (30) and a detector (40); Wherein The metalens (10) includes: an illumination modulation region (11) and a detection modulation region (12) surrounding the illumination modulation region (11); The incident optical fiber (20) connects the light source (50) and the metalens (10); The receiving optical fiber (30) connects the metalens (10) and the detector (40).

11. The system according to claim 10, wherein The metalens (10) is an adjustable metalens, and the adjustable metalens can change the phase distributions of the illumination modulation region (11) and / or the detection modulation region (12) by applying an external excitation.

12. The system according to claim 11, wherein The external excitation includes electrical excitation, thermal excitation, optical excitation, and mechanical excitation.

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