Zoom super-structure lens, preparation method thereof and optical system

Abstract

The invention provides a zoom super-structure lens, a preparation method thereof and an optical system. The zoom super-structure lens comprises a substrate; the dielectric layer is arranged on the substrate and comprises a plurality of dielectric cylinders; the liquid crystal layer is arranged on the dielectric layer; the liquid crystal layer changes the liquid crystal direction through externally applied voltage so as to adjust the focal length. By utilizing the characteristics of the integrated resonance unit, the device can accurately work under various common fluorescent dye excitation wavelengths, the focal spot distortion and asymmetry degree caused by phase mismatch are reduced, and the quality of a fluorescent slice image is further improved.

Description

Technical Field

[0001] The present invention relates to the field of optical imaging technology, and in particular to a zoom meta-lens and a preparation method thereof, and an optical system. Background Art

[0002] A variable-focus meta-lens is a lens with adjustable focal length. This lens can be used for axial scanning of a microscope to obtain multi-plane images. If combined with a fluorescence microscope, it can obtain high-contrast three-dimensional fluorescence slice images. Therefore, it is widely used in biomedical research. However, traditional variable-focus meta-lenses are large in size and have spherical aberration and distortion, which not only limits the integration capability of variable-focus meta-lenses, but also reduces the quality of slice images, hindering the application and development of optical slice fluorescence microscopes. Summary of the invention

[0003] The main purpose of the embodiments of the present invention is to provide a zoom meta-lens and a preparation method thereof, and an optical system to eliminate spherical aberration and distortion and improve image quality.

[0004] In order to achieve the above object, an embodiment of the present invention provides a zoom meta-lens, comprising:

[0005] substrate;

[0006] A dielectric layer disposed on the substrate, the dielectric layer comprising a plurality of dielectric columns;

[0007] A liquid crystal layer is arranged on the medium layer; the liquid crystal layer changes the direction of the liquid crystal through an externally applied voltage to adjust the focal length.

[0008] In one embodiment, the dielectric layer includes:

[0009] multiple media columns;

[0010] Insulating materials are filled between the plurality of dielectric pillars and between the plurality of dielectric pillars and the liquid crystal layer.

[0011] In one embodiment, the dielectric column is a cuboid, and a cross section of the dielectric column is a rectangle.

[0012] In one embodiment, the rotation angle of the dielectric column corresponds to the focal length of the zoom meta-lens.

[0013] In one embodiment, the position of the dielectric rod corresponds to the phase of the variable focus meta-lens.

[0014] An embodiment of the present invention further provides a method for preparing the zoom meta-lens as described above, comprising:

[0015] providing a substrate;

[0016] forming a dielectric layer including a plurality of dielectric pillars on the substrate;

[0017] A liquid crystal layer is formed on the dielectric layer.

[0018] In one embodiment, forming a dielectric layer including a plurality of dielectric pillars on the substrate comprises:

[0019] Disposing a plurality of dielectric columns on the substrate;

[0020] Insulating material is filled between the plurality of dielectric pillars to form a dielectric layer.

[0021] In one embodiment, providing a plurality of dielectric columns on the substrate comprises:

[0022] Determine the focal length of the zoom meta-lens corresponding to the wavelength of each dielectric column;

[0023] Determining a focal length wavelength coefficient according to the focal length of the zoom meta-lens;

[0024] Determining the position of the dielectric column according to the focal length wavelength coefficient and the phase of the dielectric column;

[0025] A plurality of dielectric columns are sequentially arranged on the substrate according to the rotation angle of the dielectric column and the position of the dielectric column.

[0026] An embodiment of the present invention further provides an optical system based on a zoom meta-lens, comprising:

[0027] A laser emitter, a left-handed circularly polarized light conversion device, a zoom meta-lens as described above, a microscope, a right-handed circularly polarized light conversion device, and an image sensor are arranged in sequence;

[0028] The laser emitted by the laser transmitter is converted into left-handed circularly polarized light by the left-handed circularly polarized light conversion device, and then converted into right-handed circularly polarized light after passing through the zoom meta-lens, the microscope and the right-handed circularly polarized light conversion device in sequence, and enters the image sensor to obtain an image.

[0029] In one embodiment, it also includes:

[0030] The half-wave plate located between the laser emitter and the left-handed circularly polarized light conversion device is used to adjust the intensity of the laser.

[0031] The zoom metalens and its preparation method and optical system of the embodiments of the present invention utilize the characteristics of the integrated resonance unit to accurately operate under a variety of common fluorescent dye excitation wavelengths, reduce the focal spot distortion and asymmetry caused by phase mismatch, and further improve the quality of fluorescent slice images. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 is a schematic diagram of a zoom meta-lens in an embodiment of the present invention;

[0034] Figure 2 is a top view of a zoom meta-lens according to an embodiment of the present invention;

[0035] Figure 3 is a top view of a zoom meta-lens according to another embodiment of the present invention;

[0036] Figure 4 is a schematic diagram of the relationship between the rotation angle of the dielectric column and the geometric phase in an embodiment of the present invention;

[0037] Figure 5 is a diagram showing the relationship between the phase and the rotation angle required for adjusting the liquid crystal layer in an embodiment of the present invention;

[0038] Figure 6 is a schematic diagram of the relationship between focal length and rotation angle in an embodiment of the present invention;

[0039] Figure 7 is a flow chart of a method for preparing a zoom meta-lens in an embodiment of the present invention;

[0040] Figure 8 is a flow chart of S102 in an embodiment of the present invention;

[0041] Fig. 9 is a flow chart of S201 in an embodiment of the present invention;

[0042] Fig.10 is a schematic diagram of the phase distribution size of the dielectric column in an embodiment of the present invention;

[0043] Fig.11 is a schematic diagram of the splicing of dielectric columns in an embodiment of the present invention;

[0044] Fig.12 is a schematic diagram of focal length variation under four wavelengths in an embodiment of the present invention;

[0045] Fig.13 Schematic diagram of an optical system based on a zoom meta-lens in an embodiment of the present invention. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] Those skilled in the art will appreciate that the embodiments of the present invention may be implemented as a system, device, apparatus, method or computer program product. Therefore, the present disclosure may be specifically implemented in the following forms, namely: complete hardware, complete software (including firmware, resident software, microcode, etc.), or a combination of hardware and software.

[0048] In view of the fact that the traditional variable focus meta-lens separate design and mechanical rotation operation will cause errors (such as lateral misalignment of components, device jitter during rotation), the embodiments of the present invention provide a variable focus meta-lens and its preparation method and optical system. Among them, the variable focus meta-lens is a variable focus plane meta-lens for optical sectioning fluorescence microscopy based on the moiré effect. The modulation method is simple. The direction of the liquid crystal is changed by applying voltage. The focal length can be changed within a certain range. The spherical aberration and distortion of the traditional variable focus meta-lens are eliminated at an ultra-compact scale, and the out-of-focus noise and the lateral mismatch of the system are reduced. In addition, the optical system utilizes the characteristics of the integrated resonance unit, and can work accurately under a variety of common fluorescent dye excitation wavelengths, reducing the focal spot distortion and asymmetry caused by phase mismatch, and further improving the quality of fluorescent section images. The present invention is described in detail below in conjunction with the accompanying drawings.

[0049] Figure 1 Schematic diagram of a zoom meta-lens in an embodiment of the present invention. Figure 2 is a top view of the zoom meta-lens in an embodiment of the present invention. Figure 3 FIG. 1 is a top view of a zoom meta-lens in another embodiment of the present invention. Figures 1 to 3 As shown, the zoom meta-lens includes:

[0050] Base 1;

[0051] A dielectric layer 2 disposed on the substrate 1, the dielectric layer comprising a plurality of dielectric columns 21;

[0052] The liquid crystal layer 3 is arranged on the medium layer 2; the liquid crystal layer 3 changes the direction of the liquid crystal through an externally applied voltage to adjust the focal length.

[0053] In one embodiment, the dielectric layer includes:

[0054] A plurality of dielectric columns 21 (eg Figure 2The dielectric column A, dielectric column B, dielectric column C, and dielectric column D are described in detail; wherein the dielectric column is a cuboid, and the cross-section of the dielectric column is a rectangle.

[0055] The insulating material 22 is filled between the dielectric pillars 21 and between the dielectric pillars 21 and the liquid crystal layer 3 .

[0056] In specific implementation, the insulating material 22 can be PMMA (polymethyl methacrylate, organic glass), which can reduce the interaction between the liquid crystal layer and the dielectric column and protect the dielectric column. The thickness of PMMA and the liquid crystal layer is preferably in the micrometer level.

[0057] In one embodiment, the rotation angle of the dielectric column corresponds to the focal length of the zoom meta-lens, and the position of the dielectric column corresponds to the phase of the zoom meta-lens.

[0058] Figure 4 FIG. 1 is a schematic diagram showing the relationship between the rotation angle of the dielectric column and the geometric phase in an embodiment of the present invention. Figure 4 As shown, when circularly polarized incident light hits the dielectric column unit structure, the outgoing cross-circularly polarized light will naturally carry a geometric phase. There is a fixed two-fold relationship between the size V of the geometric phase and the rotation angle R of the dielectric column, that is, V=2R. For example, if the rotation angle is 45°, the geometric phase is 90°. The phase distribution of the dielectric column can determine the rotation angle of the dielectric column. The focal length of the zoom meta-lens determines the phase distribution of the dielectric column. Therefore, the rotation angle of the dielectric column corresponds to the focal length of the zoom meta-lens.

[0059] like Figure 1 As shown, the present invention uses an integrated design based on the moiré effect to achieve the zoom function, with the bottom layer being the substrate, the middle layer being the dielectric column, and the upper layer being the liquid crystal. The present invention replaces the first lens in the traditional moiré lens system with a dielectric column, and uses the geometric phase to achieve the phase distribution of the first lens by rotating the angle of the dielectric column; the second lens is replaced by a liquid crystal layer, and the direction of the liquid crystal is changed by changing the voltage applied to the liquid crystal, which causes a change in the phase, so that the phase is not only consistent with the phase distribution of the second lens, achieving the function of adjustable focal length, but also avoiding lateral misalignment and device jitter.

[0060] The present invention also utilizes the characteristics of the integrated resonance unit to enable the zoom meta-lens to work at the excitation wavelengths of a variety of common fluorescent dyes, thereby improving the quality of fluorescent slice images and broadening the working band of the device. Figure 2 and Figure 3As shown, by adjusting various parameters of the dielectric column, such as length, width and even material, different dielectric columns A, B, C and D can be made to work at four different excitation wavelengths, and through reasonable design, the dielectric column can only respond to the corresponding working wavelength, thereby minimizing the crosstalk between structures.

[0061] Figure 5 4 is a diagram showing the relationship between the phase and the rotation angle required to be adjusted for the liquid crystal layer in an embodiment of the present invention. Figure 6 Schematic diagram of the relationship between focal length and rotation angle in an embodiment of the present invention. Figure 5-Figure 6 As shown, taking the traditional 532nm working band as an example, Figure 5 (a) shows the fixed phase of the dielectric column layer. Figure 5 (b1) is the phase distribution corresponding to the application of different voltages to the liquid crystal layer, which corresponds to the phase when the traditional moiré lens is rotated 30°-330°. Figure 6 The reference focal length is assumed to be 19mm.

[0062] Based on the same inventive concept, an embodiment of the present invention also provides a method for preparing a zoom meta-lens. Since the principle of solving the problem by this method is similar to that of the zoom meta-lens, the implementation of this method can refer to the implementation of the zoom meta-lens, and the repeated parts will not be repeated.

[0063] Figure 7 FIG. 1 is a flow chart of a method for preparing a zoom meta-lens according to an embodiment of the present invention. Figure 7 As shown, the method for preparing the zoom meta-lens includes:

[0064] S101: providing a substrate.

[0065] S102: forming a dielectric layer including a plurality of dielectric pillars on the substrate.

[0066] Figure 8 is a flow chart of S102 in an embodiment of the present invention. Figure 8 As shown, S102 includes:

[0067] S201: Disposing a plurality of dielectric columns on the substrate.

[0068] Fig. 9 is a flow chart of S201 in an embodiment of the present invention. Fig. 9 As shown, S201 includes:

[0069] S301: Determine the focal length of the zoom meta-lens corresponding to the wavelength of each dielectric column.

[0070] S302: Determine a focal length wavelength coefficient according to the focal length of the zoom meta-lens.

[0071] In specific implementation, the focal length wavelength coefficient can be determined by the following formula:

[0072]

[0073] Where a is the focal length wavelength coefficient, f θ is the focal length of the zoom meta-lens, θ is the relative rotation angle corresponding to the phase of the liquid crystal layer, and λ is the wavelength.

[0074] For example, there are four dielectric columns corresponding to four fluorescent dye excitation wavelengths, and the four focal length wavelength coefficients are a1, a2, a3, and a4 respectively.

[0075] S303: Determine the position of the dielectric column according to the focal length wavelength coefficient and the phase of the dielectric column.

[0076] In one embodiment, the position of the dielectric column can be determined by the following formula:

[0077]

[0078]

[0079]

[0080] Among them, φ 1 is the phase distribution of the dielectric column, φ 2 is the phase distribution of the liquid crystal layer, F 0 is the reference focal length, r is the distance between the center of the dielectric column and the center of the zoom meta-lens, θ 0 is the angle between the center of the dielectric column and the center of the zoom meta-lens. Therefore, according to the above formula, r and θ can be determined. 0 , and then determine the position of the medium column.

[0081] In the specific implementation, a1, a2, a3, and a4 are respectively substituted into φ 1 From the formula, four corresponding phase distributions Φ11, Φ12, Φ13, and Φ14 can be obtained. The above four phase distributions are combined to form the entire phase distribution of the dielectric column layer.

[0082] S304: sequentially arranging a plurality of dielectric columns on the substrate according to the rotation angle of the dielectric column and the position of the dielectric column.

[0083] The center of the dielectric column can also be made to coincide with the center of its corresponding substrate, so that the initial position of the dielectric column is the central position of the substrate.

[0084] S202: filling insulating material between the plurality of dielectric pillars to form a dielectric layer.

[0085] S103: forming a liquid crystal layer on the dielectric layer.

[0086] In a specific implementation, after the light beam passes through the meta-lens of the present application, the phase distribution is as follows:

[0087] φ integral =φ(r,θ 0 )+(-φ(r,θ 0 -θ))=ar 2 θ;

[0088] Among them, φ integral is the overall phase distribution of the meta-lens.

[0089] Fig.10 Schematic diagram of the phase distribution of dielectric columns in an embodiment of the present invention. Fig.10 As shown, different colors represent different wavelengths, corresponding to four dielectric columns. Assuming that the size of each phase distribution is 3x3, the final overall phase distribution is 6x6. Take the following four common fluorescent dyes as examples:

[0090] 1. Green fluorescent protein (GFP): excitation wavelength 395nm;

[0091] 2. Fluorescein: excitation wavelength 495nm;

[0092] 3. Red fluorescent protein (RFP): excitation wavelength 560nm;

[0093] 4. Methylene Blue: excitation wavelength 660nm.

[0094] Among them, the corresponding relationship between the medium column ABCD and the fluorescent dye responsible for detection is as follows:

[0095] Medium column A → green fluorescent protein (395nm); medium column B → fluorescein (495nm); medium column C → red fluorescent protein (560nm); medium column D → methylene blue (660nm). The four fluorescent dyes are evenly filled in the entire space, and the depth of the space is 200mm.

[0096] Fig.11 FIG. 1 is a schematic diagram of the splicing of dielectric columns in an embodiment of the present invention. Fig.11 As shown, if a1, a2, a3, and a4 are all fixed to 100 mm-2, the calculated distributions of Φ11, Φ12, Φ13, and Φ14 are completely consistent, and the corresponding rotation angles of the dielectric columns are also completely consistent. For example Fig.11 The rotation angle of the medium column in the upper left corner is 0 degrees.

[0097] Fig.12 Schematic diagram of focal length variation under four wavelengths in an embodiment of the present invention. Fig.12 As shown, the calculated focal length changes under the four wavelengths can perfectly cover 200mm. According to the curve relationship, the information of any fluorescent slice or even combined fluorescent slice at any depth (within 200mm) can be obtained. When you want to obtain a green fluorescent protein slice at 45mm, according to the 395nm curve, the corresponding rotation angle θ is 99°. Substituting 99° into the formula can get the phase distribution of φ2, and finally applying voltage to make the upper liquid crystal layer corresponding to dielectric column A realize this phase distribution. When you want to obtain a 45mm green fluorescent protein slice and a methylene blue slice at the same time, you need to apply voltage to make the upper liquid crystal layer corresponding to dielectric column A realize a phase distribution with a rotation angle of θ=99°, and the liquid crystal layer above dielectric column D realizes a phase distribution of θ=61°.

[0098] Based on the same inventive concept, an embodiment of the present invention further provides an optical system based on a zoom meta-lens. Since the principle of solving the problem by this system is similar to that of the zoom meta-lens, the implementation of this system can refer to the implementation of the zoom meta-lens, and the repeated parts will not be repeated.

[0099] Fig.13 Schematic diagram of an optical system based on a zoom meta-lens in an embodiment of the present invention. Fig.13 As shown, the optical system based on the zoom meta-lens includes:

[0100] The laser emitter 10, the left-handed circularly polarized light conversion device (6, 7), the zoom meta-lens 4 as described above, the microscope 11, the right-handed circularly polarized light conversion device (8, 9) and the image sensor 12 are arranged in sequence.

[0101] The left-handed circularly polarized light conversion device includes a first linear polarizer 6 and a first quarter-wave plate 7 , and the right-handed circularly polarized light conversion device includes a second linear polarizer 8 and a second quarter-wave plate 9 .

[0102] In one embodiment, the optical system based on the zoom meta-lens further includes:

[0103] The half-wave plate 5 located between the laser emitter 10 and the left-handed circularly polarized light conversion device is used to adjust the intensity of the laser.

[0104] In a specific implementation, the laser emitted by the laser emitter 10 is converted into left-handed circularly polarized light by the left-handed circularly polarized light conversion device, and then enters the zoom meta-lens 4. The zoom meta-lens 4 adjusts the voltage applied to the liquid crystal layer to change the corresponding phase distribution, so that the light emitted from the zoom meta-lens 4 contains both left-handed circularly polarized light and right-handed circularly polarized light; the light emitted from the zoom meta-lens 4 is converted into right-handed circularly polarized light after passing through the microscope 11 and the right-handed circularly polarized light conversion device in turn, and enters the image sensor 12 to obtain an image. Among them, the function of the right-handed circularly polarized light conversion device is to filter out the emitted left-handed circularly polarized light (i.e., block it from passing through). When it is necessary to detect a sample, the volume sample is placed between the half-wave plate 5 and the first linear polarizer 6, and the voltage applied to the liquid crystal layer is adjusted so that the light beam is focused at different depths of the volume sample, and images of different fluorescent slices are obtained on the image sensor.

[0105] In summary, the present invention constructs a variable-focus plane meta-lens for optical sectioning fluorescence microscopy based on the moiré effect, which can realize sub-wavelength variable-focus meta-lens without spherical aberration and distortion, medical microendoscope and optical coherence tomography, etc. The present invention can interact with the excitation wavelengths of various fluorescent materials, eliminate the spherical aberration and distortion of the lens at an ultra-compact scale, and reduce out-of-focus noise; the integrated design of the present invention is not only easy to focus, but also more conducive to experimental calibration, and this device can be used to achieve functions such as high-contrast optical sectioning imaging of biological samples. In addition, the present invention can tune the range of focal length and the working band by reasonably setting the material of the meta-surface and optimizing the structural size of the meta-unit.

[0106] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A zoom meta-lens, characterized in that: include: substrate; A dielectric layer disposed on the substrate, the dielectric layer comprising a plurality of dielectric columns; A liquid crystal layer disposed on the dielectric layer; The liquid crystal layer changes the direction of the liquid crystal by an externally applied voltage to adjust the focal length.

2. The zoom meta-lens according to claim 1, characterized in that: The dielectric layer comprises: multiple media columns; Insulating materials are filled between the plurality of dielectric pillars and between the plurality of dielectric pillars and the liquid crystal layer.

3. The zoom meta-lens according to claim 1, characterized in that: The dielectric column is a cuboid, and the cross section of the dielectric column is a rectangle.

4. The zoom meta-lens according to claim 1, wherein: The rotation angle of the dielectric column corresponds to the focal length of the zoom meta-lens.

5. The zoom meta-lens according to claim 4, characterized in that: The position of the dielectric rod corresponds to the phase of the variable focus meta-lens.

6. A method for preparing a variable focus meta-lens according to any one of claims 1 to 5, characterized in that: include: providing a substrate; forming a dielectric layer including a plurality of dielectric pillars on the substrate; A liquid crystal layer is formed on the dielectric layer.

7. The method for preparing a zoom meta-lens according to claim 6, characterized in that: Forming a dielectric layer including a plurality of dielectric pillars on the substrate comprises: Disposing a plurality of dielectric columns on the substrate; Insulating material is filled between the plurality of dielectric pillars to form a dielectric layer.

8. The method for preparing a zoom meta-lens according to claim 7, characterized in that: Providing a plurality of dielectric columns on the substrate comprises: Determine the focal length of the zoom meta-lens corresponding to the wavelength of each dielectric column; Determining a focal length wavelength coefficient according to the focal length of the zoom meta-lens; Determining the position of the dielectric column according to the focal length wavelength coefficient and the phase of the dielectric column; A plurality of dielectric columns are sequentially arranged on the substrate according to the rotation angle of the dielectric column and the position of the dielectric column.

9. An optical system based on a zoom meta-lens, characterized in that: include: A laser emitter, a left-handed circularly polarized light conversion device, a zoom meta-lens as claimed in any one of claims 1 to 5, a microscope, a right-handed circularly polarized light conversion device and an image sensor arranged in sequence; The laser emitted by the laser transmitter is converted into left-handed circularly polarized light by the left-handed circularly polarized light conversion device, and then converted into right-handed circularly polarized light after passing through the zoom meta-lens, the microscope and the right-handed circularly polarized light conversion device in sequence, and enters the image sensor to obtain an image.

10. The optical system based on zoom meta-lens according to claim 9, characterized in that: Also includes: The half-wave plate located between the laser emitter and the left-handed circularly polarized light conversion device is used to adjust the intensity of the laser.

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