Submicron resolution metalens-type endoscope lens with simultaneous achromatic and spherical aberration

Abstract

The present invention relates to a submicron resolution metalens-type endoscope lens that eliminates both chromatic aberration and spherical aberration, including a metalens, wherein the metalens includes a mirror, and the mirror has a plurality of structural units that focus the excitation light and the fluorescence to the same plane and the same focus. The plurality of structural units include a plurality of first structural units and a plurality of second structural units, wherein the first structural unit is used to transmit the excitation light, and the second structural unit is used to transmit the fluorescence. The present invention can simultaneously realize a single-piece lens (easy to assemble), a small lens size (capable of entering a tiny channel), and a high imaging resolution (eliminating both chromatic aberration and spherical aberration), and is expected to apply confocal fluorescence endoscope imaging technology to pancreatic and bile duct imaging. At the same time, due to the high resolution of the lens, real-time, in vivo diagnosis of pancreatic lesions can be achieved by accurately observing changes in cell morphology and structure.

Description

Technical Field

[0001] The present invention relates to the field of endoscope imaging technology, and in particular to a sub-micron resolution super lens type endoscope lens capable of simultaneously eliminating chromatic aberration and spherical aberration. Background Art

[0002] Fluorescence confocal endoscopic imaging technology relies on an endoscope probe with a small outer diameter, which can penetrate deep into the cavities of small animals and the human body to perform in vivo imaging observations. It is an important diagnostic tool for early diagnosis of cancer in vivo. In this technology, the small-sized endoscope probe is usually composed of a fiber optic bundle and a micro-microscope. Therefore, for confocal endoscopic imaging, the size of the micro-microscope (whether it can enter the narrow cavities of the human body) and the resolution capability (whether it has a high enough resolution to identify the fine structure of cells) directly determine the quality of the imaging effect.

[0003] At present, micro-microscope lenses are usually made of refractive index gradient lenses or micro-lens groups. The advantage of refractive index gradient lenses is that the size can be designed to be very small, but there are not many adjustable parameters in the design, so it is not flexible enough, and it cannot calibrate chromatic aberration and spherical aberration at the same time, so the imaging resolution is not high, which is not enough to distinguish the fine structure of the tissue. The micro-lens group is designed by combining multiple lenses, which can calibrate spherical aberration, so the imaging resolution is higher, etc., but it often contains too many lenses, resulting in a larger overall volume, and it will also increase the complexity of lens processing and the precision requirements for objective lens assembly. At the same time, whether it is a refractive index gradient lens or a micro-lens group, it is difficult to achieve ultra-fine size (<1mm external straight size) in optical design, and it cannot enter the narrow cavities of the human body (such as the pancreatic and bile ducts).

[0004] Superlens technology is an emerging technology that has emerged in recent years. It is usually composed of nano-scale structural units and substrates. According to design requirements, the structural units can be used to realize light manipulation in local areas. Compared with traditional refractive index gradient lenses and microlens groups, superlenses have smaller nanostructure units and higher spatial freedom in design, so the imaging resolution can be further improved. At the same time, superlenses have the characteristics of being light and thin, which can meet the requirements of miniaturization and micro-miniaturization. In addition to the miniaturization of the design, in terms of performance, the guarantee of high imaging resolution is also very important, which requires the elimination of chromatic aberration and spherical aberration. There are currently design methods for separately calibrating chromatic aberration or spherical aberration, but single-item calibration can often only achieve a resolution of 1-3um, and cannot be higher. Summary of the invention

[0005] The purpose of the present invention is to provide a sub-micron resolution metalens type endoscope lens that can eliminate both chromatic aberration and spherical aberration. It can eliminate both chromatic aberration and spherical aberration at the same time. It is not only small in size to meet the application scenarios of narrow channels, but also has high resolution and can identify fine structures.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] A sub-micron resolution metalens type endoscope head capable of eliminating both chromatic aberration and spherical aberration, comprising a metalens, wherein the metalens comprises a mirror having a plurality of structural units for focusing excitation light and fluorescence onto the same plane and the same focal point.

[0008] In the above scheme, several structural units enable the excitation light and fluorescence to be focused on the same plane and the same focal point, that is, achromatism and spherical aberration are achieved simultaneously, which can reduce the outer diameter and improve the resolution at the same time. Therefore, it is suitable for application scenarios with narrow channels and provides technical support for the observation of cells in the pancreatic and bile ducts.

[0009] In the optimized solution, the plurality of structural units include a plurality of first structural units and a plurality of second structural units, the first structural units are used to transmit the excitation light, and the second structural units are used to transmit the fluorescence. In this solution, different structural units are used to realize the transmission of the excitation light and the fluorescence, respectively, to provide technical support for better realization of achromatism and avoid mutual interference between the transmission of different optical signals.

[0010] In an optimized solution, the areas occupied by the plurality of first structural units and the plurality of second structural units in the mirror surface are equal.

[0011] In the optimized solution, several first structural units form a first annular area and a second annular area, several second structural units form a third annular area and a fourth annular area, and the first annular area, the third annular area, the second annular area, and the fourth annular area are distributed in sequence.

[0012] In the optimized solution, the first structural unit and the second structural unit are both elliptical column structures.

[0013] The phase distributions on the area modulated by the incident excitation light and the area modulated by the fluorescence signal satisfy the following formulas:

[0014]

[0015] in, is the modulation phase of the excitation light, is the modulation phase for fluorescence, f is the focal length, λ sec is the excitation light wavelength, λ flo is the fluorescence wavelength, is the third-order modulation coefficient for the excitation light, is the third-order modulation coefficient for fluorescence, x and y are the coordinates of the circular lens, and R is the radius of the metalens mirror.

[0016] The optimized solution also includes an optical fiber bundle, which is composed of 10,000 to 30,000 optical fibers. In this solution, the optical fiber bundle is composed of 10,000 to 30,000 single optical fibers, each of which corresponds to an imaging point. Each optical fiber can simultaneously input excitation emission and output fluorescence. There is no need for a piezoelectric ceramic scanner or other structure to move the optical fiber, so the structure is simple and the transmission effect is good.

[0017] Compared with the prior art, the present invention has the following technical advantages:

[0018] The superlens endoscope lens provided in this embodiment not only has an ultra-fine outer lens size, which can achieve an outer diameter of less than 1mm, but also has the ability to eliminate chromatic aberration and spherical aberration, and can achieve submicron resolution, with a resolution of less than 1um. It is expected that confocal fluorescence endoscope imaging technology will be applied to pancreatic and bile duct imaging. At the same time, due to the high resolution of the lens, real-time, in vivo diagnosis of pancreatic lesions can be achieved by accurately observing changes in cell morphology and structure.

[0019] For other advantages of the present invention, please refer to the relevant description in the embodiment section. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art 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.

[0021] Figure 1 (a) Figure 1 (b) are respectively a transmission optical path diagram of the excitation light and a transmission optical path diagram of the fluorescence in the endoscope lens provided in an embodiment of the present invention.

[0022] Figure 2 (a) Figure 2 (b) Figure 2 (c) Figure 2 (d) Schematic diagram of the states of non-achromatic, non-aplanatic and non-achromatic, and simultaneous achromatic and aplanatic, respectively.

[0023] Figure 3 Schematic diagram of the distribution of the first structural unit and the second structural unit in the mirror surface of the metalens used as an example in the embodiment.

[0024] Figure 4 (a) Figure 4 (b) Figure 4 (c) are the focusing effect diagram of the excitation light and fluorescence along the xz plane, the energy distribution diagram of the excitation light and fluorescence, and the energy distribution comparison diagram of the excitation light and fluorescence, respectively.

[0025] Figure 5 (a) Figure 5 (b) Figure 5 (c) Figure 5 (d) Figure 5 (e) Figure 5 (f) are respectively the focusing effect diagram of the excitation light along the xy plane without spherical aberration elimination, the focusing effect diagram of the excitation light along the xy plane with spherical aberration eliminated, the energy distribution diagram of the excitation light along the xy plane when both chromatic aberration and spherical aberration are eliminated, the energy distribution diagram of the fluorescence along the xy plane when both chromatic aberration and spherical aberration are eliminated, the resolution of the excitation light when both chromatic aberration and spherical aberration are eliminated, and the resolution of the fluorescence when both chromatic aberration and spherical aberration are eliminated.

[0026] Markings in the figure: 10 - optical fiber bundle; 20 - capsule; 30 - super lens; 40 - glass sheet; 50 - sample. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] See also Figure 1 (a) or Figure 1 (b) This embodiment provides a sub-micron resolution metalens-type endoscope head that is simultaneously free of chromatic aberration and spherical aberration, comprising an optical fiber bundle 10 , a capsule 20 , a metalens 30 , and a glass sheet 40 .

[0029] The optical fiber bundle 10 is used as an image transmission optical fiber, mainly for transmitting optical signals, that is, the incident excitation light (λ exc ) of incoming and fluorescent (λ flo ) is transmitted, and the optical fiber bundle 10 is composed of 10,000 to 30,000 cores of optical fiber. The capsule 20 is made of medical metal and is mainly used to encapsulate and fix the optical fiber bundle 10, the super lens 30 and the glass sheet 40 (to protect the surface of the super lens).

[0030] like Figure 1 As shown in (a), the spherical light (point light source) emitted from the optical fiber bundle 10 passes through the super lens 30 (achromatic, aplanatic and focused), then passes through the glass sheet 40, and finally enters the surface of the sample 50. In order to ensure clear imaging, the returned fluorescence needs to return to the image transmission fiber along the original optical path, such as Figure 1 (b) as shown.

[0031] In order to obtain higher imaging resolution and combine the needs of fiber endoscopic and fluorescence imaging, this study proposed a method of calibrating chromatic aberration and spherical aberration simultaneously based on a high degree of freedom superlens, and finally achieved sub-micron resolution. Since the wavelengths of the incident excitation light and the returned fluorescence are different in fluorescence imaging, the chromatic aberration effect will lead to different focusing depth positions (such as Figure 2 (a)). Therefore, the metalens needs to achieve function 1 in design, that is, the incident excitation light and the fluorescence are focused on the same plane, that is, achromatic. For endoscopy applications, spherical light rather than parallel light comes out of the fiber bundle. A lens that does not have the ability to eliminate spherical aberration will cause two focal points to appear in the focal plane (such as Figure 2 (b)). Therefore, the metalens needs to have function 2, that is, to eliminate spherical aberration. The metalens designed in this way has both functions 1 and 2, and can eliminate chromatic aberration and spherical aberration at the same time, as shown in Figure 2 (c) as shown.

[0032] Design of superlens: In design, the transmission phase theory is used for phase regulation, and the phase is manipulated by controlling the structure of the cell column. In this embodiment, an elliptical column structure unit is adopted, and the materials used are HfO2 and TiO2 (which have high transmittance for excitation light and fluorescence, respectively); the base material is ordinary Si or SiO2 (glass material).

[0033] Function 1, achromatic aberration adopts the technical solution: the metalens is divided into several annular equal parts according to the area, among which: half of the area (for example Figure 3 S1 and S3 in the figure are used to modulate the excitation light, while ensuring that the transmittance of the excitation light in this area is high and the fluorescence transmittance is very low (for example, using HfO2 material); the other half of the area (for example Figure 3 S2 and S4 in the figure are used to modulate the fluorescence, while ensuring that the transmittance of the fluorescence in this area is high and the transmittance of the excitation light is very low (for example, using SiO2 material).

[0034] Function 2, the technical solution adopted for aberration elimination: In order to achieve the focusing of the excitation light, the phase distribution on the area modulated for the incident excitation light and the area modulated for the fluorescence signal satisfies formula (1) and formula (2), as shown below:

[0035]

[0036] in, is the modulation phase of the excitation light, is the modulation phase for fluorescence, f is the focal length, λ sec is the excitation light wavelength, λ flo is the fluorescence wavelength, is the third-order modulation coefficient for the excitation light, is the third-order modulation coefficient for fluorescence, x and y are the coordinates of the circular lens, and R is the radius of the metalens mirror.

[0037] In order to ensure that the area of ​​excitation light modulation is equal to the area of ​​fluorescence modulation, in this design, a total of 4 circular (or ring) shapes are used, such as Figure 3 As shown. The superlens is composed of several nanoscale structural units, and one structural unit is composed of a substrate and an elliptical cylinder with phase modulation capability. The elliptical cylinder is located on the substrate, for example, in the central area of ​​the substrate. The elliptical cylinder is made of two different high-refractive index dielectric materials, so the structural units are respectively a first structural unit and a second structural unit. The elliptical cylinder of the first structural unit is made of, for example, HfO2 material, and is used to transmit excitation light. The elliptical cylinder of the second structural unit is made of, for example, TiO2 material, and is used to transmit fluorescence. In this study, the structural unit adopts the shape of an elliptical cylinder, and different phase and transmittance distributions are obtained by changing the major axis size and minor axis size of the elliptical cylinder.

[0038] When forming the annular area, the corresponding structural units are distributed along the circumference with a set radius. Theoretically, the more the number of rings, the better the achromatic effect will be, but it will also increase the complexity of processing, which may lead to an increase in the error rate. Therefore, in this embodiment, 4 rings are used, which not only solves the problem of achromatic aberration, but also ensures the product yield.

[0039] Theoretically, the distribution areas of the rings formed by the first structural unit and the second structural unit may not be equal, but when they are equal, the signal transmission effect achieved is optimal. When the transmittance η is constant: (1) when the area ratio is 50:50, the incident excitation light + the returned fluorescence 50%*50%=0.25 (maximum value); (2) for example, when the area ratio is 10:90, the incident excitation light + the returned fluorescence 10%*90%=0.09.

[0040] According to the commonly used wavelengths of confocal endoscopic imaging, the excitation wavelength is 488nm, and the material of the nano-level structural unit is selected as HfO2; the fluorescence wavelength is 525nm, and the material of the nano-level structural unit is selected as TiO2. For the elliptical cylinder of TiO2 and the elliptical cylinder of HfO2, the corresponding relationship between different major and minor axes and phase and transmittance is obtained through experiments, and a data table of phase and transmittance when the major and minor axes change is established. In actual application, phase modulation is realized by referring to the data table.

[0041] In this embodiment, the excitation light wavelength is 488nm and the fluorescence wavelength is 525nm, and other corresponding wavelength signals can also be used as examples. For example, the absorption rate of 405nm, 560nm, 610nm and other bands in biological tissues is good. 525nm is the wavelength of sodium fluorescein (a certain dye), and other fluorescein dyes can also be used. For different design experiments, different incident light wavelengths and fluorescent dye wavelengths can be changed, and corresponding data tables of phase and transmittance when the major and minor axes change can be established through experiments.

[0042] For the nanometer-level unit column at the position (x, y) in the region of the excitation light wavelength (S1 and S3), the target phase is designed according to formula (1). At this time, λ exc The target phase is 488 nm, and the focal length f is 24 μm. Select parameters close to the target phase and with high transmittance from the HfO2 elliptical cylinder data table, and place the elliptical cylinder at each (x, y) until all S1 and S3 areas are covered; similarly, in the fluorescence wavelength (S2 and S4) region, the target phase of the nanostructure at each (x, y) is designed according to formula (2), at this time λ flo The phase angle of the target is 525nm, the focal length f is 24μm, and the parameters close to the target phase and with high transmittance are selected from the TiO2 elliptical cylinder data table, and the elliptical cylinder is placed at (x, y) until all S2 and S4 areas are covered. In this way, the surface design of the superlens is completed.

[0043] The actual lens diameter of the product measured by micrometer is 0.90mm. In order to verify the feasibility of this design, relevant experiments were also carried out. The achromatic ability verification results of the super lens are as follows: Figure 4 (a)-(c) show the results of the verification of the spherical aberration elimination ability of the metalens Figure 5 As shown in (a)-(b), the imaging resolution results with both achromatic and spherical aberration are as follows Figure 5 As shown in (c)-(f).

[0044] For 488nm excitation light, the focusing effect of the superlens is as follows Figure 4 (a) As shown in the left figure, the energy distribution of the far field along the xz axis is as follows Figure 4 (b) The left image shows that the focus is at 24.31 μm, which is close to the theoretical focal length (24 μm). For 525 nm fluorescence, the focusing effect of the superlens is as follows: Figure 4 (a) Right figure, the energy of the far field along the xz axis is Figure 4 (a) In the right figure, it can be seen that the focus is at 24.28μm, which is also close to the theoretical focal length. At the same time, the focus deviation of these two different wavelengths (488nm and 525nm) is 0.03μm (24.28μm-24.31μm, as shown in Figure 2). Figure 4(c)), that is, 0.125%*f (about 1.2% of the focal length). Based on the above results, the superlens of this study can focus two different wavelengths of light onto the same focal plane, that is, it has the ability to achromatize.

[0045] Figure 5 (a) is the beam convergence when the imaging depth is the focal plane z = 24.3um. It can be seen that in addition to the first main focus (full width at half maximum is 0.76um), there is also a secondary focus due to the failure to eliminate spherical aberration. Figure 5 (b) is the beam convergence after eliminating spherical aberration, with no secondary focus and only one focus (full width at half maximum is 0.79um). This result proves that the superlens proposed in this study has the ability to eliminate spherical aberration.

[0046] Figure 5 (c) and (d) are the imaging results of the excitation light (488 nm) and fluorescence (525 nm) at the focal plane, respectively, that is, the energy distribution along the xy axis. Figure 5 (e) shows that when the wavelength of light is 488nm, its half-maximum full width (i.e. lateral resolution) is 0.45μm. Figure 5 (f) shows that when the wavelength of light is 525nm, its half-maximum full width (i.e., lateral resolution) is 0.65μm. Therefore, it can be considered that the lateral resolution of this metalens is 0.65μm, and it ultimately reaches the submicron level due to the simultaneous elimination of chromatic aberration and spherical aberration.

[0047] It can be seen that the metalens endoscope lens provided in this embodiment not only has an ultra-fine outer lens size, which can achieve an outer diameter size of less than 1mm, but also has the ability to eliminate chromatic aberration and spherical aberration, and can achieve submicron level resolution, with a resolution of less than 1um. In the design of metalens, there is usually only a separate method for eliminating chromatic aberration, or a separate method for eliminating spherical aberration, so the imaging resolution cannot reach the submicron level. The metalens endoscope lens provided in this embodiment has the elimination of chromatic aberration and spherical aberration at the same time, because the resolution is better than 1um.

[0048] Existing confocal endoscope objectives use refractive index gradient lenses or micro-lens group solutions. The resolution based on the design method of refractive gradient lenses is usually 1.23μm and the outer diameter is 1.9mm. The resolution based on the design method of micro-lens groups is usually 1.95μm and the outer diameter is 2.6mm. This will cause problems such as bulky volume and difficulty in precise assembly due to too many lenses.

[0049] Therefore, the superlens endoscope lens proposed in this design can simultaneously realize a single lens (easy to assemble), a small lens size (can enter tiny channels), and a high imaging resolution (eliminating both chromatic aberration and spherical aberration), and is expected to apply confocal fluorescence endoscope imaging technology to pancreatic and bile duct imaging. At the same time, due to the high resolution of the lens, it can accurately observe changes in cell morphology and structure to achieve real-time, in vivo diagnosis of pancreatic lesions.

[0050] The above-described embodiments are only specific implementations of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications, replacements and improvements within the technical scope disclosed by the present invention, and these modifications, replacements and improvements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A sub-micron resolution metalens-type endoscope lens with both chromatic aberration and spherical aberration, characterized in that: The super lens includes a mirror surface, and the mirror surface has a plurality of structural units that focus the excitation light and the fluorescence light to the same plane and the same focal point; The phase distributions on the area modulated by the incident excitation light and the area modulated by the fluorescence signal satisfy the following formulas: in, is the modulation phase of the excitation light, is the modulation phase for fluorescence, f is the focal length, λ sec is the excitation light wavelength, λ flo is the fluorescence wavelength, is the third-order modulation coefficient for the excitation light, is the third-order modulation coefficient for fluorescence, x and y are the coordinates of the circular lens, and R is the radius of the metalens mirror.

2. The sub-micron resolution metalens type endoscope lens with simultaneous achromatic and spherical aberration elimination according to claim 1, characterized in that: The plurality of structural units include a plurality of first structural units and a plurality of second structural units. The first structural units are used to transmit the excitation light, and the second structural units are used to transmit the fluorescence.

3. The sub-micron resolution metalens type endoscope lens with simultaneous achromatic and spherical aberration elimination according to claim 2, characterized in that: The areas occupied by the plurality of first structural units and the plurality of second structural units in the mirror surface are equal.

4. The sub-micron resolution metalens type endoscope lens with simultaneous achromatic and spherical aberration elimination according to claim 3, characterized in that: A plurality of first structural units form a first annular region and a second annular region, a plurality of second structural units form a third annular region and a fourth annular region, and the first annular region, the third annular region, the second annular region, and the fourth annular region are distributed in sequence.

5. The sub-micron resolution metalens type endoscope lens with simultaneous achromatic and spherical aberration elimination according to claim 2, characterized in that: The first structural unit and the second structural unit are both elliptical column structures.

6. The sub-micron resolution metalens type endoscope lens with simultaneous achromatic and spherical aberration elimination according to claim 2, characterized in that: The first structural unit is made of HfO2 material, and the second structural unit is made of TiO2 material.

7. The sub-micron resolution metalens-type endoscope lens with simultaneous achromatic and spherical aberration elimination according to claim 1, characterized in that: It also includes an optical fiber bundle, which is composed of 10,000 to 30,000 optical fibers.

8. The sub-micron resolution metalens-type endoscope head having both chromatic aberration and spherical aberration abrogated according to claim 7, characterized in that: It also includes a sealing shell and a glass sheet. The super lens is located between the optical fiber bundle and the glass sheet in the transmission light path. The sealing shell is used to encapsulate and fix the optical fiber bundle, the super lens and the glass sheet.

9. The sub-micron resolution metalens type endoscope lens with simultaneous achromatic and spherical aberration elimination according to claim 1, characterized in that: The outer diameter of the endoscope lens is less than 1 mm, and the resolution is less than 1 um.

Images