Microsphere lens auxiliary super-resolution imaging device fused with pupil filter

Abstract

The microsphere-assisted super-resolution imaging device comprises an illumination light source, light emitted by the illumination light source sequentially passes through a collimating lens, a narrow-band filter and a semi-reflecting and semi-transmitting mirror, and light beams are spread downwards after being reflected by the semi-reflecting and semi-transmitting mirror. Sequentially entering a pupil filter and a microscope objective, focusing to a focal plane behind the microscope objective, and focusing to the surface of the imaging sample again through a microsphere lens to form a superfine focal spot on the surface of the imaging sample; light reflected by the imaging sample passes through the microsphere lens, the microscope objective, the pupil filter and the semi-reflecting and semi-transmitting mirror again, enters the barrel lens through a transmission light field of the semi-reflecting and semi-transmitting mirror and is converged to the imaging detector at the focal plane position of the barrel lens, so that super-resolution imaging is realized; the single crystal cell metasurface unit structure of the pupil filter can simultaneously regulate and control the amplitude, the phase and the polarization of a light field, reduces the focal spot size of the microsphere lens, and improves the resolution of the imaging device under the condition that the imaging quality of the microsphere lens is not affected.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical imaging, and particularly relates to a microsphere lens assisted super-resolution imaging device fusing a pupil filter. BACKGROUND

[0002] Due to the existence of the diffraction limit, the imaging resolution of an optical microscope is difficult to break through the limit of half wavelength. For example, when visible light with a wavelength of 400 nm is used for illumination, the imaging resolution limit is about 200 nm. Among numerous super-resolution imaging technologies, super-resolution fluorescence microscopes (such as STED, STORM, PALM and other technologies) use control of fluorescent molecules to achieve nanoscale imaging resolution, greatly promoting the development and progress of the fields of biology, medicine and the like, but for more non-biological samples that cannot be dyed, non-fluorescent super-resolution imaging technology needs to be used to improve the imaging resolution.

[0003] Among non-fluorescent super-resolution imaging technologies, microsphere assisted super-resolution imaging technology is a relatively mature super-resolution imaging technology, which has the advantages of high resolution, simple structure and easy operation, and does not need to change the traditional microscope light path. Through the microsphere lens placed on the sample surface, the evanescent wave on the sample surface can be collected and converted into a conducting wave, so as to improve the imaging resolution of the microscope system. However, after the refractive index, size and shape of the microsphere lens are adjusted and optimized by researchers, the imaging resolution of the technology has been difficult to continue to improve. Therefore, combining other super-resolution technologies will be the inevitable way to continue to improve the resolution of the microsphere assisted super-resolution imaging system. SUMMARY

[0004] In order to overcome the deficiencies of the prior art, the purpose of the present application is to provide a microsphere lens assisted super-resolution imaging device fusing a pupil filter, which combines pupil filtering technology and microsphere assisted super-resolution imaging technology, and can further reduce the focal spot size of the microsphere lens by simultaneously regulating the amplitude, phase and polarization characteristics of the light field through the single-cell metasurface unit structure of the pupil filter, without affecting the imaging quality of the microsphere lens, thereby improving the resolution of the microsphere assisted super-resolution imaging device. Compared with the traditional amplitude type or phase type pupil filter, the multi-dimensional light field modulation type pupil filter can realize further improvement of the resolution of the microsphere assisted super-resolution imaging system through simultaneous optimization of more parameters.

[0005] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] The application discloses a microsphere-assisted super-resolution imaging device with a fused pupil filter, which comprises an illumination light source 1, wherein light emitted by the illumination light source 1 sequentially passes through a collimating lens 2, a narrow-band filter 3 and a half mirror 4, is reflected by the half mirror 4 and then propagates downward into a pupil filter 5, and then enters a microscope objective 6 and is focused on a focal plane behind the microscope objective 6, is focused again on the surface of an imaging sample 8 by a microsphere lens 7, and forms a super-fine focal spot on the surface of the imaging sample 8; light reflected by the imaging sample 8 again passes through the microsphere lens 7, the microscope objective 6, the pupil filter 5 and the half mirror 4, enters a barrel lens 9 by the transmission field of the half mirror 4, and is focused on an imaging detector 10 at the focal plane position of the barrel lens 9, so that super-resolution imaging is realized.

[0007] The pupil filter 5 comprises a substrate and a plurality of single-cell supercell units on the surface of the substrate, wherein the single-cell supercell units are silicon nano-fin structures and are used for simultaneously modulating the amplitude, phase and polarization state of an incident light field.

[0008] The length, width and height of the silicon nano-fin structure are all in the order of 100 nanometers, and the azimuth angle modulation range is 0-180°.

[0009] The polarization state of the incident light field is modulated by changing the length-width ratio of the supercell supercell unit, the phase of the incident light field is modulated by changing the height of the supercell supercell unit, and the amplitude of the incident light field is modulated by rotating the azimuth angle of the supercell supercell unit.

[0010] The pupil filter 5 is divided into three parts, i.e., a central region, an intermediate region and an edge region, the phase of the central region and the edge region is 0, and the phase of the intermediate region is different from that of the central region and the edge region by π; the polarization direction of each single-cell supercell unit after the plane incident wave passes through the pupil filter 5 is a radial direction, that is, the generated light field is radial polarization light; meanwhile, the spatial distribution of the light intensity presents the phenomenon that the light intensity of the central region and the edge region is weaker than that of the intermediate region, which is consistent with the light field characteristics of a vector light beam.

[0011] The illumination light source 1 is a halogen lamp with a central wavelength of 550 nm.

[0012] Compared with the prior art, the application has the following beneficial effects:

[0013] The application introduces a pupil filter based on a single-cell metasurface above the micro-lens, which not only does not change the original microscope imaging light path, but also realizes the modulation of the incident light field by the single-cell metasurface unit structure of the pupil filter, so that the focal spot size of the micro-lens can be further reduced, and the resolution of the imaging device can be improved. In addition, through the phase modulation technology of the pupil filter, the aberration (mainly spherical aberration) introduced by the micro-lens can be compensated, and the imaging quality of the micro-lens assisted super-resolution imaging system can be improved. Compared with the resolution improvement effect of about 20% of the traditional phase type pupil filter (Guo Shuwen, Guo Hanming, Zhuang Songlin. Asymmetric three-zone pupil filter for one-dimensional lateral super-resolution, Acta Photonica Sinica, 2008), the pupil filter of the application fuses the multi-dimensional light field modulation into the micro-lens assisted super-resolution imaging system, and realizes the resolution improvement effect of about 26%, which greatly improves the resolution of the imaging device, so that the application has wide application prospect in the field of nanometer imaging and micro-detection. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The application is a kind of micro-lens assisted super-resolution imaging device of fusion pupil filter.

[0015] In the figure: 1, illumination light source; 2, collimating lens; 3, narrowband filter; 4, half mirror; 5, pupil filter; 6, microscope objective; 7, micro-lens; 8, imaging sample; 9, barrel lens; 10, imaging detector.

[0016] Figure 2 The application is a kind of micro-lens assisted super-resolution imaging device of fusion pupil filter.

[0017] Figure 3 The application is a kind of micro-lens assisted super-resolution imaging device of fusion pupil filter. Figure 3 (a) is a structure diagram of the pupil filter based on the single-cell metasurface; Figure 3 (b) is the phase distribution of the plane incident wave after the pupil filter; Figure 3 (c) is the intensity and polarization state distribution of the plane incident wave after the pupil filter.

[0018] Figure 4 The application is a kind of micro-lens assisted super-resolution imaging device of fusion pupil filter. Figure 4 (a) is the focusing effect of the single microscope objective; Figure 4 (b) is the focusing effect of the micro-lens below the microscope objective; Figure 4 (c) is the focusing effect of the micro-lens below the microscope objective after inserting the pupil filter.

[0019] Figure 5The imaging resolution of the microsphere-assisted super-resolution imaging device with the fused pupil filter is compared, wherein, Figure 5 (a) is the imaging result of the imaging sample; Figure 5 (b) is the imaging result of the single microscope objective; Figure 5 (c) is the imaging result of the microsphere lens below the microscope objective; Figure 5 (d) is the imaging result of the microsphere lens below the microscope objective after the insertion of the pupil filter. DETAILED DESCRIPTION

[0020] In order to make the technical problems solved by the present application, technical solutions and beneficial effects clearer, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application, and the detailed description is as follows.

[0021] REFERENCE Figure 1 A microsphere-assisted super-resolution imaging device with a fused pupil filter comprises an illumination light source 1, a collimating lens 2, a narrow-band filter 3, a half mirror 4, a pupil filter 5, a microscope objective 6, a microsphere lens 7, an imaging sample 8, a barrel lens 9 and an imaging detector 10. The light emitted by the illumination light source 1 passes through the collimating lens 2, the narrow-band filter 3 and the half mirror 4 in sequence, and the light beam is transmitted downward after being reflected by the half mirror 4, enters the pupil filter 5 for three-dimensional modulation of phase, amplitude and polarization, and then enters the microscope objective 6 and is focused to the focal plane behind the microscope objective 6, is focused again to the surface of the imaging sample 8 by the microsphere lens 7, and forms a super-fine focal spot on the surface of the imaging sample 8. The light reflected by the imaging sample 8 passes through the microsphere lens 7, the microscope objective 6, the pupil filter 5 and the half mirror 4 again, enters the barrel lens 9 through the transmission light field of the half mirror 4, converges to the imaging detector 10 at the focal plane position of the barrel lens 9, and forms an image of the sample. In this process, the illumination spot interacts with the micro-nano structure on the surface of the imaging sample 8, forms an evanescent field with high-frequency information of the sample surface, and is coupled and transmitted to the far field by the microsphere lens 7, thereby forming the imaging result of the imaging sample 8, and thus having a super-resolution imaging effect.

[0022] The illumination light source 1 is a common halogen lamp with a center wavelength of 550 nm; the collimating lens 2 is used to adjust the divergence angle of the incident light to convert it into a parallel light beam; the narrow-band filter 3 is used to convert the wide-band incident light into quasi-monochromatic light with a center wavelength of 550 nm required by the pupil filter 5; and the pupil filter 5 is used to modulate the phase, amplitude and polarization information of the incident light field.

[0023] As Figure 2As shown, a pupil filter 5 based on a unit cell metasurface, which is composed of a substrate and a plurality of unit cell metasurface units processed on the surface of the substrate, the substrate material is SiO2, and the unit cell metasurface units are silicon nanofin structures, the length, width, height, unit period and azimuth angle of the silicon nanofin structure are represented by L, W, H, C and theta respectively, wherein the length, width and height are all in the order of hundreds of nanometers, and the azimuth angle is adjustable within the range of 0-180°. By changing the aspect ratio of the metasurface unit to modulate the polarization state of the incident light field, by changing the height of the metasurface unit to modulate the phase of the incident light field, and by rotating the azimuth angle of the metasurface unit to modulate the amplitude of the incident light field, the three-dimensional modulation of the phase, amplitude and polarization information of the incident light field by a single metasurface unit is realized.

[0024] The present application uses the finite difference time domain (FDTD) algorithm to simulate the regulation of the pupil filter on the optical field parameters, such as Figure 3 (a) shows that the pupil filter based on a unit cell metasurface is divided into three parts: a central region, an intermediate region and an edge region, and different phases, amplitudes and polarization states are set respectively. Figure 3 (b) is the phase distribution of the plane incident wave after passing through the pupil filter, from Figure 3 (b) can be seen that the phases of the central region and the edge region are both 0, and the phase of the intermediate region is different by π. Figure 3 (c) is the intensity distribution and polarization state distribution of the plane incident wave after passing through the pupil filter, wherein the arrow represents the polarization direction, and the color depth represents the light intensity; from Figure 3 (c) can be seen that the polarization direction of each unit cell metasurface unit after the plane incident wave passes through the pupil filter 5 is the radial direction, i.e. the generated light field is radial polarization light; at the same time, the spatial distribution of its light intensity also appears an approximate three-region distribution, and the light intensity of the central region and the edge region is weaker than that of the intermediate region, which conforms to the light field characteristics of the vector beam. As can be seen, by modulating the size parameters of the metasurface unit, the required phase, amplitude and polarization can be realized at the same time.

[0025] Figure 4 (a) is the focal spot formed after the incident light is converged by the microscope objective 6 with a numerical aperture of 0.9, and the full width at half maximum (FWHM) is about 380 nm, wherein the wavelength of the incident light is 550 nm; Figure 4 (b) is the focal spot formed after the incident light is converged by the microscope objective 6 and the microsphere lens 7 in sequence, and the full width at half maximum (FWHM) is about 286 nm, which is compressed by about 25% compared with the focal spot size of the microscope objective 6 without the assistance of the microsphere lens 7; Figure 4(c) After the pupil filter 5 designed for the application is inserted, the incident light is converged by the microscope objective 6 and the micro-lens 7 in turn to form a focal spot with a full width at half maximum (FWHM) of about 212 nm, which is further compressed by about 26% compared with the focal spot size of the micro-lens 7 without the pupil filter 5. It can be seen that the micro-lens 7 has a very obvious effect on improving the focusing performance of the microscope objective 6, and the pupil filter 5 can further improve the focusing performance of the micro-lens 7.

[0026] Figure 5 The resolution simulation test of the micro-sphere assisted super-resolution imaging device with fused pupil filtering. Among them Figure 5 (a) The imaging sample is composed of four groups of point pairs with different intervals. The center interval d1 between the points in the first group is 250 nm, the interval d2 in the second group is 300 nm, the interval d3 in the third group is 350 nm, and the interval d4 in the fourth group is 400 nm. Figure 5 (b) The imaging result of the microscope objective 6 only. As can be seen from the figure, only the point pairs with an interval of 400 nm can be distinguished, and the other point pairs cannot be distinguished. The imaging effect will be obviously improved by adding the micro-lens 7 below the microscope objective 6, and the imaging result is as shown in Figure 5 (c). Except for the point pairs with an interval of 250 nm, the other point pairs can be clearly distinguished. The imaging resolution is further improved by adding the pupil filter 5 above the microscope objective 6, and the imaging result is as shown in Figure 5 (d). The 250 nm point pairs that cannot be distinguished before can now be distinguished, and the point pairs that can be distinguished before are now clearer. The simulation results prove that the micro-lens 7 improves the imaging resolution, and also verify that the pupil filter 5 designed in the application can greatly improve the resolution of the micro-sphere imaging system, and can be widely applied to various optical imaging systems.

[0027] The above is a further detailed description of the application in combination with specific preferred embodiments, and the specific implementation of the application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the application belongs, without departing from the concept of the application, a number of simple deductions or substitutions can be made, which should be regarded as falling within the protection scope of the application.

Claims

1. A microsphere-assisted super-resolution imaging device with fused pupil filter, characterized in that: The light source (1) emits light that passes through a collimating lens (2), a narrow-band filter (3), and a semi-reflective lens (4) in sequence. After being reflected by the semi-reflective lens (4), the light beam propagates downward and enters the pupil filter (5). Then it enters the microscope objective (6) and is focused to the focal plane behind the microscope objective (6). It is then focused again to the surface of the imaging sample (8) by the microsphere lens (7) to form an ultra-fine focal spot on the surface of the imaging sample (8). The light reflected back from the imaging sample (8) passes through the microsphere lens (7), the microscope objective (6), the pupil filter (5), and the semi-reflective lens (4). The transmitted light field of the semi-reflective lens (4) enters the tube lens (9) and converges to the imaging detector (10) at its focal plane position, thus achieving super-resolution imaging.

2. The microsphere-assisted super-resolution imaging device with fused pupil filter according to claim 1, characterized in that: The pupil filter (5) includes a substrate and several single-cell metasurface units on its surface. The single-cell metasurface units are silicon nanofin structures used to simultaneously modulate the amplitude, phase and polarization state of the incident light field.

3. The microsphere-assisted super-resolution imaging device with fused pupil filter according to claim 2, characterized in that: The length, width, and height dimensions of the silicon nanofin structure are all in the hundreds of nanometers range, and its azimuth angle modulation range is 0-180°.

4. The microsphere-assisted super-resolution imaging device with fused pupil filter according to claim 2, characterized in that: The polarization state of the incident light field is modulated by changing the aspect ratio of the supercell metasurface unit, the phase of the incident light field is modulated by changing the height of the supercell metasurface unit, and the amplitude of the incident light field is modulated by rotating the azimuth angle of the supercell metasurface unit.

5. The microsphere-assisted super-resolution imaging device with fused pupil filter according to claim 1, characterized in that: The pupil filter (5) is divided into a central region, an intermediate region and an edge region. The phase of the central region and the edge region are both 0, and the phase difference between the central region and the intermediate region is π. After the plane incident wave passes through the pupil filter (5), the polarization direction of each unit cell metasurface unit is the radial direction, that is, the generated light field is radially polarized light. At the same time, the spatial distribution of its light intensity shows that the light intensity of the central region and the edge region is weaker than that of the intermediate region, which is consistent with the light field characteristics of a vector beam.

6. The microsphere-assisted super-resolution imaging device with fused pupil filter according to claim 1, characterized in that: The lighting source (1) is a halogen lamp with a center wavelength of 550nm.

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