Metastructure lens condenser and microscopic imaging lighting device

Abstract

The invention provides a super-structure lens condenser and a microscopic imaging lighting device, and belongs to the technical field of microscopic imaging. The technical problems that a traditional Kohler illumination collecting lens is large in caliber, thickness and weight, high in price and not beneficial to light weight and miniaturization of a microscopic system are solved, the technical scheme is that the super-structure lens collecting lens achieves abrupt change of a light field phase through interaction of a micro-nano structure and the light field, and the light field phase change is achieved through the super-structure lens collecting lens. Therefore, the light propagation direction is changed, and the micro-nano structures of the plane lens and the super-structure lens condenser for realizing light beam convergence are periodically arranged according to a certain interval. The beneficial effects are that the super-structure lens is utilized to perform light beam deflection and convergence on a plane by utilizing phase mutation, the limitation that a traditional lens needs a convex surface type or a plurality of lenses to realize large numerical aperture condensation is solved, the limitation on the surface curvature and the transverse size during processing is solved, the longitudinal size of the condensing lens is reduced, and the processing efficiency is improved. And miniaturization of a microscopic imaging system is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of microscopic imaging technology, and particularly to a metasurface condenser and a microscopic imaging illumination device. Background Art

[0002] Existing microscopic imaging illumination devices usually work in the way of Kohler illumination, that is, using a condenser to image the light source at infinity to obtain relatively uniform illumination on the object surface, and the illumination aperture can be controlled by the aperture stop to obtain flexible illumination conditions. The traditional refractive lenses used in the traditional Kohler illumination system, such as glass, resin lenses, etc., need to have a convex surface morphology to converge light by refraction. Under the limitation of the current refractive lens manufacturing process, that is, when the surface curvature increases, the lens aperture and thickness cannot be infinitely reduced. The traditional Kohler illumination condenser generally requires multiple combinations or a relatively convex surface shape to achieve large numerical aperture or large-angle illumination, and such a condenser has a large aperture, thickness, weight and high price. The traditional illumination device composed of it is not conducive to the further lightening and miniaturization of the microscopic system. In addition, when the condenser aperture is large, in order to make the illumination light cover the entire aperture, a large surface light source must be used or a small light source must be enlarged. A large light source will also cause the system to be huge, with serious heat generation and short service life. A small light source, such as an LED light source, although it has a long service life, the brightness will inevitably decrease after being enlarged, affecting the imaging effect. Summary of the Invention

[0003] The purpose of the present invention is to overcome the problems in the background art, and provide a metasurface and a microscopic imaging illumination device. By introducing a metasurface condenser into the microscopic imaging illumination device, the miniaturization of the microscopic imaging illumination device is realized, so as to solve the problems of large volume and heaviness of the microscopic imaging illumination device caused by factors such as condensers, light collectors, light sources, etc.

[0004] In order to achieve the above-mentioned invention purpose, the technical solution adopted by the present invention is specifically: a metasurface condenser, the metasurface condenser is a planar lens that realizes the sudden change of the light field phase by using the interaction between the micro-nano structure and the light field, thereby changing the light propagation direction to achieve beam convergence. The micro-nano structures of the metasurface condenser are arranged periodically at a certain interval, and the phase distribution of the metasurface condenser adopts an aspherical focusing phase distribution or a spherical focusing phase distribution

[0005] The aspherical focusing phase distribution The expression is:

[0006]

[0007] The spherical focusing phase distribution The expression is:

[0008]

[0009] Among them, λ is the central wavelength of the LED light source, f is the focal length of the metasurface lens condenser, and x and y are the in-plane coordinates of the metasurface lens condenser.

[0010] Furthermore, the thickness of the micro-nano structure of the metasurface lens condenser is on the order of micrometers, and the overall thickness is less than 1 mm.

[0011] Furthermore, the periodic arrangement of the inner micro-nano structure of the metasurface lens condenser is a square grid or a hexagonal grid, and both the period size and the height of the inner micro-nano structure of the metasurface lens condenser can be adjusted specifically according to the working wavelength and lens parameters.

[0012] Furthermore, the morphology of the inner micro-nano structure of the metasurface lens condenser remains unchanged in the height direction, and the characteristic dimensions in the cross-section can be adjusted according to the phase requirements.

[0013] Furthermore, the metasurface lens condenser can select different materials according to different working bands;

[0014] In the visible light band, the metasurface lens condenser uses the following materials: titanium dioxide, silicon nitride, gallium nitride, or silicon;

[0015] In the infrared band, the metasurface lens condenser uses the following materials: silicon or germanium;

[0016] In the ultraviolet band, the metasurface lens condenser uses hafnium dioxide material.

[0017] Furthermore, the geometric shape of the metasurface lens condenser is rectangular, square, circular, elliptical or polygonal.

[0018] The present invention also provides a microscopic imaging illumination device, including an LED light source and a condenser lens, a first aperture, and a metasurface lens condenser arranged in sequence along the same optical axis.

[0019] Furthermore, the condenser lens uses a refractive lens condenser, a diffractive lens condenser or a metasurface lens condenser, and the metasurface lens condenser has the same material as the metasurface lens condenser.

[0020] Furthermore, a linear polarizer and a quarter-wave plate are arranged in sequence between the condenser lens and the first aperture, and by adjusting the angle between the optical axis of the quarter-wave plate and the main axis of the polarizer, the polarization state of the outgoing light can be adjusted.

[0021] Furthermore, a second aperture is arranged between the condenser lens and the linear polarizer.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. The present invention uses a metasurface lens as a condenser lens. The metasurface lens has a powerful optical field modulation ability and can precisely control the amplitude, phase, dispersion, and polarization state of light waves at the sub-wavelength scale. The metasurface lens is formed by arranging sub-wavelength scattering unit structures, can manipulate the optical field at the sub-wavelength scale, and realize functions such as focusing. The metasurface lens usually has only a sub-wavelength thickness, so it is thinner and lighter, can meet the increasingly miniaturized requirements of optical systems, and the metasurface lens condenser has higher design freedom and flexibility.

[0024] 2. This microscopic imaging illumination device uses a metasurface lens as the condenser lens in the Köhler illumination optical path. By utilizing the ability of the metasurface lens to deflect and converge light beams using phase mutations on a plane, it solves the limitation that traditional lenses require a relatively convex surface or multiple lenses to achieve high numerical aperture condensation, reduces the longitudinal size of the condenser lens, and facilitates the construction of a more compact and integrated microscopic imaging system.

[0025] 3. This microscopic imaging illumination device uses a metasurface lens as the condenser lens. Thanks to the ability of the metasurface lens to deflect and converge light beams using phase mutations on a plane, it solves the limitations on surface curvature and lateral size during the processing of traditional condenser lenses, can further reduce the lateral size of the condenser lens, and reduce the limitation on the size of the light source. Therefore, small-sized and long-life LED lamp beads can be used as the illumination light source, and the overall miniaturization of the device can still be ensured during high numerical aperture condensation.

[0026] 4. This microscopic imaging illumination device replaces the condenser lens with a diffractive lens or a metasurface lens. Based on the ability of the diffractive lens or the metasurface lens to deflect and converge light beams in a plane, and in cooperation with the metasurface lens condenser, on the premise of reasonably designing the focal lengths of these planar lenses, the volume of the Köhler illumination device can be further reduced, solving the problem that the volume of the Köhler illumination optical path based on traditional lenses is large and bulky.

[0027] 5. The manufacturing process of the metasurface lens used in the present invention is highly compatible with the microelectronics manufacturing process, suitable for large-scale production, and can reduce the production cost of the overall illumination device. Description of the Drawings

[0028] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention, and do not constitute a limitation to the present invention.

[0029] Figure 1 It is a schematic diagram of the light transmission process of this microscopic imaging illumination device.

[0030] Figure 2(a) is the layout diagram of the micro-nano structure of the metasurface lens, and (b) is the focusing result diagram of the simulation of the metasurface lens.

[0031] Figure 3 (a) The partial topography diagram of the condenser of the metasurface lens under microscope shooting, (b) is the front image of the condenser of the metasurface lens, (c) is the side image of the condenser of the metasurface lens, and (d) the left figure is the light intensity distribution along the transmission direction of the focused light field of the condenser of the metasurface lens obtained by measurement, and the right figure is the transverse light intensity distribution of the focused light field at the focal length.

[0032] Figure 4 In (a), (b), and (c), the illuminated surfaces respectively correspond to images of the second aperture with different sizes.

[0033] Figure 5 Shows along Figure 4 (a)-(b)-(c) The light intensity distribution curve of the central section line of the illuminated area.

[0034] Among them, the reference numerals are: 1. LED light source; 2. Condenser; 3. Second aperture; 4. Linear polarizer; 5. Quarter-wave plate; 6. First aperture; 7. Condenser of the metasurface lens. Detailed implementation mode

[0035] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Of course, the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0036] The present invention provides a condenser of a metasurface lens. The condenser 7 of the metasurface lens is a planar lens that uses the interaction between micro-nano structures and light fields to achieve a sudden change in the phase of the light field, thereby changing the propagation direction of light and achieving beam convergence. The thickness of the micro-nano structure of the condenser 7 of the metasurface lens is on the micron scale, and the overall thickness of the metasurface lens is generally less than 1 mm. These micro-nano structures are generally arranged periodically at a certain interval; in order to achieve beam convergence, the required phase mutations at different positions on the plane are different. Therefore, the topography of the micro-nano structures within each period will be different to achieve the phase distribution required for light concentration. The phase distribution of the condenser 7 of the metasurface lens adopts an aspherical focusing phase distribution Or spherical focusing phase distribution

[0037] Aspherical focusing phase distribution The expression is:

[0038]

[0039] Spherical focusing phase distribution The expression is:

[0040]

[0041] Among them, λ is the central wavelength of the LED light source, f is the focal length of the metasurface lens condenser, and x and y are the in-plane coordinates of the metasurface lens condenser;

[0042] The periodic arrangement of the micro-nano structures in the metasurface lens condenser 7 can be a square grid or a hexagonal grid, and the period size can be adjusted according to the wavelength and lens parameters;

[0043] The height of the micro-nano structures in the metasurface lens condenser 7 can be adjusted according to the working wavelength and lens parameters of the metasurface lens;

[0044] The morphology of the micro-nano structures in the metasurface lens condenser 7 remains unchanged in the height direction, but the characteristic size in the cross-section changes according to the phase requirements, and its cross-section can be circular, square, rectangular, elliptical or other shapes that can achieve in-plane phase mutation;

[0045] The metasurface lens condenser 7 can select different materials according to different working bands. Materials such as titanium dioxide, silicon nitride, gallium nitride, or silicon can be used in the visible light band, materials such as silicon or germanium can be used in the infrared band, and materials such as hafnium dioxide can be used in the ultraviolet band;

[0046] The geometric shape of the metasurface lens condenser 7 can be rectangular, square, circular, elliptical or polygonal.

[0047] Embodiment 1

[0048] This embodiment verifies the accuracy of the metasurface lens focusing design. First, the focusing performance of the metasurface lens condenser 7 is evaluated by using simulation software (Lumerical FDTD Solutions). Since the simulation calculation requires a large amount of computing resources and it is impossible to directly simulate the actual focusing effect of a large-aperture metasurface lens processed in reality, the metasurface lens is scaled down proportionally during the simulation calculation, that is, the focusing numerical aperture is kept unchanged and the lens aperture is reduced. The focusing numerical aperture of the lens is set to 0.58, the width is 10 microns, the working wavelength is 450 nanometers, and the corresponding theoretical focal length is 7 microns. The arrangement of the micro-nano structures in the metasurface lens is as Figure 2 (a) shown. Here, the lens is square, and the micro-nano structure units are arranged in a square grid. The cross-section of each micro-nano structure is square. These micro-nano structures achieve different phase mutations through different widths, and finally meet the aspherical focusing phase distribution Among them, λ is the central wavelength of the LED light source, f is the focal length of the metasurface lens condenser 7, and x and y are the in-plane coordinates of the metasurface lens condenser 7. The simulation focusing result is as Figure 2(b), an obvious focusing effect can be seen in the normalized electric field intensity distribution along the transmission direction. The focal length obtained by simulation is about 6.89 microns, which is basically consistent with the theory, indicating that the designed metasurface lens condenser 7 can achieve the designed focusing numerical aperture.

[0049] Example 2

[0050] In this example, a metasurface lens condenser 7 with a diameter of 2 mm, a working wavelength of 450 nm, and a focusing numerical aperture of 0.58 was fabricated using electron beam lithography and dry etching. The corresponding theoretical focal length is 1.4 mm. Figure 3 (a) shows the local morphology of the condenser under a microscope. Figure 3 (b)-(c) show the illumination of its front and side. The metasurface lens condenser 7 is located at the center of a square silica wafer and is circular. The thickness of the metasurface lens itself is less than 1 micron and can be ignored. The thickness of the entire condenser is approximately the thickness of the silicon wafer, i.e., 0.5 mm. Figure 3 (d) On the left is the normalized light intensity distribution of the focused light field along the transmission direction behind the actually measured condenser, and on the right is the focal spot light intensity distribution at 1.4 mm. It can be seen that the focal length of the actually fabricated condenser is also approximately 1.4 mm, which basically meets the requirements of the theoretical design.

[0051] Example 3

[0052] As Figure 1 shown, this example provides a microscopic imaging illumination device, which includes an LED light source 1, a condenser 2, a first aperture 6, and a metasurface lens condenser 7 arranged in sequence along the same optical axis. The metasurface lens condenser 7 uses the metasurface lens fabricated in Example 2 as Figure 1 the metasurface lens condenser 7 in the device shown. The condenser 2 generally uses a refractive lens, but for application scenarios with higher miniaturization requirements, a metasurface lens can be used instead; the condenser 2 and the metasurface lens condenser 7 based on the metasurface lens have the same design principle and processing method, but according to specific implementation requirements such as the divergence angle of the LED light source 1 and the device size, they can be arranged by different micro-nano structures and have different phase distributions and lateral dimensions.

[0053] During operation, the LED light source 1 emits a light beam with a certain divergence angle. The light beam travels a certain distance (s) and reaches the condenser lens 2. The condenser lens 2 collects the divergent light beam, deflects and converges the light beam onto the first diaphragm 6 after a distance (s’), ensuring a high energy utilization rate of the system. Due to the converging effect of the condenser lens 2, the magnified image of the LED light source (magnification is s’ / s) covers the entire first diaphragm 6. The first diaphragm 6 is located on the front focal plane of the metasurface lens condenser 7, that is, at a position one focal length (f) away from the front surface of the metasurface lens condenser 7. Its size can control the angle of the illumination light received by the object. Finally, the metasurface lens condenser 7 converges the light passing through the first diaphragm 6 at a position slightly greater than its focal length (f), forming a uniform and converging illumination light field. Depending on the design, the metasurface lens condenser 7 can have different focusing numerical apertures. At the same time, by adjusting the size of the first diaphragm 6, the illumination aperture of the object space light field can be flexibly controlled within its own focusing numerical aperture range.

[0054] Embodiment 4

[0055] To provide more flexible control of the illumination polarization state, as Figure 1 shown, based on Embodiment 3, this illumination device further includes a linear polarizer 4 and a quarter-wave plate 5. The linear polarizer 4 and the quarter-wave plate 5 are located between the condenser lens 2 and the first diaphragm 6. The quarter-wave plate 5 is placed behind the linear polarizer 4. By adjusting the angle between the optical axis of the quarter-wave plate 5 and the main axis of the linear polarizer 4, the polarization state of the outgoing light can be adjusted. The polarization states of the outgoing light include: linearly polarized light, elliptically polarized light, and circularly polarized light.

[0056] Embodiment 5

[0057] To flexibly control the intensity and illumination range of the illumination light, based on Embodiment 4, this microscopic imaging illumination device with a metasurface lens further includes a second diaphragm 3. Specifically, the second diaphragm 3 is installed between the condenser lens 2 and the linear polarizer 4, close to the condenser lens 2. The size of the second diaphragm 3 controls the size of the light beam collected and focused by the condenser lens 2. It can freely control the illumination intensity without changing the power of the LED light source 1. At the same time, through the imaging effect of the metasurface lens condenser 7, an image of the second diaphragm 3 can be formed in the object space. The size of the second diaphragm 3 can be presented proportionally in the object space according to the imaging relationship, controlling the illumination range.

[0058] This embodiment also uses the metasurface lens prepared in Embodiment 2 as Figure 1 the metasurface lens condenser 7 in the device shown. According to the device design principle, a reduced image of the second diaphragm 3 will appear at a position approximately 1.4 mm away from the back of the metasurface lens condenser 7, which is the position where the illumination device produces uniform illumination. To evaluate the illumination uniformity at this position, in this embodiment, a microscopic system is externally connected to image the illumination surface behind the metasurface lens condenser 7. The imaging result is asFigure 4 As shown in (a)-(c), the illumination surfaces shown in (a)-(c) respectively correspond to images of the second aperture 3 of different sizes, verifying that the size of the illumination range can be dynamically controlled by the size of the second aperture 3. Figure 5 (a)-(c) show along Figure 4 the light intensity distribution curves of the central cross-section of the illumination area in (a)-(c). It can be seen that a relatively uniform illumination field of view can be obtained through the microscopic imaging illumination device based on the metasurface lens.

[0059] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A meta-lens condenser, characterized in that: The meta-lens condenser (7) is a plane lens that utilizes the interaction between the micro-nano structure and the light field to achieve a sudden change in the phase of the light field, thereby changing the propagation direction of the light beam to achieve light beam convergence. The micro-nano structure of the meta-lens condenser (7) is periodically arranged at a certain interval, and the phase distribution of the meta-lens condenser (7) adopts an aspherical focusing phase distribution. Or spherical focusing phase distribution The aspheric focusing phase distribution The expression is: The spherical focusing phase distribution The expression is: Wherein, λ is the central wavelength of the LED light source (1), f is the focal length of the meta-lens condenser (7), and x and y are the in-plane coordinates of the meta-lens condenser (7).

2. The meta-lens condenser according to claim 1, characterized in that: The micro-nano structure thickness of the meta-lens condenser (7) is in the micrometer range, and the overall thickness is less than 1 millimeter.

3. The meta-lens condenser according to claim 1, characterized in that: The periodic arrangement of the micro-nano structures inside the meta-lens condenser (7) is a square grid or a hexagonal grid, and the period size and the height of the micro-nano structures inside the meta-lens condenser (7) can be specifically adjusted according to the working wavelength and lens parameters.

4. The metalens condenser according to claim 1, characterized in that: The morphology of the internal micro-nano structure of the meta-lens condenser (7) remains unchanged in the height direction, and the characteristic size in the cross section can be adjusted according to the phase requirement.

5. A meta-lens condenser according to claim 1, characterized in that: The meta-lens condenser (7) can be made of different materials according to different working bands; In the visible light band, the meta-lens condenser (7) is made of the following materials: titanium dioxide, silicon nitride, gallium nitride, or silicon; In the infrared band, the meta-lens condenser (7) is made of the following materials: silicon or germanium; In the ultraviolet band, the meta-lens condenser (7) is made of hafnium dioxide material.

6. A meta-lens condenser according to claim 1, characterized in that: The geometric shape of the meta-lens condenser (7) is rectangular, square, circular, elliptical or polygonal.

7. A microscopic imaging lighting device, the microscopic imaging lighting device adopts a meta-lens condenser according to any one of claims 1 to 6, characterized in that: It comprises an LED light source (1), and a light collecting mirror (2), a diaphragm (6), and a meta-lens light collecting mirror (7) which are sequentially arranged along the same optical axis.

8. A microscopic imaging lighting device according to claim 7, characterized in that: The light collecting mirror (2) is a refractive lens light collecting mirror, a diffractive lens light collecting mirror or a meta-lens light collecting mirror, and the meta-lens light collecting mirror is made of the same material as the meta-lens condenser (7).

9. The microscopic imaging lighting device according to claim 7, characterized in that: A linear polarizer (4) and a quarter-wave plate (5) are arranged in sequence between the light collecting mirror (2) and the aperture 1 (6); and the polarization state of the outgoing light can be adjusted by adjusting the angle between the optical axis of the quarter-wave plate (5) and the main axis of the polarizer (4).

10. The microscopic imaging lighting device according to claim 7, characterized in that: A second aperture (3) is arranged between the light collecting mirror (2) and the linear polarizing plate (4).

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