A three-dimensional optical manipulation method based on a metasurface

Abstract

The application relates to a three-dimensional optical manipulation method based on a super-structured surface, which comprises the following steps: scanning a nano-pillar unit structure to construct a phase library, selecting a high-efficiency half-wave plate nano-pillar with a phase coverage of pi to pi from the phase library for the construction of the super-structured surface, synergistically introducing a geometric phase and a transmission phase regulation mechanism, combining spatial multiplexing arrangement, realizing the independent regulation of different circular polarization state light fields under different wavelengths, and generating four switchable optical manipulation focal points in a three-dimensional space; and through the switching of the polarization state or the working wavelength of incident light, the stable capture and controllable transfer of particles in the space are realized. Compared with the prior art, the application has the advantages of realizing the three-dimensional optical manipulation of particles in a structure on a chip, high manipulation freedom, and simple and efficient manipulation adjustment mode.

Description

Technical Field

[0001] This invention relates to the field of micro-nano photonics and optical manipulation technology, and in particular to a three-dimensional optical manipulation method based on metasurfaces. Background Technology

[0002] Three-dimensional manipulation has significant application value. Optical tweezers technology utilizes momentum transfer between light and matter to achieve high-precision, non-invasive manipulation of micron- or nano-scale particles and biological cells. By controlling parameters such as the phase, amplitude, and polarization of light, multifunctional particle manipulation can be achieved. However, traditional optical manipulation systems typically rely on bulky optical components and complex optical paths, making miniaturization and integration difficult and limiting their application in systems-on-chips or microdevices.

[0003] In recent years, metasurfaces, as artificially designed two-dimensional structures, have provided new solutions for integrated optical manipulation. Metasurfaces can serve as compact alternatives to traditional optical lenses, enabling on-chip particle capture and manipulation. By utilizing geometric phase modulation, metasurfaces can spatially separate left-handed and right-handed light, thus achieving switchable optical capture and particle rotation. Furthermore, by spatially multiplexing the geometric phase metasurface, polarization-dependent dual focal points can be generated in the longitudinal direction, enabling axial movement of particles. However, existing metasurface-based optical manipulation schemes are mainly limited to two-dimensional manipulation; on-chip three-dimensional optical manipulation has not yet been explored.

[0004] Chinese invention patent CN120802409A discloses a fully dielectric adjustable optical tweezers based on a composite phase superlens. The invention integrates geometric phase and transmission phase control methods into a periodic structure of a dielectric metasurface, arranging them into a circular lens surface according to a specific mapping and arrangement. Due to the control of the composite phase, the superlens can generate two different output electric fields under linearly polarized light input, and these two electric fields can exist independently under circularly polarized light input with opposite chirality. Adjusting the polarization type of the incident light source allows for free switching between various optical capture methods for particles in the field. This invention flexibly adjusts the manipulation method without changing the device structure, addressing more diverse particle capture needs. However, existing technologies based on metasurfaces still suffer from limitations such as two-dimensional manipulation and a single, difficult-to-switch particle manipulation method.

[0005] In summary, there is currently a lack of a three-dimensional optical manipulation method based on metasurfaces to solve or partially solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by providing a three-dimensional optical manipulation method based on metasurfaces, so as to solve or partially solve the problems that the optical manipulation based on metasurfaces in the prior art is limited to two-dimensional manipulation and that the particle manipulation mode is singular and difficult to switch.

[0007] The objective of this invention can be achieved through the following technical solutions: This invention provides a three-dimensional optical manipulation method based on metasurfaces, specifically including: S1. Using a high refractive index medium material, subwavelength nanopillars are constructed on a substrate as unit structures to build a metasurface. The geometric parameters of the periodicity of the nanopillars and unit structures are scanned to obtain a parameter set. S2. Based on the obtained parameter set, select suitable nanopillars, set the orientation angle of the nanopillars, so that left-handed and right-handed light obtain equal and opposite geometric phases after transmission, and superimpose the transmission phase to realize independent phase modulation of light fields of different spin states. S3. For the metasurface, spatial multiplexing arrangement is performed at different working wavelengths so that the optical field modulation function of the metasurface at different wavelengths does not interfere with each other; S4. By setting the phases of the left-handed and right-handed light, under different wavelengths and different circular polarization states of incident conditions, the metasurface forms focal points with different spatially separated locations in three-dimensional space. Based on the focal points, an optical gradient force is generated to achieve stable capture of micron-scale particles. S5. By switching the polarization state or working wavelength of the incident light, the optical potential well is excited by the focal points separated by different spatial positions, so as to complete the controllable movement of the particles in the lateral and longitudinal directions and realize three-dimensional optical manipulation based on metasurface.

[0008] As a preferred technical solution, the metasurface is configured to simultaneously utilize the geometric phase, the transmission phase, and the spatial multiplexing arrangement to independently control the phase of left-handed and right-handed light of different wavelengths, forming focal points at different spatial locations.

[0009] As a preferred technical solution, the nanopillar has a half-wave plate structure with a rectangular cross-section.

[0010] As a preferred technical solution, the phase coverage of the parameter group is from -π to π.

[0011] As a preferred technical solution, the high refractive index medium material is titanium dioxide, and the substrate is made of silicon dioxide.

[0012] As a preferred technical solution, the spatial reuse arrangement is achieved by arranging nanopillars corresponding to different wavelengths in an alternating or partitioned manner within the plane of the metasurface.

[0013] As a preferred technical solution, the phase distribution of the metasurface satisfies: In the formula, It is the phase applied to left-handed light. It is the phase applied to right-handed light. It is the focal point of the left-handed optical system. It is the focal point of the right-handed optical rotation. λ is the wavelength.

[0014] As a preferred technical solution, the working wavelength is set to 457nm and 532nm, the light enters from the substrate side, the height of the nanopillar is set to 600nm, and the period is 360nm.

[0015] As a preferred technical solution, at a working wavelength of 457nm, the metasurface forms two spatially separated focal points in the lateral direction under left- and right-hand circularly polarized incident conditions, respectively, to realize the controllable movement of particles in the x-direction. At a working wavelength of 532nm, the metasurface forms vertically separated focal points in the yz plane, to realize the movement of particles in the longitudinal and lateral directions.

[0016] As a preferred technical solution, the particles achieve three-dimensional controllable motion in a liquid environment.

[0017] Compared with the prior art, the present invention has at least one of the following beneficial effects: (1) This invention utilizes nanopillars to construct metasurfaces, synergistically introduces geometric phase and transmission phase modulation mechanisms and combines them with spatial reuse to achieve independent modulation of light fields with different circular polarization states at different wavelengths, thereby generating switchable optical manipulation focal points in three-dimensional space, realizing stable capture and controllable transfer of particles, solving the problem that optical manipulation based on metasurfaces in the prior art is limited to two-dimensional manipulation, realizing the technical effect of three-dimensional optical manipulation based on a single metasurface, and significantly improving the degree of freedom of manipulation.

[0018] (2) This invention adjusts and switches the polarization state and working wavelength of the incident light, and combines the focal points separated by different spatial positions to excite the optical potential well, thereby completing the manipulation of particles in the lateral and longitudinal directions, realizing the stable capture and controllable transfer of particles, solving the problem of the single and difficult switching of particle manipulation mode, reducing the sensitivity of the system alignment accuracy and external disturbances during particle manipulation, and realizing the technical effect of simple and efficient particle manipulation adjustment mode, and good stability and reliability of the manipulation process.

[0019] (3) Based on a single-layer metasurface, this invention realizes the spatial multiplexing and control of multi-wavelength and multi-polarization light fields without the need to introduce multi-layer optical elements or complex mechanical adjustment structures. Combined with the metasurface arrangement design, it solves the problems of complex structure and low integration of existing three-dimensional optical manipulation systems, and achieves the technical effect of compact structure, easy integration, and good scalability of the manipulation system. It is suitable for micro-nano particle manipulation, on-chip optical manipulation and related integrated optical application scenarios. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2 This is a schematic diagram of three-dimensional optical manipulation based on metasurfaces and the structure of metasurfaces. Figure 3 The results are shown in the transmittance and phase library of the metasurface structure scan at a wavelength of 457 nm, as well as the results of the selected half-wave plate nanopillar. Figure 4 The results are shown in the transmittance and phase library of the metasurface structure scan at a wavelength of 532 nm, as well as the results of the selected half-wave plate nanopillar. Figure 5 Field distribution diagrams for the four separation foci formed at the metasurface; Figure 6 This is an optical path diagram and video frames for on-chip 3D optical manipulation experiments based on metasurfaces. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0022] To address the problems existing in the prior art, this embodiment provides a three-dimensional optical manipulation method based on metasurfaces, such as... Figure 1 As shown, the method specifically includes: S1. Using a high refractive index medium material, subwavelength nanopillars are constructed on a substrate as unit structures to build a metasurface. The period of the unit structure and the geometric parameters of the nanopillars are scanned to obtain a parameter set with high transmittance, high polarization conversion efficiency and phase coverage from -π to π, so that it has both transmission phase control capability and geometric phase control capability.

[0023] TiO2 nanopillars were constructed on a SiO2 substrate. To achieve the desired phase distribution, light was incident from the substrate side at operating wavelengths of 457 nm and 532 nm. The nanopillar height was selected to be 600 nm, and the period was 360 nm. The length d1 and width d2 of the nanopillars were scanned at both wavelengths to construct a phase library, with a scanning range of 85–275 nm. Seventeen nanopillars with high transmittance and a transmission phase coverage of -π to π for TM polarization were selected to realize the half-wave plate function.

[0024] S2. Based on the obtained parameter set, the orientation angle of the nanopillar is set so that left-handed and right-handed light obtain geometric phases with equal amplitudes and opposite signs after transmission. The nanopillar is designed as a half-wave plate structure, and the orientation angle of the nanopillar is set to θ. After transmission, left-handed and right-handed light obtain geometric phases ±2θ, and the required transmission phase is superimposed, thereby realizing independent phase modulation of light fields with different spin states.

[0025] S3. Further construct a dual-wavelength spatially multiplexed metasurface, designed for working wavelengths of 457nm and 532nm, and arrange them spatially multiplexed on the same metasurface so that the optical field modulation functions at different wavelengths are independent of each other.

[0026] S4. By setting the phases of left-handed and right-handed light, under different wavelengths and different circular polarization states of incident conditions, the metasurface forms four spatially separated focal points in three-dimensional space. Based on the focal points at different positions, optical gradient forces are generated to achieve stable capture of micron-scale particles.

[0027] To focus LCP and RCP light at different spatial locations, the metasurface needs to satisfy the following phase distribution: In the formula, It is the phase applied to left-handed light. It is the phase applied to right-handed light. It is the focal point of the left-handed optical system. It is the focal point of the right-handed optical rotation. λ is the wavelength.

[0028] Through phase design, a 43.56 μm metalens, under 457 nm laser incident light, has left-handed and right-handed light focal points at (+0.23 μm, 0, 23.26 μm) and (-0.23 μm, 0, 23.26 μm), respectively; at 532 nm, the left-handed and right-handed light focal points are at (0, +0.23 μm, 32.57 μm) and (0, -0.23 μm, 33.50 μm), respectively. Based on simulation guidance, a 1872 μm metalens was fabricated, with four focal points located at (+13 μm, 0, 1000 μm), (-13 μm, 0, 1000 μm), (0, +13 μm, 1400 μm), and (0, -13 μm, 1490 μm), respectively.

[0029] S5. By switching the polarization state or operating wavelength of the incident light, optical potential wells at different positions are selectively excited in the same on-chip optical device, thereby realizing the controllable movement of particles in the lateral and longitudinal directions, thus completing three-dimensional optical manipulation based on metasurface.

[0030] Three-dimensional manipulation of particles is achieved by switching the polarization state or operating wavelength of the incident light. At an operating wavelength of 457 nm, the metasurface forms two spatially separated focal points in the lateral direction under left- and right-hand circularly polarized incident light conditions, enabling controllable particle motion in the x-direction. At an operating wavelength of 532 nm, the metasurface forms vertically separated focal points in the yz plane, enabling particle motion in both the longitudinal and lateral directions. Based on this method, an on-chip three-dimensional optical manipulation platform based on the metasurface was constructed, achieving stable and controllable three-dimensional particle motion, with lateral displacements of approximately 25.9 μm and longitudinal displacements of approximately 90 μm.

[0031] This embodiment verifies the above method.

[0032] Figure 2 This illustrates on-chip 3D optical manipulation based on metasurfaces and a schematic diagram of the metasurface structure. (Example) Figure 1 As shown on the left, under 457nm incident light, the metasurface focuses the incident left-handed polarization light and converts it into right-handed polarization, forming a focal point on the right side of the x-axis; conversely, the incident right-handed polarization light is converted into left-handed polarization, forming a focal point on the left side of the x-axis. When a particle is near the focal point, it can be stably trapped at the focal position due to the optical gradient force. By switching the incident polarization from left-handed to right-handed, the focal position moves accordingly, causing the particle to move from right to left along the x-axis. Figure 1As shown on the right, under 532nm incident light, the incident left-handed light is converted to right-handed light and focused at a focal point below the z-axis, while the incident right-handed light is converted to left-handed light and focused at a focal point above the z-axis. The two focal points are also offset along the y-axis; particle manipulation in the yz plane can be achieved through polarization switching. The metasurface consists of unit structures designed for different wavelengths arranged diagonally to achieve spatial reuse.

[0033] Figure 3 A phase library constructed by scanning nanopillars with length d1 and width d2 on a metasurface at a wavelength of 457 nm is shown. (a) shows the transmittance and phase response of TM and TE polarized light. Seventeen nanopillars with high transmittance and TM polarization transmission phase covering -π to π were selected. Their performance and phase are shown in (b). TM and TE light have a phase difference of π, which acts as a half-wave plate.

[0034] Figure 4 A phase library constructed using the length d1 and width d2 of metasurface scanning nanopillars at a wavelength of 532 nm is presented. (a) shows the transmittance and phase response of TM and TE polarized light. Seventeen nanopillars with high transmittance and TM polarization transmission phase covering -π to π were selected, and their performance and phase are shown in (b). TM and TE light have a phase difference of π, acting as a half-wave plate.

[0035] Figure 5 Simulation results of the focusing effect of a metalens with a side length of 43.56 μm are shown. At 457 nm, the LCP and RCP focal points are located at (+0.23 μm, 0, 23.26 μm) and (-0.23 μm, 0, 23.26 μm), respectively; at 532 nm, the LCP and RCP focal points are located at (0, +0.23 μm, 32.57 μm) and (0, -0.23 μm, 33.50 μm), respectively.

[0036] Figure 6 (a) illustrates the optical path setup of an on-chip 3D optical manipulation platform based on a metasurface. Two lasers, one at 457 nm and the other at 532 nm, are used to obtain circularly polarized light through a linear polarizer (LP) and a quarter-wave plate (QWP), while a half-wave plate (HWP) is used to switch the polarization. After beam combining, the metasurface is illuminated by an approximate plane wave through a beam expander system (L1, L2). A beam splitter introduces a white light source to illuminate the particles; the experiment uses polystyrene microspheres with a diameter of 20 μm immersed in water. Figure 6 (b) shows video frames of particle manipulation in the experiment. In the first row, the sample is located near the 532nm focal plane, and the polarization switching causes the particle to move in the yz plane. In the second row, the sample moves to the 457nm focal plane, and the particle moves laterally along the x-axis.

[0037] Utilizing the above method, this invention achieves on-chip three-dimensional optical manipulation based on metasurfaces, significantly improving the degrees of freedom of manipulation. Manipulation modes are switched by alternating polarization states and wavelengths, resulting in a simple and efficient control method. Specifically, this invention employs a single-layer planar metasurface as the core functional device. By designing the geometric parameters of nanopillars within the subwavelength scale, it integrates independent control of incident light of different wavelengths and polarization states, thereby achieving multi-degree-of-freedom optical manipulation without introducing multiple optical components. Since the thickness of the metasurface is much smaller than the operating wavelength, the system structure is compact, significantly reducing the system's volume and optical path complexity. It is easily integrated with on-chip optical systems and possesses good mass production potential. Furthermore, the optical manipulation mechanism employed in this method is based on the stable capture of particles by optical gradient forces, independent of the specific morphology or material properties of the particles. It is applicable to various liquid environments and micro / nano particles of different sizes, exhibiting good versatility.

[0038] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A three-dimensional optical manipulation method based on metasurfaces, characterized in that, The method includes: S1. Using a high refractive index medium material, subwavelength nanopillars are constructed on a substrate as unit structures to build a metasurface. The geometric parameters of the periodicity of the nanopillars and unit structures are scanned to obtain a parameter set. S2. Based on the obtained parameter set, select suitable nanopillars, set the orientation angle of the nanopillars, so that left-handed and right-handed light obtain equal and opposite geometric phases after transmission, and superimpose the transmission phase to realize independent phase modulation of light fields of different spin states. S3. For the metasurface, spatial multiplexing arrangement is performed at different working wavelengths so that the optical field modulation function of the metasurface at different wavelengths does not interfere with each other; S4. By setting the phases of the left-handed and right-handed light, under different wavelengths and different circular polarization states of incident conditions, the metasurface forms focal points with different spatially separated locations in three-dimensional space. Based on the focal points, an optical gradient force is generated to achieve stable capture of micron-scale particles. S5. By switching the polarization state or working wavelength of the incident light, the optical potential well is excited by the focal points separated by different spatial positions, so as to complete the controllable movement of the particles in the lateral and longitudinal directions and realize three-dimensional optical manipulation based on metasurface. The metasurface is configured to simultaneously utilize the geometric phase, the transmission phase, and the spatial multiplexing arrangement to independently phase-modulate left-handed and right-handed light of different wavelengths, forming focal points at different spatial locations. The spatial reuse arrangement is achieved by arranging nanopillars corresponding to different wavelengths in an alternating or partitioned manner within the plane of the metasurface. The operating wavelengths are set to 457nm and 532nm, with light entering from the substrate side. The height of the nanopillars is set to 600nm, and the period is 360nm.

2. The three-dimensional optical manipulation method based on metasurfaces according to claim 1, characterized in that, The nanopillars are half-wave plate structures with rectangular cross-sections.

3. The three-dimensional optical manipulation method based on metasurfaces according to claim 1, characterized in that, The transmission phase of the parameter group covers the range from -π to π.

4. The three-dimensional optical manipulation method based on metasurfaces according to claim 1, characterized in that, The high refractive index medium material is titanium dioxide, and the substrate is made of silicon dioxide.

5. The three-dimensional optical manipulation method based on metasurfaces according to claim 1, characterized in that, The phase distribution of the metasurface satisfies: In the formula, It is the phase applied to left-handed light. It is the phase applied to right-handed light. It is the focal point of the left-handed optical system. It is the focal point of the right-handed optical rotation. λ is the wavelength.

6. The three-dimensional optical manipulation method based on metasurfaces according to claim 1, characterized in that, At a working wavelength of 457nm, the metasurface forms two spatially separated focal points in the lateral direction under left- and right-hand circularly polarized incident conditions, enabling controllable movement of particles in the x-direction. At a working wavelength of 532nm, the metasurface forms vertically separated focal points in the yz plane, enabling movement of particles in the y and z directions.

7. The three-dimensional optical manipulation method based on metasurfaces according to claim 1, characterized in that, The particles achieve three-dimensional controllable motion in a liquid environment.

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