Micro-nano Particle Manipulator Based on Capillary Optical Fiber

Abstract

The present invention provides a micro-nano particle manipulator based on capillary optical fiber. Its characteristics are as follows: It consists of a wavelength tunable laser (1), a single-core optical fiber (2), a coreless optical fiber (3), and a capillary optical fiber (4). The present invention designs a unique structure, which successively fuses and welds the single-core optical fiber, the coreless optical fiber, and the capillary optical fiber into one body, and realizes the splitting of the light beam by using the divergence effect of the coreless optical fiber on the light beam and the tapered transition region formed by the heat fusion and collapse of the capillary optical fiber. Due to the divergence of the light beam, the hollow light beam transmitted in the tubular cladding will form multiple strong convergence points in the air holes or near the fiber end after reflection and refraction, thereby capturing multiple micro-nano particles. Also, by using the characteristic that the positions of multiple convergence points will move axially when the wavelength changes, the functions of storing, oscillating, and transporting multiple micro-nano particles are finally realized. The present invention can be used for the screening, capture, and directional ejection of biological cells, nano clusters, dielectric particles, etc.

Description

(1) Technical Field

[0001] The present invention relates to a micro-nano particle manipulation device based on single-fiber integration. It is mainly used for screening, capturing, detecting, oscillating, and ejecting of tiny particles such as biomolecules, biological cells, nano clusters, colloidal particles, and dielectric particles, and belongs to the field of optical fiber technology. (2) Background Art

[0002] Traditional optical tweezers are usually constructed based on an optical microscope system. It focuses a laser beam through a microscope objective lens, and forms an optical trap using the gradient force field near the focus center to capture and manipulate tiny particles. Traditional optical tweezers technology is mature, but its structure is complex and lacks flexibility, with a large volume, high price, and a complex optical trap movement system, requiring high operation skills. Therefore, an optical waveguide optical tweezers technology solution was proposed, which realizes the capture of tiny particles by means of multiple waveguide channels on the same material substrate [Chinese Patent CN1740831A]. Considering the disadvantages of the large volume and high preparation difficulty of the optical waveguide optical tweezers end, people further developed the optical fiber optical tweezers technology [Optics Letters, 1993, 18(21): 1867 - 9, and Optics Express, 2006, 14(25): 12510 - 6]. The optical fiber optical tweezers have a simple structure and can be made in the form of a microprobe. The optical trap and its manipulation are separated from the optical microscopy system, so the optical trap manipulation is flexible and the system has a large degree of freedom.

[0003] Optical fiber connection technology is the most basic specialized technology in the field of optical fiber applications. The connection of optical fibers refers to joining the end faces of two optical fibers together. The basic requirement for the connection is to maximize the coupling and transition of optical energy from the input optical fiber to the receiving optical fiber. For optical fiber connection technology, in addition to requiring low connection loss and high return loss, it also requires stable performance when the environmental temperature changes and sufficient mechanical strength. Therefore, precise mechanical and optical design and processing and assembly are required to ensure high-precision matching of the two optical fiber ends.

[0004] To achieve three-dimensional capture operation of particles using an optical fiber, the tip of the optical fiber needs to be specially processed. Specific processing methods include the fused biconical taper method [Optics Express, 14(25): 12510 - 12516, 2006] and the method of grinding with a special grinding machine. The common purpose of different processing methods is to be able to construct a suitable tapered end of the optical fiber to realize the construction of a large-gradient optical capture field.

[0005] The invention patent with the publication number CN1963583A melts and draws one end of a section of optical fiber into an optical fiber needle with a parabolic microstructure. Laser is coupled into the other end of the optical fiber. After the laser exits from the optical fiber needle, a converging light field with a waist spot diameter less than 1 μm is formed at the front end of the optical fiber needle, which can form a stable three-dimensional optical potential well, thus realizing a single-fiber optical tweezer; the Chinese invention patent with the publication number CN101118300 provides a small-core ultra-high numerical aperture tapered optical fiber tweezer and its manufacturing method. It is processed by a small-core ultra-high numerical aperture optical fiber, and the optical fiber end is ground into a tapered shape. The diverging light field formed due to the large numerical aperture at the tip of the optical fiber can form a large optical field gradient force potential well, so that the self-weight of the particle can be overcome, and three-dimensional single-fiber capture of micro-particles can be realized; in order to further control the attitude of the captured micro-particles, the Chinese invention patent document with the publication number CN101149449 provides a dual-core optical fiber tweezer; the invention patent with the publication number CN101339274A provides a hollow capillary optical fiber tweezer with an annular core layer, and a gas pressure adjustment device is connected in the air hole, which can realize the storage and manipulation of micro-particles.

[0006] In order to expand the structure and function of optical fiber devices, the present invention makes a unique design of the optical fiber structure. By using the beam divergence effect of the coreless optical fiber and the tapered transition region formed by the heat fusion and collapse of the capillary optical fiber, the splitting of the beam is realized. The hollow beam transmitted in the tubular cladding of the capillary optical fiber will form a strongly focused beam with multiple converging points on the optical axis in the air hole or near the fiber end after reflection and refraction, so as to capture multiple micro-nano particles simultaneously. Moreover, the positions of multiple capture points are regulated by the wavelength, and finally the functions of storing, oscillating and ejecting the micro-nano particles are realized. The design of the present invention not only makes the optical fiber tweezer device more miniaturized and integrated, but also provides a brand-new idea for manufacturing the capillary optical fiber tweezer device and then capturing and manipulating micro-nano particles. (III) Summary of the Invention

[0007] The purpose of the present invention is to provide a single-fiber integrated device that uses the tapered transition region after melting of the coreless optical fiber and the capillary optical fiber to realize the splitting of the beam, and stably captures and optically manipulates multiple micro-nano particles.

[0008] The purpose of the present invention is achieved as follows:

[0009] The micro-nano particle manipulation device is composed of a wavelength-tunable laser, a single-core optical fiber, a coreless optical fiber, and a capillary optical fiber. The wavelength-tunable laser consists of a data input end and different wavelength output ends. The single-core optical fiber consists of a core and a cladding. The coreless optical fiber consists of a cladding. The capillary optical fiber consists of air holes and a tubular cladding. The single-core optical fiber, the coreless optical fiber, and the capillary optical fiber are successively fusion-welded into one body. At the welding point of the coreless optical fiber and the capillary optical fiber, a tapered transition region is formed due to the thermal melting and collapse of the air holes. In the device, when the conduction light wave in the core of the single-core optical fiber passes through the divergence of the coreless optical fiber and the division of the tapered transition region, a hollow beam is formed. By precisely controlling the length of the coreless optical fiber, the two parts of the beam can be fully divided and propagated towards the fiber end. Then, the hollow beam transmitted in the tubular cladding of the capillary optical fiber will form a strong convergent beam with multiple convergence points on the optical axis inside the air holes or near the fiber end after reflection and refraction, realizing the three-dimensional optical trapping of multiple micro-nano particles at multiple optical trap positions. When the wavelength of the light wave passing through the single-core optical fiber is periodically regulated by the wavelength-tunable laser, the axial positions of the multiple convergence points formed by the strong convergent beam in the capillary optical fiber will also change correspondingly, realizing the function of storing or periodically oscillating multiple micro-nano particles captured near the fiber end.

[0010] Micro-nano particles with a special structure are adopted, such as one of dielectric materials, biological materials, or other transparent materials. Optionally, the material of the micro-nano particles can also be a mixed or laminated material of transparent materials and non-transparent materials. Particles of this structure will respond to changes in the light wavelength, that is, there are phenomena of Fano resonance or surface plasmon resonance. Fano resonance is a scattering resonance phenomenon that produces an asymmetric line shape. The interference between the background and the resonant scattering produces an asymmetric line shape. The line shape of Fano resonance comes from the interference of two scattering amplitudes, one is the scattering of the continuous state (related to the background), and the other is the excitation of the discrete state (related to the resonance). The energy of the resonant state must be within the energy range of the continuous state for this effect to occur. Near the resonant energy, the amplitude of the background scattering usually changes very gently with energy; but the amplitude and phase of the resonant scattering amplitude change quite rapidly, resulting in the occurrence of asymmetry. When the energy is far from the resonant energy, the background scattering dominates. When the energy is within the range of about 2Γ res on both sides of the resonant energy, the phase of the resonant scattering amplitude will differ by π. It is this drastic change in phase that causes the asymmetric line shape. Fano proved that the total scattering cross-section σ is approximately of the following form:

[0011]

[0012] where Γ resis the peak width of the resonance energy, and q is the Fano variable, representing the amplitude ratio between resonant scattering and direct (background) scattering.

[0013] Surface plasmon resonance, abbreviated as SPR in English. It refers to the resonance that occurs when an evanescent wave and a plasmon wave meet at the interface of a medium. When resonance occurs, the intensity of the reflected light will be greatly reduced. Energy is transferred from photons to surface plasmons, and most of the energy of the incident light is absorbed by the surface plasmon wave, causing the energy of the reflected light to decrease sharply.

[0014] The Fano resonance or surface plasmon resonance phenomenon, that is, the direction of the resultant force on the micro-nano particle produces unusual forward and backward directions axially. This phenomenon is closely related to the wavelength of the light wave and is manifested as the assisted capture and directional ejection of particles in particle capture. Utilizing this mechanism, when a light wave of this specific wavelength is introduced into the micro-nano particle manipulator based on capillary optical fiber, the forward radiation pressure generated by the strongly focused light beam converging near the fiber end on the micro-nano particle is greater than the negative gradient force. Under the action of the optical resultant force, the micro-nano particle is ejected in the propagation direction of the strongly focused light beam, realizing the transport function of the micro-nano particle.

[0015] The bottom angle θ of the conical frustum at the fiber end of the capillary optical fiber satisfies the following relationship:

[0016] θ≥arcsin(n m / n 1 ) (2)

[0017] where n m is the refractive index of the environment around the fiber end of the optical fiber, and n 1 is the refractive index of the tubular cladding of the capillary optical fiber. When this condition is met, the light beam introduced into the capillary optical fiber satisfies the condition of total reflection when passing through this conical frustum, so that the light beam does not leak and is all reflected onto the fiber end face. Then, the two parts of the light beam are strongly converged at the fiber end, generating an optical trap that can capture micro-nano particles. Optionally, a metal film (reflective film) can also be deposited on the grinding or tapering area of the conical frustum. At this time, the cone angle will not be restricted, so as to collect the light beam more effectively.

[0018] Analyze the feasibility of the micro-nano particle manipulation device based on capillary optical fiber. The results of theoretical analysis are shown in Figures 5(a)-(b). Figure (a) shows the two-dimensional plane optical field diagram of the single-mode optical fiber, the coreless optical fiber, and the capillary optical fiber connected and then the single-mode optical fiber is illuminated. From the figure, we can see that there are multiple light intensity maxima in the section from 800um to 1000um in the z direction, representing the positions of multiple strong focusing points, so as to capture multiple micro-nano particles. When using a wavelength-tunable laser to modulate the optical field, the longitudinal optical trap force curves of the same radius particles at different positions in the section from 800um to 1000um are shown in Figure (b). The distance of each curve deviating from the reference line represents the magnitude of the longitudinal optical trap force on the particles at this wavelength. When the illumination wavelength is 980nm, the multi-optical trap region is near 925um, and at this time the optical trap force is relatively large and the capture range is relatively small; when the illumination wavelength is 1130nm, the multi-optical trap region is near 938um, and at this time the optical trap force is moderate and the capture range is moderate; when the illumination wavelength is 1280nm, the multi-optical trap region is near 958um, and at this time the optical trap force is relatively small and the capture range is relatively large. And the device has different longitudinal optical trap force magnitudes for different radius particles at the same position. When the particle radius is relatively small, the optical trap force is relatively small and the capture efficiency is higher; when the particle radius is relatively large, the optical trap force is relatively large and the capture efficiency is lower; when the particle radius is too large, the multi-optical trap region is not sufficient to capture the micro-nano particles, and the particles are pushed out of the air holes of the capillary optical fiber under the combined action of the optical resultant force.

[0019] The micro-nano particle manipulator based on capillary optical fiber of the present invention may further include:

[0020] 1. The single-core optical fiber is one of a single-mode optical fiber, a few-mode optical fiber or a multi-mode optical fiber, and the shape of the core can be one of: circular, annular, triangular, rectangular or other polygons.

[0021] 2. The coreless optical fiber can also be a step-index multi-mode optical fiber or a graded-index multi-mode optical fiber.

[0022] 3. The shape of the air holes of the capillary optical fiber can be one of: circular, equilateral triangular, square or other regular polygons, and the shape of the tubular cladding can be one of circular, square or other regular polygons.

[0023] 4. The conical surface of the frustum-shaped fiber end can directly perform total reflection on the transmitted light wave in the tubular cladding, or a metal reflection film can be deposited to enhance the total reflection effect.

[0024] The manufacturing method of the micro-nano particle manipulator based on capillary optical fiber of the present invention is:

[0025] In an optical fusion splicer, two rotatable optical fiber clamps are respectively used to fix two optical fibers to be fused (single-core optical fiber, coreless optical fiber, capillary optical fiber). The optical fiber cutter is used to cut the two optical fibers to be fused respectively to form optical fiber end faces for fusion. The optical fiber end face positioning unit is used to display the structure of the optical fiber end face. The optical fiber fusion unit fuses the optical fiber end faces of the two optical fibers to be fused together. Fabrication of the conical end of the capillary optical fiber: The first method: Fix the capillary optical fiber with an optical fiber clamp, and then place the fiber end on a polishing disc. Both the optical fiber clamp and the optical fiber polishing disc can rotate around their respective central axes. By controlling the angle between the optical fiber and the normal of the polishing disc surface, conical ends with different opening angles can be fabricated. The second method: Place the optical fiber on an optical fiber tapering machine, draw it to an appropriate taper length and cut it at an appropriate position in the tapering area to form a conical end with an arc-shaped conical surface.

[0026] The advantages of the present invention are mainly reflected in overcoming the deficiencies of the prior art. By utilizing the beam divergence effect of the coreless optical fiber and the conical transition region formed by the heat melting and collapse of the capillary optical fiber, the splitting of the beam is realized. The hollow beam transmitted in the tubular cladding of the capillary optical fiber will form a strong focusing beam with multiple convergence points on the optical axis inside the air hole or near the fiber end after reflection and refraction, thereby simultaneously capturing multiple micro-nano particles. Moreover, the positions of multiple capture points are regulated by the wavelength, and finally the functions of storing, oscillating, and ejecting the micro-nano particles are realized. The whole device has a small structure and strong integration. It can be rotated at any angle or translated over a long distance, and has strong operability. The unique design not only makes the fiber optical tweezer device more miniaturized and integrated, but also provides a new idea for fabricating the capillary optical fiber optical tweezer device, making it have wide application value in the fields of biomedical research, particle transport, etc. (IV) Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of a micro-nano particle manipulator based on a capillary optical fiber. It is composed of a wavelength-tunable laser 1, a single-core optical fiber 2, a coreless optical fiber 3, and a capillary optical fiber 4.

[0028] Figure 2(a) is a schematic diagram of the fusion splicing of each section of optical fiber by an optical fusion splicer. It is composed of a single-core optical fiber 201, a coreless optical fiber 202, a capillary optical fiber 203, a movable clamping device 204, a clamping device 205, and a fusion unit 206. Figure 2(b) is a process flow chart of the optical fiber fusion splicing. It is composed of four parts: optical fiber cutting, optical fiber end face cleaning, angular positioning, and optical fiber fusion.

[0029] Figure 3(a) is a schematic diagram of the preparation of a conical fiber end with an arc-shaped conical surface obtained by tapering. It consists of a CMOS camera 301, a left-hand tapering platform 302, a heating platform 303, a right-hand tapering platform 304, a heating system 305, a fiber alignment and tapering system 306, a fiber image detection system 307, a hardware system control platform 308, a fiber image 309, and a computer control system 310. Figure 3(b) is a schematic diagram of the structure of the conical fiber end with an arc-shaped conical surface.

[0030] Figure 4 is a schematic diagram of the preparation of a conical fiber end obtained by grinding the taper. It consists of a fiber fixture 401, a capillary fiber 402, and a grinding disc 403. Figure 4(b) is a schematic diagram of the structure of the conical fiber end.

[0031] Figure 5 is a diagram showing the results of the feasibility analysis of a micro-nano particle manipulator based on a capillary fiber.

[0032] Figure 6 shows the refractive index distributions when a coreless fiber is replaced with a multimode fiber. They are schematic diagrams of the structures of a step-index multimode fiber and a graded-index multimode fiber, respectively.

[0033] Figure 7 shows schematic diagrams of different core shapes of a single-core fiber. Diagram (a) shows the schematic diagram of the structure when the core shape is triangular. Diagram (b) shows the schematic diagram of the structure when the core shape is square. Diagram (c) shows the schematic diagram of the structure when the core shape is annular. Diagram (d) shows the schematic diagram of the structure when the core shape is polygonal.

[0034] Figure 8 shows schematic diagrams of different air holes and the shapes of the tubular cladding of a capillary fiber. Diagram (a) shows the schematic diagram of the structure when the air hole shape is square and the tubular cladding shape is circular. Diagram (b) shows the schematic diagram of the structure when the air hole shape is square and the tubular cladding shape is square.

[0035] Figure 9 is a schematic diagram of the application structure of a micro-nano particle manipulator based on a capillary fiber. (V) Specific implementation manners

[0036] The present invention will be further described below by way of examples with reference to the accompanying drawings.

[0037] Combined with Figure 1 and Figure 9, in the embodiment of the present invention, a single-core optical fiber, a coreless optical fiber, and a capillary optical fiber are sequentially fusion-welded into one body. At the solder joint of the coreless optical fiber and the capillary optical fiber, a conical transition region is formed due to the thermal melting and collapse of air holes. In the device, when the guided light wave in the core of the single-core optical fiber passes through the divergence of the coreless optical fiber and the segmentation of the conical transition region, a hollow beam is formed. By precisely controlling the length of the coreless optical fiber, the two parts of the beam can be fully segmented and propagated towards the fiber end. Then, the hollow beam transmitted in the tubular cladding of the capillary optical fiber will form a strongly focused beam with multiple convergence points on the optical axis inside the air holes or near the fiber end after reflection and refraction, realizing the three-dimensional optical trapping of multiple micro-nano particles at multiple optical trap positions. When a wavelength-tunable laser is used to periodically regulate the wavelength of the light wave passing through the single-core optical fiber, the axial positions of the multiple convergence points formed by the strongly focused beam in the capillary optical fiber will also change correspondingly, enabling the function of storing or periodically oscillating multiple micro-nano particles captured near the fiber end.

[0038] Special-structured micro-nano particles are used, such as one of dielectric materials, biological materials, or other transparent materials. Optionally, the material of the micro-nano particles can also be a mixture or laminated material of transparent materials and non-transparent materials. Particles of this structure will respond to changes in the light wavelength, that is, there are phenomena of Fano resonance or surface plasmon resonance, that is, the direction of the resultant force on the micro-nano particles produces unusual forward and backward phenomena in the axial direction. This phenomenon is closely related to the light wave wavelength and is manifested as assisting the capture and directional ejection of particles in particle capture. Using this mechanism, when a light wave of a specific wavelength is introduced into the micro-nano particle manipulator based on the capillary optical fiber, the positive radiation pressure generated by the strongly focused beam converging near the fiber end on the micro-nano particles is greater than the negative gradient force. Under the action of the optical resultant force, the micro-nano particles are ejected in the propagation direction of the strongly focused beam, realizing the transport function of the micro-nano particles.

[0039] The preparation process of the particle manipulation device formed by fusing the coreless optical fiber and the capillary optical fiber can be divided into the following two steps (see Figures 2 - 4):

[0040] Step 1: Fusion splicing of each section of optical fiber (see Figure 2). Positioning members matching the shape or size of the rotatable optical fiber clamp are provided on the optical fiber cutter, the optical fiber end face positioning unit, and the optical fiber fusion splicing unit. Through the positioning members, the rotatable optical fiber clamp can be quickly installed with the optical fiber cutter, the optical fiber end face positioning unit, or the optical fiber fusion splicing unit and maintain the installation position fixed. The positioning member can be a positioning hole, a positioning groove, or a fixed position, etc. The optical fiber cutter automatically fixes the position of the rotatable optical fiber fixture through a fixing member to ensure that the cutting position is consistent each time. The optical fiber end face positioning unit is quickly installed and fixed with the rotatable optical fiber fixture through a fixing member to ensure the accuracy of the observed optical fiber end face structure and operation consistency. The fixing member on the optical fiber fusion splicing unit 206 can fix two rotatable optical fiber clamps at the same time, and can be symmetrically arranged left and right, so that the two rotatable optical fiber clamps after installation and the two optical fibers to be fused respectively fixed by them can be quickly and accurately fused;

[0041] Step 2: Microfabrication of the optical fiber end (this step can be prepared in two ways): Optical fiber tapering (see Figure 3). After removing the coating layer of the optical fiber, it is fixed on the optical fiber fixture. The control system drives the left hand electric control displacement platform 302 and the right hand electric control displacement platform 304 carrying the optical fiber to send the optical fiber into the field of view of the CMOS camera 301. In the field of view area, the optical fiber is focused through the autofocus system to obtain a clear image 309, and the image can be displayed through the computer control system 310. Calculate the geometric parameters and pose information of the optical fiber and use them as feedback quantities. By adjusting the micro motion actuators in five dimensions of the left and right hands, the alignment of the optical fiber waveguide and the heating device is achieved. Drive the electric heating device 308 to send the melting zone to the waveguide alignment position for heating, and stretch the optical fiber at a certain speed with the left and right hand electric control displacement platforms. After the tapering is completed, cut at the center point with an optical fiber cutter to finally form a conical frustum optical fiber end with an arc-shaped conical surface. Optical fiber end face grinding (see Figure 4). Fix the capillary optical fiber 402 with the optical fiber fixture 401, and then place the optical fiber end on the grinding disc 403. The optical fiber fixture and the optical fiber grinding disc are each connected with a DC motor drive to rotate around their respective central axes; keep the capillary optical fiber at a fixed angle θ with the normal line of the grinding disc surface, and a conical frustum optical fiber end with an opening angle of θ can be ground through the rotation of the optical fiber fixture and the grinding disc.

[0042] Optionally, when the coreless optical fiber is replaced with a multimode optical fiber, the refractive index distribution can be one of a step-index multimode optical fiber and a graded-index multimode optical fiber, as shown in Figures 6(a)-(b).

[0043] Optionally, the single-core optical fiber is one of a single-mode optical fiber, a few-mode optical fiber, or a multimode optical fiber, and the shape of the fiber core can be one of a circle, an annulus, a triangle, a rectangle, or other polygons, as shown in Figures 7(a)-(c).

[0044] Optionally, the shape of the air holes in the capillary fiber can be one of: circular, equilateral triangular, square, or other regular polygons, and the shape of the tubular cladding can be one of circular, square, or other regular polygons, as shown in Figures 8(a)-(b).

[0045] In addition, by controlling the length of the coreless fiber and the angle of the conical end of the capillary fiber, a beam with the best focusing effect can be obtained, so as to more accurately capture and manipulate micro-nano particles.

[0046] The following will further elaborate on the present invention in combination with specific embodiments.

[0047] Step 1, device preparation: Fabricate 10 sets of devices formed by melting and welding single-core fiber, coreless fiber, and capillary fiber according to the fiber preparation method of the embodiment. The lengths of the coreless fibers and the angles of the conical frustums in the 10 sets of devices are different. Use a wavelength-tunable laser with a pigtail and a common single-mode fiber for light injection (see Figure 1 Figure 2, Figure 9 );

[0048] Step 2, microfabrication of the fiber end (this step can be prepared in two ways): Fiber tapering: Fabricate a conical frustum fiber end structure with an arc-shaped conical surface according to the fiber tapering method of the embodiment (see Figure 3), Fiber end grinding: Fabricate a conical frustum fiber end structure according to the fiber end grinding method of the embodiment (see Figure 4);

[0049] Step 3, storage and oscillation functions of micro-nano particles (see Figure 1 , Figure 9 ): Use a wavelength-tunable laser to inject a beam with a fixed optical power into the core of the single-core fiber. After the beam reaches the connection between the single-core fiber and the coreless fiber, utilize the divergence effect of the coreless fiber on the beam and the conical transition region formed after the melting of the capillary fiber to achieve the splitting of the beam. The length of the coreless fiber can be precisely controlled so that the two parts of the beam can be fully separated and propagate towards the fiber end. Then, the hollow beam transmitted in the tubular cladding of the capillary fiber will form a strong focusing beam with multiple focusing points on the optical axis inside the air holes or near the fiber end after reflection and refraction, realizing the three-dimensional optical trapping of multiple micro-nano particles at multiple optical trap positions. When the wavelength of the light wave injected into the single-core fiber is periodically regulated by a wavelength-tunable laser, the axial positions of the multiple focusing points formed by the strong focusing beam in the capillary fiber will also change correspondingly, thus realizing the function of storing or periodically oscillating multiple micro-nano particles captured near the fiber end. Replace each set of prepared devices in turn, observe the capture effect on multiple micro-particles and record it, and obtain the length of the coreless fiber and the angle of the conical frustum when the capture effect is the best;

[0050] Step 4, directional ejection function of micro-nano particles (see Figure 1 ,Figure 9 ):Using micro-nano particles with a special structure, such as one of dielectric materials, biological materials, other transparent materials, or materials formed by mixing or laminating transparent and non-transparent materials. When particles of this structure are in an optical field with a changing light wavelength, there will be phenomena of Fano resonance or plasmon resonance. Then, when a light wave of a specific wavelength is introduced into the micro-nano particle manipulator based on capillary optical fiber, the forward radiation pressure generated by the strongly focused light beam converging near the fiber end on the micro-nano particles is greater than the negative gradient force. Under the action of the optical resultant force, the micro-nano particles are pushed outside the air hole along the propagation direction of the strongly focused light beam. According to actual requirements, the fiber optical tweezer device is moved as a whole, and multiple micro-nano particles are directed and ejected into different channels of the microfluidic multi-channel 8 along a predetermined path, thereby completing the precise optical manipulation of micro-nano particles using this device.

Claims

1. A micro-nano particle manipulator based on a capillary optical fiber, characterized in that: It consists of a wavelength tunable laser (1), a single-core optical fiber (2), a coreless optical fiber (3), and a capillary optical fiber (4). The wavelength tunable laser (1) consists of a data input end (101) and different wavelength output ends (102). The single-core optical fiber (2) consists of a core (201) and a cladding (202). The coreless optical fiber (3) consists of a cladding (301). The capillary optical fiber (4) consists of an air hole (401) and a tubular cladding (402). The single-core optical fiber, the coreless optical fiber, and the capillary optical fiber are sequentially fusion-welded and connected into one body. At the solder joint (7) between the coreless optical fiber (3) and the capillary optical fiber (4), a conical transition region (403) is formed due to the thermal melting and collapse of the air hole (401). When the guided light wave in the core (201) of the single-core optical fiber (2) passes through the coreless optical fiber (3) and the conical transition region (403), it is split into a hollow light beam. Then, the hollow light beam transmitted in the tubular cladding (402) of the capillary optical fiber (4) will form a strong converging light beam (5) with multiple converging points on the optical axis inside the air hole or near the fiber end after reflection and refraction, so as to simultaneously perform optical trapping on multiple micro-nano particles (6). When the wavelength of the light wave passing through the single-core optical fiber (2) is periodically regulated by the wavelength tunable laser (1), the axial positions of the multiple converging points formed by the strong converging light beam (5) in the capillary optical fiber (4) will change periodically, and the storage or periodic oscillation function of the micro-nano particles (6) trapped near the fiber end can be realized. If the micro-nano particles (6) have surface plasmon resonance or Fano resonance phenomena for light waves of a specific wavelength, then when the light wave of this specific wavelength is introduced into the micro-nano particle manipulator based on the capillary optical fiber, the positive radiation pressure generated by the strong converging light beam (5) converging near the fiber end on the micro-nano particles (6) is greater than the negative gradient force. Under the action of the optical resultant force, the micro-nano particles (6) are ejected in the propagation direction of the strong converging light beam (5), realizing the transport function of the micro-nano particles (6).

2. The preparation method of the micro-nano particle manipulator based on the capillary optical fiber according to claim 1 is as follows: (1) Fusion welding: Use a wire bonding machine to sequentially fusion-weld the single-core optical fiber, the coreless optical fiber, and the capillary optical fiber together; (2) The fiber end of the capillary optical fiber adopts a frustum-shaped fiber end structure. Fabrication of the frustum-shaped fiber end: The first method: Fix the capillary optical fiber with a fiber fixture, and then place the fiber end on a polishing disc. Both the fiber fixture and the fiber polishing disc can rotate around their respective central axes. By controlling the angle between the optical fiber and the normal line of the polishing disc surface, frustum-shaped fiber ends with different opening angles can be prepared; The second method: Place the optical fiber on an optical fiber taper machine, draw it into an appropriate taper length and taper angle, and cut it at an appropriate position in the taper region to form a frustum-shaped fiber end with an arc-shaped taper surface.

3. The micro-nano particle manipulator based on the capillary optical fiber according to claim 1, characterized in that: The single-core optical fiber is one of single-mode optical fiber, few-mode optical fiber or multi-mode optical fiber, and the core shape is one of circular, annular, triangular and rectangular.

4. The micro-nano particle manipulator based on capillary optical fiber according to claim 1, characterized in that: The coreless optical fiber is one of step-index multi-mode optical fiber or graded-index multi-mode optical fiber.

5. The micro-nano particle manipulator based on capillary optical fiber according to claim 1, characterized in that: The shape of the air holes of the capillary optical fiber is one of circular, equilateral triangular and square, and the shape of the tubular cladding is one of circular and square.

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