Particle driving device

Abstract

The utility model discloses a particle driving device which comprises a first light source, a second light source, a 3db coupler and a focusing vortex beam generator, and the first light source and the second light source are connected with the focusing vortex beam generator through the 3db coupler. Wherein the first light source is used for emitting a resonant wavelength light beam; the second light source is used for emitting a non-resonant wavelength light beam; the 3db coupler is used for coupling the resonant wavelength light beam and the non-resonant wavelength light beam into the focusing vortex light beam generator according to a preset proportion; and the focusing vortex beam generator is used for converting the resonant wavelength beam and the non-resonant wavelength beam into a first focusing vortex beam and a second focusing vortex beam respectively. The particle driving device can output the first focusing vortex light beam and the second focusing vortex light beam at the same time to drive particles to rotate.

Description

Technical Field

[0001] The utility model relates to the field of micro-motors, in particular to a micro-particle driving device. Background Art

[0002] Vortex beams have been widely used in communication, sensing, particle manipulation and other fields due to their unique spiral wavefront structure and central singularity characteristics. Existing particle driving devices convert Gaussian beams into vortex beams by focusing a vortex beam generator, and focus the converted vortex beams on particles to drive the particles to rotate.

[0003] The traditional lens-type optical tweezers system consists of multiple devices, including a laser source, a beam expander, a high-power objective lens, etc., and forms a light trap through optical focusing to control tiny particles. However, this type of optical tweezers system is complex and limited by optical components. It has problems such as limited operation and inability to handle particles in narrow positions, and requires a large number of expensive optical components. Dual-fiber optical tweezers use two optical fibers to form a focused light trap at a certain angle. Compared with traditional lens-type optical tweezers, dual-fiber optical tweezers are more compact, simple, reduce costs and structural complexity, and have advantages in improving light trap force, operation accuracy and stability. However, this type of optical tweezers has high requirements for the mechanical accuracy of the experimental system, the spatial position of the optical fiber, the matching of the output light power, and the experimental operation skills. Moreover, the existing single-fiber optical tweezers drive device only outputs a focused vortex beam, its driving force is limited, and the driving method for the particles is single, which can only drive the particles to rotate in one direction. Utility Model Content

[0004] In order to solve the above-mentioned deficiencies of the prior art, the utility model provides a particle driving device, which can simultaneously output a first focused vortex light beam and a second focused vortex light beam to drive the particles to rotate.

[0005] The technical problem to be solved by the utility model is achieved through the following technical solutions:

[0006] A particle driving device comprises a first light source, a second light source, a 3db coupler and a focused vortex beam generator, wherein the first light source and the second light source are connected to the focused vortex beam generator through the 3db coupler;

[0007] The first light source is used to emit a light beam of a resonant wavelength;

[0008] The second light source is used to emit a non-resonant wavelength light beam;

[0009] The 3db coupler is used to couple the resonant wavelength light beam and the non-resonant wavelength light beam into the focused vortex beam generator according to a preset ratio;

[0010] The focused vortex beam generator is used to convert the resonant wavelength beam and the non-resonant wavelength beam into a first focused vortex beam and a second focused vortex beam respectively.

[0011] Furthermore, the foci of the first focused vortex light beam and the second focused vortex light beam coincide with each other, or are staggered along the optical axis to form a double focus.

[0012] Furthermore, the 3db coupler has a first incident port, a second incident port and an exit port, wherein the first incident port is connected to the first light source via an optical fiber, the second incident port is connected to the second light source via an optical fiber, and the exit port is directly connected to the focused vortex beam generator.

[0013] Furthermore, the focused vortex beam generator comprises:

[0014] A combined optical fiber having an incident end face and an output end face for transmitting the resonant wavelength light beam and the non-resonant wavelength light beam;

[0015] A spiral long-period fiber grating is arranged between the incident end face and the output end of the combined optical fiber, and is used for mode coupling the resonant wavelength light beam transmitted in the combined optical fiber to form a first vortex light beam;

[0016] The spiral zone plate is arranged on the output end face of the combined optical fiber, and is used to perform topological charge conversion on the first vortex light beam and focus it to form a first focused vortex light beam, and to perform spiral phase modulation on the non-resonant wavelength light beam output from the combined optical fiber and focus it to form a second focused vortex light beam.

[0017] Furthermore, the combined optical fiber includes a first optical fiber and a graded-index multimode optical fiber, and the end faces of the first optical fiber and the graded-index multimode optical fiber are connected; the other end face of the first optical fiber opposite to its connected end face serves as the incident end face of the combined optical fiber, and the other end face of the graded-index multimode optical fiber opposite to its connected end face serves as the output end face of the combined optical fiber, and the helical long-period fiber grating is formed in the core or cladding of the first optical fiber.

[0018] Furthermore, the first optical fiber is a single-mode optical fiber, a few-mode optical fiber, a combination of a single-mode optical fiber and a few-mode optical fiber, or a combination of a single-mode optical fiber and a ring-core optical fiber.

[0019] Furthermore, the spiral long-period fiber grating satisfies the following formula:

[0020] N CO -N F =m·λ / Λ 0

[0021] J CO =JF +m·σ

[0022] Where N CO 、N F is the effective refractive index of the fundamental mode and the effective refractive index of the higher-order mode in the first optical fiber, m is the topological order of the spiral long-period fiber grating, λ is the resonant wavelength of the spiral long-period fiber grating, Λ 0 is the period of the helical long-period fiber grating, J CO and J F is the total angular momentum of the fundamental mode and the higher-order modes in the first optical fiber, and σ=±1 is the helical direction of the helical long-period fiber grating.

[0023] Furthermore, the length of the graded-index multimode optical fiber is equal to or less than (2n+1) / 4 pitches, where the pitch is the unit optical fiber length corresponding to a complete sinusoidal wave cycle transmitted by the resonant wavelength light beam and the non-resonant wavelength light beam in the graded-index multimode optical fiber, and n is a natural number.

[0024] Furthermore, the transmittance function of the spiral zone plate satisfies the following formula:

[0025]

[0026] Wherein λ and f are the wavelength and focal length of the focused vortex beam, respectively, l is the waveband order of the spiral waveband plate, and r and φ are polar coordinates.

[0027] The utility model has the following beneficial effects: the particle driving device of the utility model outputs the resonant wavelength light beam λ1 and the non-resonant wavelength light beam λ2 to the focused vortex beam generator 15 through the first light source 12 and the second light source 13 respectively, so that the focused vortex beam generator 15 can convert the resonant wavelength light beam λ1 and the non-resonant wavelength light beam λ2 into the first focused vortex beam and the second focused vortex beam respectively and then output them; the focused vortex beam generator 15 can output two focused vortex beams at the same time, and can improve the driving force on the particles and drive the particles to realize forward rotation, reverse rotation and stop rotation through the coordination between the order direction and the order value between the first focused vortex beam and the second focused vortex beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the principle of the particle driving device provided by the utility model.

[0029] Figure 2 This is a schematic structural diagram of the focused vortex beam generator provided by the utility model.

[0030] Figure 3This is a schematic diagram of the structure of the spiral zone plates in the focused vortex beam generator provided by the utility model when they are of 0th order, 1st order and 2nd order respectively. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments, examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0032] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0033] In addition, the terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first", "second", and "third" may explicitly or implicitly include one or more of the features. In the description of the present utility model, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0034] In the present invention, unless otherwise clearly specified and limited, the terms "install", "connect", "connect", "fix", "set" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] Embodiment 1

[0036] like Figure 1 As shown, a particle driving device includes a first light source 12, a second light source 13, a 3db coupler 14 and a focused vortex beam generator 15, wherein the first light source 12 and the second light source 13 are connected to the focused vortex beam generator 15 through the 3db coupler 14;

[0037] The first light source 12 is used to emit a resonant wavelength light beam λ1;

[0038] The second light source 13 is used to emit a non-resonant wavelength light beam λ2;

[0039] The 3db coupler 14 is used to couple the resonant wavelength light beam λ1 and the non-resonant wavelength light beam λ2 into the focused vortex beam generator 15;

[0040] The focused vortex beam generator 15 is used to convert the resonant wavelength beam λ1 and the non-resonant wavelength beam λ2 into a first focused vortex beam and a second focused vortex beam, respectively.

[0041] The particle driving device of the utility model outputs the resonant wavelength light beam λ1 and the non-resonant wavelength light beam λ2 to the focused vortex beam generator 15 through the first light source 12 and the second light source 13 respectively, so that the focused vortex beam generator 15 can convert the resonant wavelength light beam λ1 and the non-resonant wavelength light beam λ2 into the first focused vortex beam and the second focused vortex beam respectively and then output them. The focused vortex beam generator 15 can output two focused vortex beams at the same time, and can improve the driving force on the particles and drive the particles to realize forward rotation, reverse rotation and stop rotation through the coordination between the order direction and the order value between the first focused vortex beam and the second focused vortex beam.

[0042] In this embodiment, the resonant wavelength light beam λ1 and the non-resonant wavelength light beam λ2 are coupled into the focused vortex beam generator 15 in a ratio of 50:50.

[0043] The 3db coupler 14 has a first input port, a second input port and an output port, wherein the first input port is connected to the first light source 12 via an optical fiber, the second input port is connected to the second light source 13 via an optical fiber, and the output port is connected to the incident end face of the combined optical fiber 100.

[0044] In one of the usage methods of the present invention, the first light source 12 and the second light source 13 are controlled to simultaneously emit the resonant wavelength beam λ1 and the non-resonant wavelength beam λ2, so that the resonant wavelength beam λ1 and the non-resonant wavelength beam λ2 are coupled into the combined optical fiber 100 through the 3db coupler 14, so that the focused vortex beam generator 15 simultaneously outputs the first focused vortex beam and the second focused vortex beam, and by adjusting the output power of the resonant wavelength beam λ1 and the non-resonant wavelength beam λ2, the torque formed by the first focused vortex beam and the second focused vortex beam on the particle is controlled.

[0045] In another method of using the present invention, the first light source 12 is controlled to emit the resonant wavelength beam λ1 and the second light source 13 is turned off, or the first light source 12 is controlled to be turned off and the second light source 13 is controlled to emit the non-resonant wavelength beam λ2, and one of the resonant wavelength beam λ1 and the non-resonant wavelength beam λ2 is selectively coupled into the combined optical fiber 100, and the focused vortex beam generator 15 selectively outputs one of the first focused vortex beam and the second focused vortex beam.

[0046] Embodiment 2

[0047] As an optimization solution of the first embodiment, in this embodiment, if Figure 2 As shown, the focused vortex beam generator 15 comprises:

[0048] The combined optical fiber 100 has an incident end face and an output end face, and is used to transmit a light beam;

[0049] The spiral long-period fiber grating 200 is disposed between the incident end face and the output end of the combined optical fiber 100 and is used for mode coupling the resonant wavelength light beam λ1 transmitted in the combined optical fiber 100 to form a first vortex light beam;

[0050] The spiral zone plate 300 is arranged on the output end face of the combined optical fiber 100, and is used to perform topological charge conversion on the first vortex beam and focus it to form a first focused vortex beam, and to perform spiral phase modulation on the non-resonant wavelength beam λ2 output from the combined optical fiber 100 and focus it to form a second focused vortex beam.

[0051] The particle driving device of the utility model uses the combined optical fiber 100 as the main body of the focused vortex beam generator 15, and integrates the spiral long-period fiber grating 200 and the spiral zone plate 300 in the combined optical fiber 100 at the same time. The spiral long-period fiber grating 200 can excite the fundamental mode in the optical fiber into a high-order mode with orbital angular momentum, so as to perform mode coupling on the resonant wavelength light beam λ1 to convert it into a first vortex light beam with a high-order mode, and the spiral zone plate 300 has a spiral phase, which can add a spiral phase with orbital angular momentum to all light beams, so as to perform topological charge conversion on the first vortex light beam and perform spiral phase modulation on the non-resonant wavelength light beam λ2 and focus to form the first focused spiral light beam and the second focused spiral light beam respectively. Through the cooperation of the spiral long-period fiber grating 200 and the spiral zone plate 300, the first focused vortex light beam and the second focused vortex light beam with opposite topological charges can be output, and then the first focused vortex light beam and the second focused vortex light beam are used to drive the particles to realize forward rotation, reverse rotation and stop rotation.

[0052] The spiral zone plate 300 has a dual function: on the one hand, for the first vortex light beam transmitted by the combined optical fiber 100, the spiral zone plate 300 can realize topological charge conversion and further focus it to generate the first focused vortex light beam; on the other hand, for the non-resonant wavelength light beam λ2 transmitted by the combined optical fiber 100, the spiral zone plate 300 is responsible for spiral phase modulation thereof and then focusing it as well to construct the second focused vortex light beam.

[0053] The spiral long-period fiber grating 200 has a resonant wavelength and a non-resonant wavelength. When the resonant wavelength beam λ1 is input into the combined optical fiber 100, the spiral long-period fiber grating 200 can generate a high-order mode (i.e., a first vortex beam) with orbital angular momentum, while when the non-resonant wavelength beam λ2 is input into the combined optical fiber 100, the spiral long-period fiber grating 200 does not undergo mode coupling and only outputs a Gaussian beam of the fundamental mode. That is, the spiral long-period fiber grating 200 can only perform mode coupling on the resonant wavelength beam λ1, but cannot perform mode coupling on the non-resonant wavelength beam λ2.

[0054] When in use, if the resonant wavelength light beam λ1 is coupled into the combined optical fiber 100, when the resonant wavelength light beam λ1 passes through the spiral long-period fiber grating 200, since its wavelength is the same as the resonant wavelength of the spiral long-period fiber grating 200, it can carry orbital angular momentum through the mode coupling of the spiral long-period fiber grating 200, and then be converted into the first vortex light beam. When the first vortex light beam is emitted from the exit end face of the combined optical fiber 100, it is modulated by the spiral phase of the spiral zone plate 300 and the order of the spiral zone plate 300 is superimposed to realize the conversion of the topological charge number. Finally, the first vortex light beam is transmitted through the spiral phase modulation of the spiral zone plate 300. The first focused vortex beam is formed by the diffraction focusing of the spiral zone plate 300; if the non-resonant wavelength beam λ2 is coupled into the combined optical fiber 100, when the non-resonant wavelength beam λ2 passes through the spiral long-period fiber grating 200, since its wavelength is different from the resonant wavelength of the spiral long-period fiber grating 200, it cannot be mode-coupled through the spiral long-period fiber grating 200, so it still remains a Gaussian beam of the base film. When it is emitted from the output end face of the combined optical fiber 100, it is spirally phase modulated and diffraction-focused by the spiral zone plate 300 to form the second focused vortex beam.

[0055] The order directions of the first focused vortex beam and the second focused vortex beam may be the same or different, and the order values ​​may be the same or different. The motion state of the particles is determined by the joint action of the first focused vortex beam λ1 and the second focused vortex beam λ2.

[0056] In one of the usage methods of the present invention, the resonant wavelength beam λ1 and the non-resonant wavelength beam λ2 are coupled together into the combined optical fiber 100, so that the focused vortex beam generator 15 simultaneously outputs a symmetrical first focused vortex beam and a second focused vortex beam, and by adjusting the output power of the resonant wavelength beam λ1 and the non-resonant wavelength beam λ2, the magnitude of the torque formed by the first focused vortex beam and the second focused vortex beam on the particle is controlled.

[0057] For example, the order of the spiral long-period fiber grating 200 is +2, and the order of the spiral zone plate 300 is -1. After the mode coupling of the spiral long-period fiber grating 200, the resonant wavelength light beam λ1 forms a first vortex light beam with a topological charge of +2. After the spiral phase modulation and diffraction focusing of the spiral zone plate 300, the first vortex light beam is converted into a first focused vortex light beam with a topological charge of +1; and the non-resonant wavelength light beam λ2 forms a second focused vortex light beam with a topological charge of -1 after the spiral phase modulation and focusing diffraction of the spiral zone plate 300. It can be seen that the first focused vortex light beam and the second focused vortex light beam have opposite order directions but the same order values, and a symmetrical relationship between the positive rotation and the negative rotation.

[0058] If the output power of the resonant wavelength beam λ1 is greater than the output power of the non-resonant wavelength beam λ2, the force of the first focused vortex beam is greater than the force of the second focused vortex beam, the particle obtains positive angular momentum, and can rotate forward or decelerate in the reverse direction and stop; if the output power of the resonant wavelength beam λ1 is less than the output power of the non-resonant wavelength beam λ2, the force of the first focused vortex beam is less than the force of the second focused vortex beam, the particle obtains reverse angular momentum, and can rotate reversely or decelerate in the forward direction and stop.

[0059] In another method of using the present invention, by controlling the on and off of the resonant wavelength beam λ1 and the non-resonant wavelength beam λ2, one of the resonant wavelength beam λ1 and the non-resonant wavelength beam λ2 is selectively coupled into the combined optical fiber 100, and the focused vortex beam generator 15 selectively outputs one of the symmetrical first focused vortex beam and the second focused vortex beam.

[0060] For example, when the order of the spiral long-period fiber grating 200 is +2 and the order of the spiral zone plate 300 is -1, the resonant wavelength light beam λ1 forms a first vortex light beam with a topological charge of +2 after mode coupling of the spiral long-period fiber grating 200, and the first vortex light beam is converted into a first focused vortex light beam with a topological charge of +1 after spiral phase modulation and diffraction focusing of the spiral zone plate 300; and the non-resonant wavelength light beam λ2 forms a second focused vortex light beam with a topological charge of -1 after spiral phase modulation and focusing diffraction of the spiral zone plate 300. It can be seen that the first focused vortex light beam and the second focused vortex light beam have opposite order directions but the same order values, and a symmetrical relationship between the positive rotation and the negative rotation.

[0061] If the non-resonant wavelength beam λ2 is controlled to be disconnected and only the resonant wavelength beam λ1 is coupled into the combined optical fiber 100, the focused vortex beam generator 15 alone outputs a first focused vortex beam with a topological charge of +1 to drive the particle to rotate forward or to decelerate and stop in the reverse direction. If the resonant wavelength beam λ1 is controlled to be disconnected and only the non-resonant wavelength beam λ2 is coupled into the combined optical fiber 100, the focused vortex beam generator 15 alone outputs a second focused vortex beam with a topological charge of -1 to drive the particle to rotate reversely or to decelerate and stop in the forward direction.

[0062] Of course, the angular momentum of the vortex beam is also related to the value of its topological charge. The larger the value of the topological charge, the larger the angular momentum of the vortex beam. Therefore, in another method of using the present invention, the order of the spiral long-period fiber grating 200 and the spiral wave zone plate 300 can also be matched according to the angular momentum required by the first focused vortex beam and the second focused vortex beam, so that the focused vortex beam generator 15 can simultaneously output an asymmetric first focused vortex beam and a second focused vortex beam, or selectively output one of the asymmetric first focused vortex beam and the second focused vortex beam to meet specific application scenarios.

[0063] For example, the order of the spiral long-period fiber grating 200 is -3, and the order of the spiral zone plate 300 is +1. After the mode coupling of the spiral long-period fiber grating 200, the resonant wavelength light beam λ1 forms a first vortex light beam with a topological charge of -3. After the spiral phase modulation and focusing diffraction of the spiral zone plate 300, the first vortex light beam is converted into a first focused vortex light beam with a topological charge of -2; and the non-resonant wavelength light beam λ2 forms a second focused vortex light beam with a topological charge of +1 after the spiral phase modulation and focusing diffraction of the spiral zone plate 300. It can be seen that the order directions of the first focused vortex light beam and the second focused vortex light beam are opposite but the order values ​​are different, and the positive rotation and the negative rotation are in an asymmetric relationship.

[0064] For another example, the order of the spiral long-period fiber grating 200 is +1, and the order of the spiral zone plate 300 is +1. After mode coupling of the spiral long-period fiber grating 200, the resonant wavelength light beam λ1 forms a first vortex light beam with a topological charge of +1. After the spiral phase modulation and focusing diffraction of the spiral zone plate 300, the first vortex light beam is converted into a first focused vortex light beam with a topological charge of +2; and the non-resonant wavelength light beam λ2 forms a second focused vortex light beam with a topological charge of +1 after the spiral phase modulation and focusing diffraction of the spiral zone plate 300. It can be seen that the first focused vortex light beam and the second focused vortex light beam have the same order direction and an asymmetric relationship of both being positive rotations. The angular momentum of the two is superimposed on each other to drive the particles to rotate forward or to decelerate and stop in the reverse direction.

[0065] For another example, the order of the spiral long-period fiber grating 200 is -1, and the order of the spiral zone plate 300 is -1. After mode coupling of the spiral long-period fiber grating 200, the resonant wavelength light beam λ1 forms a first vortex light beam with a topological charge of -1. After the spiral phase modulation and focusing diffraction of the spiral zone plate 300, the first vortex light beam is converted into a first focused vortex light beam with a topological charge of -2; and the non-resonant wavelength light beam λ2 forms a second focused vortex light beam with a topological charge of -1 after the spiral phase modulation and focusing diffraction of the spiral zone plate 300. It can be seen that the first focused vortex light beam and the second focused vortex light beam have the same order direction and are both anti-rotational asymmetric relations, and the angular momentums of the two are superimposed on each other to drive the particles to rotate in the opposite direction or to decelerate and stop in the forward direction.

[0066] In summary, the order matching of the spiral long-period fiber grating 200 and the spiral zone plate 300 needs to ensure that the focused vortex beam generator 15 can output two focused vortex beams simultaneously.

[0067] The combined optical fiber 100 includes a first optical fiber 110 and a graded-index multimode optical fiber 120, wherein one end face of the first optical fiber 110 serves as the incident end face, and one end face of the graded-index multimode optical fiber 120 serves as the output end face; the other end face of the first optical fiber 110 opposite to the incident end face is connected to the other end face of the graded-index multimode optical fiber 120 opposite to the output end face; the spiral long-period fiber grating 200 can be formed by modulating the core or cladding of the first optical fiber 110 by a CO2 laser method or a femtosecond laser direct writing method.

[0068] The refractive index of the graded-index multimode optical fiber 120 is the highest at the center and is gradually decreasing along the radial direction. The propagation path of the light beam in the graded-index multimode optical fiber 120 presents a sinusoidal waveform. After the light beam is coupled from the first optical fiber 110 into the graded-index multimode optical fiber 120, due to the gradual change of the refractive index of the graded-index multimode optical fiber 120, its light beam mode field is expanded, achieving a beam expansion effect, so that the spiral zone plate 300 has a larger design space. This is conducive to forming a sufficiently large modulation range on the output end face to design a spiral zone plate 300 with a high numerical aperture, so as to integrate more wavebands to modulate the light beam, so as to generate a strongly focused vortex beam to perform rotational manipulation of the particles.

[0069] In this embodiment, the other end face of the first optical fiber 110 opposite to the incident end face is directly fused with the other end face of the graded-index multimode optical fiber 120 opposite to the emitting end face.

[0070] During preparation, the first optical fiber 110 and the graded-index multimode optical fiber 120 may be fusion-spliced ​​by a fiber fusion splicer, and then the graded-index multimode optical fiber 120 may be cut to a desired length by a fiber precision cutter.

[0071] The first optical fiber 110 includes a first core 111 and a first cladding 112, and the first cladding 112 surrounds the outer circumference of the first core 111; the graded-index multimode optical fiber 120 includes a second core 121 and a second cladding 122, and the second cladding 122 surrounds the outer circumference of the second core 121; the diameter of the second core 121 is greater than the diameter of the first core 111, and the outer diameter of the first cladding 112 is equal to the outer diameter of the second cladding 122.

[0072] Because the core diameter of the first optical fiber 110 is smaller than the core diameter of the graded-index multimode optical fiber 120, during preparation, it is only necessary to consider aligning the outer diameter of the first optical fiber 110 with the outer diameter of the graded-index multimode optical fiber 120, so that the first optical fiber 110 and the graded-index multimode optical fiber 120 can be directly aligned and fused by a fusion splicer. This method is simple, easy to operate and low in cost. At the connection portion after direct fusion splicing, the second core 121 and the first core 111 are in a stepped shape.

[0073] Among them, the length of the graded-index multimode optical fiber 120 is equal to or less than (2n+1) / 4 pitches, where the pitch is the unit optical fiber length corresponding to a complete sinusoidal wave cycle transmitted by the light beam in the graded-index multimode optical fiber 120, and n is a natural number.

[0074] Optimally, when the length of the graded-index multimode optical fiber 120 is equal to (2n+1) / 4 pitches, the light beam emitted from the graded-index multimode optical fiber 120 is exactly at the peak of the sine wave. At this time, the lateral range of the light beam transmitted in the graded-index multimode optical fiber is the largest, and the beam expansion effect is the best. At the same time, the slope of the sine wave peak of the light beam at the exit end face of the graded-index multimode optical fiber 120 is 0, so during the light beam transmission process, it can be understood that the divergence angle of the light beam is close to 0, which means that the light beam is similar to parallel light when it is emitted, and the collimation effect is also the best.

[0075] During preparation, when determining the length of (2n+1) / 4 pitches of the graded-index multimode optical fiber 120, the following steps are included:

[0076] Prepare a plurality of combined optical fiber 100 samples, wherein the lengths of the graded-index optical fibers in different combined optical fiber 100 samples are different, wherein the lengths of the graded-index multimode optical fibers 120 in different combined optical fiber 100 samples start with L1, and are sampled at preset intervals, and the lengths are L1, 2*L1, 3*L1, ..., 20*L1 in sequence; the range of L1 is 10-100 μm, and L1 is further preferably 30-70 μm;

[0077] The divergence angles of the output end faces of the graded-index multimode optical fibers 120 in different combined optical fiber 100 samples are measured, and the length of the graded-index multimode optical fiber 120 in the combined optical fiber 100 sample with the smallest divergence angle is determined to be (2n+1) / 4 pitches.

[0078] Specifically, the method for measuring the divergence angle includes the following steps:

[0079] The graded-index multimode optical fiber 120 in the combined optical fiber 100 sample is fixed on a displacement platform, with the output end face facing the CCD camera, and then the incident end face of the first optical fiber 110 in the combined optical fiber 100 sample is connected to a single-wavelength light source, the wavelength of which is the corresponding design wavelength of the spiral zone plate 300;

[0080] Starting from the distance L2, the distance between the output end face of the gradient refractive index multimode optical fiber 120 and the CCD camera is sequentially increased by the displacement platform and the spot image is recorded each time, wherein the range of L2 is 1 to 10 mm;

[0081] Through software processing, the change rate of the spot diameter as the distance between the exit end face and the CCD camera changes is obtained. Half of this change rate is the tangent value of the half divergence angle of the gradient refractive index multimode optical fiber 120. The size of the divergence angle can be obtained based on the tangent value.

[0082] Specifically, according to the formula Get the size of the divergence angle, where θ is the beam divergence angle, is the rate of change of the spot diameter as the distance from the camera changes. Since the divergence angle is very small, the tangent value of the divergence angle is approximately equal to the size of the divergence angle, and the divergence angle is approximately:

[0083] The first optical fiber 110 is a single-mode fiber, a few-mode fiber, a combination of a single-mode fiber and a few-mode fiber, or a combination of a single-mode fiber and a ring-core fiber. The core of the single-mode fiber only has the fundamental mode. Although there are other high-order modes in the core of the few-mode fiber, the fundamental mode is still the main mode, and the proportion of other modes is very small. The ring-core fiber is a special type of few-mode fiber. Therefore, writing the spiral long-period fiber grating 200 on the single-mode fiber or the few-mode fiber can excite the fundamental mode in the single-mode fiber or the few-mode fiber into a high-order mode carrying orbital angular momentum. The spiral long-period fiber grating 200 satisfies the following formula:

[0084] N CO -N F =m·λ / Λ 0

[0085] J CO =J F +m·σ

[0086] Where N CO 、N F is the effective refractive index of the fundamental mode and the effective refractive index of the higher-order mode in the first optical fiber 110, m is the harmonic order of the spiral long-period fiber grating 200, λ is the resonant wavelength of the spiral long-period fiber grating 200, Λ 0 is the period of the helical long-period fiber grating, J CO and J F is the total angular momentum of the fundamental mode and the higher-order modes in the first optical fiber 110 (the sum of the spin angular momentum and the orbital angular momentum), σ=±1 is the spiral direction of the spiral long-period fiber grating 200, + is the positive rotation (also called positive rotation, left rotation or clockwise rotation), and - is the reverse rotation (also called reverse rotation, right rotation or counterclockwise rotation).

[0087] The spiral zone plate 300 includes two parts: a spiral phase structure and a Fresnel zone structure. The spiral phase structure is used to add a spiral phase to the light beam, and its transmittance function is exp(ilφ). The Fresnel zone structure is used to diffract and focus the light beam, and its transmittance function is Therefore, the transmittance function of the spiral zone plate 300 satisfies the following formula:

[0088]

[0089] Wherein λ and f are the wavelength and focal length of the focused vortex beam (the first focused vortex beam or the second focused vortex beam), l is the waveband order of the spiral zone plate 300, and r and φ are polar coordinates. Figure 2 The spiral zone plate 300 is shown with the wave zone order l being 0, 1 and 2. It can be seen that when the wave zone order l=0, the structure of the spiral zone plate 300 is a Fresnel zone plate with a concentric circle structure.

[0090] In this embodiment, the spiral zone plate 300 is prepared by focused ion beam etching technology (FIB). First, a light-shielding film layer is formed on the output end face of the gradient refractive index multimode optical fiber 120. The light-shielding film layer is preferably a metal film layer. The metal film layer is firmly combined with the optical fiber end face and can block light with stable performance. For example, the metal film layer can be a gold film, a silver film or a copper film, etc., with a thickness between 50nm-150nm; then the high-energy ion beam is focused on the light-shielding film layer, and the gradient refractive index multimode optical fiber 120 is driven to move by a three-dimensional displacement platform, so that the high-energy ion beam is The shape of the spiral wave zone plate 300 is etched on the shading film layer, and the spiral wave zone plate 300 includes a light-transmitting wave zone and a light-shielding wave zone. The light-transmitting wave zone is formed by the area on the light-shielding film layer that is removed by the high-energy ion beam etching, and the light-shielding wave zone is formed by the area on the light-shielding film layer that is not etched by the high-energy ion beam and retained. The light-transmitting wave zone and the light-shielding wave zone are arranged in sequence at intervals along the circumference of the end face of the gradient refractive index multimode optical fiber 120 and are spirally wound around each other to form an amplitude-type wave zone plate.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the utility model rather than to limit them. Although the embodiments of the utility model are described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the embodiments of the utility model can still be modified or replaced by equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the scope of the technical solutions of the embodiments of the utility model.

Claims

1. A particle driving device, characterized in that: The invention comprises a first light source, a second light source, a 3db coupler and a focused vortex beam generator, wherein the first light source and the second light source are connected to the focused vortex beam generator through the 3db coupler; The first light source is used to emit a light beam of a resonant wavelength; The second light source is used to emit a non-resonant wavelength light beam; The 3db coupler is used to couple the resonant wavelength light beam and the non-resonant wavelength light beam into the focused vortex beam generator according to a preset ratio; The focused vortex beam generator is used to convert the resonant wavelength beam and the non-resonant wavelength beam into a first focused vortex beam and a second focused vortex beam respectively.

2. The particle driving device according to claim 1, characterized in that: The foci of the first focused vortex light beam and the second focused vortex light beam coincide with each other, or are staggered along the optical axis to form a double focus.

3. The particle driving device according to claim 1, characterized in that: The 3db coupler has a first input port, a second input port and an output port, wherein the first input port is connected to the first light source via an optical fiber, the second input port is connected to the second light source via an optical fiber, and the output port is directly connected to the focused vortex beam generator.

4. The particle driving device according to claim 1, characterized in that: The focused vortex beam generator comprises: A combined optical fiber having an incident end face and an output end face for transmitting the resonant wavelength light beam and the non-resonant wavelength light beam; A spiral long-period fiber grating is arranged between the incident end face and the output end of the combined optical fiber, and is used for mode coupling the resonant wavelength light beam transmitted in the combined optical fiber to form a first vortex light beam; The spiral zone plate is arranged on the output end face of the combined optical fiber, and is used to perform topological charge conversion on the first vortex light beam and focus it to form a first focused vortex light beam, and to perform spiral phase modulation on the non-resonant wavelength light beam output from the combined optical fiber and focus it to form a second focused vortex light beam.

5. The particle driving device according to claim 4, characterized in that: The combined optical fiber includes a first optical fiber and a graded-index multimode optical fiber, and the first optical fiber and the graded-index multimode optical fiber are connected at their end faces; the other end face of the first optical fiber opposite to its connected end face serves as the incident end face of the combined optical fiber, and the other end face of the graded-index multimode optical fiber opposite to its connected end face serves as the output end face of the combined optical fiber, and the spiral long-period fiber grating is formed in the core or cladding of the first optical fiber.

6. The particle driving device according to claim 5, characterized in that: The first optical fiber is a single-mode optical fiber, a few-mode optical fiber, a combination of a single-mode optical fiber and a few-mode optical fiber, or a combination of a single-mode optical fiber and a ring-core optical fiber.

7. The particle driving device according to claim 5, characterized in that: The spiral long-period fiber grating satisfies the following formula: N CO -N F =m·λ / Λ0 I CO =J F +m·σ Where N CO 、N F is the effective refractive index of the fundamental mode and the effective refractive index of the higher-order mode in the first optical fiber, m is the topological order of the spiral long-period fiber grating, λ is the resonant wavelength of the spiral long-period fiber grating, Λ0 is the period of the spiral long-period fiber grating, J CO and J F is the total angular momentum of the fundamental mode and the higher-order modes in the first optical fiber, and v=±1 is the helical direction of the helical long-period fiber grating.

8. The particle driving device according to claim 5, characterized in that: The length of the graded-index multimode optical fiber is equal to or less than (2n+1) / 4 pitches, where the pitch is the unit optical fiber length corresponding to a complete sinusoidal wave cycle transmitted by the resonant wavelength light beam and the non-resonant wavelength light beam in the graded-index multimode optical fiber, and n is a natural number.

9. The particle driving device according to claim 4, characterized in that: The transmittance function of the spiral zone plate satisfies the following formula: Wherein λ and f are the wavelength and focal length of the focused vortex beam, respectively, l is the waveband order of the spiral waveband plate, and r and φ are polar coordinates.

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