Optical fiber optical tweezer probe for multi-particle trapping, method of manufacture and use

Abstract

The present disclosure relates to a kind of optical fiber optical tweezers probe for multi-particle capture, preparation method and application.The optical fiber optical tweezers probe includes a single-mode optical fiber, and the end of the single-mode optical fiber is a conical end, and the end surface of the conical end is attached with black porous carbon-based thermoplastic polyurethane polymer.The optical fiber optical tweezers probe is manufactured according to the following path: the end of the single-mode optical fiber is twisted and electrode discharged in sequence;the other end of the single-mode optical fiber is twisted, the thermoplastic polyurethane fiber coating is placed in the exposed fiber twisted area, and the taper treatment is carried out, so that the other end of the single-mode optical fiber has a black porous carbon-based thermoplastic polyurethane polymer conical transition zone.After the treatment, the other end of the single-mode optical fiber has a black porous carbon-based thermoplastic polyurethane polymer conical transition zone.The application of this scheme can realize low-cost and high-efficiency particle aggregation capture based on single-mode optical fiber without inserting other additional optical elements and additional experimental materials during the preparation of optical fiber optical tweezers probe.

Description

Technical Field

[0001] This disclosure relates to the field of all-fiber technology, and more specifically, to a method for capturing large-scale aggregations of yeast particles using a single-mode fiber optical tweezers probe. Background Technology

[0002] In the field of optical micromanipulation, optical tweezers (OTs), with their unique "invisible hand" power, are able to capture and manipulate microscopic particles, making them an important tool for scientific research. With the continuous development of OT technology, various specialized techniques have emerged to address different experimental needs, each with its own specific advantages and limitations.

[0003] Existing optical tweezers based on spatial light modulators (SLMs) can form complex optical fields, such as spiral beams or optical arrays, by manipulating the phase, amplitude, or polarization of light, thereby achieving high-precision manipulation of single or multiple particles. This method is highly flexible and adaptable, but the equipment is expensive and requires precise alignment of optical components, making operation complex, especially challenging in high-precision applications. Existing silicon-based optical tweezers utilize nanofabrication technology to enhance localized optical fields through the design of micro / nanostructured silicon arrays, thus providing powerful particle manipulation capabilities. However, silicon-based optical tweezers have limited capture range and lower flexibility, making it difficult to perform multi-particle manipulation over large spatial areas. Existing fiber optic tweezers (OFTs) are gradually becoming important tools for optical capture due to their compactness, economy, and flexibility. Generally, by adjusting the geometry of the fiber tip (such as tapered, spherical, or truncated) or the geometry of the middle region of the fiber, OFTs can generate highly localized electromagnetic fields for particle capture. For example, Deng Hongchang et al. proposed a tunable fiber tweezers based on a biconical freeform surface (Chinese patent document: CN 117766190 A). This device uses a capillary fiber side-thrown and filled with a high-refractive-index material, utilizing total internal reflection to form a continuous optical potential trap near the fiber, achieving multi-point capture and dynamic manipulation of particles. Yuan Libo et al. proposed a fiber-optic tweezers device based on lateral movement (Chinese patent document: CN 117766191 A). This invention integrates particle capture, manipulation, and detection functions by using multi-core fibers and a lateral capture region. However, existing fiber tweezers technologies are generally limited to the near-field region near the fiber tip and are mostly suitable for capturing single particles or single-chain particles, which limits their application in multi-particle operations. Furthermore, the required technology is costly, and the position and intensity of the optical potential trap require complex external control, limiting the device's performance in rapid capture and flexible operation.

[0004] In summary, there is a lack of a relatively simple and low-cost method for capturing large numbers of particles using ordinary single-mode optical fibers in the current technology. Summary of the Invention

[0005] To address the technical problems existing in the background art, this disclosure proposes a fiber optic tweezers probe for multi-particle trapping, its fabrication method, and its application. In this technical solution, only a single-mode fiber (SMF) is used. By twisting one end of the fiber by 225° and discharging twice, the LP11 mode can be excited from the LP01 mode, and further discharge forms the OAM mode. Subsequently, the untreated end of the fiber is also twisted by 225°, and a thermoplastic polyurethane (TPU) coating stripped from the fiber is placed on the upper surface of the twisted area. A hot-melt tapering process is then performed to obtain a tapered fiber optic probe with a black carbon-based thermoplastic polyurethane (TPU) polymer tip. Finally, the fabricated fiber optic tweezers probe is placed in a yeast solution, and a 980nm wavelength laser is passed through the fiber, ultimately achieving a large-scale aggregation and trapping phenomenon of yeast particles at the fiber tip. No other complex operations such as multi-fiber coupling or optical device modulation are required.

[0006] One aspect of this disclosure provides an optical fiber tweezers probe for multi-particle trapping, comprising a single-mode optical fiber, characterized in that: one end of the single-mode optical fiber is a tapered end, and the end surface of the tapered end is coated with a black porous carbon-based thermoplastic polyurethane polymer.

[0007] A second aspect of this disclosure provides a method for fabricating the aforementioned fiber optic tweezers probe:

[0008] One end of a single-mode optical fiber is twisted and then subjected to electrode discharge in sequence.

[0009] The other end of a single-mode optical fiber is twisted, a thermoplastic polyurethane fiber coating is placed in the exposed twisted area of ​​the fiber, and then tapered. After the treatment, the other end of the single-mode optical fiber has a black porous tapered transition region with carbon-based thermoplastic polyurethane polymer.

[0010] Furthermore, the process of twisting and discharging electrodes at one end of a single-mode optical fiber is performed sequentially, following the path described below.

[0011] Applications include a Z-axis rotary table and an optical fiber fusion splicer;

[0012] Strip the thermoplastic polyurethane coating from one end of a single-mode optical fiber and fix it on the fiber holder of the Z-axis rotary table. Twist the fiber at a preset twist angle and adjust its relative position in the X-axis direction to ensure that the twisted area is between the two electrodes of the fiber fusion machine. Then fix the other end of the single-mode optical fiber on the fiber holder of the fiber fusion machine.

[0013] The fiber fusion splicer was modulated into a discharge mode and discharged twice: after the first discharge, the diameter of the twisted region became thinner, and the LP01-LP11 mode conversion was obtained; after the second discharge, the optical fibers on both sides of the twisted region were heated and expanded, and their shape changed to a hemispherical shape, and the LP11-OAM mode conversion was obtained.

[0014] Heat shrink tubing is applied to the area on a single-mode optical fiber that is subjected to torsional discharge, and then fixed using the heating module of the optical fiber fusion machine.

[0015] Furthermore, the process of twisting the other end of the single-mode optical fiber, applying a thermoplastic polyurethane fiber coating to the exposed twisted area of ​​the bare fiber, and then tapering it is carried out according to the following path:

[0016] Use an electric taper and an alcohol lamp;

[0017] The outermost transparent thermoplastic polyurethane coating is stripped from the other end of a single-mode optical fiber, exposing part of the fiber.

[0018] The middle section of a single-mode optical fiber is fixed on the Z-axis rotary table;

[0019] One end of the exposed optical fiber is fixed to the optical fiber clamp of the electric tapering machine;

[0020] Rotate the Z-axis rotary table clockwise by a preset rotation angle to form a fiber twisting region in the exposed part of the optical fiber;

[0021] The stripped transparent thermoplastic polyurethane coating is placed on the upper surface of the optical fiber twist region;

[0022] The lower surface of the optical fiber twisted region is heated to the optical fiber melting point from directly below using the outer flame of an alcohol lamp;

[0023] Set the initial speed V1 of the X-axis motor of the electric taper and start it. After a delay time T, suddenly transition to speed V2. The speed V2 must ensure that the breakage time of the optical fiber torsion region does not exceed 10 seconds.

[0024] After the optical fiber twisted region breaks, the end of the single-mode optical fiber is tapered and covered with black porous carbon-based thermoplastic polyurethane polymer.

[0025] Further, the preferred embodiment is as follows: the preset torsion angle and rotation angle are both 225°; the discharge intensity of the fiber optic fusion splicer is +100 bits, and the discharge time is 0.5 s; the length of the thermoplastic polyurethane coating that is peeled off is controlled within 3 cm to 4 cm, the initial speed V1 is set to 0.03 mm / s, the delay time T is set to 3 s, and the speed V2 is set to 0.5 mm / s.

[0026] The third aspect of this disclosure proposes applications for multi-particle trapping using fiber optic tweezers probes, including:

[0027] The application method includes using a laser, an optical fiber fixed three-dimensional stage, a solution fixed three-dimensional stage, and an optical fiber tweezers probe; the optical fiber tweezers probe is obtained by the aforementioned optical fiber tweezers probe manufacturing method.

[0028] The fiber optic tweezers probe is fixed on the capillary stainless steel tube of the fiber optic fixed three-dimensional stage;

[0029] Connect the end of the fiber optic tweezers probe that has not been tapered to the laser.

[0030] The conical tip of the fiber optic tweezers probe is inserted into the solution of particles to be captured.

[0031] Activate the laser to achieve multi-particle capture.

[0032] Preferably, the particle solution to be captured is a yeast solution; the laser is a 980nm laser, and the input power of the laser is adjusted to 10mW to pass in a 980nm wavelength laser, so as to achieve the aggregation and capture of yeast particles at the tip of the optical fiber.

[0033] The following example of capturing yeast particles illustrates that at least one of the above-mentioned technical solutions employed in one or more embodiments of this specification can achieve the following beneficial effects:

[0034] First, the method provided in this disclosure can obtain an optical fiber tweezers probe and capture a large number of yeast particles in an aqueous solution by operating only a single ordinary single-mode optical fiber, which has the characteristics of low cost and good applicability.

[0035] Secondly, after performing a 225° twist and two discharges on one end of the optical fiber according to the method provided in this disclosure, the circular symmetry of the optical fiber will be destroyed when an LP01 mode SMF fiber is subjected to stress with a 225° twist angle. According to the birefringence effect of the stressed fiber, the fiber will be decomposed into two linearly polarized components along the fast axis F and the slow axis S, with the fast axis component F leading the slow axis component S. Because of the phase difference, when the fiber fusion splicer discharges the twisted region, the diameter of the twisted region becomes thinner, changing the fiber mode. This allows the excitation of a polarized LP11 mode with the same twist angle in a standard single-mode LP01 fiber. Based on this, an approximately hemispherical fiber lens is fabricated at both ends of the twisted region using the electrode discharge function of the fiber fusion splicer. This is equivalent to introducing a phase difference. A circular polarizer is used to superimpose light spots with phase differences to form an OAM mode. This method can obtain higher-order polarization modes and OAM modes of LP11 by combining fiber twisting tapering with a hemispherical lens fabricated at the tip. A 225° twist and thermoplastic polyurethane (TPU) coating are applied to the other end of the fiber to form a tapered fiber tweezer probe with a black porous carbon-based TPU polymer at the end. Due to the optical properties of the resulting polymer, the porous carbon-based black region embedded at the fiber tip has a porous structure. Due to the material's inhomogeneity and gradient refractive index effect, the light field undergoes multiple scattering and standing wave superposition. Under the influence of the gradient refractive index characteristics, the porous structure acts like a microlens to modulate the light field, resulting in a significant light field focusing effect and local light intensity enhancement, ultimately enabling the large-scale aggregation and capture of yeast particles. The process involves three steps, is simple to operate, and can be repeatedly reproduced. Furthermore, the entire process does not require any fiber coupling or optical component modulation, resulting in low operating costs and a high success rate.

[0036] Furthermore, the method for capturing large numbers of yeast particles using a single-mode fiber tweezers probe disclosed in this disclosure can convert the single-mode fiber into different modes, generating an OAM mode optical field distribution and enhancing the multi-dimensional capture efficiency of the fiber tweezers. Additionally, a fiber probe with a porous aggregated structure is formed at the other end of the fiber, amplifying the local electromagnetic field intensity, optimizing the balance between optical gradient and scattering force, and introducing unique optical field dynamics. This optimized fiber tweezers probe is expected to improve the efficiency of capturing large numbers of yeast particles, providing a robust framework for scalable, low-cost, and energy-efficient optical capture systems.

[0037] In summary, the method provided in this disclosure achieves the large-scale aggregation and capture of yeast particles by a single single-mode fiber tweezer probe through three steps: fiber mode conversion (torsion + discharge), fiber tapering (torsion + thermoplastic polyurethane (TPU) hot-melt tapering), and fiber tweezer probe yeast particle capture. It does not require other complex operations such as multi-fiber coupling or optical device modulation, and is a relatively simple, low-cost, and efficient fiber tweezer yeast particle capture method.

[0038] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure.

[0039] Other features and aspects of this disclosure will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0040] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the specification, serve to illustrate the technical solutions of this disclosure.

[0041] Figure 1 This is a mode conversion diagram of a common single-mode fiber in a specific embodiment formed by applying the scheme described in this disclosure.

[0042] Figure 2 This is an optical field distribution diagram of the fiber optic tweezers probe prepared in a specific embodiment formed by applying the scheme described in this disclosure.

[0043] Figure 3 This is a schematic diagram of the process for manufacturing fiber optic tweezers probes using the scheme described in this disclosure.

[0044] Figure 4 This is a diagram of an optical fiber tweezers particle trapping experimental apparatus prepared using the scheme described in this disclosure.

[0045] Figure 5 The images show electron microscope (EM) images and elemental spectra of the black porous carbon-based thermoplastic polyurethane polymer formed by incomplete combustion of TPU in a specific embodiment of the scheme described in this disclosure.

[0046] Figure 6 This is a force analysis diagram of yeast particles captured by optical fiber tweezers prepared in a specific embodiment of the scheme described in this disclosure.

[0047] Figure 7 This is a diagram showing the trajectory of yeast particle capture under a 980nm wavelength laser light, prepared by optical tweezers in a specific embodiment of the scheme described in this disclosure.

[0048] Figure 8 This is a diagram showing the trajectory of yeast particles captured by optical tweezers prepared in a specific embodiment of the scheme described in this disclosure under a 980nm wavelength laser cut-off.

[0049] Figure 9 This is a comparative analysis of the results of a particle trapping experiment using a fiber optic tweezers probe prepared in a specific embodiment of the scheme described in this disclosure and a conventional fiber optic tweezers probe of the same size.

[0050] Figure 10 This is a force analysis diagram of the particles under different power 980nm wavelength lasers when the optical fiber tweezers prepared in a specific embodiment of the scheme described in this disclosure capture yeast particles.

[0051] Figure 11 It is a force analysis diagram of simulation experiments on different particles using the scheme described in this disclosure.

[0052] In the figure, 1-Ordinary single-mode optical fiber G.652D, 2-Z-axis rotary stage, 3-Fiber fusion splicer, 4-Electric tapering machine, 5-Alcohol lamp, 6-980nm laser, 7-Fiber optic fixed three-dimensional stage, 8-Capillary stainless steel tube, 9-Yeast solution fixed three-dimensional stage, 10-Microscope, 11-Host computer PC, 12-Fiber optic tweezers probe, 13-Charge-coupled device camera (CCD). Detailed Implementation

[0053] Various exemplary embodiments, features, and aspects of this disclosure will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0054] Furthermore, to better illustrate this disclosure, numerous specific details are set forth in the following detailed description. Those skilled in the art will understand that this disclosure can be practiced without certain specific details. In some instances, methods and means well-known to those skilled in the art have not been described in detail in order to highlight the main points of this disclosure.

[0055] This disclosure provides a method for capturing large-scale aggregation of yeast particles using a single-mode fiber tweezers probe. The application potential of the obtained fiber tweezers probe can be extended to biological and medical experiments to improve particle capture efficiency.

[0056] The specific embodiment below uses an SMF optical fiber as the operating object, and utilizes a torsion and discharge method to excite the LP11 mode and OAM mode with corresponding torsional orthogonal angles from the LP01 mode of the SMF. A tapered optical fiber probe with black porous thermoplastic polyurethane (TPU) carbon-based polymer is then fabricated using a torsion and thermoplastic polyurethane (TPU) polymer tapering method. Placing the prepared optical fiber tweezers probe in a yeast particle solution results in a large-scale aggregation and trapping of particles.

[0057] In this example, the single-mode fiber is G.652D Corning, SMF-28e, with a cladding diameter of 125μm and a fiber core diameter of 8.2μm. It is necessary to first convert the mode of the laser input port of the single-mode fiber and then perform a tapering process with a thermoplastic polyurethane (TPU) coating on the laser output end to form a tapered fiber tip with a porous carbon-based thermoplastic polyurethane (TPU) polymer.

[0058] like Figure 1 As shown, the single-mode fiber optical tweezers probe is fabricated by twisting one end of the fiber by 225° and discharging it twice. This process enables the single-mode fiber to be excited from the LP01 mode to the LP11 mode, and after the second discharge, the OAM mode is formed.

[0059] A single-mode fiber tweezers probe can be obtained by twisting the untreated end of the fiber by 225°, placing the stripped thermoplastic polyurethane (TPU) coating on the upper surface of the twisted area, and then performing a hot-melt tapering process. This produces a tapered fiber probe with a black carbon-based thermoplastic polyurethane (TPU) polymer tip.

[0060] First, a single-mode fiber optic tweezers probe is fabricated. The specific steps include:

[0061] Step 1: The single-mode optical fiber is G.652D Corning SMF-28e with a cladding diameter of 125μm and a core diameter of 8.2μm. The thermoplastic polyurethane (TPU) coating is stripped from one end of the single-mode optical fiber, while the other end remains untreated. The stripped TPU-coated single-mode optical fiber is then fixed to the fiber optic holder on the Z-axis rotary table. The fiber is twisted 225°, and its relative position along the X-axis is adjusted to ensure the twisted area is between the two electrodes of the fusion splicer. The other end of the fiber is then fixed to the fiber optic holder of the fusion splicer.

[0062] The fiber fusion splicing system was modulated into discharge mode, with a discharge intensity set to +100 bits and a discharge time of 0.5 seconds, for a total of two discharges. After the first discharge, the diameter of the twisted region became thinner, achieving LP01-LP11 mode conversion. After the second discharge, due to the thermal expansion of the fibers on both sides of the twisted region, a hemispherical shape was achieved, achieving LP11-OAM mode conversion. Finally, a heat-shrink tubing was fitted over the twisted discharge area, and the heating module of the fiber fusion splicing machine was used to fix the heat-shrink tubing to the treated area of ​​the fiber for protection.

[0063] The Z-axis rotary table on the XZ-axis electric tapering machine 2 is selected to have a torsion angle that is an odd multiple of 225°. Its characteristic is that the number of modes propagating in the optical fiber depends on the normalized frequency parameter of the transmitted light wave in the optical fiber. Normalized parameter V and laser wavelength Fiber core diameter ρ, fiber core refractive index n core and cladding refractive index n cladding This is relevant. When V < 2.405, the fiber maintains the LP01 mode. When 2.405 ≤ V ≤ 3.832, the fiber begins to generate the LP11 mode. As the value of V increases, the number of modes supported by the fiber increases, and the fiber gradually transforms into a low-mode and multimode fiber. When V > 3.832, higher-order modes will be excited in the fiber. This can be achieved by utilizing the rotation angle. By applying rotational stress-stretching to the SMF to excite birefringence in the fiber, and by changing the value of ρ, and thus the value of V, it is possible to generate a birefringence with a phase difference from the LP01 mode. LP11 mode.

[0064] If a hemispherical fiber lens is fabricated using the arc discharge function of a fiber fusion splicer based on θ, this is equivalent to introducing... A circular polarizer can superimpose light spots with phase differences at the tapered end of an optical fiber, ultimately forming an approximate OAM mode. Based on this principle, further experimental results show that a 225° rotation angle provides the highest conversion efficiency for the OAM mode. By rotating the SMF by 225° and performing partial discharge treatment on the twisted region at the fiber end using a fusion splicer, the fiber core diameter is reduced, exciting the LP11 mode. Simultaneously, the partial discharge treatment of the fusion splicer causes the twisted region at the fiber end to expand due to heat, forming a structure similar to a hemispherical lens. The modulation effect of this expanded region on the optical field causes the two lobes of the LP11 mode light spot to superimpose in the expanded region of the fiber, thereby realizing the conversion of the optical vortex (OAM) mode. By changing the rotation angle and geometry of the optical fiber, we can adjust the core diameter of the fiber, thereby changing the normalized frequency V and achieving the excitation of different modes. For example, when rotating by 225°, the core diameter of the fiber decreases, and the change in the normalized frequency V causes the LP01 mode to convert to the LP11 mode. Further partial discharge modulates the geometry of the optical fiber, causing the two modes to superimpose at the fiber end, ultimately producing an optical field distribution with orbital angular momentum (OAM) characteristics.

[0065] In this process, the light field distribution of the OAM mode can be expressed as: Where A(r) is the radial amplitude distribution, θ is the azimuth angle, and l is the topological charge. The core radius ρ can be adjusted to control V by regulating θ and the discharge power. For wavelength... =980 nm, core refractive index n core =1.45, cladding refractive index n cladding For optical fibers with a core radius of 1.44 μm, the core radius required for LP11 mode excitation ranges from approximately 2.55 μm to 4.05 μm. These principles form the theoretical basis for efficient LP01 to LP11 and OAM mode conversion in single-mode optical fibers.

[0066] Step 2: Peel off the outermost transparent thermoplastic polyurethane (TPU) coating from the untreated end of the optical fiber, exposing approximately 5cm of fiber. Fix one end of the fiber to a Z-axis rotary table and the other end to the fiber clamp of an electric tapering machine. Rotate the Z-axis rotary table clockwise to 225°. Gently place the peeled-off TPU transparent coating onto the upper surface of the exposed twisted area of ​​the fiber using tweezers (leaving the lower surface exposed). Place an alcohol lamp directly below the twisted area, approximately 3cm from the fiber end, and heat the lower surface of the twisted area to the fiber's melting point using the outer flame of the alcohol lamp. By controlling the length of the thermoplastic polyurethane (TPU) coating within the range of (3cm, 4cm), setting the initial acceleration of the X-axis motor of the electric tapering machine to 0.03 mm / s², and then suddenly transitioning to 0.5 mm / s² after a 3-second delay, the optical fiber can be rapidly broken in the torsion region, thus obtaining a tapered optical fiber tweezer probe with a black porous carbon-based thermoplastic polyurethane (TPU) polymer tip.

[0067] The Z-axis rotary table on the XZ-axis electric fiber optic tapering machine 2 is twisted at an angle of 225°, and a thermoplastic polyurethane (TPU) coating is placed on the upper surface of the twisted area, ultimately forming a tapered fiber optic tweezers probe with a black porous carbon-based thermoplastic polyurethane (TPU) polymer tip.

[0068] Thermoplastic polyurethane (TPU) polymers that do not completely burn on the probe surface can propagate evanescent waves to the surrounding environment, summoning nearby yeast particles. Thermoplastic polyurethane (TPU) is a polyurethane-based material, specifically used as the outer coating of the transparent SMF (superficial microfiber) used in its implementation. Due to its high carbon chain, hydrogen, and oxygen content, it may undergo thermal decomposition, oxidation, and carbonization processes when heated in air at high temperatures (approximately 800°C - 1200°C) using the outer flame of an alcohol lamp. Heating the thermoplastic polyurethane (TPU) material coated on the optical fiber tip with the outer flame of an alcohol lamp forms a black substance with a porous structure. Its formation mechanism includes the thermal decomposition, carbonization, and pore formation during gas escape of the thermoplastic polyurethane (TPU). At high temperatures, the urethane bonds in the thermoplastic polyurethane (TPU) break, generating small molecule products (such as amines and alcohols) which further decompose into volatile gases.

[0069] R-NH-CO-O-R'→ R-NH2+ R'-OH (1)

[0070] S-NH2 → NH3+ Hydrocarbons (2)

[0071] R'-OH→ H2O+ Alkenes (3)

[0072] As the heating time increases, some carbon chains further carbonize, forming amorphous carbon (carbon black). Simultaneously, the escaped gases form a porous structure within the material. The main reactions are as follows:

[0073] CxHyOz→ C+ CO2 + H2O + CO (4)

[0074] The final product is a black, porous carbon-based polymer that exhibits optical properties similar to organic polymers. The effective refractive index of the porous carbon-based black region embedded at the fiber tip was measured to be approximately n. black-block =1.5, and the refractive index n at the fiber tip tip =1.46 and cladding refractive index n cladding There is a certain difference between 1.45 and 1.45. This difference in refractive index causes a redistribution of the light field at the interface, with some light being reflected and some transmitted into the porous material. The light reflection and transmission phenomena at the interface can be described by Fresnel's equations:

[0075] ,

[0076] in, and These represent parallel and perpendicularly polarized light, respectively. θ i It is the angle of incidence (determined by the twist angle of the optical fiber and the direction of the incident light), θ t The transmission angle can be solved using Snell's law, n tip = 1.46. The calculated reflectance is: R ll ≈2.89×10⁻⁶, R ≈ 6.76 × 10⁻⁴. This indicates that the vast majority of light enters the black carbon-based polymer region. This region has a porous structure. Due to the material's inhomogeneity and gradient refractive index effect, the light field undergoes multiple scattering and standing wave superposition, resulting in a localized enhancement of the electromagnetic field. This phenomenon can be expressed by the local light intensity enhancement factor G:

[0077] ,

[0078] Among them, E local It is the local electric field intensity in the porous structure, E incident It is the electric field intensity of the incident light. Under the influence of gradient refractive index characteristics, porous structures are formed by the stacking of microspheres with multiple spacings (such as...). Figure 5The electron microscope image shown illustrates how a microlens modulates the light field, resulting in a significant focusing effect and enhanced local light intensity. Therefore, in practical implementation, a single SMF is converted to LP01-LP11-OAM mode through twisting and discharge. Then, a thermoplastic polyurethane (TPU) coating stripped from the transparent fiber surface is used to further conicalize the modified fiber into an OFT (off-the-fiber) shape while maintaining the twist angle, ultimately forming a tapered fiber probe with a black carbon-based polymer tip. This novel probe structure significantly enhances the local electromagnetic field strength, improves the optical gradient force and scattering force at the fiber tip, thereby enhancing the particle capture efficiency and stability.

[0079] The specific steps for capturing large-scale aggregations of yeast particles using the fabricated probe are as follows:

[0080] The prepared fiber optic probe was fixed onto a capillary stainless steel tube on a three-dimensional fiber optic stage. The untapered end was connected to a 980nm laser, and the laser's input power was adjusted to 10mW. The tapered tip of the prepared fiber optic probe was inserted into a yeast solution, which was placed on the three-dimensional yeast solution stage. The stage consisted of a coverslip and a slide, spaced 2-3 mm apart to form a chamber. The images of solution particles captured by the prepared fiber optic probe were monitored and recorded in real-time on a PC via a microscope connected to a CCD, demonstrating the phenomenon of a large number of yeast particles being captured by the probe.

[0081] The conical tip of the prepared optical fiber probe was inserted into a yeast solution, resulting in the observation of a large number of yeast particles being captured. Its characteristics are as follows:

[0082] The fabricated OFT probe was immersed in a solution of yeast particles. The yeast particles began to move under the influence of optical forces, including optical gradient forces and scattering forces. These optical forces can be expressed as the surface integral of the target particle surface S:

[0083] ,

[0084] Where n is the outward normal unit vector of surface S; <T M > is the time-averaged Maxwell stress tensor, which can be obtained by formula (9), expressed as:

[0085] ,

[0086] Where E is the electric field, H is the magnetic field, ε is the permittivity of the surrounding medium, µ is the permeability of the surrounding medium, and I is the unit second tensor.

[0087] Therefore, if F gradient =F scatteringTherefore, particles in the optical field can be captured by a fabricated OFT probe. Force analysis of yeast particles in solution. Figure 6 As shown.

[0088] Figure 7 The fiber optic tweezers prepared according to the specific embodiments provided in this disclosure are used to capture the movement trajectory of yeast particles under the influence of a 980nm wavelength laser.

[0089] Figure 8 This is a diagram showing the trajectory of yeast particles captured by optical tweezers prepared under a 980nm wavelength laser cut-off, according to a specific embodiment provided in this disclosure.

[0090] Devices that utilize single-mode fiber optical tweezers probes to achieve mass aggregation and capture of yeast particles include single-mode fiber (SMF) mode conversion devices, fiber taper fabrication devices, and yeast particle capture devices.

[0091] The single-mode fiber (SMF) mode conversion device is responsible for twisting and discharging pretreatment of the optical fiber to obtain LP11 mode and OAM mode with corresponding twist angles. The device includes: 1. a common single-mode fiber G.652D, 2. a Z-axis rotary table, and 3. an optical fiber fusion splicer.

[0092] The single-mode optical fiber is G.652D Corning SMF-28e with a cladding diameter of 125 μm and a core diameter of 8.2 μm. One end of the single-mode optical fiber has its thermoplastic polyurethane (TPU) coating stripped, while the other end remains untreated. The stripped TPU-coated single-mode optical fiber is then fixed to the fiber holder on the Z-axis rotary table, twisted 225°, and its relative position along the X-axis is adjusted to ensure the twisted area is between the two electrodes of the fusion splicer. The other end of the fiber is then fixed to the fiber holder of the fusion splicer.

[0093] The fiber fusion splicing system was modulated into discharge mode, with a discharge intensity set to +100 bits and a discharge time of 0.5 seconds, for a total of two discharges. After the first discharge, the diameter of the twisted region became thinner, achieving LP01-LP11 mode conversion. After the second discharge, due to the thermal expansion of the fibers on both sides of the twisted region, a hemispherical shape was achieved, achieving LP11-OAM mode conversion. Finally, a heat-shrink tubing was fitted over the twisted discharge area, and the heating module of the fiber fusion splicing machine was used to fix the heat-shrink tubing to the treated area of ​​the fiber for protection.

[0094] The fiber optic tapering apparatus is responsible for twisting and tapering optical fibers to obtain tapered fiber tweezers probes with black carbon-based TPU polymer tips. The apparatus includes: 1. an electric tapering machine, 2. an alcohol lamp, and 3. a Z-axis rotary table.

[0095] The yeast particle capture device is responsible for capturing a large number of yeast particles in water using a fabricated fiber optic tweezers probe, thereby obtaining LP11 mode and OAM mode with corresponding torsion angles. The device includes: 1. a 980nm laser; 2. a fiber optic fixed three-dimensional stage; 3. a capillary stainless steel tube; 4. a yeast solution fixed three-dimensional stage; 5. a microscope; 6. a CCD; 7. a host computer PC; and 8. the fabricated fiber optic tweezers probe.

[0096] The prepared fiber optic tweezers probe was fixed onto a capillary stainless steel tube on a three-dimensional fiber optic stage. The untapered end was connected to a 980 nm laser, and the laser's input power was adjusted to 10 mW. The tapered tip of the prepared fiber optic probe was inserted into a yeast solution placed on the three-dimensional yeast solution stage. The stage consisted of a coverslip and a slide, spaced 2-3 cm apart to form a chamber. The capture of solution particles by the prepared fiber optic probe was monitored and recorded in real-time on a PC via a microscope connected to a CCD. The observation of a large-scale aggregation and capture of yeast particles in the probe tip region was ultimately obtained.

[0097] The method for capturing large-scale aggregation of yeast particles using a single-mode fiber optic tweezers probe provided in this disclosure can be applied to the multi-dimensional capture technology of fiber optic tweezers. Figure 9 This is a comparative analysis of the results of particle trapping experiments using fiber optic tweezers probes prepared according to specific embodiments of this disclosure and conventional fiber optic tweezers probes. The comparison shows the performance of conventional fiber optic tweezers probes and the fiber optic tweezers probes prepared according to the embodiments of this disclosure in four indicators: local electromagnetic field strength, particle trapping quantity, trapping range, and minimum trapping power. The local electromagnetic field strength of the fiber optic tweezers probe prepared according to the embodiments of this disclosure is 1293.10 V / m, while that of the conventional fiber optic tweezers probe is 1104.48 V / m. The comparative data reflects that the fiber optic tweezers probe prepared according to the embodiments of this disclosure has enhanced trapping efficiency, resulting in stronger optical manipulation and particle interaction. Porous polymers play a crucial role in the redistribution and amplification of the local electromagnetic field. Furthermore, compared to the typical 1-3 particles trapped by conventional probes, the fiber optic tweezers probe prepared according to the embodiments of this disclosure has a significant advantage in particle trapping, capable of simultaneously trapping more than 10 particles, highlighting the advantages of the optical field redistribution characteristics of porous carbon-based polymers, thereby promoting stable multi-particle aggregation. The fiber optic tweezers probe prepared according to embodiments of this disclosure expands the capture range—including the black porous region and the fiber tip. Furthermore, the minimum capture power required by the fiber optic tweezers probe prepared according to embodiments of this disclosure can be reduced to as low as 1 mW, compared to the 10 mW required by conventional probes.

[0098] Figure 10This is a force analysis diagram of the fiber optic tweezers prepared according to specific embodiments of this disclosure when capturing yeast particles under different powers of 980 nm wavelength laser light. Comparison of different input powers shows that the magnitude of the optical force increases with increasing power, while the positions of stable and unstable capture points remain unaffected. Even at the lowest power of 1 mW, the fiber optic tweezers probe prepared according to embodiments of this disclosure successfully captured yeast particles, demonstrating its capture capability at low power levels. However, for biological particles like yeast, excessive input power (e.g., 20 mW) can lead to photothermal effects, potentially damaging cells. Therefore, for biological applications, it is recommended to use lower power levels (e.g., 1 mW or 10 mW) to achieve effective capture while minimizing thermal damage. This result highlights the robustness and versatility of the OFT system, maintaining consistent performance across various input power levels while preserving biocompatibility with sensitive samples.

[0099] In summary, the technical solution of this disclosure can efficiently achieve the large-scale aggregation and capture of yeast particles using a single-mode fiber optic tweezers probe, with simple operation and low cost. Because the fiber optic probe tip has a porous carbon-based polymer that amplifies the local electromagnetic field intensity and provides a more concentrated and stable capture field, the particle capture efficiency is significantly improved. This simple yet effective design paves the way for potential advancements in optical tweezers technology and other particle manipulation applications. Furthermore, the application potential of this optical fiber probe can be extended to biological and medical experiments to improve particle capture efficiency.

[0100] To verify whether the technical solution proposed in this disclosure has an aggregation and trapping effect on particles other than yeast particles, simulation experiments were conducted for different particles. The experimental results are as follows: Figure 11 As shown, the researchers conducted force analysis on yeast with n=1.39, SiO2 with n=1.46, and PS particles with n=1.59 (all with a particle radius of 1.5 μm), and found that a large number of trapping phenomena were obtained in the XY axis direction.

[0101] The embodiments of this disclosure have been described above. These descriptions are exemplary and not exhaustive, and are not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical applications, or technological improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for manufacturing an optical fiber tweezers probe for multi-particle trapping, the optical fiber tweezers probe comprising a single-mode optical fiber, one end of the single-mode optical fiber being a tapered end, and the end surface of the tapered end being coated with a black porous carbon-based thermoplastic polyurethane polymer. The manufacturing method is carried out according to the following path: One end of a single-mode optical fiber is twisted and then subjected to electrode discharge in sequence. The other end of a single-mode optical fiber is twisted, a thermoplastic polyurethane fiber coating is placed in the exposed twisted area of ​​the fiber, and then tapered. After the treatment, the other end of the single-mode optical fiber has a black porous tapered transition area with carbon-based thermoplastic polyurethane polymer. The process involves sequentially twisting and discharging electrodes at one end of a single-mode optical fiber, following the path described below. Applications include a Z-axis rotary table and an optical fiber fusion splicer; Strip the thermoplastic polyurethane coating from one end of a single-mode optical fiber and fix it on the fiber holder of the Z-axis rotary table. Twist the fiber at a preset twist angle and adjust its relative position in the X-axis direction to ensure that the twisted area is between the two electrodes of the fiber fusion machine. Then fix the other end of the single-mode optical fiber on the fiber holder of the fiber fusion machine. The fiber fusion splicer was modulated into a discharge mode and discharged twice: after the first discharge, the diameter of the twisted region became thinner, and the LP01-LP11 mode conversion was obtained; after the second discharge, the optical fibers on both sides of the twisted region were heated and expanded, and their shape changed to a hemispherical shape, and the LP11-OAM mode conversion was obtained. Heat shrink tubing is applied to the area on a single-mode optical fiber that is subjected to torsional discharge, and then fixed using the heating module of the optical fiber fusion splicer. Its features are: The process of twisting the other end of a single-mode optical fiber, applying a thermoplastic polyurethane fiber coating to the exposed twisted area of ​​the bare fiber, and then tapering it is carried out according to the following path. Use an electric taper and an alcohol lamp; The outermost transparent thermoplastic polyurethane coating is stripped from the other end of a single-mode optical fiber, exposing part of the fiber. The middle section of a single-mode optical fiber is fixed on the Z-axis rotary table; One end of the exposed optical fiber is fixed to the optical fiber clamp of the electric tapering machine; Rotate the Z-axis rotary table clockwise by a preset rotation angle to form a fiber twisting region in the exposed part of the optical fiber; The stripped transparent thermoplastic polyurethane coating is placed on the upper surface of the optical fiber twist region; The lower surface of the optical fiber twisted region is heated to the optical fiber melting point from directly below using the outer flame of an alcohol lamp; Set the initial speed V1 of the X-axis motor of the electric taper and start it. After a delay time T, suddenly transition to speed V2. The speed V2 must ensure that the breakage time of the optical fiber torsion region does not exceed 10 seconds. After the optical fiber twisted region breaks, the end of the single-mode optical fiber is tapered and covered with black porous carbon-based thermoplastic polyurethane polymer.

2. The method for manufacturing an optical fiber tweezers probe for multi-particle trapping according to claim 1, characterized in that: The preset torsion angle and rotation angle are both 225°; The fiber optic fusion splicer has a discharge intensity of +100 bits and a discharge time of 0.5 seconds. The length of the thermoplastic polyurethane coating that was peeled off was controlled within 3cm to 4cm. The initial speed V1 was set to 0.03 mm / s, the delay time T was set to 3 seconds, and the speed V2 was set to 0.5 mm / s.

3. An application method for multi-particle trapping using fiber optic tweezers probes, characterized in that: The application method includes using a laser, an optical fiber fixed three-dimensional stage, a solution fixed three-dimensional stage, and an optical fiber tweezers probe; the optical fiber tweezers probe is manufactured by the method for manufacturing optical fiber tweezers probes according to any one of claims 1-2; The fiber optic tweezers probe is fixed on the capillary stainless steel tube of the fiber optic fixed three-dimensional stage; Connect the end of the fiber optic tweezers probe that has not been tapered to the laser. The conical tip of the fiber optic tweezers probe is inserted into the solution of particles to be captured. Activate the laser to achieve multi-particle capture.

4. The application method for multi-particle capture using fiber optic tweezers probe according to claim 3, characterized in that: The particle-to-capture solution is a yeast solution; The laser is a 980nm laser. By adjusting the input power of the laser to 10mW and introducing a 980nm wavelength laser, the aggregation and capture of yeast particles at the tip of the optical fiber can be achieved.

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