CN112068249A - A kind of optical fiber optical tweezers and system based on special optical fiber - Google Patents

Abstract

The invention provides an optical fiber optical tweezers and a system based on special optical fibers. It is characterized in that it is composed of a coaxial double waveguide fiber 1, a large core diameter coaxial double waveguide fiber 2, a truncated cone 3, a Fresnel diffraction lens 4, a coaxial double waveguide fiber connector 5, and a laser (6, 7). . In the system, the lasers (6, 7) are respectively connected to the intermediate core and the annular core of the coaxial dual-waveguide fiber 1 through the coaxial dual-waveguide fiber connector 5 . The other end of the coaxial dual-waveguide fiber 1 is spliced with a large-core-diameter coaxial dual-waveguide fiber 2, and the other end of the large-core-diameter coaxial dual-waveguide fiber 2 is processed into a truncated cone 3. Potential well of particles; Fresnel diffractive lens 4 is processed in the middle core of large core diameter coaxial dual-waveguide fiber 2, and light is converged by Fresnel diffractive lens 4 into another potential well capable of stably capturing particles. The invention can be used for capturing and ejecting particles, and can be widely used in the fields of photodynamic manipulation and the like.

Description

A kind of optical fiber optical tweezers and system based on special optical fiber

(1) Technical field

The invention relates to an optical fiber optical tweezers and a system based on special optical fibers, which can be used for capturing and ejecting cells or particles, and belongs to the technical field of photodynamic manipulation.

(2) Background technology

In 1986, Askin and his colleagues first proposed the concept of "optical tweezers" [Optical Letters, 18(5): 288-290, 1986], opening up a new field of research on light-harvesting particles. At present, optical tweezers technology has become a general scientific research tool for exploring the microscopic world.

Optical tweezers, which use light to grasp objects. But the difference is that optical tweezers make particles bound by light to achieve the effect of "grasping". Optical tweezers can achieve nanometer spatial resolution, pico-new force resolution, and millisecond temporal resolution. This makes it possible to study living organisms from the single-cell level as well as the single-molecule level. Developments over the past few decades have transformed these tools from precision instruments to highly versatile molecular biophysics instruments. At present, optical tweezers have become the most widely used high-precision positioning technology and measurement of pico-new force in biological sciences.

Although conventional optical tweezers have achieved remarkable results, their use remains limited in a considerable number of contexts. For example, it is difficult to focus beams in thick samples or turbid media using conventional optical tweezers systems, which typically have a small working distance. In addition, cost and portability issues are barriers to their widespread use.

In order to solve the above problems, in 2016, Su Chenguang et al. disclosed an automatic capture method of microspheres in an optical tweezers system (application number: 201610832084.4), which can automatically identify and capture 800nm-10μm particles, effectively improving the efficiency of the experiment , reducing the workload of the experimenter and improving the stability of the experimental data. In the same year, Huang Wei et al. disclosed a fiber optical tweezers based on a four-core helical fiber and a manufacturing method thereof (application number: 201610412841.2). After twisting the four-core optical fiber, a helical optical fiber is formed, thereby forming the optical fiber optical tweezers. In 2017, Zhang Yonghui et al. disclosed a step-by-step multimode fiber optical tweezers based on an oblique light ring light field (application number: 201721083580.0). In the multimode fiber core, a ring light field composed entirely of oblique light rays is constructed. After grinding the fiber tip, a gradient field of light intensity is formed, which captures microdroplets of cells or femtoliters.

In addition, in 2010, the applicant disclosed a throughput optical fiber optical tweezers based on a coaxial dual-waveguide structure and a preparation method (application number: 201010215424.1). Using coaxial dual-waveguide fibers to manipulate the particles, and by adjusting and changing the optical power of the light source, the throughput, emission, and even absorption of the captured particles can be stably achieved. At the same time, the capture of particles is more flexible, accurate, and adjustable, which greatly improves the practicability of fiber optic tweezers technology.

Although the above patents can control particles such as capture, throughput, etc., most of them can only control one particle at a time, and the function is relatively simple.

The invention discloses an optical fiber optical tweezers based on special optical fibers. It can be used for capturing and ejecting cells or particles, and can be widely used in cell manipulation and other fields. A small section of coaxial double-waveguide fiber with large core diameter is spliced at one end of the small-core-diameter coaxial double-waveguide fiber. The end of the large core diameter coaxial double waveguide fiber is ground into a cone frustum, so that the annular core can converge to form a three-dimensional stable trapping potential well. The Fresnel lens is engraved on the middle core of the large-core coaxial dual-waveguide fiber by femtosecond laser processing technology, so that the middle core can also form a stable focused light field. Compared with the prior art, the advantages of the present invention are: on the one hand, the annular core forms a focal point through the frustum, and the intermediate core forms a focal point through the diffractive lens, which can capture two particles with a certain distance at the same time; The intermediate core and the annular core are separately light-passed, capturing only one particle at a time. On the other hand, by designing the focal length of the intermediate core binary diffractive lens so that the focal length of the lens is similar to the focal length of the annular core, the annular core can be used to capture particles, and the intermediate core is used to eject the particles; The beam is compressed, resulting in a longer ejection acceleration area compared to a direct exit Gaussian beam.

(3) Contents of the invention

The purpose of the present invention is to provide a multifunctional composite optical fiber optical tweezers and a system with simple structure, capturing single or multiple cells, and ejecting functions at the same time.

The object of the present invention is achieved in this way:

It is composed of coaxial double waveguide fiber 1, large core diameter coaxial double waveguide fiber 2, cone 3, optical fiber end Fresnel diffraction lens 4, coaxial double waveguide fiber connector 5, and lasers (6, 7). The laser 6 is connected to the middle core 101 of the coaxial dual waveguide fiber 1 through the coaxial dual waveguide fiber connector 5 , and the laser 7 is connected to the annular core 102 of the coaxial dual waveguide fiber 1 through the coaxial dual waveguide fiber connector 5 . The other end of the coaxial dual-waveguide fiber 1 is spliced with a section of the large-core-diameter coaxial dual-waveguide fiber 2, and the other end of the large-core-diameter coaxial dual-waveguide fiber 2 is ground into a truncated cone, so that the light transmitted by the annular core 202 is converged to form an energy source. Stabilize the potential well for trapping particles; the middle core of the coaxial dual-waveguide fiber 2 with large core diameter is engraved with a Fresnel diffraction lens 4 on its end face by a femtosecond laser processing system, so that the light transmitted by the middle core 201 passes through the Fresnel diffraction lens 4 Convergence into another potential well that stably traps particles.

The outer diameter of the coaxial dual-waveguide fiber 1 is D ₁ , preferably, D ₁ is 125 μm. It consists of an intermediate waveguide 101 and an annular core waveguide 102. The diameter of the intermediate core waveguide 101 is A ₁ , preferably A ₁ is 10 μm, the inner diameter of the annular core waveguide 102 is B ₁ , and the outer diameter is C ₁ , preferably , B ₁ is 84 μm, and the outer diameter is C ₁ is 94 μm. The intermediate core waveguide 101 and the annular core waveguide 102 are coaxial.

The outer diameter of the coaxial dual-waveguide fiber 2 is D ₂ , preferably, D ₂ is 125 μm. It consists of an intermediate core waveguide 201 and a ring core waveguide 202. The diameter of the intermediate core waveguide 201 is A ₂ , preferably A ₂ is 70 μm, the inner diameter of the annular core waveguide 2 is B ₂ , and the outer diameter is C ₂ , preferably , B2 is 84 μm, and _C2 is ₉₄ μm. The intermediate core waveguide 201 and the annular core waveguide 202 are coaxial. The annular core of the coaxial dual-waveguide fiber 2 has the same size as the annular core of the coaxial dual-waveguide fiber 1 .

The length of the coaxial dual-waveguide fiber 2 is L, preferably, L is 300 μm.

Zhang et al. (Zhang Y, Liu Z, Yang J, et al. An annular core single fiber tweezers[J]. Sensor Letters, 2012, 10(7): 1374-1377.) used the finite element method to analyze the The optical trap force under different grinding angles. Finally, it is concluded that when the angle between the cone-shaped outgoing beams from the ring-core fiber optical tweezers is a right angle, the amplitudes of the axial and lateral optical trapping forces are the largest, that is, when the angle between the ring beams approaches a right angle, the power of the light source is at a right angle. Under the premise of the same refractive index and size of the captured particles, the optical fiber optical tweezers probe has the strongest light capture ability.

The truncated cone 3 is formed by finely grinding the fiber ends of the large-core-diameter coaxial dual-waveguide fiber 2, and its cone angle is β, and the preferred β is 17°.

The diameter of the end face of the large-core-diameter coaxial dual-waveguide optical fiber 2 after grinding is D, preferably, D is 80 μm.

The optical fiber end Fresnel diffractive lens 4 is directly processed on the middle core 201 of the large-core-diameter coaxial dual-waveguide optical fiber 2 by using the femtosecond laser micromachining technology. The band radius R is determined by the Fresnel equation, and the optical path difference between adjacent bands is λ. From the knowledge of geometric optics, the radius of the nth band can be obtained as:

where f ₀ is the prime focal length corresponding to the first diffraction order, and λ ₀ is the design wavelength.

When f ₀ >>λ ₀ , the radius of the nth band is approximately:

The design wavelength λ ₀ used in the system is 980 nm, and the focal length f ₀ is 45 μm.

The radius rn of the Fresnel diffractive lens 4, where _n is 12, the values (unit: μm) of r ₁ to r ₁₂ are: 6.6, 9.4, 11.5, 13.28, 14.85, 16.27, 17.57, 18.78, 19.92, 21 , 22.02, 23.

Fabrication of Fresnel diffractive lens 4: A ring groove with a depth of d is etched with a femtosecond laser micromachining system on the even-numbered half-wave band to produce a phase difference of π with the odd-numbered half-wave band. Preferably, d is 3.66 μm .

Compared with the prior art, the outstanding advantages of the present invention are:

(1) It integrates capture of single particles and multiple particles, and the ejection function is integrated into one optical fiber, with high integration, simple structure, and flexible and convenient operation.

(2) By designing the focal length of the intermediate core binary diffractive lens, the focal length of the lens is similar to the focal length of the annular core, the annular core is used to capture particles, and the intermediate core is used to eject the particles. Compared to Gaussian beams that eject particles, the ejection acceleration area is longer.

(4) Description of drawings

Figure 1 is a system structure diagram of a special optical fiber-based optical fiber optical tweezers and system. It is composed of coaxial dual waveguide fiber 1, large core diameter coaxial dual waveguide fiber 2, cone truncated 3, optical fiber end Fresnel diffraction lens 4, coaxial dual waveguide fiber connector 5, and lasers (6, 7). 101 is the middle core of the coaxial double waveguide fiber 1, 102 is the annular core of the coaxial double waveguide fiber 1; 201 is the middle core of the large core diameter coaxial double waveguide fiber 2, 202 is the large core diameter coaxial double waveguide fiber 2 the annular core. 401 is where the femtosecond laser is processed on the fiber end face.

FIG. 2 is an end view of a coaxial dual-waveguide fiber 1 of a special fiber-based fiber optical tweezers and system.

FIG. 3 is an end view of a coaxial dual-waveguide fiber 2 of a special fiber-based fiber optical tweezers and system.

Fig. 4 is a schematic diagram of a kind of optical fiber optical tweezers and system based on special optical fiber to capture particles in the annular core 202, wherein 5 is the condensing beam of the light field emitted by the annular core, 6 is the captured particle, and 8 is the schematic diagram of the transmission direction of light in the annular core .

FIG. 5 is a graph showing the transverse optical trapping force of a special optical fiber-based optical fiber optical tweezers and the particles captured by the annular core 202 of the system.

FIG. 6 is a graph of the axial optical trapping force suffered by a special optical fiber-based optical fiber optical tweezers and the particles captured by the annular core 202 of the system.

Figure 7 is a schematic diagram of a special optical fiber-based optical fiber tweezers and a system intermediate core 201 that transmits light through the Fresnel diffractive lens 4 to capture particles, where 7 is a converging beam, 6 is a captured particle, and 8 is light transmitted in the intermediate core Orientation diagram.

FIG. 8 is a graph of the transverse optical trapping force received by the optical fiber optical tweezers based on a special optical fiber and the light transmitted by the intermediate core 201 of the system passing through the Fresnel diffraction lens 4 and captured by the particles.

FIG. 9 is a graph of the axial optical trapping force received by the optical fiber optical tweezers based on a special optical fiber and the light transmitted by the intermediate core 201 of the system passing through the Fresnel diffraction lens 4 and captured by the particles.

Fig. 10 A schematic diagram of a special optical fiber-based optical fiber optical tweezers and system for capturing two particles.

Figure 11 is a schematic diagram of a special optical fiber-based optical fiber optical tweezers and a system for realizing the ejection function.

FIG. 12 shows the propagation of the light field after the optical fiber optical tweezers based on the special optical fiber and the light transmitted by the intermediate core 201 of the system are condensed by the Fresnel diffractive lens 4 .

(5) Specific implementation methods

The present invention will be further described below in conjunction with specific embodiments.

Example 1: A preparation process of optical fiber optical tweezers based on special optical fibers.

Step 1: Take each section of coaxial dual-waveguide fiber 1 and large-core-diameter coaxial dual-waveguide fiber 2, remove the coating layer, cut the fiber end face with a cleaver, and wipe it with alcohol.

Step 2: Put the two pieces of optical fiber into the optical fiber fusion splicer and splicing.

Step 3: The large-core-diameter coaxial dual-waveguide optical fiber 2 is cut by a fixed-length cutting system, so that the length of the large-core-diameter coaxial dual-waveguide optical fiber 2 is 300 μm.

Step 4: Wipe the welded optical fiber with alcohol to remove dust, and then put the optical fiber on the stage of the femtosecond micromachining system;

Step 5: Set the frequency to 60kHz, the power to 0.5mW, select the objective lens of 50× and the numerical aperture of 0.42, so that the femtosecond laser can be focused on the surface of the fiber end through the microscope objective lens;

Step 6: Draw graphics on the host computer software written by yourself, generate executable code, and execute the code. After the execution is completed, the fiber end has two parts, one part is the unmodified part, and the other part is the modified part;

Step 7: The sample processed by femtosecond laser scanning is placed in a hydrofluoric acid solution with a concentration of 5%, assisted by an ultrasonic cleaning machine, and corroded for about 25 minutes.

Step 8: Put the optical fiber sample in Step 7 into the optical fiber grinder to grind out the truncated cone 3, and the angle is 17°.

Example 2: Capture of single particles.

FIG. 4 is a schematic diagram of the trapped particles after the light transmitted in the annular core is converged by the frustum. Turn on the laser 7, the light in the laser 7 is coupled to the ring core 102 of the coaxial dual waveguide fiber 1 through the coaxial dual waveguide fiber connector 5, and then transmitted to the ring core 202 of the large core diameter coaxial dual waveguide fiber 2, Finally, after converging through the frustum 3, a good three-dimensional trapping potential well can be formed.

For the structure of the captured particles in Figure 4, the finite element method is used to simulate the force of the sphere, where the background refractive index is 1.33, the sphere refractive index is 1.41, the refractive index of the annular cores 102 and 202 is 1.46, and the frustum angle is 17°. The results are shown in FIGS. 5 and 6 . Figure 5 is a graph of the lateral optical trapping force on the sphere, and it can be seen that its lateral trapping range is -20 μm to 20 μm. Figure 6 is a graph of the axial optical trapping force on the sphere, the lateral trapping range is from 20 μm to 60 μm, and the focus is at 50 μm.

FIG. 7 is a schematic diagram of captured particles after the intermediate core is converged by the Fresnel diffractive lens 4 . Turn on the laser 6, the light in the laser 6 is coupled to the middle core 101 of the coaxial double waveguide fiber 1 through the coaxial double waveguide fiber connector 5, and then transmitted to the middle core 201 of the large core diameter coaxial double waveguide fiber 2, Finally, it converges through the Fresnel diffractive lens 4 to form a focal point that can capture cells.

For the structure of the captured particles in Figure 7, the finite element method is used to simulate the force of the sphere, where the background refractive index is 1.33, the refractive index of the sphere is 1.41, the refractive index of the intermediate core is 1.45, and the focal length of the lens is 20 μm, the results are shown in Figure 8 , as shown in Figure 9. Figure 8 is a graph of the lateral optical trapping force on the sphere, and it can be seen that its lateral trapping range is -30 μm to 30 μm. Figure 9 is a graph of the axial optical trap force on the sphere, and its lateral trapping range is 0 μm to 40 μm.

Example 3: Capture of double particles.

Figure 10 is a schematic diagram of capturing two particles at the same time, and the focal length of the Fresnel diffractive lens 4 is designed to be 20 μm. Turn on laser 6 and laser 7 at the same time. The light in the laser 6 is coupled to the middle core 101 of the coaxial double waveguide fiber 1 through the coaxial double waveguide fiber connector 5; then transmitted to the middle core 201 of the large core diameter coaxial double waveguide fiber 2, and finally passes through Fresnel The diffraction lens 4 converges to form a three-dimensional potential well capable of stably trapping particles. The light in the laser 7 is coupled into the annular core 102 of the coaxial dual waveguide fiber 1 through the coaxial dual waveguide fiber connector 5, and then transmitted to the annular core 202 of the large core diameter coaxial dual waveguide fiber 2, and then passes through the frustum 3 converge to form a three-dimensional potential well that stably traps particles.

Example 4: Particle ejection example.

Figure 11 is a schematic diagram of particle ejection. The focal length of the Fresnel diffractive lens 4 is designed to be 50 μm, which is equal to the potential well distance formed by the converging annular core beam of the truncated cone 3 . Turn on the laser 7, the light in the laser 7 is coupled to the annular core 102 of the coaxial dual waveguide fiber 1 through the coaxial dual waveguide fiber connector 5, and then transmitted to the annular core 202 of the large core diameter coaxial dual waveguide fiber 2, Convergence through the frustum 3 forms a three-dimensional potential well that can stably capture particles. After the particles are stably captured, the laser 6 is turned on, and the light in the laser 6 is coupled to the intermediate core 101 of the coaxial dual-waveguide fiber 1 through the coaxial dual-waveguide fiber connector 5; and then transmitted to the large-core-diameter coaxial dual-waveguide fiber In the middle core 201 of 2, it finally converges through the Fresnel diffractive lens 4 to form a long focus, which acts on the small ball, so that the small ball is accelerated and ejected by force. Figure 12 shows the light field distribution after the Fresnel diffractive lens 4 converges. It can be seen that after passing through the Fresnel diffractive lens 4, an elongated focus will be formed, the length of which is about 10 μm and the width is about 2 μm.

Claims (6)

1. An optical fiber optical tweezers and system based on a special optical fiber, which consists of a coaxial dual-waveguide optical fiber (1), a large-core-diameter coaxial dual-waveguide optical fiber (2), a frustum (3), and an optical fiber end Fresnel lens ( 4), a coaxial dual-waveguide optical fiber connector (5) and a laser (6, 7) are composed, in the system, the laser (6) is connected to the coaxial dual-waveguide optical fiber (1) through the coaxial dual-waveguide optical fiber connector (5) ) is connected to the intermediate core (101) of the laser (7), and the laser (7) is connected to the annular core (102) of the coaxial dual-waveguide fiber (1) through the coaxial dual-waveguide fiber connector (5). The other end of the coaxial dual-waveguide optical fiber (1) is spliced with a section of the large-core-diameter coaxial dual-waveguide optical fiber (2), and the other end of the large-core-diameter coaxial dual-waveguide optical fiber (2) is ground into a truncated cone (3), so that the annular core (202) The transmitted light converges to form a potential well capable of stably trapping particles; the end face of the middle core of the large-core coaxial dual-waveguide fiber (2) is processed with a Fresnel lens (4), so that the middle core (201) transmits The light passing through the Fresnel lens (4) can be converged into another potential well that can stably trap particles. 2. A kind of optical fiber optical tweezers based on special optical fiber and the coaxial dual waveguide fiber (1) in the system according to claim 1, it is characterized in that: its annular core (102) and the large core diameter coaxial dual waveguide fiber (102) 2) The annular cores (202) are of the same size. 3. A kind of optical fiber optical tweezers based on special optical fiber according to claim 1 and the large-core-diameter coaxial dual-waveguide fiber (2) in the system, is characterized in that: the large-core-diameter coaxial dual-waveguide fiber (2) can also be For coreless fiber. 4. A kind of optical fiber optical tweezers based on special optical fiber and the frustum (3) in the system according to claim 1, it is characterized in that: the frustum (3) is directly processed at one end of the coaxial dual-waveguide fiber (2) to form a frustum (3). to make. 5 . The optical fiber optical tweezers based on special optical fibers and the truncated cone ( 3 ) in the system according to claim 1 , wherein the angle range of the cone angle is 0° to 60°. 6 . 6. A special fiber-based optical fiber optical tweezers and a Fresnel diffraction lens (4) at the fiber end in the system according to claim 1. It is characterized in that the etching depth of the even half-wave band for femtosecond laser processing is 3.66 μm.

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