CN112068250A

CN112068250A - Combined optical fiber optical tweezers based on special optical fiber

Info

Publication number: CN112068250A
Application number: CN202010931945.0A
Authority: CN
Inventors: 苑立波; 杜佳豪
Original assignee: Guilin University of Electronic Technology
Current assignee: Guilin University of Electronic Technology
Priority date: 2020-09-06
Filing date: 2020-09-06
Publication date: 2020-12-11
Anticipated expiration: 2040-09-06
Also published as: CN112068250B

Abstract

The invention provides a combined type optical fiber optical tweezers based on a special optical fiber. The method is characterized in that: the optical fiber consists of a coaxial double-waveguide optical fiber 1, an annular core optical fiber 2, a frustum 3 and a Fresnel diffraction lens 4. One end of the coaxial double-waveguide fiber 1 is welded with a section of annular core fiber 2, the frustum 3 is formed by grinding the fiber end of the annular core fiber 2, and the Fresnel diffraction lens 4 is formed by processing the end face of a cladding 201 of the annular core fiber 2 by a femtosecond laser micro-processing system. Light transmitted by the annular fiber core 202 is converged into a potential well capable of stably capturing particles through the frustum 3, and light transmitted by the cladding 201 is converged into another potential well capable of capturing particles through the Fresnel diffraction lens 4. The invention can be used for capturing and ejecting particles and can be widely used in the fields of photodynamic control and the like.

Description

Combined optical fiber optical tweezers based on special optical fiber

(I) technical field

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

(II) background of the invention

In 1986, the concept of "Optical tweezers" was first proposed by Askin and his colleagues [ Optical Letters, 18 (5): 288-. Currently, the optical tweezers technology becomes a general tool for scientific research in the exploration of the micro world.

Optical tweezers, i.e. using light to grab an object. In contrast, optical tweezers are designed to provide a "grab" effect by optically confining particles. The optical tweezers can enable the spatial resolution to reach the nanometer magnitude, enable the force resolution to reach the piconiumber magnitude and enable the time resolution to reach the millisecond magnitude. This allows one to study life forms from single cell levels to single molecule levels. Developments over the past decades have transformed these tools from precision instruments to highly versatile molecular biophysical instruments. Currently, optical tweezers have become the most widely used high-precision positioning technology and technology for measuring the strength of a cow in bioscience.

Although conventional optical tweezers have achieved significant results, their use is still limited in a considerable number of environments. For example, it is difficult to focus a light beam in a thick sample or turbid medium using conventional optical tweezers systems, which typically have a small working distance. In addition, cost and portability issues are obstacles to their widespread use.

In order to solve the above problems, 2016, suchenguang et al disclose an automatic microsphere capturing method (application number: 201610832084.4) in an optical tweezers system, which can automatically identify and capture particles of 800nm to 10um, effectively improve the efficiency of experiments, reduce the workload of experimenters, and improve the stability of experimental data. In the same year, Huangwei et al disclosed a four-core helical fiber-based fiber optical tweezers and a method for making the same (application number: 201610412841.2). In 2017, Zhangyonghui et al disclose a step multimode fiber optical tweezers (application number: 201721083580.0) based on oblique annular light field, wherein in the fiber core of the multimode fiber, an annular light field completely composed of oblique light is constructed, and after the fiber head is ground, a light intensity gradient field is formed, thereby capturing cells or micro-droplets of flying-up level.

In addition, the applicant discloses a throughput type optical fiber optical tweezers based on a coaxial dual-waveguide structure in 2010 and a preparation method (application number: 201010215424.1). The coaxial double-waveguide fiber is utilized to control the particles, the light power of the light source is changed through adjustment, the handling and the emission of the particles can be stably captured, and even the particles are sucked back.

Although the above patents can perform operations such as capturing and handling on particles, most of them can only operate one particle at a time and have a single function.

The invention discloses a special fiber-based combined optical tweezers. Can be used for capturing and ejecting cells or particles, and can be widely used in the fields of cell manipulation and the like. And a small section of annular core optical fiber is welded at one end of the coaxial double-waveguide optical fiber. And grinding the annular core optical fiber end into a frustum, so that the annular cores can converge to form a three-dimensional stable capture potential well. After the light transmitted in the middle fiber core in the coaxial double-waveguide fiber reaches the cladding of the annular core fiber, the light is converged into another focus through the Fresnel lens. Compared with the prior art, the invention has the advantages that: on one hand, the annular core forms a focus through the frustum, and the middle cladding of the annular core fiber forms a focus point through the diffraction lens, so that two particles with a certain distance can be captured simultaneously; the light can also be respectively transmitted to the middle core and the annular core of the coaxial double-waveguide fiber, and only one particle is captured at a time. On the other hand, the focal length of the Fresnel diffraction lens on the end face of the cladding layer is designed to enable the focal length of the Fresnel diffraction lens to be close to that of the annular core, the annular core can be used for capturing particles, the intermediate focus is used for ejecting the particles, the intermediate core is a light beam converged by the diffraction lens, the light beam is compressed, and compared with a Gaussian light beam which is directly emitted, the ejection acceleration area is longer.

Disclosure of the invention

The invention aims to provide multifunctional composite optical fiber tweezers and a system, which have simple structure, capture single or multiple cells and have ejection function.

The purpose of the invention is realized as follows:

the optical fiber consists of a coaxial double-waveguide optical fiber 1, an annular core optical fiber 2, a frustum 3 and a Fresnel diffraction lens 4. One end of the coaxial double-waveguide fiber 1 is welded with a section of annular core fiber 2, namely, an annular fiber core 102 in the coaxial double-waveguide is connected with an annular fiber core 202 in the annular core fiber 2, and a middle fiber core 101 in the coaxial double-waveguide fiber 1 is butted with a cladding 201 in the annular core fiber 2; the frustum 3 is formed by finely grinding the fiber end of the annular core optical fiber 2, and the Fresnel diffraction lens 4 is formed by processing the end face of the cladding 201 of the annular core optical fiber 2 by a femtosecond laser micro-processing system. Light transmitted by the annular fiber core 202 is converged into a potential well capable of stably capturing particles through the frustum 3; after light transmitted in the middle fiber core 101 in the coaxial double-waveguide fiber 1 is transmitted to the cladding 201 of the annular core fiber 2, the light can be converged into another potential well capable of stably capturing particles through the Fresnel diffraction lens 4.

The coaxial double-waveguide fiber 1 has an outer diameter D₁Preferably, D₁And 125 μm. It is composed of an intermediate core waveguide 101 and an annular core waveguide 102, the diameter of the intermediate core waveguide 101 being A₁Preferably A₁10 μm, and an inner diameter B of the annular core waveguide 102₁Outer diameter of C₁Preferably, B₁84 μm, outer diameter C₁And 94 μm. The intermediate core waveguide 101 and the annular core waveguide 102 are coaxial.

The annular core optical fiber 2 has an outer diameter D₂Preferably, D₂And 125 μm. It comprises a ring core waveguide 102, the ring core waveguide 102 having an inner diameter B1 and an outer diameter C1, preferably B1 of 84 μm and an outer diameter C1 of 94 μm. The annular core 102 in the coaxial dual-waveguide fiber 1 and the annular core 202 in the annular-core fiber 2 are equal in size.

The length of the annular core optical fiber 2 is L, preferably, L is 350 μm.

Zhang et al (Zhang Y, Liu Z, Yang J, et al, an annular core single fibers tweezers [ J ]. Sensor Letters,2012,10(7):1374-1377.) analyzed the magnitude of the optical trapping force on the ring core fiber at different polishing angles by using the finite element method. Finally, it is concluded that when the included angle of the conical outgoing light beam from the annular core fiber optical tweezers is a right angle, the amplitudes of the axial and transverse light trapping forces are the largest, that is, when the included angle of the annular light beam approaches the right angle, the optical trapping capability of the fiber optical tweezers probe is the strongest on the premise that the light source power, the refractive index of the trapped particles and the size are the same.

The frustum 3 is formed by finely grinding the optical fiber end of the annular core optical fiber 2, and the cone angle is beta, preferably, the beta is 17 degrees.

The end face diameter of the ring-core optical fiber 2 after polishing is D μm, preferably, D is 80.

The Fresnel diffraction lens 4 is directly processed on the end surface of the cladding 201 of the annular core optical fiber 2 by using a femtosecond laser micromachining technology. The radius R of the wave band is determined by Fresnel equation, the optical path difference of the adjacent wave bands is lambda, and the radius of the nth wave band can be obtained by geometric optics knowledge as follows:

wherein f is₀Is the principal focal length, λ, corresponding to the first diffraction order₀Is the design wavelength.

When f is₀＞＞λ₀Then the radius of the nth band is approximately:

design wavelength lambda used in the system₀980nm, focal length f₀And was 45 μm.

Radius r of the binary Fresnel diffraction lens 4_nWherein n is 12, r₁To r₁₂The values (unit: μm) of (d) are respectively: 6.6, 9.4, 11.5, 13.28, 14.85, 16.27, 17.57, 18.78, 19.92, 21, 22.02, 23.

Manufacturing a binary Fresnel diffraction lens 4: and etching a ring groove with the depth of d mu m on the even half-wave band by using the femtosecond laser micro-processing system to generate pi phase difference with the odd half-wave band, wherein d is preferably 3.86 mu m.

Compared with the prior art, the invention has the outstanding advantages that:

(1) single particles and a plurality of particles are collected and captured, the ejection function is realized on one optical fiber, the integration level is high, the structure is simple, and the operation is flexible and convenient.

(2) The focal length of the Fresnel diffraction lens of the middle core is designed to enable the focal length of the lens to be close to that of the annular core, the annular core is used for capturing particles, light converged by the annular core fiber cladding is used for ejecting the particles, and because the light of the cladding is light beams converged by the diffraction lens, compared with the Gaussian light beam ejection particles which are directly emitted, the ejection acceleration area is longer.

(IV) description of the drawings

Fig. 1 is a system structure diagram of a combined fiber optical tweezers based on special optical fibers. The optical fiber laser comprises a coaxial double-waveguide optical fiber 1, an annular core optical fiber 2, a frustum 3, a Fresnel diffraction lens 4, a coaxial double-wave optical fiber connector 5 and lasers (6 and 7). 101 is the middle core of the coaxial double-

waveguide fiber

1, and 102 is the annular core of the coaxial double-waveguide fiber 1; 201 is a cladding of the ring-core

optical fiber

2, and 202 is a ring-core of the ring-core optical fiber 2. 401 is where the femtosecond laser is processed on the fiber end face.

Fig. 2 is a schematic cross-sectional view of a coaxial dual-waveguide fiber 1 of a combined fiber optical tweezers and system based on a special fiber.

Fig. 3 is a schematic cross-sectional view of a ring-core optical fiber 2 of a combined optical fiber tweezers and system based on a special optical fiber.

Fig. 4 is a schematic diagram of particles captured by the annular fiber core 202 of the combined fiber optical tweezers based on special optical fibers, wherein 5 is a convergent beam of an emergent optical field of the annular core, 6 is the captured particles, and 8 is a schematic diagram of the transmission direction of light in the annular fiber core.

Fig. 5 is a graph of the lateral optical trapping force experienced by particles trapped by the combined fiber optical tweezers and system annular core 202 based on a specialty fiber.

Fig. 6 is a graph showing the axial optical trapping force of particles trapped by the combined optical tweezers and system annular fiber core 202 based on a special optical fiber.

Fig. 7 is a schematic diagram of a special fiber-based combined optical tweezers and system, in which light transmitted through an intermediate fiber core 201 captures particles through a fresnel diffraction lens 4, where 7 is a converging beam, 6 is the captured particles, and 8 is a schematic diagram of the direction of light transmission in the intermediate core.

Fig. 8 is a graph of the lateral light trapping force of the particles captured by the fresnel diffraction lens 4, which is applied to the light transmitted by the special fiber-based combined fiber optical tweezers and the system intermediate cladding 201.

Fig. 9 is a graph showing an axial light trapping force applied to particles captured by the fresnel diffraction lens 4 by light transmitted through the special fiber-based combined fiber optical tweezers and the system intermediate cladding 201.

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

Fig. 11 is a schematic diagram of a combined fiber optical tweezers based on a special fiber and a system for realizing an ejection function.

Fig. 12 shows the propagation condition of the light field after the light transmitted by the special fiber-based combined fiber optical tweezers and the system cladding 201 is converged by the fresnel diffraction lens 4.

(V) detailed description of the preferred embodiments

The invention is further illustrated below with reference to specific examples.

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

Step 1: taking a section of the coaxial double-waveguide fiber 1 and a section of the annular core fiber 2 respectively, removing the coating layer, cutting the end face of the fiber by a cutter, and wiping the fiber by alcohol.

Step 2: and putting the two sections of optical fibers into an optical fiber fusion splicer for fusion splicing.

And step 3: the ring-core optical fiber 2 was cut with a fixed-length cutting system so that the length of the ring-core optical fiber 2 was 350 μm.

And 4, step 4: wiping the welded optical fiber with alcohol to remove dust, and then placing the optical fiber on a displacement table of a femtosecond micro-processing system;

and 5: setting the frequency to be 60kHz, setting the power to be 0.5mW, selecting an objective lens with the numerical aperture of 0.42 multiplied by 50, and focusing the femtosecond laser to the end surface of the optical fiber through a microscope objective lens;

step 6: drawing a graph on the upper computer software written by the user, generating an executable code, and executing the code. After the execution is finished, the optical fiber end has two parts, one part is an unmodified part, and the other part is a modified part;

and 7: and (3) placing the sample processed by the femtosecond laser scanning into a hydrofluoric acid solution with the concentration of 5%, and carrying out auxiliary corrosion on the sample for about 25min by using an ultrasonic cleaning machine.

And 8: and (4) cleaning the optical fiber obtained in the step (7) by using deionized water, putting the optical fiber into an optical fiber end grinding system, and grinding the optical fiber end into a frustum with an angle of 17 degrees.

Example 2: and (4) capturing single particles.

Fig. 4 is a schematic diagram of a particle captured after light transmitted in the toroidal core is converged by a frustum. And (3) turning on the laser 7, coupling the light in the laser 7 into the annular core 102 of the coaxial double-waveguide fiber 1 through the coaxial double-wave optical fiber connector 5, transmitting the light into the annular fiber core 202 of the annular core fiber 2, and finally converging the light through the frustum 3 to form a good three-dimensional capture potential well.

For the structure of the trapped particle of fig. 4, the pellet was force simulated using the finite element method, where the background index is 1.33, the pellet index is 1.41, the

annular cores

102, 202 have indices of 1.46, and the frustum angle is 17 °. The results are shown in fig. 5 and 6. FIG. 5 is a graph of the lateral optical trapping force experienced by the pellet, which can be seen to range from-20 μm to 20 μm lateral trapping. FIG. 6 is a graph of axial optical trapping force experienced by a pellet with a lateral trapping range of 20 μm to 60 μm and a focal point at 50 μm.

Fig. 7 is a schematic diagram of the trapped particles after the intermediate core has been converged by the fresnel diffractive lens 4. And (3) turning on the laser 6, coupling the light in the laser 6 into the middle core 101 of the coaxial double-waveguide fiber 1 through the coaxial double-wave optical fiber connector 5, transmitting the light into the cladding 201 of the annular core fiber 2, and finally converging the light through the Fresnel diffraction lens 4 to form a focus capable of capturing cells.

For the structure of the trapped particle of fig. 7, the force simulation was performed using a finite element method pellet, in which the background refractive index was 1.33, the pellet refractive index was 1.41, the intermediate core refractive index was 1.45, and the focal length of the lens was 20 μm, and the results are shown in fig. 8 and 9. FIG. 8 is a graph of the lateral optical trapping force experienced by a pellet, which can be seen to range from-30 μm to 30 μm lateral trapping. FIG. 9 is a graph of the axial optical trapping force experienced by a pellet with a lateral trapping range of 0 μm to 40 μm.

Example 3: and (4) capturing double particles.

Fig. 10 is a schematic diagram of two particles captured simultaneously, and the focal length of the fresnel diffraction lens 4 is designed to be 20 μm. The laser 6 and the laser 7 are switched on simultaneously. The light in the laser 6 is coupled into the middle core 101 of the coaxial double waveguide fiber 1 through the coaxial double-wave optical fiber connector 5; and then transmitted into a cladding 201 of the annular core fiber 2, and finally converged by a Fresnel diffraction lens 4 to form a three-dimensional potential well capable of stably capturing particles. The light in the laser 7 is coupled into the annular core 102 of the coaxial double waveguide fiber 1 through the coaxial double-wave optical fiber connector 5, then is transmitted into the annular core 202 of the annular core fiber 2, and then is converged through the frustum 3 to form a three-dimensional potential well capable of stably capturing particles. That is, two particles can be captured simultaneously.

Example 4: particles eject embodiments.

Fig. 11 is a schematic view of particle ejection. The focal length of the Fresnel diffraction lens 4 is designed to be 50 μm, so that the distance between the Fresnel diffraction lens and a potential well formed by the annular core light beam converged by the frustum 3 is equal. And (3) turning on the laser 7, coupling the light in the laser 7 into the annular core 102 of the coaxial double-waveguide fiber 1 through the coaxial double-wave optical fiber connector 5, transmitting the light into the annular core 202 of the annular core fiber 2, and converging the light through the frustum 3 to form a three-dimensional potential well capable of stably capturing particles. After the particles are stably captured, the laser 6 is turned on, and the light in the laser 6 is coupled into the middle core 101 of the coaxial double-waveguide fiber 1 through the coaxial double-wave optical fiber connector 5; and then the light is transmitted into a cladding 201 of the annular core optical fiber 2, finally the light is converged by a Fresnel diffraction lens 4 to form a long focus, and the long focus is acted on a small ball, so that the small ball is accelerated to be ejected out under stress. Fig. 12 shows the distribution of the light field after being converged by the fresnel diffraction lens 4, and it can be seen that after passing through the fresnel diffraction lens 4, an elongated focal point is formed, which has a length of about 10 μm and a width of about 2 μm.

Claims

1. A combined optical fiber optical tweezers based on special optical fibers is composed of a coaxial double-waveguide optical fiber (1), an annular core optical fiber (2), a frustum (3) and a Fresnel diffraction lens (4), wherein one end of the coaxial double-waveguide optical fiber (1) is welded with a section of the annular core optical fiber (2), and light transmitted by the annular core (202) is converged into a potential well capable of stably capturing particles through the frustum (3); after light transmitted in a middle fiber core (101) in the coaxial double-waveguide fiber (1) is transmitted to a cladding (201) of the annular core fiber (2), the light can be converged into another particle-capturing potential well through a Fresnel diffraction lens (4).

2. The combined optical fiber tweezers based on the special optical fiber and comprising the coaxial double waveguide fiber (1) and the ring core fiber (2) according to claim 1, wherein the ring core (102) of the coaxial double waveguide fiber (1) and the ring core (202) of the ring core fiber (2) are equal in size.

3. The annular core optical fiber (2) in the combined optical fiber tweezers based on special optical fibers as claimed in claim 1, wherein: the annular core optical fiber (2) can also be a coreless optical fiber.

4. A combined fiber optical tweezers frustum (3) based on a special optical fiber as claimed in claim 1, wherein: directly processed at the fiber end of the ring-shaped core optical fiber (2).

5. A combined fiber optical tweezers frustum (3) based on a special optical fiber as claimed in claim 1, wherein: the angle interval of the cone angle is 0 DEG to 60 deg.

6. A special fiber based combined fiber optical tweezers Fresnel diffraction lens (4) according to claim 1. The method is characterized in that: the etching depth of the even half-wave band processed by the femtosecond laser is 3.86 mu m.