Micro-droplet long-distance optical force traction system based on nanometer optical fiber

Abstract

The invention discloses a micro-droplet long-distance optical force traction system based on a nanometer optical fiber. The system comprises an optical fiber laser, a nano optical fiber, micro-droplets, an imaging optical element and an imaging camera, the nanometer optical fiber comprises a first optical fiber non-tapering area, a second optical fiber non-tapering area, a first optical fiber taper area, a second optical fiber taper area and a uniform waist area located in the middle. And the micro-droplets coat the uniform waist region of the nano optical fiber. The transmission loss of the nanometer optical fiber is low, the total length can reach the meter level, a transmission light field in the uniform waist area of the nanometer optical fiber interacts with the micro-droplets, forward scattering is enhanced through momentum exchange, and therefore long-range optical traction force is applied to the micro-droplets. According to the invention, the problem of short luminous traction action distance (millimeter level) based on a single light beam in the prior art is solved, and the device has the advantages of long-distance control (centimeter to meter level), high precision, high flexibility, good stability and good biocompatibility, and can be applied to the biochemical fields of cell control and sorting, biological detection, micro-droplet reaction and the like.

Description

Technical Field

[0001] This invention relates to a microdroplet photomechanical manipulation system, and more particularly to a microdroplet long-range photomechanical traction system based on nanofibers, belonging to the field of optical manipulation technology. Background Technology

[0002] Optical manipulation is an important research tool in fields such as nanotechnology, atomic physics, quantum science, and biochemistry. As a novel method of optical manipulation, optical traction can pull transparent objects toward a light source, providing a new degree of freedom for particle manipulation. The most common method to achieve optical traction is to enhance the forward momentum of photons when light is scattered by an object. Although research on optical traction has made a series of advances over the past two decades, limitations such as optical diffraction, long-distance structure fabrication, and insufficient flexibility in optical field manipulation have restricted the current range of single-beam optical traction to the millimeter scale, hindering the further development of optical manipulation technology and applications.

[0003] Nanofibers, fabricated by high-temperature stretching of standard glass fibers, are typical micro / nano optical waveguide structures with structural characteristics such as subwavelength diameter, atomic-level surface smoothness, and good flexibility. Due to the large refractive index difference between the core and cladding, most of the energy of light propagating along its interior exists in the form of an evanescent field, meaning that light can be confined to the vicinity of its surface for low-loss propagation, and can be considered as a long-range, diffraction-free Bessel beam. Microdroplets, liquids with diameters ranging from micrometers to millimeters, can coat the surface of nanofibers through surface tension, forming a non-uniform dielectric background structure, providing the possibility for controlling photon momentum transfer and generating long-range optical traction forces. Therefore, this invention constructs a long-range optical traction system for microdroplets based on nanofibers, extending the effective range of optical traction forces to the centimeter or even meter level, providing platform support for research on high-throughput cell sorting, single-cell biosensing and detection, and microdroplet biochemical reactions. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a long-range optical traction system for microdroplets based on nanofibers, which overcomes the short working distance of existing microparticle optical traction technology and realizes long-distance optical traction of microdroplets.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is: a long-range optical force traction system for microdroplets based on nanofibers. The system includes a fiber laser, a nanofiber, and a microdroplet. The nanofiber includes a first untapered region, a first taper region, a uniform waist region, a second taper region, and a second untapered region connected in sequence. The first untapered region is connected to the output end of the fiber laser. The microdroplet covers the uniform waist region of the nanofiber. After the light field transmitted inside the uniform waist region interacts with the microdroplet, an optical traction force is generated along the axial direction of the nanofiber, thereby performing long-range optical force traction on the microdroplet.

[0006] Furthermore, the system also includes an imaging optical element and an imaging camera, the imaging camera performing real-time observation and imaging of microdroplets through the imaging optical element.

[0007] Furthermore, the system also includes an optical fiber support, with the first untapered region and the second untapered region of the nanofiber fixed on both sides of the optical fiber support, and the first taper region, the uniform waist region and the second taper region of the nanofiber suspended in the air.

[0008] Furthermore, the microdroplets are suspended on the uniform waist region of the nanofiber. Based on the surface tension of the liquid, the microdroplets exhibit a spherical shape with a diameter of 5μm to 100μm.

[0009] Furthermore, the output light of the fiber laser passes sequentially through the first untapered region and the first taper region of the nanofiber to reach the uniform waist region, where it interacts with the microdroplet. The output light from the uniform waist region passes through the second taper region and reaches the second untapered region. The end of the second untapered region is provided with an optical signal output port.

[0010] Furthermore, most of the energy of the transmitted light field in the uniform waist region exists in the form of an evanescent field. After the transmitted light field passes through the microdroplet and exits, it is focused in the uniform waist region. The forward scattering is enhanced through momentum exchange, which applies an optical traction force to the microdroplet and pulls it toward the light source.

[0011] Furthermore, the nanofiber is prepared by a high-temperature stretching and melting method for standard glass fibers and a flame brush scanning technique, and the morphology of the first and second fiber cone regions both meet the thermal insulation requirements.

[0012] Furthermore, the nanofiber is a silicon oxide nanofiber, the diameter of its uniform waist region is less than 1 / 3 of the output wavelength of the fiber laser, and the total transmission loss of the nanofiber at the output wavelength of the fiber laser is less than 0.1 dB / cm.

[0013] Furthermore, the connection between one end of the first fiber of the nanofiber (without tapering) and the output end of the fiber laser is a fiber fusion splice, and the splice loss at the output wavelength of the fiber laser is less than 0.1 dB.

[0014] Furthermore, by adjusting the output wavelength of the fiber laser, the flexible switching between optical propulsion and optical traction of the microdroplets can be achieved.

[0015] Furthermore, by changing the output optical power of the fiber laser, the magnitude of the axial optical force acting on the microdroplet is adjusted, thereby controlling the movement speed of the microdroplet; under the action of the axial optical force, the microdroplet gradually accelerates until the viscous resistance between it and the uniform waist region and the axial optical force are balanced, and the microdroplet enters a state of uniform motion.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] (1) Existing optical traction technologies rely on special structural light sources or complex micro / nano photonic structures, which are difficult to fabricate and expensive. The microdroplet long-range optical traction system of this invention adopts an all-fiber integrated structure, which is easy to fabricate and inexpensive. By controlling the transmission light field in the uniform waist region and the photon momentum transfer between the microdroplet, forward optical scattering can be enhanced, and stable and efficient optical traction of the microdroplet can be achieved.

[0018] (2) Existing optical traction technologies are limited by the optical diffraction limit, scattering loss, and insufficient flexibility in optical field manipulation, making it difficult to achieve long-range optical traction of microparticles at the macroscopic scale. The microdroplet long-range optical traction system of this invention uses low-loss nanofibers as optical waveguide structures. Its waist diameter is uniform, and its usable length is large, enabling stable photon momentum transfer over long distances. By adjusting the waist diameter, input light wavelength, and other methods, the evanescent field of its internal conduction mode and the photon momentum distribution can be flexibly controlled, making it easy to achieve long-range optical traction of microdroplets at the centimeter scale.

[0019] (3) This invention utilizes the optical scattering force generated by photon momentum transfer to perform photodynamic traction on microdroplets, which differs from particle manipulation systems that rely on photothermal effects. This invention is suitable for manipulating transparent microdroplets, and its mechanism is that light energy is directly converted into mechanical energy without the need for photothermal effects, thus resulting in a faster response.

[0020] (4) The microdroplet long-range optical traction system of the present invention is not limited to manipulating microdroplets, but can also be used to optically transport microparticles such as biological cells and solid particles embedded within them. At the same time, microdroplets have good biocompatibility, are suitable for simulating cellular environments, and help develop high-throughput cell sorting, single-cell biosensing and detection technologies. Attached Figure Description

[0021] Figure 1This is a schematic diagram of the structure of the microdroplet long-range optical force traction system based on nanofibers of the present invention;

[0022] In the figure: 1-fiber laser, 2-1-first fiber untapered region, 2-2-second fiber untapered region, 3-1-first fiber taper region, 3-2-second fiber taper region, 4-uniform waist region, 5-microdroplet, 6-imaging optical element, 7-imaging camera, 8-fiber support;

[0023] Figure 2 This is a normalized transmittance curve of continuous light at a wavelength of 1552 nm during the fabrication process of silicon oxide nanofibers provided in this embodiment of the invention.

[0024] Figure 3 This is a longitudinal light intensity distribution diagram of the fundamental mode conducted by the nanofiber provided in the embodiment of the present invention after being scattered by microdroplets. The white dashed line represents the outline of the microdroplets.

[0025] Figure 4 This is a graph showing the variation of axial optical force acting on microdroplets as a function of input light wavelength, provided by an embodiment of the present invention.

[0026] Figure 5 This is an optical microscope time series diagram of the movement of microdroplets along nanofibers under different wavelength input light driving provided by the embodiments of the present invention, wherein the diameter of the microdroplets is 20 μm and the diameter of the uniform waist region of the nanofiber is 370 nm.

[0027] Figure 6 This is a graph showing the change in microdroplet velocity with input light power under 1552nm wavelength input light drive provided by an embodiment of the present invention.

[0028] Figure 7 This is a diameter distribution diagram of the ultra-long waist region of the optical fiber provided in an embodiment of the present invention;

[0029] Figure 8 This is a time trajectory diagram of the microdroplet long-range photodynamic traction system provided in this embodiment of the invention, which controls the movement of microdroplets up to 40cm. Detailed Implementation

[0030] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described examples are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] See Figure 1As a first embodiment of the present invention, the microdroplet long-range optical force traction system based on nanofiber includes a fiber laser 1, a nanofiber, a microdroplet 5, an imaging optical element 6, and an imaging camera 7; the nanofiber includes a first untapered region 2-1, a second untapered region 2-2, a first taper region 3-1, a second taper region 3-2, and a uniform waist region 4; the microdroplet 5 is coated with the uniform waist region 4 of the nanofiber; the imaging camera 7 performs real-time observation and imaging of the microdroplet 5 through the imaging optical element 6;

[0032] The output end of the fiber laser 1 is connected to one end of the first untapered region 2-1 of the nanofiber, the other end of the first untapered region 2-1 is connected to one end of the first taper region 3-1, the other end of the first taper region 3-1 is connected to one end of the uniform waist region 4, the other end of the uniform waist region 4 is connected to one end of the second taper region 3-2, and the other end of the second taper region 3-2 is connected to one end of the second untapered region 2-2. After the light field transmitted inside the uniform waist region 4 of the nanofiber interacts with the microdroplet 5, an optical traction force is generated along the axial direction of the nanofiber, which performs long-range optical force traction on the microdroplet 5.

[0033] See Figure 1 As a preferred embodiment of the present invention, in order to improve the stability of the long-range optical traction system of microdroplets, the long-range optical traction system of microdroplets based on nanofibers further includes an optical fiber support 8. The first untapered region 2-1 and the second untapered region 2-2 of the nanofiber are respectively fixed on both sides of the optical fiber support 8, and the first taper region 3-1, the uniform waist region 4 and the second taper region 3-2 of the nanofiber are suspended.

[0034] See Figure 1 The microdroplet 5 is suspended on the uniform waist region 4 of the nanofiber. Based on the surface tension of the liquid, the microdroplet 5 exhibits a spherical shape with a diameter of 5μm to 100μm.

[0035] The following describes the transmission path of light in the microdroplet long-range optical force traction system based on nanofibers of the present invention. The output light of the fiber laser 1 passes sequentially through the first untapered region 2-1 and the first taper region 3-1 of the nanofiber to reach the uniform waist region 4, where it interacts with the microdroplet 5. The output light from the uniform waist region 4 passes through the second taper region 3-2 and then reaches the second untapered region 2-2. The end of the second untapered region 2-2 is provided with an optical signal output port.

[0036] Furthermore, most of the energy of the transmitted light field in the uniform waist region 4 of the nanofiber exists in the form of an evanescent field. After the transmitted light field passes through the microdroplet 5 and exits, it is focused in the uniform waist region 4. The forward scattering is enhanced through momentum exchange, which applies an optical traction force to the microdroplet 5 and pulls it toward the light source.

[0037] Furthermore, the nanofibers were prepared by high-temperature stretching and melting of standard glass fibers and flame brush scanning technology, and the morphologies of the first fiber taper region 3-1 and the second fiber taper region 3-2 both met the thermal insulation requirements.

[0038] Furthermore, for silica nanofibers, the diameter of the uniform waist region 4 is less than 1 / 3 of the output wavelength of the fiber laser 1, and the length can reach the centimeter level. The total transmission loss of the nanofiber at the output wavelength of the fiber laser 1 is less than 0.1 dB / cm, which can maintain long-distance optical momentum exchange and forward scattering amplification, thereby realizing stable long-distance optical force traction of microdroplets.

[0039] Furthermore, the connection between one end of the untapered region 2-1 of the first fiber of the nanofiber and the output end of the fiber laser 1 is fiber fusion splicing, and the fusion loss at the output wavelength of the fiber laser 1 is less than 0.1dB.

[0040] The following example illustrates this. In this example, a 1552nm wavelength continuous-wave single-mode fiber laser 1 is selected, with an output fiber type of SMF-28e+. See [link / reference] Figure 2 The nanofiber is prepared by stretching fused silica fiber at high temperature and combining it with flame brush scanning technology. The prepared nanofiber has a uniform waist diameter of 370nm, a waist length of 2cm, a total length of 5cm, an optical transmittance of over 95%, and a single-mode transmission loss of less than 0.045dB / cm.

[0041] After preparation, the nanofibers are fixed, encapsulated, and transferred using a U-shaped aluminum alloy fiber optic bracket 8. The first untapered region 2-1 and the second untapered region 2-2 of the nanofibers are fixed to both sides of the fiber optic bracket 8 using UV-curable adhesive. The first taper region 3-1, the uniform waist region 4, and the second taper region 3-2 of the nanofibers are suspended and kept taut. One end of the first untapered region 2-1 of the nanofibers is connected to the output end of the fiber laser 1 by fiber fusion splicing, with a splicing loss of less than 0.1 dB. The end of the second untapered region 2-2 of the nanofibers is connected to a photodetector to collect and measure the output optical signal.

[0042] In this example, the material for microdroplet 5 is dimethyl silicone oil, model number Xiameter. TM PMX-200, with a viscosity of 1000 cst. Microdroplets 5 were sampled using an optical fiber probe and transferred to the uniform waist region 4 of the nanofiber using a three-dimensional precision displacement stage. Based on the surface tension of the liquid, the microdroplets 5 exhibited a quasi-spherical shape with a diameter of 5 μm to 100 μm and a cross-sectional eccentricity of less than 0.6.

[0043] In this example, most of the energy of the transmitted optical field in the nanofiber exists in the form of an evanescent field. After passing through the microdroplet 5, the axial optical force acting on the microdroplet 5 is determined by the photon momentum exchanged between the photons distributed in the air and silica media and the microdroplet 5. Since this involves photon momentum transfer between multiple background media, the photon momentum exhibits the form of Minkowski momentum, meaning the magnitude of the photon momentum is proportional to the refractive index of the background media. See also... Figure 3 The longitudinal light intensity distribution of the fundamental mode propagated in the uniform waist region 4 of the nanofiber, scattered by the microdroplet 5, was calculated using the three-dimensional finite-difference time-domain method. The diameter of the uniform waist region of the nanofiber is 370 nm, and the input light wavelength is 1552 nm. The fundamental mode propagated inside the uniform waist region 4 (i.e., HE) 11 99.8% of the energy in the model is distributed in the external air environment (refractive index n = 1.0003). After it passes through the microdroplet 5 with a diameter of 20 μm, based on the refraction and reflection of light, most of the energy is focused in the uniform waist region 4 (refractive index n = 1.44), which enhances the forward momentum of photons and optical scattering. This can apply an axial optical traction force to the microdroplet 5, pulling it towards the light source.

[0044] By performing the Minkowski tensor integral on the outer envelope surface S of microdroplet 5, the axial optical force F acting on microdroplet 5 can be calculated. The specific formula is as follows:

[0045] F=∫ S <T M >·n S dS (1)

[0046] In formula (1), <T M > is the time-averaged Minkowski tensor, T M =DE + BH - (B·H + D·E)I / 2, where D and E are the electric displacement vector and electric field intensity vector, respectively; B and H are the magnetic induction vector and magnetic field intensity vector, respectively; I is the unit vector; n S It is the unit vector in the direction of the normal to the outer envelope surface.

[0047] See Figure 4According to formula (1), the axial optical force acting on the microdroplet 5 with input light of different wavelengths was calculated. When the input light wavelength is less than 1150 nm, the axial optical force acting on the microdroplet 5 is optical thrust (F>0); when the input light wavelength is greater than 1150 nm, the axial optical force acting on the microdroplet 5 is optical traction (F<0). Therefore, by adjusting the output light wavelength of the fiber laser 1, the flexible switching between optical propulsion and optical traction of the microdroplet 5 can be achieved, greatly improving the freedom and flexibility of single-beam manipulation of the microdroplet 5. Taking the typical output light of the fiber laser 1 as an example, when the wavelength is set to 980 nm, the normalized axial optical force acting on the microdroplet 5 is 0.64 nN / W, which is optical thrust; when the wavelength is set to 1552 nm, the normalized axial optical force acting on the microdroplet 5 is -1.86 nN / W, which is optical traction.

[0048] See Figure 5 Under continuous light drive at a wavelength of 980 nm, when the input optical power is 0.1 W, the microdroplet 5 moves at a constant speed (exhibiting optical propulsion) away from the light source along the uniform waist region 4 of the nanofiber, with a speed of 6.0 μm / s. After the input light wavelength is switched to 1552 nm, when the input optical power is 0.05 W, the microdroplet 5 moves at a constant speed (exhibiting optical traction) towards the light source along the uniform waist region 4 of the nanofiber, with a speed of -4.3 μm / s.

[0049] By changing the output optical power of the fiber laser 1, the magnitude of the axial optical force acting on the microdroplet 5 can be adjusted, thereby controlling the velocity of the microdroplet 5. Under the action of the axial optical force, the microdroplet 5 gradually accelerates until the viscous resistance between it and the uniform waist region 4 and the axial optical force are balanced, at which point the microdroplet 5 enters a state of uniform motion. According to the theory of viscous dissipation, its velocity is expressed as:

[0050]

[0051] In formula (2), v is the velocity of the microdroplet 5, F is the axial optical force, μ is the dynamic viscosity of the microdroplet 5, and D is the diameter of the uniform waist region 4 of the nanofiber. Indicates the integration along the radial direction of microdroplet 5, d s Let be the diameter of the microdroplet 5, and b ≈ 0.1 nm be the thickness of the monomolecular film. According to formula (2), for a dimethyl silicone oil microdroplet 5 with a diameter of 20 μm, its dynamic viscosity at room temperature is μ = 0.96 Pa·s, l = 12.2, and the velocity along the uniform waist region 4 of the nanofiber is proportional to the magnitude of the axial optical force. See [reference needed] Figure 6As the input optical power at a wavelength of 1552nm increases, the movement speed of microdroplet 5 increases significantly. When the input optical power is 0.5W, the measured movement speed of microdroplet 5 can reach -78μm / s. The actual measured value is in good agreement with the theoretical calculation value.

[0052] The following describes the long-range optical-mechanical traction of microdroplet 5 using a light field stably propagating in the waist region of an ultralong uniform nanofiber. (See also...) Figure 7 A nanofiber with a waist length of 40 cm and a waist diameter of 325 ± 15 nm was fabricated using flame brush scanning technology. It exhibits extremely high uniformity, low optical transmission loss, and can maintain stable photon momentum transfer over long distances, making it suitable for constructing long-range photodynamic traction systems for microdroplets. In this example, the imaging optics 6 and imaging camera 7 are mounted on a long-stroke optical guide rail to track and record the motion trajectory of the microdroplet 5 in real time. See also... Figure 8 Driven by 1W of continuous light at a wavelength of 1552nm, a 45μm diameter microdroplet 5 moved along the uniform waist region 4 of a nanofiber towards the light source for 1.5 hours, with a total displacement of -40cm. In this example, the long-range optical traction system for microdroplets based on nanofibers can achieve stable optical traction of microdroplets with a length of centimeters, exceeding the millimeter-level effective distance of previously reported single-beam microparticle optical traction.

[0053] The above description is merely a preferred embodiment of the present invention. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the scope of the technical solutions of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A long-range optical-mechanical traction system for microdroplets based on nanofibers, characterized in that, The system includes a fiber laser, a nanofiber, and a microdroplet. The nanofiber comprises a first untapered region, a first taper region, a uniform waist region, a second taper region, and a second untapered region connected in sequence. The first untapered region is connected to the output end of the fiber laser. The microdroplet covers the uniform waist region of the nanofiber. After the light field transmitted inside the uniform waist region interacts with the microdroplet, it generates an optical traction force along the axial direction of the nanofiber, thereby exerting long-range optical force traction on the microdroplet.

2. The microdroplet long-range optical-mechanical traction system based on nanofibers according to claim 1, characterized in that, The system also includes imaging optics and an imaging camera, which uses the imaging optics to observe and image microdroplets in real time.

3. The microdroplet long-range optical-mechanical traction system based on nanofibers according to claim 1, characterized in that, The system also includes an optical fiber support, with the first untapered region and the second untapered region of the nanofiber fixed on both sides of the optical fiber support, and the first taper region, the uniform waist region and the second taper region of the nanofiber suspended in the air.

4. The microdroplet long-range optical-mechanical traction system based on nanofibers according to claim 1, characterized in that, The microdroplets are suspended on the uniform waist region of the nanofiber. Based on the surface tension of the liquid, the microdroplets exhibit a spherical shape with a diameter of 5μm to 100μm.

5. The microdroplet long-range optical-mechanical traction system based on nanofibers according to claim 1, characterized in that, Most of the energy of the transmitted light field in the uniform waist region exists in the form of an evanescent field. After the transmitted light field passes through the microdroplet and exits, it is focused in the uniform waist region. The forward scattering is enhanced through momentum exchange, which applies an optical traction force to the microdroplet and pulls it toward the light source.

6. The microdroplet long-range optical-mechanical traction system based on nanofibers according to claim 1, characterized in that, The nanofibers are prepared by high-temperature stretching and melting of standard glass fibers and flame brush scanning technology. The morphologies of the first and second fiber cone regions both meet the thermal insulation requirements.

7. The microdroplet long-range optical-mechanical traction system based on nanofibers according to claim 1, characterized in that, The nanofiber is a silica nanofiber, and the diameter of its uniform waist region is less than 1 / 3 of the output wavelength of the fiber laser. The total transmission loss of the nanofiber at the output wavelength of the fiber laser is less than 0.1 dB / cm.

8. The microdroplet long-range optical-mechanical traction system based on nanofibers according to claim 1, characterized in that, The connection between one end of the untapered region of the first fiber of the nanofiber and the output end of the fiber laser is fiber fusion splicing, and the splicing loss at the output wavelength of the fiber laser is less than 0.1dB.

9. The microdroplet long-range optical-mechanical traction system based on nanofibers according to claim 1, characterized in that, By adjusting the output wavelength of the fiber laser, the flexible switching between optical propulsion and optical traction of microdroplets can be achieved.

10. The microdroplet long-range optical-mechanical traction system based on nanofibers according to claim 1, characterized in that, By changing the output optical power of the fiber laser, the magnitude of the axial optical force acting on the microdroplet is adjusted, thereby controlling the movement speed of the microdroplet. Under the action of the axial optical force, the microdroplet gradually accelerates until the viscous resistance between it and the uniform waist region and the axial optical force are balanced, and the microdroplet enters a state of uniform motion.

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