CN111025466A

CN111025466A - Multi-focus diffraction lens based on optical fiber

Info

Publication number: CN111025466A
Application number: CN201911377605.1A
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: 2019-12-27
Filing date: 2019-12-27
Publication date: 2020-04-17

Abstract

The invention provides a multifocal diffractive lens based on an optical fiber. The method is characterized in that: the coaxial dual-waveguide fiber coaxial optical fiber consists of a single-mode fiber 1, a coaxial dual-waveguide fiber 2, a coreless fiber 3 and a binary diffraction lens 4. In the composition, the binary diffraction lens 4 is directly processed at the fiber end of the coreless optical fiber 3 by a femtosecond processing system. The invention can be used for preparing the multifocal diffraction lens based on the optical fiber, and can be widely used in the fields of single cell manipulation and analysis, micro-electro-mechanical system real-time monitoring, optical imaging, optical communication and the like.

Description

Multi-focus diffraction lens based on optical fiber

Technical Field

The invention relates to a multifocal diffraction lens based on an optical fiber, which can be used for preparing a diffraction lens based on an optical fiber end, can be used in the fields of single cell manipulation and analysis, micro-electro-mechanical system real-time monitoring, optical imaging, optical communication and the like, and belongs to the technical field of fiber integrated optics.

Background

The first concept of integrated optics was introduced in the 60 s of the 20 th century, and the miniaturization of optical elements and systems was therefore uncovered. With the continuous progress of information technology, optical devices are developing towards miniaturization and integration without breaking new views in the optical field.

With the continuous development of integrated optics, some optical wavelength division multiplexers, optical switches and lasers can be integrated on a microchip, so that various functions are integrated together, and the system structure is greatly reduced.

Lenses are one of the traditionally optically important components, and are also being developed toward more miniaturization, for example, the fabrication process of silicon microlens arrays for MOEMS devices is reported by the royal (fabrication process of silicon microlens arrays for MOEMS devices [ J ] meter technology and sensors, 2019(10): 5-7.). Microlenses are small in size, easy to integrate, and widely used in the fields of light manipulation (YuanL, Liu Z, Yang J, et al. twin-core fiber optical tweeters [ J ]. Optics Express,2008,16(7):4559-66.) and optical imaging (liujianan. research and design of microlens array integral field imaging spectrometer [ D ]. university of academy of sciences of china (changchun optical precision machinery and physical institute of academy of sciences of china), 2019.).

Optical fibers are widely used in optical fiber devices and optical fiber sensing as a low-loss, long-distance light-transmitting element. The large divergence angle of the optical fiber causes the large loss of emergent light after a certain distance, and the sensitivity of the experiment is seriously influenced. It needs to add lens group or self-collimating lens on the end face of the optical fiber to reduce its divergence angle, but the size of this structure is in millimeter, and the size is much larger than the size of the optical fiber. Because the system is too large to penetrate into the micro-wells, it is not advantageous to use the experiment such as measurement in the micro-wells. In this case, a microlens, i.e., a "fiber microlens", is directly formed on the end face of the optical fiber to focus and collimate the light beam.

In 2017, Liuxin Wei et al reported a micro-grinding beveled lensed fiber flatness test study (Liuxin Wei, Luyushan, Yintiong, Li Weifan, Li Yufei, Zhao national Wei. micro-grinding beveled lensed fiber flatness test study [ J ]. applied optics, 2017,38(01):94-98.), tested by an orthogonal test method for micro-grinding 30 ° beveled lensed fiber of a 125 μm diameter single mode fiber, and ground a 30 ° beveled lensed fiber with a flatness error of 3 μm by the test. The small-angle inclined plane is generally used for reducing reflected light, the large-angle inclined plane is generally used for optical fiber sensing, and because the light receiving area of the inclined plane is larger than that of the plane, the optical fiber micro-lens manufactured by the grinding method can meet the requirement of a single experiment, but one optical fiber is intelligently processed every time, parameters such as the grinding angle, the processing speed and the like need to be continuously adjusted in the grinding process, the process is complex, and the success rate is low.

In 2018, Zhao Fusheng et al disclose an optical fiber with Fresnel lens on its end face and a sensor using the same (application No. 201821263256.1). The inverse model of the lens structure is first engraved on the rigid substrate, and then the lens structure model and the substrate are treated with silane to facilitate the detachment of the structure. And coating liquid PDMS on the anti-sticking pattern layer on the surface of the substrate, fully removing gas, heating the PDMS to solidify the PDMS, activating the PDMS structure and the end face of the optical fiber body by using oxygen plasma, aligning the optical fiber body to the center of the Fresnel lens, inserting the optical fiber body on the PDMS structure until the two form permanent adhesion, and removing the redundant PDMS structure by using a blade to complete the preparation of the optical fiber with the Fresnel lens on the end face. The PDMS is used for manufacturing the lens on the end face of the optical fiber, a mask needs to be manufactured, and a series of complicated steps such as casting, curing, optical fiber alignment and the like need to be performed, so that the process is complicated and complicated.

In 2019, Shaohuajiang et al disclose an adjustable bifocal microlens array, which realizes a long focal depth characteristic based on the microlens array, realizes adjustable bifocal distances from a single focus to bifocal points by rotating along the intersecting line direction of the cylindrical surfaces of the microlens array and matching with a focusing lens based on a micro curved surface light splitting characteristic, and greatly increases the bifocal focusing beam focal depth. Although the function of adjustable bifocal is realized, the side mirror is composed of dozens to hundreds of micro-cylindrical array units, and has large volume and complex structure.

In addition, chemical etching and fused biconical taper methods are also used to fabricate microlenses. The optical fiber conical micro lens manufactured by the chemical corrosion method has rough surface and poor mechanical strength, and can cause great loss of light intensity; the size of the hot melting tapering method is not easy to control.

The invention discloses a multifocal diffraction lens based on an optical fiber end, which integrates a binary diffraction lens into the optical fiber end and can be used in the fields of single cell manipulation and analysis, micro-electro-mechanical system real-time monitoring, optical imaging, optical communication and the like. And welding a section of single mode fiber at one end of the coaxial double-waveguide fiber for laser input, welding a section of coreless fiber at the other end of the coaxial double-waveguide fiber for optical field regulation, and directly processing a binary diffraction lens at the fiber end of the coreless fiber by using a femtosecond processing technology to finish the preparation of the multifocal diffraction lens based on the fiber end. Compared with the prior art, the invention integrates the binary diffraction mirror at the optical fiber end, realizes the simultaneous focusing of multiple points and can capture multiple particles simultaneously; the femtosecond laser processing system is used for directly processing the binary diffraction lens at the optical fiber end, so that the integration level is high, the volume is small, and the use is easy; the femtosecond laser processing technology is utilized, the precision is high, the processing period is short, the yield is high, and the method can be used for batch production.

Disclosure of Invention

The invention aims to provide a binary diffraction lens based on an optical fiber end and a preparation method thereof, wherein the binary diffraction lens is simple in structure, convenient to process, high in precision and high in yield.

The purpose of the invention is realized as follows:

an optical fiber based multifocal diffractive lens. The method is characterized in that: the coaxial dual-waveguide fiber coaxial optical fiber consists of a single-mode fiber 1, a coaxial dual-waveguide fiber 2, a coreless fiber 3 and a binary diffraction lens 4. And (3) tapering the coaxial double-waveguide fiber 2 until the diameter of the tapered region is the same as that of the single-mode fiber 1, cutting off the coaxial double-waveguide fiber from the taper waist by using a cutting knife, and welding the coaxial double-waveguide fiber with the single-mode fiber 1. And after the other end of the coaxial double-waveguide fiber 2 is welded with a section of coreless fiber 3, the coreless fiber is trimmed by a fixed-length cutting system, and the optimal length of the coreless fiber is obtained. The binary diffraction lens 4 is directly processed by a femtosecond processing system at the fiber end of the coreless fiber 3.

The length of the coreless fiber is L, preferably L450 μm.

The single-mode fiber 1 is a common single-mode fiber, the outer diameter of a cladding is 125 mu m, and the diameter of a fiber core is 9 mu m. The size of the coaxial double-waveguide fiber 2 is preferably 125 μm in outer diameter of a cladding, 35 μm in radius of a middle core, 50 μm in radius of an annular core and 55 μm in outer radius.

The coaxial double-waveguide fiber 2 may be a multicore fiber such as a double-core fiber, a three-core fiber, a four-core fiber, a six-core fiber, or a seven-core fiber.

The coreless fiber 3 may be a large core graded index fiber.

The end binary diffraction lens of the coreless fiber 3 is carved by a femtosecond laser processing system, the binary diffraction lens 4 is preferably composed of two groups of binary Fresnel lenses, the wave band radius R of the binary Fresnel lenses is determined by a Fresnel equation, the optical path difference of adjacent wave bands is lambda, and the radius of the nth wave band can be obtained by geometric optics knowledge:

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:

so that the nth zone radius r_nComprises the following steps:

design wavelength lambda used in the system₀At 520nm, focal length f₀And 80 μm.

Preferably, the binary diffractive lens 4 comprises three groups of binary fresnel lenses, each binary fresnel lens has 10 annular zones, and r is₁To r₁₀The values (unit: μm) of (d) are respectively: 6.45, 9.12, 11.17, 12.9, 14.42, 15.8, 17.06, 18.24, 19.39, 20.4.

Manufacturing a binary Fresnel lens: and etching a ring groove with the depth of d mu m on the even half-wave band by using a femtosecond laser micro-processing system to generate pi phase difference with the odd half-wave band, wherein d is preferably 2.36 mu m.

The binary diffractive lens 4 may also be a binary dammann grating, blazed grating or array grating.

Drawings

Fig. 1 is a schematic view of an optical fiber structure of an optical fiber-based multifocal diffractive lens. Wherein 1 is a single mode fiber, 2 is a coaxial double waveguide fiber, 3 is a coreless fiber, and 4 is a binary diffractive lens.

FIG. 2 is a schematic illustration of light ray traces in an optical fiber of a fiber based multifocal diffractive lens. 201 is the ray trace in the coaxial

double waveguide fiber

2 and 202 is the trace of light in the coreless fiber 3.

Fig. 3 is a schematic diagram of a fiber end binary diffractive lens condensing light of a fiber based multifocal diffractive lens. 301 is the incident ray, 302 is the binary diffractive lens focal plane, 303 is the converging ray, and d is the etch depth.

Figure 4 is a schematic view of a coreless fiber end binary diffractive lens of a fiber based multifocal diffractive lens. 3 is a coreless fiber, R₁Is the first zone radius, R, of the binary diffractive lens at the fiber end_nIs the nth zone radius of the fiber end binary diffractive lens.

Fig. 5 is a process for manufacturing an optical fiber-based multifocal diffractive lens.

FIG. 6 is an example of a microfluidic chip system application for a fiber-based multifocal diffractive lens.

FIG. 7 is a schematic diagram of an example of an inertial force cell sorting in a microfluidic chip application with an optical fiber-based multifocal diffractive lens. Among them, 701 is a cell fluid, 702 is a target cell, and 703 is a waste liquid.

FIG. 8 is a schematic diagram of a single fiber-manipulated cell in a microfluidic chip system application using a fiber-based multifocal diffractive lens. Where 628 is a single flow channel, 702 is a captured cell, 801 is a converging light output by a diffractive lens, 603 is a fiber-based multi-focal diffractive lens, 602 is a single mode fiber, 808 is a schematic representation of the exciting and receiving light of the single mode fiber

Detailed Description

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

Example 1: optical fiber-based multifocal diffractive lens fabrication processes.

The fiber-based multifocal diffractive lens fiber soldering process is shown in fig. 5:

step 1: inserting the coaxial double-waveguide fiber 2 into a proper quartz capillary 501, generating a high-temperature region by using oxyhydrogen flame 502 to soften the quartz capillary 501, realizing fused tapering, wherein the diameter of a fiber core at the waist of the quartz capillary 501 is reduced to be equal to that of the single-mode fiber 1, and the diameter of the fiber core of the coaxial double-waveguide fiber 2 in the coaxial double-waveguide fiber is reduced to 9-10 microns and is equal to that of the fiber core of the single-mode fiber 1;

step 2: drawing the obtained cone in the step 1, and cutting the cone at the cone waist by using a cutting knife 503;

and step 3: aligning the cone obtained by cutting in the step 2 with the single-mode optical fiber 1, and performing fusion welding on the cone and the single-mode optical fiber 1 by adopting a high-temperature region generated by the electrode 504 to complete welding of the single-mode optical fiber 1 and the coaxial double-waveguide optical fiber 2;

and 4, step 4: taking a section of coreless fiber 3, and welding the coreless fiber 3 to the other end of the coaxial double-waveguide fiber 2 by adopting a high-temperature region generated by an electrode 504 on the basis of the fiber prepared in the step 3;

and 5: and cutting the length of the coreless optical fiber 3 by using a fixed-length cutting system to obtain the optimal length.

The femtosecond system processing step of the coreless optical fiber 3 and the fiber end binary diffraction lens 4 comprises the following steps:

step 1: 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;

step 2: setting the frequency to be 60kHz, setting the power to be 4mW, selecting an objective lens with 50 x and the numerical aperture of 0.42, and focusing the femtosecond laser to the end surface of the optical fiber through a microscope objective lens;

and step 3: 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 4, step 4: 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.

Example 2: an example of a microfluidic chip application for a fiber-based multifocal diffractive lens.

Fig. 6 is a system diagram of an example of a microfluidic chip application of a multi-focal diffractive lens based on an optical fiber. The microfluidic chip 601 mainly includes two parts, cell screening 620 and cell manipulation 621. First, the cell screening 620 includes a micro-flow controller 610, a sheath fluid inlet reservoir 622, a cell fluid inlet reservoir 623, a sheath fluid channel 624, a main channel 626, a primary waste fluid outlet reservoir 625, and a target cell flow channel 627; second, the cell manipulation section 621 includes a single cell flow channel 628, a secondary waste drain 629, and a target cell drain 630. The binary diffractive lens fiber 603 and the two single mode fibers 604 are embedded through microgrooves.

Two single mode fibers 604 are on one side of the single flow cell 628 and a binary diffractive lens fiber 603 is on the other side of the single flow cell 628.

The width of the channel of the microfluidic chip is W μm, and W is preferably 150; the channel depth is H μm, H preferably being 65. The main channel 626 and the single flow cell channel 628 are L cm in length, L preferably being 2.

The micro-fluidic chip has the main structure and the working process as follows: sheath fluid is injected into the sheath fluid inlet reservoir 622 via the micro-flow controller 610 and cellular fluid is injected into the cellular fluid inlet reservoir 623 via the micro-flow controller 610. In the main channel 626, large cells (such as circulating tumor cells in the cell fluid) can be separated from the cell fluid by inertial force, the separated target cells enter the inlet of the single cell channel 628, and the rest is discharged as waste from the first-stage waste discharge tank 625. The single-cell flow channel 628 has sheath fluid channels 624 on two sides, at the inlet of the single-cell flow channel 628, the target cell flow is changed into the single-cell flow to flow into the single-cell flow channel 628 under the action of the sheath fluid on the two sides, in the single-cell flow channel 628, the cells are controlled by the binary diffraction lens fiber 603 and the two single-mode fibers 604, the light transmitted by the binary diffraction lens fiber 603 is used for capturing two cells at the same time, and the two single-mode fibers 604 are used for transmitting the excitation light and collecting the scattered light of the two cells.

FIG. 7 is a schematic diagram showing the process of sorting the cell fluid in the main channel. Among them, 701 is a cell fluid, 702 is a target cell, and 703 is a waste liquid. After the cell fluid 701 enters the main channel 626 from both sides, the target cell 702 can be sorted out due to different forces applied to different cells. As shown, the large cell is subjected to a rotational force F, causing the large target cell 702 to enter the intermediate sheath fluid.

FIG. 8 is a schematic diagram of optical fiber manipulation of cells in a single cell flow channel 628 in a microfluidic chip system employing an optical fiber based multifocal diffractive lens. Combine fig. 6 and 8. Wherein 628 is a single-cell flow channel, 603 is a binary diffractive lens fiber, 801 is a convergent light output by the binary diffractive lens fiber, 602 is two single-mode fibers, and 808 is a schematic diagram of an excitation light and a received light of the single-mode fibers. The trapping light emitted by the laser 802 is converged into two points by the binary diffractive lens fiber 603 to form a light trapping force, which can trap two target cells 702 at the same time. Excitation light emitted by the laser 804 enters the # 1 port of the three-port circulator 805, is output from the # 2 port and is irradiated onto the target cell 702 through the single-mode fiber 602, reflected light of the target cell 702 is still collected by the single-mode fiber 602, a reflected light signal enters the # 2 port of the three-port circulator 805 from the single-mode fiber 602 and is output from the # 3 port, and enters the spectrometer 806, and a spectrum received by the spectrometer can be transmitted to the computer 807 to be processed.

Claims

1. An optical fiber based multifocal diffractive lens. The method is characterized in that: the coaxial dual-waveguide fiber coaxial optical fiber consists of a single-mode fiber 1, a coaxial dual-waveguide fiber 2, a coreless fiber 3 and a binary diffraction lens 4. And (3) tapering the coaxial double-waveguide fiber 2 until the diameter of the tapered region is the same as that of the single-mode fiber 1, cutting off the coaxial double-waveguide fiber from the taper waist by using a cutting knife, and welding the coaxial double-waveguide fiber with the single-mode fiber 1. And after the other end of the coaxial double-waveguide fiber 2 is welded with a section of coreless fiber 3, the coreless fiber is trimmed by a fixed-length cutting system, and the optimal length of the coreless fiber is obtained. The binary diffraction lens 4 is directly processed by a femtosecond processing system at the fiber end of the coreless fiber 3.

2. An optical fiber-based multifocal diffractive lens according to claim 1, characterized in that: the coaxial double-waveguide fiber 2 can also be a double-core fiber, a three-core fiber, a four-core fiber, a six-core fiber or a seven-core fiber.

3. An optical fiber-based multifocal diffractive lens according to claim 1, characterized in that: the coreless fiber 3 may be a large core graded index fiber.

4. An optical fiber-based multifocal diffractive lens according to claim 1, characterized in that: the binary diffractive lens 4 preferably consists of two sets of binary fresnel diffractive lenses, and may be three or four sets.

5. The binary fresnel lens of claim 4, wherein: the even number of zones of the binary fresnel lens are etched to a depth of 2.36 μm.

6. An optical fiber-based multifocal diffractive lens according to claim 1, characterized in that: the binary diffractive lens 4 may also be a binary dammann grating, blazed grating or array grating.