阅读说明：本技术 一种多孔与多芯组合型光纤的制备方法 (Preparation method of porous and multi-core combined optical fiber ) 是由 苑立波 王剑 杨世泰 于 2021-10-12 设计创作，主要内容包括：本发明提供的是一种多孔与多芯组合型光纤的制备方法。其特征是：它由不同的双包层光纤、毛细管光纤和纯石英光纤选择性插入多孔石英套管,高温下绝热拉锥至多孔与多芯组合型光纤的直径后,保持光纤直径稳定拉丝,从而制备出一段多芯与多孔组合型光纤,并且该光纤的多个纤芯可和多根标准单模光纤连接,解决多芯光纤的连接问题。光纤中的多个纤芯可以用于光信号通讯传输,也可以用于传感应用,还可以构造光纤内集成的干涉仪。光纤中的微孔可以用作微流通道。本发明具有组装灵活、制备参数可调、制备的光纤功能多样化的优点,可广泛用于光纤微流控、光纤传感等领域。(The invention provides a preparation method of a porous and multi-core combined optical fiber. The method is characterized in that: different double-clad optical fibers, capillary optical fibers and pure quartz optical fibers are selectively inserted into a porous quartz sleeve, and the diameter of the optical fibers is kept stable after adiabatic tapering to the diameter of the porous and multi-core combined optical fiber at high temperature, so that a section of multi-core and porous combined optical fiber is prepared, a plurality of fiber cores of the optical fiber can be connected with a plurality of standard single-mode optical fibers, and the connection problem of the multi-core optical fiber is solved. Multiple cores in an optical fiber can be used for optical signal communication transmission, can also be used for sensing application, and can also be used for constructing an interferometer integrated in the optical fiber. The micro-holes in the optical fiber may serve as microfluidic channels. The invention has the advantages of flexible assembly, adjustable preparation parameters and diversified functions of the prepared optical fiber, and can be widely applied to the fields of optical fiber microfluidics, optical fiber sensing and the like.)

1. A preparation method of a porous and multi-core combined optical fiber is characterized by comprising the following steps: the porous and multicore combined optical fiber is prepared from the following raw materials: porous quartz sleeve, double-clad fiber, pure quartz fiber, capillary fiber, single-mode fiber; the preparation steps are as follows:

the method comprises the following steps: the single-mode optical fiber is welded with a section of double-clad optical fiber;

step two: selectively inserting one or more of the double-clad optical fibers into the micropores of the porous quartz sleeve; selectively inserting one or more capillary optical fibers into the micropores of the porous quartz sleeve; inserting the pure quartz optical fiber into the rest holes of the porous quartz sleeve for filling; completing the steps to obtain a miniature combined prefabricated rod;

step three: the assembled prefabricated rod is arranged on a clamp of a miniature optical fiber drawing tower, and is tapered in a furnace at the temperature of more than 1700 ℃; wherein the tail end of the inserted capillary optical fiber is connected with an air pressure control device, and the diameter of the hole in the drawing process is adjusted by controlling the air pressure in the hole to form a micropore for preparing the optical fiber; the optical fiber inserted into the micropore of the pure quartz optical fiber is integrated with the porous quartz sleeve; the inserted double-clad optical fiber is tapered along with tapering, the fiber core of the double-clad optical fiber is tapered until the optical fiber can not bind light waves any more, the inner cladding is tapered into a new fiber core, and the light waves are converted from the original fiber core to the new fiber core for transmission in an insulating way;

step four: the tapering process is gentle, the drawing diameter is fed back through a laser diameter gauge, after the drawing is carried out to the preset diameter, the rod feeding speed of a displacement table of a miniature combined type preform rod clamp is adjusted, and the multi-hole and multi-core combined optical fiber tail fiber is drawn at a continuous and stable speed in cooperation with the drawing speed;

step five: coating and curing a coating layer on the tail fiber while drawing the porous and multi-core combined optical fiber tail fiber, and collecting the fiber through an optical fiber disc;

step six: and after the optical fiber tail fiber is drawn to a preset length, taking the optical fiber together with the residual micro prefabricated rod down from the optical fiber drawing tower, and putting the residual micro prefabricated rod and the gradually-changed optical fiber bundle cone into a steel pipe for packaging to protect the device.

2. The method for preparing the porous and multicore combined optical fiber according to claim 1, wherein: the porous quartz sleeve comprises a plurality of micro through holes, and double-clad optical fibers, capillary optical fibers and pure quartz optical fibers with coating layers removed can be selectively inserted into the through holes.

3. The method for preparing the porous and multicore combined optical fiber according to claim 1, wherein: the double-clad fiber comprises a single-mode fiber core and two coaxially-distributed claddings, and the refractive index distribution of the claddings is step distribution or gradual distribution.

4. The method for preparing the porous and multicore combined optical fiber according to claim 1, wherein: and in the process of drawing the optical fiber in the fourth step, adding coaxial rotation to ensure that the drawn multi-core and porous combined optical fiber has micropores and fiber cores which are spirally distributed to form the spiral multi-core and porous combined optical fiber.

Technical Field

The invention relates to a preparation method of a porous and multi-core combined optical fiber, belonging to the technical field of special optical fiber preparation.

Background

In recent years, the research on the micro-fluidic chip technology based on optical detection is promoted by the proposal of the 'Lap on/in fiber' fiber integrated optical fiber micro-fluidic (optical flow) detection technology taking optical fibers as carriers. The core meaning of the micro-fluidic device is that the micro-structural optical fiber is used as the essential attribute of an optical waveguide medium, an optical detection structure unit is constructed on the surface/inside of the optical fiber, and a micro-fluidic channel is constructed by using the optical fiber or an auxiliary structure, so that the micro-fluidic device with optical analysis performance is formed. The idea of transplanting the microfluidic unit into the optical fiber can effectively utilize the structural characteristics of the optical fiber to realize the microfluidic detection process based on various optical detection mechanisms, wherein the microfluidic detection process comprises intensity detection such as fluorescence type, chemiluminescence type and absorption type, and phase detection such as interference type, long-period optical fiber grating and Bragg optical fiber grating, so that optical signal detection based on different detection mechanisms and different sensitivity requirements can be realized. The fiber integrated optical fiber detection structure can not only omit complicated chip optical waveguide preparation steps, but also realize the full contact of the optical waveguide and the detection medium to the maximum extent and realize simple optical input and signal output. Therefore, the "Lap on/in fiber" fiber integrated optical microfluidic (optofluidic) detection technology based on the microstructure fiber technology has unique potential application value in a micro-chemical biological analysis system, and particularly, with the rapid development of special optical fibers such as photonic crystal fibers, multi-core fibers, hollow fibers, holey fibers and the like and the continuous emergence of optical fiber sensing technologies with different detection mechanisms, the integrated optical microfluidic detection system for the "Lap on/in fiber" has been put into practical use, and related basic research work is widely carried out.

The optical fiber interferometer is widely applied in the fields of refractive index measurement, chemical concentration measurement, molecular biology and the like. Compared with the traditional interference light path, the light path structure of the optical fiber interferometer can reduce wave front distortion, quickly respond to internal and external measurement environments, and has the characteristic of anti-electromagnetic interference. The detection principle is based on phase detection, so that the device based on the optical fiber interferometer has better stability, and the optical signal can avoid the influence of instability of the intensity of the optical path. The multi-core optical fiber has a plurality of fiber cores, can integrate an interference optical path in the same optical fiber, and has the characteristics of small volume and good stability. But the connection of multi-core fibers is not as simple as a common single-mode fiber, which requires precise core alignment. And the multi-core optical fiber is also provided with a fan-in/out device, so that the multi-core optical fiber can be connected with a plurality of single-mode optical fibers to realize the independent connection of each fiber core.

The micro-structure optical fiber or the perforated optical fiber has a pore channel structure with micron scale, the volume for containing gas/liquid can be as low as nano liter scale, and the micro-structure optical fiber or the perforated optical fiber is an ideal carrier for trace detection. The one-dimensional pore structure provides a long-range action field for a sample and an optical waveguide, breaks through the limitation of the traditional optical fiber optics, and shows the advantages of no substitution in the field of analysis and detection research.

Therefore, the multi-core and porous combined optical fiber is a valuable optical fiber, and patent CN109752791A proposes a micro-flow channel and light wave channel hybrid integrated dual-core optical fiber and a preparation method thereof, wherein the optical fiber has two fiber cores and a plurality of micro-flow channels, and the micro-flow channels and the light wave channel are integrated in the same optical fiber, thereby having important applications in the fields of micro-flow control and trace substance detection. Patent CN111632534A proposes a photo-thermal micro-fluidic mixer based on the multi-core porous fiber, and realizes the application function of micro-fluidic control.

At present, the preparation of the optical fiber is prepared according to the traditional optical fiber preparation process, which mainly comprises the steps of preparing a large multi-core optical fiber preform, preparing through holes by an ultrasonic punching technology, and drawing a large amount of multi-core and multi-hole combined optical fibers under the condition of pressure control. Although conventional optical fiber fabrication techniques can produce longer optical fibers, it is not easy to use these optical fibers, and special fan-in/out devices are required to complete the connection of the multi-core optical fibers. On the other hand, in general, such a multi-hole and multi-core combined optical fiber is used in the fields of sensing, measuring, and micro-fluidic control, and the usage amount of each device is not very long, so that an optical fiber device which is convenient for connecting the multi-hole and multi-core combined optical fiber is more urgently needed. The invention provides a preparation method of a porous and multi-core combined optical fiber, which is characterized in that the optical fiber prepared by the method is directly provided with fan-in/out devices, and not only can the independent connection of each fiber core be met, but also the independent connection of each microfluidic channel is met.

Disclosure of Invention

The invention aims to provide a preparation method of a porous and multi-core combined optical fiber.

The purpose of the invention is realized as follows:

a method for preparing a multi-hole and multi-core combined optical fiber can combine and prepare multi-core optical fibers with different fiber core numbers according to the practical application requirements, for example, (a) a double-core optical fiber, (b) a three-core optical fiber, (c) a four-core optical fiber, (d) a five-core optical fiber, etc. as shown in figure 1; it is also possible to produce a plurality of micro-and multi-core combined optical fibers, such as (a) a three-hole two-core optical fiber, (b) a two-hole two-core optical fiber, (c) a single-hole two-core optical fiber, etc., as shown in fig. 2.

The porous and multicore combined optical fiber is prepared from the following raw materials: double-clad optical fiber, capillary optical fiber, pure quartz optical fiber, porous quartz sleeve and single-mode optical fiber.

The end face of the double clad optical fiber 1 is shown in fig. 3a and comprises a core 1-1, at least one inner cladding 1-2 and an outer cladding 1-3. The fiber core mode field is matched with the fiber core mode field of the single-mode fiber, the fiber core can be in butt fusion with the single-mode fiber, and the fiber is used for mode field conversion transition in the process of pulling the porous and multi-core combined fiber.

The capillary fiber 2 has a middle micropore 2-1, the cladding 2-2 is made of pure quartz, the end surface is shown in figure 3b, the fiber is used for controlling the pressure in the hole in the drawing process of the porous and multi-core combined fiber, and finally forms a micropore structure with a proper size.

The pure quartz optical fiber is a coreless optical fiber 3 made of pure quartz material, and the end face of the pure quartz optical fiber is shown in fig. 3c, and the pure quartz optical fiber is used for solid filling in the drawing process of the porous and multi-core combined optical fiber.

The double-clad fiber 1, the capillary fiber 2 and the pure silica fiber 3 have a uniform diameter, preferably 125 μm.

The porous quartz sleeve 4 is made of pure quartz, and the end surface of the porous quartz sleeve is a quartz tube with a plurality of micropores with equal diameters as shown in fig. 4, and the number of the micropores is specifically designed according to the structure of the porous and multi-core combined optical fiber to be prepared actually. Preferably, the diameter of the hole is 126-.

The preparation steps of the porous and multi-core combined optical fiber are as follows:

the method comprises the following steps: the single mode fiber 5 is welded with a section of double-clad fiber 1, and the coating layer of the double-clad fiber is removed;

step two: as shown in fig. 5, one or more single-mode optical fibers to which the double-clad optical fibers are fusion-spliced are selectively inserted into the micropores of the porous quartz sleeve 4; selectively inserting one or more capillary optical fibers 2 into the micropores of a porous quartz sleeve 4; inserting the pure quartz optical fiber 3 into the rest holes of the porous quartz sleeve 4 for filling; the above steps are completed to obtain the miniature combined type prefabricated rod 6.

Step three: as shown in fig. 6, a micro-combined preform 6 is mounted on a fixture 7 of a micro-optical fiber drawing tower, tapered in a heating furnace 8 at a temperature of more than 1700 ℃, the tail end of the inserted capillary optical fiber 2 is connected with an air pressure control device 9, and the diameter of a hole in the drawing process is adjusted by controlling the air pressure in the hole to form a micropore for preparing the optical fiber; the optical fiber inserted into the micropore of the pure quartz optical fiber 3 is integrated with the porous quartz sleeve; the inserted double-clad optical fiber 1 is tapered along with tapering, the fiber core of the double-clad optical fiber is tapered until the optical fiber can not bind light waves any more, the inner cladding is tapered into a new fiber core, and the light waves are transmitted from the original fiber core to the new fiber core in an adiabatic conversion mode.

Step four: the tapering process is gentle, the drawing diameter is fed back through the laser diameter gauge 10, after the drawing is reduced to the preset diameter, the rod feeding speed of the displacement table 11 of the miniature combined type preform rod clamp is adjusted, and the multi-hole and multi-core combined optical fiber tail fiber 13 is drawn at a continuous and stable speed by matching with the drawing speed of the drawing driving wheel 12;

step five: coating the tail fiber 13 by a coating device 14 and curing the coating layer by a curing lamp 15 while drawing the multi-hole and multi-core combined optical fiber tail fiber, and finally, collecting the fiber by an optical fiber capstan 16 and an optical fiber disc 17;

step six: after the optical fiber tail fiber is drawn to a preset length, the optical fiber is taken down from the micro wire drawing tower together with the optical fiber tail fiber 13 and the residual micro preformed rod 6, and the residual micro preformed rod and the gradually-changed optical fiber bundle cone are placed into a steel pipe together for packaging to protect devices.

The resulting device should be as shown in fig. 7, comprising (1) input fibers: a capillary fiber 2 and a single mode fiber 5 in which a double clad fiber is fused; (2) a fiber bundle adiabatic transition taper 18; (3) the multi-hole and multi-core combined optical fiber pigtail 13. The pure quartz optical fiber 3 is used as a filler and is fused with the quartz capillary sleeve 4 in the drawing process, the single-mode optical fibers 5 are used as independent input ports of optical paths of each fiber core of the porous and multi-core combined optical fiber, and the capillary optical fiber 2 can be used as an injection interface of micro-liquid flow/micro-air flow.

The core of the invention is the combined preparation of the micro preform and adiabatic transition conversion of the optical fiber mode field. The combined preform is very flexible to manufacture, and can be combined into a desired multi-hole and multi-core combined optical fiber as desired. The adiabatic transition conversion of the fiber mode field means that the fiber core energy of the double-clad fiber can be adiabatically converted into the inner cladding for transmission in the tapering process, so that the independent optical path connection of a plurality of fiber cores is ensured.

The adiabatic conversion principle of the double-clad fiber is shown in fig. 8, wherein 8(a) and 8(b) are respectively an end view, a refractive index distribution and a mode field 19 distribution of the fiber before and after tapering, light waves are mainly bound in the fiber core 1-1 of the double-clad fiber 1 before tapering and transmitted, and the optical mode field 19 is diffused to the inner cladding distribution after tapering.

The double-clad fiber comprises a single-mode core and at least two coaxially-distributed claddings, and the refractive index distribution of the claddings is step distribution (shown in figure 9a) or gradual distribution (shown in figure 9 b).

And in the process of drawing the optical fiber in the fourth step, adding coaxial rotation to ensure that the drawn multi-core and porous combined optical fiber has micropores and fiber cores which are spirally distributed to form the spiral multi-core and porous combined optical fiber.

The preparation method of the porous and multi-core combined optical fiber provided by the invention at least has the following outstanding advantages:

(1) the connector and the optical fiber are integrally prepared, so that a device can be connected with one section of optical fiber, and the branching connection problem of the multi-core optical fiber is solved;

(2) the optical fiber is provided with a plurality of fiber cores and micropore channels, the combined optical fiber can be used for microfluidic optical combined application, and the combination method is flexible and changeable;

(3) if micro-holes are not needed, a small number of multi-core optical fibers can be prepared by the method, and the multi-core optical fibers and fan-in/out devices are integrally prepared.

Drawings

FIG. 1 is an end view of a multi-core optical fiber that can be prepared according to the present invention, (a) a two-core optical fiber, (b) a three-core optical fiber, (c) a four-core optical fiber, and (d) a five-core optical fiber.

FIG. 2 is an end view of a multi-hole and multi-core combined optical fiber that can be prepared according to the present invention, (a) a three-hole two-core optical fiber, (b) a two-hole two-core optical fiber, and (c) a single-hole two-core optical fiber.

Fig. 3 is a structural view of end surfaces of (a) a double-clad fiber, (b) a capillary fiber, and (c) a pure silica fiber.

FIG. 4 is an end view of a porous quartz sleeve having a plurality of pores of equal diameter.

Fig. 5 is a micro-fabricated optical fiber preform into which a plurality of optical fibers are inserted.

FIG. 6 is a manufacturing process for drawing integrated optical fibers and devices using a micro fiber draw tower.

Fig. 7 is a structure of an integrated holey and multicore combined type optical fiber with a connector.

Fig. 8 is a schematic diagram of adiabatic conversion of a double-clad fiber, in which (a) and (b) are respectively an end view, a refractive index distribution and a mode field distribution of the fiber before and after tapering, in which light waves are mainly confined in the core of the double-clad fiber before tapering and transmitted, and a mode field of the light waves is diffused to an inner cladding distribution after tapering.

Fig. 9 shows refractive index profiles of two types of double-clad fibers, in which fig. 9(a) shows a step profile and fig. 9(b) shows a graded profile.

FIG. 10 is a block diagram of a four-core optical fiber with an integrated connector.

Fig. 11 is a simulation result of mode field transitions of the center core and the side cores of the connector of the four-core optical fiber of fig. 10.

Fig. 12 is a diagram showing a method for manufacturing a holey and multicore combined type optical fiber having a spiral structure.

FIG. 13 is a block diagram of a spiral quad-core fiber with an integrated connector.

FIG. 14 is a view showing a structure of a spiral multi-hole and multi-core combined optical fiber, (a) a double-hole single-core spiral optical fiber, and (b) a single-hole double-core optical fiber.

Detailed Description

The invention is further illustrated with reference to the following figures and specific examples.

Example 1: preparation of single-hole double-core optical fiber

Taking the single-hole dual-core fiber as an example in fig. 2(c), the preparation method of the multi-hole and multi-core combined fiber is explained.

A5-hole silica sleeve 4 shown in FIG. 4 was selected, two coreless optical fibers 3 having a diameter of 125 μm were selected, a coating layer was stripped off in a length of 20 cm, and holes No. 4-2 and No. 4-4 of the 5-hole silica sleeve were inserted as filling optical fibers. Two single-mode fibers 5 are selected, and after being respectively welded with a double-clad fiber 1 with the length of 20 cm, the single-mode fibers are inserted into No. 4-3 holes and No. 4-5 holes of a quartz sleeve 4 with 5 holes. A capillary optical fiber 2 is selected, a coating layer with the length of 20 cm is stripped, and then the capillary optical fiber is inserted into a No. 4-1 hole of a 5-hole quartz sleeve 4. The above steps are completed to obtain a micro-composite preform 6, as shown in fig. 5.

As shown in fig. 6, the assembled preform 6 is mounted on a fixture 7 of a micro optical fiber drawing tower, a graphite filament heat source 8 is used for drawing a cone, the temperature of the drawing cone can reach more than 2000 ℃, the tail end of the inserted capillary optical fiber 2 is connected with an air pressure control device 9, the diameter of a hole in the drawing process is adjusted through the control of air pressure in the hole, and micropores for preparing the optical fiber are formed; the optical fiber inserted into the micropore of the pure quartz optical fiber 3 is integrated with the porous quartz sleeve; the inserted double-clad optical fiber 1 is tapered along with tapering, the fiber core of the double-clad optical fiber is tapered until the optical fiber can not bind light waves any more, the inner cladding is tapered into a new fiber core, and the light waves are transmitted from the original fiber core to the new fiber core in an adiabatic conversion mode.

The tapering process should be gentle, the drawn wire diameter is fed back by the laser diameter gauge 10, after the drawn wire is drawn to the preset diameter, the rod feeding speed of the displacement table 11 of the miniature combined type preform rod clamp is adjusted, and the single-hole double-core optical fiber pigtail 13 is drawn at a continuous and stable speed by matching with the wire drawing speed of the wire drawing driving wheel 12.

While the single-hole twin-core optical fiber pigtail is drawn, the pigtail is coated and cured with a coating layer, and is drawn by an optical fiber capstan 16 and an optical fiber capstan 17.

And after the optical fiber tail fiber is drawn to a preset length, taking the optical fiber down from the micro wire drawing tower together with the optical fiber and the residual micro preformed rod, and putting the residual micro preformed rod and the gradually-changed optical fiber bundle cone into a steel pipe for packaging to protect the device.

Example 2: and (4) preparing the four-core optical fiber.

Four-hole quartz sleeves are selected, wherein one hole is positioned in the middle of the sleeve, the other three holes are distributed in a regular triangle, the diameter of each hole is equal to 130 micrometers, the distance between each side hole and the middle hole is 294 micrometers, and the outer diameter of each sleeve is 875 micrometers.

Four single-mode fibers 5 are respectively welded with a double-clad fiber 1 of 20 cm, the relative refractive index difference between the fiber core of the double clad and the inner cladding is 0.5%, the relative refractive index difference between the inner cladding and the outer cladding is 0.5%, and the outer cladding is made of pure quartz. Four optical fibers are inserted into the four-hole quartz sleeve to form the miniature combined prefabricated rod of the four-core optical fiber.

The miniature combined preform of the four-core optical fiber is installed on a miniature optical fiber drawing tower, and a small amount of fan-in/out device integrated four-core optical fiber pigtails are prepared according to the drawing method in the embodiment 1.

FIG. 11 is a simulation of mode field transition of a central core and 1 side core of a four-core fiber micro-composite preform in a cone variation region by using a beam propagation method. It can be seen that the mode field gradually transitions from the core to the inner cladding transmission of the double clad fiber in the taper region.

Example 3: and (3) preparing the spiral four-core optical fiber.

The method for manufacturing the spiral four-core optical fiber is similar to that of the four-core optical fiber of example 2, except that, as shown in fig. 12, in the process of drawing the spiral four-core optical fiber, the clamp for clamping the four-core optical fiber micro-combined preform is coaxially rotated at the same time, resulting in spiral distribution of three side cores in the process of drawing. The resulting fan-in device integrated spiral four-core fiber is shown in fig. 13.

Example 4: and (3) preparing the spiral holey fiber.

According to the combination of example 1, a pure silica fiber, a capillary fiber, and a double-clad fiber can be used to selectively fill a five-hole silica tube, and then according to the preparation method of example 3, a spiral holey fiber as shown in fig. 14 can be prepared.