阅读说明：本技术 一种超低损耗的大模场光纤侧面泵浦合束器及其制作方法 (Ultra-low-loss large-mode-field optical fiber side pumping beam combiner and manufacturing method thereof ) 是由 熊波波 邹达 于 2020-04-29 设计创作，主要内容包括：本发明公开了一种超低损耗的大模场光纤侧面泵浦合束器及其制作方法,该方法包括以下步骤：将大模场信号光纤和泵浦光纤中对应熔融结合部处的涂覆层除去,露出内部的包层；将两根泵浦光纤中裸露的包层分别紧密贴合在大模场信号光纤中包层的两侧以形成光纤束；而后对光纤束中的包层区域进行熔烧加热；在加热至熔融状态时拉伸光纤束,使大模场信号光纤中熔融区域的尺寸被拉细变小形成两端对称的锥形结构,而后使光纤束恢复至室温后形成固态,将大模场信号光纤和泵浦光纤熔接形成一体。本发明通过在熔烧过程中适当拉细光纤,减弱机器、夹具、重力和热应力因素对大模场信号光纤产生的微小形变,从而使得基模信号通过熔烧区时发生畸变的程度非常小。(The invention discloses an ultra-low loss large mode field optical fiber side pumping beam combiner and a manufacturing method thereof, wherein the method comprises the following steps: removing the coating layer at the corresponding fusion joint part in the large mode field signal fiber and the pump fiber to expose the inner cladding; respectively and tightly attaching the bare cladding layers of the two pump optical fibers to two sides of the cladding layer of the large mode field signal optical fiber to form an optical fiber bundle; then, carrying out sintering heating on the cladding region in the optical fiber bundle; and stretching the optical fiber bundle when the large mode field signal optical fiber is heated to a molten state, so that the size of a molten area in the large mode field signal optical fiber is thinned and reduced to form a tapered structure with two symmetrical ends, then the optical fiber bundle is restored to room temperature to form a solid state, and the large mode field signal optical fiber and the pump optical fiber are welded into a whole. The invention reduces the tiny deformation of the large mode field signal optical fiber caused by machine, clamp, gravity and thermal stress factors by properly thinning the optical fiber in the sintering process, thereby ensuring that the distortion degree of the basic mode signal is very small when the basic mode signal passes through the sintering area.)

1. A manufacturing method of an ultralow-loss large-mode-field optical fiber side pumping beam combiner is used for integrating two pumping optical fibers and a large-mode-field signal optical fiber through fusion tapering, and is characterized by comprising the following steps:

s1, removing the coating layer at the corresponding fusion joint part in the large mode field signal fiber and the pump fiber to expose the cladding layers in the signal fiber and the pump fiber;

s2, respectively and tightly attaching the bare cladding of the two pump fibers to two sides of the bare cladding of the large mode field signal fiber to form a fiber bundle;

s3, then, sintering and heating the cladding region jointed with each optical fiber in the optical fiber bundle;

s4, stretching the optical fiber bundle when the jointed cladding region is heated to a molten state, so that the size of the molten region in the large-mode signal optical fiber is thinned and reduced to form a tapered structure with two symmetrical ends, gradually reducing the sintering temperature after stretching until the optical fiber bundle is completely heated, and enabling the optical fiber bundle to be recovered to room temperature to form a solid state, thereby welding the large-mode signal optical fiber and the pump optical fiber into a whole.

2. The method for manufacturing the ultra-low loss large mode field fiber side pump beam combiner of claim 1, wherein in step S1, after removing the coating layer, the bare cladding layers in the signal fiber and the pump fiber are cleaned by alcohol wiping.

3. The method for manufacturing the ultra-low loss large mode field optical fiber side pump beam combiner of claim 1, wherein in step S2, after the claddings of the large mode field signal optical fiber and the pump optical fiber are bonded, the two ends of the bonded region are fixed by gummed paper.

4. The method for manufacturing the ultra-low loss large-mode-field optical fiber side-pumped beam combiner of claim 3, wherein the steps between S2 and S3 further comprise the steps of:

s21, respectively connecting two ends of the large-mode-field signal fiber into a signal light source and a power meter, wherein a cladding region attached between the large-mode-field signal fiber and the pump fiber is positioned between the signal light source and the power meter; and the two ends of the large mode field signal optical fiber are respectively connected into the two optical fiber mode field adapters, and the optical fiber mode field adapters are communicated with the signal light source and the power meter through single mode optical fibers.

5. The method for manufacturing the ultra-low-loss large-mode-field optical fiber side-pumped beam combiner as claimed in claim 1, wherein in step S3, the optical fiber bundle is placed on a tapering machine, two symmetrically arranged clamps are used to clamp two ends of the bonding region of the optical fiber bundle respectively, oxyhydrogen flame on the tapering machine is used to burn and heat the bonding region, and then the optical fiber bundle is stretched in a manner that the clamps at two ends of the bonding region move and separate slowly in opposite directions respectively.

6. The method as claimed in claim 5, wherein in step S4, the fiber bundle is slowly drawn after the attached cladding region is heated to a molten state and the fusion heating is performed for 100S and 500S.

7. The method for fabricating the ultra-low loss large-mode-area fiber side-pumped beam combiner of any one of claims 1 to 6, wherein in step S4, the stretching speed is controlled to be 5mm/min, and the stretching length is controlled to be within 8 mm.

8. The method for manufacturing the ultra-low loss large-mode-field optical fiber side-pumped beam combiner of claim 1, wherein the steps between S1 and S2 further comprise the steps of:

s11, the pump fiber is firstly placed on a tapering machine, and then the cladding exposed in the pump fiber is thinned in a fused tapering mode.

9. The method for manufacturing the ultra-low-loss large-mode-field optical fiber side-pumped beam combiner as claimed in claim 1, wherein in step S4, the temperature of the sintering is gradually reduced in four stages after the stretching is finished, and finally the optical fiber bundle is cooled to return to room temperature; the four stages include:

the first stage is as follows: cooling to 1400 ℃, and heating for 20 s;

and a second stage: cooling to 1000 ℃, and heating for 20 s;

and a third stage: cooling to 500 ℃, and heating for 20 s;

a fourth stage: the heating is directly removed, and the optical fiber bundle is cooled to return to the room temperature.

10. An ultra-low loss large mode field optical fiber side pumping beam combiner, characterized in that it is made by the method of any claim 1-9.

Technical Field

The invention belongs to the technical field of optical fibers, and particularly relates to an ultra-low-loss large-mode-field optical fiber side pumping beam combiner and a manufacturing method thereof.

Background

High-power fiber lasers have been widely used in the fields of industrial processing, medical treatment, national defense and military, etc. In the optical fiber laser, the performance of the high-power optical fiber device is important. The large-mode-field optical fiber has a large core diameter area, so that the threshold of nonlinear effects (SPM, SBS, SRS and the like) can be improved, and the characteristics of pulse width, spectrum width and the like of signal light are ensured not to be changed. Therefore, large mode field fibers are suitable for high average power transmission and have been widely used in the field of high power fiber lasers.

There is a very important parameter in the design of optical fibers: normalizing the frequency (V parameter) to measure the number of allowable transmission modes in the fiber; when V is less than 2.405, only the fundamental mode can be transmitted, which is called a single-mode fiber, and the fiber body of the single-mode fiber is generally very small (<6um), and the NA is large; and the large mode field fiber is not a single mode fiber generally, V is greater than 2.405, the core diameter is large (10-50um), the V parameter is reduced by reducing the NA, the number of allowable transmission modes is controlled, and therefore better beam quality is maintained.

The normalized frequency (vparameter) of a large mode field fiber is large, so it is not a single mode fiber, allowing multiple modes to be transmitted in the fiber; in practical application, due to the influence of external factors or the change of the self morphological structure of the large-mode-field optical fiber, part of fundamental mode signals are converted into high-order modes, so that the quality of light beams is reduced.

When the large mode field optical fiber is used for manufacturing a high-power optical fiber device, a process step of sintering is often needed, the optical fiber is heated and softened to reach a molten state, and then is fused with other optical fibers. For example, when a side pump beam combiner with signal input and output both being large mode field optical fibers is manufactured, the pump optical fibers need to be attached to the surfaces of the large mode field signal optical fibers and be fused together. At present, the signal loss of the basic mode of the device in industrial application is generally more than 0.5 dB.

The large mode field optical fiber is subjected to micro deformation in the process of fusion sintering, and the micro deformation is mainly related to the following factors:

1) due to the influence of the machine and the clamp, the vibration of the machine can deform the optical fiber in a molten state, and the micro dislocation of the fixed clamps at the two sides causes the microscopic dislocation of a sintering area.

2) Influence of thermal stress: the sintering process only occurs in a small section of area in the middle of the large-mode-field-diameter optical fiber, the sintering area is heated to a molten state, but the optical fibers on two sides are still in a solid state, and the sintering area can be bent under the influence of thermal stress.

3) Gravity causes the molten region of the fiber to sag, bending microscopically.

In the current industrial application, the core diameter of the large mode field optical fiber is generally 10-30um, the micro deformation caused by the factors can easily reach more than 10um, the shape structure, the coaxiality and the symmetry of the core diameter are obviously changed, the injected fundamental mode signal can be excited into a high-order mode through a sintering area, and the loss of the fundamental mode signal is increased.

The large loss of the fiber device results in the laser needing higher pump power to reach the same power output, which introduces more noise, thereby reducing the overall performance and reliability, and the distorted higher-order modes also reduce the output beam quality of the laser.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a manufacturing method of an ultralow-loss large-mode-field optical fiber side pumping beam combiner.

In order to solve the technical problem, the invention provides a manufacturing method of an ultralow-loss large-mode-field optical fiber side pumping beam combiner, which is used for integrating two pumping optical fibers and a large-mode-field signal optical fiber through fused tapering, and comprises the following steps:

s1, removing the coating layer at the corresponding fusion joint part in the large mode field signal fiber and the pump fiber to expose the cladding layers inside the large mode field signal fiber and the pump fiber;

s2, pre-thinning the two pump fibers, and then respectively and tightly attaching the thinned parts to two sides of a bare cladding in the large mode field signal fiber to form a fiber bundle;

s3, then, sintering and heating the cladding region jointed with each optical fiber in the optical fiber bundle;

s4, stretching the optical fiber bundle when the jointed cladding region is heated to a molten state, so that the size of the molten region in the large-mode signal optical fiber is thinned and reduced to form a tapered structure with two symmetrical ends, gradually reducing the sintering temperature after stretching until the optical fiber bundle is completely heated, and enabling the optical fiber bundle to be recovered to room temperature to form a solid state, thereby welding the large-mode signal optical fiber and the pump optical fiber into a whole.

Further, in step S1, after removing the coating layer, the bare cladding layers in the large mode field signal fiber and the pump fiber are cleaned by alcohol wiping.

Further, in step S2, after the claddings of the large mode field signal fiber and the pump fiber are bonded, both ends of the bonded region are fixed with adhesive tape.

Further, the following steps are included between steps S2 and S3:

s21, respectively connecting two ends of the large-mode-field signal fiber into a signal light source and a power meter, wherein a cladding region attached between the large-mode-field signal fiber and the pump fiber is positioned between the signal light source and the power meter; and the two ends of the large mode field signal optical fiber are respectively connected into the two optical fiber mode field adapters, and the optical fiber mode field adapters are communicated with the signal light source and the power meter through single mode optical fibers.

Further, in step S3, the optical fiber bundle is placed on a tapering machine, two symmetrically disposed clamps are used to respectively clamp two ends of the bonding region of the optical fiber bundle, and then oxyhydrogen flame on the tapering machine is used to burn and heat the bonding region, and then the optical fiber bundle is stretched in a manner that the clamps at the two ends of the bonding region respectively slowly move and separate in opposite directions.

Further, in step S4, the bonded clad region is heated to a molten state and then is sintered and heated for 100-500 seconds, and then the optical fiber bundle is slowly drawn.

Further, in step S4, the stretching rate is controlled to 5mm/min and the stretching length is controlled to be within 8 mm.

Further, the following steps are included between steps S1 and S2:

s11, the pump fiber is firstly placed on a tapering machine, and then the cladding exposed in the pump fiber is thinned in a fused tapering mode.

Further, in step S4, after the drawing is finished, the temperature of the sintering is gradually reduced in four stages, and finally the optical fiber bundle is cooled and returned to room temperature; the four stages include:

the first stage is as follows: cooling to 1400 ℃, and heating for 20 s;

and a second stage: cooling to 1000 ℃, and heating for 20 s;

and a third stage: cooling to 500 ℃, and heating for 20 s;

a fourth stage: the heating is directly removed, and the optical fiber bundle is cooled to return to the room temperature.

The ultra-low loss large mode field optical fiber side pumping beam combiner is characterized by being manufactured by the manufacturing method of any one of claims 1 to 9.

The invention has the following beneficial effects:

the optical fiber at the fusion joint part is properly thinned in the optical fiber bundle fusion process, and the micro deformation of a machine, a clamp, gravity and thermal stress factors on the large-mode-field optical fiber is weakened under the action of a stretching force, so that the distortion degree of a base mode signal is reduced as much as possible when the base mode signal passes through the fusion zone, the insertion loss of the base mode signal during the manufacture of a large-mode-field optical fiber device can be effectively controlled, the comprehensive performance of the device is greatly improved, the signal output power and the beam quality of a laser are further improved, the performance, the reliability and the stability of a laser product are improved, and the industrial production efficiency is improved; the two ends of the large-mode-field signal optical fiber are respectively connected into the signal light source and the power meter before the optical fiber bundle is fused, so that the signal loss degree of the large-mode-field optical fiber can be tested, the change condition of the optical fiber signal passing through a fused area can be observed in real time in the fusing and stretching processes, and the quality of fused stretching is ensured; the pump optical fiber and the large-mode-field signal optical fiber are fixed by the adhesive tape after being jointed, so that the pump optical fiber and the large-mode-field signal optical fiber are effectively and tightly jointed together, the relative position between the pump optical fiber and the large-mode-field signal optical fiber is kept stable, the pump optical fiber and the large-mode-field signal optical fiber cannot shift, and the quality of the fused and stretched optical fiber is higher and; the two clamps which are symmetrically arranged are used for respectively clamping two ends of the attaching area in the optical fiber bundle, so that the relative position between the two clamps is further ensured not to move, the optical fiber bundle is stretched in a mode that the two clamps respectively move and separate slowly in opposite directions, the optical fiber bundle is stretched to form a straight line, and the problem that the optical fiber is deformed due to dislocation in the stretching process is solved; in addition, the invention controls the melting heating for 100-500s and then slowly stretches the optical fiber bundle, ensures that the cladding region is integrally molten, and avoids the problem that the surface of the cladding is molten and the center of the cladding is solid due to insufficient melting heating time, so that the optical fiber bundle is broken during stretching.

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention:

FIG. 1 is a schematic diagram of a large mode field signal fiber connected to a monitoring optical path in an embodiment;

FIG. 2 is a schematic view of two symmetrically arranged clamps according to an embodiment;

FIG. 3 is a schematic diagram illustrating an embodiment of attaching a pump fiber to two sides of a large mode field signal fiber;

FIG. 4 is a schematic diagram of the optical fiber bundle after fusion-drawing in the example.

The optical fiber clamp comprises a clamp 1, a clamp 11, a first clamping opening, a clamp 12, a second clamping opening, a pump optical fiber 2 and a large mode field signal optical fiber 3.

Detailed Description

For a fuller understanding of the technical content of the present invention, reference should be made to the following detailed description taken together with the accompanying drawings.

In order to explain the feasibility of the inventive concept, the technical contents, the achieved objects and the effects of the invention are combined for explanation.