Square fiber core optical fiber and manufacturing process thereof

Abstract

The invention discloses a manufacturing process of an optical fiber with a square fiber core. The manufacturing process comprises the following steps: S1, manufacturing an outer-layer prefabricated rod with an inner square hole; s2, inner square hole butt joint is conducted through a cross laser butt joint positioning method; s3, polishing the square inner-layer preform; s4, combining the outer-layer prefabricated rod with the inner-layer prefabricated rod, and vacuumizing a gap between the outer-layer prefabricated rod and the inner-layer prefabricated rod; and S5, performing optical fiber drawing by using a multi-section temperature control method and a gradient cooling method, forming a square hole suitable for the square fiber core in the outer-layer preform, reducing a gap between the inner layer and the outer layer, vacuumizing the gap to avoid bubbles, and reducing the chamfer of the square fiber core so as to reduce excessive deformation of the outer layer, thereby ensuring the homogenization effect and improving the quality of the optical fiber. And the out-of-roundness of the optical fiber outer cladding is controlled. The square fiber core optical fiber manufacturing process provided by the invention has the effect of manufacturing the high-performance square fiber core optical fiber.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber production, and in particular to a square core optical fiber and a manufacturing process thereof. Background Art

[0002] Traditional optical fibers usually use a circular core structure, which has certain limitations in the process of light transmission, especially in high-power transmission and special optical applications, where circular core fibers are prone to mode distortion and energy loss. In recent years, with the rapid development of optical fiber communications and laser technology, higher requirements have been placed on the performance of optical fibers, especially in high-power transmission, beam shaping and special optical systems, where traditional circular core fibers can no longer meet the requirements.

[0003] As a new type of optical fiber structure, square core quartz fiber has unique optical properties, which can effectively improve the quality of beam transmission, reduce mode distortion, and improve energy transmission efficiency. Square core fiber has a unique spot homogenization perturbation characteristic. After inputting Gaussian distributed laser, it can obtain a flat-top spot with uniform energy distribution after passing through square / rectangular / octagonal optical fiber. It is currently widely used in laser processing, astronomical observation, biological analysis and other applications.

[0004] The existing square core quartz optical fiber preparation process is complex, the cost is high, and there are certain limitations in practical applications. The existing technical solution usually adopts preform rod sleeve drawing. The preform rod is a set of square pure quartz fiber core preform rod and round fluorine-doped quartz sleeve, which is drawn on the fiber drawing tower. It has the following problems: 1. The chamfer of the square fiber core is too large, the fluorine-doped layer is severely deformed, and the homogenization effect is poor; 2. There are bubbles and gaps between the fiber core and the cladding; 3. The outer cladding of the optical fiber is out of roundness, which affects the fiber fusion alignment. Summary of the invention

[0005] In view of the above problems, a square core optical fiber and a manufacturing process thereof are now provided, aiming to solve the problems existing in the prior art.

[0006] The specific technical solutions are as follows:

[0007] A square core optical fiber and a manufacturing process thereof, comprising the following steps:

[0008] S1, manufacturing an outer preform rod with an inner square hole;

[0009] S2, using the cross laser docking positioning method to dock the inner square hole;

[0010] S3, grinding the square inner preform rod;

[0011] S4, combining the outer preform rod and the inner preform rod, and evacuating the gap between the outer preform rod and the inner preform rod;

[0012] S5. Utilize multi-stage temperature control method and gradient cooling method to perform optical fiber drawing.

[0013] The square core optical fiber and the manufacturing process thereof also have the following characteristics: the step S1 further comprises the following steps:

[0014] S11, drilling holes in the fluorine-doped quartz preform by using a CNC machine tool;

[0015] S12, using laser to chamfer the square hole of the fluorine-doped quartz preform rod.

[0016] The above-mentioned square core optical fiber manufacturing process also has the following characteristics: the cross laser docking positioning method recorded in step S2 is: two pairs of orthogonally distributed laser beams are projected onto the outer wall of the quartz rod and the side wall of the inner square hole respectively, and the laser spot displacement is captured in real time through the PSD sensor array. Based on the spot displacement data, the chuck deflection angle at both ends of the rod bed is corrected in real time through PID closed-loop control to ensure that the docking deflection of the square inner hole is less than 0.1°, and annealing treatment is performed after docking.

[0017] The above-mentioned square core optical fiber manufacturing process also has the following characteristics: the step S3 also includes grinding the core preform rod into a square column by flat grinding processing technology, and after polishing, the surface roughness Ra≤0.1μm.

[0018] The above-mentioned square core optical fiber manufacturing process also has the following characteristics: step S4 also includes placing the combined inner preform rod and outer preform rod into a vertical casing machine for casing, and evacuating the gap between the outer preform rod and the inner preform rod to -0.1 MPa to ensure that no bubbles are generated in the gap during the fusion process.

[0019] The above-mentioned square core optical fiber manufacturing process also has the following characteristics: the multi-stage temperature control method in step S5 includes dividing the drawing furnace into three independent temperature zones, wherein the upper temperature zone is 1900-2000°C, the middle temperature zone is 1800-1900°C, and the lower temperature zone is 1700-1800°C. By adjusting the temperature of each temperature zone, the viscosity ratio of the inner preform rod and the outer preform rod is controlled to suppress interface stress concentration and rounding.

[0020] The above-mentioned square core optical fiber manufacturing process also has the following characteristics: the gradient cooling method in step S5 includes that after the optical fiber comes out of the furnace mouth, it passes through the annealing tube, and the temperature of different areas of the annealing tube is controlled to cool the optical fiber in multiple stages to reduce the stress in the core and cladding areas. The annealing tube is divided into multiple cooling zones, the temperature of the first cooling zone is 800-1000°C, and forced convection cooling is performed by inert gas to quickly shape the core. The temperature of the second cooling zone is 300-500°C, and radiation cooling is combined with low-speed nitrogen flow at a rate of 10-20°C / s to release interface stress. The temperature of the third cooling zone is room temperature, and the annealing tube is equipped with heat dissipation fins to fully exchange heat with the indoor air to ensure that the optical fiber shrinks uniformly as a whole.

[0021] A square core optical fiber comprises a core layer and a cladding layer, wherein the core layer is made of high-purity quartz, the cladding layer is made of low-refractive-index quartz, the cladding layer surrounds the outer periphery of the core layer, and a gradient refractive-index layer is used as a transition between the core layer and the cladding layer.

[0022] The square core optical fiber mentioned above also has the following characteristics: the core layer is a square with a side length of 100-1000 microns, the thickness of the cladding layer is 200-2000 microns, and the thickness of the gradient refractive index layer is 1-10 microns.

[0023] In summary, the beneficial effects of this scheme are:

[0024] In the square core optical fiber manufacturing process provided by the present invention, a square hole suitable for the square core is opened in the outer preform rod to reduce the gap between the inner and outer layers, and the gap is evacuated to avoid the presence of bubbles, and the chamfer of the square core is reduced to reduce excessive deformation of the outer layer, and the non-circularity of the outer cladding of the optical fiber is controlled while ensuring the homogenization effect. The square core optical fiber manufacturing process provided by the present invention has the effect of manufacturing high-performance square core optical fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of the square core optical fiber manufacturing process of the present invention;

[0026] Figure 2 It is a schematic diagram of the cross section of a square core optical fiber of the present invention;

[0027] Figure 3 It is a schematic diagram of the cross section of an existing square core optical fiber;

[0028] Figure 4 It is a structural schematic diagram of a cross laser docking positioning device in the square core optical fiber manufacturing process of the present invention;

[0029] Figure 5 It is a structural schematic diagram of a multi-stage temperature control device in the square core optical fiber manufacturing process of the present invention;

[0030] Figure 6 It is a schematic structural diagram of a gradient cooling device in the square core optical fiber manufacturing process of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0033] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0034] Figure 1 is a flow chart of the square core optical fiber manufacturing process of the present invention, as shown in Figure 1 As shown, the square core optical fiber and the manufacturing process thereof provided in this embodiment include the following steps:

[0035] S1, manufacturing an outer preform rod with an inner square hole;

[0036] S2, using the cross laser docking positioning method to dock the inner square hole;

[0037] S3, grinding the square inner preform rod;

[0038] S4, combining the outer preform rod and the inner preform rod, and evacuating the gap between the outer preform rod and the inner preform rod;

[0039] S5. Utilize multi-stage temperature control method and gradient cooling method to perform optical fiber drawing.

[0040] In the above embodiment, step S1 further includes the following steps:

[0041] S11, drilling holes in the fluorine-doped quartz preform by using a CNC machine tool;

[0042] S12, using laser to chamfer the square hole of the fluorine-doped quartz preform rod.

[0043] It should be noted that the fluorine-doped quartz preform rod is drilled using a high-precision CNC machine tool. The outer diameter of the quartz tube is 40 mm, the side length of the inner square hole is 20+0.02 mm, the maximum depth can reach 150 mm, and the inner wall is polished with hydrofluoric acid to Ra≤0.1μm.

[0044] It should also be noted that due to the limited size of CNC machine tool tools, the limit is 150mm, so the length of a single processed outer preform rod is limited. In order to improve wire drawing efficiency and reduce material waste, it is necessary to connect multiple punched outer preform rods.

[0045] It should also be noted that the chamfer of the square hole processed by the CNC machine tool is limited by the tool, generally >2mm, and cannot meet the design requirements of the preform rod. It is necessary to use ultrafast laser (wavelength range: 1030-1064nm, pulse width ≤10ps, repetition frequency 10kHz-1MHz) to trim the chamfer. The trimming process is: fix the quartz square tube on the three-dimensional motion platform, locate the inner edge through the coaxial vision system, set the spiral scanning path, the scanning speed is 200mm / s, the defocus is -0.2mm (the focus is inside the material), and the layered processing is carried out. The depth of each layer is 5μm, and a total of 50 layers are processed. Four chamfers are trimmed, and compressed air is introduced during the correction process to remove debris.

[0046] like Figure 4 As shown, in the above embodiment, the cross laser docking positioning method recorded in step S2 is: two pairs of orthogonally distributed laser beams are projected onto the outer wall of the quartz rod and the side wall of the inner square hole respectively, and the laser spot displacement is captured in real time through the PSD sensor array. Based on the spot displacement data, the chuck deflection angles at both ends of the rod bed are corrected in real time through PID closed-loop control to ensure that the docking deflection of the square inner hole is less than 0.1°, and annealing is performed after docking.

[0047] It should be noted that the wavelength of the laser beam is 635 nm and the power is <5 mW.

[0048] It should also be noted that during the annealing process, the outer preform rod is annealed at 1200°C for 2 hours to eliminate processing stress and solve the problem of brittle cracking of the square structure.

[0049] In the above embodiment, step S3 also includes grinding the fiber core preform rod into a square column by flat grinding technology, and after polishing, the surface roughness Ra≤0.1μm.

[0050] In the above embodiment, step S4 also includes placing the combined inner preform rod and the outer preform rod into a vertical casing machine for casing, and evacuating the gap between the outer preform rod and the inner preform rod to -0.1MPa to ensure that no bubbles are generated in the gap during the fusion process.

[0051] like Figure 6As shown, in the above embodiment, the multi-stage temperature control method in step S5 includes dividing the wire drawing furnace into three independent temperature zones, wherein the upper temperature zone is 1900-2000°C, the middle temperature zone is 1800-1900°C, and the lower temperature zone is 1700-1800°C. By adjusting the temperature of each temperature zone, the viscosity ratio of the inner preform rod and the outer preform rod is controlled to suppress interface stress concentration and rounding.

[0052] like Figure 5 As shown, in the above embodiment, the gradient cooling method in step S5 includes that after the optical fiber comes out of the furnace mouth, it passes through the annealing tube, and the temperature of different areas of the annealing tube is controlled to cool the optical fiber in multiple stages to reduce the stress in the core and cladding areas. The annealing tube is divided into multiple cooling zones, the temperature of the first cooling zone is 800-1000°C, and forced convection cooling is performed by inert gas to quickly shape the core. The temperature of the second cooling zone is 300-500°C, and radiation cooling is combined with low-speed nitrogen flow at a rate of 10-20°C / s to release interface stress. The temperature of the third cooling zone is room temperature, and the annealing tube is equipped with heat dissipation fins to fully exchange heat with the indoor air to ensure that the optical fiber shrinks uniformly as a whole.

[0053] It should be noted that the annealing tube is 3 meters long. By controlling the temperature of different areas of the annealing tube, the optical fiber is cooled in multiple stages to reduce the stress in the core and cladding areas.

[0054] like Figure 2 As shown, a square core optical fiber includes a core layer and a cladding layer. The core layer material is high-purity quartz, the cladding material is low-refractive-index quartz, the cladding layer surrounds the outer periphery of the core layer, and the core layer and the cladding layer are transitioned by a gradient refractive-index layer.

[0055] In the above embodiment, the core layer is a square with a side length of 100-1000 microns, the thickness of the cladding layer is 200-2000 microns, and the thickness of the gradient refractive index layer is 1-10 microns.

[0056] like Figure 3 As shown, the square-core fluorine-doped optical fiber in the prior art will produce anisotropy of shrinkage during the shrinkage process due to internal resistance and unevenness, resulting in a large non-roundness of the outer cladding, and the core and cladding preform rods are not tightly fitted, with a large gap, resulting in microbubbles between the optical fiber core and the cladding.

[0057] Working principle: Since the square hole obtained by CNC machine tool drilling cannot meet the design requirements, the square hole is corrected by laser to obtain a precise square hole, and multiple outer preform rods are docked. The cross laser docking positioning method is used for multi-segment docking, so that the length of the outer preform rod meets the requirement and the output of a single preform rod is improved. At the same time, the inner preform rod is processed by flat grinding technology to obtain a precise square rod, and the square rod is polished. When the inner preform rod is combined with the outer preform rod, the tolerance between the two is less than 0.05mm. The whole combination is vacuumed to effectively ensure that no bubbles are generated during the fusion process. Finally, the whole combination is subjected to multi-segment temperature-controlled heating and drawing, and the obtained optical fiber is gradient cooled to suppress interface stress concentration and rounding, avoid core crystallization or microcracks, and ensure the transmission performance of the optical fiber.

[0058] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A square core optical fiber manufacturing process, characterized in that: The following steps are involved: S1, manufacturing an outer preform rod with an inner square hole; S2, using the cross laser docking positioning method to dock the inner square hole; S3, grinding the square inner preform rod; S4, combining the outer preform rod and the inner preform rod, and evacuating the gap between the outer preform rod and the inner preform rod; S5. Utilize multi-stage temperature control method and gradient cooling method to perform optical fiber drawing.

2. A square core optical fiber manufacturing process according to claim 1, characterized in that: The step S1 also includes the following steps: S11, drilling holes in the fluorine-doped quartz preform by using a CNC machine tool; S12, using laser to chamfer the square hole of the fluorine-doped quartz preform rod.

3. A square core optical fiber manufacturing process according to claim 1, characterized in that: The cross laser docking positioning method described in step S2 is as follows: two pairs of orthogonally distributed laser beams are projected onto the outer wall of the quartz rod and the side wall of the inner square hole respectively, and the laser spot displacement is captured in real time through the PSD sensor array. Based on the spot displacement data, the chuck deflection angles at both ends of the rod bed are corrected in real time through PID closed-loop control to ensure that the docking deflection of the square inner hole is less than 0.1°, and annealing treatment is performed after docking.

4. A square core optical fiber manufacturing process according to claim 1, characterized in that: The step S3 also includes grinding the fiber core preform rod into a square column by flat grinding technology, and after polishing, the surface roughness Ra≤0.1μm.

5. A square core optical fiber manufacturing process according to claim 1, characterized in that: The step S4 also includes placing the combined inner preform rod and the outer preform rod into a vertical casing machine for casing, and evacuating the gap between the outer preform rod and the inner preform rod to -0.1 MPa to ensure that no bubbles are generated in the gap during the fusion process.

6. A square core optical fiber manufacturing process according to claim 1, characterized in that: The multi-stage temperature control method in step S5 includes dividing the wire drawing furnace into three independent temperature zones, wherein the upper temperature zone is 1900-2000°C, the middle temperature zone is 1800-1900°C, and the lower temperature zone is 1700-1800°C. By adjusting the temperature of each temperature zone, the viscosity ratio of the inner preform rod and the outer preform rod is controlled to suppress interface stress concentration and rounding.

7. A square core optical fiber manufacturing process according to claim 1, characterized in that: The gradient cooling method in step S5 includes that after the optical fiber comes out of the furnace mouth, it passes through the annealing tube, and the temperature of different areas of the annealing tube is controlled to cool the optical fiber in multiple stages to reduce the stress in the core and cladding areas. The annealing tube is divided into multiple cooling zones. The temperature of the first cooling zone is 800-1000°C, and forced convection cooling is performed by inert gas to quickly shape the core. The temperature of the second cooling zone is 300-500°C, and radiation cooling is combined with low-speed nitrogen flow at a rate of 10-20°C / s to release interface stress. The temperature of the third cooling zone is room temperature, and the annealing tube is equipped with heat dissipation fins to fully exchange heat with the indoor air to ensure that the optical fiber shrinks uniformly as a whole.

8. A square core optical fiber manufactured using the process of any one of claims 1 to 7, characterized in that: It comprises a core layer and a cladding layer, wherein the core layer is made of high-purity quartz, the cladding layer is made of low-refractive-index quartz, the cladding layer surrounds the outer periphery of the core layer, and a gradient refractive-index layer is used as a transition between the core layer and the cladding layer.

9. A square core optical fiber according to claim 8, characterized in that: The core layer is a square with a side length of 100-1000 microns, the cladding layer has a thickness of 200-2000 microns, and the gradient refractive index layer has a thickness of 1-10 microns.

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