A quartz-type low-crosstalk image-transmitting optical fiber and its preparation method

Abstract

The present invention belongs to the technical field of optical fibers, and discloses a quartz-type low-crosstalk image-transmitting optical fiber and a preparation method thereof. First, the pure silica layer of the first high-NA core rod is etched, and the etched core rod is placed in a fluorine-doped glass sleeve and fused and drawn to obtain a second high-NA core rod with a numerical aperture of 0.40-0.45; then the second high-NA core rod is drawn to obtain a single-core capillary rod; a plurality of single-core capillary rods are stacked in a first pure silica outer sleeve to obtain a multifilament preform, and the multifilament preform is drawn to obtain a multifilament capillary rod; the pure silica cladding of the multifilament capillary rod is partially etched to obtain an etched multifilament capillary rod; finally, a plurality of etched multifilament capillary rods are stacked in a second pure silica outer sleeve to obtain an image-transmitting optical fiber preform, and the image-transmitting optical fiber preform is drawn to obtain a quartz-type low-crosstalk image-transmitting optical fiber. The present invention can increase the NA values of the core rod and the image-transmitting optical fiber and reduce the crosstalk between the fiber cores.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fibers, and more specifically, relates to a quartz-type low-crosstalk image transmission optical fiber and a preparation method thereof. Background Art

[0002] An image transmission optical fiber, also known as an imaging optical fiber, a multi-core image transmission bundle, or an optical fiber image transmission bundle, is a passive optical fiber image transmission device. Passive optical fiber image transmission devices are mainly of two types. One is a rigid optical fiber faceplate; the other is a flexible optical fiber image transmission bundle, which also includes a semi-flexible pure silica multi-core type image transmission optical fiber. The pure silica type image transmission optical fiber has the advantages of small volume, light weight, high temperature resistance, electromagnetic interference resistance, certain flexibility, and a relatively flexible image transmission process, and thus is widely used in fields such as endoscopes. Three particularly important indicators for characterizing the performance of an image transmission optical fiber are the numerical aperture, transmittance, and resolution. The numerical aperture of an image transmission optical fiber is the same as that of a single optical fiber filament, and its size indicates the strength of the light-gathering ability of the image transmission optical fiber; the transmittance is an important indicator for characterizing the light-transmitting performance of the image transmission optical fiber, and a high transmittance indicates good light transmittance; the resolution is a parameter for characterizing the image transmission quality of the image transmission optical fiber, which refers to the minimum distance between two point images in space that the image transmission optical fiber can distinguish, and is usually expressed by the logarithm of the line distance that can be distinguished per millimeter (lp / mm). The higher the resolution, the better the transmission quality and the higher the clarity. In addition, the crosstalk rate of the optical fiber is also one of the factors affecting the image transmission quality of the image transmission optical fiber, and how to optimize the crosstalk between optical fiber cores has always attracted the attention of many researchers.

[0003] Traditional image transmission optical fibers are bundle-type optical fiber image transmission bundles made of multi-component glass materials. Thousands or even tens of thousands of multi-component glass single filaments with a certain length and a diameter of several micrometers are glued and positioned at both ends so that the fiber pixels arranged accordingly are relatively positioned, while most of the length of the optical fiber bundle in the middle is in a free and loose state to have flexibility. The image transmission optical fiber prepared in this way has certain disadvantages, such as glue joints, complex processes, high manufacturing difficulty, high cost, and large absorption loss. Quartz-type image transmission optical fibers are formed by neatly arranging thousands of quartz optical fibers in a pure silica sleeve and heating and melting them into one body to form a single quartz-type image transmission optical fiber. The image transmission optical fiber prepared in this way has the advantages of high resolution, long drawing length, and low cost. Compared with multi-component glass image transmission optical fiber bundles, quartz-type image transmission optical fibers have the following advantages: 1) It is possible to prepare image transmission optical fibers with ultra-fine diameters, which are more suitable for the application of medical endoscopes, especially in parts such as the pancreaticobiliary duct and bronchus; 2) Excellent optical transmission performance and higher image quality; 3) Higher resolution; 4) It is possible to achieve long-distance optical transmission; 5) High chemical stability and high mechanical durability; 6) It has a broader application prospect in fields such as medical treatment, industry, and national defense and military industry.

[0004] However, the method of preparing a high numerical aperture (NA) core rod in a traditional pure silica doping system has its upper limit, and it is difficult to reach or exceed 0.4. How to further break through this upper limit to achieve a higher numerical aperture has become the main technical problem. Summary of the Invention

[0005] The present invention provides a quartz-type low-crosstalk image transmission optical fiber and a preparation method thereof, which solve the problems in the prior art that the upper limit of the NA value of the image transmission optical fiber is difficult to break through and the crosstalk between cores needs to be further reduced.

[0006] In a first aspect, the present invention provides a preparation method of a quartz-type low-crosstalk image transmission optical fiber, including the following steps:

[0007] Step 1: Corrode the pure silica layer of the first high-NA core rod, and place the corroded core rod in a fluorine-doped glass sleeve for melting and shrinking to obtain a second high-NA core rod;

[0008] Wherein, the first high-NA core rod is a core rod prepared by the PCVD process. The first high-NA core rod sequentially includes a core layer of pure silica doped with germanium, a depressed layer of pure silica doped with fluorine, and the pure silica layer as a cladding from the inside to the outside. The numerical aperture of the first high-NA core rod ranges from 0.20 to 0.35; the second high-NA core rod sequentially includes a core layer of pure silica doped with germanium, a depressed layer of pure silica doped with fluorine, and the fluorine-doped glass sleeve as a cladding from the inside to the outside. The numerical aperture of the second high-NA core rod ranges from 0.40 to 0.45;

[0009] Step 2: Draw the second high-NA core rod to obtain a single-core capillary rod;

[0010] Step 3: Stack a plurality of the single-core capillary rods in a first pure silica outer sleeve to obtain a multi-filament preform; draw the multi-filament preform to obtain a multi-filament capillary rod;

[0011] Step 4: Partially corrode the pure silica cladding of the multi-filament capillary rod to obtain a corroded multi-filament capillary rod;

[0012] Step 5: Stack a plurality of the corroded multi-filament capillary rods in a second pure silica outer sleeve to obtain an image transmission optical fiber preform; draw the image transmission optical fiber preform to obtain a quartz-type low-crosstalk image transmission optical fiber.

[0013] Preferably, in Step 1, the core layer of pure silica doped with germanium in the second high-NA core rod has a positive relative refractive index, and the range of the positive relative refractive index difference is +0.5% to +3.5%; the fluorine-doped glass sleeve in the second high-NA core rod has a negative relative refractive index, and the range of the negative relative refractive index difference is -2.0% to -0.2%.

[0014] Preferably, in the step 2, the diameter of the obtained single-core capillary rod ranges from 1.2 mm to 2.6 mm, and the length ranges from 800 mm to 1200 mm; in the step 3, the diameter of the obtained multi-filament capillary rod ranges from 1.5 mm to 3.5 mm, and the length ranges from 700 mm to 1000 mm; in the step 4, the thickness of the pure silica cladding of the obtained multi-filament capillary rod after corrosion ranges from 20 um to 200 um.

[0015] Preferably, in the step 3, the ratio of the inner diameter to the outer diameter of the first pure silica outer tube ranges from 0.30 to 0.85; in the step 5, the ratio of the inner diameter to the outer diameter of the second pure silica outer tube ranges from 0.30 to 0.85.

[0016] Preferably, in the step 5, the ratio of the diameter of a single core to the core pitch in the obtained quartz type low crosstalk image transmission fiber ranges from 0.45 to 0.85.

[0017] Preferably, in the step 5, the ratio of the image transmission surface diameter to the cladding diameter of the obtained quartz type low crosstalk image transmission fiber ranges from 0.50 to 0.95.

[0018] Preferably, in the step 5, the resolution of the obtained quartz type low crosstalk image transmission fiber ranges from 100 lp / mm to 250 lp / mm.

[0019] Preferably, in the step 5, the transmittance of the obtained quartz type low crosstalk image transmission fiber is greater than 50% / m.

[0020] Preferably, the quartz type low crosstalk image transmission fiber further includes a coating layer, and the thickness of the coating layer ranges from 20 um to 200 um.

[0021] In a second aspect, this aspect provides a quartz type low crosstalk image transmission fiber, which is prepared by using the above-mentioned preparation method of the quartz type low crosstalk image transmission fiber.

[0022] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0023] In the present invention, the mandrel preform (i.e., the second high-NA mandrel) has a core layer - depressed layer - cladding structure. The core layer is made of pure silica doped with germanium to achieve a high refractive index. The depressed layer is made of pure silica doped with fluorine. The cladding uses a fluorine-doped glass sleeve to achieve a lower refractive index cladding. Through the above design, the mandrel has a higher NA, which can break through the upper limit of the NA value of the mandrel prepared by the traditional pure silica doping system. The higher NA value can effectively suppress the mutual coupling between the cores. Therefore, the present invention can reduce the crosstalk between the cores and obtain a clearer transmission image. In addition, the mandrel preform of the present invention is prepared by combining the PCVD (Plasma Chemical Vapor Deposition) technology and the in-tube mandrel collapsing technology. First, a conventional high-NA mandrel is prepared by PCVD. The core layer has a high germanium doping content, and the depressed layer is doped with fluorine to prevent light leakage from the core layer and thus reduce the crosstalk between the cores. Then, after removing the pure silica layer of this preform by corrosion, it is combined with a fluorine-doped glass sleeve and assembled, and then melted and solidified into a mandrel preform by in-tube mandrel collapsing. Compared with the case where doping by FCVD (Flame Vapor Deposition Method) may result in the doping elements not being incorporated when the doping amount is large and not reaching the pre-designed state, the present invention can ensure that the doping elements are effectively incorporated and meet the preset requirements by using the PCVD technology. The present invention can avoid the situation of mandrel cracking caused by mechanical external forces when preparing the preform by mechanical processing in some existing preparation methods through corrosion, which can effectively improve the yield. Moreover, in the present invention, the core layer and the cladding are prepared separately first, and it is easier to obtain a core layer with a larger refractive index and a cladding with a lower refractive index. After combination, a mandrel preform with a larger refractive index difference is obtained, that is, a larger numerical aperture. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flowchart for preparing a quartz-type low-crosstalk image transmission optical fiber provided by an embodiment of the present invention;

[0025] Figure 2 is a schematic diagram of the refractive index profile of the second high-NA mandrel;

[0026] Figure 3 is a schematic diagram of the end face of the multifilament preform;

[0027] Figure 4 is a schematic diagram of the end face of the corroded multifilament capillary rod;

[0028] Figure 5 is a schematic diagram of the end face of the image transmission optical fiber preform. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in conjunction with the accompanying drawings of the specification and specific embodiments.

[0030] This embodiment provides a method for preparing a quartz-type low-crosstalk image transmission optical fiber. Refer toFigure 1 , including the following steps:

[0031] Step 1, melt and shrink the core inside the tube.

[0032] Etch the pure silica layer of the first high-NA core, place the etched core in a fluorine-doped glass sleeve and melt and shrink it to obtain a second high-NA core.

[0033] Specifically, the first high-NA core is a core prepared by the PCVD process. The first high-NA core includes, from the inside to the outside, a core layer of pure silica doped with germanium, a depressed layer of pure silica doped with fluorine, and the pure silica layer as the cladding. The numerical aperture of the first high-NA core ranges from 0.20 to 0.35. See Figure 2 , the second high-NA core includes, from the inside to the outside, a core layer of pure silica doped with germanium ( Figure 2 where a in Figure 2 is the core layer radius), a depressed layer of pure silica doped with fluorine ( Figure 2 where b in

[0034] is the depressed layer radius) and the fluorine-doped glass sleeve as the cladding (

[0035] where c in

[0036] is the cladding radius), that is, the core rod structure is three-layer coaxial: core layer - depressed layer - cladding; the numerical aperture of the second high-NA core ranges from 0.40 to 0.45.

[0037] The relative refractive index range of the depressed layer is -2.2% to -0.4%. The depressed layer is used to prevent light leakage from the core layer and reduce crosstalk between cores. The ratio of the core layer to the cladding, i.e., the core-cladding ratio (a / c), ranges from 0.45 to 0.85, and the ratio of the depressed layer to the core layer ranges from 0.05 to 0.50.

[0037] That is, in step 1 of the present invention, the outer pure silica layer of the conventional high numerical aperture core rod prepared by the PCVD technology is etched, and the etching degree is precisely controlled. Then, the etched core rod is placed in a fluorine-doped glass sleeve, and a core rod preform with a high NA (0.40 ≤ NA ≤ 0.45) is prepared by the core rod collapsing technology inside the tube.

[0038] Step 2: Prepare a single-core capillary rod.

[0039] The second high-NA core rod is drawn to obtain a single-core capillary rod.

[0040] Specifically, the above-mentioned core rod preform is made into equal-length single-core capillary rods with the same diameter, and the numerical aperture is greater than or equal to 0.40; the diameter of the single-core capillary rod ranges from 1.2 mm to 2.6 mm, and the length ranges from 800 mm to 1200 mm.

[0041] For example, the second high-NA core is drawn on a wire drawing tower into a single-core capillary rod with a diameter of 2.5 mm and a length of 1200 mm, and then cleaned and dried.

[0042] Step 3: Prepare a multi-filament preform and a multi-filament capillary rod.

[0043] See Figure 3 , stack a number of the single-core capillary rods 1 in the first pure silica outer sleeve 2 to obtain a multi-filament preform; draw the multi-filament preform to obtain a multi-filament capillary rod.

[0044] Specifically, the above-mentioned single-core capillary rods are randomly arranged in a certain number in a pure silica outer sleeve with a certain inner diameter, and are fixed inside the sleeve to prepare a multi-filament preform. The ratio of the outer diameter to the inner diameter of the pure silica outer sleeve ranges from 0.30 to 0.85; during the stacking process, the pure silica outer sleeve is placed horizontally, and the single-core capillary rods naturally form a tight stack under the action of gravity.

[0045] The above-mentioned multi-filament preform is made into multi-filament capillary rods with the same diameter and equal length. The diameter of the multi-filament capillary rod ranges from 1.5 mm to 3.5 mm, and the length ranges from 700 mm to 1000 mm.

[0046] For example, the above-mentioned cleaned and dried single-core capillary rods are stacked in a pure silica outer sleeve with an inner diameter of 29 mm and a wall thickness of 8 mm until the entire inner diameter of the outer sleeve is filled. At this time, the number of single-core capillary rods filled is about 100 - 110. When filling, the outer sleeve is placed horizontally, and the single-core capillary rods naturally form a tight stack under the action of gravity. The single-core capillary rods are fixed in the outer sleeve without relative sliding, and finally a fixed multi-filament preform is obtained. Then, the above-mentioned multi-filament preform is drawn on a wire drawing tower into a multi-filament capillary rod with a diameter of 2.9 mm and a length of 1000 mm.

[0047] Step 4: Etch the multi-filament capillary rod.

[0048] Partially etch the pure silica cladding of the multi-filament capillary rod to obtain the etched multi-filament capillary rod 3, as shown in Figure 4 .

[0049] Specifically, etch the pure silica cladding of the multi-filament capillary rod by the etching method, and precisely control the etching degree to a suitable thickness, and the value range of the thickness is 20um to 200um.

[0050] For example, etch away part of the pure silica cladding of the above multi-filament capillary rod. The diameter of the etched multi-filament capillary rod is 1.90 - 1.95mm, and then wash and dry the etched multi-filament capillary rod.

[0051] Step 5: Prepare the image transmission fiber preform and the image transmission fiber.

[0052] As shown in Figure 5 , stack a number of the etched multi-filament capillary rods 3 in the second pure silica outer tube 4 to obtain the image transmission fiber preform; draw the image transmission fiber preform to obtain a quartz-type low-crosstalk image transmission fiber.

[0053] Specifically, randomly arrange the etched multi-filament capillary rods in a certain number in a pure silica outer tube with a certain inner diameter, and fix them inside the tube to prepare the image transmission fiber preform. The value range of the ratio of the outer diameter to the inner diameter of the pure silica outer tube is 0.30 - 0.85.

[0054] Draw the above image transmission fiber preform to obtain the image transmission fiber. In the obtained quartz-type low-crosstalk image transmission fiber, the value range of the ratio of the diameter of a single core to the core pitch is 0.45 - 0.85, the value range of the ratio of the image transmission surface diameter to the cladding diameter is 0.50 - 0.95, the resolution range is 100lp / mm - 250lp / mm, and the transmittance is greater than 50% / m.

[0055] The image transmission surface in the fiber is composed of independent cores, and the number of cores ranges from ten thousand to several hundred thousand. The number of cores of the quartz-type image transmission fiber can be adjusted by the number of capillary rods stacked each time.

[0056] In addition, the quartz-type low-crosstalk image transmission fiber further includes a coating layer, and the thickness of the coating layer is 20um - 200um.

[0057] For example, stack the corroded multifilament capillary rods after the above cleaning and drying inside a pure silica outer sleeve with an inner diameter of 21.5 mm and a wall thickness of 4.75 mm until the entire outer sleeve is filled. At this time, the number of single-core capillary rods filled is approximately 100 to 110. When filling, the outer sleeve is placed horizontally, and the corroded multifilament capillary rods are naturally and tightly stacked under the action of gravity, fixing the corroded multifilament capillary rods in the outer sleeve without relative sliding, and finally obtaining a fixed image transmission optical fiber preform. Draw the above image transmission optical fiber preform into a quartz-type low-crosstalk image transmission optical fiber on a drawing tower, with the number of fiber cores being approximately 10,000 and the outer diameter being approximately 650 μm.

[0058] In summary, the present invention uses a core rod with a high numerical aperture to prepare a single fiber core of an image transmission optical fiber, and the cladding of the image transmission optical fiber is pure silica. The core preform consists of a germanium-doped core layer - a fluorine-doped depressed layer - a fluorine-doped glass sleeve. The single-core capillary rods are randomly arranged and stacked inside the pure silica outer sleeve to form multifilament capillary rods; the corroded multifilament capillary rods are randomly arranged and stacked again inside the pure silica outer sleeve and drawn into an image transmission optical fiber. The present invention can increase the NA values of the core rod and the image transmission optical fiber, reduce the crosstalk between the fiber cores, can better improve the image transmission resolution of the fiber end face, improve the image transmission quality, and is of great significance to the development of fields such as biomedical endoscopes.

[0059] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the examples, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a quartz - type low - crosstalk image - transmitting optical fiber, characterized in that, it comprises the following steps: Step 1: Corrode the pure silica layer of the first high - NA core rod, and place the corroded core rod in a fluorine - doped glass sleeve for collapsing to obtain a second high - NA core rod; Among them, the first high - NA core rod is a core rod prepared by the PCVD process. The first high - NA core rod sequentially includes a core layer of pure silica doped with germanium, a depressed layer of pure silica doped with fluorine, and the pure silica layer as the cladding from the inside to the outside. The numerical aperture of the first high - NA core rod ranges from 0.20 to 0.35; the second high - NA core rod sequentially includes a core layer of pure silica doped with germanium, a depressed layer of pure silica doped with fluorine, and the fluorine - doped glass sleeve as the cladding from the inside to the outside. The numerical aperture of the second high - NA core rod ranges from 0.40 to 0.45; Step 2: Draw the second high - NA core rod to obtain a single - core capillary rod; Step 3: Stack a plurality of the single - core capillary rods in a first pure silica outer sleeve to obtain a multi - filament preform; draw the multi - filament preform to obtain a multi - filament capillary rod; Step 4: Partially corrode the pure silica cladding of the multi - filament capillary rod to obtain a corroded multi - filament capillary rod; Step 5: Stack a plurality of the corroded multi - filament capillary rods in a second pure silica outer sleeve to obtain an image - transmitting optical fiber preform; draw the image - transmitting optical fiber preform to obtain a quartz - type low - crosstalk image - transmitting optical fiber.

2. The method for preparing a quartz - type low - crosstalk image - transmitting optical fiber according to claim 1, characterized in that, in the step 1, the core layer of pure silica doped with germanium in the second high - NA core rod has a positive relative refractive index, and the range of the positive relative refractive index difference is + 0.5% to + 3.5%; the fluorine - doped glass sleeve in the second high - NA core rod has a negative relative refractive index, and the range of the negative relative refractive index difference is - 2.0% to - 0.2%.

3. The method for preparing a quartz - type low - crosstalk image - transmitting optical fiber according to claim 1, characterized in that, in the step 2, the diameter of the obtained single - core capillary rod ranges from 1.2 mm to 2.6 mm, and the length ranges from 800 mm to 1200 mm; in the step 3, the diameter of the obtained multi - filament capillary rod ranges from 1.5 mm to 3.5 mm, and the length ranges from 700 mm to 1000 mm; in the step 4, the thickness of the pure silica cladding of the obtained corroded multi - filament capillary rod ranges from 20 μm to 200 μm.

4. The method for preparing a quartz - type low - crosstalk image - transmitting optical fiber according to claim 1, characterized in that, in the step 3, the ratio of the inner diameter to the outer diameter of the first pure silica outer sleeve ranges from 0.30 to 0.85; in the step 5, the ratio of the inner diameter to the outer diameter of the second pure silica outer sleeve ranges from 0.30 to 0.

85.

5. The method for preparing a quartz - type low - crosstalk image - transmitting optical fiber according to claim 1, characterized in that, In the step 5, the value range of the ratio of the diameter of a single core to the core pitch in the obtained quartz type low crosstalk image transmission optical fiber is 0.45 to 0.

85.

6. The method for preparing a quartz type low crosstalk image transmission optical fiber according to claim 1, characterized in that in the step 5, the value range of the ratio of the image transmission surface diameter to the cladding diameter in the obtained quartz type low crosstalk image transmission optical fiber is 0.50 to 0.

95.

7. The method for preparing a quartz type low crosstalk image transmission optical fiber according to claim 1, characterized in that in the step 5, the resolution range of the obtained quartz type low crosstalk image transmission optical fiber is 100 lp / mm to 250 lp / mm.

8. The method for preparing a quartz type low crosstalk image transmission optical fiber according to claim 1, characterized in that in the step 5, the transmittance of the obtained quartz type low crosstalk image transmission optical fiber is greater than 50% / m.

9. The method for preparing a quartz type low crosstalk image transmission optical fiber according to claim 1, characterized in that the quartz type low crosstalk image transmission optical fiber further includes a coating layer, and the thickness of the coating layer is 20 um to 200 um.

10. A quartz type low crosstalk image transmission optical fiber, characterized in that it is prepared by using the method for preparing a quartz type low crosstalk image transmission optical fiber according to any one of claims 1-9.

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