A low-melting-point image transmission optical fiber, core rod and preparation method thereof

Abstract

This invention relates to a low-melting-point image-transmitting optical fiber, a core rod, and a method for fabricating the same. The fiber comprises an image-transmitting layer and an outer cladding covering the image-transmitting layer. The image-transmitting layer includes a common cladding and an image-transmitting fiber core spaced apart within the common cladding. The image-transmitting fiber core includes a core layer and a transition layer. The core layer is a germanium- and alkali metal-doped quartz glass layer with a power-law gradient refractive index profile. The transition layer is a fluorine- and alkali metal-doped quartz glass layer. The common cladding and outer cladding are fluorine-doped quartz glass layers. This invention not only reduces the drawing temperature and achieves balanced viscosity matching between layers, but also optimizes the optical and material properties of the optical fiber, improving its refractive index, transmittance, and photodetector (NA). By doping and rationally designing the refractive index profile of the image-transmitting fiber core, its image transmission resolution is optimized.

Description

Technical Field

[0001] This invention relates to a low-melting-point optical fiber for image transmission, a core rod, and a method for preparing the same, belonging to the field of optical fiber technology. Background Technology

[0002] Imaging fiber, also known as a transmission fiber, is a passive fiber optic device used in endoscopes. Similar to ordinary communication fibers, its working principle is based on total internal reflection of light. However, unlike ordinary communication fibers, imaging fibers typically operate at visible wavelengths and contain thousands or even tens of thousands of cores within their cladding. In endoscopes, imaging fibers serve as samples; each core acts as a "lens," transmitting signal light from the sample end to the observation end, enabling real-time, high-resolution image transmission. Due to its high resolution, high flexibility, extremely small size, real-time imaging, interference resistance, and relatively low cost, imaging fiber is increasingly used in medical and industrial fields.

[0003] In existing technologies, the drawing of imaging optical fibers requires ultra-high temperatures of up to 2000℃ or even higher. These ultra-high temperatures not only lead to significant energy consumption but also increase the requirements for production equipment and the complexity of the production process, undoubtedly increasing production costs. For example, Chinese patent documents CN111635124A discloses a fabrication process for randomly distributed multi-core imaging optical fibers, and CN111635125A discloses a fabrication method for high duty cycle multi-core microstructure imaging optical fiber bundles. Both use pure quartz glass as raw material, with pure quartz as the fiber core and air as the cladding. Although this eliminates the doping step, the drawing process is relatively complex, and the high softening temperature of pure quartz glass results in high energy consumption during fabrication. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a low melting point image transmission optical fiber, a core rod and its preparation method, which not only has a relatively low drawing temperature, but also optimizes its optical performance.

[0005] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: it includes an image transmission layer and an outer cladding layer covering the image transmission layer. The image transmission layer includes a common cladding layer and image transmission fiber cores spaced apart in the common cladding layer. The image transmission fiber core includes a core layer and a transition layer. The core layer is a quartz glass layer co-doped with germanium and alkali metals. The refractive index profile of the core layer is a power function gradually changing distribution (parabolic). The transition layer is a quartz glass layer co-doped with fluorine and alkali metals. The common cladding layer and the outer cladding layer are fluorine-doped quartz glass layers.

[0006] According to the above scheme, the core layer radius r1 is 0.4 to 1.4 μm, the transition layer radius r2 is 0.5 to 1.5 μm, and satisfies (r2-r1) / r1 = 10 to 25%.

[0007] According to the above scheme, the refractive index distribution index α of the core layer is 2 to 3, and the highest relative refractive index difference (relative to the refractive index of pure silicon dioxide) Δ at the center of the core layer is... 1[max] The relative refractive index difference is 2-3.5%, and the relative refractive index difference at the core edge is 0.

[0008] According to the above scheme, the relative refractive index difference of the transition layer increases with the increase of the radius, and the relative refractive index difference Δ at the lowest point... 2[min] The relative refractive index difference Δ at the highest point is between -1 and -0.2%. 2[max] The range is -0.5% to 0%, and the difference between the highest and lowest relative refractive index difference is 0.2% to 0.5%.

[0009] According to the above scheme, the relative refractive index difference of the transition layer satisfies the condition of the radius. In the formula, Δ2(r) is the relative refractive index difference at the radius r of the transition layer, and k is the slope, which takes the value of r is the radius of the point corresponding to the transition layer, and r1 and r2 are the core radius and the transition layer radius, respectively.

[0010] According to the above scheme, the relative refractive index difference Δ3 of the common cladding is -0.5 to -0.2%; the relative refractive index difference Δ4 of the outer cladding is -0.5 to -0.2%.

[0011] According to the above scheme, the core spacing Λ of the image transmission fiber is 2-5 μm, the radius r3 of the image transmission layer is 50-475 μm, the radius r4 of the outer cladding layer is 75-500 μm, and the ratio of r3 to r4 is 0.4-0.95.

[0012] According to the above scheme, the number of image transmission fiber cores is greater than or equal to 1000.

[0013] According to the above scheme, the alkali metal element is one or more of lithium, sodium, and potassium, and its doping amount is 1000 to 10000 ppm.

[0014] According to the above scheme, in order to reduce the softening temperature of the image transmission fiber, in addition to the core layer, the doping elements in other layers can also be one or more of boron, phosphorus, tellurium, vanadium, barium, copper, etc.

[0015] According to the above scheme, the outer coating layer is covered with a resin coating layer, and the radius r5 of the resin coating layer is 100-600μm.

[0016] According to the above scheme, the NA value of the image transmission fiber is 0.3 to 0.5, the transmittance is 70 to 90%, and the resolution is ≥128 lp / mm.

[0017] The technical solution of the image transmission fiber fabrication method of the present invention is as follows:

[0018] The low-melting-point mandrel is prepared by using a fluorine-doped quartz glass liner as the substrate, and depositing a transition layer and a core layer using a PCVD process. After deposition, the mandrel is melted and shrunk into a low-melting-point mandrel. The mandrel consists of a core layer, a transition layer, and a cladding layer from the inside out.

[0019] Low-melting-point capillary rod drawing: The low-melting-point mandrel is heated and drawn into a low-melting-point capillary rod.

[0020] The low-melting-point image-transmitting fiber preform is prepared by stacking and fixing the low-melting-point capillary rods in a fluorine-doped quartz glass sleeve to obtain the image-transmitting fiber preform.

[0021] Image transmission fiber drawing: The image transmission fiber preform is drawn into a low melting point image transmission fiber.

[0022] According to the above scheme, the ratio of the low melting point mandrel core layer radius R1 to the mandrel radius R3 is 40-60%.

[0023] According to the above scheme, the relative refractive index difference Δ3 of the low melting point core cladding is -0.5 to -0.2%, and the relative refractive index difference Δ4 of the fluorine-doped quartz glass sleeve is the same as Δ3.

[0024] According to the above scheme, the radius of the low-melting-point capillary rod is 0.1-1 mm, and the radius R3 of the low-melting-point core rod cladding is 10-20 mm.

[0025] According to the above scheme, the low melting point core rod, low melting point capillary rod, low melting point image transmission fiber preform and the glass part of the image transmission fiber have a low softening temperature of 1400~1600℃.

[0026] According to the above scheme, the temperature for drawing the image transmission optical fiber preform is 1600-1800℃, and the drawing speed is 100-1000m / min.

[0027] The low-melting-point core rod technology for image transmission optical fiber of the present invention is as follows:

[0028] From the inside out, it includes a core layer, a transition layer, and a cladding layer. The core layer is a quartz glass layer co-doped with germanium and alkali metal, and the refractive index profile of the core layer is a power function-based gradual distribution. The transition layer is a quartz glass layer co-doped with fluorine and alkali metal, and the cladding layer is a fluorine-doped quartz glass layer.

[0029] According to the above scheme, the core layer refractive index distribution index α is 2 to 3, and the highest relative refractive index difference Δ at the center of the core layer is... 1[max] The relative refractive index difference is 2-3.5%, and the relative refractive index difference at the core edge is 0.

[0030] According to the above scheme, the relative refractive index difference of the transition layer increases with the increase of the radius, and the relative refractive index difference Δ at the lowest point... 2[min] The relative refractive index difference Δ at the highest point is between -1 and -0.2%. 2[max] The range is -0.5% to 0%, and the difference between the highest and lowest relative refractive index difference is 0.2% to 0.5%.

[0031] According to the above scheme, the relative refractive index difference Δ3 of the cladding is -0.5 to -0.2%.

[0032] According to the above scheme, the ratio of the core radius R1 to the cladding radius R3 is 40-60%, and the cladding radius R3 is 10-20 mm.

[0033] The beneficial effects of this invention are as follows: 1. By using a low-refractive-index fluorine-doped quartz glass liner as the substrate for preparing a low-melting-point core rod, and doping the core rod with germanium, fluorine, alkali metals, or other doping elements, germanium and fluorine play a role in regulating the glass refractive index, regulating the glass viscosity, and reducing the glass softening temperature; alkali metals, on the one hand, can reduce the absorption of light by the glass, thereby increasing the visible light transmittance, and on the other hand, can regulate the viscosity of the glass, further reducing the glass softening temperature. The drawing temperature is reduced by 200-400℃, achieving energy saving and consumption reduction; 2. Through doping of each layer, not only is the drawing temperature reduced, but the viscosity matching between each layer is also balanced, and the optical and material properties of the optical fiber are optimized, resulting in improved refractive index, transmittance, and NA; 3. By doping and rationally designing the refractive index profile of the image transmission fiber core, the waveguide of the transmitted image signal light is constrained, thereby suppressing crosstalk between cores and optimizing its image transmission resolution. At the same time, it also helps to improve its bending performance, enabling it to maintain good image transmission capability when bent in narrow spaces inside the human body or in complex industrial environments. 4. Using an incrementally varying transition layer to connect the core and cladding layers can, on the one hand, constrain the waveguide of the signal light in the fiber core and reduce crosstalk, and on the other hand, help improve the viscosity matching between the layers of the fiber, avoiding fiber deformation during the drawing process, which would lead to the degradation of the performance of the image transmission fiber. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the radial cross-section of the mandrel in one embodiment of the present invention.

[0035] Figure 2 This is a cross-sectional view of the refractive index of the mandrel in one embodiment of the present invention.

[0036] Figure 3 This is a distribution diagram of fluorine in a mandrel according to an embodiment of the present invention.

[0037] Figure 4This is a distribution diagram of alkali metal elements in a mandrel according to an embodiment of the present invention.

[0038] Figure 5 This is a schematic diagram of the radial cross-section of the image transmission optical fiber in one embodiment of the present invention.

[0039] Figure 6 This is a schematic diagram of the radial cross-section of the image transmission optical fiber in one embodiment of the present invention. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0041] To facilitate the introduction of the invention, the following terms are first defined:

[0042] Power-law refractive index distribution: refers to the radial refractive index distribution of an optical fiber following the formula: In the formula, n(r) is the refractive index of each point in the radial direction of the core layer, n1 is the refractive index at the center of the core layer, Δ1 is the relative refractive index difference at the center of the core layer, r is the radius of the corresponding point in the core layer, a is the radius of the core layer, and α is the refractive index distribution index. When α = 1, the refractive index is triangularly distributed; when α = 2, it is parabolic; and when α approaches infinity, it is step distribution.

[0043] Relative refractive index difference Δ i : Where n i Let n be the refractive index of each layer of the optical fiber. c is the refractive index of pure quartz glass.

[0044] Numerical aperture: Where n1 is the refractive index of the fiber core and n2 is the refractive index of the cladding.

[0045] Core spacing Λ: The distance between the geometric center of a certain image transmission fiber core and the geometric center of the nearest adjacent image transmission fiber core.

[0046] The low-melting-point image-transmitting optical fiber of the present invention includes an image-transmitting layer 2 and an outer cladding layer 3 covering the image-transmitting layer. The image-transmitting layer includes a common cladding and an image-transmitting fiber core 1 spaced apart within the common cladding. The image-transmitting fiber core includes a core layer and a transition layer. The core layer is a silica glass layer co-doped with germanium and alkali metals, and the refractive index profile of the core layer has a power function gradient distribution (parabolic). The core layer radius r1 is 0.4–1.4 μm. The transition layer is a silica glass layer co-doped with fluorine and alkali metals, and the transition layer radius r2 is 0.5–1.5 μm, satisfying (r2–r1) / r1 = 10–25%. The common cladding and the outer cladding are fluorine-doped silica glass layers.

[0047] The core layer is composed of quartz glass co-doped with germanium and alkali metals. This co-doping increases the refractive index of the core layer, lowers its softening temperature, and helps reduce light absorption, thus increasing transmittance. The transition layer is composed of quartz glass co-doped with fluorine and alkali metals. This co-doping also lowers the drawing temperature and helps control the glass viscosity.

[0048] Embodiment 1 of the present invention: A low-melting-point imaging optical fiber, the parameters of which and its preparation method are as follows:

[0049] Mandrel fabrication: Low-melting-point mandrels were fabricated using a fluorine-doped quartz glass liner via PCVD process. The ratio of the core layer radius R1 to the mandrel radius R3 was 49.9%, and the relative refractive index difference Δ between the core layers was [missing information]. 1[max] The refractive index is 2.13%, and the refractive index distribution parameter α is 2.36; the radius of the transition layer is R2, the ratio of the thickness of the transition layer (R2-R1) to the radius of the core layer R1 is 20.2%, and the relative refractive index difference Δ2 of the transition layer is -0.15 to 0%; the radius of the core rod R3 is 10.19 mm, and the relative refractive index difference Δ3 of its cladding is -0.32%.

[0050] The end face structure of the prepared low-melting-point mandrel is as follows Figure 1 As shown, from the inside out, it consists of a core layer 1-1, a transition layer 1-2, and a cladding layer 1-3; its refractive index profile is as follows. Figure 2 As shown.

[0051] Low-melting-point capillary rod drawing: A low-melting-point mandrel is heated and drawn into a low-melting-point capillary rod with a radius of 0.1 to 1 mm.

[0052] Image transmission fiber preform preparation: Approximately 3,000 low-melting-point capillary rods are densely packed in a fluorinated quartz glass sleeving until the sleeving is completely filled. The relative refractive index difference Δ4 of the fluorinated quartz glass sleeving is equal to that of the core rod cladding.

[0053] Image transmission fiber drawing: The above-mentioned image transmission fiber preform is heated and drawn on a drawing tower at a drawing temperature T of 1650℃ and a drawing speed of 50-200 m / min. This yields a low-melting-point image transmission fiber with the following characteristics: core radius r1 of 0.71 μm, transition layer radius (i.e., image transmission core radius) r2 of 0.85 μm, core spacing Λ of 2.72 μm, image layer radius r3 of 76 μm, cladding radius r4 of 85 μm, and coating layer radius r5 of 121 μm. The NA of this image transmission fiber is 0.308, the transmittance of a 4m fiber is 85.13%, and the resolution is 128 lp / mm.

[0054] The main parameters of other embodiments provided by this invention are shown in Tables 1 and 2:

[0055] Table 1 Production Parameters

[0056]

[0057]

[0058] Table 2 Optical and Performance Parameters

[0059]

Claims

1. A low-melting-point image-transmitting optical fiber, comprising an image-transmitting layer and an outer cladding covering the image-transmitting layer, wherein the image-transmitting layer comprises a common cladding and image-transmitting fiber cores spaced apart within the common cladding, characterized in that... The image transmission fiber core comprises a core layer and a transition layer. The core layer is a germanium-alkali metal co-doped quartz glass layer with a power-law gradient refractive index profile. The transition layer is a fluorine-alkali metal co-doped quartz glass layer. The common cladding and outer cladding are fluorine-doped quartz glass layers. The highest relative refractive index difference Δ at the center of the core layer is... 1[max] The relative refractive index difference is 2-3.5%, and the relative refractive index difference at the core edge is 0; the relative refractive index difference of the transition layer increases with the increase of the radius, and the lowest relative refractive index difference Δ 2[min] The relative refractive index difference Δ at the highest point is between -1 and -0.2%. 2[max] The range is -0.5% to 0%, and the difference between the highest and lowest relative refractive index difference is 0.2% to 0.5%.

2. The low-melting-point optical fiber according to claim 1, characterized in that... The core layer radius r1 is 0.4~1.4 μm, the transition layer radius r2 is 0.5~1.5 μm, and (r2-r1) / r1 = 10~25%.

3. The low-melting-point optical fiber according to claim 1 or 2, characterized in that... The core layer refractive index distribution index α is 2~3.

4. The low-melting-point optical fiber according to claim 1, characterized in that... The relative refractive index difference of the transition layer satisfies the radius. In the formula, Δ2(r) is the radius of the transition layer. r The relative refractive index difference at the location, k Let be the slope, and its value is... , r Let r1 be the radius of the point corresponding to the transition layer, and r2 be the radius of the core layer and the radius of the transition layer, respectively.

5. The low-melting-point imaging optical fiber according to claim 1 or 2, characterized in that... The relative refractive index difference Δ3 of the common cladding is -0.5 to -0.2%; the relative refractive index difference Δ4 of the outer cladding is -0.5 to -0.2%.

6. The low-melting-point optical fiber according to claim 1 or 2, characterized in that... The core spacing Λ of the image transmission fiber is 2~5 μm, the radius r3 of the image transmission layer is 50~475 μm, the radius r4 of the outer cladding layer is 75~500 μm, and the ratio of r3 to r4 is 0.4~0.

95.

7. The low-melting-point optical fiber according to claim 1 or 2, characterized in that... The number of image transmission fiber cores is greater than or equal to 1000.

8. The low-melting-point optical fiber according to claim 1 or 2, characterized in that... The alkali metal element is lithium, sodium, or potassium. One or more of the following, with a doping amount of 1000~10000 ppm.

9. The low-melting-point optical fiber according to claim 1 or 2, characterized in that... The outer coating layer is coated with resin. The coating layer has a radius r5 of 100~600 μm.

10. The low-melting-point imaging optical fiber according to claim 1 or 2, characterized in that... The image transmission fiber has an NA value of 0.3~0.5, a transmittance of 70~90%, and a resolution of ≥128 lp / mm.

11. A method for preparing a low-melting-point imaging optical fiber according to any one of claims 1-10, characterized in that... Low-melting-point mandrel fabrication involves using a fluorine-doped quartz glass liner as the substrate and employing a PCVD process to fabricate the transition layer and core layer. Doping and deposition are performed, and after deposition, the material is melted and condensed into a low-melting-point mandrel. The mandrel consists of a core layer, a transition layer, and a cladding layer from the inside out. Low-melting-point capillary rod drawing: The low-melting-point mandrel is heated and drawn into a low-melting-point capillary rod. The low-melting-point image-transmitting fiber preform is prepared by stacking and fixing the low-melting-point capillary rods in a fluorine-doped quartz glass sleeve to obtain the image-transmitting fiber preform. Image transmission fiber drawing: The image transmission fiber preform is drawn into a low melting point image transmission fiber.

12. The method for preparing the low-melting-point imaging optical fiber according to claim 11, characterized in that... The ratio of the core radius R1 to the core radius R3 of the low-melting-point mandrel is 40-60%.

13. The method for preparing the low-melting-point imaging optical fiber according to claim 11, characterized in that... The relative refractive index difference Δ3 of the low-melting-point mandrel cladding is -0.5 to -0.2%, and the relative refractive index difference Δ4 of the fluorine-doped quartz glass sleeve is the same as Δ3.

14. The method for preparing the low-melting-point imaging optical fiber according to claim 11, characterized in that... The low-melting-point capillary rod has a radius of 0.1 to 1 mm, and the low-melting-point core rod cladding has a radius R3 of 10 to 20 mm.

15. The method for preparing the low-melting-point imaging optical fiber according to claim 11, characterized in that... The low-melting-point core rod, low-melting-point capillary rod, low-melting-point image transmission fiber preform, and the glass portion of the image transmission fiber have a low softening temperature of 1400~1600 ℃.

16. The method for preparing the low-melting-point imaging optical fiber according to claim 11, characterized in that... The fiber optic preform is drawn at a temperature of 1600~1800℃ and at a drawing speed of 100~1000 m / min.

17. A low-melting-point image transmission fiber core rod, characterized in that... From the inside out, it comprises a core layer, a transition layer, and a cladding layer. The core layer is a germanium- and alkali metal-doped quartz glass layer with a power-law gradually changing refractive index profile. The transition layer is a fluorine- and alkali metal-doped quartz glass layer, and the cladding layer is a fluorine-doped quartz glass layer. The highest relative refractive index difference Δ at the center of the core layer is... 1[max] The relative refractive index difference is 2-3.5%, and the relative refractive index difference at the core edge is 0; the relative refractive index difference of the transition layer increases with the increase of the radius, and the lowest relative refractive index difference Δ 2[min] The relative refractive index difference Δ at the highest point is between -1 and -0.2%. 2[max] The value ranges from -0.5% to 0%, and the difference between the highest and lowest relative refractive index difference is 0.2% to 0.5%.

18. The low-melting-point image transmission fiber core rod according to claim 17, characterized in that... The core layer refractive index distribution index α is 2 to 3.

19. The low-melting-point image transmission fiber core rod according to claim 17, characterized in that... The relative refractive index difference Δ3 of the cladding is -0.5 to -0.2%.

20. The low-melting-point image transmission fiber core rod according to claim 17, characterized in that... The ratio of the core radius R1 to the cladding radius R3 is 40-60%, and the cladding radius R3 is 10-20 mm.

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