Low-melting-point image transmitting optical fiber, core rod and preparation method of core rod

Abstract

The invention relates to a low-melting-point image transmitting optical fiber, a core rod and a preparation method thereof, the low-melting-point image transmitting optical fiber comprises an image transmitting layer and an outer wrapping layer wrapping the image transmitting layer, the image transmitting layer comprises a common wrapping layer and image transmitting fiber cores densely distributed in the common wrapping layer at intervals, and each image transmitting fiber core comprises a core layer and a transition layer. The core layer is a germanium and alkali metal co-doped quartz glass layer, the refractive index profile of the core layer is in power function gradient distribution, the transition layer is a fluorine and alkali metal co-doped quartz glass layer, and the common cladding and the outer cladding are fluorine-doped quartz glass layers. According to the invention, the drawing temperature is reduced, the viscosity matching among the layers is balanced, the optical and material properties of the optical fiber are optimized, the refractive index, transmittance and NA of the optical fiber are improved, and the image transmission resolution of the optical fiber is optimized by doping and reasonably designing the refractive index profile of the image transmission fiber core.

Description

Technical Field

[0001] The invention relates to a low-melting-point image transmission optical fiber, a core rod and a preparation method thereof, and belongs to the technical field of optical fibers. Background Art

[0002] Image transmission fiber, also known as imaging fiber, is a passive fiber optic device used in endoscopes. Similar to ordinary communication optical fibers, its working principle is also based on the total internal reflection of light, but the difference is that the working wavelength of image transmission fiber is usually visible light, and there are thousands or even tens of thousands of fiber cores in its cladding. Image transmission fiber plays a sampling role in endoscopes, and each of its cores can be used as a "lens" to transmit signal light from the sample end to the observation end to achieve real-time high-resolution image transmission. Based on the high resolution, high flexibility, extremely small size, real-time imaging, anti-interference and relatively low cost of image transmission fiber, it has been increasingly used in medical and industrial fields.

[0003] In the prior art, the drawing of image transmission optical fiber requires ultra-high temperature of up to 2000°C or even higher, which not only brings great energy consumption, but also increases the requirements for production equipment and the complexity of production process, which undoubtedly increases production costs. For example, the preparation process of a randomly distributed multi-core imaging optical fiber disclosed in Chinese patent document CN111635124A and the preparation method of a high duty cycle multi-core microstructure imaging optical fiber bundle disclosed in CN111635125A both use pure quartz glass as raw material, pure quartz as the fiber core, and air as the cladding. Although the doping link is omitted, the drawing process is relatively complicated, and the softening temperature of pure quartz glass is high, and the energy consumption during production is high. 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 a preparation method thereof in view of the deficiencies in the above-mentioned prior art, which not only has a relatively low drawing temperature but also can optimize 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 coated outside the image transmission layer, the image transmission layer includes a common cladding and image transmission fiber cores densely spaced in the common cladding, 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 metal, the refractive index profile of the core layer is a power function gradient distribution (parabolic), the transition layer is a quartz glass layer co-doped with fluorine and alkali metal, and the common cladding and the outer cladding are fluorine-doped quartz glass layers.

[0006] According to the above scheme, 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%.

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

[0008] According to the above scheme, the relative refractive index difference of the transition layer increases with the increase of radius, and the relative refractive index difference at the lowest point is Δ 2[min] The relative refractive index difference at the highest point is -1 to -0.2%. 2[max] It 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 and radius of the transition layer satisfy Where Δ2(r) is the relative refractive index difference at the transition layer radius r, and k is the slope, which is r is the radius of the corresponding point of the transition layer, r1 and r2 are the radius of the core layer and the radius of the transition layer 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 2-5μm, the radius r3 of the image transmission layer is 50-475μm, the radius r4 of the outer cladding is 75-500μm, and the ratio of r3 to r4 is 0.4-0.95.

[0012] According to the above scheme, the number of the 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 the doping amount thereof is 1000 to 10000 ppm.

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

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

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

[0017] The technical solution of the method for preparing the image transmission optical fiber of the present invention is:

[0018] Preparation of low melting point core rod: fluorine-doped quartz glass liner is used as substrate, and transition layer and core layer are doped and deposited by PCVD process. After deposition, it is melted into low melting point core rod. From inside to outside, core rod is composed of core layer, transition layer and cladding.

[0019] Low melting point capillary rod drawing, the low melting point core rod is heated and stretched into a low melting point capillary rod,

[0020] Preparation of low melting point image transmission optical fiber preform rod, stacking, filling and fixing the low melting point capillary rod in a fluorine-doped quartz glass sleeve to obtain an image transmission optical fiber preform rod,

[0021] The image transmission optical fiber is drawn by drawing the image transmission optical fiber preform rod to prepare a low melting point image transmission optical fiber.

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

[0023] According to the above scheme, the relative refractive index difference Δ3 of the low-melting-point core rod 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 optical fiber preform rod and the glass part of the image transmission optical fiber have a low softening temperature, and the softening temperature is 1400-1600°C.

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

[0027] The technical solution of the low melting point core rod for image transmission optical fiber of the present invention is:

[0028] From the inside to the outside, 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 metals. The refractive index profile of the core layer is a power function gradient distribution. The transition layer is a quartz glass layer co-doped with fluorine and alkali metals. 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 1[max] It is 2-3.5%, and the relative refractive index difference at the edge of the core layer is 0.

[0030] According to the above scheme, the relative refractive index difference of the transition layer increases with the increase of radius, and the relative refractive index difference at the lowest point is Δ 2[min] The relative refractive index difference at the highest point is -1 to -0.2%. 2[max] It 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 solution, 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 the present 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 metal elements or other doping elements, germanium and fluorine play the role of regulating the glass refractive index, regulating the glass viscosity and reducing the glass softening temperature; alkali metals can reduce the absorption of light by glass on the one hand, play the role of improving the visible light transmittance, and on the other hand, can regulate the viscosity of glass, further reduce the softening temperature of glass, and reduce the drawing temperature by 200-400°C, thereby achieving the effect of energy saving and consumption reduction; 2. Through the doping of each layer, not only the drawing temperature is reduced, the viscosity matching between each layer is balanced, but also the optical and material properties of the optical fiber are optimized, so that its refractive index, transmittance and NA are improved; 3. By doping and reasonably designing the refractive index profile of the image transmission fiber core, the waveguide of the transmitted image signal light is constrained, so that its core crosstalk is suppressed and its image transmission resolution is optimized. At the same time, it is also beneficial to improve its bending performance, so that it still has good image transmission ability when it is bent in a narrow space inside the human body or in a complex industrial environment. 4. Using an incremental transition layer to connect the core layer and the cladding can, on the one hand, constrain the waveguide of the signal light in the core and reduce crosstalk. On the other hand, it can also help improve the viscosity matching between the optical fiber layers and avoid deformation of the optical fiber during the drawing process, which will lead to degradation of the performance of the image transmission optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of a radial cross section of a core rod in one embodiment of the present invention.

[0035] Figure 2 FIG. 4 is a refractive index profile diagram of a core rod in one embodiment of the present invention.

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

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

[0038] Figure 5 Schematic diagram of radial cross section of the image transmission optical fiber in one embodiment of the present invention.

[0039] Figure 6 Schematic diagram of radial cross section of the image transmission optical fiber in one embodiment of the present invention. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0041] In order to facilitate the introduction of the present invention, the following terms are first defined:

[0042] Power function refractive index distribution: refers to the radial refractive index distribution of optical fiber following the formula: Where n(r) is the refractive index of each radial point 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 of the core layer, a is the radius of the core layer, α is the refractive index distribution index, when α = 1, the refractive index is triangular distribution, when α = 2, it is parabolic distribution, and when α approaches infinity, it is step distribution.

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

[0044] Numerical Aperture: Where n1 is the refractive index of the optical 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-transmitting fiber core and the geometric center of the adjacent nearest image-transmitting fiber core.

[0046] The low melting point image transmission optical fiber of the present invention comprises an image transmission layer 2 and an outer cladding 3 coated outside the image transmission layer, the image transmission layer comprises a common cladding and an image transmission fiber core 1 spaced and densely distributed in the common cladding, the image transmission fiber core comprises a core layer and a transition layer, the core layer is a quartz glass layer co-doped with germanium and alkali metal, the refractive index profile of the core layer is a power function gradient distribution (parabola), the core layer radius r1 is 0.4-1.4μm, the transition layer is a quartz glass layer co-doped with fluorine and alkali metal, the transition layer radius r2 is 0.5-1.5μm, and satisfies (r2-r1) / r1=10-25%, and the common cladding and the outer cladding are fluorine-doped quartz glass layers.

[0047] The core layer is composed of quartz glass co-doped with germanium and alkali metal elements. The co-doping of germanium and alkali metal elements in the core layer can improve the refractive index of the core layer on the one hand, and on the other hand, it can not only reduce its softening temperature, but also help reduce the absorption of light by the glass and improve the transmittance. The transition layer is composed of quartz glass co-doped with fluorine and alkali metal elements. The co-doping of fluorine and alkali metal elements in the transition layer also plays a role in reducing the drawing temperature and can also regulate the viscosity of the glass.

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

[0049] Core rod preparation: A low-melting-point core rod is prepared by PCVD process using a fluorine-doped quartz glass liner. The ratio of the core layer radius R1 to the core rod radius R3 of the low-melting-point core rod is 49.9%, and the relative refractive index difference of the core layer is Δ 1[max] It is 2.13%, and the refractive index distribution parameter α is 2.36; the transition layer radius is R2, the ratio of the transition layer thickness (R2-R1) to the core layer radius R1 is 20.2%, and the transition layer relative refractive index difference Δ2 is -0.15~0%; the core rod radius R3 is 10.19mm, and its cladding relative refractive index difference Δ3 is -0.32%.

[0050] The end surface structure of the prepared low melting point core rod is as follows: Figure 1 As shown, from the inside to the outside, it is composed 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 shown.

[0051] Low melting point capillary rod drawing: The low melting point core rod is heated and stretched to become a low melting point capillary rod, and the radius of the low melting point capillary rod is 0.1 to 1 mm.

[0052] Preparation of image transmission optical fiber preform: about 3000 low melting point capillary rods are densely stacked in a fluorine-doped quartz glass sleeve until the sleeve is completely filled, and the relative refractive index difference Δ4 of the fluorine-doped quartz glass sleeve is equal to that of the core rod cladding.

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

[0054] The main parameters of other embodiments provided by the present invention are shown in Table 1 and Table 2:

[0055] Table 1 Production parameters

[0056]

[0057]

[0058] Table 2 Optical and performance parameters

[0059]

Claims

1. A low melting point image transmission optical fiber, comprising an image transmission layer and an outer cladding coated outside the image transmission layer, wherein the image transmission layer comprises a common cladding and image transmission fiber cores densely spaced in the common cladding, characterized in that The image transmission fiber core comprises a core layer and a transition layer, wherein the core layer is a quartz glass layer co-doped with germanium and alkali metal, the refractive index profile of the core layer is a power function gradient distribution, the transition layer is a quartz glass layer co-doped with fluorine and alkali metal, and the common cladding and outer cladding are fluorine-doped quartz glass layers.

2. The low melting point image transmission 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 image transmission optical fiber according to claim 1 or 2, characterized in that The core layer refractive index distribution index α is 2 to 3, and the highest relative refractive index difference Δ 1[max] It is 2-3.5%, and the relative refractive index difference at the edge of the core layer is 0.

4. The low melting point image transmission optical fiber according to claim 1 or 2, characterized in that The relative refractive index difference of the transition layer increases with the increase of radius, and the relative refractive index difference at the lowest point is Δ 2[min] The relative refractive index difference at the highest point is -1 to -0.2%. 2[max] It is -0.5 to 0%, and the difference between the highest and lowest relative refractive index difference is 0.2 to 0.5%.

5. The low melting point image transmission optical fiber according to claim 4, characterized in that The relative refractive index difference and radius of the transition layer satisfy Where Δ2(r) is the relative refractive index difference at the transition layer radius r, and k is the slope, which is r is the radius of the corresponding point of the transition layer, r1 and r2 are the radius of the core layer and the radius of the transition layer respectively.

6. The low melting point image transmission 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%.

7. The low melting point image transmission 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 is 75-500 μm, and the ratio of r3 to r4 is 0.4-0.

95.

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

9. The low melting point image transmission optical fiber according to claim 1 or 2, characterized in that The alkali metal element is one or more of lithium, sodium and potassium, and the doping amount thereof is 1000 to 10000 ppm.

10. The low melting point image transmission optical fiber according to claim 1 or 2, characterized in that The outer cladding layer is covered with a resin coating layer, and the radius r5 of the resin coating layer is 100-600 μm.

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

12. A method for preparing any low melting point image transmission optical fiber according to any one of claims 1 to 11, characterized in that Preparation of low melting point core rod: fluorine-doped quartz glass liner is used as substrate, and transition layer and core layer are doped and deposited by PCVD process. After deposition, it is melted into low melting point core rod. From inside to outside, core rod is composed of core layer, transition layer and cladding. Low melting point capillary rod drawing, the low melting point core rod is heated and stretched into a low melting point capillary rod, Preparation of low melting point image transmission optical fiber preform rod, stacking, filling and fixing the low melting point capillary rod in a fluorine-doped quartz glass sleeve to obtain an image transmission optical fiber preform rod, The image transmission optical fiber is drawn by drawing the image transmission optical fiber preform rod to prepare a low melting point image transmission optical fiber.

13. The method for preparing the low melting point image transmission optical fiber according to claim 12, characterized in that The ratio of the core layer radius R1 of the low-melting-point core rod to the core rod radius R3 is 40-60%.

14. The method for preparing the low melting point image transmission optical fiber according to claim 12, characterized in that The relative refractive index difference Δ3 of the low-melting-point core rod 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.

15. The method for preparing the low melting point image transmission optical fiber according to claim 12, characterized in that 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.

16. The method for preparing the low melting point image transmission optical fiber according to claim 12, characterized in that The low-melting-point core rod, the low-melting-point capillary rod, the low-melting-point image-transmitting optical fiber preform rod preparation and the glass part of the image-transmitting optical fiber have a low softening temperature of 1400-1600°C.

17. The method for preparing the low melting point image transmission optical fiber according to claim 12, characterized in that The temperature of the image transmission optical fiber preform for drawing is 1600-1800° C., and the drawing speed is 100-1000 m / min.

18. A low melting point image transmission optical fiber core rod, characterized in that From the inside to the outside, 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 metals. The refractive index profile of the core layer is a power function gradient distribution. The transition layer is a quartz glass layer co-doped with fluorine and alkali metals. The cladding layer is a fluorine-doped quartz glass layer.

19. The low melting point image transmission optical fiber core rod according to claim 18, characterized in that The core layer refractive index distribution index α is 2 to 3, and the highest relative refractive index difference Δ 1[max] It is 2-3.5%, and the relative refractive index difference at the edge of the core layer is 0.

20. The low melting point image transmission optical fiber core rod according to claim 18, characterized in that The relative refractive index difference of the transition layer increases with the increase of radius, and the relative refractive index difference at the lowest point is Δ 2[min] The relative refractive index difference at the highest point is -1 to -0.2%. 2[max] It is -0.5 to 0%, and the difference between the highest and lowest relative refractive index difference is 0.2 to 0.5%.

21. The low melting point imaging optical fiber core rod according to claim 18, characterized in that The relative refractive index difference Δ3 of the cladding is -0.5 to -0.2%.

22. The low melting point image transmission optical fiber core rod according to claim 18, 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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