Low crosstalk and high-resolution image transmission optical fiber and preparation method thereof

Abstract

This invention relates to a low-crosstalk, high-resolution image transmission fiber and its fabrication method. The fiber includes an image transmission layer and an outer cladding covering the image transmission layer. The image transmission layer comprises a common cladding and image transmission cores spaced apart within the common cladding. The image transmission cores have five or more different core diameters, and the numerical aperture of the image transmission fiber is 0.6–0.85. The image transmission fiber of this invention is fabricated from multi-component doped silica, achieving a very high numerical aperture. This is beneficial for optimizing inter-pixel crosstalk, increasing the field of view, and improving contrast. While expanding the field of view of the fiber, it significantly improves image quality, and the multi-component silica material has a lower cost. This invention effectively reduces the proportion of the common cladding in the image transmission plane, resulting in lower grid lines and clearer, more coherent images. The random distribution of five or more different core diameters further reduces inter-core crosstalk and improves resolution.

Description

Technical Field

[0001] This invention relates to a low-crosstalk, high-resolution imaging optical fiber and its fabrication method, belonging to the field of optical fiber technology. Technical Background

[0002] Imaging fiber, also known as imaging fiber, multi-core image bundle, or fiber optic image bundle, is a passive fiber optic imaging device and a core component of endoscopes. With advancements in endoscope technology, the requirements for imaging performance from imaging fibers are becoming increasingly stringent. The main indicators characterizing the imaging performance of imaging fibers are resolution and contrast. Resolution is a parameter characterizing the image quality transmitted by the imaging fiber, referring to the minimum distance between two spatial points that the fiber can resolve. It is usually expressed as the logarithm of line spacing (lp / mm) that can be resolved per millimeter. Higher resolution results in better transmission quality and higher clarity. Resolution primarily depends on the inter-core spacing between two pixels. Smaller inter-core spacing leads to higher resolution, but as the inter-core spacing decreases, crosstalk between cores increases. Therefore, the crosstalk rate of pixels is also a factor affecting the image transmission quality of imaging fibers, and optimizing inter-core crosstalk has always been a focus of attention. Optimizing inter-core crosstalk is often achieved by increasing the numerical aperture or increasing the inter-core spacing. Increasing the intercore spacing leads to a decrease in the resolution of the image transmission fiber, thus affecting the image transmission quality. Numerical aperture (NAP) is related to the refractive index difference between the fiber core and cladding; the greater the refractive index difference, the higher the NAP. The size of the NAP indicates the light-gathering ability of the image transmission fiber, and strong light-gathering ability increases the contrast of the image transmission fiber. Simultaneously, increasing the NAP can effectively reduce intercore crosstalk. Therefore, how to increase the NAP of the image transmission fiber is a key factor in improving its image transmission quality. Patent CN116239294 A discloses a method for manufacturing an image transmission fiber and the fiber itself, employing a double-fiber method to ensure neat pixel arrangement, but multiple hexagons are aggregated at the fiber end face, resulting in an uneven image transmission surface. Patent 117023972A discloses a quartz-type low-crosstalk image transmission fiber and its manufacturing method. The NAP of this fiber is 0.40–0.45, which is currently a relatively high NAP for quartz-type image transmission fiber pixels, but its improvement in image transmission quality is not yet ideal. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a low crosstalk high resolution imaging optical fiber and its preparation method, which addresses the problems existing in the prior art, with low inter-core crosstalk and high image transmission quality.

[0004] 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 and densely distributed in the common cladding layer. The image transmission fiber cores have 5 or more different core diameters, and the NA value of the image transmission fiber is 0.6 to 0.85.

[0005] According to the above scheme, the diameter of the image transmission fiber core is 0.5 to 1.5 μm, the center distance between adjacent image transmission fiber cores is 1.5 to 3.2 μm, and the diameter of the outer cladding layer is 200 to 800 μm.

[0006] According to the above scheme, the diameter of the image transmission fiber core is 0.7 to 1.2 μm, and the center distance between adjacent image transmission fiber cores is 1.8 to 2.5 μm.

[0007] According to the above scheme, the proportion of each type of image transmission fiber core to the total number of cores is 10-40%, and the minimum diameter difference between the two different diameter image transmission fiber cores is ≥7%, that is, the ratio of the larger diameter to the smaller diameter is ≥1.07.

[0008] According to the above scheme, the difference between the maximum and minimum diameters of the five or more different core diameter image transmission fiber cores is ≤50%.

[0009] According to the above scheme, the image transmission fiber core is a doped silicon dioxide glass layer, which includes the following components by weight: BaO2 2-31%, Na2O 2-6%, K2O 0-5%, Li2O 0-2%, Al2O3 1-7%, B2O3 0.5-10%, MgO 1-7%, CaO 0-3%, SrO 0-3%, La2O3 5-15%, Sb2O3 0.5-3%, ZnO 4-7%, ZrO2 2-3%, and SiO2 balance.

[0010] According to the above scheme, the common cladding and outer cladding are doped silica glass layers, which include the following components by weight: Al2O3 3-6%, B2O3 1-3%, MgO 0-5%, CaO 4-7%, Li2O 0-2%, Na2O 7-15%, K2O 0-5%, and SiO2 balance.

[0011] According to the above scheme, the total amount of SiO2 and B2O3 in the common cladding and outer cladding is 68-85%, and the total amount of alkali metal oxides Li2O, Na2O and K2O is 8-22%.

[0012] According to the above scheme, the refractive index n1 of the image transmission core layer is 1.65 to 1.75, and the refractive index n2 of the common cladding and outer cladding is 1.49 to 1.51.

[0013] According to the above scheme, the area ratio of the fiber core to the common cladding of the image transmission layer is 0.72 to 0.82.

[0014] According to the above scheme, the number of cores in the image transmission layer is 1000 or more.

[0015] The technical solution of the image transmission fiber fabrication method of the present invention is as follows:

[0016] Mandrel fabrication: Fabrication of multi-component doped silica mandrels, comprising a multi-component doped silica fiber mandrel and a multi-component doped silica liner.

[0017] The capillary rod is drawn by placing the multi-component doped silica core rod on a drawing tower to produce capillary rods of five or more different diameters, cutting them into the same length, and then cleaning and drying them. The capillary rod comprises a multi-component doped silica core layer and a multi-component doped silica cladding layer.

[0018] The image transmission fiber preform is prepared by tightly and randomly stacking and fixing five or more capillary rods of the same length but different diameters inside a multi-component doped glass jacket tube to obtain the image transmission fiber preform.

[0019] Image transmission fiber drawing: The image transmission fiber preform is drawn to prepare a low crosstalk, high resolution image transmission fiber.

[0020] According to the above scheme, the multi-component doped silica core rod is prepared by the sleeve method, comprising a multi-component doped silica fiber core rod and a multi-component doped silica liner. The diameter of the fiber core rod is 15-35 mm, the outer diameter of the liner is 18-40 mm, the wall thickness is 1-2.5 mm, the core-to-closing ratio of the core rod is 0.72-0.82, and the numerical aperture NA is 0.6-0.85.

[0021] According to the above scheme, the diameter of the core rod is 22-35mm, the outer diameter of the liner is 24-31mm, the wall thickness is 1-1.5mm, and the numerical aperture is 0.7-0.85.

[0022] According to the above scheme, the fiber core rod is a multi-component doped silica glass layer rod, which includes the following components by weight: BaO 22-31%, Na2O 2-6%, K2O 0-5%, Li2O 0-2%, Al2O3 1-7%, B2O3 0.5-10%, MgO 1-7%, CaO 0-3%, SrO 0-3%, La2O3 5-15%, Sb2O3 0.5-3%, ZnO 4-7%, ZrO2 2-3%, and SiO2 balance.

[0023] A more preferred composition is: BaO 25-30%, Na2O 2-4%, K2O 0-3%, Li2O 0-2%, Al2O3 1.5-5%, B2O3 0-5%, MgO 1-7%, CaO 0-3%, SrO 0-3%, La2O3 8-13%, Sb2O3 0.5-3%, ZnO 5-7%, ZrO2 2-3%, and SiO2 balance.

[0024] According to the above scheme, the liner and outer sleeve are multi-component doped silica glass tubes, which include the following components by weight: Al2O3 3-6%, B2O3 1-3%, MgO 0-5%, CaO 4-7%, Li2O 0-2%, Na2O 7-15%, K2O 0-5%, and SiO2 balance.

[0025] A more preferred composition is: Al2O3 4-5%, B2O3 1-2%, MgO 0-3%, CaO 5-6%, Li2O 0-2%, Na2O 11-13%, K2O 0-3%, and SiO2 as the balance; wherein the total amount of SiO2 and B2O3 is 70-77%, and the total amount of alkali metal oxides Li2O, Na2O and K2O is 11-18%.

[0026] According to the above scheme, the diameter of the capillary rod is 0.2mm to 1mm and the length is 400mm to 700mm.

[0027] More preferably, the capillary rod has a diameter of 0.3 mm to 0.6 mm and a length of 400 mm to 600 mm.

[0028] According to the above scheme, the proportion of each type of capillary rod to the total number of capillary rods is 10-40%, and the minimum diameter difference between the two different diameter capillary rods is ≥7%, that is, the ratio of the larger diameter to the smaller diameter is ≥1.07.

[0029] According to the above scheme, the duty cycle of the image transmission fiber preform is 0.8 to 0.9; more preferably, the duty cycle is 0.85 to 0.9.

[0030] The beneficial effects of this invention are as follows: 1. The image transmission fiber is made of multi-component doped silica, which can achieve a very high numerical aperture. This is beneficial for optimizing crosstalk between pixels, increasing the field of view, and improving contrast. While expanding the field of view of the fiber, it significantly improves the imaging quality, and the multi-component silica material has a low cost. 2. The numerical aperture of this invention is almost twice that of fluorine-doped silica, which will reduce the critical core spacing for crosstalk. The core-cladding ratio of the corresponding fiber core preform can be designed to be larger, thereby reducing the distance between the fiber cores and further increasing the area ratio of the pixels on the entire image transmission surface. On the one hand, this improves the transmittance of the image transmission fiber, and on the other hand, it can effectively reduce the proportion of the common cladding in the image transmission surface, making the transmitted image less grid-like and the image clearer and more coherent. 3. Using five or more different core diameters randomly distributed can effectively suppress inter-core crosstalk, thereby further reducing the core spacing and improving resolution. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the radial cross-section of a capillary rod in one embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of the refractive index profile of a capillary rod in one embodiment of the present invention.

[0033] Figure 3 This is a partial end face diagram of the image transmission fiber preform in one embodiment of the present invention. The capillary rods with different numbers in the figure represent capillary rods with different outer diameters.

[0034] Figure 4 This is a schematic diagram and a partial enlarged view of the radial cross-section of the image transmission fiber in one embodiment of the present invention.

[0035] Figure 5 This is a cross-sectional view of an image transmission fiber actually manufactured according to an embodiment of the present invention.

[0036] Figure 6 This is a diagram illustrating the image transmission effect of an image transmission fiber optic cable according to an embodiment of the present invention. Detailed Implementation

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0038] Example 1: First, a multi-component doped silica core rod was prepared. The core rod includes a multi-component doped silica fiber core rod and a multi-component doped silica liner. The fiber core rod is a multi-component doped silica glass rod, comprising the following components by weight: BaO 25%, Na2O 2%, K2O 2%, Li2O 2%, Al2O3 2%, B2O3 2%, MgO 3%, CaO 1%, SrO 1%, La2O3 11%, Sb2O3 2%, ZnO 5%, ZrO2 2%, and SiO2 balance; the refractive index n1 of the core rod glass is 1.69. The liner is a multi-component doped silica glass layer tube, comprising the following components by weight: Al2O3 4%, B2O3 2%, MgO 3%, CaO 5%, Li2O 1%, Na2O 12%, K2O 3%, and SiO2 balance; the refractive index n2 of the liner glass is 1.51. Multi-component doped silica mandrels were prepared using a sleeve method. The prepared multi-component doped silica fiber core material was rolled into a 20mm diameter core rod. The cladding glass material was then molded into a 26mm outer diameter, 2.5mm wall thickness tube. The core rod and cladding tube were then assembled using the sleeve method to form the mandrel. The mandrel was placed on a stretching tower, turned around, and then vacuumed. It was drawn at 800℃ and 60m / min. At least five different outer diameter capillary rods, numbered 1-5, were drawn from the same mandrel. The core layer 1 of the capillary rod has a radius of R1, and the cladding layer 2 has a radius of R2. The relevant parameters of the capillary rod are shown in Table 1. The capillary rods were then cut to the same length and cleaned and dried.

[0039] Table 1: Main parameters of 5 types of capillary rods

[0040]

[0041] Preparation of multi-component image transmission fiber preform: The image transmission fiber preform is prepared by tightly and randomly stacking capillary rods inside a multi-component glass jacket tube. The material composition of the multi-component glass jacket tube is the same as that of the multi-component doped silica liner tube. The outer diameter of the preform tube is 40 mm and the wall thickness is 2 mm. The preform tube is filled with the above 5 types of pixel capillary rods randomly until there are no obvious gaps visible to the naked eye (about 6000±100 rods). One end of the multi-component image transmission fiber preform is closed so that the capillary rods cannot fall out.

[0042] Multi-component imaging fiber drawing: The preform is placed on a drawing tower, turned around, and a vacuum is applied. Drawing is performed at 800℃ and a speed of 60 m / min to obtain fiber filaments with a glass portion diameter of 350 ± 20 μm. After coating, an optical fiber with a diameter of 450 ± 20 μm is obtained. The refractive index curves of the fiber core and the cladding surrounding the core are shown below. Figure 2 As shown, the local end face of the optical fiber is as follows Figure 4As shown, it includes an image-transmitting layer and an outer cladding layer 5 covering the image-transmitting layer, and an outer coating layer 6 around the outer cladding layer. The image-transmitting layer includes a common cladding layer 7 and image-transmitting fiber cores 8 spaced apart within the common cladding layer. The image-transmitting fiber cores have five different core diameters, and the number of fiber cores ranges from 6000±100, with a core diameter of 0.8~1.1μm. Figure 6 The 4m image-transmitting fiber prepared in Example 1 is shown in Table 2 for image transmission to a USAF 1951 resolution plate at 510nm. The main parameters of the fiber are shown in Table 2.

[0043] Comparative Example 1: An optical fiber preform was prepared and drawn according to the conditions described in CN114200575A, and its image transmission effect on a USAF 1951 resolution plate at 510 nm was observed. The main parameters of the optical fiber are shown in Table 2.

[0044] Table 2: Main parameters of the optical fiber in Example 1

[0045]

[0046] As can be seen from Table 2, the embodiment and Comparative Example 1, the resolution of the optical fiber of the present invention has been significantly improved.

[0047] Example 2-10:

[0048] The multi-component doped silica fiber core rods and multi-component doped silica liner tubes in Examples 2-6 have the same composition as in Example 1. The mass percentage composition of the fiber core rods in Examples 7-10 is as follows: BaO 27%, Na2O 2%, K2O 2%, Li2O 2%, Al2O3 2%, B2O3 2%, MgO 3%, CaO 1%, SrO 1%, La2O3 12%, Sb2O3 2%, ZnO 6%, ZrO2 2%, SiO2 balance; the refractive index n1 of the core glass is 1.71. The composition of the liner tube is as follows: Al2O3 4%, B2O3 2%, MgO 3%, CaO 5%, Li2O 1%, Na2O 12%, K2O 3%, SiO2 balance; the refractive index n2 of the liner tube glass is 1.51. The preparation process of Examples 2-10 is the same as in Example 1, and the capillary rod parameters of each example are shown in Table 3.

[0049] Table 3: Main parameters of capillary rods in Examples 2-10

[0050]

[0051]

[0052] The fabrication process of the multi-component image transmission fiber in each embodiment is the same as that in Embodiment 1. After the fiber is cut off, it is drawn at a speed of 40 to 100 m / min in the temperature range of 650℃ to 1000℃ to obtain 9 different sizes of multi-component image transmission fibers. The main parameters of the fiber are shown in Table 4. The resolution is the test data of 4-meter fiber at 510 nm on the USAF 1951 resolution board.

[0053]

Claims

1. A low-crosstalk, high-resolution image transmission optical fiber, comprising an image transmission layer and an outer cladding covering the image transmission layer, wherein the image transmission layer comprises a common cladding and image transmission fiber cores spaced apart within the common cladding, characterized in that... The image-transmitting fiber core has five or more different core diameters, and the numerical aperture of the image-transmitting fiber is 0.6~0.

85. The image-transmitting fiber core is a doped silica glass layer, comprising the following components by weight: BaO 22-31%, Na2O 2-6%, K2O 0-5%, Li2O 0-2%, Al2O3 1-7%, B2O3 0.5-10%, MgO 1-7%, CaO 0-3%, SrO 0-3%, La2O3 5-15%, Sb2O3 0.5-3%, ZnO 4-7%, ZrO2 2-3%, and SiO2 balance. The common cladding and outer cladding are doped silica glass layers, comprising the following components by weight: Al2O3 3-6%, B2O3 1-3%, MgO 0-5%, CaO 4-7%, Li2O 0-2%, Na2O 7-15%, K2O 0-5%, SiO2 balance.

2. The low crosstalk, high-resolution imaging optical fiber according to claim 1, characterized in that... The diameter of the image transmission fiber core is 0.5~1.5μm, the center distance between adjacent image transmission fiber cores is 1.5~3.2μm, and the diameter of the outer cladding layer is 200~800μm.

3. The low crosstalk, high-resolution imaging optical fiber according to claim 2, characterized in that... The diameter of the image transmission fiber core is 0.7~1.2μm, and the center distance between adjacent image transmission fiber cores is 1.8~2.5μm.

4. The low crosstalk, high-resolution imaging optical fiber according to claim 1 or 2, characterized in that... The proportion of each type of image transmission fiber core to the total number of cores is 10-40%, and the minimum diameter difference between any two different diameter image transmission fiber cores is ≥7%, that is, the ratio of the larger diameter to the smaller diameter is ≥1.

07.

5. The low crosstalk, high-resolution imaging optical fiber according to claim 4, characterized in that... The difference between the maximum and minimum diameters of the five or more different image transmission fiber cores 50%.

6. The low crosstalk, high-resolution imaging optical fiber according to claim 1, characterized in that... The total amount of SiO2 and B2O3 in the common cladding and outer cladding is 68-85%, and the total amount of alkali metal oxides Li2O, Na2O and K2O is 8-22%.

7. The low crosstalk, high-resolution imaging optical fiber according to claim 1 or 2, characterized in that... The refractive index n1 of the image transmission layer is 1.65 to 1.75, and the refractive index n2 of the common cladding and the outer cladding is 1.49 to 1.

51.

8. The low crosstalk, high-resolution imaging optical fiber according to claim 1 or 2, characterized in that... The area ratio of the fiber core to the common cladding of the image transmission layer is 0.72 to 0.

82.

9. The low crosstalk, high-resolution imaging optical fiber according to claim 1 or 2, characterized in that... The image transmission layer has 1000 or more cores.

10. A method for fabricating a low-crosstalk, high-resolution imaging optical fiber according to any one of claims 1-9, characterized in that... Includes the following steps: S1: Mandrel preparation, fabricating multi-component doped silica mandrels, the mandrels including multi-component doped silica fiber mandrels and multi-component doped silica liner tubes; S2: Capillary rod drawing, the multi-component doped silica core rod is placed on a drawing tower and drawn into 5 or more different diameter capillary rods, cut into the same length and cleaned and dried, the capillary rod includes a multi-component doped silica core layer and a multi-component doped silica cladding layer. S3: Image transmission fiber preform preparation: Five or more capillary rods of the same length but different diameters are tightly and randomly stacked and fixed inside a multi-component doped glass jacket tube to obtain an image transmission fiber preform. S4: Image transmission fiber drawing: The image transmission fiber preform is drawn to form a low crosstalk, high resolution image transmission fiber.

11. The method for fabricating low-crosstalk, high-resolution imaging optical fiber according to claim 10, characterized in that... The aforementioned A multi-component doped silica core rod is prepared by a sleeve method, comprising a multi-component doped silica fiber core rod and a multi-component doped silica liner. The diameter of the fiber core rod is 15-35 mm, the outer diameter of the liner is 18-40 mm, the wall thickness is 1-2.5 mm, the core-to-closing ratio of the core rod is 0.72-0.82, and the numerical aperture (NA) is 0.6-0.

85.

12. The method for fabricating low-crosstalk, high-resolution imaging optical fiber according to claim 11, characterized in that... The diameter of the core rod is 22-35 mm, the outer diameter of the liner is 24-31 mm, the wall thickness is 1-1.5 mm, and the numerical aperture is 0.7-0.

85.

13. The method for fabricating low-crosstalk, high-resolution imaging optical fiber according to claim 11, characterized in that... The fiber core rod is a multi-component doped silica glass layer rod, comprising the following components by weight: BaO 22-31%, Na2O 2-6%, K2O 0-5%, Li2O 0-2%, Al2O3 1-7%, B2O3 0.5-10%, MgO 1-7%, CaO 0-3%, SrO 0-3%, La2O3 5-15%, Sb2O3 0.5-3%, ZnO 4-7%, ZrO2 2-3%, and SiO2 balance.

14. The method for fabricating low-crosstalk, high-resolution imaging optical fiber according to claim 13, characterized in that... The fiber core rod is a multi-component doped silica glass layer rod, comprising the following components by weight: BaO 25-30%, Na2O 2-4%, K2O 0-3%, Li2O 0-2%, Al2O3 1.5-5%, B2O3 0.5-5%, MgO 1-7%, CaO 0-3%, SrO 0-3%, La2O3 8-13%, Sb2O3 0.5-3%, ZnO 5-7%, ZrO2 2-3%, and SiO2 balance.

15. The method for fabricating low-crosstalk, high-resolution imaging optical fiber according to claim 13, characterized in that... The liner and outer sleeve are multi-component doped silica glass tubes, comprising the following components by weight: Al2O3 3-6%, B2O3 1-3%, MgO 0-5%, CaO 4-7%, Li2O 0-2%, Na2O 7-15%, K2O 0-5%, and SiO2 balance.

16. The method for fabricating low-crosstalk, high-resolution imaging optical fiber according to claim 15, characterized in that... The liner and outer sleeve are multi-component doped silica glass tubes, comprising the following components by weight: Al2O3 4-5%, B2O3 1-2%, MgO 0-3%, CaO 5-6%, Li2O 0-2%, Na2O 11-13%, K2O 0-3%, and SiO2 balance; wherein the total amount of SiO2 and B2O3 is 70-77%, and the total amount of alkali metal oxides Li2O, Na2O, and K2O is 11-18%.

17. The method for fabricating low-crosstalk, high-resolution imaging optical fiber according to claim 10 or 11, characterized in that... The capillary rod has a diameter of 0.2 mm to 1 mm and a length of 400 mm to 700 mm.

18. The method for fabricating low-crosstalk, high-resolution imaging optical fiber according to claim 10 or 11, characterized in that... The capillary rod has a diameter of 0.3mm to 0.6mm and a length of 400mm to 600mm.

19. The method for fabricating low-crosstalk, high-resolution imaging optical fiber according to claim 10 or 11, characterized in that... The proportion of capillary rods of each diameter to the total number of capillary rods is 10-40%, and the minimum diameter difference between two different diameter capillary rods is ≥7%, that is, the ratio of the larger diameter to the smaller diameter is ≥1.

07.

20. The method for fabricating low-crosstalk, high-resolution imaging optical fiber according to claim 10 or 11, characterized in that... The duty cycle of the image transmission fiber preform is 0.8 to 0.9.

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