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

Abstract

The invention relates to a low-crosstalk high-resolution image-transmitting optical fiber and a preparation method thereof.The low-crosstalk high-resolution 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, the image-transmitting fiber cores have five or more different core diameters, and the core diameters of the image-transmitting fiber cores are different. And the numerical aperture of the image transmitting optical fiber is 0.6-0.85. The image transmitting optical fiber is prepared from multiple components doped with silicon dioxide, a very high numerical aperture can be achieved, crosstalk among pixels can be optimized, the field angle is increased, the contrast ratio is improved, the field angle of the optical fiber is enlarged, meanwhile, the imaging quality is greatly improved, and the cost of the multi-component silicon dioxide material is low. According to the invention, the proportion of the common cladding in the image transmission plane is effectively reduced, the grid sense of the transmitted image is lower, the image is clearer and more coherent, five or more kinds of fiber cores with different core diameters are randomly distributed, the inter-core crosstalk can be further reduced, and the resolution is improved.

Description

Technical Field

[0001] The invention relates to a low-crosstalk and high-resolution image transmission optical fiber and a preparation method thereof, belonging to the technical field of optical fibers. Technical Background

[0002] Image transmission fiber, also known as imaging fiber, multi-core image transmission bundle or fiber image transmission bundle, is a passive fiber image transmission device and the core component of endoscope. With the advancement of endoscope-related technologies, the requirements for the imaging effect of image transmission fiber are getting higher and higher. The main indicators that characterize the imaging effect of image transmission fiber are the following two parameters: resolution and contrast. Resolution is a parameter that characterizes the image quality of image transmission fiber. It refers to the minimum distance between two points in space that the image transmission fiber can distinguish. It is usually expressed by the logarithm of the line spacing that can be distinguished per millimeter (lp / mm). The higher the resolution, the better the transmission quality and the higher the clarity. The resolution mainly depends on the core spacing between two pixels. The smaller the core spacing, the higher the resolution. However, as the core spacing becomes smaller, the crosstalk between the cores becomes larger. Therefore, the crosstalk rate of the pixel is also one of the factors affecting the image transmission quality of the image transmission fiber. How to optimize the crosstalk between the optical fiber cores has always been the focus of the audience. Optimizing the crosstalk between the cores is often achieved by increasing the numerical aperture or increasing the core spacing. Increasing the core spacing will lead to a decrease in the resolution of the image transmission fiber, thereby affecting the image transmission quality; the numerical aperture is related to the refractive index difference between the core layer and the cladding of the optical fiber. The greater the refractive index difference, the higher the numerical aperture. The size of the numerical aperture indicates the strength of the light collection ability of the image transmission fiber. A strong light collection ability will increase the contrast of the image transmission fiber; at the same time, increasing the numerical aperture can effectively reduce the crosstalk between the cores; therefore, how to increase the numerical aperture of the image transmission fiber is a key factor in improving its image transmission quality. Patent CN116239294 A discloses a method for making an image transmission fiber and an image transmission fiber, which adopts a secondary multifilament method to ensure that the pixel is neatly arranged, but it will gather into multiple hexagons on the end face of the optical fiber, and the image transmission surface is not uniform enough. Patent 117023972A discloses a quartz low crosstalk image transmission fiber and its preparation method. The numerical aperture of the pixel is 0.40-0.45, which is a relatively high numerical aperture of the current quartz image transmission fiber pixel, but the improvement of the image transmission quality is not ideal. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a low-crosstalk, high-resolution image transmission optical fiber and a preparation method thereof in view of the problems existing in the above-mentioned prior art, with small crosstalk between cores and high image transmission quality.

[0004] The technical solution adopted by the present invention to solve the above-mentioned problems is: 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, and is characterized in that the image transmission fiber core has 5 or more different core diameters, and the NA value of the image transmission optical fiber is 0.6 to 0.85.

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

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

[0007] According to the above scheme, the proportion of each diameter of the imaging fiber core to the total number of cores is 10-40%, and the minimum diameter difference between the two imaging fiber cores with different diameters 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 diameter and the minimum diameter of the 5 or more imaging fiber cores with different core diameters is ≤50%.

[0009] According to the above scheme, the image transmission fiber core is a doped silica 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 the 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 the 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 1.65-1.75, and the refractive index n2 of the common cladding and the outer cladding is 1.49-1.51.

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

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

[0015] The technical solution of the method for preparing the image transmission optical fiber of the present invention is:

[0016] Core rod preparation, making multi-component doped silica core rod, the core rod includes a multi-component doped silica fiber core rod and a multi-component doped silica liner,

[0017] Capillary rod drawing, placing the multi-component doped silica core rod on a drawing tower and drawing it into 5 or more capillary rods with different diameters, cutting them into the same length and washing and drying them, wherein the capillary rod comprises a multi-component doped silica core layer and a multi-component doped silica cladding layer,

[0018] Preparation of an image transmission optical fiber preform rod, wherein five or more capillary rods of the same length but different diameters are tightly and randomly stacked, filled and fixed in a multi-component doped glass outer sleeve to obtain an image transmission optical fiber preform rod,

[0019] The image transmission optical fiber is drawn by drawing the image transmission optical fiber preform rod to prepare a low crosstalk and high-resolution image transmission optical fiber.

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

[0021] According to the above scheme, 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.

[0022] According to the above scheme, the 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 component 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%, Sb2O30.5-3%, ZnO 5-7%, ZrO2 2-3%, and SiO2 balance.

[0024] According to the above scheme, the liner tube and outer sleeve are multi-component doped silica glass layer tubes, which include the following components by weight: Al2O3 3-6%, B2O3 1-3%, MgO 0-5%, CaO 4-7%, Li2O 0-2%, Na2O7-15%, K2O 0-5%, and SiO2 balance.

[0025] A more preferred component composition is: Al2O3 4-5%, B2O3 1-2%, MgO 0-3%, CaO 5-6%, Li2O0-2%, 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 capillary rod has a diameter of 0.2 mm to 1 mm and a length of 400 mm to 700 mm.

[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 the capillary rods of each diameter to the total number of capillary rods is 10-40%, and the minimum diameter difference between the two capillary rods of different diameters 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 optical fiber preform is 0.8 to 0.9; a more preferred duty cycle is 0.85 to 0.9.

[0030] The beneficial effects of the present invention are as follows: 1. The image transmission optical fiber is prepared from multi-component doped silica, which can achieve a very high numerical aperture, which is conducive to optimizing the crosstalk between pixels, increasing the field of view angle, and improving the contrast. While expanding the field of view of the optical fiber, the imaging quality is greatly improved, and the cost of multi-component silica materials is relatively low. 2. The numerical aperture of the present invention is almost twice that of fluorine-doped quartz, and the critical core spacing for crosstalk will become smaller. The core-to-shell ratio of the corresponding fiber core preform can be designed to be larger accordingly, thereby reducing the distance between the fiber cores and further increasing the area proportion of the pixel in the entire image transmission surface. On the one hand, the transmittance of the image transmission optical fiber is improved, and the proportion of the common cladding in the image transmission surface can also be effectively reduced, so that the grid sense of the transmitted image is lower and the image is clearer and more coherent. 3. The use of 5 or more cores with different core diameters randomly distributed can effectively suppress crosstalk between cores, thereby further reducing the core spacing and improving resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 FIG. 4 is a schematic diagram of a radial cross section of a capillary rod in one embodiment of the present invention.

[0032] Figure 2 FIG. 4 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 schematic diagram of a partial end face of an image transmission optical fiber preform in one embodiment of the present invention. Capillary rods with different numbers in the figure represent capillary rods with different outer diameters.

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

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

[0036] Figure 6 This is a diagram showing the image transmission effect of an image transmission optical fiber according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0038] Embodiment 1: A multi-component doped silica core rod is first prepared, the core rod includes a multi-component doped silica fiber core rod and a multi-component doped silica liner tube, the fiber core rod is a multi-component doped silica glass rod, and includes 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%, SiO2 balance; the refractive index n1 of the core rod glass is 1.69. The liner tube is a multi-component doped silica glass layer tube, and includes the following components by weight: Al2O3 4%, B2O32%, MgO 3%, CaO 5%, Li2O1%, Na2O 12%, K2O 3%, SiO2 balance, and the refractive index n2 of the liner tube glass is 1.51. The multi-component doped silica core rod is prepared by the sleeve method, wherein the prepared multi-component doped silica core rod glass material is rolled into a core rod material with a diameter of 20 mm, and the cladding glass material is molded into a tube with an outer diameter of 26 mm and a wall thickness of 2.5 mm. The core rod and the cladding liner are assembled into a core rod by the sleeve method, and the rod is placed on the stretching tower, and the vacuum is turned on after turning around. The wire is drawn at 800°C and 60m / min. The same core rod is used to draw ≥5 capillary rods with different outer diameters, which are numbered 1-5. The radius of the core layer 1 of the capillary rod is R1, and the radius of the cladding 2 is R2. The relevant parameters of the capillary rod are shown in Table 1. The capillary rod is cut into the same length and cleaned and dried.

[0039] Table 1: Main parameters of five capillary rods

[0040]

[0041] Preparation of multi-component image transmission optical fiber preform: The capillary rods are tightly and randomly stacked in a multi-component glass outer sleeve to prepare an image transmission optical fiber preform. The material composition of the multi-component glass outer sleeve is the same as that of the multi-component doped silica liner. The outer diameter of the preform is 40mm and the wall thickness is 2mm. The above-mentioned 5 kinds of pixel capillary rods are randomly filled in the preform sleeve until there is no obvious gap to the naked eye (about 6000±100 rods). One end of the multi-component image transmission optical fiber preform is closed until the capillary rod cannot fall out.

[0042] Drawing of multi-component image transmission optical fiber: The above preform rod is placed on the drawing tower, turned around and vacuumed, and drawn at 800℃ and 60m / min to obtain an optical fiber with a glass portion diameter of 350±20μm. After coating, an optical fiber with a diameter of 450±20μm is obtained. The refractive index curves of the optical fiber core layer and the cladding surrounding the core layer are as follows: Figure 2 As shown, the local end face of the optical fiber is Figure 4As shown. It includes an image transmission layer and an outer cladding 5 coated outside the image transmission layer, and a coating layer 6 outside the outer cladding. The image transmission layer includes a common cladding 7 and image transmission fiber cores 8 densely spaced in the common cladding. The image transmission fiber cores have 5 different core diameters. The number of fiber cores of the image transmission optical fiber ranges from 6000±100, and the diameter of the fiber core is 0.8 to 1.1μm. Figure 6 The image transmission effect of the 4 m image transmission optical fiber prepared in Example 1 on the USAF 1951 resolution plate at 510 nm. The main parameters of the optical 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 the imaging effect of the USAF 1951 resolution plate at 510 nm was measured. 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] It can be seen from the embodiment in Table 2 and the comparative example 1 that the resolution of the optical fiber of the present invention is significantly improved.

[0047] Embodiment 2-10:

[0048] The components of the multi-component doped silica core rod and the multi-component doped silica liner of Examples 2-6 are the same as those of Example 1. The mass percentages of the components of the core rods of Examples 7-10 are: BaO 27%, Na2O2%, K2O2%, Li2O 2%, Al2O3 2%, B2O3 2%, MgO 3%, CaO 1%, SrO 1%, La2O3 12%, Sb2O32%, ZnO 6%, ZrO2 2%, and the balance of SiO2; the refractive index n1 of the core glass is 1.71. The components of the liner are: Al2O3 4%, B2O32%, MgO 3%, CaO 5%, Li2O 1%, Na2O 12%, K2O 3%, and the balance of SiO2; the refractive index n2 of the sleeve glass is 1.51. The preparation process of Examples 2-10 is the same as that of 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 preparation process of the multi-component image-transmitting optical fiber of each embodiment is the same as that of embodiment 1. After turning, the multi-component image-transmitting optical fiber is drawn at a speed of 40 to 100 m / min in the temperature range of 650°C to 1000°C to obtain 9 multi-component image-transmitting optical fibers of different sizes. The main parameters of the optical fiber are shown in Table 4, where the resolution is the test data of 4 meters of optical fiber at 510 nm for the USAF 1951 resolution plate.

[0053]

Claims

1. A low crosstalk high-resolution 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 has 5 or more different core diameters, and the numerical aperture of the image transmission fiber is 0.6-0.

85.

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

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

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

07.

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

6. The low crosstalk high-resolution image transmission optical fiber according to claim 1 or 2, characterized in that The image transmission fiber core is a doped silica glass layer, 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%, La2O35-15%, Sb2O3 0.5-3%, ZnO 4-7%, ZrO2 2-3%, and SiO2 balance.

7. The low crosstalk high-resolution image transmission optical fiber according to claim 6, characterized in that The common cladding and the outer cladding are doped silica glass layers, which include the following components by weight: Al2O3 3-6%, B2O3 1-3%, MgO0-5%, CaO 4-7%, Li2O 0-2%, Na2O 7-15%, K2O 0-5%, and SiO2 balance.

8. The low crosstalk high-resolution image transmission optical fiber according to claim 7, characterized in that The total amount of SiO2 and B2O3 in the common cladding and the outer cladding is 68-85%, and the total amount of alkali metal oxides Li2O, Na2O and K2O is 8-22%.

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

51.

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

82.

11. The low crosstalk high-resolution image transmission optical fiber according to claim 1 or 2, characterized in that The number of cores of the image transmission layer is 1000 or more.

12. A method for preparing a low crosstalk high-resolution image transmission optical fiber, characterized in that The steps include: S1: core rod preparation, making a multi-component doped silica core rod, the core rod includes a multi-component doped silica fiber core rod and a multi-component doped silica liner; S2: capillary rod drawing, placing the multi-component doped silica core rod on a drawing tower and drawing it into 5 or more capillary rods with different diameters, cutting them into the same length and cleaning and drying them, the capillary rod includes a multi-component doped silica core layer and a multi-component doped silica cladding; S3: preparing an image transmission optical fiber preform, by densely and randomly stacking and filling the above-mentioned five or more capillary rods with the same length and different diameters and fixing them in a multi-component doped glass outer sleeve to obtain an image transmission optical fiber preform; S4: Drawing the image transmission optical fiber, drawing the image transmission optical fiber preform rod to prepare a low crosstalk and high-resolution image transmission optical fiber.

13. The method for preparing a low crosstalk high-resolution image transmission optical fiber according to claim 12, characterized in that The multi-component doped silica core rod is prepared by a sleeve method, including a multi-component doped silica core rod and a multi-component doped silica liner. The diameter of the core rod is 15 to 35 mm, the outer diameter of the liner is 18 to 40 mm, the wall thickness is 1 to 2.5 mm, the core-to-wrapper ratio of the core rod is 0.72 to 0.82, and the numerical aperture NA is 0.6 to 0.

85.

14. The method for preparing a low crosstalk high-resolution image transmission optical fiber according to claim 13, 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.

15. The method for preparing a low crosstalk high-resolution image transmission optical fiber according to claim 13, characterized in that 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.

16. The method for preparing a low crosstalk high-resolution image transmission optical fiber according to claim 15, characterized in that The fiber core rod is a multi-component doped silica glass layer rod, which includes the following components by weight: 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.

17. The method for preparing a low crosstalk high-resolution image transmission optical fiber according to claim 13, characterized in that The liner and outer sleeve are multi-component doped silica glass layer 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.

18. The method for preparing a low crosstalk high-resolution image transmission optical fiber according to claim 17, characterized in that The liner and outer sleeve are multi-component doped silica glass layer tubes, which include 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 as the balance; 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%.

19. The method for preparing a low crosstalk high-resolution image transmission optical fiber according to claim 12 or 13, 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.

20. The method for preparing a low crosstalk high-resolution image transmission optical fiber according to claim 12 or 13, characterized in that The capillary rod has a diameter of 0.3 mm to 0.6 mm and a length of 400 mm to 600 mm.

21. The method for preparing a low crosstalk high-resolution image transmission optical fiber according to claim 12 or 13, characterized in that The proportion of the capillary rods of each diameter to the total number of capillary rods is 10-40%, and the minimum diameter difference between the two capillary rods of different diameters is ≥7%, that is, the ratio of the larger diameter to the smaller diameter is ≥1.

07.

22. The method for preparing a low crosstalk high-resolution image transmission optical fiber according to claim 12 or 13, characterized in that The duty cycle of the image transmission optical fiber preform is 0.8-0.9.

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