Preparation method of high-resolution image transmission fiber and image transmission fiber

Abstract

The application relates to a preparation method of a high-resolution image transmission optical fiber and the image transmission optical fiber, which comprises the following steps: manufacturing a core rod, drawing a single wire, manufacturing a porous sleeve, preparing an image transmission optical fiber preform, inserting the same length single wires into each small-diameter through hole of the porous sleeve, each small-diameter through hole matching one single wire, and preparing an image transmission optical fiber preform; and finally drawing the image transmission optical fiber, and each single wire and the small-diameter through hole spacing layer of the porous sleeve are combined into a common cladding layer after being fused. The application uses a dense small-diameter porous sleeve to replace a traditional large single-hole sleeve, the single wire is inserted into the porous sleeve to prepare the image transmission optical fiber preform, the shape distortion of each core of the optical fiber is small after being drawn, the core arrangement is regular, the crosstalk between the cores is small, the resolution and contrast of the optical fiber are high, the image transmission quality of the optical fiber is good, and the optical fiber is especially suitable for use in endoscopes.

Description

Technical Field

[0001] This invention relates to a method for preparing a high-resolution image transmission fiber and the prepared image transmission fiber, belonging to the field of image transmission fiber technology. Technical Background

[0002] Image transmission fiber refers to optical fiber used for optical image transmission. A single image transmission fiber consists of multiple cores, each transmitting one pixel. The performance of image transmission fiber is mainly evaluated by its numerical aperture, transmittance, and resolution. The numerical aperture of an image transmission fiber is the same as that of a single fiber filament, and its size indicates the strength of the fiber's light-gathering ability. The numerical aperture of an image transmission fiber depends on the refractive index of each core. Transmittance is an important indicator of the light transmission performance of an image transmission fiber; higher transmittance means better light transmission. Resolution is a parameter characterizing the image quality transmitted by an image transmission fiber, referring to the minimum distance between two points in space that the fiber can resolve. Higher resolution means better transmission quality and higher clarity. The transmittance and resolution of image transmission fiber are related to the degree of coupling between fiber cores and the fiber core density. Specifically, the higher the refractive index of the fiber core, the smaller the core diameter, and the farther the spacing between adjacent cores, the less likely it is to couple with adjacent transmitted signals. From the perspective of eliminating coupling between fiber cores, it is beneficial to improve the transmittance and resolution of image transmission fiber. However, if the core diameter is too small and the spacing between adjacent cores is too far, each pixel will not be bright enough. At the same time, the pixels will be sparse, resulting in a decrease in resolution. Therefore, it is necessary to balance the diameter relationship of various parameters of the fiber profile.

[0003] There are three existing methods for fabricating optical fibers for image transmission: the lamination method, the acid dissolution method, and the multifilament method. The lamination method involves arranging drawn monofilament optical fibers into bundles, bonding and curing them, and then polishing them to obtain the optical fiber image bundle. Because the lamination method uses monofilament optical fibers to form bundles, the optical fiber image bundle has good flexibility (as described in CN 2833630 Y). However, the diameter of the monofilaments in the optical fiber image bundle produced by this method is relatively large, or as described in CN 103951184 A, the fiber fabrication process is prone to introducing contamination, making it difficult to achieve high resolution and transmittance.

[0004] The acid dissolution method, as described in CN 112573819 B, involves adding an acid-soluble outer cladding layer to the traditional optical fiber cladding, drawing monofilament optical fibers, combining them, and then drawing a multifilament fiber rod. The ends of the multifilament fiber rod are sealed according to the required length, and the rod is placed in an acidic solution to dissolve the outermost cladding layer of the monofilament optical fiber, thus obtaining a flexible image bundle. The acid dissolution method can produce high-resolution optical fiber image bundles through multifilament technology. However, when the diameter of the monofilament of the required optical fiber image bundle is too small, as in CN 104614804A using the acid dissolution method, the fibers are prone to breakage, making the manufacturing process relatively difficult.

[0005] The multifilament method involves filling the entire interior of a ferrule with single filaments and then drawing them to obtain the fiber. This method avoids the drawbacks of the lamination and acid-solution methods. As described in patent CN101178460B, 10,000 fiber optic cables (single filaments) are inserted together into a quartz tube and stretched to obtain a multi-core fiber with a diameter of 500µm. This preparation method has the following shortcomings: First, the single filaments are directly stacked in the ferrule without constraint or regularity, making it impossible to achieve a neat arrangement; in some areas, the single filaments intersect each other. The density between the single filaments is also difficult to unify, leading to stripes in the drawn fiber. Secondly, during the process of transforming the core rod into optical fiber, the gaps between the monofilaments are filled by the melting and flowing of all the monofilaments, inevitably leading to core deformation. In areas where the monofilaments are arranged regularly, the core layer will become hexagonal. In areas where the monofilaments are not arranged regularly (such as crossovers, missing strands, or uneven tension), the core layer will become various irregular shapes such as ellipses, semicircles, rhombuses, and triangles. In short, the final produced optical fiber deviates significantly from the initial design concept of a circular core with a hexagonal arrangement. The fiber end face also clearly shows that the core has become various shapes, none of which are circular (see appendix). Figure 6 At the same time, the cladding width around each fiber core becomes irregular, meaning the spacing between cores becomes irregular, which disrupts the weak coupling between fiber cores, increases the coupling between the signal transmitted by each fiber core and the adjacent fiber cores, and reduces the resolution of the optical fiber. The optical fiber prepared by this patent has a resolution of only about 115 lp / mm over a length of 3 meters. Summary of the Invention

[0006] To facilitate the explanation of this invention, some terms are defined as follows:

[0007] The diameter is 2r, and the radius r is the distance between the outer boundary of the layer and the center point.

[0008] Refractive index profile: The relationship between the glass refractive index and the radius in different regions of an optical fiber.

[0009] Relative refractive index difference: Δ% = [(n i 2 -n0 2 ) / 2n i 2 ]×100%≈(n i -n0) / n0×100%, n i n and n0 are the refractive indices of the corresponding optical fibers and the refractive index of the common cladding, i.e., pure silica glass, respectively.

[0010] The technical problem to be solved by the present invention is to provide a method for preparing high-resolution image transmission optical fiber and an image transmission optical fiber in order to overcome the shortcomings of the prior art. The prepared image transmission optical fiber has a regular core arrangement, small distortion, and high fiber resolution.

[0011] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0012] Manufacture of core rod: Deposit a cladding layer and a core layer inside a pure silica quartz liner. After deposition, melt and shrink the deposited liner to obtain a solid core rod.

[0013] Drawing monofilaments: The mandrel is placed on a drawing tower and drawn into monofilaments, cut into the same lengths and cleaned and dried. The monofilaments include a core layer, a recessed cladding layer and a monofilament cladding layer from the inside out.

[0014] Fabrication of a porous sleeve: The sleeve is made of pure silica glass, and parallel, spaced small-diameter through holes are densely arranged along the axial direction in the sleeve. The number of small-diameter through holes is the same as the number of cores of the image transmission fiber.

[0015] Preparing the image transmission fiber preform: Insert the monofilaments of the same length into each small-diameter through hole of the porous sleeve, with one monofilament matching each small-diameter through hole, to prepare the image transmission fiber preform.

[0016] Drawing the image transmission fiber: The image transmission fiber preform is placed on a drawing tower for drawing to obtain the image transmission fiber. At this time, the cladding of each monofilament and the small-diameter through-hole spacer layer (hole wall) of the porous sleeve are fused together to form a common cladding.

[0017] According to the above scheme, an inner cladding layer is provided between the core layer of the monofilament and the sunken cladding layer.

[0018] According to the above scheme, the relative refractive index difference Δ1 of the core layer is greater than 2%, the relative refractive index difference Δ2 of the recessed cladding layer is -1.5 to -0.4%, and the inner cladding layer and the monofilament cladding layer are pure silica glass layers.

[0019] According to the above scheme, the diameters of the core layer, inner cladding, sunken cladding and monofilament cladding of the monofilament are a1, a2, a3 and D, respectively. The diameter D of the monofilament cladding is 0.2 to 1.2 mm and the length is 200 to 2000 mm, and 0.35 < a1 / D < 0.65.

[0020] According to the above scheme, the monofilament cladding diameter D has k possible values, denoted as D1, D2, D3...D k k≥1, where different outer diameters refer to any D1, D2, D3...D k There are differences of 8% or more between them.

[0021] According to the above scheme, the porous sleeve is prepared by 3D printing or by laser etching or mechanical drilling using a glass rod.

[0022] According to the above scheme, the outer diameter of the porous sleeve is 20-200mm, the sleeve wall thickness (single-sided thickness of the outer sheath) is 0.08-1mm, the length is 200-2000mm, and the number of small-diameter through holes is ≥2000.

[0023] According to the above scheme, the inner diameter of the small-diameter through hole is 0.25-1.25 mm, and the hole spacing is 0.33-2 mm.

[0024] According to the above scheme, monofilaments with different cladding diameters are inserted into the adjacent small-diameter through holes.

[0025] According to the above scheme, the optical fiber preform is placed on the drawing tower and the drawing temperature is 1700-2000℃, the drawing speed is 30-1000m / min, and a resin coating layer is applied to the outer cladding layer during the drawing process.

[0026] The image-transmitting optical fiber prepared by the above method according to the present invention is characterized in that the diameter of the glass cladding layer of the image-transmitting optical fiber is 125-1200 μm, the outer diameter of the resin coating layer is 180-1800 μm, the number of cores m≥2000, and the core diameter A is 1.1-10 μm, with the minimum value being A. min (μm), with the maximum value being A. max (μm), the inter-core spacing B between adjacent core layers is 2.5–20 μm, with the minimum value being B. min (μm), with a maximum value of B. max (μm), and simultaneously satisfy A min / B max >0.35, A max / B min <0.65.

[0027] According to the above scheme, the 4-meter-long optical fiber has a transmittance of >92% in the 510nm band and a resolution of ≥143lp / mm.

[0028] According to the above scheme, the image transmission fiber matching jacket, lens, receiving device, etc. are assembled into an image transmission device.

[0029] The beneficial effects of this invention are as follows: 1. By using a dense, small-diameter, multi-hole sleeve instead of the traditional large single-hole sleeve, a preform of the image-transmitting fiber is prepared by inserting single filaments into the multi-hole sleeve, and then drawing the fiber to obtain the image-transmitting fiber. This overcomes the shortcomings of existing preparation methods where single filaments cannot be neatly stacked and the gaps between single filaments are filled by the single filaments themselves during drawing. The multi-hole sleeve constrains the neat arrangement of single filaments, and the gaps between single filaments are filled by the walls of the multi-hole sleeve. After drawing, each fiber core can maintain a neat arrangement according to the design requirements, with small core shape distortion, neat core arrangement, and low crosstalk between cores. This results in high fiber resolution and contrast, and good fiber image transmission quality, making it particularly suitable for use in endoscopes. 2. By setting an inner cladding outside the core layer, the distortion of the core can be further reduced, improving the quality of fiber image transmission. 3. The preparation method of this invention is reasonable and reliable. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of one embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram of a partial end face of a porous sleeve according to an embodiment of the present invention.

[0032] Figure 3 This is a partial end face diagram of a preform after a porous sleeve is matched with a monofilament, according to an embodiment of the present invention. The numbers in the diagram represent the different diameter types and distributions of the monofilaments.

[0033] Figure 4 This is a refractive index distribution curve of a portion of the core cladding in one embodiment of the present invention.

[0034] Figure 5 A microscope image of the end face of the imaging fiber prepared according to an embodiment of the present invention.

[0035] Figure 6 Microscopic image of the image transmission fiber end face prepared for Comparative Example 1.

[0036] Figure 7 The image transmission effect of a 4m imaging fiber prepared according to an embodiment of the present invention in the 510nm band is shown.

[0037] Figure 8 The image transmission effect of the 4m image transmission fiber prepared for Comparative Example 1 in the 510nm band is shown. Detailed Implementation

[0038] The present invention will be further illustrated below with reference to the embodiments.

[0039] Example 1: The production process of optical fiber for image transmission is shown in the diagram. Figure 1 As shown.

[0040] Mandrel and monofilament preparation: Using PCVD deposition technology with a pure silicon liner, a high-refractive-index mandrel was prepared through deposition and shrinkage processes. Then, three monofilaments with different outer diameters were drawn on a stretching tower. After cleaning and etching away part of the outer cladding, three different specifications of monofilaments were obtained, labeled 1-3. The relevant parameters of the monofilaments are shown in Table 1.

[0041] Table 1: Main parameters of three types of monofilaments

[0042]

[0043] Preparation of porous sleeve and preform: A porous sleeve is prepared by 3D printing process. Ten thousand holes are distributed inside the sleeve, and the inner diameter of each hole is between 0.29-0.35mm. The monofilament in Table 1 is inserted into the porous sleeve. The type of mandrel in adjacent holes can be the same or different.

[0044] Fiber Drawing: The preform is placed on the drawing tower, turned around, and vacuum is applied. At 1840℃, the fiber is drawn at a speed of 50 m / min to obtain an optical fiber with a glass portion of approximately 350 μm and a coated portion of approximately 450 μm. The refractive index curves of the fiber core and the surrounding cladding are shown below. Figure 4 As shown, a partial end-face view of the optical fiber is as follows. Figure 5 As shown, Figure 7 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.

[0045] Comparative Example 1:

[0046] Optical fiber preforms were prepared and drawn according to the conditions described in CN101178460B. A partial end-face view of the optical fiber is shown below. Figure 6 As shown, Figure 8 The image transmission effect of the 4m image-transmitting fiber prepared for Comparative Example 1 on a USAF 1951 resolution plate at 510nm is shown in Table 2. The main parameters of the fiber are shown in Table 2.

[0047] Table 2: Main parameters of optical fibers in Example 1 and Comparative Example 1

[0048]

[0049] As can be seen from the comparison between the embodiments and the comparative examples in Table 2, the transmittance and resolution of the optical fiber prepared by the present invention have been significantly improved.

[0050] Example 2-10:

[0051] Mandrel and monofilament preparation: Each embodiment used PCVD deposition process, followed by deposition and shrinkage steps to prepare mandrels with different profiles. Then, on a stretching tower, monofilaments of the same or different outer diameters were drawn from each mandrel. Afterward, part of the outer cladding was cleaned and etched away. The relevant parameters of the monofilaments are shown in Table 3.

[0052] Table 3: Main parameters of monofilaments in Examples 2-10

[0053]

[0054] Preparation of porous sleeves and preforms: Nine porous sleeves were prepared using 3D printing technology. The number of holes in the sleeves ranged from 15,000 to 100,000, the inner diameter of each hole was between 0.28 and 0.41 mm, and the maximum hole spacing was 0.5 mm. The monofilaments in Examples 2-10 were matched and the monofilaments in Table 3 were inserted into the porous sleeves.

[0055] Fiber drawing: The preformed rod is placed on the drawing tower, turned around and vacuumed. The fiber is drawn at a speed of 30-200m / min in the temperature range of 1800℃-1900℃ to obtain 9 different sizes of image transmission optical fibers. The main parameters of the optical fibers are shown in Table 4. The resolution is the test data of 4-meter optical fiber at 510nm on the USAF 1951 resolution board.

[0056] Table 4: Main parameters of optical fiber in Examples 2-10

[0057]

Claims

1. A method for fabricating a high-resolution image transmission optical fiber, characterized in that... include Manufacture of core rod: Deposit a cladding layer and a core layer inside a pure silica quartz liner. After deposition, melt and shrink the deposited liner to obtain a solid core rod. Drawing monofilaments: The mandrel is placed on a drawing tower and drawn into monofilaments, cut into the same lengths and cleaned and dried. The monofilaments include a core layer, a sunken cladding layer and a monofilament cladding layer from the inside out. Fabrication of a porous sleeve: The sleeve is made of pure silica glass, and parallel, spaced small-diameter through holes are densely arranged along the axial direction in the sleeve. The number of small-diameter through holes is the same as the number of cores of the image transmission optical fiber. The outer diameter of the porous sleeve is 20~200mm, the sleeve wall thickness is 0.08~1mm, the length is 200~2000mm, and the number of small-diameter through holes is ≥2000. Preparing the image transmission fiber preform: Insert monofilaments of the same length into each small-diameter through hole of the porous sleeve, with one monofilament matching each small-diameter through hole, to prepare the image transmission fiber preform. Drawing the image transmission fiber: The image transmission fiber preform is placed on a drawing tower for drawing to obtain the image transmission fiber. At this time, the cladding of each monofilament and the small-diameter through-hole spacer layer of the porous sleeve are fused together to form a common cladding.

2. The method for fabricating high-resolution imaging optical fiber according to claim 1, characterized in that... An inner cladding layer is provided between the core layer of the monofilament and the sunken cladding layer.

3. The method for fabricating high-resolution image transmission optical fiber according to claim 2, characterized in that... The core layer has a relative refractive index difference Δ1 > 2%, the sunken cladding has a relative refractive index difference Δ2 of -1.5 to -0.4%, and the inner cladding and monofilament cladding are pure silica glass layers.

4. The method for fabricating high-resolution imaging optical fiber according to claim 2, characterized in that... The diameters of the core layer, inner cladding, sunken cladding, and monofilament cladding of the monofilament are a1, a2, a3, and D, respectively. The diameter D of the monofilament cladding is 0.2~1.2mm, the length is 200~2000mm, and 0.35 < a1 / D < 0.

65.

5. The method for fabricating high-resolution imaging optical fiber according to claim 4, characterized in that... There are k types of monofilament cladding diameters D, denoted as D1, D2, D3...Dk, where k>1. Among the k types of cladding diameters, there is a difference of 8% or more between any D1, D2, D3...Dk.

6. The method for fabricating high-resolution imaging optical fiber according to claim 1 or 2, characterized in that... The porous sleeve is prepared by 3D printing or by laser etching or mechanical drilling using a glass rod.

7. The method for fabricating high-resolution image transmission optical fiber according to claim 1, characterized in that... The inner diameter of the small-diameter through hole is 0.25~1.25mm, and the hole spacing is 0.33~2mm.

8. The method for fabricating high-resolution image transmission optical fiber according to claim 5, characterized in that... Monofilaments with different cladding diameters are inserted into adjacent small-diameter through holes.

9. The method for fabricating high-resolution imaging optical fiber according to claim 1 or 2, characterized in that... The optical fiber preform is placed on a drawing tower and drawn at a temperature of 1700~2000℃ and a drawing speed of 30~1000m / min. During the drawing process, a resin coating layer is applied to the outer cladding layer.

10. A high-resolution imaging optical fiber prepared according to any one of claims 1-9, characterized in that... The outer cladding diameter of the optical fiber is 125~1200μm, the outer diameter of the resin coating layer is 180~1800μm, the number of fiber cores m≥2000, the core diameter A is 1.1~10μm, the minimum value is Amin, the maximum value is Amax, the core spacing B between adjacent core layers is 2.5~20μm, the minimum value is Bmin, the maximum value is Bmax, and simultaneously satisfy Amin / Bmax>0.35, Amax / Bmin<0.

65.

11. The high-resolution image transmission optical fiber according to claim 10, characterized in that... The 4-meter-long optical fiber has a transmittance of >92% in the 510nm band and a resolution of ≥143lp / mm.

12. An image transmission device, characterized in that... An image transmission device is assembled from the image transmission fiber matching jacket, lens, and receiving device as described in any one of claims 10-11.

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