Preparation method of large-size gradient refractive index plastic optical fiber preform

Abstract

The present invention discloses a method for preparing a large-size gradient refractive index plastic optical fiber preform. The device includes a prepolymerization chamber, a dopant chamber, a feed pump, a coextrusion head, a polymerization film forming area, rollers connected to a power device, and a winding and traction device. Polymer monomer M1 is prepolymerized at a temperature of 60°C to 80°C for 6 to 12 hours to obtain an M1 prepolymer. The M1 prepolymer is then pushed to the coextrusion head by the action of a screw in the screw zone. Simultaneously, a dopant M2 in the dopant chamber is transported to the coextrusion head by a feed pump. The amount of dopant M2 entering the coextrusion head is regulated by adjusting the speed of the feed pump. The mixed M1 prepolymer and dopant M2 enter the polymerization film forming chamber and polymerize into a polymer film. The polymer film is passed through a conveyor belt with the roller controlling the thickness. The polymer film is then wound into a large-size gradient refractive index plastic optical fiber preform by a winding and traction device. The method is simple, stable, and reliable. The refractive index gradient can be flexibly and precisely designed, and is adjustable and controllable.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic optical fiber preparation, and particularly relates to a method for preparing a large-size gradient refractive index plastic optical fiber preform. Background Art

[0002] In recent years, gradient-type (GI) plastic optical fiber has attracted much attention due to its great potential in optical fiber communications and optical integrated circuits based on polymer materials. For example, gradient lens arrays composed of hundreds of gradient cylindrical lenses have been used in small copiers; the bandwidth of gradient plastic optical fiber has reached the order of hundreds of megahertz, which is very important for fast data transmission, short-distance optical fiber communications and local area networks (LANs). GI plastic optical fiber preform is the precursor of GI plastic optical fiber, and most of the performance of GI optical fiber is largely determined by the GI plastic optical fiber preform. The refractive index in the GI plastic optical fiber preform is parabolic, with the highest refractive index at the central axis of the plastic rod, and decreases according to the square of the radius along the radial direction. There are currently four main methods for preparing GI plastic optical fiber:

[0003] (1) Interfacial gel polymerization. This process first uses PMMA to make a PMMA tube. A mixed solution composed of two different monomers is placed in this PMMA tube. One monomer, M1, has a high refractive index and a large molecular weight, while the other monomer, M2, has a low refractive index and a small molecular weight. The PMMA tube containing the mixed solution is placed in a drying oven and heated to 80°C. The inner wall of the PMMA tube begins to liquefy, forming a gel layer and accelerating the polymerization reaction from the PMMA tube wall to the center of the tube. The small molecular weight M2 easily diffuses into this gel layer, causing the concentration (refractive index) of M1 to gradually increase from the edge of the PMMA tube to the center. The resulting concentration gradient distribution is actually a gradient refractive index distribution structure.

[0004] (2) Centrifugal polymerization method: The process of preparing the gradient refractive index preform rod is to load the monomer mixture of two monomers with different refractive indices into three reaction tubes (one glass tube and two polymer tubes) of the same length, thickness and different inner diameter for heating and polymerization reaction. The temperature of the reactor is 60℃, and the rotation speed of the reaction tubes containing the three monomer mixtures with different refractive indices is 1000-2000r / min. The temperature of the reactor and the viscosity of the mixture change in the same way as the preparation of the polymer tube. Finally, in order to achieve the purpose of complete polymerization, the polymer preform rod is continuously polymerized at a temperature of 60℃ and a pressure of 0.2mmHg for 8 hours, thus preparing a transparent gradient refractive index preform rod with a length of 500mm and a diameter of 50mm.

[0005] (3) Continuous production method: First, a SI-POF is extruded, and then the SI-POF is passed through a heating tube. The dopant contained in the fiber core is heated and diffused, thereby producing GI-POF. Specifically, CYTOP + dopant raw materials are first added to the fiber core extruder, and the cladding is extruded by the cladding extruder. The SI-POF is produced by the core and cladding co-extrusion head. Then, the SI-POF is passed through a heating tube. The dopant in the SI-POF is heated in the heating tube and diffuses from the fiber core to the cladding, thereby realizing the transformation of the refractive index distribution from SI to GI. Finally, a 500-micron-thick PMMA protective layer is applied to the outer surface of the GI-POF to produce the PF-GI-POF product.

[0006] (4) Diffusion and rotation combined method. The principle of this method is that the monomer solution is placed in a cylindrical glass reaction tube, and a solid polymer material rod with a high refractive index is placed in the center of the tube. Through rotation and diffusion reaction, the high refractive index material rod slowly diffuses into the surrounding monomers to form the required gradient refractive index distribution structure.

[0007] In summary, these four methods all control the gradient refractive index of the refractive index by diffusing the high refractive index material in the low refractive index material. These methods have the following shortcomings: 1) The gradient refractive index of the plastic optical fiber rod cannot be precisely controlled, and the diffusion process is time-consuming, which slows down the entire preform preparation time; 2) It is difficult to prepare preforms with large diameters because large-diameter preforms require a long diffusion time. After the diffusion time becomes longer, as the degree of polymerization of the polymer monomer increases, the diffusion of the dopant will be inhibited, making it difficult to successfully prepare preforms with large diameters. Summary of the Invention

[0008] In view of the defects or shortcomings in the above-mentioned prior art, the object of the present invention is to provide a method for preparing a large-sized gradient refractive index plastic optical fiber preform. The plastic optical fiber preform prepared by this method can not only ensure the consistency of the gradient refractive index, but also is simple in method, has good stability and reliability, and the refractive index gradient can be flexibly designed.

[0009] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0010] The first technical solution:

[0011] A method for preparing a large-size gradient refractive index plastic optical fiber preform, characterized in that the method uses an apparatus comprising a prepolymerization chamber and a dopant chamber, wherein the prepolymerization chamber contains a low-refractive-index, low-molecular-weight polymer monomer M1, and the dopant chamber contains a high-refractive-index, high-molecular-weight dopant M2;

[0012] The prepolymerization chamber is connected to the first feeding pump, which is connected to the co-extrusion head through the screw zone, and the co-extrusion head is connected to the polymerization film forming zone. The polymerization film forming chamber is provided with a conveyor belt, a roller connected to a power device, and a winding traction device;

[0013] The dopant chamber is connected to a second feeding pump, and the second feeding pump is connected to the polymerization film forming area through a linear feeding hole at the upper end of the co-extrusion head outlet;

[0014] The method for preparing a large-size gradient refractive index plastic optical fiber preform is as follows:

[0015] The low refractive index and small molecular weight polymer monomer M1 in the prepolymerization chamber is prepolymerized at a temperature of 60°C to 80°C for 6h to 12h to obtain the prepolymer of M1, and then the prepolymer of M1 is sent to the screw zone by the first feeding pump. Under the action of the screw, the prepolymer of M1 is pushed to the co-extrusion head; at the same time, the dopant M2 with a high refractive index and a large molecular weight in the dopant chamber is sent to the co-extrusion head by the second feeding pump, and the speed of the second feeding pump is adjusted to adjust the amount of dopant M2 entering the co-extrusion head. The dopant M2 enters a linear feed hole with a port width of 1mm-3mm at the co-extrusion head. The feed hole is located at the upper end of the co-extrusion head outlet. The mixed prepolymer M1 and dopant M2 enter the polymerization film forming chamber. The temperature of the polymerization film forming chamber is controlled between 150°C and 240°C. The polymer is polymerized into a polymer film in the polymerization film forming chamber. The polymer film is conveyed by a conveyor belt with the thickness controlled by a roller. The polymer film is then wound into a large-sized gradient refractive index plastic optical fiber preform rod through a winding and traction device.

[0016] By controlling the addition amount of dopant M2 at different time periods, i.e., different positions of the polymer film, corresponding to different radii of the final large-size gradient refractive index plastic optical fiber preform, the different radii r x The refractive index n(r x ), thereby accurately controlling the refractive index gradient of the large-size gradient refractive index plastic optical fiber preform;

[0017] The refractive index at a certain radius satisfies the following formula:

[0018] Where x = 0, 1, 2, 3, ..., k;

[0019] Where n(r x ) is the refractive index at radius r; n0 is the refractive index at the central axis; A is a constant; r x is the radius;

[0020] r x Satisfies the following formula:

[0021]

[0022] Where v is the linear velocity of the polymer film, t k For time, l k t k The total length of the polymer film at that moment.

[0023] Polymer film Within the location area, the corresponding time period is:

[0024] When , the refractive index is:

[0025] Wherein, x=0, 1, 2, 3, ...., k.

[0026] n(r x ) also satisfies the following formula:

[0027] n(r x )=n1(1-ρ x )+n2ρ x , ρ x =ρ0(1-t / k),

[0028] n1 is the refractive index of the monomer, n2 is the refractive index of the dopant, and ρ x is the doping concentration of the dopant, and ρ0 is the initial doping concentration.

[0029] The refractive index n0 at the central axis can be expressed by the following formula:

[0030] n0=n1(1-ρ0)+n2ρ0;

[0031] Therefore, the formula for refractive index can be expressed as a function of t:

[0032]

[0033] The second technical solution:

[0034] A method for preparing a large-size gradient refractive index plastic optical fiber preform, characterized in that the method uses an apparatus comprising a prepolymerization chamber and a dopant chamber, wherein the prepolymerization chamber contains a low-refractive-index, low-molecular-weight polymer monomer M1, and the dopant chamber contains a high-refractive-index, high-molecular-weight dopant M2;

[0035] The prepolymerization chamber is connected to the first feed pump, the dopant chamber is connected to the second feed pump, the first feed pump and the second feed pump are respectively connected to the co-extrusion head, the co-extrusion head is connected to the die head through the screw mixing zone, and the die head is connected to the polymerization film forming chamber. A conveyor belt, a roller connected to a power device, and a winding traction device are provided in the polymerization film forming chamber;

[0036] The method for preparing a large-size gradient refractive index plastic optical fiber preform is as follows:

[0037] The low-refractive-index, low-molecular-weight polymer monomer M1 in the prepolymerization chamber is prepolymerized at a temperature of 60°C to 80°C for 1h to 12h, and then the prepolymer of M1 is delivered to the coextrusion head by the first feeding pump. At the same time, the high-refractive-index, high-molecular-weight dopant M2 in the raw material chamber is delivered to the coextrusion head by the second feeding pump. The prepolymer of M1 and the dopant M2 are mixed under the action of the screw in the screw mixing zone, and the mixture is pushed to the die head; the discharge port of the die head is a linear hole with a width of 0.01mm-0.5mm. The mixture extruded from the discharge port of the die head enters the polymerization film-forming chamber for further polymerization. The temperature of the polymerization film-forming chamber is controlled between 150°C and 240°C. In the polymerization film-forming chamber, the mixture is polymerized into a polymer film. The polymer film is wound into a large-size gradient refractive-index plastic optical fiber preform rod by a winding and traction device with a conveyor belt and a roller controlling the thickness;

[0038] By controlling the addition amount of dopant M2 at different time periods, i.e., different positions of the polymer film, corresponding to different radii of the final polymer rod, and by controlling the speed of the second feeding pump, the addition amount of dopant M2 can be adjusted, and different radii r can be controlled. x The refractive index n(r x ), thereby being able to accurately control the refractive index gradient of the large-size gradient refractive index plastic optical fiber preform;

[0039] The refractive index at a certain radius satisfies the following formula:

[0040] Where x = 0, 1, 2, 3, ..., k;

[0041] Where n(r x ) is the refractive index at radius r; n0 is the refractive index at the central axis; A is a constant; r x is the radius;

[0042] r x Satisfies the following formula:

[0043]

[0044] Where v is the linear velocity of the polymer film, t k For time, l k t k The total length of the polymer film at that moment.

[0045] Polymer film Within the location area, the corresponding time period is:

[0046] When , the refractive index is:

[0047] Wherein, x=0, 1, 2, 3, ...., k.

[0048] n(r x ) also satisfies the following formula:

[0049] n(r x )=n1(1-ρ x )+n2ρ x , ρ x =ρ0(1-t / k);

[0050] Where n1 is the refractive index of the monomer, n2 is the refractive index of the dopant, and ρ x is the doping concentration of the dopant, and ρ0 is the initial doping concentration.

[0051] The refractive index n0 at the central axis can be expressed by the following formula:

[0052] n0=n1(1-ρ0)+n2ρ0

[0053] Therefore, the formula for refractive index can be expressed as a function of t:

[0054]

[0055] The third technical solution:

[0056] A method for preparing a large-size gradient refractive index plastic optical fiber preform, characterized in that the method uses an apparatus comprising a prepolymerization chamber and a dopant chamber, wherein the prepolymerization chamber contains a low-refractive-index, low-molecular-weight polymer monomer M1, and the dopant chamber contains a high-refractive-index, high-molecular-weight dopant M2;

[0057] The prepolymerization chamber is connected to the first feeding pump, the dopant chamber is connected to the second feeding pump, the first feeding pump and the second feeding pump are respectively connected to the co-extrusion head, the co-extrusion head is connected to the die head through the screw mixing zone, and the die head outlet end is provided with a winding traction device;

[0058] The method for preparing a large-size gradient refractive index plastic optical fiber preform is as follows:

[0059] The low-refractive-index, low-molecular-weight polymer monomer M1 in the prepolymerization chamber is prepolymerized at a temperature of 60°C to 80°C for 1h to 12h, and then the M1 prepolymer is delivered to the coextrusion head by a first feeding pump. At the same time, the high-refractive-index, high-molecular-weight dopant M2 in the dopant chamber is delivered to the coextrusion head by a second feeding pump. The M1 prepolymer and the dopant M2 are mixed by the screw in the screw mixing zone, and the mixture is pushed to the die head; the discharge port of the die head is a linear hole with a width of 0.01mm-0.5mm. The mixed prepolymer after extrusion is coated on the rotating shaft of the winding and traction device. The temperature of the winding zone of the rotating shaft is controlled between 150°C and 240°C. As the rotating shaft rotates, a large-sized gradient refractive-index plastic optical fiber preform is produced;

[0060] By controlling the addition amount of dopant M2 in different time periods, that is, corresponding to different radii of the final large-size gradient refractive index plastic optical fiber preform, the addition amount of dopant M2 can be adjusted by controlling the speed of the second feeding pump to regulate the different radii r x The refractive index n(r x ), and thus the refractive index gradient of large-size gradient refractive index plastic optical fiber preform can be accurately controlled;

[0061] The refractive index at a certain radius satisfies the following formula:

[0062] Where x = 0, 1, 2, 3, ..., k;

[0063] Where n(r x ) is the refractive index at radius r; n0 is the refractive index at the central axis; A is a constant; r x is the radius;

[0064] r x Satisfies the following formula:

[0065]

[0066] Where v is the linear velocity of the polymer film, t k For time, l k t k The total length of the polymer film at that moment.

[0067] Polymer film Within the location area, the corresponding time period is:

[0068] hour,

[0069] The refractive index is:

[0070] Wherein, x=0, 1, 2, 3, ...., k.

[0071] n(r x ) also satisfies the following formula:

[0072] n(r x )=n1(1-ρ x )+n2ρ x , ρ x =ρ0(1-t / k),

[0073] Where n1 is the refractive index of the monomer, n2 is the refractive index of the dopant, and ρ x is the doping concentration of the dopant, and ρ0 is the initial doping concentration.

[0074] The refractive index n0 at the central axis can be expressed by the following formula:

[0075] n0=n1(1-ρ0)+n2ρ0

[0076] Therefore, the formula for refractive index can be expressed as a function of t:

[0077]

[0078] The method for preparing a large-size gradient-refractive-index plastic optical fiber preform of the present invention can rapidly and stably produce large-diameter plastic optical fiber preforms. Not only can the consistency of the gradient refractive index of the prepared plastic optical fiber preform be ensured, but the method is also simple, stable, and reliable, and the refractive index gradient can be flexibly designed, adjusted, and controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 This is a schematic diagram of a first device for a large-size gradient refractive index plastic optical fiber preform according to the present invention;

[0080] Figure 2 This is a schematic diagram of a second device for the large-size gradient refractive index plastic optical fiber preform of the present invention;

[0081] Figure 3 This is a schematic diagram of a third device for a large-size gradient refractive index plastic optical fiber preform according to the present invention;

[0082] The marks in the figure respectively represent: 1. prepolymerization chamber, 2. first feed pump, 3. screw zone, 4. dopant chamber, 5. second feed pump, 6. co-extrusion head, 7. polymerization film forming zone, 8. roller, 9. power device, 10. winding and traction device, 11. linear feed hole, 12. die head, 13. screw mixing zone.

[0083] The present invention is further described in detail below with reference to the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0084] Example 1:

[0085] See also Figure 1 This embodiment provides a method for preparing a large-size gradient refractive index plastic optical fiber preform. The device used includes a prepolymerization chamber 1 and a dopant chamber 4. The prepolymerization chamber 1 contains a low-refractive-index, low-molecular-weight polymer monomer M1, and the dopant chamber 4 contains a high-refractive-index, high-molecular-weight dopant M2.

[0086] The prepolymerization chamber 1 is connected to the first feeding pump 2, which is connected to the co-extrusion head 6 through the screw zone 3. The co-extrusion head 6 is connected to the polymerization film forming zone 7. The polymerization film forming chamber 7 is provided with a conveyor belt, a roller 8 connected to a power device 9, and a winding and traction device 10;

[0087] The dopant chamber 4 is connected to the second feeding pump 5, and the second feeding pump 5 is connected to the polymerization film forming area 7 through the linear feeding hole 11 at the upper end of the discharge port of the co-extrusion head 6;

[0088] The method for preparing a large-size gradient refractive index plastic optical fiber preform is as follows:

[0089] The low refractive index and small molecular weight polymer monomer M1 in the prepolymerization chamber 1 is prepolymerized at a temperature of 60°C to 80°C for 6h to 12h to obtain the prepolymer of M1. The prepolymer of M1 is then fed to the screw zone by the first feeding pump. Under the action of the screw, the prepolymer of M1 is pushed to the coextrusion head 6. At the same time, the dopant M2 with a high refractive index and a large molecular weight in the dopant chamber 4 is fed to the coextrusion head 6 by the second feeding pump 5. By adjusting the speed of the second feeding pump 5, the dopant M2 is adjusted to enter the coextrusion head 6. The dopant M2 enters the linear feed hole 11 with a port width of 1mm-3mm of the co-extrusion head 6, and the mixed prepolymer M1 and dopant M2 enter the polymerization film forming chamber 7, and are polymerized into a polymer film in the polymerization film forming chamber 7 (the temperature of the polymerization film forming chamber 7 is controlled in the range of 150℃~240℃). The polymer film is wound into a large-size gradient refractive index plastic optical fiber preform rod by a conveyor belt and a winding and traction device 10.

[0090] By controlling the addition amount of dopant M2 at different time periods, i.e., different positions of the polymer film, corresponding to different radii of the final large-size gradient refractive index plastic optical fiber preform (also called GI plastic optical fiber preform), the different radii r can be controlled. x The refractive index n(r x ), and thus the refractive index gradient of the GI plastic optical fiber preform can be precisely controlled.

[0091] The refractive index at a certain radius satisfies the following formula:

[0092] Where x = 0, 1, 2, 3, ..., k;

[0093] Where n(r x ) is the refractive index at radius r; n0 is the refractive index at the central axis; A is a constant; r x is the radius;

[0094] r x Satisfies the following formula:

[0095]

[0096] Where v is the linear velocity of the polymer film, t k For time, l k t k The total length of the polymer film at that moment.

[0097] Polymer film Within the location area, the corresponding time period is:

[0098] When , the refractive index is:

[0099] Wherein, x=0, 1, 2, 3, ...., k.

[0100] n(r x ) also satisfies the following formula:

[0101] n(r x )=n1(1-ρ x )+n2ρ x , ρ x =ρ0(1-t / k),

[0102] Where n1 is the refractive index of the monomer, n2 is the refractive index of the dopant, and ρ x is the doping concentration of the dopant, and ρ0 is the initial doping concentration.

[0103] The refractive index n0 at the central axis can be expressed by the following formula:

[0104] n0=n1(1-ρ0)+n2ρ0

[0105] Therefore, the formula for refractive index can be expressed as a function of t:

[0106]

[0107] Example 2:

[0108] See also Figure 2This embodiment provides a method for preparing a large-size gradient refractive index plastic optical fiber preform. The device used includes a prepolymerization chamber 1 and a dopant chamber 4. The prepolymerization chamber 1 contains a low-refractive-index, low-molecular-weight polymer monomer M1, and the dopant chamber 4 contains a high-refractive-index, high-molecular-weight dopant M2.

[0109] The prepolymerization chamber 1 is connected to the first feed pump 2, the dopant chamber 4 is connected to the second feed pump 5, the first feed pump 2 and the second feed pump 5 are respectively connected to the co-extrusion head 6, the co-extrusion head 6 is connected to the die head 12 through the screw mixing zone 13, the die head 12 is connected to the polymerization film forming chamber 7, and a conveyor belt, a roller 8 connected to the power device 9 and a winding and traction device 10 are provided in the polymerization film forming chamber 7;

[0110] The method for preparing a large-size gradient refractive index plastic optical fiber preform is as follows:

[0111] The low refractive index and small molecular weight polymer monomer M1 in the prepolymerization chamber 1 is prepolymerized at a temperature of 60°C to 80°C for 1h to 12h, and then the prepolymer of M1 is fed to the coextrusion head 6 by the first feeding pump 1, and at the same time, the dopant M2 with a high refractive index and a large molecular weight in the dopant chamber 4 is transported to the coextrusion head 6 by the second feeding pump 5. The prepolymer of M1 and the dopant M2 are mixed under the action of the screw in the screw mixing zone 13, and the mixture is pushed to the die 12; the discharge port of the die 12 is a linear hole with a width of 0.01mm-0.5mm. The extruded mixture enters the polymerization film forming chamber 7 for further polymerization (the temperature of the polymerization film forming chamber 7 is controlled in the range of 150°C to 240°C). In the polymerization film forming chamber 7, the mixture is polymerized into a polymer film. The polymer film is wound into a large-size gradient refractive index plastic optical fiber preform (i.e., GI optical fiber preform) by a winding and traction device 10 under the condition that the thickness of the polymer film is controlled by a conveyor belt and a roller 8.

[0112] By controlling the amount of dopant M2 added at different time periods (i.e., different positions of the polymer film, corresponding to different radii of the final GI optical fiber preform) (the amount of dopant M2 added can be adjusted by controlling the speed of the second feeding pump 5), the different radii r x The refractive index n(r x ), and thus the refractive index gradient of large-size gradient refractive index plastic optical fiber preform (GI plastic optical fiber preform) can be precisely controlled.

[0113] The refractive index at a certain radius satisfies the following formula:

[0114] Where x = 0, 1, 2, 3, ..., k;

[0115] Where n(r x) is the refractive index at radius r; n0 is the refractive index at the central axis; A is a constant; r x is the radius;

[0116] r x Satisfies the following formula:

[0117]

[0118] Where v is the linear velocity of the polymer film, t k For time, l k t k The total length of the polymer film at that moment.

[0119] Polymer film Within the location area, the corresponding time period is:

[0120] When , the refractive index is:

[0121] Wherein, x=0, 1, 2, 3, ...., k.

[0122] n(r x ) also satisfies the following formula:

[0123] n(r x )=n1(1-ρ x )+n2ρ x , ρ x =ρ0(1-t / k),

[0124] Where n1 is the refractive index of the monomer, n2 is the refractive index of the dopant, and ρ x is the doping concentration of the dopant, and ρ0 is the initial doping concentration.

[0125] The refractive index n0 at the central axis can be expressed by the following formula:

[0126] n0=n1(1-ρ0)+n2ρ0

[0127] Therefore, the formula for refractive index can be expressed as a function of t:

[0128]

[0129] Example 3:

[0130] See also Figure 3 This embodiment provides a method for preparing a large-size gradient refractive index plastic optical fiber preform. The device used includes a prepolymerization chamber 1 and a dopant chamber 4. The prepolymerization chamber 1 contains a low-refractive-index, low-molecular-weight polymer monomer M1, and the dopant chamber 4 contains a high-refractive-index, high-molecular-weight dopant M2.

[0131] The prepolymerization chamber 1 is connected to the first feed pump 2, the dopant chamber 4 is connected to the second feed pump 5, the first feed pump 2 and the second feed pump 5 are respectively connected to the co-extrusion head 6, the co-extrusion head 6 is connected to the die head 12 through the screw mixing zone 13, and the outlet end of the die head 12 is provided with a winding and traction device 10;

[0132] The method for preparing a large-size gradient refractive index plastic optical fiber preform is as follows:

[0133] The low refractive index and small molecular weight polymer monomer M1 in the prepolymerization chamber 1 is prepolymerized at a temperature of 60°C to 80°C for 1h to 12h, and then the prepolymer of M1 is fed to the coextrusion head 6 by the first feeding pump 1. At the same time, the dopant M2 with a high refractive index and a large molecular weight in the dopant chamber 4 is fed to the coextrusion head 6 by the second feeding pump 5. The prepolymer of M1 and the dopant M2 are mixed under the action of the screw in the screw mixing zone 13, and the mixture is pushed to the die 12; the discharge port of the die 12 is a linear hole with a width of 0.01mm-0.5mm. The mixed prepolymer after extrusion is coated on the rotating shaft of the winding and traction device 10 (the temperature of the winding zone of the rotating shaft is controlled in the range of 150°C to 240°C), and is prepared into a large-size gradient refractive index plastic optical fiber preform (GI optical fiber preform) as the rotating shaft rotates.

[0134] By controlling the amount of dopant M2 added in different time periods (corresponding to different radii of the final GI optical fiber preform) (the amount of dopant M2 added can be adjusted by controlling the speed of the second feeding pump 5), the different radii r x The refractive index n(r x ), and thus the refractive index gradient of large-size gradient refractive index plastic optical fiber preform can be precisely controlled.

[0135] The refractive index at a certain radius satisfies the following formula:

[0136] Where x = 0, 1, 2, 3, ..., k;

[0137] Where n(r x ) is the refractive index at radius r; n0 is the refractive index at the central axis; A is a constant; r x is the radius;

[0138] r x Satisfies the following formula:

[0139]

[0140] Where v is the linear velocity of the polymer film, t k For time, l k t k The total length of the polymer film at that moment.

[0141] Polymer film Within the location area, the corresponding time period is:

[0142] When , the refractive index is:

[0143] Wherein, x=0, 1, 2, 3, ...., k.

[0144] n(r x ) also satisfies the following formula:

[0145] n(r x )=n1(1-ρ x )+n2ρ x , ρ x =ρ0(1-t / k),

[0146] n1 is the refractive index of the monomer, n2 is the refractive index of the dopant, and ρ x is the doping concentration of the dopant, and ρ0 is the initial doping concentration.

[0147] The refractive index n0 at the central axis can be expressed by the following formula:

[0148] n0=n1(1-ρ0)+n2ρ0

[0149] Therefore, the formula for refractive index can be expressed as a function of t:

[0150]

Claims

1. A method for preparing a large-size gradient refractive index plastic optical fiber preform, characterized in that: The device used in the method includes a prepolymerization chamber and a dopant chamber, wherein the prepolymerization chamber contains a polymer monomer M1 with a low refractive index and a small molecular weight, and the dopant chamber contains a dopant M2 with a high refractive index and a large molecular weight; The prepolymerization chamber is connected to the first feeding pump, the first feeding pump is connected to the co-extrusion head through the screw zone, the co-extrusion head is connected to the polymerization film forming chamber, and the polymerization film forming chamber is provided with a conveyor belt, a roller connected to a power device and a winding traction device; The dopant chamber is connected to the second feeding pump, and the second feeding pump is connected to the polymerization film forming chamber through the linear feeding hole at the upper end of the co-extrusion head outlet; The method for preparing a large-size gradient refractive index plastic optical fiber preform is as follows: The low refractive index and small molecular weight polymer monomer M1 in the prepolymerization chamber is prepolymerized at a temperature of 60°C to 80°C for 6h to 12h to obtain the prepolymer of M1, and then the prepolymer of M1 is sent to the screw zone by the first feeding pump. Under the action of the screw in the screw zone, the prepolymer of M1 is pushed to the co-extrusion head; at the same time, the dopant M2 with a high refractive index and a large molecular weight in the dopant chamber is sent to the co-extrusion head by the second feeding pump, and the speed of the second feeding pump is adjusted to adjust the speed of the dopant M2 entering the co-extrusion head. The dopant M2 enters the linear feed hole with a port width of 1mm-3mm of the co-extrusion head, and the linear feed hole is located at the upper end of the co-extrusion head outlet. The mixed prepolymer M1 and dopant M2 enter the polymerization film forming chamber, and the temperature of the polymerization film forming chamber is controlled between 180℃ and 240℃; the polymer is polymerized into a polymer film in the polymerization film forming chamber, and the polymer film is wound into a large-sized gradient refractive index plastic optical fiber preform rod by a winding and traction device under the condition that the thickness of the polymer film is controlled by a roller on a conveyor belt; By controlling the addition amount of dopant M2 at different time periods, i.e., different positions of the polymer film, corresponding to different radii of the final large-size gradient refractive index plastic optical fiber preform, the different radii r x The refractive index n(r x ), thereby accurately controlling the refractive index gradient of the large-size gradient refractive index plastic optical fiber preform; The refractive index at a certain radius satisfies the following formula: ; where x = 0, 1, 2, 3, ...., k; Where, n ( r x ) is the refractive index at radius r; n0 is the refractive index at the central axis; A is a constant; r x is the radius; r x Satisfies the following formula: v·t k =l k = in, v is the linear velocity of the polymer film, t k For the moment, l k for t k The total length of the polymer film at the moment; Polymer films in ~ Within the location area, the corresponding time period is: / v ~ / v The refractive index is: ； n( r x ) also satisfies the following formula: ， ； Where n1 is the refractive index of the monomer, n2 is the refractive index of the dopant, and ρ x is the doping concentration of the dopant, ρ0 is the initial doping concentration; The refractive index n0 at the central axis is expressed by the following formula: ； Therefore, the formula for the refractive index is expressed as a function of t: 。 2. A method for preparing a large-size gradient refractive index plastic optical fiber preform, characterized in that: The device used in the method includes a prepolymerization chamber and a dopant chamber, wherein the prepolymerization chamber contains a polymer monomer M1 with a low refractive index and a small molecular weight, and the dopant chamber contains a dopant M2 with a high refractive index and a large molecular weight; The prepolymerization chamber is connected to the first feed pump, the dopant chamber is connected to the second feed pump, the first feed pump and the second feed pump are respectively connected to the co-extrusion head, the co-extrusion head is connected to the die head through the screw mixing zone, and the die head is connected to the polymerization film forming chamber. A conveyor belt, a roller connected to a power device, and a winding traction device are provided in the polymerization film forming chamber; The method for preparing a large-size gradient refractive index plastic optical fiber preform is as follows: The low-refractive-index, low-molecular-weight polymer monomer M1 in the prepolymerization chamber is prepolymerized at a temperature of 60°C to 80°C for 1h to 12h, and then the prepolymer of M1 is delivered to the coextrusion head by the first feeding pump. At the same time, the dopant M2 with a high-refractive-index and high-molecular-weight in the dopant chamber is delivered to the coextrusion head by the second feeding pump. The prepolymer of M1 and the dopant M2 are mixed under the action of the screw in the screw mixing zone, and the mixture is pushed to the die head; the discharge port of the die head is a linear hole with a width of 0.01mm-0.5mm. The mixture extruded from the discharge port of the die head enters the polymerization film-forming chamber for further polymerization. The temperature of the polymerization film-forming chamber is controlled between 150°C and 240°C. In the polymerization film-forming chamber, the mixture is polymerized into a polymer film. The polymer film is wound into a large-size gradient refractive-index plastic optical fiber preform rod by a winding and traction device with a conveyor belt and a roller controlling the thickness; By controlling the addition amount of dopant M2 at different time periods, i.e., different positions of the polymer film, corresponding to different radii of the final large-size gradient refractive index plastic optical fiber preform, and by controlling the speed of the second feeding pump, the addition amount of dopant M2 can be adjusted, and the different radii r can be controlled. x The refractive index n(r x ), thereby being able to accurately control the refractive index gradient of the large-size gradient refractive index plastic optical fiber preform; The refractive index at a certain radius satisfies the following formula: ; where x = 0, 1, 2, 3, ...., k; Where n( r x ) is the refractive index at radius r; n0 is the refractive index at the central axis; A is a constant; r x is the radius; r x Satisfies the following formula: v·t k =l k = in, v is the linear velocity of the polymer film, t k For the moment, l k for t k The total length of the polymer film at the moment; Polymer films in ~ Within the location area, the corresponding time period is: / v ~ / v The refractive index is: ； n( r x ) also satisfies the following formula: ， ， Where n1 is the refractive index of the monomer, n2 is the refractive index of the dopant, and ρ x is the doping concentration of the dopant, ρ0 is the initial doping concentration; The refractive index n0 at the central axis is expressed by the following formula: ； Therefore, the formula for the refractive index is expressed as a function of t: 。 3. A method for preparing a large-size gradient refractive index plastic optical fiber preform, characterized in that: The device used in the method includes a prepolymerization chamber and a dopant chamber, wherein the prepolymerization chamber contains a polymer monomer M1 with a low refractive index and a small molecular weight, and the dopant chamber contains a dopant M2 with a high refractive index and a large molecular weight; The prepolymerization chamber is connected to the first feeding pump, the dopant chamber is connected to the second feeding pump, the first feeding pump and the second feeding pump are respectively connected to the co-extrusion head, the co-extrusion head is connected to the die head through the screw mixing zone, and the die head outlet end is provided with a winding traction device; The method for preparing a large-size gradient refractive index plastic optical fiber preform is as follows: The low-refractive-index, low-molecular-weight polymer monomer M1 in the prepolymerization chamber is prepolymerized at a temperature of 60°C to 80°C for 1h to 12h, and then the M1 prepolymer is delivered to the co-extrusion head by a first feeding pump. At the same time, the high-refractive-index, high-molecular-weight dopant M2 in the dopant chamber is delivered to the co-extrusion head by a second feeding pump. The M1 prepolymer and the dopant M2 are mixed by the screw in the screw mixing zone, and the mixture is pushed to the die head; the discharge port of the die head is a linear hole with a width of 0.01mm-0.5mm. The mixed prepolymer after extrusion is coated on the rotating shaft of the winding and traction device. The temperature of the winding zone of the rotating shaft is controlled between 150°C and 240°C. As the rotating shaft rotates, a large-sized gradient refractive-index plastic optical fiber preform is produced. By controlling the addition amount of dopant M2 in different time periods, that is, corresponding to different radii of the final large-size gradient refractive index plastic optical fiber preform, the addition amount of dopant M2 can be adjusted by controlling the speed of the second feeding pump to regulate the different radii r x The refractive index n(r x ), and thus the refractive index gradient of large-size gradient refractive index plastic optical fiber preform can be accurately controlled; The refractive index at a certain radius satisfies the following formula: ; where x = 0, 1, 2, 3, ...., k; Where n( r x ) is the refractive index at radius r; n0 is the refractive index at the central axis; A is a constant; r x is the radius; r x Satisfies the following formula: v·t k =l k = ； in, v is the linear velocity of the polymer film, t k For the moment, l k for t k The total length of the polymer film at the moment; Polymer films in ~ Within the location area, the corresponding time period is: / v ~ / v The refractive index is: ； n( r x ) also satisfies the following formula: ， ， Where n1 is the refractive index of the monomer, n2 is the refractive index of the dopant, and ρ x is the doping concentration of the dopant, ρ0 is the initial doping concentration; The refractive index n0 at the central axis is expressed by the following formula: ； Therefore, the formula for the refractive index is expressed as a function of t: 。

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