Simulation Method for Drawing Multilayer Tubular Anti-Resonant Hollow Core Fibers

Abstract

A simulation method for drawing a multi-layer tubular anti-resonant hollow fiber is disclosed. In the method, the multi-layer tubular anti-resonant hollow fiber to be drawn includes an outer sleeve, a plurality of cladding tubes located within the outer sleeve, and a plurality of insert tubes located within the cladding tubes. Predetermined drawing parameters of the multi-layer tubular anti-resonant hollow fiber to be drawn are input, and based on the Fitt model formula, the changes of the outer and inner diameters of the outer sleeve and the glass viscosity coefficient with the drawing distance are calculated, and the rationality of the calculation results of the outer diameter and inner diameter of the outer sleeve with the increase of the drawing distance is judged; at the same time, the changes of the outer diameter and inner diameter of the cladding tubes with the drawing distance are calculated, and the changes of the outer diameter and inner diameter of the insert tubes with the drawing distance are calculated.

Description

Technical Field

[0001] The present invention belongs to the technical field of anti-resonant hollow fiber drawing, and particularly relates to a simulation method for drawing a multi-layer tube type anti-resonant hollow fiber. Background Art

[0002] The main preparation process of the existing anti-resonant hollow fiber is: stacking and drawing, which mainly includes the following steps: (a) preparing a fiber preform by the stacking method; (b) drawing the fiber preform; (c) drawing the fiber. Among them, step (c) is a very complex and sensitive process with many influencing factors. To make the final fiber become the designed structure, it is necessary to accurately control the drawing parameters, such as temperature, air pressure, rod feeding speed, wire drawing speed, etc. Otherwise, it will cause the deformation of the air holes and result in the inability to achieve the designed structure. However, the accurate control of these drawing parameters still greatly depends on the trial-and-error adjustment during operation at present, which leads to a low drawing success rate, high manufacturing cost of the preform, and a great waste.

[0003] The above information disclosed in the background art is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention proposes a simulation method for drawing a multi-layer tube type anti-resonant hollow fiber, which can accurately simulate the drawing process of the anti-resonant hollow fiber with a multi-layer tube cladding structure in a high-temperature furnace, making the drawing process of the anti-resonant hollow fiber theoretical and stable, reducing the waste of preforms, increasing the fiber yield, and reducing the cost.

[0005] The object of the present invention is achieved through the following technical solutions. A simulation method for drawing a multi-layer tube type anti-resonant hollow fiber includes,

[0006] Step 1, the multi-layer tube type anti-resonant hollow fiber preform to be drawn includes an outer tube, a plurality of cladding tubes located inside the outer tube, and a plurality of insert tubes located inside the cladding tubes. Input the predetermined drawing parameters of the multi-layer tube type anti-resonant hollow fiber to be drawn, which include the drawing distance z of the fiber, the initial outer diameter R j (0) of the outer tube preform, the initial inner diameter r j (0) of the outer tube preform, the target outer diameter R j (L) of the outer tube after drawing, the target inner diameter r j (L) of the outer tube after drawing, the rod feeding speed w, the core air pressure P core , the unit distance speed change rate dw / dz of the rod feeding speed, the initial outer diameter R c (0) of the cladding tube preform, the initial inner diameter r c(0)、The air pressure difference Δp1 between the inside and outside of the cladding tube, the outer diameter R of the preform of the insert tube in the initial state n (0)、The inner diameter r of the preform of the insert tube in the initial state n (0)、The air pressure difference Δp2 between the inside and outside of the insert tube;

[0007] Step 2, Calculate the changes of the outer and inner diameters of the outer tube and the glass viscosity coefficient with the drawing distance z based on the Fitt model formula. The Fitt model formula is as follows:

[0008]

[0009]

[0010] Among them, ρ is the density of fused silica, with the unit of kg / m 3 ; Rj is the outer diameter of the outer tube, with the unit of mm; rj is the inner diameter of the outer tube, with the unit of mm; w is the lower rod speed, with the unit of mm / min; g is the acceleration due to gravity, with the unit of m / s 2 ; μ is the glass viscosity coefficient, with the unit of pa*s; γ is the surface tension coefficient of fused silica, with the unit of N / m; P core is the core air pressure; C p is the specific heat capacity of glass, with the unit of J / kgK; σ is the Stefan-Boltzmann constant; T α (z) is the furnace temperature distribution, with the unit of K; N is the heat transfer coefficient, with the unit of W / m 2 K; T is the glass temperature, with the unit of K;

[0011] Step 3, ① Define the flow rate f = π(R j (z) 2 - r j (z) 2 )w. The flow rate is not negative. ② Define the outer diameter R j (l) and the inner diameter r j (l) of the outer tube in the actually calculated completed drawing state as: R j (L) / 20 < R j (l) < 20×R j (L), r j (L) / 20 < r j (l) < 20×r j (L), where R j (L) is the target outer diameter of the outer tube in the completed drawing state, and r j (L) is the target inner diameter of the outer tube in the completed drawing state. After satisfying ① and ②, according to abs(R j (l) / R j(L)-1) < RATIO to determine that the rate of change of the lower rod speed per unit distance dw / dz is reasonable. RATIO is a quantity to measure the calculation accuracy and is input together with the drawing parameters. Otherwise, adjust the rate of change of the lower rod speed per unit distance dw / dz and substitute it into the Fitt model formula for recalculation until abs(R j (l) / R j (L)-1) < RATIO to determine that the rate of change of the lower rod speed per unit distance dw / dz is reasonable; then based on abs(r j (l) / r j (L)-1) < RATIO to determine that the core air pressure P core is reasonable. Otherwise, adjust the core air pressure P core and substitute its value into the Fitt model equation for recalculation until abs(R j (l) / R j (L)-1) < RATIO to determine that the core air pressure P core is reasonable, thereby determining the rationality of the calculation results of the outer sleeve outer diameter R j (z) and the outer sleeve inner diameter r j (z) with the drawing distance z;

[0012] Step 4, input the initial state outer diameter R of the cladding tube preform c (0), the initial state inner diameter r of the cladding tube preform c (0), and the cladding tube internal and external air pressure difference Δp1 to calculate the change of the cladding tube outer diameter R c (z) and the cladding tube inner diameter r c (z) with the drawing distance z. The calculation formula is as follows,

[0013] wherein, the lower rod speed w and the viscosity coefficient μ are taken from the calculation results of the adjusted outer sleeve in the said step 3;

[0014] At the same time, input the initial state outer diameter R of the inlay tube preform n (0), the initial state inner diameter r of the inlay tube preform n (0), and the inlay tube internal and external air pressure difference Δp2 to calculate the change of the inlay tube outer diameter R n (z) and the inlay tube inner diameter r n (z) with the drawing distance z. The calculation formula is as follows, wherein, the lower rod speed w and the viscosity coefficient μ are taken from the calculation results of the adjusted outer sleeve in the said step 3.

[0015] In the multi-layer tube anti-resonant hollow core fiber drawing simulation method described above, in step 1, the drawing distance z of the optical fiber, the initial state outer diameter R of the outer sleeve preform j (0) is 9.4 mm, the initial state inner diameter r of the outer sleeve preformj (0) is the target outer diameter R of the outer tube in the completed state of drawing j (L) is the target inner diameter r of the outer tube in the completed state of drawing j (L) is 80μm, the lower rod speed w is 4m / min, and the core air pressure P core is 2×10 5 KPa, and the rate of change of the lower rod speed per unit distance dw / dz is 7×10 -7 1 / s. The outer diameter R of the preform of the cladding tube in the initial state c (0) is 0.73mm, and the inner diameter r of the preform of the cladding tube in the initial state c (0) is 0.6438mm, the pressure difference Δp1 between the inside and outside of the cladding tube is 6050KPa, and the outer diameter R of the preform of the embedding tube n (0) is 0.73mm, and the inner diameter r of the preform of the embedding tube in the initial state n (0) is 0.6438mm, and the pressure difference Δp2 between the inside and outside of the embedding tube is 1000Kpa.

[0016] In the method for simulating the drawing of the multi-layer tube type anti-resonant hollow optical fiber, in step 2, the density ρ of fused quartz is 2200kg / m 3 ; the glass viscosity coefficient μ is:

[0017] T is the glass temperature, with the unit of K; the unit is pa*s; the surface tension coefficient γ of fused quartz is 0.3N / m, and the specific heat capacity C of glass p is 1345J / kgK; the Stefan-Boltzmann constant σ is 5.67x108 W / m 2 K 4 ; the furnace temperature distribution T α (z) is 2098.15*exp(-(z - 0.0005) 2 / (2*0.06 2 )), with the unit of K; the heat transfer coefficient N is 100W / m 2 K W / m 2 K.

[0018] In the method for simulating the drawing of the multi-layer tube type anti-resonant hollow optical fiber, in step 3, when adjusting the rate of change of the lower rod speed per unit distance dw / dz, three adjustment parameters are selected. The rate of change of the lower rod speed per unit distance dw / dz is multiplied by the value ranked second in size among the three adjustment parameters. Among the three adjustment parameters, two are constants 1.3 and 0.7, and the third is a variable (R j (l) / R j (L)) 2The adjustment parameters selected by this method are within the range of 0.7 - 1.3, neither too large nor too small, and will not cause the non - convergence of step 3.

[0019] In the multi - layer tubular anti - resonant hollow fiber drawing simulation method described above, in step 3, when adjusting the core air pressure P core the core air pressure P core is multiplied by the value ranked second in size among the three adjustment parameters. Among these three adjustment parameters, two are constants 1.3 and 0.7, and the third variable is (R j (l) 2 -r j (l) 2 ) / (R j (L) 2 -r j (L) 2 ). The adjustment parameters selected by this method are within the range of 0.7 - 1.3 and will not cause the non - convergence of step 3.

[0020] Compared with the prior art, the present invention has the following advantages: The multi - layer tubular anti - resonant hollow fiber drawing simulation method described in the present invention realizes the drawing structure simulation of the anti - resonant hollow fiber with a multi - layer capillary (or semi - circular tube) as the cladding structure, and through the setting of a unique rationality judgment mechanism and adjustment mechanism for the outer sleeve core air pressure P core and the increase amount of the lower rod unit distance speed dw / dz, it realizes the rapid and accurate calculation of the fiber drawing parameter simulation. The present invention predicts the influence of the change of drawing parameters on the structural change, and reduces the waste of expensive preforms caused by the trial - and - error adjustment during drawing. The physical effects involved in the Fitt simulation model for anti - resonant hollow fiber drawing include thermal effects and mechanical effects. The thermal effects can be specifically divided into thermal radiation and heat conduction generated when the preform is heated by the high - temperature furnace of the drawing tower. The mechanical effects can be specifically divided into the surface tension at the glass - air interface, the normal air pressure on the air side, and the viscous force inside the glass. The regulation of the competition state of these three forces determines whether the final structure of the anti - resonant hollow fiber can meet the expectations. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The accompanying drawings in the specification are only for the purpose of showing the preferred embodiments and are not considered as limiting the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts. Moreover, throughout the drawings, the same reference numerals are used to represent the same components.

[0022] In the drawings:

[0023] Figure 1 It is a fiber structure diagram of a simulation method for drawing a multi-layer tubular anti-resonant hollow fiber according to an embodiment of the present invention;

[0024] Figure 2 It is a flowchart of a simulation method for drawing a multi-layer tubular anti-resonant hollow fiber according to an embodiment of the present invention;

[0025] Figure 3 It is a schematic diagram of experimental verification simulation results of the prior art;

[0026] Figure 4 It is a schematic diagram of simulation results of a simulation method for drawing a multi-layer tubular anti-resonant hollow fiber according to an embodiment of the present invention.

[0027] The present invention will be further explained below in conjunction with the drawings and embodiments. Specific Embodiments

[0028] The following will refer to the attached Figures 1 to 4 The specific embodiments of the present invention will be described in more detail. Although specific embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0029] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different terms to refer to the same component. The specification and claims do not distinguish components by the difference in terms, but by the difference in functions of the components. As used throughout the specification and claims, the term "comprising" or "including" is an open-ended term and should be interpreted as "including but not limited to". The following description is a preferred embodiment for implementing the present invention, but the description is for the purpose of the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be defined by the appended claims.

[0030] For the convenience of understanding the embodiments of the present invention, the following will further explain with specific embodiments as examples in conjunction with the drawings, and the drawings do not limit the embodiments of the present invention.

[0031] For better understanding, as Figure 1 、 Figure 2 shown, the simulation method for drawing a multi-layer tubular anti-resonant hollow fiber includes:

[0032] Step 1, the multi-layer tubular anti-resonant hollow fiber preform to be drawn includes an outer sleeve, a plurality of cladding tubes located inside the outer sleeve, and a plurality of embedded tubes located inside the cladding tubes. Input the predetermined drawing parameters of the multi-layer tubular anti-resonant hollow fiber to be drawn, which include the drawing distance z of the fiber, the initial outer diameter R j (0) of the outer sleeve preform, the initial inner diameter r j (0) of the outer sleeve preform, the target outer diameter R j (L) of the outer sleeve after drawing, the target inner diameter r j (L) of the outer sleeve after drawing, the lower rod speed w, the core air pressure P core , the rate of change of the lower rod speed per unit distance dw / dz, the initial outer diameter R c (0) of the cladding tube preform, the initial inner diameter r c (0) of the cladding tube preform, the air pressure difference Δp1 between the inside and outside of the cladding tube, the initial outer diameter R n (0) of the embedded tube preform, the initial inner diameter r n (0) of the embedded tube preform, the air pressure difference Δp2 between the inside and outside of the embedded tube;

[0033] Step 2, calculate the change of the outer and inner diameters of the outer sleeve and the glass viscosity coefficient with the drawing distance z based on the Fitt model formula. The Fitt model formula is as follows:

[0034]

[0035]

[0036] Among them, ρ is the density of fused silica, with the unit of kg / m 3 ; Rj is the outer diameter of the outer sleeve, with the unit of mm; rj is the inner diameter of the outer sleeve, with the unit of mm; w is the lower rod speed, with the unit of mm / min; g is the acceleration due to gravity, with the unit of m / s 2 ; μ is the glass viscosity coefficient, with the unit of pa*s; γ is the surface tension coefficient of fused silica, with the unit of N / m; P core is the core air pressure; C p is the specific heat capacity of glass, with the unit of J / kgK; σ is the Stefan-Boltzmann constant; T α (z) is the furnace temperature distribution, with the unit of K; N is the heat transfer coefficient, with the unit of W / m 2 K; T is the glass temperature, with the unit of K;

[0037] Step 3, ① Define the flow rate f = π(R j (z) 2 -r j (z) 2) w, the flow rate is not negative. ② Define the outer diameter R j (l) and the inner diameter r j (l) of the outer sleeve in the actually calculated drawn - completed state are: R j (L) / 20 < R j (l) < 20×R j (L), r j (L) / 20 < r j (l) < 20×r j (L), where R j (L) is the target outer diameter of the outer sleeve in the drawn - completed state, r j (L) is the target inner diameter of the outer sleeve in the drawn - completed state. After satisfying ① and ②, according to abs(R j (l) / R j (L) - 1) < RATIO to judge that the change rate of the rod speed per unit distance dw / dz is reasonable. RATIO is a quantity to measure the calculation accuracy and is input together with the drawing parameters. Otherwise, adjust the change rate of the rod speed per unit distance dw / dz and substitute it into the Fitt model formula to recalculate until abs(R j (l) / R j (L) - 1) < RATIO to judge that the change rate of the rod speed per unit distance dw / dz is reasonable; then according to abs(r j (l) / r j (L) - 1) < RATIO to judge that the core air pressure P core is reasonable. Otherwise, adjust the core air pressure P core value and substitute it into the Fitt model equation to recalculate until abs(R j (l) / R j (L) - 1) < RATIO to judge that the core air pressure P core is reasonable, so as to judge the rationality of the calculation results of the outer diameter R j (z) and the inner diameter r j (z) of the outer sleeve with the drawing distance z;

[0038] Step 4, simultaneously input the outer diameter R c (0) and the inner diameter r c (0) of the preform of the cladding tube, and the pressure difference Δp1 between the inside and outside of the cladding tube to calculate the changes of the outer diameter R c (z) and the inner diameter r c (z) of the cladding tube with the drawing distance z. The calculation formula is as follows,

[0039] Among them, the rod speed w and the viscosity coefficient μ are taken from the calculation results of the adjusted outer sleeve in the said Step 3,

[0040] Input the initial outer diameter R of the sleeve preform at the same time n (0), the initial inner diameter r of the sleeve preform n (0), the pressure difference Δp2 between the inside and outside of the sleeve, and calculate the outer diameter R of the sleeve n (z) and the inner diameter r of the sleeve n (z) changes with the drawing distance z, and the calculation formula is as follows Among them, the lower rod speed w and the viscosity coefficient μ are taken from the calculation results of the adjusted outer sleeve in the step 3

[0041] In the preferred embodiment of the multi-layer tube type anti-resonant hollow fiber drawing simulation method, in step 1, the drawing distance z of the fiber, the initial outer diameter R of the outer sleeve preform j (0) is 9.4 mm, the initial inner diameter r of the outer sleeve preform j (0) is 2 mm, the target outer diameter R of the outer sleeve in the completed drawing state j (L) is 255 μm, the target inner diameter r of the outer sleeve in the completed drawing state j (L) is 80 μm, the lower rod speed w is 4 m / min, the core air pressure P core is 2×10 5 KPa, the unit distance speed change rate dw / dz of the lower rod speed is 7×10 -7 1 / s, the initial outer diameter R of the cladding tube preform c (0) is 0.73 mm, the initial inner diameter r of the cladding tube preform c (0) is 0.6438 mm, the pressure difference Δp1 between the inside and outside of the cladding tube is 6050 KPa, the initial outer diameter R of the sleeve preform n (0) is 0.73 mm, the initial inner diameter r of the sleeve preform n (0) is 0.6438 mm, the pressure difference Δp2 between the inside and outside of the sleeve is 1000 Kpa

[0042] In the preferred embodiment of the multi-layer tube type anti-resonant hollow fiber drawing simulation method, in step 2, the density ρ of fused quartz is 2200 kg / m 3 ; the glass viscosity coefficient μ is T is the glass temperature, in units of K; in units of pa*s; the surface tension coefficient γ of fused quartz is 0.3 N / m, the specific heat capacity C of glass p is 1345 J / kgK; the Stefan-Boltzmann constant σ is 5.67x108 W / m 2 K 4 ; the furnace temperature distribution T α (z) is 2098.15*exp(-(z - 0.0005) 2 / (2 * 0.06 2 )) and the unit is K; the heat transfer coefficient N is 100 W / m 2 K · W / m 2 K.

[0043] In the preferred embodiment of the simulation method for drawing multi-layer tube-type anti-resonant hollow-core optical fiber, in step 3, when adjusting the rate of change of the lower rod speed per unit distance dw / dz, three adjustment parameters are selected. The rate of change of the lower rod speed per unit distance dw / dz is multiplied by the value ranked second in size among the three adjustment parameters. Among the three adjustment parameters, two are constants 1.3 and 0.7, and the third is a variable (R j (l) / R j (L)) 2 .

[0044] In the preferred embodiment of the simulation method for drawing multi-layer tube-type anti-resonant hollow-core optical fiber, in step 3, when adjusting the core air pressure P core , the core air pressure P core is multiplied by the value ranked second in size among the three adjustment parameters. Among the three adjustment parameters, two are constants 1.3 and 0.7, and the third variable is (R j (l) 2 -r j (l) 2 ) / (R j (L) 2 -r j (L) 2 ).

[0045] In one embodiment, the method includes,

[0046] Inputting the NANF optical fiber drawing parameters simultaneously: z represents the drawing distance of the optical fiber, z = 0 is the initial state, and z = L is the completed drawing state. The initial outer inner diameter of the outer sleeve preform

[0047] (R j (0) = 9.4 mm, r j (0) = 2 mm), the target outer inner diameter of the outer sleeve in the completed drawing state (R j (L) = 255 μm, r j (L) = 80 μm), the lower rod speed w = 4 m / min, the peak furnace temperature T p = 2098.15 K, the core air pressure P core = 2 × 10 5 KPa, and the rate of change of the lower rod speed per unit distance dw / dz = 7 × 10 -7 1 / s.

[0048] Calculating the outer inner diameter R j (z), rj (z), the variation of the glass viscosity coefficient μ(z) with the drawing distance z. The Fitt model formula is as follows:

[0049]

[0050]

[0051]

[0052] Judge the outer diameter R of the outer sleeve j (z), r j (z) for the rationality of the calculation results with the drawing distance z: ① Define the flow rate f = π(R j (z) 2 -r j (z) 2 )w, the flow rate is not negative ② Define R j (l) and r j (l) as the outer diameter and inner diameter of the outer sleeve in the completed drawing state calculated actually, R j (L) / 20 < R j (l) < 20×R j (L), r j (L) / 20 < r j (l) < 20×r j (L), after satisfying ① and ②, then judge the rationality of the unit distance speed change rate dw / dz = 7×10 -7 1 / s at the beginning guessed lower rod speed, and the judgment basis is abs(R j (l) / R j (L) - 1) < RATIO (a quantity used to measure the calculation accuracy, determined according to the required calculation accuracy). If it is not less than, the value of dw / dz needs to be adjusted, and substitute it into the Fitt model equation to recalculate. The way to adjust dw / dz is to select 3 adjustment parameters. Multiply dw / dz by the value ranked second in size among the three adjustment parameters. Two of the three adjustment parameters are two constants 1.3 and 0.7 selected through multiple experiments, and the third is a variable, defined as (R j (l) / R j (L)) 2 , which is also an empirical adjustment parameter obtained through multiple experiments. After completing the rationality judgment of dw / dz, it is necessary to judge the rationality of the core air pressure P core again. The judgment basis is abs(r j (l) / r j (L) - 1) < RATIO. If it is not less than, P coreThe value is substituted into the Fitt model equation for recalculation. The way to adjust dw / dz is to select three adjustment parameters. dw / dz is multiplied by the value ranked second in size among the three adjustment parameters. Two of the three adjustment parameters are two constants 1.3 and 0.7 selected through multiple experiments, and the third is a variable defined as (R j (l) 2 -r j (l) 2 ) / (R j (L) 2 -r j (L) 2 ), which is also an empirical adjustment parameter obtained through multiple experiments.

[0053] Meanwhile, input the initial outer and inner diameters of the preform of the cladding tube (R c (0) = 0.73 mm, r c (0) = 0.6438 mm), and the pressure difference Δp between the inside and outside of the cladding tube = 6050 KPa. Calculate the variations of R c (z) and r c (z) with the drawing distance z. The calculation formula is as follows. The drawing speed w of the lower rod and the viscosity coefficient μ in the formula are both taken from the calculation results of the above preform of the outer sleeve.

[0054]

[0055] Meanwhile, input the initial outer and inner diameters of the preform of the insert tube (R n (0) = 0.73 mm, r n (0) = 0.6438 mm), and the pressure difference Δp between the inside and outside of the insert tube = 1000 KPa. Calculate the variations of R n (z) and r n (z) with the drawing distance z. The calculation formula is as follows. The drawing speed w of the lower rod and the viscosity coefficient μ in the formula are both taken from the calculation results of the above preform of the outer sleeve.

[0056]

[0057] Verification of the correctness of the simulation results

[0058] The simulation results of drawing the outer sleeve are as Figure 4 shown, which are compared with those in the paper T. Gregory et al, "Fabrication of tubular anti-resonant hollow core fibers: modelling, draw dynamics and process optimization," Opt. Express 27, 20567 - 20582 (2)(2019). Figure 3The simulation results are consistent. The functional relationship between the abscissa Draw tension, i.e., the drawing tension τ when drawing the optical fiber, and the viscosity coefficient μ is as follows:

[0059]

[0060] Although the embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments and application fields. The above specific embodiments are merely illustrative and guiding, rather than restrictive. Those of ordinary skill in the art can also make many forms under the inspiration of this specification and without departing from the scope protected by the claims of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A simulation method for drawing a multi-layer tubular anti-resonant hollow optical fiber, characterized in that, It includes Step 1, the multi-layer tubular anti-resonant hollow fiber preform to be drawn includes an outer sleeve, a plurality of cladding tubes located within the outer sleeve, and a plurality of insert tubes located within the cladding tubes. Input the predetermined drawing parameters of the multi-layer tubular anti-resonant hollow fiber to be drawn, which include the drawing distance z of the fiber, the initial outer diameter R j (0) of the outer sleeve preform, the initial inner diameter r j (0) of the outer sleeve preform, the target outer diameter R j (L) of the outer sleeve after drawing is completed, the target inner diameter r j (L) of the outer sleeve after drawing is completed, the lower rod speed w, the core air pressure P core , the rate of change of the lower rod speed per unit distance dw / dz, the initial outer diameter R c (0) of the cladding tube preform, the initial inner diameter r c (0) of the cladding tube preform, the pressure difference Δp1 between the inside and outside of the cladding tube, the initial outer diameter R n (0) of the insert tube preform, the initial inner diameter r n (0) of the insert tube preform, the pressure difference Δp2 between the inside and outside of the insert tube; Step 2: Calculate the changes of the outer diameter and inner diameter of the outer sleeve and the glass viscosity coefficient with the drawing distance z based on the Fitt model formula. The Fitt model formula is as follows: ， ， , where ρ is the density of fused silica, with the unit of kg / m 3 ; R j is the outer diameter of the outer tube, with the unit of mm; r j is the inner diameter of the outer tube, with the unit of mm; w is the speed of the lower rod, with the unit of mm / min; is the acceleration due to gravity, with the unit of m / s 2 ; μ is the glass viscosity coefficient, with the unit of pa·s; γ is the surface tension coefficient of fused silica, with the unit of N / m; P core is the core air pressure; C p is the specific heat capacity of glass, with the unit of J / kgK; σ is the Stefan-Boltzmann constant; is the thermal radiation emissivity, with the unit of 1 / m, T α (z) is the furnace temperature distribution, with the unit of K; N is the heat transfer coefficient, with the unit of W / m 2 K; is the glass temperature, with the unit of K; Step 3, ① Define the flow rate f = π(R j (z) 2 - r j (z) 2 )w, where the flow rate is non - negative. ② Define the outer diameter R j (l) and the inner diameter r j (l) of the outer sleeve in the actually calculated drawn - completed state as: R j (L) / 20 < R j (l) < 20×R j (L), r j (L) / 20 < r j (l) < 20×r j (L), where R j (L) is the target outer diameter of the outer sleeve in the drawn - completed state, r j (L) is the target inner diameter of the outer sleeve in the drawn - completed state. After satisfying ① and ②, according to abs(R j (l) / R j (L)-1) < RATIO, where RATIO is a quantity measuring the calculation accuracy and is input together with the drawing parameters, to judge whether the rate of change of the rod speed per unit distance dw / dz is reasonable. Otherwise, adjust the rate of change of the rod speed per unit distance dw / dz and substitute it into the Fitt model formula for recalculation until abs(R j (l) / R j (L)-1) < RATIO to judge that the rate of change of the rod speed per unit distance dw / dz is reasonable; then according to abs(r j (l) / r j (L)-1) < RATIO to judge whether the core air pressure P core is reasonable. Otherwise, adjust the value of the core air pressure P core and substitute it into the Fitt model equation for recalculation until abs(R j (l) / R j (L)-1) < RATIO to judge that the core air pressure P core is reasonable, so as to judge the rationality of the calculation results of the outer diameter R j (z) and the inner diameter r j (z) of the outer sleeve with the drawing distance z. Step 4, input the initial outer diameter R of the cladding tube preform c (0), the initial inner diameter r of the cladding tube preform c (0), calculate the outer diameter R of the cladding tube from the pressure difference Δp1 between the inside and outside of the cladding tube c (z) and the inner diameter r of the cladding tube c (z) vary with the drawing distance z, and the calculation formula is as follows , where the lower rod speed w and the viscosity coefficient μ are taken from the calculation results of the adjusted outer sleeve in the step 3; Simultaneously input the outer diameter R of the sleeve preform in the initial state n (0), the inner diameter r of the sleeve preform in the initial state n (0), the air pressure difference Δp2 between the inside and outside of the sleeve, and calculate the outer diameter R of the sleeve n (z) and the inner diameter r of the sleeve n (z) changes with the drawing distance z, and the calculation formula is as follows , wherein the lower rod speed w and the viscosity coefficient μ are taken from the calculation results of the adjusted outer sleeve in the step 3.

2. The simulation method for drawing a multi-layer tubular anti-resonant hollow optical fiber according to claim 1, characterized in that, In Step 1, the drawing distance z of the optical fiber, the initial outer diameter R j (0) is 9.4 mm, and the initial inner diameter r j (0) of the outer tube preform is 2 mm. The target outer diameter R j (L) of the outer tube after drawing is 255 μm, and the target inner diameter r j (L) is 80 μm. The speed w of the lower rod is 4 m / min, and the core air pressure P core is 2×10 5 kPa. The rate of change of the speed per unit distance of the lower rod dw / dz is 7×10 -7 1 / s. The initial outer diameter R c (0) of the cladding tube preform is 0.73 mm, and the initial inner diameter r c (0) of the cladding tube is 0.6438 mm. The pressure difference Δp1 between the inside and outside of the cladding tube is 6050 kPa. The initial outer diameter R n (0) of the insert tube preform is 0.73 mm, and the initial inner diameter r n (0) of the insert tube is 0.6438 mm. The pressure difference Δp2 between the inside and outside of the insert tube is 1000 kPa.

3. The simulation method for drawing a multi-layer tubular anti-resonant hollow optical fiber according to claim 1, wherein In step 2, the density ρ of fused silica is 2200 kg / m 3 ; the glass viscosity coefficient μ is: , where is the glass temperature in K; the unit is pa·s; the surface tension coefficient γ of fused silica is 0.3 N / m, and the specific heat capacity C of the glass p is 1345 J / kgK; the Stefan-Boltzmann constant σ is 5.67x108 W / m 2 K 4 ; the furnace temperature distribution T α (z) is 2098.15*exp(-(z - 0.0005) 2 / (2 * 0.06 2 )) in K; the heat transfer coefficient N is 100 W / m 2 K W / m 2 K.

4. The simulation method for drawing a multi-layer tubular anti-resonant hollow optical fiber according to claim 1, wherein In step 3, when adjusting the rate of change of the lower rod speed per unit distance dw / dz, three adjustment parameters are selected. The rate of change of the lower rod speed per unit distance dw / dz is multiplied by the value ranked second in magnitude among the three adjustment parameters. Among the three adjustment parameters, two are constants 1.3 and 0.7, and the third is a variable (R j (l) / R j (L)) 2 .

5. The simulation method for drawing a multi-layer tubular anti-resonant hollow fiber according to claim 1, wherein In step 3, adjust the core air pressure P core When the core air pressure P core is multiplied by the value ranked second in size among the three adjustment parameters. Among the three adjustment parameters, two are constants 1.3 and 0.7, and the third variable is (R j (l) 2 -r j (l) 2 ) / (R j (L) 2 -r j (L) 2 ).

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