CN114349327A - Low-cost processing technology of bending insensitive single-mode optical fiber - Google Patents

Abstract

The invention provides a low-cost processing technology of a bending insensitive single-mode optical fiber, which can solve the problems of complex technology and high manufacturing cost of the existing method. Firstly, preparing an optical fiber preform and then carrying out wire drawing treatment on the optical fiber preform; the bending insensitive single mode optical fiber comprises a central core layer and a cladding layer surrounding and contacting with the core layer, wherein the cladding layer comprises an inner cladding layer and an outer cladding layer from inside to outside; the inner cladding comprises at least two layers, and at least two layers of inner cladding form at least one step-like concave structure from inside to outside; preparing an optical fiber preform, namely depositing by deposition equipment by using VAD (vapor deposition) process to obtain a core rod loose body formed by a core layer and an inner cladding; then sintering, dehydrating and stretching the loose core rod body to obtain the transparent glass core rod; finally, an OVD process is applied to deposit on the outer surface of the core rod to form an outer cladding layer, and the outer cladding layer is sintered to obtain an optical fiber preform; the inner cladding blowtorch of the deposition equipment is at least provided with two inner cladding blowtorches, and each inner cladding blowtorch is respectively corresponding to one inner cladding.

Description

A low-cost fabrication process for bend-insensitive single-mode fibers

technical field

The invention relates to the production field of bending-insensitive single-mode optical fibers, in particular to a low-cost processing technology for bending-insensitive single-mode optical fibers.

Background technique

Compared with ordinary G.652 single-mode fiber, bend-insensitive single-mode fiber has the characteristics of small additional loss under extremely small bending radius. In the application of FTTH technology, a bending radius of 5mm to 15mm often occurs, and the actual complex laying environment has higher requirements on the bending performance of the optical fiber. The bending loss-insensitive single-mode fiber of the conventional scheme adopts increasing the content of germanium (Ge) in the core layer to increase the refractive index of the core layer, and at the same time doping fluorine (F) in the inner cladding layer to reduce the refractive index of the inner cladding layer.

For example, the Chinese invention patent with the publication number CN102730961B discloses a method of doping germanium element (Ge) in the core layer during deposition, and introducing carbon tetrafluoride (CF ₄ ) during the sintering process to increase the subsidence depth of the inner cladding. The preparation process is long, but introducing CF ₄ during sintering will reduce the service life of the sintering furnace and increase the manufacturing cost; another example is the Chinese invention patent application with publication number CN112904474A which discloses a PCVD/VAD+ liner shrinkage+OVD scheme, This solution is easy to obtain a stable refractive index profile, but the manufacturing process of the mandrel is complicated, and the F-doped tube is shrunk on the outside of the mandrel. The existing bending-insensitive single-mode optical fiber processing technology generally has the problems of complicated process and high manufacturing cost.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention provides a low-cost processing technology for a bend-insensitive single-mode optical fiber, which can solve the problems of complicated process and high manufacturing cost existing in the existing method.

A low-cost processing technology for a bend-insensitive single-mode optical fiber, wherein an optical fiber preform is prepared first, and then the optical fiber preform is drawn to obtain a bend-insensitive optical fiber; the bend-insensitive single-mode optical fiber includes a central core layer, a cladding surrounding and in contact with the core layer, the cladding including an inner cladding and an outer cladding from the inside out; it is characterized in that:

The inner cladding layer includes at least two layers, and the at least two inner cladding layers form at least one stepped-like recessed structure from the inside to the outside;

The preparation of the optical fiber preform includes: step (1), applying a VAD process to deposit a core rod loose body formed by the core layer and the inner cladding layer by deposition equipment; step (2), sequentially depositing the core rod loose body After sintering and dehydration treatment and stretching treatment, a transparent glass core rod is obtained; in step (3), the outer cladding is formed by depositing the outer surface of the core rod with an OVD process, and finally the optical fiber preform is obtained by sintering;

In the step (1), the deposition equipment includes a cavity, and a core layer torch and an inner cladding torch disposed in the cavity, the inner cladding torches are provided with at least two and each of the inner cladding torches is provided. One-to-one correspondence with an inner cladding layer, the core layer burner and the inner cladding burner are both annular multi-layer nozzle structures; the initial target rod extends into the cavity from the top and is controlled by the control system to set the desired value. The speed is rotated and raised upward, the control system controls the core layer burner to deposit the core layer at the end of the initial target rod at a preset deposition gas flow rate, and the control system is based on the refractive index profile of the inner cladding of the optical fiber The structure sequentially controls each of the inner cladding torches to deposit and form each layer of the inner cladding layer at the end of the core layer at a preset gas flow rate of each inner cladding layer from the inside out.

Further, the deposition equipment further includes an air intake system and an air extraction system, the air intake system is provided on one side of the cavity, and the air extraction system is provided on the opposite side.

Further, the inner cladding layer includes a first inner cladding layer and a second inner cladding layer from the inside out, and a stepped recessed structure is formed between the first inner cladding layer and the second inner cladding layer; the core The relative refractive index difference Δn1 of the layers is 0.35% to 0.45%, the relative refractive index difference Δn2 of the first inner cladding layer is 0.02% to 0.04%, and the relative refractive index difference Δn3 of the second inner cladding layer is 0.1 %～0.18%.

Further, the inner cladding torch includes a first inner cladding torch for depositing the first inner cladding layer and a second inner cladding torch for depositing the second inner cladding layer; the core layer torch, the first inner cladding torch The layer burner and the second inner cladding burner are all annular eight-layer spray hole structures, which sequentially include a central spray hole, a first annular spray hole, a second annular spray hole, a third annular spray hole, and a fourth annular spray hole from inside to outside. The injection hole, the fifth annular injection hole, the sixth annular injection hole and the seventh annular injection hole.

Further, the central orifice of the core layer burner is provided with SiCl ₄ gas with a preset flow rate of 0.4-0.8slpm and GeCl ₄ gas with a preset flow rate of 0.02-0.06slpm; the first annular shape of the core layer burner The orifice passes through the hydrogen gas with a preset flow rate of 3-6 slpm, the second annular spray hole of the core layer burner passes through the argon gas with a preset flow rate of 2-4 slpm, and the third annular spray hole of the core layer burner passes through the gas with a preset flow rate of 2-4 slpm There is oxygen with a preset flow rate of 18 to 26 slpm, the fourth annular orifice of the core layer burner has a preset flow rate of 3 to 4.6 slpm of argon gas, and the fifth annular orifice of the core layer burner has a preset flow rate. The flow rate is 18-24 slpm of hydrogen, the sixth annular orifice of the core layer burner has a preset flow rate of 3.2-4.8 slpm of argon gas, and the seventh annular orifice of the core layer burner has a preset flow rate. For 18 ~ 22slpm of oxygen.

Further, the gas and airflow flow through each nozzle hole of the first inner cladding torch from the inside to the outside are set as follows: the central nozzle hole is filled with SiCl4 gas with a preset flow rate of 3 to 4.2 slpm, and the first annular nozzle hole is connected with the gas. There are hydrogen gas with a preset flow rate of 6 to 8 slpm and carbon tetrafluoride gas with a preset flow rate of 0.4 to 0.6 slpm, the second annular orifice is connected with argon gas with a preset flow of 3 to 5 slpm, and the third annular spray hole is connected with There is oxygen with a preset flow rate of 25 to 45 slpm, the fourth annular orifice is passed through with argon with a preset flow of 4 to 6 slpm, the fifth annular orifice is passed with hydrogen with a preset flow of 60 to 80 slpm, and the sixth annular spray hole has a preset flow of 60 to 80 slpm. Argon gas with a preset flow rate of 4-6 slpm passes through the holes, and oxygen with a preset flow rate of 25-45 slpm passes through the seventh annular nozzle; the control range of the loose body density of the first inner cladding is 0.35-0.38 g/cm ³ .

Further, the gas and airflow flow through each nozzle hole of the second inner cladding torch from the inside to the outside are set as follows: the central nozzle hole is filled with SiCl4 gas with a preset flow rate of 4-5.4 slpm, and the first annular nozzle hole is connected There are hydrogen gas with a preset flow rate of 8 to 10.6 slpm and carbon tetrafluoride gas with a preset flow rate of 1 to 1.6 slpm, the second annular orifice is connected with argon gas with a preset flow of 3 to 5 slpm, and the third annular nozzle hole Oxygen with a preset flow rate of 25-45 slpm is passed through, the fourth annular orifice is passed with argon with a preset flow rate of 4-6 slpm, the fifth annular spray hole is passed with hydrogen with a preset flow of 60-80 slpm, and the sixth annular spray hole is passed with hydrogen with a preset flow rate of 60-80 slpm. Argon gas with a preset flow rate of 4-6 slpm passes through the orifice, and oxygen with a preset flow rate of 25-45 slpm passes through the seventh annular spray hole; the second inner cladding loose body density control range is 0.26-0.3 g/cm ³ .

Further, in the step (2), chlorine gas and helium gas are introduced into the sintering and dehydration treatment.

The low-cost processing technology of the bending-insensitive single-mode optical fiber of the present invention adopts the VAD process + OVD process to prepare the optical fiber preform, especially when the core layer and the inner cladding layer are deposited by the VAD process, the core layer and the inner cladding layer of each layer are The layer deposition is carried out by a core layer torch and an inner cladding torch. Meanwhile, the core layer torch and each inner cladding torch all adopt a ring-shaped multi-layer nozzle structure, and are controlled from the inside to the outside according to the refractive index profile structure of the inner cladding of the optical fiber. Each inner cladding torch deposits an inner cladding layer at the end of the core layer with a preset flow rate of each inner cladding gas, thereby greatly simplifying the production process of the optical fiber preform and the entire optical fiber production process, improving production efficiency and reducing production costs; in addition On the one hand, during the processing of the optical fiber preform, the inner cladding of the bend-insensitive single-mode optical fiber is designed to include at least two layers, and at least two inner cladding layers form at least one step-like concave structure from the inside to the outside. Meet the requirements of the difference in the refractive index of the inner cladding, and at the same time, through the adaptation of the flow rates of the core layer torch and each inner cladding torch during the deposition of the loose body, the loose body can obtain better macrobending performance, so that the produced fiber can meet ITU-T requirements. G.657 fiber optic standard.

Description of drawings

1 is a schematic cross-sectional view of the refractive index of a bend-insensitive optical fiber according to an embodiment of the present invention;

2 is a schematic diagram of a radial cross-sectional structure of a bend-insensitive optical fiber according to an embodiment of the present invention;

3 is a schematic diagram of the annular multi-layer orifice structure adopted by the core layer burner and the inner clad burner in the embodiment of the present invention;

FIG. 4 is a schematic diagram of deposition of a core layer torch and two inner clad layer torches in an embodiment of the present invention.

Reference numerals: 10-core layer, 21a-first inner cladding layer, 21b-second inner cladding layer, 22-outer cladding layer, 23-mandrel loose body, 30-deposition equipment, 31-cavity, 32-core layer torch , 33a-the first inner cladding burner, 33b-the second inner cladding burner, 34a-the central spray hole, 34b-the first annular spray hole, 34c-the second annular spray hole, 34d-the third annular spray hole, 34e-the first annular spray hole Four annular nozzle holes, 34f- fifth ring nozzle hole, 34g- sixth ring nozzle hole, 34h- seventh ring nozzle hole, 35- air inlet system, 36- exhaust system, 36- initial target rod

Detailed ways

Example 1:

A low-cost processing process for a bend-insensitive single-mode optical fiber, which first prepares an optical fiber preform, and then performs a wire drawing process on the optical fiber preform to obtain a bend-insensitive optical fiber; see Figures 1 and 2, the bend-insensitive single-mode optical fiber The optical fiber includes a core layer 10 in the center, a cladding layer surrounding and in contact with the core layer, and the cladding layer includes an inner cladding layer and an outer cladding layer 22 from the inside out; in this embodiment, the inner cladding layer includes two layers, which are the first inner cladding layer 21a respectively. and the second inner cladding layer 21b, and the first inner cladding layer and the second inner cladding layer form a stepped concave structure from the inside out; the relative refractive index difference Δn1 of the core layer 10 is 0.35% to 0.45%, and the first inner cladding layer The relative refractive index difference Δn2 of 21a is 0.02% to 0.04%, and the relative refractive index difference Δn3 of the second inner cladding layer 21b is 0.1% to 0.18%.

Among them, the preparation of the optical fiber preform includes:

Step (1), applying the VAD process to deposit through the deposition equipment to obtain the loose core rod 23 formed by the core layer and the inner cladding layer; as shown in FIG. 4 , the deposition equipment 30 includes a cavity 31 and a core layer torch disposed in the cavity 31 32. The first inner cladding torch 33a, the second inner cladding torch 33b, the first inner cladding torch 33a is used to deposit the first inner cladding 21a, the second inner cladding torch 33b is used to deposit the second inner cladding 21b; the core torch 32 , The first inner cladding torch 33a and the second inner cladding torch 33b are annular multi-layer nozzle structures, and in this embodiment, the core layer torch 32, the first inner cladding torch 33a, and the second inner cladding torch 33c are all annular The eight-layer orifice structure, as shown in Figure 3, includes a central injection hole 34a, a first annular injection hole 34b, a second annular injection hole 34c, a third annular injection hole 34d, a fourth annular injection hole 34e, The fifth annular spray hole 34f, the sixth annular spray hole 34g and the seventh annular spray hole 34h; the initial target rod 37 extends into the cavity 31 from the top and is controlled by the control system to rotate at a set speed and lift upward, The control system controls the core layer torch 32 to deposit the core layer 10 at the end of the initial target rod with a preset deposition gas flow rate. A corresponding first inner cladding layer 21a and a second inner cladding layer 21b are deposited at the end of the core layer 10 for each set inner cladding gas flow rate.

The deposition apparatus 30 further includes an air inlet system 35 and an air extraction system 36 . The air inlet system 35 is provided on one side of the cavity 31 , and the air extraction system 36 is provided on the opposite side.

In this embodiment, the central orifice 34a of the core layer torch 32 is connected with SiCl ₄ gas with a preset flow rate of 0.46slpm and GeCl ₄ gas with a preset flow rate of 0.035slpm; the first annular nozzle hole 34b of the core layer torch 32 is connected to There is hydrogen with a preset flow rate of 4.1slpm, the second annular nozzle hole 34c of the core layer burner 32 is connected with argon gas with a preset flow rate of 2.6slpm, and the third annular nozzle hole 34d of the core layer burner 32 is connected with a preset flow rate of 2.6slpm. 18.2 slpm of oxygen, the fourth annular orifice 34e of the core layer torch 32 is supplied with argon with a preset flow rate of 3.6 slpm, and the fifth annular orifice 34f of the core layer torch 32 is supplied with hydrogen with a preset flow rate of 20.4 slpm, Argon gas with a preset flow rate of 4 slpm is passed through the sixth annular orifice 34g of the core layer torch 32, and oxygen gas with a preset flow rate of 19.3 slpm is passed through the seventh annular orifice 34h of the core layer torch 32.

The first inner cladding torch 33a passes through the gas and the airflow flow rate of each spray hole from the inside to the outside is set as follows: the central spray hole passes through the SiCl4 gas with a preset flow rate of 4 slpm, and the first annular spray hole passes through the preset flow rate of 7.2 slpm. Hydrogen gas and carbon tetrafluoride gas with a preset flow rate of 0.42slpm, the second annular orifice is connected with argon with a preset flow rate of 3.2slpm, the third annular spray hole is connected with oxygen with a preset flow rate of 30slpm, and the fourth annular nozzle is connected with oxygen with a preset flow rate of 30slpm Argon gas with a preset flow rate of 5 slpm is passed through the orifice, hydrogen gas with a preset flow rate of 76 slpm is passed through the fifth annular spray hole, argon gas with a preset flow rate of 4.8 slpm is passed through the sixth annular spray hole, and the seventh annular spray hole is passed with a preset flow rate of 4.8 slpm. Oxygen with a preset flow rate of 35 slpm is passed through; the control range of the loose body density of the first inner cladding is 0.365 g/cm ³ .

The second inner cladding torch 33b passes through the gas and the flow rate of the gas flow through each orifice from the inside to the outside. The hydrogen gas and carbon tetrafluoride gas with a preset flow rate of 1.4slpm are passed through the second annular nozzle hole with a preset flow rate of argon gas of 4slpm, the third annular nozzle hole with a preset flow rate of 38slpm oxygen gas, and the fourth annular nozzle hole has a preset flow rate of 38slpm oxygen gas. Argon gas with a preset flow rate of 5.3 slpm is passed through the orifice, hydrogen with a preset flow rate of 78 slpm is passed through the fifth annular spray hole, argon gas with a preset flow rate of 5.3 slpm is passed through the sixth annular spray hole, and the seventh annular spray hole is passed with a preset flow rate of 5.3 slpm. Oxygen with a preset flow rate of 42 slpm passes through the holes; the control range of the loose body density of the second inner cladding is 0.272 g/cm ³ .

The obtained mandrel loose body had a diameter of 210 mm and an overall density of 0.316 g/cm ³ .

Step (2), the mandrel loose body is successively subjected to sintering dehydration treatment and stretching treatment to obtain a transparent glass mandrel with a diameter of 40mm, wherein chlorine and helium are introduced into the sintering dehydration treatment;

In step (3), an OVD process is applied to deposit an outer cladding on the outer surface of the transparent glass core rod, and the deposited outer cladding is pure silica dust, which is then sintered to obtain an optical fiber preform.

The typical parameters of the optical fibers prepared in this example are shown in the following table:

The above-mentioned optical fibers manufactured by the process of this embodiment all meet the ITU-T G.657 optical fiber standard.

Embodiment 2:

The difference between this embodiment and the first embodiment is only in that the core layer torch 32, the first inner clad torch 33a and the first inner clad torch 33a and the third The preset flow rates of the gas passing through each layer of the nozzle holes of the two inner cladding torches 33b are different:

In the present embodiment: the central nozzle hole 34a of the core layer torch 32 is connected with SiCl ₄ gas with a preset flow rate of 0.4slpm and GeCl ₄ gas with a preset flow rate of 0.06slpm; the first annular nozzle hole 34b of the core layer torch 32 is connected to There is hydrogen with a preset flow rate of 4.5slpm, the second annular nozzle hole 34c of the core layer burner 32 is connected with argon gas with a preset flow rate of 3slpm, and the third annular nozzle hole 34d of the core layer burner 32 is connected with a preset flow rate of 18slpm. The fourth annular orifice 34e of the core layer torch 32 is supplied with argon with a preset flow rate of 4.6 slpm, and the fifth annular orifice 34f of the core layer torch 32 is supplied with hydrogen with a preset flow rate of 21 slpm. Argon gas with a preset flow rate of 4.8 slpm is passed through the sixth annular orifice 34g of 32 , and oxygen gas with a preset flow rate of 18 slpm is passed through the seventh annular orifice 34h of the core layer torch 32 .

The first inner cladding torch 33a passes through the gas and the airflow flow rate of each spray hole from the inside to the outside is set as follows: the central spray hole passes through the SiCl4 gas with a preset flow rate of 3.6slpm, and the first annular spray hole passes through the preset flow rate of 7slpm. Hydrogen gas and carbon tetrafluoride gas with a preset flow rate of 0.4slpm, the second annular orifice is passed with argon with a preset flow rate of 5slpm, the third annular spray hole is passed with oxygen with a preset flow rate of 35slpm, and the fourth annular spray hole is passed through. Argon gas with a preset flow rate of 4 slpm passes through the orifice, hydrogen gas with a preset flow rate of 70 slpm passes through the fifth annular spray hole, argon gas with a preset flow rate of 6 slpm passes through the sixth annular spray hole, and the seventh annular spray hole passes with a preset flow rate of 6 slpm. The preset flow rate is 45slpm of oxygen; the control range of the bulk density of the first inner cladding is 0.38g/cm ³ .

The second inner cladding torch 33b from the inside to the outside through the gas and gas flow through the nozzle holes are set as follows: the central nozzle hole has a preset flow of SiCl4 gas of 4slpm, the first annular nozzle has a preset flow of 9.3slpm of SiCl4 gas. Hydrogen gas and carbon tetrafluoride gas with a preset flow rate of 1.6slpm, the second annular orifice is passed with argon with a preset flow rate of 4slpm, the third annular spray hole is passed with oxygen with a preset flow rate of 25slpm, and the fourth annular spray hole is passed through. Argon gas with a preset flow rate of 5 slpm is passed through the holes, the fifth annular spray hole is passed with hydrogen gas with a preset flow rate of 80 slpm, the sixth annular spray hole is passed with argon gas with a preset flow rate of 4 slpm, and the seventh annular spray hole is passed with a preset flow rate of 4 slpm. The preset flow rate is 35slpm of oxygen; the second inner cladding loose body density control range is 0.28g/cm ³ .

Embodiment three:

The difference between the third embodiment and the first to second embodiments is only in that the core layer burner 32, the first inner clad burner 32 and the first inner clad burner are in the process of obtaining the mandrel loose body formed by the core layer and the inner cladding layer by applying the VAD process to deposit by the deposition equipment. The preset flow rates of the gases passing through the orifices of each layer of the second inner cladding torch 33a and the second inner cladding torch 33b are different:

In this embodiment, the central orifice of the core layer torch 32 is passed through with SiCl ₄ gas with a preset flow rate of 0.6slpm and GeCl ₄ gas with a preset flow rate of 0.04slpm; The preset flow rate of hydrogen gas is 3slpm, the second annular nozzle hole of the core layer burner has a preset flow rate of 4slpm of argon gas, and the third annular nozzle hole of the core layer burner has a preset flow rate of 22slpm oxygen gas. , the fourth annular orifice of the core layer torch passes through the argon gas with a preset flow rate of 3.8 slpm, the fifth annular orifice of the core layer torch passes through the hydrogen gas with a preset flow rate of 18 slpm, and the core layer torch passes through the gas with a preset flow rate of 18 slpm. The sixth annular orifice of the core layer burner passes through argon with a preset flow rate of 4 slpm, and the seventh annular orifice of the core layer burner passes through oxygen with a preset flow rate of 20 slpm.

In this embodiment, the gas and airflow flow through each nozzle hole of the first inner cladding torch 33a from the inside to the outside are set as follows: the central nozzle hole has a preset flow rate of 4.2slpm of SiCl4 gas, and the first annular nozzle hole has a preset flow rate of 4.2 slpm. Set the flow rate of 8slpm of hydrogen gas and the preset flow rate of 0.5slpm of carbon tetrafluoride gas, the second annular orifice is connected with argon with a preset flow rate of 3slpm, and the third annular orifice is connected with oxygen with a preset flow rate of 45slpm , the fourth annular orifice has a preset flow rate of 5slpm of argon, the fifth annular orifice has a preset flow of 60slpm of hydrogen, the sixth annular orifice has a preset flow of 5slpm of argon, the seventh Oxygen with a preset flow rate of 25 slpm passes through the annular orifice; the density control range of the loose body of the first inner cladding layer is 0.363 g/cm ³ .

In this embodiment, the gas and airflow flow through the nozzle holes of the second inner cladding torch 33b from the inside to the outside are set as follows: the central nozzle hole is filled with SiCl4 gas with a preset flow rate of 4.7 slpm, and the first annular nozzle hole is filled with a predetermined flow rate of SiCl4 gas. Set the flow rate of 8slpm of hydrogen gas and the preset flow rate of 1.3slpm of carbon tetrafluoride gas, the second annular orifice has a preset flow rate of 5slpm of argon gas, and the third annular orifice is passed through with a preset flow rate of 35slpm of oxygen gas , the fourth annular orifice passes through the argon gas with a preset flow of 4 slpm, the fifth annular orifice passes through the hydrogen with a preset flow of 70 slpm, the sixth annular orifice passes through the argon gas with a preset flow of 6 slpm, and the seventh Oxygen with a preset flow rate of 25 slpm passes through the annular orifice; the density control range of the loose body of the second inner cladding is 0.3 g/cm ³ .

Embodiment 4:

The difference between this embodiment and the first to third embodiments is only in that the core layer burner 32 and the first inner clad burner 33a are in the process of obtaining the mandrel loose body formed by the core layer and the inner cladding layer by applying the VAD process to deposit by the deposition equipment. It is different from the preset flow rate of the gas passing through the orifices of each layer of the second inner cladding torch 33b:

In this embodiment, the central orifice of the core layer torch 32 is passed through with SiCl ₄ gas with a preset flow rate of 0.8slpm and GeCl ₄ gas with a preset flow rate of 0.02slpm; The preset flow rate is 6slpm of hydrogen gas, the second annular nozzle hole of the core layer burner has a preset flow rate of 2slpm of argon, and the third annular nozzle hole of the core layer burner has a preset flow rate of 26slpm oxygen gas , the fourth annular orifice of the core layer torch passes through argon with a preset flow rate of 3 slpm, the fifth annular orifice of the core layer torch is passed through with hydrogen gas with a preset flow rate of 24 slpm, and the core layer torch has a flow rate of 24 slpm. Argon gas with a preset flow rate of 3.2 slpm passes through the sixth annular orifice, and oxygen with a preset flow rate of 22 slpm passes through the seventh annular orifice of the core layer burner.

In this embodiment, the gas and airflow flow through the nozzle holes of the first inner cladding torch 33a from the inside to the outside are set as follows: the central nozzle hole has a preset flow rate of 3slpm of SiCl4 gas, and the first annular nozzle hole has a preset flow rate of 3 slpm. Hydrogen with a flow rate of 6 slpm and carbon tetrafluoride gas with a preset flow rate of 0.6 slpm, the second annular orifice is connected with argon with a preset flow rate of 4 slpm, and the third annular spray hole is connected with oxygen with a preset flow rate of 25 slpm, The fourth annular orifice passes through argon with a preset flow of 6 slpm, the fifth annular orifice passes through hydrogen with a preset flow of 80 slpm, the sixth annular orifice passes through with argon with a preset flow of 4 slpm, and the seventh annular Oxygen with a preset flow rate of 35 slpm passes through the orifice; the density control range of the loose body of the first inner cladding is 0.35 g/cm ³ .

In this embodiment, the gas and airflow flow through the nozzle holes of the second inner cladding torch 33b from the inside to the outside are set as follows: the central nozzle hole is filled with SiCl4 gas with a preset flow rate of 5.4 slpm, and the first annular nozzle hole is filled with a predetermined flow rate of SiCl4 gas. The hydrogen gas with a flow rate of 10.6slpm and a carbon tetrafluoride gas with a preset flow rate of 1 slpm are set, the second annular orifice is connected with argon with a preset flow rate of 3slpm, and the third annular spray hole is connected with oxygen with a preset flow rate of 45slpm. Argon gas with a preset flow rate of 6 slpm passes through the fourth annular orifice, hydrogen with a preset flow rate of 60 slpm passes through the fifth annular spray hole, and argon gas with a preset flow rate of 5 slpm passes through the sixth annular spray hole. Oxygen with a preset flow rate of 45 slpm passes through the annular orifice; the density control range of the loose body of the second inner cladding is 0.26 g/cm ³ .

The low-cost processing technology of the bend-insensitive optical fiber of the present invention adopts the combined process of VAD+OVD, by incorporating F into the loose body during the production process of the mandrel, and controlling the gas flow rate of different torches, thereby controlling the loose body package The density of the cladding layer, and the amount of CF4 introduced into it, completes the control of the refractive index of the outer cladding. After sintering, the inner cladding structure like a stepped descending depression is obtained. This structure greatly reduces the viscosity matching problem between the core cladding, and the optical rod is prepared by OVD. After drawing, the fiber macrobend attenuation meets the ITU-T G.657 fiber standard under the condition that the fiber performance remains unchanged.

The specific implementation of the present invention has been described in detail above, but the content is only a preferred embodiment of the present invention, and cannot be considered to limit the implementation scope of the present invention. All equivalent changes and improvements made according to the scope of the application of the invention should still fall within the scope of the patent of the present invention.

Claims (8)

1. A low-cost processing technology of a bending insensitive single-mode optical fiber is characterized in that an optical fiber perform is prepared, and then drawing processing is carried out on the optical fiber perform to obtain the bending insensitive optical fiber; the bend insensitive single mode optical fiber comprises a central core layer, a cladding layer surrounding and in contact with the core layer, the cladding layer comprising from inside to outside an inner cladding layer and an outer cladding layer; the method is characterized in that:

the inner cladding comprises at least two layers, and at least two layers of inner cladding form at least one step-like concave structure from inside to outside;

the preparation of the optical fiber preform includes: depositing by using VAD (vapor deposition) technology through deposition equipment to obtain a core rod loose body formed by the core layer and the inner cladding layer; step (2), sintering, dehydrating and stretching the core rod loose body to obtain a transparent glass core rod; depositing the outer cladding layer on the outer surface of the core rod by using an OVD (over-voltage direct current) process, and finally sintering to obtain the optical fiber preform;

in the step (1), the deposition equipment comprises a cavity, and a core layer blowtorch and an inner cladding blowtorch which are arranged in the cavity, wherein the inner cladding blowtorch is at least two, each inner cladding blowtorch is respectively in one-to-one correspondence with an inner cladding, and the core layer blowtorch and the inner cladding blowtorch are both in an annular multilayer spray hole structure; the initial target rod extends into the cavity from the top and is controlled by the control system to rotate at a set speed and lift upwards, the control system controls the core layer blowtorch to deposit at the tail end of the initial target rod at a preset deposition gas flow rate to form the core layer, and the control system controls each inner cladding blowtorch to deposit at the tail end of the core layer at a preset inner cladding gas flow rate to form each inner cladding layer from inside to outside in sequence according to the refractive index profile structure of the inner cladding layer of the optical fiber.

2. A low cost process of fabricating a bend insensitive single mode optical fiber as claimed in claim 1 wherein: the deposition equipment further comprises an air inlet system and an air exhaust system, wherein the air inlet system is arranged on one side of the cavity, and the air exhaust system is arranged on the opposite side of the cavity.

3. A low cost process of fabricating a bend insensitive single mode optical fiber as claimed in claim 1 wherein: the inner cladding comprises a first inner cladding and a second inner cladding from inside to outside, and the first inner cladding and the second inner cladding form a stepped concave structure; the relative refractive index difference delta n1 of the core layer is 0.35-0.45%, the relative refractive index difference delta n2 of the first inner cladding layer is 0.02-0.04%, and the relative refractive index difference delta n3 of the second inner cladding layer is 0.1-0.18%.

4. A low cost process of fabricating a bend insensitive single mode optical fiber as claimed in claim 3 wherein: the inner cladding blowtorch comprises a first inner cladding blowtorch for depositing the first inner cladding and a second inner cladding blowtorch for depositing the second inner cladding; the core layer blowtorch, the first inner cladding blowtorch and the second inner cladding blowtorch are all of an annular eight-layer spray hole structure and sequentially comprise a central spray hole, a first annular spray hole, a second annular spray hole, a third annular spray hole, a fourth annular spray hole, a fifth annular spray hole, a sixth annular spray hole and a seventh annular spray hole from inside to outside.

5. The low-cost process of fabricating a bend insensitive single mode optical fiber as claimed in claim 4, wherein: the central spray hole of the core layer blast lamp is communicated with SiCl with preset flow of 0.4-0.8 slpm₄Gas and GeCl with preset flow of 0.02-0.06 slpm₄A gas; the first annular orifice of sandwich layer blowtorch leads to and has predetermine the hydrogen that flow is 3 ~ 6slpm, the second annular orifice of sandwich layer blowtorch leads to and has predetermine the argon gas that flow is 2 ~ 4slpm, the third annular orifice of sandwich layer blowtorch leads to and has predetermine the oxygen that flow is 18 ~ 26slpm, the fourth annular orifice of sandwich layer blowtorch leads to and has predetermine the argon gas that flow is 3 ~ 1.6slpm, the fifth annular orifice of sandwich layer blowtorch leads to and has predetermine the hydrogen that flow is 18 ~ 24slpm, the sixth annular orifice of sandwich layer blowtorch leads to and predetermines the argon gas that flow is 3.2 ~ 4.8slpm, the seventh annular orifice of sandwich layer blowtorch leads to and has predetermine the oxygen that flow is 18 ~ 22 slpm.

6. The low-cost process of fabricating a bend insensitive single mode optical fiber as claimed in claim 4, wherein: the flow rates of gas and air flow communicated with each spray hole from inside to outside of the first inner cladding blowtorch are set as follows: the central spray hole is filled with SiCl4 gas with the preset flow rate of 3-4.2 slpm, the first annular spray hole is filled with hydrogen with the preset flow rate of 6-8 slpm and carbon tetrafluoride gas with the preset flow rate of 0.4-0.6 slpm, the second annular spray hole is filled with argon with the preset flow rate of 3-5 slpm, and the third annular spray hole is filled with preset gasOxygen with the flow rate of 25-45 slpm is introduced into the fourth annular spray hole, argon with the preset flow rate of 4-6 slpm is introduced into the fifth annular spray hole, hydrogen with the preset flow rate of 60-80 slpm is introduced into the fifth annular spray hole, argon with the preset flow rate of 4-6 slpm is introduced into the sixth annular spray hole, and oxygen with the preset flow rate of 25-45 slpm is introduced into the seventh annular spray hole; the control range of the first inner cladding loose body density is 0.35-0.38 g/cm³。

7. The low-cost process of fabricating a bend insensitive single mode optical fiber as claimed in claim 4, wherein: the flow rates of the gas and the gas flow communicated with each spray hole from inside to outside of the second inner cladding blowtorch are set as follows: SiCl4 gas with the preset flow rate of 4-5.4 slpm is introduced into the central spray hole, hydrogen with the preset flow rate of 8-10.6 slpm and carbon tetrafluoride gas with the preset flow rate of 1-1.6 slpm are introduced into the first annular spray hole, argon with the preset flow rate of 3-5 slpm is introduced into the second annular spray hole, oxygen with the preset flow rate of 25-45 slpm is introduced into the third annular spray hole, argon with the preset flow rate of 4-6 slpm is introduced into the fourth annular spray hole, hydrogen with the preset flow rate of 60-80 slpm is introduced into the fifth annular spray hole, argon with the preset flow rate of 4-6 slpm is introduced into the sixth annular spray hole, and oxygen with the preset flow rate of 25-45 slpm is introduced into the seventh annular spray hole; the control range of the loose body density of the second inner cladding is 0.26-0.3 g/cm³。

8. A low cost process of fabricating a bend insensitive single mode optical fiber as claimed in claim 1 wherein: and (3) introducing chlorine and helium in the sintering dehydration treatment in the step (2).

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