Air pressure regulating device and method for hollow core optical fiber

Abstract

The application provides a kind of hollow optical fiber internal gas pressure regulating device and method, device includes 2 high pressure gas chamber, the optical fiber interface of second high pressure gas chamber and the optical fiber interface of a row of first high pressure gas chamber are used to communicate with the two ends of hollow optical fiber respectively;Gas path is connected with the gas inlet and outlet of 2 high pressure gas chamber respectively;Vacuum pump is connected with the gas inlet and outlet through gas path;High pressure gas source is connected with the gas inlet and outlet through gas path;Optical detection assembly is same with the number of hollow optical fiber, each optical detection assembly is connected with pigtail, each pigtail is connected with the optical fiber interface of another row of first high pressure gas chamber, and is aligned and coupled with corresponding hollow optical fiber in the interior of first high pressure gas chamber.The application extracts residual gas and fills high pressure gas from the two ends of hollow optical fiber using a set of gas path equipment, can quickly improve the internal pressure of optical fiber, and then improve the additional attenuation problem caused by gas absorption, enhance the long-term use stability of optical fiber.

Description

Technical Field

[0001] The present invention belongs to the technical field of hollow-core optical fibers, and in particular relates to a device and method for regulating the internal gas pressure of a hollow-core optical fiber. Background Art

[0002] Hollow-core optical fiber consists of a hollow capillary structure with gas trapped within it. During the hollow-core optical fiber production process, the preform is typically drawn from a high-temperature furnace into the hollow-core fiber. This causes the gas inside the fiber to experience a sudden drop in temperature. According to the ideal gas equation of state, when the total volume of the fiber's interior remains constant, a drop in temperature will cause a decrease in gas pressure. Therefore, if the pressure inside the preform is close to ambient pressure at the beginning of the drawing process, the pressure inside the hollow-core fiber after drawing is complete and the temperature has dropped significantly below ambient pressure, resulting in a negative pressure differential within the fiber.

[0003] The negative pressure differential within a hollow-core fiber has a certain impact on its long-term stability. For example, if a hollow-core fiber breaks unexpectedly, the fiber end will be exposed to the external environment. Due to the negative pressure differential within the fiber, water and gas from the external environment can easily be absorbed into the fiber and quickly penetrate into the fiber, causing distortion of the communication signal and reducing the effective length of the fiber.

[0004] Chinese invention application CN115390194A discloses a miniaturized hollow-core fiber gas cavity connection device with adjustable internal air pressure. By connecting the two ends of the hollow-core fiber to air chambers, the internal gas pressure of the hollow-core fiber can be conveniently adjusted. However, this solution cannot guarantee the purity of the introduced gas, and may introduce new "contaminated gas" during the pressure regulation process, thereby degrading the performance of the hollow-core fiber. Furthermore, this solution does not provide real-time monitoring and feedback on the progress of pressure regulation. Summary of the Invention

[0005] In response to the above-mentioned defects or improvement needs of the prior art, the present invention proposes a device and method for regulating the gas pressure inside a hollow-core optical fiber.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a hollow-core optical fiber internal gas pressure regulating device is provided, comprising:

[0007] Two high-pressure air chambers, wherein the second high-pressure air chamber is provided with at least one optical fiber interface and at least one gas inlet and outlet; the first high-pressure air chamber is provided with at least one gas inlet and outlet and two rows of symmetrically arranged optical fiber interfaces, and the number of optical fiber interfaces in each row is the same as the number of optical fiber interfaces in the second high-pressure air chamber; the optical fiber interface of the second high-pressure air chamber and the row of optical fiber interfaces of the first high-pressure air chamber are respectively used to communicate with the two ends of the hollow-core optical fiber;

[0008] The gas circuit is connected to the gas inlet and outlet of the two high-pressure gas chambers respectively;

[0009] A vacuum pump is connected to the gas inlet and outlet through a gas path and is used to extract residual gas in the hollow-core optical fiber from both ends of the hollow-core optical fiber;

[0010] A high-pressure gas source is connected to the gas inlet and outlet through a gas path and is used to fill the hollow-core optical fiber with high-pressure gas from both ends thereof;

[0011] The optical detection components have the same number as the hollow-core optical fibers. Each optical detection component is connected to a pigtail. Each pigtail is connected to another row of optical fiber interfaces of the first high-pressure air chamber and is aligned and coupled with the corresponding hollow-core optical fiber inside the first high-pressure air chamber.

[0012] According to the above scheme, the optical fiber interface is a detachable ferrule, the outer surface of the ferrule is detachably connected to the high-pressure gas chamber, the inner diameter of the ferrule is the same as the outer diameter of the hollow-core optical fiber, and after the hollow-core optical fiber is inserted, the hollow-core optical fiber is sealed and connected at the optical fiber interface through sealant.

[0013] According to the above scheme, the gas circuit includes a mixing branch, a charging branch, a pumping branch and a deflation branch; wherein,

[0014] The mixing branch includes two mixing branch roads, one end of the two mixing branch roads is connected to the gas inlet and outlet of the two high-pressure gas chambers respectively, and the other ends of the two mixing branch roads are connected to one end of the inflation branch road, the exhaust branch road and the deflation branch road respectively after merging;

[0015] The other end of the inflation branch is connected to the high-pressure gas source, the other end of the exhaust branch is connected to the vacuum pump, and the other end of the deflation branch is connected to the outside world;

[0016] The mixing branch, the charging branch, the exhaust branch and the deflation branch are respectively provided with switch valves.

[0017] According to the above scheme, pressure gauges are respectively connected to the inflation branch, the exhaust branch and the high-pressure gas chamber.

[0018] According to the above scheme, a pressure reducer, a gas purifier and a booster pump are connected in series on the inflation branch.

[0019] According to the above scheme, the high-pressure gas is an inactive gas whose molecules have no obvious absorption effect on electromagnetic waves in the commonly used bands of optical communications.

[0020] According to a second aspect of the present invention, a method for regulating the gas pressure inside a hollow-core optical fiber using the hollow-core optical fiber internal gas pressure regulating device is provided, comprising the following steps:

[0021] S1. Use a vacuum pump to evacuate the air path, the two high-pressure air chambers, and both ends of the hollow-core optical fiber to achieve a predetermined low pressure in the hollow-core optical fiber.

[0022] S2. Filling the gas path, the two high-pressure gas chambers, and both ends of the hollow-core optical fiber with high-pressure gas through a high-pressure gas source, and after the two high-pressure gas chambers reach a predetermined high pressure, continuously keeping the two high-pressure gas chambers sealed and within a certain pressure range, so that the high-pressure gas enters the hollow-core optical fiber from both ends simultaneously;

[0023] S3. Monitor the process of high-pressure gas passing into the hollow-core optical fiber, and stop when the high-pressure gas passing from both ends of the hollow-core optical fiber converges in the middle section of the hollow-core optical fiber.

[0024] According to the above method, S1 specifically includes:

[0025] S101, evacuating the two high-pressure gas chambers by a vacuum pump until the pressure reaches a first predetermined low pressure;

[0026] S102, closing the valves in the gas path connected to the two high-pressure gas chambers to maintain a certain low pressure in the two high-pressure gas chambers, thereby gradually discharging the gas in the hollow-core optical fiber from both ends of the hollow-core optical fiber; and simultaneously monitoring the gas extraction process in the hollow-core optical fiber until the hollow-core optical fiber reaches a second predetermined low pressure.

[0027] S103, opening the valve in the gas path connected to the two high-pressure gas chambers, and exhausting the gas exhausted from both ends of the hollow-core optical fiber through a vacuum pump.

[0028] According to the above method, S2 specifically includes:

[0029] S201, purifying the gas introduced from the high-pressure gas source;

[0030] S202, pressurizing the purified gas;

[0031] S203, introducing the pressurized gas into two high-pressure gas chambers, continuously keeping the two high-pressure gas chambers sealed and maintaining the air pressure within a certain range, so that the high-pressure gas enters the hollow-core optical fiber from both ends at the same time.

[0032] According to the above method, the length of the hollow-core optical fiber is less than or equal to 10 km.

[0033] According to the above method, S3 specifically includes:

[0034] After inflation, the optical reflection intensity of a portion of the hollow-core fiber length at both ends of the hollow-core fiber monitored by optical time domain reflectometry increased significantly, i.e., a bulge appeared, indicating that high-pressure gas successfully entered the hollow-core fiber from both ends. The range covered by the bulge indicates the length of the high-pressure gas immersed in the hollow-core fiber.

[0035] As the inflation time increases, the bulges at both ends gradually advance toward the middle section of the hollow-core fiber. When the high-pressure gases at both ends converge, the light reflection intensity curves finally intersect, indicating that the high-pressure gas has filled the entire hollow-core fiber and stopped.

[0036] According to a third aspect of the present invention, there is provided a hollow-core optical fiber obtained by using the hollow-core optical fiber internal gas pressure regulation method, comprising an internal gas having a certain pressure, wherein the pressure distribution of the internal gas is:

[0037] Immediately after the treatment, the air pressure at both ends of the hollow-core fiber is much higher than that in the middle section, and both are higher than the outside atmospheric pressure;

[0038] After the treatment is completed and the hollow fiber is sealed and placed for a certain period of time, the air pressure inside the hollow fiber is evenly distributed.

[0039] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0040] 1. A set of gas path equipment is used to extract residual gas from both ends of the hollow-core optical fiber and fill it with high-pressure gas. When extracting gas, the gas inside the hollow-core optical fiber is discharged from both ends of the optical fiber, and the introduced external impurities can be discharged together; when replenishing gas, high-pressure gas is introduced from both ends of the hollow-core optical fiber, which can quickly improve the internal pressure of the optical fiber, thereby improving the additional attenuation problem caused by gas absorption and enhancing the long-term stability of the optical fiber.

[0041] 2. By rationally setting the connection of the gas circuit and the layout of the components in the gas circuit, the efficiency of the pressure regulation process can be further improved. Specifically, by adjusting the pressure valves on the gas circuit branches leading to the first high-pressure gas chamber and the second high-pressure gas chamber, the pressures in the two gas chambers can be controlled separately, thereby controlling the speed at which the gas enters the hollow-core optical fiber from both ends; the supplementary gas is purified by a gas purifier, avoiding the increase in the absorption loss of the optical fiber caused by possible impurities in the supplementary gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A structural diagram provided for an embodiment of the present invention.

[0043] Figure 2 A schematic diagram of a method flow chart provided in one embodiment of the present invention.

[0044] Figure 3 The real-time monitoring results of a typical gas extraction process using optical time domain reflectometry.

[0045] Figure 4 The real-time monitoring results of a typical gas replenishment process using optical time domain reflectometry.

[0046] Figure 5 The results of optical time domain reflectometry monitoring of a hollow-core optical fiber sealed and placed after gas extraction and replenishment.

[0047] In the figure, the meanings of the various numbers are as follows:

[0048] 1. Hollow-core optical fiber; 2. Optical time domain reflectometer; 3. First high-pressure gas chamber; 4. Second high-pressure gas chamber; 5. Gas circuit; 6. High-pressure gas source; 7. Gas purifier; 8. Booster pump; 9. Vacuum pump;

[0049] 21. Pigtail; 31. Sealing insert on the left side of the first high-pressure gas chamber; 32. Sealing insert on the right side of the first high-pressure gas chamber; 33. Pressure gauge of the first high-pressure gas chamber; 34. Safety valve of the first high-pressure gas chamber; 41. Sealing insert of the second high-pressure gas chamber; 42. Pressure gauge of the second high-pressure gas chamber; 43. Safety valve of the second high-pressure gas chamber; 51. Pressure gauge of the booster pump; 52. Pressure gauge of the vacuum pump; 53. Control valve of the booster pump; 54. Control valve of the vacuum pump; 55. Exhaust valve; 56. Branch control valve of the first high-pressure gas chamber; 57. Branch control valve of the second high-pressure gas chamber; 58. Vent branch; 61. Pressure reducer. DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0051] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0052] According to the first aspect of the present invention, this embodiment provides a hollow core optical fiber internal gas pressure regulating device, such as Figure 1 As shown, it includes a first high-pressure gas chamber 3, a second high-pressure gas chamber 4, an air circuit 5, a vacuum pump 9, a high-pressure gas source 6 and an optical detection component.

[0053] The first high-pressure gas chamber 3 and the second high-pressure gas chamber 4 are pressure vessels capable of withstanding a pressure of at least 10 MPa. A first high-pressure gas chamber pressure gauge 33 and a second high-pressure gas chamber pressure gauge 42 are provided above the first high-pressure gas chamber 3 and the second high-pressure gas chamber 4, respectively. Safety valves, a first high-pressure gas chamber safety valve 34 and a second high-pressure gas chamber safety valve 43, are provided, respectively, to automatically release pressure to the rated operating pressure when the pressure exceeds the pressure range of the high-pressure gas chamber.

[0054] The second high-pressure air chamber 4 is provided with at least one optical fiber interface and at least one gas inlet and outlet; the first high-pressure air chamber 3 is provided with at least one gas inlet and outlet and two rows of symmetrically arranged optical fiber interfaces, the number of optical fiber interfaces in each row being the same as the number of optical fiber interfaces in the second high-pressure air chamber 4; the optical fiber interfaces of the second high-pressure air chamber 4 and the row of optical fiber interfaces of the first high-pressure air chamber 3 are respectively used to connect to the two ends of the hollow-core optical fiber 1. The number of optical detection components is the same as the number of hollow-core optical fibers, and each optical detection component is connected to a pigtail 21. Each pigtail 21 is aligned and coupled with the corresponding hollow-core optical fiber 1 inside the first high-pressure air chamber 3. The pigtail 21 should be a hollow-core optical fiber with a cross-sectional structure similar to that of the hollow-core optical fiber 1.

[0055] The optical fiber interface is a detachable ferrule, the outer surface of which is detachably connected to the high-pressure gas chamber. The inner diameter of the ferrule is the same as the outer diameter of the hollow-core fiber. After the hollow-core fiber is inserted, a sealant is used to seal the hollow-core fiber at the optical fiber interface. In this embodiment, the optical fiber interface of the second high-pressure gas chamber 4 is a second high-pressure gas chamber sealing ferrule 41. The optical fiber interface of the first high-pressure gas chamber 3 includes a first high-pressure gas chamber left sealing ferrule 31 and a first high-pressure gas chamber right sealing ferrule 32. The first high-pressure gas chamber right sealing ferrule 32 and the second high-pressure gas chamber sealing ferrule 41 are respectively connected to the two ends of the hollow-core fiber 1, so that the two ends of the hollow-core fiber 1 are connected to the interior of the first high-pressure gas chamber 3 and the second high-pressure gas chamber 4. In this embodiment, the optical detection component is an optical time domain reflectometer 2. The pigtail 21 is connected to the first high-pressure gas chamber left sealing ferrule 31 and is aligned and coupled with the end of the hollow-core fiber 1 in the first high-pressure gas chamber 3, so that the optical time domain reflectometer 2 can monitor the internal pressure state of the hollow-core fiber 1 in real time during the evacuation and inflation process.

[0056] Gas circuit 5 is a high-pressure pipeline capable of withstanding at least 20 MPa of pressure. It is connected to the gas inlets and outlets of the two high-pressure gas chambers. In this embodiment, gas circuit 5 includes a mixing branch, an inflation branch, an exhaust branch, and a deflation branch 58. The mixing branch includes two mixing branches, one end of each of which is connected to the gas inlets and outlets of the two high-pressure gas chambers. The other ends of the two mixing branches merge and are then connected to one end of the inflation branch, the exhaust branch, and the deflation branch 58, respectively. A first high-pressure gas chamber branch control valve 56 and a second high-pressure gas chamber branch control valve 57 are provided on each of the two mixing branches.

[0057] The other end of the inflation branch is connected to a high-pressure gas source 6. Starting from the high-pressure gas source 6, the inflation branch is connected in series with a pressure reducer 61, a gas purifier 7, a booster pump 8, a booster pump pressure gauge 51, and a booster pump control valve 53. The rated pressure of the high-pressure gas source 6 is generally 15 MPa. The high-pressure gas contained in the gas source 6 is an inert gas whose molecules do not significantly absorb electromagnetic waves in the wavelength band commonly used in optical communications, including but not limited to nitrogen, argon, and helium. The gas source can be changed based on actual usage. The pressure reducer 61 reduces the gas pressure to meet the inlet pressure of the gas purifier 7. The gas purifier 7 removes impurities such as water vapor from the gas at the outlet of the high-pressure gas source 6 and then passes the gas to the booster pump 8. The booster pump 8 regulates the pressure of the gas entering the high-pressure gas chamber, which should be between 1 MPa and 10 MPa. The outlet pipeline of the booster pump 8 is equipped with a booster pump pressure gauge 51 to monitor the outlet pressure and a booster pump control valve 53 to control the opening and closing of the pipeline.

[0058] The other end of the exhaust branch is connected to a vacuum pump 9, which is equipped with a vacuum pump pressure gauge 52 and a vacuum pump control valve 54. The vacuum pump 9 is primarily used in the extraction process of the hollow-core optical fiber 1. The vacuum pump control valve 54 can be controlled according to the value indicated by the vacuum pump pressure gauge 52 to roughly adjust the vacuum level in the first high-pressure gas chamber 3 and the second high-pressure gas chamber 4.

[0059] The other end of the deflation branch 58 is connected to the outside world, and an exhaust valve 55 is provided on the deflation branch 58. The deflation branch 58 is used to exhaust excess gas in the gas path 5. For example, after the gas replenishment process is completed, the exhaust valve 55 can be opened to exhaust the high-pressure gas in the gas path 5.

[0060] According to the second aspect of the present invention, this embodiment provides a method for regulating the gas pressure inside a hollow-core optical fiber using the hollow-core optical fiber internal gas pressure regulating device, comprising the following steps:

[0061] S1. Use a vacuum pump to evacuate the air path, two high-pressure air chambers, and both ends of the hollow-core optical fiber to achieve a predetermined low pressure in the hollow-core optical fiber. S1 specifically includes:

[0062] S101, evacuating the two high-pressure gas chambers by a vacuum pump until the pressure reaches a first predetermined low pressure;

[0063] S102, closing the valves in the gas path connected to the two high-pressure gas chambers to maintain a certain low pressure in the two high-pressure gas chambers, thereby gradually discharging the gas in the hollow-core optical fiber from both ends of the hollow-core optical fiber; and simultaneously monitoring the gas extraction process in the hollow-core optical fiber until the hollow-core optical fiber reaches a second predetermined low pressure.

[0064] S103, opening the valve in the gas path connected to the two high-pressure gas chambers, and exhausting the gas exhausted from both ends of the hollow-core optical fiber through a vacuum pump.

[0065] S2: Fill the gas path, two high-pressure gas chambers, and both ends of the hollow-core optical fiber with high-pressure gas through a high-pressure gas source, and after the two high-pressure gas chambers reach a predetermined high pressure, continue to keep the two high-pressure gas chambers sealed and within a certain pressure range, so that high-pressure gas can be simultaneously introduced into the hollow-core optical fiber from both ends of the hollow-core optical fiber. S2 specifically includes:

[0066] S201, purifying the gas introduced from the high-pressure gas source;

[0067] S202, pressurizing the purified gas;

[0068] S203, introducing the pressurized gas into two high-pressure gas chambers, continuously keeping the two high-pressure gas chambers sealed and maintaining the air pressure within a certain range, so that the high-pressure gas enters the hollow-core optical fiber from both ends at the same time.

[0069] S3. Monitor the process of high-pressure gas passing into the hollow-core optical fiber, and stop when the high-pressure gas passing from both ends of the hollow-core optical fiber converges in the middle section of the hollow-core optical fiber.

[0070] like Figure 2 As shown, Figure 2 The figure is a flow chart of a method for extracting and replenishing gas inside a hollow-core optical fiber according to the present invention. The method comprises the following steps:

[0071] 1. After the hollow core optical fiber 1 is drawn, one end thereof is connected to the first high-pressure gas chamber 3 and coupled to the pigtail 21 of the optical time domain reflectometer 2, and the other end is connected to the second high-pressure gas chamber 4.

[0072] 2. Open the vacuum pump control valve 54, the first high-pressure gas chamber branch control valve 56, and the second high-pressure gas chamber branch control valve 57, close the booster pump control valve 53 and the exhaust valve 55, and turn on the vacuum pump 9 to vacuum the gas path 5, the first high-pressure gas chamber 3, and the second high-pressure gas chamber 4 to discharge the contaminated gas that may have existed in the gas path 5 and the two high-pressure gas chambers.

[0073] 3. When the pressure gauges 33 and 42 of the first high-pressure gas chamber decrease and stop changing, it can be considered that the two gas chambers are close to vacuum. At this time, close the first high-pressure gas chamber branch control valve 56 and the second high-pressure gas chamber branch control valve 57, and then close the vacuum pump control valve 54 to keep the two high-pressure gas chambers in a vacuum pressure-maintaining state, so that the contaminated gas in the hollow-core optical fiber is continuously extracted and discharged from both ends of the hollow-core optical fiber.

[0074] 4. After the gas extraction is completed, the pressure reducer 61 of the high-pressure gas source 6 is opened and adjusted to make the gas meet the working pressure of the gas purifier 7 and then introduced into the gas purifier 7. After the gas is purified by the gas purifier, the impurity content is less than 1 ppb.

[0075] 5. Set the pressure 8 of booster pump 8. After the purified gas is introduced into booster pump 8, the pressure is increased to the set value. After booster pump control valve 53 and first and second high-pressure chamber branch control valves 56 and 57 are opened, the high-pressure gas flows through the gas path and is introduced into first and second high-pressure chambers 3 and 4. In some embodiments, the booster pump increases the pressure of the supplemented gas to 1 MPa to 10 MPa.

[0076] 6. When the readings on the first and second high-pressure chamber pressure gauges 33 and 42 reach the values ​​set by booster pump 8, close the first and second high-pressure chamber branch control valves 56 and 57. At this point, both high-pressure chambers are in a high-pressure holding state. High-pressure gas enters both ends of hollow-core optical fiber 1 from the first and second high-pressure chambers 3 and 4, respectively. Close the pressure reducer 61 and booster pump 8, open the exhaust valve 55, and allow the high-pressure gas in gas path 5 to be discharged through the venting branch 58. Then close the booster pump control valve 53.

[0077] 7. After entering hollow-core fiber 1, high-pressure gas intrudes from both ends toward the middle section. The pressure in hollow-core fiber 1 gradually increases at both ends, and the length of the high-pressure section increases over time. The pressure changes within hollow-core fiber 1 can be monitored using the readings from optical time-domain reflectometry 2. Because the interior of hollow-core fiber 1 is very confined, the pressures within first and second high-pressure gas chambers 3 and 4 will slowly decrease. Based on the real-time readings from optical time-domain reflectometry 2, when the high-pressure gas in hollow-core fiber 1 converges in the middle section, the first and second high-pressure gas chamber branch control valves 56 and 57 are opened, allowing the gas in the two high-pressure gas chambers to be discharged through the venting branch 58. Remove hollow-core fiber 1 and seal both ends for storage.

[0078] Figure 3 This is the real-time monitoring result of a typical gas extraction process by optical time domain reflectometer 2. Figure 3 As can be seen, before gas extraction, the optical fiber absorbs "contaminated gas," causing a localized increase in light reflection intensity near the fiber end, creating a "bulge." This is because the absorption of gas by the hollow-core fiber increases the number of gas molecules at the fiber entrance, leading to enhanced light backscattering in this section of the fiber. As gas extraction time increases, the "bulge" gradually flattens, indicating that the absorbed "contaminated gas" is gradually expelled, which helps reduce additional attenuation due to gas absorption.

[0079] Figure 4 This is the real-time monitoring result of a typical gas replenishment process by optical time domain reflectometer 2. Figure 4As can be seen, after inflation, "bulges" appear near the ends of the fiber, indicating that the high-pressure gas has successfully entered the fiber from both ends. The extent of the "bulge" indicates the length of the fiber that the high-pressure gas has penetrated. As inflation time increases, the "bulges" at both ends gradually advance toward the middle of the fiber. When the high-pressure gas at both ends converges, the light reflection intensity curve eventually approaches a "V" shape, indicating that the high-pressure gas has nearly filled the entire hollow-core fiber. At this point, the pressure inside the fiber is much higher than the external air pressure.

[0080] In the wavelength range of 1600nm to 1601nm, carbon dioxide gas has three relatively high absorption peaks. The average amount of additional attenuation of these three absorption peaks is used as a typical value to measure the degree of gas contamination of the optical fiber.

[0081] Table 1

[0082]

[0083] Table 1 gives several embodiments of the method for extracting and replenishing gas inside a hollow-core optical fiber. As shown in Table 1, after the gas extraction and replenishment process, the additional gas attenuation involved in the optical fiber is much less than before the gas replacement. In addition, since the pressure inside the optical fiber is higher than that of the external environment, it can increase the entry of external contaminant gases, so that the optical fiber will not experience an increase in additional gas attenuation for a long time. It can also be seen from Table 1 that the longer the optical fiber or the higher the gas pressure used, the stronger the ability of the optical fiber to resist the entry of external gas after gas replacement. Generally speaking, after gas extraction and replenishment, the gas accessory attenuation of the optical fiber will not exceed 10% within at least 30 days, and can be up to 105 days.

[0084] After the gas extraction and replenishment process is completed, both ends of the optical fiber are sealed and placed. Figure 5 The optical time domain reflectometer readings for different placement times are shown in the figure. As can be seen from the figure, with the increase of placement time, the readings at both ends of the optical fiber inflation slowly decrease, while the readings in the middle section of the optical fiber, especially at the bottom of the "V", rise rapidly. By the fourth day, the overall curve is close to a straight line, indicating that the air pressure inside the optical fiber is close to uniform distribution.

[0085] Table 2

[0086]

[0087] Table 2 shows the time required for the optical fiber to achieve uniform internal pressure distribution after gas replacement under several typical embodiments. It can be seen from the table that the longer the optical fiber or the greater the high-pressure gas pressure, the longer it takes to achieve uniform internal pressure distribution. Generally speaking, after the gas extraction and replenishment process in the optical fiber is completed, the internal pressure can be close to uniform distribution in about 19 days at the latest.

[0088] In some embodiments, the length of the hollow-core optical fiber is less than or equal to 10 km. When the gas is extracted, the first air chamber and the second air chamber are kept under vacuum pressure for 2-7 days. When the gas is replenished, the first high-pressure air chamber and the second high-pressure air chamber are kept under pressure for up to 25 days, so that the high-pressure gas can be completely passed into the entire optical fiber. The shorter the optical fiber length or the greater the gas pressure, the shorter the time required. After the gas replenishment is completed, the air pressure at both ends of the hollow-core optical fiber is higher than the air pressure in the middle section, but both are higher than the external atmospheric pressure. After the hollow-core optical fiber is sealed and placed for up to 20 days after the treatment is completed, the internal air pressure is close to uniform distribution. The shorter the optical fiber length or the greater the gas pressure, the shorter the time required. After the treatment is completed, the additional attenuation value of gas absorption of the hollow-core optical fiber in the 1460nm to 1625nm band is reduced by more than 50% compared with that before treatment. After the treatment, if the hollow-core optical fiber is opened at both ends and placed in the external atmospheric environment for at least 30 days, the increase in the additional attenuation value of gas absorption in the 1460nm to 1625nm band will not exceed 10%. The longer the optical fiber or the greater the pressure used for gas replenishment, the longer the open-end placement time, up to a maximum of 105 days.

[0089] Therefore, according to the third aspect of the present invention, this embodiment provides a hollow-core optical fiber obtained by using the hollow-core optical fiber internal gas pressure regulation method, including internal gas with a certain pressure, and the pressure distribution of the internal gas is:

[0090] Immediately after the treatment, the air pressure at both ends of the hollow-core fiber is much higher than that in the middle section, and both are higher than the outside atmospheric pressure;

[0091] After the treatment is completed, the air pressure inside the hollow fiber is evenly distributed after being sealed and placed for a certain period of time. The certain period of time is 2-20 days, and the specific time is related to the length of the fiber and / or the air pressure. The shorter the fiber length or the higher the air pressure, the shorter the time required.

[0092] The device described in the present invention uses the same set of gas path equipment, which can realize the extraction and replenishment functions of the gas inside the hollow-core optical fiber as needed. When the gas is extracted, the gas inside the hollow-core optical fiber is discharged from both ends of the optical fiber, and the introduced external impurities can be discharged together. When the gas is replenished, high-pressure gas is introduced from both ends of the hollow-core optical fiber, which can quickly improve the internal pressure of the optical fiber. At the same time, the present invention purifies the supplementary gas through a gas purifier, avoiding the increase in the absorption loss of the optical fiber caused by the possible presence of impurities in the supplementary gas; in addition, the optical time domain reflectometer can conveniently and quickly monitor the degree of high-pressure gas entering from both ends in real time; by adjusting the pressure valves on the gas path branches leading to the first high-pressure gas chamber and the second high-pressure gas chamber, the pressure in the two gas chambers can be controlled respectively, thereby controlling the speed of gas entry from both ends of the hollow-core optical fiber; in addition, the safety valves on the first high-pressure gas chamber and the second high-pressure gas chamber will automatically release the pressure when the pressure exceeds the rated value, further ensuring the safety of the gas replenishment process.

[0093] The method of the present invention can, on the one hand, extract the contaminated gas already present inside the hollow-core optical fiber, improving the additional attenuation problem caused by gas absorption; on the other hand, it can quickly increase the gas pressure inside the hollow-core optical fiber, enhancing the long-term stability of the optical fiber.

[0094] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0095] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A hollow-core optical fiber internal gas pressure regulating device, characterized by: include: Two high-pressure air chambers, wherein the second high-pressure air chamber is provided with at least one optical fiber interface and at least one gas inlet and outlet; the first high-pressure air chamber is provided with at least one gas inlet and outlet and two rows of symmetrically arranged optical fiber interfaces, and the number of optical fiber interfaces in each row is the same as the number of optical fiber interfaces in the second high-pressure air chamber; the optical fiber interface of the second high-pressure air chamber and the row of optical fiber interfaces of the first high-pressure air chamber are respectively used to communicate with the two ends of the hollow-core optical fiber; The gas circuit is connected to the gas inlet and outlet of the two high-pressure gas chambers respectively; A vacuum pump is connected to the gas inlet and outlet through a gas path and is used to extract residual gas in the hollow-core optical fiber from both ends of the hollow-core optical fiber; A high-pressure gas source is connected to the gas inlet and outlet through a gas path and is used to fill the hollow-core optical fiber with high-pressure gas from both ends thereof; The optical detection components have the same number as the hollow-core optical fibers. Each optical detection component is connected to a pigtail. Each pigtail is connected to another row of optical fiber interfaces of the first high-pressure air chamber and is aligned and coupled with the corresponding hollow-core optical fiber inside the first high-pressure air chamber.

2. The hollow-core optical fiber internal gas pressure regulating device according to claim 1, characterized in that: The optical fiber interface is a detachable ferrule, the outer surface of the ferrule is detachably connected to the high-pressure air chamber, the inner diameter of the ferrule is the same as the outer diameter of the hollow-core optical fiber, and after the hollow-core optical fiber is inserted, the hollow-core optical fiber is sealed and connected at the optical fiber interface through sealant.

3. The hollow-core optical fiber internal gas pressure regulating device according to claim 1, characterized in that: The gas circuit includes a mixing branch, an inflation branch, an exhaust branch and a deflation branch; wherein, The mixing branch includes two mixing branch roads, one end of the two mixing branch roads is connected to the gas inlet and outlet of the two high-pressure gas chambers respectively, and the other ends of the two mixing branch roads are connected to one end of the inflation branch road, the exhaust branch road and the deflation branch road respectively after merging; The other end of the inflation branch is connected to the high-pressure gas source, the other end of the exhaust branch is connected to the vacuum pump, and the other end of the deflation branch is connected to the outside world; The mixing branch, the charging branch, the exhaust branch and the deflation branch are respectively provided with switch valves.

4. The hollow-core optical fiber internal gas pressure regulating device according to claim 3, characterized in that: The inflation branch, the exhaust branch and the high-pressure gas chamber are respectively connected with pressure gauges.

5. The hollow-core optical fiber internal gas pressure regulating device according to claim 3, characterized in that: The inflation branch is connected in series with a pressure reducer, a gas purifier and a booster pump.

6. The hollow-core optical fiber internal gas pressure regulating device according to claim 1, characterized in that: High-pressure gas is an inactive gas whose molecules have no obvious absorption effect on electromagnetic waves in the band commonly used in optical communications.

7. A method for regulating the gas pressure inside a hollow-core optical fiber using the hollow-core optical fiber internal gas pressure regulating device according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Use a vacuum pump to evacuate the air path, the two high-pressure air chambers, and both ends of the hollow-core optical fiber to achieve a predetermined low pressure in the hollow-core optical fiber. S2. Filling the gas path, the two high-pressure gas chambers, and both ends of the hollow-core optical fiber with high-pressure gas through a high-pressure gas source, and after the two high-pressure gas chambers reach a predetermined high pressure, continuously keeping the two high-pressure gas chambers sealed and within a certain pressure range, so that the high-pressure gas enters the hollow-core optical fiber from both ends simultaneously; S3. Monitor the process of high-pressure gas passing into the hollow-core optical fiber, and stop when the high-pressure gas passing from both ends of the hollow-core optical fiber converges in the middle section of the hollow-core optical fiber.

8. The method for regulating gas pressure inside a hollow-core optical fiber according to claim 7, wherein: S1 specifically includes: S101, evacuating the two high-pressure gas chambers by a vacuum pump until the pressure reaches a first predetermined low pressure; S102, closing the valves in the gas path connected to the two high-pressure gas chambers to maintain a certain low pressure in the two high-pressure gas chambers, thereby gradually discharging the gas in the hollow-core optical fiber from both ends of the hollow-core optical fiber; and simultaneously monitoring the gas extraction process in the hollow-core optical fiber until the hollow-core optical fiber reaches a second predetermined low pressure. S103, opening the valve in the gas path connected to the two high-pressure gas chambers, and exhausting the gas exhausted from both ends of the hollow-core optical fiber through a vacuum pump.

9. The method for regulating gas pressure inside a hollow-core optical fiber according to claim 7, wherein: S2 specifically includes: S201, purifying the gas introduced from the high-pressure gas source; S202, pressurizing the purified gas; S203, introducing the pressurized gas into two high-pressure gas chambers, continuously keeping the two high-pressure gas chambers sealed and maintaining the air pressure within a certain range, so that the high-pressure gas enters the hollow-core optical fiber from both ends at the same time.

10. The method for regulating gas pressure inside a hollow-core optical fiber according to claim 7, wherein: The length of the hollow core optical fiber is less than or equal to 10 km.

11. The method for regulating gas pressure inside a hollow-core optical fiber according to claim 7, wherein: S3 specifically includes: After inflation, the optical reflection intensity of a portion of the hollow-core fiber length at both ends of the hollow-core fiber monitored by optical time domain reflectometry increased significantly, i.e., a bulge appeared, indicating that high-pressure gas successfully entered the hollow-core fiber from both ends. The range covered by the bulge indicates the length of the high-pressure gas immersed in the hollow-core fiber. As the inflation time increases, the bulges at both ends gradually advance toward the middle section of the hollow-core fiber. When the high-pressure gases at both ends converge, the light reflection intensity curves finally intersect, indicating that the high-pressure gas has filled the entire hollow-core fiber and stopped.

12. A hollow-core optical fiber obtained by the method for regulating the pressure of gas inside a hollow-core optical fiber according to any one of claims 7 to 11, characterized in that: Including internal gas with a certain pressure, the pressure distribution of the internal gas is: Immediately after the treatment, the air pressure at both ends of the hollow-core fiber is much higher than that in the middle section, and both are higher than the outside atmospheric pressure; After the treatment is completed and the hollow fiber is sealed and placed for a certain period of time, the air pressure inside the hollow fiber is evenly distributed.

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