A device and method for suppressing the roughness of the inner wall of a hollow photonic crystal fiber core.

Abstract

This application discloses a device and method for suppressing the roughness of the inner wall of a hollow photonic crystal fiber, relating to optical fiber application technology. The device includes: a light source (1), whose emitted light is split into two paths by a coupler (2); one path passes through an attenuator (3) to a dual-channel power meter (4); the other path is connected to a hollow photonic crystal fiber (7) via a first fiber flange (5), and the hollow photonic crystal fiber (7) is connected to a solid fiber (8) via a second fiber flange (6); a dual-channel power meter (4), connected to the attenuator (3) and the solid fiber (8); a vacuum chamber (9), in which the head end and / or tail end of the hollow photonic crystal fiber (7) are placed; a high-temperature furnace (10), in which the hollow photonic crystal fiber (7) is placed; and an air-floating active vibration isolation platform (11), on which the high-temperature furnace (10) is placed to counteract the influence of external vibrations during annealing and polishing. This application utilizes the surface tension during annealing to suppress surface roughness, achieving universality in suppressing the roughness of the inner wall of the optical fiber.

Description

Technical Field

[0001] This application relates to the field of optical fiber application technology, and in particular to a device and method for suppressing the roughness of the inner wall of a hollow photonic crystal fiber core. Background Technology

[0002] Hollow-core photonic crystal fibers possess unparalleled advantages over traditional optical fibers due to their unique structure, transmission medium, and light guiding mechanism. For example, because light waves propagate within an air core, they theoretically exhibit lower transmission loss, superior environmental adaptability, lower nonlinearity, and higher transmission bandwidth. Furthermore, the large core size, high damage threshold, and quasi-single-mode transmission characteristics of hollow-core fibers enable high-beam-quality, high-energy fiber laser transmission, making them an ideal choice for future fiber laser transmission and fiber optic sensing.

[0003] Since the successful first drawing of hollow-core photonic crystal fiber (HCV) in 1999, over two decades of development have reduced its loss from approximately ~1 dB / m to 6.5 dB / km. Some international companies offer mature commercial HCV products, such as the HC-1550-02 HCV, with a loss of ~20 dB / km. Overall, however, the loss of HCV remains significantly higher than that of traditional optical fibers (~0.15 dB / km), severely limiting its application in high-energy laser transmission and fiber optic sensing. The main sources of loss in HCV are confinement loss and scattering loss. Confinement loss can be suppressed by designing multi-cladding structures. Scattering loss is related to the surface roughness of the fiber core; the immaturity of the HCV drawing process leads to a larger surface roughness, resulting in greater scattering loss. Currently, scattering loss is generally considered the primary source of loss in HCV, and the surface roughness of the fiber core determines the limiting loss of the HCV. Meanwhile, during high-energy laser transmission, a large amount of scattered light will cause the fiber temperature to rise, which can easily damage the fiber waveguide structure and cause system failure. Furthermore, the backscattered light will interfere with the forward light, severely disrupting its phase and amplitude and damaging the stability of the laser output.

[0004] Currently, the most common method to reduce scattering loss in hollow-core photonic crystal fibers (HDFs) is through fiber design, such as increasing the duty cycle and enlarging the core. However, this method introduces more higher-order modes and surface modes. Annealing and polishing can significantly improve the roughness of quartz glass materials and is currently commonly used to process fiber preforms. Annealing and polishing involves heating quartz glass to its softening temperature, allowing microcracks, microdeformations, and minor defects on the surface to self-heal. Quartz glass is solid at room temperature, but becomes fluid when heated above its softening temperature, reducing its viscosity. At this point, under the influence of surface tension, the minor deformations and defects on the surface can be smoothed out, thereby reducing surface roughness. However, fluctuations in drawing parameters during the preform drawing process into HDFs, such as air pressure fluctuations and vibrations, can still lead to roughness on the inner wall of the core. Therefore, the drawn HDFs need to undergo annealing and polishing again. Due to the small size of optical fibers and their susceptibility to environmental influences, traditional annealing and polishing methods are not applicable, and there is currently a lack of annealing and polishing methods and devices specifically for HDFs. Summary of the Invention

[0005] This application provides a device and method for suppressing the roughness of the inner wall of a hollow photonic crystal fiber. It utilizes the surface tension during annealing to suppress surface roughness and is applicable to all types of hollow optical fibers, achieving universality in suppressing the roughness of the inner wall of the fiber.

[0006] This application provides a device for suppressing the roughness of the inner wall of a hollow photonic crystal fiber core, comprising:

[0007] Light source 1 emits light that is split into two paths by coupler 2. One path passes through attenuator 3 and reaches dual-channel power meter 4.

[0008] Another path is connected to the hollow-core photonic crystal fiber 7 through the first fiber flange 5, and the hollow-core photonic crystal fiber 7 is connected to the solid fiber 8 through the second fiber flange 6.

[0009] A dual-channel power meter 4 is connected to the attenuator 3 and the solid fiber 8, wherein the path through the attenuator 3 is the reference path and the path through the solid fiber 8 is the measurement path.

[0010] Vacuum chamber 9, into which the head end and / or tail end of the hollow-core photonic crystal fiber 7 is placed, is used to evacuate the air core and air cladding within the hollow-core photonic crystal fiber 7.

[0011] A high-temperature furnace 10 is used to anneal and polish the hollow photonic crystal fiber 7.

[0012] An air-float active vibration isolation platform 11 is placed on which the high-temperature furnace 10 is placed to counteract the influence of external vibrations during the annealing and polishing process.

[0013] This application also proposes a method for suppressing the roughness of the inner wall of a hollow-core photonic crystal fiber, including:

[0014] The hollow photonic crystal fiber 7 to be annealed and polished is placed in the high-temperature furnace 10, and both ends are led out from the high-temperature furnace 10 so that the fiber end face is placed in the vacuum chamber 9.

[0015] The two end faces of the hollow-core photonic crystal fiber 7 are connected to the pigtail and solid-core fiber 8 of the coupler 2 respectively through the first fiber flange 5 and the second fiber flange 6, and the vacuum chamber 9 is evacuated.

[0016] With the air pressure in the vacuum chamber 9 kept stable, the attenuator 3 is adjusted so that the difference between the two optical power readings displayed by the dual-channel power meter 4 via the attenuator 3 and the solid fiber 8 is maximized to be close to zero.

[0017] Turn on the air flotation active vibration isolation platform 11, and then turn on the high temperature furnace 10 to gradually increase the temperature from room temperature until the difference between the optical power readings of the reference path and the measurement path on the dual-channel power meter 4 reaches its maximum value.

[0018] Cool the high-temperature furnace 10 to room temperature, shut down the air-float active vibration isolation platform 11, restore the vacuum chamber 9 to normal pressure, remove the hollow-core photonic crystal fiber 7, and complete the annealing and polishing.

[0019] This application utilizes the surface tension during annealing to suppress surface roughness, applicable to all types of hollow optical fibers, achieving universality in suppressing the roughness of the inner wall of the optical fiber.

[0020] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0021] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0022] Figure 1 This is the end face structure of a hollow-core photonic crystal fiber according to an embodiment of this application;

[0023] Figure 2 This is a schematic diagram of the inner wall roughness of the hollow-core photonic crystal fiber in an embodiment of this application.

[0024] Figure 3This is a schematic diagram of a device for suppressing the roughness of the inner wall of a hollow photonic crystal fiber according to an embodiment of this application.

[0025] Figure 4 This is a flowchart of a method for suppressing the roughness of the inner wall of a hollow photonic crystal fiber according to an embodiment of this application. Detailed Implementation

[0026] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0027] Hollow-core photonic crystal fiber end-face structure, such as Figure 1 As shown, hollow-core photonic crystal fiber is composed of It consists of a cladding formed by regular arrangement of air and an air core. Figure 2 This is a schematic diagram of the cross-section of the air-core fiber along the optical fiber axis. Due to factors such as air pressure fluctuations and vibrations during the fiber drawing process, the inner wall of the fiber core becomes rough and uneven. When the output light comes into contact with the rough inner wall, it generates strong scattered secondary waves, which in turn cause scattering loss. Scattered light can also cause the fiber temperature to rise, damaging the fiber waveguide structure and causing system failure. In addition, backscattered light can interfere with the forward light, disrupting the stability of the laser output.

[0028] This application provides a device for suppressing the roughness of the inner wall of a hollow photonic crystal fiber core, used for suppressing the roughness of the inner wall of the fiber core, such as... Figure 3 As shown, the suppression device includes:

[0029] Light source 1 emits light that is split into two paths by coupler 2. One path passes through attenuator 3 and reaches dual-channel power meter 4.

[0030] Another path is connected to the hollow-core photonic crystal fiber 7 through the first fiber flange 5, and the hollow-core photonic crystal fiber 7 is connected to the solid fiber 8 through the second fiber flange 6.

[0031] A dual-channel power meter 4 is connected to the attenuator 3 and the solid fiber 8, wherein the path through the attenuator 3 is the reference path and the path through the solid fiber 8 is the measurement path.

[0032] Vacuum chamber 9, into which the head end and / or tail end of the hollow-core photonic crystal fiber 7 is placed, is used to evacuate the air core and air cladding within the hollow-core photonic crystal fiber 7.

[0033] A high-temperature furnace 10 is used to anneal and polish the hollow photonic crystal fiber 7.

[0034] An air-float active vibration isolation platform 11 is used to counteract the effects of external vibrations during the annealing and polishing process, upon which the high-temperature furnace 10 is placed. Another cause of roughness in the fiber core inner wall is vibration during the fiber drawing process, which includes high-frequency (>10Hz) and low-frequency (0.5Hz~10Hz) vibrations. Traditional air-float platforms can passively isolate high-frequency vibrations but cannot isolate low-frequency vibrations. This embodiment employs an air-float active vibration isolation platform 11, which can both passively and actively isolate high-frequency vibrations.

[0035] The light emitted by light source 1 is split into two paths by coupler 2. One path passes through attenuator 3 to reach dual-channel power meter 4, and the other path is connected to hollow-core photonic crystal fiber 7 through fiber optic flange A5, then connected to traditional solid-core fiber 8 through fiber optic flange B6, and finally reaches dual-channel power meter 4. Vacuum chamber 9 is used to evacuate the air core and air cladding inside hollow-core photonic crystal fiber 7. High-temperature furnace 10 is used to anneal and polish hollow-core photonic crystal fiber 7. Air-floating active vibration isolation platform 11 can avoid the influence of external vibrations during annealing and polishing.

[0036] One of the main causes of roughness on the inner wall of fiber core is pressure fluctuation during fiber drawing. Vacuuming is a measure taken to avoid pressure fluctuations during annealing. Hollow-core photonic crystal fibers (7) in a vacuum state experience extremely weak pressure fluctuations during annealing, which plays a very positive role in maintaining the smoothness of the fiber's inner wall. Existing mechanical pumps can achieve a vacuum level of ~5× Pa, in the embodiments of this application, the combination of mechanical pump and molecular pump can achieve... - Both Pa and Pa have some effect, and the lower the vacuum level, the better the effect.

[0037] In some embodiments of this application, the splitting ratio of the coupler 2 is such that the splitting ratio of the reference path is greater than that of the measurement path, and the initial power between the two is kept consistent by adjusting the attenuator 3. In a specific example, the coupler 2 uses a splitting ratio such as 60:40 or 70:30, and the initial power between the two is kept substantially consistent by adjusting the attenuator 3.

[0038] In some embodiments of this application, the high-temperature furnace 10 is set to operate within a temperature range of 25℃-1000℃. Since the optimal annealing temperature varies for different types or batches of hollow-core photonic crystal fibers 7, annealing tests should be conducted on fibers of the same type and batch before mass annealing and polishing. The high-temperature furnace 10 should be set with a large temperature variation range, such as 25℃-1000℃. The temperature corresponding to the maximum difference between the two optical power readings displayed by the dual-channel power meter 4 is the optimal annealing temperature for that type and batch of hollow-core photonic crystal fiber 7. Mass annealing and polishing will then be performed at this temperature.

[0039] This application also proposes a roughness suppression method for a hollow-core photonic crystal fiber core inner wall roughness suppression device, such as... Figure 4 The process includes the following steps:

[0040] The hollow-core photonic crystal fiber 7 to be annealed and polished is placed in a high-temperature furnace 10, with both ends extended from the furnace 10 so that the fiber end faces are placed in a vacuum chamber 9. In some embodiments of this application, the coating layer of the hollow-core photonic crystal fiber 7 is removed before placing it in the high-temperature furnace 10. Since the coating layer will burn first during the heating process, and the burning process may damage the structure of the hollow-core photonic crystal fiber 7, this application removes the coating layer of the hollow-core photonic crystal fiber 7 before placing it in the high-temperature furnace 10. The hollow-core photonic crystal fiber 7 extends a certain length from the high-temperature furnace 10 to facilitate the placement of the fiber end faces in the vacuum chamber 9.

[0041] The two end faces of the hollow-core photonic crystal fiber 7 are connected to the pigtail of the coupler 2 and the solid-core fiber 8 via the first fiber flange 5 and the second fiber flange 6, respectively, to evacuate the vacuum chamber 9. In this specific example, the coupler pigtail and the solid-core fiber 8 are both traditional solid-core fibers. The hollow-core photonic crystal fiber 7 and the solid-core fiber are connected by fiber flanges rather than by fusion splicing, intentionally maintaining an air gap between the two fibers so that gas can be extracted from the air gap during the evacuation process.

[0042] With the air pressure in vacuum chamber 9 maintained at a stable value, attenuator 3 is adjusted to maximize the difference between the two optical power readings displayed on the dual-channel power meter 4, which are transmitted through attenuator 3 and the solid fiber 8, to near zero. Annealing and polishing reduces the roughness of the fiber core inner wall, decreasing scattering loss and increasing output power. However, the output power of light source 1 also drifts over time. To avoid the combined effect of these two phenomena on the judgment of the annealing and polishing effect, a reference optical path is directly split from the light source using coupler 2. The output power of the measurement path is subtracted from that of the reference path, and attenuator 3 is adjusted to bring the difference as close to zero as possible. This allows for a more intuitive judgment of the annealing and polishing effect when the power of the measurement path increases. Coupler 2 should be selected so that the splitting ratio of the reference path is greater than that of the measurement path, for example, a coupler with a splitting ratio of 60:40 or 70:30.

[0043] Turn on the air-bearing active vibration isolation platform 11, then turn on the high-temperature furnace 10 to gradually increase the temperature from room temperature until the difference between the optical power readings of the reference path and the measurement path on the dual-channel power meter 4 reaches its maximum value. Another reason for the roughness of the fiber core inner wall is the vibration during the fiber drawing process, which includes high-frequency (>10Hz) and low-frequency vibrations (0.5Hz~10Hz). Traditional air-bearing platforms can passively isolate high-frequency vibrations but cannot isolate low-frequency vibrations. This application uses the air-bearing active vibration isolation platform 11, which can both passively isolate high-frequency vibrations and actively isolate low-frequency vibrations. The high-temperature furnace 10 should be set with a large temperature range, such as 25℃-1000℃. The temperature corresponding to the maximum difference between the two optical power readings on the dual-channel power meter 4 is the optimal annealing temperature for this type and batch of hollow-core photonic crystal fiber 7. At this time, mass annealing and polishing will be carried out according to this temperature.

[0044] Cool the high-temperature furnace 10 to room temperature, shut down the air-float active vibration isolation platform 11, restore the vacuum chamber 9 to normal pressure, remove the hollow-core photonic crystal fiber 7, and complete the annealing and polishing.

[0045] In some embodiments of this application, the method further includes: first cooling the annealed and polished hollow-core photonic crystal fiber 7 to room temperature, then shutting down the air-bearing active vibration isolation platform 11, and restoring the vacuum chamber 9 to normal pressure. This avoids vibration and air pressure disturbance at high temperatures from affecting the roughness of the fiber core inner wall again.

[0046] In some embodiments of this application, after the hollow-core photonic crystal fiber 7 is removed, the process further includes: recoating the portion of the hollow-core photonic crystal fiber 7 that has been stripped of its coating layer, thereby completing the final annealing and polishing.

[0047] This application utilizes the surface tension during annealing to suppress surface roughness, achieving better roughness suppression compared to traditional polishing methods. The device described in this application is simple and easy to assemble, facilitating engineering applications. Furthermore, the suppression method and device proposed in this application are applicable to all types of hollow optical fibers, increasing the universality of this application.

[0048] It should be noted that, in the embodiments of this application, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0049] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0050] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims. All of these forms are within the protection scope of this application.

Claims

1. A device for suppressing the roughness of the inner wall of a hollow photonic crystal fiber core, characterized in that, include: The light source (1) emits light that is split into two paths by a coupler (2). One path passes through an attenuator (3) and reaches a dual-channel power meter (4). The splitting ratio of the coupler (2) makes the splitting ratio of the reference path greater than that of the measurement path. Another path is connected to the hollow-core photonic crystal fiber (7) through the first fiber flange (5), and the hollow-core photonic crystal fiber (7) is connected to the solid fiber (8) through the second fiber flange (6); A dual-channel power meter (4) is connected to the attenuator (3) and the solid fiber (8), wherein the path through the attenuator (3) is the reference path and the path through the solid fiber (8) is the measurement path. A vacuum chamber (9) is provided in which the head end and / or tail end of the hollow-core photonic crystal fiber (7) are placed to evacuate the air core and air cladding of the hollow-core photonic crystal fiber (7). Under the condition that the air pressure value in the vacuum chamber (9) is kept stable, the difference between the two optical power values ​​displayed by the dual-channel power meter (4) via the attenuator (3) and the solid-core fiber (8) is maximized to be close to zero by adjusting the attenuator (3). A high-temperature furnace (10) is used to anneal and polish the hollow photonic crystal fiber (7). An air-float active vibration isolation platform (11) is placed on which the high-temperature furnace (10) is placed to counteract the influence of external vibrations during the annealing and polishing process. The air-float active vibration isolation platform (11) is turned on, and then the high-temperature furnace (10) is turned on to gradually increase the temperature from room temperature. The temperature corresponding to the maximum difference between the two optical power readings displayed by the dual-channel power meter (4) is the optimal annealing temperature for hollow core photonic crystal fibers (7) of the same type and batch.

2. The device for suppressing the roughness of the inner wall of a hollow photonic crystal fiber as described in claim 1, characterized in that, The vacuum chamber (9) is constructed using a combination of mechanical pumps and molecular pumps.

3. The device for suppressing the roughness of the inner wall of the hollow photonic crystal fiber as described in claim 1, characterized in that, The operating temperature range of the high-temperature furnace (10) is 25℃-1000℃.

4. A roughness suppression method based on the roughness suppression device for the inner wall of the hollow photonic crystal fiber core as described in any one of claims 1-3, characterized in that, include: The hollow-core photonic crystal fiber (7) to be annealed and polished is placed in a high-temperature furnace (10), and both ends are led out from the high-temperature furnace (10) so that the fiber end face is placed in a vacuum chamber (9). The two end faces of the hollow-core photonic crystal fiber (7) are connected to the pigtail and solid-core fiber (8) of the coupler (2) respectively through the first fiber flange (5) and the second fiber flange (6), and the vacuum chamber (9) is evacuated. While maintaining a stable air pressure in the vacuum chamber (9), the attenuator (3) is adjusted so that the difference between the two optical power readings displayed by the dual-channel power meter (4) via the attenuator (3) and the solid optical fiber (8) is maximized to be close to zero. Turn on the air-float active vibration isolation platform (11), and then turn on the high-temperature furnace (10) to gradually increase the temperature from room temperature until the difference between the optical power readings of the reference path and the measurement path on the dual-channel power meter (4) reaches the maximum value. The corresponding temperature is the optimal annealing temperature for hollow core photonic crystal fiber (7) of the same type and batch. Cool the high-temperature furnace (10) to room temperature, shut down the air-float active vibration isolation platform (11), restore the vacuum chamber (9) to normal pressure, take out the hollow core photonic crystal fiber (7), and complete the annealing and polishing.

5. The roughness suppression method as described in claim 4, characterized in that, Before placing the hollow photonic crystal fiber (7) to be annealed and polished in a high-temperature furnace (10), the coating layer of the hollow photonic crystal fiber (7) is removed.

6. The roughness suppression method as described in claim 4, characterized in that, Also includes: First, the annealed and polished hollow photonic crystal fiber (7) is cooled to room temperature, then the air-floating active vibration isolation platform (11) is turned off, and the vacuum chamber (9) is restored to normal pressure.

7. The roughness suppression method as described in claim 6, characterized in that, After removing the hollow-core photonic crystal fiber (7), the following is also included: The portion of the hollow photonic crystal fiber (7) that has had its coating removed is then recoated.

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