A method for testing the attenuation of hollow optical fiber using mode filtering technology

Abstract

This invention discloses a method for testing the attenuation of hollow-core optical fiber using mode filtering technology, relating to the field of hollow-core optical fiber attenuation testing technology. The method includes: using a single-mode pigtail fused to a hollow-core optical fiber as the test pigtail, or using a single-mode pigtail fused to a mode-matching fiber or mode adapter as the test pigtail; at the coupling point between the test pigtail and the hollow-core optical fiber under test, using a coupler with fiber axial rotation function to modulate the output mode field of the light source pigtail to match the mode field of the light source pigtail and the hollow-core optical fiber under test; when using the truncation method for attenuation testing, after measuring the optical power at the output end of the hollow-core optical fiber under test, the fiber is cut back, and the optical power of the hollow-core optical fiber under test is measured again at the cut-back position; the difference between the two measured optical power values ​​is the loss of the hollow-core optical fiber under test. This invention can reduce the excitation of higher-order modes in the hollow-core optical fiber under test, thereby achieving mode filtering and reducing the impact of higher-order modes on the attenuation of the test fiber.

Description

Technical Field

[0001] This invention relates to the field of hollow fiber attenuation testing technology, and specifically to a method for testing hollow fiber attenuation using mode filtering technology. Background Technology

[0002] Hollow-core antiresonant fiber has become one of the most prominent research topics in fiber optics in recent years. Unlike traditional silica fiber with single-mode cutoff characteristics, the fundamental mode and higher-order modes of hollow-core antiresonant fiber can satisfy the antiresonance condition of the glass wall, thus it is essentially a "multimode fiber". To achieve single-mode optical transmission in hollow-core antiresonant fiber, the ratio of cladding tube diameter to core diameter can be designed to enhance the first higher-order mode (LP). 11 Matching and coupling with the cladding pattern improves LP. 11 The loss of modes is reduced, thus enabling quasi-single-mode transmission in the optical fiber. However, when testing the attenuation of this optical fiber, whether using the cut-off method or the backscattering method, the coupling of the fiber will inevitably excite a small number of higher-order modes in the hollow fiber. This poses a challenge to the accuracy and repeatability of the fiber attenuation test. Therefore, some methods are needed to reduce the excitation of higher-order modes and filter out higher-order modes, so as to obtain a more accurate single-mode transmission attenuation of the optical fiber.

[0003] Due to its unique light-guiding mechanism, the looping method and refractive index matching liquid method used in conventional fiber optic mode filtering are not applicable to hollow-core optical fibers. When testing the attenuation of hollow-core optical fibers using the truncation method, the existing solution generally involves directly coupling the hollow-core fiber with a single-mode pigtail and filtering modes by increasing the back-cut fiber length. The back-cut length is typically greater than 20m, thus filtering out the influence of higher-order modes on the attenuation test results. This method is time-consuming and more difficult to operate when testing hollow-core optical cables. Summary of the Invention

[0004] This invention provides a method for modulating the output mode field of a light source pigtail, thereby achieving mode field matching between the light source pigtail and the hollow fiber under test, reducing the excitation of higher-order modes in the hollow fiber under test, thus achieving mode filtering, reducing the impact of higher-order modes on the attenuation of the test fiber, improving the efficiency of hollow fiber attenuation testing, and ensuring the accuracy and repeatability of the test.

[0005] This invention provides a method for testing the attenuation of hollow optical fiber using mode filtering technology, comprising:

[0006] The light source pigtail is a single-mode pigtail fused with hollow fiber as the test pigtail, or the light source pigtail is a single-mode pigtail fused with a mode adapter fiber or mode adapter device as the test pigtail.

[0007] At the coupling point between the test pigtail and the hollow fiber under test, a coupler with fiber axial rotation function is used to modulate the output mode field of the light source pigtail so that the mode fields of the light source pigtail and the hollow fiber under test are matched.

[0008] When using the cut-off method for attenuation testing, after measuring the optical power at the output end of the hollow fiber under test, the fiber is cut back, and the optical power of the hollow fiber under test is measured again at the cut-back position. The difference between the two measured optical powers is the loss of the fiber under test.

[0009] In some instances, the light source pigtail uses a first hollow fiber with a single-mode pigtail spliced ​​to ≥20m as the test pigtail. The first hollow fiber and the hollow fiber under test have the same mode field diameter (MFD) and numerical aperture (NA).

[0010] In some instances, a hollow fiber fusion splicer is used to align the inner cladding ring structure and the cladding XY alignment of the first hollow fiber, so that the test pigtail matches the mode field of the hollow fiber under test.

[0011] In some instances, the light source pigtail uses a second hollow fiber with a single-mode pigtail spliced ​​to ≥2m as the test pigtail. The area of ​​the air pores in the inner cladding of the second hollow fiber divided by the area of ​​the air core is greater than or equal to 0.3. The second hollow fiber and the hollow fiber under test have the same mode field diameter (MFD) and numerical aperture (NA).

[0012] In some instances, the area of ​​the air pores in the inner cladding of the second hollow fiber divided by the area of ​​the air core is greater than or equal to 0.5.

[0013] In some instances, a hollow fiber fusion splicer is used to align the inner cladding ring structure and the cladding XY alignment of the second hollow fiber, so that the test pigtail matches the mode field of the hollow fiber under test.

[0014] In some instances, when the light source pigtail is a single-mode pigtail spliced ​​with a mode-matching fiber or mode adapter device and used as a test pigtail, the beam incident on the hollow fiber under test is matched with the MFD and NA of the hollow fiber under test by adjusting the XYZ axial distance between the light source pigtail and the hollow fiber under test.

[0015] In some instances, the process of matching the incident beam on the hollow fiber under test with the MFD and NA of the hollow fiber under test by adjusting the XYZ axial distance between the light source pigtail and the hollow fiber under test includes:

[0016] At the fiber coupling point, adjust the coupler and manually adjust the XYZ axial distance between the test pigtail and the hollow fiber under test, while observing the output optical power of the hollow fiber under test. When the output optical power reaches its maximum value, the MFD and NA matching of the incident beam on the hollow fiber under test and the mode field of the fiber under test are achieved.

[0017] In some instances, the back-cut fiber length is ≥1m.

[0018] In some instances, when using an OTDR to test the attenuation of hollow fiber, the light source is replaced with a single-mode OTDR, the test pigtail is selected, and the coupling between the test pigtail and the hollow fiber under test is adjusted to perform the hollow fiber attenuation test.

[0019] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0020] 1. A method for modulating the output mode field of a light source pigtail is adopted to achieve mode field matching between the light source pigtail and the hollow fiber under test, thereby reducing the excitation of higher-order modes in the hollow fiber under test, thus achieving mode filtering and reducing the impact of higher-order modes on the attenuation of the test fiber.

[0021] 2. The light source pigtail uses a general hollow fiber with a single-mode pigtail spliced ​​for ≥20m as the test pigtail, and a specially designed hollow fiber with a spliced ​​for ≥2m as the test pigtail. The light source beam is filtered out of higher-order modes in the test pigtail before being incident on the hollow fiber under test, reducing the influence of higher-order modes on the attenuation test.

[0022] 3. The light source pigtail is made of single-mode fiber fused with a mode-matching fiber / device to ensure collimation of the output beam. A small-step adjustment fiber coupler is used, and the XYZ axial distance between the test pigtail and the hollow fiber under test is manually adjusted to achieve MFD and NA matching between the incident beam and the mode field of the hollow fiber under test. This minimizes the excitation of higher-order modes in the hollow fiber under test, reducing their impact on attenuation testing. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of light source pigtail modulation provided in an embodiment of the present invention;

[0025] Figure 2 This is another schematic diagram of light source pigtail modulation provided in an embodiment of the present invention;

[0026] Figure 3 This is another schematic diagram of light source fiber modulation provided in an embodiment of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In the following description, specific embodiments of the invention will be illustrated with reference to steps and symbols performed by one or more computers, unless otherwise stated. Therefore, these steps and operations will be referred to several times as being performed by a computer, and computer execution as referred to herein includes operations by a computer processing unit representing electronic signals of data in a structured format. This operation transforms the data or maintains it at a location in the computer's memory system, which can be reconfigured or otherwise alter the operation of the computer in a manner well known to those skilled in the art. The data structure maintained by the data is the physical location of the memory, which has specific characteristics defined by the data format. However, the principles of the invention described above are not intended to be limiting, and those skilled in the art will understand that many of the following steps and operations can also be implemented in hardware.

[0029] The terms "module" or "unit" as used herein can be considered as software objects executing on the computing system. Different components, modules, engines, and services described herein can be considered as implementations on the computing system. The apparatus and methods described herein are preferably implemented in software, but can also be implemented in hardware, both of which are within the scope of this invention.

[0030] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements. Furthermore, “connected” or “coupled” as used herein can include wireless connections or wireless coupling. The term “and / or” as used herein includes all or any units and all combinations of one or more associated listed items.

[0031] In this embodiment of the invention, the test method uses two types of light source pigtails. One type is a single-mode fiber fusion spliced ​​with a hollow-core fiber. The length of this hollow-core fiber is preferably ≥20m, and its structure is consistent with that of the hollow-core fiber under test. Its mode field diameter (MFD) and numerical aperture (NA) are also consistent with those of the hollow-core fiber under test. Furthermore, this hollow-core fiber can be a structurally designed hollow-core fiber. The ratio of the air pore area to the air core area of ​​the inner cladding of this hollow-core pigtail is greater than or equal to 0.3, preferably greater than or equal to 0.5. It has excellent single-mode characteristics, and its MFD and NA are consistent with those of the hollow-core fiber under test. The length of this hollow-core pigtail is ≥2m. Another type of light source pigtail uses single-mode fiber fusion splicing transition fiber technology to fusion splice single-mode fiber with mode-matching fiber / device to form a mode field adapter (MFA). By adjusting the XYZ axial distance between the pigtail and the hollow fiber under test, the beam incident on the hollow fiber under test can be matched with the MFD and NA of the hollow fiber under test.

[0032] In another embodiment of the invention, such as Figure 1 As shown, a hollow-core fiber fusion spliced ​​with a single-mode pigtail of ≥20m is used as the test pigtail. This hollow-core pigtail has the same MFD and NA as the hollow-core fiber under test. The beam is output after undergoing a certain amount of higher-order mode filtering in the test pigtail. At the coupling point between the test pigtail and the fiber under test, a coupler with fiber axial rotation function is used. Preferably, a hollow-core fiber fusion splicer is used to align the inner cladding ring structure and cladding XY alignment of the hollow-core fiber, ensuring mode field matching between the pigtail and the hollow-core fiber under test, and minimizing the excitation of higher-order modes. During the attenuation test using the truncation method, after measuring the optical power at the output end of the fiber under test, the fiber is cut back by ≥1m, and the optical power is measured again at the cut-back position. The difference between the two measured optical power values ​​is the loss of the fiber under test.

[0033] In another embodiment of the invention, such as Figure 2 As shown, a quasi-single-mode hollow fiber fusion spliced ​​with a single-mode pigtail of ≥2m is used as the test pigtail. The porosity of the inner cladding of this hollow pigtail divided by the air core area is greater than or equal to 0.3, and further greater than or equal to 0.5, exhibiting excellent single-mode characteristics. Furthermore, this hollow pigtail and the hollow fiber under test have consistent MFD and NA. The beam is output after undergoing a certain amount of higher-order mode filtering in this test pigtail. At the coupling point between the test pigtail and the fiber under test, a coupler with fiber axial rotation function is used. Preferably, a hollow fiber fusion splicer is used to align the inner cladding ring structure and cladding XY alignment of the hollow fiber, ensuring mode field matching between the pigtail and the hollow fiber under test, minimizing the excitation of higher-order modes. During the attenuation test using the truncation method, after measuring the optical power at the output end of the fiber under test, the fiber is cut back by ≥1m, and the optical power is measured again at the cut-back position. The difference between the two measured optical power values ​​is the loss of the fiber under test.

[0034] Among them, the pore area refers to the pore area of ​​a single nested capillary in the inner cladding, and the air core area refers to the cross-sectional area of ​​the near-polygonal core surrounded by multiple nested capillary tubes.

[0035] In another embodiment of the invention, such as Figure 3 As shown, a single-mode fiber is fused with a mode-matching fiber or mode adapter to form a test pigtail. The outgoing light MFD after passing through the mode-matching fiber is close to that of the hollow fiber under test. At the fiber coupling point, a small-step adjustment (e.g., 5μm step, or other step parameters, not limited to a single step in this embodiment) is used to adjust the XYZ axial distance between the test pigtail and the hollow fiber under test. Simultaneously, the output optical power of the hollow fiber under test is observed. When the output optical power reaches its maximum value, the MFD and NA of the incident beam on the hollow fiber under test are matched with those of the fiber under test, and a very small number of higher-order modes are excited in the hollow fiber under test. During the truncation attenuation test, after measuring the optical power at the output end of the fiber under test, the fiber is cut back by ≥1m, and the optical power is measured again at the cut-back position. The difference between the two measured optical powers is the loss of the fiber under test.

[0036] In another embodiment of the present invention, when using an OTDR to test the attenuation of hollow fiber, the light source is replaced with a single-mode OTDR. The use of the pigtail and the coupling method can be referred to in Embodiment 1, Embodiment 2 or Embodiment 3. Simply select the pigtail and adjust the coupling between the pigtail and the fiber under test according to the above embodiments, and click on the device to test and obtain the results.

[0037] The above provides a detailed description of a method for testing the attenuation of hollow optical fiber using filter technology, as provided in the embodiments of the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for testing the attenuation of hollow optical fiber using mode filtering technology, characterized in that, include: The light source pigtail is a single-mode pigtail fused with hollow fiber as the test pigtail, or the light source pigtail is a single-mode pigtail fused with a mode adapter fiber or mode adapter device as the test pigtail. At the coupling point between the test pigtail and the hollow fiber under test, a coupler with fiber axial rotation function is used to modulate the output mode field of the light source pigtail so that the mode fields of the light source pigtail and the hollow fiber under test are matched. When using the cut-off method for attenuation testing, after measuring the optical power at the output end of the hollow fiber under test, the fiber is cut back, and the optical power of the hollow fiber under test is measured again at the cut-back position. The difference between the two measured optical powers is the loss of the fiber under test.

2. The method according to claim 1, characterized in that, The light source pigtail uses a first hollow fiber with a single-mode pigtail spliced ​​to ≥20m as the test pigtail. The first hollow fiber and the hollow fiber under test have the same mode field diameter (MFD) and numerical aperture (NA).

3. The method according to claim 2, characterized in that, A hollow fiber fusion splicer was used to align the inner cladding ring structure and the cladding XY alignment of the first hollow fiber, so that the test pigtail and the hollow fiber under test were matched in mode field.

4. The method according to claim 1, characterized in that, The light source pigtail uses a second hollow fiber with a single-mode pigtail spliced ​​to ≥2m as the test pigtail. The area of ​​the air pores in the inner cladding of the second hollow fiber divided by the area of ​​the air core is greater than or equal to 0.

3. The second hollow fiber and the hollow fiber under test have the same mode field diameter (MFD) and numerical aperture (NA).

5. The method according to claim 4, characterized in that, The area of ​​the air pores in the inner cladding of the second hollow fiber divided by the area of ​​the air core is greater than or equal to 0.

5.

6. The method according to claim 5, characterized in that, A hollow fiber fusion splicer was used to align the inner cladding ring structure and the cladding XY alignment of the second hollow fiber, so that the test pigtail and the hollow fiber under test were matched in mode field.

7. The method according to claim 1, characterized in that, When the light source pigtail is a single-mode pigtail spliced ​​with a mode-matching fiber or mode adapter as a test pigtail, the beam incident on the hollow fiber under test is matched with the MFD and NA of the hollow fiber under test by adjusting the XYZ axial distance between the light source pigtail and the hollow fiber under test.

8. The method according to claim 7, characterized in that, The method of matching the incident light beam on the hollow fiber under test with the MFD and NA of the hollow fiber under test by adjusting the XYZ axial distance between the light source pigtail and the hollow fiber under test includes: At the fiber coupling point, adjust the coupler and manually adjust the XYZ axial distance between the test pigtail and the hollow fiber under test, while observing the output optical power of the hollow fiber under test. When the output optical power reaches its maximum value, the MFD and NA matching of the incident beam on the hollow fiber under test and the mode field of the fiber under test are achieved.

9. The method according to claim 1, characterized in that, The length of the back-cut fiber is ≥1m.

10. The method according to any one of claims 1 to 9, characterized in that, When testing the attenuation of hollow fiber using an OTDR, replace the light source with a single-mode OTDR, select the test pigtail and adjust the coupling between the test pigtail and the hollow fiber under test to perform the hollow fiber attenuation test.

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