Anti-resonant hollow core fiber size parameter measurement system and measurement method

Abstract

The disclosure describes a kind of anti-resonant hollow fiber size parameter measurement system and measurement method, the measurement system includes sequentially connected incident light source, light source processing module, fiber to be measured, data acquisition module and data processing module, data processing module is filtered to the spectrum formed by the coherent superposition of multiple scattering light beams, Fourier transform group delay spectrum is obtained, and peak retrieval is carried out to the group delay spectrum, and the group delay difference caused by the coherent superposition of each light beam in group delay spectrum is obtained, and the size parameters of anti-resonant hollow fiber are obtained based on the multi-beam interference geometric optics model and the group delay difference between each light beam. Thus, the simultaneous on-line measurement of multiple parameters of anti-resonant hollow fiber can be realized, and the drawing efficiency and output efficiency of anti-resonant hollow fiber can be further improved, and the fiber manufacturing cost is reduced.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of optical fiber, in particular to a measurement system and method for size parameters of a counter-resonant hollow-core fiber. BACKGROUND

[0002] With the continuous improvement of the performance of counter-resonant hollow-core fiber, its application field is rapidly expanding. In order to promote the industrialization development of counter-resonant hollow-core fiber, improve the production of counter-resonant hollow-core fiber, and reduce the cost, the counter-resonant hollow-core fiber needs to be drawn in a more intelligent way. During the drawing process of the counter-resonant hollow-core fiber, the microstructure size parameters of the fiber need to be monitored continuously, and then the drawing parameters of the fiber, including the temperature of the heating furnace, the air pressure, and the fiber feeding speed, are adjusted according to the monitored microstructure size parameters.

[0003] However, the existing commercial equipment can only monitor the single size parameter of the fiber outer diameter, which cannot meet the needs of the adjustment of the drawing parameters. Therefore, researchers and engineers have to manually cut off the fiber during the drawing process, and observe the cross section of the fiber through a microscope to obtain the required internal microstructure size parameters of the fiber. This method not only takes a long time and is low in efficiency, but also causes a huge waste of materials, which seriously limits the production of the fiber.

[0004] In the prior art, based on the microstructure characteristics of the counter-resonant hollow-core fiber, MICHAEL H. FROSZ proposed an online monitoring technology based on the spectrum of whispering gallery mode (WGM) (Document 1: M. H. Frosz, et al., "Non-invasive real-time characterization of hollow-core photonic crystal fibers using whispering gallery mode spectroscopy," Opt. Express, 2019. 27(21), 30842.). This technology can non-contactly and online monitor the internal microstructure size of the counter-resonant hollow-core fiber by combining the white light Fourier transform method and the WGM model. However, the WGM model can only calculate the single size parameter of the cladding tube diameter, which cannot meet the needs of the adjustment of the drawing parameters. SUMMARY

[0005] The present disclosure is proposed in view of the above-mentioned prior art, and aims to provide a measurement system and method for size parameters of a counter-resonant hollow-core fiber based on a geometric optics model, which can realize the online measurement of multiple parameters, further improve the drawing efficiency and output efficiency of the counter-resonant hollow-core fiber, and reduce the manufacturing cost of the fiber.

[0006] To this end, the first aspect of the present disclosure provides a size parameter measurement system of a counter-resonant hollow-core fiber based on a geometric optics model, comprising an incident light source, a light source processing module, a fiber to be measured, a data acquisition module, and a data processing module connected in sequence. The light beam emitted by the incident light source is irradiated to the fiber to be measured after being processed by the light source processing module, and forms a plurality of scattered light beams after passing through the fiber to be measured in different paths. Then, the plurality of scattered light beams are input to the data processing module after being collected by the data acquisition module. The data processing module obtains the group delay spectrum by filtering and Fourier transforming the spectrum formed by the coherent superposition of the plurality of scattered light beams, and obtains the group delay difference caused by the coherent superposition of each light beam by peak searching the group delay spectrum. The data processing module obtains a plurality of size parameters of the fiber to be measured based on a multi-beam interference geometric optics model and the group delay difference between each light beam.

[0007] In the first aspect of the present disclosure, the data processing module obtains the group delay difference caused by the coherent superposition of each light beam by filtering, Fourier transforming, and peak searching the spectrum formed by the coherent superposition of the plurality of scattered light beams collected from the fiber to be measured. The data processing module can obtain a plurality of size parameters of the counter-resonant hollow-core fiber based on a multi-beam interference geometric optics model and the group delay difference between each light beam. Thus, the simultaneous online measurement of multiple parameters of the counter-resonant hollow-core fiber can be realized, and the drawing efficiency and output efficiency of the counter-resonant hollow-core fiber can be further improved, and the cost of fiber manufacturing can be reduced.

[0008] In addition, in the size parameter measurement system of the counter-resonant hollow-core fiber according to the first aspect of the present disclosure, the light source processing module can comprise a collimation module and a polarization module connected with the collimation module.

[0009] In addition, in the size parameter measurement system of the counter-resonant hollow-core fiber according to the first aspect of the present disclosure, the collimation module can be an off-axis parabolic mirror or a single lens, and the polarization module can be a polarization controller.

[0010] In addition, in the size parameter measurement system of the counter-resonant hollow-core fiber according to the first aspect of the present disclosure, the data acquisition module can comprise a signal acquisition optical fiber and a spectrometer connected with the signal acquisition optical fiber.

[0011] In addition, in the size parameter measurement system of the counter-resonant hollow-core fiber according to the first aspect of the present disclosure, the fiber to be measured can comprise a hollow sleeve and a plurality of cladding tubes arranged in the hollow sleeve.

[0012] In addition, in the anti-resonant hollow core fiber size parameter measurement system of the first aspect of the present disclosure, optionally, the light beam emitted by the light source is processed by the light source processing module, and then irradiated to different positions of the fiber to be measured, and forms a plurality of scattered light beams after passing through the hollow sleeve and the cladding tube of the fiber to be measured in at least four different paths, and then input to the data processing module after being collected by the data collection module.

[0013] In addition, in the anti-resonant hollow core fiber size parameter measurement system of the first aspect of the present disclosure, optionally, the data processing module obtains three size parameters of the fiber to be measured based on a four-beam interference geometric optics model and the group delay difference, including the inner diameter r of the fiber to be measured, the outer diameter R of the fiber to be measured, and the diameter d of the cladding tube.

[0014] In addition, in the anti-resonant hollow core fiber size parameter measurement system of the first aspect of the present disclosure, optionally, the calculation formulas of the inner diameter r of the fiber to be measured, the outer diameter R of the fiber to be measured, and the diameter d of the cladding tube are as follows:

[0015]

[0016]

[0017] ΔD 14 = 2R[-cos(a4) + n silica sin(a4+a1) + cos(a1)] + l / 2,

[0018] ΔD 24 = -2R(cos(a4) - cos(a2)) + 2n silica [Rsin(a4+a1) - U],

[0019]

[0020] ΔD 23 = -R·[cos(a3) + cos(a'3) - 2cos(a2)] + n silica (U' + U" - 2U) + L tube ,

[0021] wherein τ jk is the group delay difference between the light beam j and the light beam k, ΔD jk is the optical path difference between the light beam j and the light beam k, j = 1, 2, 3, or 4, k = 1, 2, 3, or 4, n silica is the refractive index of the fiber to be measured, n eff is the effective refractive index of the third light beam propagating in the cladding tube, v is the optical frequency, a i(i = 1, 2, 3, 4) is the incident angle of the i-th light beam, a'3 is the exit angle of the third light beam, γ is the circumferential angle formed by the intersection of the cladding tube in the optical fiber to be measured and the inner wall of the hollow sleeve, θ is the included angle between the line connecting the center of the cladding tube and the center of the optical fiber to be measured and the normal line of the first light beam, and λ is the wavelength of the light wave.

[0022] In addition, in the anti-resonant hollow core fiber size parameter measurement system according to the first aspect of the present disclosure, the data processing module can optionally filter the scattered light through a window function filter.

[0023] In addition, in the anti-resonant hollow core fiber size parameter measurement system according to the first aspect of the present disclosure, the data processing module can be a computer.

[0024] The second aspect of the present disclosure provides an anti-resonant hollow core fiber size parameter measurement method based on a geometric optics model, including the following steps:

[0025] A preparation process is provided for sequentially connecting an incident light source, a light source processing module, an optical fiber to be measured, a data acquisition module, and a data processing module;

[0026] A light beam acquisition process is provided, in which the light beam emitted by the incident light source is processed by the light source processing module, irradiated to different positions of the optical fiber to be measured, and forms a plurality of scattered light beams after passing through the optical fiber to be measured in different paths, and then input to the data processing module after being collected by the data acquisition module;

[0027] A data processing process is provided, in which the data processing module filters and Fourier transforms the spectrum formed by the coherent superposition of a plurality of scattered light beams to obtain a group delay spectrum, and performs peak value retrieval on the group delay spectrum to obtain the group delay difference caused by the coherent superposition of each light beam in the group delay spectrum;

[0028] A calculation process is provided, in which the data processing module obtains a plurality of size parameters of the anti-resonant hollow core fiber based on a multi-beam interference geometric optics model and the group delay difference between each light beam.

[0029] In addition, in the anti-resonant hollow core fiber size parameter measurement system according to the second aspect of the present disclosure, the data processing module can optionally obtain three size parameters of the optical fiber to be measured based on a four-beam interference geometric optics model and the group delay, including the inner diameter r of the optical fiber, the outer diameter R of the optical fiber to be measured, and the diameter d of the cladding tube, and the calculation formulas of the inner diameter r of the optical fiber to be measured, the outer diameter R of the optical fiber to be measured, and the diameter d of the cladding tube are as follows:

[0030]

[0031]

[0032] ΔD 14 = 2R[-cos(a4) + n silica sin(a4 + a1) + cos(a1)] + λ / 2,

[0033] ΔD 24 = -2R(cos(a4) - cos(a2)) + 2n silica [Rsin(a4 + a1) - U],

[0034]

[0035] ΔD 23 = -R - [cos(a3) + cos(a'3) - 2cos(a2)] + n silica (U' + U" - 2U) + L tube ,

[0036] wherein τ jk is the group delay difference between beam j and beam k, ΔD jk is the optical path difference between beam j and beam k, j = 1, 2, 3, or 4, k = 1, 2, 3, or 4, n silica is the refractive index of the fiber under test, n eff is the effective refractive index of the third beam propagating in the cladding tube, v is the optical frequency, a i (i = 1, 2, 3, 4) is the incidence angle of the ith beam, a'3 is the exit angle of the third beam, g is the circumferential angle formed by the intersection of the cladding tube and the inner wall of the hollow jacket in the fiber under test, q is the included angle between the line connecting the center of the cladding tube and the center of the fiber under test and the normal line of the first beam, and l is the wavelength of the light wave.

[0037] In the second aspect of the present disclosure, the data processing module can obtain the group delay difference caused by the coherent superposition of each beam after sequentially performing filtering processing, Fourier transform, and peak retrieval on the multiple scattered beams collected from the fiber under test. The data processing module can obtain multiple size parameters of the anti-resonant hollow fiber based on the multi-beam interference geometric optics model and the group delay difference between the beams, thereby achieving simultaneous online measurement of multiple parameters of the anti-resonant hollow fiber, further improving the drawing efficiency and output efficiency of the anti-resonant hollow fiber, and reducing the fiber manufacturing cost.

[0038] According to the present disclosure, a geometric optics model-based anti-resonant hollow fiber size parameter measurement system and method for realizing simultaneous online measurement of multiple parameters, further improving the drawing efficiency and output efficiency of the anti-resonant hollow fiber, and reducing the fiber manufacturing cost can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0039] Embodiments of the present disclosure will now be explained in further detail by way of example only with reference to the drawings, in which:

[0040] Figure 1 is a functional module diagram showing an anti-resonant hollow core fiber size parameter measurement system involved in the embodiments of the present disclosure.

[0041] Figure 2 is a functional module diagram showing one example of a light source processing module involved in the embodiments of the present disclosure.

[0042] Figure 3 is a functional module diagram showing one example of a data acquisition module involved in the embodiments of the present disclosure.

[0043] Figure 4 is a structural diagram showing an anti-resonant hollow core fiber involved in the embodiments of the present disclosure.

[0044] Figure 5 is a flow chart showing one example of an anti-resonant hollow core fiber size parameter measurement method involved in the embodiments of the present disclosure.

[0045] Figure 6 is a flow chart showing another example of an anti-resonant hollow core fiber size parameter measurement method involved in the embodiments of the present disclosure.

[0046] Figure 7 is a propagation path diagram showing a plurality of light beams in an anti-resonant hollow core fiber involved in the embodiments of the present disclosure.

[0047] SYMBOL EXPLANATION

[0048] 1…incident light source, 2…light source processing module, 3…fiber to be measured, 4…data acquisition module, 5…data processing module, 21…collimation module, 22…polarization module, 31…hollow sleeve, 32…cladding tube, 41…signal acquisition light beam, 42…spectrometer. DETAILED DESCRIPTION

[0049] Hereinafter, preferred embodiments of the present disclosure will be explained in detail with reference to the drawings. In the following description, the same parts are assigned the same reference numerals, and repetitive explanation will be omitted. In addition, the drawings are only schematic, and the ratio of the sizes of the components to each other or the shape of the components, etc. can be different from the actual.

[0050] It should be noted that the terms "comprising" and "having" and any variations thereof, such as the processes, methods, systems, products or devices comprising or having a series of steps or units, are not necessarily limited to those clearly listed steps or units, but can include or have other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0051] Figure 1 is a functional module schematic diagram showing the anti-resonant hollow fiber size parameter measurement system involved in the embodiment of the present disclosure.

[0052] Referring to Figure 1 The anti-resonant hollow fiber size parameter measurement system based on the geometric optics model involved in the embodiment can include an incident light source 1, a light source processing module 2, a fiber to be measured 3, a data acquisition module 4, and a data processing module 5 connected in sequence. And the fiber to be measured 3 can be an anti-resonant hollow fiber.

[0053] Specifically, the light beam emitted by the incident light source 1 can be irradiated to different positions of the fiber to be measured 3 after being processed by the light source processing module 2, and can form multiple scattering lights after passing through the fiber to be measured 3 in different paths. The multiple scattering light beams emitted by the fiber to be measured 3 can be input to the data processing module 5 after being collected by the data acquisition module 4. The data processing module 5 obtains the group delay spectrum by filtering processing and Fourier transform on the spectrum formed by the coherent superposition of the multiple scattering light beams, and obtains the group delay difference caused by the coherent superposition of each light beam by peak value retrieval on the group delay spectrum. The data processing module 5 can obtain multiple size parameters of the fiber to be measured based on the multi-beam interference geometric optics model and from the group delay difference between the light beams.

[0054] In the present disclosure, the data processing module 5 can obtain the group delay difference caused by the coherent superposition of each light beam by filtering processing, Fourier transform, and peak value retrieval on the multiple scattering light beams collected from the fiber to be measured. The data processing module 5 can obtain multiple size parameters of the anti-resonant hollow fiber based on the multi-beam interference geometric optics model and from the group delay difference between the light beams. Thus, the simultaneous online measurement of multiple parameters of the anti-resonant hollow fiber can be realized, and the drawing efficiency and output efficiency of the anti-resonant hollow fiber can be further improved, and the fiber manufacturing cost can be reduced.

[0055] Figure 2 is a functional module schematic diagram showing one example of the light source processing module involved in the embodiment of the present disclosure. Figure 3 is a functional module schematic diagram showing one example of the data acquisition module involved in the embodiment of the present disclosure.

[0056] Referring to Figure 2 and Figure 3In some examples, the light source processing module 2 can include a collimation module 21 and a polarization module 22 connected to the collimation module 21. In this case, the light beam emitted by the incident light source 1 can be converted into linearly polarized parallel light after collimation by the collimation module 21 and polarization by the polarization module 22, which can facilitate irradiation to the optical fiber 3 to be measured.

[0057] In some examples, the collimation module can be an off-axis parabolic mirror. In some examples, the collimation module can also be a single lens.

[0058] In some examples, the polarization module can be a polarization controller.

[0059] In some examples, the data acquisition module 4 can include a signal acquisition optical fiber 41 and a spectrometer 42 connected to the signal acquisition optical fiber 41. In this case, the signal acquisition optical fiber 41 can facilitate the collection of scattered light emitted by the optical fiber 3 to be measured, and the spectrometer 42 can perform pretreatment such as collection and light splitting on the light beam collected by the signal acquisition optical fiber 41.

[0060] In some examples, the incident light source 1 can be a supercontinuum broadband laser source, which can be used to emit a supercontinuum broadband laser source.

[0061] Figure 4 is a structural schematic diagram showing the anti-resonant hollow core optical fiber involved in the embodiments of the present disclosure.

[0062] In some examples, the optical fiber 3 to be measured can include a hollow sleeve 31 and a plurality of cladding tubes 32 arranged in the hollow sleeve 31.

[0063] In some examples, the light beam emitted by the incident light source can be processed by the collimation module 21 and the polarization module 22 and then irradiated to different positions of the optical fiber 3 to be measured, and can form a plurality of scattered light beams after passing through the hollow sleeve 31 and the cladding tubes 32 of the optical fiber 3 to be measured in at least four different paths (such as Figure 7 shown) and then collected by the signal acquisition optical fiber 41 and the spectrometer 42 and input to the data processing module 5. The four light beams (i.e., the scattered light beams) emitted can be scattered from the optical fiber to be measured at the same scattering angle (i.e., the collection angle of the signal acquisition optical fiber 41).

[0064] In some examples, the data processing module 5 can obtain three size parameters of the optical fiber 3 to be measured based on a four-beam interference geometric optics model and from the group delay difference, including the inner diameter r of the optical fiber 3 to be measured, the outer diameter R of the optical fiber 3 to be measured, and the diameter d of the cladding tube 32.

[0065] In some examples, referring to Figure 7 , the four beams can be Figure 6The four beams, numbered 1, 2, 3, and 4 respectively, are referred to below as the first beam, second beam, third beam, and fourth beam. They can be incident parallel to the horizontal axis of the fiber cross-section and can illuminate one side of the fiber under test. Figure 7 The fiber under test is shown at different positions on the left side, and then from the other side (as shown). Figure 7 The beams emerge from different positions on the right side of the fiber under test (as shown). Furthermore, the data processing module can calculate three dimensional parameters of the anti-resonant fiber based on the incident and exit paths of the four beams, the acquisition angle parameters of the acquisition fiber 41, and the angle parameters of the anti-resonant fiber itself.

[0066] In some examples, the different paths through the fiber under test 3 can be determined by the internal structure and refractive index of the fiber under test. In some further examples, the different paths through the fiber under test 3 can be determined by factors such as the structure of the hollow sleeve 31, the structure of the cladding tube 32, and the refractive index of the light passing through the hollow sleeve 31 and the cladding tube 32.

[0067] In some examples, different paths through the fiber under test 3 may include the light path of a fourth beam passing through the hollow sleeve 31, the light path of a third beam passing through the hollow sleeve 31 and the cladding tube 32 in sequence, the light path of a second beam passing through the hollow sleeve 31 and formed by reflection from the inner wall of the hollow sleeve 31, and the light path of a first beam formed by reflection from the outer wall of the hollow sleeve 31.

[0068] In some examples, the first beam may consist of incident light rays incident on the outer wall of the hollow sleeve 31 and reflected light rays reflected by the outer wall of the hollow sleeve 31. That is, the first beam can be directly reflected by the outer wall of the hollow sleeve 31.

[0069] In some examples, the second beam may consist of an incident ray, a first refracted ray penetrating the hollow sleeve 31, a reflected ray reflected from the inner wall of the hollow sleeve 31, and a second refracted ray penetrating the outer wall of the hollow sleeve 31. That is, the second beam can be refracted from the outer wall of the hollow sleeve 31 into the hollow sleeve 31, reflected by the inner wall of the hollow sleeve 31, and then refracted out from the outer wall of the hollow sleeve 31.

[0070] In some examples, the third beam can consist of an incident ray, a first refracted ray passing through the hollow sleeve 31, a second refracted ray passing through the cladding tube 32, a third refracted ray exiting the cladding tube 32, and an outgoing ray. That is, the third beam can be refracted from the outer wall of the hollow sleeve 31 into the hollow sleeve 31, and enter the storage layer 32 from one coupling point between the hollow sleeve 31 and the storage layer 32. Then, it propagates around the circumference of the storage layer 32 to another coupling point between the hollow sleeve 31 and the storage layer 32, and finally refracted from the outer wall of the hollow sleeve 31.

[0071] It can be understood that since the propagation in the cladding tube 32 is a waveguide propagation, the effective refractive index n eff .

[0072] In some examples, the fourth light beam can be composed of the incident light ray, the refracted light ray, and the emergent light ray. That is, the fourth light beam can be refracted into the hollow sleeve 31 from the outer wall of the hollow sleeve 31 and refracted out of the outer wall of the hollow sleeve.

[0073] In some examples, the different positions can be the intersection positions of the 4 light beams and one side of the fiber under test 3.

[0074] In some examples, the calculation formula of the inner diameter r of the fiber under test, the outer diameter R of the fiber under test, and the diameter d of the cladding tube can be as follows:

[0075]

[0076]

[0077] ΔD 14 = 2R[-cos(a4) + n silica sin(a4 + a1) + cos(a1)] + l / 2,

[0078] ΔD 24 =-2R(cos(a4)-cos(a2))+2n silica [R sin(a4 + a1) - U],

[0079]

[0080] ΔD 23 =-R·[cos(a3) + cos(a'3) - 2cos(a2)] + n silica (U' + U" - 2U) + L tube ,

[0081] where τ jk is the group delay difference between the light beam j and the light beam k, ΔD jk is the optical path difference between the light beam j and the light beam k, j = 1, 2, 3, or 4, k = 1, 2, 3, or 4, n silica is the refractive index of the fiber under test, n eff is the effective refractive index of the third light beam propagating in the cladding tube, v is the optical frequency, a i(i=1,2,3,4) is the incident angle of the i-th beam, α′3 is the exit angle of the third beam, γ is the circumferential angle formed by the intersection of the cladding tube and the inner wall of the hollow sleeve in the fiber under test, d is the diameter of the cladding tube, θ is the angle between the line connecting the center of the cladding tube and the center of the fiber under test and the normal of the first beam, and λ is the wavelength of the light wave.

[0082] In some examples, the group delay difference between the j-th beam and the k-th beam is

[0083]

[0084] Specifically, the calculation process for the three dimensional parameters—the inner diameter r of the fiber under test 3, the outer diameter R of the fiber under test 3, and the diameter d of the cladding tube 32—can be as follows:

[0085] The optical path difference between the first beam and the fourth beam is

[0086] ΔD 14 =2R[-cos(α4)+nsin(α4+α1)+cos(α1)]+λ / 2, formula (1)

[0087] The incident angles α1 and α4 in formula (3) can be expressed according to the law of refraction as follows:

[0088]

[0089] Where n silica Let be the refractive index of the optical fiber under test. The scattering angle (also the acquisition angle of the signal acquisition fiber) is a known quantity;

[0090] The group delay time difference τ between the first beam and the fourth beam 14 for:

[0091]

[0092] According to the group delay time difference τ between the first and fourth beams in formula (3) 14 The optical path difference ΔD between the first and fourth beams can be obtained. 14 According to ΔD 14 The outer diameter R of the optical fiber 3 to be tested can be obtained by formulas (1) and (2).

[0093] The optical path difference between the second beam and the fourth beam is:

[0094] For α2 in formula (4), according to the law of refraction

[0095]

[0096] The group delay difference τ between the second light beam and the fourth light beam 24 is:

[0097]

[0098] The group delay difference τ between the second light beam and the fourth light beam according to equation (6) 24 The optical path difference ΔD between the second light beam and the fourth light beam can be derived as 24 , according to ΔD 24 , equation (4), equation (5), and the outer diameter R of the fiber under test 3.

[0099] In addition, the optical path difference ΔD between the second light beam and the third light beam 23 is:

[0100]

[0101] L in equation (7) tube and the auxiliary angles β1 and β2 can be expressed as

[0102]

[0103] For the incident angle α3 and the exit angle α3', according to the refraction law, the following equation can be given

[0104]

[0105] and the group delay difference τ between the second light beam and the third light beam 23 is:

[0106]

[0107] The group delay difference τ between the second light beam and the third light beam according to equation (10) 23 The optical path difference ΔD between the second light beam and the third light beam can be derived as 23 For a given γ and n eff , according to ΔD 23 , equation (9), equation (8), equation (7), and the outer diameter R of the fiber under test 3, the inner diameter r of the fiber under test 3, the diameter d of the cladding tube 32 can be derived.

[0108] In some examples, the data processing module 5 can filter the scattering spectrum by a window function filter.

[0109] In some examples, the data processing module 5 can be a computer.

[0110] Figure 5 is a flowchart illustrating one example of a method for measuring the size parameters of a reverse-hollow-core optical fiber according to an embodiment of the present disclosure.Figure 6 is a flow chart showing another example of a method for measuring the size parameters of a counter- resonant hollow core fiber according to an embodiment of the present disclosure.

[0111] With reference to Figure 5 and Figure 6 , the present disclosure also provides a method for measuring the size parameters of a counter- resonant hollow core fiber based on a geometric optics model, which can be a measurement method implemented based on the counter- resonant hollow core fiber size parameter measurement system described above. The method can include the following steps:

[0112] Step S100, preparation procedure, prepare the sequentially connected incident light source 1, light source processing module 2, fiber to be measured 3, data acquisition module 4, and data processing module 5;

[0113] Step S200, light beam acquisition procedure, the light beam emitted by the incident light source 1 can irradiate different positions of the fiber to be measured 3 after being processed by the light source processing module 2. The multiple scattered light beams emitted by the fiber to be measured 3 are collected by the data acquisition module 4 and input to the data processing module 5;

[0114] Step S300, data processing procedure, the data processing module 5 can obtain the group delay spectrum by filtering and Fourier transforming the scattering spectrum, and obtain the group delay difference caused by the coherent superposition of each light beam in the group delay spectrum by peak searching.

[0115] Step S400, calculation procedure, the data processing module can obtain multiple size parameters of the counter- resonant hollow core fiber based on the multi- beam interference geometric optics model and the group delay difference between each light beam.

[0116] Figure 7 is a diagram showing the propagation paths of multiple light beams in a counter- resonant hollow core fiber according to an embodiment of the present disclosure. Among them, Figure 7 (a) is a walking path diagram of 4 light beams, Figure 7 (b) is a walking path diagram of 4 light beams, Figure 7 (c) is an angle diagram of the walking path of 4 light beams and the internal structure of the fiber to be measured 3.

[0117] With reference to Figure 7 , in some examples, in the calculation procedure of step S400, the data processing module 5 can obtain three size parameters of the fiber to be measured based on the 4-beam interference geometric optics model and the group delay difference between each light beam, including the inner diameter r of the fiber to be measured 3, the outer diameter R of the fiber to be measured 3, and the diameter d of the cladding tube 32. The calculation process of the inner diameter r of the fiber to be measured, the outer diameter R of the fiber to be measured, and the diameter d of the cladding tube 32 can be as follows:

[0118] The optical path difference between the first light beam and the fourth light beam is

[0119] ΔD14 = 2R[-cos(a4) + nsin(a4 + a1) + cos(a1)] + λ / 2, Equation (1)

[0120] The incident angles a1 and a4 in Equation (3) can be expressed according to the refraction law as:

[0121]

[0122] where n silica is the refractive index of the fiber to be measured, is the scattering angle (also the collection angle of the signal collection light), both of which are known quantities;

[0123] The group delay difference τ 14 between the first beam and the fourth beam is:

[0124]

[0125] According to the group delay difference τ 14 between the first beam and the fourth beam in Equation (3), the optical path difference ΔD 14 between the first beam and the fourth beam can be obtained, and according to ΔD 14 and Equation (2), the outer diameter R of the fiber to be measured 3 can be obtained.

[0126] The optical path difference between the second beam and the fourth beam is:

[0127] For a2 in Equation (4), according to the refraction law

[0128]

[0129] The group delay difference τ 24 between the second beam and the fourth beam is:

[0130]

[0131] According to the group delay difference τ 24 between the second beam and the fourth beam in Equation (6), the optical path difference ΔD 24 between the second beam and the fourth beam can be obtained, and according to ΔD 24 , Equation (5), Equation (4), and the outer diameter R of the fiber to be measured 3, the inner diameter r of the fiber to be measured 3 can be obtained.

[0132] In addition, the optical path difference ΔD 23 between the second beam and the third beam is:

[0133]

[0134] L tubeand the auxiliary angles β1 and β2 can be expressed as

[0135]

[0136] For the incident angle α3 and the exit angle α3', according to the refraction law, the following equation can be given

[0137]

[0138] and the group delay difference τ between the second light beam and the third light beam 23 is:

[0139]

[0140] According to the group delay difference τ of the second light beam and the third light beam in formula (10) 23 The optical path difference ΔD of the second light beam and the third light beam 23 can be obtained. For a given γ and n eff , according to ΔD 23 , formula (9), formula (8), formula (7), and the outer diameter R of the measured optical fiber 3 and the inner diameter r of the measured optical fiber 3, the diameter d of the cladding tube 32 can be obtained.

[0141] In some examples, the optical frequency where T is the optical wave period, and c is the speed of light in vacuum.

[0142] The introductions of other modules refer to the descriptions of the measurement system part, which will not be repeated here.

[0143] In the measurement method of the present disclosure, the data processing module 5 can obtain the group delay difference caused by the coherent superposition of each light beam after filtering processing, Fourier transform, and peak retrieval of the spectrum formed by the coherent superposition of the collected multiple scattered light beams from the measured optical fiber. Based on the multi-beam interference geometric optics model and the group delay difference between each light beam, the data processing module 5 can obtain multiple size parameters of the anti-resonant hollow optical fiber. Thus, the simultaneous online measurement of multiple parameters of the anti-resonant hollow optical fiber can be realized, and the drawing efficiency and output efficiency of the anti-resonant hollow optical fiber can be further improved, and the optical fiber manufacturing cost can be reduced.

[0144] On the basis of the WGM (Whispering Gallery Mode) spectrum method, the present disclosure proposes a geometric optics model based on 4-beam interference according to the structural characteristics of the anti-resonant hollow optical fiber. According to the model, multiple key parameters of the anti-resonant hollow optical fiber can be calculated, so that online monitoring of multiple key parameters of the optical fiber can be realized according to the anti-resonant hollow optical fiber size parameter measurement system and the measurement method based on the geometric optics model.

[0145] Although the present disclosure has been specifically shown and described above with reference to the drawings and embodiments, it will be understood by those skilled in the art that the above description is not in any form limiting the present disclosure. Those skilled in the art can modify and change the present disclosure as needed without departing from the essential spirit and scope of the present disclosure, and such modifications and changes fall within the scope of the present disclosure.

Claims

1. A system for measuring size parameters of a counter- resonant hollow-core optical fiber, the system comprising: The system comprises sequentially connected incident light source, light source processing module, optical fiber to be measured, data acquisition module and data processing module, the light beam emitted by the incident light source is irradiated to different positions of the optical fiber to be measured after being processed by the light source processing module, and forms multiple scattered light beams after passing through the optical fiber to be measured in different paths, and then is input to the data processing module after being collected by the data acquisition module, the data processing module obtains group delay spectrum by filtering and Fourier transform on the spectrum formed by the coherent superposition of multiple scattered light beams, and obtains the group delay difference caused by the coherent superposition of each light beam in the group delay spectrum by peak value retrieval on the group delay spectrum, and the data processing module obtains multiple size parameters of the optical fiber to be measured based on the multi-beam interference geometric optics model and the group delay difference between each light beam; The optical fiber to be measured comprises a hollow sleeve and multiple cladding tubes arranged in the hollow sleeve; The light beam emitted by the incident light source is irradiated to different positions of the optical fiber to be measured after being processed by the light source processing module, and forms multiple scattered light beams after passing through the hollow sleeve and the cladding tubes of the optical fiber to be measured in at least four different paths, and then is input to the data processing module after being collected by the data acquisition module; The data processing module obtains three size parameters of the optical fiber to be measured based on a 4-beam interference geometric optical model and from the group delay difference, including an inner diameter of the optical fiber to be measured r , an outer diameter of the optical fiber to be measured R , and a diameter of the cladding tube d； an inner diameter of the optical fiber to be measured r an outer diameter of the optical fiber to be measured R a diameter of the cladding tube d The calculation formula is as follows: ， ， ， ， wherein, is a group delay difference between the light beam j and the light beam k, is an optical path difference between the light beam j and the light beam k, j = 1, 2, 3, 4, k = 1, 2, 3, 4, is a refractive index of the fiber under test, is an effective refractive index of the third light beam when propagating in the cladding tube, is an optical frequency, is an incident angle of the i-th light beam, is an exit angle of the third light beam, is a circumferential angle formed by the intersection of the cladding tube in the fiber under test and the inner wall of the hollow jacket, is an angle between the line connecting the center of the cladding tube and the center of the fiber under test and the normal line of the first light beam, is a wavelength of the light wave.

2. The anti-resonant hollow core fiber size parameter measurement system according to claim 1, wherein The light source processing module comprises a collimation module and a polarization module connected with the collimation module.

3. The anti-resonant hollow core fiber size parameter measurement system according to claim 2, wherein The collimation module is an off-axis parabolic mirror or a single lens, and the polarization module is a polarization controller.

4. The anti-resonant hollow core fiber size parameter measurement system according to claim 1, wherein The data acquisition module comprises a signal acquisition optical fiber and a spectrometer connected with the signal acquisition optical fiber.

5. A method for measuring size parameters of an anti-resonant hollow core fiber based on a geometric optics model, characterized in that, The system comprises the following steps: A preparation process of preparing sequentially connected incident light source, light source processing module, optical fiber to be measured, data acquisition module and data processing module; A light beam collection process, the light beam emitted by the incident light source is irradiated to different positions of the optical fiber to be measured after being processed by the light source processing module, and forms multiple scattered light beams after passing through the optical fiber to be measured in different paths, and then is input to the data processing module after being collected by the data acquisition module; A data processing process, the data processing module obtains group delay spectrum by filtering and Fourier transform on the spectrum formed by the coherent superposition of multiple scattered light beams, and obtains the group delay difference caused by the coherent superposition of each light beam in the group delay spectrum by peak value retrieval on the group delay spectrum; A calculation process, the data processing module obtains multiple size parameters of the optical fiber to be measured based on the multi-beam interference geometric optics model and the group delay difference between each light beam; The optical fiber to be measured comprises a hollow sleeve and multiple cladding tubes arranged in the hollow sleeve; The light beams emitted by the incident light source are irradiated to different positions of the optical fiber to be measured after being processed by the light source processing module, and form a plurality of scattered light beams after passing through the hollow sleeve and the cladding tube of the optical fiber to be measured in at least four different paths, and then are input to the data processing module after being collected by the data collection module. The data processing module obtains three size parameters of the optical fiber to be measured based on a 4-beam interference geometric optical model and the group delay difference, including an inner diameter of the optical fiber to be measured r , an outer diameter of the optical fiber to be measured R , and a diameter of the cladding tube d , and the calculation formulas of the inner diameter of the optical fiber to be measured r , the outer diameter of the optical fiber to be measured R , and the diameter of the cladding tube d are ， ， ， ， wherein, is the group delay difference between the light beam j and the light beam k, is the optical path difference between the light beam j and the light beam k, j = 1, 2, 3, 4, k = 1, 2, 3, 4, is the refractive index of the fiber under test, is the effective refractive index of the third light beam when propagating in the cladding tube, is the optical frequency, is the incidence angle of the i-th light beam, is the exit angle of the third light beam, is the circumferential angle formed by the intersection of the cladding tube in the fiber under test and the inner wall of the hollow jacket, is the angle between the line connecting the center of the cladding tube and the center of the fiber under test and the normal of the first light beam, is the wavelength of the light wave.

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