A method and apparatus for evaluating the coupling loss of hollow-core optical fiber fusion splice

Abstract

This invention discloses a method and apparatus for evaluating the coupling loss of hollow-core optical fiber fusion splices. The method first acquires a cross-sectional image of the fusion splice end of the first hollow-core optical fiber, then acquires an image of the light field distribution of the emitted light after passing a laser beam through it, and fits the circumcircle of the nested tube with a regular polygon fitted to the light field. The two hollow-core optical fibers are then fused together, and a cross-sectional image of the non-fusion splice end of the second hollow-core optical fiber and an image of the light field distribution after passing a laser beam are acquired, completing the same fitting. Finally, the relevant geometric parameters before and after fusion are input into a preset evaluation model to obtain the fusion loss. This invention achieves accurate and real-time evaluation of fusion loss.

Description

Technical Field

[0001] This invention relates to the field of hollow fiber testing technology, specifically to a method and apparatus for evaluating the fusion splice coupling loss of hollow fiber. Background Technology

[0002] Hollow-core antiresonant fiber, as a next-generation fiber technology, confines light to a low-refractive-index hollow core region through the antiresonant reflection waveguide effect. With its advantages of ultra-low loss, high damage threshold, and low nonlinearity, it has broad application prospects in optical communication, high-power laser transmission, and sensing. In practical applications of hollow-core fiber, fiber splicing is a critical step, and the magnitude of splice loss directly affects the performance of the entire transmission system. Traditional splice loss assessment methods mainly include the truncation method and the backscattering method, but these methods have significant limitations: the truncation method requires damaging the fiber and cannot achieve real-time assessment; the backscattering method relies on a complex optical system and is susceptible to interference from fiber background noise, resulting in low assessment accuracy.

[0003] The transmission mode field of hollow anti-resonant fiber is mainly concentrated in the hollow core region of the fiber. During optical power transmission, most of the optical power (usually >90%) is confined to the air-filled fiber core. This working principle can significantly reduce material absorption and waveguide dispersion.

[0004] Mode field confinement efficiency determines the fundamental loss. The more concentrated the mode field is in the hollow core (fitting the hollow core region), the less optical power penetrates into the high-loss cladding, and the lower the material absorption and scattering loss. Mode field symmetry affects scattering loss: when the mode field deviates from circular symmetry (such as ellipticization or distortion), it easily induces interface scattering and mode coupling, resulting in decreased fit and increased loss.

[0005] Losses mainly include leakage loss, material loss, surface scattering loss, and bending loss. Among these, leakage loss is strongly coupled with mode field fit, and its precise control can be achieved by optimizing structural parameters. Key influencing factors of mode field fit include core size, cladding structure, and operating wavelength, which can be accurately analyzed using numerical simulation methods such as the finite element method and the finite-difference time-domain method.

[0006] Meanwhile, the splice loss of hollow-core optical fibers is closely related to the optical field morphology of the core layer. During splicing, if the fiber end faces are misaligned, the splicing temperature is inappropriate, or the structure is deformed, it will lead to problems such as changes in the mode diameter of the core layer optical field, a decrease in the power constraint factor, and a reduction in mode purity, thus resulting in splice loss. Existing evaluation methods often ignore the direct impact of changes in the optical field morphology on splice loss, and cannot establish a quantitative relationship between the two, making it difficult to meet the needs of high-precision splice quality inspection. Therefore, there is an urgent need for a splice loss evaluation method and device based on the optical field morphology of the hollow-core fiber core layer to achieve accurate and real-time evaluation of splice loss. Summary of the Invention

[0007] The purpose of this invention is to provide a method and apparatus for evaluating the fusion splice coupling loss of hollow optical fibers, so as to achieve accurate and real-time evaluation of the fusion splice loss of hollow optical fibers.

[0008] To address the aforementioned technical problems, this invention provides a method for evaluating the coupling loss of hollow-core optical fiber fusion splices, comprising:

[0009] S1. Acquire a first cross-sectional image of the fusion splice end of the first hollow fiber; pass a laser beam through the first hollow fiber and acquire a first optical field distribution image of the emitted light from the fusion splice end of the first hollow fiber.

[0010] S2. Obtain the circumcircle of each nested tube in the first cross-sectional image and the fitted regular polygon of the field intensity distribution in the first light field distribution image by fitting.

[0011] S3. The first hollow fiber and the second hollow fiber are fused together, and the second cross-sectional image of the non-fused end of the second hollow fiber is acquired; a laser is passed through the hollow fiber obtained after fusion, and the second light field distribution image of the emitted light from the non-fused end of the second hollow fiber is acquired.

[0012] S4. Obtain the circumcircle of each nested tube in the second cross-sectional image and the fitted regular polygon of the field intensity distribution in the second light field distribution image by fitting.

[0013] S5. Input the geometric parameters of the circumscribed fitting circle of each nested tube in the first cross-sectional image, the fitted regular polygon of the field intensity distribution in the first optical field distribution image, the circumscribed fitting circle of each nested tube in the second cross-sectional image, and the fitted regular polygon of the field intensity distribution in the second optical field distribution image into the pre-constructed fusion loss evaluation model to obtain the fusion loss after the first hollow fiber and the second hollow fiber are fused together.

[0014] According to the above scheme, the geometric parameters include: the center coordinates and radius of the circumscribed circle corresponding to the first cross-sectional image; the center coordinates and radius of the circumscribed circle corresponding to the second cross-sectional image; the side length and included angle of the fitted regular polygon corresponding to the first light field distribution image; the side length and included angle of the fitted regular polygon corresponding to the second light field distribution image; the concentricity of the circumscribed circle corresponding to the first cross-sectional image and the fitted regular polygon corresponding to the first light field distribution image; and the concentricity of the circumscribed circle corresponding to the second cross-sectional image and the fitted regular polygon corresponding to the second light field distribution image.

[0015] According to the above scheme, the fusion loss assessment model is based on a neural network, which includes several input layer neurons with different geometric parameters, several hidden layer neurons, and output layer neurons; the output layer neurons output the fusion loss.

[0016] According to the above scheme, the fusion splice loss evaluation model includes a correction layer connected to the output layer; the correction layer corrects the fusion splice loss output by the output layer based on the hollow diameter, cladding tube thickness and inter-tube gap of the first hollow fiber or the second hollow fiber, and obtains the corrected fusion splice loss.

[0017] According to the above scheme, the welding loss assessment model is constructed based on a BP neural network.

[0018] According to the above scheme, the geometric parameters of different hollow optical fibers before and after fusion splicing are obtained by acquiring images and fitting, and the actual fusion loss of different hollow optical fibers after fusion splicing is measured by the truncation method. The obtained geometric parameters and actual fusion loss are used to construct a training dataset, and the fusion loss evaluation model is trained using the training dataset.

[0019] According to the above scheme, when actually evaluating the welding loss, if the difference between the welding loss output by the welding loss evaluation model and the measured actual welding loss is greater than a set threshold, then the welding loss output by the welding loss evaluation model and the measured actual welding loss are added to the training dataset; the updated training dataset is used to train and update the welding loss evaluation model.

[0020] According to the above scheme, before acquiring the cross-sectional image and light field distribution image of the hollow fiber, the hollow fiber is cut and cleaned at the end face.

[0021] This invention also provides an evaluation device for the fusion splice coupling loss of hollow optical fibers, used to implement the evaluation method for the fusion splice coupling loss of hollow optical fibers described above, comprising:

[0022] The light source module is used to transmit laser light into the hollow fiber.

[0023] The image acquisition module is used to acquire cross-sectional images and light field distribution images of hollow optical fibers;

[0024] The fitting module is used to obtain the circumscribed circle based on the cross-sectional image and to obtain the fitted regular polygon based on the light field distribution image.

[0025] The geometric parameter analysis module is used to analyze and obtain geometric parameters based on the circumscribed fitted circle and the fitted regular polygon.

[0026] The welding loss estimation module is equipped with a pre-built welding loss evaluation model, which is used to estimate welding loss based on geometric parameters.

[0027] According to the above scheme, the image acquisition module includes a near-field scanning camera.

[0028] Beneficial effects

[0029] This invention comprehensively captures the structural state and optical field distribution characteristics of the hollow fiber before and after fusion by acquiring a first cross-sectional image of the fusion splice end of the first hollow fiber and a first optical field distribution image of the emitted light, as well as a second cross-sectional image of the non-fusion splice end of the second hollow fiber and a second optical field distribution image of the emitted light. This avoids the shortcomings of traditional evaluation methods that ignore the influence of optical field morphology changes on fusion loss. By fitting the circumscribed circles of each nested tube in the cross-sectional image and the fitted regular polygons of the field intensity distribution in the optical field distribution image, intuitive image information is transformed into quantifiable geometric parameters, providing a specific and effective method for accurate evaluation of fusion loss. With the support of data, the problem of establishing a quantitative relationship between optical field morphology and fusion loss has been solved. By inputting the key geometric parameters before and after fusion into a pre-constructed fusion loss evaluation model, the core factors affecting fusion loss, such as fiber alignment deviation, structural deformation, and changes in optical field symmetry reflected by the geometric parameters, can be fully utilized to achieve direct quantitative evaluation of fusion loss. Compared with the traditional truncation method, it does not require damage to the optical fiber, and compared with the backscattering method, it is less affected by interference. It not only ensures the integrity and accuracy of the evaluation, but also achieves efficient real-time evaluation of fusion loss, meeting the demand for high-precision detection of fusion quality in hollow fiber applications. Attached Figure Description

[0030] Figure 1 This is a flowchart of a method for evaluating the coupling loss of hollow-core optical fiber fusion splicing according to an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of data collection before welding according to an embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram of data acquisition after fusion welding according to an embodiment of the present invention;

[0033] Figure 4 This is a light field distribution image according to an embodiment of the present invention;

[0034] Figure 5 This is a schematic diagram of the circumscribed circle according to an embodiment of the present invention;

[0035] Figure 6 This is a schematic diagram of a fitted regular polygon according to an embodiment of the present invention.

[0036] In the figure: 1. Circumscribed fitted circle; 2. Fitted regular polygon; 3. Light source module; 4. Image acquisition module; 5. First hollow fiber; 6. Second hollow fiber; 7. Fusion splice. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0038] See Figures 1-6 This embodiment discloses a method for evaluating the coupling loss of hollow-core optical fiber fusion splice, including:

[0039] S1. Acquire a first cross-sectional image of the fusion splice end of the first hollow fiber 5; pass a laser to the first hollow fiber 5 and acquire a first light field distribution image of the light emitted from the fusion splice end of the first hollow fiber 5.

[0040] S2. By fitting, the circumcircle of each nested tube in the first cross-sectional image is obtained as 1, and the fitted regular polygon of the field intensity distribution in the first light field distribution image is obtained as 2.

[0041] S3. The first hollow fiber 5 and the second hollow fiber 6 are fused together, and the second cross-sectional image of the non-fused end of the second hollow fiber is acquired; a laser is passed through the hollow fiber obtained after fusion, and the second light field distribution image of the emitted light from the non-fused end of the second hollow fiber 6 is acquired.

[0042] S4. Obtain the circumcircle of each nested tube in the second cross-sectional image by fitting, and the fitted regular polygon 2 of the field intensity distribution in the second light field distribution image.

[0043] S5. Input the geometric parameters of the circumscribed fitting circle 1 of each nested tube in the first cross-sectional image, the fitting regular polygon 2 of the field intensity distribution in the first optical field distribution image, the circumscribed fitting circle 1 of each nested tube in the second cross-sectional image, and the fitting regular polygon 2 of the field intensity distribution in the second optical field distribution image into the pre-constructed fusion loss evaluation model to obtain the fusion loss after the first hollow fiber 5 and the second hollow fiber 6 are fused together.

[0044] Understandably, before proceeding with the evaluation method, the first hollow fiber 5 and the second hollow fiber 6 need to be pre-processed. Pre-processing includes end-face cutting and cleaning to ensure the hollow fiber end faces are flat and free of impurities. In this embodiment, an optical fiber cleaver is used for end-face cutting, and an optical fiber end-face inspection device is used for inspection to ensure that the cutting angle error does not exceed 0.5°, thus guaranteeing the flatness of the optical fiber end faces.

[0045] In this embodiment, a fiber optic fusion splicer is used to splice two pre-treated hollow optical fibers, controlling the splicing temperature, splicing time, and advance distance to form a fusion joint 7; for example, for... Figure 5 , Figure 6 The hollow fiber end face structure shown can be set with a fusion temperature of 1800~2200℃, a fusion time of 0.1~1s, and a push distance of 0.1~1μm. During the fusion process, the fusion status is monitored in real time by the control module to ensure that the alignment deviation of the fiber end face does not exceed 1μm, thus forming a qualified fusion joint 7.

[0046] Furthermore, the geometric parameters include: the center coordinates and radius of the circumscribed fitted circle 1 corresponding to the first cross-sectional image; the center coordinates and radius of the circumscribed fitted circle 1 corresponding to the second cross-sectional image; the side length and interior angle of the fitted regular polygon 2 corresponding to the first light field distribution image; the side length and interior angle of the fitted regular polygon 2 corresponding to the second light field distribution image; the concentricity of the circumscribed fitted circle 1 and the fitted regular polygon 2 corresponding to the first light field distribution image corresponding to the first cross-sectional image; and the concentricity of the circumscribed fitted circle 1 and the fitted regular polygon 2 corresponding to the second light field distribution image corresponding to the second cross-sectional image.

[0047] Furthermore, the fusion loss assessment model is based on a neural network, which includes several input layer neurons with different geometric parameters, several hidden layer neurons, and output layer neurons; the output layer neurons output the fusion loss.

[0048] Furthermore, the fusion splice loss assessment model includes a correction layer connected to the output layer; the correction layer corrects the fusion splice loss output by the output layer based on the hollow diameter of the first hollow fiber 5 or the second hollow fiber 6, the cladding tube thickness, and the inter-tube gap, to obtain the corrected fusion splice loss.

[0049] Specifically, in this embodiment, the corrected weld loss is expressed as:

[0050] Initial model output loss × (1 + 0.01 × (hollow core diameter deviation / 5 + cladding tube thickness deviation / 50 + tube gap deviation / 2))

[0051] In the above formula, the hollow core diameter deviation, cladding tube thickness deviation, and inter-tube gap deviation are the differences in structural parameters between the first hollow fiber 5 or the second hollow fiber 6 and the pre-set standard hollow fiber; 0.01 is the set deviation coefficient of 0.01dB / um, and 1 / 5, 1 / 50, and 1 / 2 are the set calculation factors for hollow core diameter deviation, cladding tube thickness deviation, and inter-tube gap deviation, respectively. The above coefficients are all set according to process requirements. The specific setting method is not described in this invention. It should be understood that the coefficients can be adjusted and modified according to actual needs.

[0052] Furthermore, the weld loss assessment model is constructed based on a BP neural network.

[0053] Furthermore, the geometric parameters of different hollow optical fibers before and after fusion splicing are obtained by acquiring images and fitting them, and the actual fusion loss of different hollow optical fibers after fusion splicing is measured by the truncation method. The obtained geometric parameters and actual fusion loss are used to construct a training dataset, and the fusion loss evaluation model is trained using the training dataset.

[0054] Specifically, this embodiment selects 25 hollow fiber samples with different structural parameters, including hollow core diameters of 20-50 μm, cladding tube thicknesses of 300-800 nm, and inter-tube gaps of 5-20 μm. Twenty fusion splicing experiments are performed on each sample. The geometric parameters before and after fusion are recorded for each experiment. The actual fusion loss is measured using the cut-off method (measuring the fiber output power P1 before fusion, and after fusion, cutting the fiber behind the splice joint 7 and measuring the output power P2 at the cut-off point; the fusion loss is...). ), resulting in 500 sets of data, which constitute the training dataset.

[0055] Furthermore, when actually evaluating the welding loss, if the difference between the welding loss output by the welding loss evaluation model and the measured actual welding loss is greater than a set threshold (set to 5% in this embodiment), then the welding loss output by the welding loss evaluation model and the measured actual welding loss are added to the training dataset; the updated training dataset is used to train and update the welding loss evaluation model.

[0056] Furthermore, before acquiring cross-sectional and optical field distribution images of the hollow fiber, the hollow fiber is end-faced cut and cleaned.

[0057] This embodiment also provides an evaluation device for the fusion splice coupling loss of hollow optical fibers, used to implement the evaluation method for the fusion splice coupling loss of hollow optical fibers described above, including:

[0058] Light source module 3 is used to transmit laser light into the hollow fiber;

[0059] Image acquisition module 4 is used to acquire cross-sectional images and light field distribution images of hollow optical fibers;

[0060] The fitting module is used to obtain the circumscribed circle 1 by fitting the cross-sectional image and to obtain the fitted regular polygon 2 by fitting the light field distribution image.

[0061] The geometric parameter analysis module is used to analyze the geometric parameters based on the circumscribed fitted circle 1 and the fitted regular polygon 2.

[0062] The welding loss estimation module is equipped with a pre-built welding loss evaluation model, which is used to estimate welding loss based on geometric parameters.

[0063] Furthermore, the image acquisition module 4 includes a near-field scanning camera.

[0064] In this embodiment, the light source module 3 includes a laser and a collimator. The wavelength of the laser light source output by the laser is matched with the wavelength of the hollow fiber (for example, a 1550nm laser with a linewidth of less than 10kHz and an output power adjusted to 5mW). The collimator couples the laser into the hollow fiber (the coupling efficiency should be ensured to be no less than 90%). The near-field scanning camera is a CCD camera with a frame rate of 30fps and a dynamic range of 60dB. The image acquisition module 4 also includes an image acquisition card, which transmits the cross-sectional image or light field distribution image to the fitting module.

[0065] The method and apparatus described in this invention have the advantages of high evaluation accuracy, fast response speed and convenient operation, and can be widely used in splicing, coupling quality detection and loss determination in fields such as hollow fiber communication and high-power laser transmission.

[0066] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0067] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for evaluating the coupling loss of hollow-core optical fiber fusion splice, characterized in that, include: S1. Acquire the first cross-sectional image of the fusion splice end of the first hollow optical fiber; A laser is passed through the first hollow fiber to acquire the first optical field distribution image of the light emitted from the splice end of the first hollow fiber. S2. Obtain the circumcircle of each nested tube in the first cross-sectional image and the fitted regular polygon of the field intensity distribution in the first light field distribution image by fitting. S3. The first hollow fiber and the second hollow fiber are fused together, and the second cross-sectional image of the non-fused end of the second hollow fiber is acquired; a laser is passed through the hollow fiber obtained after fusion, and the second light field distribution image of the emitted light from the non-fused end of the second hollow fiber is acquired. S4. Obtain the circumcircle of each nested tube in the second cross-sectional image and the fitted regular polygon of the field intensity distribution in the second light field distribution image by fitting. S5. Input the geometric parameters of the circumscribed fitting circle of each nested tube in the first cross-sectional image, the fitted regular polygon of the field intensity distribution in the first optical field distribution image, the circumscribed fitting circle of each nested tube in the second cross-sectional image, and the fitted regular polygon of the field intensity distribution in the second optical field distribution image into the pre-constructed fusion loss evaluation model to obtain the fusion loss after the first hollow fiber and the second hollow fiber are fused together.

2. The method for evaluating the coupling loss of hollow-core optical fiber fusion splice according to claim 1, characterized in that, The geometric parameters include: the center coordinates and radius of the circumscribed circle corresponding to the first cross-sectional image; the center coordinates and radius of the circumscribed circle corresponding to the second cross-sectional image; the side length and interior angle of the fitted regular polygon corresponding to the first light field distribution image; the side length and interior angle of the fitted regular polygon corresponding to the second light field distribution image; the concentricity between the circumscribed circle corresponding to the first cross-sectional image and the fitted regular polygon corresponding to the first light field distribution image; and the concentricity between the circumscribed circle corresponding to the second cross-sectional image and the fitted regular polygon corresponding to the second light field distribution image.

3. The method for evaluating the coupling loss of hollow-core optical fiber fusion splice according to claim 2, characterized in that, The fusion loss assessment model is based on a neural network, which includes several input layer neurons with different geometric parameters, several hidden layer neurons, and output layer neurons; the output layer neurons output the fusion loss.

4. The method for evaluating the coupling loss of hollow-core optical fiber fusion splice according to claim 3, characterized in that, The fusion splice loss assessment model includes a correction layer connected to the output layer. The correction layer corrects the fusion splice loss output by the output layer based on the hollow diameter, cladding tube thickness, and inter-tube gap of the first or second hollow fiber, thus obtaining the corrected fusion splice loss.

5. The method for evaluating the coupling loss of hollow-core optical fiber fusion splice according to claim 2, characterized in that, The weld loss assessment model is constructed based on a BP neural network.

6. The method for evaluating the coupling loss of hollow-core optical fiber fusion splice according to claim 1, characterized in that, The geometric parameters of different hollow optical fibers before and after fusion splicing were obtained by acquiring images and fitting them. The actual fusion loss of different hollow optical fibers after fusion splicing was measured by the truncation method. The obtained geometric parameters and actual fusion loss were used to construct a training dataset, and the fusion loss evaluation model was trained using the training dataset.

7. The method for evaluating the coupling loss of hollow-core optical fiber fusion splice according to claim 6, characterized in that, When actually evaluating weld loss, if the difference between the weld loss output by the weld loss evaluation model and the measured actual weld loss is greater than a set threshold, then the weld loss output by the weld loss evaluation model and the measured actual weld loss are added to the training dataset; the updated training dataset is used to train and update the weld loss evaluation model.

8. The method for evaluating the coupling loss of hollow-core optical fiber fusion splice according to claim 1, characterized in that, Before acquiring cross-sectional and optical field distribution images of hollow optical fibers, the hollow optical fibers are cut and cleaned at the end face.

9. An evaluation device for fusion splice coupling loss of hollow optical fiber, characterized in that, The method for evaluating the coupling loss of hollow-core optical fiber fusion splicing as described in claim 1 includes: The light source module is used to transmit laser light into the hollow fiber. The image acquisition module is used to acquire cross-sectional images and light field distribution images of hollow optical fibers; The fitting module is used to obtain the circumscribed circle based on the cross-sectional image and to obtain the fitted regular polygon based on the light field distribution image. The geometric parameter analysis module is used to analyze and obtain geometric parameters based on the circumscribed fitted circle and the fitted regular polygon. The welding loss estimation module is equipped with a pre-built welding loss evaluation model, which is used to estimate welding loss based on geometric parameters.

10. The apparatus for evaluating the coupling loss of hollow-core optical fiber fusion splice according to claim 9, characterized in that, The image acquisition module includes a near-field scanning camera.

Images