Apparatus, method and test method for preparing a double-clad fiber cladding mode strippings sample

Abstract

This invention discloses a device, method, and testing method for preparing cladding mode stripping samples of double-clad optical fibers. The device features a groove bent along a smooth path. The sample preparation method includes the following steps: taking a double-clad optical fiber to be tested; using a predetermined length of the beginning of the double-clad fiber as a cladding mode stripping segment; and bending the cladding mode stripping segment along a predetermined smooth path to form a pre-fabricated test sample. The testing method includes the following steps: preparation of the cladding mode stripped sample; and light injection testing. This invention cleanly strips the cladding mode from the test sample prepared from the optical fiber to be tested, rather than from the testing device end. Thus, while ensuring the accuracy of the test results, cladding mode stripping and light injection testing are separated into two completely independent steps, executed simultaneously in parallel. This makes the test results more accurate and unaffected by the cladding mode, while also improving the test efficiency.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber testing, and more specifically, relates to an apparatus, method and testing method for preparing a sample of double-clad optical fiber cladding mode stripping. Background Technology

[0002] With the continuous development of high-power lasers, in order to improve the efficiency of pump light coupling into the inner cladding, cladding pumping technology has been applied to lasers. The market demand for its core components, double-clad ytterbium-doped fiber and passive double-clad matching fiber, has gradually increased, and the research on corresponding testing methods for double-clad fiber has gradually become a hot topic.

[0003] Double-clad optical fibers have an additional low-refractive-index cladding compared to conventional communication fibers. The structure includes a core, a low-refractive-index glass cladding (inner cladding), an outer cladding (low-refractive-index coating), and an outer coating. The inner cladding can be irregularly shaped (e.g., octagonal) or a conventional circular cladding. The optical core has a slightly higher refractive index than the glass inner cladding, and a low-refractive-index polymer coating is used as the outer cladding, resulting in a numerical aperture of 0.46 between the inner and outer claddings.

[0004] Fiber optic testing, including geometric dimension testing, numerical aperture testing, attenuation testing, and laser testing, is a crucial step in fiber optic production and R&D. The efficiency of fiber optic testing significantly impacts production efficiency. Generally, to improve testing efficiency, a coupling method is used to inject test light, and the detection light is then coupled into the testing instrument to obtain the fiber optic test results.

[0005] However, coupling errors are unavoidable when performing the tests listed above on double-clad fibers. Coupling errors can cause light to leak from the fiber core beyond its diameter, or, due to beam quality issues, directly couple into the fiber cladding. Cladding mode stripping is necessary during testing; incomplete or improper stripping will lead to inaccurate measurement results due to cladding mode propagation.

[0006] Currently, to address interference caused by cladding modes in double-clad fiber testing, a cladding mode stripping device is typically added to the light injection end of the testing apparatus. Furthermore, the fiber under test must be connected to the double-clad fiber testing apparatus using a fusion splice alignment method to avoid cladding mode propagation in the fiber under test due to coupling errors. Simultaneously, this cladding mode stripping device requires the use of high-refractive-index adhesive at the splice to filter out any cladding light generated at the splice point. If necessary, the cladding mode stripping device must also be connected via fusion splicing to ensure effective cladding mode filtering and thus guarantee the accuracy of the test results. For example, see Chinese patent document CN113203548A. If alignment coupling is used, complete cladding light filtering cannot be guaranteed, making it impossible to obtain accurate measurement results. Summary of the Invention

[0007] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a preparation apparatus, method, and testing method for double-clad fiber cladding mode stripping samples. The aim is to prepare double-clad fiber samples capable of stripping the cladding mode, rather than adding a cladding mode stripping device to the testing apparatus. This ensures clean stripping of the cladding mode regardless of the coupling method used, guaranteeing test results. More importantly, it completely separates the testing and sample preparation steps, enabling streamlined testing scheduling. This solves the technical problems of inconvenience or low efficiency in double-clad fiber testing caused by the need for fusion coupling of the test laser or the requirement to perform cladding mode stripping during test optical path setup in existing technologies.

[0008] To achieve the above objectives, according to one aspect of the present invention, an apparatus for preparing a double-clad fiber cladding mode stripping sample is provided, characterized in that it includes: a groove bent along a smooth path;

[0009] The path is divided into multiple segments according to the curve inflection points and the endpoints of the curve and straight line segments, including at least curve segments; the curve segments include positive curvature segments and negative curvature segments, which have opposite bending directions along the fiber axis; adjacent curve segments are arranged alternately with positive curvature segments and negative curvature segments.

[0010] Preferably, in the apparatus for preparing the cladding mode stripping sample of the double-clad optical fiber, the absolute value of the radius of curvature of the curved segment is between 20 and 40 mm, and the included angle between the tangential directions at both ends is less than or equal to 180°.

[0011] Preferably, in the apparatus for preparing the cladding mode stripping sample of the double-clad optical fiber, the curved segments are arranged in ascending order of absolute value of radius of curvature from upstream to downstream along the path.

[0012] Preferably, the preparation device for the cladding mode stripping sample of the double-clad optical fiber includes at least a filter mode segment whose absolute value of the radius of curvature is close to the minimum bending radius of the optical fiber, wherein the minimum bending radius of the optical fiber is the minimum bending radius for normal operation; and the absolute value of the radius of curvature of the filter mode segment is within 15mm ± 5mm.

[0013] Preferably, in the apparatus for preparing the cladding mode stripping sample of the double-clad optical fiber, the smooth path further includes a straight segment, both ends of which are connected to positive curvature segments or both are connected to negative curvature segments.

[0014] Preferably, in the apparatus for preparing the cladding mode stripping sample of the double-clad optical fiber, the bottom of the groove is filled with an elastic solid high-refractive-index medium and / or filled with a liquid high-refractive-index medium; the high-refractive-index medium is an optical transmission medium with a refractive index higher than that of the low-refractive-index glass cladding of the double-clad optical fiber to be tested; the refractive index of the high-refractive-index medium is preferably above 1.5.

[0015] Preferably, in the apparatus for preparing the cladding mode stripping sample of the double-clad optical fiber, the bottom of the groove is filled with an elastic solid high refractive index medium and a liquid high refractive index medium is injected, and the difference between the height of the elastic solid high refractive index medium and the height of the groove sidewall is 2-4 mm.

[0016] Preferably, in the apparatus for preparing the cladding mode stripping sample of the double-clad optical fiber, the groove has an outer wall formed by a thermally conductive material; the groove has a pressure foot, and the contact surface between the pressure foot and the optical fiber sample has an elastic solid high-refractive-index medium, with each curve segment having at least one pressure foot.

[0017] According to another aspect of the present invention, a method for preparing a double-clad optical fiber cladding mode stripping sample is provided, comprising the following steps:

[0018] Take the double-clad optical fiber to be tested;

[0019] A section of a predetermined length at the beginning of the double cladding to be tested is taken as the cladding mold removal section. The cladding mold removal section is bent along a predetermined smooth path to form a pre-made test sample.

[0020] The path is divided into multiple segments according to the curve inflection points and the endpoints of the curve and straight line segments, including at least curve segments; the curve segments include positive curvature segments and negative curvature segments, which have opposite bending directions along the fiber axis; adjacent curve segments are arranged alternately with positive curvature segments and negative curvature segments.

[0021] Preferably, in the method for preparing the cladding mode stripping sample of the double-clad optical fiber, the absolute value of the radius of curvature of the curved segment is between 20 and 40 mm, and the included angle between the tangential directions at both ends is less than or equal to 180°.

[0022] The path includes at least a filter mode segment and / or a straight segment whose absolute value of curvature radius is close to the minimum bending radius of the optical fiber, and both ends of the straight segment are connected to positive curvature segments or both are connected to negative curvature segments.

[0023] Preferably, the method for preparing the double-clad fiber cladding mode stripping sample includes the following steps:

[0024] The low-refractive-index coating of the cladding stripping section is removed, so that the glass cladding of the cladding stripping section is covered with a high-refractive-index medium; the high-refractive-index medium preferably has a refractive index of 1.5 or higher; the high-refractive-index medium is: an elastic solid high-refractive-index medium is a highly transparent rubber and / or a liquid high-refractive-index medium;

[0025] In the preferred embodiment, the high refractive index medium is in contact with a thermally conductive material, wherein the thermal conductivity of the thermally conductive material is above 200 W / m·K.

[0026] Preferably, the method for preparing the double-clad fiber cladding mode stripping sample, using the apparatus for preparing the double-clad fiber cladding mode stripping sample provided by the present invention, includes the following steps:

[0027] The cladding mode stripped section of the optical fiber to be tested is fixed in the groove of the preparation device for the cladding mode stripped sample of the double-clad optical fiber;

[0028] In a preferred embodiment, the low-refractive-index coating is removed from the cladding stripping section, exposing the low-refractive-index glass cladding, and it is fixed in a groove at the bottom filled with an elastic solid high-refractive-index medium and / or filled with a liquid high-refractive-index medium, so that the glass cladding of the cladding stripping section is covered with the high-refractive-index medium.

[0029] According to another aspect of the present invention, a testing method for a double-clad optical fiber in cladding mode stripping state is provided, comprising the following steps:

[0030] Preparation of cladding mode stripping sample: The double-clad optical fiber to be tested is prepared into a cladding mode stripping sample according to the preparation method of the double-clad optical fiber cladding mode stripping sample provided by the present invention;

[0031] Optical injection test: Connect the beginning of the cladding mode stripped sample to the test laser, and connect the end of the cladding mode stripped sample to the double-clad fiber test equipment to complete the test optical path construction and perform double-clad fiber test.

[0032] Preferably, the testing method for the cladding mode stripped state of the double-clad fiber includes connecting the beginning end of the cladding mode stripped sample to the test laser by means of fusion splicing or alignment coupling; and coupling the end end of the cladding mode stripped sample to the double-clad fiber testing equipment by means of fusion splicing or alignment coupling.

[0033] Preferably, the testing method for the double-clad fiber under the stripped cladding mode first involves connecting the end of the stripped cladding mode sample to a geometric testing device to confirm that the cladding mode has been completely stripped; then, the end of the stripped cladding mode sample is connected to other double-clad fiber testing devices for further testing; the other double-clad fiber testing devices include, but are not limited to: a geometric dimension meter, a numerical aperture meter, an attenuation spectrum meter, a laser conversion efficiency meter, a beam quality meter, a spot size meter, and a mode meter.

[0034] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0035] The double-clad fiber prefabricated test sample provided by this invention utilizes bends of varying sizes formed in the fiber under test to increase the loss of modes distributed in the fiber cladding, thereby cleanly stripping the cladding mode on the test sample prepared from the fiber under test, rather than at the test device end. Thus, while ensuring the accuracy of the test results, cladding mode stripping and light injection testing are separated into two completely independent steps, executed simultaneously in parallel. This makes the test results more accurate and unaffected by the cladding mode, while also improving the test efficiency.

[0036] Furthermore, the cladding stripping and optical injection testing steps can be time-matched to enable batch, pipelined fiber testing. For example, in double-clad fiber geometry testing, since the testing time is relatively short, time matching can be performed. Multiple test samples can be fabricated in a batch, and the samples fabricated in the batch can be tested sequentially, making the sample fabrication time comparable to the time required for sequential testing of multiple samples. Similarly, in fiber core absorption coefficient testing, since the testing steps are complex and time-consuming, time matching can be performed. Multiple testing platforms can be established, and after fiber samples are fabricated, they can be tested separately on each platform, making the fabrication time of multiple test samples comparable to the total testing time. Time matching avoids downtime, thereby improving efficiency. Time matching can also be performed when performing multiple tests simultaneously, enabling pipelined testing of double-clad fibers and improving overall testing efficiency. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the apparatus for preparing a double-clad optical fiber cladding mode stripping sample provided in Embodiment 1 of the present invention;

[0038] Figure 2 This is the optical path assembly diagram of the double-clad fiber geometric testing system of Embodiment 2 of the present invention;

[0039] Figure 3 This is a core imaging image of the geometric test core of the 50 / 400 double-clad passive matched fiber according to Embodiment 50 of the present invention;

[0040] Figure 4 This is a strength signal-to-noise ratio diagram of the fiber core and cladding in the geometric test of the 50 / 400 double-clad passive matched fiber of the present invention.

[0041] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0042] 1 to 7 are curved segments, 8 is the filter segment, 9 to 15 are pressure feet, 16 is a straight segment, 17 is a groove, 18 is the light source output end, 19 is the beginning of the test fiber sample, 20 is the coating stripping segment of the test fiber sample, 21 is the output fiber segment, and 22 is the test end. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0044] Existing technologies require a cladding mode stripping device at the optical injection end of the testing apparatus, necessitating a fusion splicing connection. After connection, mode stripping must be performed again, meaning the testing and mode stripping steps must be performed sequentially. In other words, a single test requires completing both the cladding mode stripping and optical injection testing steps sequentially, resulting in significant time consumption and low efficiency. To improve testing efficiency, this invention separates the cladding mode stripping and optical injection testing steps, allowing them to be performed independently. This enables the cladding mode stripping and optical injection testing steps to proceed in parallel, thereby improving testing efficiency.

[0045] The apparatus for preparing a double-clad fiber cladding mode stripping sample provided by the present invention includes: a groove bent along a smooth path;

[0046] The path is divided into multiple segments based on the curve inflection points and the endpoints of curve and straight segments, including at least curved segments. Each curved segment includes positive and negative curvature segments, which have opposite bending directions along the fiber optic axis. Adjacent curved segments are arranged alternately with positive and negative curvature segments. This arrangement combines positive and negative curvature in areas with relatively uniform density laterally, resulting in gentler stress changes. This significantly reduces interference at the corners of the geometric structures, thereby reducing compressive stress in the same direction and effectively preventing fiber breakage. The absolute value of the curvature radius of each curved segment is between 20 and 40 mm, and the angle between its two tangential ends is less than or equal to 180°.

[0047] In a preferred embodiment, the curve segments are arranged in ascending order of absolute value of radius of curvature from upstream to downstream along the path, so that the test light passes through the curve segments with smaller absolute value of radius of curvature first, in order to strip away more complex modes transmitted over short distances and to minimize the excitation of higher-order modes in the core layer, while the curve segments with larger absolute value of radius of curvature are used to ensure that cladding modes are completely filtered out.

[0048] The path includes at least one filter mode segment whose absolute value of the radius of curvature is close to the minimum bending radius of the optical fiber, which is the minimum bending radius for normal operation. The absolute value of the radius of curvature of the filter mode segment is within 15mm ± 5mm. This filter mode segment maximally reduces the bending radius of the optical fiber, maximizing the loss of modes distributed in the fiber cladding, while also increasing the loss of higher-order modes. This ensures that the primary transmission mode in the core of the double-clad fiber is the fundamental mode, minimizing or eliminating the influence of higher-order modes during fiber testing, resulting in more accurate results.

[0049] The smooth path also includes a straight segment, both ends of which can be connected to positive curvature segments or negative curvature segments, thereby changing the direction of the optical fiber axis under test, so that the optical fiber under test is coiled in a small area, without breaking or being damaged due to the accumulation of bending stress.

[0050] The bottom of the groove is filled with an elastic solid high-refractive-index medium and / or filled with a liquid high-refractive-index medium; the high-refractive-index medium is an optical transmission medium with a refractive index higher than that of the low-refractive-index glass cladding of the double-clad optical fiber under test; the high-refractive-index medium has a refractive index of 1.5 or higher; the elastic solid high-refractive-index medium is, for example, highly transparent rubber; the liquid high-refractive-index medium is, for example, a refractive index matching liquid.

[0051] When the groove is simultaneously filled with an elastic solid high-refractive-index medium at the bottom and filled with a liquid high-refractive-index medium to form a low-refractive-index glass cladding of the optical fiber under test with a high-refractive-index medium, that is, the bottom is filled with an elastic solid high-refractive-index medium and filled with a liquid high-refractive-index medium. The difference between the height of the elastic solid high-refractive-index medium and the height of the groove sidewall is 2 to 4 mm, so that the test sample of the double-clad optical fiber is in a position that is easy to fix and circumferentially covered with a high-refractive-index medium, avoiding or reducing the risk of breakage caused by lateral bending of the sample when it is pressed down and fixed on the path.

[0052] The groove has an outer wall formed of a thermally conductive material with a thermal conductivity of 200 W / m·K or higher, such as an aluminum heat sink or a copper heat sink.

[0053] The groove has pressure feet for fixing the optical fiber sample under test, and the contact surface between the groove and the optical fiber sample is an elastic solid high-refractive-index medium. Generally, each curve segment has at least one pressure foot.

[0054] This invention provides a method for preparing a cladding mode stripping sample of a double-clad optical fiber, comprising the following steps:

[0055] Take the double-clad optical fiber to be tested;

[0056] A section of a predetermined length at the beginning of the double cladding to be tested is taken as the cladding mold removal section. The cladding mold removal section is bent along a predetermined smooth path to form a pre-made test sample.

[0057] The path is divided into multiple segments based on the curve inflection points and the endpoints of curve and straight segments, including at least curved segments. Each curved segment includes positive and negative curvature segments, which have opposite bending directions along the fiber optic axis. Adjacent curved segments are arranged alternately with positive and negative curvature segments. This arrangement combines positive and negative curvature in areas with relatively uniform density laterally, resulting in gentler stress changes. This significantly reduces interference at the corners of the geometric structures, thereby reducing compressive stress in the same direction and effectively preventing fiber breakage. The absolute value of the curvature radius of each curved segment is between 20 and 40 mm, and the angle between its two tangential ends is less than or equal to 180°.

[0058] The path includes at least one filter mode segment whose absolute value of the radius of curvature is close to the minimum bending radius of the optical fiber, which is the minimum bending radius for normal operation. The absolute value of the radius of curvature of the filter mode segment is within 15mm ± 5mm. This filter mode segment maximally reduces the bending radius of the optical fiber, maximizing the loss of modes distributed in the fiber cladding, while also increasing the loss of higher-order modes. This ensures that the primary transmission mode in the core of the double-clad fiber is the fundamental mode, minimizing or eliminating the influence of higher-order modes during fiber testing, resulting in more accurate results.

[0059] Since this invention requires cladding mode stripping on the test sample rather than on the fixed components of the test instrument, a cladding mode stripping method that is as convenient as possible is needed to save test sample preparation time. Based on experience, bending the optical fiber is the simplest and fastest way to completely remove the cladding mode from the test sample.

[0060] To reduce the area occupied by the test sample, the smoothing path also includes a straight segment. Both ends of the straight segment can be connected to positive curvature segments or negative curvature segments, thereby changing the axial direction of the fiber under test, so that the fiber under test is coiled within a smaller area and does not break or get damaged due to the accumulation of bending stress.

[0061] To further improve the cladding removal efficiency, the low-refractive-index coating of the cladding removal section is removed, allowing the glass cladding of the cladding removal section to be coated with a high-refractive-index medium. This guides the cladding mold from the cladding removal section into the high-refractive-index medium, thus removing the cladding mold. By combining this cladding mold removal principle, the length of the bent cladding mold removal section required for cladding mold attenuation is shortened, thereby reducing the risk of loss and breakage of the test sample due to bending.

[0062] The refractive index difference of the high refractive index medium is preferably above 1.5; the high refractive index medium is: an elastic solid high refractive index medium is a highly transparent rubber and / or a liquid high refractive index medium; the elastic solid high refractive index medium is such as highly transparent rubber, and the liquid high refractive index medium is such as a refractive index matching liquid.

[0063] In the preferred embodiment, the high refractive index medium is in contact with a thermally conductive material, wherein the thermal conductivity of the thermally conductive material is above 200 W / m·K, such as an aluminum heat sink or a copper heat sink.

[0064] The preferred embodiment, using the preparation apparatus for double-clad fiber cladding mode stripping samples provided by the present invention, specifically includes the following steps:

[0065] The cladding mode stripped section of the optical fiber to be tested is fixed in the groove of the preparation device for the cladding mode stripped sample of the double-clad optical fiber;

[0066] In a preferred embodiment, the low-refractive-index coating is removed from the cladding stripping section, exposing the low-refractive-index glass cladding, and it is fixed in a groove at the bottom filled with an elastic solid high-refractive-index medium and / or filled with a liquid high-refractive-index medium, so that the glass cladding of the cladding stripping section is covered with the high-refractive-index medium.

[0067] To further stabilize the optical fiber under test, it is preferable to use the pressure foot of the preparation device for the cladding mode stripping sample of double-clad optical fiber to fix the cladding mode stripped section of the optical fiber under test in the groove of the preparation device.

[0068] The testing method for double-clad optical fiber under cladding mode stripping state provided by the present invention includes the following steps:

[0069] Preparation of cladding mode stripping sample: The double-clad optical fiber to be tested is prepared into a cladding mode stripping sample according to the preparation method of the double-clad optical fiber cladding mode stripping sample provided by the present invention;

[0070] Optical injection test: Connect the beginning of the cladding mode stripped sample to the test laser, and connect the end of the cladding mode stripped sample to the double-clad fiber test equipment to complete the test optical path construction and perform double-clad fiber test;

[0071] The process of connecting the cladding mode stripped sample to the test laser can be carried out by either fusion splicing or alignment coupling. Alignment coupling is preferred as it provides higher connection efficiency. Regardless of whether fusion splicing or alignment coupling is used, there is no need to strip the cladding mode again at the fusion point at the light injection end.

[0072] The process of connecting the cladding mode stripped sample end to the double-clad fiber test equipment can be carried out by fusion splicing or alignment coupling, with alignment coupling being preferred.

[0073] In a preferred embodiment, the end of the cladding mode stripped sample is first connected to a geometric testing device to confirm that the cladding mode has been completely stripped; then, the end of the cladding mode stripped sample is connected to other double-clad fiber testing devices for other double-clad fiber testing; the other double-clad fiber testing devices include, but are not limited to: a geometric dimension tester, a numerical aperture tester, an attenuation spectrum tester, a laser conversion efficiency tester, a beam quality tester, a spot size tester, and a mode tester.

[0074] In a preferred embodiment, multiple cladding stripping samples and / or multiple test platforms are tested in parallel to achieve time matching, ensuring that the preparation step of the cladding stripping sample takes a comparable time to at least one of the multiple test steps sequentially executed in the light injection test step. More preferably, the preparation step of the cladding stripping sample takes a comparable time to all the test steps in the multiple test steps sequentially executed in the light injection test step, achieving pipelined testing.

[0075] The following is an example:

[0076] Example 1

[0077] An apparatus for preparing samples of double-clad optical fiber cladding mode stripping, such as... Figure 1 As shown, it includes a groove 17 that curves along a smooth path;

[0078] The path of groove 17 is as follows Figure 1 As shown, the curve is divided into multiple segments according to its inflection points and the endpoints of the curve and straight line segments, including curve segments 1, 2, 3, 4, 5, 6, 7, filter segment 8, and straight line segment 16, where:

[0079] Curve segments 1, 2, 3, 4, 5, 6, and 7 are all semicircular arcs. Curve segments 1, 4, and 6 are positive curvature segments, while curve segments 2, 3, 5, and 7 are negative curvature segments. The absolute value of the curvature radius of curve segments 1, 2, 3, and 4 is 20–25 mm, and the absolute value of the curvature radius of curve segments 5, 6, and 7 is 38–40 mm.

[0080] The filter module section has an absolute radius of curvature of 15mm, a width of 30mm, a length of at least 70mm, and a U-shape.

[0081] Straight segment 16, with a length of 100mm.

[0082] Smoothly connect curve segments 1 and 2, filter segment, curve segments 3 and 4, straight segment 16, and curve segments 5, 6, and 7 in sequence. Connect two adjacent semi-circular curve segments to form an S-shape.

[0083] The groove depth is 3-4 mm, and the groove bottom width is 1.5-2.5 mm;

[0084] The bottom of the groove 17 is filled with highly transparent silicone rubber with a refractive index greater than that of the outer cladding of the optical fiber to be tested. It cures naturally, and the height difference between the silicone rubber and the side wall of the groove is 2-4 mm. It is used to place the bare optical fiber and to pour in a high refractive index matching liquid to cover the bare optical fiber.

[0085] Pressure feet 9, 10, 11, 12, 15, 14, and 13 are respectively located on curve segments 1, 2, 3, 4, 5, 6, and 7, and are used to fix the optical fiber. The bottom of each pressure foot uses V-shaped high-transparency rubber to contact the optical fiber. The refractive index should be greater than or equal to the refractive index of the optical fiber cladding.

[0086] The groove is the outer wall formed by a copper heat sink.

[0087] Example 2

[0088] This embodiment uses a 50 / 400 double-clad passive matched fiber as an example to illustrate the testing process of double-clad fiber:

[0089] Sample preparation method: Using the sample preparation apparatus for double-clad fiber cladding mode stripping provided in Example 1, fiber optic sample testing is performed, including the following steps:

[0090] Take the double-clad fiber to be tested: Remove the coating layer of a section of fiber 20 from any end of the fiber 20 at a distance of 20cm from the beginning of the fiber to be tested. The length of the stripped section is the total length of the groove along the cladding stripping device. Use a large-diameter fiber cleaver to process the end faces of both ends of the fiber.

[0091] The fiber with the coating stripped is placed into the groove of the preparation device for the double-clad fiber cladding mold stripping sample provided in Example 1, and is smoothly bent along the groove path. The fiber is then fixed with a pressure foot, and a flowing high refractive index matching liquid is used to cover the surface of the bare fiber.

[0092] The geometric testing procedure for 50 / 400 double-clad passive matched fiber is as follows:

[0093] like Figure 2 As shown, one end 19 of the prepared double-clad fiber cladding mode stripped sample is aligned with the light source output end 18 of the test end of the coupled geometric test equipment; the fiber segment 21 output from curve segment 7 is aligned with the test end 22 of the coupled geometric test equipment.

[0094] The results are obtained by processing images using the software of the geometric testing equipment, such as... Figure 3 As shown, the intensity signal is as follows Figure 4 As shown, the higher the signal-to-noise ratio of the fiber core to the cladding, the stronger the fiber core signal that can be detected.

[0095] Depend on Figure 3 , Figure 4 It is known that samples prepared using the double-clad fiber cladding mode stripping sample preparation device can cleanly strip the cladding mode, and the optical transmission mode within the fiber core is the fundamental mode. Since geometric testing can intuitively determine whether the cladding mode stripping is clean and determine the optical transmission mode, samples confirmed by geometric testing can be directly applied to other tests, making it easier to obtain more accurate test results, including: numerical aperture testing, attenuation testing, laser testing, etc.

[0096] Furthermore, the path curve parameters can be adjusted for different test samples and test light sources to ensure that the prepared test samples have their cladding and higher-order modes completely removed and will not re-excite the cladding mode. This enables pipeline scheduling of testing and sample preparation, saves testing time, and is suitable for large-scale testing.

[0097] 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 device for preparing a sample of a cladding mode of a double-clad optical fiber, characterized in that it comprises: include: Grooves that curve along a smooth path; The path is divided into multiple segments according to the curve inflection points and the endpoints of curve and straight line segments, including at least curve segments; The curve segment includes a positive curvature segment and a negative curvature segment, which have opposite bending directions along the fiber axis; adjacent curve segments are arranged alternately with positive curvature segments and negative curvature segments; the curve segments are arranged in ascending order of the absolute value of the radius of curvature from upstream to downstream along the path; The groove is used to fix the cladding stripped section of the optical fiber under test therein.

2. The device for preparing a sample of a double-clad fiber cladding mode according to claim 1, wherein The absolute value of the radius of curvature of the curve segment is between 20 and 40 mm, and the included angle between the tangential directions at both ends is less than or equal to 180°.

3. The device for preparing a sample of a cladding mode of a double- cladding optical fiber according to claim 1, wherein The path includes at least one filter segment whose absolute value of the radius of curvature is close to the minimum bending radius of the optical fiber, wherein the minimum bending radius of the optical fiber is the minimum bending radius for normal operation; the absolute value of the radius of curvature of the filter segment is 15mm ± 5mm.

4. The device for preparing a sample for cladding mode stripping of a double- clad optical fiber according to claim 1, wherein The smooth path also includes straight line segments, both ends of which are connected to positive curvature segments or both are connected to negative curvature segments.

5. The device for preparing a sample for cladding mode stripping of a double- clad optical fiber according to any one of claims 1 to 4, characterized in that The bottom of the groove is filled with an elastic solid high-refractive-index medium and / or filled with a liquid high-refractive-index medium; the high-refractive-index medium is an optical transmission medium with a refractive index higher than that of the low-refractive-index glass cladding of the double-clad optical fiber under test.

6. The apparatus for preparing a double-clad optical fiber cladding mode stripping sample as described in claim 5, characterized in that, The high refractive index medium has a refractive index of 1.5 or higher.

7. The apparatus for preparing a double-clad optical fiber cladding mode stripping sample as described in claim 5, characterized in that, The bottom of the groove is filled with an elastic solid high refractive index medium and a liquid high refractive index medium. The difference between the height of the elastic solid high refractive index medium and the height of the groove sidewall is 2~4mm.

8. The apparatus for preparing a double-clad optical fiber cladding mode stripping sample as described in claim 5, characterized in that, The groove has an outer wall formed of thermally conductive material; the groove has a pressure foot, the contact surface of which with the optical fiber sample has an elastic solid high refractive index medium, and each curve segment has at least one pressure foot.

9. A testing method for double-clad optical fiber under cladding mode stripping condition, characterized in that, Includes the following steps: Preparation of cladding mode stripping samples: The double-clad optical fiber to be tested is prepared with cladding mode stripping samples according to the following method: Take the double-clad optical fiber to be tested; A section of a predetermined length at the beginning of the double cladding to be tested is taken as the cladding mold removal section. The cladding mold removal section is bent along a predetermined smooth path to form a pre-made test sample. The path is divided into multiple segments according to the curve inflection points and the endpoints of curve and straight line segments, including at least curve segments; the curve segments include positive curvature segments and negative curvature segments, which have opposite bending directions along the fiber axis; adjacent curve segments are arranged in alternating positive and negative curvature segments; The method for preparing a double-clad fiber cladding mode stripping sample utilizes a device for preparing a double-clad fiber cladding mode stripping sample, which includes a groove bent along a smooth path. The path is divided into multiple segments according to the curve inflection points and the endpoints of curve and straight line segments, including at least curve segments; the curve segments include positive curvature segments and negative curvature segments, which have opposite bending directions along the fiber axis; adjacent curve segments are arranged in alternating positive and negative curvature segments; The curve segments are arranged in ascending order of the absolute value of their radius of curvature from upstream to downstream along the path; Optical injection test: Connect the beginning of the cladding mode stripped sample to the test laser, and connect the end of the cladding mode stripped sample to the double-clad fiber test equipment to complete the test optical path construction and perform double-clad fiber test; The preparation of the cladding stripping sample and the pipeline scheduling of the light injection testing steps are described.

10. The test method for double-clad optical fiber under cladding mode stripping state as described in claim 9, characterized in that, The process involves connecting the beginning of the cladding mode stripped sample to the test laser using fusion splicing or alignment coupling; and connecting the end of the cladding mode stripped sample to the double-clad fiber test equipment using fusion splicing or alignment coupling.

11. The test method for double-clad optical fiber in cladding mode stripping state as described in claim 9, characterized in that, First, the end of the cladding mode stripped sample is connected to a geometric testing device to confirm that the cladding mode has been completely stripped. Then, the end of the cladding mode stripped sample is connected to other double-clad fiber testing devices for other double-clad fiber tests. The other double-clad fiber testing devices include, but are not limited to: geometric dimension testers, numerical aperture testers, attenuation spectrum testers, laser conversion efficiency testers, beam quality testers, spot size testers, and mode testers.

12. The test method for double-clad optical fiber under cladding mode stripping state as described in claim 9, characterized in that, The absolute value of the radius of curvature of the curve segment is between 20 and 40 mm, and the included angle between the tangential directions at both ends is less than or equal to 180°. The path includes at least a filter mode segment and / or a straight segment whose absolute value of curvature radius is close to the minimum bending radius of the optical fiber, and both ends of the straight segment are connected to positive curvature segments or both are connected to negative curvature segments.

13. The test method for double-clad optical fiber in cladding mode stripping state as described in claim 9, characterized in that, Includes the following steps: The low-refractive-index coating of the cladding stripping section is removed, so that the glass cladding of the cladding stripping section is covered with a high-refractive-index medium.

14. The test method for double-clad optical fiber in cladding mode stripping state as described in claim 13, characterized in that, The high refractive index medium has a refractive index of 1.5 or higher; the high refractive index medium is: an elastic solid high refractive index medium is a highly transparent rubber and / or a liquid high refractive index medium.

15. The test method for double-clad optical fiber in cladding mode stripping state as described in claim 14, characterized in that, The high refractive index medium is in contact with the thermally conductive material, and the thermally conductive material has a thermal conductivity of 200 W / m·K or higher.

16. The test method for double-clad optical fiber in cladding mode stripping state as described in claim 9, characterized in that, The absolute value of the radius of curvature of the curve segment is between 20 and 40 mm, and the included angle between the tangential directions at both ends is less than or equal to 180°.

17. The test method for double-clad optical fiber in cladding mode stripping state as described in claim 9, characterized in that, The path includes at least one filter segment whose absolute value of the radius of curvature is close to the minimum bending radius of the optical fiber, wherein the minimum bending radius of the optical fiber is the minimum bending radius for normal operation; the absolute value of the radius of curvature of the filter segment is 15mm ± 5mm.

18. The test method for double-clad optical fiber in cladding mode stripping state as described in claim 9, characterized in that, The smooth path also includes straight line segments, both ends of which are connected to positive curvature segments or both are connected to negative curvature segments.

19. The test method for double-clad optical fiber under cladding mode stripping state as described in any one of claims 9 to 18, characterized in that, The bottom of the groove is filled with an elastic solid high-refractive-index medium and / or filled with a liquid high-refractive-index medium; the high-refractive-index medium is an optical transmission medium with a refractive index higher than that of the low-refractive-index glass cladding of the double-clad optical fiber under test.

20. The test method for double-clad optical fiber in cladding mode stripping state as described in claim 19, characterized in that, The high refractive index medium has a refractive index of 1.5 or higher.

21. The test method for double-clad optical fiber in cladding mode stripping state as described in claim 19, characterized in that, The bottom of the groove is filled with an elastic solid high refractive index medium and a liquid high refractive index medium. The difference between the height of the elastic solid high refractive index medium and the height of the groove sidewall is 2~4mm.

22. The test method for double-clad optical fiber in cladding mode stripping state as described in claim 19, characterized in that, The groove has an outer wall formed of thermally conductive material; the groove has a pressure foot, the contact surface of which with the optical fiber sample has an elastic solid high refractive index medium, and each curve segment has at least one pressure foot.

23. The test method for double-clad optical fiber in cladding mode stripping state as described in claim 19, characterized in that, The preparation of the cladding stripping sample includes the following steps: The cladding mode stripped section of the optical fiber to be tested is fixed in the groove of the preparation device for the cladding mode stripped sample of the double-clad optical fiber.

24. The test method for double-clad optical fiber in cladding mode stripping state as described in claim 23, characterized in that, The low-refractive-index coating is removed from the cladding stripping section, exposing the low-refractive-index glass cladding, and it is fixed in a groove at the bottom filled with an elastic solid high-refractive-index medium and / or filled with a liquid high-refractive-index medium, so that the glass cladding of the cladding stripping section is covered with the high-refractive-index medium.

25. A method for preparing a double-clad optical fiber cladding mode stripping sample, characterized in that, Using the apparatus for preparing double-clad fiber cladding mode stripping samples as described in any one of claims 1 to 8, Includes the following steps: Includes the following steps: The cladding mode stripped section of the optical fiber to be tested is fixed in the groove of the preparation device for the cladding mode stripped sample of the double-clad optical fiber.

26. The method for preparing a double-clad optical fiber cladding mode stripping sample as described in claim 25, characterized in that, The low-refractive-index coating is removed from the cladding stripping section, exposing the low-refractive-index glass cladding, and it is fixed in a groove at the bottom filled with an elastic solid high-refractive-index medium and / or filled with a liquid high-refractive-index medium, so that the glass cladding of the cladding stripping section is covered with the high-refractive-index medium.

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