Method for testing absorption coefficient of fiber core of high-doping-concentration double-cladding erbium-doped optical fiber
By setting cladding light filtering modules and low-loss fusion splice protection at both ends of high-doped double-clad erbium-doped fiber, the problem of difficult stripping and oil immersion operations of short-size fiber is solved, and the core signal and cladding light are effectively separated, improving test accuracy and system stability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-12
- Publication Date
- 2026-03-13
AI Technical Summary
Existing technologies make it difficult to accurately measure the core absorption coefficient of highly doped double-clad erbium-doped fibers. The stripping and oiling process is also difficult, leading to fiber damage, cladding light leakage, and signal interference, which affects test accuracy and repeatability.
An input cladding light filtering module and an output cladding light filtering module are respectively installed at both ends of the optical fiber under test. A U-shaped structure is formed by high refractive index glue to filter out the cladding light. Combined with low-loss fusion splicing and splice protection, the fiber core signal and cladding light are effectively separated.
It improves testing accuracy and system stability, reduces insertion loss and return reflection, and is suitable for accurate measurement of short-size double-clad optical fibers.
Smart Images
Figure CN121655836A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for testing the absorption coefficient of a high-doped double-clad erbium-doped fiber core, belonging to the field of fiber laser technology. Background Technology
[0002] As the core gain medium for high-power fiber lasers and amplifiers, the accurate measurement of the core absorption coefficient of double-clad erbium-doped fiber is crucial for device design and performance optimization. With the continuous increase in laser output power demands, high doping concentration has become a key approach to achieving high gain density and compact cavity structures. However, high doping concentration leads to a significant increase in the absorption coefficient per unit length of the fiber, drastically reducing the fiber length required for testing, typically to the centimeter level.
[0003] In existing testing methods, cladding mode removal is often performed by stripping and oil immersion in double-clad rare-earth-doped fibers to accurately obtain the core absorption characteristics. However, when the fiber under test is too short, performing stripping and oil immersion on the fiber itself presents significant difficulties: on the one hand, insufficient operating space can easily lead to fiber damage or breakage; on the other hand, the oil immersion area is difficult to control precisely, easily introducing additional cladding light leakage or core signal interference, severely affecting test accuracy and repeatability. Furthermore, the cladding modes present in double-clad fibers can interfere with the measurement of transmitted light signals; if not effectively filtered out, the measured core absorption coefficient will deviate from the true value. Therefore, there is an urgent need to develop a core absorption coefficient testing method suitable for high-doping-concentration double-clad erbium-doped fibers to solve the cladding light filtering problem and improve the accuracy and operability of the test. Summary of the Invention
[0004] The technical problem to be solved by the present invention is to provide a test method for the absorption coefficient of the core of a high-doped double-clad erbium-doped optical fiber, which solves the problem that short-sized double-clad optical fibers under test cannot be directly stripped and immersed in oil for testing. This method achieves effective separation of the core signal and the cladding light, reduces the interference of the cladding mode on the core transmitted light, and improves the test accuracy.
[0005] The technical solution adopted by this invention to solve the above problems is as follows: a method for testing the absorption coefficient of a high-doped double-clad erbium-doped optical fiber core, comprising the following steps: Step 1: Prepare the first matching passive optical fiber, perform end face treatment on both ends of the first matching passive optical fiber, and connect one end of the treated first matching passive optical fiber to the output end of the light source. Step 2: Prepare the double-clad erbium-doped fiber to be tested, and perform end-face treatment on both ends of the double-clad erbium-doped fiber to be tested to form a double-clad erbium-doped fiber with an initial length of L1. Step 3: Construct the input cladding light filtering module. The first matched passive fiber is equipped with the input cladding light filtering module. Step 4: First fusion splice operation. The other end of the processed first matching passive fiber is clamped in the left clamp of the fusion splicer, and the other end of the processed double-clad erbium-doped fiber to be tested is clamped in the right clamp of the fusion splicer. The two are arranged coaxially and fused together to form the first fusion splice. The input cladding light filtering module is placed near the first fusion splice. Step 5: Protect the first fusion splice. Take out the first matched passive optical fiber and the double-clad erbium-doped optical fiber to be tested, which are fused together, and place the first fusion splice on the protective sheet. Apply low refractive index adhesive evenly around the first fusion splice to form a protective layer. Step 6: Prepare the second matched passive optical fiber and construct the output cladding light filtering module. Perform end face processing on both ends of the second matched passive optical fiber. After processing, one end of the second matched passive optical fiber is connected to the input end of the optical signal receiving device. The output cladding light filtering module is provided on the second matched passive optical fiber and is located close to the optical signal receiving device. Step 7: Second fusion splice operation. The other end of the processed second matching passive fiber is clamped in the left clamp of the fusion splicer, and the other end of the processed double-clad erbium-doped fiber to be tested is clamped in the right clamp of the fusion splicer. The two are arranged coaxially and fused together to form the second fusion splice. Step 8: Protect the second fusion splice. Take out the second matched passive optical fiber and the double-clad erbium-doped optical fiber to be tested, which are fused together, and place the second fusion splice on the protective sheet. Apply low refractive index adhesive evenly around the second fusion splice to form a protective layer. Step 9: Measure the transmitted light power of the double-clad erbium-doped fiber of length L1. Turn on the light source, set the output wavelength, and after the output power stabilizes, record the transmitted light power P1 displayed by the optical signal receiving device. Step 10: Cut the double-clad erbium-doped fiber under test, turn off the light source, disconnect the second fusion splice, cut the double-clad erbium-doped fiber under test to a length of L2, and process the new end face of the cut double-clad erbium-doped fiber under test and the end face of the second matching passive fiber connection end. Step 11: Measure and process the transmitted light power of the double-clad erbium-doped fiber of length L2. Re-fuse the processed double-clad erbium-doped fiber of length L2 with the second matching passive fiber to form a new second fusion point. Turn on the light source again and record the new transmitted light power P2 displayed by the optical power meter after the output stabilizes. Obtain the core absorption coefficient value of the double-clad erbium-doped fiber of length L2 using the absorption coefficient calculation formula α = (P2 - P1) / (L1 - L2).
[0006] The first matched passive optical fiber input end is connected to the light source output end through the first FC interface, and the second matched passive optical fiber output end is connected to the optical signal receiving device through the second FC interface.
[0007] The core-cladding dimensions of the first and second matched passive optical fibers are matched with the dimensions of the double-clad erbium-doped optical fiber under test.
[0008] The light source is a tunable laser or a semiconductor laser source, and the optical signal receiving device is an optical power meter.
[0009] The protective sheet has an adhesive groove at the center of its top surface, and symmetrical slots on both sides of the adhesive groove, which are connected to the adhesive groove. A heating element is provided at the bottom of the protective sheet.
[0010] In step three, a portion of the coating layer on the first matched passive fiber is stripped to expose the bare fiber cladding. The bare fiber cladding is then bent into a U-shaped structure. The stripped section is uniformly coated with high-refractive-index adhesive, extending to the coating layer boundary. After curing, an input cladding light filtering module is formed. In step six, a portion of the coating layer on the second matched passive fiber is stripped to expose the bare fiber cladding. The bare fiber cladding is then bent into a U-shaped structure. The stripped section is uniformly coated with high-refractive-index adhesive, extending to the coating layer boundary. After curing, an output cladding light filtering module is formed.
[0011] The high-refractive-index adhesive has a refractive index >1.50, and the low-refractive-index adhesive has a refractive index <1.46.
[0012] The input cladding light filtering module in step three and the output cladding light filtering module in step six are both cladding mode power filters, which are respectively fused to the first matched passive optical fiber and the second matched passive optical fiber.
[0013] Compared with existing technologies, the advantages of this invention are as follows: A method for testing the absorption coefficient of the core of a high-doped double-clad erbium-doped fiber includes: 1. A prefabricated input cladding light filtering module on a first matched passive fiber and a prefabricated output cladding light filtering module on a second matched passive fiber. These modules are located at both ends of the double-clad erbium-doped fiber under test, filtering out cladding light and eliminating interference from the cladding mode to the transmitted light from the core. This effectively solves the problem that short-sized double-clad erbium-doped fibers cannot be directly stripped and oiled, achieving effective separation of the core signal and cladding light, and improving test accuracy. 2. Low-loss fusion splicing and splice protection technology reduces insertion loss and return reflection in the optical path, improving the stability and repeatability of the test system. 3. This application is not only applicable to double-clad erbium-doped active fibers but can also be extended to the absorption coefficient testing of other types of double-clad rare-earth-doped fibers, exhibiting good versatility and scalability. Attached Figure Description
[0014] Figure 1 This is a schematic diagram of a testing device used in an embodiment of the present invention for testing the absorption coefficient of a high-doped double-clad erbium-doped optical fiber core; Figure 2This is a schematic diagram of the protective film; In the figure, 1 is the light source, 2 is the first FC interface, 3 is the first matching passive fiber, 4 is the input cladding light filtering module, 5 is the first fusion splice, 6 is the double-clad erbium-doped fiber under test, 7 is the second fusion splice, 8 is the second matching passive fiber, 9 is the output cladding light filtering module, 10 is the second FC interface, 11 is the optical signal receiving device, 12 is the protective sheet, 12.1 is the glue coating groove, 12.2 is the card slot, and 13 is the heating element. Detailed Implementation
[0015] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.
[0016] like Figure 1 As shown, this embodiment of the high-doping-concentration double-clad erbium-doped fiber core absorption coefficient testing device includes a first matched passive fiber 3 and a second matched passive fiber 8. The output end of the light source 1 is connected to one end of the first matched passive fiber 3 via a first FC interface 2. The other end of the first matched passive fiber 3 is fused to one end of the double-clad erbium-doped fiber 6 under test, forming a first fusion point 5. An input cladding light filtering module 4 is provided on the first matched passive fiber adjacent to the first fusion point 5. The other end of the double-clad erbium-doped fiber 6 under test is fused to one end of the second matched passive fiber 8, forming a second fusion point 7. The other end of the second matched passive fiber is connected to an optical signal receiving device 11 via a second FC interface 10. An output cladding light filtering module 9 is provided on the second matched passive fiber adjacent to the second FC interface. Protective layers are provided on the first fusion point 5 and the second fusion point 7. Example 1
[0017] A method for testing the absorption coefficient of the core of a highly doped double-clad erbium-doped optical fiber includes the following steps: Step 1: Prepare the first matching passive fiber. The size of the first matching passive fiber should be the same as the core cladding size of the double-clad erbium-doped fiber to be tested. Use a fiber cleaver to precisely cut both ends of the first matching passive fiber, ensuring the cut surfaces are flat, clean, and perpendicular to the fiber axis, with an end-face angle of less than 0.5°. Connect one end of the processed first matching passive fiber to the output of the tunable laser via the first FC interface.
[0018] Step 2: Prepare the double-clad erbium-doped fiber to be tested. Perform end-face treatment on both ends of the double-clad erbium-doped fiber to be tested, ensuring that the cut surfaces meet the same flatness and perpendicularity requirements. Use a precision ruler to measure and cut the fiber to form a double-clad erbium-doped fiber with an initial length of L1.
[0019] Step 3: Construction of the input cladding optical filtering module. Using fiber strippers, the coating on the first matched passive fiber is stripped to a length of 7 cm, exposing the bare fiber cladding. The bare fiber cladding is then bent into a U-shape, and a high-refractive-index adhesive (refractive index > 1.50) is uniformly applied to this area. The high-refractive-index adhesive completely covers the stripped section and extends to the coating boundary. Subsequently, it is cured under UV irradiation at 25 °C for 20 minutes on a temperature-controlled stage to form a stable input cladding optical filtering module. The input cladding optical filtering module utilizes bending loss and the extraction effect of the high-refractive-index medium to effectively leak and dissipate the fiber cladding mode.
[0020] Step 4: First fusion splice operation. The other end of the processed first matched passive fiber is clamped in the left clamp of the fusion splicer, and the other end of the processed double-clad erbium-doped fiber under test is clamped in the right clamp of the fusion splicer. Both are aligned axially. The fusion parameters are selected and fusion is performed to form the first fusion splice. The cladding optical filtering module is then positioned close to the first fusion splice. After fusion, the fusion splicer estimates the loss at the first fusion splice to be less than 0.01 dB.
[0021] Step 5: Protect the first fusion splice. Take the first matched passive optical fiber and the double-clad erbium-doped optical fiber to be tested, which are fused together, out of the fusion splicer and place the first fusion splice on the protective sheet 12. Apply low refractive index adhesive (refractive index <1.46) evenly around the first fusion splice to ensure that the low refractive index adhesive completely covers the first fusion splice without air bubbles, forming a protective layer.
[0022] like Figure 2 As shown, a coating groove 12.1 is formed on the top surface of the protective sheet 12, located at the center of the protective sheet. Slots 12.2 are symmetrically formed on both sides of the coating groove, communicating with it. A heating element 13 is provided at the bottom of the protective sheet. The first matching passive optical fiber and the double-clad erbium-doped optical fiber to be tested are respectively placed in the slots, and the first splice is placed in the coating groove. Low-refractive-index adhesive is dripped into the coating groove using a micro-syringe, ensuring that the adhesive completely covers the splice without air bubbles. Then, the heating element is activated, and the heating temperature is set to 45 ℃ for 5 minutes to accelerate adhesive curing.
[0023] Step Six: Prepare the second matching passive fiber and construct the output cladding optical filter module. The second matching passive fiber should have the same core-cladding size as the double-clad erbium-doped fiber under test. Use a fiber cleaver to precisely cut both ends of the second matching passive fiber, ensuring the cut surfaces are flat, clean, and perpendicular to the fiber axis with an end-face angle of less than 0.5°. Use fiber strippers to remove the coating from the second matching passive fiber, removing a 7 cm length to expose the bare fiber cladding. Bend the bare fiber cladding into a U-shape and uniformly apply high-refractive-index adhesive (refractive index > 1.50) to this area, ensuring the adhesive completely covers the stripped section and extends to the coating boundary. Then, cure the adhesive on a temperature-controlled platform at 25 °C for 20 minutes under UV irradiation to form a stable output cladding optical filter module. One end of the second matching passive fiber with the output cladding optical filter module is connected to the input of the optical power meter via a second FC interface.
[0024] Step 7: Second fusion splice operation. The other end of the processed second matching passive fiber is clamped in the left clamp of the fusion splicer, and the other end of the processed double-clad erbium-doped fiber to be tested is clamped in the right clamp of the fusion splicer. The two are arranged axially and fused using the same splicing parameters as in Step 4 to form the second fusion splice. After the fusion is completed, the fusion splicer estimates that the loss of the second fusion splice is less than 0.01 dB.
[0025] Step 8: Protect the second fusion splice. Remove the second matched passive fiber and the double-clad erbium-doped fiber to be tested from the fusion splicer and place the second fusion splice on the protective sheet. Apply low refractive index adhesive (refractive index <1.46) evenly around the second fusion splice to ensure that the low refractive index adhesive completely covers the second fusion splice without air bubbles, forming a protective layer.
[0026] The second matching passive fiber and the erbium-doped double-clad fiber under test were placed in the slots, and the second splice was placed in the adhesive coating tank. Low-refractive-index adhesive was dripped into the coating tank using a micro-syringe, ensuring the adhesive completely covered the splice without air bubbles. Then, the heating element was activated, and the heating temperature was set to 45 °C for 5 minutes to accelerate adhesive curing.
[0027] Step 9: Measure the transmitted light power of the double-clad erbium-doped fiber of length L1. Turn on the tunable laser and set the output wavelength to 1535 nm (typical absorption peak of erbium-doped fiber). After the output power stabilizes (about 2 minutes), record the transmitted light power value P1 displayed by the optical power meter.
[0028] Step 10: Shorten the double-clad erbium-doped fiber under test. Turn off the tunable laser, disconnect the second fusion splice, and use a large-core fiber cleaver to shorten the double-clad erbium-doped fiber to a length of L2 (e.g., 5.0 cm). Process the new end face of the shortened double-clad erbium-doped fiber; simultaneously, clean or reprocess the end face of the second matching passive fiber connection to ensure consistent optical coupling efficiency.
[0029] Step 11: Measure and process the transmitted light power of the double-clad erbium-doped fiber of length L2. Re-fuse the processed L2-length double-clad erbium-doped fiber with the second matching passive fiber to form a new second splice point. Turn on the tunable laser again (wavelength still 1535 nm). After the output stabilizes, record the new transmitted light power P2 displayed on the optical power meter. Using the absorption coefficient calculation formula α = (P2 - P1) / L, where L is L1 - L2 in meters, obtain the core absorption coefficient value of the double-clad erbium-doped fiber. When L1 is 0.10 m, L2 is 0.05 m, P1 is measured to be -41.35 dBm, and P2 is measured to be -35.38 dBm. The calculated core absorption coefficient of the double-clad erbium-doped fiber at 1535 nm is approximately 115.4 dB / m. Example 2
[0030] A method for testing the absorption coefficient of the core of a highly doped double-clad erbium-doped optical fiber includes the following steps: Step 1: Prepare the first matching passive fiber. The size of the first matching passive fiber should be the same as the core-cladding size of the double-clad erbium-doped fiber to be tested. Use a fiber cleaver to precisely cut both ends of the first matching passive fiber, ensuring the cut surfaces are flat, clean, and perpendicular to the fiber axis, with an end-face angle of less than 0.5°. Connect one end of the processed first matching passive fiber to the output of the semiconductor laser source via the first FC interface.
[0031] Step 2: Prepare the double-clad erbium-doped fiber to be tested. Perform end-face treatment on both ends of the double-clad erbium-doped fiber to be tested, ensuring that the cut surfaces meet the same flatness and perpendicularity requirements. Use a precision ruler to measure and cut the fiber to form a double-clad erbium-doped fiber with an initial length of L1.
[0032] Step 3: Construction of the input cladding optical filtering module. End face treatment is performed on both ends of a cladding mode power filter (CPS). The other end of the treated first matching passive fiber is clamped in the left clamp of the fusion splicer. The input end of the treated cladding mode power filter is clamped in the right clamp of the fusion splicer. A fusion splicing operation is performed, fusing the cladding mode power filter onto the first matching passive fiber, forming a stable input cladding optical filtering module that effectively leaks and dissipates the input cladding mode. Then, the fusion splicer clamps are removed.
[0033] Step 4: First fusion splice operation. The output end of the processed cladding mode power filter is clamped in the left clamp of the fusion splicer, and one end of the processed double-clad erbium-doped fiber under test is clamped in the right clamp of the fusion splicer. Both are aligned axially. The fusion parameters are selected and fusion is performed to form the first fusion splice. The input cladding optical filter module is placed near the first fusion splice. After fusion, the fusion splicer estimates the loss at the first fusion splice to be less than 0.01 dB.
[0034] Step 5: Protect the first fusion splice. Take the first matched passive optical fiber and the double-clad erbium-doped optical fiber to be tested, which are fused together, out of the fusion splicer and place the first fusion splice on the protective sheet. Apply low refractive index adhesive (refractive index <1.46) evenly around the first fusion splice to ensure that the low refractive index adhesive completely covers the first fusion splice without air bubbles, forming a protective layer.
[0035] like Figure 2 As shown, a coating groove is formed on the top surface of the protective sheet, located at the center of the sheet. Symmetrical slots are formed on both sides of the coating groove, communicating with it. A heating element is located at the bottom of the protective sheet. The first matching passive optical fiber and the erbium-doped double-clad optical fiber under test are placed in the slots, with the first splice positioned in the coating groove. Low-refractive-index adhesive is dripped into the coating groove using a micro-syringe, ensuring the adhesive completely coats the splice without air bubbles. The heating element is then activated, and the heating temperature is set to 45°C for 5 minutes to accelerate adhesive curing.
[0036] Step Six: Prepare the second matching passive fiber and construct the output cladding optical filtering module. The second matching passive fiber should have the same core-cladding size as the double-clad erbium-doped fiber under test. Precision cut both ends of the second matching passive fiber using a fiber cleaver, ensuring the cut surfaces are flat, clean, and perpendicular to the fiber axis with an end-face angle less than 0.5°. After processing, clamp one end of the second matching passive fiber in the left clamp of the fusion splicer. Process the end faces of the other cladding mode power filter (CPS). After processing, clamp the input end of the CPS in the right clamp of the fusion splicer and perform the fusion splicing operation, fusing the other CPS onto the second matching passive fiber to form a stable output cladding optical filtering module, effectively leaking and dissipating the output cladding mode. Connect one end of the second matching passive fiber with the output cladding optical filtering module to the input of the optical power meter via the second FC interface. Then, remove it from the fusion splicer clamp.
[0037] Step 7: Second fusion splice operation. The other end of the processed second matching passive fiber is clamped in the left clamp of the fusion splicer, and the other end of the processed double-clad erbium-doped fiber to be tested is clamped in the right clamp of the fusion splicer. The two are arranged axially and fused using the same splicing parameters as in Step 4 to form the second fusion splice. After the fusion is completed, the fusion splicer estimates that the loss of the second fusion splice is less than 0.01 dB.
[0038] Step 8: Protect the second fusion splice. Remove the second matched passive fiber and the double-clad erbium-doped fiber to be tested from the fusion splicer and place the second fusion splice on the protective sheet. Apply low refractive index adhesive (refractive index <1.46) evenly around the second fusion splice to ensure that the low refractive index adhesive completely covers the second fusion splice without air bubbles, forming a protective layer.
[0039] The second matching passive fiber and the erbium-doped double-clad fiber under test were placed in the slots, and the second splice was placed in the adhesive coating tank. Low-refractive-index adhesive was dripped into the coating tank using a micro-syringe, ensuring the adhesive completely covered the splice without air bubbles. Then, the heating element was activated, and the heating temperature was set to 45 °C for 5 minutes to accelerate adhesive curing.
[0040] Step 9: Measure the transmitted light power of the double-clad erbium-doped fiber of length L1. Turn on the semiconductor laser source and set the output wavelength to 1535 nm (typical absorption peak of erbium-doped fiber). After the output power stabilizes (about 2 minutes), record the transmitted light power value P1 displayed by the optical power meter.
[0041] Step 10: Shorten the double-clad erbium-doped fiber under test, turn off the semiconductor laser source, disconnect the second fusion splice, and shorten the double-clad erbium-doped fiber under test to a length of L2 (e.g., 5.0 cm). Use a large-core fiber cleaver to process the new end face of the shortened double-clad erbium-doped fiber under test. At the same time, clean or reprocess the end face of the second matching passive fiber connection end to ensure consistent optical coupling efficiency.
[0042] Step 11: Measure and process the transmitted light power of the double-clad erbium-doped fiber of length L2. Re-fuse the processed L2-length double-clad erbium-doped fiber with the second matching passive fiber to form a new second splice point. Re-activate the semiconductor laser source (wavelength still 1535 nm). After the output stabilizes, record the new transmitted light power P2 displayed on the optical power meter. Using the absorption coefficient calculation formula α = (P2 - P1) / L, where L is L1 - L2 in meters, obtain the core absorption coefficient value of the double-clad erbium-doped fiber. When L1 is 0.10 m, L2 is 0.05 m, P1 is measured to be -41.35 dBm, and P2 is measured to be -35.38 dBm. The calculated core absorption coefficient of the double-clad erbium-doped fiber at 1535 nm is approximately 115.4 dB / m.
[0043] 1. An input cladding light filtering module and an output cladding light filtering module are prefabricated on the first and second matched passive optical fibers, respectively. The input and output cladding light filtering modules are located at both ends of the double-clad erbium-doped fiber under test. They have the function of filtering out cladding light and eliminating the interference of the cladding mode on the transmitted light of the fiber core. This effectively solves the problem that short-size double-clad erbium-doped fibers cannot be directly stripped and impregnated with oil, and achieves effective separation of the fiber core signal and cladding light, thereby improving the accuracy of the test.
[0044] 2. Low-loss fusion splicing and splice protection technology reduces insertion loss and return reflection in the optical path, improving the stability and repeatability of the test system.
[0045] 3. This application is not only applicable to double-clad erbium-doped active optical fibers, but can also be extended to the absorption coefficient testing of other types of double-clad rare-earth-doped optical fibers, and has good versatility and scalability.
[0046] In addition to the above embodiments, the present invention also includes other embodiments. All technical solutions formed by equivalent transformation or equivalent substitution should fall within the protection scope of the claims of the present invention.
Claims
1. A method for testing the absorption coefficient of the core of a highly doped double-clad erbium-doped optical fiber, characterized in that: Includes the following steps: Step 1: Prepare the first matching passive optical fiber, perform end face treatment on both ends of the first matching passive optical fiber, and connect one end of the treated first matching passive optical fiber to the output end of the light source. Step 2: Prepare the double-clad erbium-doped fiber to be tested, and perform end-face treatment on both ends of the double-clad erbium-doped fiber to be tested to form a double-clad erbium-doped fiber with an initial length of L1. Step 3: Construct the input cladding light filtering module. The first matched passive fiber is equipped with the input cladding light filtering module. Step 4: First fusion splice operation. The other end of the processed first matching passive fiber is clamped in the left clamp of the fusion splicer, and the other end of the processed double-clad erbium-doped fiber to be tested is clamped in the right clamp of the fusion splicer. The two are arranged coaxially and fused together to form the first fusion splice. The input cladding light filtering module is placed near the first fusion splice. Step 5: Protect the first fusion splice. Take out the first matched passive optical fiber and the double-clad erbium-doped optical fiber to be tested, which are fused together, and place the first fusion splice on the protective sheet. Apply low refractive index adhesive evenly around the first fusion splice to form a protective layer. Step 6: Prepare the second matched passive optical fiber and construct the output cladding light filtering module. Perform end face processing on both ends of the second matched passive optical fiber. After processing, one end of the second matched passive optical fiber is connected to the input end of the optical signal receiving device. The output cladding light filtering module is provided on the second matched passive optical fiber and is located close to the optical signal receiving device. Step 7: Second fusion splice operation. The other end of the processed second matching passive fiber is clamped in the left clamp of the fusion splicer, and the other end of the processed double-clad erbium-doped fiber to be tested is clamped in the right clamp of the fusion splicer. The two are arranged coaxially and fused together to form the second fusion splice. Step 8: Protect the second fusion splice. Take out the second matched passive optical fiber and the double-clad erbium-doped optical fiber to be tested, which are fused together, and place the second fusion splice on the protective sheet. Apply low refractive index adhesive evenly around the second fusion splice to form a protective layer. Step 9: Measure the transmitted light power of the double-clad erbium-doped fiber of length L1. Turn on the light source, set the output wavelength, and after the output power stabilizes, record the transmitted light power P1 displayed by the optical signal receiving device. Step 10: Cut the double-clad erbium-doped fiber under test, turn off the light source, disconnect the second fusion splice, cut the double-clad erbium-doped fiber under test to a length of L2, and process the new end face of the cut double-clad erbium-doped fiber under test and the end face of the second matching passive fiber connection end. Step 11: Measure and process the transmitted light power of the double-clad erbium-doped fiber of length L2. Re-fuse the processed double-clad erbium-doped fiber of length L2 with the second matching passive fiber to form a new second fusion point. Turn on the light source again and record the new transmitted light power P2 displayed by the optical power meter after the output stabilizes. Obtain the core absorption coefficient value of the double-clad erbium-doped fiber of length L2 using the absorption coefficient calculation formula α = (P2 - P1) / (L1 - L2).
2. The method for testing the absorption coefficient of a high-doped double-clad erbium-doped optical fiber core according to claim 1, characterized in that: The first matched passive optical fiber input end is connected to the light source output end through the first FC interface, and the second matched passive optical fiber output end is connected to the optical signal receiving device through the second FC interface.
3. The method for testing the absorption coefficient of a high-doped double-clad erbium-doped optical fiber core according to claim 1, characterized in that: The core-cladding dimensions of the first and second matched passive optical fibers are matched with the dimensions of the double-clad erbium-doped optical fiber under test.
4. The method for testing the absorption coefficient of a high-doped double-clad erbium-doped optical fiber core according to claim 1, characterized in that: The light source is a tunable laser or a semiconductor laser source, and the optical signal receiving device is an optical power meter.
5. The method for testing the absorption coefficient of a high-doped double-clad erbium-doped optical fiber core according to claim 1, characterized in that: The protective sheet has an adhesive groove at the center of its top surface, and symmetrical slots on both sides of the adhesive groove, which are connected to the adhesive groove. A heating element is provided at the bottom of the protective sheet.
6. The method for testing the absorption coefficient of a high-doped double-clad erbium-doped optical fiber core according to claim 1, characterized in that: In step three, a portion of the coating layer on the first matched passive fiber is stripped to expose the bare fiber cladding. The bare fiber cladding is then bent into a U-shaped structure. The stripped section is uniformly coated with high-refractive-index adhesive, extending to the coating layer boundary. After curing, an input cladding light filtering module is formed. In step six, a portion of the coating layer on the second matched passive fiber is stripped to expose the bare fiber cladding. The bare fiber cladding is then bent into a U-shaped structure. The stripped section is uniformly coated with high-refractive-index adhesive, extending to the coating layer boundary. After curing, an output cladding light filtering module is formed.
7. The method for testing the absorption coefficient of a high-doped double-clad erbium-doped optical fiber core according to claim 6, characterized in that: The high-refractive-index adhesive has a refractive index >1.50, and the low-refractive-index adhesive has a refractive index <1.
46.
8. The method for testing the absorption coefficient of a high-doped double-clad erbium-doped optical fiber core according to claim 1, characterized in that: The input cladding light filtering module in step three and the output cladding light filtering module in step six are both cladding mode power filters, which are fused to the first matched passive optical fiber and the second matched passive optical fiber.