A method for measuring cladding optical power distribution of triple-clad optical fiber combiner

Abstract

The present invention discloses a method for measuring the cladding light power distribution of a three-clad optical fiber combiner, firstly, a reference light spot diameter is obtained by using a first cladding light calibration optical path, then the second cladding light of the three-clad optical fiber is stripped by using a second cladding light stripping optical path, and then the cladding light power measurement optical path is used to obtain the cladding light power transmitted in the first cladding of the three-clad optical fiber combiner, and finally the cladding light power distribution of the three-clad optical fiber combiner is calculated. The present invention can completely strip the second cladding light in the optical fiber through the obtained second cladding light stripper, and accurately measure the cladding light of the three-clad optical fiber combiner under high power conditions, thereby improving the accuracy of measuring the cladding light power distribution of the three-clad optical fiber combiner, and further promoting the optimization of the beam quality of the three-clad optical fiber combiner.

Description

Technical Field

[0001] The invention belongs to the technical field of laser detection, and in particular relates to a method for measuring the cladding optical power distribution of a triple-cladding optical fiber combiner. Background Art

[0002] High-power fiber lasers have the advantages of high conversion efficiency, good beam quality, compact structure, and easy thermal management. They are widely used in industrial processing, national defense and military fields. Fiber combiners are important components of high-power fiber lasers. They can combine multiple fiber-coupled semiconductor lasers into one fiber output, thereby providing a pump source for fiber lasers. The performance of the combiner directly determines the upper limit of the output power of the fiber laser.

[0003] Due to its high damage threshold and upper limit of pump power, triple-clad gain fiber is the future development trend for further improving the single-fiber power of high-power fiber lasers. In triple-clad fiber lasers, the first cladding of triple-clad ytterbium-doped fiber has a higher pump absorption efficiency than the second cladding. At the fusion point between the fiber combiner and the triple-clad ytterbium-doped fiber, the pump beam will inevitably leak into the external polymer coating, causing light absorption and heating at the fusion point, even exceeding the temperature threshold of the external coating, affecting the overall safety of the fiber laser. Therefore, the pump light should be constrained to be transmitted within the first cladding of the triple-clad fiber as much as possible to ensure the optical-to-optical conversion efficiency and system safety of the fiber laser. Therefore, measuring the cladding light power distribution of the triple-clad fiber combiner can determine the efficiency and safety of the fiber laser.

[0004] In the article "6.7kW Domestically Produced Narrow Linewidth Triple-Clad Fiber Laser", Han Zhigang et al. studied the effect of the second cladding power ratio in large mode field triple-cladding fiber on fiber temperature and upper limit of pump power. The results show that the combiner with low second cladding power ratio has a higher upper limit of pump power. The cladding optical power distribution measurement method based on the NA method has a large measurement error due to the diffraction effect of the output laser and the error of the aperture distance and size, and cannot be measured under high-power laser output due to the damage threshold of the aperture. Summary of the invention

[0005] The purpose of the present invention is to provide a method for measuring the cladding optical power distribution of a triple-clad optical fiber combiner, by using a stripper to calibrate the optical fiber to obtain a triple-clad optical fiber second cladding optical stripper, thereby accurately measuring the cladding optical power distribution of the triple-clad optical fiber combiner, and also being able to accurately and quickly measure the triple-clad optical fiber combiner with the same output fiber.

[0006] The technical solution to realize the present invention is: a method for measuring the cladding optical power distribution of a triple-clad optical fiber combiner, the steps are as follows:

[0007] Step 1: Use the first cladding cursor to determine the optical path and obtain the reference spot diameter D1:

[0008] The first cladding light calibration optical path includes an adjustable DC power supply, a semiconductor laser, a stripper calibration optical fiber, a power attenuator and a near-infrared camera arranged along the optical path.

[0009] The adjustable DC power supply controls the laser output of the semiconductor laser. The output laser of the semiconductor laser enters the stripper calibration optical fiber through the first fusion point, and then exits through the stripper calibration optical fiber. After the output laser power is attenuated by the power attenuator, the output laser spot diameter D1 of the stripper calibration optical fiber is captured by the near-infrared camera.

[0010] Step 2: Use the second cladding light to strip the optical path to strip the second cladding light of the triple-clad optical fiber:

[0011] A triple-clad fiber combiner and a triple-clad energy transfer fiber are used to replace the stripper calibration fiber in the first clad optical calibration optical path to obtain a second clad optical repair stripping optical path.

[0012] The adjustable DC power supply controls the laser output of the semiconductor laser. The output laser passes through the triple-clad fiber combiner, triple-clad energy transfer fiber and power attenuator in sequence, and then the output laser spot diameter D2 is captured by the near-infrared camera.

[0013] The triple-clad energy transfer fiber is processed by chemical etching until the spot diameter D2 collected by the near-infrared camera is equal to the spot diameter D1 collected when the fiber is calibrated using a stripper, and the second cladding light of the triple-clad fiber is stripped. At this time, the triple-clad energy transfer fiber serves as a triple-clad fiber second cladding light stripper.

[0014] Step 3: Use the cladding optical power measurement optical path to obtain the cladding optical power P1 transmitted in the first cladding of the three-cladding optical fiber combiner:

[0015] A lens group and an optical power meter are used to replace the power attenuator and the near-infrared camera in the second cladding optical repair and stripping optical path to obtain the cladding optical power measurement optical path.

[0016] The adjustable DC power supply controls the laser output of the semiconductor laser. After the output laser passes through the triple-clad fiber combiner and the optical fiber second cladding light stripper, it is collimated and focused by the lens group to the target surface of the optical power meter. The optical power meter is used to measure the cladding light power P1 transmitted in the first cladding of the triple-clad fiber combiner.

[0017] Step 4: Calculate the power distribution of the cladding light of the triple-clad fiber combiner:

[0018] According to the power P of the laser output by the semiconductor laser and the cladding light power P1 transmitted in the first cladding of the three-cladding fiber combiner, the cladding light power P2 transmitted in the second cladding of the three-cladding fiber combiner is calculated:

[0019] P2=P-P1

[0020] The power distribution η of the cladding light of the triple-clad fiber combiner is calculated based on P1 and P2:

[0021] η=P1 / P2.

[0022] Furthermore, the parameters of the triple-clad energy transfer fiber are the same as the output fiber parameters of the triple-clad fiber combiner.

[0023] Furthermore, the stripper calibration optical fiber is a single-clad coreless optical fiber, which has the same first cladding numerical aperture and cladding diameter as the output optical fiber of the triple-clad optical fiber combiner.

[0024] Compared with the prior art, the present invention has the following significant advantages:

[0025] (1) Based on the spot size of the output laser, the stripper is used to calibrate the optical fiber to obtain the second cladding light stripper of the triple-clad optical fiber. This method ensures the complete stripping of the second cladding light and the transmission of the first cladding light, thereby achieving higher accuracy in measurement.

[0026] (2) Based on the obtained triple-clad optical fiber second cladding light stripper, the triple-clad optical fiber combiner with the same output fiber can be measured, and the cladding optical power distribution of the triple-clad optical fiber combiner with different structures can be quickly determined, which has good universality.

[0027] (3) Based on the obtained triple-clad optical fiber second cladding light stripper, the cladding light power distribution measurement of the triple-clad optical fiber combiner under the condition of high-power pump light injection can be achieved, and the cladding light power distribution of the triple-clad optical fiber combiner under different powers can be obtained with good measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the first cladding cursor positioning optical path of the present invention.

[0029] Figure 2 It is a schematic diagram of the optical path of the second cladding light stripping of the present invention.

[0030] Figure 3 It is a schematic diagram of the optical path for measuring the cladding optical power of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0032] The method for measuring the cladding optical power distribution of a triple-clad optical fiber combiner described in the present invention comprises the following steps:

[0033] Step 1: Use the first cladding cursor to determine the optical path and obtain the reference spot diameter D1:

[0034] Combination Figure 1 The first cladding light calibration optical path includes an adjustable DC power supply 1, a semiconductor laser 2, a stripper calibration optical fiber 4, a power attenuator 6 and a near-infrared camera 7 arranged along the optical path; the adjustable DC power supply 1 controls the laser output of the semiconductor laser 2, and the output laser of the semiconductor laser 2 enters the stripper calibration optical fiber 4 through the first fusion point 3, and then exits through the stripper calibration optical fiber 4. After the output laser power is attenuated by the power attenuator 6, the output laser spot diameter D1 of the stripper calibration optical fiber 4 is captured by the near-infrared camera 7. Among them, the type of semiconductor laser 2 is a fiber-coupled semiconductor laser, and its output wavelength is the absorption wavelength for ytterbium-doped optical fiber in the field of industrial fiber lasers, such as 915nm, 976nm, etc.; in order to alleviate the problem of leakage light during fiber fusion splicing, the numerical aperture of the output fiber of semiconductor laser 2 should be ≤0.22; the laser is coupled to the stripper calibration optical fiber 4 by fiber fusion splicing, and the fusion loss of the stripper calibration optical fiber 4 and the semiconductor laser 2 pump fiber should be less than 0.05dB to ensure the efficiency of the injected pump beam and the safety of the semiconductor laser 2 during the test; The stripper calibration fiber 4 is a single-clad coreless fiber, which has the same numerical aperture and cladding diameter as the first cladding of the output fiber of the three-clad fiber combiner 9 to ensure that it passes; during the test, the bending diameter of the fiber should not be less than 8cm to ensure the accuracy and safety during the test; the output end of the stripper calibration fiber 4 is cut at a 0° angle to ensure that the output laser is not affected by the fiber end face; the output end of the stripper calibration fiber 4 is clamped by a fiber clamp 5, which is set on a three-dimensional adjustment table. The three-dimensional adjustment table posture is adjusted to achieve that the optical axis in the optical path passes through the center of each optical element at the same time. Based on the first cladding cursor to calibrate the optical path, the spot diameter corresponding to the first cladding of the three-clad fiber combiner to be tested can be obtained, that is, the reference spot diameter D1, which provides a basis standard for completely stripping the second cladding light.

[0035] Step 2: Use the second cladding light to strip the optical path to strip the second cladding light of the triple-clad optical fiber:

[0036] Combination Figure 2, a triple-clad fiber combiner 9 and a triple-clad energy transfer fiber 10 are used to replace the stripper calibration fiber 4 in the first clad light calibration optical path to obtain a second clad light stripping optical path; an adjustable DC power supply 1 controls the laser output of the semiconductor laser 2, and the output laser passes through the triple-clad fiber combiner 9, the triple-clad energy transfer fiber 10 and the power attenuator 6 in sequence, and the output laser spot diameter D2 is captured by the near-infrared camera 7; the pigtails of the semiconductor laser 2 and the triple-clad fiber combiner 9 are connected through the second fusion point 8, and the output fiber of the triple-clad fiber combiner 9 is connected to the triple-clad energy transfer fiber 10 through the third fusion point 15. To ensure the laser transmission efficiency, the loss between the second fusion point 8 and the third fusion point 15 is not greater than 0.05dB. The triple-clad energy transfer fiber 10 is processed by chemical etching until the spot diameter D2 collected by the near-infrared camera 7 is equal to the spot diameter D1 collected when the stripper is used to calibrate the optical fiber 4, and the second cladding light of the triple-clad optical fiber is stripped. At this time, the triple-clad energy transfer fiber 10 serves as a triple-clad optical fiber second cladding light stripper 16. Among them, the use of chemical etching to process the triple-clad energy transfer fiber 10 should follow the principle of short-term and multiple times to ensure that the second cladding light is completely stripped and the first cladding is not corroded. Based on the second cladding light stripping optical path, the second cladding light stripper 16 can be obtained, which can completely strip the influence of the second cladding light when measuring the cladding light power to achieve accurate measurement.

[0037] Step 3: Use the cladding optical power measurement optical path to obtain the cladding optical power P1 transmitted in the first cladding of the three-cladding optical fiber combiner:

[0038] Combination Figure 3 , use lens group 11 and optical power meter 14 to replace power attenuator 6 and near-infrared camera 7 in the second cladding optical stripping optical path, and obtain the cladding optical power measurement optical path; adjustable DC power supply 1 controls the laser output of semiconductor laser 2, and the output laser passes through three-cladding fiber combiner 9 and optical fiber second cladding optical stripper 16, and then is collimated and focused by lens group 11 to the target surface of optical power meter 14, and the cladding optical power P1 transmitted in the first cladding of the three-cladding fiber combiner is measured by optical power meter 14; wherein, the relative positions of the first lens 12 and the second lens 13 of lens group 11 are adjusted to meet the requirements of the optical power meter for the spot size. Based on the optical power measured by the cladding optical power measurement optical path, the cladding optical power distribution can be obtained by further data processing.

[0039] Step 4: Calculate the power distribution of the cladding light of the triple-clad fiber combiner:

[0040] According to the power P of the laser output by the semiconductor laser 2 and the cladding light power P1 transmitted in the first cladding of the three-cladding optical fiber combiner 9, the cladding light power P2 transmitted in the second cladding of the three-cladding optical fiber combiner 9 is calculated:

[0041] P2=P-P1

[0042] The power distribution η of the cladding light of the triple-cladding fiber combiner 9 is calculated based on P1 and P2:

[0043] η=P1 / P2

[0044] The present invention uses the calibration optical fiber 4 to obtain the second cladding light stripper 16 of the three-cladding optical fiber. Based on the second cladding light stripper 16 of the three-cladding optical fiber, accurate cladding light power measurement can be achieved under high-power laser output conditions, solving the measurement error caused by the diffraction of the output light when using the NA method to measure the cladding light power distribution, and the limitation of only being able to output at low power lasers due to the aperture damage threshold. The cladding light power distribution η measured by the present invention can effectively determine the cladding distribution of the pump light beam in the three-cladding optical fiber after being combined by the three-cladding optical fiber combiner 9. On this basis, the fiber temperature and power distribution are obtained by combining the power density formula of the three-cladding gain optical fiber heat source and the fiber laser rate equation theory, so as to analyze the output characteristics and reliability of the three-cladding optical fiber laser. The cladding light power distribution measurement method of the three-cladding optical fiber combiner based on the second cladding light stripper 16 can accurately measure the cladding light power distribution under high-power laser output conditions, providing a reference standard for the optimization of the coupling scheme of the three-cladding optical fiber combiner.

Claims

1. A method for measuring the cladding optical power distribution of a triple-clad optical fiber combiner, characterized in that: Here are the steps: Step 1: Use the first cladding cursor to determine the optical path and obtain the reference spot diameter D1: The first cladding light calibration optical path comprises an adjustable direct current power supply (1), a semiconductor laser (2), a stripper calibration optical fiber (4), a power attenuator (6) and a near-infrared camera (7) arranged along the optical path; The adjustable direct current power supply (1) controls the laser output of the semiconductor laser (2); the output laser of the semiconductor laser (2) enters the stripper calibration optical fiber (4) through the first fusion point (3), and then is emitted through the stripper calibration optical fiber (4); after the output laser power is attenuated by the power attenuator (6), the output laser spot diameter D1 of the stripper calibration optical fiber (4) is captured by the near-infrared camera (7); Step 2: Use the second cladding light to strip the optical path to strip the second cladding light of the triple-clad optical fiber: A triple-clad optical fiber combiner (9) and a triple-clad energy transmission optical fiber (10) are used to replace the stripper calibration optical fiber (4) in the first clad light calibration optical path to obtain a second clad light stripping optical path; The adjustable DC power supply (1) controls the laser output of the semiconductor laser (2), and the output laser passes through the triple-clad fiber combiner (9), the triple-clad energy transfer fiber (10) and the power attenuator (6) in sequence, and the output laser spot diameter D2 is captured by the near-infrared camera (7); The triple-clad energy transmission optical fiber (10) is processed by a chemical etching method until the spot diameter D2 collected by the near-infrared camera (7) is equal to the spot diameter D1 collected when the stripper is used to calibrate the optical fiber (4), and the second cladding light of the triple-clad optical fiber is stripped. At this time, the triple-clad energy transmission optical fiber (10) serves as a triple-clad optical fiber second cladding light stripper (16); Step 3: Use the cladding optical power measurement optical path to obtain the cladding optical power P1 transmitted in the first cladding of the three-cladding optical fiber combiner: A lens group (11) and an optical power meter (14) are used to replace a power attenuator (6) and a near-infrared camera (7) in the second cladding optical repair and stripping optical path, thereby obtaining a cladding optical power measurement optical path; An adjustable direct current power supply (1) controls the laser output of a semiconductor laser (2); after the output laser passes through a three-clad optical fiber combiner (9) and an optical fiber second clad optical stripper (16), it is collimated and focused by a lens group (11) onto a target surface of an optical power meter (14); and the optical power meter (14) is used to measure the cladding optical power P1 transmitted in the first cladding of the three-clad optical fiber combiner; Step 4: Calculate the power distribution of the cladding light of the triple-clad fiber combiner: According to the power P of the laser output by the semiconductor laser (2) and the cladding light power P1 transmitted in the first cladding of the three-cladding optical fiber combiner, the cladding light power P2 transmitted in the second cladding of the three-cladding optical fiber combiner is calculated: P2=P-P1 The power distribution η of the cladding light of the triple-clad fiber combiner is calculated based on P1 and P2: η=P1 / P2.

2. The method for measuring the cladding optical power distribution of a triple-clad optical fiber combiner according to claim 1, characterized in that: The parameters of the triple-clad energy transmission optical fiber (10) are the same as the output optical fiber parameters of the triple-clad optical fiber combiner (9).

3. The method for measuring the cladding optical power distribution of a triple-clad optical fiber combiner according to claim 2, characterized in that: It also comprises an optical fiber clamp (5), which is arranged on a three-dimensional adjustment table to enable the optical axis in the optical path to pass through the center of each optical element at the same time.

4. The method for measuring the cladding optical power distribution of a triple-clad optical fiber combiner according to claim 3, characterized in that: In step one, the output fiber of the semiconductor laser (2) is connected to the stripper calibration fiber (4) through the first fusion point (3); the output end of the stripper calibration fiber (4) is cut at a 0° angle and placed on a fiber clamp (5); the posture of the fiber clamp (5) is adjusted so that the optical axis passes through the center of each optical element at the same time.

5. The method for measuring the cladding optical power distribution of a triple-clad optical fiber combiner according to claim 4, characterized in that: In step 2, the output fiber of the semiconductor laser (2) is connected to the tail fiber of the triple-clad fiber combiner (9) through the second fusion point (8); the output fiber of the triple-clad fiber combiner (9) is connected to the triple-clad energy transfer fiber (10) through the third fusion point (15); the output end of the triple-clad energy transfer fiber (10) is cut at a 0° angle and placed on the fiber clamp (5), the distance from the output end of the triple-clad energy transfer fiber (10) to the near-infrared camera (7) is kept equal to the distance from the output end of the stripper calibration fiber (4) to the near-infrared camera (7), and the posture of the fiber clamp (5) is adjusted so that the optical axis passes through the center of each optical element at the same time.

6. The method for measuring the cladding optical power distribution of a triple-clad optical fiber combiner according to claim 1, characterized in that: The stripper calibration optical fiber (4) is a single-clad coreless optical fiber, and has the same first cladding numerical aperture and cladding diameter as the output optical fiber of the three-clad optical fiber combiner (9).

7. The method for measuring the cladding optical power distribution of a triple-clad optical fiber combiner according to claim 5, characterized in that: In step three, the lens group (11) is adjusted to include a first lens (12) and a second lens (13). Both the first lens (12) and the second lens (13) are convex lenses. The first lens (12) collimates the divergent light emitted from the optical fiber into parallel light, and the second lens (13) converges the parallel light onto the target surface of the optical power meter (14).

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