Device and method for measuring absorption coefficient of fiber core of large-mode-field active optical fiber

Abstract

The invention provides a device and method for measuring the absorption coefficient of a large-mode-field active optical fiber core, and the device comprises a seed light source, an adjustable optical attenuator, a cladding mode filter and a data processing system which are sequentially connected in a direction from an input end to an output end. A large-mode-field active optical fiber to be detected is connected between the cladding mode filter and the data processing system, and the data processing system is used for detecting the optical power output by the large-mode-field active optical fiber to be detected; obtaining a fiber core absorption coefficient of the to-be-measured large-mode-field active optical fiber according to the optical power variation of the to-be-measured large-mode-field active optical fiber after each time of truncation processing, the truncation length of each time of truncation processing, and the fiber core layer area and the inner cladding area of the to-be-measured large-mode-field active optical fiber; the measuring device provided by the invention can accurately measure the fiber core absorption coefficient of the to-be-measured large-mode-field active optical fiber, the structure is simple, the used to-be-measured large-mode-field active optical fiber is short, and large-batch sampling inspection test is facilitated.

Description

Technical Field

[0001] The invention relates to the field of optical fiber laser technology, and in particular to a device and a method for measuring the absorption coefficient of a large mode field active optical fiber core. Background Art

[0002] Optical fiber is an important material in the fields of optical fiber communication, optical fiber sensing and laser technology. With the rapid development of these fields in recent years, active optical fiber materials have been widely used in military, medical, exploration and communication fields. Among them, large mode field active optical fiber has been favored in various fields due to its high amplification efficiency, large output power and good working stability. The core absorption coefficient of active optical fiber is an important parameter. As the active gain medium in the fiber laser, its core absorption coefficient directly determines the use length of the active optical fiber in the fiber laser, which indirectly affects the structure of the fiber laser.

[0003] Generally, the absorption coefficient test of optical fiber core with small core diameter is a mature technology in the current industry. However, the absorption coefficient of optical fiber core with large core diameter is generally large, so the length used in the test process will be short, generally less than 50cm. At the same time, in order to ensure the accurate test of the measuring instrument and reduce the test error, the operation will be very difficult. In particular, for step-type large mode field optical fiber with base design, due to its base design, the core power is easily affected by the base layer during transmission, which greatly increases the difficulty of testing.

[0004] Therefore, there is an urgent need for a device and method for measuring the absorption coefficient of a large mode field active optical fiber core to solve the above technical problems. Summary of the invention

[0005] The purpose of the present invention is to provide a device and method for measuring the absorption coefficient of a large mode field active optical fiber core, so as to improve the technical problem that the existing technology cannot accurately measure the absorption coefficient of a large mode field active optical fiber core.

[0006] In order to solve the above technical problems, the present invention first provides a device for measuring the core absorption coefficient of a large mode field active optical fiber, comprising a seed light source, an adjustable optical attenuator, a cladding mode filter and a data processing system connected in sequence along the direction from the input end to the output end, and the cladding mode filter and the data processing system are used to connect the large mode field active optical fiber to be measured; The data processing system is used to detect the optical power output by the large mode field active optical fiber to be tested, and obtain the core absorption coefficient of the large mode field active optical fiber to be tested according to the optical power change after each shortening process of the large mode field active optical fiber to be tested, the cut length of each shortening process, the core layer area and the inner cladding area of ​​the large mode field active optical fiber to be tested.

[0007] Preferably, the seed light source is used to output seed signal light, and the adjustable optical attenuator is used to adjust the optical power of the seed signal light to between -20dBm and -10dBm.

[0008] Preferably, the measuring device also includes a first active connector and a second active connector, the first end of the first active connector is connected to the seed light source, and the second end of the first active connector is connected to the adjustable optical attenuator; the first end of the second active connector is connected to the adjustable optical attenuator, and the second end of the second active connector is connected to the first end of the cladding mode filter.

[0009] Preferably, the measuring device further comprises a passive optical fiber matching the structure of the large mode field active optical fiber to be measured, the first end of the passive optical fiber is connected to the second end of the cladding mode filter, and the second end of the passive optical fiber is fused with the large mode field active optical fiber to be measured.

[0010] Preferably, the initial length of the large mode field active optical fiber to be tested is 10 to 20 cm, the remaining length of the large mode field active optical fiber to be tested after the nth shortening process is greater than or equal to 1 cm, and n is a positive integer greater than or equal to 1; the length of the large mode field active optical fiber to be tested after each shortening process is 3 to 5 cm.

[0011] Accordingly, the present invention also provides a method for measuring the absorption coefficient of a large mode field active optical fiber core, the method comprising: S10, providing any of the above measuring devices, connecting the large mode field active optical fiber to be measured between the cladding mode filter and the data processing system; S20, outputting seed signal light through a seed light source, so that the seed signal light enters a data processing system through the large mode field active optical fiber to be measured, and the data processing system measures the optical power of the large mode field active optical fiber to be measured; S30, shortening the large mode field active optical fiber to be tested, and recording the cut length of the large mode field active optical fiber to be tested; S40, connecting the shortened large mode field active optical fiber to be tested between the cladding mode filter and the data processing system; S50, outputting seed signal light through a seed light source, so that the seed signal light enters a data processing system through the shortened large mode field active optical fiber to be tested, and the data processing system measures the optical power of the shortened large mode field active optical fiber to be tested; S60, obtaining a core absorption coefficient of the large mode field active optical fiber to be tested according to the optical power variation of the large mode field active optical fiber to be tested before and after each shortening process, the shortened length of each shortening process, the core layer area and the inner cladding area of ​​the large mode field active optical fiber to be tested.

[0012] Preferably, step S60 specifically includes: S601, obtaining a fiber cladding coefficient of the large mode field active optical fiber to be tested after the nth truncation process according to the optical power variation of the large mode field active optical fiber to be tested before and after the nth truncation process and the truncation length of the nth truncation process, where n is a positive integer greater than or equal to 1; S602, obtaining the core absorption coefficient of the large mode field active optical fiber to be tested after the n-th shortening process according to the optical fiber cladding coefficient, the core layer area and the inner cladding area of ​​the large mode field active optical fiber to be tested.

[0013] Preferably, in step S601, the calculation formula of the optical fiber cladding coefficient of the large mode field active optical fiber to be tested after the n-th truncation process is as follows: ; in, n It represents the fiber cladding coefficient of the large mode field active fiber to be tested for the seed signal light with wavelength λ after the nth truncation process, P n It represents the optical power of the large mode field active optical fiber to be tested after the nth shortening process, P n-1 It indicates the optical power of the large mode field active optical fiber to be tested after the n-1th shortening process. It indicates the cut length of the large mode field active optical fiber to be tested after the nth shortening process.

[0014] Preferably, in step S602, the calculation formula of the fiber core absorption coefficient is as follows: ; in, It represents the core absorption coefficient of the large mode field active optical fiber to be tested for the seed signal light with a wavelength of λ after the nth truncation process, s represents the core layer area of ​​the large mode field active optical fiber to be tested, and S represents the inner cladding area of ​​the large mode field active optical fiber to be tested.

[0015] Preferably, after step S602, the method further includes: taking an average value of multiple groups of core absorption coefficients after the 1st to nth truncation processes to obtain an average core absorption coefficient. The calculation formula of the average core absorption coefficient is as follows: ; in, It represents the average core absorption coefficient of the large mode field active optical fiber to be tested for the seed signal light with a wavelength of λ. k It represents the core absorption coefficient of the large mode field active optical fiber to be tested for the seed signal light with a wavelength of λ after the k-th truncation process, 1≤k≤n, and k is a positive integer.

[0016] The beneficial effects of the present invention are as follows: Different from the prior art, the present invention provides a device for measuring the absorption coefficient of the core of a large mode field active optical fiber and a method for measuring the absorption coefficient of the core of a large mode field active optical fiber. The above-mentioned measuring device comprises a seed light source, an adjustable optical attenuator, a cladding mode filter and a data processing system which are sequentially connected along the direction from the input end to the output end. The cladding mode filter and the data processing system are used to connect the large mode field active optical fiber to be tested. The data processing system is used to detect the optical power output by the large mode field active optical fiber to be tested, and according to the optical power change amount of the large mode field active optical fiber to be tested after each shortening process, the cut length of each shortening process, the core layer area of ​​the large mode field active optical fiber to be tested and The core absorption coefficient of the large mode field active optical fiber to be tested is obtained by measuring the inner cladding area; the measuring device for the core absorption coefficient of the large mode field active optical fiber provided by the present invention detects the optical power output by the large mode field active optical fiber to be tested through a data processing system, and can accurately measure the core absorption coefficient of the large mode field active optical fiber to be tested according to the optical power change amount of the large mode field active optical fiber to be tested after each shortening process, the cut length of each shortening process, the core layer area and the inner cladding area of ​​the large mode field active optical fiber to be tested; at the same time, the structure of the above-mentioned measuring device is simple, and the large mode field active optical fiber to be tested used is relatively short, which is convenient for large-scale spot check testing of the large mode field active optical fiber to be tested, and is conducive to reducing the testing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic diagram of the connection of a device for measuring the absorption coefficient of a large mode field active optical fiber core provided by an embodiment of the present invention; Figure 2 A flow chart of a method for measuring the absorption coefficient of a large mode field active optical fiber core provided by an embodiment of the present invention; In the figure: 100 - measuring device; 101 - seed light source; 102 - adjustable optical attenuator; 103 - cladding mode filter; 104 - data processing system; 105 - first active connector; 106 - second active connector; 20 - large mode field active optical fiber to be measured. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] The purpose of the present invention is to provide a device and method for measuring the core absorption coefficient of a large mode field active optical fiber in view of the defects of the prior art, which can accurately measure the core absorption coefficient of the large mode field active optical fiber to be tested, facilitate large-scale random sampling tests on the large mode field active optical fiber to be tested, and help reduce testing costs.

[0020] See also Figure 1 , Figure 1 A connection diagram of a device 100 for measuring the absorption coefficient of a large mode field active optical fiber core provided by an embodiment of the present invention; wherein the device 100 for measuring the absorption coefficient of a large mode field active optical fiber core provided by an embodiment of the present invention comprises a seed light source 101, an adjustable optical attenuator 102, a cladding mode filter 103 and a data processing system 104 connected in sequence along the direction from the input end to the output end, and the cladding mode filter 103 and the data processing system 104 are used to connect the large mode field active optical fiber 20 to be measured; The data processing system 104 is used to detect the optical power output by the large mode field active optical fiber 20 to be tested, and obtain the core absorption coefficient of the large mode field active optical fiber 20 to be tested according to the optical power change of the large mode field active optical fiber 20 to be tested after each shortening process, the cut length of each shortening process, the core layer area and the inner cladding area of ​​the large mode field active optical fiber 20 to be tested.

[0021] In the embodiment of the present invention, the seed light source 101 is used to output seed signal light; wherein, the seed light source 101 is preferably a single-wave laser light source, which is used to output a single-wave signal light of 1535nm.

[0022] In the embodiment of the present invention, the variable optical attenuator 102 (VOA) is a very important fiber optic passive component, which can attenuate the optical signal energy as required by the user, and is mainly used to adjust the input signal optical power.

[0023] Specifically, when the optical power of the seed signal light input to the large mode field active optical fiber 20 to be tested is too large, it will cause stimulated emission in the large mode field active optical fiber 20 to be tested. The stimulated emission process will be accompanied by energy conversion, which may generate heat in the large mode field active optical fiber 20 to be tested. If too much heat accumulates, it may affect the performance and life of the large mode field active optical fiber 20 to be tested, and even cause damage to the large mode field active optical fiber 20 to be tested; when the optical power of the seed signal light input to the large mode field active optical fiber 20 to be tested is too small, it will cause the test result of the core absorption coefficient to be small and irregular, thereby increasing the test error.

[0024] Preferably, in order to avoid the result error caused by the large mode area active optical fiber 20 to be tested emitting at the test wavelength, the input light needs to be reduced as much as possible during the process of outputting the signal light. Generally, the range of -20dBm to -10dBm is a more suitable optical power range of the seed signal light.

[0025] In the embodiment of the present invention, the measuring device 100 also includes a first active connector 105, a first end of the first active connector 105 is connected to the seed light source 101, and a second end of the first active connector 105 is connected to the adjustable optical attenuator 102; wherein the first active connector 105 is mainly used to connect the seed light source 101 and the adjustable optical attenuator 102, which ensures that the seed signal light can be efficiently and stably transmitted between these two key components.

[0026] In the embodiment of the present invention, the cladding mode filter is used to filter out the wide spectrum signal light transmitted in the optical fiber cladding. It is understandable that when the seed signal light output by the seed light source 101 enters the large mode field active optical fiber 20 to be tested for transmission, a part of it will leak into the cladding of the large mode field active optical fiber 20 to be tested for transmission. Since the refractive index of the outer cladding is less than the refractive index of the inner cladding, only the inner cladding passes light during the actual light transmission process; therefore, in order to accurately measure the core absorption coefficient of the large mode field active optical fiber 20 to be tested, it is necessary to filter out the light transmitted in the cladding, and try to make the optical power measured by the data processing system 104 the optical power of the seed signal light transmitted in the core layer.

[0027] Specifically, the cladding mode filter 103 generally utilizes the principle of mode coupling to remove the cladding mode. When light is transmitted in an optical fiber, coupling occurs between different modes. The cladding mode filter 103 is designed with a specific structure so that the cladding mode can couple with the absorbing material or scattering material in the filter, thereby transferring the energy of the cladding mode to these materials to achieve cladding mode filtering.

[0028] In the embodiment of the present invention, the measuring device 100 further includes a second active connector 106 , a first end of the second active connector 106 is connected to the adjustable optical attenuator 102 , and a second end of the second active connector 106 is connected to a first end of the cladding mode filter 103 .

[0029] In an embodiment of the present invention, the measuring device 100 also includes a passive optical fiber that matches the structure of the large mode field active optical fiber 20 to be measured, the first end of the passive optical fiber is connected to the second end of the cladding mode filter 103, and the second end of the passive optical fiber is fused with the large mode field active optical fiber 20 to be measured; at this time, the passive optical fiber can be used as a device pigtail of the cladding mode filter 103.

[0030] Specifically, using a passive optical fiber of the same structure to fuse with the large mode field active optical fiber 20 to be tested can enable the seed signal light to maintain a stable propagation mode during the core layer transmission of the large mode field active optical fiber 20 to be tested, and reduce the seed signal light escaping to the inner cladding area during the core transmission, resulting in a reduction in output optical power. This can make the test results more regular; at the same time, adding a passive optical fiber can avoid the device tail fiber of the cladding mode filter 103 being too short, resulting in the cladding mode filter 103 being unusable.

[0031] In the embodiment of the present invention, the core feature of the large mode field active optical fiber 20 to be tested is that it has a large mode field area. Compared with traditional optical fibers, the core diameter of large mode field active optical fibers is larger, which can accommodate more optical power and reduce the optical power density, thereby reducing the risk of nonlinear effects and optical fiber damage.

[0032] Preferably, the large mode field active optical fiber 20 to be tested is a step-type double-clad large core diameter doped optical fiber with a base design; the refractive index distribution of this optical fiber is step-type, that is, there is an obvious refractive index mutation between the core and the cladding. The refractive index of the core is higher, and the refractive index of the cladding is lower. The light propagates in the core by total reflection; the refractive index of the base is usually between the core and the cladding, playing a transition and supporting role. The base design can improve the mode characteristics and transmission performance of the optical fiber. It can reduce the refractive index mutation between the core and the cladding, reduce the coupling loss between modes, and improve the mode stability and transmission efficiency of the optical fiber. At the same time, the base can also increase the mechanical strength and bending resistance of the optical fiber, and improve the reliability and service life of the optical fiber.

[0033] Preferably, the initial length of the large mode field active optical fiber 20 to be tested is 10 to 20 cm, and the remaining length of the large mode field active optical fiber 20 to be tested after the n-th shortening process is greater than or equal to 1 cm, where n is a positive integer greater than or equal to 1; this is because when the length of the large mode field active optical fiber 20 to be tested is less than 1 cm, the test of its optical power will be more easily affected by external factors and produce fluctuations.

[0034] Preferably, the cut length of each shortening process of the large mode field active optical fiber 20 to be tested is 3 to 5 cm; when the cut length is less than 3 cm each time, the change in optical power before and after the shortening process is too small, which will increase the measurement error; when the cut length is greater than 5 cm each time, the data of the core absorption coefficient obtained subsequently is small, which will affect the accuracy of the measurement result.

[0035] In the embodiment of the present invention, the data processing system 104 is used to detect the optical power output by the large mode field active optical fiber 20 to be tested, and obtain the core absorption coefficient of the large mode field active optical fiber 20 to be tested according to the optical power change of the large mode field active optical fiber 20 to be tested after each shortening process, the cut length of each shortening process, the core layer area and the inner cladding area of ​​the large mode field active optical fiber 20 to be tested.

[0036] Specifically, the data processing system 104 includes an optical power meter, one end of which is connected to the large mode area active optical fiber 20 to be tested, and the optical power meter is used to detect the optical power output by the large mode area active optical fiber 20 to be tested.

[0037] Specifically, the data processing system 104 also includes an I / V converter, a voltage amplifier, a filtering circuit, an ADC analog-to-digital converter, an MCU unit and a terminal; the function of the I / V conversion module is to convert the current signal generated by the optical power meter into a voltage signal; the voltage amplifier is used to amplify the voltage signal after the I / V converter; the purpose of the filtering circuit is to filter out the noise and interference that may exist in the circuit and retain the effective voltage signal; the ADC analog-to-digital conversion is responsible for converting the filtered and amplified analog voltage signal into a digital signal; the MCU unit: the MCU (Micro controller Unit) is the central processor of the system, responsible for overall control and data processing, the MCU receives the digital signal from the ADC analog-to-digital converter, performs data analysis, processing and storage, and obtains the core absorption coefficient of the large mode field active optical fiber 20 to be tested according to the optical power change amount of the large mode field active optical fiber 20 to be tested after each shortening process, the cut length of each shortening process, the core layer area and the inner cladding area of ​​the large mode field active optical fiber 20 to be tested; the terminal is the human-computer interaction interface of the system, responsible for intuitively displaying the processed core absorption coefficient data and analysis results to the user.

[0038] See also Figure 2 , Figure 2 A flow chart of a method for measuring the absorption coefficient of a large mode field active optical fiber core provided by an embodiment of the present invention; wherein the above-mentioned measurement method specifically includes: S10 , providing a measuring device 100 as described in any one of the above items, and connecting the large mode field active optical fiber 20 to be measured between the cladding mode filter 103 and the data processing system 104 .

[0039] Specifically, step S10 also includes: The above-mentioned measuring device 100 is provided, and the large mode field active optical fiber 20 to be measured is connected between the cladding mode filter 103 and the data processing system 104; wherein, the seed light source 101 and the adjustable attenuator are connected with the first active connector 105, and the adjustable optical attenuator and the cladding mode filter 103 are connected with the second active connector 106; the large mode field active optical fiber 20 to be measured is fused to one end of the cladding mode filter 103 away from the seed light source 101, and the other end is cut at an 8° angle for output and connected to the optical power meter in the data processing system 104.

[0040] Among them, by cutting the output at an 8° angle, on the one hand, the output power test error caused by the reflection of the optical fiber end face can be reduced, thereby improving the test accuracy; on the other hand, after cutting at an 8° angle, the angle at which the light is emitted from the large mode field active optical fiber 20 to be tested will change. This change in angle can make the light better coupled to the optical power meter, thereby improving the light collection efficiency.

[0041] S20, the seed light source 101 outputs seed signal light, so that the seed signal light enters the data processing system 104 through the large mode field active optical fiber 20 to be tested, and the data processing system 104 measures the optical power of the large mode field active optical fiber 20 to be tested.

[0042] Specifically, step S20 also includes: The seed signal light is outputted by the seed light source 101, so that the seed signal light is coupled to the cladding mode filter 103 through the adjustable optical attenuator 102, and enters the data processing system 104 through the large mode field active optical fiber 20 to be tested. The optical power of the large mode field active optical fiber 20 to be tested before truncating is measured by the optical power meter in the data processing system 104.

[0043] S30 , shortening the large mode field active optical fiber 20 to be tested, and recording the shortened length of the large mode field active optical fiber 20 to be tested.

[0044] Specifically, step S30 also includes: The large mode field active optical fiber 20 to be tested is shortened by using tools such as scissors, and the cut length of the large mode field active optical fiber 20 to be tested is recorded.

[0045] S40 , connecting the shortened large mode field active optical fiber 20 to be tested between the cladding mode filter 103 and the data processing system 104 .

[0046] Specifically, step S40 also includes: The shortened large mode field active optical fiber 20 to be tested is fused to one end of the cladding mode filter 103 away from the seed light source 101 , and the other end is cut at an 8° angle and connected to the optical power meter in the data processing system 104 .

[0047] S50, the seed light source 101 outputs seed signal light, so that the seed signal light enters the data processing system 104 through the shortened large mode field active optical fiber 20 to be tested, and the data processing system 104 measures the optical power of the shortened large mode field active optical fiber 20 to be tested.

[0048] Specifically, step S50 also includes: The seed signal light is outputted through the seed light source 101, so that the seed signal light is coupled to the cladding mode filter 103 through the adjustable optical attenuator 102, and the large mode field active optical fiber 20 to be tested after being shortened enters the data processing system 104, and the optical power of the large mode field active optical fiber 20 to be tested after being shortened is measured by the optical power meter in the data processing system 104.

[0049] S60, obtaining the core absorption coefficient of the large mode field active optical fiber 20 to be tested according to the optical power variation of the large mode field active optical fiber 20 to be tested before and after each shortening process, the cut length of each shortening process, the core layer area and the inner cladding area of ​​the large mode field active optical fiber 20 to be tested.

[0050] Specifically, step S60 includes: S601, obtaining the fiber cladding coefficient of the large mode field active optical fiber 20 to be tested after the nth truncation process according to the optical power variation of the large mode field active optical fiber 20 to be tested before and after the nth truncation process and the truncation length of the nth truncation process, where n is a positive integer greater than or equal to 1; S602, obtaining the core absorption coefficient of the large mode field active optical fiber 20 to be tested after the n-th shortening process according to the optical fiber cladding coefficient, the core layer area and the inner cladding area of ​​the large mode field active optical fiber 20 to be tested.

[0051] In step S601, the calculation formula of the optical fiber cladding coefficient of the large mode field active optical fiber 20 to be tested after the n-th shortening process is as follows: (1); in, n represents the fiber cladding coefficient of the large mode field active optical fiber 20 to be tested for the seed signal light with a wavelength of λ after the nth truncation process, P n represents the optical power of the large mode field active optical fiber 20 to be tested after the nth truncation process, P n-1 represents the optical power of the large mode field active optical fiber 20 to be tested after the n-1th shortening process, It represents the cut length of the large mode field active optical fiber 20 to be tested after the nth shortening process.

[0052] In step S602, the calculation formula of the fiber core absorption coefficient is as follows: (2); in, represents the core absorption coefficient of the large mode field active optical fiber 20 to be tested for the seed signal light with a wavelength of λ after the nth truncation process, s represents the core layer area of ​​the large mode field active optical fiber 20 to be tested, and S represents the inner cladding area of ​​the large mode field active optical fiber 20 to be tested.

[0053] Furthermore, since the large mode field active optical fiber 20 to be tested is a double-clad optical fiber with a pedestal layer design, and since the present test method uses a cladding mode filter 103, the seed signal light is only transmitted in the core layer of the large mode field active optical fiber 20 to be tested, but due to the existence of the pedestal layer design, a portion of the seed signal light will enter the pedestal layer for transmission. Therefore, in the large mode field active optical fiber with a pedestal layer design alone, the pedestal layer is equivalent to the cladding of the large mode field active optical fiber, so when the large mode field active optical fiber with a pedestal design is tested by the above method, the core absorption coefficient calculated by the test is actually the absorption coefficient including the pedestal layer.

[0054] Therefore, according to the following relationship between cladding absorption and core absorption in double-clad optical fiber: (3); and then the core absorption coefficient is obtained The calculation formula (2) is:

[0055] Furthermore, after step S602, the method further includes: taking an average value of the multiple groups of core absorption coefficients after the 1st to nth truncation processes to obtain an average core absorption coefficient. The calculation formula (4) of the average core absorption coefficient is as follows: (4); in, represents the average core absorption coefficient of the large mode field active optical fiber 20 to be tested for the seed signal light with a wavelength of λ, k represents the core absorption coefficient of the large mode field active optical fiber 20 to be tested for the seed signal light with a wavelength of λ after the k-th truncation process, 1≤k≤n, and k is a positive integer.

[0056] Specifically, when measuring the fiber core absorption coefficient, the results obtained from multiple measurements may fluctuate within a certain range. Taking the average of these measured values ​​can reduce this random error and improve the accuracy of the measurement.

[0057] The present invention will now be further described with reference to specific embodiments.

[0058] Embodiment 1: Embodiment 1 of the present invention first provides a device 100 for measuring the core absorption coefficient of a large mode field active optical fiber, comprising a seed light source 101, an adjustable optical attenuator 102, a cladding mode filter 103 and a data processing system 104 connected in sequence along the direction from the input end to the output end, and the cladding mode filter 103 and the data processing system 104 are used to connect the large mode field active optical fiber 20 to be measured; The data processing system 104 is used to detect the optical power output by the large mode field active optical fiber 20 to be tested, and obtain the core absorption coefficient of the large mode field active optical fiber 20 to be tested according to the optical power change of the large mode field active optical fiber 20 to be tested after each shortening process, the cut length of each shortening process, the core layer area and the inner cladding area of ​​the large mode field active optical fiber 20 to be tested.

[0059] Specifically, the measuring device 100 also includes a first active connector 105 and a second active connector 106, the first end of the first active connector 105 is connected to the seed light source 101, and the second end of the first active connector 105 is connected to the adjustable optical attenuator 102; the first end of the second active connector 106 is connected to the adjustable optical attenuator 102, and the second end of the second active connector 106 is connected to the first end of the cladding mode filter 103.

[0060] In Embodiment 1 of the present invention, the measuring device 100 further comprises a passive optical fiber that matches the structure of the large mode field active optical fiber 20 to be measured, the first end of the passive optical fiber is connected to the second end of the cladding mode filter 103, and the second end of the passive optical fiber is fused to the large mode field active optical fiber 20 to be measured.

[0061] In Example 1 of the present invention, the seed light source 101 selects a 1535nm single-wave laser light source; the optical power input to the output of the cladding mode filter 103 is adjusted between -20dBm and -10dBm through the adjustable optical attenuator 102; after adjusting the optical power, the passive optical fiber is fused with the large mode field active optical fiber 20 to be tested, and the length of the large mode field active optical fiber 20 to be tested is 20cm.

[0062] In Example 1 of the present invention, the large mode field active optical fiber 20 to be tested is a 25 / 300 Er-Yb co-doped optical fiber, wherein 25 / 300 means that the core diameter is 25 μm and the inner cladding diameter is 300 μm. Then, the core area s of the large mode field active optical fiber 20 to be tested is 490.625 μm. 2 The inner cladding area S of the large mode field active optical fiber 20 to be tested is 70159.375 μm 2 .

[0063] Specifically, the method for measuring the absorption coefficient of the large mode field active optical fiber core provided in Example 1 of the present invention is as follows: Step (1), providing the above-mentioned measuring device 100, welding the first end of the 25 / 300 erbium-ytterbium co-doped optical fiber with a length of 20 cm to be measured to the rear of the cladding mode filter 103, and after welding, cutting the other end of the 25 / 300 erbium-ytterbium co-doped optical fiber at an angle of 8°, and after cutting, connecting the 25 / 300 erbium-ytterbium co-doped optical fiber to the power meter probe of the data processing system 104; Step (2), outputting seed signal light through a 1535nm single-wave laser light source, so that the seed signal light enters the power meter probe of the data processing system 104 through the 25 / 300 erbium-ytterbium co-doped optical fiber, and the optical power P0 of the 25 / 300 erbium-ytterbium co-doped optical fiber measured by the power meter is -21.56dBm; Step (3), performing a first shortening process on the 25 / 300 Erbium-Ytterbium co-doped optical fiber to be tested, and recording the shortening length L1 during the first shortening process as 5.2 cm; Step (4), connecting the 25 / 300 Er-Yb co-doped optical fiber after the first shortening process between the cladding mode filter 103 and the data processing system 104 through an operation similar to step (1); Step (5), outputting seed signal light through a 1535nm single-wave laser light source, so that the seed signal light enters the power meter probe of the data processing system 104 through the 25 / 300 erbium-ytterbium co-doped optical fiber after the first truncation process, and the optical power P1 of the 25 / 300 erbium-ytterbium co-doped optical fiber measured by the power meter is -20.2dBm; Step (6), substitute the optical power P0, optical power P1 and cut length L1 into formula (1) to obtain the fiber cladding coefficient of the 25 / 300 Erbium-Ytterbium co-doped fiber to be tested after the first cut treatment: 1, and the fiber cladding coefficient after the first truncation is Substituting 1 into formula (2), we can obtain the core absorption coefficient of the seed signal light with a wavelength of 1535 nm for the 25 / 300 Er-Yb co-doped fiber to be tested after the first truncation treatment: 104.62dB / m; Step (7), performing a second shortening process on the 25 / 300 Erbium-Ytterbium co-doped optical fiber to be tested, and recording the shortening length L2 during the second shortening process as 5.3 cm; Step (8), connecting the 25 / 300 Er-Yb co-doped optical fiber after the second shortening process between the cladding mode filter 103 and the data processing system 104 through an operation similar to step (1); Step (9), outputting seed signal light through a 1535nm single-wave laser light source, so that the seed signal light enters the power meter probe of the data processing system 104 through the 25 / 300 erbium-ytterbium co-doped optical fiber after the second truncation process, and the optical power P2 of the 25 / 300 erbium-ytterbium co-doped optical fiber measured by the power meter is -18.81dBm; Step (10), substituting the optical power P1, optical power P2 and cut length L2 into formula (1) to obtain the fiber cladding coefficient of the 25 / 300 Erbium-Ytterbium co-doped fiber to be tested after the second shortening process 2, and Substituting 2 into formula (2), we can obtain the core absorption coefficient of the seed signal light with a wavelength of 1535 nm for the 25 / 300 Er-Yb co-doped fiber to be tested after the second shortening treatment: 104.91dB / m; Step (11), performing a third shortening process on the 25 / 300 Erbium-Ytterbium co-doped optical fiber to be tested, and recording the shortening length L3 during the third shortening process as 5.2 cm; Step (12), connecting the 25 / 300 Er-Yb co-doped optical fiber after the third shortening process between the cladding mode filter 103 and the data processing system 104 through an operation similar to step (1); Step (13), outputting seed signal light through a 1535nm single-wave laser light source, so that the seed signal light enters the power meter probe of the data processing system 104 through the 25 / 300 erbium-ytterbium co-doped optical fiber after the third truncation process, and the optical power P3 of the 25 / 300 erbium-ytterbium co-doped optical fiber measured by the power meter is -17.43dBm; Step (14), substituting the optical power P2, optical power P3 and cut length L3 into formula (1) to obtain the fiber cladding coefficient of the 25 / 300 Erbium-Ytterbium co-doped fiber to be tested after the third shortening process: 3, and Substituting 3 into formula (2), we can obtain the core absorption coefficient of the seed signal light with a wavelength of 1535 nm for the 25 / 300 Er-Yb co-doped fiber to be tested after the third truncation treatment: 106.16dB / m; Step (15), , as well as Substitute it into formula (4) and take the average value to get the average core absorption coefficient 105.2dB / m, at this time, the average core absorption coefficient The test results are within the error range and consistent with the design theoretical value.

[0064] The measuring device 100 and the measuring method of the large mode field active optical fiber core absorption coefficient provided by the embodiment of the present invention can be used to measure the core absorption coefficient of doped optical fibers such as erbium-doped large mode field optical fibers and erbium-ytterbium co-doped large mode field optical fibers; the measuring device 100 is simple, and the large mode field active optical fibers used are relatively short, which is convenient for large-scale sampling tests, and the test results are accurate and reliable. In particular, in this test device, when testing large mode field active optical fibers of different sizes, it is necessary to connect a passive optical fiber of corresponding size structure after the cladding mode filter 103 to ensure the accuracy of the test results.

[0065] In summary, different from the prior art, the present invention provides a device 100 for measuring the absorption coefficient of the core of a large mode field active optical fiber and a method for measuring the absorption coefficient of the core of a large mode field active optical fiber. The device 100 comprises a seed light source 101, an adjustable optical attenuator 102, a cladding mode filter 103 and a data processing system 104 which are sequentially connected along the direction from the input end to the output end. The cladding mode filter 103 and the data processing system 104 are used to connect the large mode field active optical fiber 20 to be measured. The data processing system 104 is used to detect the optical power output by the large mode field active optical fiber 20 to be measured, and to obtain the optical power of the large mode field active optical fiber 20 to be measured according to the optical power change amount after each shortening treatment of the large mode field active optical fiber 20 to be measured, the cut length of each shortening treatment, and the core layer of the large mode field active optical fiber 20 to be measured. The core absorption coefficient of the large mode field active optical fiber 20 to be tested is obtained by measuring the core absorption coefficient of the large mode field active optical fiber 20 to be tested; the measuring device 100 for the core absorption coefficient of the large mode field active optical fiber provided by the present invention detects the optical power output by the large mode field active optical fiber 20 to be tested through the data processing system 104, and can accurately measure the core absorption coefficient of the large mode field active optical fiber 20 to be tested according to the optical power change amount of the large mode field active optical fiber 20 to be tested after each shortening treatment, the cut length of each shortening treatment, the core layer area and the inner cladding area of ​​the large mode field active optical fiber 20 to be tested; at the same time, the structure of the above-mentioned measuring device 100 is simple, and the large mode field active optical fiber 20 to be tested used is relatively short, which is convenient for large-scale spot check testing of the large mode field active optical fiber 20 to be tested, which is beneficial to reducing the testing cost.

[0066] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For details not described in individual embodiments, reference may be made to the description in other embodiments.

[0067] The above embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for those of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A device for measuring the absorption coefficient of a large mode field active optical fiber core, characterized in that: It includes a seed light source, an adjustable optical attenuator, a cladding mode filter and a data processing system which are sequentially connected along the direction from the input end to the output end, wherein the cladding mode filter and the data processing system are used to connect the large mode field active optical fiber to be tested; The data processing system is used to detect the optical power output by the large mode field active optical fiber to be tested, and obtain the core absorption coefficient of the large mode field active optical fiber to be tested according to the optical power change of the large mode field active optical fiber to be tested after each shortening process, the cut length of each shortening process, the core layer area and the inner cladding area of ​​the large mode field active optical fiber to be tested.

2. The device for measuring the absorption coefficient of a large mode field active optical fiber core according to claim 1, characterized in that: The seed light source is used to output the seed signal light, and the adjustable optical attenuator is used to adjust the optical power of the seed signal light to between -20dBm and -10dBm.

3. The device for measuring the absorption coefficient of a large mode field active optical fiber core according to claim 1, characterized in that: The measuring device also includes a first active connector and a second active connector, wherein the first end of the first active connector is connected to the seed light source, and the second end of the first active connector is connected to the adjustable optical attenuator; the first end of the second active connector is connected to the adjustable optical attenuator, and the second end of the second active connector is connected to the first end of the cladding mode filter.

4. The device for measuring the absorption coefficient of a large mode field active optical fiber core according to claim 3, characterized in that: The measuring device also includes a passive optical fiber that matches the structure of the large mode field active optical fiber to be measured, the first end of the passive optical fiber is connected to the second end of the cladding mode filter, and the second end of the passive optical fiber is fused with the large mode field active optical fiber to be measured.

5. The device for measuring the absorption coefficient of a large mode field active optical fiber core according to claim 1, characterized in that: The initial length of the large mode field active optical fiber to be tested is 10 to 20 cm, and the remaining length of the large mode field active optical fiber to be tested after the nth shortening process is greater than or equal to 1 cm, where n is a positive integer greater than or equal to 1; the cut length of the large mode field active optical fiber to be tested after each shortening process is 3 to 5 cm.

6. A method for measuring the absorption coefficient of a large mode field active optical fiber core, characterized in that: The method comprises: S10, providing the measuring device according to any one of claims 1 to 5, connecting the large mode field active optical fiber to be measured between the cladding mode filter and the data processing system; S20, outputting the seed signal light through the seed light source, so that the seed signal light enters the data processing system through the large mode field active optical fiber to be tested, and the data processing system measures the optical power of the large mode field active optical fiber to be tested; S30, shortening the large mode field active optical fiber to be tested, and recording the cut length of the large mode field active optical fiber to be tested; S40, connecting the shortened large mode field active optical fiber to be tested between the cladding mode filter and the data processing system; S50, outputting the seed signal light through the seed light source, so that the seed signal light enters the data processing system through the shortened large mode field active optical fiber to be tested, and the data processing system measures the optical power of the shortened large mode field active optical fiber to be tested; S60, obtaining the core absorption coefficient of the large mode field active optical fiber to be tested according to the optical power change of the large mode field active optical fiber to be tested before and after each shortening process, the shortening length of each shortening process, the core layer area and the inner cladding area of ​​the large mode field active optical fiber to be tested.

7. The method for measuring the absorption coefficient of the large mode field active optical fiber core according to claim 6, characterized in that: The S60 step specifically includes: S601, obtaining a fiber cladding coefficient of the large mode field active optical fiber to be tested after the nth truncation process according to the optical power variation of the large mode field active optical fiber to be tested before and after the nth truncation process and the cut length of the nth truncation process, where n is a positive integer greater than or equal to 1; S602, obtaining the core absorption coefficient of the large mode field active optical fiber to be tested after the n-th shortening process according to the optical fiber cladding coefficient, the core layer area and the inner cladding area of ​​the large mode field active optical fiber to be tested.

8. The method for measuring the absorption coefficient of the large mode field active optical fiber core according to claim 7, characterized in that: In the step S601, the calculation formula of the optical fiber cladding coefficient of the large mode field active optical fiber to be tested after the n-th truncation process is as follows: ； in, n represents the fiber cladding coefficient of the seed signal light with a wavelength of λ after the large mode field active fiber to be tested is shortened for the nth time, P n represents the optical power of the large mode field active optical fiber to be tested after the nth truncation process, P n-1 represents the optical power of the large mode field active optical fiber to be tested after the n-1th shortening process, It indicates the cut length of the large mode field active optical fiber to be tested after the nth shortening process.

9. The method for measuring the absorption coefficient of a large mode field active optical fiber core according to claim 8, characterized in that: In the step S602, the calculation formula of the core absorption coefficient is as follows: ； in, represents the core absorption coefficient of the seed signal light with a wavelength of λ after the large mode field active optical fiber to be tested has been shortened for the nth time, s represents the core layer area of ​​the large mode field active optical fiber to be tested, and S represents the inner cladding area of ​​the large mode field active optical fiber to be tested.

10. The method for measuring the core absorption coefficient of a large mode field active optical fiber according to claim 9, characterized in that: After the step S602, the method further includes: taking an average value of the plurality of groups of the core absorption coefficients after the 1st to nth truncation processes to obtain an average core absorption coefficient, wherein the calculation formula of the average core absorption coefficient is as follows: ； in, represents the average core absorption coefficient of the large mode field active optical fiber to be tested to the seed signal light with a wavelength of λ, k represents the core absorption coefficient of the large mode field active optical fiber to be tested for the seed signal light with a wavelength of λ after the k-th truncation process, 1≤k≤n, and k is a positive integer.

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