CN108931486B - Fiber core absorption coefficient testing system and method of ytterbium-doped optical fiber - Google Patents

Fiber core absorption coefficient testing system and method of ytterbium-doped optical fiber Download PDF

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CN108931486B
CN108931486B CN201810499750.6A CN201810499750A CN108931486B CN 108931486 B CN108931486 B CN 108931486B CN 201810499750 A CN201810499750 A CN 201810499750A CN 108931486 B CN108931486 B CN 108931486B
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optical fiber
ytterbium
fiber
doped
doped optical
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CN108931486A (en
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孙程
黄宏琪
曹蓓蓓
陶金金
刘琦
何亮
张承炎
王鹏
蔡杰
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Changfei Guangfang Wuhan Technology Co ltd
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Yangtze Optical Fibre and Cable Co Ltd
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Abstract

The invention discloses a system and a method for testing the absorption coefficient of a fiber core of an ytterbium-doped optical fiber. The system comprises a light injection device, a mode filtering device and a spectrum analyzer which are sequentially arranged; one end of the ytterbium-doped optical fiber to be detected is connected with the light injection device; the other end of the filter is connected with the filter die device. The method comprises the following steps: (1) loading an ytterbium-doped optical fiber to be tested to the system, and enabling one end of the ytterbium-doped optical fiber to be connected with the output end matched with the core diameter of the optical injection device and the other end of the ytterbium-doped optical fiber to be connected with the input end matched with the core diameter of the filter module device; (2) monitoring an absorption spectrum from 600nm to 1000nm in real time by adopting a leveling spectrum analyzer, and monitoring an alpha coefficient; (3) adjusting the length of the measured optical fiber until the alpha coefficient is in a confidence interval; and calculating the absorption coefficients of the 915nm wavelength and the 976nm wavelength of the ytterbium-doped optical fiber to be detected at the moment as the absorption coefficients of the fiber core of the optical fiber to be detected. The invention has accurate and reliable test result and good consistency.

Description

Fiber core absorption coefficient testing system and method of ytterbium-doped optical fiber
Technical Field
The invention belongs to the field of optical fiber testing, and particularly relates to a system and a method for testing the absorption coefficient of a fiber core of an ytterbium-doped optical fiber.
Background
Yb-doped optical fiber is formed by doping Yb into the core rod of optical fiber preform3+Ion doping of Yb in optical fibers3+The purpose of the ions is to make a common passive transmission fiber an active fiber with amplification capability. Yb of3+The absorption and emission cross-section of ions in quartz glass directly influences Yb doping3+Fluorescence output of fiber lasers and amplifiers. The ytterbium-doped fiber has high efficiency for 915nm and 976nm wavelength lightThe strong absorption characteristic is that the absorption peak at the wavelength of 915nm is small but the absorption spectrum is wide, and the absorption coefficient corresponding to the absorption peak at 976nm is large but the absorption peak is narrow.
The current technological methods for preparing ytterbium-doped optical fibers mainly include liquid phase doping and gas phase doping. With the rapid development of the market of high-power ytterbium-doped fiber lasers, higher requirements are put forward on the performance of ytterbium-doped fibers, particularly the doping uniformity; meanwhile, as the process route of the large-size optical fiber preform becomes mature gradually, the improvement of the productivity and the consistency of the optical fiber is a key important factor.
To obtain a high doped amount, the doping mechanism and the doping process of the optical fiber need to be studied deeply, and the absorption performance and the doping uniformity of the ytterbium-doped optical fiber have a significant influence on the active function of the doped optical fiber. The method is a method for directly judging the absorption performance and uniformity of the optical fiber preform by quickly and effectively detecting the absorption coefficient of the multipoint fiber core of the ytterbium-doped optical fiber.
The absorption coefficient of the ytterbium-doped fiber is divided into a fiber core absorption coefficient and a cladding absorption coefficient, the cladding is divided into an inner cladding and an outer cladding, and the influence factors comprise loss, the shape of the cladding and the geometric dimension, and are relatively complex. The absorption coefficient of the fiber core of the optical fiber can also be tested, the circular ytterbium-doped optical fiber can be tested, and the optical fiber preform which is polished into an octagonal shape is not needed in the process experiment, so that the experimental research cost and time can be further reduced. At present, the absorption coefficient of the optical fiber is measured, and the absorption coefficient of the fiber core obtained by testing the long optical fiber is mainly influenced by transmission loss, cladding absorption and gain, so that the doping performance of the fiber core cannot be accurately evaluated. And the short optical fiber is adopted for testing, the mode control is complex, and the accurate testing is difficult.
Disclosure of Invention
Aiming at the defects or improvement requirements in the prior art, the invention provides a fiber core absorption coefficient testing system and method of an ytterbium-doped optical fiber, and aims to realize the test of the fiber core absorption coefficient under the transmission of a ytterbium-doped optical fiber fundamental mode by adopting a short optical fiber and a mode filtering device, obtain the accurate and good-repeatability test result of the fiber core absorption coefficient of the ytterbium-doped optical fiber, and solve the technical problems that the existing absorption coefficient test of the ytterbium-doped optical fiber cannot simply test the fiber core absorption coefficient, the result is inaccurate and the consistency is low.
In order to achieve the above object, according to an aspect of the present invention, there is provided a system for testing an absorption coefficient of a core of an ytterbium-doped optical fiber, comprising a light injection device, a mode filtering device, and a spectrum analyzer, which are sequentially disposed; one end of the ytterbium-doped optical fiber to be detected is connected with the light injection device; the other end of the filter is connected with the filter die device;
and laser in the interested waveband is excited by the light injection device and injected into the ytterbium-doped optical fiber to be detected, enters the spectrum analyzer through the filter module device, and determines the absorption coefficient of the ytterbium-doped optical fiber to be detected according to an analysis result output by the spectrum analyzer.
Preferably, the fiber core absorption coefficient test system of the ytterbium-doped optical fiber, the filter module device of which is a multi-channel optical fiber coupler, includes a plurality of input ends and corresponding output ends thereof, the input ends are bare fibers matched with the core diameter of the optical fiber to be tested and used for being aligned and welded with the optical fiber to be tested through the fiber core, the output ends are cut-off wavelength optical fibers with cut-off wavelengths smaller than 900nm, and the bare fibers at the input ends are welded and coupled with the cut-off wavelength optical fibers at the corresponding output ends after tapering.
Preferably, in the core absorption coefficient test system for the ytterbium-doped optical fiber, the cut-off wavelength optical fiber is a jumper.
Preferably, the optical injection device of the fiber core absorption coefficient test system of the ytterbium-doped optical fiber comprises a supercontinuum light source and a multichannel optical fiber coupler; the multichannel optical fiber coupler comprises a plurality of integrated coupling jumper wires, wherein the input end of the multichannel optical fiber coupler is a jumper wire head, and the output end of the multichannel optical fiber coupler is a bare optical fiber and is used for screening modes and matching ytterbium-doped optical fibers to be detected.
Preferably, in the fiber core absorption coefficient test system of the ytterbium-doped optical fiber, the supercontinuum light source outputs laser light with a wavelength range of 600-1000 nm.
Preferably, the system for testing the core absorption coefficient of the ytterbium-doped optical fiber further comprises a first and/or second cladding mode stripping device;
one end of the ytterbium-doped optical fiber to be tested is welded with the light injection device, and the welding point of the ytterbium-doped optical fiber to be tested and the light injection device is arranged in the first cladding mold stripping device; the other end of the filter mould device is welded with the filter mould device, and the welding point of the filter mould device and the filter mould device is arranged in a second cladding mould stripping device; the two cladding mode stripping devices are the same, and when the optical fiber to be tested is short, the two welding points are arranged in one cladding mode stripping device.
Preferably, the core absorption coefficient test system of the ytterbium-doped optical fiber, wherein the cladding mode stripping device comprises a heat conduction material groove, and the material is preferably copper or aluminum; the groove is filled with high-refractive-index liquid glue, and the relative refractive index of the glue at the wavelength of 589nm is larger than or equal to 1.47.
According to another aspect of the present invention, there is provided a method for measuring the core absorption coefficient of an ytterbium-doped optical fiber, comprising the steps of:
(1) loading the ytterbium-doped optical fiber to be tested to the fiber core absorption coefficient test system of the ytterbium-doped optical fiber, so that one end of the ytterbium-doped optical fiber is connected with the output end matched with the core diameter of the light injection device, and the other end of the ytterbium-doped optical fiber is connected with the input end matched with the core diameter of the filter module device;
(2) monitoring an absorption spectrum from 600nm to 1000nm in real time by adopting a leveling spectrum analyzer, and monitoring an alpha coefficient; wherein the alpha coefficient is calculated according to the following method:
Figure BDA0001669991060000031
wherein
Figure BDA0001669991060000032
To test the optical power value of the length of ytterbium-doped fiber to be tested at 915nm wavelength,
Figure BDA0001669991060000033
the optical power value of the ytterbium-doped optical fiber to be tested with the standard length at the wavelength of 915nm,
Figure BDA0001669991060000034
the ytterbium-doped optical fiber to be tested for testing the length is at 976nmThe value of the light power at the long side,
Figure BDA0001669991060000035
the optical power value of the ytterbium-doped optical fiber to be detected with the standard length at the wavelength of 976nm is obtained;
(3) adjusting the length of the optical fiber to be detected until the alpha coefficient is in a confidence interval; calculating the absorption coefficients of the 915nm wavelength and the 976nm wavelength of the ytterbium-doped optical fiber to be detected at the moment as the absorption coefficients of the fiber core of the optical fiber to be detected; the method comprises the following specific steps:
Figure BDA0001669991060000041
Figure BDA0001669991060000042
wherein the ABS915ABS as the fiber core absorption coefficient at 915nm wavelength under the length of the ytterbium-doped optical fiber to be measured976The fiber core absorption coefficient L at the wavelength of 976nm under the length of the ytterbium-doped optical fiber to be detected1The length L of the ytterbium-doped fiber to be measured at the moment0Is of standard length.
Preferably, the confidence interval of the alpha coefficient of the method for testing the core absorption coefficient of the ytterbium-doped optical fiber is [2.5, 3.5 ].
Preferably, in the method for testing the core absorption coefficient of the ytterbium-doped optical fiber, the leveling spectrum analyzer takes a non-absorption wavelength range below the cut-off wavelength of the mode filtering device as a leveling base section.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
the system and the method provided by the invention furthest eliminate the interference caused by a high-order optical mode, test the fiber core absorption coefficient of the ytterbium-doped optical fiber during the transmission of a fundamental mode under the full injection condition, and have accurate and reliable result, good repeatability and good consistency.
The preferred scheme can test the fiber core absorption spectrum of the ytterbium-doped optical fiber with large core diameter and common core diameter and the absorption coefficients of two characteristic absorption peak wavelengths to test various types of ytterbium-doped optical fibers, only matched filter mode coupling optical fibers need to be replaced, an all-optical-path system is adopted, the system is modularized in building, the protection system can be fine, the assembly is simple, an operator can easily get on the hand, and the later maintenance is simple. Meanwhile, the test system is a faster test system in the optical test of the ytterbium-doped optical fiber, can feed back in time to guide the process, and provides effective help for the research of the high-doping-concentration ytterbium-doped optical fiber and the improvement of the capacity and the batch consistency.
Drawings
FIG. 1 is a schematic structural diagram of an absorption coefficient testing system for a fiber core of an ytterbium-doped fiber provided by the present invention;
FIG. 2 is a core absorption spectrum and absorption coefficients at two characteristic absorption peak wavelengths for an ytterbium-doped fiber of example 10/125 of the present invention;
FIG. 3 is a core absorption spectrum and absorption coefficients at two characteristic absorption peak wavelengths for an ytterbium-doped fiber of example 20/125 of the present invention;
FIG. 4 is a core absorption spectrum and absorption coefficients at two characteristic absorption peak wavelengths for an ytterbium-doped fiber of example 25/250 of the present invention.
The same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein: 1 is a light injection device, 2 is a first or second cladding mode stripping device, 3 is a filter mode device, and 4 is a spectrum analyzer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The fiber core absorption coefficient testing system of the ytterbium-doped optical fiber, as shown in fig. 1, comprises a light injection device, a cladding mode stripping device, a mode filtering device and a spectrum analyzer which are arranged in sequence; one end of the ytterbium-doped optical fiber to be tested is connected with the light injection device, preferably is welded with the light injection device, and the welding point of the ytterbium-doped optical fiber to be tested and the light injection device is arranged in the first cladding mold stripping device; the other end of the filtering mold device is connected with the filtering mold device, preferably welded with the filtering mold device, and the welding point of the filtering mold device and the filtering mold device is arranged in a second cladding mold stripping device;
and laser in the interested waveband is excited by the light injection device and injected into the ytterbium-doped optical fiber to be detected, enters the spectrum analyzer through the filter module device, and determines the absorption coefficient of the ytterbium-doped optical fiber to be detected according to an analysis result output by the spectrum analyzer.
The light injection device comprises a supercontinuum light source and a multi-channel optical fiber coupler. Preferably, the laser output tail fiber is a CS1060 optical fiber, and is connected with the multi-channel optical fiber coupler through an optical fiber adapter flange plate, so that the operation is simple, and equipment is protected. The super-continuum spectrum laser has high brightness and wide spectrum output characteristics, is suitable for being used as a laser source for testing the absorption coefficient of the optical fiber by a truncation method, and is suitable for testing the fiber core absorption performance of the ytterbium-doped optical fiber within the wavelength range of 600-1000 nm. However, the output pigtail of the laser is generally a CS1060 fiber, and if the output pigtail is directly fusion-spliced with a measured fiber, it is very inconvenient to adjust the length of the ytterbium-doped fiber to be measured and match different ytterbium-doped fibers to be measured, and may also cause that the laser cannot be fully injected, and excite a high-order mode to cause an inaccurate test result and a poor consistency, so that a multi-channel fiber coupler is required to be added to the measured fiber. The multichannel optical fiber coupler comprises a plurality of integrated coupling jumper wires, wherein the input end of the multichannel optical fiber coupler is a jumper wire head, and the output end of the multichannel optical fiber coupler is a bare optical fiber and is used for screening modes and matching ytterbium-doped optical fibers to be detected. Preferably, the multichannel optical fiber coupler is an optical fiber coupler formed by three optical coupling units made of 1.2 m coupling jumper wires, and the screening mode ensures that a fundamental mode is transmitted to optical fibers to be tested with various diameters from a tail fiber of the multichannel optical fiber coupler, so that a high-order mode is prevented from being excited, and a large mode field diameter meets the incidence condition of full injection. Specifically, the input end of the optical fiber cable is an FC/PC jumper wire head which is connected with a super-continuum spectrum light source, and the output end of the optical fiber cable is a bare optical fiber which is directly welded with an optical fiber to be detected. The three 1.2-meter coupling jumper wires are respectively a G.652 single-mode optical fiber jumper wire, a single-package matched optical fiber jumper wire (NA0.062 +/-0.005) with the core package diameter of 30/250 mu m and a single-package matched optical fiber (NA0.06 +/-0.005) with the core package diameter of 30/400 mu m, the flange plate of the optical fiber adapter is of an FC/PC type, the insertion loss is 0.2dB, the test output power can be guaranteed to be attenuated to the acceptable range of a system detector, and therefore system equipment is protected.
The two cladding die stripping devices comprise heat conduction material grooves with triangular bottoms for preventing liquid from overflowing, and the material is preferably copper or aluminum; high-refractive-index liquid glue is injected into the groove, and the relative refractive index of the glue at the wavelength of 589nm is larger than or equal to 1.47. Stripping all coating layers on the surface of the optical fiber glass completely, wherein no coating is left on the surface, one end of the ytterbium-doped optical fiber to be detected is in fusion joint with the light injection device, and the fusion joint point of the ytterbium-doped optical fiber to be detected and the light injection device is arranged in the first cladding mold stripping device; the other end of the filter mould device is welded with the filter mould device, and the welding point of the filter mould device and the second cladding mould stripping device is arranged in the second cladding mould stripping device.
The mode filtering device is a multi-channel optical fiber coupler, the output end of the mode filtering device comprises a plurality of input ends and corresponding output ends, the input ends are bare fibers matched with the core diameter of an optical fiber to be detected and used for being aligned and welded with the optical fiber to be detected through the fiber cores, the output ends are cut-off wavelength optical fibers with cut-off wavelengths smaller than 900nm, and the bare fibers at the input ends are welded and coupled with the cut-off wavelength optical fibers at the corresponding output ends after tapering. Preferably, the optical fiber patch board comprises four input end bare optical fibers which are used for being matched with optical fibers to be detected through fiber cores to carry out fiber core alignment fusion, and a special cut-off wavelength optical fiber C-SMF jumper produced by the Long-fly optical fiber cable company Limited, a single-package matching optical fiber with 20/125 mu m core package diameter, a single-package matching optical fiber with 30/250 mu m core package diameter and a single-package matching optical fiber with 30/400 mu m core package diameter; the corresponding output end is a special cut-off wavelength optical fiber C-SMF jumper wire, the cut-off wavelength of the special cut-off wavelength optical fiber C-SMF jumper wire is less than 900nm, the interested test section (915nm and 976nm) is ensured to be in a single mode condition, when other mode tests are inhibited, the corresponding optical fiber line jumper wire head is connected with an optical spectrum analyzer, and four input end optical fibers and four output end optical fibers are respectively tapered and then are welded and coupled to form four coupling channels.
The invention provides a method for testing the fiber core absorption coefficient of an ytterbium-doped optical fiber, and a system for testing the fiber core absorption coefficient of the ytterbium-doped optical fiber, which is applied, comprises the following steps:
(1) connecting one end of the ytterbium-doped optical fiber to be tested with the output end of the light injection device, preferably welding the ytterbium-doped optical fiber with the output end of the light injection device, and placing a welding point in glue of the first coating mold stripping device; connecting the other end of the ytterbium-doped optical fiber to be tested with the input end of the filter module device, preferably welding the other end of the ytterbium-doped optical fiber to the input end of the filter module device, and placing a welding point in glue of a second coating module stripping device; preferably, the welding is performed in a core alignment mode, and welding loss can be kept relatively stable.
(2) Monitoring an absorption spectrum from 600nm to 1000nm in real time by adopting a leveling spectrum analyzer, and monitoring an alpha coefficient; wherein the alpha coefficient is calculated according to the following method:
Figure BDA0001669991060000071
wherein
Figure BDA0001669991060000072
To test the optical power value of the length of ytterbium-doped fiber to be tested at 915nm wavelength,
Figure BDA0001669991060000073
the optical power value of the ytterbium-doped optical fiber to be tested with the standard length at the wavelength of 915nm,
Figure BDA0001669991060000074
in order to test the optical power value of the ytterbium-doped optical fiber to be tested at the wavelength of 976nm,
Figure BDA0001669991060000075
the optical power value of the ytterbium-doped optical fiber to be detected with the standard length at the wavelength of 976nm is obtained;
the leveling spectrum analyzer takes a non-absorption wavelength range below the cut-off wavelength of the filter module device as a leveling base section, and preferably the leveling base section is 600nm to 800 nm. Analyzing and processing the system reliability of the power detected by the spectrum analyzer, and removing the system self-error to the maximum extent by a preset instruction; through the wavelength range without absorption below the cut-off wavelength, the preset instruction leveling maximally removes errors caused by two times of welding points, and balance is performed on the precision and the test time so as to reduce the errors.
(3) Adjusting the length of the optical fiber to be detected until the alpha coefficient is in a confidence interval; calculating the absorption coefficients of the 915nm wavelength and the 976nm wavelength of the ytterbium-doped optical fiber to be detected at the moment as the absorption coefficients of the fiber core of the optical fiber to be detected; the method comprises the following specific steps:
Figure BDA0001669991060000081
Figure BDA0001669991060000082
wherein the ABS915ABS as the fiber core absorption coefficient at 915nm wavelength under the length of the ytterbium-doped optical fiber to be measured976The fiber core absorption coefficient L at the wavelength of 976nm under the length of the ytterbium-doped optical fiber to be detected1The length L of the ytterbium-doped fiber to be measured at the moment0Is of standard length.
The confidence interval of the alpha coefficient is [2.5, 3.5], the ytterbium-doped optical fiber has very strong absorption characteristics at the wavelengths of 915nm and 976nm, and the principle judgment and test accuracy of the absorption coefficient of 976nm light waves in the ytterbium-doped optical fiber is nearly 3 times that of 915nm light waves.
The absorption coefficient of the fiber core obtained by short fiber test is used for simply measuring the absorption coefficient of the fiber core of unit fiber length to pumping light, so that Yb can be accurately evaluated3+Ion core absorption, and Yb3+And the doping uniformity effect of ions in the fiber core of the prefabricated rod is further evaluated. However, the short ytterbium-doped fiber test is easy to have the problems of insufficient spectral injection and excitation of high-order mode, so that the test result is inaccurate and poor in consistencyThe method has accurate effect and good consistency, and is convenient to match ytterbium-doped optical fibers of various specifications.
The following are examples:
example 1
A fiber core absorption coefficient test system of an ytterbium-doped optical fiber comprises a light injection device, a first cladding mode stripping device, a second cladding mode stripping device, a mode filtering device and a spectrum analyzer which are sequentially arranged; one end of the ytterbium-doped optical fiber to be tested is welded with the light injection device, and the welding point of the ytterbium-doped optical fiber to be tested and the light injection device is arranged in the first cladding mold stripping device; the other end of the filter mould device is welded with the filter mould device, and the welding point of the filter mould device and the filter mould device is arranged in the second cladding mould stripping device;
and laser in the interested waveband is excited by the light injection device and injected into the ytterbium-doped optical fiber to be detected, enters the spectrum analyzer through the filter module device, and determines the absorption coefficient of the ytterbium-doped optical fiber to be detected according to an analysis result output by the spectrum analyzer.
The light injection device comprises a supercontinuum light source and a multi-channel optical fiber coupler. The super-continuum spectrum laser outputs a wavelength range of 600-1000 nm, and the output tail fiber is CS1060 and is connected with the multichannel optical fiber coupler through an optical fiber adapter flange plate. The multichannel optical fiber coupler is an optical fiber coupler consisting of optical coupling units made of three 1.2-meter coupling jumpers, the input end of the multichannel optical fiber coupler is an FC/PC jumper wire head, the insertion loss is 0.2dB, and the output end of the multichannel optical fiber coupler is bare optical fibers. The three 1.2-meter coupling jumper wires are respectively a G.652 single-mode optical fiber jumper wire, a single-package matched optical fiber jumper wire (NA0.062 +/-0.005) with the core package diameter of 30/250 mu m and a single-package matched optical fiber (NA0.06 +/-0.005) with the core package diameter of 30/400 mu m.
The first and second cladding die stripping devices comprise a copper groove which is provided with a triangular bottom and prevents liquid from overflowing; high-refractive-index liquid glue is injected into the groove, and the relative refractive index of the glue at the wavelength of 589nm is larger than or equal to 1.47.
The input end of the filter module device comprises four input end optical fibers, the four input end optical fibers are used for being matched with optical fibers to be detected through fiber cores to carry out fiber core alignment fusion welding, the four input end optical fibers are respectively a long-flying special cut-off wavelength optical fiber C-SMF, a single-package matching optical fiber with the core package diameter of 20/125 mu m, a single-package matching optical fiber with the core package diameter of 30/250 mu m and a single-package matching optical fiber with the core package diameter of 30/400 mu m, the corresponding output end of the filter module device is a long-flying special cut-off wavelength optical fiber C-SMF jumper wire, the cut-off wavelength of the filter module device is 900nm, other three input end optical fibers and output end optical.
Example 2
A method for testing the absorption coefficient of a fiber core of an ytterbium-doped optical fiber applies a system for testing the absorption coefficient of the fiber core of the ytterbium-doped optical fiber provided by embodiment 1, and comprises the following steps:
(1) stripping all coating layers on the surface of ytterbium-doped optical fiber glass to be detected completely, wherein no coating layer is left on the surface, one end of the ytterbium-doped optical fiber glass is welded with the output end of the multi-channel optical fiber coupler of the light injection device in a fiber core alignment mode, and a welding point is arranged in the first cladding mode stripping device and is immersed in high-refractive-index liquid glue; the other end of the filter module is welded with the input end of the filter module device, and the welding point is arranged in the first cladding module stripping device and is immersed in the high-refractive-index liquid glue.
(2) Monitoring an absorption spectrum from 600nm to 1000nm in real time by adopting a leveling spectrum analyzer, and monitoring an alpha coefficient; wherein the alpha coefficient is calculated according to the following method:
Figure BDA0001669991060000101
wherein
Figure BDA0001669991060000102
To test the optical power value of the length of ytterbium-doped fiber to be tested at 915nm wavelength,
Figure BDA0001669991060000103
the optical power value of the ytterbium-doped optical fiber to be tested with the standard length at the wavelength of 915nm,
Figure BDA0001669991060000104
in order to test the optical power value of the ytterbium-doped optical fiber to be tested at the wavelength of 976nm,
Figure BDA0001669991060000105
the optical power value of the ytterbium-doped optical fiber to be detected with the standard length at the wavelength of 976nm is obtained;
the leveling spectrum analyzer takes a non-absorption wavelength range below the cut-off wavelength of the filter module device as a leveling base section, and preferably the leveling base section is 600nm to 800 nm. Analyzing and processing the system reliability of the power detected by the spectrum analyzer, and removing the system self-error to the maximum extent by a preset instruction; through the wavelength range without absorption below the cut-off wavelength, the preset instruction leveling maximally removes errors caused by two times of welding points, and balance is performed on the precision and the test time so as to reduce the errors.
(3) Adjusting the length of the optical fiber to be detected until the alpha coefficient is in a confidence interval; calculating the absorption coefficients of the 915nm wavelength and the 976nm wavelength of the ytterbium-doped optical fiber to be detected at the moment as the absorption coefficients of the fiber core of the optical fiber to be detected; the method comprises the following specific steps:
Figure BDA0001669991060000106
Figure BDA0001669991060000107
wherein the ABS915ABS as the fiber core absorption coefficient at 915nm wavelength under the length of the ytterbium-doped optical fiber to be measured976The fiber core absorption coefficient L at the wavelength of 976nm under the length of the ytterbium-doped optical fiber to be detected1The length L of the ytterbium-doped fiber to be measured at the moment0The standard length is in the range < 1.5cm, with 1cm being chosen for this example. The confidence interval of the alpha coefficient is [2.5, 3.5]。
When the optical fiber to be tested is 5/125, 7/128, 10/125 and 10/130 mu m ytterbium-doped optical fiber, the tail fiber of the supercontinuum laser is connected with the input port G.652 single-mode optical fiber jumper of the multi-channel optical fiber coupler through the optical fiber adapter flange plate, the output end G.652 single-mode optical fiber of the multi-channel optical fiber coupler is welded with the ytterbium-doped optical fiber to be tested, and the output end of the ytterbium-doped optical fiber to be tested is welded with the ytterbium-doped optical fiber to beThe fiber is welded with the input end of a first channel cut-off wavelength fiber C-SMF of a multi-channel coupler of the filter module device, and an FC/PC jumper wire joint at the output end of the first channel of the multi-channel coupler of the filter module device is connected with a spectrum analyzer and a spectrum analyzer; l is1Is 5 cm.
When the optical fiber to be tested is an 20/125 and 20/130 mu m ytterbium-doped optical fiber, a tail fiber of the supercontinuum laser is connected with a G.652 single-mode optical fiber jumper of a first channel input port of a multi-channel optical fiber coupler through an optical fiber adapter flange plate, a G.652 single-mode optical fiber of a first channel output end of the multi-channel optical fiber coupler is welded with the ytterbium-doped optical fiber to be tested, an output end of the ytterbium-doped optical fiber to be tested is welded with an input end of a 20/125 mu m single-package matching optical fiber of a second channel of the multi-channel coupler of a mode filtering device, and an FC/PC jumper head of an output end of the second channel of the multi-channel coupler; l is1Is 5 cm.
When the optical fiber to be tested is an 25/250 and 30/250 mu m ytterbium-doped optical fiber, a tail fiber of the supercontinuum laser and a second channel 30/250 mu m single-packet matching optical fiber jumper input port of a multi-channel optical fiber coupler are connected through an optical fiber adapter flange plate, the output end of the second channel 30/250 mu m single-packet matching optical fiber of the multi-channel optical fiber coupler is welded with the ytterbium-doped optical fiber to be tested, the output end of the ytterbium-doped optical fiber to be tested is welded with the input end of a third channel 30/250 mu m single-packet matching optical fiber of a multi-channel coupler optical fiber of a filter module device, and an output end FC/PC jumper head of a third channel of the multi-channel coupler of the filter module device; l is1Is 5 cm.
When the optical fiber to be tested is an 20/400, 25/400 and 30/400 mu m ytterbium-doped optical fiber, a tail fiber of the supercontinuum laser is connected with a third channel 30/400 mu m single-packet matched optical fiber jumper input port of a multi-channel optical fiber coupler through an optical fiber adapter flange plate, the output end of the third channel 30/400 mu m single-packet matched optical fiber of the multi-channel optical fiber coupler is welded with the ytterbium-doped optical fiber to be tested, the output end of the ytterbium-doped optical fiber to be tested is welded with the input end of a fourth channel 30/400 mu m single-packet matched optical fiber of a multi-channel coupler of a filter module device, and an output end FC/PC jumper head of the fourth channel of the multi-channel coupler of the filter module device; l is1Is 40 cm.
In this embodiment, the core absorption spectrum of the 10/125 ytterbium-doped fiber obtained by analysis and processing after the test and the absorption coefficients at two characteristic absorption peak wavelengths are shown in fig. 2; in this embodiment, the core absorption spectrum of the 20/125 ytterbium-doped fiber obtained by analysis and processing after the test and the absorption coefficients at two characteristic absorption peak wavelengths are shown in fig. 3; the core absorption spectrum of the 25/250 ytterbium-doped fiber obtained by analysis and processing after the test of this example and the absorption coefficients at two characteristic absorption peak wavelengths are shown in fig. 4.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (8)

1. A fiber core absorption coefficient test system of an ytterbium-doped optical fiber is characterized by comprising a light injection device, a mode filtering device and a spectrum analyzer which are sequentially arranged; one end of the ytterbium-doped optical fiber to be detected is connected with the light injection device; the other end of the filter is connected with the filter die device; the output end of the filter module device is a special cut-off wavelength optical fiber, and the cut-off wavelength is less than 900 nm;
laser of an interested waveband is excited by the light injection device and injected into the ytterbium-doped optical fiber to be detected, the ytterbium-doped optical fiber enters a spectrum analyzer through a filter module device, and the fiber core absorption coefficient of the ytterbium-doped optical fiber to be detected is determined according to an analysis result output by the spectrum analyzer;
the mode filtering device is a multi-channel optical fiber coupler and comprises a plurality of input ends and corresponding output ends, the input ends are bare fibers matched with the core diameter of an optical fiber to be detected and are used for aligning and welding with the optical fiber to be detected through fiber cores, and the bare fibers at the input ends are welded and coupled with the cut-off wavelength optical fibers at the corresponding output ends after tapering;
the system further comprises first and second overcladding die stripping apparatus;
one end of the ytterbium-doped optical fiber to be tested is welded with the light injection device, and the welding point of the ytterbium-doped optical fiber to be tested and the light injection device is arranged in the first cladding mold stripping device; the other end of the filter mould device is welded with the filter mould device, and the welding point of the filter mould device and the filter mould device is arranged in the second cladding mould stripping device; the two cladding die stripping devices are the same, and when the optical fiber to be tested is short, the two welding points are arranged in one cladding die stripping device;
the cladding die stripping device comprises a heat conduction material groove; the groove is filled with high-refractive-index liquid glue, and the relative refractive index of the glue at the wavelength of 589nm is larger than or equal to 1.47.
2. The system for testing the core absorption coefficient of ytterbium-doped fiber of claim 1, wherein the fiber with an output end cutoff wavelength less than 900nm is a jumper.
3. The system for testing the core absorption coefficient of an ytterbium-doped fiber as claimed in claim 1, wherein the light injection device comprises a supercontinuum light source and a multichannel fiber coupler; the multichannel optical fiber coupler comprises a plurality of integrated coupling jumper wires, wherein the input end of the multichannel optical fiber coupler is a jumper wire head, and the output end of the multichannel optical fiber coupler is a bare optical fiber and is used for screening modes and matching ytterbium-doped optical fibers to be detected.
4. The system for testing the absorption coefficient of the core of an ytterbium-doped fiber according to claim 3, wherein the supercontinuum light source is capable of outputting laser light in a wavelength range of 600 to 1000 nm.
5. The system for testing the core absorption coefficient of an ytterbium-doped fiber according to claim 1, wherein the cladding mode stripping means is preferably made of copper or aluminum.
6. A method for testing the absorption coefficient of a fiber core of an ytterbium-doped optical fiber is characterized by comprising the following steps:
(1) loading a ytterbium-doped optical fiber to be tested to the fiber core absorption coefficient test system of the ytterbium-doped optical fiber according to any one of claims 1 to 4, so that one end of the ytterbium-doped optical fiber is connected with the output end matched with the core diameter of the light injection device, and the other end of the ytterbium-doped optical fiber is connected with the input end matched with the core diameter of the mode filtering device;
(2) monitoring an absorption spectrum from 600nm to 1000nm in real time by adopting a leveling spectrum analyzer, and monitoring an alpha coefficient; wherein the alpha coefficient is calculated according to the following method:
Figure FDA0002709214770000021
wherein
Figure FDA0002709214770000022
The optical power value of the ytterbium-doped optical fiber to be tested at the wavelength of 915nm in the initial test length,
Figure FDA0002709214770000023
the optical power value of the ytterbium-doped optical fiber to be tested with the standard length at the wavelength of 915nm,
Figure FDA0002709214770000024
the optical power value of the ytterbium-doped optical fiber to be tested at the wavelength of 976nm in the initial test length,
Figure FDA0002709214770000025
the optical power value of the ytterbium-doped optical fiber to be detected with the standard length at the wavelength of 976nm is obtained;
(3) adjusting the length of the optical fiber to be detected until the alpha coefficient is in a confidence interval; calculating the absorption coefficients of the 915nm wavelength and the 976nm wavelength of the ytterbium-doped optical fiber to be detected at the moment as the absorption coefficients of the fiber core of the optical fiber to be detected; the method comprises the following specific steps:
Figure FDA0002709214770000026
Figure FDA0002709214770000027
wherein the ABS915ABS as the fiber core absorption coefficient at 915nm wavelength under the length of the ytterbium-doped optical fiber to be measured976The fiber core absorption coefficient L at the wavelength of 976nm under the length of the ytterbium-doped optical fiber to be detected1The length L of the ytterbium-doped fiber to be measured at the moment0Is of standard length.
7. The method of claim 6, wherein the confidence interval for the α -coefficient is [2.5, 3.5 ].
8. The method for testing the core absorption coefficient of an ytterbium-doped optical fiber according to claim 6, wherein the leveling spectrum analyzer uses a non-absorption wavelength range below a cutoff wavelength of the mode filter as a leveling baseline.
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