CN119143378B - Rare earth doped optical fiber for inhibiting mode instability effect and preparation method thereof - Google Patents
Rare earth doped optical fiber for inhibiting mode instability effect and preparation method thereof Download PDFInfo
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 75
- 229910052761 rare earth metal Inorganic materials 0.000 title claims abstract description 44
- 230000000694 effects Effects 0.000 title claims abstract description 42
- 150000002910 rare earth metals Chemical class 0.000 title claims abstract description 39
- 238000002360 preparation method Methods 0.000 title claims abstract description 23
- 230000002401 inhibitory effect Effects 0.000 title claims abstract description 22
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 39
- 239000010453 quartz Substances 0.000 claims abstract description 36
- 229910052782 aluminium Inorganic materials 0.000 claims description 19
- 238000000034 method Methods 0.000 claims description 17
- 238000000151 deposition Methods 0.000 claims description 16
- 238000005253 cladding Methods 0.000 claims description 15
- 229910004298 SiO 2 Inorganic materials 0.000 claims description 14
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 12
- 150000001875 compounds Chemical class 0.000 claims description 12
- 238000005229 chemical vapour deposition Methods 0.000 claims description 10
- 150000002500 ions Chemical class 0.000 claims description 10
- 239000007787 solid Substances 0.000 claims description 7
- 238000004090 dissolution Methods 0.000 claims description 6
- 238000012681 fiber drawing Methods 0.000 claims description 6
- 230000008569 process Effects 0.000 claims description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 229910001427 strontium ion Inorganic materials 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 claims description 2
- 239000000835 fiber Substances 0.000 abstract description 51
- 230000001808 coupling effect Effects 0.000 abstract description 13
- 230000005764 inhibitory process Effects 0.000 abstract description 10
- 239000000463 material Substances 0.000 abstract description 10
- 230000007246 mechanism Effects 0.000 abstract description 5
- 238000013461 design Methods 0.000 abstract description 4
- 238000005516 engineering process Methods 0.000 description 20
- 230000000052 comparative effect Effects 0.000 description 14
- 230000006872 improvement Effects 0.000 description 7
- 230000008878 coupling Effects 0.000 description 4
- 238000010168 coupling process Methods 0.000 description 4
- 238000005859 coupling reaction Methods 0.000 description 4
- 239000006185 dispersion Substances 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 230000036961 partial effect Effects 0.000 description 4
- 230000001737 promoting effect Effects 0.000 description 4
- 230000003313 weakening effect Effects 0.000 description 4
- 238000005452 bending Methods 0.000 description 3
- 238000001914 filtration Methods 0.000 description 3
- 230000002829 reductive effect Effects 0.000 description 3
- 230000001629 suppression Effects 0.000 description 3
- 239000007789 gas Substances 0.000 description 2
- 230000000670 limiting effect Effects 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 238000011056 performance test Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- 238000009210 therapy by ultrasound Methods 0.000 description 2
- 238000004017 vitrification Methods 0.000 description 2
- PSNPEOOEWZZFPJ-UHFFFAOYSA-N alumane;yttrium Chemical compound [AlH3].[Y] PSNPEOOEWZZFPJ-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000006731 degradation reaction Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000005368 silicate glass Substances 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 239000002918 waste heat Substances 0.000 description 1
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- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
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- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
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- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
- C03B37/01—Manufacture of glass fibres or filaments
- C03B37/012—Manufacture of preforms for drawing fibres or filaments
- C03B37/014—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD]
- C03B37/018—Manufacture of preforms for drawing fibres or filaments made entirely or partially by chemical means, e.g. vapour phase deposition of bulk porous glass either by outside vapour deposition [OVD], or by outside vapour phase oxidation [OVPO] or by vapour axial deposition [VAD] by glass deposition on a glass substrate, e.g. by inside-, modified-, plasma-, or plasma modified- chemical vapour deposition [ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod
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Abstract
The invention provides a rare earth doped optical fiber for inhibiting a mode instability effect and a preparation method thereof, and relates to the technical field of special optical fiber preparation. According to the preparation method, a channel region with a low refractive index is deposited in a quartz tube, and then a fiber core passive region and a fiber core active region with different doping components are sequentially prepared, so that the difference of thermo-optical coefficients of local regions of the fiber core is realized. The invention reduces the thermooptic coefficient of the optical fiber by introducing the material with negative thermooptic coefficient, weakens the coupling effect between nonlinear modes, realizes the effective inhibition of MI, simultaneously adopts the mode of rare earth ion center doping, reduces the gain of a high-order mode under the condition of a large fiber core, inhibits the generation of the high-order mode by a mode competition mechanism, increases the occupation ratio of a basic mode, and has higher high-order mode loss, inhibits the coupling effect of the basic mode and the high-order mode by the design of a low numerical aperture and a channel structure, thereby further improving the MI threshold value and the quality of light beams.
Description
Technical Field
The invention relates to the technical field of special optical fiber preparation, in particular to a rare earth doped optical fiber for inhibiting a mode instability effect and a preparation method thereof.
Background
Mode instability refers to the abrupt change of the high-power fiber laser from steady-state fundamental mode output to unsteady-state high-order mode output along with the increase of output power, which can lead to the reduction of beam quality and limit the increase of the output power of the diffraction limit beam quality fiber laser. Mode instability can lead to rapid degradation of laser beam quality and severely limits the application of fiber laser, and has become one of the biggest limiting factors for improving the power of ytterbium-doped fiber laser with diffraction limit beam quality and large mode field area, and has attracted extensive attention of researchers in recent years.
It is widely believed that factors such as fiber waste heat, higher order modes, photodarkening, etc. may cause mode instability effects or a reduction in mode instability thresholds. Patent publication No. CN 115611508B discloses a rare earth doped optical fiber for inhibiting mode instability effect and a preparation method thereof. The fiber core of the optical fiber comprises a central area and an outer ring area, wherein the central area is rare earth doped quartz glass with low loss and low heat conductivity, and the outer ring area is yttrium aluminum silicate glass with high loss and high heat conductivity. The high-loss outer ring region of the fiber core is utilized to inhibit high-order modes in the fiber, so that the coupling of a fundamental mode and the high-order modes is inhibited, and further, the effect of inhibiting the mode instability effect is achieved. However, the scheme adopts a single means to inhibit MI effect, the MI inhibition effect is not ideal, the MI effect threshold is relatively low, and under the condition that the consistency of external conditions such as test conditions, preparation conditions and the like is ensured, the MI threshold can be raised to more than 3kW, and the MI threshold of the patent CN 115611508B is only 2.5KW.
In view of the foregoing, there is a need for an improved rare earth doped fiber for suppressing mode instability effects and a method of making the same.
Disclosure of Invention
The invention aims to provide a rare earth doped optical fiber for inhibiting mode instability effect and a preparation method thereof. The preparation method comprises the steps of firstly depositing a channel region with a low refractive index in a quartz tube, then sequentially preparing a fiber core passive region and a fiber core active region with different doping components, realizing different thermo-optical coefficients (dn/dT) of local regions of the fiber core, reducing the thermo-optical coefficients of the fiber by introducing a negative thermo-optical coefficient material, weakening the coupling effect between nonlinear modes, realizing the effective inhibition of MI, simultaneously adopting a rare earth ion center doping mode, reducing the gain of a high-order mode under the condition of a large fiber core, inhibiting the generation of the high-order mode by a mode competition mechanism, increasing the occupation ratio of a basic mode, inhibiting the coupling effect of the basic mode and the high-order mode, further improving the MI threshold value and improving the quality of light beams.
In order to achieve the above object, the present invention provides a method for preparing a rare earth doped optical fiber for suppressing a mode instability effect, comprising the steps of:
s1, depositing a low-refractive-index channel region in a quartz tube by adopting an MCVD (chemical vapor deposition) process, wherein the width of the channel is 1-3um, and the refractive index depth of the channel is-0.0005 to-0.001;
S2, depositing a SiO 2 loose layer on the inner wall of a quartz tube, then taking down the quartz tube on which the SiO 2 loose layer is deposited, putting the quartz tube into a P, B, sr mixed doping solution, taking out and airing, wherein the ion concentration of P, B, sr in the mixed doping solution is respectively 0.5-1.5M, 1-1.5M and 0.2-0.6M;
S3, depositing a SiO 2 loose layer on the inner wall of the quartz tube, taking down the quartz tube on which the SiO 2 loose layer is deposited, putting the quartz tube into a mixed doping solution of Al, P, sr, yb, taking out and airing, wherein the ion concentration of Al, P, sr, yb in the mixed doping solution is respectively 1.5-2M, 0.2-0.6M and 0.5-1M;
S4, collapse is completed at 2000-2200 ℃ to obtain a compact solid optical fiber preform;
and S5, placing the solid optical fiber preform on an optical fiber drawing tower, and drawing the optical fiber to obtain the rare earth doped optical fiber for inhibiting the mode instability effect.
As a further improvement of the invention, in the step S2, the preparation method of the P, B, sr mixed doping solution comprises the steps of dissolving a P, B, sr-containing compound in water or ethanol solution, and promoting the dissolution of the compound by a dispersion mode such as shaking and ultrasonic to form a P, B, sr ion-containing mixed doping solution.
As a further improvement of the invention, in the step S3, the preparation method of the Al, P, sr, yb mixed doping solution comprises the steps of dissolving a Al, P, sr, yb-containing compound in water or ethanol solution, and promoting the dissolution of the compound by a dispersion mode such as shaking and ultrasonic to form a Al, P, sr, yb ion-containing mixed doping solution.
In order to achieve the above object, the present invention further provides a rare earth doped optical fiber for suppressing a mode instability effect, which is prepared by adopting the above scheme, and the rare earth doped optical fiber for suppressing a mode instability effect includes a core active region, a core passive region, a channel region and a cladding layer, which are sequentially arranged from inside to outside.
As a further improvement of the invention, the core active region is of a different doping composition than the core inactive region.
As a further improvement of the present invention, the doping component of the active region of the core is Al, P, sr, yb, F and the doping component of the inactive region of the core is P, B, sr, F.
As a further improvement of the present invention, the thermo-optic coefficient of the active region of the fiber core is (0.6-0.9) ×10 -5/k, and the thermo-optic coefficient of the passive region of the fiber core is (0.6-0.9) ×10 -5/k.
As a further improvement of the invention, the numerical aperture of the rare earth doped optical fiber is 0.035-0.055.
As a further improvement of the invention, the MI threshold value of the rare earth doped optical fiber with the fiber core/cladding diameter of 25um/400um is more than or equal to 3kW, the beam quality factor M2 is 1.5, the MI threshold value of the rare earth doped optical fiber with the fiber core/cladding diameter of 30um/400um is more than or equal to 2kW, and the beam quality factor M2 is 2.
The beneficial effects of the invention are as follows:
The invention relates to a preparation method of a rare earth doped optical fiber for inhibiting a mode instability effect, which comprises the steps of firstly depositing a channel region with a low refractive index in a quartz tube to enable the optical fiber to have higher high-order mode loss (more than 30 dB/m), and then sequentially preparing a fiber core passive region and a fiber core active region with different doping components to realize different thermo-optical coefficients (dn/dT) of local regions of the fiber core. Specifically, the passive fiber core region is doped with element F P, B, sr to lower the thermal optical coefficient of the passive fiber core region and to lower the refractive index of the material, and the active fiber core region is doped with element F Al, P, sr, yb to lower the thermal optical coefficient of the active fiber core region and to lower the refractive index of the material.
The method comprises the steps of introducing negative thermo-optic coefficient materials (B, sr and P), reducing the thermo-optic coefficient of an optical fiber, weakening the coupling effect between nonlinear modes, realizing the effective inhibition of MI, simultaneously adopting a rare earth ion center doping mode, reducing the gain of a high-order mode under the condition of a large fiber core, inhibiting the generation of the high-order mode through a mode competition mechanism, increasing the duty ratio of a basic mode, inhibiting the coupling effect of the basic mode and the high-order mode, further improving the MI threshold value and the quality of a light beam, and further realizing the inhibition of MI effect, and simultaneously ensuring that the large-core optical fiber still can realize the output of the basic mode with higher duty ratio and has good light beam quality due to the low numerical aperture and channel structural design.
The invention integrates various advantageous characteristics, and uses multiple MI effect suppression technologies such as a low-heat-light material technology, a partial doping technology, a low numerical aperture bending mode filtering technology, a high-order mode coupling loss technology, a high-order mode self-loss technology and the like to continuously suppress the MI effect, greatly improve the MI threshold value and simultaneously ensure the beam quality of laser output by a large-core fiber. The MI threshold value of the rare earth doped optical fiber with the core/cladding diameter of 25um/400um is more than or equal to 3kW, the light beam quality factor M2 is 1.5, the MI threshold value of the rare earth doped optical fiber with the core/cladding diameter of 30um/400um is more than or equal to 2kW, the light beam quality factor M2 is 2, and the performance is far better than that of the traditional optical fiber.
Drawings
FIG. 1 is a graph showing refractive index profiles corresponding to regions of a rare earth doped fiber for suppressing mode instability effects prepared in accordance with example 1 of the present invention.
Reference numerals
1-Core active region, 2-core inactive region, 3-channel region, 4-core, 5-cladding.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.
It should be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and/or processing steps closely related to aspects of the present invention are shown in the drawings, and other details not greatly related to the present invention are omitted.
In addition, it should be further noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The invention provides a preparation method of rare earth doped optical fiber for inhibiting mode instability effect, which comprises the following steps:
s1, depositing a low-refractive-index channel region in a quartz tube by adopting an MCVD (chemical vapor deposition) process, wherein the width of the channel is 1-3um, and the refractive index depth of the channel is-0.0005 to-0.001;
S2, depositing a SiO 2 loose layer on the inner wall of a quartz tube, then taking down the quartz tube on which the SiO 2 loose layer is deposited, putting the quartz tube into a P, B, sr mixed doping solution, taking out and airing, wherein the ion concentration of P, B, sr in the mixed doping solution is respectively 0.5-1.5M, 1-1.5M and 0.2-0.6M;
Specifically, the preparation method of the P, B, sr mixed doping solution comprises the steps of dissolving a P, B, sr-containing compound in water or ethanol solution, and promoting the dissolution of the compound by means of dispersion such as shaking and ultrasonic treatment to form a P, B, sr-ion-containing mixed doping solution.
S3, depositing a SiO 2 loose layer on the inner wall of the quartz tube, taking down the quartz tube on which the SiO 2 loose layer is deposited, putting the quartz tube into a mixed doping solution of Al, P, sr, yb, taking out and airing, wherein the ion concentration of Al, P, sr, yb in the mixed doping solution is respectively 1.5-2M, 0.2-0.6M and 0.5-1M;
Specifically, the preparation method of the Al, P, sr, yb mixed doping solution comprises the steps of dissolving a Al, P, sr, yb-containing compound in water or ethanol solution, and promoting the dissolution of the compound by means of dispersion such as shaking and ultrasonic treatment to form a Al, P, sr, yb-ion-containing mixed doping solution.
By preparing the fiber core passive region and the fiber core active region with different doping components, the low thermo-optical coefficient (dn/dT) of the fiber core local region is realized, the mode coupling effect in the optical fiber is reduced to a certain extent, and the mode instability effect of the optical fiber is restrained.
S4, collapse is completed at 2000-2200 ℃ to obtain a compact solid optical fiber preform;
And S5, placing the solid optical fiber preform on an optical fiber drawing tower, and drawing the optical fiber to obtain the rare earth doped optical fiber for inhibiting the mode instability effect.
Referring to fig. 1, the rare earth doped optical fiber for suppressing mode instability effect prepared by the method includes a core active region 1, a core inactive region 2, a channel region 3 and a cladding 5 sequentially arranged from inside to outside. The core active region 1 is different from the doping composition of the core inactive region 2. Specifically, the doping component of the active core region 1 is Al, P, sr, yb, F, and the doping component of the inactive core region 2 is P, B, sr, F.
The thermo-optic coefficients of the active area and the passive area of the fiber core are (0.6-0.9) multiplied by 10 -5/k. Compared with the common fiber thermo-optic coefficient (1.0-1.2) multiplied by 10 -5/k, the invention reduces the fiber thermo-optic coefficient, weakens the coupling effect between nonlinear modes, and realizes the effective inhibition of MI.
The numerical aperture of the rare earth doped optical fiber is 0.035-0.055.
The method comprises the steps of introducing negative thermo-optic coefficient materials (B, sr and P), reducing the thermo-optic coefficient of an optical fiber, weakening the coupling effect between nonlinear modes, realizing the effective inhibition of MI, simultaneously adopting a rare earth ion center doping mode, reducing the gain of a high-order mode under the condition of a large fiber core, inhibiting the generation of the high-order mode through a mode competition mechanism, increasing the duty ratio of a basic mode, inhibiting the coupling effect of the basic mode and the high-order mode, further improving the MI threshold value and the quality of a light beam, and further realizing the inhibition of MI effect, and simultaneously ensuring that the large-core optical fiber still can realize the output of the basic mode with higher duty ratio and has good light beam quality due to the low numerical aperture and channel structural design.
The invention integrates various advantageous characteristics, and uses multiple MI effect suppression technologies such as a low-heat-light material technology, a partial doping technology, a low numerical aperture bending mode filtering technology, a high-order mode coupling loss technology, a high-order mode self-loss technology and the like to continuously suppress the MI effect, greatly improve the MI threshold value and simultaneously ensure the beam quality of laser output by a large-core fiber.
The method for preparing the rare earth doped optical fiber for suppressing the mode-unstable effect provided by the invention is described below with reference to specific examples.
Example 1
The preparation method of the rare earth doped optical fiber for inhibiting the mode instability effect mainly comprises the following steps:
S1, depositing a low-refractive-index channel region in a tube by using a conventional MCVD (chemical vapor deposition) process, wherein the channel width is 1-3um, and the refractive index depth is-0.0005 to-0.001;
S2, depositing a SiO 2 loose layer on the inner wall of a quartz tube, taking down the quartz tube with the deposited loose layer, putting the quartz tube into a P, B, sr mixed doping solution, taking out and airing, putting the quartz tube with the ion concentration of 1.5M, 1M and 0.2M on an MCVD lathe, doping F element by using a gas phase technology, completing sintering at 1300-1600 ℃, completing vitrification at 1850 ℃ and completing preparation of a fiber core passive region;
s3, depositing a SiO 2 loose layer on the inner wall of the quartz tube, taking down the quartz tube with the deposited loose layer, putting the quartz tube into a Al, P, sr, yb mixed doping solution, taking out and airing the quartz tube with the ion concentration of 1.5M, 0.2M and 0.5M respectively, putting the quartz tube back on an MCVD lathe, doping F element by using a gas phase technology, completing sintering at 1300-1600 ℃, completing vitrification at 1850 ℃ and completing preparation of an active area of a fiber core;
S4, collapse is completed at 2000-2200 ℃ to obtain a compact solid optical fiber preform;
s5, placing the optical fiber preform on an optical fiber drawing tower, and drawing the optical fiber to obtain the quartz optical fiber with the core/cladding diameter of 25um/400um and the numerical aperture of 0.04.
The optical fiber has the characteristics of low numerical aperture, low thermo-optical coefficient, channel structure, partial doping and the like.
FIG. 1 is a graph of refractive index corresponding to each region of a rare earth doped fiber for suppressing mode instability effects prepared in example 1. It can be seen that the refractive indexes of the active region and the passive region of the fiber core are basically consistent, the low-loss transmission of the fundamental mode light in the fiber core is ensured, the refractive index of the channel region is reduced by 0.0005-0.001 compared with that of the pure quartz cladding, the width is usually 3um, the high-order mode is further filtered, and the mode field area is reduced.
Example 2
Example 2 differs from example 1 mainly in that in step S5, an optical fiber preform is placed on an optical fiber drawing tower, and optical fiber drawing is performed to obtain a silica optical fiber having a core/cladding diameter of 30um/400um, the core diameter being increased to 30um. The other points are substantially the same as those of embodiment 1, and will not be described here again.
Comparative example 1
Comparative example 1 differs from example 1 mainly in that the B element was not introduced in step S2, i.e., the loss of the passive region mode of the core was not significantly increased. The other points are substantially the same as those of embodiment 1, and will not be described here again.
Comparative example 2
Comparative example 2 differs from example 1 mainly in that the mixed doping solutions in step S2 and step S3 are both Al, P, sr, yb in composition, i.e., the doping composition of the core passive region and the core active region are the same. The other points are substantially the same as those of embodiment 1, and will not be described here again.
Comparative example 3
Comparative example 3 differs from example 1 mainly in that the operation of step S1 was not performed, i.e., no channel was deposited. The other points are substantially the same as those of embodiment 1, and will not be described here again.
Comparative example 4
Comparative example 4 differs from example 1 mainly in that the core number aperture is 0.06 in step S1. The other points are substantially the same as those of embodiment 1, and will not be described here again.
The optical fibers prepared in examples 1-2 and comparative examples 1-4 were subjected to performance test, and the results obtained are shown in Table 1.
TABLE 1 Performance test data for conventional optical fibers, optical fibers prepared in examples 1-2, comparative examples 1-4
As is clear from Table 1, the MI threshold of the rare earth doped fiber having a core/cladding diameter of 25um/400um was 3kW or more, the beam quality factor M2 was 1.5, and the MI threshold of the rare earth doped fiber having a core/cladding diameter of 30um/400um was 2kW or more, the beam quality factor M2 was 2.
The MI threshold of comparative example 1 was 2.9kW, and the beam quality was greater than 2, and it was found that both the MI threshold and the beam quality were deteriorated when the high-order mode high-loss condition of the core passive region was not provided, in comparison with example 1.
In comparative example 2, in which the MI threshold was 2.3kW and the beam quality was greater than 2, it was found that both the MI threshold and the beam quality were deteriorated when the center doping condition was not provided, as compared with example 1.
In comparative example 3, in which the MI threshold was 2.2kW and the beam quality was greater than 2, it was found that both the MI threshold and the beam quality were deteriorated when no trench deposition was provided, as compared with example 1.
The MI threshold of comparative example 4 was 1.8kW, and the beam quality was greater than 2, and it was found that both the MI threshold and the beam quality were deteriorated when the numerical aperture was not low, as compared with example 1.
In summary, the method comprises the steps of firstly depositing a channel region with low refractive index in a quartz tube to enable the optical fiber to have higher high-order mode loss, and then sequentially preparing a fiber core passive region and a fiber core active region with different doping components to realize different thermo-optical coefficients of local regions of the fiber core. The method comprises the steps of introducing a negative thermo-optic coefficient material, reducing the thermo-optic coefficient of an optical fiber, weakening the coupling effect between nonlinear modes, realizing the effective inhibition of MI, adopting a rare earth ion center doping mode, reducing the gain of a high-order mode under the condition of a large fiber core, inhibiting the generation of the high-order mode through a mode competition mechanism, increasing the duty ratio of a basic mode, inhibiting the coupling effect of the basic mode and the high-order mode, further improving the MI threshold value, improving the quality of a light beam, and further realizing the inhibition of MI effect by adopting a low numerical aperture and channel structural design, wherein the optical fiber has higher high-order mode loss and the coupling effect between modes, and simultaneously ensuring that the large-core-diameter optical fiber still can realize the output of the basic mode with higher duty ratio and has good light beam quality. The patent integrates various advantageous characteristics, and is overlapped with multiple MI effect suppression technologies such as a low-heat-light material technology, a partial doping technology, a low numerical aperture bending mode filtering technology, a high-order mode coupling loss technology, a high-order mode self-loss technology and the like, so that MI effect is continuously suppressed, MI threshold value is greatly improved, and meanwhile, the beam quality of laser output by a large-core-diameter optical fiber is ensured.
The above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the technical solution of the present invention.
Claims (7)
1. The preparation method of the rare earth doped optical fiber for inhibiting the mode instability effect is characterized by comprising the following steps of:
S1, depositing a low-refractive-index channel region in a quartz tube by adopting an MCVD (chemical vapor deposition) process, wherein the width of the channel is 1-3um, and the refractive index depth of the channel is-0.0005 to-0.001;
S2, depositing a SiO 2 loose layer on the inner wall of a quartz tube, then taking down the quartz tube on which the SiO 2 loose layer is deposited, putting the quartz tube into a P, B, sr mixed doping solution, taking out and airing, wherein the ion concentration of P, B, sr in the mixed doping solution is respectively 0.5-1.5M, 1-1.5M and 0.2-0.6M;
S3, depositing a SiO 2 loose layer on the inner wall of the quartz tube, taking down the quartz tube on which the SiO 2 loose layer is deposited, putting the quartz tube into a mixed doping solution of Al, P, sr, yb, taking out and airing, wherein the ion concentration of Al, P, sr, yb in the mixed doping solution is respectively 1.5-2M, 0.2-0.6M and 0.5-1M;
S4, collapse is completed at 2000-2200 ℃ to obtain a compact solid optical fiber preform;
and S5, placing the solid optical fiber preform on an optical fiber drawing tower, and drawing the optical fiber to obtain the rare earth doped optical fiber for inhibiting the mode instability effect.
2. The method for preparing a rare earth doped optical fiber for suppressing mode-unstable effect according to claim 1, wherein in step S2, the preparation method of the P, B, sr mixed doped solution is that a compound containing P, B, sr is dissolved in water or ethanol solution, and dispersed by shaking ultrasonic manner to promote the dissolution of the compound, so as to form a mixed doped solution containing P, B, sr ions.
3. The method for preparing a rare earth doped optical fiber for suppressing mode-unstable effect according to claim 1, wherein in step S3, the preparation method of the Al, P, sr, yb mixed doped solution is that a compound containing Al, P, sr, yb is dissolved in water or ethanol solution, and dispersed by shaking ultrasonic manner to promote the dissolution of the compound, so as to form a mixed doped solution containing Al, P, sr, yb ions.
4. A rare earth doped optical fiber for suppressing a mode-unstable effect, characterized in that it comprises a core active region, a core passive region, a channel region and a cladding layer which are sequentially arranged from inside to outside, and is manufactured by the manufacturing method according to any one of claims 1 to 3.
5. The rare earth doped optical fiber according to claim 4, wherein the thermo-optic coefficient of the core active region is (0.6-0.9) x 10 -5/k and the thermo-optic coefficient of the core passive region is (0.6-0.9) x 10 -5/k.
6. The rare earth doped optical fiber for suppressing mode instability effects according to claim 4, wherein the numerical aperture of the rare earth doped optical fiber is 0.035-0.055.
7. The rare earth doped optical fiber for suppressing mode instability effects according to claim 4, wherein the MI threshold of the rare earth doped optical fiber with a core/cladding diameter of 25um/400um is 3kW or more, the beam quality factor M2 is 1.5, and the MI threshold of the rare earth doped optical fiber with a core/cladding diameter of 30um/400um is 2kW or more, the beam quality factor M2 is 2.
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