Rare earth doped optical fiber for suppressing mode instability effect and preparation method thereof

Abstract

The present invention provides a rare earth-doped optical fiber for suppressing mode instability effects and a preparation method thereof, and relates to the technical field of special optical fiber preparation. The preparation method first deposits a channel region with a low refractive index in a quartz tube, and then sequentially prepares a core passive region and a core active region with different doping components to achieve different thermo-optic coefficients in the local region of the core. The present invention reduces the thermo-optic coefficient of the optical fiber and weakens the nonlinear inter-mode coupling effect by introducing a negative thermo-optic coefficient material, thereby effectively suppressing MI; at the same time, the method of rare earth ion center doping is adopted to reduce the high-order mode gain in the case of a large core, and then suppress the generation of high-order modes through a mode competition mechanism, thereby increasing the proportion of the fundamental mode; the low numerical aperture and channel structure design enable the optical fiber to have a higher high-order mode loss, suppress the fundamental mode-high-order mode coupling effect, further increase the MI threshold, and improve the beam quality.

Description

Technical Field

[0001] The present invention relates to the technical field of special optical fiber preparation, and in particular to a rare earth doped optical fiber for suppressing mode instability effect and a preparation method thereof. Background Art

[0002] Mode instability refers to the sudden change of the steady-state fundamental mode output to the non-steady-state high-order mode output when the output power of high-power fiber laser increases, which will lead to the degradation of beam quality and limit the increase of output power of diffraction-limited beam quality fiber laser. Mode instability will lead to the rapid degradation of laser beam quality, severely restricting the application of fiber laser. It has become one of the biggest limiting factors for the increase of power of diffraction-limited beam quality large mode area ytterbium-doped fiber laser, and has attracted widespread attention of researchers in recent years.

[0003] It is generally believed that factors such as optical fiber waste heat, high-order modes, and photodarkening can lead to mode instability effects or cause a decrease in the threshold of mode instability. The patent with publication number CN 115611508B discloses a rare-earth-doped optical fiber for suppressing mode instability effects and a preparation method thereof. The core of the optical fiber includes a central region and an outer ring region; the central region is a rare-earth-doped quartz glass with low loss and low thermal conductivity, and the outer ring region is a yttrium aluminum silicate glass with high loss and high thermal conductivity. The optical fiber utilizes the high loss of the outer ring region of the core to suppress the high-order modes in the optical fiber, suppress the coupling of the fundamental mode and the high-order mode, and thus play a role in suppressing the mode instability effect; at the same time, the high thermal conductivity outer ring region can export the heat of the core, suppress the mode instability effect caused by the thermal effect, and achieve an increase in the threshold of the mode instability effect. However, this solution adopts a single means to suppress the MI effect, the MI suppression effect is not ideal, and the MI effect threshold is relatively low. When the external conditions such as test conditions and preparation conditions are consistent, the MI threshold of this application can be increased to more than 3kW, and the MI threshold of patent CN 115611508B is only 2.5KW.

[0004] In view of this, it is necessary to design an improved rare-earth-doped optical fiber for suppressing the mode instability effect and a preparation method thereof to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to provide a rare earth doped optical fiber for suppressing the mode instability effect and a preparation method thereof. The preparation method first deposits a channel region with a low refractive index in a quartz tube, and then sequentially prepares a core passive region and a core active region with different doping components to achieve different thermo-optic coefficients (dn / dT) in the local region of the core; by introducing negative thermo-optic coefficient materials, the thermo-optic coefficient of the optical fiber is reduced, the nonlinear inter-mode coupling effect is weakened, and the MI is effectively suppressed; at the same time, the rare earth ion center doping method is adopted to reduce the high-order mode gain in the case of a large core, and then the high-order mode generation is suppressed through the mode competition mechanism, the fundamental mode proportion is increased, the fundamental mode-high-order mode coupling effect is suppressed, and the MI threshold and the beam quality are further improved.

[0006] To achieve the above-mentioned object of the invention, the present invention provides a method for preparing a rare earth-doped optical fiber for suppressing mode instability effects, comprising the following steps:

[0007] S1, using MCVD process, using vapor deposition technology to deposit a low refractive index channel area in the quartz tube, the channel width is 1-3um, and the refractive index depth of the channel is -0.0005~ -0.001;

[0008] S2, depositing SiO on the inner wall of the quartz tube 2 Loose layer, then deposit the SiO 2 The quartz tube of the loose layer is removed, and placed in a mixed doping solution of P, B, and Sr, and then taken out and dried; wherein, in the mixed doping solution, the ion concentrations of P, B, and Sr are 0.5-1.5M, 1-1.5M, and 0.2-0.6M, respectively; after drying, the quartz tube is put back on the MCVD lathe, and the F element is doped by gas phase technology, and then sintering and vitrification treatment are carried out in sequence to complete the preparation of the passive area of ​​the fiber core;

[0009] S3, deposit SiO on the inner wall of the quartz tube 2 Loose layer, then deposit the SiO 2 The quartz tube of the loose layer is removed, and placed in a mixed doping solution of Al, P, Sr, and Yb, and then taken out and dried; wherein the ion concentrations of Al, P, Sr, and Yb in the mixed doping solution are 1.5-2M, 1.5-2M, 0.2-0.6M, and 0.5-1M, respectively; after drying, the quartz tube is put back on the MCVD lathe, and the F element is doped using the gas phase technology, and then sintering and vitrification treatment are performed in sequence to complete the preparation of the core active area;

[0010] S4, completing collapse at 2000°C-2200°C to obtain a dense solid core optical fiber preform;

[0011] S5, placing the solid core optical fiber preform on an optical fiber drawing tower to draw the optical fiber, thereby obtaining the rare earth-doped optical fiber for suppressing mode instability effect.

[0012] As a further improvement of the present invention, in step S2, the preparation method of the mixed doping solution of P, B and Sr is: dissolving the compound containing P, B and Sr in water or ethanol solution, promoting the dissolution of the compound by dispersion methods such as oscillation and ultrasound, and forming a mixed doping solution containing P, B and Sr ions.

[0013] As a further improvement of the present invention, in step S3, the preparation method of the mixed doping solution of Al, P, Sr and Yb is: dissolving the compound containing Al, P, Sr and Yb in water or ethanol solution, and promoting the dissolution of the compound by dispersion methods such as oscillation and ultrasound to form a mixed doping solution containing Al, P, Sr and Yb ions.

[0014] To achieve the above-mentioned purpose of the invention, the present invention also provides a rare-earth-doped optical fiber for suppressing mode instability effects prepared by the above-mentioned scheme, wherein the rare-earth-doped optical fiber for suppressing mode instability effects comprises a core active region, a core passive region, a channel region and a cladding arranged in sequence from the inside to the outside.

[0015] As a further improvement of the present invention, the doping components of the core active region and the core passive region are different.

[0016] As a further improvement of the present invention, the doping components of the core active region are Al, P, Sr, Yb, and F, and the doping components of the core passive region are P, B, Sr, and F.

[0017] 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, the thermo-optic coefficient of the passive region of the core is (0.6-0.9)×10 -5 / k.

[0018] As a further improvement of the present invention, the numerical aperture of the rare-earth-doped optical fiber is 0.035-0.055.

[0019] As a further improvement of the present invention, the MI threshold of the rare-earth-doped optical fiber with a core / cladding diameter of 25um / 400um is greater than or equal to 3kW, and the beam quality factor M2 is 1.5; the MI threshold of the rare-earth-doped optical fiber with a core / cladding diameter of 30um / 400um is greater than or equal to 2kW, and the beam quality factor M2 is 2.

[0020] The beneficial effects of the present invention are:

[0021] The method for preparing rare earth-doped optical fiber for suppressing mode instability effect of the present invention first deposits a channel region with a low refractive index in a quartz tube, so that the optical fiber has a higher high-order mode loss (greater than 30dB / m), and then sequentially prepares a core passive region and a core active region with different doping components to achieve different thermo-optic coefficients (dn / dT) in the local region of the core. Specifically, the core passive region is doped with P, B, and Sr, and then doped with F element, so that the core passive region has a lower thermo-optic coefficient and a lower material refractive index; the core active region is doped with Al, P, Sr, and Yb, and then doped with F element, so that the core active region has a lower thermo-optic coefficient and a lower material refractive index.

[0022] By introducing negative thermo-optic coefficient materials (B, Sr, P), the thermo-optic coefficient of the optical fiber is reduced, the nonlinear inter-mode coupling effect is weakened, and the effective suppression of MI is achieved; at the same time, the rare earth ion center doping method is used to reduce the high-order mode gain in the case of a large fiber core, and then through the mode competition mechanism, the generation of high-order modes is suppressed, the proportion of fundamental mode is increased, and the fundamental mode-higher-order mode coupling effect is suppressed, further increasing the MI threshold and improving the beam quality; the low numerical aperture and channel structure design make the optical fiber have a higher high-order mode loss, suppressing the inter-mode coupling effect, thereby further suppressing the MI effect, while ensuring that the large-core fiber can still achieve a higher proportion of fundamental mode output with good beam quality.

[0023] The present invention integrates multiple advantageous features, using multiple MI effect suppression technologies such as low-thermal optical material technology, partial doping technology, low numerical aperture bending filter technology, high-order mode coupling loss technology, and high-order mode self-loss technology to continuously suppress the MI effect, greatly improve the MI threshold, and at the same time ensure the beam quality of the large-core fiber output laser. The MI threshold of the rare-earth-doped optical fiber with a core / cladding diameter of 25um / 400um is greater than or equal to 3kW, and the beam quality factor M2 is 1.5; the MI threshold of the rare-earth-doped optical fiber with a core / cladding diameter of 30um / 400um is greater than or equal to 2kW, and the beam quality factor M2 is 2, and the performance is far better than that of traditional optical fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a refractive index curve corresponding to each region of the rare-earth-doped optical fiber for suppressing mode instability effect prepared in Example 1 of the present invention.

[0025] Reference numerals

[0026] 1-fiber core active region, 2-fiber core passive region, 3-channel region, 4-fiber core, 5-cladding. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0029] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0030] The present invention provides a method for preparing a rare earth-doped optical fiber for suppressing mode instability effects, comprising the following steps:

[0031] S1, using MCVD process, using vapor deposition technology to deposit a low refractive index channel area in the quartz tube, the channel width is 1-3um, and the refractive index depth of the channel is -0.0005~ -0.001;

[0032] S2, depositing SiO on the inner wall of the quartz tube 2 Loose layer, then deposit the SiO 2 The quartz tube of the loose layer is removed, and placed in a mixed doping solution of P, B, and Sr, and then taken out and dried; wherein, in the mixed doping solution, the ion concentrations of P, B, and Sr are 0.5-1.5M, 1-1.5M, and 0.2-0.6M, respectively; after drying, the quartz tube is put back on the MCVD lathe, and the F element is doped by gas phase technology, and then sintering and vitrification treatment are carried out in sequence to complete the preparation of the passive area of ​​the fiber core;

[0033] Specifically, the preparation method of the mixed doping solution of P, B and Sr is: dissolving the compound containing P, B and Sr in water or ethanol solution, promoting the dissolution of the compound by dispersion methods such as oscillation and ultrasound, and forming a mixed doping solution containing P, B and Sr ions.

[0034] S3, deposit SiO on the inner wall of the quartz tube 2 Loose layer, then deposit the SiO 2 The quartz tube of the loose layer is removed, and placed in a mixed doping solution of Al, P, Sr, and Yb, and then taken out and dried; wherein the ion concentrations of Al, P, Sr, and Yb in the mixed doping solution are 1.5-2M, 1.5-2M, 0.2-0.6M, and 0.5-1M, respectively; after drying, the quartz tube is put back on the MCVD lathe, and the F element is doped using the gas phase technology, and then sintering and vitrification treatment are performed in sequence to complete the preparation of the core active area;

[0035] Specifically, the preparation method of the mixed doping solution of Al, P, Sr and Yb is: dissolving the compound containing Al, P, Sr and Yb in water or ethanol solution, promoting the dissolution of the compound by dispersion methods such as oscillation and ultrasound, and forming a mixed doping solution containing Al, P, Sr and Yb ions.

[0036] By preparing the core passive region and core active region with different doping components, the thermo-optic coefficient (dn / dT) of the local area of ​​the core is lowered, which reduces the mode coupling effect in the optical fiber to a certain extent, thereby suppressing the mode instability effect of the optical fiber.

[0037] S4, completing collapse at 2000°C-2200°C to obtain a dense solid core optical fiber preform;

[0038] S5, placing the solid core optical fiber preform on an optical fiber drawing tower to draw the optical fiber, thereby obtaining a rare earth-doped optical fiber for suppressing mode instability effects.

[0039] See also Figure 1 As shown, a rare earth-doped optical fiber for suppressing mode instability effect prepared by the above method comprises a core active region 1, a core passive region 2, a channel region 3 and a cladding 5 arranged in sequence from the inside to the outside. The doping components of the core active region 1 are different from those of the core passive region 2. Specifically, the doping components of the core active region 1 are Al, P, Sr, Yb, and F, and the doping components of the core passive region 2 are P, B, Sr, and F.

[0040] The thermo-optic coefficient of the core active region and the core passive region is (0.6-0.9)×10 -5 / k. Compared with the thermo-optical coefficient of ordinary optical fiber (1.0-1.2) ×10 -5 / k, the present invention reduces the thermal-optical coefficient of the optical fiber, weakens the nonlinear inter-mode coupling effect, and realizes the effective suppression of MI.

[0041] The numerical aperture of rare earth doped optical fiber is 0.035-0.055.

[0042] By introducing negative thermo-optic coefficient materials (B, Sr, P), the thermo-optic coefficient of the optical fiber is reduced, the nonlinear inter-mode coupling effect is weakened, and the effective suppression of MI is achieved; at the same time, the rare earth ion center doping method is used to reduce the high-order mode gain in the case of a large fiber core, and then through the mode competition mechanism, the generation of high-order modes is suppressed, the proportion of fundamental mode is increased, and the fundamental mode-higher-order mode coupling effect is suppressed, further increasing the MI threshold and improving the beam quality; the low numerical aperture and channel structure design make the optical fiber have a higher high-order mode loss, suppressing the inter-mode coupling effect, thereby further suppressing the MI effect, while ensuring that the large-core fiber can still achieve a higher proportion of fundamental mode output with good beam quality.

[0043] The present invention integrates multiple advantageous features and uses multiple MI effect suppression technologies such as low-thermal optical material technology, partial doping technology, low numerical aperture bent filter technology, high-order mode coupling loss technology, and high-order mode self-loss technology to continuously suppress the MI effect and greatly improve the MI threshold while ensuring the beam quality of the large-core optical fiber output laser.

[0044] The preparation method of the rare earth-doped optical fiber for suppressing mode instability effect provided by the present invention is described below with reference to specific embodiments.

[0045] Example 1

[0046] A method for preparing a rare earth-doped optical fiber for suppressing mode instability effects mainly comprises the following steps:

[0047] S1, using the traditional MCVD process, using vapor deposition technology to deposit a low refractive index channel area in the tube, with a channel width of 1-3um and a refractive index depth of -0.0005~ -0.001;

[0048] S2, deposition of SiO 2 The loose layer is on the inner wall of the quartz tube. The quartz tube with the loose layer deposited is removed and placed in a mixed doping solution of P, B, and Sr. The tube is taken out and dried. The ion concentrations are 1.5M, 1M, and 0.2M respectively. The tube is put back on the MCVD lathe and F element is doped using the gas phase technology. The tube is sintered at 1300-1600°C and vitrified at 1850°C to complete the preparation of the passive area of ​​the fiber core.

[0049] S3, deposition of SiO 2 The loose layer is on the inner wall of the quartz tube. The quartz tube with the loose layer deposited is removed and placed in a mixed doping solution of Al, P, Sr, and Yb with ion concentrations of 1.5M, 1.5M, 0.2M, and 0.5M, respectively. The tube is taken out and dried, and then placed back on the MCVD lathe. The F element is doped using the gas phase technology, and the sintering is completed at 1300-1600°C. The vitrification is completed at 1850°C to complete the preparation of the core active area.

[0050] S4, completing collapse at 2000°C-2200°C to obtain a dense solid core optical fiber preform;

[0051] S5, placing the optical fiber preform on an optical fiber drawing tower, and drawing the optical fiber to obtain a quartz optical fiber with a core / cladding diameter of 25um / 400um and a numerical aperture of 0.04.

[0052] This optical fiber has many characteristics such as low numerical aperture, low thermo-optical coefficient, channel structure, and partial doping.

[0053] Figure 1The refractive index curve corresponding to each region of the rare earth-doped optical fiber for suppressing the mode instability effect prepared in Example 1. It can be seen that the refractive index of the core active region and the core passive region is basically the same, ensuring low-loss transmission of the fundamental mode light in the core, and the refractive index of the channel region is 0.0005-0.001 lower than that of the pure silica cladding, and the width is usually 3um, which further filters out the high-order mode and reduces the mode field area.

[0054] Example 2

[0055] The difference between Example 2 and Example 1 is that in step S5, the optical fiber preform is placed on an optical fiber drawing tower to draw the optical fiber to obtain a quartz optical fiber with a core / cladding diameter of 30um / 400um, and the core diameter is increased to 30um. The rest is substantially the same as Example 1 and will not be described in detail.

[0056] Comparative Example 1

[0057] The difference between comparative example 1 and embodiment 1 is mainly that: the B element is not introduced in step S2, that is, the mode loss of the passive region of the core is not significantly increased. The rest is substantially the same as embodiment 1 and will not be described again.

[0058] Comparative Example 2

[0059] The difference between Comparative Example 2 and Example 1 is that the mixed doping solution components in step S2 and step S3 are the same, both are mixed doping solutions of Al, P, Sr, and Yb, that is, the doping components of the core passive region and the core active region are the same. The rest is substantially the same as in Example 1 and will not be described here.

[0060] Comparative Example 3

[0061] The difference between Comparative Example 3 and Example 1 is that step S1 is not performed, that is, the channel is not deposited. The rest is substantially the same as Example 1 and will not be described again.

[0062] Comparative Example 4

[0063] The difference between Comparative Example 4 and Example 1 is that in step S1, the numerical aperture of the fiber core is 0.06. The rest is substantially the same as Example 1 and will not be described in detail here.

[0064] The optical fibers prepared in Examples 1-2 and Comparative Examples 1-4 were subjected to performance tests, and the results are shown in Table 1.

[0065] Table 1 Performance test data of conventional optical fibers, optical fibers prepared in Examples 1-2, and Comparative Examples 1-4

[0066]

[0067] It can be seen from Table 1 that the MI threshold of the rare-earth-doped optical fiber with a core / cladding diameter of 25um / 400um is greater than or equal to 3kW, and the beam quality factor M2 is 1.5; the MI threshold of the rare-earth-doped optical fiber with a core / cladding diameter of 30um / 400um is greater than or equal to 2kW, and the beam quality factor M2 is 2.

[0068] The MI threshold of comparative example 1 is 2.9 kW, and the beam quality is greater than 2. Compared with example 1, it can be seen that when the high-order mode high loss condition of the core passive region is not met, the MI threshold and the beam quality will deteriorate.

[0069] The MI threshold of comparative example 2 is 2.3 kW, and the beam quality is greater than 2. Compared with example 1, it can be seen that when the central doping condition is not met, both the MI threshold and the beam quality will deteriorate.

[0070] The MI threshold of comparative example 3 is 2.2 kW, and the beam quality is greater than 2. Compared with example 1, it can be seen that when channel deposition is not provided, both the MI threshold and the beam quality will deteriorate.

[0071] The MI threshold of comparative example 4 is 1.8 kW, and the beam quality is greater than 2. Compared with example 1, it can be seen that when a low numerical aperture is not provided, both the MI threshold and the beam quality will deteriorate.

[0072] In summary, the present invention first deposits a low-refractive-index channel region in a quartz tube, so that the optical fiber has a higher high-order mode loss; then, the core passive region and the core active region with different doping components are sequentially prepared to achieve different thermo-optic coefficients in the local area of ​​the core. By introducing negative thermo-optic coefficient materials, the optical fiber thermo-optic coefficient is reduced, the nonlinear inter-mode coupling effect is weakened, and the effective suppression of MI is achieved; at the same time, the rare earth ion center doping method is adopted to reduce the high-order mode gain in the case of a large core, and then the mode competition mechanism is used to suppress the generation of high-order modes, increase the proportion of fundamental modes, suppress the coupling effect of fundamental mode-high-order modes, further increase the MI threshold, and improve the beam quality; the low numerical aperture and channel structure design make the optical fiber have a higher high-order mode loss, suppress the inter-mode coupling effect, thereby further realizing the suppression of the MI effect, while ensuring that the large-core optical fiber can still achieve a higher proportion of fundamental mode output, with good beam quality. This patent integrates multiple advantageous features, superimposing multiple MI effect suppression technologies such as low-thermal optical material technology, partial doping technology, low numerical aperture bent filter technology, high-order mode coupling loss technology, and high-order mode self-loss technology, to continuously suppress the MI effect and significantly increase the MI threshold while ensuring the beam quality of the large-core optical fiber output laser.

[0073] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a rare earth-doped optical fiber for suppressing mode instability effects, characterized in that: The steps include: S1, using MCVD process, using vapor deposition technology to deposit a low refractive index channel area in the quartz tube, the channel width is 1-3um, and the refractive index depth of the channel is -0.0005 to -0.001; S2, depositing a loose SiO2 layer on the inner wall of the quartz tube, then removing the quartz tube with the deposited loose SiO2 layer, placing it in a mixed doping solution of P, B, and Sr, taking it out and drying it; wherein, in the mixed doping solution, the ion concentrations of P, B, and Sr are 0.5-1.5M, 1-1.5M, and 0.2-0.6M, respectively; after drying, placing the quartz tube back on the MCVD lathe, doping F element using gas phase technology, and then sintering and vitrification treatment are performed in sequence to complete the preparation of the passive area of ​​the fiber core; S3, depositing a SiO2 loose layer on the inner wall of the quartz tube, then removing the quartz tube with the SiO2 loose layer deposited, and placing it in a mixed doping solution of Al, P, Sr, and Yb, taking it out and drying it; wherein, in the mixed doping solution, the ion concentrations of Al, P, Sr, and Yb are 1.5-2M, 1.5-2M, 0.2-0.6M, and 0.5-1M, respectively; after drying, placing the quartz tube back on the MCVD lathe, doping F element using gas phase technology, and then sintering and vitrification treatment are performed in sequence to complete the preparation of the core active area; S4, completing collapse at 2000°C-2200°C to obtain a dense solid core optical fiber preform; S5, placing the solid core optical fiber preform on an optical fiber drawing tower to draw the optical fiber, thereby obtaining the rare earth-doped optical fiber for suppressing mode instability effect.

2. The method for preparing a rare earth-doped optical fiber for suppressing mode instability effect according to claim 1, characterized in that: In step S2, the preparation method of the mixed doping solution of P, B and Sr is: dissolving the compound containing P, B and Sr in water or ethanol solution, dispersing by oscillation ultrasound to promote the dissolution of the compound, and forming a mixed doping solution containing P, B and Sr ions.

3. The method for preparing a rare earth-doped optical fiber for suppressing mode instability effect according to claim 1, characterized in that: In step S3, the preparation method of the mixed doping solution of Al, P, Sr and Yb is: dissolving the compound containing Al, P, Sr and Yb in water or ethanol solution, dispersing by oscillation ultrasound to promote the dissolution of the compound, and forming a mixed doping solution containing Al, P, Sr and Yb ions.

4. A rare earth doped optical fiber for suppressing mode instability effects, characterized in that: According to the preparation method according to any one of claims 1 to 3, the rare-earth-doped optical fiber for suppressing mode instability effects comprises a core active region, a core passive region, a channel region and a cladding arranged in sequence from the inside to the outside.

5. The rare earth-doped optical fiber for suppressing mode instability effect according to claim 4, characterized in that: The thermo-optic coefficient of the active region of the core is (0.6-0.9)×10 -5 / k, the thermo-optic coefficient of the passive region of the core is (0.6-0.9)×10 -5 / k.

6. The rare earth-doped optical fiber for suppressing mode instability effect according to claim 4, characterized in that: 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 effect according to claim 4, characterized in that: The MI threshold of rare-earth-doped optical fiber with a core / cladding diameter of 25um / 400um is greater than or equal to 3kW, and the beam quality factor M2 is 1.5; the MI threshold of rare-earth-doped optical fiber with a core / cladding diameter of 30um / 400um is greater than or equal to 2kW, and the beam quality factor M2 is 2.

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