CN114114527B - Active optical fiber for homogenizing light intensity distribution of fundamental mode and preparation method thereof - Google Patents
Active optical fiber for homogenizing light intensity distribution of fundamental mode and preparation method thereof Download PDFInfo
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Abstract
The invention discloses an active optical fiber for homogenizing light intensity distribution of a fundamental mode and a preparation method thereof. According to the invention, through the arrangement mode that the inner fiber core is doped with rare earth ions and the outer fiber core is not doped with rare earth ions, the homogenization of the light intensity distribution of the transmission fundamental mode of the fiber core is realized, the power density difference between the radial positions of the fiber core is reduced, the mode field area of the fiber core is enlarged, and the overlapping factor of a high-order mode and a gain region doped with rare earth ions is obviously reduced by utilizing the outer fiber core not doped with rare earth ions, so that the effect of inhibiting the gain of the high-order mode is achieved; meanwhile, the highest power density borne by the fiber core of the optical fiber is also reduced, so that the nonlinear threshold of the active optical fiber is improved.
Description
Technical Field
The invention relates to the technical field of optical fibers, in particular to an active optical fiber for homogenizing light intensity distribution of a fundamental mode and a preparation method thereof.
Background
At present, the advent of lasers has greatly facilitated the development of modern industrial, defense, medical and scientific applications, where fiber lasers with the advantages of high slope efficiency, good beam quality, excellent thermal management, etc. are more favored. Generally, in order to avoid the nonlinear effect of the fiber laser due to the power boost, the simplest and most effective measure is to enlarge the core size of the gain fiber to increase the mode field area. However, in the practical implementation process, the number of transmission modes in the fiber core increases with the increase of the diameter of the fiber core, so that the quality of the light beam of the output light field is degraded, and the practical performance of the fiber laser is affected. In order to expand the mode field and inhibit the high-order mode, researchers have proposed many new-structure optical fibers, such as bragg optical fibers, photonic band-gap optical fibers, large-pitch optical fibers, and chiral coupling core optical fibers, which are difficult to prepare and are not suitable for mass production. For a traditional Step Index Fiber (SIF) which is simple to manufacture and widely used, the light intensity distribution of a fundamental mode transmitted by a Fiber core is close to gaussian distribution, so that the center of the Fiber core bears the highest power density, and the nonlinear effect is naturally easy to trigger. Therefore, a new optical fiber design is needed to solve the shortcomings of the existing optical fiber.
Disclosure of Invention
The invention aims to provide an active optical fiber for homogenizing light intensity distribution of a fundamental mode and a preparation method thereof, which are used for solving the problems that the light intensity distribution of a conventional step-index optical fiber is uneven and a nonlinear effect is easily triggered.
In order to solve the above technical problem, a first solution provided by the present invention is: the active optical fiber comprises an optical fiber core, an inner cladding and an outer cladding which are sequentially arranged from inside to outside, wherein the optical fiber core comprises an inner fiber core doped with rare earth ions and an outer fiber core not doped with rare earth ions, the refractive index of the inner fiber core is lower than that of the outer fiber core, the difference between the refractive index of the inner fiber core and that of the inner cladding is 0.0010-0.0015, and the difference between the effective refractive index corresponding to a transmission fundamental mode in the optical fiber core and that of the inner fiber core is smaller than 0.0001.
Preferably, the cross section of the inner cladding is an octagonal structure.
Preferably, the inner core is made of SiO2The rare earth element is a substrate, is co-doped with Al with the mol percentage of 0.5-1 mol% and F with the mol percentage of 0.1-0.2 mol%, and is doped with rare earth elements Yb and Ce, the mol percentage range of the rare earth elements Yb and Ce is 0.1-0.5 mol%, and the mol ratio of Ce/Yb is 0.5-1.
Preferably, the outer core is formed of SiO2The substrate is doped with 1-10 mol% of element Ge.
Preferably, the ratio of the diameter of the inner core to the diameter of the optical fiber core is greater than 0.5.
In order to solve the above technical problem, a second solution provided by the present invention is: base mold for homogenizationA method for manufacturing an active optical fiber having a light intensity distribution, which is used for manufacturing the active optical fiber for homogenizing a light intensity distribution of a fundamental mode in the aforementioned first solution, comprising the steps of: (1) depositing a first loose body on the inner wall of the quartz glass tube by adopting a chemical vapor deposition method, and sintering the first loose body for one time to form an outer fiber core; (2) depositing a second loose body on the inner wall of the outer fiber core, immersing the quartz glass tube in a solution containing rare earth ions for doping, and drying after doping to form a second loose body doped with rare earth ions; (3) at O2Oxidizing the second loose body doped with rare earth ions in the environment, performing secondary sintering to form an inner fiber core, and performing rod-shrinking treatment to obtain an optical fiber core; (4) and after acid washing and polishing the fiber core of the optical fiber, sequentially arranging an inner cladding layer and an outer cladding layer to obtain the active optical fiber for homogenizing the light intensity distribution of the fundamental mode.
Preferably, SiCl is introduced into the reaction solution in the step (1) under the condition that the reaction temperature is 1600-1800 DEG C4、GeCl4And O2Depositing a first loose body on the inner wall of the quartz glass tube, wherein the first loose body is SiO2-GeO2A composite loose structure; the temperature of the primary sintering is 2000-2200 ℃, and the time of the primary sintering is 10-20 min.
Preferably, SiCl is introduced into the reaction solution in the step (2) under the condition that the reaction temperature is 1600-1800 DEG C4、O2And SF6Depositing a second loose body on the inner wall of the outer fiber core, wherein the second loose body is SiO2Loose structure, solution containing rare-earth ions made of YbCl3、AlCl3、CeCl3Mixing with solvent, and introducing Cl2Drying is carried out.
Preferably, in the step (3), the oxidation reaction temperature of the second loose body doped with the rare earth ions is 1400-1500 ℃; the temperature of the secondary sintering is 2000-2200 ℃, and the time of the secondary sintering is 10-20 min; the rod shrinking treatment comprises the following steps: heating to 2100-2300 deg.C at O2And (5) reversely collapsing the atmosphere to obtain the fiber core of the optical fiber.
Preferably, in the step (4), sleeving the outer surface of the optical fiber core, and grinding and polishing the outer surface to form an inner cladding with an octagonal cross-section structure; sleeving a sleeve on the outer surface of the inner cladding to form an outer cladding to obtain a prefabricated rod; and (4) placing the polished preform into a heating furnace of a wire drawing tower, melting into wires and carrying out double-layer coating to obtain the active optical fiber for homogenizing the light intensity distribution of the base mode.
The invention has the beneficial effects that: the invention provides an active optical fiber for homogenizing the light intensity distribution of a fundamental mode and a preparation method thereof, which are different from the prior art, the homogenization of the light intensity distribution of the fundamental mode transmitted by a fiber core is realized by the arrangement mode that rare earth ions are doped into an inner fiber core and rare earth ions are not doped into an outer fiber core, the power density difference between the radial positions of the fiber cores is reduced, the mode field area of the fiber core is enlarged, and the overlapping factor of a high-order mode and a gain region doped with rare earth ions is obviously reduced by utilizing the outer fiber core not doped with rare earth ions, so that the effect of inhibiting the gain of the high-order mode is achieved; meanwhile, the highest power density borne by the fiber core of the optical fiber is also reduced, so that the nonlinear threshold of the active optical fiber is improved.
Drawings
FIG. 1 is a schematic cross-sectional view of an embodiment of an active optical fiber for homogenizing the intensity distribution of a fundamental mode in accordance with the present invention;
FIG. 2 is a schematic view of the refractive index profile of an embodiment of the active optical fiber of the present invention for homogenizing the intensity distribution of the fundamental mode light;
FIG. 3 is a comparison graph of light intensity distribution in example 1 of the present invention;
FIG. 4 is a comparison graph of light intensity distribution in example 2 of the present invention;
FIG. 5 is a comparison graph of light intensity distribution in example 3 of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art based on the embodiments of the present invention without any creative effort, fall within the protection scope of the present invention.
Referring to fig. 1, the active optical fiber for homogenizing the light intensity distribution of the fundamental mode of the present invention includes an optical fiber core 1, an inner cladding layer 2 and an outer cladding layer 3 arranged in sequence from inside to outside, the optical fiber core 1 includes an inner fiber core 11 doped with rare earth ions and an outer fiber core 12 not doped with rare earth ions; in the embodiment, the cross section of the inner cladding 2 is of an octagonal structure, and the octagonal structure of the inner cladding is utilized to enable the pump light in the inner cladding to be fully absorbed by the optical fiber core 1; inner core made of SiO2Co-doping Al and F as a matrix, and doping rare earth elements Yb and Ce; the outer core is made of SiO2As a host, elemental Ge is doped. Here, the arrangement in which the inner core is doped with rare earth and the outer core is not doped with rare earth is adopted, and the purpose is to suppress the gain of the high-order mode in the outer core, thereby avoiding a decrease in the laser performance of the optical fiber.
Referring to FIG. 2, in the present embodiment, the refractive index n of the inner core 113Lower than the refractive index n of the outer core 122Refractive index n of inner core 113Greater than the refractive index n of the inner cladding 21The difference between the refractive index of the inner core 11 and the refractive index of the inner cladding 2 is preferably 0.0010 to 0.0015; the effective refractive index corresponding to the transmission fundamental mode in the fiber core needs to be as close as possible to the refractive index of the inner fiber core, and preferably, the difference between the effective refractive index corresponding to the transmission fundamental mode in the fiber core and the refractive index of the inner fiber core is less than 0.0001 so as to obtain the uniform light intensity distribution effect of the fundamental mode. In addition, through experimental tests, on the premise of ensuring the refractive index relationship, the thickness of the outer fiber core and the difference between the refractive indexes of the inner fiber core and the outer fiber core have a mutual influence relationship, specifically, the narrower the width of the outer fiber core ring relative to the thickness of the inner fiber core, the larger the difference between the refractive indexes of the inner fiber core and the outer fiber core is, so that the difference between the refractive indexes of the inner fiber core and the outer fiber core can be adjusted by adjusting the relative thicknesses of the inner fiber core and the outer fiber core; preferably, the diameter of the optical fiber core is 20 to 30 μm, and the ratio of the diameter of the inner core to the diameter of the optical fiber core is greater than 0.5.
As for the second solution provided by the present invention, there is provided a method for manufacturing an active optical fiber for homogenizing a light intensity distribution of a fundamental mode, the method for manufacturing an active optical fiber for homogenizing a light intensity distribution of a fundamental mode in the aforementioned first solution, comprising the steps of:
(1) and depositing a first loose body on the inner wall of the quartz glass tube by adopting a chemical vapor deposition method, and sintering the first loose body once to form the outer fiber core. Before the step is executed, MCVD (Modified Chemical Vapor Deposition) equipment can be adopted to polish the inner wall of the high-purity quartz glass tube so as to remove impurities on the surface of the inner wall; in the process of executing the step, MCVD equipment is adopted, and SiCl is introduced under the condition that the reaction temperature is 1600-1800 DEG C4、GeCl4And O2Depositing a first loose body on the inner wall of the quartz glass tube, then sintering for the first time, and carrying out high-temperature vitrification sintering on the first loose body to obtain an outer fiber core; wherein the first loose body is SiO2-GeO2The composite loose structure is formed, the temperature of primary sintering is 2000-2200 ℃, and the time of primary sintering is 10-20 min.
(2) And depositing a second loose body on the inner wall of the outer fiber core, immersing the quartz glass tube in a solution containing rare earth ions for doping, and drying after doping to form the second loose body doped with the rare earth ions. In the step, MCVD equipment is adopted, and SiCl is introduced under the condition that the reaction temperature is 1600-1800 DEG C4、O2And SF6Depositing a second loose body on the inner wall of the outer fiber core, wherein the second loose body is SiO2A loose structure; using YbCl3、AlCl3、CeCl3Mixing with solvent to prepare solution containing rare earth ions, immersing quartz glass tube in the solution containing rare earth ions for doping, taking out the quartz glass tube after doping, and adopting N2Drying water, connecting the dried substrate tube into MCVD equipment again, and introducing Cl2Drying is carried out.
(3) At O2Oxidizing the second loose body doped with rare earth ions in the environment, performing secondary sintering to form an inner fiber core, and performing rod shrinkage to obtain the fiber core of the optical fiber. In the step, rare earth doped ions in the second loose body are oxidized by oxygen at 1400-1500 ℃, and then secondary sintering is carried out to mix the second loose body with the rare earth doped ionsThe loose body is subjected to high-temperature vitrification sintering to obtain an inner fiber core; wherein the temperature of the secondary sintering is 2000-2200 ℃, and the time of the secondary sintering is 10-20 min; then heating to 2100-2300 deg.C in O2And (4) reversely collapsing the atmosphere to obtain the fiber core of the optical fiber.
(4) And after acid washing and polishing the fiber core of the optical fiber, sequentially arranging an inner cladding layer and an outer cladding layer to obtain the active optical fiber for homogenizing the light intensity distribution of the fundamental mode. In the step, the optical fiber core rod body is treated by acid washing and high-temperature polishing so as to remove impurities and fine cracks in the optical fiber core rod body; then, sleeving a sleeve on the outer surface of the fiber core of the optical fiber, and processing the sleeve into a structure with an octagonal cross section through grinding and polishing treatment to form an inner cladding; sleeving a sleeve on the outer surface of the inner cladding to form an outer cladding to obtain a prefabricated rod; and finally, placing the polished preform into a heating furnace of a drawing tower, melting the preform into filaments at the high temperature of 2000 ℃, and performing double-layer coating to obtain the active optical fiber for homogenizing the light intensity distribution of the base mode.
The effect of the above-described active optical fiber for homogenizing the light intensity distribution of the fundamental mode is tested and analyzed by the following embodiments.
Example 1
The preparation steps of the active optical fiber for homogenizing the light intensity distribution of the fundamental mode in the embodiment are as follows:
(1) selecting a high-purity quartz glass tube with the outer diameter of 20 micrometers, depositing a first loose body on the inner wall of the quartz glass tube by MCVD equipment, then performing primary sintering at 1600 ℃, wherein the time of the primary sintering is 15min, and performing high-temperature vitrification sintering on the first loose body to obtain an outer fiber core; the outer core had a thickness of 3 μm and a refractive index of 1.4523.
(2) Depositing a second loose body on the inner wall of the outer fiber core by MCVD equipment, preparing a solution containing rare earth ions by mixing, immersing the quartz glass tube in the solution containing the rare earth ions for doping, taking out the quartz glass tube after doping is finished, and introducing Cl2Drying is carried out.
(3) At O2Oxidizing the second loose body doped with rare earth ions under the environment, and then performing secondary sintering at the temperature of 2000 DEGPerforming high-temperature vitrification sintering on the second loose body to obtain an inner fiber core, wherein the secondary sintering time is 15 min; the inner core had a diameter of 14 μm and a refractive index of 1.4512.
(4) Acid washing and high-temperature polishing are adopted to treat the optical fiber core rod body so as to remove impurities and fine cracks in the optical fiber core rod body; then, sleeving a sleeve on the outer surface of the optical fiber core, and processing the sleeve into a structure with an octagonal cross section through grinding and polishing treatment to form an inner cladding, wherein the refractive index of the inner cladding is 1.45; sleeving a sleeve on the outer surface of the inner cladding to form an outer cladding to obtain a prefabricated rod; and finally, placing the polished preform into a heating furnace of a wire drawing tower, melting into wires and carrying out double-layer coating to obtain the active optical fiber for homogenizing the light intensity distribution of the base mold.
The active optical fiber prepared in this example was tested, and two SIF fibers, which had refractive indices of 1.4523 and 1.4512, and a wavelength of 1.08 μm for both test laser, were used as a comparative group. In this example, the effective mode field area of the prepared active optical fiber fundamental mode is 367 μm2Base mold, LP11The overlapping factors of the mode and the doped region are 0.507 and 0.320 respectively; SIF fiber with refractive index n =1.4523 and effective mode field area of fundamental mode of 227 μm2Base mold, LP11The overlapping factors of the mode and the doped region are 0.754 and 0.510 respectively; SIF optical fiber with refractive index n =1.4512 and effective mode field area of fundamental mode of 271 μm2Base mold, LP11The overlap factors of the mode and the doped region are 0.684 and 0.379 respectively. Specifically, as shown in fig. 3, the light intensity distribution pairs of the three optical fibers are combined with the above data, and it can be seen that the effective mode field area of the fundamental mode of the active optical fiber prepared in this embodiment is significantly larger than that of the other two conventional SIF optical fibers; meanwhile, the optical fiber LP of the present invention11The overlapping factor of the mode and the doped region is minimum, so that the high-order mode gain can be effectively inhibited; as can be seen from the comparison of the light intensity distributions, the active fiber prepared in this example can effectively homogenize the light intensity distribution of the fundamental mode.
Example 2
The preparation procedure of this example is based on the preparation procedure of the previous example 1, except that the diameter of the inner core is 16 μm, the thickness of the outer core is 2 μm, and the refractive index of the outer core 12 is 1.4529; meanwhile, one of the SIF fibers to be compared had a refractive index of 1.4529, and the other conditions were the same as in example 1.
In this example, the effective mode field area of the prepared active optical fiber fundamental mode is 396 μm2Base mold, LP11The overlapping factors of the mode and the doped region are 0.596 and 0.431 respectively; SIF fiber with refractive index n =1.4529 and effective mode field area of fundamental mode of 216 μm2Base mold, LP11The overlapping factors of the mode and the doped region are 0.873 and 0.716 respectively; SIF optical fiber with refractive index n =1.4512 and effective mode field area of fundamental mode of 271 μm2Base mold, LP11The overlap factors of the mode and the doped region are 0.789 and 0.523 respectively. Specifically, as shown in fig. 4, the light intensity distribution pairs of the three optical fibers are combined with the above data, and it can be seen that the effective mode field area of the fundamental mode of the active optical fiber prepared in this embodiment is significantly larger than that of the other two conventional SIF optical fibers; meanwhile, the optical fiber LP of the present invention11The overlapping factor of the mode and the doped region is minimum, so that the high-order mode gain can be effectively inhibited; as can be seen from the comparison of the light intensity distributions, the active fiber prepared in this example can effectively homogenize the light intensity distribution of the fundamental mode.
Example 3
The preparation procedure of this example is based on the preparation procedure of the aforementioned example 1 except that the outer diameter of the silica glass tube is 30 μm, the diameter of the inner core is 24 μm, the thickness of the outer core is 3 μm, and the refractive index of the outer core is 1.4522; meanwhile, one of the SIF fibers to be compared had a refractive index of 1.4522, and the other conditions were the same as in example 1.
In this example, the effective mode field area of the prepared active optical fiber fundamental mode is 784 μm2Base mold, LP11The overlapping factors of the mode and the doped region are 0.654 and 0.512 respectively; SIF fiber with refractive index n =1.4522 and fundamental mode effective mode field area of 445 μm2Base mold, LP11The overlapping factors of the mode and the doped region are 0.901 and 0.777 respectively; SIF optical fiber with refractive index n =1.4512 and effective mode field area of fundamental mode of 494 μm2Base mold, LP11Of modes and doped regionsThe overlap factors are 0.867 and 0.703, respectively. Specifically, as shown in fig. 5, the light intensity distribution ratio of the three optical fibers is combined with the above data, and it can be seen that the effective mode field area of the fundamental mode of the active optical fiber prepared in this embodiment is significantly larger than that of the other two conventional SIF optical fibers; meanwhile, the optical fiber LP of the present invention11The overlapping factor of the mode and the doped region is minimum, so that the high-order mode gain can be effectively inhibited; as can be seen from the comparison of the light intensity distributions, the active fiber prepared in this example can effectively homogenize the light intensity distribution of the fundamental mode.
Comparative example 1
The preparation procedure of this example is based on the preparation procedure of example 1 above, except that the refractive index of the inner core is 1.4522, the refractive index of the outer core is 1.4530, and the others are identical to example 1, with the difference between the refractive index of the inner core and the refractive index of the inner cladding being greater than 0.0015.
In this example, the effective mode field area of the prepared active fiber fundamental mode is 326 μm2Base mold, LP11The overlapping factors of the mode and the doped region are 0.495 and 0.270 respectively; comparing the data with the data of example 1, it is easy to see that the effective mode field area and the overlap factor of the fundamental mode of the active optical fiber prepared in comparative example 1 are both smaller than those of example 1, because the refractive index of the inner fiber core is adjusted and exceeds the parameter limit requirement of the present invention, the homogenization effect of the fundamental mode light intensity distribution is poor, and it is proved that a better homogenization effect of the fundamental mode light intensity distribution can be obtained only by using the parameter range defined by the present invention.
The invention provides an active optical fiber for homogenizing light intensity distribution of a fundamental mode and a preparation method thereof, which are different from the prior art, through the arrangement mode that an inner fiber core is doped with rare earth ions and an outer fiber core is not doped with the rare earth ions, the homogenization of the light intensity distribution of the fundamental mode transmitted by the fiber core is realized, the power density difference between the radial positions of the fiber core is reduced, the mode field area of the fiber core is enlarged, and the overlapping factor of a high-order mode and a gain area doped with the rare earth ions is obviously reduced by utilizing the outer fiber core not doped with the rare earth ions, so that the effect of inhibiting the gain of the high-order mode is achieved; meanwhile, the highest power density borne by the fiber core is also reduced, so that the nonlinear threshold of the active optical fiber is improved.
It should be noted that the above embodiments belong to the same inventive concept, and the description of each embodiment has a different emphasis, and reference may be made to the description in other embodiments where the description in individual embodiments is not detailed.
The above-mentioned embodiments only express the embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (9)
1. An active optical fiber for homogenizing light intensity distribution of a fundamental mode is characterized by comprising an optical fiber core, an inner cladding and an outer cladding which are sequentially arranged from inside to outside, wherein the optical fiber core comprises an inner fiber core doped with rare earth ions and an outer fiber core not doped with rare earth ions, the refractive index of the inner fiber core is lower than that of the outer fiber core, the difference between the refractive index of the inner fiber core and that of the inner cladding is 0.0010-0.0015, and the difference between the effective refractive index corresponding to a transmission fundamental mode in the optical fiber core and that of the inner fiber core is less than 0.0001;
the inner fiber core, the outer fiber core and the inner cladding are arranged in a step index distribution mode;
the inner fiber core is made of SiO2The rare earth element is a substrate, is co-doped with Al with the mol percentage of 0.5-1 mol% and F with the mol percentage of 0.1-0.2 mol%, and is doped with rare earth elements Yb and Ce, the mol percentage range of the rare earth elements Yb and Ce is 0.1-0.5 mol%, and the mol ratio of Ce/Yb is 0.5-1.
2. The active optical fiber for homogenizing the intensity distribution of a fundamental mode light according to claim 1, wherein the cross-section of the inner cladding has an octagonal structure.
3. The method according to claim 1, wherein the intensity distribution of the fundamental mode light is homogenizedThe active optical fiber of (1), wherein the outer core is formed of SiO2The substrate is doped with 1-10 mol% of element Ge.
4. The active fiber for homogenizing the fundamental mode intensity profile of claim 1, wherein the ratio of the diameter of the inner core to the fiber core is greater than 0.5.
5. A method for preparing an active optical fiber for homogenizing the intensity distribution of a fundamental mode light as claimed in any one of claims 1 to 4, comprising the steps of:
(1) depositing a first loose body on the inner wall of the quartz glass tube by adopting a chemical vapor deposition method, and sintering the first loose body for one time to form an outer fiber core;
(2) depositing a second loose body on the inner wall of the outer fiber core, immersing the quartz glass tube in a solution containing rare earth ions for doping, and drying after doping to form a second loose body doped with rare earth ions;
(3) at O2Oxidizing the second loose body doped with rare earth ions in the environment, performing secondary sintering to form an inner fiber core, and performing rod-shrinking treatment to obtain an optical fiber core;
(4) and after acid washing and polishing the fiber core of the optical fiber, sequentially arranging an inner cladding layer and an outer cladding layer to obtain the active optical fiber for homogenizing the light intensity distribution of the fundamental mode.
6. The method for preparing an active optical fiber for homogenizing the intensity distribution of a fundamental mode light according to claim 5, wherein SiCl is introduced into the fiber at a reaction temperature of 1600-1800 ℃ in the step (1)4、GeCl4And O2Depositing a first loose body on the inner wall of the quartz glass tube, wherein the first loose body is SiO2-GeO2A composite loose structure; the temperature of the primary sintering is 2000-2200 ℃, and the time of the primary sintering is 10-20 min.
7. According to claim 5The preparation method of the active optical fiber for homogenizing the light intensity distribution of the fundamental mode is characterized in that SiCl is introduced into the active optical fiber in the step (2) under the condition that the reaction temperature is 1600-1800 DEG C4、O2And SF6Depositing a second loose body on the inner wall of the outer fiber core, wherein the second loose body is SiO2Loose structure, the solution containing rare earth ions is composed of YbCl3、AlCl3、CeCl3Mixing with solvent, and introducing Cl2Drying is carried out.
8. The method for preparing an active optical fiber for homogenizing a light intensity distribution of a fundamental mode according to claim 5, wherein the oxidation reaction temperature of the second bulk doped with rare earth ions in the step (3) is 1400 to 1500 ℃;
the temperature of the secondary sintering is 2000-2200 ℃, and the time of the secondary sintering is 10-20 min;
the rod shrinking treatment comprises the following steps: heating to 2100-2300 deg.C at O2And (4) reversely collapsing the atmosphere to obtain the optical fiber core.
9. The method for preparing an active optical fiber for homogenizing the intensity distribution of the fundamental mode light according to claim 5, wherein in the step (4), the outer surface of the core of the optical fiber is sleeved and processed into a cross-sectional octagonal structure by polishing to form an inner cladding;
sleeving a sleeve on the outer surface of the inner cladding to form an outer cladding to obtain a prefabricated rod;
and (3) placing the polished preform into a heating furnace of a wire drawing tower, melting into wires and carrying out double-layer coating to obtain the active optical fiber for homogenizing the light intensity distribution of the base mode.
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