Active optical fiber preform, preparation method thereof and optical fiber

Abstract

The embodiment of the invention provides an active optical fiber preform, a preparation method thereof and an optical fiber, and the preparation method comprises the following steps: introducing first silicon tetrachloride, first oxygen and first helium into a quartz base tube, carrying out pre-deposition treatment, and forming a silicon oxide pre-deposition layer in the quartz base tube to obtain a first base tube; second silicon tetrachloride, second oxygen and second helium are introduced into the first base tube for deposition treatment, a silicon oxide deposition layer is formed in the first base tube, and a second base tube is obtained; soaking the second base tube in a rare earth ion solution to obtain a third base tube; and carrying out melting shrinkage treatment on the third base tube to obtain the active optical fiber preform. The method is used for achieving the effect of improving the rare earth doping concentration and the bonding strength between the loose layer and the base tube at the same time.

Description

Technical Field

[0001] This application relates to the field of optical fiber manufacturing technology, and in particular to an active optical fiber preform and its preparation method, and an optical fiber. Background Technology

[0002] Rare-earth-doped fiber, as the core gain medium of fiber lasers, directly determines the laser's output power, wavelength stability, and nonlinear effect control capabilities. In the communications field, rare-earth-doped fiber is widely used in full-band fiber amplifiers to achieve relay amplification for long-distance optical signal transmission; in contrast, traditional glass fiber is mainly used for signal transmission and lacks gain capabilities. In industrial processing (such as laser cutting and welding), high-power fiber lasers rely on the high-efficiency energy conversion capabilities of rare-earth-doped fiber. With the increasing power demands of lasers, the requirement for rare-earth doping concentration has significantly increased to enhance light absorption efficiency and suppress nonlinear effects.

[0003] Currently, the process for fabricating active optical fiber preforms using the solution immersion method requires first depositing a porous layer in a quartz tube before solution immersion to achieve rare earth ion doping. The doping concentration of the porous material obtained through solution immersion is related to the structure of the porous material and the solution immersion parameters. Theoretically, the more porous the material, the higher the concentration of rare earth ions that can be doped. However, the concentration of rare earth ions cannot be increased indefinitely; excessive ion doping can cause the porous powder to detach from the quartz tube wall after immersion, leading to the shedding of the porous layer.

[0004] Therefore, there is an urgent need to provide an optical fiber preform with high rare earth doping concentration and high bonding strength between the loose layer and the base tube wall, so as to solve the contradiction between the loose layer structure and doping concentration in the existing technology. Summary of the Invention

[0005] This application provides an active optical fiber preform and its preparation method, as well as an optical fiber, to achieve the effect of simultaneously increasing the rare earth doping concentration and the bonding force between the deposited layer and the base tube wall.

[0006] In a first aspect, embodiments of this application provide a method for preparing an active optical fiber preform, comprising: introducing a first silicon tetrachloride, a first oxygen gas, and a first helium gas into a quartz base tube, performing a pre-deposition treatment, forming a silicon oxide pre-deposition layer in the quartz base tube, and obtaining a first base tube;

[0007] A second silicon tetrachloride, a second oxygen gas, and a second helium gas are introduced into the first base tube for deposition treatment, forming a silicon oxide deposition layer inside the first base tube to obtain a second base tube.

[0008] The second base tube was immersed in a rare earth ion solution to obtain the third base tube;

[0009] The third base tube is fused and shrunk to obtain the active optical fiber preform.

[0010] In one possible implementation, the porosity of the silicon oxide pre-deposited layer is 35% to 45%.

[0011] And / or, the porosity of the silicon oxide deposited layer is 45% to 55%.

[0012] In one possible implementation, the pre-deposition treatment is carried out at a temperature of 1200°C-1600°C;

[0013] And / or, the flow rate of the first silicon tetrachloride is 2 g / min-5 g / min;

[0014] And / or, the flow rate of the first oxygen is 1000 sccm-2000 sccm;

[0015] And / or, the flow rate of the first helium gas is 500 sccm-2000 sccm;

[0016] And / or, the deposition treatment temperature is 1150℃-1500℃;

[0017] And / or, the flow rate of the second silicon tetrachloride is 2 g / min - 5 g / min;

[0018] And / or, the flow rate of the second oxygen is 1000 sccm-2000 sccm;

[0019] And / or, the flow rate of the second helium gas is 500 sccm-2000 sccm.

[0020] In one possible implementation, the pre-deposition treatment may be performed 1 to 5 times.

[0021] In one possible implementation, the processing temperature of each pre-deposition treatment is 10°C-30°C lower than the processing temperature of the previous pre-deposition treatment.

[0022] In one possible implementation, the deposition process is performed at a temperature 5°C to 20°C lower than the temperature of the final pre-deposition process.

[0023] In one possible implementation, the rare earth chloride comprises at least one element selected from Y, Ce, Nd, Yb, Tm, Er, La, Bi, Ho, Pm, Sm, and Lu.

[0024] And / or, the rare earth ion solution includes at least one solvent selected from methanol, ethanol, and ethylene glycol;

[0025] And / or, the rare earth ion solution further includes at least one element selected from Al, P, and Ge.

[0026] In one possible implementation, the inner wall of the quartz tube is etched and polished before the pre-deposition treatment is performed on the quartz tube.

[0027] Secondly, embodiments of this application provide an active optical fiber preform prepared by the above-described preparation method.

[0028] Thirdly, embodiments of this application provide an optical fiber, which is obtained from an optical fiber preform prepared by the above-described preparation method or from the above-described optical fiber preform after drawing and coating.

[0029] This application provides an active optical fiber preform and its preparation method, as well as an optical fiber. By introducing a silica pre-deposition step before the silica loose layer deposition process, a loose layer system with a gradient pore structure is constructed, thereby enhancing the rare earth ion adsorption capacity and strengthening the bonding force between the loose layer and the base tube wall, achieving stable process control of high-concentration rare earth doping. Detailed Implementation

[0030] Exemplary embodiments will be described in detail below. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0031] Unlike traditional glass fibers, existing technologies for preparing active optical fiber preforms using solution immersion methods present a technical challenge: achieving a balance between rare earth doping concentration and the bonding strength of the loose layer.

[0032] Unlike ordinary glass fibers used only for optical signal transmission in the prior art, the active optical fiber preform preparation method provided in this application introduces silicon oxide pre-deposition before silicon oxide loose layer deposition treatment to construct a loose layer system with gradient pore structure, which solves the technical problem that the rare earth doping concentration and the bonding strength of the loose layer cannot be balanced at the same time.

[0033] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments.

[0034] This application provides a method for preparing an active optical fiber preform. The method includes: introducing a first silicon tetrachloride, a first oxygen gas, and a first helium gas into a quartz base tube for pre-deposition treatment to form a silicon oxide pre-deposition layer inside the quartz base tube, thus obtaining a first base tube; introducing a second silicon tetrachloride, a second oxygen gas, and a second helium gas into the first base tube for deposition treatment to form a silicon oxide deposition layer inside the first base tube, thus obtaining a second base tube; immersing the second base tube in a rare earth ion solution to obtain a third base tube; and performing a melting and shrinking treatment on the third base tube to obtain an active optical fiber preform. The porosity of the silicon oxide pre-deposition layer is less than the porosity of the silicon oxide deposition layer.

[0035] In this application, a relatively dense silicon oxide pre-deposited layer is first formed inside the quartz substrate, followed by a uniform amorphous silicon oxide layer on the substrate surface. On one hand, the amorphous silicon oxide layer can form strong chemical bonds with the quartz substrate surface, creating a continuous and robust interface. On the other hand, the silicon oxide pre-deposited layer serves as a thermal expansion gradient transition layer, alleviating stress generated during deposition temperature and cooling, preventing interface peeling, and thus enhancing the interfacial bonding between the silicon oxide deposited layer (loose layer) and the quartz substrate. Furthermore, the presence of the silicon oxide pre-deposited layer increases the effective specific surface area of ​​the subsequent silicon oxide deposited layer, providing more active sites for rare earth ion adsorption. Simultaneously, the high hydroxyl density on the surface of the silicon oxide pre-deposited layer allows it to form coordination bonds or ion exchange sites with rare earth ions. During subsequent solution doping, rare earth ions are adsorbed and uniformly distributed within the silicon oxide deposited layer (loose layer), thereby increasing the doping concentration of rare earth ions in the active optical fiber preform. Moreover, the silicon oxide pre-deposited layer also acts as a diffusion barrier layer, preventing rare earth ions from diffusing into the quartz tube during high-temperature deposition or sintering, thereby increasing the local concentration and doping efficiency of rare earth metals in the porous layer.

[0036] In some specific implementations, the porosity of the silicon oxide pre-deposited layer is 35% to 45%.

[0037] Since the silica pre-deposited layer is formed before the silica deposited layer, by controlling the porosity of the silica pre-deposited layer to 35%~45%, a more densely packed silica pre-deposited layer is obtained. During subsequent sintering, the contact area between particles is larger and the mass transfer path is shorter, which helps to achieve rapid and uniform densification and reduce internal stress. Moreover, the silica pre-deposited layer is close to the central region of the optical fiber preform, and eventually forms the core or inner cladding of the optical fiber. The lower porosity reduces the risk of incomplete collapse of pores during sintering, avoids the formation of bubbles or microcracks, and thus reduces the scattering loss and nonlinear effects of the optical fiber.

[0038] For example, the porosity of the silicon oxide pre-deposited layer can be a range of 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, or any combination thereof.

[0039] In some specific implementations, the porosity of the silicon oxide deposited layer is 45-55%.

[0040] The porosity of the silica deposited layer is controlled at 45%–55%. Maintaining a high porosity in the silica deposited layer provides more interconnected channels, which is more conducive to the escape of residual impurities (such as OH⁻, metal ions) or reaction byproducts during sintering, thereby improving the purity of the material. In addition, the silica deposited layer is usually relatively thick, and the high porosity can buffer the stress caused by the difference in shrinkage between the inner and outer layers during sintering, preventing cracking or delamination.

[0041] For example, the porosity of the silicon oxide deposited layer can be a range of 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, or any combination thereof.

[0042] In some specific implementations, the pre-deposition treatment temperature is 1200℃-1600℃.

[0043] In this embodiment, the pre-deposition processing temperature is controlled at 1200℃-1600℃. At this temperature, the silicon source (silicon tetrachloride) and oxygen source (oxygen) used for pre-deposition processing can obtain sufficient activation energy to ensure efficient and complete oxidation reaction (SiCl4 + O2 → SiO2 + 2Cl2↑). The pre-deposition rate is moderate and stable, which is conducive to the formation of a silicon oxide pre-deposition layer with appropriate nanopores and abundant surface silanol groups. This provides sufficient rare earth adsorption sites without collapsing in subsequent steps due to excessive structural fragility. Moreover, within this temperature range, the newly deposited SiO2 particles can not only physically adhere to the surface of the quartz tube, but also undergo interdiffusion of surface atoms / ions and direct formation of chemical bonds (Si-O-Si), thereby achieving a "glass-glass" level dense bond and ensuring the mechanical strength and long-term reliability of the active photovoltaic preform. More importantly, within this temperature window, through precise control, a semi-dense transition layer that is neither completely loose nor completely dense can be deposited. It acts as a bridge between the quartz base tube and the subsequent loose silica deposition layer, effectively mitigating the stress caused by the difference in thermal expansion coefficients.

[0044] For example, the pre-deposition treatment temperature can be a range of 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, 1500°C, 1550°C, 1600°C, or any combination thereof.

[0045] In some specific implementations, the flow rate of the first oxygen is 1000 sccm-2000 sccm.

[0046] At this flow rate, the initial oxygen supply provides sufficient oxygen for the pre-deposition process, ensuring complete reaction and purity of the silica pre-deposited layer. It also allows for a smoother reaction and more uniform deposition, resulting in a more controllable structure and fewer defects in the deposited layer. This helps achieve the appropriate porosity and ideal surface morphology required for the pre-deposited layer.

[0047] For example, the flow rate of the first oxygen can be a range of 1000 sccm, 1100 sccm, 1200 sccm, 1300 sccm, 1400 sccm, 1500 sccm, 1600 sccm, 1700 sccm, 1800 sccm, 1900 sccm, 2000 sccm or any combination thereof.

[0048] In some specific implementations, the flow rate of the first helium gas is 500 sccm-2000 sccm.

[0049] In the pre-deposition process, chlorine gas primarily serves as an environmental control gas. At high temperatures, it reacts violently with hydroxyl groups (-OH) and moisture (H2O) in the pre-deposition layer and quartz tube (SiO2-OH + Cl2 → SiO2-Cl + HCl↑, H2O + Cl2 → 2HCl + 1 / 2O2), generating volatile HCl and Cl2 which are carried away by the carrier gas. This significantly reduces the OH groups in the pre-deposition layer. - Content. At the same time, a moderate chlorine atmosphere can perform slight synchronous etching on the surface of the growing pre-deposited layer, which helps to smooth the pre-deposited front, reduce nodular growth, and obtain a more uniform layer structure.

[0050] For example, the flow rate of the first helium gas can be a range of 500 sccm, 600 sccm, 700 sccm, 800 sccm, 900 sccm, 1000 sccm, 1200 sccm, 1400 sccm, 1600 sccm, 1800 sccm, 2000 sccm, or any combination thereof.

[0051] In some specific implementations, the deposition process is carried out at a temperature of 1150℃-1500℃.

[0052] By controlling the deposition temperature to 1150℃-1500℃, it is ensured that the SiO2 particles formed during the deposition process are deposited in the form of "smoke ash," with loosely packed particles forming a nanoscale, interconnected pore network, thereby increasing the porosity and specific surface area of ​​the silica deposition layer. The high porosity and high activity structure ensured by the low temperature allows the rare earth ion solution to uniformly fill all pores, with sufficient active sites for adsorption in every corner, thus achieving high doping concentration and excellent radial uniformity.

[0053] For example, the deposition temperature can be a range of 1150°C, 1200°C, 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, 1500°C, or any combination thereof.

[0054] In some specific implementations, the flow rate of the second oxygen is 1000 sccm-2000 sccm.

[0055] In some specific implementations, the flow rate of the second helium gas is 500 sccm-2000 sccm.

[0056] Similar to the mechanism of controlling the flow rates of the first oxygen and second helium in the pre-deposition treatment, in order to achieve a more ideal deposition rate and obtain better structural porosity and thermal stability of the silicon oxide deposition layer, the flow rate of the second oxygen in the deposition treatment can be controlled to be 1000 sccm-2000 sccm and the flow rate of the second helium can be controlled to be 500 sccm-2000 sccm.

[0057] For example, the flow rate of the second oxygen gas can be a range of 1000 sccm, 1100 sccm, 1200 sccm, 1300 sccm, 1400 sccm, 1500 sccm, 1600 sccm, 1700 sccm, 1800 sccm, 1900 sccm, 2000 sccm or any combination thereof, and the flow rate of the second helium gas can be a range of 500 sccm, 600 sccm, 700 sccm, 800 sccm, 900 sccm, 1000 sccm, 1200 sccm, 1400 sccm, 1600 sccm, 1800 sccm, 2000 sccm or any combination thereof.

[0058] In some specific implementations, the number of pre-deposition treatments ranges from 1 to 5.

[0059] In this embodiment, each pre-deposition treatment alters the microstructure of the quartz tube surface. By controlling the number of pre-deposition treatments to 1-5 times, an ideal surface with a certain degree of micro-roughness or nanostructure is formed within the quartz tube, which is beneficial for the "anchoring" of the subsequent silica deposition layer and the wetting of the rare earth solution. Moreover, the number of depositions affects the density and distribution of hydroxyl groups on the surface of the silica pre-deposition layer. The surface of the silica pre-deposition layer after 1-5 pre-deposition treatments provides more uniform and highly active adsorption sites.

[0060] For example, the pre-deposition treatment can be performed once, twice, three times, four times, or five times.

[0061] In some specific implementations, the processing temperature of each pre-deposition treatment is 10°C-30°C lower than the processing temperature of the previous pre-deposition treatment.

[0062] It is understood that in this embodiment, the initial pre-deposition treatment has the highest processing temperature. At this time, the quartz substrate is a dense and robust quartz glass, and the higher pre-deposition treatment temperature facilitates the full decomposition and deposition of the first oxygen and first helium gases, forming a first layer firmly bonded to the quartz substrate. When subsequent pre-deposition treatments are performed, a silica pre-deposition layer already exists beneath it. By lowering the processing temperature during subsequent pre-deposition treatments, the existing silica deposition layer is protected, ensuring the overall porosity of the final silica pre-deposition layer, which is beneficial for the penetration of rare earth solutions, increasing the total amount of rare earth ion adsorption, and homogenizing its axial and radial distribution within the quartz substrate. Moreover, the higher processing temperature of the initial pre-deposition treatment results in a relatively dense pre-deposition layer with a microstructure close to that of quartz glass and a thermal expansion coefficient close to that of the quartz substrate. As the pre-deposition treatment temperature gradually decreases, the pre-deposition layer gradually becomes looser and more porous, and its thermal expansion coefficient gradually increases, approaching that of the subsequently deposited silica deposition layer (loose layer). In this way, the change in the coefficient of thermal expansion of the obtained active photovoltaic preform in the radial direction is continuous and gradual. This causes the thermal stress to be redistributed throughout the entire transition zone thickness from the quartz base tube to the silicon oxide deposited layer (loose layer). The original sharp stress peak becomes a stress curve with a wider distribution and lower peak value. This enables the silicon oxide pre-deposited layer to act as a thermal expansion gradient transition layer to alleviate thermal stress and prevent the silicon oxide deposited layer from falling off.

[0063] For example, the processing temperature of each pre-deposition treatment can be 10°C, 12°C, 14°C, 16°C, 18°C, 20°C, 22°C, 24°C, 26°C, 28°C, 30°C or any combination thereof lower than the processing temperature of the previous pre-deposition treatment.

[0064] In some specific implementations, the deposition temperature is 5°C-20°C lower than the temperature of the final pre-deposition treatment.

[0065] It is understandable that the purpose of pre-deposition treatment is to establish a strong and highly active transition layer on the quartz substrate. Therefore, a relatively high starting temperature can be used during pre-deposition treatment to ensure that the silica pre-deposited layer forms a strong chemical bond with the quartz substrate. The purpose of deposition treatment is to rapidly deposit a thick, highly porosity-rich, and large specific surface area loose body as a matrix for adsorbing rare earth ions. Therefore, by controlling the deposition treatment temperature to be 5℃-20℃ lower than the pre-deposition treatment temperature, it is possible to ensure that the pre-deposited layer is not damaged by high temperature, maintain the bonding strength between the deposited layer and the quartz substrate, and keep the newly deposited particles in a loose state, obtaining an extremely high specific surface area and hydroxyl density, ultimately forming an overall loose structure with excellent adsorption potential from the inside out.

[0066] For example, the deposition temperature can be 5°C, 10°C, 12°C, 14°C, 16°C, 18°C, 20°C or any combination thereof lower than the temperature of the last pre-deposition treatment.

[0067] In some specific embodiments, the rare earth ion solution contains at least one element selected from Nd, Yb, Er, Tm, Ho, Sm, Pm, Y, La, Lu, Ce, and Bi.

[0068] As rare earth elements, ions such as Nd, Yb, Er, Tm, Ho, Sm, and Pm possess unique electronic energy level structures, enabling the emission and amplification of light at specific wavelengths. They provide optical gain through a "pump-absorption-stimulated emission" process. Ions such as Y, La, Lu, and Ce typically do not directly generate lasers, but they can improve the glass network structure of silicon oxide deposits, enhance doping uniformity and concentration, control ion valence states, and improve the radiation resistance and anti-darkening properties of optical fibers. Low-valence bismuth ions of Bi (such as Bi...) + Ultrawide fluorescence emission (from visible light to over 1700 nm) can be generated in certain glass matrices, enabling the fabrication of ultrawide fiber amplifiers and tunable lasers.

[0069] In some specific embodiments, the rare earth ion solution also includes at least one element selected from Al, P, and Ge.

[0070] As a co-doper, Al 3+ Entering the network in the form of [AlO4] tetrahedra, its connection with [SiO4] is relatively flexible, which can significantly disrupt and loosen the quartz network, creating more and more suitable "homes" for larger rare earth ions, effectively suppressing ion aggregation and concentration quenching, and facilitating high-concentration, high-efficiency doping. Furthermore, aluminosilicate glass has good high-temperature stability, which is beneficial for the sintering and drawing of active optical fiber preforms. 5+It exists in the form of a [PO4] tetrahedron, but with double oxygen bonds, exhibiting a strong chain-severing and modification effect on the network, and can greatly isolate rare earth ions, preventing concentration quenching. Meanwhile, P... 5+ It can also replace Si 4+ The generation of a positive charge surplus helps to balance trivalent rare earth ions (REs). 3+ ) replaces tetravalent silicon (Si) 4+ The negative charge defects generated during the process make rare earth ions more stable in the crystal lattice. Furthermore, P... 5+ The presence of these molecules can significantly broaden the absorption and emission spectra of rare earth ions (for Er). 3+ (Especially evident) This is beneficial for manufacturing broadband amplifiers and mode-locked lasers. GeO2 can increase the refractive index of silicon dioxide. In active optical fibers, it is also responsible for forming optical waveguides. At the same time, it coexists with rare earth elements, helping to improve the rare earth environment and forming unique light-emitting centers.

[0071] In some specific embodiments, the rare earth ion solution includes at least one solvent selected from methanol, ethanol, and ethylene glycol.

[0072] In some specific embodiments, the third base tube needs to be dried before it undergoes melting and shrinking treatment. Specifically, the drying treatment includes: introducing third oxygen, third helium and chlorine into the third base tube and drying it at 400℃-500℃ for 4h-6h.

[0073] For example, the drying temperature can be a range of 400°C, 420°C, 440°C, 460°C, 480°C, 500°C or any combination thereof; the drying time can be a range of 4h, 5h, 6h or any combination thereof.

[0074] In some embodiments, the flow rate of the third oxygen gas is 200 sccm-500 sccm; the flow rate of the third helium gas is 500 sccm-1000 sccm; and the flow rate of the chlorine gas is 200 sccm-400 sccm.

[0075] For example, the flow rate of the third oxygen gas can be a range of 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, 450 sccm, 500 sccm, or any combination thereof; the flow rate of the third helium gas can be a range of 500 sccm, 600 sccm, 700 sccm, 800 sccm, 900 sccm, 1000 sccm, or any combination thereof; and the flow rate of the chlorine gas can be a range of 200 sccm, 250 sccm, 300 sccm, 350 sccm, 400 sccm, or any combination thereof.

[0076] In some specific implementations, the inner wall of the quartz base tube is etched and polished before pre-deposition treatment.

[0077] Before pre-depositing the quartz tube, surface defects and microcracks on the inner wall of the quartz tube can be removed by etching and polishing to obtain controllable surface roughness, which greatly increases the surface area of ​​the deposition and provides more "anchor points" for the subsequent pre-deposited layer.

[0078] The active optical fiber preform fabrication method provided in this application constructs a loose layer system with a gradient porosity by introducing a silica pre-deposition step before the silica deposition layer. The silica pre-deposition layer (dense silica layer) and the silica deposition layer (porous silica layer) form a physical and chemical gradient interface. The silica pre-deposition layer enhances the adhesion strength of the silica deposition layer through surface activity regulation, while providing directional channels for rare earth ion diffusion. Furthermore, the dense structure of the silica pre-deposition layer forms a strong bond with the quartz substrate wall through thermal stress matching and chemical bonding (such as Si-O-Si bonds), while its surface microporous structure provides anchoring points for the subsequent loose layer, reducing the risk of loose layer detachment. The difference in interlayer thermal expansion is controlled by decreasing the pre-deposition treatment temperature, and the porosity distribution is regulated by the deposition treatment temperature gradient, forming a composite loose layer with both high specific surface area and structural stability. Ultimately, this achieves the effect of improving the rare earth ion adsorption capacity while enhancing the bonding force between the loose layer and the substrate wall.

[0079] This application also provides an active optical fiber preform prepared by the above-described method. The rare earth ion doping concentration in this active optical fiber preform can reach over 5000 ppm, and the bonding strength between the silicon oxide layer and the quartz substrate can reach over ... MPa.

[0080] This application also provides an optical fiber, which is obtained by drawing and coating an active optical fiber preform prepared by the above preparation method or by drawing and coating the above active optical fiber preform.

[0081] The optical fiber provided in this embodiment can perform the method provided in the above method embodiment. Its implementation principle and technical effect are similar, and will not be described in detail here.

[0082] The technical solution of this application will be further described below using specific embodiments.

[0083] Example 1

[0084] An active optical fiber preform is prepared by the following method:

[0085] 1) Etching and polishing: The quartz base tube is mounted on an MCVD lathe, and SF6 is introduced into the tube for preheating and polishing at a temperature of 1600℃;

[0086] 2) Silica pre-deposition: Silicon tetrachloride, oxygen, and helium were added to a quartz substrate via carrier gas at flow rates of 3 g / min, 2000 sccm, and 2000 sccm, respectively. The initial pre-deposition temperature was 1350℃, and the silica pre-deposition was performed 5 times. The temperature of each pre-deposition layer decreased by 15℃ compared to the previous pre-deposition temperature, with the final pre-deposition temperature at 1290℃, resulting in the first substrate.

[0087] 3) Silica deposition: Second silicon tetrachloride, second oxygen, and second helium are added to the first base tube via carrier gas at flow rates of 3 g / min, 1000 sccm, and 1000 sccm, respectively, and the heating temperature is 1270℃; thus, a second base tube is obtained.

[0088] 4) Solution immersion: After cutting off the tail tube of the second base tube, immerse it in a rare earth ion solution containing ytterbium chloride (YbCl3) and aluminum chloride (AlCl3) (ytterbium chloride concentration of 1.0 mol.% and aluminum chloride concentration of 5.1 mol.%), with methanol as the solvent; to obtain the third base tube;

[0089] 5) Drying treatment: Reconnect the third base tube to the MCVD lathe and introduce the third oxygen, third helium and chlorine gas at flow rates of 250 sccm, 500 sccm and 300 sccm respectively. The drying time is 4 hours and the drying temperature is 400℃.

[0090] 6) Sintering and shrinking: The third base tube doped with rare earth ions is sintered and shrunk to finally obtain a solid active optical fiber preform.

[0091] Example 2

[0092] An active optical fiber preform is prepared by the following method:

[0093] 1) Etching and polishing: The quartz base tube is mounted on an MCVD lathe, and SF6 is introduced into the tube for preheating and polishing at a temperature of 1600℃;

[0094] 2) Silica pre-deposition: First silicon tetrachloride, first oxygen and first helium are added to the quartz base tube via carrier gas at flow rates of 4 g / min, 1000 sccm and 1000 sccm respectively. The initial pre-deposition temperature is 1300℃, and the silica pre-deposition is performed 4 times. The processing temperature of each pre-deposition is 20℃ lower than the previous pre-deposition temperature, and the final pre-deposition temperature is 1240℃, resulting in the first base tube.

[0095] 3) Silica deposition: Second silicon tetrachloride, second oxygen, and second helium are added to the first base tube via carrier gas at flow rates of 4 g / min, 1000 sccm, and 1500 sccm, respectively, and the heating temperature is 1230℃; thus, a second base tube is obtained.

[0096] 4) Solution immersion: After cutting off the tail tube of the second base tube, immerse it in a rare earth ion solution containing erbium chloride (ErCl3) and aluminum chloride (AlCl3) (erbium chloride concentration of 0.1 mol.% and aluminum chloride concentration of 6.5 mol.%), with ethanol as the solvent; to obtain the third base tube;

[0097] 5) Drying treatment: Reconnect the third base tube to the MCVD lathe and introduce the third oxygen, third helium and chlorine gas at flow rates of 500 sccm, 1000 sccm and 200 sccm respectively. The drying time is 6 hours and the drying temperature is 500℃.

[0098] 6) Sintering and shrinking: The third base tube doped with rare earth ions is sintered and shrunk to finally obtain a solid optical fiber preform.

[0099] Example 3

[0100] An active optical fiber preform is prepared by the following method:

[0101] 1) Etching and polishing: The quartz base tube is mounted on an MCVD lathe, and SF6 is introduced into the tube for preheating and polishing at a temperature of 1600℃;

[0102] 2) Pre-deposition of silicon dioxide: First silicon tetrachloride, first oxygen and first helium are added to the quartz base tube by means of carrier gas, with flow rates of 2 g / min, 2000 sccm and 1000 sccm respectively. The pre-deposition treatment temperature is 1200℃ and the silicon dioxide pre-deposition is performed once; the first base tube is obtained.

[0103] 3) Silica deposition: Second silicon tetrachloride, second oxygen, and second helium are added to the first base tube via carrier gas at flow rates of 3 g / min, 1500 sccm, and 500 sccm, respectively, and the heating temperature is 1180℃; thus, a second base tube is obtained.

[0104] 4) Solution immersion: After cutting off the tail tube of the second base tube, immerse the second base tube in a rare earth ion solution containing thulium chloride (TmCl3) and aluminum chloride (AlCl3) (thulium chloride concentration of 0.7 mol.% and aluminum chloride concentration of 2.2 mol.%), with ethanol as the solvent; to obtain the third base tube;

[0105] 5) Drying treatment: Reconnect the third base tube to the MCVD lathe and introduce the third oxygen, third helium and chlorine gas at flow rates of 200 sccm, 500 sccm and 400 sccm respectively. The drying time is 5 hours and the drying temperature is 450℃.

[0106] 6) Sintering and shrinking: The third base tube doped with rare earth ions is sintered and shrunk to finally obtain a solid optical fiber preform.

[0107] Example 4

[0108] An active optical fiber preform is prepared in a manner that is basically the same as that in Example 1, except that in step 2), the processing temperature of the first pre-deposition treatment is 1600℃ and the processing temperature of the last pre-deposition treatment is 1540℃; at the same time, the processing temperature of the deposition treatment in step 3) is set to 1520℃.

[0109] Example 5

[0110] An active optical fiber preform is prepared using a method basically the same as in Example 1, except that in step 2), the processing temperature of each pre-deposition treatment decreases by 10°C compared to the previous pre-deposition treatment temperature, and the processing temperature of the last pre-deposition treatment is 1310°C. Simultaneously, in step 3), the deposition treatment temperature is set to 1290°C.

[0111] Example 6

[0112] An active optical fiber preform is prepared in a manner that is basically the same as that in Example 1, except that in step 2), the number of pre-deposition treatments is 3, and the temperature of the last pre-deposition treatment is 1320℃; at the same time, the temperature of the deposition treatment in step 3) is set to 1300℃.

[0113] Example 7

[0114] An active optical fiber preform is prepared in a manner that is basically the same as that in Example 1, except that in step 3), the deposition treatment temperature is 1290°C, and the temperature of the final pre-deposition treatment is the same as that of the deposition treatment.

[0115] Comparative Example 1

[0116] An optical fiber preform is prepared using a method that is basically the same as that in Example 1, except that step 2 is not performed.

[0117] Comparative Example 2

[0118] An optical fiber preform is prepared using a method that is basically the same as that in Example 2, except that step 2 is not performed.

[0119] Comparative Example 3

[0120] An optical fiber preform is prepared using a method that is basically the same as in Example 3, except that step 2 is not performed.

[0121] The porosity of the silicon oxide pre-deposited layer and the silicon oxide deposited layer obtained by pre-deposition treatment in the above embodiments and comparative examples was measured, and the results are detailed in Table 1:

[0122] Table 1

[0123]

[0124] Performance testing

[0125] Rare earth ion concentration: The concentration of rare earth ions contained in the optical fiber preforms prepared by the active optical fiber preforms prepared in Examples 1-7 above was measured by EPMA testing.

[0126] The test results are detailed in Table 2.

[0127] Table 2

[0128]

[0129] As can be seen from the data in Table 2, the active optical fiber preform prepared by the preparation method provided in this application can obtain a rare earth ion doping concentration of not less than 1000 ppm, and the silicon oxide deposition layer on the base tube does not fall off when it is impregnated with rare earth ions.

[0130] In Example 1, the active optical fiber preform obtained achieved a Raman intensity of 48 dB under a full output power of 3000 W. Compared to Examples 1-3, the active optical fiber preforms obtained without pre-deposition treatment in Comparative Examples 1-3 experienced deposit layer detachment during rare earth ion impregnation, resulting in failure to form the preform. Therefore, the active optical fiber preform and its preparation method provided in this application can simultaneously improve the doping concentration of rare earth ions in the optical fiber preform and the bonding strength between the silicon oxide deposit layer and the substrate, preventing detachment during deposition and successfully obtaining an optical fiber preform with a high rare earth ion doping concentration.

[0131] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and various modifications and changes may be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for preparing an active optical fiber preform, characterized in that, include: A first silicon tetrachloride, a first oxygen gas, and a first helium gas are introduced into a quartz base tube for pre-deposition treatment, forming a silicon oxide pre-deposition layer inside the quartz base tube to obtain a first base tube; A second silicon tetrachloride, a second oxygen gas, and a second helium gas are introduced into the first base tube for deposition treatment, forming a silicon oxide deposition layer inside the first base tube to obtain a second base tube. The second base tube was immersed in a rare earth ion solution to obtain the third base tube; The third base tube is fused and shrunk to obtain the active optical fiber preform. The porosity of the pre-deposited silicon oxide layer is less than that of the deposited silicon oxide layer.

2. The preparation method according to claim 1, characterized in that, The porosity of the silicon oxide pre-deposited layer is 35%~45%; And / or, the porosity of the silicon oxide deposited layer is 45% to 55%.

3. The preparation method according to claim 1 or 2, characterized in that, The pre-deposition treatment temperature is 1200℃-1600℃; And / or, the flow rate of the first silicon tetrachloride is 2 g / min-5 g / min; And / or, the flow rate of the first oxygen is 1000 sccm-2000 sccm; And / or, the flow rate of the first helium gas is 500 sccm-2000 sccm; And / or, the deposition treatment temperature is 1150℃-1500℃; And / or, the flow rate of the second silicon tetrachloride is 2 g / min - 5 g / min; And / or, the flow rate of the second oxygen is 1000 sccm-2000 sccm; And / or, the flow rate of the second helium gas is 500 sccm-2000 sccm.

4. The preparation method according to claim 3, characterized in that, The number of pre-deposition treatments ranges from 1 to 5.

5. The preparation method according to claim 4, characterized in that, The processing temperature of each pre-deposition treatment is 10°C-30°C lower than the processing temperature of the previous pre-deposition treatment.

6. The preparation method according to any one of claims 1-5, characterized in that, The processing temperature of the deposition treatment is 5°C-20°C lower than the processing temperature of the last pre-deposition treatment.

7. The preparation method according to any one of claims 1-6, characterized in that, The rare earth ion solution contains at least one element selected from Nd, Yb, Er, Tm, Ho, Sm, Pm, Y, La, Lu, Ce, and Bi. And / or, the rare earth ion solution further includes at least one element selected from Al, P, and Ge; And / or, the rare earth ion solution includes at least one solvent selected from methanol, ethanol, and ethylene glycol.

8. The preparation method according to any one of claims 1-7, characterized in that, Also includes: Before performing the pre-deposition treatment on the quartz base tube, the inner wall of the quartz base tube is subjected to corrosion and polishing treatment.

9. An active optical fiber preform, characterized in that, Prepared by the preparation method according to any one of claims 1-8.

10. An optical fiber, characterized in that, The active optical fiber preform prepared by any one of the preparation methods of claims 1-8 or the active optical fiber preform of claim 9 is obtained by drawing and coating.

Images