Channel type gain optical fiber and preparation method thereof

Abstract

The invention discloses a channel type gain optical fiber and a preparation method thereof. The optical fiber comprises a rare earth doped fiber core layer (1), a quartz layer (2), a non-rare earth doped fiber core layer (3), an inner cladding (4), an outer cladding (5) and a coating layer (6) which are sequentially arranged from inside to outside. The rare earth doped fiber core layer (1) is prepared by combining an MCVD (modified chemical vapor deposition) process with a liquid phase doping process; the quartz layer (2) and the non-rare earth doped fiber core layer (3) are prepared through a PCVD process; the refractive index of the non-rare earth doped fiber core layer (3) is the same as that of the rare earth doped fiber core layer (1); the refractive index of the quartz layer (2) is the same as that of the inner cladding (4); the MCVD technology is combined with the liquid phase doping technology and the PCVD technology, the channel type gain optical fiber is prepared through a sleeve method, the size and the structure of the optical fiber are effectively controlled, the attenuation coefficient of the optical fiber is reduced, and high-quality light beam output and high-efficiency laser conversion are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber communication, and more specifically, relates to a channel-type gain optical fiber and a preparation method thereof. Background Art

[0002] Fiber lasers are widely used in industrial processing and military fields due to their small size, good beam quality, excellent heat dissipation and high conversion efficiency. With the development of high-performance double-clad optical fibers and optical fiber devices, the output power of high-power ytterbium-doped fiber lasers has increased rapidly. However, the generation of nonlinear effects such as stimulated Brillouin and stimulated Raman effects has greatly limited the further increase of fiber laser output power. Although the use of large mode area optical fiber can effectively increase the threshold of nonlinear effects, increasing the core diameter will support more high-order modes, which will lead to the deterioration of the beam quality of the fiber laser and the mode instability effect, making it difficult to achieve high beam quality and high power output in fiber lasers. Summary of the invention

[0003] In view of the above defects or improvement needs of the prior art, the present invention provides a channel-type gain optical fiber and a preparation method thereof. The optical fiber core rod is prepared by MCVD process, and the channel formation is precisely controlled by PCVD. By combining the two, a gain optical fiber capable of achieving precise control of the channel refractive index is prepared, which can achieve high beam quality and high power output in a fiber laser.

[0004] In order to achieve the above object, one aspect of the present invention provides a channel-type gain optical fiber, comprising a rare earth-doped core layer, a silica layer, a non-rare earth-doped core layer, an inner cladding layer, an outer cladding layer and a coating layer arranged in sequence from the inside to the outside; wherein:

[0005] The rare earth doped core layer is prepared by MCVD process combined with liquid phase doping process;

[0006] The quartz layer and the non-rare earth doped core layer are prepared by PCVD process;

[0007] The refractive index of the non-rare earth doped core layer is the same as that of the rare earth doped core layer, and the thickness of both layers is 1-2 mm;

[0008] The refractive index of the quartz layer is the same as that of the inner cladding, and the thickness of both is 0.5-1 mm;

[0009] The MCVD process is combined with the liquid phase doping process and the PCVD process to prepare the channel-type gain fiber through the sleeve method, which effectively controls the size and structure of the fiber, reduces the attenuation coefficient of the fiber, and achieves high-quality beam output and high-efficiency laser conversion.

[0010] A second aspect of the present invention provides a method for preparing a channel-type gain optical fiber, comprising the following steps:

[0011] S1: taking a quartz liner tube, and depositing a non-rare earth doped core layer inside the quartz liner tube by a PCVD process to obtain a quartz liner tube including a non-rare earth doped core layer;

[0012] S2: by a PCVD process, a quartz layer is further deposited on the inner surface of the quartz liner tube comprising a non-rare earth doped core layer to obtain a quartz liner tube comprising a non-rare earth doped core layer and a quartz layer;

[0013] S3: repeating steps S1 and S2 according to design requirements, so that the non-rare earth doped core layer and the quartz layer are alternately deposited to form a required number of channels, and obtaining a multi-channel sleeve including the non-rare earth doped core layer and the quartz layer;

[0014] S4: taking another quartz liner tube, depositing a rare earth doped core layer inside the other quartz liner tube by MCVD process combined with liquid phase doping process, and melting and shrinking into a solid preform rod including the rare earth doped core layer;

[0015] S5: using hydrofluoric acid to clean the surface of the solid preform rod containing the rare earth-doped core layer to obtain a core rod with the outer pure silica layer etched away; grinding and polishing the core rod with the outer pure silica layer etched away to obtain a grinded and polished core rod;

[0016] S6: Combine the polished core rod obtained in step S5 with the multi-channel sleeve including the non-rare earth doped core layer and the quartz layer obtained in step S3, and draw a channel-type gain optical fiber of a required size on a drawing tower; and perform double-layer coating and UV curing.

[0017] Furthermore, the thickness of the non-rare earth doped core layer in step S1 is 1-2 mm;

[0018] The core layer thickness of the solid preform rod containing the rare earth doped core layer in step S4 is 1-2 mm, and the core numerical aperture is 0.01-0.1.

[0019] Furthermore, the non-rare earth doped core layer is obtained by depositing germanium dioxide.

[0020] Furthermore, the quartz layer in step S2 is obtained by depositing silicon dioxide.

[0021] Furthermore, in step S3, the number of channels formed by the non-rare earth doped core layer and the quartz layer is 1-100 layers.

[0022] Furthermore, the thickness of the non-rare earth doped core layer in each channel is the same as that of the quartz layer.

[0023] Furthermore, the thickness of each of the channels is different from the thickness of other channels.

[0024] Furthermore, the refractive index of the non-rare earth doped core layer and the silica layer in each of the channels is the same as the refractive index of the non-rare earth doped core layer and the silica layer in other channels.

[0025] Furthermore, the refractive index of the non-rare earth doped core layer and the silica layer in each of the channels is different from the refractive index of the non-rare earth doped core layer and the silica layer in other channels.

[0026] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0027] The present invention discloses a channel-type gain optical fiber and a preparation method thereof. A rare earth-doped core is prepared by an MCVD process, and a non-rare earth-doped core and a quartz layer are prepared by a PCVD process. The MCVD process is combined with a liquid phase doping process to prepare the characteristics of high rare earth doping concentration and uniform rare earth ion distribution, and the PCVD process has the advantages of high-precision refractive index distribution control and high deposition efficiency. The channel-type gain optical fiber is prepared by a casing method, and the size and structure of the optical fiber are effectively controlled to reduce the attenuation coefficient of the optical fiber. This optical fiber can be used in the field of high-power optical fiber lasers, optimize the beam quality of the optical fiber laser, improve the nonlinear effect threshold of the optical fiber laser, and realize high-power laser output. The optical fiber laser can achieve a very high light-to-light conversion efficiency by selecting a semiconductor laser with a matching emission wavelength and absorption characteristics of doped rare earth elements as a pump source. The preparation method of the channel-type gain optical fiber of the present invention combines the advantages of the MCVD and PCVD processes, and prepares high-performance optical fibers by a casing method. These optical fibers have important applications in the field of high-power optical fiber lasers and can provide high-quality beam output and high-efficiency laser conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic structural diagram of a channel-type gain optical fiber according to an embodiment of the present invention;

[0029] Figure 2 A schematic diagram of a process for preparing a channel-type gain optical fiber according to an embodiment of the present invention;

[0030] Figure 3 The figure is a schematic diagram of the refractive index distribution of a channel-type gain optical fiber according to an embodiment of the present invention.

[0031] In all the drawings, the same reference numerals represent the same technical features, specifically: 1-rare earth doped core layer, 2-quartz layer, 3-non-rare earth doped core layer, 4-inner cladding, 5-outer cladding, 6-coating layer. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, when an element is referred to as being "fixed to", "disposed on" or "provided on" another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or indirectly connected to the other element; the terms "installed", "connected", "connected" and "provided with" should be understood in a broad sense, for example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the internal connection of the two elements or the interaction relationship between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0034] like Figure 1 and Figure 3 As shown, one aspect of the present invention provides a channel-type gain optical fiber, comprising a rare earth-doped core layer 1, a quartz layer 2, a non-rare earth-doped core layer 3, an inner cladding 4, an outer cladding 5 and a coating layer 6 arranged in sequence from the inside to the outside; the rare earth-doped core layer 1 is prepared by an MCVD process; the quartz layer 2 and the non-rare earth-doped core layer 3 are prepared by a PCVD process; the refractive index of the non-rare earth-doped core layer 3 is the same as that of the rare earth-doped core layer 1, and the thickness of both is 1-2 mm; the refractive index of the quartz layer 2 is the same as that of the inner cladding 4, and the thickness of both is 0.5-1 mm; the present invention utilizes the advantages of the MCVD process combined with the liquid phase doping process and the PCVD process to prepare a channel-type gain optical fiber by a sleeve method, which can effectively control the size and structure of the optical fiber and reduce the attenuation coefficient of the optical fiber; and can provide high-quality beam output and high-efficiency laser conversion.

[0035] Furthermore, the rare earth doped core layer 1 is the innermost layer of the optical fiber and is prepared by an improved chemical vapor deposition (MCVD) process; this core layer is doped with rare earth elements, which can amplify optical signals, so this layer is a key part of the optical fiber amplifying and transmitting optical signals; the quartz layer 2 is located outside the rare earth doped core layer 1 and is prepared by a plasma chemical vapor deposition (PCVD) process; the refractive index of the quartz layer 2 is the same as that of the inner cladding 4, which serves to isolate the rare earth doped core layer 1 and the non-rare earth doped core layer 3, and also helps to maintain the strength and structural integrity of the optical fiber; the non-rare earth doped core layer 3 is located outside the quartz layer 2 and is also prepared by a PCVD process; the refractive index of the non-rare earth doped core layer 3 is the same as that of the rare earth doped core layer 1, and the thickness is The inner cladding 4 is located outside the non-rare earth doped core layer 3, and its refractive index is the same as that of the quartz layer 2, and its thickness is between 0.5-1mm; the inner cladding is used to provide internal support for the optical fiber and protect the core layer from the external environment; the outer cladding 5 is located outside the inner cladding 4, and the outer cladding adopts a modified low-refractive index coating to improve the heat tolerance of the gain optical fiber when it is used in a high-power fiber laser; the main function of the outer cladding is to protect the optical fiber from external physical damage and environmental influences; the coating layer 6 is the outermost layer of the optical fiber, usually composed of a polymer material, and uses a high-refractive index coating to protect the optical fiber from mechanical damage and chemical corrosion. The channel-type gain optical fiber of the present invention can transmit or process optical signals between different core layers while maintaining the isolation and integrity of the signal. By precisely controlling the refractive index and thickness of each layer, high-quality beam output and high-efficiency laser conversion can be achieved, which has important value in the field of high-power fiber lasers.

[0036] Furthermore, PCVD (high temperature plasma vapor deposition) is a cladding deposition process with high raw material utilization and good refractive index control.

[0037] Furthermore, MCVD (Modified Chemical Vapor Deposition) is a process technology used to manufacture optical fiber preforms. The following are the main steps and characteristics of the MCVD process:

[0038] Process principle: MCVD is based on the principle of chemical vapor deposition. It deposits a loose layer of silica on the pre-prepared optical fiber shell to finally produce an optical fiber with good optical properties.

[0039] Main steps:

[0040] Pre-preparation of optical fiber housing: First, a hollow tube needs to be prepared with a suitable material to form a pre-prepared optical fiber housing;

[0041] Atmosphere control and impurity deposition: Place the fiber housing at a suitable temperature and deposit the loose layer by precisely controlling the flow of dopants;

[0042] Synthesis of the central core: pour the prepared rare earth doping solution into the loose layer, and sinter it at high temperature after adsorption to obtain the designed refractive index distribution, thereby synthesizing the central core;

[0043] Process characteristics:

[0044] Materials diversity: MCVD can be used to deposit a wide range of materials, including different types of rare-earth doped materials, making it suitable for a wide range of applications from telecommunications to microelectronics;

[0045] Scalability: One of the main advantages of MCVD is its scalability. The process can be used to produce fibers on a large scale, making it ideal for industrial applications.

[0046] Control and repeatability: MCVD provides excellent control over the deposition process, resulting in reproducible results, which is critical for both R&D and industrial applications;

[0047] Environmental and safety considerations: While MCVD does involve the use of potentially hazardous precursors, the process is designed to minimize risk;

[0048] The MCVD process is widely used in the field of optical fiber manufacturing, especially in the production of high-quality single-mode and multi-mode optical fibers. Through this process, optical fiber structures with complex refractive index structures can be manufactured, and it has great flexibility in terms of optical fiber material selection and optical fiber size design.

[0049] like Figure 2 As shown, the second aspect of the present invention provides a method for preparing a channel-type gain optical fiber, comprising the following steps:

[0050] S1: Take a quartz liner tube, and deposit a non-rare earth doped core layer 3 inside the quartz liner tube by PCVD process to obtain a quartz liner tube including a non-rare earth doped core layer;

[0051] S2: by means of a PCVD process, a quartz layer 2 is further deposited on the inner surface of the quartz liner tube comprising a non-rare earth doped core layer to obtain a quartz liner tube comprising a non-rare earth doped core layer and a quartz layer;

[0052] S3: repeating steps S1 and S2 according to design requirements, so that the non-rare earth doped core layer 3 and the quartz layer 2 are alternately deposited to form a required number of channels, and obtaining a multi-channel sleeve including a non-rare earth doped core layer and a quartz layer;

[0053] S4: taking another quartz liner tube, depositing a rare earth doped core layer 1 inside the other quartz liner tube by using an MCVD process combined with a liquid phase doping process, and melting and shrinking the quartz liner tube into a solid preform rod including the rare earth doped core layer;

[0054] S5: using hydrofluoric acid with a concentration of 10% to 25% to clean the surface of the solid preform rod containing the rare earth doped core layer, to obtain a core rod with the outer pure silica layer etched away; grinding and polishing the core rod with the outer pure silica layer etched away, to obtain a grinded and polished core rod;

[0055] S6: Combine the polished core rod obtained in step S5 with the multi-channel sleeve including the non-rare earth doped core layer and the quartz layer obtained in step S3, and draw a channel-type gain optical fiber of a required size on a drawing tower; and perform double-layer coating and UV curing.

[0056] Furthermore, the thickness of the non-rare earth doped core layer 3 in step S1 is 1-2 mm; the non-rare earth doped core layer 3 is obtained by depositing germanium dioxide (GeO2); specifically comprising the following steps:

[0057] Preparation of the liner and deposition environment: construct a deposition chamber, take a quartz liner, and clamp the quartz liner on the PCVD deposition machine in the deposition chamber; the quartz liner passes through the microwave resonant cavity and is placed in a heat preservation furnace, with both ends clamped by a rotating chuck; gradually increase the temperature of the heat preservation furnace to 800-1200° C., start the translation and rotation mechanism of the deposition machine, and start the microwave plasma power output, so that the microwave resonant cavity generates high-frequency power to reciprocate along the axial direction of the quartz liner for PCVD deposition;

[0058] Gas introduction and deposition: using fluorine-containing gas to etch and clean the inner substrate of the quartz liner; specifically, using 150 sccm to 300 sccm C2F6 gas to etch and clean the substrate of the quartz liner; then, introducing an appropriate amount of reaction gas;

[0059] Plasma generation: The reactive gas is energized by plasma generated by radio frequency, direct current or microwave energy in a microwave resonant cavity; the plasma includes ions, free electrons, free radicals, excited atoms and molecules;

[0060] Chemical reaction: The plasma provides the necessary energy to dissociate the reactive gas, initiating a chemical reaction that results in the formation of a thin film on the inner substrate of the quartz liner;

[0061] Thin film deposition: the inner substrate of the quartz liner is exposed to the plasma-activated gas, and the interaction between the plasma and the gas deposits a thin film on the inner substrate of the quartz liner;

[0062] Controlling deposition parameters: Precisely controlling the flow of reactive gases, the temperature of the deposition chamber, and the energy of the plasma to ensure the quality and uniformity of the film;

[0063] Channel layer deposition: Depositing germanium dioxide (GeO2) to form a non-rare earth doped core layer 3, and forming a multilayer structure through multiple cycles of deposition;

[0064] Post-processing: After the deposition is completed, the liner tube with the germanium dioxide deposited is cleaned, etched or polished to remove the outer pure silicon dioxide layer, and then ground and polished;

[0065] Quality inspection: Perform quality inspection on the deposited non-rare earth doped core layer 3 to ensure that its purity and performance meet the requirements;

[0066] Furthermore, after the reaction gas undergoes chemical reaction and plasma reaction, a solid film is formed on the surface of the quartz liner. In the PCVD process, gaseous halides such as SiCl4 (silicon tetrachloride) and GeCl4 (germanium tetrachloride) are commonly used reaction gases. These gases undergo redox reactions with oxygen under high temperature conditions to generate SiO2 (silicon dioxide) and GeO2 (germanium dioxide), which are used to form the main component and dopant of the optical fiber core layer, respectively. Oxygen is used as an oxidant, and oxygen reacts with gaseous halides to generate oxides, which are used to form the optical fiber core layer. Indispensable reaction gases; in the PCVD process, SF6 (sulfur hexafluoride) can be used to remove OH- (hydroxyl) to reduce the water peak loss in the optical fiber; HF (hydrofluoric acid) etches the surface OH- contamination layer to eliminate the OH- contamination layer; these reaction gases are directly converted into glass through chemical reactions in the PCVD process, deposited on the inner wall of the quartz liner, and form the core layer of the optical fiber; by precisely controlling the flow and proportion of these reaction gases, the deposition process can be precisely controlled to produce an optical fiber core layer with a specific refractive index distribution and performance;

[0067] Furthermore, in the PCVD (plasma chemical vapor deposition) process, controlling the flow rate of the reaction gas is a key step to achieve accurate deposition and film quality control; the following are several methods for controlling the flow rate of the reaction gas:

[0068] Use gas flow meter: Use a large-range gas flow meter to directly control the gas flow. For gaseous reaction gases, the gas flow meter can be used directly to control the flow;

[0069] Regulating device: The gas source needs to use a gas purifier to remove moisture and other impurities, and then the required flow rate is obtained through the regulating device, and then it is sent into the deposition chamber together with the source material;

[0070] Flow coefficient adjustment: determine the flow coefficient of the process gas relative to the reference gas, and calculate the corrected flow value of the process gas based on the flow setting value of the process gas and the flow coefficient;

[0071] Over-range alarm: If the corrected flow value of the process gas is greater than the maximum range of the gas flow meter, an over-range alarm will be triggered, and the maximum range of the gas flow meter will be used as the flow control value of the process gas to execute the process program;

[0072] Precise control technology solution: For liquid raw materials, such as SiCl4 or GeCl4, pure steam or premixed steam can be used for feeding to achieve precise control of large flow rates of gas or steam;

[0073] Monitor and adjust:

[0074] During the PCVD process, process parameters such as temperature, pressure, and gas flow rate must be carefully monitored and adjusted as necessary to achieve the desired film properties;

[0075] Relationship between deposition efficiency and flow rate: As the high-frequency output power increases, the deposition efficiency gradually approaches 100%; the actual deposition efficiency is controlled according to the actual deposition rate. As the deposition rate increases, the deposition efficiency corresponding to the appropriate high-frequency power decreases, but remains above 90%;

[0076] Through the above method, the reaction gas flow rate in the PCVD process can be accurately controlled.

[0077] Furthermore, the quartz layer 2 in step S2 is obtained by depositing silicon dioxide; specifically comprising the following steps:

[0078] Gas introduction and deposition: the mixed gas involved in the deposition enters the quartz liner tube containing the non-rare earth doped core layer from one end thereof, the other end of the liner tube being the exhaust end, the exhaust end being connected to a vacuum pump through a pipeline; a quartz glass dust collecting intubation tube is installed in the exhaust end of the liner tube to collect the dust deposited at the exhaust end;

[0079] Dust handling during deposition:

[0080] When the dust collected in the dust collecting cannula reaches a certain amount, the deposition is suspended, the mixed gas control valve is closed, the liner stops rotating, the resonance cavity stops working, the exhaust end rotary chuck is loosened, the dust collecting cannula is replaced, the rotary chuck is tightened again, and the deposition continues, and this process is repeated until the deposition is completed;

[0081] Deposition parameter control during deposition: During deposition, the pressure in the liner is controlled to be 5-20mbar; the microwave resonant cavity generates a high-frequency deposition power of 3kw-15kw; the resonant cavity performs axial reciprocating motion relative to the liner, with a moving speed of 12-40m / min;

[0082] Deposition gas types: The mixed gas types involved in deposition include silicon tetrachloride vapor, germanium tetrachloride vapor, pure oxygen, phosphorus oxychloride, sulfur hexafluoride and other vapors;

[0083] Post-deposition treatment: remove the dust collecting tube, and melt the deposited liner in an electric melting furnace to obtain a solid core rod;

[0084] Doping element deposition:

[0085] Then, SiCl4, GeCl4 and SF6 are introduced into the reaction gas to deposit the optical cladding at high temperature. Ge (germanium) and F (fluorine) elements are doped into the SiO2 cladding to make the refractive index of the optical cladding consistent with the refractive index of the external liner, effectively reducing the fiber attenuation and improving the red light performance of the fiber;

[0086] Relationship between deposition efficiency and flow rate: With the increase of high-frequency output power, deposition efficiency gradually approaches 100%. The actual deposition efficiency should be controlled according to the actual deposition rate. With the increase of deposition rate, the deposition efficiency corresponding to the appropriate high-frequency power decreases, but it is maintained above 90%.

[0087] The above steps provide a detailed process of quartz layer deposition, including preparation, deposition environment setting, gas introduction and deposition, dust treatment, deposition parameter control, deposition gas type, deposition post-treatment, and the relationship between deposition efficiency and flow rate. These steps ensure the uniform deposition of the quartz layer and the preparation of high-quality optical fiber preforms; the whole process of silicon dioxide deposition of the quartz layer inside the quartz liner tube through the PCVD process, from the preparation of the substrate tube to the final melting and deposition, ensures the quality and performance of the optical fiber preform.

[0088] Furthermore, in step S3, the number of channels formed by the non-rare earth doped core layer 3 and the quartz layer 2 is 1-100 layers, and the number of channels is precisely controlled according to design requirements; the thickness of the non-rare earth doped core layer 3 and the quartz layer 2 in each layer of the channel can be the same or different; the thickness of each channel can be the same as or different from the thickness of other channels to achieve a specific refractive index distribution and optical fiber performance; the refractive index of the non-rare earth doped core layer 3 and the quartz layer 2 in each channel can be the same as or different from the refractive index of the non-rare earth doped core layer 3 and the quartz layer 2 in other channels to further optimize the performance of the optical fiber; during the entire PCVD process, parameters such as gas flow, temperature, pressure and microwave power need to be precisely controlled to ensure uniform deposition and quality of the channel layer; through steps S1 to S3, a multilayer channel structure composed of a non-rare earth doped core layer and a quartz layer can be precisely constructed inside a quartz liner using the PCVD process, and these channel structures are crucial to achieving specific optical properties of the optical fiber.

[0089] Furthermore, step S3 also includes: sintering the multi-channel liner tube containing the non-rare earth doped core layer and the quartz layer in a high-temperature sintering system; sintering the quartz liner tube using the high temperature of the oxyhydrogen flame and the pressure inside the tube to obtain a multi-channel quartz sleeve containing the non-rare earth doped core layer and the quartz layer (i.e., doped germanium dioxide and silicon dioxide).

[0090] Further, in step S4, the core layer thickness of the solid preform rod containing the rare earth doped core layer is 1-2 mm, and the core numerical aperture is 0.01-0.1; the rare earth doped core layer 1 is deposited inside the separately taken quartz liner tube by the MCVD process combined with the liquid phase doping process, and melted into a solid preform rod containing the rare earth doped core layer; comprising:

[0091] Prepare the quartz liner: First, take a high-purity quartz glass tube as the liner, which is the basis of the MCVD process;

[0092] MCVD deposition: The two ends of the quartz liner are connected to the chemical raw material supply system and the reaction tail gas collection system respectively; the movable heat source placed at the bottom of the liner provides heat for chemical reaction, deposition and melting;

[0093] Raw gas supply: SiCl4, GeCl4 and high-purity O2 are used as raw gas, and POCl3, Cl2, He, etc. are added according to the preform type and process requirements;

[0094] Rare earth doping: During the deposition process, rare earth dopants are introduced into the deposition area in gaseous form, reacting with raw gas such as SiCl4, GeCl4 and high-purity O2 to deposit on the inner wall of the quartz liner to form a rare earth doped fiber core layer. During the deposition process, the flow rate of the dopant needs to be precisely controlled to obtain the required refractive index distribution.

[0095] Solution doping: The quartz deposition tube with a loose SiO2 layer deposited on the inner wall is removed from the deposition lathe and vertically immersed in a solution containing rare earth doping ions and co-doping ions. After a certain period of time, the doping ions enter the loose core layer;

[0096] Thermal drying: The solution-doped deposition tube is placed back on the deposition lathe for thermal drying;

[0097] Ventilation dehydration: During the drying process, gas is introduced to remove moisture from the doping layer;

[0098] Sintering into rods: After drying and dehydration, sintering is performed to transform the loose layer into a dense glass structure, forming a fiber core refractive index distribution with design requirements;

[0099] Melting into a solid preform: The deposited hollow high-purity quartz glass tube is melted into a solid optical fiber preform core rod. This step is to increase the temperature to melt and shrink the material in the deposited tube, and finally form a solid optical fiber preform.

[0100] The preparation method of the channel-type gain optical fiber of the present invention is described below with a specific embodiment:

[0101] (1) A 1 mm thick germanium dioxide region and a 1 mm thick silicon dioxide region were deposited on a quartz liner tube with a length of 500 mm, an outer diameter of 25 mm, and a wall thickness of 3 mm by PCVD equipment. The refractive index difference between the germanium dioxide region and the liner tube is 2*10 -3 , the refractive index of the silica region is consistent with that of the liner;

[0102] (2) removing the deposited quartz liner tube and sintering it in a high-temperature sintering system, using the high temperature of the hydrogen-oxygen flame and the pressure inside the tube to sinter the quartz liner tube to obtain a quartz sleeve doped with germanium dioxide and silicon dioxide with an inner diameter of 1 mm;

[0103] (3) Using MCVD equipment combined with vapor phase doping technology, a 3 mm thick active region was deposited in a quartz liner tube with a length of 500 mm, an outer diameter of 25 mm, and a wall thickness of 3 mm. The ytterbium doping concentration was 0.5% wt, and the refractive index difference between the active region and the liner was 2*10 -3 ;

[0104] (4) cleaning and etching the liner in step (2) in an acid-base solution to etch away the outer pure silicon dioxide region to obtain a 2 mm thick active region, and grinding and polishing the core rod to eliminate surface defects;

[0105] (5) The core rod in step (3) is combined with the preform rod sleeve in step (1), and finally a channel-type gain optical fiber is drawn on a drawing tower, wherein the first region of the core is 20 μm, the second region is 1 μm, the third region is 1 μm, and the core numerical aperture is 0.076.

[0106] The present invention provides a channel-type gain optical fiber and a preparation method thereof. The optical fiber core rod is prepared by MCVD process, and the formation of the channel is precisely controlled by PCVD process. The gain optical fiber capable of realizing precise control of the channel refractive index is prepared by combining the two processes, and high beam quality and high power output can be achieved in an optical fiber laser.

[0107] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A channel-type gain optical fiber, characterized in that: The invention comprises a rare earth doped core layer (1), a quartz layer (2), a non-rare earth doped core layer (3), an inner cladding layer (4), an outer cladding layer (5) and a coating layer (6) which are arranged in sequence from the inside to the outside; wherein: The rare earth doped core layer (1) is prepared by a MCVD process combined with a liquid phase doping process; The quartz layer (2) and the non-rare earth doped core layer (3) are prepared by a PCVD process; The refractive index of the non-rare earth doped core layer (3) is the same as the refractive index of the rare earth doped core layer (1), and the thickness of both is 1-2 mm; The refractive index of the quartz layer (2) is the same as that of the inner cladding (4), and the thickness of both is 0.5-1 mm; The MCVD process is combined with the liquid phase doping process and the PCVD process to prepare the channel-type gain fiber through the sleeve method, which effectively controls the size and structure of the fiber, reduces the attenuation coefficient of the fiber, and achieves high-quality beam output and high-efficiency laser conversion.

2. A method for preparing a channel-type gain optical fiber, characterized in that: The method for preparing the channel-type gain optical fiber according to claim 1 comprises the following steps: S1: taking a quartz liner tube, and depositing a non-rare earth doped core layer (3) inside the quartz liner tube by a PCVD process, to obtain a quartz liner tube comprising a non-rare earth doped core layer; S2: by means of a PCVD process, a quartz layer (2) is further deposited on the inner surface of the quartz liner tube comprising a non-rare earth doped core layer, so as to obtain a quartz liner tube comprising a non-rare earth doped core layer and a quartz layer; S3: repeating steps S1 and S2 according to design requirements, so that the non-rare earth doped core layer (3) and the quartz layer (2) are alternately deposited to form a required number of channels, and obtaining a multi-channel sleeve comprising a non-rare earth doped core layer and a quartz layer; S4: taking another quartz liner tube, depositing a rare earth doped core layer (1) inside the other quartz liner tube by using a MCVD process combined with a liquid phase doping process, and melting and shrinking the layer into a solid preform rod including the rare earth doped core layer; S5: using hydrofluoric acid to clean the surface of the solid preform rod containing the rare earth-doped core layer to obtain a core rod with the outer pure silica layer etched away; grinding and polishing the core rod with the outer pure silica layer etched away to obtain a grinded and polished core rod; S6: Combine the polished core rod obtained in step S5 with the multi-channel sleeve including the non-rare earth doped core layer and the quartz layer obtained in step S3, and draw a channel-type gain optical fiber of a required size on a drawing tower; and perform double-layer coating and UV curing.

3. A method for preparing a channel-type gain optical fiber according to claim 2, characterized in that: The thickness of the non-rare earth doped core layer (3) in step S1 is 1-2 mm; The core layer thickness of the solid preform rod containing the rare earth doped core layer in step S4 is 1-2 mm, and the core numerical aperture is 0.01-0.

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4. A method for preparing a channel-type gain optical fiber according to claim 2, characterized in that: The non-rare earth doped core layer (3) is obtained by depositing germanium dioxide.

5. A method for preparing a channel-type gain optical fiber according to claim 2, characterized in that: The quartz layer (2) in step S2 is obtained by depositing silicon dioxide.

6. A method for preparing a channel-type gain optical fiber according to claim 2, characterized in that: In step S3, the number of channels formed by the non-rare earth doped core layer (3) and the quartz layer (2) is 1-100 layers.

7. A method for preparing a channel-type gain optical fiber according to any one of claims 2 to 6, characterized in that: The thickness of the non-rare earth doped core layer (3) in each channel is the same as that of the quartz layer (2).

8. A method for preparing a channel-type gain optical fiber according to any one of claims 2 to 6, characterized in that: The thickness of each of the channels is different from the thickness of the other channels.

9. A method for preparing a channel-type gain optical fiber according to any one of claims 2 to 6, characterized in that: The refractive index of the non-rare earth doped core layer (3) and the quartz layer (2) in each channel is the same as the refractive index of the non-rare earth doped core layer (3) and the quartz layer (2) in other channels.

10. A method for preparing a channel-type gain optical fiber according to any one of claims 2 to 6, characterized in that: The refractive index of the non-rare earth doped core layer (3) and the quartz layer (2) in each channel is different from the refractive index of the non-rare earth doped core layer (3) and the quartz layer (2) in other channels.

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