Rare-earth-doped optical fiber having adjustable thermo-optical coefficient, and preparation method therefor and use thereof

Abstract

Provided in the present application are a rare-earth-doped optical fiber having an adjustable thermo-optical coefficient, and a preparation method therefor and the use thereof. The optical fiber comprises a fiber core and a cladding, wherein the fiber core comprises the following components in molar percentages: 80-95 mol% of SiO2, 0.1-0.3 mol% of a rare earth oxide Re2O3, 0.5-10 mol% of P2O5, 0.5-10 mol% of Al2O3, 0.1-10 mol% of SiF4, and 0.1-10 mol% of a first alkali metal oxide R2O; and the cladding comprises the following components in molar percentages: 95-100 mol% of SiO2, 0.1-5 mol% of GeO2, 0.1-10 mol% of SiF4, 0.1-5 mol% of a second alkali metal oxide R2O and 0.1-5 mol% of Fe2O3. According to the rare-earth-doped optical fiber having an adjustable thermo-optical coefficient of the present application, by means of the components having different effects, the thermo-optical coefficient of the fiber core and the cladding layer is adjusted, and the loss of the cladding in a specific wave band is adjusted; and after the rare-earth-doped optical fiber is applied to an optical fiber laser, the working stability and the output power of the laser can be improved.

Description

A rare earth-doped optical fiber with adjustable thermo-optical coefficient, its preparation method and application Technical Field

[0001] The present application belongs to the field of optical fiber manufacturing technology, and more specifically, relates to a rare earth-doped optical fiber with adjustable thermo-optical coefficient, a preparation method thereof, and an application thereof. Background Art

[0002] The application scope of high-power fiber lasers in industry, military, and scientific research continues to expand. As the output power of lasers continues to increase, for example, the average power of continuous lasers has reached hundreds of kilowatts, and the average power of ultrafast lasers is also developing towards several kilowatts.

[0003] In high-power fiber lasers, large-mode-field rare-earth-doped quartz fiber is used as the gain medium. Due to intrinsic fiber loss, quantum loss, quenching, and other factors, a portion of the pump energy is converted into heat in the fiber core, causing the temperature of the rare-earth-doped core and pure quartz cladding to rise to varying degrees, forming a temperature gradient. The thermal effect causes the refractive index of the core and cladding to change. The thermo-optical coefficient dn / dT of existing quartz fiber is positive, and its refractive index increases with increasing temperature.

[0004] The doped fiber core acts as the center of the heat source. Heat is conducted from the center of the fiber to the fiber cladding. A temperature difference is formed between the core and the cladding, that is, the increase in the refractive index of the core is higher than the increase in the refractive index of the cladding, which leads to an increase in the actual effective numerical aperture of the fiber and an increase in the number of transmittable modes in the core. Irregular coupling occurs between different modes, which not only affects the stability of the laser operation, but also limits the further increase in the laser output power. This problem has become a key issue restricting the power increase of fiber lasers.

[0005] Summary of the Invention

[0006] The purpose of this application is to provide a rare earth-doped optical fiber with adjustable thermo-optical coefficient, a preparation method and application thereof, so as to solve the technical problems of poor laser working stability and limited laser output power in the prior art.

[0007] To achieve the above objectives, in a first aspect, the present application provides a rare-earth-doped optical fiber with adjustable thermo-optical coefficient, the optical fiber comprising a core and a cladding, the core comprising the following molar percentage composition: SiO2 80-95 mol%, rare earth oxide Re2O3 0.1-0.3 mol%, P2O5 0.5-10 mol%, Al2O3 0.5-10 mol%, SiF4 0.1-10 mol%, and a first alkali metal oxide R2O 0.1-10 mol%;

[0008] The cladding layer contains the following molar percentage composition: SiO2 95-100 mol%, GeO2 0.1-5 mol%, SiF4 1-10 mol%, second alkali metal oxide R2O 0.1-5% mol, Fe2O3 0.1-5 mol%.

[0009] Furthermore, the rare earth oxide Re2O3 includes at least one of Yb2O3, Nd2O3, and Er2O3.

[0010] Furthermore, the first alkali metal oxide R2O includes at least one of Li2O, Na2O, and K2O; and / or the second alkali metal oxide R2O includes at least one of Li2O, Na2O, and K2O.

[0011] In a second aspect of the present application, a method for preparing the above-mentioned optical fiber is provided, which adopts an improved chemical vapor deposition method and a high-temperature chelate doping system for preparation.

[0012] Further, the following steps are included:

[0013] Using O2 as the carrier gas, the flow rate of the carrier gas O2 is controlled by MFC (mass flow controller) through bubbling to control SiCl4 and GeO2. The flow rates of O2, He, and SF6 are independently controlled by MFC. The flow rate of the carrier gas He is controlled by MFC to control the doping amount of Fe chelate and K chelate. At the same time, the above gases are introduced into a quartz tube, and a hydrogen-oxygen flame is used to deposit the cladding back and forth in the tube multiple times. The amount of doping elements in each layer can be radially controlled by adjusting the flow rate of different substances.

[0014] Using O2 as the carrier gas, the MFC is used to control the flow rate of the carrier gas O2 through bubbling to control SiCl4 and POCl3. The flow rates of O2, He, and SF6 are independently controlled by MFC. At the same time, the MFC is used to control the flow rate of the carrier gas He to control the doping amount of Yb chelate, K chelate, and AlCl3. At the same time, the above gases are introduced into a quartz tube, and a hydrogen-oxygen flame is used to deposit the core layer in the tube multiple times. The amount of doping elements in each layer can be radially controlled by adjusting the flow rate of different substances.

[0015] After the deposition is completed, He, Cl2, and O2 are introduced into the tube, and a solid preform is fired on the MCVD lathe using an oxyhydrogen flame at 1900-2050°C in multiple passes.

[0016] The melted core rod is inserted into a high-purity quartz tube and drawn into optical fiber in a fiber drawing tower.

[0017] The third aspect of the present application provides an application of the above-mentioned rare-earth-doped optical fiber with adjustable thermo-optical coefficient in a fiber laser.

[0018] Compared with the existing technology, this application has the following technical effects:

[0019] In the rare-earth-doped optical fiber with adjustable thermo-optical coefficient of the present application, P2O5 can effectively suppress the photodarkening problem of the optical fiber, Al2O3 can effectively improve the dispersion of Yb2O3 and reduce agglomeration, SiF4 can effectively control the increase in the refractive index of the fiber core caused by various doping, and the alkali metal oxide R2O can not only increase the excitation emission cross section of the quartz glass, but also adjust the thermo-optical coefficient of the quartz glass.

[0020] This application introduces P2O5 and Al2O3 in the core co-doping, which are the main solutions for gain fibers used in current commercial lasers. SiF4 is used to balance the increase in the core refractive index caused by high-concentration doping and control the numerical aperture of the fiber within a reasonable range. In order to reduce the impact of heat generation during the operation of this type of optical fiber on the stability of laser operation, the intrinsic loss of the optical fiber within the pump wavelength and operating wavelength range is generally reduced through process optimization and material purification. However, the thermo-optical coefficient of the matrix material SiO2 doped with components Al2O3 and Re2O3 (Yb2O3, Nd2O3, Er2O3) is positive, and the thermo-optical coefficient of the optical fiber cladding is pure SiO2, which is also positive. Based on this, the thermo-optical coefficient of the alkali metal oxides R2O (Li2O, Na2O, K2O), P2O5, and SiF4 introduced in the core doping of this application is negative. As an alkali metal oxide, R2O has a lower refractive index than pure SiO2 and has no absorption peak in the infrared band. Core doping can reduce the refractive index without increasing the loss of pump and signal light in the laser. By adjusting the core component content, the thermo-optic coefficient (dn / dT) of the quartz fiber core can be reduced, even to zero or a negative value. As the core heats up, the refractive index increases less, remains unchanged, or even decreases.

[0021] The radial distribution of the components of the fiber core of the present application can be precisely controlled through the preparation process. Since the distribution of laser energy in the fiber core varies depending on the application scenario, the radial distribution of temperature in the fiber core is also different. By adjusting the radial components of the fiber core and thus controlling the radial thermo-optical coefficient and refractive index distribution of the fiber core, the refractive index consistency and controllability of the fiber core during operation are improved.

[0022] In the present application, the cladding of the optical fiber is doped with a certain amount of Fe2O3, GeO2, SiF4, R2O, P2O5, etc., while maintaining the same refractive index as pure SiO2. The purpose of adjusting the thermo-optical coefficient dn / dT of the quartz optical fiber core and cladding can be achieved by adjusting the composition. The temperature of the optical fiber cladding can also be controlled within a certain range by adjusting the loss of the cladding.

[0023] The present invention discloses a rare-earth-doped optical fiber with adjustable thermo-optic coefficient, which adjusts the thermo-optic coefficients of the core and cladding through different components, and regulates the loss of the cladding in a specific wavelength band. When applied to a fiber laser, it can improve the stability of the laser operation and the output power of the laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0025] FIG1 is a diagram showing mode degradation of the optical fiber provided in Comparative Example 1 of the present application at 1500W;

[0026] FIG2 is a diagram showing mode degradation of the optical fiber provided in Example 1 of the present application at 2000 W;

[0027] FIG3 is a diagram showing mode degradation of the optical fiber provided in Comparative Example 2 of the present application at 80W;

[0028] FIG4 is a diagram showing mode degradation of the optical fiber provided in Example 2 of the present application at 150 W;

[0029] FIG5 is a schematic diagram of the optical fiber structure provided in Example 1 of the present application;

[0030] FIG6 is a schematic diagram of the optical fiber structure provided in Example 2 of the present application. DETAILED DESCRIPTION

[0031] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0032] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0033] In this application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0034] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0035] The terms used in the embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0036] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass described in the examples of this application may be a mass unit known in the chemical industry, such as μg, mg, g, kg, etc.

[0037] The terms "first" and "second" are used solely for descriptive purposes to distinguish objects, such as substances, from one another and should not be understood to indicate or imply relative importance or to implicitly specify the quantity of the technical features being referred to. For example, without departing from the scope of the embodiments of this application, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of such features.

[0038] The following describes a rare-earth-doped optical fiber with adjustable thermo-optical coefficient, a preparation method thereof, and an application thereof through multiple specific embodiments.

[0039] Example 1

[0040] Example 1 of the present application provides a rare earth-doped optical fiber with adjustable thermo-optical coefficient and a preparation method thereof, wherein an optical fiber preform is produced using MCVD (modified chemical vapor deposition) and a high-temperature chelate doping system, comprising the following steps:

[0041] (1) Preparation of doped optical fiber cladding: A high-purity quartz tube (impurity concentration is lower than the detection limit of ICP-MS (inductively coupled plasma mass spectrometer)) 28mm*22mm*800mm is used, O2 is used as the carrier gas, and the flow rate of the carrier gas O2 is controlled by bubbling with an MFC (mass flow controller) to control SiCl4 and GeO2. The flow rates of O2, He, and SF6 are independently controlled by MFCs, and the flow rate of the carrier gas He is controlled by MFCs to control the doping amount of Fe chelate and K chelate. At the same time, the above gases are introduced into the quartz tube, and a cladding with a refractive index of 1.4573 is gradually deposited in multiple layers at 1860°C in the tube using an oxyhydrogen flame;

[0042] (2) Preparation of doped optical fiber core: using a high-purity quartz tube of 28mm*22mm*800mm, with O2 as carrier gas, and controlling the flow rate of carrier gas O2 by bubbling with an MFC (mass flow controller) to control the amount of SiCl4 and POCl3, wherein the flow rates of O2, He, and SF6 are independently controlled by high-precision MFCs, and the flow rate of carrier gas He is controlled by MFC to control the doping amount of Yb chelate, K chelate, and AlCl3. At the same time, the above gases are introduced into the quartz tube, and a core layer with a refractive index of 1.4586 is gradually deposited in multiple layers at 1800-1860°C in the tube using an oxyhydrogen flame;

[0043] (3) After the deposition is completed, He, Cl2, and O2 are introduced into the tube, and a hydrogen-oxygen flame is used on the MCVD lathe at 1900-2050℃ for multiple round trips to form a solid preform rod;

[0044] (4) The melted core rod is inserted into a high-purity octagonal quartz tube with an inner diameter of 17.5 mm and an appropriate outer diameter side-to-side distance, and then drawn into an optical fiber in an optical fiber drawing tower.

[0045] The preparation method of the embodiment of the present application is applicable to the preparation method of a commonly used general all-solid optical fiber. It is also possible to increase the number of deposition layers in step (1) above and then melt and shrink directly into a solid rod, remove the regulated fiber core by etching, and use it as a raw material as the cladding in a PCF (photonic crystal) optical fiber. It is also possible to increase the number of deposition layers in step (2) above and then melt and shrink directly into a solid rod, then grind the outer pure quartz layer by cold working, and remove the regulated fiber core by etching, and use it as a raw material as the fiber core in a PCF optical fiber.

[0046] The refractive index and refractive index temperature coefficient of the preform in the embodiment of the present application are measured using an optical fiber preform analyzer and a refractive index temperature coefficient meter, respectively.

[0047] The composition of the core and cladding of the optical fiber prepared in the present embodiment is shown in Table 1, and the structure of the prepared optical fiber is shown in Figure 5. The double-clad ytterbium-doped optical fiber prepared in the present embodiment has a core diameter of 20 μm and a cladding diameter of 400 μm. Using a 976 nm semiconductor pump, a single-cavity all-fiber structure test showed mode degradation at 2000 W, as shown in Figure 2.

[0048] Comparative Example 1

[0049] This example differs from Example 1 in that the components and their contents in the core and cladding of the optical fiber are different, as shown in Table 1. The preparation method is the same, and the optical fiber structure prepared is the same as in Example 1. The double-clad ytterbium-doped optical fiber prepared in this comparative example has a core diameter of 20 μm and a cladding diameter of 400 μm. Using a 976 nm semiconductor pump, a single-cavity all-fiber structure test exhibits mode degradation at 1500 W, as shown in Figure 1.

[0050] Example 2

[0051] This embodiment differs from Example 1 in that the components and their contents in the core and cladding of the optical fiber are different, as shown in Table 1. The preparation method is the same, and the prepared optical fiber structure is shown in Figure 6. The double-clad ytterbium-doped optical fiber prepared in this embodiment has a core diameter of 40 μm, a cladding diameter of 200 μm, an intercept of 10 μm, and an air hole diameter of 1 μm in the cladding. Using a 976 nm semiconductor pump, the spatial optical path test of the MOPA structure shows that mode degradation occurs at 150 W, as shown in Figure 4.

[0052] Comparative Example 2

[0053] This example differs from Example 2 in that the components and their contents in the core and cladding of the optical fiber are different, as shown in Table 1. The preparation method is the same, and the optical fiber structure prepared is the same as in Example 2. The double-clad ytterbium-doped optical fiber prepared in this comparative example has a core diameter of 40 μm, a cladding diameter of 200 μm, an intercept of 10 μm, and an air hole diameter of 1 μm in the cladding. Using a 976 nm semiconductor pump, a MOPA structure spatial optical path test showed mode degradation at 80 W, as shown in Figure 3.

[0054] Table 1

[0055] Compared with Comparative Example 1, Example 1 reduces the thermo-optical coefficient of the core due to the regulation of the optical fiber core and cladding components, so that the increase in the refractive index of the core is smaller than that of Comparative Example 1 when working at high power, and at the same time increases the loss of the cladding in the pump band. When the thermo-optical coefficient of the cladding is basically consistent with that of Comparative Example 1, the increase in the refractive index of the cladding in Example 1 is higher than that of the cladding in Comparative Example 1, and the increase in the numerical aperture of the core-cladding in Example 1 is smaller than that of the core-cladding in Comparative Example 1, thereby obtaining a higher mode instability threshold.

[0056] Compared with Comparative Example 2, Example 2 maintains the same core refractive index as Comparative Example 2 due to the regulation of the optical fiber core and cladding components, further reduces the thermo-optical coefficient of the core, and makes the refractive index of the core increase less than that of Comparative Example 2 when working at high power. At the same time, the loss of the optimized pump band is used to assemble into microstructure units. When the thermo-optical coefficient of the cladding is basically consistent with that of the cladding in Comparative Example 2, the refractive index increase of the cladding is higher than the refractive index increase of the cladding in Comparative Example 2. The increase in the numerical aperture of the core-cladding of Example 2 is smaller than that of the core-cladding of Comparative Example 2, and a higher mode instability threshold is obtained.

[0057] The above embodiments merely illustrate several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A rare earth doped optical fiber with adjustable thermo-optical coefficient, characterized in that: The optical fiber comprises a core and a cladding, wherein the core contains the following molar percentage composition: SiO2 80-95 mol%, rare earth oxide Re2O3 0.1-0.3 mol%, P2O5 0.5-10 mol%, Al2O3 0.5-10 mol%, SiF4 0.1-10 mol%, first alkali metal oxide R2O 0.1-10 mol%; The cladding layer contains the following molar percentage composition: SiO2 95-100 mol%, GeO2 0.1-5 mol%, SiF4 0.1-10 mol%, second alkali metal oxide R2O 0.1-5% mol, Fe2O3 0.1-5 mol%.

2. The rare earth doped optical fiber with adjustable thermo-optical coefficient according to claim 1, characterized in that: The rare earth oxide Re2O3 includes at least one of Yb2O3, Nd2O3, and Er2O3.

3. The rare earth doped optical fiber with adjustable thermo-optical coefficient according to claim 1, characterized in that: The first alkali metal oxide R2O includes at least one of Li2O, Na2O, and K2O; and / or the second alkali metal oxide R2O includes at least one of Li2O, Na2O, and K2O.

4. The rare earth doped optical fiber with adjustable thermo-optical coefficient according to claim 1, characterized in that: The content of P2O5 in the core is 3-6 mol%.

5. The rare earth doped optical fiber with adjustable thermo-optical coefficient according to claim 1, characterized in that: The content of Al2O3 in the core is 1-3 mol%.

6. The rare earth doped optical fiber with adjustable thermo-optical coefficient according to claim 1, characterized in that: The content of SiF4 in the core is 1-10 mol%.

7. The rare earth doped optical fiber with adjustable thermo-optical coefficient according to claim 1, characterized in that: The content of GeO2 in the cladding is 0.1-2 mol% and or the content of Fe2O3 is 0.1-2 mol%.

8. A method for preparing a rare earth-doped optical fiber with adjustable thermo-optical coefficient according to any one of claims 1 to 7, characterized in that: The optical fiber is prepared by adopting an improved chemical vapor deposition method and a high-temperature chelate doping system.

9. The method for preparing a rare earth-doped optical fiber with adjustable thermo-optical coefficient according to claim 8, characterized in that: The following steps are involved: (1) Preparation of doped optical fiber cladding: using a high-purity quartz tube and O2 as carrier gas, the flow rate of O2 carrier gas is controlled by MFC through bubbling to control SiCl4 and GeO2, wherein the flow rates of O2, He and SF6 are independently controlled by MFC, and the flow rate of He carrier gas is controlled by MFC to control the doping amount of Fe chelate and K chelate, and the above gases are introduced into the quartz tube at the same time, and the cladding is deposited by multiple trips of hydrogen-oxygen flame in the tube; (2) Preparation of doped optical fiber core: using a high-purity quartz tube and O2 as carrier gas, the amount of SiCl4 and POCl3 is controlled by MFC through bubbling, where O2, He, and SF6 are independently controlled by high-precision MFC, and the amount of Yb chelate, K chelate, and AlCl3 is controlled by MFC while the above gases are introduced into the quartz tube, and a hydrogen-oxygen flame is used to deposit the core layer in the tube multiple times; After the deposition is completed, He, Cl2, and O2 are introduced into the tube, and the solid preform is fired on the MCVD lathe using an oxyhydrogen flame at 1900-2050°C for multiple round trips; The melted core rod is inserted into a high-purity quartz tube and drawn into optical fiber in a fiber drawing tower.

10. Application of the rare earth-doped optical fiber with adjustable thermo-optical coefficient as claimed in any one of claims 1 to 7 in optical fiber laser.

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