High-power all-fiber optical isolator and preparation method thereof

Abstract

The invention discloses a high-power all-fiber optical isolator and a preparation method in the field of optical devices, the high-power all-fiber optical isolator comprises an integrated optical fiber, the integrated optical fiber comprises a core layer and a cladding located on the periphery of the core layer, the integrated optical fiber further comprises a distributed micro-nano structure, the inner end of the micro-nano structure is located in the core layer, and the outer end of the micro-nano structure is located in the cladding. The outer end of the micro-nano structure is located in the cladding, and the micro-nano structure is configured to conduct light transmitted in the forward direction of the integrated optical fiber, couple light transmitted in the reverse direction of the integrated optical fiber and guide the light out of the core layer; the method comprises the steps of constructing an integrated optical fiber model, constructing an optical waveguide model, debugging parameters, preparing in batches, testing and optimizing performance and the like. According to the high-power optical isolator, light transmitted in the forward direction in the optical fiber can be conducted, light transmitted in the reverse direction in the optical fiber can be led out and consumed, and the requirement of the high-power optical fiber laser field on the aspect of the high-power optical isolator is met.

Description

Technical Field

[0001] The present invention relates to the field of optical devices, and in particular to a high-power all-fiber optical isolator and a preparation method thereof. Background Art

[0002] In the field of high-power fiber laser systems and their applications, fiber lasers, with their significant advantages such as high efficiency, compact size, good beam quality, stable and reliable operation, and strong environmental adaptability, have shown extremely important application prospects in many fields such as industrial processing, medical treatment, and national defense. With the continuous development of high-power semiconductor laser pumping technology and double-clad fiber manufacturing processes, the output power of high-power fiber lasers and amplifiers continues to increase. Currently, the output power of high-beam-quality single-fiber lasers has exceeded 20kW.

[0003] However, further increasing its output power faces numerous challenges, severely constrained by factors such as pump source brightness, nonlinear effects, and thermal effects. For narrow-linewidth fiber laser systems, stimulated Brillouin scattering (SBS) becomes the primary factor restricting power increases. Once the SBS threshold is reached, the forward laser power experiences stagnation, and the injected laser energy is completely converted into backward Stokes light, which not only severely impacts system performance but can even damage it.

[0004] In order to prevent the impact of return light on high-power fiber laser systems during applications, or even damage, it is usually necessary to add an optical isolator to the system. However, currently available isolators generally adopt an "optical fiber + spatially independent element" structure. The internal spatial structure is based on Faraday crystals and permanent magnets, and only the input / output ends are optically coupled. This structure severely restricts the high-power handling capacity of the optical isolator. The highest power handling level of optical isolators currently on the market is only in the hundreds of watts, and they are large in size. In actual use, there are many inconveniences and they cannot meet the urgent demand of 100,000-watt high-power fiber lasers for optical isolators that can withstand hundreds or even kilowatts of power.

[0005] The above defects are worth solving. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the present invention provides a high-power all-fiber optical isolator and a preparation method. Based on a distributed tree-like coupling mechanism, a micro-nanostructure is added to the optical fiber to form a coupler, allowing forward-transmitting light to pass while reverse-transmitting light is guided out and attenuated, thereby meeting the needs of the high-power fiber laser field for high-power optical isolators.

[0007] The technical solution of the present invention is as follows:

[0008] On the one hand, a high-power all-fiber optical isolator is characterized by comprising an integrated optical fiber, wherein the integrated optical fiber comprises a core layer and a cladding layer located outside the core layer;

[0009] The integrated optical fiber further comprises a distributed micro-nano structure, wherein the inner end of the micro-nano structure is located in the core layer, and the outer end thereof is located in the cladding layer;

[0010] The micro-nano structure is configured to conduct light transmitted in a forward direction along the integrated optical fiber, couple light transmitted in a reverse direction along the integrated optical fiber, and guide the light out of the core layer.

[0011] The present invention according to the above solution is characterized in that the micro-nano structures are distributed in pairs within the integrated optical fiber.

[0012] The present invention according to the above solution is characterized in that the micro-nano structure is formed by writing along the axial direction of the integrated optical fiber.

[0013] Furthermore, the angle between the micro-nano structure and the forward transmission direction of the integrated optical fiber is less than 90°.

[0014] The present invention according to the above solution is characterized in that the length of the micro-nanostructure located in the core layer is smaller than the length of the micro-nanostructure located in the cladding layer.

[0015] On the other hand, a method for preparing a high-power all-fiber optical isolator is characterized by comprising the following steps:

[0016] S1. Build an integrated fiber model using multi-physics simulation software;

[0017] S2. constructing a distributed micro-nanostructured optical waveguide model, with its inner end located in the core layer of the integrated optical fiber model and its outer end located in the cladding layer of the integrated optical fiber model;

[0018] S3. Based on the constructed simulation model, analyze the influence of different parameters on the coupling effect and determine the optimal writing parameters;

[0019] S4. Based on the optimal writing parameters obtained through debugging, batch writing of micro-nano structures is performed on the integrated optical fiber;

[0020] S5. Perform a performance test on the prepared all-fiber optical isolator, reversely infer the deviation of the writing parameters based on the test results, further optimize the process, and obtain the best curing processing technology.

[0021] The present invention according to the above scheme is characterized in that in step S3, the coupling effects under different waveguide angles, different distribution densities, different waveguide shapes, different waveguide thicknesses, and different refractive index changes are simulated respectively to determine the optimal writing parameters.

[0022] Furthermore, the data of isolation, insertion loss, return loss and withstand power under different parameters are analyzed to determine the optimal writing parameters.

[0023] The present invention according to the above scheme is characterized in that in step S5, an all-fiber optical isolator is obtained by writing under different actual writing parameters, and performance tests are performed to analyze the impact of different parameters on the performance of the all-fiber optical isolator and determine the optimal processing technology.

[0024] Furthermore, the actual writing parameters include femtosecond laser wavelength, intensity, spot size and focal depth, movement speed and trajectory, and the number of branch couplers.

[0025] The beneficial effect of the present invention according to the above scheme is that the micro-nano structure of the present invention allows forward light to pass through and isolates reverse light, and can filter out backward Stokes light or return light feedback in the application to protect the stability and reliability of the entire system.

[0026] The present invention uses a single optical fiber to replace the traditional optical isolator, which is small in size and easy to use. Moreover, due to the application of the spatial structure without Radius crystals and permanent magnets, it can provide higher power tolerance, higher stability and resistance to laser damage.

[0027] This invention uses a femtosecond laser direct writing process to fabricate micro-nanocouplers within optical fibers. The micro-nanostructures do not require strict distribution control, simplifying the process. Once the optimal process is established, the process parameters can be inferred based on actual applications to achieve the best coupling effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic diagram of a first embodiment of the present invention;

[0029] Figure 2 for Figure 1 Schematic side view of

[0030] Figure 3 is a schematic diagram of a second embodiment of the present invention;

[0031] Figure 4 is a schematic diagram of a third embodiment of the present invention;

[0032] Figure 5 is a schematic diagram of a fourth embodiment of the present invention;

[0033] Figure 6 Flowchart of the present invention.

[0034] In the drawings, the reference numerals are:

[0035] 1. Core layer; 2. Cladding layer; 3. Micro-nano structure. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0037] In high-power fiber laser systems, optical isolators and other devices are required to prevent the effects of light return. However, isolators utilize fiber-coupled inputs and outputs, and their internal structure is based on a spatial structure based on Faraday crystals and permanent magnets. This severely limits their high-power handling capabilities, with the current maximum power rating being only in the hundreds of watts. Furthermore, they are bulky and inconvenient to use. Therefore, to overcome the numerous drawbacks of optical isolators in existing fiber laser systems, the present invention proposes a high-power all-fiber optical isolator. This integrates the light return isolation function within a single optical fiber, eliminating the need for separate spatial components, saving space, and addressing the instability associated with spatial component coupling.

[0038] like Figures 1 to 5 As shown, the high-power all-fiber optical isolator includes an integrated optical fiber, which replaces the existing optical isolator. The integrated optical fiber includes a core layer 1 and a cladding layer 2 located outside the core layer 1. The integrated optical fiber targeted by the present invention is a large-core double-clad optical fiber, whose cladding includes an inner cladding and an outer cladding.

[0039] To achieve return light isolation, the integrated optical fiber also includes a distributed micro-nanostructure 3, the inner end of which is located within the core layer 1 and the outer end of which is located within the cladding layer 2. The micro-nanostructure 3 is configured to conduct light transmitted in the forward direction along the integrated optical fiber, couple light transmitted in the reverse direction along the integrated optical fiber, and guide it out of the core layer 1.

[0040] Figure 1 The present invention shows the principle of using micro-nano structures to achieve high-power optical fiber applications. By using the configuration of the micro-nano structure 3, the present invention can achieve high-power optical fiber applications without hindering the forward transmission of light (such as Figure 1 In the case of the solid arrow pointing right in the figure), the reverse transmission light (such as Figure 1 Specifically, when the reverse light encounters the micro-nano structure 3, the micro-nano structure 3 can couple and waveguide the reverse light and couple it to the cladding 2 (as shown by the dotted arrow to the left in the figure). Figure 1 The invention is based on the principle that when light is transmitted in the forward direction, the angle between its propagation direction and the micro-nanostructure is small, and the scattering, absorption, or coupling effect of the micro-nanostructure 3 on the forward-transmitting light is very small and negligible, thus achieving a "conduction" effect and reducing insertion loss. However, the angle between the reverse-transmitting light and the micro-nanostructure 3 is large, making it easy to couple with the micro-nanostructure 3 and be waveguided by the micro-nanostructure 3 to the cladding, thus achieving an "isolation" effect and achieving high isolation.

[0041] The present invention directly incorporates the micro-nanostructure 3 into the integrated optical fiber through inscription, eliminating the need for large equipment such as isolators, achieving a miniaturized design, and simultaneously enhancing stability. Furthermore, the micro-nanostructure 3 replaces spatial components such as the Faraday crystal and permanent magnet in the isolator, offering a high power handling capability. The micro-nanostructure 3 in the present invention avoids coupling losses between the optical fiber and the Faraday crystal, as well as beam collimation losses between the optical fibers. Furthermore, the energy from the return light is channeled into the cladding and dissipated as heat, preventing thermal damage. This allows the integrated optical fiber to withstand higher powers, enabling its application in high-power laser systems.

[0042] The micro-nano structures are distributed in pairs in the integrated optical fiber, that is, Figure 1 In the embodiment, every two micro-nanostructures 3 form a pair (or a group). In the present invention, each micro-nanostructure 3 can be regarded as a branch-like coupler, which is used to achieve forward light conduction and reverse light coupling isolation. Combined with water cooling or TEC cooling of the integrated optical fiber segment, it can achieve rapid heat attenuation at the reverse light isolation position, avoid thermal damage, and improve power tolerance.

[0043] In order to achieve the effect of forward light conduction and reverse light isolation, the micro-nano structure 3 in the present invention is formed along the axial direction of the integrated optical fiber, and the angle between the micro-nano structure 3 and the forward transmission direction of the integrated optical fiber is less than 90 degrees. Therefore, when the forward light is transmitted, it will not couple with the micro-nano structure 3 and can be transmitted normally; when the reverse light is transmitted, it will couple with the micro-nano structure 3 when it contacts the micro-nano structure 3, and will be lost when it is waveguided to the cladding 2 to achieve the purpose of isolation. It should be pointed out that in Figure 1 In the figure, the direction indicated by the arrow (from left to right) is the direction of forward transmission, and the above-mentioned 90° means that the angle between the micro-nano structure and the left side of the optical fiber axis is less than 90°.

[0044] Of course, in order to achieve a better forward conduction effect and ensure effective isolation of reverse light, the angle θ between the micro-nano structure 3 and the forward transmission direction of the integrated optical fiber in the present invention satisfies: 30°≤θ≤60°.

[0045] exist Figure 1 、 Figure 2 In the embodiment shown, the angles between the micro-nano structure 3 and the forward transmission direction of the integrated optical fiber are equal. Figure 3 In other embodiments shown, the angle between the micro-nano structure 3 and the forward transmission direction of the integrated optical fiber may be different.

[0046] The length of the micro-nanostructure 3 in the core layer 1 is shorter than that in the cladding layer 2, so that in the process of coupling the reverse light of the core layer 1 to the cladding layer 2, the cladding layer 2 can be used to attenuate more energy and achieve rapid cooling. Figure 1 、 Figure 2 In the embodiment shown, the micro-nano structures 3 are located in the core layer 1 with the same size. Figure 4 In the illustrated embodiment, the dimensions of the micro-nanostructure 3 within the core layer 1 can vary, as long as they do not affect normal light transmission. To ensure that forward light transmission is not affected and to better isolate reverse light, the depth of the micro-nanostructure 3 extending into the core layer 1 in the present invention is no greater than the radius of the core layer 1. Preferably, the depth of the micro-nanostructure 3 extending into the core layer 1 is no greater than 15% of the diameter of the core layer 1. This reduces the precision requirements for writing the micro-nanostructure 3 while meeting the forward conduction and reverse isolation requirements of the present invention.

[0047] exist Figure 1 、 Figure 2 In the embodiment shown, the micro-nanostructures 3 are evenly distributed in the integrated optical fiber; Figure 5 In other embodiments shown, the micro-nanostructures do not need to be uniformly distributed.

[0048] By comparison Figure 1 Examples and Figure 3-Figure 5 As can be seen from the embodiments shown, the present invention does not require narrowband filtering like traditional tilted fiber Bragg gratings, so the micro-nano structure does not require strict periodicity. Therefore, the present invention does not have strict requirements on the tilt angle, insertion length, and distribution density of the micro-nano structure, thereby reducing the difficulty of femtosecond writing of the micro-nano structure.

[0049] like Figure 6 As shown, the present invention also provides a method for preparing a high-power all-fiber optical isolator, including simulation, emulation, parameter determination, actual engraving, testing, etc. The specific preparation method is as follows.

[0050] 1. Build an integrated fiber model: Use multi-physics simulation software to build an integrated fiber model.

[0051] For example, COMSOL multiphysics simulation software can be used to build a double-clad fiber model. During this process, the corresponding dimensions and refractive indices of the core, inner cladding, and outer cladding layers in the double-clad fiber model are determined, as well as the corresponding materials. Alternatively, the fiber type can be determined based on the specific application, and then a model corresponding to its parameters can be built in the simulation software.

[0052] 2. Construct an optical waveguide model: Construct a distributed micro-nano structure so that its inner end is located in the core layer of the integrated optical fiber model and its outer end is located in the cladding layer of the integrated optical fiber model.

[0053] Specifically, a tree-like micro-nanostructure is constructed along the axial direction of the optical fiber to form a coupler. Preferably, two micro-nanostructures form a pair of couplers to form a module. During the construction of the complete optical waveguide model, the module is used as a unit to construct the coupling structure in the high-power all-fiber optical isolator.

[0054] 3. Parameter debugging: Based on the constructed simulation model, analyze the impact of different parameters on the coupling effect and determine the optimal writing parameters.

[0055] (1) Simulate the coupling effects under different waveguide angles, distribution densities, waveguide shapes, waveguide thicknesses, and refractive index variations to determine the optimal writing parameters.

[0056] Since the optical isolation effect can be evaluated from aspects such as isolation and withstand power, the present invention analyzes the impact of different parameters on the coupling effect. It is necessary to analyze the data of isolation, insertion loss, return loss, and withstand power under different parameters to determine the optimal writing parameters. It should be noted that the optimal writing parameters here refer to the parameters corresponding to isolation ≥ 28dB, based on meeting the power requirements of the fiber laser system and insertion loss ≤ 1dB.

[0057] (2) After the required waveguide angle, distribution density, waveguide shape, waveguide thickness, and refractive index change are obtained through simulation, the final parameter combination is constructed based on the determined parameters, and this parameter combination forms the parameter basis for the subsequent preparation of the fiber optic isolator.

[0058] 4. Batch preparation: Based on the optimal writing parameter combination obtained through debugging, batch writing of micro-nano structures is performed on integrated optical fibers.

[0059] Specifically, the parameters of the femtosecond laser equipment are initially determined, and the focal depth is controlled at the interface between the core layer and the inner cladding to achieve batch writing of micro-nano structures.

[0060] 5. Performance testing and optimization: The prepared all-fiber optical isolator is subjected to performance testing. The deviation of the writing parameters is deduced based on the test results, and the process is further optimized to obtain the optimal curing processing technology.

[0061] Specifically, all-fiber optical isolators were created under different actual writing parameters and performance tests were conducted to analyze the impact of different parameters on the performance of the all-fiber optical isolators and determine the optimal processing technology. The actual writing parameters include femtosecond laser wavelength, intensity, spot size and focal depth, motion speed and trajectory, and the number of branch coupler pairs. The femtosecond laser wavelength, intensity, spot size and focal depth, motion speed and trajectory determine the refractive index change, lateral size and shape, and coupler depth of the written branch coupler. The number of branch coupler pairs determines the return light isolation effect. A larger number of pairs means a stronger isolation effect, but it is important to balance this with the actual insertion loss of the device.

[0062] The preparation process of the present invention has the advantages of both simplicity and high efficiency in batch production, and achieves the combination of low insertion loss and high isolation. The following table shows the specific test results of different indicators of the present invention compared with two comparative examples.

[0063] Indicator name The present invention Isolator In-line isolators Isolation ≥28dB 28dB 33dB Power handling capacity ≥200W 120W 10W Insertion loss ≤1dB ≤1.2dB 1.2dB Return loss ≥50dB ≥50dB ≥50dB Full fiber optic yes no no cost Low high high Mass production efficiency high Low Low

[0064] From the analysis of the above table, it can be seen that the present invention has the following advantages:

[0065] (1) The present invention is based on the coupling mechanism of distributed dendritic waveguides, coupling reverse light from the core layer into the cladding to achieve optical isolation. Unlike the narrowband filtering method of tilted fiber Bragg gratings to suppress reverse light, the present invention does not require strict periodicity, which can effectively reduce the difficulty of femtosecond writing in preparation. At the same time, the micro-nanostructure can be distributed over a long distance, which can disperse the heat introduced into the cladding by the reverse light, avoiding performance degradation caused by local overheating, thereby achieving an isolation of ≥28dB and ensuring effective isolation of the reverse light.

[0066] (2) By adopting an all-fiber structure, the present invention completely eliminates the spatially independent components and Faraday rotator crystals found in traditional isolators, thus avoiding coupling losses between the optical fiber and the Faraday rotator crystal, as well as collimation losses between the optical fibers. Furthermore, the all-fiber structure simplifies water cooling of the optical fiber, effectively removing heat generated by the components during the optical isolation process and preventing thermal damage. This significantly improves the power tolerance of the optical isolator, which is expected to withstand power levels of ≥200W, far exceeding the power tolerance of traditional in-line optical isolators.

[0067] (3) By optimizing the parameters and preparation process of the tree-shaped coupled waveguide, the present invention can achieve an insertion loss of ≤1dB for the all-fiber optical isolator, which has lower energy loss than traditional isolators and improves the transmission efficiency of optical signals.

[0068] (4) The present invention has a return loss of ≥50dB, which can effectively reduce the reflection of optical signals and reduce the interference of reflected light on the system, further improving the performance and stability of the system.

[0069] (5) Unlike conventional optical isolators, the present invention integrates a micro-nanostructure etched along the fiber axis using a femtosecond laser onto a single optical fiber to form an optical isolator. This eliminates the optical coupling issue between independent spatial components and thus offers greater stability. This structural design fundamentally addresses the stability issues inherent in conventional isolators due to spatial component coupling, enabling the optical isolator to maintain stable performance in complex operating environments and improving overall system reliability.

[0070] (6) The all-fiber structure design greatly reduces the size of the optical isolator, getting rid of the disadvantage of the traditional isolator that is large in size due to the inclusion of spatially independent components. It is more flexible and convenient in practical applications and facilitates system integration and installation.

[0071] (7) Compared with the existing fiber-optic integrated isolator based on magneto-optical effect, the present invention will not be affected by the anti-laser damage prefabrication of magneto-optical materials, has high power bearing capacity, and does not require high-precision assembly of magneto-optical crystals. It has a simple process and low cost, which is conducive to large-scale production.

[0072] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes should fall within the scope of protection of the appended claims of the present invention.

[0073] The above is an exemplary description of the patent of the present invention in conjunction with the accompanying drawings. It is obvious that the implementation of the patent of the present invention is not limited to the above-mentioned method. As long as various improvements are made by adopting the method concept and technical solution of the patent of the present invention, or the concept and technical solution of the patent of the present invention are directly applied to other occasions without improvement, they are all within the scope of protection of the present invention.

Claims

1. A high-power all-fiber optical isolator, characterized in that: The integrated optical fiber comprises a core layer and a cladding layer located outside the core layer; The integrated optical fiber further comprises a distributed micro-nano structure, wherein the inner end of the micro-nano structure is located in the core layer, and the outer end thereof is located in the cladding layer; The micro-nano structure is configured to conduct light transmitted in a forward direction along the integrated optical fiber, couple light transmitted in a reverse direction along the integrated optical fiber, and guide the light out of the core layer.

2. The high-power all-fiber optical isolator according to claim 1, characterized in that: The micro-nano structures are distributed in pairs within the integrated optical fiber.

3. The high-power all-fiber optical isolator according to claim 1, characterized in that: The micro-nano structure is formed by writing along the axial direction of the integrated optical fiber.

4. The high-power all-fiber optical isolator according to claim 3, characterized in that: The angle between the micro-nano structure and the forward transmission direction of the integrated optical fiber is less than 90°.

5. The high-power all-fiber optical isolator according to claim 1, characterized in that: The length of the micro-nano structure located in the core layer is smaller than the length of the micro-nano structure located in the cladding layer.

6. A method for preparing a high-power all-fiber optical isolator, characterized in that: The following steps are involved: S1. Build an integrated fiber model using multi-physics simulation software; S2. constructing a distributed micro-nanostructured optical waveguide model, with its inner end located in the core layer of the integrated optical fiber model and its outer end located in the cladding layer of the integrated optical fiber model; S3. Based on the constructed simulation model, analyze the influence of different parameters on the coupling effect and determine the optimal writing parameters; S4. Based on the optimal writing parameters obtained through debugging, batch writing of micro-nano structures is performed on the integrated optical fiber; S5. Perform a performance test on the prepared all-fiber optical isolator, reversely infer the deviation of the writing parameters based on the test results, further optimize the process, and obtain the best curing processing technology.

7. The method for preparing a high-power all-fiber optical isolator according to claim 6, characterized in that: In step S3, the coupling effects under different waveguide angles, different distribution densities, different waveguide shapes, different waveguide thicknesses, and different refractive index variations are simulated to determine the optimal writing parameters.

8. The method for preparing a high-power all-fiber optical isolator according to claim 7, characterized in that: The data of isolation, insertion loss, return loss and withstand power under different parameters are analyzed respectively to determine the optimal writing parameters.

9. The method for preparing a high-power all-fiber optical isolator according to claim 6, characterized in that: In step S5, all-fiber optical isolators are obtained by writing under different actual writing parameters, and performance tests are performed to analyze the effects of different parameters on the performance of the all-fiber optical isolator and determine the optimal processing technology.

10. The method for preparing a high-power all-fiber optical isolator according to claim 9, characterized in that: The actual writing parameters include femtosecond laser wavelength, intensity, spot size and focal depth, movement speed and trajectory, and branch coupler logarithm.

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