Space-time mode locking mode separation device based on symmetric fused biconical taper coupler

Abstract

The invention provides a space-time mode locking mode separation device based on a symmetric fused biconical taper coupler, and belongs to the technical field of laser. The device comprises a space-time mode-locked fiber laser used for generating mixed mode space-time solitons containing an LP01 mode and an LP11 mode; the symmetric fused biconical taper coupler is connected with the output end of the space-time mode-locked fiber laser and is used for separating the mixed mode space-time soliton into an independent LP01 mode and an independent LP11 mode; and the measuring assembly is connected with the output end of the symmetric fused biconical taper coupler and is used for measuring the time domain pulse sequence, the spectral information, the light spot shape and the pulse repetition frequency of the modes before and after separation. According to the invention, information-crosstalk-free accurate separation of a low-order mode (such as an LP01 mode) and a high-order mode (such as an LP11 mode) can be realized, the separation is not limited to a time domain, and effective separation of the two modes can be realized in space, so that the requirements of research on dynamic characteristics in different mode cavities and interaction between the modes are met, and the method has a wide application prospect. And powerful support is provided for the technical development of the space-time mode-locked fiber laser.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler. Background Technology

[0002] In the field of modern laser technology, the development of high-performance light sources is crucial for numerous industries. Spacetime mode-locked fiber lasers, as an advanced light source, occupy a central position in high-dimensional nonlinear physics research and the development of next-generation high-performance lasers due to their unique working mechanism. They fully utilize the spatial degrees of freedom of multimode fibers, successfully overcoming the power and energy bottlenecks of traditional single-mode fiber lasers, and providing an ideal research platform for related fields.

[0003] Multimode fiber transverse modes are a key component of spacetime mode-locked fiber lasers, and their different characteristics directly affect the laser's output performance. Mode separation is a crucial step in deeply exploring the internal characteristics of spacetime mode-locked fiber lasers. Only by achieving precise mode separation can we more effectively study the intracavity dynamics of different modes and the interactions between modes, thereby further promoting the development and application of this technology.

[0004] Currently, there are several technical solutions for mode separation of spatiotemporally mode-locked pulses: 1. Mode conversion device technology: such as mode couplers, long-period fiber gratings, photonic lanterns, etc. This technology can convert low-order modes into high-order mode outputs, and can simultaneously obtain both low-order and high-order modes.

[0005] 2. Spatial sampling technology: By adjusting the size and position of the aperture, information from different regions of the output light spot is sampled, thereby obtaining the relevant characteristics of different transverse mode components.

[0006] 3. Mode stretching technology based on multimode step fiber: It can achieve complete separation of two modes.

[0007] However, the aforementioned prior art has the following significant drawbacks: 1. When mode conversion technology converts a low-order mode to a high-order mode output, the time-frequency domain information of the high-order mode comes from the low-order mode in the original cavity, which will lead to information loss and make it impossible to achieve pure separation between the low-order mode and the high-order mode without information crosstalk.

[0008] 2. Spatial sampling technology can only acquire module information of different transverse mode components, and cannot accurately separate individual modes independently, making it difficult to meet the needs of in-depth research on the characteristics of a single mode.

[0009] 3. Although the mode stretching technique based on multimode step fiber can achieve complete separation of two modes in the time domain, it cannot separate them in the spatial dimension, which is not conducive to in-depth exploration of the spatial characteristics of the modes. Summary of the Invention

[0010] In view of this, and to address the aforementioned shortcomings of the existing technology, the present invention provides a spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler, capable of realizing low-order modes (such as LP modes). 01 (e.g., LP) and higher-order modules (e.g., LP) 11 The system achieves precise separation of modes without crosstalk, and the separation is not limited to the time domain but can also achieve effective separation of two modes in the space, thereby meeting the needs of studying the intracavity dynamics characteristics of different modes and the interaction between modes, and providing strong support for the further development of spatiotemporal mode-locked fiber laser technology.

[0011] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler, comprising: Spacetime mode-locked fiber lasers for generating LP 01 Model and LP 11 Hybrid mode spacetime solitons; A symmetric fused tapered coupler, connected to the output of the spacetime mode-locked fiber laser, is used to separate the hybrid-mode spacetime solitons into independent LPs. 01 Model and LP 11 mold; The measurement component, connected to the output of the symmetrical fused tapered coupler, is used to measure the time-domain pulse sequence, spectral information, spot shape, and pulse repetition frequency of the modes before and after separation.

[0012] The present invention has the following advantages over the prior art: (1) Achieving spatial dimensional pattern separation without crosstalk: Existing technologies either cannot achieve complete spatial separation of a single pattern without crosstalk, or require expensive and bulky spatial equipment, increasing application costs and operational difficulties. This invention utilizes the structural design of a symmetrical fused tapered coupler, taking advantage of LP... 11 The characteristic of the mode leaking first as a cladding mode allows it to couple to the output of another fiber; LP 01 The module is then constrained to the direct output of the fiber core, achieving LP. 01 With LP 11 The mode has independent output in space and no information crosstalk, which meets the needs of studying the characteristics of a single mode.

[0013] (2) Reduced cost and simplified device structure: The present invention uses low-cost optical fiber (such as SMF-28e) to prepare symmetrical fused tapered couplers, replacing the expensive and bulky space equipment in the prior art. This not only reduces the application cost, but also simplifies the device structure and makes operation convenient.

[0014] (3) Supports precise measurement of multi-dimensional characteristics: This invention uses a measurement component consisting of an oscilloscope, a spectrometer, a CCD (charge-coupled device), and an RF spectrum to acquire complete data such as time-domain pulse sequences, spectral information, spot shapes, and pulse repetition frequencies of modes before and after separation, providing comprehensive experimental basis for exploring the intracavity dynamics characteristics of different modes and the interactions between modes.

[0015] (4) Parameter optimization ensures efficient separation: This invention uses Comsol simulation to determine the optimal range of cone diameter (35-100µm) and cone length (mm level), and verifies it experimentally. For example, the separation effect when the cone diameter is 30-40µm ensures LP 11 The mode is fully coupled while the LP 01 The modules are almost uncoupled, enabling precise mode separation.

[0016] (5) Facilitating in-depth research on spatiotemporal mode-locking mechanism: Experimental results show that the pulse intervals of different modes after separation are equal and the repetition frequencies are the same (proving that spatiotemporal mode-locking is achieved); there are differences in the center wavelength of the spectrum (reflecting the nonlinear effects and interactions between modes), providing key experimental data for the study of the internal dynamics of spatiotemporal mode-locked fiber lasers.

[0017] In summary, this invention utilizes a low-cost fiber-based symmetric fused taper coupler as a mode separation device, which not only reduces equipment costs but also simplifies the device structure. This device enables the spatial separation of mixed modes from spatiotemporally mode-locked pulses without crosstalk. Subsequent measurement equipment can accurately acquire information such as the pulse sequence, spectral characteristics, and RF characteristics of individual transverse modes. This technology provides an effective research tool for investigating the differences in intracavity effects experienced by different transverse modes in spatiotemporally mode-locked fiber lasers and the dynamic processes such as interactions between transverse modes. Furthermore, the overall device structure is simple, low-cost, and easy to use, demonstrating broad application prospects. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the working principle of the present invention; Figure 2 This is a schematic diagram of the principle of a symmetrical fused tapered coupler; Figure 3 A schematic diagram for reading the diameter of the cone region using a microscope; Figure 4 This is the effective refractive index variation curve for the mode, where the blue curve represents LP. 01 The red curve represents the LP (Low Potential). 11 The modulus, with the x-axis representing the diameter of the cone region and the y-axis representing the effective refractive index; Figure 5The mode coupling process is when the cone region diameter is 35 μm; Figure 6 This is a schematic diagram of the light spot distribution, where (a) is the mixed light spot before coupling, and (b) is the LP after coupling. 11 Model double-lobed light spot; Figure 7 This is a schematic diagram of a symmetrical fused tapered coupler, where (a) the total output (LP) 01 Model + LP 11 (a) Pulse sequence of mode (b) with inset as light spot; 01 (c) LP pulse sequence, inset as light spot; 11 The pulse sequence of the mode, with the inset showing the light spot; (d) Total output, LP 01 Model and LP 11 (e) Spectrum of the mode; (b) Spectrum of the total output, LP01 mode and LP11 mode. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] Terminology Explanation Spatiotemporally mode-locked fiber lasers are advanced light sources whose core structure includes a pump source, a gain medium (such as multimode doped fiber), and a resonant cavity. Through precise nonlinear dynamic control, the phases of the longitudinal modes (time dimension) and transverse modes (spatial dimension) within the resonant cavity can be locked simultaneously, generating unified spatiotemporal solitons that are ultrashort pulses in time and complex structured optical fields in space. This can overcome the power and energy bottlenecks of traditional single-mode fiber lasers.

[0021] Transverse mode: A stable electromagnetic field mode with a specific transverse field distribution and propagation constant, formed under boundary conditions when light propagates in the core of a multimode optical fiber. Different transverse modes have different propagation constants, and the intensity patterns on the cross-section perpendicular to the propagation direction also differ, such as the low-order mode LP. 01 The mode spot is a Gaussian circle, and the higher-order mode LP 11 The mode light field is distributed in a double-lobed pattern. The modes mentioned in this invention all refer to transverse modes.

[0022] Mode separation: Due to the differences in mode field distribution and propagation constants among different modes within a spacetime mode-locked fiber laser, they experience varying effects from gain, saturable absorption, and filtering within the cavity, ultimately resulting in differences in pulse shape, pulse width, and spectral shape at the output. Precise separation of spacetime mode-locked pulses of different modes using technical means allows for the exploration of the intracavity dynamics of different modes and the interactions between modes.

[0023] Symmetrical fused taper coupler: This coupler uses two identical optical fibers (e.g., SMF-28e fiber, preferably used in this invention) to support LP in the 1.0 band. 01 Model and LP 11 An optical device made by tightly bonding, heating, and stretching two transverse modes (transmission modes). When two optical fibers satisfy the phase-matching condition (equal propagation constants), the two modes will couple, and the optical power can oscillate periodically between the two fibers. When the tapered diameter decreases to a certain extent, higher-order modes (LP modes)... 11 The higher-order mode (LP mode) cannot propagate in the fiber core and transforms into the cladding mode, making coupling easier. With a suitable coupling end length, the higher-order mode can be completely coupled to the output of another fiber, while the lower-order mode (LP mode)... 01 The mode is bound to the fiber core and cannot be coupled, thus achieving mode separation.

[0024] like Figure 1 As shown, the present invention provides a spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler, comprising: Spacetime mode-locked fiber lasers for generating LP 01 Model and LP 11 Hybrid mode spacetime soliton.

[0025] A symmetric fused tapered coupler, connected to the output of the spacetime mode-locked fiber laser, is used to separate the hybrid-mode spacetime solitons into independent LPs. 01 Model and LP 11 mold.

[0026] The measurement component, connected to the output of the symmetrical fused tapered coupler, is used to measure the time-domain pulse sequence, spectral information, spot shape, and pulse repetition frequency of the modes before and after separation.

[0027] This technical solution enables hybrid mode separation and multi-parameter measurement, overcoming three major shortcomings of existing technologies. These shortcomings include crosstalk in mode conversion devices, the inability of spatial sampling techniques to accurately separate individual modes, and the fact that multimode step fibers can only separate modes in the time domain. This solution achieves LP... 01 Model and LP 11The model achieves information-free crosstalk spatial separation, and simultaneously acquires the time-domain pulse sequence, spectrum, spot size, and radio frequency characteristics of the model before and after separation using components such as oscilloscopes and spectrometers, providing complete experimental data for exploring the intracavity dynamics and interactions of the models.

[0028] In this invention, the diameter of the conical region of the symmetrical fused tapered coupler is 30-40 μm, and the length of the conical region is on the order of mm. In this technical solution, this parameter range is the optimal range verified by Comsol simulation. A conical region diameter of 30-40 μm falls within the "LP" range. 11 Model leakage is cladding model, LP 01 The critical range of "the mold is still bound to the fiber core" can be ensured by combining it with a millimeter-level tapered section length. 11 The mode is fully coupled to another fiber, LP 01 The modules are almost uncoupled, enabling efficient and accurate pattern separation.

[0029] In this invention, the core function of the symmetric fused tapered coupler is to separate the mixed-mode spacetime soliton containing LP01 and LP11 modes into individual LP modes. 01 Model and LP 11 Model, LP 01 The LP mode is one of the intrinsic modes of a two-mode fiber, and its light spot exhibits a Gaussian circular shape; 11 This mode is also one of the intrinsic modes of two-mode fiber, similar to LP. 01 Depending on the model, the light spot will appear as a double-lobed pattern. A schematic diagram of its principle is shown below. Figure 2 As shown.

[0030] In this invention, the method for manufacturing the symmetrical fused tapered coupler is as follows: Step (1): Select two identical two-mode optical fibers, strip the coating layer between the two fibers, and then bond them tightly together at both ends. Specifically: In step (1), two identical two-mode optical fibers are selected. A 2-3 cm long coating layer is stripped from the middle section and cleaned with alcohol. The two fibers are then tightly bonded together, and UV glue is used to bond both ends of the fibers. This ensures that the two fibers remain tightly parallel and bonded during the tapering process, guaranteeing efficient mode coupling. In this technique, the 2-3 cm coating layer removal length balances the fiber bonding area and mechanical strength; UV glue bonding ensures that the fibers remain tightly parallel during the tapering process, enhancing mode coupling efficiency and preventing a decrease in separation effect due to fiber misalignment.

[0031] Step (2): After heating and melting, stretch the material and then seal it with a glass slide for preservation. Specifically: The bonded optical fibers were heated using a heat source until they reached a molten state, then stretched in both directions to create a symmetrical fused tapered coupler. The tapering process was performed using a laboratory manual displacement platform with an alcohol lamp. The tapered fibers were then encapsulated and stored on glass slides to prevent damage that could affect performance.

[0032] Step (3): Measure the diameter and length of the cone region. Specifically: After tapering, the diameter (the diameter of the thinner portion of the fiber after fused tapering) and length (the length of the thinner portion of the fiber after fused tapering) of the tapered region are measured using a microscope and a ruler, respectively. A schematic diagram of reading the tapered region diameter under the microscope is shown below. Figure 3 As shown in the figure, the sum of the diameters of the two coupled optical fibers is 60.1 μm, meaning the diameter of a single optical fiber is approximately 30 μm. Under specific taper diameter and taper length conditions, this coupler can achieve LP (Liquidity Limiting)... 01 The mode is coupled to the lower fiber and output from the coupling end, while the LP... 01 The modes exhibit almost no coupling, outputting from the through-hole, thus achieving mode separation. This technique precisely acquires key parameters of the cone region to ensure the coupler conforms to "LP". 11 Mode coupling, LP 01 The design requirement of "mode decoupling" improves the accuracy of mode separation and provides a replicable quality standard for mass production.

[0033] In this technical solution, a standardized manufacturing process ensures that the two optical fibers are tightly and parallelly bonded, avoiding structural displacement during the tapering process; glass slide encapsulation prevents damage to the optical fibers, ensuring the stability and reliable performance of the coupler structure; and measuring the tapered region parameters provides a quality control basis for the mode separation effect.

[0034] In this invention, the symmetrical fused tapered coupler is made of two identical SMF-28e optical fibers, supporting LP in the 1.0 band. 01 and LP 11 Mode-to-mode transmission. In this technical solution, two optical fibers of identical type naturally satisfy the phase-matching condition (equal propagation constants for the same mode), promoting LP (Limited-mode) transmission. 11 The efficient coupling of modes provides a physical basis for mode separation; the 1.0 band is compatible with the operating wavelength of the spatiotemporally mode-locked laser, ensuring signal transmission compatibility.

[0035] In this invention, LP 01 The light spot of the model appears as a Gaussian circle, LP 11 The light spot of the mode appears as a double-lobed pattern. In this technical solution, the type of the separated mode can be intuitively distinguished by the shape of the light spot, and the mode separation effect can be quickly verified; it provides intuitive image evidence for studying the spatial characteristics of different modes and helps to analyze the interaction between modes.

[0036] In this invention, the spatiotemporal mode-locked fiber laser includes a pump source, a beam combiner, a gain fiber, a saturable absorber, a two-mode passive fiber, a polarization controller, and a filter. The polarization controller is used to regulate the operating state of the laser. By adjusting its parameters, the laser can output pulses with different characteristics. Specifically: The function of a polarization controller is to regulate the operating state of the laser. By adjusting its parameters, the laser can output pulses with different characteristics, such as single pulse, double pulse, dual-wavelength, and pulsating pulses. Because two-mode passive optical fibers can accommodate LP... 01 Model and LP 11 The laser has two modes, therefore the output of this laser is from the LP mode. 01 Patterns and LPs 11 The mixed light spot formed by the superposition of modes contains light field information from both modes.

[0037] In this technical solution, the polarization controller can flexibly output pulses with various characteristics such as single pulse, double pulse, and dual wavelength, adapting to different separation scenarios, enriching the parameter range of experimental research, and improving the versatility of the device.

[0038] In this invention, the symmetrical fused tapered coupler achieves mode separation in the following manner: LP 11 As the diameter of the memetic cone region decreases, it leaks first into the cladding mode, which couples to another fiber for output. LP 01 The module is confined within the fiber core and output from the through end, achieving separation without information crosstalk.

[0039] This technical solution utilizes the differences in leakage characteristics between the two modes to achieve precise separation without information crosstalk, avoiding information loss caused by mode switching in existing technologies, and ensuring the complete preservation of the temporal, spectral, and spatial characteristics of a single mode.

[0040] In this invention, the measuring component includes: An oscilloscope is used to measure the time-domain pulse sequence before and after mode separation. Specifically, the oscilloscope is mainly used to measure the mixed-mode LP before separation. 01 +LP 11 Model and LP after separation 01 Model and LP 11 The time-domain pulse sequence of the mode. By displaying the pulse sequence waveform on an oscilloscope, the type of pulse output by the laser can be determined, such as whether it is a single pulse, a double pulse, or a pulsating characteristic, providing a basis for analyzing the time-domain characteristics of different modes.

[0041] A spectrometer is used to measure the spectral information of the modes before and after separation. Specifically, the spectrometer is used to measure the LP mixing mode before separation.01 +LP 11 Model and LP after separation 01 Model and LP 11 Spectral information of the mode. Based on the spectrum obtained by the spectrometer, it can be determined whether the output pulse is single-wavelength, dual-wavelength, or whether there is a four-wave mixing phenomenon, which helps to understand the optical processes and characteristic changes of different modes in the cavity.

[0042] Charge-coupled devices (CCDs) are used to measure the spot shape of the mixed modes before and after separation. Specifically, the function of a CCD is to measure the mixed mode LP before separation. 01 +LP 11 Model and LP after separation 01 Model and LP 11 The transverse electromagnetic field distribution of the mode, i.e., the shape of the light spot. The light spot image captured by CCD can intuitively determine the mode components contained in the pulse, providing intuitive image data for verifying the mode separation effect and studying the mode characteristics.

[0043] The emission spectrum is used to measure the pulse repetition frequency of the modes before and after separation. Specifically, it refers to a charge-coupled device (CCD) that measures the LP of the mixed mode before separation. 01 +LP 11 Model and LP after separation 01 Model and LP 11 The transverse electromagnetic field distribution of the mode, i.e., the shape of the light spot. The light spot image captured by CCD can intuitively determine the mode components contained in the pulse, providing intuitive image data for verifying the mode separation effect and studying the mode characteristics.

[0044] In this technical solution, the time-domain pulse sequence (oscilloscope), spectral information (spectrometer), spot shape (CCD), and pulse repetition frequency (radio spectrum) of the mode before and after separation are measured in multiple dimensions to comprehensively acquire mode characteristic data and provide multi-dimensional support for in-depth analysis of mode cavity dynamics and interactions.

[0045] like Figure 1 As shown, the working principle of this invention is as follows: A spacetime soliton is generated by a spacetime mode-locked fiber laser. This invention employs a two-mode fiber laser containing LP01 and LP11 modes, resulting in an output spacetime soliton with a mixed beam pattern, i.e., LP01 + LP11 modes. This mixed-mode spacetime soliton is transmitted to a self-made symmetric fused tapered coupler, where mode separation is achieved, separating the soliton into LP11 modes. 01 Model and LP 11 mold.

[0046] LP before separation 01 +LP 11 Model and separated LP01 Model, LP 11 The modes are connected to an oscilloscope, spectrometer, CCD, and RF spectrometer respectively, and the pulse sequence, spectrum, spot size, and repetition frequency before and after separation are measured to obtain the characteristic parameters of different modes.

[0047] The following section verifies and explains in detail the principle of mode separation achieved by the symmetrical fused tapered coupler of this invention, using specific experimental procedures.

[0048] (1) Coupled Mode Theory Ideally, the intrinsic modes propagating in an optical fiber are orthogonal to each other, and mode coupling does not occur. However, when a perturbation is introduced or the transverse refractive index distribution of the fiber changes, mode coupling will occur between two modes that satisfy phase matching (equal propagation constants β), resulting in energy exchange. In a symmetrical biconical coupler, the other fiber can be considered as perturbing the transverse refractive index distribution of the first fiber; therefore, two modes that satisfy the phase matching condition will couple. Since the two optical fibers used in this invention are exactly the same type (SMF-28e fiber, supporting LP in the 1.0 band)... 01 and LP 11 (Mode transmission), LP of two optical fibers 01 The propagation constants of the modes are naturally equal, satisfying the phase matching condition, LP 11 The same principle applies to modes. When the same mode in two optical fibers meets the phase matching condition, coupling will occur, and the energy will flow in a cosine manner. By controlling the length of the cone region, the energy can be completely transferred to the other optical fiber and output.

[0049] In the process of implementing schema separation, it is necessary to ensure LP 11 The mode is coupled to another fiber, while the LP 01 Mode coupling is almost nonexistent. As the fiber diameter decreases, LP... 11 The first mode to fail to meet the propagation conditions of the fiber core will escape its constraints and become the cladding mode. Cladding modes exist in the outer layer of the fiber and are more likely to interact with the LP (Laminated Propagation Mode) of another fiber. 11 Mode coupling and energy exchange occur; while LP 01 The mode is confined within the fiber core, making it difficult to interact with the LP of another fiber. 01 Mode coupling and energy exchange are generated, thereby achieving mode separation.

[0050] (2) Simulation parameter calculation To determine the cone diameter and cone length parameters required for pattern separation, calculations were performed using Comsol simulation software. Figure 4 For LP 01 Model and LP 11 The refractive index variation curves of the model under different cone diameters.

[0051] As can be seen from the figure, LP 11 When the diameter of the cone region is less than 100 μm, the mode will leak into the cladding for transmission, LP 01 When the module diameter is below 35µm in the cone region, some leakage will occur into the cladding for transmission. To enable LP... 11 To achieve optimal coupling between the LP01 and LP01 modes while preventing coupling, the cone diameter needs to be controlled between 35µm and 100µm. However, even if the fiber diameter is slightly less than 35µm, LP... 11 The coupling length of the mode is also much smaller than that of the LP. 01 Therefore, controlling the cone length can also ensure LP. 11 Mode coupling and LP 01 The modes do not couple, thus achieving mode separation.

[0052] The coupling lengths (the fiber length required for energy to flow completely from fiber 1 to fiber 2) corresponding to different cone diameters were calculated, and the specific data are shown in Table 1. Table 1. LP under different waist diameters 01 Model and LP 11 Mode coupling length

[0053] The data in the table shows that the smaller the cone diameter, the shorter the coupling length; that is, the shorter the cone length needed to ensure complete energy flow. Furthermore, the cone diameter LP... 11 The coupling length of the mode is on the order of mm, while the LP 01 The coupling length of the module is on the order of centimeters. Therefore, when the cone region length is controlled on the order of millimeters, LP can be guaranteed. 01 The modules are almost uncoupled, thus achieving mode separation.

[0054] (3) Simulation verification The mode separation scheme of this invention was verified using Rsoft software, and the simulation results are as follows: Figure 5 , Figure 6 As shown.

[0055] In the diagram, the red and cyan lines represent the LPs of the right and left optical fibers, respectively. 11 The modulus content is represented by the blue and green lines, which represent the LP of the right and left optical fibers, respectively. 01 Mode content. With a single fiber taper diameter of 35 μm, as light propagates (z increases), it can be observed that at a propagation distance z of approximately 3700 μm (corresponding to Table 1), the LP11 mode completely transfers from the right fiber to the left fiber output, while the LP01 mode is almost not coupled to the left fiber. The slight oscillations in the curve are due to the conversion between the core mode and the cladding mode. From... Figure 6The light spot pattern also shows that before coupling began, the right fiber contained both LP01 and LP11 modes simultaneously. When the light propagated 3700µm in the conical region, the LP... 11 The mode is fully coupled to the left fiber, therefore the output spot of the left fiber exhibits a double-lobed structure, indicating that the output is LP. 11 The mode, while the right fiber LP 01 The inability of modes to couple results in a Gaussian circular output beam, indicating that the output is LP. 01 The model further verifies the feasibility of the model separation scheme of the present invention.

[0056] (4) Experimental results and analysis Through experimental measurements, the mixed modes of the spatiotemporally mode-locked fiber laser output and the individual LP modes after mode separation were obtained. 01 Model and LP 11 The pulse characteristics, spectral characteristics, spot size, and radio frequency characteristics of the mode are shown in the experimental results. Figure 7 As shown.

[0057] Because the two-mode fiber laser used in this experiment contains LP... 11 With fewer modes, the overall output beam shape closely resembles the fundamental mode; however, the two modes were still separated experimentally. Experimental results show that the pulse intervals of the pulse sequences for different modes are equal, and the repetition frequencies displayed in the RF spectra are also the same. This demonstrates that the different modes achieved simultaneous locking, i.e., spatiotemporal mode locking. Regarding spectral characteristics, the center wavelengths of the spectra of different modes differ, and also differ from the center wavelength of the overall spectrum after mixing and superposition. This indicates that the nonlinear effects and filtering effects experienced by different modes within the cavity vary, and there may also be interactions between modes. This provides experimental evidence for further research into the internal dynamics of spatiotemporally mode-locked fiber lasers.

[0058] In summary, this invention designs a unique experimental scheme for spatiotemporal mode-locked pulse mode separation based on a symmetrical fused tapered coupler, and successfully implements the scheme, including the overall structural design of the device, the selection and connection of each component, and the specific experimental operation procedures.

[0059] The principle of spatiotemporal mode-locking separation using a symmetrical fused tapered coupler was thoroughly studied and elucidated, including analysis based on coupled-mode theory, correction of coupled-mode equations considering ultrashort pulse characteristics, and verification of the principle through simulation and experiments, providing a solid theoretical foundation for mode separation technology.

[0060] Key parameters for achieving efficient mode separation were determined, such as the cone diameter (30um-40um) and cone length (mm level) of the symmetrical melt tapered coupler. Optimization of these parameters is an important guarantee for achieving accurate separation of low-order and high-order modes.

[0061] The above description is merely a preferred embodiment of the present invention. However, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention should be covered within the scope of protection of the present invention.

Claims

1. A spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler, characterized in that, include: Spacetime mode-locked fiber lasers for generating LP 01 Model and LP 11 Hybrid mode spacetime solitons; A symmetric fused tapered coupler, connected to the output of the spacetime mode-locked fiber laser, is used to separate the hybrid-mode spacetime solitons into independent LPs. 01 Model and LP 11 mold; The measurement component, connected to the output of the symmetrical fused tapered coupler, is used to measure the time-domain pulse sequence, spectral information, spot shape, and pulse repetition frequency of the modes before and after separation.

2. The spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler according to claim 1, characterized in that, The diameter of the cone region of the symmetrical fused tapered coupler is 30um-40um, and the length of the cone region is on the order of mm.

3. The spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler according to claim 1, characterized in that, The method for manufacturing the symmetrical fused tapered coupler is as follows: Step (1): Select two identical two-mode optical fibers, strip the coating layer between the two fibers, and then bond them tightly together and secure the ends with adhesive. Step (2): After heating and melting, stretch the material and seal it with a glass slide for preservation. Step (3): Measure the diameter and length of the cone area.

4. The spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler according to claim 3, characterized in that, In step (1), a 2-3 cm long coating layer is stripped from the middle part of the two optical fibers, and UV glue is used to bond the two ends of the optical fibers together.

5. The spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler according to claim 3, characterized in that, In step (3), the diameter and length of the cone area are measured using a microscope and a ruler, respectively.

6. The spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler according to claim 3, characterized in that, The symmetrical fused tapered coupler is made of two identical SMF-28e optical fibers and supports LP in the 1.0 band. 01 Model and LP 11 Modular transmission.

7. The spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler according to claim 1, characterized in that, LP 01 The light spot of the model appears as a Gaussian circle, LP 11 The light spot of the model appears as a double-lobed pattern.

8. The spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler according to claim 1, characterized in that, The spatiotemporal mode-locked fiber laser includes a pump source, a beam combiner, a gain fiber, a saturable absorber, a two-mode passive fiber, a polarization controller, and a filter. The polarization controller is used to adjust the working state of the laser. By adjusting its parameters, the laser can output pulses with different characteristics.

9. The spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler according to claim 1, characterized in that, The symmetrical fused tapered coupler achieves mode separation in the following manner: LP 11 As the diameter of the memetic cone region decreases, it leaks first into the cladding mode, which couples to another fiber for output. LP 01 The module is confined within the fiber core and output from the through end, achieving separation without information crosstalk.

10. A spatiotemporal mode-locking separation device based on a symmetrical fused tapered coupler according to any one of claims 1-9, characterized in that, The measurement component includes: An oscilloscope is used to measure time-domain pulse sequences before and after pattern separation. A spectrometer is used to measure the spectral information of the modes before and after separation. Charge-coupled device (CCD) used to measure the spot shape before and after mode separation; Radio frequency spectrum, used to measure the pulse repetition frequency of modes before and after separation.

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