STED Dual-Beam Generator Based on Single-Mode Fiber and Its Preparation Method

Abstract

An embodiment of the present application relates to a STED dual-beam generator based on a single-mode optical fiber and a preparation method thereof. The generator includes: a single-mode optical fiber including a core; a dual light source arranged on one side of a first end face of the core and capable of emitting dual beams with different wavelengths to be input into the core through the first end face; and a three-dimensional microstructure integrated on a second end face of the core coaxially with the core, and the size of the three-dimensional microstructure is designed to be associated with the wavelengths of the beams emitted by the dual light source, so that the dual beams can form STED dual beams after passing through the core and the three-dimensional microstructure; the three-dimensional microstructure includes a plurality of cylindrical stepped portions stacked along the axial direction of the core, the axes of the stepped portions coincide and have radii gradually decreasing in a direction away from the second end face, and adjacent stepped portions have the same height. The generator avoids additional design of the fiber core layer or the refractive index of the optical fiber, greatly reduces the difficulty and cost of overall preparation, and has better overall structural stability.

Description

Technical Field

[0001] This application relates to the field of STED dual-beams, and more specifically, to a STED dual-beam generator based on a single-mode fiber and a method for preparing the same. Background Art

[0002] Generally speaking, a STED dual-beam includes two focused beams with different wavelengths, namely a laser beam and a STED beam, corresponding to a circular spot distribution and a hollow "doughnut" distribution respectively. It is a super-resolution technology that breaks through the diffraction limit and thus becomes one of the important technologies in super-resolution fields such as super-resolution processing and super-resolution imaging. The key to this technology lies in preparing a STED beam with the property of a vector beam.

[0003] As an excellent optical transmission medium, an optical fiber can support the transmission of a cylindrical vector beam, and the light intensity distribution of its propagation cross-section has a circular dark area in the middle. The STED beam generated based on an optical fiber waveguide has been proven to be able to improve the resolution of tip-scanning imaging, nonlinear imaging, stimulated emission depletion (STED) microscopy, super-oscillation imaging, etc. Currently, the technical solutions for generating a STED beam based on an optical fiber waveguide are mainly divided into two categories: functional optical fibers based on additional structural designs and special optical fibers based on the design of the optical fiber itself. In the former solution, the simplest way is to use chemical etching means to prepare a tapered structure with an inward or outward taper angle at the end face of the optical fiber to achieve a single STED beam. However, there are problems such as poor preparation accuracy and high risk of the etching solution when preparing microstructures by this method, and there is no structural matching design for the dual-beam. With the rapid development of the preparation process, methods for achieving a single STED beam by preparing complex structures such as long-period gratings, spiral phase plates, fork-shaped gratings, and superlenses on the optical fiber waveguide have emerged one after another. However, only the long-period grating structure and the superlens structure can achieve a STED dual-beam in an optical fiber. All of the above methods involve complex structural designs and structural processing, resulting in high overall preparation difficulty, high cost, and low efficiency. In the latter solution, to achieve a STED dual-beam based on an optical fiber, there is a reported method of preparing a coupler by coupling a few-mode fiber and a multi-mode fiber. Although the overall structure of this method is simple, there are problems such as high requirements for coupling control, poor overall structural stability, and unstable waveguide modes. There is also a reported work on developing a special optical fiber with a double-clad double-step refractive index distribution to achieve a STED dual-beam in an optical fiber through the coupling method of spatial core misalignment of the optical fiber. This method has problems such as poor overall structural stability, high difficulty and high requirements for preparing special optical fibers, high requirements for misalignment coupling alignment accuracy, and large spatial volume.

[0004] As a common commercial waveguide, the single-mode fiber is also the waveguide carrier that is most easily compatible with the fiber optic system. It has the characteristics of low fundamental mode transmission loss, stable waveguide mode, and easy integration. This makes it an option to integrate microstructures on its end face to achieve STED double beams. Therefore, researching a STED double-beam generator based on single-mode fiber with a simple structure, low preparation difficulty, and excellent beam quality, as well as its preparation method, has important value and significance for the application and development in the field of super-resolution technology. Summary of the Invention

[0005] To solve the above problems, the present application provides an all-fiber STED double-beam generator based on single-mode fiber and its preparation method. An axisymmetric three-dimensional microstructure is integrated at the center of the core on the end face of the single-mode fiber. The three-dimensional dimensions of this microstructure are all at the micro-nano level, which plays a diffraction role to change the phase of the output beam. Therefore, adjusting the microstructure size can achieve the regulation of the optical characteristics of the output beam. At the same time, its structure is simple, the preparation difficulty and cost are low, and the overall structural stability is relatively good.

[0006] In the first aspect of the present application, the present application provides a STED double-beam generator based on single-mode fiber, including: the single-mode fiber, which includes a core; a dual light source, which is arranged on one side of the first end face of the core and is configured to be able to emit double beams with different wavelengths and input the double beams into the core through the first end face; and a three-dimensional microstructure, which is integrated on the second end face of the core in a coaxial manner with the core. The first end face is opposite to the second end face, and the size of the three-dimensional microstructure is designed to be associated with the wavelengths of the beams emitted by the dual light source, so that after the double beams pass through the core and the three-dimensional microstructure, the STED double beams can be formed; wherein, the three-dimensional microstructure includes a plurality of cylindrical stepped portions stacked along the axial direction of the core. The axes of the plurality of cylindrical stepped portions coincide and have radii that gradually decrease along the direction away from the second end face, and adjacent cylindrical stepped portions have the same height.

[0007] In the second solution of the present application, the present application further provides a preparation method of the STED dual-beam generator based on a single-mode optical fiber in the first solution, including the following steps: providing the single-mode optical fiber including a core; arranging a dual light source on one side of the first end face of the core, the dual light source being configured to be capable of emitting dual beams with different wavelengths and inputting the dual beams into the core through the first end face; and integrating a three-dimensional microstructure coaxially with the core on the second end face of the core, wherein the first end face is opposite to the second end face, and the size of the three-dimensional microstructure is designed to be associated with the wavelengths of the beams emitted by the dual light source, so that after the dual beams pass through the core and the three-dimensional microstructure, the STED dual beams can be formed; wherein the three-dimensional microstructure includes a plurality of cylindrical stepped portions stacked along the axial direction of the core, the axes of the plurality of cylindrical stepped portions coincide and have radii gradually decreasing in a direction away from the second end face, and adjacent cylindrical stepped portions have the same height.

[0008] Compared with the prior art, the STED dual-beam generator provided by the present application has the following remarkable advantages:

[0009] 1) The present application uses a common commercial single-mode optical fiber, avoiding the complex design of the optical fiber integration structure or the additional design of the optical fiber refractive index, greatly reducing the overall preparation difficulty and cost, and taking into account the characteristics of low loss and stable mode transmission;

[0010] 2) The overall structure of the single-mode optical fiber end face microstructure designed in the present application is simple, reducing the design difficulty and preparation difficulty of the overall structure;

[0011] 3) The microstructure size designed in the present application is flexibly controllable and has many optimizable parameters, which is beneficial to preparing STED dual beams with excellent beam performance;

[0012] 4) The present application realizes the STED dual beams with two wavelengths based on the combination of a single-mode optical fiber and end face integration, which is a full-fiber structure, easy to be compatible with an optical fiber communication system, small in volume and light in weight, and is conducive to high integration and commercialization. Description of the Drawings

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present application. At an appropriate time, the same reference numerals will be used throughout all the drawings to refer to the same or similar parts. Such embodiments are illustrative and are not intended to be an exhaustive or exclusive embodiment of the present device or method. In the drawings:

[0014] Figure 1Schematic diagram of the structure of a STED dual-beam generator based on a single-mode optical fiber according to an embodiment of the present application;

[0015] Figure 2 and Figure 3 Schematic side view and top view of the structure of the dual-beam generating component in the STED dual-beam generator according to an embodiment of the present application, respectively;

[0016] Figure 4 is Figure 2 and Figure 3 Schematic side view of the structure of the three-dimensional microstructure in the STED dual-beam generator in

[0017] Figure 5 Schematic side view of the structure of the dual-beam generating component in the STED dual-beam generator according to another embodiment of the present application;

[0018] Figure 6 and Figure 7 Schematic flowchart of a method for preparing a STED dual-beam generator according to an embodiment of the present application;

[0019] Figures 8a - 8c Theoretical transverse optical field distribution diagrams and theoretical one-dimensional light intensity distributions of the "doughnut" shape distribution and solid circular spot distribution generated by simulation calculation according to an embodiment of the present application, respectively;

[0020] Figures 9a - 9c Schematic diagrams of the solid circular spot distribution, "doughnut" shape distribution, and STED dual-beam distribution generated according to an embodiment of the present application, respectively;

[0021] Figures 10a - 10c Actual transverse optical field distribution diagrams and actual one-dimensional light intensity distributions of the "doughnut" shape distribution and solid circular spot distribution generated in the experiment according to an embodiment of the present application, respectively. Detailed implementation manners

[0022] In order to make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present application without creative efforts shall fall within the scope of protection of the present application.

[0023] Unless otherwise defined, technical terms or scientific terms used in this application shall have the ordinary meanings as understood by those of ordinary skill in the art to which this application pertains. The terms "first", "second" and similar words used in this application do not denote any order, quantity or importance, but are only used to distinguish different components. Words such as "comprising" or "including" mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects. Words such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Upper", "lower", "left", "right", etc. are only used to indicate relative positional relationships, and when the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0024] To keep the following description of the embodiments of this application clear and concise, detailed descriptions of known functions and known components are omitted in this application.

[0025] Figure 1 The schematic diagram of the structure of the STED dual-beam generator 100 based on a single-mode optical fiber provided by this application is shown. As Figure 1 shown, the STED dual-beam generator 100 may at least include a dual light source 110 and an STED dual-beam generating component 120. Specifically, the dual light source 110 is arranged on one side of the first end face of the fiber core 130, and it may include a first light source 110A that emits a first input beam with a first wavelength and a second light source 110B that emits a second input beam with a second wavelength. The STED dual-beam generating component 120 may include the fiber core 130 (for simplicity, the fiber core 130 is only used to represent the single-mode optical fiber in the text) and a three-dimensional microstructure 140 integrated on the second end face of the fiber core 130. In this configuration, along Figure 1 the dotted line in, the dual light source 110 emits the first input beam and the second input beam. After the two are coupled, the dual beam formed after coupling, after passing through the fiber core 130 and the three-dimensional microstructure 140 in sequence, obtains an STED dual beam on the beam output side of the three-dimensional microstructure 140.

[0026] As Figure 2 and Figure 3 shown, the side view and top view of the detailed structure of the STED dual-beam generating component 120 according to an embodiment are shown.

[0027] Combined with Figure 1 and Figure 2It can be seen that in the STED dual-beam generating component 120, the three-dimensional microstructure 140 is integrated on the second end face of the core 130 in a coaxial manner with the core 130 (i.e., the axes of the two coincide), where the first end face and the second end face are the two opposite end faces of the core 130. In Figure 1 , for example, the first end face of the core 130 is defined as the top end face, and the second end face is defined as the bottom end face. As Figure 2 shown, the three-dimensional microstructure 140 includes a plurality of cylindrical stepped portions 141 stacked along the axial direction of the core 130. The axes of these cylindrical stepped portions 141 coincide with each other and the axis coincides with the axis of the core 130, and these cylindrical stepped portions 141 have radii that gradually decrease in the direction away from the second end face, as Figure 2 and Figure 3 shown. Through the above arrangement, when observed from the side view direction, the three-dimensional microstructure 140 has a conical-like shape.

[0028] With the STED dual-beam generator 100 constructed as above, the setting of the three-dimensional microstructure 140 forms a plurality of steps along the optical path direction, which can diffract the input dual-beam and change the phase of the output beam. Therefore, by adjusting the microstructure size, optical specific control of the output beam can be achieved, and the optimal STED dual-beam (i.e., excellent beam quality) can be obtained.

[0029] In the above structure, the size of the three-dimensional microstructure 140 needs to be designed to be associated with the wavelength of the beam emitted by the dual light source 110, so that after the dual-beam passes through the core 130 and the three-dimensional microstructure 140, an STED dual-beam can be formed. As Figure 4 shown, the size parameters of the three-dimensional microstructure 140 may include the overall height H, the radius of the largest cylindrical stepped portion (i.e., the radius of the cylindrical stepped portion 141 closest to the core 130) r (which preferably does not exceed the radius of the core 130), the radius difference dr between adjacent cylindrical stepped portions 141, and the height h of each cylindrical stepped portion 141. The matching between these parameters enables a better STED dual-beam distribution to be obtained.

[0030] To reduce the calculation amount and the difficulty of device preparation, in a preferred embodiment, it can be stipulated that the radius difference dr between adjacent cylindrical stepped portions 141 is a fixed value (i.e., equal), and each cylindrical stepped portion 141 has the same height h. In this embodiment, generally, in order to enable the first input beam and the second input beam incident from the first end face of the core 130 to obtain an STED dual-beam after passing through the STED dual-beam generating component 120, the size (shape) of the three-dimensional microstructure 140 needs to satisfy the following formula:

[0031]

[0032] Wherein, H is the overall height of the three-dimensional microstructure 140, r is the radius of the largest cylindrical step portion, dr is the radius difference, and h is the height of the cylindrical step portion 141.

[0033] In addition, in order to obtain the desired STED dual beam, the three-dimensional microstructure 140 should have a refractive index close to or equal to that of the core 130. Preferably, the three-dimensional microstructure 140 is made of the same material as the core 130, such as silica.

[0034] In one embodiment, the three-dimensional microstructure 140 is a separate component separated from the core 130 formed by stacking a plurality of individual cylinders (i.e., cylindrical step portions 141), and is attached to the second end face of the core 130, such as Figure 2 and Figure 4 shown.

[0035] In another embodiment, the three-dimensional microstructure 140 can be formed on the second end face of the core 130 by processes such as focused ion beam process, electron beam lithography process, two-photon polymerization process or 3D printing process, so that the three-dimensional microstructure 140 and the core 130 are of an integral structure, such as Figure 5 shown. By this processing method, it is possible to avoid the adverse effect on the distribution effect of the finally obtained STED dual beam caused by the installation error between the two, and improve the preparation efficiency and reduce the preparation difficulty.

[0036] Next, the process of the preparation method 200 of the STED dual beam generator 100 according to the present application will be described in conjunction with Figures 6 - 7 As shown, the preparation method 200 includes:

[0037] As Figure 6 shown, the preparation method 200 includes:

[0038] S210, providing a single-mode optical fiber including the core 130;

[0039] S220, arranging a dual light source 110 on one side of the first end face of the core 130, and the dual light source 110 is configured to be able to emit dual beams with different wavelengths and input them into the core 130 through the first end face; and

[0040] S230, integrating a three-dimensional microstructure 140 coaxially with the core 130 on the second end face of the core 130, wherein the first end face is opposite to the second end face, and the size of the three-dimensional microstructure 140 is designed to be associated with the wavelength of the beam emitted by the dual light source 110, so that after the dual beam passes through the core 130 and the three-dimensional microstructure 140, the STED dual beam can be formed.

[0041] In S210, the provided single-mode optical fiber can be a common commercial optical fiber, having a single-mode bandwidth of hundreds of nanometers, a core radius R (as Figure 2 shown) and a certain refractive index.

[0042] Specifically, as Figure 7 shown, S230 may include the following steps S231 - S233.

[0043] S231, determine, within the bandwidth of the single-mode optical fiber, a first wavelength and a second wavelength corresponding to the desired STED dual-beam, where the first wavelength and the second wavelength respectively correspond to the first light source 110A and the second light source 110B that constitute the dual light source 110.

[0044] S232, through physical simulation, determine, when the first input beam with the first wavelength passes through the core 130 and the three-dimensional microstructure 140 and forms a first output beam with a "doughnut"-shaped distribution in the propagation cross-section, the multiple size combinations of the three-dimensional microstructure 140 corresponding thereto.

[0045] S233, continue through physical simulation, from the multiple size combinations, determine, when the second input beam with the second wavelength passes through the core 130 and the three-dimensional microstructure 140 and forms a second output beam with a distribution having a solid circular spot at the positive center in the propagation cross-section, one or more sizes of the three-dimensional microstructure 140 corresponding thereto as the target sizes.

[0046] As mentioned above, the size of the three-dimensional microstructure 140 should be associated with the wavelengths of the beams emitted by the dual light source 110, so the formed dual-beam is specific to the dual light source 110. Therefore, for a specific single-mode optical fiber and dual light source, it is necessary to customize the size of the three-dimensional microstructure 140 based on the parameters of the provided single-mode optical fiber and dual light source.

[0047] Specifically, the wavelength of the first input beam emitted by the first light source 110A is the first wavelength, and the wavelength of the second input beam emitted by the second light source 120A is the second wavelength. The first wavelength and the second wavelength are different in size and are within the bandwidth of the provided single-mode optical fiber. Therefore, before preparing the STED dual-beam generator 100, it is necessary to first determine, within the bandwidth of the provided single-mode optical fiber, the first wavelength and the second wavelength corresponding to the first input beam and the second input beam respectively, for outputting the first output beam and the second output beam in the STED dual-beam respectively, where the propagation cross-section of the first output beam has a "doughnut"-shaped distribution, and the propagation cross-section of the second output beam has a distribution with a solid circular spot at the positive center. The combination of the two forms the STED dual-beam.

[0048] In this embodiment, for the selected first wavelength and second wavelength, a first output beam with a "doughnut" - shaped distribution is obtained through a first input beam with the first wavelength, and then a second output beam with a distribution having a solid circular spot at the positive center is obtained through a second input beam with the second wavelength to determine the target size of the three - dimensional microstructure 140. Since there may be more than one size of the three - dimensional microstructure 140 that can produce a better dual - beam distribution effect, optionally, any one of one or more matching sizes of the three - dimensional microstructure 140 can be used as the target size to fabricate the STED dual - beam generator 100. Most preferably, the size of the three - dimensional microstructure 140 with the optimal distribution effect can be selected from multiple matching sizes as the target size to fabricate the STED dual - beam generator 100.

[0049] Here, since the beam with a "doughnut" - shaped distribution is relatively sensitive to the change of the device size, the range of the size combination of the three - dimensional microstructure 140 is efficiently narrowed by first obtaining a first output beam with a "doughnut" - shaped distribution in the propagation cross - section, and then the target size is determined by obtaining a second output beam with a distribution having a solid circular spot at the positive center in the propagation cross - section. In this way, the fabrication difficulty can be reduced and the efficiency can be improved. However, the present invention is not limited to this. Alternatively, the range of the size combination of the three - dimensional microstructure 140 can be first narrowed by obtaining a second output beam with a distribution having a solid circular spot at the positive center in the propagation cross - section, and then the target size is determined by obtaining a first output beam with a "doughnut" - shaped distribution in the propagation cross - section.

[0050] It should be understood that in the present application, the first wavelength can be specified to be greater than the second wavelength, for example. In one embodiment, a first output beam with a "doughnut" - shaped distribution in the propagation cross - section can be obtained through a first input beam with the first wavelength (long - wave wavelength), and a second output beam with a distribution having a solid circular spot at the positive center in the propagation cross - section can be obtained through a second input beam with the second wavelength (short - wave wavelength). However, the present invention is not limited to this. Alternatively, a first output beam with a "doughnut" - shaped distribution in the propagation cross - section can be obtained through a second input beam with the second wavelength (short - wave wavelength), and a second output beam with a distribution having a solid circular spot at the positive center in the propagation cross - section can be obtained through a first input beam with the first wavelength (long - wave wavelength).

[0051] Return Figure 1 In the STED dual - beam generator 100 provided in the present application, a wavelength - division multiplexing optical fiber 150 can also be included, which is arranged between the dual - light source 110 and the first end face of the core 130 to couple the first input beam and the second input beam, and input the coupled dual - beam into the core 130 through the first end face.

[0052] In this embodiment, wavelength division multiplexing technology is used to couple light beams through wavelength division multiplexing optical fiber 150 to obtain dual light beams. However, the present invention is not limited thereto. As long as dual light beams can be obtained, the light beams can also be coupled by other means, such as using a lens assembly to couple the light beams through free space optical coupling technology to obtain dual light beams.

[0053] Furthermore, as Figure 1 shown, the STED dual light beam generator 100 may further include a detector 160, which is arranged on the light beam output side of the three-dimensional microstructure 140 for detecting the generated STED dual light beams. Optionally, the detector 160 may be an imaging detector or an intensity detector.

[0054] In a specific embodiment, for example, the provided single-mode optical fiber is a commercial single-mode optical fiber SM400, having a bandwidth of about 130 nm (which can support single-mode transmission in the wavelength range of 405 nm - 532 nm), and the radius R of its core 130 is 1.5 μm, the refractive index is 1.4769, and the length is 1 μm. In addition, a first wavelength of 532 nm and a second wavelength of 405 nm are determined within the bandwidth of the single-mode optical fiber.

[0055] First, a simulation calculation model of integrating an axially symmetric three-dimensional microstructure 140 on the second end face of the core 130 is constructed using professional optical software FDTD, as Figure 2 and Figure 3 shown.

[0056] Secondly, in this simulation calculation model, the first input light beam with a first wavelength of 532 nm emitted by the first light source 110A propagates in free space after passing through the STED dual light beam generating component 120. When the theoretical transverse light field on the propagation cross-section of the corresponding first output light beam presents a "doughnut" shape distribution (as Figure 8a shown), record the combination of multiple dimensions of the corresponding three-dimensional microstructure 140 at this time.

[0057] Then, turn off the first light source 110A. Continuing in this simulation calculation model, on the basis of the combination of the above multiple dimensions, the second input light beam with a second wavelength of 405 nm emitted by the second light source 110B propagates in free space through the STED dual light beam generating component 120. When the theoretical transverse light field on the propagation cross-section of the corresponding second output light beam presents a distribution with a solid circular spot at the center (as Figure 8bAs shown, one or more dimensions of the corresponding three-dimensional microstructure 140 are determined as target dimensions. For example, as the optimal matching dimensions, the three-dimensional microstructure 140 is formed by stacking 5 cylindrical stepped portions 141. Its maximum cylindrical stepped radius r is 0.6 μm, the height h of the cylindrical stepped portion 141 is 26 μm, and the radius difference dr between adjacent cylindrical stepped portions 141 is 150 nm.

[0058] During the simulation calculation process, the transverse optical field distributions of the distributed light beams corresponding to the two-wavelength light sources detected are also respectively recorded and analyzed to obtain the one-dimensional light intensity distribution of the transverse optical field under the target dimensions. Figure 8c Shows the theoretical one-dimensional light intensity distribution obtained by simulation calculation under the target dimensions of the three-dimensional microstructure 140 in this embodiment, where the ordinate represents the normalized intensity, and the abscissa corresponds to the dashed line passing through the center in Figure 8a and Figure 8b and represents the distance to the center of the light beam (negative on the left side and positive on the right side). To calibrate the beam characteristic attributes of the all-fiber STED dual-beam generator 100 and judge the accuracy of the integrated processing method, the full width at half maximum (FWHM) value corresponding to the circular spot beam (i.e., the second output beam) and the logarithm of the ratio of the central peak to the first side peak light intensity (I CR ) are used to evaluate the quality of its beam characteristics, and the size of the inner diameter of the "doughnut" beam (i.e., the first output beam) (PPD) is used to evaluate the quality of its beam characteristics. In Figure 8c , the theoretical values of I CR and PPD of the "doughnut" beam are 5.76 dB and 0.808 μm respectively, and the theoretical values of I CR and FWHM of the circular spot beam are 13 dB and 0.48 μm respectively.

[0059] For the device size parameters calculated by simulation, verification processing is required. The specific experimental method is as follows: Using wavelength division multiplexing technology, the first input beam emitted by the first light source 110A (corresponding to the first wavelength of 532 nm) and the second input beam emitted by the second light source 110B (corresponding to the second wavelength of 405 nm) are coupled at the first end face of the fiber core 130 by using a wavelength division multiplexing fiber 150. After the coupled dual-beam is transmitted through the waveguide of the STED dual-beam generating component 120 and output from the beam output side of the three-dimensional microstructure 140, it is detected by the detector 160, so as to test whether the STED dual-beam generator 100 calculated by simulation can generate the desired STED dual-beam. When the first light source 110A corresponding to the wavelength of 532 nm is turned off, a distribution with a solid circular spot at the center appears on the detector 160, as shown in Figure 9a ; when the second light source 110B corresponding to the wavelength of 405 nm is turned off, a "doughnut" type distribution appears, as shown in Figure 9bAs shown; when the above-mentioned first light source 110A and second light source 110B are turned on simultaneously, if the beam centers overlap, as Figure 9c shown, the preparation of the all-fiber STED dual-beam generator 100 based on single-mode fiber is completed.

[0060] The following provides a specific experimental case. Through FIB micro-nano processing technology, the theoretical microstructures as shown in Figure 2 and Figure 3 are processed on one end face of a commercial single-mode fiber SM400. In the experiment, a 520nm light source is specifically used as the first input beam to obtain the "doughnut" distribution as shown in Figure 10a shown, and a 405nm light source is used as the second input beam to obtain the distribution with a solid circular spot at the exact center as shown in Figure 10b shown. The transverse optical field distributions of the distributed beams corresponding to the two-wavelength light sources are detected, recorded, and analyzed by a CCD detector to obtain the one-dimensional light intensity distribution of the transverse optical field at the target size. Figure 10c The figure shows the actual one-dimensional light intensity distribution obtained at the target size of the three-dimensional microstructure 140 in this embodiment, where the ordinate represents the normalized intensity, and the abscissa corresponds to the dotted line passing through the exact center in Figure 10a and Figure 10b , indicating the number of detection pixels used by the CCD detector to detect the transverse optical field (counting from the 0th pixel on the left until the 3683rd pixel at the right end). To quickly judge the transverse optical field distribution, the number of pixels can be directly used as the abscissa. If you want to specifically determine the actual size of the light spot, you can convert it into the corresponding actual size abscissa after determining the magnification of the detection. Through data processing and analysis, it can be seen that due to reasons such as the end face of the fiber output not being perpendicular to the imaging detection surface during detection, interference phenomena occur, but it does not affect the overall distribution of the beam; among them, the 520nm light source corresponds to the output of a "doughnut" beam, and its I CR and PPD experimental values are 6.38dB±0.5dB and 1.07±0.1um respectively; the 405nm light source corresponds to the output of a circular spot beam, and its I CR and FWHM experimental values are 12dB±1dB and 0.98±0.1um respectively. On the other hand, compared with the theoretical first input light source of 532nm, in the experiment, a 520nm input light source can also generate a "doughnut" beam, indicating that there is a certain bandwidth for the input light source that generates the "doughnut" beam during the actual preparation process. This also reduces the precision requirements for the preparation of the microstructural size and increases the processing tolerance of the target size. In addition, there are various measurement errors in the actual preparation. Through repeated experiments, relative value comparisons are made for the three experimental values of I CR , FWHM, and PPD, and absolute value comparisons are made with their theoretical values to evaluate the beam properties of the actually prepared all-fiber STED dual-beam generator 100 in order to pursue a more excellent one.

[0061] This application uses common commercial single-mode optical fibers, avoiding the complex design of the integrated microstructure of the fiber core layer or the additional design of the refractive index of the optical fiber, greatly reducing the overall preparation difficulty and cost, and taking into account the characteristics of low loss and stable mode transmission. The overall structure of the single-mode optical fiber end-face microstructure designed in this application is simple, reducing the design difficulty and preparation difficulty of the overall structure. The microstructure designed in this application has flexible and controllable dimensions and many parameters that can be optimized, which is beneficial to the preparation of STED dual beams with excellent beam performance. This application realizes STED dual beams with two wavelengths based on the combination of a single-mode optical fiber and end-face integration. It is a fully fiber-optic structure, easy to be compatible with fiber-optic communication systems, small in size and light in weight, which is conducive to high integration and commercialization.

[0062] The above description is only a preferred embodiment of this application and an explanation of the applied technical principles. Those skilled in the art should understand that the scope of disclosure involved in this application is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the above disclosure concept. For example, the technical solutions formed by mutually replacing the above features with the (but not limited to) technical features with similar functions disclosed in this application.

[0063] In addition, although the operations are depicted in a particular order, this should not be construed as requiring that the operations be performed in the particular order shown or in sequential order. In certain environments, multitasking and parallel processing may be advantageous. Similarly, although several specific implementation details are included in the above discussion, these should not be construed as limiting the scope of the invention. Certain features described in the context of separate embodiments can also be implemented combinatorially in a single embodiment. Conversely, the various features described in the context of a single embodiment can also be implemented separately or in any suitable sub-combination in multiple embodiments.

[0064] Although the subject matter has been described in language specific to structural features and / or methodological logical acts, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. On the contrary, the specific features and acts described above are merely example forms for implementing the claims.

[0065] The above has described multiple embodiments of this application in detail, but this application is not limited to these specific embodiments. Those skilled in the art can make various variations and modifications to the embodiments based on the concept of this application, and these variations and modifications should all fall within the scope claimed by this application.

Claims

1. A STED dual-beam generator based on single-mode optical fiber, characterized in that: include: The single-mode optical fiber comprises a core; A dual light source, which is arranged on one side of the first end face of the fiber core and is configured to emit dual light beams with different wavelengths and input them into the fiber core through the first end face; as well as a three-dimensional microstructure, which is integrated on the second end face of the fiber core in a coaxial manner with the fiber core, the first end face is opposite to the second end face, and the size of the three-dimensional microstructure is designed to be associated with the wavelength of the light beams emitted by the dual light sources, so that the dual light beams can form the STED dual light beams after passing through the fiber core and the three-dimensional microstructure; The three-dimensional microstructure includes a plurality of cylindrical step portions stacked along the axial direction of the fiber core, the axes of the plurality of cylindrical step portions coincide and have a radius that gradually decreases in a direction away from the second end face, and adjacent cylindrical step portions have the same height.

2. The STED dual-beam generator according to claim 1, characterized in that: The radius differences between adjacent cylindrical step portions are equal, and the size of the three-dimensional microstructure satisfies the following formula: Wherein, H is the overall height of the three-dimensional microstructure, r is the maximum radius of the cylindrical step portion, dr is the radius difference, and h is the height of the cylindrical step portion.

3. The STED dual-beam generator according to claim 1 or 2, characterized in that: The dual light source comprises: A first light source configured to emit a first input light beam having a first wavelength; and a second light source configured to emit a second input light beam having a second wavelength; The first wavelength and the second wavelength are within the bandwidth of the single-mode optical fiber, and after the first input light beam and the second input light beam pass through the fiber core and the three-dimensional microstructure, they respectively form a first output light beam and a second output light beam constituting the STED double light beam, the propagation cross section of the first output light beam has a "donut" type distribution, and the propagation cross section of the second output light beam has a distribution with a solid circular spot at the center.

4. The STED dual-beam generator according to claim 1 or 2, characterized in that: The refractive index of the three-dimensional microstructure is equal to the refractive index of the fiber core.

5. The STED dual-beam generator according to claim 4, characterized in that: The three-dimensional microstructure and the fiber core are an integrated structure, which is formed on the second end face of the fiber core by a focused ion beam process, an electron beam lithography process, a two-photon polymerization process or a 3D printing process.

6. The STED dual-beam generator according to claim 4, characterized in that: The cylindrical step portion is a separate cylinder, and a plurality of cylinders are stacked to form the three-dimensional microstructure and attached to the second end surface of the fiber core.

7. The STED dual-beam generator according to claim 3, characterized in that: Also includes: A wavelength division multiplexing optical fiber, which is used to couple the first input light beam and the second input light beam and input them into the fiber core through the first end face; as well as A detector is arranged at the beam output side of the three-dimensional microstructure to detect the STED double beams.

8. The STED dual-beam generator according to claim 7, characterized in that: The detector is an imaging detector or an intensity detector.

9. The STED dual-beam generator according to claim 2, characterized in that: The maximum cylindrical step portion radius does not exceed the radius of the fiber core.

10. A method for preparing a STED dual-beam generator based on a single-mode optical fiber, characterized in that: The steps include: Providing the single-mode optical fiber including a core; A dual light source is arranged on one side of the first end face of the fiber core, and the dual light source is configured to emit dual light beams with different wavelengths and input into the fiber core through the first end face; as well as integrating a three-dimensional microstructure on the second end face of the fiber core in a coaxial manner with the fiber core, wherein the first end face is opposite to the second end face, and the size of the three-dimensional microstructure is designed to be associated with the wavelength of the light beams emitted by the dual light sources, so that the dual light beams can form the STED dual light beams after passing through the fiber core and the three-dimensional microstructure; The three-dimensional microstructure includes a plurality of cylindrical step portions stacked along the axial direction of the fiber core, the axes of the plurality of cylindrical step portions coincide and have a radius that gradually decreases in a direction away from the second end face, and adjacent cylindrical step portions have the same height.

11. The preparation method according to claim 10, characterized in that: The radius differences between adjacent cylindrical step portions are equal, and the size of the three-dimensional microstructure satisfies the following formula: Wherein, H is the overall height of the three-dimensional microstructure, r is the maximum radius of the cylindrical step portion, dr is the radius difference, and h is the height of the cylindrical step portion.

12. The preparation method according to claim 11, characterized in that: The size of the three-dimensional microstructure is determined by the following steps: Determining a first wavelength and a second wavelength within the bandwidth of the single-mode optical fiber, wherein the first wavelength and the second wavelength correspond to a first light source and a second light source constituting the dual light source, respectively; Determine, by physical simulation, a plurality of size combinations of the three-dimensional microstructures corresponding to a first output light beam having a propagation cross section with a "donut" distribution after a first input light beam having the first wavelength passes through the fiber core and the three-dimensional microstructure; as well as Through the physical simulation, one or more sizes of the three-dimensional microstructure corresponding to when a second input light beam with the second wavelength passes through the fiber core and the three-dimensional microstructure to form a second output light beam with a propagation cross-section having a distribution with a solid circular spot at the center is determined from the multiple size combinations as the target size.

13. The preparation method according to any one of claims 10 to 12, characterized in that: The three-dimensional microstructure is formed on the second end face of the fiber core by a focused ion beam process, an electron beam lithography process, a two-photon polymerization process or a 3D printing process.

14. The preparation method according to claim 12, characterized in that: The first light source and the second light source are coupled by optical fiber or free space light, thereby emitting the double light beams.

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