阅读说明：本技术 一种基于多阶光纤模式复用的光纤sted显微镜 (Optical fiber STED microscope based on multi-order optical fiber mode multiplexing ) 是由 苑立波 王东辉 孟令知 于 2021-10-12 设计创作，主要内容包括：本发明提供的是一种基于多阶光纤模式复用的光纤STED显微镜。其特征是：它由激发光输入端口1、损耗光输入端口2、荧光输出端口3、多孔毛细管4、扇入扇出拉锥区5、异质多芯光纤6、低折射率套管7、模式转换拉锥区8、低模间串扰少模光纤9、扩束无芯光纤10、特制光纤聚焦透镜11和待测荧光物质12组成。本发明可用于超分辨率显微照明和成像系统,可广泛用于生物学和医学领域。(The invention provides an optical fiber STED microscope based on multi-order optical fiber mode multiplexing. The method is characterized in that: the device comprises an exciting light input port 1, a loss light input port 2, a fluorescence output port 3, a porous capillary tube 4, a fan-in fan-out tapering region 5, a heterogeneous multi-core fiber 6, a low-refractive-index sleeve 7, a mode conversion tapering region 8, a low-mode crosstalk few-mode fiber 9, a beam-expanding coreless fiber 10, a special fiber focusing lens 11 and a fluorescent substance 12 to be detected. The invention can be used for super-resolution microscopic illumination and imaging systems and can be widely applied to the fields of biology and medicine.)

1. A kind of optic fibre STED microscope based on multiplexing of multi-order optic fibre mode, its characteristic is: the system consists of an exciting light input port (1), a loss light input port (2), a fluorescence output port (3), a porous capillary tube (4), a fan-in fan-out biconical region (5), a heterogeneous multi-core fiber (6), a low-refractive-index sleeve (7), a mode conversion biconical region (8), a low-intermode crosstalk few-mode fiber (9), a beam-expanding coreless fiber (10), a special fiber focusing lens (11) and a fluorescent substance to be detected (12), wherein exciting light with the wavelength matched with the fluorescent substance is injected into the exciting light input port (1) in the system, the exciting light passes through the fan-in fan-out biconical region (5) prepared by the double-cladding transition fiber and the porous capillary tube (4) jack biconical region, is coupled to a certain fiber core in the heterogeneous multi-core fiber (6), and then passes through the mode conversion biconical region (8) formed by the low-refractive-index sleeve (7) and the heterogeneous multi-core fiber (6), the exciting light forms an LP01 fundamental mode in the low-mode crosstalk few-mode optical fiber (9), and the LP01 fundamental mode passes through a beam-expanding coreless optical fiber (10) and then is incident to a special optical fiber focusing lens (11) and then is focused on a fluorescent substance (12) to be detected to form Gaussian-distributed light spots; the loss light with the wavelength matched with the stimulated radiation loss effect of the fluorescent substance is input through a loss light input port (2), the loss light in the wavelength matched with the stimulated radiation loss effect of the fluorescent substance forms an LP02 mode in a few-mode optical fiber through a fan-in fan-out tapered region (5) and a mode conversion tapered region (8), the light wave is expanded through an expanded beam expanding coreless fiber (10) and then enters a special optical fiber focusing lens (11), the outer ring of an LP02 mode can be independently modulated by the edge of the lens due to a large divergence angle of a high-order mode, the modulated outer ring of the LP02 mode and an inner light spot are simultaneously focused on the surface of the fluorescent substance (12) to be detected, a phase difference value of pi is formed between an inner light wave focusing point and an outer light wave focusing point, the inner light wave focusing point and the outer light wave focusing point are interfered to form an annular light spot with a central coherence weakening edge, the central coherence is enhanced, the annular light spot of the loss light inhibits the fluorescent excitation of the substance, the Gaussian light is promoted by the Gaussian light spot of the excitation light of the annular light, and the central coherence of the Gaussian light spot, a small fluorescent excitation region is formed, the fluorescence generated by the area can be received by the optical fiber end, and the energy received by the optical fiber can reversely pass through the whole device and is finally output to a receiver through a fluorescence output port (3).

2. The fiber-optic STED microscope as claimed in claim 1, wherein: the heterogeneous multi-core optical fiber has different refractive index, diameter or refractive index section types of partial fiber cores, the number of the fiber cores is N, N is an integer, and N is not less than 3.

3. The fiber-optic STED microscope as claimed in claim 1, wherein: the refractive index profile of the fiber core in the heterogeneous multi-core fiber is in a step type, a parabolic type or a Gaussian type.

4. The fiber-optic STED microscope as claimed in claim 1, wherein: the mode conversion tapering region is formed by inserting heterogeneous multi-core optical fibers with special structures into a low-refractive-index sleeve to be tapered, the tapered structure meets the adiabatic conversion condition, the Gaussian fundamental mode of an input end can be converted into a scalar mode in the few-mode optical fiber, and the two modes have one-to-one correspondence.

5. The fiber-optic STED microscope as claimed in claim 1, wherein: the cladding structure of the heterogeneous multi-core fiber is a single cladding or a double cladding, and the matching of the mode field area and the numerical aperture is realized between the fiber structure formed at the inner cladding boundary after the tail end of the mode conversion tapered region is contracted and the rear-end output few-mode fiber.

6. The fiber-optic STED microscope as claimed in claim 1, wherein: the heterogeneous multi-core optical fiber is provided with air holes and small-core-diameter fiber core structures between fiber cores, and aims to control the phase difference value of a symmetric supermode and an anti-symmetric supermode in a mode conversion tapered region.

7. The fiber-optic STED microscope as claimed in claim 1, wherein: the few-mode optical fiber is a single-core few-mode or multi-core few-mode optical fiber, and when the few-mode optical fiber is a multi-core few-mode optical fiber, a mode conversion cone-drawing area, a fan-in fan-out cone-drawing area and an input/output optical fiber which are matched at the front end are all used in multiple parts, so that the array type STED microscope is formed.

8. The fiber-optic STED microscope as claimed in claim 1, wherein: the optical fiber focusing lens is a ball lens, an optical fiber end Fresnel lens or an optical fiber cone grinding lens, and is characterized in that an outer ring and an inner light spot of an LP02 mode can be focused on a focal plane at the same time, and the phases of the outer ring and the inner light spot at a focal point are opposite.

Technical Field

The invention relates to an optical fiber STED microscope based on multi-order optical fiber mode multiplexing, which can be used for super-resolution microscopic illumination and imaging systems and belongs to the fields of biology and medicine.

Background

With the development of modern bioscience and medical science, researchers put more and more requirements on microstructure observation, the traditional optical microscope is limited by the fact that the diffraction limit cannot distinguish the material structure under the half-wavelength scale, and with the requirement, heler in 1994 proposes a stimulated emission depletion (STED) microscopic imaging technology, the core of the technology is that when fluorescent materials are subjected to fluorescence excitation generated by illumination, annular light beams (called STED light beams and depletion light beams) with different wavelengths are superposed on the periphery of the excitation light beams, the annular light beams can force fluorescent dye atoms in the illumination range to perform stimulated radiation, so that normal fluorescent signals cannot be emitted, while dark areas in the centers of the annular light beams can still normally emit fluorescence, the technology greatly reduces the minimum resolution size of the microscope and is not limited by diffraction effect, namely, theoretically, the dark center areas can be adjusted to be infinitely small, making it a very promising microscopic technique.

Most of the STED microscopy techniques currently on the market are based on a spatial light modulator to generate an annular STED beam and to keep the excitation beam coaxially matched to the STED beam. Such a spatial light type experimental scheme is quite complex, the system calibration needs to be performed for a long time before the experiment, and interference factors such as vibration, temperature change and the like in the experiment cause the response of the spatial light path to further influence the position and the shape of the annular light spot in the STED microscope, and all of the factors cause the performance of the whole STED system to be reduced. Just because the conventional STED microscope faces such problems, the fiber-based STED microscope has come to work, and the fiber-based STED system can greatly simplify the complexity of the system and improve the flexibility and stability of the system, but at the same time how to realize the ring beam in the fiber is called a main problem.

The photon lantern is a waveguide device which is emerging in recent ten years, can realize the function of mode low-loss coupling between a single-mode fiber and a multimode fiber, and is an ideal fiber communication mode division multiplexing device. The photonic lantern connects a single multimode waveguide with a plurality of single mode waveguides, and is generally prepared by constraining a plurality of heterogeneous single mode fibers by a low-refractive-index capillary sleeve to be fused and tapered. The photon lantern is a reciprocal device which can realize the function of a mode multiplexer for converting a fundamental mode of an optical fiber into a specific high-order mode and also can realize the demodulation and the coupling of the high-order mode to a corresponding single-mode port.

The patent with publication number CN109752830B proposes an optical fiber-based STED super-resolution micro-lighting device, which uses spatial light to excite a high-order mode of an optical fiber inner cladding in a double-clad optical fiber to form a ring beam, but the excitation mode cannot be specified, and fine adjustment is still needed to realize the ring beam.

Patent publication No. CN111653380A proposes an STED super-resolution microscopic imaging device based on a single optical fiber. The invention uses the spiral optical fiber to couple the loss light to the optical fiber vortex mode, and forms an annular output optical field without influencing the emergent state of the exciting light.

The patent with publication number CN111653378A proposes an STED super-resolution microscopic imaging device based on multi-fiber optical tweezers. The method provided by the patent is that loss light is converted into an optical fiber high-order vortex mode through the spiral optical fiber, the optical fiber high-order vortex mode is distributed on a plurality of single-mode optical fibers around particles to be measured, and the motion position of the particles can be adjusted by utilizing the action of the optical tweezers, so that the high-precision STED microscope is realized.

The invention provides an optical fiber STED microscope based on multi-order optical fiber mode multiplexing. The device utilizes a photon lantern prepared from heterogeneous multi-core fibers to convert loss light incident from a single-mode input end into an LP02 mode of a few-mode fiber, and utilizes the characteristic of separation of an outer ring and an inner light spot of the mode to design a focusing lens in a targeted manner, so that the outer ring and the inner light spot of the LP02 mode are focused on the surface of a fluorescent substance to be detected at the same time, a pi phase difference value is formed between the inner light wave focus point and the outer light wave focus point, and the interference of the two forms a central coherence weakening edge enhanced annular light spot; meanwhile, fluorescence excitation light is emitted to the surface of the sample through the optical fiber fundamental mode to excite the fluorescent substance in the center of the annular loss light wave; meanwhile, the fluorescence of the substance can be received by the few-mode optical fiber and returns to the fluorescence output port, the device realizes the integration of the input end and the output end of the STED microscope, and is different from other optical fiber STED microscopes which need to utilize an optical fiber high-order mode to generate annular loss light.

Disclosure of Invention

The invention aims to provide a fiber STED microscope based on multi-order fiber mode multiplexing.

The purpose of the invention is realized as follows:

the system consists of an exciting light input port 1, a loss light input port 2, a fluorescence output port 3, a porous capillary 4, a fan-in fan-out biconical region 5, a heterogeneous multi-core fiber 6, a low-refractive-index sleeve 7, a mode conversion biconical region 8, a low-intermode crosstalk few-mode fiber 9, an expanded beam coreless fiber 10, a specially-made fiber focusing lens 11 and a fluorescent substance 12 to be detected, wherein exciting light with the wavelength matched with the fluorescent substance is injected into the exciting light input port 1 in the system, passes through the fan-in fan-out biconical region 5 prepared by double-clad transition fibers and the jack biconical taper of the porous capillary 4, is coupled to a certain fiber core in the heterogeneous multi-core fiber 6, passes through the mode conversion biconical region 8 formed by combining and tapering the low-intermode sleeve 7 and the heterogeneous multi-core fiber 6, forms an LP01 fundamental mode in the low-intermode crosstalk few-mode fiber 9, passes through the expanded beam coreless fiber 10, is incident to the specially-made fiber focusing lens 11 and then is focused on the fluorescent substance 12 to be detected, forming light spots in Gaussian distribution; the loss light with the wavelength matched with the stimulated radiation loss effect of the fluorescent substance is input from a loss light input port 2, a low-mode fiber LP02 mode is formed by a fan-in fan-out tapered region 5 and a mode conversion tapered region 8, the light wave is expanded by an expanded beam coreless fiber 10 and then enters a special fiber focusing lens 11, the divergence angle of a high-order mode is large, so that the outer ring of a LP02 mode can be independently modulated by the edge of the lens, the modulated outer ring of the LP02 mode and the modulated inner light spot are focused on the surface of the fluorescent substance 12 to be detected at the same time, a phase difference value of pi is formed between the focusing points of the inner light wave and the outer light wave, and the interference of the two forms a central coherent weakening edge-enhanced annular light spot; the annular light spot of the loss light inhibits the fluorescence excitation of the substance, the Gaussian light spot of the excitation light promotes the fluorescence excitation of the substance, a small fluorescence excitation area is formed in the center of the coincidence of the annular light spot and the Gaussian light spot, the fluorescence generated in the area can be received by the optical fiber end, the energy received by the optical fiber can reversely pass through the whole device, and finally the energy is output to the receiver through the fluorescence output port 3.

The mechanism of LP02 mode formation, the method of modulating LP02 mode by a special fiber focus lens, and the principle of backward transmission of fluorescence through few-mode fibers to the output port will be explained in detail below.

A fiber mode division multiplexer (or Photon Lantern, PL) is a fiber bundle tapered waveguide, which is generally made of a plurality of single mode fibers, a low refractive index porous capillary, and a few-mode fiber fusion taper, and can convert a fundamental mode conducted in a single mode fiber into each order mode in a taper region end few-mode fiber. The invention discloses a mode conversion method for a photonic lantern, which is characterized in that a mode conversion tapered region formed by heterogeneous multi-core fibers and a low-refractive-index sleeve is used as the photonic lantern for mode conversion.

The heterogeneous multi-core optical fiber at the front end of the mode conversion tapered region comprises a plurality of different fiber cores, and the guided modes of the single fiber cores are Gaussian fundamental modes. The single fiber guided modes in the heterogeneous multicore fiber can be converted into fiber output end scalar modes using a photonic lantern, where the mode in the core with the largest propagation constant can be shifted to the LP01 fundamental mode of the few-mode fiber and the mode in the core with the lowest transmission constant (when the number of cores is 6) can be shifted to at least the LP02 mode of the mode fiber. The other cores correspond to four modes of the optical fiber, namely LP11a, LP11b, LP21a and LP21b, and the modes are degenerate pairwise.

In addition, the basic principle of mode conversion is adiabatic conversion in a graded structure, namely, in an optical waveguide with slowly changing shape parameters and refractive index profile, a certain mode at an incident end can be converted to a certain same-order mode at an output end without loss. The whole tapering region satisfies adiabatic coupling conditions as shown below

The subscripts j and l in the formula represent a guided fundamental mode and other modes respectively, β is a transmission constant of a local mode, Ψ is a normalized electromagnetic field distribution of the local mode, k is 2 π/λ is a wave number of an electromagnetic wave, z is an axial coordinate of a tapered structure, ρ is a shrinkage ratio of a cladding, n is a refractive index distribution function of a tapered region, and A is a cross section of the tapered structure. The formula defines a judgment condition related to the length of the tapered cone and the shape expression rho (z), and the judgment condition can measure the theoretical performance of the mode conversion tapered area.

In order to enable the LP02 mode to be transmitted in a few-mode optical fiber with a longer distance without loss, the invention selects a few-mode optical fiber with low inter-mode crosstalk, and the optical fiber can inhibit the energy coupling of the LP01 and LP02 modes and other modes, and maximally ensure that the two mode states at the output end are the same as the states at the input end. Other modes inevitably have coupling phenomena for reasons of degeneracy.

The design of the special fiber focusing lens also has some requirements, and the purpose of the special fiber focusing lens is to ensure that the outer ring and the inner light spot of the LP02 mode of the lost light can be focused on the surface of the fluorescent object to be detected, and the phase difference between the outer ring and the inner light spot is pi, so that the annular light spot can be formed. The processing method can be a femtosecond laser end face carving method, and Fresnel lenses with different parameters are carved at different positions of the end face of the coreless optical fiber to form interference annular light spots. In addition, the processing can also be carried out by using an additive manufacturing method, such as a two-photon polymerization nano 3D printer and the like.

The collection of fluorescence is also an important innovation point of the invention, the fluorescence emitted by the fluorescent substance to be detected is weak, the general collection method is collection by using an objective lens with high numerical aperture, and the invention utilizes an imaging optical fiber to collect scattered light waves and outputs the scattered light waves to a certain single-mode port through the whole device in a backward direction. The scattered light waves can reversely pass through the device and are output to the fluorescent output port 3 through the mode conversion tapering region and the fan-in fan-out transition region, and the excitation light and the loss light component in the feedback light waves can be removed by the optical filter.

The heterogeneous multi-core optical fiber has different refractive index, diameter or refractive index section types of partial fiber cores, the number of the fiber cores is N, N is an integer, and N is not less than 3.

The refractive index profile of the fiber core in the heterogeneous multi-core fiber is in a step type, a parabolic type or a Gaussian type.

The mode conversion tapering region is formed by inserting heterogeneous multi-core optical fibers with special structures into a low-refractive-index sleeve to be tapered, the tapered structure meets the adiabatic conversion condition, the Gaussian fundamental mode of an input end can be converted into a scalar mode in the few-mode optical fiber, and the two modes have one-to-one correspondence.

The cladding structure of the heterogeneous multi-core fiber is a single cladding or a double cladding, and the matching of the mode field area and the numerical aperture is realized between the fiber structure formed at the inner cladding boundary after the tail end of the mode conversion tapered region is contracted and the rear-end output few-mode fiber.

The heterogeneous multi-core optical fiber is provided with air holes and small-core-diameter fiber core structures between fiber cores, and aims to control the phase difference value of a symmetric supermode and an anti-symmetric supermode in a mode conversion tapered region. The phase difference value between the supermodes has a significant relation with the end surface structure of the fiber core, and if the fiber core distance is changed, the fiber core air holes are increased or the auxiliary fiber core is added, the evolution of the supermodes in the cone area is different, and the phase difference values are also different.

The few-mode optical fiber is a single-core few-mode or multi-core few-mode optical fiber, and when the few-mode optical fiber is a multi-core few-mode optical fiber, a mode conversion cone-drawing area, a fan-in fan-out cone-drawing area and an input/output optical fiber which are matched at the front end are all used in multiple parts, so that the array type STED microscope is formed. Compared with the traditional photon lantern in the form of fiber bundles, the photon lantern based on heterogeneous multi-core fibers increases the integration level and the stability of devices, so that the multi-core few-mode photon lantern is possible. Otherwise, taking a seven-core six-mode as an example, it is totally necessary to insert 42 different single-mode fibers into the low-refractive-index fluorine-doped tube, and to control the taper angle shape, which is obviously impossible, and only by using a plurality of heterogeneous multi-core fibers and matching with a fan-in fan-out device, the design of tapering a plurality of photon lanterns at a time can be realized to form the array type STED microscope system.

The optical fiber focusing lens is a ball lens, an optical fiber end Fresnel lens or an optical fiber cone grinding lens, and is characterized in that an outer ring and an inner light spot of an LP02 mode can be focused on a focal plane at the same time, and the phases of the outer ring and the inner light spot at a focal point are opposite.

Compared with other types of fiber STED microscopes, the invention provides the freely movable low-mode crosstalk fiber, and the fiber can move, bend and twist when in use, so that the size of an imaging lens is reduced, the use range of a device is expanded, and the possibility of larger-scale microscopic imaging is provided.

The invention provides an optical fiber STED microscope based on multi-order optical fiber mode multiplexing. The device utilizes a photon lantern prepared from heterogeneous multi-core fibers to convert loss light incident from a single-mode input end into an LP02 mode of a few-mode fiber, and utilizes the characteristic of separation of an outer ring and an inner light spot of the mode to design a focusing lens in a targeted manner, so that the outer ring and the inner light spot of the LP02 mode are focused on the surface of a fluorescent substance to be detected at the same time, a pi phase difference value is formed between the inner light wave focus point and the outer light wave focus point, and the interference of the two forms a central coherence weakening edge enhanced annular light spot; meanwhile, fluorescence excitation light is emitted to the surface of the sample through the optical fiber fundamental mode to excite the fluorescent substance in the center of the annular loss light wave; meanwhile, the fluorescence of the substance can be received by the few-mode optical fiber and returns to the single-mode fluorescence output port, the device realizes the integration of the input end and the output end of the STED microscope, and is different from other optical fiber STED microscopes which need to utilize an optical fiber high-order mode to generate annular loss light.

Drawings

Fig. 1 is an overall configuration diagram of a fiber-optic STED microscope based on multi-step fiber mode multiplexing. The device comprises an exciting light input port 1, a loss light input port 2, a fluorescence output port 3, a porous capillary tube 4, a fan-in fan-out tapering region 5, a heterogeneous multi-core fiber 6, a low-refractive-index sleeve 7, a mode conversion tapering region 8, a low-mode crosstalk few-mode fiber 9, a beam-expanding coreless fiber 10, a special fiber focusing lens 11 and a fluorescent substance 12 to be detected.

FIG. 2 is a schematic cross-sectional view of a mode-switching taper region and a fan-in fan-out transition region in a multi-step fiber-mode multiplexing-based fiber STED microscope.

Fig. 3 is a schematic end view of a heterogeneous multi-core fiber used in the present invention, (a) a heterogeneous six-core fiber, (b) a heterogeneous three-core fiber, (c) a double-clad heterogeneous six-core fiber, (d) a double-clad heterogeneous three-core fiber, (e) a double-clad heterogeneous five-core fiber, and (f) a double-clad heterogeneous ten-core fiber. In FIG. e, the center of the cross section of the optical fiber is a cladding or a void.

Fig. 4 is a graph of the propagation constants of the eigenmodes for each cross section in the mode-switched tapered region. The curves are respectively a multi-core supermode corresponding to a few-mode end LP01 mode, a multi-core supermode corresponding to a few-mode end LP11a mode and LP11b mode, a multi-core supermode corresponding to a few-mode end LP21a mode and LP21b mode, and a multi-core supermode propagation constant corresponding to a few-mode end LP02 mode along with the drawing cone proportion change diagram from top to bottom.

Fig. 5 is a diagram of the process of light beam evolution in the mode conversion tapered region. The Gaussian guided modes of all fiber cores in the heterogeneous multi-core fiber at the left end of the tapering region gradually evolve into few modes of the fiber at the right end, and the process is reciprocal. The right end of the figure is a mode field distribution diagram of each mode of the few-mode optical fiber.

FIG. 6 is a graph of the conversion efficiency and noise results of a mode conversion taper region in a multi-order fiber STED microscope based on multi-order fiber mode multiplexing. The vertical pictures are standard modes in few-mode fibers, the horizontal pictures are patterns output by a photon lantern after single-mode fibers are injected, and data in the patterns are integration results between two groups of modes. The data on the diagonal line of the graph represents the loss of the vortex mode in the mode conversion tapering region, and the data on the off-diagonal line represents the signal crosstalk of the few-mode in the mode conversion tapering region. The purity of the output fiber modes is greater than 95%. The data unit in the figure is dB.

FIG. 7 is a schematic diagram of the ring-shaped light spot formed by the LP02 mode of the optical fiber passing through a special fiber focusing lens, in which different line segments represent light waves with different components, and two groups of light waves are focused to form a ring-shaped loss light beam.

Detailed Description

The invention is further illustrated below with reference to specific examples.

Example 1: the design of a fiber STED microscope based on multi-order fiber mode multiplexing;

the low-intermode crosstalk few-mode optical fiber uses a six-mode optical fiber with the core diameter of 18.5um and the numerical aperture of 0.12. It can accommodate six modes, LP01, LP11a, LP11b, LP21a, LP21b, LP 02. The fiber cores of the heterogeneous multi-core fiber are 6, and the core diameter of each fiber core is 11um, 9um, 9um, 8um, 8um and 6.5 um. The cladding index is 1.444 and the core cladding numerical aperture is 0.12. The refractive index of the low-index sleeve is 1.439, and the inner diameter of the sleeve is equal to the outer diameter of the heterogeneous multi-core fiber and is 125 um.

And inserting the heterogeneous multi-core optical fiber into the low-refractive-index sleeve to perform adiabatic tapering, so as to obtain the mode conversion tapered region. The shape and length of the tapered cone may be determined by simulation. A typical cone length is 4cm, and the cone is a linear cone.

The fan-in fan-out transition region is prepared by inserting a double-clad transition fiber into a porous capillary medium-drawing cone.

The beam expanding coreless fiber has a length of 150um to 300 um.

The specific parameters of the special fiber focusing lens should be determined according to the results of finite element simulation.

Typical specially made fiber focusing lenses use fresnel lenses.

Exciting light input into the device from a port 1 is changed into an LP01 basic mode of the few-mode optical fiber through a fan-in fan-out transition region and a mode conversion tapering region, and is irradiated on the surface of a fluorescent substance to be detected after being focused by a specially-made optical fiber focusing lens to form a Gaussian light spot; the loss light input into the device from the port 2 is changed into an LP02 mode of few-mode optical fibers through a fan-in fan-out transition region and a mode conversion tapering region, and the divergence angle of the mode is larger, so that the edge of the special optical fiber focusing lens only acts on the outer ring of the LP02 mode, and the LP02 mode outer ring and the central light spot passing through the lens are focused on the surface of the fluorescent substance to be detected to form an annular light spot; the annular light spot and the Gaussian light spot are natural coaxial, so only a small part in the center of the annular light spot can excite fluorescence, and the scale of the dark ring is smaller than the optical diffraction limit.

The fluorescence emitted by the fluorescence substance to be tested enters at least a mode fiber, wherein light waves belonging to modes LP11a, LP11b, LP21a and LP21b can reversely pass through the device and are output to a 3-port through a mode conversion tapering region and a fan-in fan-out region, and then the interference of excitation light and loss light can be removed by means of optical filters and the like, so that super-resolution imaging is realized.