CN114415362B - All-fiber step microscope based on vortex rotation - Google Patents
All-fiber step microscope based on vortex rotation Download PDFInfo
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Abstract
The invention provides an all-fiber step microscope based on vortex rotation. The method is characterized in that: the optical fiber comprises an input/output optical fiber 1, a 1X2 coupler 2, an optical attenuation and phase modulator 3, a double-cladding transition optical fiber 4, a porous capillary 5, a fan-in fan-out cone pulling area 6, a heterogeneous multi-core optical fiber 7, a low refractive index sleeve 8, a mode conversion cone pulling area 9, an output few-mode optical fiber 10, a low-mode inter-mode crosstalk optical fiber 11, an optical fiber focusing lens 12 and a fluorescent substance 13 to be measured. The invention can be used for super-resolution microscopic illumination and imaging systems, and can be widely used in the fields of biology and medicine.
Description
Technical Field
The invention relates to an all-fiber step microscope based on vortex rotation, which can be used for a super-resolution microscopic illumination and imaging system and belongs to the fields of biology and medicine.
Background
With the development of modern bioscience and medical science, researchers have put higher and higher demands on microstructure observation, the traditional optical microscope is limited by a material structure with diffraction limit incapable of resolving at half wavelength scale, under the demands, helter has put forward a stimulated emission loss (step) microscopic imaging technology in 1994, the core of the technology is that when fluorescent substances are excited by fluorescence generated by illumination, an annular light beam (called step light beam and loss light beam) with different wavelengths is overlapped on the periphery of an excitation light beam, the annular light beam can force fluorescent dye atoms in the irradiation range of the annular light beam to be stimulated to emit stimulated radiation, so that normal fluorescent signals cannot be emitted, and a dark area in the center of the annular light beam can still emit fluorescence normally, the minimum resolution size of the microscope is greatly reduced, and the technology is not limited by diffraction effect, namely, the dark center area can be regulated to be infinitely small theoretically, so that the technology is a microscopic technology with very high application potential.
Most of the step microscopy techniques currently on the market are based on spatial light modulators to generate a circular step beam and to keep the excitation beam coaxially matched to the step beam. Such spatial light type of experimental protocols are quite complex, often requiring long system corrections before experiments, and interference factors in the experiments, such as vibration, temperature changes, etc., can cause the response of the spatial light path to further affect the position and shape of the annular spot in the step microscope, which can lead to reduced performance of the overall step system. Just as conventional step microscopes face such problems, fiber-based step microscopes have grown, fiber-based step systems can greatly simplify the complexity of the system, improve the flexibility and stability of the system, but at the same time how to implement a ring beam in a fiber is called a major problem.
The photon lantern is a waveguide device which is rising in more than ten years, can realize the mode low-loss coupling function between a single mode fiber and a multimode fiber, and is an ideal optical fiber communication mode division multiplexing device. The photon lantern is connected with a single multimode waveguide and a plurality of single-mode waveguides and is generally prepared by constraining a plurality of heterogeneous single-mode optical fibers to be fused and tapered through a low-refractive-index capillary sleeve. The photon lantern is a reciprocal device which can realize the function of a mode multiplexer for converting the fundamental mode of an optical fiber into a specific higher-order mode and can also realize the demodulation and the coupling of the higher-order mode to a corresponding single-mode port.
The patent with publication number CN109752830B proposes a fiber-based step super-resolution microscopic lighting device, which uses spatial light to excite a higher-order mode of an inner cladding of an optical fiber in a double-clad optical fiber to form an annular light beam, but cannot designate an excitation mode, and still needs fine adjustment to realize the annular light beam.
Patent publication number CN111653380a proposes a single fiber-based step super-resolution microscopic imaging device. The spiral optical fiber is used for leading the loss light to be coupled to the optical fiber vortex mode, so that an annular output light field is formed without influencing the emergent state of excitation light.
Patent publication No. CN111653378A proposes a step super-resolution microscopic imaging device based on multi-fiber optical tweezers. The method provided by the patent converts the loss light into an optical fiber high-order vortex mode through the spiral optical fiber, and simultaneously distributes the loss light into a plurality of single-mode optical fibers around the particles to be detected, and can adjust the movement position of the particles by utilizing the action of optical tweezers, so that the high-precision step microscope is realized.
The invention provides an all-fiber step microscope based on vortex rotation. The device converts the loss light incident from a single-mode input end into an optical fiber vortex mode by utilizing the vortex photon lantern prepared by the heterogeneous multi-core optical fiber, so that an annular output field is formed, meanwhile, the scanning range can be greatly conveniently expanded by introducing the low-mode inter-mode crosstalk optical fiber, the annular mode damage caused by the optical fiber disturbance can be counteracted by matching with the optical attenuation and the phase modulator of the input end, and the purity of the annular vortex rotation of the output end is ensured. Meanwhile, fluorescence energy of the substance is received by the few-mode optical fiber and returns to the single-mode output port, the device realizes integration of the input end and the output end of the step microscope, and the interference of the optical fiber bending equivalent to the vortex mode is counteracted by using the controller, so that the device is a novel optical fiber step microscope device with great potential.
Disclosure of Invention
The invention aims to provide an all-fiber step microscope based on vortex rotation.
The purpose of the invention is realized in the following way:
the optical fiber comprises an input/output optical fiber 1, a 1X2 coupler 2, an optical attenuation and phase modulator 3, a double-cladding transition optical fiber 4, a porous capillary 5, a fan-in fan-out cone pulling area 6, a heterogeneous multi-core optical fiber 7, a low refractive index sleeve 8, a mode conversion cone pulling area 9, an output few-mode optical fiber 10, a low-mode inter-mode crosstalk optical fiber 11, an optical fiber focusing lens 12 and a fluorescent substance 13 to be measured. The input/output optical fiber 1 in the system inputs two light waves, wherein one light wave is excitation light, and the other light wave is loss light; excitation light is input from an optical fiber port 1-2, is subjected to fanning-in fanout tapering region 6 prepared by tapering through double-cladding transition optical fiber 4 and jack tapering of a porous capillary 5, so that the excitation light is coupled to a certain fiber core in heterogeneous multi-core optical fiber 7, is subjected to mode conversion tapering region 9 formed by tapering through combination of low refractive index sleeve 3 and heterogeneous multi-core optical fiber 7, forms a fundamental mode in output few-mode optical fiber 10, is transmitted to optical fiber focusing lens 12 through low-mode intermodal interference optical fiber 11, and finally is projected on the surface of fluorescent substance 13 to be measured, and the light spot is Gaussian; the loss light is input by an optical fiber port 1-3 or 1-4, the light wave is divided into two beams with equal success rate by a 1X2 coupler 2, the two beams are respectively connected into a rear-end double-cladding transition optical fiber 4 through the output end of the coupler, each path is internally provided with light attenuation and a phase modulator 3 for controlling the light power and the phase, the two paths of light waves are converted into guide fundamental modes of two identical fiber cores in a heterogeneous multi-core optical fiber through a fan-in fan-out cone pulling area 6, the group of fundamental modes are converted into vortex modes by a mode conversion cone pulling area 9, the light spots are projected on the surface of a fluorescent substance 13 to be detected through a low-mode inter-interference optical fiber 11 and an optical fiber focusing lens 12, and the light spots are annular; the annular light spot of the loss light suppresses 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 at the center of the superposition of the annular light spot and the Gaussian light spot, fluorescence generated by the area can be received by the optical fiber end, energy received by the optical fiber can reversely pass through the whole device, and finally the energy is output to the receiver through the output port.
The mechanism of vortex light formation of the annular light spot, the compensation of the optical loss and phase modulator for the vortex mode affected by bending and the principle of reverse transmission of fluorescence to the output port via the few-mode fiber will be described in detail below.
The key to realize the conversion from the single-mode Gaussian beam to the vortex beam is the design of a mode conversion tapering region, and the region can separate light waves loaded with different orders of orbital angular momentum in the input vortex beam and respectively convert the light waves into each output channel, wherein the orbital angular momentum beams of each order correspond to Gaussian beams in each output channel one by one.
The eigenmodes of the few-mode fiber are vector modes or scalar modes, while the vortex modes in the fiber can be combined from the vector modes or scalar modes, the following expression is between the vortex modes and the modes of each order of the fiber,
in the formula, OAM represents a high-order vortex beam mode with orbital angular momentum in the optical fiber, the topological charge number and the order of the mode are determined by a first subscript of the expression, a second subscript represents the radial node number of the mode, and a mode superscript represents the polarization state of the mode. HE, EH, TE, TM at the right end of the formula is the vector mode of the optical fiber, the superscripts even and odd represent the symmetry of the mode, and the subscript definition is the same as the vortex mode. The imaginary symbol i in the formula represents the phase difference between the modes that is pi/2. This expression illustrates that the vector mode and vortex mode in the fiber are mutually switchable.
The heterogeneous multi-core optical fiber at the front end of the mode conversion tapering zone comprises a plurality of different fiber cores, and the guided modes of the single fiber cores are all Gaussian fundamental modes, but in the patent of the invention, the super-mode characteristics of the multi-core optical fiber are needed to be considered as a whole. In the heterogeneous multi-core optical fiber, at most, two fiber cores have the same structural parameters, and the fundamental modes of the two fiber cores are mutually coupled to form an ultra-mode with energy distributed in the two fiber cores, the energy distribution is still in a Gaussian shape of the fundamental mode, but the wave front phases in the two identical fiber cores are different, if the phases of the fundamental modes in the two fiber cores are the same, the two fiber cores are called symmetrical ultra-mode, and the other ultra-mode with pi phase difference is called antisymmetric ultra-mode. The symmetrical supermode and the antisymmetric supermode are in a nearly degenerate state, and the effective refractive indexes are very close. If the symmetrical supermode and the antisymmetric supermode with equal power exist at the same time, the phase between the two modes will determine the light field distribution in the multi-core optical fiber, if the phase difference is pi or the same, the Gaussian fundamental mode of one core is excited respectively, and can be led out to a single-mode optical fiber by the fan-in fan-out device, if the phase difference is not 0 or pi, the two cores in the multi-core optical fiber can generate the Gaussian fundamental mode with unequal power, and can not be output to the same single-mode optical fiber by the fan-in fan-out device.
The photon lantern can be used for converting the supermode in the heterogeneous multi-core optical fiber into a scalar mode at the output end of the optical fiber, wherein the symmetrical supermode can be converted into an LP11a mode or an LP21a mode (corresponding to different ports) of the optical fiber, and the anti-symmetrical supermode is converted into an LP11b mode or an LP21b mode, so that a phase difference value can be generated in the conversion process. When the phase difference value reaches pi/2, the output result of the photon lantern is a vortex mode.
In addition, the fundamental principle of mode conversion is adiabatic conversion in a slowly varying structure, i.e. in an optical waveguide with slowly varying shape parameters and refractive index profile, a certain mode at the input end can be converted into a certain same-order mode at the output end without damage. The whole tapering region meets the adiabatic coupling condition as follows
The symbol subscripts j and l in the formula respectively represent a guided fundamental mode and other modes, beta is a transmission constant of a local mode, ψ is normalized electromagnetic field distribution of the local mode, k=2pi/λ is wave number of electromagnetic waves, z is axial coordinate of a tapered structure, ρ is shrinkage of a cladding layer, 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 taper length and the shape expression ρ (z), which can measure the theoretical performance of the mode conversion taper region.
In addition to adiabatic conversion conditions, the phase relationship between modes in the mode-converting tapered region also determines the conversion efficiency of vortex light into gaussian beams. The conversion process from the input mode to the output mode in the whole process of inserting the heterogeneous multi-core optical fiber into the low refractive index sleeve and tapering the heterogeneous multi-core optical fiber is determined by a local coupling mode process. In this process, a single input vortex beam can be decomposed into even component of vector mode and odd mode with pi/2 phase difference. The evolution process and the result of the two modes in the cone region are slightly different, generally, the even mode of the optical fiber can evolve to the symmetrical supermode of the heterogeneous multi-core optical fiber end, and the odd mode of the optical fiber can evolve to the antisymmetric supermode of the heterogeneous multi-core optical fiber. If a non-0 or non-pi phase difference exists between the two evolved supermodes, gaussian fundamental modes in the two fiber cores are excited simultaneously, and a one-to-one correspondence between vortex light beams and Gaussian fundamental modes in a single fiber core cannot be formed.
The mode phase transformation resulting from the mode evolution in the mode-converting tapered region is mainly divided into two parts, one part being called the kinetic phase, which is determined by integrating the propagation constants of the eigenmodes of each profile in the tapered region along the tapered length and the shape expression ρ (z). The other part of the phase, which may be called the geometric phase, is determined by the energy distribution evolution process of each mode in the tapering region, irrespective of the tapering length of the tapering region. By calculating the geometric phase and the kinetic phase, the optimal length and shape of the mode conversion tapering region can be obtained to realize that the accumulated phase difference between the input odd mode and even mode is pi/2, so that the accumulated phase difference is overlapped with the initial phase difference of the odd mode and even mode which form vortex light beams to obtain 0 or pi phase difference, and the light waves injected from the input end can pass through the fan-in fan-out transition region and the mode conversion tapering region to form vortex light waves which can be stably transmitted in the few-mode optical fibers.
It is known that vortex light waves cannot be transmitted and maintained in optical fibers for a long distance, because bending, torsion, stress deformation and the like of the optical fibers can lead to degeneracy of vector modes forming vortex rotation, namely, the propagation constant separation of the vortex light waves cannot maintain a stable phase difference value, and finally, the mode energy is split, so that annular light beam output cannot be realized. However, if no significant loss of degenerate vector mode energy occurs during this process, a swirling output can be achieved at the output if this phase difference can be compensated for from the source side. The invention designs the optical loss and the phase modulator at the input end of the optical fiber, and the optical loss and the phase modulator are controlled by the driver, when the annular light spot outputting the loss light is detected to generate the split phenomenon, the phase movement of different modes in the section of the optical fiber can be compensated by the energy and the phase control of the input optical fiber, and the annular vortex light output is realized.
The low-mode crosstalk optical fiber used in the invention only can generate energy coupling between degenerate modes during bending and torsion, and can not generate mode crosstalk, namely, the energy of vortex mode can not be coupled to the optical fiber fundamental mode, and the excitation light beam is not influenced.
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 common collection method is to collect by using an objective lens with high numerical aperture, and the invention utilizes an imaging optical fiber to collect scattered light waves, and the scattered light waves are output to a single-mode port through reversing through the whole device. Wherein the scattered light waves couple at least the components of the LP02 mode of the mode fiber, can pass back through the device, are output to the single-mode output port 1-1 via the mode conversion tapering region and the fan-in fan-out transition region, and the excitation light and the loss light components in the feedback light waves can be removed by the optical filter.
The refractive index, diameter or refractive index profile type of part of fiber cores of the heterogeneous multi-core fiber are different, the number of the fiber cores is N, N is an integer, and N is more than or equal to 3. Wherein the corresponding core parameters with degenerate vortex modes are the same, e.g., the two core parameters corresponding to oam= ±1 modes are the same, and the core corresponding to the mode without degeneracy is unique, e.g., the core parameters corresponding to LP01 or LP02 modes at the output.
The refractive index profile of the fiber core in the heterogeneous multi-core fiber is step type, parabolic type and 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 for tapering, the tapering structure meets the conditions of adiabatic conversion and vortex phase matching, and single vortex mode energy can be converted into a guided mode of one fiber core in the heterogeneous multi-core optical fibers and has a corresponding relationship.
The few-mode optical fiber is few-mode optical fiber, annular core optical fiber or spiral few-mode optical fiber, and is characterized by being capable of conducting vortex modes.
The cladding structure of the heterogeneous multi-core optical fiber is a single cladding or double cladding, and the optical fiber structure formed by the inner cladding boundary after the tail end of the mode conversion tapering region is contracted and the rear end output few-mode optical fiber realize the matching of the mode field area and the numerical aperture.
And air holes and small-core-diameter fiber core structures are arranged between fiber cores in the heterogeneous multi-core fiber, so that the phase difference value of the symmetrical supermode and the antisymmetric supermode in the mode conversion tapering region is controlled. The phase difference between the supermodes has a remarkable relation with the end face 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 increased, the evolution of the supermodes in the cone region is different, and the phase difference is 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, the mode conversion tapering area, the fan-in fan-out tapering area and the input/output optical fiber matched with the front end all use multiple parts, so that the array-type step microscope is formed.
The optical fiber focusing lens is a spherical lens, an optical fiber end Fresnel lens or an optical fiber grinding cone lens, and has a focusing function.
Compared with the traditional photon lantern in the form of an optical fiber bundle, the vortex photon lantern based on the heterogeneous multi-core optical fiber increases the integration level and the stability of devices, so that the multi-core few-mode vortex photon lantern is possible. Otherwise, taking seven-core six-mode as an example, 42 different single-mode fibers are required to be inserted into the fluorine-doped tube with low refractive index in total, and the phase difference value is obviously impossible to control, and only a plurality of heterogeneous multi-core fibers are used and matched with a fan-in fan-out device, the vortex light wave output of a plurality of photon lantern by one-time tapering can be realized.
Compared with other types of optical fiber step microscopes, the invention provides the freely movable optical fiber with low intermodal crosstalk, and the optical fiber can move, bend and twist when in use, so that the size of an imaging lens is reduced, the application range of a device is widened, and the possibility is provided for larger-scale microscopic imaging.
The invention provides an all-fiber step microscope based on vortex rotation. The device converts the loss light incident from the single-mode input end into the optical fiber vortex mode by utilizing the vortex photon lantern prepared by the heterogeneous multi-core optical fiber, so that an annular output field is formed, meanwhile, the introduction of the low-mode inter-mode crosstalk optical fiber can greatly facilitate the expansion of the scanning range, the annular mode damage caused by the bending of the optical fiber can be counteracted by matching with the optical attenuation and the phase modulator of the input end, and the purity of the annular vortex rotation of the output end is ensured. Meanwhile, fluorescence energy of the substance is received by the few-mode optical fiber and returns to the single-mode output port, the device realizes integration of the input end and the output end of the step microscope, and the interference of the optical fiber bending equivalent to the vortex mode is counteracted by using the controller, so that the device is a novel optical fiber step microscope device with great potential.
Drawings
FIG. 1 is an overall block diagram of an all-fiber step microscope based on vortex rotation. The optical fiber comprises an input/output optical fiber 1, a 1X2 coupler 2, an optical attenuation and phase modulator 3, a double-cladding transition optical fiber 4, a porous capillary 5, a fan-in fan-out cone pulling area 6, a heterogeneous multi-core optical fiber 7, a low refractive index sleeve 8, a mode conversion cone pulling area 9, an output few-mode optical fiber 10, a low-mode inter-mode crosstalk optical fiber 11 and a fluorescent substance 12 to be measured. The figure shows the driver 14 of the optical attenuation and phase modulator, the single-mode output port 1-1, the excitation light input port 1-2, and the loss light input ports 1-3 and 1-4. The reason for using two loss optical ports is to use both the vortex beam of oam=1 and the vortex beam of oam=2.
FIG. 2 is a schematic cross-sectional view of a mode-switching cone-pull zone and fan-in-fan-out transition zone in an all-fiber step microscope based on a vortex photon lantern.
FIG. 3 is a schematic diagram of an end-face of a heterogeneous multi-core optical fiber used in the present invention, (a) a heterogeneous six-core optical fiber, (b) a heterogeneous three-core optical fiber, (c) a double-clad heterogeneous six-core optical fiber, (d) a double-clad heterogeneous three-core optical fiber, (e) a double-clad heterogeneous five-core optical fiber, and (f) a double-clad heterogeneous ten-core optical fiber. Wherein, the center of the optical fiber section in the figure (e) is a cladding or an air hole.
Fig. 4 is a schematic diagram of gaussian fundamental mode and heterogeneous multicore fiber supermode superposition switching for a single core. As can be seen from the figure, a single gaussian fundamental mode in two identical cores in a heterogeneous multi-core fiber can consist of a symmetrical supermode (the two cores are in the same phase) and an antisymmetric supermode (the two cores are in opposite phases). As shown in the figure, when two overmodes are directly overlapped, the two overmodes are equivalent to a Gaussian fundamental mode of a certain fiber core; when the antisymmetric supermode is subjected to 180-degree phase shift, the aliasing of the two supermodes is equivalent to the Gaussian fundamental mode in the other identical fiber core.
FIG. 5 is a plot of the propagation constants of the eigenmodes of the various sections in the mode-converting tapered region. The curves are respectively from top to bottom modes corresponding to 0-order vortex light, symmetrical supermodes related to +/-1-order vortex, antisymmetric supermodes related to +/-1-order vortex, symmetrical supermodes related to +/-2-order vortex, antisymmetric supermodes related to +/-2-order vortex and modes corresponding to radial 1-order light beams of 0-order vortex light beams.
FIG. 6 is a graph of the evolution of the various orders of vortex beam in the mode transition tapering region. The Gaussian guided mode of each fiber core in the heterogeneous multi-core fiber at the left end of the tapering region gradually evolves into each order vortex mode at the right end, and the process is reciprocal. The right end of the figure is the mode field distribution and the phase distribution of each order vortex beam.
FIG. 7 is a graph of conversion efficiency and noise results for a mode-converted tapered region in an all-fiber step microscope based on vortex rotation. The vertical column pictures are standard vortex modes in the few-mode optical fiber, the horizontal row pictures are patterns output by the vortex photon lantern after single-mode optical fiber injection, and the data in the pictures are integral results between two groups of modes. The data on the diagonal of the graph represents the loss of the vortex pattern in the mode conversion taper region, and the data on the off-diagonal represents the crosstalk of the vortex pattern in the mode conversion taper region. The purity of the output vortex mode is greater than 95%. The data units in the figure are dB.
Fig. 8 is an energy field simulation of a focused vortex beam in the propagation direction and an annular beam simulation on the focal plane with a small central dark hole radius and a scale less than the diffraction limit.
Detailed Description
The invention is further illustrated below in conjunction with specific examples.
Example 1: an all-fiber step microscope design based on vortex rotation.
Wherein the few-mode fiber uses a six-mode fiber with a core diameter of 18.5um and a numerical aperture of 0.12. Which can accommodate a variety of vortex beams with orbital angular momentum of + -2, + -1, 0. The heterogeneous multi-core optical fiber has 6 fiber cores, and each fiber core has 11um,9um, 8um and 6.5um core diameters, and a typical core spacing is 40um. The cladding index was 1.444 and the core cladding numerical aperture was 0.12. The low refractive index ferrule has a refractive index of 1.4398, and the ferrule inner diameter is equal to the outer diameter of the heterogeneous multicore fiber, 125um.
And inserting the heterogeneous multi-core optical fiber into a low-refractive-index sleeve for heat insulation tapering, so as to obtain the mode conversion tapering region. The shape and length of the taper can be determined by simulation. The length or shape of the cone region is adjusted, and aiming at vortex beams with different orders, the air holes among cores, the core spacing and the distance between small fiber cores and the center of the fiber cores are designed in a targeted manner, so that vortex beams with orbital angular momentum of + -2, + -1, 0 have phase movement of (N+0.5) pi, and a one-to-one correspondence is established between Gaussian beams in a single fiber core and output vortex states, and the relation diagram is shown in figure 7. A typical taper length is 4.2cm and the taper is a linear taper.
The fan-in and fan-out transition area is prepared by inserting double-clad transition optical fibers into a porous capillary tube and tapering.
Light waves with corresponding wavelengths which meet the stimulated radiation loss of fluorescent substances are injected through ports 1-3 and 1-4, are transmitted into corresponding fiber cores of heterogeneous multi-core optical fibers through fan-in and fan-out transition areas, are converted into annular vortex modes through mode conversion tapering areas, are output into at least mode light, are output to an optical fiber focusing lens through low-mode inter-mode crosstalk optical fibers, and are transmitted to the surface of the fluorescent substances to be measured. At this point a ring-shaped depletion beam is formed as shown in the central dark edge of fig. 8. When the back end low-mode inter-mode crosstalk optical fiber splits into optical fiber scalar modes due to bending, when the annular optical field is destroyed, the optical attenuation and the phase modulator can be adjusted to compensate the variation so that the optical attenuation and the phase modulator still output the vortex optical field.
The port 1-2 is used for injecting excitation light which accords with the excitation wavelength of fluorescent substances, the excitation light is transmitted into the corresponding fiber cores of heterogeneous multi-core optical fibers through a fan-in and fan-out transition region, the light waves are converted into Gaussian fundamental modes in few-mode optical fibers through a mode conversion tapering region, the Gaussian fundamental modes are output to an optical fiber focusing lens through a low-mode inter-mode crosstalk optical fiber, the focused excitation light is transmitted to the surface of the fluorescent substances to be detected, the loss light inhibits the fluorescence excitation of an annular region, so that only a central dark region can excite the fluorescence of the substances, and the region scale is smaller than the wavelength, so that super-resolution imaging can be realized.
The fluorescence emitted by the fluorescent substance to be detected is incident into at least a mode optical fiber, wherein light waves belonging to the LP02 mode can reversely pass through the device, the light waves are output to a 1-1 port through a mode conversion tapering area and a fan-in fan-out area, and interference of excitation light and loss light can be removed by means of an optical filter and the like, so that super-resolution imaging is realized.
Claims (9)
1. An all-fiber step microscope based on vortex rotation is characterized in that: the system consists of an input/output optical fiber (1), a 1X2 coupler (2), an optical attenuation and phase modulator (3), a double-cladding transition optical fiber (4), a porous capillary tube (5), a fan-in fan-out tapering region (6), a heterogeneous multi-core optical fiber (7), a low refractive index sleeve (8), a mode conversion tapering region (9), an output few-mode optical fiber (10), a low-mode inter-mode crosstalk optical fiber (11), an optical fiber focusing lens (12) and a fluorescent substance (13) to be detected, wherein two light waves are input into the input/output optical fiber (1) in the system, one is excitation light, and the other is loss light; excitation light is input from an optical fiber port (1-2), is subjected to fanning-in fanning-out tapering region 6 prepared by tapering through jacks of a double-clad transition optical fiber (4) and a porous capillary (5), is coupled to a certain fiber core in a heterogeneous multi-core optical fiber (7), is subjected to mode conversion tapering region (9) formed by tapering by combining a low refractive index sleeve (8) and the heterogeneous multi-core optical fiber (7), forms a fundamental mode in an output few-mode optical fiber (10), is transmitted to an optical fiber focusing lens (12) through a low-mode crosstalk optical fiber (11), and is finally projected on the surface of a fluorescent substance (13) to be detected, wherein a light spot is Gaussian; the loss light is input by an optical fiber port (1-3) or (1-4), the light wave is divided into two equal power beams by a 1X2 coupler (2), the two equal power beams are respectively connected into a rear-end double-cladding transition optical fiber (4) through the output end of the coupler, each path is provided with a light attenuation and phase modulator (3) for controlling the light power and the phase, the two light waves are converted into the guiding fundamental modes of two identical fiber cores in a heterogeneous multi-core optical fiber through a fan-in fan-out tapering region (6), the fundamental modes are converted into vortex modes by a mode conversion tapering region (9), and the vortex modes are projected on the surface of a fluorescent substance (13) to be detected through a low-mode inter-interference optical fiber (11) and an optical fiber focusing lens (12), and the light spots are annular; the annular light spot of the loss light suppresses 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 at the center of the superposition of the annular light spot and the Gaussian light spot, fluorescence generated by the area can be received by the optical fiber end, energy received by the optical fiber can reversely pass through the whole device, and finally, the energy is output to a receiver through a single-mode output port (1-1).
2. An all-fiber, vortex-based, step microscope system according to claim 1, characterized in that: the refractive index, diameter or refractive index profile type of part of fiber cores of the heterogeneous multi-core fiber are different, the number of the fiber cores is N, N is an integer, and N is more than or equal to 3.
3. An all-fiber, vortex-based, step microscope system according to claim 1, characterized in that: the refractive index profile of the fiber core in the heterogeneous multi-core fiber is step type, parabolic type and Gaussian type.
4. An all-fiber, vortex-based, step microscope system according to claim 1, characterized in that: the mode conversion tapering region is formed by inserting heterogeneous multi-core optical fibers with special structures into a low refractive index sleeve for tapering, the tapering structure meets the conditions of adiabatic conversion and vortex phase matching, and single vortex mode energy can be converted into a guided mode of one fiber core in the heterogeneous multi-core optical fibers and has a corresponding relationship.
5. An all-fiber, vortex-based, step microscope system according to claim 1, characterized in that: the few-mode optical fiber is few-mode optical fiber, annular core optical fiber or spiral few-mode optical fiber, and is characterized by being capable of conducting vortex modes.
6. An all-fiber, vortex-based, step microscope system according to claim 1, characterized in that: the cladding structure of the heterogeneous multi-core optical fiber is a single cladding or double cladding, and the optical fiber structure formed by the inner cladding boundary after the tail end of the mode conversion tapering region is contracted and the rear end output few-mode optical fiber realize the matching of the mode field area and the numerical aperture.
7. An all-fiber, vortex-based, step microscope system according to claim 1, characterized in that: and air holes and small-core-diameter fiber core structures are arranged between fiber cores in the heterogeneous multi-core fiber, so that the phase difference value of the symmetrical supermode and the antisymmetric supermode in the mode conversion tapering region is controlled.
8. An all-fiber, vortex-based, step microscope system according to claim 1, characterized in that: 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, the mode conversion tapering area, the fan-in fan-out tapering area and the input/output optical fiber matched with the front end all use multiple parts, so that the array-type step microscope is formed.
9. An all-fiber, vortex-based, step microscope system according to claim 1, characterized by: the optical fiber focusing lens is a spherical lens, an optical fiber end Fresnel lens or an optical fiber grinding cone lens, and has a focusing function.
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