An asymmetrically tapered optical fiber probe and method and apparatus

Abstract

The application provides an asymmetric pyramid optical fiber probe and a method and device, wherein the asymmetric pyramid optical fiber probe comprises: an asymmetric pyramid optical fiber core layer, the surface of the asymmetric pyramid optical fiber core layer is covered with a metal film layer; when the number of pyramid edges of the asymmetric pyramid optical fiber core layer is odd, the asymmetric pyramid optical fiber core layer comprises an arbitrary pyramid geometric shape; when the number of pyramid edges of the asymmetric pyramid optical fiber core layer is even, the geometric shape of the asymmetric pyramid optical fiber core layer is not symmetric about any axis of space and is not symmetric about any axis center. Under the incidence of linear polarization laser, the application can excite surface plasmons on the asymmetric pyramid surface of the probe and propagate to the probe tip to form a focused light field, so that high-resolution and high-signal-intensity near-field optical measurement is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of near-field optical imaging, and relates to an asymmetric pyramidal optical fiber probe and a method and device. BACKGROUND

[0002] With the advent of near-field optical microscopy, people can break through the limit of the diffraction limit, detect near-field optical signals in the near-field range of the sample surface, and realize optical measurement with nanoscale resolution.

[0003] In the traditional near-field optical microscopy based on the optical fiber probe, people usually use an aperture optical fiber probe with a hundred-nanometer-diameter small hole at the tip or a conical optical fiber probe covered with a metal thin film layer for near-field optical detection. The aperture optical fiber probe collects near-field optical information through a hundred-nanometer-diameter light transmission hole at the tip, which determines that the signal strength is closely related to the size of the aperture. The larger the aperture, the stronger the signal. However, an excessively large aperture size will restrict the resolution, making it difficult to break through the hundred-nanometer scale. The conical optical fiber probe covered with a metal thin film layer excites surface plasmons on the surface of the conical metal thin film layer through the incidence of radially polarized light, and the surface plasmons propagate along the metal thin film layer to the tip to form a nanoscale focused light field, greatly enhancing the intensity of the near-field optical signal while improving the resolution. However, the modulation and coupling conditions of the radially polarized light are very harsh, requiring a large and complex spatial modulation and coupling light path, and the mode is easily distorted during transmission in the optical fiber, leading to mode distortion. Moreover, in the practice of probe preparation, the conical geometry of the needle tip is difficult to ensure accurate preparation, and the imperfections of the geometric symmetry and the flatness of the needle tip surface greatly reduce the conversion of radially polarized light to surface plasmons and the propagation and focusing efficiency, thereby affecting the detection signal strength. SUMMARY

[0004] In order to solve the problems in the prior art, the present application provides an asymmetric pyramidal optical fiber probe and a method and device, which can excite surface plasmons on the asymmetric pyramidal surface of the probe under the incidence of linearly polarized laser and propagate to the probe tip to form a focused light field, realizing high-resolution and high-signal-strength near-field optical measurement.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical scheme: an asymmetric pyramidal optical fiber probe, comprising: an asymmetric pyramidal optical fiber core layer, the surface of the asymmetric pyramidal optical fiber core layer being covered with a metal thin film layer; when the number of pyramidal edges of the asymmetric pyramidal optical fiber core layer is odd, the asymmetric pyramidal optical fiber core layer contains any pyramidal geometric shape; when the number of pyramidal edges of the asymmetric pyramidal optical fiber core layer is even, the geometric shape of the asymmetric pyramidal optical fiber core layer is not symmetric about any one axis in space and not symmetric about any one axis center.

[0006] Further, the pyramidal curvature radius is 1nm-1000nm, and the aspect ratio of the pyramidal seen from any direction is 0.5-10.

[0007] Further, the thickness of the metal film layer is 1nm-300nm, and the material of the metal film layer includes but is not limited to one of gold, silver, platinum, copper, aluminum and chromium.

[0008] The application further provides a preparation method of the asymmetric pyramidal optical fiber probe.

[0009] After the optical fiber is horizontally cut, the chemical etching method is used to insert into hydrofluoric acid for etching, and after the etching is completed, the optical fiber is inserted into an organic solvent to dissolve and soften the organic coating layer on the outer wall of the optical fiber, and after the coating layer is removed, the optical fiber core layer with a conical nanoscale tip is obtained.

[0010] The conical optical fiber core layer is cut and modified into an asymmetric pyramidal optical fiber core layer from the side by using a focused ion beam.

[0011] A metal film layer is prepared on the surface of the asymmetric pyramidal optical fiber core layer to obtain the asymmetric pyramidal optical fiber probe.

[0012] Further, after the optical fiber is horizontally cut, the end face of the optical fiber is inserted into hydrofluoric acid with a concentration of 30%-40% for etching for 1h-4h, the end face of the optical fiber forms a conical needle tip, the end face of the conical needle tip of the optical fiber is inserted into an organic solvent to dissolve for 30s-120s, the organic coating layer on the outer wall of the optical fiber is dissolved and softened, and after the coating layer is removed, the optical fiber core layer with a conical nanoscale tip is obtained.

[0013] Further, the organic solvent includes but is not limited to one of acetone, butanone, methanol, ethanol and carbon tetrachloride.

[0014] Further, the focused ion beam is a gallium ion beam, and the current is 1A-10A.

[0015] Further, the metal film layer is prepared on the surface of the asymmetric pyramidal optical fiber core layer by using an electron beam evaporation method or a magnetron sputtering method. -5 Bar, the metal evaporation rate is 0.1nm / s-0.5nm / s; the process condition of the magnetron sputtering method is that the temperature is 25℃-150℃, the vacuum degree in the cavity is less than 1×10 -5 Bar, the voltage is 360V-400V, the current of the metal target material is controlled to be 0.5A-6A, and the deposition rate of the metal film layer is 0.1nm / s-0.5nm / s.

[0016] The application further provides a near-field optical microscope using the asymmetric pyramidal optical fiber probe.

[0017] Further, when the near-field optical microscope is used for sample testing, linearly polarized light is incident from the tail end of the fiber core of the asymmetric conical fiber probe, surface plasmons are excited on the surface of the metal thin film layer, the surface plasmons propagate along the metal thin film layer to the tip of the asymmetric conical fiber probe, and a focused light field is formed at the tip; when the tip of the asymmetric conical fiber probe interacts with the surface of the sample, the near-field optical information of the surface of the sample to be measured excited by the focused light field of the tip of the asymmetric conical fiber probe returns to the fiber in the form of plasmons, and the detected near-field optical signal is collected at the tail of the light.

[0018] Compared with the prior art, the present application has at least the following beneficial effects:

[0019] The present application provides an asymmetric conical fiber probe, which is designed in an asymmetric conical geometric shape, so that the probe can excite surface plasmons and focus to form a nanoscale light field under the simplest linearly polarized light incidence, has extremely high processing precision and focusing effect. When surface plasmons are excited and focused, it has high polarization direction insensitivity, can realize excitation and focusing of surface plasmons in a wide range of polarization directions, and increases the flexibility and application range.

[0020] The preparation method of the asymmetric conical fiber probe of the present application obtains a conical tip by chemical etching method, greatly saves the time and cost of subsequent focused ion beam processing, and improves the preparation efficiency. The method combining chemical etching method and focused ion beam cutting modification has simple and controllable preparation process, and can accurately prepare a fiber probe with asymmetric conical geometric shape. During preparation and processing, as long as the asymmetric characteristic is met, excitation and focusing of surface plasmons can be realized, which has high fault tolerance and reduces the preparation difficulty.

[0021] The asymmetric conical fiber probe of the present application is used in a near-field optical microscope, which can realize high-resolution imaging at the nanoscale and provide a more delicate observation means for scientific research. The focused light field of the probe tip can interact with the surface of the sample to be measured, excite near-field optical information in the form of plasmons, return to the fiber, and realize sensitive detection of the near-field optical information of the sample surface. The near-field optical microscope of the present application has wide application prospects in the fields of material science, biology, physics, etc., and can be used for studying the structure and properties of substances at the nanoscale, providing a powerful tool for scientific research and technological innovation. BRIEF DESCRIPTION OF DRAWINGS

[0022] The drawings described herein are used to provide further understanding of the present application, constitute a part of the present application, and do not constitute an improper limitation on the present application, and in the drawings:

[0023] Figure 1is a schematic diagram of an asymmetric odd number of pyramid fiber probe structure represented by an asymmetric four-pyramid;

[0024] Figure 2 is a schematic diagram of an asymmetric odd number of pyramid fiber probe structure;

[0025] Figure 3 is the simulation result of the fiber probe of embodiment 1;

[0026] Figure 4 is the simulation result of the fiber probe of embodiment 2;

[0027] Figure 5 is the simulation result of the fiber probe of embodiment 3.

[0028] In the figure: 1, fiber core layer; 2, metal film layer; 3, surface plasmon; 4, focused light field; 5, nanofocused light field. DETAILED DESCRIPTION

[0029] The application will be further described below in conjunction with the drawings and specific embodiments.

[0030] The application provides an asymmetric pyramid fiber probe based on linearly polarized light incidence, using a chemical etching method to etch a fiber base material to form a large-angle conical needle tip, using a focused ion beam etching to cut and modify the needle tip into an asymmetric pyramid, and then covering a metal film layer 2 on the surface of the asymmetric pyramid to obtain an asymmetric pyramid fiber probe, and a preparation method of the asymmetric pyramid fiber probe, comprising the following steps.

[0031] Step 1, after the fiber is horizontally cut, a chemical etching method is used, one end of the fiber is inserted into hydrofluoric acid with a concentration of 30% to 40% for etching for 1h to 4h. After etching is completed, the fiber is inserted into an organic solvent for 30s to 120s to dissolve and soften the organic coating layer on the outer wall of the fiber, and after the coating layer is removed, a fiber core layer 1 with a conical nanoscale tip is obtained.

[0032] Preferably, the fiber is a standard single-mode fiber or a multi-mode fiber;

[0033] Preferably, the organic solvent includes but is not limited to one of acetone, butanone, methanol, ethanol, and carbon tetrachloride

[0034] Step 2, a focused ion beam is used to cut and modify the conical fiber core layer into an asymmetric pyramid fiber core layer 1 from the side.

[0035] Preferably, the focused ion beam is a gallium ion beam with a current of 1A to 10A.

[0036] Step 3, a 1nm~300nm thick metal film layer 2 is coated on the surface of the asymmetric prism fiber core layer 1 by using electron beam evaporation or magnetron sputtering method, to obtain the asymmetric prism fiber probe.

[0037] Preferably, the electron beam evaporation method is as follows: the asymmetric prism fiber core layer in step 2 is placed in the evaporation cavity, the fiber is perpendicular to the target material direction, the hatch is closed to vacuumize, the vacuum degree in the cavity is less than 1×10 -5 Bar, the metal evaporation rate is set to 0.1nm / s~0.5nm / s until the target thickness;

[0038] The magnetron sputtering method is as follows: the asymmetric prism fiber core layer in step 2 is placed in the evaporation cavity, the temperature of the magnetron sputtering deposition equipment is adjusted to 25℃~150℃, the vacuum degree in the cavity is less than 1×10 -5 Bar, the voltage is 300~400V, the current of the metal target material is controlled to 0.5A~6A, and the deposition rate of the metal film layer 2 is 0.1nm / s~0.5nm / s.

[0039] Preferably, the material of the metal film layer 2 is gold, silver, aluminum, chromium or titanium.

[0040] Preferably, the shape of the asymmetric prism fiber probe is a prism with a number of prisms between 3 and 15.

[0041] Preferably, when the number of prisms of the asymmetric prism fiber probe is even, the geometric shape of the asymmetric prism fiber probe is not symmetric about any one axis of space and not symmetric about the center of any one axis.

[0042] Preferably, when the number of prisms of the asymmetric prism fiber probe is odd, the geometric shape of the asymmetric prism fiber probe is not limited.

[0043] Preferably, the radius of curvature of the probe prism tip is 1nm~1000nm, and the smaller the radius of curvature of the needle tip, the smaller the nanometer light field scale formed by focusing, and the higher the near-field optical resolution.

[0044] Preferably, the aspect ratio of the asymmetric prism fiber probe in any direction is 0.5~10.

[0045] When the asymmetric prism fiber probe of the application is used, under the irradiation of linearly polarized laser in the fiber, the metal film layer 2 can effectively excite surface plasmon resonance, the surface plasmon propagates along the tapered metal film layer 2 to the tip, and due to the geometric asymmetry of the probe tip prism, the surface plasmon excited on each side and prism by linearly polarized laser does not satisfy the interference cancellation condition when reaching the needle tip, so a focused enhanced light field can be formed at the needle tip for near-field optical detection.

[0046] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0047] Example 1

[0048] The preparation of asymmetric even-numbered pyramid fiber probe is as follows:

[0049] Step 1: After horizontally cutting a standard single-mode optical fiber, one end of the fiber is etched in 40% hydrofluoric acid for three hours. After etching, the fiber is immersed in acetone to dissolve and soften the organic coating on the outer surface of the fiber. After removing the coating, the fiber core with a conical nanometer-scale tip is obtained.

[0050] Step 2: Using a focused ion beam, the conical optical fiber core layer is cut and modified from the side into an asymmetric even-numbered pyramid optical fiber core layer 1, wherein the number of edges is 4, the curvature radius of the pyramid tip is 20 nm, and the aspect ratio viewed in any direction is 2;

[0051] Step 3: Using electron beam evaporation, the vacuum degree in the cavity is less than 1×10 -5 Bar, set the metal evaporation rate to 0.1nm / s, and cover the surface of the asymmetric even-numbered pyramid optical fiber core layer 1 with a 100nm thick silver metal film layer, as shown below: Figure 1 The asymmetric even-pyramid optical fiber probe shown in the figure has the following asymmetric characteristics: it is not axisymmetric with respect to any axis in space and is not centrally symmetric about any axis.

[0052] Under the incident of linearly polarized laser light, surface plasmons 3 are excited on the surface of the silver metal film layer. Surface plasmons 3 propagate along the conical silver metal film layer toward the tip. Due to the geometric asymmetry of the pyramid at the tip of the probe of the present invention, the surface plasmons excited by the linearly polarized laser light on each side and edge do not meet the interference destructive condition when reaching the tip. Therefore, a focused light field 4 is formed at the tip. The simulation results are as follows: Figure 3 As shown, a nano-focused light field 5 is formed at the needle tip for near-field optical detection.

[0053] Example 2

[0054] The preparation of the asymmetric odd number pyramid optical fiber probe is specifically as follows:

[0055] Step 1, after the standard multimode optical fiber is horizontally cut, the etching method is used to insert one end of the optical fiber into hydrofluoric acid with a concentration of 40% for 4 hours. After the etching is completed, the optical fiber outer wall organic coating layer is dissolved and softened by inserting into acetone, and the fiber core layer with a conical shape nanometer scale tip is obtained after the coating layer is removed.

[0056] Step 2, the focused ion beam is used to cut and modify the conical shape fiber core layer into an asymmetric odd number pyramid optical fiber probe fiber core layer 1 from the side, the number of edges is 3, the pyramid tip curvature radius is 100 nm, and the aspect ratio viewed in any direction view is 3;

[0057] Step 3, the magnetron sputtering method is used, the temperature of the magnetron sputtering deposition equipment is adjusted to 100 ℃, the cavity vacuum degree is less than 1×10 -5 Bar, the voltage is 350 V, the current of the metal target is 6 A, the metal thin film layer deposition rate is 0.2 nm / s, a 200 nm thick aluminum metal thin film layer is covered on the surface of the asymmetric even number pyramid optical fiber core layer 1, and the asymmetric odd number pyramid optical fiber probe as shown in Figure 2 is obtained.

[0058] Under the incidence of linear polarized laser, surface plasmons 3 are excited on the surface of the aluminum metal thin film layer and propagate towards the tip, and finally form a focused light field 4 at the tip, and the simulation result is as shown in Figure 4 , and a nanometer focused light field 5 is formed at the tip.

[0059] Example 3

[0060] The preparation of the asymmetric odd number pyramid optical fiber probe is specifically as follows:

[0061] Step 1, after the standard single mode optical fiber is horizontally cut, the etching method is used to insert one end of the optical fiber into hydrofluoric acid with a concentration of 40% for 1 hour. After the etching is completed, the optical fiber outer wall organic coating layer is dissolved and softened by inserting into acetone, and the fiber core layer with a conical shape nanometer scale tip is obtained after the coating layer is removed.

[0062] Step 2, the focused ion beam is used to cut and modify the conical shape fiber core layer into an asymmetric odd number pyramid optical fiber core layer 1 from the side, the number of edges is 5, the pyramid tip curvature radius is 20 nm, and the aspect ratio viewed in any direction view is 5;

[0063] Step 3, the electron beam evaporation method is used, the cavity vacuum degree is less than 1×10 -5Bar, set the metal evaporation rate 0.5nm / s, on the surface of the asymmetric even number of pyramid optical fiber core layer 1 covered with a layer of 100nm thick gold metal film layer, get asymmetric even number of pyramid optical fiber probe, its asymmetric characteristics include not with space any axis axisymmetric and not about any axis center symmetric.

[0064] Under the incidence of linearly polarized laser, surface plasmons 3 are excited on the surface of the gold metal film layer, and the surface plasmons 3 propagate along the tapered silver metal film layer to the tip direction. Because the tip pyramid of the probe has geometric asymmetry, the surface plasmons excited on each side and the ridge by the linearly polarized laser do not satisfy the interference cancellation condition when they reach the needle tip, so a focused light field 4 is formed at the needle tip, which is used for near-field optical detection.

[0065] Under the incidence of linearly polarized laser, surface plasmons 3 are excited on the surface of the gold metal film layer, and the surface plasmons 3 propagate along the tapered silver metal film layer to the tip direction. Because the tip pyramid of the probe has geometric asymmetry, the surface plasmons excited on each side and the ridge by the linearly polarized laser do not satisfy the interference cancellation condition when they reach the needle tip, so a focused light field 4 is formed at the needle tip, which is used for near-field optical detection. Figure 5 As shown in the simulation results, a nanometer focused light field 5 is formed at the needle tip.

[0066] Example 4

[0067] The difference between this embodiment and example 2 is that in step 2, the asymmetric even number of pyramid optical fiber core layer 1 has 3 ridges, and the curvature radius of the pyramid tip is 1nm, and the aspect ratio viewed in any direction is 0.5.

[0068] Example 5

[0069] The difference between this embodiment and example 2 is that in step 2, the asymmetric even number of pyramid optical fiber core layer 1 has 15 ridges, and the curvature radius of the pyramid tip is 1000nm, and the aspect ratio viewed in any direction is 10.

[0070] Example 6

[0071] The difference between this embodiment and example 1 is that in step 3, an electron beam evaporation method is used, and a metal evaporation rate of 0.5nm / s is set to cover a layer of 1nm thick titanium metal film layer 2 on the surface of the asymmetric even number of pyramid optical fiber core layer 1.

[0072] Example 7

[0073] The difference between this embodiment and example 1 is that in step 3, an electron beam evaporation method is used, and a metal evaporation rate of 0.3nm / s is set to cover a layer of 300nm thick chromium metal film layer 2 on the surface of the asymmetric even number of pyramid optical fiber core layer 1.

[0074] Example 8

[0075] The difference between the embodiment and the embodiment 1 is that in step 3, the temperature of the magnetron sputtering deposition device is adjusted to 25 DEG C by using the magnetron sputtering method, the vacuum degree in the cavity is less than 1*10 -5 The Bar voltage is 400 V, the current of the metal target is 0.5 A, and the deposition rate of the metal thin film layer is 0.1 nm / s.

[0076] Embodiment 9

[0077] The difference between the embodiment and the embodiment 1 is that in step 3, the temperature of the magnetron sputtering deposition device is adjusted to 150 DEG C by using the magnetron sputtering method, the vacuum degree in the cavity is less than 1*10 -5 The Bar voltage is 300 V, the current of the metal target is 5 A, and the deposition rate of the metal thin film layer is 0.5 nm / s.

[0078] Embodiment 10

[0079] The difference between the embodiment and the embodiment 1 is that in step 1, the optical fiber is inserted into the hydrofluoric acid with a concentration of 30% for etching for 1 hour by using the etching method.

[0080] Embodiment 11

[0081] The difference between the embodiment and the embodiment 1 is that in step 1, the optical fiber is inserted into the hydrofluoric acid with a concentration of 30% for etching for 3 hours by using the etching method.

[0082] Embodiment 12

[0083] The difference between the embodiment and the embodiment 1 is that in step 1, the optical fiber is inserted into the hydrofluoric acid with a concentration of 30% for etching for 4 hours by using the etching method.

[0084] Embodiment 13

[0085] The application provides a working method of the above-mentioned pyramidal tip optical fiber probe for exciting and collecting near-field optical signals, and the working method comprises the following processes:

[0086] The asymmetric pyramidal optical fiber probe for exciting and collecting near-field optical signals is installed on a near-field optical microscope.

[0087] When the sample is tested, linearly polarized laser beams are incident on the cone through the fiber core to excite surface plasmons, the surface plasmons propagate along the cone to the tip to form a nanoscale local light spot.

[0088] When the tip and the surface of the sample interact, the near-field light of the sample surface scatters to the far field, and at this time, the scattered light signal can be directly collected by an objective lens on the side or directly below the sample.

[0089] In addition, the near-field optical information of the measured sample surface excited by the focused light field of the asymmetric pyramid fiber probe tip can also return to the optical fiber in the form of plasmons, and the detected near-field optical signal can be collected at the tail of the light.

[0090] Compared with the conventional fiber probe, the asymmetric pyramid geometry of the tip of the present application can directly excite surface plasmons under the incidence of linearly polarized laser (the laser light is generally linearly polarized laser) and form a focused spot at the tip. It is not necessary to modulate the linearly polarized laser into radial polarization light to excite and focus plasmons, which greatly reduces the complexity of the system optical path. And because there is no need to modulate the radial polarization light in the spatial optical path, the illumination and collection process of the probe can be completed in the fiber optical path, greatly improving the signal-to-noise ratio.

[0091] In the preparation of the asymmetric pyramid fiber probe of the present application, the conical tip is obtained by using chemical etching method, which saves a lot of time and cost for subsequent focused ion beam processing and modification, and further using focused ion beam etching method has high processing precision. The asymmetric pyramid geometry formed can excite surface plasmons under the incidence of the simplest linearly polarized light and focus to form a nanoscale light field, without the need to modulate special polarization state laser. And the asymmetric pyramid geometry of the fiber probe of the present application has high polarization direction insensitivity when exciting and focusing surface plasmons. Surface plasmons can be excited and focused to form a focused light field in a wide range of polarization directions, thereby realizing high-resolution and high-signal-intensity near-field optical measurement.

[0092] The present application is not limited to the above embodiments. Based on the technical solutions disclosed in the present application, those skilled in the art can make some substitutions and modifications to some technical features without creative labor, and these substitutions and modifications are within the protection scope of the present application.

Claims

1. An asymmetric pyramidal optical fiber probe, characterized in that: include: An asymmetric pyramid optical fiber core layer (1), wherein the surface of the asymmetric pyramid optical fiber core layer is covered with a metal thin film layer (2); When the number of pyramid edges of the asymmetric pyramid optical fiber core layer (1) is an odd number, any pyramid geometric shape is included; when the number of pyramid edges of the asymmetric pyramid optical fiber core layer (1) is an even number, the geometric shape of the asymmetric pyramid optical fiber core layer (1) is not axisymmetric about any axis in space and is not centrosymmetric about any axis.

2. The asymmetric pyramid optical fiber probe according to claim 1, characterized in that: The pyramid curvature radius is 1 nm to 1000 nm, and the aspect ratio of the pyramid viewed from any viewing angle is 0.5 to 10.

3. The asymmetric pyramid optical fiber probe according to claim 1, characterized in that: The thickness of the metal film layer (2) is 1 nm to 300 nm, and the material used for the metal film layer (2) includes but is not limited to one of gold, silver, platinum, copper, aluminum, and chromium.

4. A method for preparing an asymmetric pyramid optical fiber probe according to any one of claims 1 to 3, characterized in that: The following steps are involved: After cutting the optical fiber horizontally, the fiber is etched in hydrofluoric acid using a chemical etching method. After the etching is completed, the fiber is inserted into an organic solvent to dissolve and soften the organic coating on the outer wall of the optical fiber. After removing the coating, the optical fiber core layer with a conical nanometer-scale tip is obtained. Using a focused ion beam to cut and modify the conical fiber core from the side into an asymmetric pyramidal fiber core (1); A metal film layer (2) is prepared on the surface of an asymmetric pyramid optical fiber core layer (1) to obtain an asymmetric pyramid optical fiber probe.

5. The method for preparing an asymmetric pyramid optical fiber probe according to claim 4, characterized in that: After cutting the optical fiber horizontally, the end face of the optical fiber is inserted into hydrofluoric acid with a concentration of 30% to 40% for etching for 1 hour to 4 hours to form a conical needle tip on the end face of the optical fiber. The conical needle tip of the optical fiber is then inserted into an organic solvent for 30 seconds to 120 seconds to dissolve and soften the organic coating on the outer wall of the optical fiber. After removing the coating, the optical fiber core layer with a conical nanoscale tip is obtained.

6. The method for preparing an asymmetric pyramid optical fiber probe according to claim 5, characterized in that: The organic solvent includes but is not limited to one of acetone, butanone, methanol, ethanol, and carbon tetrachloride.

7. The method for preparing an asymmetric pyramid optical fiber probe according to claim 4, characterized in that: The focused ion beam is a gallium ion beam, and the current is 1A-10A.

8. The method for preparing an asymmetric pyramid optical fiber probe according to claim 4, characterized in that: The metal thin film layer (2) is prepared on the surface of the asymmetric pyramid optical fiber core layer (1) by electron beam evaporation or magnetron sputtering. The process condition of the electron beam evaporation method is that the vacuum degree is less than 1×10 -5 Bar, metal evaporation rate 0.1nm / s~0.5nm / s; the process conditions of magnetron sputtering are temperature 25℃~150℃, vacuum degree in the chamber is less than 1×10 -5 Bar, voltage is 360V~400V, the current of the metal target is controlled to be 0.5A~6A, and the deposition rate of the metal thin film layer is 0.1nm / s~0.5nm / s.

9. A near-field optical microscope, characterized in that The asymmetric pyramid optical fiber probe according to any one of claims 1 to 3 is used.

10. The near-field optical microscope according to claim 9, characterized in that: When the near-field optical microscope is used to test a sample, linearly polarized light is incident from the tail end of the optical fiber core (1) of the asymmetric pyramid optical fiber probe, exciting surface plasmons (3) on the surface of the metal film layer (2), and the surface plasmons (3) propagate along the metal film layer (2) toward the tip of the asymmetric pyramid optical fiber probe, forming a focused light field (4) at the tip; when the tip of the asymmetric pyramid optical fiber probe interacts with the surface of the sample, the near-field optical information of the surface of the sample being tested excited by the focused light field (4) of the tip of the asymmetric pyramid optical fiber probe returns to the optical fiber in the form of plasmons, and the detected near-field optical signal is collected at the tail end of the light.

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