Surface encapsulated micro-nano fiber based on evanescent field photocuring and surface coating preparation device and method

Abstract

This invention discloses a micro / nano optical fiber and surface coating preparation device and method based on evanescent field photocuring for surface encapsulation. The device includes standard optical fibers at both ends, a middle waist fiber, and two transition fiber sections connecting the standard and waist fibers. An ultraviolet (UV) adhesive coating is attached to the waist fiber. Low-refractive-index UV adhesive is cured in situ using an evanescent field transmitted on the outer surface of the micro / nano optical fiber, forming a surface coating that conforms to the fiber's own structure. The coating thickness is as low as the micrometer level. This effectively isolates the evanescent field and avoids surface contamination of the optical fiber, while reducing the size of the micro / nano optical fiber sensor, achieving a spatial resolution at the micrometer level, which is beneficial for miniaturization and integration. The use of low-refractive-index UV adhesive as the coating material ensures that the coating refractive index is lower than that of the optical fiber, allowing the optical signal transmission to meet the total internal reflection waveguide condition, ensuring low-loss transmission. Furthermore, the UV adhesive cures instantaneously within 0.1–1 s under UV light irradiation, supporting the formation of the surface coating during rapid movement.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber surface functionalization and sensing applications, specifically relating to a micro / nano optical fiber and surface coating preparation device and method based on evanescent field photocuring to achieve surface encapsulation. Background Technology

[0002] Micro- and nano-fibers are optical waveguides with diameters close to or smaller than their transmission wavelength. When light propagates through micro- and nano-fibers, a significant portion of the energy exists as an evanescent field on the fiber surface, which is highly sensitive to changes in the refractive index of the environment. This characteristic gives them unique advantages in constructing highly sensitive, fast-response, and small-sized sensors. However, micro- and nano-fibers without surface coatings are susceptible to various environmental factors. For example, the surface of micro- and nano-fibers easily attracts dust from the air, leading to strong scattering loss and affecting the normal operation of micro- and nano-fiber sensors. Although the detection of piconewton-level and even femtonew-level forces has been achieved using micro- and nano-fibers without surface coatings, these sensors have high requirements for the cleanliness, temperature stability, and airflow stability of the testing environment.

[0003] To avoid the influence of environmental factors on micro / nano fiber optic sensors, researchers have proposed encapsulating micro / nano fiber optic sensing structures with low-refractive-index materials. Commonly used materials include polydimethylsiloxane, Teflon, cellulose, and low-refractive-index UV-curable adhesives. These materials typically form a large-area thin-film structure when encapsulating micro / nano fibers. While this method effectively avoids surface contamination of the micro / nano fiber, it also significantly increases the size of the sensor, affects its ability to detect weak stimuli, and limits its spatial resolution. Therefore, constructing a coating on the surface of micro / nano fibers that protects them from dust interference without significantly affecting the sensor's structural dimensions remains a challenge in the field of micro / nano fiber fabrication and sensing.

[0004] The existing technology has the following technical problems:

[0005] 1) The encapsulation layer formed usually has a large area, which significantly increases the overall volume of the micro-nano fiber optic sensor, limits the spatial resolution of the sensor, and affects the sensor's resolution sensitivity.

[0006] 2) The establishment of the encapsulation layer structure cannot be done quickly and in real time, and the control of parameters such as the shape, thickness, and length of the encapsulation layer is relatively rough;

[0007] 3) The packaging process is usually carried out after the overall micro-nano fiber optic sensing structure is completed. This may introduce unnecessary changes to the micro-nano fiber optic sensing structure during the packaging process. Summary of the Invention

[0008] The purpose of this invention is to provide a device and method for preparing micro / nano optical fibers and surface coatings based on evanescent field photopolymerization for surface encapsulation in the fields of optical fiber surface functionalization and sensing applications. This invention is achieved through the following technical solutions:

[0009] This invention discloses a micro / nano optical fiber with surface encapsulation based on evanescent field photopolymerization, comprising standard optical fibers at both ends, a middle waist optical fiber, and two transition optical fibers connecting the standard optical fiber and the waist optical fiber, wherein the waist optical fiber is coated with a UV adhesive coating.

[0010] As a further improvement, the UV coating of the present invention has a thickness of about 2-3 μm and a coating length of 5-10 mm.

[0011] The present invention also discloses a device for preparing surface coatings of micro / nano optical fibers based on evanescent field curing, comprising: a three-dimensional adjustment frame, an electrically controlled displacement stage fixed on the three-dimensional adjustment frame, an optical microscope located directly above the micro / nano optical fiber to be operated for observing the state of the micro / nano optical fiber, and an ultraviolet laser connected to a standard optical fiber at one end of the micro / nano optical fiber to be operated as an input light source; the electrically controlled displacement stage is moved by the three-dimensional adjustment frame.

[0012] A method for preparing surface coatings for micro / nano optical fibers based on evanescent field photocuring, specifically as follows:

[0013] 1) Draw a micro / nano fiber to be operated, and keep the micro / nano fiber in a horizontal and taut state;

[0014] 2) A small amount of uncured UV adhesive is dipped into a single-cone optical fiber to form a UV adhesive droplet at the tip of the single-cone optical fiber. The tail end of the single-cone optical fiber is fixed on an electrically controlled displacement stage. Under the observation of an optical microscope, the position of the single-cone optical fiber is controlled and adjusted by the three-dimensional adjustment frame below the electrically controlled displacement stage, which moves the UV adhesive droplet to the scanning start position and makes the UV adhesive droplet completely wet and wrap the micro-nano optical fiber at this position.

[0015] 3) Connect a standard fiber to the ultraviolet laser at one end of the micro-nano fiber, determine the output power of the ultraviolet laser, start the electronically controlled displacement stage to control the single-cone fiber to drive the ultraviolet adhesive droplet to move at a certain scanning speed on the micro-nano fiber. When it reaches the target film formation start position, start the ultraviolet laser and input ultraviolet light into the micro-nano fiber to start film formation.

[0016] 4) When the UV-coated droplet reaches the target film-forming termination position, turn off the UV laser to stop film formation. The UV-coated droplet will continue to move a certain distance before stopping, and the scanning ends.

[0017] 5) Remove the single-cone fiber, add a small amount of alcohol solution to the micro / nano fiber for surface cleaning, remove any residual uncured UV adhesive, form a UV adhesive coating on the fiber surface in the waist region, and the encapsulation is complete.

[0018] As a further improvement, the ultraviolet laser described in this invention is a laser with wavelength parameters in the range of 300nm-400nm.

[0019] As a further improvement, the UV adhesive described in this invention is a low refractive index UV adhesive with a refractive index in the range of 1.4-1.45.

[0020] As a further improvement, the film formation start position and film formation end position described in this invention are determined by the target encapsulation length, and the encapsulation layer is located within the waist region of the micro / nano fiber.

[0021] As a further improvement, the scanning speed described in this invention is adjustable within the range of 5-10 mm / s.

[0022] As a further improvement, the output power of the ultraviolet laser described in this invention is adjustable in the range of 10-20 mW.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1) Low-refractive-index UV adhesive is cured in situ using the evanescent field transmitted on the outer surface of micro- and nano-fibers to form a surface coating that fits the structure of the micro- and nano-fibers themselves. The coating thickness is as low as micrometers. While effectively isolating the evanescent field and avoiding surface contamination of the fiber, the size of the micro- and nano-fiber sensor is significantly reduced, and the spatial resolution reaches the micrometer level, which is conducive to miniaturization and integration.

[0025] 2) Using low-refractive-index UV adhesive as the coating material can ensure that the coating refractive index is lower than that of the optical fiber, so that the optical signal transmission meets the total internal reflection waveguide condition, ensuring low-loss transmission. Moreover, the UV adhesive can be cured instantly within 0.1-1 s under UV light irradiation, supporting the formation of surface coating during rapid movement. The low surface tension of the UV adhesive makes it better able to form a smooth surface coating.

[0026] 3) The UV gel technology is mature, readily available, and offers flexible and diverse formulations, resulting in high cost-effectiveness;

[0027] 4) The thin and lightweight design that fits the micro-nano fiber itself greatly reduces the impact on the sensitivity of the micro-nano fiber sensor, thus better preserving the advantage of the high sensitivity of the micro-nano fiber detection.

[0028] 5) This invention requires no special conditions for the micro / nano optical fibers to be manipulated; only the fibers need to be adjusted to a suspended and taut state. Simultaneously, the fabrication device can be flexibly moved according to needs, resulting in a highly flexible overall fabrication process.

[0029] 6) Through rapid scanning and photopolymerization, millisecond-level local instantaneous curing is achieved, which improves manufacturing efficiency. The structural parameters such as the length and thickness of the surface coating can be precisely controlled by adjusting factors such as scanning speed, scanning distance, and input ultraviolet laser power.

[0030] 7) The apparatus of the present invention for preparing surface coatings of micro-nano optical fibers is applicable to pre-drawn micro-nano optical fibers that meet the diameter requirements. The encapsulation process is carried out after the micro-nano optical fibers are drawn, and the encapsulated micro-nano optical fibers can be subjected to relevant operations to directly obtain the sensing structure required by the target. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a micro / nano fiber structure for surface encapsulation based on evanescent field photopolymerization, provided by an embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of a device for preparing a micro / nano optical fiber surface coating based on evanescent field photocuring, according to an embodiment of the present invention.

[0033] Figure 3 This is a schematic diagram of a micro / nano optical fiber surface coating preparation process based on evanescent field photocuring, provided by an embodiment of the present invention.

[0034] Figure 4 This is a scanning electron microscope image of a micro / nano fiber optic cable with a UV adhesive coating on its surface, provided in an embodiment of the present invention.

[0035] Figure 5 This is the result of quantitative elemental analysis of a micro / nano optical fiber with a surface encapsulated with a UV adhesive coating, provided by an embodiment of the present invention.

[0036] In the figure, 1-micro / nano fiber, 2-UV adhesive coating, 101-waist region fiber, 102-transition region fiber, 103-standard fiber, 3-UV adhesive droplet, 4-single-cone fiber, 5-fiber clamp, 601-electrically controlled displacement stage, 602-three-dimensional adjustment frame, 603-optical microscope, 604-UV laser. Detailed Implementation

[0037] This invention discloses a micro / nano optical fiber and surface coating preparation device and method based on evanescent field photopolymerization for surface encapsulation. The technical solution of the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0038] Example 1

[0039] like Figure 1The image shows a micro / nano fiber with surface encapsulation based on evanescent field curing. The micro / nano fiber includes standard fibers 103 at both ends, a waist fiber 101 in the middle, and transition fibers 102 at both ends connecting the standard fibers 103 and the waist fiber 101. A thin UV adhesive coating 2 is attached to the middle of the waist fiber 101. The UV adhesive coating 2 has a uniform thickness of about 2-3 μm and a coating length less than or equal to the length of the waist fiber 101. The coating length is determined by the length of the waist fiber 101 and the required target length and is adjustable within the range of 5-10 mm.

[0040] like Figure 2 The diagram shows a schematic of an apparatus for fabricating a surface coating on micro / nano optical fibers based on evanescent field curing. The apparatus includes a three-dimensional adjustment frame 602, an electrically controlled displacement stage 601 fixed on the frame 602, an optical microscope 603 positioned directly above the micro / nano optical fiber 1 for observing its state, and an ultraviolet laser 604 connected to a standard optical fiber 103 at one end of the fiber 1 as an input light source. During operation, the initial position of the electrically controlled displacement stage 601 is controlled by the three-dimensional adjustment frame 602 below it.

[0041] like Figure 2 As shown, the fabrication process of the micro / nano fiber surface coating based on evanescent field photocuring is presented. The following section combines... Figure 2 and Figure 3 The specific preparation method is described.

[0042] S1: A micro / nano fiber 1 to be operated is drawn, and the micro / nano fiber 1 is kept in a horizontally taut state. The specific operation includes: fixing the two ends of the standard fiber 103 of the micro / nano fiber 1 with the target diameter drawn beforehand to the fiber clamp 5, so that the waist fiber 101 in the center of the micro / nano fiber 1 is in a horizontally suspended and taut state.

[0043] S2: A small amount of uncured UV adhesive is applied to the tip of a single-cone optical fiber 4, forming a UV adhesive droplet 3. The end of the single-cone optical fiber 4 is fixed on an electrically controlled displacement stage 601. Under the observation of an optical microscope 603, the position of the single-cone optical fiber 4 is adjusted by a three-dimensional adjustment frame 602 below the electrically controlled displacement stage 601, moving the UV adhesive droplet 3 to the scanning start position, ensuring that the UV adhesive droplet 3 completely wets and encapsulates the micro / nano optical fiber 1 at this position. Specific operations include: obtaining a micro / nano optical fiber from another optical fiber using fiber taper technology, and then breaking it at the center to obtain a single-cone optical fiber 4. A small amount of uncured UV adhesive is applied to the single-cone optical fiber 4, forming a UV adhesive droplet 3 at the tip of the single-cone optical fiber 4 under the action of surface tension. The tail end of the single-cone fiber carrying the UV adhesive droplet 3 is fixed on the electrically controlled displacement stage 601 and placed perpendicular to the micro / nano fiber 1, so that the single-cone fiber 4 and the micro / nano fiber 1 are in an orthogonal position. The electrically controlled displacement stage 601 is fixed on the three-dimensional adjustment frame 602. Under the optical microscope 603, the single-cone fiber 4 is moved by adjusting the three-dimensional adjustment frame 602, and its position is adjusted so that it is on the same focal plane as the micro / nano fiber 1, with the UV adhesive droplet 3 at the intersection of the two, and the UV adhesive droplet 3 completely enveloping and wetting the micro / nano fiber 1 at this intersection. The UV adhesive droplet 3 is then adjusted to the preset target scan start position. This scan start position is usually on the transition fiber 102 near the waist fiber 101.

[0044] S3: A standard optical fiber 103 at one end of the micro / nano fiber 1 is connected to an ultraviolet laser 604. The output power of the ultraviolet laser 604 is determined. First, the electrically controlled displacement stage 601 is activated to control the single-cone optical fiber 4, which drives the ultraviolet adhesive droplet 3 to move uniformly along the micro / nano fiber 1 at a certain scanning speed. When the droplet reaches the target film-forming start position, the ultraviolet laser 604 is activated, and ultraviolet light is input into the micro / nano fiber 1 to begin film formation. Specific operations include: taking a standard optical fiber 103 from the micro / nano fiber 1 and connecting it to the ultraviolet laser 604 through an optical fiber coupler; the ultraviolet laser 604 serves as the input light source. The scanning distance and scanning speed of the electrically controlled displacement stage 601 are preset. The stage is activated to begin moving until the ultraviolet adhesive droplet 3 reaches the target film-forming start position, at which point the ultraviolet laser 604 is activated. The ultraviolet adhesive droplet 3 is exposed to an ultraviolet evanescent field distributed outside the surface of the micro / nano fiber 1, undergoing a polymerization reaction to form an ultraviolet adhesive coating 2 at the exposed location. The rapid scanning movement of the UV adhesive droplet 3 enables the single-cone optical fiber 4 to continue moving the remaining uncured UV adhesive to the next position.

[0045] S4: When the UV-coated droplet 3 reaches the target film-forming termination position, turn off the UV laser 604 to stop film formation. The UV-coated droplet 3 continues to move a certain distance before stopping, and the scan ends. Specific operations include: upon reaching the target film-forming endpoint, turning off the UV laser 604, stopping the UV light input, and ending the UV-coated polymerization and curing reaction, i.e., film formation ends. Because the electrically controlled displacement stage 601 needs to accelerate and decelerate during startup and shutdown, it is in a non-uniform speed state. Therefore, to ensure that the UV-coated droplet 3 maintains a uniform scanning speed during the film-forming stage, the pre-set scanning distance of the electrically controlled displacement stage 601 must be greater than the target film length. After moving the preset scanning distance, the UV-coated droplet 3 stops, and the scan ends.

[0046] S5: Remove the single-cone fiber 4, add a small amount of alcohol solution to the micro / nano fiber 1 for surface cleaning, remove any remaining uncured UV adhesive, and form a UV adhesive coating 2 on the surface of the waist fiber 101, completing the encapsulation. Specific operations include: After scanning, using the 3D adjustment frame 602, remove the remaining uncured UV adhesive droplets 3 from the surface of the micro / nano fiber 1. At this point, a small amount of uncured UV adhesive remains on the surface of the micro / nano fiber 1. Carefully add alcohol solution using a dropper to the micro / nano fiber 1 for surface cleaning, dissolving and removing the remaining uncured UV adhesive. After the alcohol evaporates, a uniform UV adhesive coating 2 is formed at the waist fiber 101 of the micro / nano fiber 1, completing the encapsulation. Subsequent processing operations can be performed on the encapsulated micro / nano fiber 1, such as further fabricating micro / nano fiber sensing structures.

[0047] A 604 ultraviolet laser with wavelength parameters in the 300nm-400nm range can be selected as the input ultraviolet light source to facilitate rapid polymerization of the ultraviolet adhesive and quick curing into a film. Simultaneously, the selected ultraviolet adhesive has a low refractive index, within the range of 1.4-1.45, ensuring that its refractive index is lower than that of micro / nano optical fibers, meeting the conditions for total internal reflection and guaranteeing high transmission transmittance.

[0048] The film formation start and end positions are determined by the desired target coating length. At the same time, it is necessary to ensure that both the film formation start and end positions are within the waist region fiber 101 to ensure that the entire coating is located on the surface of the waist region fiber 101. If the film formation position is selected on the transition region fiber 102, the larger tilt angle of the transition region fiber 102 will cause more light to be scattered outward. This relatively large ultraviolet light field will cause the entire ultraviolet adhesive droplet 3 to quickly solidify and clump together at the current position, making it impossible to continue scanning and forming a film.

[0049] The thickness of the UV adhesive coating 2 is determined by two factors: the scanning speed and the output power of the UV laser 604. A slower scanning speed results in a longer residence time for the UV adhesive droplets within a given range, leading to a thicker coating. The scanning speed is adjustable within the range of 5-10 mm / s. Conversely, a higher output power of the UV laser results in a larger evanescent field range transmitted across the outer surface of the micro / nano fiber 1, leading to a greater penetration depth of the UV adhesive droplets 3 and a thicker coating. The output power of the UV laser 604 is adjustable within the range of 10-20 mW.

[0050] like Figure 4 As shown, a scanning electron microscope image of a micro / nano fiber optic cable with a UV adhesive coating on its surface is presented. Figure 4 The first inset image is a partial scanning electron microscope (SEM) image of the micro / nano fiber 1 with a UV-coated adhesive layer 2 on its surface. The remaining five images are elemental distribution maps of the micro / nano fiber 1. The first inset image clearly shows that the UV-coated adhesive layer 2 has a uniform thickness at different locations and a smooth, flat surface without any bumps or unevenness. Elemental analysis reveals that in addition to the elements carbon (C), oxygen (O), and silicon (Si) inherent in the micro / nano fiber 1, and gold (Au) introduced through pre-plating for SEM, fluorine (F) is also present. Fluorine is a constituent element of the UV-coated adhesive. The fluorine distribution map shows that its thickness and density are very uniform, and its distribution diameter is slightly larger than that of carbon, oxygen, and silicon. This confirms the presence of a uniformly thick UV-coated adhesive layer 2 on the surface of the micro / nano fiber 1.

[0051] like Figure 5 As shown, the results of quantitative elemental analysis of micro / nano optical fibers with a surface encapsulated with a UV adhesive coating are presented. These results are... Figure 4 The quantitative analysis of the elements present clearly shows the presence of fluorine in the histogram of the results, and the percentage is reasonable.

[0052] Example 2

[0053] To verify the protective effect of the UV coating 2 on the micro / nano fiber 1, a control experiment was conducted. PMMA microspheres with a diameter of 5 μm were used to simulate dust in the air. The PMMA microspheres were placed on both the uncoated and coated micro / nano fiber 1. The placement positions were all located at the center of the waist region of the fiber 101. Visual observation revealed a significant light spot at the location of the PMMA microsphere on the uncoated micro / nano fiber 1, caused by scattered light; while no scattered light spot was observed on the coated micro / nano fiber 1. The output signal showed that the output light intensity of the uncoated micro / nano fiber 1 decreased instantaneously upon the placement of the PMMA microsphere, resulting in reduced transmittance. For the coated micro / nano fiber 1, the change in light intensity before and after the placement of the microsphere was negligible. This effectively demonstrates the protective effect of the UV coating on the optical field of the micro / nano fiber 1, helping to isolate the fiber from the external environment.

[0054] Example 3

[0055] This paper explores different methods for encapsulating U-shaped micro / nano fiber optic sensors, employing both the present invention and traditional PDMS (polydimethylsiloxane) encapsulation. For the present invention, a surface encapsulation operation is first performed on the pre-tapered micro / nano fiber 1, covering the central waist region fiber 101 with a UV adhesive coating 2. Then, the encapsulated micro / nano fiber 1 is bent and twisted to prepare a U-shaped micro / nano fiber ring with a width of 100 μm. Traditional PDMS encapsulation cannot be performed by encapsulating before processing because PDMS has high fluidity and cannot solidify instantaneously, making it impossible to form a uniformly thick radial film on the micro / nano fiber. Therefore, the pre-tapered micro / nano fiber is first bent and twisted to form a U-shaped micro / nano fiber ring, which is then encapsulated with PDMS. During heating, PDMS accumulates on the U-shaped micro / nano fiber ring, forming a small sphere of a certain volume. The U-shaped micro / nano fiber ring has a width of 100 μm, and the final PDMS encapsulated sphere has a diameter of 150 μm. The results show that the final micro / nano fiber sensing structure obtained by PDMS encapsulation has a larger spatial volume, and the encapsulation is a complete wrapping rather than a bonding to the micro / nano fiber itself. This greatly limits the deformation of the U-shaped micro / nano fiber ring and reduces the test sensitivity. Pressing experiments were conducted on probes of both encapsulation types in orthogonal directions. Under the same pressing displacement (4μm), the U-shaped micro / nano fiber ring encapsulated with UV adhesive showed a significant output light signal response. In contrast, the U-shaped micro / nano fiber ring encapsulated with PDMS produced a weak output light signal, indicating its insensitivity to the small deformation of 4μm. The light intensity variation shows that the former's response sensitivity is 5 times higher than the latter, confirming that the encapsulation method based on evanescent field photocuring to form a coating on the surface of the micro / nano fiber can better leverage the high sensitivity advantage of micro / nano fibers.

[0056] It will be understood by those skilled in the art that the above description is merely a single example of the invention and is not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for preparing micro-nano fiber surface coating based on evanescent field photocuring, characterized in that, The preparation method described herein is implemented using the following preparation apparatus, which includes a three-dimensional adjustment frame, an electrically controlled displacement stage fixed on the three-dimensional adjustment frame, an optical microscope located directly above the micro / nano fiber to be operated for observing the state of the micro / nano fiber, and an ultraviolet laser connected to a standard optical fiber at one end of the micro / nano fiber to be operated as an input light source; the three-dimensional adjustment frame controls the movement of the electrically controlled displacement stage. The preparation method specifically includes the following steps: 1) Draw a micro / nano fiber to be operated, and keep the micro / nano fiber in a horizontal and taut state; 2) A small amount of uncured UV adhesive is dipped into a single-cone optical fiber to form a UV adhesive droplet at the tip of the single-cone optical fiber. The tail end of the single-cone optical fiber is fixed on an electrically controlled displacement stage. Under the observation of an optical microscope, the position of the single-cone optical fiber is controlled and adjusted by the three-dimensional adjustment frame below the electrically controlled displacement stage, which moves the UV adhesive droplet to the scanning start position and makes the UV adhesive droplet completely wet and wrap the micro-nano optical fiber at this position. 3) Connect a standard fiber to the ultraviolet laser at one end of the micro-nano fiber, determine the output power of the ultraviolet laser, start the electronically controlled displacement stage to control the single-cone fiber to drive the ultraviolet adhesive droplet to move at a certain scanning speed on the micro-nano fiber. When it reaches the target film formation start position, start the ultraviolet laser and input ultraviolet light into the micro-nano fiber to start film formation. 4) When the UV-coated droplet reaches the target film-forming termination position, turn off the UV laser to stop film formation. The UV-coated droplet will continue to move a certain distance before stopping, and the scanning ends. 5) Remove the single-cone fiber, add a small amount of alcohol solution to the micro / nano fiber for surface cleaning, remove the residual uncured UV adhesive, form a UV adhesive coating on the fiber surface in the waist region, and the encapsulation is complete; The micro / nano optical fiber prepared by the above method based on evanescent field photocuring for surface encapsulation includes standard optical fibers at both ends, a middle waist fiber, and two transition fiber sections connecting the standard optical fiber and the waist fiber. The waist fiber is coated with a UV adhesive coating. The thickness of the UV adhesive coating is about 2-3 μm, and the coating length is within 5-10 mm.

2. The method for preparing micro / nano optical fiber surface coatings based on evanescent field photocuring according to claim 1, characterized in that, The ultraviolet laser mentioned is a laser with wavelength parameters in the range of 300nm-400nm.

3. The method for preparing micro-nano fiber surface coating based on evanescent field photocuring according to claim 1 or 2, characterized in that, The UV adhesive is a low refractive index UV adhesive with a refractive index in the range of 1.4-1.

45.

4. The method for preparing micro-nano fiber surface coating based on evanescent field photocuring according to claim 3, wherein, The film formation start position and film formation end position are determined by the target encapsulation length, and the encapsulation layer is located within the waist region of the micro / nano fiber.

5. The method for preparing micro-nano fiber surface coating based on evanescent field photocuring according to claim 4, wherein, The scanning speed is adjustable within the range of 5-10 mm / s.

6. The method for preparing micro-nano fiber surface coating based on evanescent field photocuring according to claim 1 or 2 or 4 or 5, characterized in that, The output power of the ultraviolet laser is adjustable in the range of 10-20 mW.

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