Optical fiber integrated with movable liquid metal microspheres and preparation method thereof

Abstract

The invention discloses an optical fiber integrated with movable liquid metal microspheres and a preparation method of the optical fiber, and particularly belongs to the technical field of optical fibers. The optical fiber integrated with the movable liquid metal microspheres comprises a single-mode optical fiber; one end of the hollow-core optical fiber is coaxially welded with the single-mode optical fiber, and the hollow-core optical fiber is provided with a semi-closed hollow-core optical fiber microcavity; the movable indium tin liquid metal microspheres are arranged in the semi-closed hollow-core optical fiber microcavity; the NaOH solution is filled with the semi-closed hollow-core optical fiber microcavity and completely wraps the gallium-indium-tin liquid metal microspheres, and the semi-closed hollow-core optical fiber microcavity of the hollow-core optical fiber, the indium-tin liquid metal microspheres and the NaOH solution form a Fabry-Perot microcavity; and the waterproof epoxy resin layer is used for fixedly sealing the other end of the hollow fiber. The indium tin liquid metal microsphere can sensitively move in the axial direction along with the inclination of the optical fiber in the NaOH solution, so that the optical path difference in the Fabry-Perot microcavity is modulated in real time, the structure is compact, the size is small, the design is simple, the sensitive detection of the inclination state can be realized, and the method has great potential in the aspect of high-integration application in a narrow space.

Description

Technical Field

[0001] This application relates to the field of optical fiber technology, and in particular to optical fibers with integrated movable liquid metal microspheres and their fabrication methods. Background Technology

[0002] Real-time online monitoring technology for tilt states is a key technology supporting the assessment of equipment operating conditions and the safety of engineering and building environments, and is crucial for ensuring system stability and environmental safety. Currently, to meet practical application demands such as miniaturization, electromagnetic interference resistance, operational safety, and long-distance monitoring, novel fiber optic tilt state sensing devices have become a research focus in the field, demonstrating irreplaceable application value in industrial manufacturing, urban infrastructure construction, and aerospace engineering. The principle of fiber optic tilt sensing technology lies in the measurable changes in the intensity, phase, and polarization state of light waves within the optical fiber caused by the tilt state of the equipment. Monitoring the tilt state of the equipment is achieved by observing these changes in the optical signal. However, the inherent high Young's modulus and low elastic coefficient of quartz material make it difficult for traditional all-fiber sensing structures to produce an effective response to tilt states, resulting in low tilt sensing sensitivity. This has become a bottleneck restricting the development of all-fiber tilt sensors.

[0003] To improve the sensitivity of fiber optic tilt sensors, existing biaxial tilt sensors incorporate two fiber Bragg gratings (FBGs) onto a single optical fiber, achieving axial tilt resolution through the difference in the resonant wavelengths of the two FBGs. However, existing biaxial tilt sensors rely on the coordinated matching of the two FBGs. Due to the limitations of the fiber tilt sensing structure caused by the high Young's modulus and low elastic coefficient of quartz material, the sensitivity is low, and the structural design is complex, making it difficult to adapt to the miniaturization and high integration requirements of applications. Therefore, there is an urgent need to develop an optical fiber integrating movable liquid metal microspheres and its fabrication method to solve the above problems. Summary of the Invention

[0004] In view of this, this application provides an optical fiber with integrated movable liquid metal microspheres and a method for fabricating the same. The indium tin liquid metal microspheres in the optical fiber can move sensitively along the axial direction in NaOH solution as the tilt state of the optical fiber changes, thereby modulating the optical path difference in the Fabry-Perot microcavity in real time. High sensitivity sensing of the tilt state is achieved by demodulating the rapidly evolving interference spectrum. The structure is compact, small in size, and simple in design, and can realize sensitive detection of the tilt state. It has great potential for high-integration applications in confined spaces.

[0005] Specifically, the following technical solutions are included:

[0006] In a first aspect, this application provides an optical fiber integrating movable liquid metal microspheres, the optical fiber comprising:

[0007] Single-mode fiber;

[0008] A hollow fiber with one end coaxially fused to a single-mode fiber has a semi-closed hollow fiber microcavity.

[0009] Movable indium tin liquid metal microspheres placed inside a semi-enclosed hollow fiber microcavity;

[0010] A NaOH solution that fills a semi-enclosed hollow fiber microcavity and completely encapsulates gallium indium tin liquid metal microspheres forms a Fabry-Perot microcavity with the semi-enclosed hollow fiber microcavity, the indium tin liquid metal microspheres, and the NaOH solution.

[0011] A waterproof epoxy resin layer used to seal the other end of a hollow optical fiber.

[0012] In some embodiments, the single-mode optical fiber has an inner diameter of 8~10μm and an outer diameter of 125μm.

[0013] In some embodiments, the hollow optical fiber has an inner diameter of 50~60μm and an outer diameter of 125μm.

[0014] In some embodiments, the volume of the gallium indium tin liquid metal microspheres is 0.113~0.179 nL, and the mass fraction of the NaOH solution is 1~3 wt%, with a volume of 0.7~0.9 μL.

[0015] In some embodiments, the thickness of the waterproof epoxy resin layer is 20~30μm.

[0016] In some embodiments, the length of the Fabry-Perot microcavity is 80~250μm, which changes in real time with the movement of the gallium indium tin liquid metal microsphere (4) when tilted, and the length of the semi-enclosed hollow fiber microcavity is 400~500μm.

[0017] Secondly, this application provides an optical fiber integrating movable liquid metal microspheres and a method for fabricating the same, the method comprising:

[0018] Step 1: Fiber fusion is performed between one end of the hollow fiber and one end of the single-mode fiber, and the other end of the hollow fiber is cut to make the hollow fiber have a semi-closed hollow fiber microcavity, thus obtaining the first fiber.

[0019] Step 2: Inject gallium indium tin liquid metal from the other end of the hollow fiber to form a Fabry-Perot microcavity in the hollow fiber, thereby obtaining a second fiber containing gallium indium tin liquid metal droplets.

[0020] Step 3: Fill the outside of the gallium indium tin liquid metal microdroplet with NaOH solution to obtain the third optical fiber;

[0021] Step 4: Seal the other end of the hollow fiber with a waterproof epoxy resin layer to obtain an optical fiber with integrated movable liquid metal microspheres.

[0022] In some embodiments, arc fusion splicing technology is used in the fiber optic fusion splicer in steps 1 and 4, and the discharge intensity during the fusion splicing process is 3.5~4.0mA.

[0023] In some embodiments, in step 3, gallium indium tin liquid metal is slowly injected under pressure using a syringe.

[0024] In some embodiments, the mass fraction of the NaOH solution in step 3 is 1~3 wt%.

[0025] The beneficial effects of the technical solutions provided in this application include at least the following:

[0026] This application provides an optical fiber integrating movable liquid metal microspheres and its fabrication method. The optical fiber includes a single-mode optical fiber; a hollow-core optical fiber coaxially fused to the single-mode optical fiber at one end, having a semi-enclosed hollow-core optical fiber microcavity; movable indium tin (INT) liquid metal microspheres placed within the semi-enclosed hollow-core optical fiber microcavity; a NaOH solution filling the semi-enclosed hollow-core optical fiber microcavity and completely encapsulating the INT liquid metal microspheres; the semi-enclosed hollow-core optical fiber microcavity, the INT liquid metal microspheres, and the NaOH solution forming a Fabry-Perot microcavity; and a waterproof epoxy resin layer for sealing the other end of the hollow-core optical fiber. The INT liquid metal microspheres in this optical fiber can move sensitively along the axial direction in the NaOH solution according to the tilt state of the optical fiber, thereby modulating the optical path difference in the Fabry-Perot microcavity in real time. Highly sensitive sensing of the tilt state is achieved by demodulating the rapidly evolving interference spectrum. The structure is compact, small in size, and simple in design, enabling sensitive detection of the tilt state, and has great potential for highly integrated applications in confined spaces. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 A schematic diagram of the structure of an optical fiber integrating movable liquid metal microspheres provided in an embodiment of this application;

[0029] Figure 2 A schematic diagram illustrating the working principle of the optical fiber with integrated movable liquid metal microspheres provided in this embodiment of the application;

[0030] Figure 3A schematic diagram of the tilt response characteristics of the optical fiber with integrated movable liquid metal microspheres provided in the embodiments of this application under different tilt states: (a) clockwise tilt, (b) horizontal state, (c) counterclockwise tilt;

[0031] Figure 4 A schematic diagram showing the relationship between the free spectral range and the Fabry-Perot cavity length of the optical fiber with integrated movable liquid metal microspheres provided in the embodiments of this application under different tilt states;

[0032] Figure 5 Frequency domain diagrams of the optical fiber with integrated movable liquid metal microspheres provided in the embodiments of this application under different tilt states.

[0033] The reference numerals in the figure are respectively:

[0034] 1-Single-mode optical fiber, 2-Hollow-core optical fiber, 21-Semi-enclosed hollow-core optical fiber microcavity, 3-Faber microcavity, 4-GaInTin liquid metal microspheres, 5-Waterproof epoxy resin layer. Detailed Implementation

[0035] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0036] To make the technical solutions and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0037] In a first aspect, embodiments of this application provide an optical fiber structure integrating movable liquid metal microspheres, such as... Figure 1 As shown, the optical fiber includes:

[0038] Single-mode fiber 1;

[0039] A hollow fiber 2, which is fused coaxially with a single-mode fiber 1 at one end, has a semi-enclosed hollow fiber microcavity 21; the fusion of the single-mode fiber 1 and the hollow fiber 2 ensures efficient coaxial transmission of optical signals.

[0040] Indium tin liquid metal microspheres 4 are placed inside a semi-enclosed hollow fiber microcavity 21 and are movable; the semi-enclosed hollow fiber microcavity 21 provides a moving channel for the indium tin liquid metal microspheres 4.

[0041] A NaOH solution fills the semi-enclosed hollow fiber microcavity 21 and completely encapsulates the gallium indium tin liquid metal microspheres 4. The semi-enclosed hollow fiber microcavity 21, the indium tin liquid metal microspheres 4, and the NaOH solution form a Fabry-Perot microcavity 3. The NaOH solution filling the semi-enclosed hollow fiber microcavity 21 and completely encapsulating the gallium indium tin liquid metal microspheres 4 is an important structure to ensure the mobility of the indium tin liquid metal microspheres 4.

[0042] A movable gallium indium tin (GaInT) liquid metal microsphere 4 in NaOH solution serves as a sensing unit capable of real-time monitoring of tilt states. Under surface tension, it spontaneously coalesces into a regular spherical structure. A Fabry-Perot microcavity 3 senses the movement of the liquid metal microspheres with varying tilt states. When the optical fiber tilts, the GaInT liquid metal microsphere 4 moves directionally along the inner wall of the hollow optical fiber 2 under gravity. Its displacement modulates the optical path difference within the Fabry-Perot microcavity 3, altering the reflection spectral characteristics and thus achieving sensitive detection of the tilt state. This direct coupling between the displacement and optical response of the GaInT liquid metal microsphere 4 provides a simple and efficient solution for dynamic environmental tilt monitoring.

[0043] A waterproof epoxy resin layer 5 is applied to the other end of the hollow fiber 2. The waterproof epoxy resin layer 5 is used to fix the fiber end and ensure the stability of the fiber structure. In some embodiments, the inner diameter of the single-mode fiber 1 is 9 μm and the outer diameter is 125 μm. This configuration allows for single-mode transmission of optical signals, reduces mode dispersion to maintain high coherence, and provides a high-quality incident light basis for stable interference of the Fabry-Perot microcavity.

[0044] In some embodiments, the hollow fiber 2 has an inner diameter of 50 μm and an outer diameter of 125 μm. This configuration allows the outer diameter to be adapted to the single-mode fiber (outer diameter 125 μm), reducing optical loss at the splice to ensure optical signal transmission. The inner diameter is adapted to the gallium indium tin liquid metal microspheres to enable smooth movement, and the microcavity length provides sufficient space for microsphere displacement, ensuring effective modulation of the Fabry-Perot cavity length when tilted.

[0045] In some embodiments, the volume of the gallium indium tin liquid metal microsphere 4 is 0.113 nL, and the mass fraction of the NaOH solution is 1 wt%, with a volume of 0.8 μL. This concentration range is a key concentration range for adapting the gallium indium tin liquid metal microsphere 4 to the optical fiber sensing, which allows the liquid metal to stably form a regular sphere under the action of surface tension, reducing the influence of non-spherical structures on the flatness of the light reflection interface, providing a regular reflective surface for the stable interference of the Fabry-Perot microcavity, and improving the consistency of the sensing signal. In the semi-enclosed hollow optical fiber microcavity 21, it is in a dynamic adaptation state. The NaOH solution coats the gallium indium tin liquid metal microsphere 4, which moves axially as it is tilted. The NaOH solution fills the space left by the movement of the gallium indium tin liquid metal microsphere 4 in real time, always keeping the interior of the semi-enclosed hollow optical fiber microcavity 21 in a full liquid state, providing a stable medium basis for the optical path difference modulation of the Fabry-Perot microcavity. In terms of concentration, the alkaline environment provided by the 1wt% NaOH solution can efficiently dissolve the oxide layer on the surface of the gallium indium tin liquid metal microspheres 4, eliminate the adhesion between the gallium indium tin liquid metal microspheres 4 and the cavity wall, and at the same time avoid the corrosion of the quartz optical fiber by high concentration. In terms of volume, 0.8μL of NaOH solution can fill the semi-enclosed hollow fiber microcavity, ensuring that the gallium indium tin liquid metal microspheres 4 are completely immersed in the NaOH solution, reducing their movement resistance and improving tilt sensing sensitivity.

[0046] In some embodiments, the thickness of the waterproof epoxy resin layer 5 is 30 μm. This setting can effectively seal the end port of the hollow fiber 2, prevent the leakage of NaOH solution and gallium indium tin liquid metal microspheres 4 in the cavity, and block the intrusion of external impurities to ensure the sealing of the core sensing area. Furthermore, the ultra-thin thickness of 30 μm will not increase the overall volume of the sensor, making it suitable for miniaturized application scenarios.

[0047] In some embodiments, the length of the Fabry-Perot microcavity 3 is 80~250μm, which changes in real time with the movement of the gallium indium tin liquid metal microsphere 4 when tilted. The length of the semi-enclosed hollow fiber microcavity 2 is 400μm. This configuration can provide sufficient sliding space for the gallium indium tin liquid metal microsphere 4, avoid the microsphere from hitting the end due to the short cavity when tilted, ensure that the cavity length modulation range is 80~250μm, so that the interference spectrum shift can be accurately detected, and improve the resolution of tilt sensing.

[0048] Figure 2 This illustrates the working principle of an optical fiber integrating movable liquid metal microspheres, whereas a conventional Fabry-Perot interferometer consists of two parallel optical reflective surfaces. The diagram shows the optical fiber in a horizontal position. Figure 2As shown, the semi-enclosed hollow fiber microcavity 21 of the hollow fiber 2, the indium tin liquid metal microspheres 4, and the NaOH solution form a Fabry-Perot microcavity 3. This Fabry-Perot microcavity 3 includes two core reflective interfaces: Interface 1 and Interface 2. Interface 1 refers to the contact interface between the end face of the single-mode fiber 1 and the NaOH solution inside the hollow fiber 2, while Interface 2 refers to the contact interface between the NaOH solution inside the hollow fiber 2 and the indium tin liquid metal microspheres 4. Since Interface 1 is vertically perpendicular to the inner wall of the fiber, and Interface 2 is the vertical tangential surface of the gallium indium tin liquid metal microspheres 4 relative to the inner wall, the two interfaces conform to the characteristics of a Fabry-Perot interferometer. Therefore, Interface 1 and Interface 2 of the gallium indium tin liquid metal microspheres 4 inside the hollow fiber 2 form a low-precision Fabry-Perot interferometer (FPI) structure, where the Fabry-Perot cavity length (the length of the Fabry-Perot microcavity 3) is L1, and the refractive index of the cavity medium is set to n. When the incident light is transmitted through the optical fiber to interface one, part of the light undergoes an initial reflection at interface one, while the other part penetrates into the Fabry-Perot microcavity 3 and undergoes a secondary reflection at interface two. The two reflected beams superimpose within the optical fiber to form an interference signal.

[0049] When a beam of light is incident from an optically less dense medium to an optically denser medium and reflected, a half-wave loss occurs; however, when a beam of light is incident from an optically denser medium to an optically less dense medium and reflected, no half-wave loss occurs. In an optical fiber, the beam is reflected at interface one and interface two. At interface one, the light inside the fiber is incident on a 1% NaOH solution, which is an optically denser medium incident on an optically less dense medium, and there is no half-wave loss. At interface two, the light is incident from a 1% NaOH solution onto the surface of a gallium indium tin liquid metal microsphere 4, which is an optically less dense medium incident on an optically denser medium, and there is a half-wave loss. The different half-wave loss states at the two interfaces introduce an additional optical path difference of λ / 2 into the total optical path difference. Therefore, the interference spectrum must be determined by the Fabry-Perot cavity length L1 and this additional optical path difference to ensure a stable correspondence between the phase change of the interference signal and the displacement of the liquid metal microsphere (cavity length change).

[0050] When light travels from single-mode fiber 1 to hollow fiber 2 spliced ​​with it, because the semi-enclosed microcavity of hollow fiber 2 is pre-filled with a 1wt% NaOH solution, the light first passes through interface one, where partial reflection occurs, forming the first reflected light beam I1. Its intensity is controlled by the Fresnel reflection coefficient, determined by the difference in refractive index between the two media (quartz material of single-mode fiber 1 and NaOH solution). The unreflected transmitted light continues to propagate along the axis of hollow fiber 2 until it reaches the surface of gallium indium tin liquid metal microsphere 4 near the single-mode fiber 1 (i.e., interface two), where secondary reflection occurs, forming the second reflected beam I2. After the two reflected beams propagate in opposite directions and recouple back to single-mode fiber 1, due to the optical path difference (… (where L1 is the distance between interface one and interface two) generates a two-beam interference phenomenon, where the intensity I of the interference light can be expressed as Equation 2.1:

[0051]

[0052] Where the initial phase Typically 0, L1 is the cavity length of the Fabry-Perot microcavity 3. Let λ be the wavelength of the incident light, n be the refractive index of the cavity medium, and m be an integer. From Equation 2.1, we know that Equation 2.2 is obtained when the following condition is met:

[0053]

[0054] The reflection spectrum formed by the interference light shows trough positions, where the wavelength λ at the trough position is... m This can be expressed as Formula 2.3:

[0055]

[0056] From Equation 2.3, we can derive the relationship between the change in Fabry cavity length ΔL and the shift Δλ at the trough position of the reflection spectrum. m The correspondence is given by formula 2.4:

[0057]

[0058] As shown in Equation 2.4, changes in the Fabry-Perot cavity length will cause a directional shift in the position of the troughs in the reflection spectrum. When the Fabry-Perot cavity length increases, the wavelength at the trough shifts towards longer wavelengths, a phenomenon known as "redshift." When the Fabry-Perot cavity length decreases, the wavelength at the trough shifts towards shorter wavelengths, a phenomenon known as "blueshift." Furthermore, the distance between adjacent troughs, i.e., the free spectral range (FSR), can be expressed by Equation 2.5:

[0059]

[0060] Because the gallium indium tin (GaInT) liquid metal microsphere 4 is movable, when the optical fiber is horizontal, the net force on the GaInT liquid metal microsphere 4 is zero, and the GaInT liquid metal microsphere 4 is stably positioned at the geometric center of the semi-enclosed hollow fiber microcavity 21 of the hollow fiber 2. At this time, the Fabry-Perot cavity length is the initial value L0, and the corresponding valley distribution of the reflection spectrum exhibits a standard periodicity. When the optical fiber tilts clockwise, the component of gravity along the tilt direction drives the GaInT liquid metal microsphere 4 to slide along the lower right side of the semi-enclosed hollow fiber microcavity 21, causing the effective cavity length to increase to... According to FP interference theory ( Increasing the cavity length reduces the spacing between adjacent interference valleys (Free Spectral Range, FSR), resulting in an overall shift of the reflection spectrum towards longer wavelengths. Conversely, tilting counterclockwise causes the gallium indium tin liquid metal microsphere 4 to shift to the left, compressing the cavity length to... As the FSR increases, the spectrum shifts towards shorter wavelengths. By tracking the translation direction (redshift or blueshift) and offset of the reflectance spectrum in real time, the tilt direction and tilt angle can be directly determined, forming a direct optical sensing mechanism that does not require complex demodulation algorithms.

[0061] To verify the tilt response characteristics of the optical fiber integrated with movable liquid metal microspheres, the dynamic behavior of the gallium indium tin liquid metal microsphere 4 within the semi-enclosed hollow fiber microcavity 21 of the hollow fiber 2 was visually captured using microscopic imaging techniques. For example... Figure 3 As shown in (a) to (c), after the optical fiber was placed on an adjustable tilt platform, the axial direction of the microcavity was observed in real time under a microscope. When the platform tilted, the gallium indium tin liquid metal microsphere 4 slid along the axial direction of the microcavity due to gravity. The gallium indium tin liquid metal microsphere 4 was subjected to gravity, buoyancy, and the supporting force of the inner wall of the fiber core in the NaOH solution inside the optical fiber. Since the volume of the gallium indium tin liquid metal microsphere 4 was only on the sub-nanolithic scale, the change in motion due to buoyancy was negligible. Figure 3 As can be seen in (a), when the optical fiber with integrated movable liquid metal microspheres is tilted clockwise, the gallium indium tin liquid metal microsphere 4 moves to the lower right along the inner wall of the semi-enclosed hollow fiber microcavity 21 under the action of gravity, the Fabry-Perot cavity length increases, and its motion trajectory shows continuous displacement in the microscopic field of view; from Figure 3 As can be seen from (b), when the optical fiber is in a horizontal state, the gallium indium tin liquid metal microsphere 4 is stably located at the middle position of the arc-shaped interface of the semi-enclosed hollow fiber microcavity 21, and the Fabry-Perot cavity length remains unchanged; from Figure 3 As can be seen in (c), when the optical fiber tilts counterclockwise, the gallium indium tin liquid metal microsphere 4 moves to the lower left under the influence of gravity, shortening the Fabry-Perot cavity length. Through microscopic image sequence analysis, the correspondence between the boundary morphology and positional changes of the gallium indium tin liquid metal microsphere 4 can be clearly identified: as the tilt angle increases, the gallium indium tin liquid metal microsphere 4 gradually approaches the cavity wall. Microscopic observation not only directly verifies the strong correlation between the displacement and tilt direction of the gallium indium tin liquid metal microsphere 4, but also provides a visualized spatial positioning basis for subsequent spectral-mechanical coupling analysis. Furthermore, from... Figure 3 As can be seen from (a) to (c), the optical fiber with integrated movable liquid metal microspheres is stable and spontaneously moves under the influence of gravity when the external tilt changes. Under the influence of the high surface tension of the gallium indium tin liquid metal microsphere 4, the gallium indium tin liquid metal microsphere 4 always maintains a regular spherical shape in the NaOH solution, which can provide a guarantee for the optical fiber sensing structure for subsequent spectroscopic detection.

[0062] like Figure 1 , Figure 2 and Figure 3As shown in (a) to (c), in some embodiments, the hollow fiber 2 has an arcuate interface, which is generated by fusion splicing. The hollow fiber 2 is fused with the single-mode fiber 1, and partial discharge heating is applied to the microcavity region of the hollow fiber 2. Under the action of surface tension, the quartz material forms an arcuate protrusion structure, i.e., the arcuate interface. The curved surface morphology of this arcuate interface can utilize the gravitational component of the liquid metal microspheres to spontaneously return them to their apex in a horizontal state, ensuring the initial stability of the Fabry-Perot cavity length; from Figure 3 As can be seen from (c), when the optical fiber tilts counterclockwise, the gallium indium tin liquid metal microsphere 4 moves to the lower left along the arc-shaped interface under the influence of gravity, and the Fabry-Perot cavity length shortens.

[0063] In some embodiments, fusion splicing can be performed using the discharge process of a fiber optic fusion splicer.

[0064] To monitor the tilt sensing performance of the optical fiber in real time, it was placed in three tilted states: clockwise, horizontal, and counterclockwise. The reflection spectra generated under different states were measured in real time using a constructed sensing system. In the optical fiber sensing system, the incident beam undergoes retroreflection due to reflection from the fiber end face and the surface of the liquid metal microspheres. An interference effect was observed between the two returning beams within the fiber. A broadband light source (1420nm~1600nm) was bridged by an optical fiber circulator and combined with an AQ6370D spectrometer (resolution set to 0.02 nm high-precision mode) to characterize the interference spectrum of the fabricated optical fiber integrating movable liquid metal microspheres. The system configuration uses a broadband light source as the excitation source, and the entire testing process requires no additional auxiliary equipment. The experimental scheme features convenient operation, good repeatability, and excellent system stability, effectively ensuring the reliability of the measurement data. The signal light enters the optical fiber sensing structure from the light source output, and the resulting interference light, after modulation, passes through the circulator again and enters the spectrometer, from which the measured reflection spectrum is obtained. Interference spectra were observed under different tilt conditions, and experiments revealed that the spectra evolved in real time as the tilt changed. For example... Figure 4 As shown, the free spectral range (FSR) of the reflection spectrum is significantly correlated with the equivalent optical cavity length of the fiber microcavity. When the fiber with integrated movable liquid metal microspheres is in a horizontal state, the gallium indium tin liquid metal microsphere 4 is located in the central region of the microcavity, and the formed Fabry-Perot (FP) interference cavity maintains its equilibrium length. At this time, the reflection spectrum exhibits a periodic trough structure, and the measured characteristic FSR value is 10.3 nm. Tilting disrupts this mechanical balance: clockwise tilting causes the liquid metal microspheres to migrate to the right end of the microcavity, leading to an increase in the effective optical cavity length. According to Fabry-Perot interference theory, the spacing between adjacent troughs decreases to 6.2 nm. Conversely, counterclockwise tilting forces the microspheres to move to the left, compressing the cavity length and significantly broadening the FSR to 35.2 nm. This inverse relationship between FSR and cavity length (…) It provides an intuitive spectral criterion for tilting. By monitoring the dynamic contraction or widening of the trough spacing, the tilting direction and amplitude can be directly calculated, forming a direct sensing mechanism that does not require complex signal processing.

[0065] In some embodiments, to improve the real-time performance and accuracy of fiber tilt detection, Fast Fourier Transform (FFT) is introduced as the core algorithm for frequency domain analysis. FFT allows for a more intuitive and rapid understanding of the tilt state of the external environment, such as... Figure 5 As shown, frequency domain analysis based on Fast Fourier Transform (FFT) clearly reveals the mapping law between the tilt state and the spatial frequency. In the horizontal state, the gallium indium tin liquid metal microsphere 4 is located in the middle of the semi-enclosed hollow fiber microcavity 21. After the reflection spectrum is converted by FFT, its main spatial frequency peak is stable at... The optical path difference corresponding to the equilibrium position of the microspheres is periodically distributed. When tilted clockwise, the gallium indium tin liquid metal microsphere 4 slides towards the right end of the semi-enclosed hollow fiber microcavity 21 under the action of gravity, resulting in an increase in the modulation period of the optical path difference and a shift of the main peak of the FFT spectrum towards higher frequencies. When the gallium indium tin liquid metal microsphere 4 reaches the rightmost end of the semi-enclosed hollow fiber microcavity 21, the spatial frequency rises to [value missing]. Conversely, tilting counterclockwise causes the gallium indium tin liquid metal microsphere 4 to shift to the left, compressing the optical path period. The main peak frequency decreases accordingly. When the gallium indium tin liquid metal microsphere 4 reaches the leftmost end of the semi-enclosed hollow fiber microcavity 21, the spatial frequency drops to... This characteristic of spatial frequency monotonically shifting with the tilt direction provides an intuitive frequency domain feature for real-time determination of tilt direction and amplitude, and high-precision detection can be achieved without additional demodulation algorithms. Therefore, the accuracy of fiber tilt detection can be improved by using Fast Fourier Transform. This fiber has significant application value in fields such as civil engineering monitoring, precision machining, national defense, spacecraft attitude control, precision industrial equipment monitoring, and structural health.

[0066] In summary, the embodiments of this application provide an optical fiber with integrated movable liquid metal microspheres, which has the outstanding advantages of simple structure, small size, and high integration. Moreover, it does not require external auxiliary components to increase the modulation capability of the optical signal and can realize sensitive detection of tilt state.

[0067] Secondly, embodiments of this application provide an optical fiber integrating movable liquid metal microspheres and a method for fabricating the same, the method comprising:

[0068] Step 1: Fiber splice one end of hollow fiber 2 to one end of single-mode fiber 1, and cut the other end of hollow fiber 2 to make hollow fiber 2 have a semi-closed hollow fiber microcavity 21, thus obtaining the first fiber.

[0069] Step 2: Injecting gallium indium tin (GaInT) liquid metal from the other end of the hollow fiber 2 forms a Fabry-Perot microcavity 3 within the hollow fiber 2, resulting in a second optical fiber containing GaInT liquid metal droplets. The GaInT liquid metal spontaneously condenses into metal droplets under surface tension. The GaInT liquid metal generates an indium gallium selenide (IGS) metal oxide layer, which adheres to the inner wall of the semi-enclosed hollow fiber microcavity 21 of the hollow fiber 2.

[0070] Step 3: Fill the outer side of the gallium indium tin (GaInT) liquid metal microdroplet with NaOH solution to obtain the third optical fiber. The NaOH solution fills the semi-enclosed hollow fiber microcavity 21 of the hollow fiber 2 through capillary action. At this time, the oxide layer on the surface of the GaInT liquid metal microdroplet dissolves in the alkaline solution, significantly reducing the adhesion between the GaInT liquid metal microdroplet and the inner wall of the fiber. This allows the GaInT liquid metal microdroplet to ultimately maintain a microsphere shape in the NaOH solution under the influence of surface tension and remain movable.

[0071] It should be noted that before filling with NaOH solution, although the injected gallium indium tin (GaInT) liquid metal droplets condense into droplet state under the action of surface tension, the liquid metal easily forms an indium gallium tin oxide layer when exposed to air. This oxide layer adheres to the inner wall of the semi-enclosed hollow fiber microcavity 21 of the hollow fiber 2, causing the GaInT liquid metal droplets to adhere to the cavity wall, making it difficult to maintain a regular shape and unable to move freely. At this time, it is only in the state of "GaInT liquid metal droplets". After filling with NaOH solution, the alkaline environment will quickly dissolve the oxide layer on the surface of the GaInT liquid metal droplets, completely eliminating the adhesion between the GaInT liquid metal droplets and the cavity wall. At the same time, under the continuous action of surface tension, the GaInT liquid metal droplets will spontaneously adjust to a regular spherical structure, eventually forming "GaInT liquid metal microspheres", providing a structural basis for the stable interference and sensitive response of the Fabry-Perot microcavity.

[0072] Step 4: Seal the other end of the hollow fiber 2 with a waterproof epoxy resin layer 5 to obtain an optical fiber structure with integrated movable liquid metal microspheres.

[0073] In some embodiments, arc fusion splicing technology is used in the fiber optic fusion splicer in steps 1 and 4, and the discharge intensity during the fusion process is 3.5mA to avoid the collapse of the hollow fiber 2 at the interface during the fusion process.

[0074] In some embodiments, in step 3, gallium indium tin liquid metal is slowly injected under pressure using a syringe.

[0075] In some embodiments, the mass fraction of the NaOH solution in step 3 is 1 wt%.

[0076] In summary, the embodiments of this application provide a method for fabricating an optical fiber with integrated movable liquid metal microspheres. The optical fiber with integrated movable liquid metal microspheres prepared by this method has a simple structure, small size, high integration, and does not require external auxiliary components to increase the modulation capability of the optical signal, thus enabling sensitive detection of tilted states.

[0077] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The term "multiple" refers to two or more unless otherwise expressly defined.

[0078] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only.

[0079] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. An optical fiber integrating movable liquid metal microspheres, characterized in that, The optical fiber includes: Single-mode fiber (1); A hollow fiber (2) is fused to a single-mode fiber (1) at one end, and has a semi-closed hollow fiber microcavity (21). Movable indium tin liquid metal microspheres (4) placed inside a semi-enclosed hollow fiber microcavity (21). A NaOH solution fills the semi-enclosed hollow fiber microcavity (21) and completely encapsulates the gallium indium tin liquid metal microspheres (4). The semi-enclosed hollow fiber microcavity (21), the indium tin liquid metal microspheres (4) and the NaOH solution form a Fabry-Perot microcavity (3). Waterproof epoxy resin layer (5) is used to seal the other end of the hollow optical fiber (2).

2. The optical fiber with integrated movable liquid metal microspheres according to claim 1, characterized in that, The single-mode optical fiber (1) has an inner diameter of 8~10μm and an outer diameter of 125μm.

3. The optical fiber with integrated movable liquid metal microspheres according to claim 1, characterized in that, The hollow fiber (2) has an inner diameter of 50~60μm and an outer diameter of 125μm.

4. The optical fiber with integrated movable liquid metal microspheres according to claim 1, characterized in that, The volume of the gallium indium tin liquid metal microspheres (4) is 0.113~0.179 nL, and the mass fraction of the NaOH solution is 1~3 wt%, with a volume of 0.7~0.9 μL.

5. The optical fiber with integrated movable liquid metal microspheres according to claim 1, characterized in that, The thickness of the waterproof epoxy resin layer (5) is 20~30μm.

6. The optical fiber with integrated movable liquid metal microspheres according to claim 1, characterized in that, The length of the Fabry-Perot microcavity (3) is 80~250μm, which changes in real time with the movement of the gallium indium tin liquid metal microsphere (4) when tilted. The length of the semi-enclosed hollow fiber microcavity (21) is 400~500μm.

7. A method for fabricating an optical fiber integrating movable liquid metal microspheres, characterized in that, The preparation method includes: Step 1: fused one end of the hollow fiber (2) with one end of the single-mode fiber (1), and cut the other end of the hollow fiber (2) to make the hollow fiber (2) have a semi-closed hollow fiber microcavity (21) to obtain the first fiber. Step 2: Inject gallium indium tin liquid metal from the other end of the hollow fiber (2) to form a Fabry-Perot microcavity (3) in the hollow fiber (2) to obtain a second fiber containing gallium indium tin liquid metal droplets; Step 3: Fill the outside of the gallium indium tin liquid metal microdroplet with NaOH solution to obtain the third optical fiber; Step 4: Seal the other end of the hollow fiber (2) with a waterproof epoxy resin layer (5) to obtain an optical fiber with integrated movable liquid metal microspheres.

8. The method for fabricating an optical fiber with integrated movable liquid metal microspheres according to claim 7, characterized in that, In steps 1 and 4, arc fusion splicing technology is used to perform fusion splicing in an optical fiber fusion splicer, and the discharge intensity during the fusion splicing process is 3.5~4.0mA.

9. The method for fabricating an optical fiber with integrated movable liquid metal microspheres according to claim 7, characterized in that, In step 3, gallium indium tin liquid metal is slowly injected under pressure using a syringe.

10. The method for fabricating an optical fiber with integrated movable liquid metal microspheres according to claim 7, characterized in that, In step 3, the mass fraction of the NaOH solution is 1-3 wt%.

Images