Microsphere-driven dual-cavity decoupled optical fiber micro-force and temperature sensor and preparation method thereof

Abstract

The application discloses a microsphere-driven double-cavity decoupled optical fiber micro-force and temperature sensor, a preparation method thereof and a sensing device, and belongs to the technical field of optical fiber sensing. The sensor is formed by cascading a polydimethylsiloxane temperature-sensitive cavity and an air cavity in an air-core optical fiber, and covering a graphene oxide film and fixing a silica microsphere on an end face, and a double-Fabry-Perot interference structure is formed. The preparation adopts a core offset semi-filling method to introduce polydimethylsiloxane, uses a pulling method to form a film, and precisely fixes the microsphere on a three-dimensional displacement platform through trace ultraviolet glue. Changes of external temperature and micro-force cause optical path drift of the temperature-sensitive cavity and the air cavity respectively, and double-parameter decoupled measurement is realized by using spectrum separation and a sensitivity matrix. Experiments show that the temperature sensitivity of the application reaches 2.233 nm / ℃ in the range of 30-60℃, and the micro-force sensitivity reaches -1.344 nm / μN in the range of 0-10 μN. The application has compact structure, simple preparation, can realize micro-newton level contact force detection, has good temperature measurement capacity, and has wide application prospects in the fields of micro-electro-mechanical system monitoring, biomechanical detection and minimally invasive medical treatment.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a microsphere-driven dual-cavity decoupled fiber optic micro-force temperature sensor, its fabrication method, and sensing device. Background Technology

[0002] With the rapid development of microelectromechanical systems (MEMS), flexible electronic devices, biomedical detection, and minimally invasive surgery, increasingly higher demands are being placed on the high-precision synchronous monitoring of microscale contact forces and ambient temperatures. Currently, commonly used microforce sensors mainly include piezoresistive, capacitive, piezoelectric, and fiber optic sensors. Among them, fiber optic sensors have become an important research direction in the field of microforce detection due to their advantages such as small size, light weight, strong resistance to electromagnetic interference, good biocompatibility, and suitability for harsh environments. However, the inherent thermo-optical and thermal expansion effects of fiber optic materials make the sensors highly susceptible to interference from changes in ambient temperature during force application, resulting in a serious cross-sensitivity problem.

[0003] Existing fiber optic microforce sensors typically employ fiber Bragg gratings, Mach-Zehnder interferometers, or Fabry-Perot interferometers. Existing dual-parameter detection schemes for microforce and temperature often compensate for temperature effects using reference gratings, dual-wavelength measurements, external temperature compensation structures, or dual-cavity interferometry structures. While these schemes can reduce temperature crosstalk to some extent, they still have the following shortcomings: First, in micro-Newton level contact force detection, the force-sensitive region's location and loading area are difficult to stably define, leading to insufficient consistency in microforce response. Second, temperature changes simultaneously cause changes in optical path length and material refractive index, making it easy for microforce and temperature signals to couple in the reflection spectrum. Compensation methods such as reference gratings and dual-wavelength methods usually require additional structures or more complex demodulation systems. Third, some dual-parameter sensors involve numerous fabrication steps and complex end structures, hindering miniaturization and packaging. This invention constructs a double Fabry-Perot interference structure consisting of a polydimethylsiloxane temperature-sensitive cavity and an air cavity within a hollow optical fiber. It also employs silica microspheres and graphene oxide films to form a centrally loaded micro-force actuation unit, enabling the temperature-sensitive cavity to primarily respond to temperature and the air cavity to primarily respond to micro-force. Furthermore, by combining spectral separation and sensitivity matrix decoupling, the cross-interference between micro-force and temperature is reduced from both structural and demodulation perspectives. Summary of the Invention

[0004] To address the issues mentioned in the background art regarding achieving higher sensitivity in micro-force monitoring and resolving the force-temperature cross-sensitivity problem, this invention proposes a microsphere-driven dual-cavity decoupled fiber optic micro-force temperature sensor, its fabrication method, and sensing device, thereby solving problems such as low micro-force detection sensitivity, severe temperature crosstalk, and complex structure in existing technologies.

[0005] This invention proposes a microsphere-driven dual-cavity decoupled fiber optic microforce temperature sensor, comprising: a single-mode fiber, a hollow-core fiber, a polydimethylsiloxane temperature-sensitive cavity, an air cavity, a graphene oxide film, and silica microspheres. The single-mode fiber and the hollow-core fiber are connected by fusion splicing.

[0006] Preferably, a temperature-sensitive cavity is formed inside the hollow optical fiber using polydimethylsiloxane.

[0007] Preferably, a graphene oxide film covers the end face of the hollow optical fiber, and the air cavity is located between the polydimethylsiloxane temperature-sensitive cavity and the graphene oxide film.

[0008] Preferably, the silica microspheres are fixed at the center of the graphene oxide film, forming a micro-force detection unit together with the graphene oxide film and the air cavity.

[0009] This invention proposes a microsphere-driven dual-cavity decoupled fiber optic micro-force temperature sensor. This sensor constructs a polydimethylsiloxane (PDS) temperature-sensitive cavity and an air cavity within a hollow fiber, forming a double Fabry-Perot interference structure. A graphene oxide film is fabricated on the end face of the hollow fiber, and microspheres are fixed to form force-sensitive units. The PDS temperature-sensitive cavity is used for temperature sensing, while the air cavity and graphene oxide film work together for micro-force sensing. Changes in external temperature cause thermal expansion and thermo-optic effects in the PDS material, leading to a change in the optical path length of the temperature-sensitive cavity. When an external micro-force acts on the microsphere, it is transmitted through the silica microsphere to the graphene oxide film, causing the film to flex and deform, compressing the length of the air cavity and thus altering its optical path length. By monitoring the wavelength shift of the characteristic peaks corresponding to different interference cavities in the reflection spectrum, and combining this with spectral separation and sensitivity matrix demodulation methods, synchronous measurement and decoupled analysis of micro-force and temperature parameters can be achieved.

[0010] This invention also proposes a method for fabricating the above-mentioned microsphere-driven dual-cavity decoupled fiber optic micro-force temperature sensor, comprising the following steps:

[0011] S1. A single-mode optical fiber is fused with a hollow optical fiber with an inner diameter of 80 μm and a length of 50–80 μm to form a sensor substrate.

[0012] S2. Polydimethylsiloxane is introduced using the core offset semi-filling method to fill the hollow fiber with polydimethylsiloxane prepolymer to form a liquid microcavity.

[0013] S3. The liquid microcavity is heated and cured at 90°C using a constant temperature chamber. After heating for 60 minutes, the liquid microcavity is cured to form a polydimethylsiloxane temperature-sensitive cavity.

[0014] S4. On a three-dimensional displacement platform, the hollow fiber-thermal cavity structure prepared in S3 is brought into contact with a 5% graphene oxide solution using the Czochralski method to form a liquid graphene oxide film on its end face.

[0015] S5. The liquid film is heated and cured at 60°C using a constant temperature chamber. After heating for 40 minutes, the liquid film is cured to form a graphene oxide film.

[0016] S6. Using a tapered single-mode optical fiber dipped in a small amount of UV adhesive, it is then docked with the structure obtained in S5 on a precision displacement platform, leaving a small amount of UV adhesive at the center of the graphene oxide film.

[0017] S7. On an inverted optical displacement platform, the structure obtained in S6 is precisely controlled by microscopic observation to adhere the silica microspheres to the center of the graphene oxide film.

[0018] S8. Use an ultraviolet lamp to irradiate the end face of the structure obtained in S7 to cure the ultraviolet adhesive, and then a silica microsphere driven dual-cavity decoupled fiber optic micro-force and temperature sensor can be obtained.

[0019] The fabrication method of the microsphere-driven dual-cavity decoupled fiber optic micro-force temperature sensor proposed in this invention is simple, has good repeatability, and low fabrication cost, and can realize the mass production of high-sensitivity micro-force and temperature sensors.

[0020] This invention also proposes a microsphere-driven dual-cavity decoupled fiber optic sensing device, including the aforementioned microsphere-driven dual-cavity decoupled fiber optic micro-force temperature sensor. It also includes a broadband light source, a circulator, and a spectrometer; the broadband light source is used to emit detection light signals to the sensor, the circulator is used to achieve directional transmission of the light signals, and the spectrometer is used to collect and analyze the sensor's reflection spectral signals.

[0021] The proposed microsphere-driven dual-cavity decoupled fiber optic sensing device generates different responses to micro-force and temperature through a dual-cavity interference structure. Combined with fast Fourier transform spectrum separation technology and sensitivity matrix demodulation algorithm, it achieves synchronous detection and high-precision decoupling of micro-force and temperature parameters. Its technical effect is similar to that of the aforementioned fiber optic sensor, so it will not be described in detail here. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of one embodiment of a microsphere-driven dual-cavity decoupled fiber optic microforce and temperature sensor proposed in this invention.

[0023] Figure 2 This is a schematic diagram of one embodiment of a microsphere-driven dual-cavity decoupled fiber optic microforce and temperature sensing device proposed in this invention.

[0024] Figure 3 The present invention presents the reflection spectrum of a microsphere-driven dual-cavity decoupled fiber optic microforce and temperature sensor. Detailed Implementation

[0025] like Figures 1 to 3 As shown, Figure 1 This is a schematic diagram of the structure of a microsphere-driven dual-cavity decoupled fiber optic microforce and temperature sensor proposed in this invention. Figure 2 This is a schematic diagram of the experimental setup for a microsphere-driven dual-cavity decoupled fiber optic microforce and temperature sensor proposed in this invention. Figure 3 The present invention presents the reflection spectrum of a microsphere-driven dual-cavity decoupled fiber optic microforce and temperature sensor.

[0026] Reference Figure 1 This invention proposes a microsphere-driven dual-cavity decoupled fiber optic micro-force temperature sensor, comprising a single-mode fiber 1, a hollow fiber 2, a polydimethylsiloxane (PDMS) temperature-sensitive cavity 3, an air cavity 4, a graphene oxide film 5, and microspheres 6. The single-mode fiber 1 and the hollow fiber 2 are fused together to form the main sensor structure. The PMS temperature-sensitive cavity 3 is disposed inside the hollow fiber 2 for temperature detection; the air cavity 4 is located between the PMS temperature-sensitive cavity 3 and the graphene oxide film 5; the graphene oxide film 5 is encapsulated at the end face of the hollow fiber 2; the microspheres 6 are fixed to the center of the graphene oxide film 5 with UV adhesive, thereby forming a micro-force sensitive unit. In this embodiment, the PMS temperature-sensitive cavity 3 and the air cavity 4 together constitute a double Fabry-Perot interference structure. The PMS temperature-sensitive cavity 3 is mainly sensitive to temperature changes, while the air cavity 4 is mainly sensitive to changes in external micro-force, thus achieving synchronous detection of temperature and micro-force. When the ambient temperature changes, the polydimethylsiloxane material undergoes thermal expansion and thermo-optic effects, causing a change in the optical path length of the polydimethylsiloxane temperature-sensitive cavity 3, resulting in a drift in the corresponding interference spectrum. When a small external force is applied to the microsphere 6, the microsphere 6 concentrates the force and transmits it to the graphene oxide film 5, causing the graphene oxide film 5 to undergo elastic flexural deformation, thereby causing a change in the length of the air cavity 4, resulting in a drift in the corresponding interference spectrum. Because the two cavities have different response characteristics to small forces and temperature, dual-parameter detection can be achieved.

[0027] To illustrate the fabrication process of this embodiment in detail, the present invention proposes a method for fabricating a microsphere-driven dual-cavity decoupled fiber optic micro-force temperature sensor, comprising the following steps:

[0028] S1. A single-mode optical fiber is fused with a hollow optical fiber with an inner diameter of 80 μm and a length of 50–80 μm to form a sensor substrate.

[0029] S2. Polydimethylsiloxane is introduced using the core offset semi-filling method to fill the hollow fiber with polydimethylsiloxane prepolymer to form a liquid microcavity.

[0030] S3. The liquid microcavity is heated and cured at 90°C using a constant temperature chamber. After heating for 60 minutes, the liquid microcavity is cured to form a polydimethylsiloxane temperature-sensitive cavity.

[0031] S4. On a three-dimensional displacement platform, the hollow fiber-thermal cavity structure prepared in S3 is brought into contact with a 5% graphene oxide solution using the Czochralski method to form a liquid graphene oxide film on its end face.

[0032] S5. The liquid film is heated and cured at 60°C using a constant temperature chamber. After heating for 40 minutes, the liquid film is cured to form a graphene oxide film.

[0033] S6. Using a tapered single-mode optical fiber dipped in a small amount of UV adhesive, it is then docked with the structure obtained in S5 on a precision displacement platform, leaving a trace amount of UV adhesive at the center of the graphene oxide film.

[0034] S7. On an inverted optical displacement platform, the structure obtained in S6 is precisely controlled by microscopic observation to adhere the silica microspheres to the center of the graphene oxide film.

[0035] S8. Use an ultraviolet lamp to irradiate the end face of the structure obtained in S7 to cure the ultraviolet adhesive, and then a silica microsphere driven dual-cavity decoupled fiber optic micro-force and temperature sensor can be obtained.

[0036] To explain the testing method in this embodiment in detail, please refer to... Figure 2 The present invention also proposes a microsphere-driven dual-cavity decoupled fiber optic microforce and temperature sensing device, including a broadband light source 20, a circulator 21, a spectrometer 22, and a three-dimensional displacement platform 23.

[0037] The light signal emitted by the broadband light source 20 enters the sensor through the circulator 21. The reflected light signal returns to the circulator 21 and is then transmitted to the spectrometer 22 for acquisition and analysis. The three-dimensional displacement platform 23 is used to apply minute displacements and generate corresponding micro-force loads.

[0038] During the specific testing process, the sensor was driven to contact the standard probe via a three-dimensional displacement platform 23 to achieve micro-force loading. The spectral analyzer 22 acquired the sensor's reflection spectrum in real time. The initial reflection spectrum of the sensor when no force was applied was as follows: Figure 3 As shown, the spectral signals corresponding to the polydimethylsiloxane temperature-sensitive cavity 3 and the air cavity 4 can be obtained after fast Fourier transform processing. A sensitivity matrix is ​​established using the different response coefficients of the two cavities to temperature and micro-force, and synchronous demodulation of temperature and micro-force parameters is achieved by matrix inversion.

[0039] The microsphere-driven dual-cavity decoupled fiber optic microforce and temperature sensor designed in this embodiment utilizes the deformation of the graphene oxide film 5 caused by the force applied to the silica microspheres 6, thereby inducing a change in the optical path of the air cavity 4; simultaneously, the temperature response is obtained through the polydimethylsiloxane temperature-sensitive cavity 3. This structure enables microforce detection and temperature detection at the same fiber end, and reduces the cross-influence between the two through spectral separation and sensitivity matrix.

[0040] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A microsphere-driven dual-cavity decoupled fiber optic microforce and temperature sensor, characterized in that, include: Single-mode optical fiber (1); hollow-core optical fiber (2) connected to the single-mode optical fiber (1) by fusion splicing. The polydimethylsiloxane temperature-sensitive cavity (3) is disposed inside the hollow fiber (2); the air cavity (4) is located between the polydimethylsiloxane temperature-sensitive cavity (3) and the end face of the hollow fiber; the graphene oxide film (5) covers the end face of the hollow fiber; and the silica microspheres (6) are fixed in the central region of the graphene oxide film (5). The interface between the single-mode fiber (1) and the polydimethylsiloxane temperature-sensitive cavity (3), the interface between the polydimethylsiloxane temperature-sensitive cavity (3) and the air cavity (4), and the graphene oxide film (5) together constitute a cascaded double Fabry-Perot interference structure.

2. The sensor according to claim 1, characterized in that, To ensure the stability of the fusion splicing with the single-mode fiber, the hollow fiber should be selected with the largest possible inner diameter. Therefore, a hollow fiber with an inner diameter of 80μm is selected.

3. The sensor according to claim 1, characterized in that, The polydimethylsiloxane temperature-sensitive cavity is prepared by the core offset semi-filling method, and the length prepared by this method is stable at 30-40 μm.

4. The sensor according to claim 1, characterized in that, Simulation analysis shows that the sensor sensitivity increases significantly as the thickness of the graphene oxide film decreases. However, considering the actual preparation process, the minimum thickness achievable using the Czochralski method is 1–2 μm.

5. The sensor according to claim 1, characterized in that, The diameter of the silica microspheres (6) should be smaller than the inner diameter of the hollow optical fiber. Therefore, silica microspheres with a diameter of 50 to 60 μm are selected.

6. A method for manufacturing a sensor according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Fusion splice the single-mode fiber with a hollow fiber with an inner diameter of 80μm and a length of 50-80μm. S2. Polydimethylsiloxane is introduced using the core offset semi-filling method to fill the hollow fiber with polydimethylsiloxane prepolymer to form a liquid microcavity. S3. The liquid microcavity is heated and cured at 90°C using a constant temperature chamber. After heating for 60 minutes, the liquid microcavity is cured to form a polydimethylsiloxane temperature-sensitive cavity. S4. On a three-dimensional displacement platform, the hollow fiber-thermal cavity structure prepared in S3 is brought into contact with a 5% graphene oxide solution using the Czochralski method to form a liquid graphene oxide film on its end face. S5. The liquid film is heated and cured at 60°C using a constant temperature chamber. After heating for 40 minutes, the liquid film is cured to form a graphene oxide film. S6. Using a tapered single-mode optical fiber dipped in a small amount of UV adhesive, it is then docked with the structure obtained in S5 on a precision displacement platform, so that a trace amount of UV adhesive is left at the center of the graphene oxide film. S7. On an inverted optical displacement platform, the structure obtained in S6 is precisely controlled by microscopic observation to adhere the silica microspheres to the center of the graphene oxide film. S8. Use an ultraviolet lamp to irradiate the end face of the structure obtained in S7 to cure the ultraviolet adhesive, and then a silica microsphere driven dual-cavity decoupled fiber optic micro-force and temperature sensor can be obtained.

7. A fiber optic micro-force temperature sensing device, characterized in that, include: A broadband light source (20), a circulator (21), and a spectrometer (22) are provided. The broadband light source (20) is connected to a sensor via the circulator (21), and the sensor's reflected signal is transmitted to the spectrometer (22) via the circulator.

8. The sensing device according to claim 7, characterized in that, Fast Fourier transform is used to separate the interference signals corresponding to the temperature-sensitive cavity and the air cavity, respectively, and a two-parameter sensitivity matrix is ​​used to decouple the micro-force and temperature parameters.

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