A fiber optic sensing unit, a fiber optic fluorescence pressure sensor and a method of manufacture

Abstract

The application discloses an optical fiber sensing unit, an optical fiber fluorescence pressure sensor and a preparation method, relates to the field of optical fiber sensing, and the method comprises a sensing optical fiber, a fluorescence solution with a concentration effect and a pressure-sensitive flexible shell film; the fluorescence solution is encapsulated in the pressure-sensitive flexible shell film; the sensing optical fiber is inserted into the pressure-sensitive flexible shell film, and the sensing optical fiber is immersed in the fluorescence solution; the sensing optical fiber is used for transmitting an excitation light signal generated by a light source module to the fluorescence solution and transmitting a fluorescence signal change amount of the fluorescence solution; and the fluorescence signal change amount is used for realizing pressure detection. The application can reduce cost, improve sensitivity and precision.

Description

Technical Field

[0001] This application relates to the field of fiber optic sensing, and in particular to a fiber optic sensing unit, a fiber optic fluorescent pressure sensor, and a method for its fabrication. Background Technology

[0002] Fiber optic sensing technology, as a crucial technology in the field of detection, is gradually playing a vital role in various sectors. Its position has become increasingly unshakeable with the gradual maturation of its technology, and its development and progress are highly valued. Currently, fiber optic sensing technology has made significant progress in physical quantity detection in daily life, industrial manufacturing, agricultural production, marine exploration, and aerospace, and is widely used in numerous applications. Pressure sensing is a crucial element in industrial production, marine exploration, aerospace, and meteorological research, as it relates to the safety and accuracy of production, exploration, and flight activities, making it extremely important. However, current pressure sensors mostly detect pressure at a single point or on a single surface, making them difficult to operate normally in harsh and complex environments, thus limiting their application. While fiber optic pressure sensors can adapt to harsh environments, their fabrication is relatively complex and costly. Therefore, developing a fiber optic pressure sensor that can be easily fabricated, is low-cost, and possesses good sensitivity and accuracy is of great significance for the application and widespread adoption of fiber optic pressure sensing technology. Summary of the Invention

[0003] The purpose of this application is to provide an optical fiber sensing unit, an optical fiber fluorescence pressure sensor, and a method for fabricating it, which can reduce costs and improve sensitivity and accuracy.

[0004] To achieve the above objectives, this application provides the following solution:

[0005] In a first aspect, this application provides an optical fiber sensing unit, comprising: a sensing optical fiber, a fluorescent solution with a concentration effect, and a pressure-sensitive flexible outer shell membrane; the fluorescent solution is encapsulated within the pressure-sensitive flexible outer shell membrane; the sensing optical fiber is inserted into the pressure-sensitive flexible outer shell membrane and immersed in the fluorescent solution; the sensing optical fiber is used to transmit the excitation light signal generated by the light source module to the fluorescent solution and to transmit the change in the fluorescence signal of the fluorescent solution; the change in the fluorescence signal is used to realize pressure detection.

[0006] In one embodiment, the fluorescent solution is a rhodamine derivative solution or a coumarin derivative solution.

[0007] In one embodiment, the pressure-sensitive flexible outer shell film is made of PDMS, polyolefin, or styrene.

[0008] In one embodiment, the pressure-sensitive flexible outer shell membrane is shaped like a sphere or a polyhedron.

[0009] In one embodiment, the fiber optic sensing unit further includes a UV-curable adhesive; the UV-curable adhesive is used to encapsulate the boundary between the sensing fiber and the pressure-sensitive flexible outer shell membrane.

[0010] Secondly, this application provides a fiber optic fluorescence pressure sensor, comprising: the aforementioned fiber optic sensing unit, a light source module, a fiber optic spectrometer, and a computer; the fiber optic sensing unit is connected to both the light source module and the fiber optic spectrometer; the computer is also connected to the fiber optic spectrometer; the light source module is used to excite a fluorescent solution in the fiber optic sensing unit; the fiber optic sensing unit is used to detect changes in fluorescence signal and transmit these changes to the fiber optic spectrometer; the fiber optic spectrometer is used to convert the changes in fluorescence signal into spectral information and transmit the spectral information to the computer; the computer is used to determine pressure information based on the spectral information.

[0011] In one embodiment, the fiber optic fluorescent pressure sensor further includes a focusing lens group; the focusing lens group is disposed between the fiber optic sensing unit and the light source module.

[0012] In one embodiment, the fiber optic fluorescence pressure sensor further includes a filter; the filter is disposed between the fiber optic spectrometer and the fiber optic sensing unit.

[0013] Thirdly, this application provides a method for fabricating the aforementioned optical fiber sensing unit, comprising: obtaining a pressure-sensitive flexible outer shell membrane; filling the pressure-sensitive flexible outer shell membrane with a concentration-effect fluorescent solution; inserting a sensing optical fiber into the fluorescent solution and attaching the pressure-sensitive flexible outer shell membrane to the sensing optical fiber.

[0014] In one embodiment, obtaining a pressure-sensitive flexible outer shell film specifically includes: immersing a mold with a predetermined shape into a pressure-sensitive flexible material; and obtaining a pressure-sensitive flexible outer shell film by heating and curing.

[0015] According to the specific embodiments provided in this application, the following technical effects are disclosed:

[0016] This application provides an optical fiber sensing unit, an optical fiber fluorescent pressure sensor, and a fabrication method. A concentration-effect fluorescent solution is encapsulated within a pressure-sensitive flexible outer shell membrane; a sensing optical fiber is inserted into the pressure-sensitive flexible outer shell membrane and immersed in the fluorescent solution; the sensing optical fiber is used to transmit the excitation light signal generated by the light source module to the fluorescent solution and to transmit the change in the fluorescence signal of the fluorescent solution; the change in the fluorescence signal is used to achieve pressure detection. Directly utilizing a concentration-effect fluorescent solution to reflect pressure changes can improve the sensitivity and accuracy of pressure detection; pressure detection can be completed using only a sensing optical fiber, a concentration-effect fluorescent solution, and a pressure-sensitive flexible outer shell membrane, and it can be reused, reducing costs. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the 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.

[0018] Figure 1 This is a schematic diagram of an optical fiber sensing unit.

[0019] Figure 2 This is a schematic diagram of a fiber optic fluorescent pressure sensor.

[0020] Figure 3 This is a schematic diagram of the fabrication method for an optical fiber sensing unit.

[0021] Figure 4 This is a schematic diagram of the detection principle of a fiber optic fluorescent pressure sensor.

[0022] Figure labels: 1-Test environment, 2-Fiber optic sensing unit, 3-Transmission fiber optic cable, 4-Fiber optic circulator, 5-Light source module, 6-Fiber optic spectrometer, 7-Computer, 8-Fluorescent solution, 9-PDMS pressure-sensitive flexible outer shell film, 10-Fluorescent molecule, 11-Excitation light, 12-UV curing adhesive, 13-Sensing fiber optic cable, 14-Reflected fluorescence, 15-Spherical mold, 16-Increased external pressure, 17-Fluorescent molecule dimer, 18-Fluorescent molecule polymer, 19-Decreased external pressure. Detailed Implementation

[0023] 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, and 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.

[0024] As an important branch of the pressure sensing field, fiber optic pressure sensing technology is widely used in pressure sensing and detection in various occasions due to its good anti-interference ability and remote monitoring capability. It is mainly divided into intensity modulation fiber optic pressure sensing, phase modulation fiber optic pressure sensing, wavelength modulation fiber optic pressure sensing, polarization modulation fiber optic pressure sensing, and distributed fiber optic pressure sensing. Intensity-modulated fiber optic pressure sensors sense pressure by changing the intensity of light transmitted through the fiber due to external pressure affecting its loss. Their advantages include simple structure and low cost. However, they suffer from low sensitivity, susceptibility to interference from external factors, and poor stability. Phase-modulated fiber optic pressure sensors, based on the principle of interference, utilize pressure to cause changes in the interference cavity length and effective refractive index, leading to changes in the light phase. Detecting these phase changes allows for pressure sensing. They offer high sensitivity and a wide dynamic range, but require demodulation systems and sophisticated optical components, resulting in complex and costly system construction. Wavelength-modulated fiber optic pressure sensors, primarily fiber optic grating pressure sensors (including fiber Bragg gratings), utilize pressure to alter the grating period and refractive index, causing wavelength shifts. Detecting these wavelength changes allows for pressure detection. They offer the advantage of multi-point, multi-parameter detection, but require complex demodulation equipment, resulting in high costs and complex sensor unit fabrication. Polarization-modulated fiber optic pressure sensing utilizes the birefringence of optical fibers caused by pressure to detect the polarization state, achieving pressure sensing with minimal impact from light source fluctuations and high sensitivity. However, the demodulation system is extremely complex and costly. Distributed fiber optic pressure sensors employ Raman and Brillouin scattering principles, achieving location-based pressure sensing by detecting reflection time and signal intensity. They offer high resolution and low cost, but suffer from slow response and complex data processing. Given the current state of fiber optic pressure sensing technology and addressing its existing problems and limitations, this application provides a novel fiber optic pressure sensor based on a new sensing principle. This sensor is simple to fabricate, low-cost, and exhibits high sensitivity and stability, significantly expanding its application and widespread adoption in the pressure sensing field.

[0025] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] like Figure 1As shown, an optical fiber sensing unit 2 is provided, comprising: a sensing optical fiber 13, a fluorescent solution 8 with a concentration effect, and a pressure-sensitive flexible outer shell membrane; the fluorescent solution 8 is encapsulated within the pressure-sensitive flexible outer shell membrane; the sensing optical fiber 13 is inserted into the pressure-sensitive flexible outer shell membrane and immersed in the fluorescent solution 8; the sensing optical fiber 13 is used to transmit the excitation light 11 signal generated by the light source module 5 to the fluorescent solution 8 and to transmit the change in fluorescence signal of the fluorescent solution 8; the change in fluorescence signal is used to realize pressure detection.

[0027] In an exemplary embodiment, the fluorescent solution 8 is a rhodamine derivative solution or a coumarin derivative solution; wherein, the rhodamine derivative solution is a rhodamine B solution or other rhodamine derivatives, which refer to rhodamine 6G or rhodamine 110, etc., rhodamine series substances. The fiber optic sensing unit 2 uses the concentration-effect fluorescent solution 8, rhodamine B, as the sensitive substance. When the concentration of the concentration-effect rhodamine B solution decreases, the fluorescence emission peak wavelength will blue shift; when the concentration increases, rhodamine B molecules will aggregate, causing the fluorescence emission wavelength to red shift and fluorescence to be quenched. Quantitative detection of indirect pressure can be achieved by detecting the change in fluorescence emission wavelength. To meet usage requirements or the fluorescence characteristics of the solution itself, other concentration-effect fluorescent solutions 8 can be selected, such as other rhodamine derivatives, coumarin derivatives, etc., which can reduce the influence of temperature sensitivity or photobleaching effect and improve fluorescence quantum yield, etc.

[0028] The fiber optic sensing unit 2 is prepared using the fluorescent solution Rhodamine B as the sensing material. Rhodamine B material exhibits a concentration effect, showing regular fluorescence changes at different concentrations, such as regular changes in fluorescence intensity and regular shifts in fluorescence emission peak wavelength. When combined with a flexible encapsulation shell, this characteristic can be utilized to achieve qualitative and quantitative pressure sensing. Other fluorescent solutions 8 with concentration effects, such as coumarin solutions, can be used for encapsulation. Pressure sensing can be achieved by altering other fluorescence characteristics, such as regular changes in fluorescence lifetime and fluorescence quantum yield. Alternatively, special solvents can be used to prepare the fluorescent solution 8, such as solutions with different polarities, like ethanol and ethylene glycol, to improve the sensing sensitivity or detection range.

[0029] In one exemplary embodiment, the pressure-sensitive flexible outer shell membrane is made of PDMS, polyolefin, or styrene. The fiber optic sensing unit 2 is encapsulated using polydimethylsiloxane (PDMS), which not only possesses excellent ductility, mechanical properties, and resilience, but also exhibits good chemical stability and sealing properties, effectively encapsulating the fluorescent solution 8 without leakage. Furthermore, the material itself is non-toxic, harmless, and does not cause pollution, making it suitable for pressure detection in most harsh environments. Depending on the sensitivity requirements, pressure detection range, and application scenario of the fiber optic sensing unit 2, other polyolefin or styrene materials can be used as encapsulation materials, or the PDMS material can be doped to improve its physical or chemical properties.

[0030] The fiber optic sensing unit 2 is made of PDMS, which has good flexibility, sealing properties and chemical stability, as the encapsulation material. Its good flexibility and recovery ability can restore it to its initial shape after being subjected to high pressure and maintain a seal to prevent leakage of the internal encapsulated fluorescent solution 8. Special substances such as ZnO can be doped into PDMS to improve the mechanical properties of PDMS, thereby increasing the pressure range that the fiber optic sensing unit 2 can withstand and thus improving the detection range of the sensor. Alternatively, other materials with special properties, such as polyacrylamide (biocompatible), can be used to prepare fiber optic bio-pressure sensors for the detection of biological movements or pressure in internal parts of the body, thus broadening the field of sensing and application scenarios.

[0031] In one exemplary embodiment, the pressure-sensitive flexible outer shell membrane is spherical or polyhedral in shape. In this application, the fiber optic sensing unit 2 is spherical, meaning the pressure-sensitive flexible outer shell membrane is spherical. This is designed to accommodate the uniform action of liquid and gas pressures and can be modified according to the detection area or the type of pressure. For example, when detecting solid pressure, it can be set to a square shape. Because the surface of force application is different, the effect of pressure on concentration will also change, thus altering the sensor's sensitivity to adapt to pressure detection in different situations.

[0032] The shape of the pressure-sensitive flexible shell membrane formed by PDMS can be changed by changing the mold, such as cuboid or cube, which can realize the detection and sensing of unidirectional pressure. The pressure-sensitive flexible shell membrane in this application is PDMS pressure-sensitive flexible shell membrane 9. The size of PDMS pressure-sensitive flexible shell membrane 9 can also be reduced to adapt to different applications, such as detection of biological movement and internal pressure, and application of fiber optic fluorescent pressure sensor in the field of biological sign detection.

[0033] In an exemplary embodiment, the fiber optic sensing unit 2 further includes a UV-curable adhesive 12; the UV-curable adhesive 12 is used to encapsulate the boundary between the sensing fiber 13 and the pressure-sensitive flexible outer shell film.

[0034] In an exemplary embodiment, the transmission optical fiber 3 is a communication-grade optical fiber. The low-loss communication optical fiber is selected for signal transmission based on the transmission distance of the remote monitoring. In the case of high gas pressure or high liquid pressure, a protective layer with high mechanical strength can be added to the outside of the optical fiber to protect the optical fiber and reduce the impact of external pressure on transmission loss. In some high temperature or low temperature situations, a high temperature resistant or low temperature resistant coating can be added to the outside of the optical fiber to protect the transmission optical fiber 3 and ensure normal operation, thus broadening the application scenarios and fields of the sensor.

[0035] By adding a high-hardness special protective layer to the outside of the optical fiber, the influence of the surrounding environment on the transmission capability of the transmission optical fiber 3 is prevented, and the transmission optical fiber 3 can maintain normal operation under high pressure environment, thereby improving the working environment that the sensor can adapt to, such as working in the high pressure environment of the deep sea.

[0036] In another exemplary embodiment, such as Figure 2 As shown, the fiber optic fluorescence pressure sensor includes: the fiber optic sensing unit 2, the light source module 5, the fiber optic spectrometer 6, and the computer 7; the fiber optic sensing unit 2 is connected to the light source module 5 and the fiber optic spectrometer 6 respectively; the computer 7 is also connected to the fiber optic spectrometer 6; the light source module 5 is used to excite the fluorescent solution 8 of the fiber optic sensing unit 2; the fiber optic sensing unit 2 is used to detect the change in fluorescence signal and transmit the change in fluorescence signal to the fiber optic spectrometer 6; the fiber optic spectrometer 6 is used to convert the change in fluorescence signal into spectral information and transmit the spectral information to the computer 7; the computer 7 is used to determine pressure information based on the spectral information.

[0037] In practical applications, the fiber optic fluorescence pressure sensor also includes a focusing lens group; the focusing lens group is disposed between the fiber optic sensing unit 2 and the light source module 5. The fiber optic sensing unit 2 can increase the intensity of the excitation light 11 by adding optical elements such as the focusing lens group, reduce the loss of excitation light 11 caused by the excessive length of the transmission fiber 3 and the divergence angle of the fiber end face, thereby enhancing the fluorescence intensity and enabling more effective fluorescence collection.

[0038] In practical applications, the fiber optic fluorescence pressure sensor also includes a filter; the filter is positioned between the fiber optic spectrometer 6 and the fiber optic sensing unit 2. The filter added in front of the signal receiving end of the fiber optic spectrometer 6 prevents the laser light from affecting the final detection result and protects the fiber optic spectrometer 6 from damage due to excessively high laser intensity.

[0039] By placing a focusing lens assembly and filters in front of the signal receiver of the fiber optic spectrometer 6, the fluorescence intensity of the fluorescence signal can be enhanced, improving detection efficiency and reducing the influence of excitation light 11 on the fluorescence signal. This improves detection accuracy while reducing the workload on the fiber optic spectrometer 6. Placing the focusing lens assembly in front of the fiber optic spectrometer 6 means building a small optical system in front of the fiber optic spectrometer 6 and connecting it to the fiber optic spectrometer 6 via optical fiber. This effectively increases the intensity of the fluorescence signal detected by the fiber optic spectrometer 6.

[0040] In practical applications, the fiber optic fluorescence pressure sensor also includes a fiber optic circulator 4. The fiber optic circulator 4 is connected to the fiber optic sensing unit 2, the light source module 5, and the fiber optic spectrometer 6. The function of the fiber optic circulator 4 is to transmit optical signals unidirectionally. Its input end is connected to the light source module 5 and receives the laser signal for reverse transmission. Its bidirectional interface end is connected to the fiber optic sensing unit 2, enabling it to transmit the excitation signal to the fiber optic sensing unit 2 to generate a fluorescence signal and collect the fluorescence signal for transmission to the output end. The output end is connected to the fiber optic spectrometer 6 for unidirectional transmission of the fluorescence signal, minimizing the influence of the laser signal on the fluorescence signal.

[0041] The fiber optic fluorescence pressure sensor includes a light source module 5, a transmission fiber optic cable 3, a fiber optic sensing unit 2, a fiber optic spectrometer 6, and a computer 7. The light source module 5 is a laser light source that inputs signal light with the optimal absorption wavelength of the fluorescent material into the entire sensing system. The center wavelength of the light source can be changed according to the different fluorescent materials. The transmission fiber optic cable 3 connects the light source module 5, the fiber optic sensing unit 2, the fiber optic circulator 4, and the fiber optic spectrometer 6 to form an optical path. It mainly transmits the excitation light signal 11 generated by the light source module 5 to the fiber optic sensing unit 2, and then transmits the fluorescence signal to the fiber optic spectrometer 6. The fiber optic sensing unit 2 encapsulates a concentration-effect fluorescent solution, Rhodamine B, using PDMS as the encapsulation material. PDMS, due to its excellent sealing, mechanical properties, elasticity, and ability to recover elastic deformation, effectively protects the internal fluorescent solution 8 from leakage. The encapsulated fluorescent solution 8 exhibits a concentration effect; the fluorescence emission peak wavelength and fluorescence intensity change regularly with changes in concentration. Pressure can be detected by measuring the change in the fluorescence signal output by the fiber optic sensing unit 2. The fiber optic spectrometer 6 uses an internal diffraction grating to disperse and convert the fluorescence signal transmitted through the transmission fiber 3 into spectral information. The computer 7 visualizes the spectral information processed by the fiber optic spectrometer 6 and extracts and processes the fluorescence intensity and fluorescence emission peak wavelength. After the sensor is assembled, the fiber optic sensing unit 2 can be placed in the test environment 1. External pressure can increase the concentration of the fluorescent solution 8 by squeezing the PDMS, thereby affecting the wavelength and intensity of the fluorescence emission peak. The sensor is calibrated by calibrating the relationship between pressure and fluorescence intensity or fluorescence emission peak wavelength. Subsequently, quantitative detection of pressure can be achieved by detecting changes in fluorescence peak wavelength or fluorescence intensity.

[0042] The laser source generates an excitation light signal 11 at the optimal excitation wavelength (center wavelength 520nm) of the Rhodamine B fluorescent solution, ensuring that the fluorescent solution 8 can generate a sufficient fluorescence signal. This signal is then transmitted via the transmission fiber 3 to the fiber optic sensing unit 2. The transmission fiber 3 connects the light source module 5, the fiber optic circulator 4, the fiber optic sensing unit 2, and the fiber optic spectrometer 6 to form the optical path of the fiber optic fluorescence pressure sensor, responsible for transmitting the excitation light signal 11 generated by the light source module 5 and the fluorescence signal generated by the fiber optic sensing unit 2. The fiber optic sensing unit 2 uses PDMS as the encapsulation material to form a spherical pressure-sensitive flexible shell membrane with good sealing performance and chemical stability. The Rhodamine B fluorescent solution is encapsulated inside the PDMS flexible shell membrane. Finally, the sensing fiber 13 is bonded to the PDMS flexible shell membrane containing the Rhodamine B fluorescent solution using a rapidly curable UV-curable adhesive 12 to complete the encapsulation and form the fiber optic sensing probe. After receiving the excitation light signal 11 transmitted by the sensing fiber 13, the Rhodamine B solution will produce... The external pressure is indirectly transmitted to the internal Rhodamine B solution through the flexible PDMS outer shell membrane, causing a change in solution concentration and thus a change in fluorescence characteristics, ultimately achieving qualitative and quantitative detection of pressure. The main function of the fiber optic spectrometer 6 is to receive the fluorescence signal generated by the fiber optic sensing unit 2 and convert it into an electrical signal. Its detection range includes the ultraviolet-visible and near-infrared light bands, and it can detect light signals from 300nm to 1000nm, including the wavelength range of the fluorescence signal. The computer 7 is connected to the fiber optic spectrometer 6 via a data cable. The electrical signal generated after the fluorescence signal is converted by the fiber optic spectrometer 6 is transmitted to the computer 7 via the data cable, and the fluorescence signal and its change process are visualized through the accompanying software (such as spectrum diagrams, spectral data, etc.), which facilitates data processing and determination of the specific relationship between the fluorescence signal (emission peak wavelength or fluorescence intensity) and the known external pressure, thereby realizing calibration and subsequent sensing and detection of unknown pressure. The fiber optic fluorescence pressure sensor based on the principle of molecular concentration change allows for the application of highly sensitive and easily detectable fiber optic fluorescence sensing technology in pressure sensing. Compared with traditional fiber optic pressure sensors, it not only has advantages such as strong anti-interference and suitability for long-distance real-time monitoring, but also has advantages such as high cost-effectiveness, fewer preparation processes, and simple signal demodulation. This expands the application field of fiber optic fluorescence sensing technology and provides new sensing principles and ideas for fiber optic pressure sensing technology.

[0043] See Figure 2The diagram shows a fiber optic fluorescence pressure sensor based on changes in molecular concentration. This sensor includes a light source module 5, a transmission fiber optic cable 3, a fiber optic sensing unit 2, a fiber optic circulator 4, a fiber optic spectrometer 6, and a computer 7. The light source module 5 is a laser source with a specific wavelength. The center wavelength is 520 nm, the optimal excitation wavelength of the fluorescent solution Rhodamine B, which is sensitive to the solution 8. The center wavelength of the laser signal emitted by the laser source module 5 can be adjusted according to the optimal excitation wavelength of the fluorescent solution 8 to maximize fluorescence excitation, facilitating subsequent collection and processing of the fluorescence signal. The transmission fiber optic cable 3 connects the light source module 5, the fiber optic circulator 4, the fiber optic sensing unit 2, and the fiber optic spectrometer 6 to form the entire optical path of the fiber optic fluorescence pressure sensor. It transmits the laser signal generated by the laser source in the light source module 5 through the fiber optic circulator 4 to the fiber optic sensing unit 2 to excite the fluorescent solution 8 and generate a fluorescence signal. The fluorescence signal reflected back from the fiber optic sensing unit 2 is then collected by the fiber optic circulator 4 and transmitted to the fiber optic spectrometer 6 for fluorescence signal processing. The function of the fiber optic circulator 4 is to transmit optical signals unidirectionally. The input end is connected to the light source module 5 and inputs the laser signal for reverse transmission. The bidirectional interface end is connected to the fiber optic sensing unit 2, which can transmit the excitation signal to the fiber optic sensing unit 2 to generate a fluorescence signal and collect the fluorescence signal to transmit it to the output end. The output end is connected to the fiber optic spectrometer 6 to transmit the fluorescence signal unidirectionally, minimizing the influence of the laser signal on the fluorescence signal. The fiber optic sensing unit 2 uses a spherical flexible outer shell membrane made of PDMS, which has good flexibility, mechanical properties, and chemical stability, to encapsulate the fluorescent solution Rhodamine B. After encapsulation, the good hydrophobicity, airtightness, and mechanical strength of PDMS can protect the internal fluorescent solution Rhodamine B from leakage when subjected to external high pressure. In addition, the good flexibility and self-healing properties of PDMS can produce corresponding deformation after the external pressure changes, thereby compressing the volume of the internal fluorescent solution 8 to realize pressure transmission. Moreover, it can quickly recover its original shape after the pressure changes, making the fiber optic sensing unit 2 highly reusable. The sensitive material, the fluorescent solution Rhodamine B, has a good concentration effect and can change its fluorescence signal according to the concentration change. The fiber optic sensing unit 2, through the combination of the pressure-sensitive flexible outer shell membrane made of PDMS and the concentration-effect fluorescent solution Rhodamine B, can convert the change of external pressure in the test environment 1 into a regular change of fluorescence signal by compressing the solution volume.

[0044] The fiber optic spectrometer 6, acting as a fluorescence signal acquisition module, disperses the fluorescence signal transmitted from the fiber optic sensing unit 2 via the transmission fiber 3 into spectral information through a diffraction grating. The optical signal of the spectral information is then converted into an electrical signal and transmitted to the computer 7 via a data line. The computer 7 receives the spectral information electrical signal from the fiber optic spectrometer 6, converts it into spectral data, and uses corresponding software to visualize the spectral data on the screen. Based on the fluorescence characteristics (fluorescence emission peak wavelength or fluorescence intensity, etc.) and the known corresponding pressure, a specific pressure-fluorescence characteristic relationship is established to achieve qualitative and quantitative detection of unknown pressure. The entire sensor is simple to fabricate, has low production difficulty and cost, and employs a novel detection principle. Introducing high-sensitivity fiber optic fluorescence sensing technology into pressure sensing is beneficial for the innovation, development, and widespread application of fiber optic pressure sensors.

[0045] Firstly, the concentration of the fluorescent solution can be determined by the fluorescence intensity or fluorescence emission wavelength detected by the fiber optic spectrometer. The concentration is fixed at the initial manufacturing stage of the fiber optic sensor. Therefore, it will be compressed under external pressure, causing the concentration to change. The concentration effect of the fluorescent solution (the change in fluorescence intensity with concentration) follows a fixed pattern. Based on this fixed pattern, the current concentration of the fluorescent solution can be calculated from the fluorescence intensity or fluorescence emission wavelength. The current concentration also forms a fixed pattern with the external pressure. The fluorescence solution concentration corresponding to the external pressure can be pre-calibrated by computer to calculate the calibration fitting curve. Finally, the concentration of the fluorescent solution can be calculated based on the detected fluorescence intensity or fluorescence emission peak wavelength, and thus the magnitude of the unknown external pressure can be calculated.

[0046] See Figure 1 The diagram shows a schematic of the fiber optic sensing unit 2. The fiber optic sensing unit 2 mainly comprises a sensing fiber 13, a fluorescent solution 8, and a PDMS pressure-sensitive flexible outer shell 9. The PDMS pressure-sensitive flexible outer shell 9 is prepared by a molding method, filled with the fluorescent solution 8, and then bonded to the sensing fiber 13. A simple, rapid, and effective seal is achieved by curing the bonded boundary with UV-curable adhesive 12 under UV light. The fluorescent solution 8 is an aqueous solution of Rhodamine B, containing many fluorescent molecules 10 (Rhodamine molecules). These fluorescent molecules 10 exist as single molecules at low concentrations (0.5 g / L and below). The sensing fiber 13 receives the excitation light 11 signal input from the light source module 5 and transmits it to the fluorescent solution 8 to generate reflected fluorescence 14. The reflected fluorescence 14 is then transmitted out of the fiber optic sensing unit 2 through the sensing fiber 13. All the fluorescent molecules 10 are encapsulated in a liquid state, which allows for free molecular movement. This not only enables concentration changes caused by volume compression but also effectively avoids the photobleaching effect of the excitation light 11 on the fluorescent molecules 10 (prolonged exposure of fluorescent molecules 10 to high-intensity excitation light 11 will cause irreversible fluorescence quenching of the fluorescent molecules 10), thus improving the lifespan of the sensor.

[0047] See Figure 4 The diagram shows the detection principle of a fiber optic fluorescent pressure sensor based on molecular concentration changes. The fiber optic sensing unit 2 encapsulates the fluorescent solution 8 through a PDMS pressure-sensitive flexible shell membrane 9. The fluorescent solution 8 is a concentration-effect aqueous solution of Rhodamine B. In the fluorescent solution 8, Rhodamine monomer molecules are used as the luminescent source to generate fluorescence. Under the influence of the concentration effect, the Rhodamine B aqueous solution will produce fluorescence of different intensities and different emission peaks after being excited by light 11 at different concentrations. When the external pressure increases by 16, the PDMS pressure-sensitive flexible outer shell membrane 9 is squeezed, and the Rhodamine B molecules in the fluorescent solution 8 encapsulated inside gradually aggregate from monomers, causing electrons to transfer more within the rigid plane of the molecules rather than undergoing radiative transitions to produce high-energy fluorescence. This causes a red shift in the fluorescence emission peak (reduced emission energy). Some fluorescent molecules 10 even combine with each other to form fluorescent dimers 17 and fluorescent polymers 18 during the process of increasing concentration. Electrons in fluorescent dimers 17 and fluorescent polymers 18 can transfer within the monomers bound inside, greatly reducing the generation of radiative transitions, and also causing the emission peak to broaden, i.e., the bandwidth increases and monochromaticity deteriorates. When the external pressure decreases by 19, the fluorescent molecules 10 will return from the polymer state to the monomer state and become more dispersed. At this time, it is difficult for electrons to transfer inside, increasing the generation of radiative transitions. Its fluorescence emission peak undergoes a blue shift, and the fluorescence intensity also changes regularly. By detecting changes in the fluorescence emission peak wavelength or fluorescence intensity (non-linear) of fluorescent molecule 10 (Rhodamine B) and calibrating these changes with external pressure, qualitative and quantitative sensing can be achieved by detecting changes in the fluorescence emission peak wavelength or fluorescence intensity based on the calibrated relationship.

[0048] In another exemplary embodiment, such as Figure 3 As shown, a method for fabricating the optical fiber sensing unit is also provided, comprising:

[0049] Obtain a pressure-sensitive flexible outer shell film.

[0050] Fluorescent solution 8 with concentration effect is filled into pressure-sensitive flexible outer shell membrane.

[0051] The sensing fiber 13 is inserted into the fluorescent solution 8 and the pressure-sensitive flexible outer shell film is attached to the sensing fiber 13.

[0052] In practical applications, obtaining a pressure-sensitive flexible outer shell film specifically includes: immersing a mold of a predetermined shape into a pressure-sensitive flexible material; and obtaining the pressure-sensitive flexible outer shell film through heat curing. The mold used in this application is a spherical mold 15.

[0053] See Figure 3The diagram shows the fabrication process of the fiber optic sensing unit 2. The fabrication of the fiber optic sensing unit 2 is simple, mainly consisting of four steps. First, a mold method is used to prepare the encapsulation shell. A spherical mold 15 (preferably made of polytetrafluoroethylene material for easy removal of PDMS) is used. PDMS is prepared according to a specified ratio (AB glue), and then the spherical mold 15 is immersed in it and removed (leaving an encapsulation opening). After heating and curing, the PMDS forms a spherical PDMS pressure-sensitive flexible shell film 9 with good hydrophobicity and sealing properties. Next, fluorescent solution 8 is filled into the PDMS pressure-sensitive flexible shell film 9, and the sensing fiber 13 is inserted, ensuring that the end face of the fiber is immersed in the fluorescent solution 8. Finally, the PDMS pressure-sensitive flexible shell film 9 is attached to the sensing fiber 13, and UV-curable adhesive 12 is applied to the joint. After irradiation with a UV lamp, curing is achieved, completing the sealing and fabrication of the fiber optic sensing unit 2. The entire fabrication process is short, has low material costs, is easy to operate, and is time-saving, making it very suitable for mass production and offering good economic benefits.

[0054] This application utilizes a mold method to prepare a PDMS film with good chemical stability, plasticity, mechanical properties, and elasticity. An optical fiber is then inserted into the PDMS film, followed by the injection of a concentration-effect fluorescent dye. An optical fiber sensing unit is then fabricated using UV-curable adhesive. This unit leverages the concentration effect of fluorescent molecules in the fluorescent solution; under external pressure, the volume of the internal solution decreases while the number of fluorescent molecules remains unchanged, leading to a change in solution concentration and ultimately affecting the fluorescence emission spectrum. The order of optical fiber insertion and fluorescent solution filling has no impact on the performance of the optical fiber sensing unit.

[0055] Quantitative sensing and detection of external pressure can be achieved by calibrating the relationship between changes in fluorescence emission peak wavelength and fluorescence intensity and external pressure. The entire fiber optic sensing unit uses PDMS as the encapsulation material. PDMS itself is non-toxic and harmless, possessing excellent mechanical properties, chemical stability, and self-healing capabilities. It can withstand high pressure without damage, effectively protecting the internally encapsulated fluorescent solution from leakage and preventing environmental pollution. The fabrication process of this sensing unit is simple and low-cost, the sensing principle is novel and simple, and the results are intuitive. This demonstrates the potential of fiber optic fluorescent sensors in the field of pressure detection, especially showing broad application prospects in the detection of gas and liquid pressures. It can achieve better detection results in pneumatic and hydraulic pressure detection, and is expected to expand the application market by extending fiber optic pressure sensors to pressure detection in more applications. This solution overcomes the technical challenges of existing fiber optic pressure sensors, such as high manufacturing costs, insufficient stability, complex signal demodulation, and limited sensitivity.

[0056] Unlike existing technologies, this application has the following advantages:

[0057] 1. This application uses PDMS as the encapsulation material. A pressure-sensitive flexible outer shell membrane is prepared using a molding method to encapsulate the fluorescent solution. Upon sensing external pressure, the pressure-sensitive flexible outer shell membrane utilizes the excellent flexibility and mechanical properties of PDMS to compress the volume of its encapsulated liquid. This volume compression indirectly transmits external pressure, transferring it to the internal fluorescent solution and increasing its concentration to achieve qualitative and quantitative pressure sensing. This develops a novel sensing principle. Furthermore, the excellent elasticity and sealing properties of PDMS allow it to recover its original shape after withstanding high pressure, ensuring no leakage of the internally encapsulated fluorescent solution and guaranteeing the normal operation of the sensor. The stable chemical properties of PDMS ensure that it does not react with external substances in the detection environment, preventing pollution and harm.

[0058] 2. This application utilizes the prepared fluorescent solution Rhodamine B as the sensing material for qualitative and quantitative pressure sensing. Changes in external pressure directly affect the concentration of Rhodamine B. Under pressure, the Rhodamine B solution exhibits a concentration effect. Fluorescent molecules have different molecular morphologies at different concentrations; at high concentrations, they aggregate into clusters, while at low concentrations, they decompose into dispersed monomers. This results in reversible and regular changes in the fluorescence emission wavelength and fluorescence intensity of the fluorescence signal. By detecting changes in fluorescence emission wavelength or fluorescence intensity, qualitative and quantitative detection of external pressure can be achieved. This sensing principle, which differs from traditional fiber optic pressure sensing technology, provides an important reference for the application of fiber optic fluorescence sensing technology in the field of pressure detection.

[0059] 3. This application utilizes a fiber optic sensing unit prepared by encapsulating a fluorescent solution of Rhodamine B in a flexible PDMS liquid core as a fiber optic sensing probe. The liquid core encapsulation method allows fluorescent molecules to move freely in the solvent, reducing the time the fluorescent molecules are exposed to excitation light and maintaining stable fluorescence signal generation. This effectively reduces the photobleaching effect inherent in fluorescent molecules (irreversible fluorescence performance degradation occurs after prolonged exposure to high-intensity excitation light), thus fully addressing the limitations of repeatability in fiber optic fluorescent sensors. Furthermore, the fiber optic sensing probe preparation process is simple, easy to operate, and economically efficient, making it suitable for commercial mass production.

[0060] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A fiber optic sensing unit, characterized in that, The fiber optic sensing unit includes: a sensing fiber, a fluorescent solution with a concentration effect, and a pressure-sensitive flexible outer shell membrane; The fluorescent solution is encapsulated within the pressure-sensitive flexible outer shell membrane; the sensing optical fiber is inserted into the pressure-sensitive flexible outer shell membrane and immersed in the fluorescent solution; the sensing optical fiber is used to transmit the excitation light signal generated by the light source module to the fluorescent solution and to transmit the change in the fluorescence signal of the fluorescent solution; the change in the fluorescence signal is used to realize pressure detection; The fluorescent solution is a rhodamine derivative solution or a coumarin derivative solution; When the fiber optic sensing unit is placed in the environment to be tested, external pressure can increase the concentration of the fluorescent solution by squeezing the PDMS, thereby affecting the wavelength and intensity of the fluorescence emission peak. The sensor can be calibrated by calibrating the relationship between pressure and fluorescence intensity or fluorescence emission peak wavelength. Subsequently, quantitative detection of pressure can be achieved by detecting changes in fluorescence emission peak wavelength or fluorescence intensity.

2. The fiber optic sensing unit according to claim 1, characterized in that, The pressure-sensitive flexible outer shell membrane is made of PDMS, polyolefin, or styrene.

3. The fiber optic sensing unit according to claim 1, characterized in that, The shape of the pressure-sensitive flexible outer shell membrane is sphere or polyhedron.

4. The fiber optic sensing unit according to claim 1, characterized in that, The fiber optic sensing unit also includes a UV-curable adhesive; The UV-curable adhesive is used to encapsulate the boundary between the sensing optical fiber and the pressure-sensitive flexible outer shell membrane.

5. A fiber optic fluorescent pressure sensor, characterized in that, The fiber optic fluorescence pressure sensor includes: a light source module, a fiber optic spectrometer, a computer, and the fiber optic sensing unit as described in any one of claims 1-4; The fiber optic sensing unit is connected to both the light source module and the fiber optic spectrometer; the computer is also connected to the fiber optic spectrometer. The light source module is used to excite the fluorescent solution of the fiber optic sensing unit; the fiber optic sensing unit is used to detect the change in fluorescence signal and transmit the change in fluorescence signal to the fiber optic spectrometer; the fiber optic spectrometer is used to convert the change in fluorescence signal into spectral information and transmit the spectral information to the computer; the computer is used to determine pressure information based on the spectral information.

6. The fiber optic fluorescent pressure sensor according to claim 5, characterized in that, It also includes a focusing lens group; The focusing lens group is disposed between the fiber optic sensing unit and the light source module.

7. The fiber optic fluorescent pressure sensor according to claim 5, characterized in that, It also includes filters; The filter is disposed between the fiber optic spectrometer and the fiber optic sensing unit.

8. A method for fabricating an optical fiber sensing unit, characterized in that, The fiber optic sensing unit fabrication method is used to fabricate the fiber optic sensing unit according to any one of claims 1-4, and the fiber optic sensing unit fabrication method includes: Obtain a pressure-sensitive flexible shell film; A concentration-effect fluorescent solution is filled into the pressure-sensitive flexible outer shell membrane; The sensing fiber is inserted into the fluorescent solution and the pressure-sensitive flexible outer shell membrane is attached to the sensing fiber.

9. The method for fabricating an optical fiber sensing unit according to claim 8, characterized in that, Obtaining a pressure-sensitive flexible outer shell film specifically includes: A mold with a predetermined shape is immersed in a pressure-sensitive flexible material; Pressure-sensitive flexible outer shell film is obtained by heating and curing.

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