An optical fiber pressure sensor based on strontium titanate crystal substrate and its preparation method

Abstract

The purpose of the present invention is to provide an optical fiber pressure sensor based on a strontium titanate crystal substrate with high measurement accuracy, good stability and low cost, and a preparation method thereof, comprising a base, a pressure sensitive diaphragm, an FP cavity and an optical fiber, wherein the pressure sensitive diaphragm is obtained by polishing, photolithography, developing and coating the strontium titanate crystal substrate. Since strontium titanate crystal has a low expansion coefficient, good chemical stability and mechanical strength, it has a significant effect on the measurement accuracy and stability of the sensor. The pressure sensitive diaphragm prepared by strontium titanate has good biocompatibility, reduces damage to the human body, and has low cost, which can further reduce the production cost of the sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber sensors, and in particular to an optical fiber pressure sensor based on a strontium titanate matrix substrate and a preparation method thereof. Background Art

[0002] Fiber optic pressure sensors have shown great potential for application in the medical field, especially in biomedical engineering, due to their excellent performance characteristics. These sensors are not only extremely sensitive and can detect tiny pressure changes, but also compact and can be easily integrated into various medical devices. Their good biocompatibility and anti-electromagnetic interference capabilities make long-term implantation and real-time monitoring possible in complex human environments, greatly improving the accuracy and safety of medical monitoring and providing strong support for early diagnosis and treatment of diseases.

[0003] When preparing micro-fiber optic pressure sensors, the biocompatibility and optical properties of the materials need to be considered, and some of the materials currently used are relatively expensive. Summary of the invention

[0004] An object of the present invention is to provide an optical fiber pressure sensor based on a strontium titanate crystal substrate with high measurement accuracy, good stability and low cost.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: Figure 1 As shown, an optical fiber pressure sensor based on a strontium titanate crystal substrate includes a base and a pressure sensitive diaphragm; wherein the pressure sensitive diaphragm is the only structure of the optical fiber pressure sensor to sense pressure, and the base is used to form an FP cavity with the pressure sensitive diaphragm and to connect with the optical fiber.

[0006] The FP cavity is a closed cavity formed between the base and the pressure-sensitive diaphragm, and is used to convert pressure changes into optical signal changes; the optical signal emitted by the optical fiber enters the FP cavity, and is reflected multiple times between the base reflection surface and the pressure-sensitive reflection surface. The deflection of the sensitive diaphragm caused by the pressure is converted into a phase change of the interference signal of the FP cavity through an optical interferometer, and pressure measurement is achieved by demodulating the phase change of the interference signal.

[0007] The optical fiber is fixed in the optical fiber installation part of the base and is used to transmit the optical signal. The external pressure change causes the pressure sensitive diaphragm to deform, changing the length of the FP cavity, thereby changing the optical path difference. By detecting the optical signal transmitted back through the optical fiber, the size of the pressure sensitive diaphragm deformation can be obtained through demodulation.

[0008] Pressure-sensitive diaphragm pressure sensing principle: According to the principle of elastic mechanics, when external pressure acts evenly on the surface of a circular pressure-sensitive diaphragm with uniform thickness and tight edges, the expression of the deformation of each point of the pressure-sensitive diaphragm is: (1) In the above formula, P Indicates the pressure on the pressure sensitive diaphragm. R 0 represents the radius of the pressure sensitive diaphragm, r represents the radius of any point on the pressure sensitive diaphragm, D=Et 3 / 12(1-ν 2 ) is the bending stiffness of the pressure sensitive diaphragm, where t is the thickness of the pressure sensitive diaphragm, E and ν They represent Young's modulus and Poisson's ratio of the pressure sensitive diaphragm material. It can be seen that the deformation of the pressure sensitive diaphragm is proportional to the pressure on the diaphragm. r = 0, that is, the change in the center position of the pressure sensitive diaphragm can be expressed as: (2)

[0009] FP cavity center length L It can be expressed as: (3)

[0010] In the above formula, h is the depth of the Fabry-Perot cavity. In summary, the sensitivity expression can be obtained as follows: (4)

[0011] From the above formula (4), it can be seen that the pressure sensitivity is related to the mechanical properties of the pressure sensitive diaphragm material of the sensor and the structural parameters of the sensor, and is proportional to the fourth power of the radius of the pressure sensitive diaphragm, and inversely proportional to the cube of the thickness of the pressure sensitive diaphragm. Therefore, the larger the radius of the pressure sensitive diaphragm and the smaller the thickness, the higher the pressure sensitivity of the pressure sensitive diaphragm. It should be noted that in order to ensure that the linearity of the pressure sensitive diaphragm deformation with pressure is good, the deformation of the pressure sensitive diaphragm should be controlled within 20% of the thickness of the pressure sensitive diaphragm.

[0012] The pressure sensitive membrane is obtained by polishing, photolithography, developing and coating a strontium titanate crystal substrate. Using a strontium titanate crystal substrate as a pressure sensitive membrane can bring the following significant performance improvements: (1) Strontium titanate crystals have a low expansion coefficient. When the temperature changes, the sensor has good dimensional stability, thereby reducing the impact of temperature on the measurement results and improving the measurement accuracy of the sensor.

[0013] (2) Strontium titanate crystals have good chemical stability and can resist corrosion from most chemicals, ensuring reliability for long-term use.

[0014] (3) Strontium titanate crystals have excellent mechanical properties, such as high hardness and good wear resistance, which enable the sensor to maintain stable performance when under pressure and is not easily damaged.

[0015] (4) Strontium titanate crystals have excellent biocompatibility, which is particularly important for medical devices that intervene in the body.

[0016] (5) Compared with some other pressure-sensitive membranes, the preparation cost of strontium titanate crystal substrates is relatively low, which helps to reduce the overall cost of the sensor and benefit more patients.

[0017] Reflective films are provided at the two end faces of the FP cavity. The provision of the end face reflective films can significantly improve the reflectivity of light on the two end faces, which is the key to achieving multi-beam interference. By optimizing the interference effect of the FP cavity, the performance of the sensor is improved. As a preferred embodiment of the present invention, a graphene inner film is provided on the inner peripheral wall of the FP cavity. Graphene is an almost completely transparent material with a light transmittance of up to 97.7%, which means that it can be covered on the inner wall of the FP cavity without affecting the transmission of the optical fiber, ensuring the efficient transmission of the optical signal and reducing the light loss caused by reflection or absorption, thereby improving the accuracy and sensitivity of the interference measurement; secondly, graphene has excellent chemical stability, which can protect the inside of the FP cavity from the influence of external environmental factors (such as moisture, blood, etc.), prolonging the service life of the sensor and ensuring the reliability of long-term operation. In addition, the shielding effect of graphene itself can be lower than the interference of external electromagnetic waves to a certain extent, which is crucial to improving the stability of the sensor in a complex electromagnetic environment.

[0018] Similarly, a graphene outer film is provided on the peripheral wall of the sensor chip composed of the base and the pressure sensitive diaphragm. In addition to the significant advantages in measurement accuracy, chemical stability, corrosion resistance and anti-electromagnetic interference, the graphene outer film on the peripheral surface also has the following advantages: (1) Due to the high conductivity and low loss characteristics of the graphene film, it can reduce signal attenuation, thereby improving the sensitivity of the sensor; (2) The excellent mechanical properties of the graphene film enable the sensor to operate reliably for a long time in harsh environments; (3) The good thermal conductivity and low thermal expansion coefficient of graphene help maintain the stability of the sensor over a wide temperature range.

[0019] A graphene film is provided on the outer wall of the optical fiber, which can provide a more solid protective layer for the optical fiber, enhance its pressure resistance, and improve the reliability and service life of the sensor.

[0020] Furthermore, the thickness of the graphene inner film and the graphene outer film is 1nm to 4nm. That is to say, the graphene film layer is very thin, usually only a few atoms thick, so it can provide an additional functional layer without increasing weight and size. High-quality graphene films can be grown on different substrates through methods such as chemical vapor deposition, which facilitates compatibility with other manufacturing processes and supports multifunctional integration.

[0021] Because strontium titanate crystals have good mechanical properties, they can be set very thin. The thickness of the pressure sensitive diaphragm is 4um to 7um, which reduces the size of the entire sensor and makes it suitable for percutaneous medical devices (such as catheter pumps, etc.).

[0022] The base includes a first substrate, a second substrate and a third substrate arranged in sequence from near to far from the pressure sensitive membrane. The first substrate is provided with a first through hole, and the first through hole, the surface of the second substrate and the pressure sensitive membrane together enclose an FP cavity. The third substrate is provided with a third through hole, and the third through hole and the surface of the second substrate together enclose an optical fiber installation portion. The base is packaged as a whole by a multi-layer substrate through a bonding technology. The substrate where the through hole needs to be set is set as a single layer of substrate, and the through through hole is processed on it. Since the through holes are all through, the surface unevenness caused by wet etching or ion etching methods is avoided. The FP cavity end face reflective film has high flatness, better light reflection effect, and improves the measurement accuracy of the sensor. At the same time, the preparation of the through hole on the substrate does not need to consider the corrosion rate problem, which reduces the manufacturing difficulty of the base. The three layers of substrate are connected as a whole by bonding. The preparation process is simple, and the structure of the obtained base is stable and reliable.

[0023] Preferably, the FP cavity and the optical fiber mounting portion are coaxially arranged in an interval in the axial direction of the optical fiber, and the light is output through the front end of the optical fiber, passes through the FP cavity, reaches the pressure sensitive diaphragm, then reflects on the pressure sensitive diaphragm, passes through the FP cavity again, and enters the optical fiber to recover the optical signal. The diameter of the FP cavity is larger than the diameter of the optical fiber mounting portion, which can more easily realize the coupling between the light beam and the optical fiber, reduce the loss in the coupling process, and provide a more stable transmission environment for the light beam, thereby enhancing the stability of the light beam.

[0024] The first substrate, the second substrate and the third substrate are selected from sapphire, single crystal silicon, glass and quartz; preferably, the reflective film is selected from one or a mixture of two of Au, Ag, Pt, Ti, Cr, Al, Pt, Ta2O5 and Al2O3.

[0025] Another object of the present invention is to provide a method for preparing an optical fiber pressure sensor based on a strontium titanate crystal substrate with high measurement accuracy, good stability and low cost.

[0026] In order to achieve the above object, the technical solution adopted by the present invention is: a method for preparing an optical fiber pressure sensor based on a strontium titanate crystal substrate, referring to Figure 2 , Figure 3 As shown, the following steps are included: S1) polishing a strontium titanate crystal substrate to obtain a pressure-sensitive film, coating a photoresist on the surface of the pressure-sensitive film, obtaining a mask pattern through photolithography and development, hardening the film at a temperature of 100° C. to 200° C., sputtering a reflective film on the surface of the pressure-sensitive film to obtain a pressure-sensitive film; S2) taking the substrate and performing etching and corrosion to form a through hole, and coating a layer of graphene inner film on the inside of the through hole to obtain a first substrate; S3) taking a substrate and performing etching and corrosion to form a third through hole to obtain a third substrate; S4) aligning the first substrate, the second substrate and the third substrate and bonding them together, sputtering a reflective film on the surface of the second substrate in the cavity to obtain a base; S5) bonding the base and the pressure sensitive membrane to obtain a sensor chip; S6) coating a layer of graphene outer film on the outer peripheral surface of the sensor chip to obtain a coated sensor chip; S7) taking a single-mode optical fiber, and coating a layer of graphene film on the outer surface of the optical fiber to form a coated optical fiber; S8) Use UV glue to bond and fix the coated optical fiber end face to the optical fiber mounting part of the base to obtain an optical fiber pressure sensor. Since UV glue has both bonding and light guiding functions, it can not only play a fixing role, but also ensure good light guiding performance; of course, the curing method can also be selected but not limited to glass solder bonding, electromagnetic heating, laser heating, and laser welding.

[0027] There is no particular order in which the pressure sensitive membrane, the sensor chip and the coated optical fiber are prepared. The pressure sensitive membrane can be prepared first (step S1), or the sensor chip can be prepared first (steps S2 to S5), or the coated optical fiber can be prepared first (step S7).

[0028] The above scheme has at least the following beneficial effects: 1. Strontium titanate crystal substrate is used as the material of the pressure sensitive diaphragm. Because of its low expansion coefficient, good chemical stability and mechanical strength, it has a significant effect on the measurement accuracy and stability of the sensor.

[0029] 2. The pressure sensitive diaphragm prepared by strontium titanate has good biocompatibility, which reduces damage to the human body. At the same time, it is low in cost and can further reduce the production cost of the sensor.

[0030] 3. A layer of graphene inner film is coated on the inner surface of the FP cavity. As a two-dimensional material, graphene has extremely high light transmittance and mechanical strength, which greatly enhances the overall structural stability of the sensor, enabling the sensor to maintain long-term reliable operation in a more harsh working environment.

[0031] 4. A layer of graphene outer mold is plated on the periphery of the entire sensor chip, wrapping the pressure-sensitive diaphragm and the base together to improve the stability of the sensor structure and the reliability of operation; at the same time, due to the high conductivity and low loss characteristics of graphene, it can reduce signal attenuation, thereby improving the sensitivity of the sensor.

[0032] 5. A layer of graphene film is coated on the outer periphery of the optical fiber to enhance its pressure resistance and improve the reliability and service life of the sensor.

[0033] 6. The multi-level structure of the base ensures the flatness of the two end faces of the FP cavity, that is, the reflective film has high flatness, better reflection effect on light, and improves the measurement accuracy of the sensor; at the same time, it also simplifies the preparation process of the base, and the structure of the obtained base is stable and reliable. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of the optical fiber pressure sensor; Figure 2 The figure is a flow chart of the preparation of the optical fiber pressure sensor; Figure 3 for Figure 2 A partially enlarged schematic diagram of . DETAILED DESCRIPTION

[0035] The sensing principle of FP cavity type optical fiber pressure sensor is as follows: (1) Light source emission: A stable light source is used to emit a light beam, which is then transmitted to the FP cavity of the sensor through an optical fiber.

[0036] (2) Interference phenomenon: The light beam is reflected multiple times in the FP cavity, resulting in interference phenomenon. The interference pattern formed depends on the cavity length.

[0037] (3) Pressure effect: External pressure is applied to the pressure-sensitive diaphragm, causing the pressure-sensitive diaphragm to deform, thereby changing the length of the FP cavity.

[0038] (4) Changes in the interference pattern: As the cavity length changes, the characteristics of the interference pattern will also change, such as the phase change of the interference fringes.

[0039] (5) Signal detection and processing: Use a spectrum analyzer or other suitable detection device to capture and analyze the phase changes of the interference pattern, and obtain the actual pressure value after signal processing.

[0040] (6) Output result: The sensor outputs the detected pressure information in the form of digital or analog signals for the user to read or further process.

[0041] The present invention is described below through detailed embodiments in conjunction with the accompanying drawings. It should be noted that the selection of the filling lines of the components in the accompanying drawings is only regarded as the difference between the components, and does not represent the material; and the ratio between the structural layers does not represent the actual structural ratio of the product, and the materials and dimensions should be based on the text description. Example 1

[0042] Take a single-sided polished strontium titanate crystal substrate 1 with a thickness of 500 μm, and perform chemical mechanical polishing on the unpolished side to obtain a pressure-sensitive membrane 2 with a thickness of 5 μm. Then use secondary deionized water to clean the strontium titanate substrate in an ultrasonic cleaner for 5 minutes, and then blow it dry with nitrogen. This method can remove stains on the surface of the strontium titanate substrate and help maintain the flatness of the surface. Use the spin coating method to coat the surface of the pressure-sensitive membrane with photoresist, and obtain the mask pattern of the Fabry-Perot microcavity through photolithography and development, and harden the film at 145°C. Then use DC magnetron sputtering technology to coat a layer of Au reflective film a on the surface of the pressure-sensitive membrane to obtain a pressure-sensitive membrane 20.

[0043] The first substrate 11 selects a sapphire substrate with a thickness of 100μm. First, the surface of the sapphire substrate is cleaned with low-concentration HCI and NaOH solutions for 10 minutes respectively. Then, a 20um thick SiO2 mask layer is deposited on the cleaned sapphire substrate surface by plasma enhanced chemical vapor deposition. The photoresist layer is peeled off on the SiO2 layer, then exposed and removed to form a photoresist pattern of the FP cavity. The pattern is then transferred to the SiO2 layer by RIE. After that, the sapphire is etched at 280°C with a mixed solution of H3PO4 and H2SO4 in a volume ratio of 1:3 to form a cavity. Then, hydrofluoric acid is used to continue to corrode the chamber until a through hole 111 is formed. Next, a layer of graphene inner film b is plated on the inner circumference of the through hole 111 using chemical vapor deposition technology.

[0044] The second substrate 12 is made of Pyrex glass, and the third substrate 13 is made of sapphire. The second substrate 12 and the third substrate 13 are first cleaned and then blown dry, and then the first substrate 11, the second substrate 12 and the third substrate 13 are aligned from top to bottom, and the bonding process is performed in sequence. The first substrate 11 and the second substrate 12 adopt direct bonding technology. Both need to be polished before bonding to ensure the flatness and smoothness of the plane. The bonding between the second substrate 12 and the third substrate 13 also adopts direct bonding technology. After the bonding is completed, a layer of Au reflective film a is plated on the surface of the second substrate 12 in the concave cavity after bonding using DC magnetron sputtering technology to form the base 10 of the multilayer structure.

[0045] Next, the pressure sensitive membrane 20 and the base 10 are bonded, also using direct bonding technology. Before bonding, the bonding contact surface of the pressure sensitive membrane 20 and the base 10 is cleaned to ensure flatness and smoothness. After bonding, the sensor chip 3 is formed. Next, a layer of graphene outer film c is plated on the outer peripheral surface of the sensor chip 3 using chemical vapor deposition technology to form a coated sensor chip 4.

[0046] Take a single-mode optical fiber 5, and use CVD technology to coat a layer of graphene film d on the outer surface to form a coated optical fiber 6. Use UV glue to bond the end face of the coated optical fiber 6 to the optical fiber installation cavity B of the base 10 to form a micro optical fiber Fabry-Perot pressure sensor 7. Example 2

[0047] The first substrate 11 selects a quartz substrate with a thickness of 100 μm. First, the surface of the quartz substrate is cleaned with low concentration HCI and NaOH solutions for 15 minutes respectively. Then, a 20 μm thick SiO2 mask layer is deposited on the cleaned quartz substrate surface by plasma enhanced chemical vapor deposition. The photoresist layer is peeled off on the SiO2 layer, then exposed and removed to form a photoresist pattern of the FP cavity. Then the pattern is transferred to the SiO2 layer by RIE. After that, the quartz is etched at 260°C with a mixed solution of H3PO4 and H2SO4 in a volume ratio of 1:3 to form a cavity. Then, hydrofluoric acid is used to continue to corrode the chamber until a through hole 111 is formed. Next, a layer of graphene inner film b is plated on the inner circumference of the through hole 111 using chemical vapor deposition technology.

[0048] The second substrate 12 is made of Pyrex glass, and the third substrate 13 is made of quartz glass. The second substrate 12 and the third substrate 13 are first cleaned and then blown dry, and then the first substrate 11, the second substrate 12 and the third substrate 13 are aligned from top to bottom, and the bonding process is performed in sequence. The first substrate 11 and the second substrate 12 adopt direct bonding technology. Both need to be polished before bonding to ensure the flatness and smoothness of the plane. The bonding between the second substrate 12 and the third substrate 13 also adopts direct bonding technology. After the bonding is completed, a layer of Ag reflective film a is plated on the surface of the second substrate 12 in the concave cavity after bonding using DC magnetron sputtering technology to form the base 10 of the multilayer structure.

[0049] Take a single-sided polished strontium titanate crystal substrate 1 with a thickness of 500 μm, and perform chemical mechanical polishing on the unpolished side to obtain a pressure-sensitive membrane 2 with a thickness of 6 μm. Then use secondary deionized water to clean the strontium titanate substrate in an ultrasonic cleaner for 6 minutes, and then blow it dry with nitrogen. Use the spin coating method to coat the surface of the pressure-sensitive membrane 2 with photoresist, and obtain the mask pattern of the Fabry-Perot microcavity through photolithography and development, and harden the film under the temperature condition of 150°C. Then use DC magnetron sputtering technology to coat a layer of Ag reflective film a on the surface 2 of the pressure-sensitive membrane to obtain a pressure-sensitive membrane 20.

[0050] Next, the pressure sensitive membrane 20 and the base 10 are bonded, also using direct bonding technology. Before bonding, the bonding contact surface of the pressure sensitive membrane 20 and the base 10 is cleaned to ensure flatness and smoothness. After bonding, the sensor chip 3 is formed. Next, a layer of graphene outer film c is plated on the outer peripheral surface of the sensor chip 3 using chemical vapor deposition technology to form a coated sensor chip 4.

[0051] Take a single-mode optical fiber 5, and use CVD technology to coat a layer of graphene film d on the outer surface to form a coated optical fiber 6. Use UV glue to bond the end face of the coated optical fiber 6 to the optical fiber installation cavity B of the base 10 to form a micro optical fiber Fabry-Perot pressure sensor 7. Comparative Example

[0052] The sapphire substrate is placed in a solution for cleaning, a layer of photoresist is spin-coated on the substrate, and then a specific pattern is left on the sapphire substrate through exposure and development technology. First, an area with a diameter of 100um is etched on the sapphire surface using the NLD dry process, and then HF acid is used to continue etching to form a concave cavity to form the FP cavity. The same method is used to etch a concave cavity on the other side of the sapphire substrate to form a fiber installation cavity. A layer of reflective film Au is plated on the bottom of the upper FP cavity using the evaporation process to obtain the base.

[0053] The SOI wafer substrate is cleaned and activated to remove surface impurities and organic pollutants and improve surface affinity. The photoresist is evenly coated on the SOI wafer material by spin coating, and the required micro-nano structure pattern is formed on the wafer substrate. A layer of Au reflective film is grown on the substrate by physical vapor deposition to obtain a pressure sensitive diaphragm.

[0054] The base and the pressure sensitive membrane surface are chemically mechanically polished and cleaned to remove surface pollutants and chemical contamination layers, and then the two are bonded to obtain a sensor chip.

[0055] Take a single-mode optical fiber and use UV glue to bond the optical fiber end face to the optical fiber installation cavity at the base to form a miniature optical fiber Fabry-Perot pressure sensor.

[0056] The performance and process of the optical fiber pressure sensors prepared by the methods of Examples 1 and 2 and Comparative Example are compared as shown in Table 1: Table 1 category Accuracy (%FS) Resolution (%FS) Mechanical strength (N / ㎡) Service life (years) Example 1 ±0.1 ±0.01 80000 9 Example 2 ±0.1 ±0.01 100000 9.5 Comparative Example ±0.25 ±0.025 50000 8.5 According to the results in Table 1, we can find that: Accuracy and resolution: The accuracy (±0.1% FS) and resolution (±0.01% FS) of Example 1 and Example 2 are the same, and are significantly better than the comparative example (accuracy ±0.25% FS and resolution ±0.025% FS). This shows that the pressure optical fiber sensors of Example 1 and Example 2 perform better in terms of measurement accuracy.

[0057] Mechanical strength: The mechanical strength of Example 2 is 100,000 N / ㎡, which is higher than 80,000 N / ㎡ of Example 1, and higher than 50,000 N / ㎡ of the comparative example. This means that the pressure optical fiber sensor using the structure of the present application can withstand greater external pressure or stress without damage or performance degradation, and is suitable for more demanding working environments.

[0058] Service life: The service life of the sensors in Examples 1 and 2 is slightly higher than that of the sensor in the comparative example, but the difference is not too large, which indicates that under normal conditions, their long-term reliability is similar. This is because conventional measurement methods are used and they are not introduced into the human body, where the blood environment is complex. Due to the selection of pressure sensitive diaphragm materials and the influence of the surrounding environment, the service life of the pressure optical fiber sensors in Examples 1 and 2 is significantly higher than that of the pressure optical fiber sensor in the comparative example.

[0059] in, The accuracy test method is: (1) Calibration: Use a certified standard pressure source (such as a high-precision pressure gauge) to calibrate and ensure that the pressure range of the standard equipment covers the operating range of the pressure fiber optic sensor.

[0060] (2) Multi-point measurement: Select multiple evenly distributed pressure points within the working range of the sensor for measurement, compare the data with that of the standard equipment, and evaluate the error.

[0061] (3) Temperature compensation: Considering that temperature changes in medical environments may affect sensor performance, the above tests need to be repeated under different temperature conditions to verify the effectiveness of temperature compensation.

[0062] The sensitivity test method is: (1) Small signal detection: Since it is a micro sensor, it should be able to detect very small pressure changes. Apply a very small pressure increment and record the change in the sensor output.

[0063] (2) Linearity check: Test whether the sensor output presents a linear response through a series of known small pressure changes and calculate the sensitivity coefficient.

[0064] (3) Frequency response: For dynamic applications, test the sensor's response speed and stability to rapidly changing pressure and determine its bandwidth.

[0065] Mechanical strength test method is: (1) Compression test: Simulate the maximum pressure load that may occur in actual use, apply it continuously for a period of time, and observe whether the sensor has permanent deformation or functional failure.

[0066] (2) Bending and torsion testing: Since optical fiber is sensitive to bending, it is necessary to test the performance changes of the sensor at different bending radii and the effect of torsion on it.

[0067] (3) Shock and vibration testing: Simulates potential shock and vibration conditions during transportation and installation to ensure that the sensor can withstand it without losing performance.

[0068] The service life test method is: (1) Accelerated aging test: By increasing the temperature and humidity of the working environment, or increasing the rate of cyclic pressure change, the aging process of the sensor is accelerated to predict its life under normal conditions.

[0069] (2) Long-term stability test: The sensor is placed in a constant pressure environment for several months or even longer, and the data is recorded regularly to analyze the long-term stability and drift.

[0070] (3) Chemical resistance test: Given that various chemicals may exist in the medical environment, the performance changes of the sensor after contact with chemicals such as disinfectants are tested.

[0071] Of course, for those skilled in the art, the present invention is not limited to the details of the above exemplary embodiments, but also includes the same or similar structures that can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended to include all changes that fall within the meaning and scope of the equivalent elements of the claims. Any figure mark in the claims should not be regarded as limiting the claims involved. In addition, it should be understood that although this specification is described in accordance with the implementation mode, not each implementation mode contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. An optical fiber pressure sensor based on a strontium titanate crystal substrate, comprising a base (10) and a pressure sensitive diaphragm (20); The FP cavity (A) is a closed chamber formed between the base (10) and the pressure sensitive membrane (20) for converting pressure changes into light signal changes; An optical fiber (30) is fixed in the optical fiber mounting portion (B) of the base (10) and is used to transmit optical signals; Features: The pressure sensitive membrane (20) is obtained by polishing, photolithography, developing and coating a strontium titanate crystal substrate.

2. The optical fiber pressure sensor based on a strontium titanate crystal substrate according to claim 1, characterized in that: Reflective films (a) are arranged at two end faces of the FP cavity (A), and a graphene inner film (b) is arranged on the inner wall of the FP cavity (A).

3. The optical fiber pressure sensor based on a strontium titanate crystal substrate according to claim 1, characterized in that: A graphene outer film (c) is provided on the outer peripheral wall of the sensor chip composed of the base (10) and the pressure sensitive diaphragm (20).

4. The optical fiber pressure sensor based on a strontium titanate crystal substrate according to claim 1, characterized in that: A graphene film (d) is also provided on the outer wall of the optical fiber (30).

5. The optical fiber pressure sensor based on a strontium titanate crystal substrate according to claim 2, 3 or 4, characterized in that: The thickness of the graphene inner film (b) and / or the graphene outer film (c) and / or the graphene thin film (d) is 1 nm to 4 nm.

6. The optical fiber pressure sensor based on a strontium titanate crystal substrate according to claim 1, characterized in that: The thickness of the pressure sensitive membrane (20) is 4 um to 7 um.

7. The optical fiber pressure sensor based on a strontium titanate crystal substrate according to claim 1, characterized in that: The base (10) comprises a first substrate (11), a second substrate (12) and a third substrate (13) which are arranged in sequence from near to far from the pressure sensitive membrane (20); the first substrate (11) is provided with a first through hole (111); the first through hole (111), the surface of the second substrate (12) and the pressure sensitive membrane (20) together enclose an FP cavity (A); the third substrate (13) is provided with a third through hole (131); the third through hole (131) and the surface of the second substrate (12) together enclose an optical fiber installation portion (B).

8. The optical fiber pressure sensor based on a strontium titanate crystal substrate according to claim 7, characterized in that: The FP cavity (A) and the optical fiber installation portion (B) are coaxially arranged and spaced apart in the axial direction of the optical fiber (30), and the diameter of the FP cavity (A) is greater than the diameter of the optical fiber installation portion (B).

9. The optical fiber pressure sensor based on a strontium titanate crystal substrate according to claim 7, characterized in that: The first substrate (11), the second substrate (12) and the third substrate (13) are selected from sapphire, single crystal silicon, glass and quartz; preferably, the reflective film (a) is selected from Au, Ag, Pt, Ti, Cr, Al, Pt, Ta2O5, Al2O3 or a mixture of two thereof.

10. A method for preparing an optical fiber pressure sensor based on a strontium titanate crystal substrate, characterized in that: The following steps are involved: S1) polishing a strontium titanate crystal substrate (1) to obtain a pressure-sensitive film (2), coating a photoresist on the surface of the pressure-sensitive film (2), performing photolithography and development to obtain a mask pattern, hardening the film at a temperature of 100° C. to 200° C., and sputtering a layer of a reflective film (a) on the surface of the pressure-sensitive film (2) to obtain a pressure-sensitive film (20); S2) taking a substrate and performing etching and corrosion to form a first through hole (111), and coating a layer of graphene inner film (b) on the inside of the first through hole (111) to obtain a first substrate (11); S3) taking a substrate and performing etching and corrosion to form a third through hole (131), thereby obtaining a third substrate (11); S4) aligning and bonding the first substrate (11), the second substrate (12) and the third substrate (13), and sputtering a reflective film (a) on the surface of the second substrate (12) in the cavity to obtain a base (10); S5) bonding the base (10) and the pressure sensitive membrane (20) to obtain a sensor chip (3); S6) coating a layer of graphene outer film (c) on the outer peripheral surface of the sensor chip (3) to obtain a coated sensor chip (4); S7) taking a single-mode optical fiber (5), coating a layer of graphene film (e) on the outer surface of the optical fiber to form a coated optical fiber (6); S7) using UV glue to bond and fix the end face of the coated optical fiber (6) to the optical fiber mounting portion (B) of the base (10) to obtain an optical fiber pressure sensor (7); The steps for preparing the pressure sensitive membrane (20), the sensor chip (3) and the coated optical fiber (6) are not arranged in a particular order.

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