Pressure measurement device and method based on fiber optic interferometer

Abstract

The present invention provides a pressure measurement device and method based on a fiber optic interferometer, comprising a laser, a fiber optic interferometer, a Faraday rotator, and a photoelectric detector. Laser light emitted by the laser is transmitted to a sensing arm optical fiber and a reference arm optical fiber through a fiber optic coupler in the fiber optic interferometer. The sensing arm optical fiber is wound on a sensitivity-enhancing transducer structure. When external pressure acts on the sensitivity-enhancing transducer structure, the sensitivity-enhancing transducer structure will deform, and the length of the sensing arm optical fiber will change with the deformation of the sensitivity-enhancing transducer structure. The laser light transmitted by the sensing arm optical fiber and the reference arm optical fiber is reflected by the Faraday rotator and then returned to the fiber optic coupler to cause interference. The light signal generated by the interference is received by the photoelectric detector and converted into an electrical signal for calculating external pressure information.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of pressure measurement, and in particular to a pressure measurement device and method based on a fiber optic interferometer. Background Art

[0002] Pressure measurement is crucial for high-precision, high-reliability applications in aerospace, petrochemicals, ocean monitoring, and medicine, and offers broad development prospects. Currently, mainstream pressure measurement devices can be categorized into three main types: mechanical, electromagnetic, and photoelectric. Electromagnetic pressure sensors include capacitive, piezoresistive, and piezoelectric pressure sensors. Photoelectric sensors, a newer type, primarily focus on fiber Bragg grating sensors.

[0003] Traditional sensors have insufficient measurement accuracy. Mechanical sensors rely on the macroscopic deformation of elastic elements, and their typical resolution is , making it difficult to capture minute nanoscale deformations. Electromagnetic pressure sensors are limited by hysteresis and electrical signal noise, with linearity and accuracy reaching only 0.1%FS. Fiber Bragg gratings, although photoelectric, have limited sensitivity (0.01nm / MPa-0.02nm / MPa) and suffer from temperature-pressure cross-sensitivity. Temperature changes cause both grating period and refractive index drift, requiring additional temperature compensation structures and resulting in insufficient actual resolution.

[0004] Electromagnetic sensors have poor environmental adaptability. Their core relies on electrical signal transmission, which is susceptible to electromagnetic interference in space. Electronic components are sensitive to temperature and humidity and require additional protective devices such as electromagnetic shielding shells and temperature compensation circuits, resulting in complex sensor structures, large size, and high cost.

[0005] Traditional sensors offer single functions and redundant structures. Due to their principle limitations, electromagnetic sensors are limited in principle. Voltage-based sensors are only suitable for dynamic measurements, while inductive-based sensors are only suitable for static measurements. They are not effective for measuring quasi-static pressure. Electromagnetic sensors rely on complex circuitry for signal processing, resulting in bulky size and high integration difficulty.

[0006] Pressure measurement is a core requirement in fields such as industrial control, aerospace, ocean monitoring, and healthcare, requiring high accuracy (0.01%FS), high reliability, and a wide measurement range. Traditional pressure sensors, due to their environmental sensitivity and limited accuracy, have struggled to meet the demands of high-end scenarios. Emerging FBG sensors, while optoelectronic, suffer from insufficient sensitivity and cross-sensitivity, necessitating technological breakthroughs.

[0007] Currently, traditional pressure sensors primarily include mechanical, electromagnetic, and fiber Bragg grating (FBG) types. Mechanical pressure sensors measure pressure by converting the deformation of an elastic mechanical structure under pressure into pointer displacement or an electrical signal through a mechanical amplification mechanism. Their core principle is the linear relationship between the deformation and pressure of the elastic element. Mechanical pressure sensors rely on the strain of the elastic structure to measure pressure, resulting in limited accuracy and poor dynamic response. Long-term use can also lead to fatigue and creep of the elastic element, resulting in reduced measurement accuracy.

[0008] Electromagnetic pressure sensors primarily include inductive, Hall, and eddy-current types. The main components of an inductive pressure sensor are an iron core and a diaphragm. The air gap between them forms a magnetic circuit. When pressure acts on the diaphragm, the air gap changes, causing a corresponding change in magnetic resistance, resulting in a change in the output current, enabling pressure measurement. The core component of a Hall pressure sensor is the Hall element. Pressure acts on an elastic element, causing it to deform, which in turn alters the magnetic field characteristics of the magnetic circuit system and generates a Hall voltage. An eddy-current pressure sensor primarily consists of an elastic element, a conductive target, a detection coil, and an oscillator circuit. The measured pressure acts on the elastic element, causing deformation, which in turn causes displacement of the conductive target. Eddy currents are induced on the surface of the conductor, and the change in the coil's impedance is used to measure pressure. All three methods measure pressure by capturing changes in current or voltage to reflect the pressure-induced deformation of the elastic element. However, the electronic components of electromagnetic sensors are sensitive to temperature, humidity, and electromagnetic interference, requiring additional protection or compensation measures. Furthermore, the integrated magnetic circuit and coil structures of Hall and eddy-current pressure sensors are difficult to miniaturize, limiting their application in confined spaces.

[0009] The main components of a fiber Bragg grating (FBG) are the fiber Bragg grating (FBG) and an elastic encapsulation. When a fiber Bragg grating (FBG) pressure sensor is subjected to external pressure, the pressure is transmitted to the optical fiber through the encapsulation structure, causing axial strain in the grating and shifting the center wavelength of the emitted light, enabling pressure measurement. The grating exhibits temperature-pressure cross-sensitivity: temperature changes simultaneously alter the effective refractive index and grating period, resulting in a wavelength shift that is independent of pressure. Summary of the Invention

[0010] In view of the technical problems existing in the prior art, the present invention proposes a pressure measurement device and method based on a fiber optic interferometer.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] In one aspect, the present invention provides a pressure measurement device based on a fiber optic interferometer, comprising a laser, a fiber optic interferometer, a Faraday rotator, and a photodetector. The fiber optic interferometer includes a fiber optic coupler, wherein two arms on one side of the fiber optic coupler are respectively connected to the laser and the photodetector, and two arms on the other side of the fiber optic coupler are respectively connected to one end of a sensing arm optical fiber and one end of a reference arm optical fiber, and the other ends of the sensing arm optical fiber and the reference arm optical fiber are respectively connected to the Faraday rotator. An initial phase difference exists between the optical signals output by the sensing arm optical fiber and the reference arm optical fiber.

[0013] The laser emitted by the laser is transmitted to the sensing arm optical fiber and the reference arm optical fiber through the optical fiber coupler. The sensing arm optical fiber is wound on the sensitivity-enhancing transducer structure. When external pressure acts on the sensitivity-enhancing transducer structure, the sensitivity-enhancing transducer structure deforms, causing the sensing arm optical fiber to change in length along with the deformation of the sensitivity-enhancing transducer structure, while the length of the reference arm optical fiber remains unchanged. The laser transmitted through the sensing arm optical fiber and the reference arm optical fiber is reflected by the corresponding Faraday rotator mirror and then returns to the optical fiber coupler to interfere. The light signal generated by the interference is received by the photoelectric detector and converted into an electrical signal for solving the external pressure information.

[0014] Furthermore, the phase difference of the optical signals output by the sensing arm fiber and the reference arm fiber is modulated by internal modulation or external modulation to suppress the influence of random phase drift on the measurement results, wherein the internal modulation method is as follows: by setting the lengths of the sensing arm fiber and the reference arm fiber so that there is an initial length difference, i.e., an initial arm difference, between the sensing arm fiber and the reference arm fiber, and achieving optical frequency shift by dynamically tuning the laser wavelength to achieve periodic modulation of the phase difference of the optical signals output by the sensing arm fiber and the reference arm fiber;

[0015] The external modulation method is: when the lengths of the sensing arm optical fiber and the reference arm optical fiber are the same, a frequency shifter is used to perform frequency shift processing on the optical signal transmitted in the sensing arm optical fiber and the reference arm optical fiber, thereby realizing periodic modulation of the phase difference of the output optical signal of the sensing arm optical fiber and the reference arm optical fiber; or when the lengths of the sensing arm optical fiber and the reference arm optical fiber are the same, a phase modulator is used to perform phase modulation on the optical signal transmitted in the sensing arm optical fiber and the reference arm optical fiber, thereby realizing periodic modulation of the phase difference of the output optical signal of the sensing arm optical fiber and the reference arm optical fiber.

[0016] Furthermore, the enhanced sensitivity transducer structure adopts a hemispherical metal shell, and the optical fiber of the sensing arm is evenly wound along a ring and bonded to the outer surface of the hemispherical metal shell. Preferably, the optical fiber of the sensing arm is evenly wound along a ring upward from a position near the bottom of the hemispherical metal shell and bonded to the outer surface of the hemispherical metal shell.

[0017] Furthermore, the sensitivity-enhancing transducer structure also includes a cylindrical cavity, the bottom of the hemispherical metal shell is provided with a cylindrical cavity, and the reference arm optical fiber is coiled in the cylindrical cavity.

[0018] On the other hand, a pressure measurement method based on a fiber optic interferometer is provided, and pressure measurement is achieved using the pressure measurement device based on the fiber optic interferometer. When external pressure acts on the sensitive transducer structure, the length of the sensing arm optical fiber changes as the sensitive transducer structure deforms, causing the phase difference of the light signal generated by interference to change. External pressure information can be obtained by demodulating the phase difference change of the light signal generated by interference.

[0019] In one embodiment, the enhanced transducer structure utilizes a hemispherical metal shell, and the sensing arm optical fiber is uniformly wound in a ring shape and bonded to the outer surface of the hemispherical metal shell. The enhanced transducer structure also includes a cylindrical cavity, with a cylindrical cavity provided at the bottom of the hemispherical metal shell, and the reference arm optical fiber is coiled within the cylindrical cavity. The pressure measurement device based on the fiber optic interferometer provided in this embodiment implements pressure measurement, including:

[0020] Assume that the initial arm difference between the sensing arm fiber and the reference arm fiber is , calculate the initial phase difference between the sensing arm fiber and the reference arm fiber of the fiber interferometer ;

[0021] Get external axisymmetric pressure When acting on the hemispherical metal shell, the optical signal generated by the interference output by the photodetector is converted into an electrical signal, and the external axisymmetric pressure is obtained based on the electrical signal. The phase difference between the sensing arm fiber and the reference arm fiber of the fiber interferometer under the action of the external axisymmetric pressure is obtained. The phase difference change of the sensing arm fiber and the reference arm fiber of the fiber interferometer under the action of the phase difference relative to the initial phase difference of the sensing arm fiber and the reference arm fiber of the fiber interferometer ;

[0022] Based on the phase difference Axisymmetric pressure with the outside world The relationship model between the external axisymmetric pressure , where the phase difference changes Axisymmetric pressure with the outside world The relationship model is as follows:

[0023] ;

[0024] in, is the central wavelength of the laser, is the core refractive index of the sensing arm optical fiber, is the radius of the hemispherical metal shell, is Poisson's ratio, is the thickness of the hemispherical metal shell, is the elastic modulus, is the propagation constant, .

[0025] Compared with the prior art, the beneficial technical effects of the present invention are:

[0026] Electromagnetic pressure sensors use electrical signals as sensing carriers, which determines their environmental sensitivity defects. Electrical signal transmission is susceptible to electromagnetic interference in space, and the physical properties of core electronic components are sensitive to temperature. To suppress temperature interference, traditional solutions require additional electromagnetic shielding devices, temperature compensation circuits, etc., which increases the complexity of the system. The present invention adopts an all-fiber signal transmission path, combined with the dual-path differential structure of the fiber optic interferometer to effectively suppress temperature crosstalk, eliminate dependence on additional protective devices, and realize deployment and use in harsh environments.

[0027] Mechanical pressure sensors are limited by the sensitivity of elastic elements and have difficulty capturing tiny nanometer-scale deformations. Electromagnetic pressure sensors are limited by hysteresis and cannot achieve high-linearity measurements. Based on the principle of phase-sensitive interferometry, this invention converts the nanometer-scale strain of elastic elements into a demodulated optical phase. Compared to the two traditional pressure sensors, the fiber optic Michelson interferometer pressure sensor achieves an accuracy improvement of 2 to 3 orders of magnitude.

[0028] The sensing principle of electromagnetic sensors determines their single function. The piezoelectric effect is only suitable for dynamic measurements, while the inductive type is only suitable for static measurements. Furthermore, signal processing relies on complex analog circuits, resulting in bulky systems and high integration difficulties. This invention utilizes PGC modulation and demodulation technology to achieve real-time demodulation of the optical phase of the two arms of a fiber interferometer, enabling accurate measurement of quasi-static pressure. Furthermore, the all-fiber winding transducer structure eliminates the need for traditional circuit modules, simplifying the system architecture and meeting the application requirements of miniaturization and multifunctional integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0030] Figure 1 This is a schematic diagram of the principle of a pressure measurement device based on a fiber optic interferometer in one embodiment;

[0031] Figure 2 Schematic diagram of a sensitivity-enhancing transducer structure and the winding of a sensing arm optical fiber and a reference arm optical fiber in one embodiment;

[0032] Figure 3 This is a schematic structural diagram of a sensitivity-enhancing transducer structure in one embodiment;

[0033] Figure 4 Schematic diagram of the enhanced sensitivity transducer structure and the winding of the sensing arm optical fiber and the reference arm optical fiber in one embodiment, wherein Figure 4 (a) is the overall schematic diagram, Figure 4 (b) is a schematic diagram of the winding of the reference arm optical fiber;

[0034] Figure 5 This is a schematic diagram of the force applied to the sensitivity-enhancing transducer structure in an application scenario in one embodiment;

[0035] Figure 6 It is a structural diagram of a sensitivity-enhancing transducer structure in one embodiment. DETAILED DESCRIPTION

[0036] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0037] Reference Figure 1 、 Figure 2 , Figure 1 This is a schematic diagram of the principle of a pressure measurement device based on a fiber optic interferometer in one embodiment; Figure 2 This is a schematic diagram of the sensitivity-enhancing transducer structure and the winding of the sensing arm optical fiber and the reference arm optical fiber in an embodiment, a pressure measuring device based on a fiber optic interferometer, including a laser 1, a fiber optic interferometer, a Faraday rotator and a photodetector 6; the fiber optic interferometer includes a fiber optic coupler 2, the two arms on one side of the fiber optic coupler 2 are respectively connected to the laser 1 and the photodetector 6, the two arms on the other side of the fiber optic coupler 2 are respectively connected to one end of the sensing arm optical fiber 3 and the reference arm optical fiber 4, the other ends of the sensing arm optical fiber 3 and the reference arm optical fiber 4 are respectively connected to a Faraday rotator 5, and there is an initial phase difference between the optical signals output by the sensing arm optical fiber 3 and the reference arm optical fiber 4.

[0038] The phase difference of the optical signals output by the sensing arm optical fiber 3 and the reference arm optical fiber 4 is modulated by internal modulation or external modulation to suppress the influence of random phase drift on the measurement results, wherein the internal modulation method is: by setting the length of the sensing arm optical fiber 3 and the reference arm optical fiber 4, an initial length difference, i.e., an initial arm difference, exists between the sensing arm optical fiber 3 and the reference arm optical fiber 4, and optical frequency shift is achieved by dynamic tuning of the laser wavelength to achieve periodic modulation of the phase difference of the optical signals output by the sensing arm optical fiber 3 and the reference arm optical fiber 4, wherein Figure 1In the embodiment shown, an internal modulation method is adopted.

[0039] Laser light emitted by laser 1 is transmitted through a fiber coupler to a sensing arm fiber 3 and a reference arm fiber 4. The sensing arm fiber 3 is wound around a sensitivity-enhancing transducer structure. When external pressure acts on the sensitivity-enhancing transducer structure, the sensitivity-enhancing transducer structure deforms, causing the sensing arm fiber 3 to change in length along with the deformation of the sensitivity-enhancing transducer structure, while the length of the reference arm fiber 4 remains unchanged. The laser light transmitted through the sensing arm fiber 3 and the reference arm fiber 4 is reflected by the corresponding Faraday rotator 5 and then returned to the fiber coupler 2, causing interference. The light signal generated by the interference is received by a photodetector 6 and converted into an electrical signal for use in calculating external pressure information. In the present invention, external pressure causes the length of the sensing arm fiber 3 to change, while external pressure does not cause the length of the reference arm fiber 4 to change, i.e., the length of the reference arm fiber 4 remains unchanged.

[0040] In addition, it is to be explained that the external modulation method can be: when the lengths of the sensing arm optical fiber 3 and the reference arm optical fiber 4 are the same, a frequency shifter is used to perform frequency shift processing on the optical signal transmitted in the sensing arm optical fiber 3 and the reference arm optical fiber 4, so as to realize periodic modulation of the phase difference of the optical signal output by the sensing arm optical fiber 3 and the reference arm optical fiber 4, or when the lengths of the sensing arm optical fiber 3 and the reference arm optical fiber 4 are the same, a phase modulator is used to perform phase modulation on the optical signal transmitted in the sensing arm optical fiber 3 and the reference arm optical fiber 4, so as to realize periodic modulation of the phase difference of the optical signal output by the sensing arm optical fiber 3 and the reference arm optical fiber 4.

[0041] Figure 2 In the embodiment shown, the sensitivity-enhancing transducer structure adopts a hemispherical metal shell 7, as shown in FIG. Figure 2 As shown, the winding method of the sensing arm optical fiber 3 is: the sensing arm optical fiber 3 is evenly wound along a ring and bonded to the outer surface of the hemispherical metal shell 7. The winding method and specific location of the reference arm optical fiber 4 are not limited. The core requirement is that the reference arm optical fiber 4 and the sensing arm optical fiber 3 are in the same environmental conditions. External pressure will change the length of the sensing arm optical fiber through the sensitivity-enhancing transducer structure but will not change the length of the reference arm optical fiber. Figure 2 As shown, the reference arm optical fiber 4 is coiled at the bottom of the hemispherical metal shell 7 .

[0042] In addition, if the fiber optic interferometer adopts a push-pull structure, pressure changes will cause the lengths of the reference arm and the measurement arm to change in opposite directions, and the sensitivity will be twice that of the current structure.

[0043] The arm difference between the sensing fiber and the reference fiber is the basis for introducing the internal modulation signal. The arm difference between the two arms is related to the modulation depth. The relationship between the modulation depth and the arm difference between the sensing fiber and the reference fiber is as follows:

[0044] ;

[0045] Where C is the modulation depth, is the refractive index of the fiber core, is the initial arm difference between the sensing arm fiber and the reference arm fiber, is the spectrum width of the light source, is the speed of light in a vacuum.

[0046] The modulation depth is related to the signal demodulation requirements that need to be met. The greater the modulation depth, the higher the signal-to-noise ratio of the monitoring signal, but it must be within the dynamic range of the PGC demodulation algorithm. The PGC demodulated signal is:

[0047] ;

[0048] in, 、 are first-order and second-order Bessel functions respectively, C is the modulation depth, is the phase difference generated by the signal.

[0049] Different demodulation algorithms have different optimal modulation depths. The optimal modulation depth for the PGC-DCM demodulation algorithm is 2.37 rad, and the optimal modulation depth for the PGC-Arctan demodulation algorithm is 2.63 rad. In practical applications, the phase modulation depth typically ranges from 0 rad to 3.7 rad. The arm difference between the sensing and reference fiber arms is selected based on the specific device used. For this invention, the initial arm difference between the sensing and reference fiber arms is 1.56 m.

[0050] Assume that the initial arm difference between the sensing arm fiber and the reference arm fiber is , the initial phase difference between the sensing arm fiber and the reference arm fiber of the fiber interferometer can be written as:

[0051] (1)

[0052] in is the core refractive index of the optical fiber used in the sensing arm optical fiber and the reference arm optical fiber, is the initial arm difference between the sensing arm fiber and the reference arm fiber, c is the speed of light in vacuum, It is the light frequency.

[0053] Note that if the laser (wavelength is 1550.32nm) has a coherence length of , coherence theory requires , that is, the coherence length of the laser must be greater than the optical path difference between the two arms of the fiber interferometer.

[0054] The phase difference change relative to the initial phase difference caused by the external pressure change is:

[0055] (2)

[0056] in, is the initial length of the acoustic sensing arm optical fiber, is the change in the length of the optical fiber of the sensing arm caused by external pressure, is the propagation constant, , is the diameter of the sensing arm optical fiber, is the core refractive index of the sensing arm optical fiber.

[0057] As can be seen from the above formula, changes in the length, core refractive index, and diameter of the sensing arm fiber will all affect the phase of the transmitted light. Among them, the change in the fiber diameter of the sensing arm fiber has the smallest impact on the light transmission phase. It is several orders of magnitude smaller than the phase difference change caused by the change in the fiber length and core refractive index of the sensing arm fiber. Therefore, this term can be ignored, and the result is:

[0058] (3)

[0059] The change in the core refractive index of the sensing arm optical fiber is:

[0060] (4)

[0061] in is the Poisson’s ratio of the sensing arm’s optical fiber, and is the elastic-optical coefficient of the sensing arm optical fiber, is the strain of the sensitive optical fiber, ,in The length change of the optical fiber of the sensing arm caused by external pressure. The core refractive index of the optical fiber used in the sensing arm is =1.464, Poisson's ratio =0.1, elastic coefficient =0.121, =0.270, and substituting it into formula (4), it can be simplified to:

[0062] (5)

[0063] Substituting formula (5) into formula (3), the relationship between the phase difference change of the optical signal generated by interference and the change of the optical fiber length of the sensor arm is:

[0064] (6)

[0065] When external pressure When acting on the sensitivity-enhancing transducer structure, the length of the sensing arm optical fiber changes with the deformation of the sensitivity-enhancing transducer structure, causing Changes, through demodulation You can get external pressure .

[0066] In practical applications, the sensitivity of relying solely on bare optical fibers to sense pressure changes is low, making it difficult to meet high-precision measurement requirements. In order to improve the sensitivity of the sensor, it is usually necessary to design a special sensitivity-enhancing transducer structure. By wrapping the sensing arm around the sensitivity-enhancing transducer structure, the responsiveness of the pressure signal can be significantly enhanced. In one embodiment of the present invention, a hemispherical transducer structure is innovatively used as a sensitivity-enhancing transducer structure. This design not only effectively improves sensitivity, but also has the advantages of uniform stress distribution and consistent multi-directional response, providing an ideal solution for high-precision pressure measurement.

[0067] Reference Figure 1 、 Figure 3 and Figure 4 A pressure measuring device based on a fiber optic interferometer includes a laser 1, a fiber optic interferometer, a Faraday rotator 5, and a photodetector 6; the fiber optic interferometer includes a fiber optic coupler 2, the two arms on one side of the fiber optic coupler 2 are respectively connected to the laser 1 and the photodetector 6, the two arms on the other side of the fiber optic coupler 2 are respectively connected to one end of the sensing arm fiber 3 and the reference arm fiber 4, the other ends of the sensing arm fiber 3 and the reference arm fiber 4 are respectively connected to a Faraday rotator 5, and there is an initial length difference between the sensing arm fiber 3 and the reference arm fiber 4, that is, there is an initial arm difference. The sensing arm fiber 3 is wound on a sensitivity-enhancing transducer structure. In this embodiment, the sensitivity-enhancing transducer structure adopts a hemispherical metal shell 7, such as Figure 4 As shown, the winding method of the sensing arm fiber is as follows: the sensing arm fiber 3 is evenly wound along a ring and bonded to the outer surface of the hemispherical metal shell. The winding method and specific location of the reference arm fiber 4 are not limited. The core requirement is that the reference arm fiber and the sensing arm fiber are in the same environmental conditions. External pressure will change the length of the sensing arm fiber through the sensitivity-enhancing transducer structure but will not change the length of the reference arm fiber. Figure 3 and Figure 4 , Figure 3 Schematic diagram of the structure of the sensitivity-enhancing transducer structure; Figure 4 It is a schematic diagram of the sensitivity-enhancing transducer structure and the winding of the sensing arm fiber and the reference arm fiber, where Figure 4 (a) is the overall schematic diagram, Figure 4(b) is a schematic diagram of the winding of the reference arm optical fiber. The enhanced sensitivity transducer structure also includes a cylindrical cavity 8, which is provided at the bottom of the hemispherical metal shell 7. The reference arm optical fiber 5 is coiled in the cylindrical cavity 8. The ends of the reference arm optical fiber 4 and the sensing arm optical fiber 3 are Faraday rotators 5. It should be noted that the winding position and method of the reference arm optical fiber are not unique, but the loss caused by the bending radius of the optical fiber needs to be considered. The key point is that the reference arm needs to be in the same environmental conditions as the measuring arm. The common mode structure can eliminate the influence of environmental factors on the measurement results.

[0068] The laser emitted by the laser is transmitted to the sensing arm optical fiber and the reference arm optical fiber through the fiber coupler. When external pressure acts on the sensitive transducer structure, the sensitive transducer structure deforms, causing the sensing arm optical fiber to change in length along with the deformation of the sensitive transducer structure, while the length of the reference arm optical fiber remains unchanged. The laser transmitted through the sensing arm optical fiber and the reference arm optical fiber is reflected by the corresponding Faraday rotator mirror and then returns to the fiber coupler to interfere. The light signal generated by the interference is received by the photoelectric detector and converted into an electrical signal for solving the external pressure information.

[0069] Preferably, the hemispherical metal shell 7 is made of cast aluminum alloy with an inner diameter of 0.1m and a thickness of 0.002m. Cast aluminum alloy has low density, high specific strength, and is corrosion-resistant and can adapt to most harsh working conditions. The maximum pressure that the hemispherical metal shell can withstand without damaging the elastic transducer structure is 2.75MPa. However, due to the limitations of the modulation and demodulation method, the maximum measurable pressure of the measuring device is related to the frequency of the signal. The lower the signal frequency, the greater the upper limit of the signal that can be accurately measured. Excessive measurement signal will cause demodulation distortion. The maximum signal amplitude that can be accurately demodulated for a 100Hz signal is Pa.

[0070] In one embodiment, a pressure measurement method based on a fiber optic interferometer is provided. The pressure measurement device based on a fiber optic interferometer provided in the above embodiment implements pressure measurement, wherein the sensitivity-enhancing transducer structure uses a hemispherical metal shell 7, and the winding method of the sensing arm optical fiber is as follows: the sensing arm optical fiber 3 is evenly wound along a ring and bonded to the outer surface of the hemispherical metal shell. Specifically, the pressure measurement method based on a fiber optic interferometer includes:

[0071] Assume that the initial arm difference between the sensing arm fiber and the reference arm fiber is , calculate the initial phase difference between the sensing arm fiber and the reference arm fiber of the fiber interferometer ;

[0072] Get external axisymmetric pressure When acting on the hemispherical metal shell, the optical signal generated by the interference output by the photodetector is converted into an electrical signal, and the external axisymmetric pressure is obtained based on the electrical signal. The phase difference between the sensing arm fiber and the reference arm fiber of the fiber interferometer under the action of the external axisymmetric pressure is obtained. The phase difference change of the sensing arm fiber and the reference arm fiber of the fiber interferometer under the action of the phase difference relative to the initial phase difference of the sensing arm fiber and the reference arm fiber of the fiber interferometer ;

[0073] Based on the phase difference Axisymmetric pressure with the outside world The relationship model between the external axisymmetric pressure , where the phase difference changes Axisymmetric pressure with the outside world The relationship model is as follows:

[0074] ;

[0075] in, is the central wavelength of the laser, is the core refractive index of the sensing arm optical fiber, is the radius of the hemispherical metal shell, is Poisson's ratio, is the thickness of the hemispherical metal shell, is the elastic modulus, is the propagation constant, .

[0076] In the above embodiment, the boundary of the hemispherical metal shell is fixed, and a spherical coordinate system is established with the center of the hemispherical metal shell as the center. The external axisymmetric pressure is set to p To evenly distribute the load (vertical downward pressure of still water), as Figure 5 As shown, Figure 5 This is a force diagram of the enhanced sensitivity transducer structure in the application scenario. Due to the fixed constraint of the hemispherical metal shell, the bending stress is concentrated, resulting in the maximum strain area of ​​the hemispherical metal shell near its support edge (the area where the hemispherical metal shell and the bottom of the hemispherical metal shell contact the cylindrical cavity). The longer the length of the sensing arm optical fiber bonded to the outer surface of the hemispherical metal shell, the better the detection effect. However, if An angle that is too small will make it difficult to manually wind the optical fiber around the transducer surface, so the winding range is limited to 60°-90°. is the pitch angle of the spherical coordinate system, the pitch angle of the hemispherical metal shell The value range is 0°-90°, and the optical fiber of the sensing arm is bonded at the pitch angle The outer surface of the hemispherical metal shell is within the range of 60°-90°. Figure 3In the figure, the winding angle range of the sensing arm optical fiber on the outer surface of the hemispherical metal shell is 30°, and the range of 60°-90° refers to the angle formed with the positive direction of the Z axis in the spherical coordinate system, 90°-60°=30°.

[0077] When the external axisymmetric pressure p When acting on the hemispherical metal shell, the hemispherical metal shell will be deformed due to the pressure. Donnell According to shell theory, the strain-displacement relationship of a hemispherical metal shell under external axisymmetric pressure is as follows:

[0078] (7)

[0079] in, 、 is the tangential displacement component, is the normal displacement, is the radius of the hemispherical metal shell, is the hoop strain, is the axial strain.

[0080] Axisymmetric condition ( ), it is simplified to:

[0081] (8)

[0082] According to the force balance of the infinitesimal element, the equilibrium equation is established as:

[0083] (9)

[0084] in , , is the circumferential membrane force, is the axial membrane force, is the pressure load, is the thickness of the hemispherical metal shell.

[0085] The constitutive relation of linear elastic materials is as follows:

[0086] (10)

[0087] in, is the elastic modulus, is Poisson's ratio, is the hoop strain, is the radial strain, is the hoop stress, is the axial stress.

[0088] Substituting the constitutive relation of the linear elastic material into the equilibrium equation, we get:

[0089] (11)

[0090] By solving formula (11), the final general solution is obtained:

[0091] (12)

[0092] According to the boundary conditions It is valid when C=0.

[0093] The hoop strain and axial strain are:

[0094] (13)

[0095] Since the optical fiber of the sensing arm is uniformly wound along the ring and bonded to the outer surface of the hemispherical metal shell, its deformation is consistent with the hemispherical metal shell. Therefore, the length change of the optical fiber of the sensing arm can be obtained by integrating the annular strain of the hemispherical metal shell. Therefore, due to the external axisymmetric pressure p Changes in the length of the optical fiber in the sensing arm caused by for:

[0096] (14)

[0097] exist Range, when the thickness-diameter ratio When , the boundary effect causes the bending stress to be non-negligible. It is necessary to introduce a correction term for the strain. The bending displacement correction term formula is:

[0098] (15)

[0099] Used to describe the normal displacement of the shell due to bending effects, where is the amplitude coefficient, which is determined by the matching conditions between the film solution and the bending solution and characterizes the initial amplitude of the bending displacement. Represents the bending attenuation coefficient, and its physical meaning is to control the attenuation rate of the bending effect with the spatial angular distance. .

[0100] The bending strain is:

[0101] (16)

[0102] The total hoop strain is corrected to:

[0103] (17)

[0104] in, is the total hoop strain, is the hoop strain, is the bending strain caused by the boundary bending stress.

[0105] Change in the length of the sensing arm fiber for:

[0106] (18)

[0107] When the external axisymmetric pressure When acting on the hemispherical metal shell, the length of the sensing arm fiber changes with the deformation of the hemispherical metal shell. The calculation formula is:

[0108] (19)

[0109] Substituting Equation (19) into Equation (6), we can obtain the phase difference change Axisymmetric pressure with the outside world The relationship model is:

[0110] (20)

[0111] in, is the central wavelength of the laser.

[0112] The application scenario of the above embodiment is the liquid level monitoring in the container and the release of the fluid flow rate. The key lies in the monitoring of the liquid level height. Only the vertical downward pressure is considered. The pressure effect diagram is shown in FIG. Figure 4 . However, in the process of monitoring the liquid level in the container, there is a horizontal flow when the liquid in the container is released. The horizontal flow of the liquid will have an impact on the side of the sensor, causing additional strain on the optical fiber, and thus affecting the monitoring of the liquid level in the container. For this reason, a diversion enclosure structure 9 can be further designed, that is, the sensitivity-enhancing transducer structure also includes a diversion enclosure structure 9, and the periphery of the hemispherical metal shell 7 is provided with a diversion enclosure structure 9, and the external pressure load in the vertical direction directly acts on the surface of the hemispherical metal shell. The lateral impact stress generated by the horizontal flow is effectively isolated by the diversion enclosure structure 9, while ensuring that the hemispherical metal shell 7 is connected to the measured medium, and only the external pressure load in the vertical direction is allowed to directly act on the surface of the hemispherical metal shell 7, such as Figure 6 Figure 1 shows a schematic diagram of a sensitive transducer structure with a diversion enclosure structure 9 added to the periphery of a hemispherical metal shell 7. The sensing arm optical fiber is uniformly wound in a circular pattern and bonded to the outer surface of the hemispherical metal shell. The reference arm optical fiber is uniformly wound in a circular pattern and bonded to a cylindrical cavity at the bottom of the hemispherical shell. To prevent measurement errors caused by environmental disturbances on the exposed sensing arm optical fiber, a Teflon protective sleeve is used to protect the exposed sensing arm optical fiber, effectively preventing interference from external environmental disturbances on the measurement results.

[0113] The fiber optic interferometer described in the present invention is a Michelson fiber optic interferometer. With the Michelson fiber optic interferometer as the core sensing unit, an innovative pressure measurement device based on the fiber optic interferometer has been developed. This device is essentially a high-precision fiber optic pressure sensor. This sensor achieves pressure detection based on the stable transmission of optical signals within an optical fiber waveguide. Compared to traditional electromagnetic pressure sensors, it exhibits significant technical advantages under complex working conditions: the inherent electrical insulation properties of optical fiber materials give it excellent resistance to electromagnetic interference, allowing it to operate stably in strong electromagnetic radiation environments; the excellent chemical stability of high-purity quartz optical fiber enables it to effectively resist acid and alkali corrosion and salt spray erosion, greatly improving the sensor's adaptability in harsh environments such as humid, dusty, and highly corrosive environments. The dual-arm structure of the fiber optic interferometer naturally constitutes a common-mode suppression system that can effectively suppress non-target disturbances caused by environmental factors such as temperature fluctuations, further enhancing the stability of the sensing signal.

[0114] The core innovation of this invention lies in the use of a phase modulation interferometry mechanism, which fully utilizes the high sensitivity of light phase to tiny physical quantities, achieving detection accuracy far exceeding that of traditional sensors and can capture nanometer-level micro-deformations of elastic sensitive components. The phase difference change shows a good linear correspondence with the pressure load, and the theoretical sensitivity can reach -137dB. Crucially, this invention breaks through the technical bottleneck of traditional electromagnetic sensors, which are limited by their working principles (they can only selectively measure static or dynamic pressure). By using the Michelson fiber interferometer to phase-demodulate and invert pressure, it achieves the first precise measurement of quasi-static pressure, effectively expanding the application scenarios of pressure sensing.

[0115] Matters not covered by the present invention are known technologies.

[0116] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, 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.

[0117] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the spirit of the present application, and such modifications and improvements are all within the scope of protection of the present application.

[0118] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A pressure measurement method based on a fiber optic interferometer, characterized in that: Pressure measurement is achieved using a pressure measurement device based on a fiber optic interferometer. The pressure measurement device includes a laser, a fiber optic interferometer, a Faraday rotator, and a photodetector. The fiber optic interferometer includes a fiber optic coupler. Two arms on one side of the fiber optic coupler are connected to the laser and the photodetector, respectively. Two arms on the other side of the fiber optic coupler are connected to one end of a sensing arm fiber and one end of a reference arm fiber, respectively. The other ends of the sensing arm fiber and the reference arm fiber are connected to the Faraday rotator, respectively. An initial phase difference exists between the optical signals output by the sensing arm fiber and the reference arm fiber. The laser light emitted by the laser is transmitted to the sensing arm optical fiber and the reference arm optical fiber through the fiber coupler. The sensing arm optical fiber is wound on the sensitivity-enhancing transducer structure. The sensitivity-enhancing transducer structure adopts a hemispherical metal shell. The sensing arm optical fiber is evenly wound along the ring and bonded to the outer surface of the hemispherical metal shell. When external pressure acts on the sensitivity-enhancing transducer structure, the sensing arm optical fiber changes in length as the sensitivity-enhancing transducer structure deforms, causing the phase difference of the light signal generated by interference to change, while the length of the reference arm optical fiber remains unchanged. The laser light transmitted through the sensing arm optical fiber and the reference arm optical fiber is reflected by the corresponding Faraday rotator mirror and then returns to the fiber coupler to cause interference. The light signal generated by the interference is received by the photodetector and converted into an electrical signal. The external pressure information can be obtained by demodulating the phase difference change of the light signal generated by the interference, including: Assume that the initial arm difference between the sensing arm fiber and the reference arm fiber is , calculate the initial phase difference between the sensing arm fiber and the reference arm fiber of the fiber interferometer ; Get external axisymmetric pressure When acting on the hemispherical metal shell, the optical signal generated by the interference output by the photodetector is converted into an electrical signal, and the external axisymmetric pressure is obtained based on the electrical signal. The phase difference between the sensing arm fiber and the reference arm fiber of the fiber interferometer under the action of the external axisymmetric pressure is obtained. The phase difference change of the sensing arm fiber and the reference arm fiber of the fiber interferometer under the action of the phase difference relative to the initial phase difference of the sensing arm fiber and the reference arm fiber of the fiber interferometer ; Based on the phase difference Axisymmetric pressure with the outside world The relationship model between the external axisymmetric pressure , where the phase difference changes Axisymmetric pressure with the outside world The relationship model is as follows: ； in, is the central wavelength of the laser, is the core refractive index of the sensing arm optical fiber, is the radius of the hemispherical metal shell, is Poisson's ratio, is the thickness of the hemispherical metal shell, is the elastic modulus, which is determined by the material used for the hemispherical metal shell. is the propagation constant, .

2. The pressure measurement method based on fiber interferometer according to claim 1, characterized in that: The phase difference of the optical signals output by the sensing arm fiber and the reference arm fiber is modulated by internal modulation to suppress the influence of random phase drift on the measurement results. The internal modulation method is as follows: by setting the lengths of the sensing arm fiber and the reference arm fiber, an initial length difference, i.e., an initial arm difference, exists between the sensing arm fiber and the reference arm fiber. The optical frequency shift is achieved by dynamic tuning of the laser wavelength to achieve periodic modulation of the phase difference of the optical signals output by the sensing arm fiber and the reference arm fiber.

3. The pressure measurement method based on fiber interferometer according to claim 1, characterized in that: The influence of random phase drift on the measurement results is suppressed by modulating the phase difference of the optical signals output by the sensing arm optical fiber and the reference arm optical fiber. The external modulation method is as follows: when the lengths of the sensing arm optical fiber and the reference arm optical fiber are the same, a frequency shifter is used to perform frequency shift processing on the optical signals transmitted in the sensing arm optical fiber and the reference arm optical fiber to achieve periodic modulation of the phase difference of the optical signals output by the sensing arm optical fiber and the reference arm optical fiber; or when the lengths of the sensing arm optical fiber and the reference arm optical fiber are the same, a phase modulator is used to perform phase modulation on the optical signals transmitted in the sensing arm optical fiber and the reference arm optical fiber to achieve periodic modulation of the phase difference of the optical signals output by the sensing arm optical fiber and the reference arm optical fiber.

4. The pressure measurement method based on fiber interferometer according to claim 1, 2 or 3, characterized in that: The sensitivity-enhancing transducer structure further includes a cylindrical cavity. The bottom of the hemispherical metal shell is provided with the cylindrical cavity, and the reference arm optical fiber is coiled in the cylindrical cavity.

5. The pressure measurement method based on fiber interferometer according to claim 4, characterized in that: The hemispherical metal shell is made of cast aluminum alloy, with an inner diameter of 0.1m and a thickness of 0.002m.

6. The pressure measurement method based on fiber interferometer according to claim 1, 2, 3 or 5, characterized in that: A flow guide enclosure structure is provided on the periphery of the hemispherical metal shell, and the external pressure load in the vertical direction directly acts on the surface of the hemispherical metal shell.

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