A phase demodulation method for fiber-optic fabry-perot sensors

Abstract

The application describes a phase demodulation method of a fiber-optic Fabry-Perot sensor, the phase demodulation method comprising: obtaining an initial cavity length of a shortest cavity of the fiber-optic Fabry-Perot sensor, emitting an emitted light beam having a preset wavelength range, reflecting the emitted light beam by a plurality of reflecting surfaces and forming a reflected light beam, dividing the reflected light beam into a first light beam, a second light beam and a third light beam, receiving the first light beam, the second light beam and the third light beam and converting them into a first signal, a second signal and a third signal respectively, calculating a phase change parameter of the fiber-optic Fabry-Perot sensor based on the first signal, the second signal, the third signal, a first center wavelength, a second center wavelength, a third center wavelength and the initial cavity length of the shortest cavity of the fiber-optic Fabry-Perot sensor, and obtaining an external measured parameter based on the phase change parameter. Thus, a phase demodulation method of a fiber-optic Fabry-Perot sensor with high reliability and high robustness can be obtained.

Description

[0001] This application is a divisional application of the patent application filed on November 5, 2021, with application number 202111307197X and invention title: Fiber Optic Sensor Demodulation System and Demodulation Method for Obtaining Phase Change Parameters. Technical Field

[0002] This invention generally relates to a fiber optic sensor demodulation system and method for obtaining phase change parameters, and in particular to a phase demodulation method for a fiber optic Fabry-Perot sensor. Background Technology

[0003] Currently, sensors used in various fields mainly include electrical sensors, fiber optic sensors, and other types. The main drawback of traditional electrical sensors is their inability to operate in harsh environments such as high temperatures, strong electromagnetic interference, and corrosion. In contrast, fiber optic Fabry-Perot (FP) sensors offer advantages such as small size, high temperature resistance, corrosion resistance, electromagnetic interference resistance, high sensitivity, and high measurement accuracy. They have broad application prospects in aerospace, large-scale construction, and petroleum industries, particularly for measuring multiple parameters such as temperature, pressure, acceleration, acoustics, and ultrasound, where high demodulation speeds are required.

[0004] Furthermore, due to the requirements of multi-parameter measurement and limitations in fabrication and packaging methods, fiber optic FP sensors have multiple reflective surfaces. When an FP sensor has multiple reflective surfaces, traditional high-speed demodulation methods are not applicable. Demodulation methods applicable to multi-cavity FP sensors mainly include Fourier transform, cross-correlation, and non-scanning cross-correlation. Since the spectrum of a multi-cavity FP sensor consists of signals of different frequencies, the Fourier transform method is a commonly used demodulation method. The cross-correlation method finds the maximum value by cross-correlating the sensor spectrum with another ideal spectrum. The non-scanning cross-correlation method uses the principle of low-coherence interference; demodulation is achieved by obtaining the location of maximum intensity when the optical path difference (OPD) between the FP sensor and another interferometer is equal.

[0005] Due to hardware limitations, the above demodulation methods cannot meet the demodulation speed requirements for dynamic parameters such as vibration, dynamic pressure, and acoustic / ultrasonic signals. Summary of the Invention

[0006] The present invention is proposed in view of the above-mentioned state of the prior art, and its purpose is to provide a demodulation system and demodulation method for measuring parameters based on fiber optic Fabry-Perot sensors with high reliability and high robustness.

[0007] Therefore, a first aspect of the present invention provides a fiber optic sensor demodulation system for obtaining phase change parameters. This system, which obtains phase change parameters using a fiber optic Fabry-Perot sensor, includes: a transmitting module, a fiber optic Fabry-Perot sensor, a beam splitting module, a filtering module, a receiving module, and a processing module. The transmitting module emits a light beam with a preset wavelength range, the fiber optic Fabry-Perot sensor receives the light beam and forms a reflected beam, and the beam splitting module is disposed between the transmitting module and the fiber optic Fabry-Perot sensor. The beam splitting module has at least three ports, including a first port connected to the transmitting module, a second port connected to the fiber optic Fabry-Perot sensor, and a third port connected to the filtering module. The filtering module includes a first filtering unit, a second filtering unit, and a third filtering unit. The first filtering unit filters the light beam... The reflected beam is filtered to obtain a first beam with a first center wavelength. The second filtering unit filters the reflected beam to obtain a second beam with a second center wavelength. The third filtering unit filters the reflected beam to obtain a third beam with a third center wavelength. The first, second, and third filtering units are broadband filters. The receiving module receives the first, second, and third beams and converts them into a first, second, and third signal, respectively. The processing module calculates the phase change parameters of the fiber optic Fabry-Perot sensor based on the first, second, and third signals, the first center wavelength, the second center wavelength, the third center wavelength, and the initial cavity length of the shortest chamber of the fiber optic Fabry-Perot sensor.

[0008] In this configuration, multiple reflective surfaces of the fiber optic Fabry-Perot sensor can be used to emit and reflect light beams, forming a reflected beam. A beam splitting module then divides the reflected beam into a first beam, a second beam, and a third beam. These beams are received and filtered to obtain a first beam with a first center wavelength, a second beam with a second center wavelength, and a third beam with a third center wavelength. This reduces the impact of fiber jitter on phase change parameters. Furthermore, since the first, second, and third filter units are broadband filters, they can filter out the interference signal (interference light) from the shortest cavity (i.e., the first chamber).

[0009] Furthermore, in the demodulation system according to the first aspect of the present invention, optionally, the fiber optic Fabry-Perot sensor is a fiber optic Fabry-Perot multi-cavity sensor, which includes at least a first reflecting surface, a second reflecting surface, and a third reflecting surface arranged sequentially. The first reflecting surface and the second reflecting surface cooperate to form a first cavity, the second reflecting surface and the third reflecting surface cooperate to form a second cavity, and the first reflecting surface and the third reflecting surface cooperate to form a third cavity. Among the first cavity, the second cavity, and the third cavity, the initial cavity length of the first cavity is the shortest. In this case, interference information of the first cavity can be extracted by limiting the coherence length.

[0010] Furthermore, in the demodulation system according to the first aspect of the present invention, optionally, the first center wavelength, the second center wavelength, and the third center wavelength are within the preset wavelength range, and the 3dB bandwidth of the first filter unit, the 3dB bandwidth of the second filter unit, and the 3dB bandwidth of the third filter unit are within the preset wavelength range. In this case, a first beam having a first center wavelength, a second beam having a second center wavelength, and a third beam having a third center wavelength can be formed.

[0011] Furthermore, in the demodulation system according to the first aspect of the present invention, optionally, the coherence length is obtained based on the first center wavelength, the second center wavelength, and the third center wavelength, wherein the optical path difference introduced by the first cavity is less than the coherence length; the coherence length is less than a first preset multiple of the optical path difference introduced by any cavity other than the first cavity, and the first preset multiple is not less than 3. In this case, since the coherence length must be greater than the cavity length for a significant interference phenomenon to occur, the mutual interference between multiple reflecting surfaces can be eliminated using the coherence length, so that the interference phenomenon mainly exists only in the first cavity of the fiber optic FP sensor, thereby realizing the demodulation of the fiber optic FP sensor and improving the demodulation accuracy.

[0012] Furthermore, in the demodulation system according to the first aspect of the present invention, optionally, the light beam emitted by the transmitting module reaches the fiber optic Fabry-Perot sensor through the first port and the second port, and the reflected light beam from the fiber optic Fabry-Perot sensor reaches the filter module through the second port and the third port. In this case, since the beam splitter is a non-reversible device, that is, the light beam entering the first port can exit from the second port, and the light beam entering the second port can exit from the third port, the light beam emitted by the transmitting module, after entering the first port, can reach the fiber optic Fabry-Perot sensor from the second port, and the reflected light beam, after entering the second port, can reach the filter module from the third port. This allows for adjustment of the beam direction and guidance of different types of light beams to different components or devices via the beam splitter.

[0013] A second aspect of the present invention provides a fiber optic sensor demodulation method for obtaining phase change parameters. This method utilizes the fiber optic sensor demodulation system described in the first aspect of the present invention to obtain phase change parameters. The demodulation method comprises: obtaining the initial cavity length of the shortest cavity of the fiber optic Fabry-Perot sensor; and receiving beams from the fiber optic Fabry-Perot sensor, namely a first beam having a first center wavelength, a second beam having a second center wavelength, and a third beam having a third center wavelength.

[0014] Calculate the first initial phase, the second initial phase, and the third initial phase, provided that the first initial phase, the second initial phase, and the third initial phase satisfy the formula:

[0015] θ1=4πnL0 / λ1,

[0016] θ2=4πnL0 / λ2,

[0017] θ3=4πnL0 / λ3,

[0018] Where θ1 represents the first initial phase, θ2 represents the second initial phase, θ3 represents the third initial phase, n represents the refractive index of the medium, L0 represents the initial cavity length, λ1 represents the first center wavelength, λ2 represents the second center wavelength, and λ3 represents the third center wavelength. The target phase is calculated based on the first beam, the second beam, the third beam, the first initial phase, the second initial phase, and the third initial phase, and the target phase satisfies the formula:

[0019]

[0020] Wherein, △θ' represents the target phase, I1 represents the intensity of the first beam, I2 represents the intensity of the second beam, and I3 represents the intensity of the third beam. The target phase is compensated to obtain the phase change parameter.

[0021] In this configuration, by filtering the first, second, and third beams, a first beam with a first center wavelength, a second beam with a second center wavelength, and a third beam with a third center wavelength can be obtained, reducing the impact of fiber jitter on phase change parameters. Simultaneously, the target phase can be conveniently calculated using formulas, and then compensated for to obtain phase change parameters, thereby meeting the demodulation speed requirements for dynamic parameters such as vibration, dynamic pressure, and acoustic / ultrasonic signals.

[0022] Furthermore, in the demodulation method according to the second aspect of the present invention, optionally, after obtaining the phase change parameter, the cavity length change is obtained based on the target phase change parameter. If the cavity length change is greater than a threshold, a target cavity length is calculated based on the cavity length change and the initial cavity length. The phase change parameter is then recalculated using the target cavity length as the initial cavity length. In this case, the sensor can maintain a small error over a large cavity length change range.

[0023] Furthermore, in the demodulation method according to the second aspect of the present invention, optionally, the first center wavelength, the second center wavelength, and the third center wavelength are different from each other. In this case, orthogonal signals can be obtained using signals with different center wavelengths, thereby enabling the calculation of the target phase.

[0024] Furthermore, in the demodulation method according to the second aspect of the present invention, optionally, the difference between the target phase and the phase change parameter matching the target phase is a preset multiple of the compensation value, wherein the compensation value is π and the preset multiple is an integer. In this case, since the target phase obtained using the arctangent algorithm is in the range of -π / 2 to π / 2, a phase jump will occur when the target phase exceeds this range. Therefore, compensating for the target phase can obtain a more accurate phase change value.

[0025] Furthermore, in the demodulation method according to the second aspect of the present invention, optionally, when calculating the phase change parameter, the initial value of the preset multiple remains unchanged, and the preset multiple is accumulated in the following manner: in adjacent target phases, if the difference between the later target phase and the earlier target phase is less than a first preset value and greater than a second preset value, then the preset multiple is 0; if the difference between the later target phase and the earlier target phase is greater than the first preset value, then the preset multiple is decreased by 1; if the difference between the later target phase and the earlier target phase is less than the second preset value, then the preset multiple is increased by 1. In this case, the true phase change (i.e., phase change parameter) of the chamber of the fiber optic Fabry-Perot sensor can be obtained.

[0026] Furthermore, in the demodulation method according to the second aspect of the present invention, optionally, a first signal matched with a first beam, a second signal matched with a second beam, and a third signal matched with a third beam are used at a preset sampling rate, wherein the first preset value is greater than 0 and matches the preset sampling rate, and the first preset value and the second preset value are opposites of each other. In this case, accurate phase change parameters can be obtained.

[0027] According to the present invention, a demodulation system and demodulation method based on a fiber optic Fabry-Perot sensor for measuring parameters with high reliability and robustness can be provided. Attached Figure Description

[0028] The invention will now be explained in further detail by way of example only with reference to the accompanying drawings, in which:

[0029] Figure 1 This is a schematic diagram illustrating the structure of the fiber optic Fabry-Perot multicavity sensor according to an embodiment of the present invention.

[0030] Figure 2 This is a schematic diagram illustrating the structure of the demodulation system according to an embodiment of the present invention.

[0031] Figure 3 This is a schematic diagram illustrating the principle of the fiber optic Fabry-Perot multicavity sensor according to an embodiment of the present invention.

[0032] Figure 4 This is a schematic diagram illustrating the beam splitting module involved in an embodiment of the present invention.

[0033] Figure 5 This is a schematic diagram illustrating the 3dB bandwidth involved in an embodiment of the present invention.

[0034] Figure 6 This is a schematic flowchart illustrating the demodulation method according to an embodiment of the present invention.

[0035] Figure 7 This is a schematic diagram illustrating the compensation of the target phase according to an embodiment of the present invention.

[0036] Figure 8 This is a schematic flowchart illustrating another embodiment of the demodulation method involved in the present invention. Detailed Implementation

[0037] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same reference numerals are used for the same parts, and repeated descriptions are omitted. Furthermore, the drawings are merely schematic diagrams, and the proportions of the parts or the shapes of the parts may differ from the actual figures.

[0038] It should be noted that the terms "comprising" and "having" and any variations thereof in this invention, such as a process, method, system, product, or device that includes or has a series of steps or units, are not necessarily limited to those steps or units that are explicitly listed, but may include or have other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0039] Furthermore, the subheadings and similar terms used in the following description of this invention are not intended to limit the content or scope of this invention; they are merely for reading guidance. Such subheadings should not be construed as dividing the content of the article, nor should the content under a subheading be limited to the scope of that subheading.

[0040] A first aspect of the present invention provides a demodulation system for obtaining phase change parameters based on a fiber optic Fabry-Perot sensor, exhibiting high reliability and robustness. In some examples, the demodulation system for obtaining phase change parameters based on a fiber optic Fabry-Perot sensor may also be referred to as a demodulation system based on a fiber optic Fabry-Perot sensor, a demodulation system for obtaining phase change parameters, a fiber optic sensor demodulation system for obtaining phase change parameters, or a demodulation system.

[0041] In some examples, the demodulation system can obtain at least one parameter from the interference phenomenon observed by a fiber optic Fabry-Perot sensor. Specifically, the fiber optic Fabry-Perot sensor can have multiple reflecting surfaces that reflect laser beams. The multiple reflecting surfaces of the fiber optic Fabry-Perot sensor can form multiple reflected beams, and the demodulation system can receive these multiple reflected beams and calculate parameters based on the interference phenomenon between them. These parameters can refer to phase change parameters.

[0042] In some examples, the phase change parameter can be related to the cavity length of the fiber optic Fabry-Perot sensor; in other words, the phase change parameter can change accordingly when the cavity length of the fiber optic Fabry-Perot sensor changes. In some examples, the phase change parameter can be a continuously changing dynamic parameter. In some examples, the phase change parameter can be a relatively stationary static parameter. In some examples, obtaining at least one phase change parameter through a demodulation system can include both static and dynamic parameters.

[0043] In some examples, the cavity length of the fiber optic Fabry-Perot sensor is dependent on the environment in which it is located. In such cases, the phase change parameter can be used to reflect physical phenomena such as vibration, dynamic pressure, acoustic / ultrasonic signals, or temperature.

[0044] This invention discloses a fiber optic sensor demodulation system for obtaining phase change parameters. It is a demodulation system that obtains phase change parameters using a fiber optic Fabry-Perot sensor. The system comprises: a transmitting module, a fiber optic Fabry-Perot sensor, a beam splitting module, a filtering module, a receiving module, and a processing module. The transmitting module emits a light beam with a preset wavelength range. The fiber optic Fabry-Perot sensor receives the light beam and forms a reflected beam. The beam splitting module is disposed between the transmitting module and the fiber optic Fabry-Perot sensor. The beam splitting module has at least three ports: a first port connecting to the transmitting module, a second port connecting to the fiber optic Fabry-Perot sensor, and a third port connecting to the filtering module. The filtering module includes a first filtering unit, a second filtering unit, and a third filtering unit. A filtering unit filters the reflected beam to obtain a first beam with a first center wavelength, a second filtering unit filters the reflected beam to obtain a second beam with a second center wavelength, and a third filtering unit filters the reflected beam to obtain a third beam with a third center wavelength. The first, second, and third filtering units are broadband filters. A receiving module receives the first, second, and third beams and converts them into a first signal, a second signal, and a third signal, respectively. A processing module calculates the phase change parameters of the fiber optic Fabry-Perot sensor based on the first signal, the second signal, the third signal, the first center wavelength, the second center wavelength, the third center wavelength, and the initial cavity length of the shortest cavity of the fiber optic Fabry-Perot sensor.

[0045] In this configuration, multiple reflective surfaces of the fiber optic Fabry-Perot sensor can be used to emit and reflect light beams, forming a reflected beam. A beam splitting module then divides the reflected beam into a first beam, a second beam, and a third beam. These beams are received and filtered to obtain a first beam with a first center wavelength, a second beam with a second center wavelength, and a third beam with a third center wavelength. This reduces the impact of fiber jitter on phase change parameters. Furthermore, since the first, second, and third filter units are broadband filters, they can filter out the interference signal (interference light) from the shortest cavity (i.e., the first chamber).

[0046] The demodulation system involved in this invention is further illustrated below with reference to the accompanying drawings.

[0047] Figure 1 This is a schematic diagram illustrating the structure of the fiber optic Fabry-Perot multicavity sensor according to an embodiment of the present invention. Figure 2 This is a schematic diagram showing the structure of the demodulation system 2 according to an embodiment of the present invention. Figure 3 This is a schematic diagram illustrating the principle of the fiber optic Fabry-Perot multicavity sensor according to an embodiment of the present invention.

[0048] In some examples, such as Figure 1As shown, the demodulation system 2 may include a transmission module 21.

[0049] In some examples, the emitting module 21 can be used to emit a light beam. In some examples, the light beam can refer to a laser, in which case the accuracy of the measurement can be improved.

[0050] In some examples, the transmitting module 21 can be used to emit at least one beam of light having a preset wavelength range. In some examples, the preset wavelength range can be a large wavelength range, for example, a preset wavelength range of 1260 nm to 1625 nm. In some examples, the preset wavelength range can be a narrow wavelength range, for example, a preset wavelength range of 1525 nm to 1610 nm. In some examples, the preset wavelength range can be continuous. In some examples, the preset wavelength range can be discontinuous.

[0051] In some examples, the transmitting module 21 can be used to emit a beam of light having a preset wavelength range. In this case, it is possible to make the first beam, the second beam, and the third beam (described later) have the same optical parameters. In some examples, the optical parameters may include at least one of phase, amplitude (light intensity), and polarization state.

[0052] In some examples, the transmitting module 21 can be used to transmit multiple beams with preset wavelength ranges. In some examples, the three beams with preset wavelength ranges can have different center wavelengths. Specifically, the transmitting module 21 can simultaneously transmit a first beam with a first center wavelength, a second beam with a second center wavelength, and a third beam with a third center wavelength. In this case, beams with different center wavelengths can be transmitted to the fiber optic Fabry-Perot sensor 22, thereby forming reflected beams with different center wavelengths.

[0053] In some examples, the multiple beams emitted by the emitting module 21 may have the same optical parameters, such as the beams emitted by the emitting module 21 having the same phase, the beams emitted by the emitting module 21 having the same amplitude (light intensity), and the beams emitted by the emitting module 21 having the same polarization state.

[0054] In some examples, the transmitting module 21 can be an ASE broadband light source module, an SLED broadband light source, a narrow linewidth laser light source, an SLD broadband light source, a desktop laser light source, or a modular laser light source, etc.

[0055] In some examples, such as Figure 2As shown, the demodulation system 2 may also include a beam splitter module 23. In some examples, the beam splitter module 23 may be a fiber optic circulator. Specifically, the demodulation system 2 may also include a fiber optic circulator disposed between the transmitting module 21 and the fiber optic Fabry-Perot sensor 22, in which case the direction of the beam can be adjusted using the fiber optic circulator.

[0056] Figure 4 This is a schematic diagram showing the beam splitting module 23 according to an embodiment of the present invention.

[0057] In some examples, such as Figure 4 As shown, the beam splitter 23 may have at least three ports, which may include a first port connected to the transmitting module 21, a second port connected to the fiber optic Fabry-Perot sensor 22, and a third port connected to the filter module 24. In this case, since the beam splitter 23 is a non-reversible device, that is, a beam entering from the first port can exit from the second port, and a beam entering from the second port can exit from the third port, the beam emitted by the transmitting module 21 can reach the fiber optic Fabry-Perot sensor 22 from the second port after entering the first port, and the reflected beam can reach the filter module 24 from the third port after entering the second port. This allows for adjustment of the beam direction, and the beam splitter 23 can guide different types of beams to different components or devices.

[0058] In some examples, the first port of the beam splitter 23 can be connected to the transmitting module 21 via optical fiber, the second port of the beam splitter 23 can be connected to the fiber optic Fabry-Perot sensor 22 via optical fiber, and the third port of the beam splitter 23 can be connected to the filtering module 24 via optical fiber. In this case, due to the flexibility of optical fiber, the relative positions of the beam splitter 23, the transmitting module 21, the fiber optic Fabry-Perot sensor 22, and the filtering module 24 can be adjusted using optical fiber.

[0059] In some examples, such as Figure 2 As shown, demodulation system 2 may include fiber optic Fabry-Perot sensor 22. In some examples, such as Figure 3As shown, the fiber optic Fabry-Perot sensor 22 can receive a light beam and form a reflected beam. In some examples, the fiber optic Fabry-Perot sensor 22 can have at least two reflecting surfaces. Specifically, the fiber optic Fabry-Perot sensor 22 can have a first reflecting surface 11, a second reflecting surface 12, and a first cavity 10 between the first reflecting surface 11 and the second reflecting surface 12. The first reflecting surface 11 can be parallel to the second reflecting surface 12, where the first reflecting surface 11 can be the reflecting surface where the light beam arrives first. After the light beam arrives at the first reflecting surface 11, it can form a first reflected beam and a first transmitted beam. After the first transmitted beam arrives at the second reflecting surface 12, it can form a second reflected beam. The first reflected beam can interfere with the second reflected beam, and the interference phenomenon can be related to the cavity length of the first cavity 10. In this case, since the cavity length of the first cavity 10 changes when the parameters change, the parameters near the fiber optic Fabry-Perot sensor 22 can be obtained through the interference phenomenon.

[0060] In some examples, the fiber optic Fabry-Perot sensor 22 can be fabricated using microelectromechanical systems (MEMS). In this case, the fiber optic Fabry-Perot sensor 22 can have multiple reflective surfaces and multiple chambers, thereby enabling the creation of a fiber optic Fabry-Perot multi-cavity sensor. In other words, the fiber optic Fabry-Perot sensor 22 can be a fiber optic Fabry-Perot multi-cavity sensor.

[0061] In some examples, a fiber optic Fabry-Perot multicavity sensor may include at least three reflective surfaces and at least three chambers. Specifically, a fiber optic Fabry-Perot multicavity sensor may include at least three reflective surfaces, and any two reflective surfaces can form a Fabry-Perot (FP) interferometer cavity.

[0062] In some examples, such as Figure 3 As shown, a fiber optic Fabry-Perot multicavity sensor may include at least a first reflecting surface 11, a second reflecting surface 12, and a third reflecting surface 13 arranged sequentially, and these three surfaces may be parallel to each other. In some examples, the first reflecting surface 11 and the second reflecting surface 12 may cooperate to form a first cavity 10, the second reflecting surface 12 and the third reflecting surface 13 may cooperate to form a second cavity 20, and the first reflecting surface 11 and the third reflecting surface 13 may cooperate to form a third cavity 30. In this case, interference information from the first cavity can be extracted by defining the coherence length.

[0063] In some examples, among the first chamber 10, the second chamber 20, and the third chamber 30, the first chamber 10 may also be referred to as a sensitive chamber or a sensitive unit. In some examples, the first chamber 10 has the shortest length.

[0064] In some examples, the chambers of the fiber optic Fabry-Perot sensor 22 (which may include a first chamber 10, a second chamber 20, and a third chamber 30) may introduce different optical path differences.

[0065] In some examples, the coherence length can be obtained based on the first center wavelength, the second center wavelength, and the third center wavelength, where the optical path difference introduced by the first chamber 10 is less than the coherence length. In this case, since the coherence length represents the distance over which a coherent wave (e.g., an electromagnetic wave) propagates with a certain degree of coherence, a larger coherence length results in better coherence, which in turn makes the interference phenomenon more pronounced.

[0066] In some examples, the coherence length satisfies the following formula:

[0067] l1=λ1 2 / Δλ1

[0068] l2=λ2 2 / Δλ2

[0069] l3=λ3 2 / Δλ3

[0070] Wherein, l1 represents the coherence length of the first beam with the first center wavelength, λ1 represents the first center wavelength, Δλ1 represents the 3dB bandwidth of the first beam (3dB bandwidth of the first filter unit), l2 represents the coherence length of the second beam with the second center wavelength, λ2 represents the second center wavelength, Δλ2 represents the 3dB bandwidth of the second beam (3dB bandwidth of the second filter unit), l3 represents the coherence length of the third beam with the third center wavelength, λ3 represents the third center wavelength (3dB bandwidth of the third filter unit), and Δλ3 represents the 3dB bandwidth of the third beam.

[0071] Figure 5 This is a schematic diagram illustrating the 3dB bandwidth involved in an embodiment of the present invention.

[0072] In some examples, such as Figure 5 As shown, the 3dB bandwidth of the first filter unit can be the wavelength range defined when the highest point of the power spectral density of the first filter unit drops to 1 / 2.

[0073] In some examples, the coherence length can be greater than the cavity length of the first chamber 10. In some examples, the coherence length can be less than a first preset multiple of the optical path difference introduced by any one of the chambers. In some examples, the coherence length can be less than a first preset multiple of the optical path difference introduced by any one of the chambers other than the first chamber 10. In some examples, the first preset multiple can be greater than 3, for example, the first preset multiple can be 3.0, 3.1, 3.2, 3.6, 4.0, 5.0, 10.0, 20, 30, or 60. In this case, since the coherence length must be greater than the cavity length of the chamber to have a significant interference phenomenon, the mutual interference between multiple reflecting surfaces can be eliminated by using the coherence length, so that the interference phenomenon exists only mainly in the first chamber 10 of the fiber optic FP sensor 22, thereby realizing the demodulation of the fiber optic FP sensor.

[0074] In some examples, such as Figure 2 As shown, the demodulation system 2 may include a filter module 24.

[0075] In some examples, the filter module 24 can be used to receive the reflected beam and split the reflected beam into a first beam, a second beam, and a third beam.

[0076] In some examples, the filter module 24 may have an optical fiber coupler. In this case, the optical fiber coupler can split the beam received by the filter module 24 into multiple beams and release multiple beams from the port.

[0077] In some examples, the fiber optic coupler can be a 1×3 fiber optic coupler. The 1×3 fiber optic coupler can split the beam received by the filter module 24 into three beams (including a first beam, a second beam, and a third beam), and release the first beam, the second beam, and the third beam respectively using the respective ends of the three-ended port.

[0078] In some examples, the ports of the fiber optic coupler can be connected to multiple filter units, one by one. In some examples, the multiple filter units can be connected to the receiver module 25 (described later).

[0079] In some examples, multiple filter units may include a first filter unit, a second filter unit, and a third filter unit. In this case, if the emitting unit emits multiple beams with different center wavelengths, the filter module 24 can divide the beams into a first beam with a first center wavelength, a second beam with a second center wavelength, and a third beam with a third center wavelength based on the different center wavelengths; if the emitting unit emits a beam with a wide preset wavelength range, the filter module 24 can use the filter units to divide the beam into a first beam, a second beam, and a third beam, and then filter the first beam, the second beam, and the third beam to obtain a first beam with a first center wavelength, a second beam with a second center wavelength, and a third beam with a third center wavelength.

[0080] In some examples, the first filter unit can filter the light beam (e.g., the first light beam) passing through the first filter unit at a first center wavelength. In this case, light with a wavelength close to the first center wavelength can pass through the first filter unit, while light with a wavelength far from the first center wavelength can be blocked from passing through the first filter unit, thereby forming a first light beam with the first center wavelength.

[0081] In some examples, the second filter unit can filter the light beam (e.g., a second beam) passing through the second filter unit at a second center wavelength. In this case, light with wavelengths close to the second center wavelength can pass through the second filter unit, while light with wavelengths far from the second center wavelength can be blocked from passing through the second filter unit, thereby forming a second beam with a second center wavelength.

[0082] In some examples, the third filter unit can filter the light beam (e.g., the third beam) passing through the third filter unit at a third center wavelength. In this case, light with a wavelength close to the third center wavelength can pass through the third filter unit, while light with a wavelength far from the third center wavelength can be blocked from passing through the third filter unit, thereby forming a third beam with a third center wavelength.

[0083] In some examples, the first, second, and third center wavelengths can be different. In some examples, the first center wavelength can be between 1260 nm and 1625 nm, the second center wavelength can be between 1260 nm and 1625 nm, and the third center wavelength can be between 1260 nm and 1625 nm. In other examples, the first, second, and third center wavelengths are different. For example, the first center wavelength can be 1550 nm, the second center wavelength can be 1570 nm, and the third center wavelength can be 1590 nm. In this case, orthogonal signals can be obtained using signals with different center wavelengths, and thus the target phase can be calculated.

[0084] In some examples, the first, second, and third filter units are broadband filters. Broadband filters can have a 3dB bandwidth length between 10 nm and 30 nm, preferably between 13 nm and 20 nm. For example, the first filter unit filters the light beam (e.g., the first beam) passing through it at a first center wavelength of 1550 nm. Since the wavelength range defined by the highest point of the power spectral density of the first filter unit dropping to half its maximum is 1543 nm to 1557 nm, the 3dB bandwidth length of the first filter unit can be 14 nm, thus classifying it as a broadband filter. In this case, since the broadband filter can filter out the interference signal from the shortest cavity (of the first cavity 10), the phase change parameters of the first cavity 10 can be calculated.

[0085] In some examples, the first center wavelength, the second center wavelength, and the third center wavelength are within a preset wavelength range, and the 3dB bandwidth of the first filter unit, the 3dB bandwidth of the second filter unit, and the 3dB bandwidth of the third filter unit are within a preset wavelength range of the emission module 21. In this case, a first beam having a first center wavelength, a second beam having a second center wavelength, and a third beam having a third center wavelength can be formed.

[0086] In some examples, such as Figure 2 As shown, the demodulation system 2 may include a receiving module 25. In this case, the receiving module 25 is capable of receiving the first beam, the second beam, and the third beam and converting them into a first signal, a second signal, and a third signal, respectively.

[0087] In some examples, the signal can refer to an analog signal or a digital signal. Specifically, the receiving module 25 can convert the first beam into a first analog signal or a first digital signal, the receiving module 25 can convert the second beam into a first analog signal or a second digital signal, and the receiving module 25 can convert the third beam into a third analog signal or a third digital signal.

[0088] In some examples, the receiving module 25 may include a sensing unit and a sampling circuit. In some examples, the sensing unit may be connected to the filtering module 24. Specifically, the sensing unit may be a three-channel photodetector, with the first, second, and third filtering units connected to the three channels of the sensing unit via optical fibers, and the sampling circuit may be a three-channel sampling circuit, with each of its three channels paired and connected to one of the three channels of the sensing unit. In this case, the sensing unit can receive the first, second, and third light beams, convert them into first, second, and third analog signals, respectively, and the sampling circuit can convert these signals into first, second, and third digital signals, respectively. The phase change parameters can then be calculated using these digital signals.

[0089] In some examples, the receiving module 25 may not include a sampling circuit. In this case, the sensing unit can receive the first beam, the second beam, and the third beam, and convert the first beam, the second beam, and the third beam into a first analog signal, a second analog signal, and a third analog signal, respectively. Then, the phase change parameters can be obtained by calculation using the first analog signal, the second analog signal, and the third analog signal.

[0090] In some examples, the sampling circuit can sample the first analog signal, the second analog signal, and the third analog signal at a preset sampling rate. In some examples, the sampling rate can refer to the sampling frequency.

[0091] In some examples, such as Figure 2 As shown, the demodulation system 2 may include a processing module 26, which can calculate the phase change parameters of the fiber optic Fabry-Perot sensor 22 based on the first signal, the second signal, the third signal, the first center wavelength, the second center wavelength, the third center wavelength, and the initial cavity length of the shortest cavity of the fiber optic Fabry-Perot sensor 22.

[0092] In some examples, processing module 26 may include a data processing unit and a signal transmission unit.

[0093] In some examples, the data processing unit can perform calculation steps such as calculating coherence length, calculating initial phase, calculating light intensity, phase compensation, and calculating phase change parameters, and the signal transmission unit can transmit the processed data to the host computer.

[0094] A second aspect of the present invention provides a demodulation method for measuring parameters based on a fiber optic Fabry-Perot sensor 22, exhibiting high reliability and robustness. In some examples, the demodulation system 2 for measuring parameters based on the fiber optic Fabry-Perot sensor 22 may also be referred to as a demodulation method based on the fiber optic Fabry-Perot sensor 22 or a fiber optic sensor demodulation system 2 for obtaining phase change parameters; the demodulation system 2 for measuring parameters based on the fiber optic Fabry-Perot sensor 22 may also be simply referred to as a demodulation method.

[0095] In some examples, the demodulation method of the present invention can be applied to various demodulation systems 2. Preferably, the demodulation method of the present invention can be applied to the demodulation system 2 described above.

[0096] Figure 6 This is a schematic flowchart illustrating the demodulation method according to an embodiment of the present invention.

[0097] In some examples, such as Figure 6 As shown, the demodulation method may include: obtaining the initial cavity length of the shortest chamber of the fiber optic Fabry-Perot sensor 22 (step S100); receiving beams from the fiber optic Fabry-Perot sensor 22, namely a first beam having a first center wavelength, a second beam having a second center wavelength, and a third beam having a third center wavelength (step S200); calculating a first initial phase, a second initial phase, and a third initial phase (step S300); calculating a target phase (step S400); and compensating the target phase to obtain the phase change parameter (step S500).

[0098] In this configuration, by filtering the first, second, and third beams, a first beam with a first center wavelength, a second beam with a second center wavelength, and a third beam with a third center wavelength can be obtained, reducing the impact of fiber jitter on phase change parameters. Simultaneously, the target phase can be conveniently calculated using formulas, and then compensated for to obtain phase change parameters, thereby meeting the demodulation speed requirements for dynamic parameters such as vibration, dynamic pressure, and acoustic / ultrasonic signals.

[0099] In some examples, in step S100, the cavity length of the shortest cavity (first cavity 10) of the fiber optic Fabry-Perot sensor 22 can be measured. In some examples, the cavity length of the first cavity 10 can be measured using a sensor cavity length testing device.

[0100] In some examples, in step S200, the reflected beam formed by the fiber optic Fabry-Perot sensor 22 can be obtained. In some examples, a beam with a first center wavelength, a second center wavelength, and a third center wavelength can be obtained by the beam splitter 23 and the filter 24. In some examples, as described above, the first center wavelength, the second center wavelength, and the third center wavelength can be different from each other.

[0101] In some examples, in step S300, a first initial phase, a second initial phase, and a third initial phase are calculated. The first initial phase, the second initial phase, and the third initial phase can satisfy the formula:

[0102] θ1=4πnL0 / λ1,

[0103] θ2=4πnL0 / λ2,

[0104] θ3=4πnL0 / λ3,

[0105] Wherein, θ1 represents the first initial phase obtained based on the first center wavelength and cavity length, θ2 represents the second initial phase obtained based on the second center wavelength and cavity length, θ3 represents the third initial phase obtained based on the third center wavelength and cavity length, n represents the refractive index of the medium, L0 represents the cavity length of the shortest cavity of the fiber optic Fabry-Perot sensor 22, λ1 represents the first center wavelength, λ2 represents the second center wavelength, and λ3 represents the third center wavelength.

[0106] In some examples, step S400 may calculate the target phase. In some examples, step S400 may be performed collaboratively by receiving module 25 and processing module 26. Specifically, receiving module 25 may receive a first beam with a first center wavelength and convert it into a first signal with the first center wavelength; receiving module 25 may receive a second beam with a second center wavelength and convert it into a second signal with the second center wavelength; and receiving module 25 may receive a third beam with a third center wavelength and convert it into a third signal with the third center wavelength. Processing module 26 may calculate the target phase based on the first beam, second beam, third beam, first initial phase, second initial phase, and third initial phase.

[0107] In some examples, the first beam, the second beam, and the third beam can be represented by the following formula:

[0108] I1=A+Bcosθ1

[0109] I² = A + Bcosθ²

[0110] I3=A+Bcosθ3

[0111] Wherein, I1 represents the light intensity of the first beam, I2 represents the light intensity of the second beam, I3 represents the light intensity of the third beam, A represents the DC component of the interference signal, B represents the amplitude of the interference signal, θ1 represents the initial phase of the first beam in the first chamber 10 of the fiber optic Fabry-Perot sensor 22, θ2 represents the initial phase of the second beam in the first chamber 10 of the fiber optic Fabry-Perot sensor 22, and θ3 represents the initial phase of the third beam in the first chamber 10 of the fiber optic Fabry-Perot sensor 22.

[0112] In some examples, the first, second, and third beams, after the cavity length of the first chamber 10 of the fiber optic Fabry-Perot sensor 22 changes, can be represented by the following formula:

[0113] I1 = A + Bcos(θ1 + Δθ)

[0114] I² = A + Bcos(θ² + Δθ)

[0115] I3 = A + Bcos(θ3 + Δθ)

[0116] Wherein, △θ represents the phase change (i.e., the target phase) caused by the change in the cavity length of the first chamber 10 of the fiber optic Fabry-Perot sensor 22.

[0117] In some examples, processing module 26 can correct three optical signals into two quadrature phase signals. The two quadrature phase signals can be obtained using the following formula:

[0118]

[0119]

[0120] F1 and F2 represent mutually orthogonal signals.

[0121] The formulas for calculating the initial phase θ1 of the first beam in the first chamber 10 of the fiber optic Fabry-Perot sensor 22, the initial phase θ2 of the second beam in the first chamber 10 of the fiber optic Fabry-Perot sensor 22, and the initial phase θ3 of the third beam in the first chamber 10 of the fiber optic Fabry-Perot sensor 22 can be:

[0122] θ1=4πnL0 / λ1

[0123] θ2=4πnL0 / λ2

[0124] θ3=4πnL0 / λ3

[0125] Where n represents the refractive index of the medium, L0 represents the initial cavity length of the first chamber 10, λ1 represents the first center wavelength, λ2 represents the second center wavelength, and λ3 represents the third center wavelength.

[0126] In some examples, the target phase of the sensor can be obtained using the arctangent algorithm. The formula for calculating the target phase is as follows:

[0127]

[0128] In some examples, the target phase can satisfy the formula:

[0129]

[0130] Figure 7 This is a schematic diagram illustrating the compensation of the target phase according to an embodiment of the present invention.

[0131] In some examples, in step S500, the processing module 26 can compensate for the target phase to obtain phase change parameters.

[0132] In some examples, such as Figure 7 As shown, the difference between the target phase and the phase change parameter that matches the target phase is a preset multiple of the compensation value. In some examples, the compensation value is π, and the preset multiple is an integer. In this case, since the target phase obtained using the arctangent algorithm is in the range of -π / 2 to π / 2, a phase jump will occur when the target phase exceeds this range. Therefore, compensating for the target phase can obtain a more accurate phase change value.

[0133] In some examples, the target phase can be compensated for to obtain the phase change parameters using the following method. The formula for calculating the phase change parameters is as follows:

[0134] Δθ'=Δθ±kπ

[0135] Where k represents a preset multiple, Δθ represents the target phase, and Δθ' represents the actual phase change (i.e., phase change parameter) of the chamber of the fiber optic Fabry-Perot sensor 22.

[0136] In some examples, the initial value of the preset multiplier can be set to 0. The preset multiplier is accumulated as follows: After the above steps, multiple target phases can be obtained. Among adjacent target phases, if the difference between the later target phase and the earlier target phase is less than a first preset value or greater than a second preset value, the preset multiplier remains unchanged. If the difference between the later target phase and the earlier target phase is greater than the first preset value, the preset multiplier is decreased by 1. If the difference between the later target phase and the earlier target phase is less than the second preset value, the preset multiplier is increased by 1. In other words, among adjacent target phases, if the difference between the later target phase and the earlier target phase is less than the first preset value or greater than the second preset value, the preset multiplier k remains unchanged; if the difference between the later target phase and the earlier target phase is greater than the first preset value, the preset multiplier k can be replaced with k-1; if the difference between the later target phase and the earlier target phase is less than the second preset value, the preset multiplier k can be replaced with k+1. In this case, the true phase change (i.e., phase change parameter) of the chamber of the fiber optic Fabry-Perot sensor 22 can be obtained.

[0137] In some examples, among the adjacent phase change parameters obtained through compensation, the difference between the later phase change parameter and the earlier phase change parameter is less than a first preset value and greater than a second preset value.

[0138] In some examples, the first preset value can be greater than 0 and less than π / 2. In some examples, the second preset value can be less than 0 and greater than -π / 2. In some examples, the first and second preset values ​​can be opposites of each other. In these cases, accurate phase change parameters can be obtained.

[0139] In some examples, the first preset value can be matched with the preset sampling rate; specifically, the larger the preset sampling rate, the larger the first preset value can be. In this case, the size of the first preset value can be controlled by adjusting the preset sampling rate.

[0140] Figure 8 This is a flowchart illustrating another embodiment of the demodulation method involved in the present invention.

[0141] like Figure 8 As shown, the demodulation method disclosed herein may further include determining whether the absolute value of the cavity length change is greater than a threshold (step S600). If the absolute value of the cavity length change is greater than the threshold, the initial cavity length of the first chamber 10 is replaced and step S200 (step S700) is executed. If the absolute value of the cavity length change is not greater than the threshold, the external measured parameters are obtained based on the phase change parameters (step S800). These steps enable the cavity length change to maintain a small error over a large range.

[0142] In some examples, in step S600, the change in cavity length can be calculated and it can be determined whether the change in cavity length is greater than a threshold.

[0143] In some examples, after obtaining the phase change parameters, the cavity length change is obtained based on the target phase change parameters. The formula for calculating the cavity length change can be:

[0144] ΔL==λ2Δθ' / 4π

[0145] Where ΔL represents the cavity length change, λ2 represents the second center wavelength, and Δθ' represents the phase change parameter.

[0146] In some examples, a threshold can be preset. When the absolute value of the cavity length change is greater than the threshold, step S700 can be executed. In other words, when the threshold and the cavity length change satisfy the formula |ΔL|≥L′, step S700 can be executed. Here, L′ represents the threshold.

[0147] In some examples, the threshold value can range from 300nm to 700nm, and a smaller threshold will result in a smaller demodulation error.

[0148] In some examples, in step S700, the initial cavity length of the first cavity 10 can be replaced with the target cavity length (i.e., the actual cavity length of the first cavity 10). In other words, the phase change parameter can be recalculated after using the target cavity length as the initial cavity length.

[0149] In some examples, after replacing the initial cavity length of the first chamber 10 with the target cavity length, step S200 can be re-executed (see [reference]). Figure 8 In some examples, the phase change parameters can be recalculated after replacing the initial cavity length of the first chamber 10 with the target cavity length.

[0150] In some examples, in step S700, the target cavity length can be calculated based on the cavity length change and the initial cavity length. In some examples, the formula for calculating the target cavity length can be:

[0151] L=L0+ΔL

[0152] In some examples, step S800 can obtain the external measured parameter based on the phase change parameter. In other examples, the change of the external measured parameter can be obtained based on the sensitivity of the calibrated sensor and the actual cavity length.

[0153] While the invention has been specifically described above in conjunction with the accompanying drawings and examples, it is to be understood that the above description does not limit the invention in any way. Those skilled in the art can make modifications and variations to the invention as needed without departing from its essential spirit and scope, and all such modifications and variations fall within the scope of the invention.

Claims

1. A method of phase demodulation of a fiber-optic Fabry-Perot sensor comprising at least three reflecting surfaces and at least three cavities, characterized in that, The phase demodulation method includes: Obtain the initial cavity length of the shortest chamber of the fiber optic Fabry-Perot sensor. Emit a beam of light with a preset wavelength range. The at least three reflecting surfaces reflect the emitted beam and form a reflected beam. The reflected beam is received and divided into a first beam having a first center wavelength, a second beam having a second center wavelength, and a third beam having a third center wavelength. The system receives the first beam, the second beam, and the third beam, and converts them into a first signal, a second signal, and a third signal, respectively. The phase change parameters of the fiber optic Fabry-Perot sensor are calculated based on the first signal, the second signal, the third signal, the first center wavelength, the second center wavelength, the third center wavelength, and the initial cavity length of the shortest chamber of the fiber optic Fabry-Perot sensor. The first center wavelength, the second center wavelength, and the third center wavelength are all different. The external measured parameters are obtained based on the phase change parameters. After obtaining the phase change parameters, the cavity length change is obtained based on the phase change parameters. If the absolute value of the cavity length change is greater than a threshold, the target cavity length is calculated based on the cavity length change and the initial cavity length. The phase change parameters are then recalculated using the target cavity length as the initial cavity length. The calculation of the phase change parameters includes: Calculate the first initial phase, the second initial phase, and the third initial phase, which satisfy the formula: ， Wherein, θ1 represents the first initial phase, θ2 represents the second initial phase, θ3 represents the third initial phase, n represents the refractive index of the medium, L0 represents the initial cavity length, λ1 represents the first center wavelength, λ2 represents the second center wavelength, and λ3 represents the third center wavelength; Calculate the target phase, which satisfies the formula: ， Wherein, △θ' represents the target phase, I1 represents the intensity of the first beam, I2 represents the intensity of the second beam, I3 represents the intensity of the third beam, θ1 represents the first initial phase, θ2 represents the second initial phase, and θ3 represents the third initial phase; The target phase is compensated to obtain the phase change parameter. The difference between the target phase and the phase change parameter that matches the target phase is a preset multiple of the compensation value. The compensation value is π, and the preset multiple is an integer.

2. The phase demodulation method according to claim 1, characterized in that, When calculating the phase change parameter, the initial value of the preset multiple is 0, and the preset multiple is accumulated in the following manner: In adjacent target phases, If the difference between the phase of the later target and the phase of the earlier target is less than a first preset value and greater than a second preset value, then the preset multiple remains unchanged. If the difference between the phase of the later target and the phase of the earlier target is greater than a first preset value, then the preset multiplier is reduced by 1. If the difference between the target phase in the later stage and the target phase in the earlier stage is less than the second preset value, then the preset multiple is increased by 1.

3. The phase demodulation method according to claim 2, characterized in that, The first preset value is greater than 0 and less than π / 2. The second preset value is less than 0 and greater than -π / 2, and the first preset value and the second preset value are opposites of each other.

4. The phase demodulation method according to claim 2, characterized in that, The first preset value is matched with a preset sampling rate, and the first signal, the second signal, and the third signal are sampled at the preset sampling rate.

5. A demodulation system based on a fiber-optic Fabry-Perot sensor, which is a demodulation system for obtaining a phase change parameter using the phase demodulation method of the fiber-optic Fabry-Perot sensor according to any one of claims 1 to 4, characterized in that, The demodulation system includes: a transmitting module, a fiber optic Fabry-Perot sensor, a beam splitting module, a filtering module, a receiving module, and a processing module. The transmitting module emits a light beam with a preset wavelength range. The fiber optic Fabry-Perot sensor receives the light beam and forms a reflected beam. A beam splitting module is disposed between the transmitting module and the fiber optic Fabry-Perot sensor. The beam splitting module has at least three ports, including a first port connected to the transmitting module, a second port connected to the fiber optic Fabry-Perot sensor, and a third port connected to the filtering module. The filtering module receives the reflected light beam from the fiber optic Fabry-Perot sensor and splits the reflected light beam into a first beam with a first center wavelength, a second beam with a second center wavelength, and a third beam with a third center wavelength. The receiving module receives the first beam, the second beam, and the third beam and converts them into a first signal, a second signal, and a third signal, respectively. The processing module calculates the phase change parameters of the fiber optic Fabry-Perot sensor based on the first signal, the second signal, the third signal, the first center wavelength, the second center wavelength, the third center wavelength, and the initial cavity length of the shortest cavity of the fiber optic Fabry-Perot sensor.

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