CN119573861A - Cavity length modulated FP interferometric optical acoustic sensor and calibration method - Google Patents

Abstract

The present disclosure provides a cavity length modulated FP interference type optical acoustic sensor and a calibration method, the method comprising: providing an optical acoustic sensor, comprising a laser light source, an optical interference type acoustic probe, a photoelectric detector, a voltage output module, a piezoelectric ceramic and a signal acquisition and processing module; outputting an alternating voltage applied to the piezoelectric ceramic through the voltage output module, controlling the piezoelectric ceramic to drive the optical fiber or the grating to generate single-frequency vibration, so that the interference cavity of the optical interference type acoustic probe responds to the single-frequency vibration to modulate the optical signal; after the optical signal is converted into an electrical signal through the photoelectric detector, Fourier transforming the electrical signal through the signal acquisition and processing module to obtain a spectrum data digital signal; identifying a main frequency signal and a frequency multiplication signal from the spectrum data digital signal through the signal acquisition and processing module; when the intensity of the frequency multiplication signal does not meet a preset condition, automatically controlling the voltage output module through a preset program to adjust the bias voltage applied to the piezoelectric ceramic to adjust the cavity length of the interference cavity.

Description

Cavity length modulation FP interference type optical acoustic sensor and calibration method

Technical Field

The disclosure relates to the technical field of optical acoustic sensing, in particular to a cavity length modulation FP interference type optical acoustic sensor and a calibration method.

Background

Because of the advantages of high detection precision of light waves, wide optical fiber working frequency band, small transmission loss and the like, compared with the traditional electrical acoustic sensor, the optical acoustic sensor has higher sensitivity and signal-to-noise ratio and wider frequency band response. Meanwhile, the optical acoustic sensor has the advantages of simple structure, low cost, electromagnetic interference resistance and the like, and can be applied to environments such as high temperature, high pressure, strong corrosion, strong radiation and the like in which the traditional electrical acoustic sensor is difficult to work normally. The optical acoustic sensor has wide application prospect in the fields of military, industry, environmental protection and the like, and can be used for industrial fault diagnosis, noise control, safety field monitoring, acoustic test of medical equipment and detection of urban noise. Among them, the optical interference type acoustic sensor has the outstanding advantages of high accuracy, high sensitivity and wide frequency range, but has the bottleneck problem that the practical application is restricted when the working point is deviated.

The optical interferometry acoustic sensor exhibits optimal acoustic response sensitivity, linearity and dynamic range at an optimal operating point. However, due to manufacturing errors and environmental influences, particularly environmental temperature fluctuations, the static operating point of the sensor may shift, resulting in a reduced response of the sensor to acoustic waves, limiting its practical application potential. To address this challenge, the current mainstream solution is to design a multi-wavelength or broadband detection optical path, and perform phase demodulation by using a quadrature detection signal, so as to alleviate the problem of operating point offset.

Although the method for alleviating the problem of the shift of the working point by designing a multi-wavelength or broadband detection light path and utilizing the orthogonal detection signal to carry out phase demodulation is very effective, the method is highly dependent on a high-precision optical component and a complex algorithm, thereby obviously improving the cost and the energy consumption of the system and preventing the large-scale application of the system. Therefore, it is becoming particularly urgent to find a simpler and more efficient solution to the problem of offset of the operating point of the optical interference type acoustic sensor. The stability of the sensor performance is improved, the cost is reduced, and the wide application and development of the optical interference type acoustic sensor in more fields are promoted.

Disclosure of Invention

Accordingly, it is a primary object of the present disclosure to provide a cavity length modulated FP interferometric optical acoustic sensor and a calibration method, so as to at least partially solve at least one of the above-mentioned technical problems.

In order to achieve the above purpose, the technical scheme of the present disclosure is as follows:

The calibration method comprises the steps of providing a cavity length modulation FP interference type optical acoustic sensor, wherein the optical acoustic sensor comprises a laser light source, an optical interference type acoustic probe, a photoelectric detector, a voltage output module, piezoelectric ceramics and a signal acquisition and processing module, the piezoelectric ceramics are arranged in the optical interference type acoustic probe, the optical interference type acoustic probe comprises an interference cavity with one end face being an optical fiber end face or a grating surface, alternating voltage is output through the voltage output module to be applied to the piezoelectric ceramics, the piezoelectric ceramics is controlled to drive an optical fiber or a grating of the optical interference type acoustic probe to vibrate in a single frequency mode, the interference cavity of the optical interference type acoustic probe responds to the single frequency vibration, optical signals sent by the laser light source are modulated and output optical signals modulated by the single frequency vibration, after the optical signals are received through the photoelectric detector and converted into electric signals, fourier transform processing is carried out on the electric signals through the signal acquisition and processing module, frequency spectrum data digital signals are obtained, the main frequency signals and frequency doubling signals of the same frequency and frequency doubling signals of the main frequency are identified from the frequency spectrum data digital signals through the signal acquisition and processing module, the frequency doubling signals are automatically controlled under the condition that the frequency doubling conditions are met, the preset condition is not met, the preset condition is met, the intensity is met, the optical signal is adjusted, and the preset condition is met, and the preset condition is achieved, and the pressure is controlled through the pressure is met, and the preset condition is achieved through the pressure, the pressure is adjusted, and the piezoelectric cavity.

As another aspect of the disclosure, a cavity length modulation FP interferometric optical acoustic sensor is provided, which comprises a laser light source, an optical interferometric acoustic probe, a voltage output module, a signal acquisition and processing module, a photoelectric detector, a main frequency signal and a frequency multiplication signal, wherein the laser light source is suitable for emitting optical signals, the optical interferometric acoustic probe comprises an interferometric cavity with an end face being an optical fiber end face or a grating surface, the interferometric cavity is suitable for responding to mechanical vibration capable of causing the cavity length change of the interferometric cavity and modulating the optical signals from the laser light source, the photoelectric detector is suitable for converting the modulated optical signals from the optical interferometric acoustic probe into electric signals, the piezoelectric ceramic is fixedly connected with one end of an optical fiber or a grating of the interferometric cavity and is suitable for generating single-frequency vibration under the action of alternating voltage, the single-frequency vibration is enabled to act on the interferometric cavity, the elongation is changed under the action of bias voltage to adjust the cavity length of the interferometric cavity, the voltage output module is suitable for applying alternating voltage and bias voltage to the piezoelectric ceramic, the signal acquisition and processing module is electrically connected with the voltage output module, the signal acquisition and the processing module is suitable for carrying out Fourier transform processing on the electric signals from the photoelectric detector to obtain frequency spectrum data digital signals, the main frequency signals and frequency doubling signals of the same frequency from the frequency spectrum data digital signals, the main frequency signals and the main frequency signals under the condition that the single frequency vibration and the frequency doubling signals are automatically different from the preset condition, the preset condition is met, and the preset condition of the preset condition is met, and the strength is adjusted, and the preset condition is achieved by the preset condition.

As can be seen from the above technical solutions, the cavity length modulation FP interferometric optical acoustic sensor and the calibration method of the present disclosure have at least one or a part of the following advantages:

(1) The method is based on the frequency multiplication signal caused by the deviation of the working point as a discriminant standard, and can automatically identify the state of the working point of the optical acoustic sensor and control the optical acoustic sensor to be adjusted to the optimal position by driving the piezoelectric ceramic to provide a reference signal and adjusting the cavity length.

(2) The method and the device have the advantages that the wavelength of the laser is not required to be repeatedly adjusted by means of an external reference sound source, the high-precision optical assembly and the complex algorithm are not required to be relied on, the working state of the optical acoustic sensor is stable, the performance requirement on the laser is low, in-situ (or on-site) real-time adjustment can be realized, the control precision is high, and the like, so that the method and the device are particularly suitable for acoustic detection equipment working in complex severe environments.

(3) The portable device has the advantages of small volume, low power consumption, convenient application of the portable device, simple structure, low cost, easy realization and extremely high popularization and application value because no additional optical devices and optical path design are added.

Drawings

The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of embodiments thereof with reference to the accompanying drawings in which:

FIG. 1 is a schematic block diagram of a cavity length modulated FP interferometric optical acoustic sensor of embodiment 1 of the present disclosure;

FIG. 2 is a schematic diagram of the structure of an optical interference type acoustic probe according to embodiment 1 of the present disclosure;

FIG. 3 is a method of calibrating a cavity length modulated FP interferometric optical acoustic sensor of embodiment 2 of the present disclosure;

FIG. 4 is a flow chart of a calibration procedure in the optical acoustic sensor method of embodiment 2 of the present disclosure;

FIG. 5A is a first spectral data plot of the dominant frequency portion of the optical acoustic sensor of the present disclosure in a state of operating point deviation;

FIG. 5B is a first spectral data plot of a frequency doubled portion of the optical acoustic sensor of the present disclosure in a state of operating point deviation;

FIG. 6A is a second spectral data plot of the dominant frequency portion of the optical acoustic sensor of the present disclosure in a state of operating point deviation;

FIG. 6B is a second spectral data plot of a frequency doubled portion of the optical acoustic sensor of the present disclosure in a state of operating point deviation;

FIG. 7A is a second spectral data plot of the dominant frequency portion of the optical acoustic sensor of the present disclosure at an optimal state of operation;

fig. 7B is a second spectral data plot of the frequency multiplied portion of the optical acoustic sensor of the present disclosure at its operating point to an optimal state.

Reference numerals illustrate:

1-laser light source

2-Optical interference type acoustic probe

21-Elastic vibrating diaphragm

22-Optical fiber

23-Connection mechanism

231-Insulator

232-Optical fiber ferrule

24-Base

25-Probe internal Cavity

3-Photodetector

4-Voltage output module

5-Piezoceramics

51-Wire

6-Signal acquisition and processing module

7-Circuit module

71-Power supply unit

72-Preamplification processing unit

73-Piezoelectric ceramic driving amplifying unit

74-Power interface

75 A-first input port

75 B-first output port

75 C-second input port

75 D-second output port

Detailed Description

For the purposes of promoting an understanding of the principles and advantages of the disclosure, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The terms "comprises," "comprising," and/or the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components.

In the drawings or description, like or identical parts are provided with the same reference numerals. Implementations not shown or described in the drawings are forms known to those of ordinary skill in the art. Additionally, although examples of parameters including particular values may be provided herein, it should be appreciated that the parameters need not be exactly equal to the corresponding values, but may be approximated to the corresponding values within acceptable error margins or design constraints. Directional terms such as "upper", "lower", "front", "rear", "left", "right", etc. mentioned in the embodiments are merely directions referring to the drawings. Accordingly, the directional terminology is used for purposes of illustration and is not intended to limit the scope of the disclosure.

All terms, including technical and scientific terms, used herein have the meaning commonly understood by one of ordinary skill in the art unless otherwise defined. It should be noted that the terms used herein should be construed to have meanings consistent with the context of the present specification and should not be construed in an idealized or overly formal manner.

The invention provides a cavity length modulation FP interference type optical acoustic sensor and a calibration method, which take a frequency multiplication signal caused by working point deviation as a discrimination reference, utilize piezoelectric ceramic to control the cavity length and combine with an automatic adjustment algorithm, realize the calibration of the working point based on a conventional optical interference type acoustic sensing system, enable the working point of the optical acoustic sensor to be kept at an optimal position, and obtain optimal acoustic response performance. The method can realize automatic in-situ real-time adjustment of the working point of the optical interference type optical acoustic sensor, is based on a conventional acoustic sensing system, has low power consumption, small volume, low cost, easy realization, does not need an external sound source, and is particularly suitable for portable acoustic detection equipment working in complex environments.

Example 1

In a first exemplary embodiment of the present disclosure, a cavity length modulation FP interferometric optical acoustic sensor is provided, and fig. 1 is a schematic block diagram of the structure of the cavity length modulation FP interferometric optical acoustic sensor of embodiment 1 of the present disclosure, and as shown in fig. 1, the optical acoustic sensor of the present disclosure mainly includes a laser light source 1, an optical interference type acoustic probe 2, a photodetector 3, a voltage output module 4, a piezoelectric ceramic 5, and a signal acquisition and processing module 6. The laser light source 1 is suitable for emitting light signals, the optical interference type acoustic probe 2 comprises an interference cavity with an optical fiber end face or a grating surface, the optical interference type acoustic probe 2 is suitable for responding to mechanical vibration which can cause the cavity length change of the interference cavity and modulating the light signals from the laser light source, the photoelectric detector 3 is suitable for converting the modulated light signals from the optical interference type acoustic probe 2 into electric signals, the piezoelectric ceramic 5 is fixedly connected with one end of the optical fiber or the grating forming the interference cavity and is suitable for driving the optical fiber to vibrate in a single frequency mode under the action of alternating voltage so that the single frequency vibration acts on the interference cavity and the elongation is changed under the action of bias voltage to adjust the cavity length of the interference cavity, the voltage output module 4 is suitable for applying alternating voltage and bias voltage to the piezoelectric ceramic, the signal acquisition and processing module 6 is electrically connected with the voltage output module 4 and is suitable for carrying out Fourier transform processing on the electric signals from the photoelectric detector 3 to obtain frequency spectrum data digital signals, the main frequency signals and frequency doubling signals of the same frequency with the single frequency vibration are identified from the frequency spectrum digital signals, and the frequency doubling signals of the main frequency signals are automatically controlled by the preset voltage output module under the condition that the intensity of the frequency doubling signals does not meet preset condition, the preset condition is achieved, the preset condition of the preset voltage is met, the preset condition is met, and the long-time condition is adjusted, and the interference condition is achieved.

It should be noted that, the optical interference type acoustic probe 2 of the present disclosure has an interference cavity, one surface of the interference cavity is an elastic diaphragm with reflectivity, and is suitable for sensing acoustic signals to vibrate, and the other surface is a fixed surface with semi-transparent and semi-reflective characteristics, which may be an end surface of an optical fiber after optical polishing or a grating surface. When the acoustic signal acts on the optical interference type acoustic probe 2, the elastic vibrating diaphragm is deformed, and the cavity length of the interference cavity is modulated by the acoustic signal.

However, due to factors such as manufacturing errors and environmental influences, particularly the influence of environmental temperature fluctuation, the working point of the optical acoustic sensor when in a static state can deviate from the optimal position, so that the response characteristic of the optical acoustic sensor to acoustic signals can be reduced, signal distortion is caused, and the accuracy and sensitivity of actual detection are limited.

The design principle of the embodiment of the disclosure is that a frequency multiplication signal caused by deviation of a working point is taken as a discrimination standard, a signal acquisition and processing module 6 is utilized to identify a main frequency signal with the same frequency as single frequency vibration generated by driving a piezoelectric ceramic 5 by a voltage output module 4 and a frequency multiplication signal of the main frequency signal, the intensity of the frequency multiplication signal is obtained, the intensity of the frequency multiplication signal is compared with a preset condition to judge whether the working point of an optical acoustic sensor deviates, if the preset condition is not met, the working point is judged to deviate, the offset voltage output by the voltage output module 4 is automatically regulated through a preset program, the interference cavity length of the optical interference type acoustic probe can be changed until the intensity of the frequency multiplication signal is regulated to meet the preset condition, and the working point is regulated to the optimal position at the moment, thereby realizing the calibration of the working point.

The respective constituent parts of the optical acoustic sensor of the present embodiment are described in detail below.

In this embodiment, the laser light source 1 may be a single wavelength light source, the wavelength of which may be tunable or non-tunable, and in various embodiments, the laser light source 1 and/or the photodetector 3 and the circuit module 7 may be integrated as one body, but is not limited thereto.

In this embodiment, as shown in fig. 1, the optical interference type acoustic probe 2 may be optically connected to the laser light source 1 and the photodetector 3, respectively, and the optical connection may be implemented by an optical fiber, but is not limited thereto, and in different embodiments, may be implemented by an optical waveguide, or may be implemented by spatial optical path transmission.

Fig. 2 is a schematic structural diagram of an optical interference type acoustic probe according to embodiment 1 of the present disclosure, as shown in fig. 2, the optical interference type acoustic probe 2 mainly includes an elastic diaphragm 21, an optical fiber 22 and a connection mechanism 23, wherein the elastic diaphragm 21 is adapted to sense acoustic signals to generate mechanical vibration and has a reflective surface, one end surface of the optical fiber 22 is disposed opposite to the reflective surface of the elastic diaphragm 21 after optical polishing to form a fabry-perot (FP) interference cavity, and the connection mechanism 23 is adapted to fixedly connect the optical fiber 22 with the piezoelectric ceramic 5. Further, the connection mechanism 23 may comprise an insulator 231 and a fiber stub 232, wherein the insulator 231 is adapted to mount the piezoelectric ceramic 5 and the fiber stub 231, and the fiber stub 232 is adapted to mount the optical fiber 22. Although not limited thereto, in other embodiments, the optical fiber 22 may be replaced by a grating, and the grating is disposed opposite to the reflective surface of the elastic diaphragm 21, so as to form a fabry-perot interference cavity.

It should be noted that, as shown in fig. 2, the optical interference type acoustic probe 2 further includes a base 24 and an elastic diaphragm 21 to form a probe internal cavity 25, and the interference cavity is only a space between the light emitting end surface of the optical fiber and the elastic diaphragm, and belongs to a part of the probe internal cavity 25. The piezoceramic is located within the probe interior cavity 25 but not within the interference cavity.

In the present embodiment, the inverse piezoelectric effect of the piezoelectric ceramic 5 is utilized, and when a voltage signal is applied to the piezoelectric ceramic 4, it is deformed, and the cavity length of the interference cavity is changed by the piezoelectric ceramic 4. By controlling the piezoelectric ceramic to generate single-frequency vibration, the interference cavity of the optical interference type acoustic probe 2 responds to the single-frequency vibration to modulate the optical signal emitted by the laser light source 1 and output the modulated optical signal, wherein the modulated optical signal comprises the optical signal with the same frequency as the single-frequency vibration.

Further, the piezoelectric ceramic 5 of the present embodiment may be a common piezoelectric ceramic such as lead zirconate titanate (PZT), lithium niobate (LiNbO ₃) single crystal piezoelectric ceramic, or barium titanate (BaTiO ₃) piezoelectric ceramic, preferably PZT5 piezoelectric ceramic, which has a high inverse piezoelectric effect, but is not limited thereto. The single-frequency vibration generated by the piezoelectric ceramic 5 is a high-frequency vibration, and the vibration frequency may be 3kHz or more, for example, 3kHz, 3.5kHz, 4kHz, 4.5kHz, 5kHz, 5.5kHz, 6kHz, 6.5kHz, 7kHz, 7.5kHz, 8kHz, or the like. The proper vibration frequency is selected to be in the frequency response range of the optical interference type acoustic probe 2, and lower background noise is sought to make the intensity measurement of double frequency more accurate.

In this embodiment, the voltage output module 4 is electrically connected to the piezoelectric ceramic 5 through the lead 51, and further, the ac voltage applied to the piezoelectric ceramic 5 by the voltage output module 4 is suitable for driving the piezoelectric ceramic 5 to generate the single-frequency vibration. The bias voltage applied to the piezoelectric ceramic 5 by the voltage output module 4 is suitable for adjusting the elongation of the piezoelectric ceramic 5.

In this embodiment, the signal collecting and processing module 6 and the voltage output module 4 may be independently operated through electrical connection, or integrated into one body, for example, integrated into a single chip microcomputer or FPGA to achieve the same function, but not limited thereto.

In this embodiment, as shown in fig. 1, the optical acoustic sensor further includes a circuit module including a pre-amplification processing unit 72, a piezoelectric ceramic driving amplification unit 73 and a power supply unit 71, wherein the pre-amplification processing unit 72 is adapted to provide a bias voltage for the photodetector 3, and amplify and output an electrical signal output from the photodetector 3 to the signal acquisition and processing module 6, the piezoelectric ceramic driving amplification unit 73 is adapted to amplify and output a voltage signal output from the voltage output module 4 to the piezoelectric ceramic 5, and the power supply unit 71 provides power for the pre-amplification processing unit 72, the piezoelectric ceramic driving amplification unit 73, the voltage output module 4 and the signal acquisition and processing module 5.

Specifically, as shown in fig. 1, the circuit module 7 further includes a power interface 74, a first input port 75a, a first output port 75b, a second input port 75c, and a second output port 75d. Wherein an external power source is connected to the power source interface 74 and connected to the power source unit 71. The pre-amplification processing unit 72 is electrically connected with the photodetector 3 through a first input port 75a, the pre-amplification processing unit 72 is electrically connected with the signal acquisition and processing module 6 through a first output port 75b, the piezoelectric ceramic driving amplification module 73 is electrically connected with the voltage output module 4 through a second input port 75c, and the piezoelectric ceramic driving amplification module 73 is electrically connected with the piezoelectric ceramic 5 through a second output port 75d.

The interference type optical acoustic sensor based on the present embodiment described above realizes calibration of the operating point thereof so as to maintain the operating point of the optical acoustic sensor at an optimal position, and obtain optimal acoustic response performance.

Example 2

In a second exemplary embodiment of the present disclosure, fig. 3 is a calibration method of a cavity length modulation FP interferometric optical acoustic sensor of embodiment 2 of the present disclosure, as shown in fig. 1 and 3, the calibration method of the embodiment of the present disclosure includes operations S1 to S5:

In operation S1, a cavity length modulation FP interference type optical acoustic sensor is provided, the optical acoustic sensor includes a laser light source 1, an optical interference type acoustic probe 2, a photodetector 3, a voltage output module 4, a piezoelectric ceramic 5, and a signal acquisition and processing module 6, the piezoelectric ceramic 5 is disposed inside the optical interference type acoustic probe 2, and the optical interference type acoustic probe 2 includes an interference cavity with an end face being an optical fiber end face or a grating surface;

in this embodiment, the specific structure can be referred to the description of embodiment 1, and will not be described here.

In operation S2, an ac voltage is output by the voltage output module 4 to be applied to the piezoelectric ceramic 5, so that the piezoelectric ceramic 5 is controlled to drive the optical fiber or the grating of the optical interference type acoustic probe 2 to vibrate in a single frequency, so that the interference cavity responds to the single frequency vibration, modulates the optical signal emitted by the laser light source 1, and outputs the optical signal modulated by the single frequency vibration;

In this embodiment, the modulated optical signal includes an optical signal of the same frequency as the single frequency vibration whose frequency is within the frequency response range of the optical interference type acoustic probe 2.

In operation S3, after receiving the optical signal through the photodetector 3 and converting it into an electrical signal, fourier transform processing is performed on the electrical signal through the signal acquisition and processing module 6 to obtain a spectrum data digital signal;

In this embodiment, the electric signal received by the signal acquisition and processing module 6 is preferably amplified by the pre-amplifying unit 72, and the electric signal also includes a main frequency signal with the same frequency as the frequency of the single-frequency vibration.

In operation S4, a main frequency signal of the same frequency as the single frequency vibration and a frequency multiplication signal of the main frequency signal are identified from the spectrum data digital signal through the signal acquisition and processing module 6;

The frequency-doubled signal may include a frequency-doubled signal with a frequency 2 times that of the main frequency signal, but is not limited thereto, and may be a higher order signal. The intensity of the frequency-multiplied signal is an intensity level, and in different embodiments, the intensity may be the absolute intensity of the frequency-multiplied signal, the relative intensity of the frequency-multiplied signal with respect to the noise floor of the spectrum data digital signal, or the relative intensity of the frequency-multiplied signal with respect to the main frequency signal.

In the embodiment, the main frequency signal is a high frequency signal with the frequency larger than 3KHz, the main frequency signal is positioned in the frequency response range of the optical interference type acoustic probe, and noise interference near the frequency multiplication signal is small.

In operation S5, if the intensity of the frequency multiplication signal does not satisfy the preset condition, the voltage output module 4 is automatically controlled to adjust the bias voltage applied to the piezoelectric ceramic 5 by the preset program, so as to adjust the cavity length of the interference cavity until the intensity of the frequency multiplication signal satisfies the preset condition.

In this embodiment, the preset condition is that the intensity of the frequency multiplication signal is less than or equal to a preset threshold value, fig. 4 is a flowchart of a calibration procedure in the optical acoustic sensor method of embodiment 2 of the present disclosure, and as shown in fig. 4, the preset procedure includes a calibration procedure, which may be executed by the signal acquisition and processing module, and specifically includes (1) inputting the intensity of the frequency multiplication signal into the calibration procedure, (2) calculating a deviation value between the intensity of the frequency multiplication signal and the preset threshold value, (3) judging whether the deviation value is greater than 0, and under the condition that the deviation value is greater than 0, determining that the intensity of the frequency multiplication signal does not satisfy the preset condition, (4) controlling the voltage output module 4 to adjust the bias voltage applied to the piezoelectric ceramic 5 until the intensity of the frequency multiplication signal satisfies the preset condition, and (5) stopping adjusting the bias voltage.

In different embodiments, the signal acquisition and processing module 6 may continuously monitor and determine the deviation of the working point, find the deviation problem and automatically start and operate the calibration procedure to perform modulation, but not limited thereto, and may stop the calibration procedure so far, wait for the manual operation of the peripheral device, and then start the calibration procedure.

As shown in fig. 4, the calibration method of the embodiment further includes, when the intensity of the frequency multiplication signal meets a preset condition, that is, when the intensity of the frequency multiplication signal is less than or equal to a preset threshold, judging that the working point of the optical acoustic sensor is not deviated, locking the bias voltage applied to the piezoelectric ceramic 5, so that the optical acoustic sensor works under the extension of the piezoelectric ceramic 5 regulated by the current bias voltage.

Further, the intensity of the frequency-multiplied signal is specifically the intensity ratio of the frequency-multiplied signal to the main frequency signal, and the preset threshold is 0.0001 to 0.5, for example, 0.0001, 0.0005, 0.001, 0.005, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, etc., and preferably, the preset discrimination threshold is 0.01 to 0.1.

Of course, not limited thereto, in other embodiments, the intensity of the multiplied signal is the intensity ratio of the multiplied signal to the noise floor of the spectrum digital signal, and the preset threshold is 1 to 5, for example, 1,2,3, 4, 5, and preferably 1 to 3.

In the present embodiment, the operation S5 may specifically include sub-operations S51 to S53:

In sub-operation S51, feedback control operation is performed by the signal acquisition and processing module according to the deviation value between the intensity of the frequency multiplication signal and the preset threshold value, so as to obtain an operation result, wherein the algorithm of the feedback control operation may be a PID algorithm, but is not limited thereto, and may be a high-efficiency algorithm optimized or simplified by the user.

In sub-operation S52, the bias voltage applied to the piezoelectric ceramic is adjusted by the voltage output module according to the operation result to adjust the cavity length of the interference cavity;

In sub-operation S53, operations of obtaining the frequency multiplication signal, feedback control operation, and adjusting the bias voltage are repeated for the optical interference type acoustic probe with the adjusted cavity length until the intensity of the frequency multiplication signal is less than or equal to the preset threshold.

In this embodiment, the comparison between the intensity of the multiplied frequency signal and the preset threshold is used to determine the deviation of the working point of the optical acoustic sensor, and the offset voltage output by the monolithic electro-mechanical output module 4 is adjusted to realize the calibration of the working point of the deviation of the optical acoustic sensor according to the following criteria:

The interference cavity length of the optical interference type acoustic probe 2 is the shortest distance from the optical fiber end face or the grating surface close to the elastic vibrating diaphragm: Wherein, the method comprises the steps of, For the static cavity length of the optical interference type acoustic probe 2,Is the length variation of the interference cavity of the optical interference type acoustic probe.

The relation between the intensity of the output optical signal of the optical interference type acoustic probe 2 and the length of the interference cavity is as follows:

(1)

Wherein, the intensity of the main frequency signal is:

the intensity of the multiplied signal is:

is the wavelength of the laser light source, Is the intensity of the direct current signal;

When the optical acoustic sensor is at the optimal working point, the relation between the wavelength of the laser light source and the length of the static cavity of the interference cavity of the optical interference type acoustic probe is that (m=0、1、2、3、......)。

This is because the number of the components of the device,(M=0, 1,2, 3.,) at the time of,The frequency multiplication signal disappears, and the obtained time domain response data of the optical acoustic sensor only comprises the direct current signal and the main frequency signal, namely when the condition of the optimal working point is met(M=0, 1,2, 3,) the output optical signal intensity is only related to the optical interference type acoustic probe interference cavity length variation amount caused by the acoustic wave actionThe ac quantity related and used to characterize the acoustic signal has the highest duty cycle:

It is thereby determined that the operating point of the optical acoustic sensor is not deviated.

When the wavelength lambda of the laser light source and the static cavity length d ₀ of the Fabry-Perot interference type acoustic probe do not meet the relation(M=0, 1,2, 3.,) at the time of,The frequency multiplication signal exists, and the obtained time domain response data of the optical acoustic sensor comprises the direct current signal, the frequency multiplication signal and the main frequency signal, so that the working point of the optical acoustic sensor is judged to deviate.

In the present embodiment, the principle can be fully explained by the time domain signal outputted from the optical interference type acoustic sensor and the spectrum data sequence obtained by the operation. As shown in fig. 5A, 5B, 6A and 6B, when the operating point deviates during the calibration process, the calculated spectrum data column shows that the peak value of the frequency doubling signal is higher at the moment, and as shown in fig. 7A and 7B, when the operating point is adjusted to the optimal position after the calibration, the calculated spectrum data column shows that the peak intensity of the main frequency signal is enhanced at the moment, the frequency doubling signal is very weak and almost disappears. It can be seen that the calibration method of the present disclosure takes the frequency multiplied signal as a reference, and facilitates adjusting the working point to an optimal position by adjusting the cavity length.

Thus, embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It should be noted that, in the drawings or the text of the specification, implementations not shown or described are all forms known to those of ordinary skill in the art, and not described in detail. Furthermore, the above definitions of the elements and methods are not limited to the specific structures, shapes or modes mentioned in the embodiments, and may be modified or replaced simply by one skilled in the art, for example:

In the embodiment, the number of the photodetectors may be more than 1, so that the number of the photodetectors is used for detecting different output optical signals, and the number of the photodetectors input to the signal acquisition and processing module may be more than 1.

The embodiments of the present disclosure are described above. These examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Although the embodiments are described above separately, this does not mean that the measures in the embodiments cannot be used advantageously in combination. The scope of the disclosure is defined by the appended claims and equivalents thereof. Various alternatives and modifications can be made by those skilled in the art without departing from the scope of the disclosure, and such alternatives and modifications are intended to fall within the scope of the disclosure.

Claims (10)

1. A method of calibrating a cavity length modulated FP interferometric optical acoustic sensor, comprising:

Providing a cavity length modulation FP interference type optical acoustic sensor, wherein the optical acoustic sensor comprises a laser light source, an optical interference type acoustic probe, a photoelectric detector, a voltage output module, piezoelectric ceramics and a signal acquisition and processing module, the piezoelectric ceramics are arranged in the optical interference type acoustic probe, and the optical interference type acoustic probe comprises an interference cavity with an end face being an optical fiber end face or a grating surface;

The voltage output module outputs alternating voltage to be applied to the piezoelectric ceramic, and controls the piezoelectric ceramic to drive the optical fiber or the grating of the optical interference type acoustic probe to vibrate in a single frequency mode, so that the interference cavity responds to the single frequency vibration, modulates the optical signal emitted by the laser light source, and outputs the optical signal modulated by the single frequency vibration;

After receiving the optical signal through a photoelectric detector and converting the optical signal into an electric signal, carrying out Fourier transform processing on the electric signal through the signal acquisition and processing module to obtain a frequency spectrum data digital signal;

Identifying a main frequency signal with the same frequency as the single-frequency vibration and a frequency multiplication signal of the main frequency signal from the frequency spectrum data digital signal through the signal acquisition and processing module;

and under the condition that the intensity of the frequency multiplication signal does not meet the preset condition, adjusting the cavity length of the interference cavity by automatically controlling the voltage output module to adjust the bias voltage applied to the piezoelectric ceramic through a preset program until the intensity of the frequency multiplication signal meets the preset condition.

2. The calibration method according to claim 1, wherein the preset condition is that the intensity of the frequency multiplication signal is less than or equal to a preset threshold value, and the step of adjusting the cavity length of the interference cavity by adjusting the bias voltage applied to the piezoelectric ceramic by the automatic control voltage output module of the preset program until the intensity of the frequency multiplication signal meets the preset condition comprises:

Performing feedback control operation according to the intensity of the frequency multiplication signal and the deviation value of the preset threshold value through the signal acquisition and processing module to obtain an operation result, wherein the algorithm of the feedback control operation is preferably a PID algorithm;

The bias voltage applied to the piezoelectric ceramic is regulated according to the operation result through the voltage output module so as to regulate the cavity length of the interference cavity;

and repeating the operations of obtaining the frequency multiplication signal, carrying out feedback control operation and adjusting the bias voltage aiming at the optical interference type acoustic probe with the adjusted cavity length until the intensity of the frequency multiplication signal is smaller than or equal to a preset threshold value.

3. The calibration method according to claim 1 or 2, further comprising determining that an operating point of the optical acoustic sensor is not deviated in a case where the intensity of the frequency-multiplied signal satisfies a preset condition, and locking a bias voltage applied to the piezoelectric ceramic.

4. Calibration method according to claim 2, wherein the intensity of the multiplied signal is the intensity ratio of the multiplied signal to the main frequency signal, the preset threshold value being 0.0001 to 0.5, preferably 0.01 to 0.1.

5. Calibration method according to claim 2, wherein the intensity of the multiplied signal is the intensity ratio of the multiplied signal to the noise floor of the spectral digital signal, the preset threshold being 1 to 5, preferably 1 to 3.

6. The calibration method of claim 1, wherein:

the main frequency signal is a high frequency signal with the frequency more than 3 kHz and/or

The frequency multiplication signal is a frequency doubling signal of the main frequency signal.

7. A cavity length modulated FP interferometric optical acoustic sensor comprising:

The laser light source is suitable for emitting optical signals;

The optical interference type acoustic probe comprises an interference cavity with an end face being an optical fiber end face or a grating surface, is suitable for responding to mechanical vibration which can cause the cavity length of the interference cavity to change, and modulates an optical signal from a laser light source;

The photoelectric detector is suitable for converting the modulated optical signal from the optical interference type acoustic probe into an electric signal;

The piezoelectric ceramic is fixedly connected with one end of an optical fiber or a grating forming the interference cavity and is suitable for generating single-frequency vibration under the action of alternating voltage, so that the single-frequency vibration acts on the interference cavity, and the elongation is changed under the action of bias voltage to adjust the cavity length of the interference cavity;

a voltage output module adapted to apply the alternating voltage and the bias voltage to the piezoelectric ceramic, and

The signal acquisition and processing module is electrically connected with the voltage output module and is suitable for carrying out Fourier transform processing on the electric signal from the photoelectric detector to obtain a frequency spectrum data digital signal, identifying a main frequency signal with the same frequency as the single frequency vibration and a frequency multiplication signal of the main frequency signal from the frequency spectrum data digital signal, and automatically controlling the voltage output module to output offset voltage through a preset program under the condition that the intensity of the frequency multiplication signal does not meet the preset condition until the intensity of the frequency multiplication signal meets the preset condition.

8. The optical acoustic sensor of claim 7, further comprising a circuit module, the circuit module comprising:

The pre-amplification processing unit is suitable for providing bias voltage for the photoelectric detector, amplifying the electric signal output by the photoelectric detector and outputting the electric signal to the signal acquisition and processing module;

A piezoelectric ceramic driving amplifying unit adapted to amplify the voltage signal outputted from the voltage output module and output the amplified voltage signal to the piezoelectric ceramic, and

And the power supply unit is used for supplying power to the pre-amplification processing unit, the piezoelectric ceramic driving amplification unit, the voltage output module and the signal acquisition and processing module.

9. The optical acoustic sensor of claim 7, wherein the optical interferometric acoustic probe comprises:

the elastic vibrating diaphragm is suitable for sensing acoustic signals to generate mechanical vibration and is provided with a reflecting surface;

An optical fiber, one end face of which is arranged opposite to the reflecting face of the elastic vibrating diaphragm after optical polishing to form a Fabry-Perot interference cavity, and

The connecting mechanism is suitable for fixedly connecting the optical fiber with the piezoelectric ceramic.

10. The optical acoustic sensor of claim 7, wherein the optical interferometric acoustic probe comprises:

the elastic vibrating diaphragm is suitable for sensing acoustic signals to generate mechanical vibration and is provided with a reflecting surface;

a grating arranged opposite to the reflecting surface of the elastic diaphragm to form a Fabry-Perot interference cavity, and

And the connecting mechanism is suitable for fixedly connecting the grating with the piezoelectric ceramic.