CN114543971B - FP interference type sound wave detector and sound wave detection method - Google Patents
FP interference type sound wave detector and sound wave detection method Download PDFInfo
- Publication number
- CN114543971B CN114543971B CN202210167330.4A CN202210167330A CN114543971B CN 114543971 B CN114543971 B CN 114543971B CN 202210167330 A CN202210167330 A CN 202210167330A CN 114543971 B CN114543971 B CN 114543971B
- Authority
- CN
- China
- Prior art keywords
- phase
- spectrum
- demodulation
- sound wave
- real
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
- G01H9/006—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors the vibrations causing a variation in the relative position of the end of a fibre and another element
Abstract
The invention discloses an FP interference type sound wave detector and a sound wave detection method, which belong to the technical field of sound wave detection and comprise a light source, an optical fiber circulator, an FP sensing head, a spectrum real-time acquisition module and a signal processing demodulation module. The FP sensing head is composed of an optical fiber collimator, a ceramic ferrule, a metal sleeve and a thin film, and the optical fiber collimator is designed to a certain extent. By using the improved Fourier phase demodulation algorithm, the spectral phase variation which is in direct proportion to the cavity length variation can be obtained, and the improved demodulation algorithm greatly widens the dynamic range of the detection system. Aiming at the extrinsic high-fineness FP sensor, the phase demodulation method provided by the invention can realize phase multiplication and increase the phase sensitivity of the sensor by performing Fourier phase demodulation at a high-order characteristic frequency peak on a Fourier spectrum of a spectrum.
Description
Technical Field
The invention belongs to the technical field of sound wave detection, and particularly relates to an FP (Fabry-Perot) interference type sound wave detector and a sound wave detection method.
Background
The sound wave detection technology has wide application prospect in the fields of infrastructure, medical health, national defense and military, disaster early warning and the like. The currently practical acoustic wave detectors are mainly capacitive and piezoelectric electrical acoustic wave detectors. Although the structure mechanism of the electric sensor is simple and the sensitivity is good, the electric sensor has great application limitation in the environments of strong electromagnetism, inflammability and explosiveness, long-distance transmission and the like.
The optical fiber acoustic wave sensor is anti-electromagnetic interference, easy to miniaturize in size, high in sensitivity, anti-electromagnetic interference, easy to multiplex and network, and avoids many problems of an electrical sensor. In the past, the research of acoustic wave sensors pursues the goals of high sensitivity, large dynamic range, stable performance and simple structure, and FP (Fabry-Perot) interference type optical fiber acoustic wave sensors have the simplest structure, high sensitivity, low noise level and easy miniaturization, show great potential, and how to optimally design the sensitive structural unit and the optical detection structure of the sensor is greatly emphasized by researchers.
The quality of the demodulation method of the acoustic wave signal can greatly influence the detection performance of the system, and the method is an important research direction of the optical fiber acoustic wave sensor. Common demodulation methods of the interference type acoustic wave sensor include a bevel edge demodulation method and a phase demodulation method. The phase demodulation method can directly demodulate the phase of the output signal of the interferometer, has high sensitivity, large dynamic range and strong anti-interference, and solves the defect that the working wavelength needs to lock the Q point of the interference spectrum in the bevel edge demodulation method.
Common phase demodulation methods include a phase generation carrier method, a 3 × 3 coupler method and a spectrum demodulation method, and the former two methods all belong to passive homodyne demodulation methods. The phase carrier generation demodulation method needs to generate strict carriers, and the demodulation algorithm is relatively complex; the 3 × 3 coupler method needs to use a 3 × 3 coupler, and needs to strictly control the coupling ratio to be 1; the improved 3 × 3 coupling method needs to be matched with algorithms such as ellipse fitting and the like, the requirements on the coupling ratio and the phase difference can be relaxed, but the demodulation of small signals is limited. For a spectrum demodulation algorithm, an interference phase is obtained by calculating an interference spectrum of an interferometer, and the method has the advantages of high precision, strong anti-interference and small influence of system noise, is suitable for demodulating low-frequency signals, but relates to a calculation step of calculating the phase reversely, and often introduces the problem of phase jump.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide an FP interference type sound wave detector and a sound wave detection method, aiming at realizing phase amplification by using a phase demodulation algorithm without changing the structure of a sensor, improving the phase sensitivity of a system and expanding the dynamic range of the system so as to realize the aims of simple structure, high sensitivity, low noise level and easy miniaturization.
One aspect of the present invention provides an FP interference type acoustic wave probe, including: the device comprises a light source, an optical fiber circulator, an FP sensing head, a spectrum real-time acquisition module and a signal processing demodulation module; the output end of the light source is connected with the input end of the optical fiber circulator; the optical fiber circulator comprises three ports, wherein a first port is connected to the output end of the optical fiber attenuator, a second port is connected with the FP sensing head, and a third port is connected to the input end of the spectrum real-time acquisition module; the input end of the spectrum real-time acquisition module is connected to the third port of the optical fiber circulator, and the output end of the spectrum real-time acquisition module is connected to the signal processing demodulation module. The optical fiber circulator is used for controlling optical signals generated by the light source to be transmitted to the FP sensing head, carries sound wave signals to be detected and then reflects the sound wave signals to the spectrum real-time acquisition module, the spectrum real-time acquisition module is used for acquiring spectrum signals in real time, and the signal processing demodulation module is used for demodulating phases and further demodulating the sound wave signals to be detected.
Further, the FP sensor head comprises: the optical fiber collimator, the inserting core, the sleeve and the thin film; the optical fiber collimator is inserted into the ferrule, the optical fiber collimator is fixed through the ferrule, the film is adhered to the end face of the sleeve, the ferrule is inserted into the sleeve and fixed, and a cavity is formed between the film and the end face of the optical fiber collimator to form the optical fiber external cavity type FP interferometer. The film is used for converting sound waves into film vibration, so that the cavity length of the FP cavity is changed, and sound wave detection is converted into phase change of demodulation interference light.
Still further, the fiber collimator includes: single mode fiber, antireflection coating, self-focusing lens and antireflection coating. The end face of the single-mode optical fiber is coupled with the inner surface of the self-focusing lens at an angle of 0 degree, and an antireflection film is covered to control return loss. The outer surface of the self-focusing lens is plated with a reflection increasing film to be used as one reflecting surface of the FP, the reflectivity needs to be designed according to the principle of multi-beam interference, the reflectivity is about 60% for the second-order peak, the reflectivity is about 70% for the third-order peak, and the other reflecting surface is a thin film. The light is transmitted in the optical fiber, the Gaussian beam is changed into parallel light through the self-focusing lens, and a part of light is reflected by the light splitting film and is coupled into the optical fiber again; the rest light is transmitted into the FP cavity, and multiple reflections occur in the cavity to form multiple-beam interference.
Furthermore, the reflectivity of the reflection increasing film on the end face of the self-focusing lens can be designed theoretically, and selected high-order characteristic frequency peaks on the Fourier spectrum of the spectrum are made more obvious by designing the reflectivity, so that the improved Fourier phase demodulation algorithm can carry out peak searching (the first three orders are more obvious).
Furthermore, the film is a circular film, and the material of the film is a film with high reflectivity, including metal films such as aluminum, gold, silver and the like, and also including a multi-layer composite film with high reflectivity, and the reflectivity is more than 95%.
Has the beneficial effects that: existing FP acoustic detectors, typically low-finesse sensors, consider only two-beam interference between reflected light that passes back and forth in the FP cavity and reflected light that does not enter the FP cavity. The FP acoustic wave detector provided by the invention can realize the multiplication of phase sensitivity on the premise of not increasing the structural size of the sensor. Because multi-beam interference needs to be generated, the single-mode fiber output light has a divergence angle, the light loss after multiple reflections is large, and the problem cannot be solved only by plating an antireflection film on the end face of the fiber. Therefore, the invention reduces the spatial scattering loss of light by using the optical fiber collimator, reduces the loss of multiple reflections of light in the cavity by plating the reflection increasing film and using the high-reflectivity film, forms a high-fineness reflection spectrum, and uses the reflection spectrum to perform phase demodulation to improve the sensitivity.
The invention provides a sound wave detection method based on the sound wave detector provided by the first aspect of the invention, aiming at the demodulation of the high-fineness FP interference spectrum, the method comprises the following steps:
s1, collecting a reflection spectrum of an FP sensing head in real time, wherein the reflection spectrum causes membrane vibration by sound waves to be measured, and the phase change of reflected interference light signals is generated;
s2, carrying out Fourier transform on the collected reflection spectrum, wherein a series of characteristic frequency peaks can be observed on the Fourier transform spectrum;
s3, locking a D-order frequency peak on the Fourier spectrum of each frame of reflection spectrum and obtaining a real part and an imaginary part of the frequency spectrum component, wherein D is more than or equal to 2;
s4, calculating the real part and the imaginary part of the frequency spectrum component at the D-order frequency to obtain phase change caused by sound waves, namely a phase demodulation result;
s5, performing phase cycle correction on the point in the phase demodulation result, where the absolute value of the phase difference between each moment and the previous moment is greater than a threshold value;
and S6, obtaining the acoustic wave signal to be detected according to the corrected phase demodulation result and the calibration result of the standard sensor.
Furthermore, the Fourier phase demodulation algorithm is suitable for double-beam interference and multi-beam interference, and phase multiplication can be realized for the multi-beam interference. The Fourier spectrum of the multi-beam interference reflection spectrum has a plurality of characteristic frequency peaks, and can be seen as the result of the superposition of countless two-beam interference. For interference between light reflected N times back and forth and M times back and forth within the cavity (M)>N), the interference intensity is:
the sum of all interference intensities satisfying M-N = D is:
reflected at the D-th characteristic frequency peak on the fourier spectrum, the D-th characteristic frequency can be expressed as: f. of D ≈2nD[L 0 +ΔL(t)]/λ 2 N is the refractive index of the medium in the cavity, L is the real-time cavity length, L 0 The initial cavity length, A, B are constants. At this time, the phase value 4 pi DnL/lambda obtained by demodulation at the D-th order characteristic frequency peak is the demodulation phase at the first order characteristic frequencyD times of.
Furthermore, the improved fourier phase demodulation algorithm proposed by the present invention differs in the order of the characteristic frequency peak used. For the high-fineness spectrum with the obvious high-order frequency peak, the first-order characteristic frequency with the largest amplitude is not selected for demodulation, but the high-order characteristic frequency is selected for Fourier phase demodulation, and the phase value after D multiplication can be demodulated. For each acquired frame of spectrum, assuming that the characteristic frequency of the D-th order is at the k-th point of the spectrum fourier spectrum, the k-th point of each frame of spectrum is locked to obtain the real part and the imaginary part of the spectrum component, and then the phase change caused by the sound wave can be expressed as:
Furthermore, the improved Fourier phase demodulation algorithm provided by the invention is improved in algorithm to a certain extent, and phase correction is carried out on the phase jump (when the phase value is greater than pi/2, the value obtained by the arctangent operation is different from the true value by integral times of pi) which is commonly existed in the arctangent operation in the phase demodulation. Selecting a threshold, carrying out cyclic detection on the phase signal demodulated by the Fourier phase demodulation algorithm, carrying out phase cyclic correction if the absolute value of the difference between the phase value of a certain point and the previous phase value is greater than the threshold, subtracting pi if the phase is greater than the previous phase value in the cyclic process, and adding pi if the phase is less than the previous phase value until the absolute value of the phase difference between two adjacent points is less than the threshold.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
(1) The invention provides an improved Fourier phase demodulation algorithm, which is matched with a high-fineness FP interference spectrum to lock the same high-order frequency peak on the Fourier spectrum of a reflection spectrum at different moments, and obtain the real part and the imaginary part of the frequency component at the position for demodulation. The idea can multiply the phase sensitivity of the sensing system without changing the structure and the size of the sensor, and the multiplication factor is related to the order D of the selected high-order characteristic frequency peak.
(2) The invention provides an improved Fourier phase demodulation algorithm, which is a spectrum demodulation algorithm, compared with a phase carrier generation method and a 3 x 3 coupling method, the phase carrier generation method and the 3 x 3 coupling method can demodulate both double-beam interference and multi-beam interference, are only suitable for the double-beam interference condition, have higher algorithm precision, have superior demodulation performance on small signals and have strong interference resistance. The method for correcting the circulating threshold value is used for correcting the phase mutation caused by the arc tangent operation in the phase demodulation, so that the dynamic range of the sensing system for detecting the sound wave is greatly expanded.
(3) The invention provides an improved Fourier phase demodulation algorithm, which has certain advantages compared with the conventional bevel edge demodulation method for demodulating a high-fineness spectrum. In the case of the hypotenuse demodulation, the slope of the hypotenuse of the high-fineness spectrum is larger, the sensitivity of the sensor can be improved, but the demodulation dynamic range is too small, the influence of the spectral jitter drift is large, and the wavelength locking is difficult. The spectrum demodulation algorithm is only limited by the sampling rate of the spectrum acquisition module, and a stable multiplied phase demodulation result can be obtained for low-frequency sound wave signals.
(4) The invention provides an acoustic wave detector based on high-fineness FP interference, which has the advantages of electromagnetic interference resistance, easiness in multiplexing and networking, low transmission loss, suitability for long-distance monitoring and the like compared with the conventional electrical acoustic wave detector. Compared with the existing optical acoustic wave detector, the optical acoustic wave detector has the characteristics of small structural size, high phase sensitivity, good low-frequency response and the like.
Drawings
Fig. 1 is a system block diagram of an FP interference type acoustic wave detector according to an embodiment of the present invention;
fig. 2 is a schematic system structure diagram of an FP interference type acoustic wave detector according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of an FP sensor head of an FP interferometric acoustic wave detector according to an embodiment of the present invention;
fig. 4 is a spectrum (a) and a fourier transform spectrum (b) of an FP interference type acoustic wave detector according to an embodiment of the present invention;
fig. 5 is a flowchart of a demodulation algorithm of a high-fineness optical fiber fabry-perot acoustic wave sensor based on improved fourier phase demodulation according to an embodiment of the present invention;
fig. 6 is a schematic diagram of first-order and second-order demodulation results of a high-fineness optical fiber fabry-perot acoustic wave sensor based on improved fourier phase demodulation according to an embodiment of the present invention;
fig. 7 is a flowchart of a phase jump correction algorithm of a high-finesse fiber fabry-perot acoustic wave sensor based on improved fourier phase demodulation according to an embodiment of the present invention.
In all the drawings, the same reference numerals are used to denote the same elements or structures, where 1 is a light source, 2 is a fiber circulator, 3 is an FP sensor head, 4 is a spectrum real-time acquisition module, 5 is a signal processing demodulation module, 6 is a fiber collimator, 7 is a ferrule, 8 is a sleeve, 9 is a thin film, 10 is a single-mode fiber, 11 is an antireflection film, 12 is a self-focusing lens, and 13 is an antireflection film.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Aiming at the requirement of high sensitivity of the existing sound wave detection, the invention provides a sound wave detection system based on high-fineness FP interference and a phase demodulation algorithm, wherein multi-beam interference occurs between the end face of a self-focusing lens plated with an anti-reflection film and a high-reflectivity film to form an FP cavity, and demodulation is carried out at a high-order peak of a Fourier spectrum of a reflection spectrum through an improved Fourier phase demodulation algorithm to realize phase amplification and multiplication of phase sensitivity.
One aspect of the present invention provides an FP interference type acoustic wave probe, including: the device comprises a light source, an optical fiber circulator, an FP sensing head, a spectrum real-time acquisition module and a signal processing demodulation module; the output end of the light source is connected with the input end of the optical fiber circulator; the optical fiber circulator comprises three ports, wherein a first port is connected to the output end of the optical fiber attenuator, a second port is connected with the FP sensing head, and a third port is connected to the input end of the spectrum real-time acquisition module; the input end of the spectrum real-time acquisition module is connected to the third port of the optical fiber circulator, and the output end of the spectrum real-time acquisition module is connected to the signal processing demodulation module. The optical fiber circulator is used for controlling optical signals generated by the light source to be transmitted to the FP sensing head, the optical signals to be detected are carried and then reflected to the spectrum real-time acquisition module, the spectrum real-time acquisition module is used for acquiring spectrum signals in real time, and the signal processing demodulation module is used for demodulating phases and further demodulating the acoustic signals to be detected.
Specifically, the FP sensor head comprises: the optical fiber collimator, the inserting core, the sleeve and the thin film; the optical fiber collimator is inserted into the ferrule, the optical fiber collimator is fixed through the ferrule, the film is adhered to the end face of the sleeve, the ferrule is inserted into the sleeve and fixed, and a cavity is formed between the film and the end face of the optical fiber collimator to form the optical fiber external cavity type FP interferometer. The film is used for converting sound waves into film vibration, so that the cavity length of the FP cavity is changed, and sound wave detection is converted into phase change of demodulation interference light.
Specifically, the optical fiber collimator includes: single mode fiber, antireflection coating, self-focusing lens and antireflection coating. The end face of the single-mode optical fiber is coupled with the inner surface of the self-focusing lens at an angle of 0 degree, and an antireflection film is covered to control return loss. And plating a reflection increasing film on the outer surface of the self-focusing lens to serve as one reflecting surface of the FP, wherein the other reflecting surface is a thin film. The light is transmitted in the optical fiber, the Gaussian beam is converted into parallel light through the self-focusing lens, and a part of light is reflected by the light splitting film and is coupled into the optical fiber again; the rest light is transmitted into the FP cavity, and multiple reflections occur in the cavity to form multi-beam interference.
Specifically, the reflectivity of the reflection increasing film on the end face of the self-focusing lens can be designed theoretically, and the selected high-order characteristic frequency peak on the Fourier spectrum of the spectrum is made more obvious by designing the reflectivity, so that the improved Fourier phase demodulation algorithm can carry out peak searching (the first three orders are more obvious).
Specifically, the film is a circular film, and the material of the film is a high-reflectivity film, including a metal film such as aluminum, gold, silver, and the like, and also including a high-reflectivity multilayer composite film.
The invention also provides an acoustic wave detection method based on the acoustic wave detector, aiming at the demodulation of the high-fineness FP interference spectrum, comprising the following steps:
s1, collecting a reflection spectrum of an FP sensing head in real time, wherein the reflection spectrum causes membrane vibration by sound waves to be measured, and the phase change of reflected interference light signals is generated;
s2, carrying out Fourier transform on the collected reflection spectrum, wherein a series of characteristic frequency peaks can be observed on the Fourier transform spectrum;
s3, locking a D-order frequency peak on the Fourier spectrum of each frame of reflection spectrum and obtaining a real part and an imaginary part of a frequency spectrum component at the D-order frequency peak, wherein D is more than or equal to 2;
s4, calculating the real part and the imaginary part of the frequency spectrum component at the D-order frequency to obtain phase change caused by sound waves, namely a phase demodulation result;
s5, performing phase cycle correction on the point in the phase demodulation result, where the absolute value of the phase difference between each moment and the previous moment is greater than a threshold value;
and S6, obtaining the acoustic wave signal to be detected according to the corrected phase demodulation result and the calibration result of the standard sensor.
Specifically, the fourier phase demodulation algorithm of the present invention is suitable for both two-beam interference and multi-beam interference, and can realize phase multiplication for multi-beam interference. The Fourier spectrum of the multi-beam interference reflection spectrum has a plurality of characteristic frequency peaks, and can be seen as the result of countless double-beam interference superposition. For interference between light reflected N times back and forth and M times back and forth within the cavity (M)>N), the interference light intensity is:
the sum of all interference intensities satisfying M-N = D is:
reflected at the D-th characteristic frequency peak on the fourier spectrum, the D-th characteristic frequency can be expressed as: f. of D ≈2nD[L 0 +ΔL(t)]/λ 2 N is the refractive index of the cavity, L is the real-time cavity length, L 0 The initial cavity length, A, B are constants. At the moment, the phase value 4 pi DnL/lambda obtained by demodulation at the D-th order characteristic frequency peak is D times of the demodulation phase at the first order characteristic frequency.
In particular, the improved fourier phase demodulation algorithms proposed by the present invention differ in the order of the characteristic frequency peaks used. For a high-fineness spectrum with an obvious high-order frequency peak, a first-order characteristic frequency with the maximum amplitude is not selected for demodulation, but a high-order characteristic frequency is selected for Fourier phase demodulation, and a phase value after D multiplication can be demodulated. For each acquired frame of spectrum, assuming that the characteristic frequency of the D-th order is at the kth point of the spectrum fourier spectrum, locking the kth point of each frame of spectrum to obtain the real part and the imaginary part of the spectrum components thereof, the phase change caused by the sound wave can be expressed as:
Specifically, the improved fourier phase demodulation algorithm provided by the invention is improved to a certain extent on the algorithm, and phase correction is performed on the phase jump (when the phase value is greater than pi/2, the value obtained by the arctangent operation is equal to the integral multiple of pi of the true value) which is universally existed in the arctangent operation in the phase demodulation. Selecting a threshold value, carrying out cyclic detection on the phase signal demodulated by the Fourier phase demodulation algorithm, carrying out phase cyclic correction if the absolute value of the difference between the phase value of a certain point and the previous phase value is greater than the threshold value, subtracting pi if the phase is greater than the previous phase value in the cyclic process, and adding pi if the phase is less than the previous phase value until the absolute value of the phase difference between two adjacent points is less than the threshold value.
The embodiment of the invention provides an FP interference type acoustic wave detector, the basic block diagram of which is shown in figure 1, comprising: the light source is used for generating and outputting an original optical signal, the light source used in the embodiment of the invention is a wide-spectrum light source, and the wavelength range is 1525 nm-1565 nm; the optical fiber sound wave detection module is used for modulating the sound wave signal to be detected to the phase of the original optical signal to generate a modulated optical signal; the spectrum real-time acquisition module is used for acquiring the FP reflection spectrum in real time so as to be convenient for subsequently demodulating a phase signal at a corresponding moment; and the signal processing and demodulating module is used for converting the acquired spectrum into phase information at corresponding moments through a series of operations so as to calculate the phase sensitivity of the sensor.
The invention provides a sound wave detection system based on high-fineness FP interference, which has a structure schematic shown in figure 2 and comprises: the device comprises a light source 1, an optical fiber circulator 2, an FP sensing head 3, a spectrum real-time acquisition module 4 and a signal processing and demodulation module 5. In embodiment 1, light emitted from a light source 1 is input to a fiber attenuator to control light intensity, and then input to an FP sensor head through a fiber circulator 2 to provide a light source for an acoustic wave detector. The reflected broadband light spectrum loaded with the sound wave signal is collected by the spectrum real-time collection module 4, and the sound wave signal is demodulated by the signal processing demodulation module 5.
In the embodiment of the invention, the structure of the high-fineness optical fiber FP sensing head is shown in FIG. 3 and comprises an optical fiber collimator 6, an insertion core 7, a sleeve 8 and a film 9. The optical fiber collimator 6 is composed of a single-mode optical fiber 10, an antireflection film 11, a self-focusing lens 12, and an antireflection film 13. The end face of the single-mode fiber 10 is coupled with the inner surface of the self-focusing lens 12 at an angle of 0 degree, and an antireflection film is covered to control return loss. And plating a reflection increasing film on the outer surface of the self-focusing lens to serve as one reflecting surface of the FP, wherein the other reflecting surface is a thin film. The light is transmitted in the optical fiber, the Gaussian beam is changed into parallel light through the self-focusing lens, and a part of light is reflected by the light splitting film and is coupled into the optical fiber again; the rest light is transmitted into the FP cavity, and multiple reflections occur in the cavity to form multi-beam interference.
In the embodiment of the invention, the cavity length needs to be controlled in the manufacturing process of the FP sensing head, in order to achieve a good demodulation result, the spectrum acquired in real time needs to be ensured to contain a complete free spectrum range, and the number of sampling points in one free spectrum range is not less than 10.
In the embodiment of the invention, the diameter of the round film is 3-5 mm, and the thickness is 0.3-0.5 um, subject to the requirements of miniaturization and high sensitivity and the processing size of the metal sleeve; the smaller the diameter of the film, the lower the sensitivity, the larger the frequency response range, the more complex the sensor manufacturing process, the smaller the film thickness and the higher the sensor sensitivity.
In the embodiment of the present invention, the transmittance of the antireflection film is 99.5%, the return loss is reduced, and in order to achieve a better second-order (D = 2) demodulation effect, the reflectance of the antireflection film is designed to be 60%, the obtained interference spectrum and its fourier spectrum are shown in (a) and (b) in fig. 4, a significant second-order characteristic frequency peak can be observed, and the fineness of the spectrum obtained by calculation is about 6.4, and by simulating multi-beam interference, the second characteristic frequency peak is more significant when the reflectance is 60% under different spatial losses in consideration of the influence of spatial light scattering loss.
In the embodiment of the invention, because the high-fineness interference spectrum is generated, the light reflected for many times can still have certain intensity, and the reflectivity of two end faces of the FP has certain requirements, the film can be a metal film, such as a metal film made of aluminum, gold, silver and the like, or a multilayer composite film with high reflectivity, wherein the composite metal film is adopted.
In the embodiment of the invention, 353ND glue is used for adhesion between the film and the metal sleeve in the manufacturing process of the FP sensor head, the film is heated for one and a half hours at 80 ℃ until the film is solidified, and the film is transferred by using a sacrificial layer wet transfer method.
In the embodiment of the present invention, the ferrule 7 is a ceramic ferrule and the sleeve 8 is a metal sleeve.
In an embodiment of the present invention, a flow chart of an improved phase demodulation algorithm is shown in fig. 5. For each frame of spectrum acquired in real time, the number of points is N, and the sampling interval is delta lambda 0 ，λ 1 As starting wavelength, λ j Is the wavelength at the jth point on the spectrum. If the second-order characteristic frequency peak is supposed to be locked for demodulation, if the second-order characteristic frequency peak f 2 At the kth point of the Fourier spectrum of the spectrum, f 2 The spectral components at (a) are represented as:
f 2 the spectrum of (b):
wherein the content of the first and second substances,
is the phase of the initial spectrum of light,
due to F' (F) 2 ) The real part is:
the imaginary part is:
when the number of sampling points N is large, the real part is simplified as follows:
the imaginary part is simplified as:
the imaginary part is divided by the real part to obtain
Thus, by taking the fourier transform of the acquired spectral data, the phase value can be obtained by performing an arctangent operation after dividing the values of the imaginary and real parts of the spectral component at the second frequency peak, at which point the phase value is obtainedThe phase change is expressed as:
wherein the content of the first and second substances,
the method can be obtained through the first frame of spectral data, and finally pi/2 is selected as a threshold value to carry out phase correction. The phase demodulation algorithm of the present invention is applied to a group of spectra in the time domain, the demodulation result is shown in fig. 6, the phase change can be demodulated, and it is observed that the phase demodulated at the second-order characteristic frequency peak is twice as large as the phase demodulated at the first-order characteristic frequency peak, that is, the phase amplification effect is achieved.
In the embodiment of the present invention, the phase demodulation method is an improved fourier phase demodulation method, and the method corrects a phase jump phenomenon that is commonly present in an arc tangent operation in phase demodulation, and an algorithm flow is shown in fig. 7. Selecting pi/2 as a threshold, carrying out cyclic detection on each point of the phase signal demodulated by the Fourier phase demodulation algorithm, carrying out phase cyclic correction on the point of which the absolute value of the difference with the previous phase value is larger than pi/2, subtracting pi if the phase is larger than the previous phase value, and adding pi if the phase is smaller than the previous phase value until the absolute value of the phase difference between two adjacent points is smaller than pi/2.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (3)
1. An acoustic wave detection method of an FP interference type acoustic wave probe, the FP interference type acoustic wave probe comprising: the device comprises a light source (1), a fiber circulator (2), an FP sensing head (3), a spectrum real-time acquisition module (4) and a signal processing demodulation module (5); the optical fiber circulator (2) comprises three ports, a first port is connected to the output end of the light source (1), a second port is connected with the FP sensing head (3), a third port is connected to the input end of the spectrum real-time acquisition module (4), and the optical fiber circulator (2) is used for controlling the transmission of an optical signal generated by the light source (1) to the FP sensing head (3) and reflecting the optical signal to the spectrum real-time acquisition module (4) after carrying a sound wave signal to be detected; the input end of the spectrum real-time acquisition module (4) is connected to the third port of the optical fiber circulator (2), and the output end of the spectrum real-time acquisition module is connected to the signal processing demodulation module (5) and is used for acquiring spectrum signals in real time; the signal processing and demodulating module (5) is used for demodulating a phase and further demodulating a sound wave signal to be detected;
the method is characterized by comprising the following steps:
s1, collecting a reflection spectrum of an FP sensing head in real time, wherein the reflection spectrum causes the vibration of a film by a sound wave to be detected, so that the phase change of a reflected interference light signal is generated;
s2, carrying out Fourier transform on the collected reflection spectrum, wherein a series of characteristic frequency peaks can be observed on the Fourier spectrum;
s3, locking a D-order frequency peak on the Fourier spectrum of each frame of reflection spectrum and obtaining a real part and an imaginary part of a frequency spectrum component at the D-order frequency peak, wherein D is more than or equal to 2;
s4, calculating the real part and the imaginary part of the frequency spectrum component at the D-order frequency to obtain phase change caused by sound waves, namely a phase demodulation result;
s5, performing phase cycle correction on the point in the phase demodulation result, where the absolute value of the phase difference between each moment and the previous moment is greater than a threshold value;
and S6, obtaining the acoustic wave signal to be detected according to the corrected phase demodulation result and the calibration result of the standard sensor.
2. The acoustic detection method of claim 1, wherein the phase values demodulated at the characteristic frequency peak of order D of the Fourier spectrum of the reflection spectrum will be a multiple of D demodulated at the characteristic frequency peak of order D.
3. The acoustic wave detection method according to claim 1, wherein the phase cycle correction in S5 is specifically: and phase correction is carried out on the point of the demodulated phase, the absolute value of the difference between the demodulated phase and the previous phase value is greater than a threshold value, if the phase is greater than or equal to the previous phase, pi is subtracted, if the phase is less than the previous phase value, pi is added until the absolute value of the phase difference between the two adjacent points is less than the threshold value, and phase jump is considered to be absent.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210167330.4A CN114543971B (en) | 2022-02-23 | 2022-02-23 | FP interference type sound wave detector and sound wave detection method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210167330.4A CN114543971B (en) | 2022-02-23 | 2022-02-23 | FP interference type sound wave detector and sound wave detection method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN114543971A CN114543971A (en) | 2022-05-27 |
| CN114543971B true CN114543971B (en) | 2022-11-11 |
Family
ID=81677637
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202210167330.4A Active CN114543971B (en) | 2022-02-23 | 2022-02-23 | FP interference type sound wave detector and sound wave detection method |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN114543971B (en) |
Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102080972A (en) * | 2009-11-30 | 2011-06-01 | 西门子公司 | External cavity-type optical fiber Fabry-Perot sensor and system and method for vibration monitoring |
| DE102010044245B3 (en) * | 2010-09-02 | 2011-12-29 | Krohne Messtechnik Gmbh | demodulation |
| CN105181112A (en) * | 2015-10-22 | 2015-12-23 | 哈尔滨工业大学 | Diaphragm type low-fineness F-P optical fiber sound pressure transducer based on FBG |
| CN107907203A (en) * | 2017-11-30 | 2018-04-13 | 大连理工大学 | A kind of demodulation method of optical fiber F P cavate sonic sensors |
| CN109088670A (en) * | 2018-08-10 | 2018-12-25 | 华中科技大学 | A kind of method and system of determining acoustic signals |
| CN109374109A (en) * | 2018-09-01 | 2019-02-22 | 哈尔滨工程大学 | A kind of mini optical fibre extrinsic type Michelson sound pressure sensor of light channel structure altogether |
| CN111780856A (en) * | 2020-06-01 | 2020-10-16 | 哈尔滨工业大学 | Optical fiber distributed vibration measurement method based on Rayleigh scattering spectrum phase spectrum analysis |
| CN111854923A (en) * | 2020-07-31 | 2020-10-30 | 重庆邮电大学 | Acoustic wave measurement system, cantilever beam type optical fiber acoustic wave sensor demodulation system and method |
| CN111982270A (en) * | 2020-09-02 | 2020-11-24 | 金华伏安光电科技有限公司 | Vibration detection device and system based on Fabry-Perot resonant cavity |
-
2022
- 2022-02-23 CN CN202210167330.4A patent/CN114543971B/en active Active
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102080972A (en) * | 2009-11-30 | 2011-06-01 | 西门子公司 | External cavity-type optical fiber Fabry-Perot sensor and system and method for vibration monitoring |
| DE102010044245B3 (en) * | 2010-09-02 | 2011-12-29 | Krohne Messtechnik Gmbh | demodulation |
| CN105181112A (en) * | 2015-10-22 | 2015-12-23 | 哈尔滨工业大学 | Diaphragm type low-fineness F-P optical fiber sound pressure transducer based on FBG |
| CN107907203A (en) * | 2017-11-30 | 2018-04-13 | 大连理工大学 | A kind of demodulation method of optical fiber F P cavate sonic sensors |
| CN109088670A (en) * | 2018-08-10 | 2018-12-25 | 华中科技大学 | A kind of method and system of determining acoustic signals |
| CN109374109A (en) * | 2018-09-01 | 2019-02-22 | 哈尔滨工程大学 | A kind of mini optical fibre extrinsic type Michelson sound pressure sensor of light channel structure altogether |
| CN111780856A (en) * | 2020-06-01 | 2020-10-16 | 哈尔滨工业大学 | Optical fiber distributed vibration measurement method based on Rayleigh scattering spectrum phase spectrum analysis |
| CN111854923A (en) * | 2020-07-31 | 2020-10-30 | 重庆邮电大学 | Acoustic wave measurement system, cantilever beam type optical fiber acoustic wave sensor demodulation system and method |
| CN111982270A (en) * | 2020-09-02 | 2020-11-24 | 金华伏安光电科技有限公司 | Vibration detection device and system based on Fabry-Perot resonant cavity |
Non-Patent Citations (2)
| Title |
|---|
| 全光纤光栅F_P腔微弱磁场传感器研究;张旭辉;《中国优秀硕士学位论文全文数据库 信息科技辑》;20180315;i140-262 * |
| 自聚焦平板波导透镜及其应用;刘德明;《红外与激光工程》;20061031;第35卷;84-90 * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN114543971A (en) | 2022-05-27 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN108955734B (en) | Cavity length demodulation method of optical fiber F-P temperature/pressure composite sensor | |
| CN108534811B (en) | Cavity length demodulation algorithm of short-cavity optical fiber Fabry-Perot sensor | |
| CN106644036A (en) | Sound wave detector based on polymer thin film and dual-wavelength demodulation method | |
| CN101105532A (en) | All-fiber Raman scattering laser radar system based on wavelength-division multiplex technology for diffracting | |
| CN109724685B (en) | Fiber grating underwater acoustic sensing array demodulation method and system based on Fizeau interference | |
| CN101603857B (en) | Method for demodulating phase carrier in Fabry-Perot interference type optical fiber hydrophon | |
| CN113406838B (en) | Method and system for realizing double-frequency comb system double-frequency doubling | |
| Zhu et al. | A high-precision wavelength demodulation method based on optical fiber fabry-perot tunable filter | |
| CN105444793A (en) | Fiber Bragg raster sensing device based on high-speed pulse laser | |
| CN110530531B (en) | Michelson interference-based fountain type atomic gravimeter light beam phase change measuring device and method | |
| CN114543971B (en) | FP interference type sound wave detector and sound wave detection method | |
| CN109696418B (en) | Heterodyne balance detection system and detection method applied to TDLAS direct absorption method under low signal-to-noise ratio | |
| Corbitt et al. | Optical cavities as amplitude filters for squeezed fields | |
| CN110553715B (en) | Optical fiber array type sound wave signal acquisition device based on laser interference | |
| CN104048617B (en) | Sensing modulating method for high-precision fiber bragg grating insensitive to polarization state changes | |
| CN210571001U (en) | Common-path dual-wavelength quadrature phase demodulation system | |
| CN108204827A (en) | A kind of phase-shifted fiber grating demodulating system | |
| CN110470378A (en) | A kind of three Wavelength demodulation formula optical fiber sound sensor-based systems and method of quadrature phase holding | |
| CN110057439A (en) | A kind of low quick sensing device of resonance eccentric core fiber sound based on F-P interference | |
| CN112050942B (en) | Optical fiber interference spectrum cavity length correction method based on phase compensation | |
| CN113188452B (en) | Displacement measurement method based on laser self-mixing interference spectrum mapping fringe multiplication | |
| CN110440899B (en) | Common-path dual-wavelength quadrature phase demodulation system | |
| CN115265615A (en) | Sensing system and method for measuring static pressure and sound pressure double parameters based on Fabry-Perot etalon | |
| Liu et al. | Simultaneous distributed acoustic and temperature sensing system based on ultra-weak chirped fiber Bragg grating array | |
| CN107402027A (en) | Physical amount measuring method based on intensity modulation optical fiber sensor |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |