Acoustic signal measuring device and method based on asymmetric interference preposed time difference

Abstract

The invention provides an acoustic signal measurement device and method based on asymmetric interference preposed time difference. The device comprises an asymmetric interference measurement light path and an acoustic transduction sensing part. Wherein the asymmetric interference measurement light path comprises a light source, a front selection part, a polarization beam splitting system, a rear selection part, a photoelectric detection part and a data acquisition part; the acoustic transduction sensing part comprises a first acoustic signal sensing channel and a second acoustic signal sensing channel, and each channel is composed of an optical time delayer and an acoustic transducer. Light emitted by the light source becomes linearly polarized light after passing through the front selection device, is divided into two light beams with orthogonal polarization directions by the polarization beam splitting system, is reflected by the acoustic transducer, generates different time delays through different optical time delayers, and then is combined to enter the rear selection device. After phase modulation and polarization state post selection, the two orthogonal component light beams form asymmetric interference meeting a weak value amplification condition at a photoelectric detection end, and an acoustic signal is reconstructed from a time difference signal measured by interference through an inverse solution algorithm.

Description

Technical Field

[0001] The present invention relates to the technical field of asymmetric interference measurement, and particularly relates to an acoustic signal measurement device and method based on asymmetric interference pre-time difference. Background Art

[0002] The asymmetric interference measurement technology is an optical phase measurement technology that generates interference signals by changing the laser optical path. In essence, it uses the weak value amplification principle to amplify extremely tiny measured quantities and then detect them to obtain high-precision measurement results. The asymmetric interference measurement technology introduces a pre-selection state and a post-selection state before and after the weak coupling process between the instrument and the system. When the pre-selection and post-selection of the system are close to orthogonal, the offset of the pointer to be measured will far exceed the eigen-spectrum range of the system observable quantity, so that its measurement accuracy is much higher than that of traditional interference measurement technology, and it has been effectively applied to the precision measurement fields of various physical quantities such as displacement, surface shape, acoustic signal, and refractive index.

[0003] The time difference technology obtains its change information by comparing the states or data of the same object or system at different times, and then analyzes the dynamic characteristics, trends, etc. of the object. It has gradually formed and improved in the development process of multiple signal processing fields such as position positioning and image recognition. The patent with the publication number CN112198537A records a high-precision Loran positioning solution method based on difference. It synthesizes signals by calculating the time difference of signals received at different times in the positioning system, improves the quality and anti-interference ability of the signals, helps to more accurately extract positioning information, realizes more accurate position solution, and ensures the positioning accuracy and reliability of the system. The advantage of the time difference technology is that it can reduce or weaken the influence of some error factors through signal difference, thereby improving the accuracy of signal recognition.

[0004] The time difference component of the acoustic signal is a high-order small quantity of the direct signal detection quantity. When the time difference interval is smaller, the time difference component of the signal is also smaller. Therefore, the detection accuracy and signal-to-noise ratio of the signal time difference component are insufficient, which become the main factors restricting the development of the acoustic signal time difference sensing technology. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the present invention proposes an acoustic signal measurement device and method based on asymmetric interference pre-time difference, and constructs a high-precision asymmetric interference measurement of the acoustic signal time difference weak value. The measurement system effectively reduces the noise in the non-working frequency band by differential subtraction at the front end of optical interference, and realizes the selection and extraction of the acoustic signal through an inverse solution algorithm, which can improve the detection signal-to-noise ratio and accuracy.

[0006] The technical solution adopted by the present invention is as follows:

[0007] In a first aspect, an acoustic signal measurement device based on asymmetric interference pre-time difference is provided, including: a light source for emitting a light beam;

[0008] A pre-selection module for converting the light beam emitted by the light source into linearly polarized light;

[0009] A polarization beam splitting system for splitting the linearly polarized light into two component light beams with orthogonal polarization states;

[0010] An acoustic signal sensing part, including an optical time delay device and a transducer. The optical time delay device is used to generate different time delays for the two component light beams. The transducer is used to convert the acoustic signal into mechanical deformation or displacement, and is also used to reflect the two component light beams; the transducer has a consistent acoustic signal frequency response function;

[0011] A post-selection module for performing phase and polarization state modulation on the two reflected component light beams to satisfy the weak value amplification condition;

[0012] A photodetector for detecting the light intensity of the asymmetric interference signal formed at the input end of the photodetector by the two post-selection modulated component light beams;

[0013] A data acquisition module for converting the light intensity signal into a digital signal;

[0014] A data processing module for performing data processing on the digital signal to recover the acoustic signal within the working bandwidth.

[0015] Further, the light source, the pre-selection module, a three-port fiber optic circulator, the polarization beam splitting system, and the acoustic signal sensing part are sequentially arranged on the incident optical path; the acoustic signal sensing part, the polarization beam splitting system, the three-port fiber optic circulator, the post-selection module, and the photodetector are sequentially arranged on the reflected optical path.

[0016] Further, the pre-selection module includes: an optical fiber, a first fiber optic coupler, a first polarizer, and a second fiber optic coupler sequentially arranged on the incident optical path.

[0017] Further, the polarization beam splitting system includes two optical paths. On one optical path, a third fiber optic coupler, a polarization beam splitting prism, and a fourth fiber optic coupler are sequentially arranged. On the other optical path, a third fiber optic coupler, a polarization beam splitting prism, and a fifth fiber optic coupler are sequentially arranged; the polarization beam splitting prism is the same polarization beam splitting prism.

[0018] Further, the acoustic signal sensing part includes a first acoustic signal sensing channel and a second acoustic signal sensing channel. In the incident light path of the first acoustic signal sensing channel, a first optical time delay device, a sixth fiber optic coupler mirror, and a first reflective transducer are sequentially arranged. In the incident light path of the second acoustic signal sensing channel, a second optical time delay device, a seventh fiber optic coupler mirror, and a second reflective transducer are sequentially arranged.

[0019] Further, the reflective transducer includes a diaphragm transducer; the diaphragm transducer includes a flywheel type vibrating film, a corrugated diaphragm, a circular diaphragm, a cantilever type diaphragm, or a composite diaphragm.

[0020] Further, the post-selection module includes an eighth fiber optic coupler mirror, a half-wave plate, a quarter-wave plate, a second polarizer, and a ninth fiber optic coupler mirror sequentially arranged in the reflected light path; the half-wave plate and the quarter-wave plate together form a phase modulation component.

[0021] Further, the polarization beam splitting system includes a fiber optic polarization beam splitter and a fiber optic polarization combiner.

[0022] Further, the post-selection module includes a linear polarizer, and an electro-optic modulator or a magneto-optic modulation crystal.

[0023] Further, the weak value amplification condition required for the post-selection is to modulate the phase and polarization state of the return beam to make it close to orthogonal to the polarization direction of the pre-selection state, that is, to satisfy the condition, so that the observable weak value of the asymmetric interference system becomes very large to obtain a significantly amplified measurable quantity.

[0024] In a second aspect, an acoustic signal measurement method based on asymmetric interference pre-time difference is provided. The measurement is performed using the acoustic signal measurement device as described in the first aspect, including:

[0025] A light source emits a beam of light that forms linearly polarized light through pre-selection;

[0026] The linearly polarized light is divided into two component beams with orthogonal polarization states through polarization beam splitting; the two component beams generate different time delays in the optical path through different optical time delay devices;

[0027] An acoustic signal is converted into mechanical deformation or displacement using a transducer, and the two component beams carry acoustic signal information after being reflected by the transducer;

[0028] The two component beams carrying acoustic signal information enter the post-selection again through polarization beam splitting, and the phase and polarization state of the optical signal carrying acoustic signal information are modulated through the post-selection;

[0029] The two component beams after post-selection form an asymmetric interference signal at the interference point;

[0030] The optical intensity is measured using a photodetector for an asymmetric interference signal, and the acoustic signal within the working bandwidth is calculated based on the optical intensity.

[0031] As can be seen from the above technical solutions, the beneficial technical effects of the present invention are as follows:

[0032] 1. For the measurement method provided by the present invention, the time-difference processing is advanced to the optical measurement stage. By optical difference, the introduction of environmental disturbances and self-noise at the front end of the optoelectronic conversion is eliminated, further reducing the system noise and improving the recognition sensitivity of weak change acoustic signals and the measurement signal-to-noise ratio.

[0033] 2. The time-difference component is a high-order small quantity of the original signal to be measured. The present invention uses a high-precision asymmetric interference measurement technology to measure the high-order small quantity of the time difference of the signal. Based on the weak value amplification effect of asymmetric interference, it can amplify the differential component to be measured without amplifying the measurement self-noise, thereby enabling the system to obtain a higher detection signal-to-noise ratio.

[0034] 3. The measurement system provided by the present invention can reduce the dependence on high-precision frequency-stabilized lasers and constant-temperature optical paths, reducing the system complexity; it has a certain inhibitory effect on environmental disturbances such as temperature drift and mechanical vibration, and is applicable to non-ideal environments such as field stations and industrial sites. Description of the Drawings

[0035] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0036] Figure 1 It is a block diagram of an acoustic signal measurement system based on pre-time difference of asymmetric interference of the present invention;

[0037] Figure 2 It is a schematic structural diagram of an acoustic signal measurement device based on pre-time difference of asymmetric interference in the first embodiment of the present invention;

[0038] Figure 3 It is a schematic diagram of the propagation and conversion process of the acoustic signal to be measured in the acoustic signal measurement method of the embodiment of the present invention;

[0039] FIG. 4(A) and FIG. 4(B) show schematic diagrams of a second embodiment of the polarization beam splitting system of an acoustic signal measurement device based on pre-time difference of asymmetric interference according to the present invention;

[0040] Figure 5Shows a schematic diagram of an alternative embodiment of the post-selection module according to the first embodiment of the present invention;

[0041] Reference numerals:

[0042] 1 - narrowband light source, 2 - pre-selection module, 3 - three-port fiber optic circulator, 4 - polarization beam splitting system, 5 - first acoustic signal sensing channel, 6 - second acoustic signal sensing channel, 7 - post-selection module, 8 - photodetector, 9 - data acquisition module, 10 - data processing module, 11 - acoustic signal source.

[0043] 21 - first fiber optic coupler mirror, 22 - first polarizer, 23 - and second fiber optic coupler mirror;

[0044] 41 - third fiber optic coupler mirror, 42 - polarization beam splitting prism, 43 - fourth fiber optic coupler mirror, 44 - fifth fiber optic coupler mirror;

[0045] 51 - first optical time delay device, 52 - sixth fiber optic coupler mirror, 53 - first reflective transducer;

[0046] 61 - second optical time delay device, 62 - seventh fiber optic coupler mirror, 63 - second reflective transducer;

[0047] 71 - eighth fiber optic coupler mirror, 72 - half-wave plate, 73 - quarter-wave plate, 74 - second polarizer, 75 - ninth fiber optic coupler mirror;

[0048] 4' - fiber optic polarization beam splitter, 4'' - fiber optic polarization combiner, 41' - fiber optic coupler mirror, 41'' - fiber optic coupler mirror, 42' - non-polarizing semi-reflective semi-transmissive beam splitter, 42'' - birefringent crystal;

[0049] 72' - electro-optic modulator or magneto-optic modulation crystal, 74' - linear polarizer. Specific embodiments

[0050] The embodiments of the technical solution of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to illustrate the technical solution of the present invention more clearly, so they are only examples and cannot be used to limit the protection scope of the present invention.

[0051] It should be noted that unless otherwise specified, the technical terms or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art to which the present invention belongs.

[0052] Figure 1 Shown is a block diagram of an acoustic signal measurement system based on asymmetric interference pre-time difference of the present invention, which mainly includes:

[0053] Light source; pre-selection module;

[0054] A polarization beam splitting system, which can be implemented by a polarization beam splitting prism or by a fiber polarization beam splitter, a waveguide polarization beam splitter, etc.; a first optical time delay device and a second optical time delay device; a first transducer and a second transducer, and the transducer includes, but is not limited to, various structural transducers such as a diaphragm type, a cantilever beam type, a composite type, etc., as long as it is ensured that the first transducer and the second transducer have a consistent acoustic signal frequency response function;

[0055] The post-selection module is mainly used to modulate the phase and polarization state of the returned light beam to meet the weak value amplification condition, and the phase modulation can be implemented by a wave plate combination or by an electro-optic modulator, a liquid crystal modulator, etc.;

[0056] A photodetector; a data acquisition module; a data processing module.

[0057] Figure 2 Fig. shows a schematic structural diagram of an acoustic signal measurement device based on an asymmetric interference pre-time difference according to the first embodiment of the present invention. The acoustic signal measurement device based on an asymmetric interference pre-time difference includes: a narrowband light source 1, a pre-selection module 2, a three-port fiber optic circulator 3, a polarization beam splitting system 4, and an acoustic signal sensing part sequentially arranged on the incident optical path; an acoustic signal sensing part, a polarization beam splitting system 4, a three-port fiber optic circulator 3, a post-selection module 7, and a photodetector 8 are sequentially arranged on the reflected optical path; the acoustic signal measurement device further includes a data acquisition module 9 and a data processing module 10 electrically connected to the photodetector 8; and an acoustic signal source 11 arranged beside the acoustic signal sensing part.

[0058] Among them, the narrowband light source, the pre-selection module, the polarization beam splitting system, and the post-selection module constitute a weak measurement optical path; specifically, the pre-selection module is sequentially provided with: an optical fiber, a first fiber optic coupler 21, a first polarizer 22, and a second fiber optic coupler 23 on the incident optical path; the polarization beam splitting system includes two optical paths, on one optical path, a third fiber optic coupler 41, a polarization beam splitting prism 42, and a fourth fiber optic coupler 43 are sequentially arranged, and on the other optical path, a third fiber optic coupler 41, a polarization beam splitting prism 42, and a fifth fiber optic coupler 44 are sequentially arranged.

[0059] The acoustic signal sensing part includes a first acoustic signal sensing channel 5 and a second acoustic signal sensing channel 6. The first acoustic signal sensing channel 5 is sequentially provided with a first optical time delay device 51, a sixth fiber optic coupler 52, and a first reflective transducer 53 on the incident optical path, and the second acoustic signal sensing channel 6 is sequentially provided with a second optical time delay device 61, a seventh fiber optic coupler 62, and a second reflective transducer 63 on the incident optical path.

[0060] The post-selection module includes an eighth fiber optic coupling mirror 71, a half-wave plate 72, a quarter-wave plate 73, a second polarizer 74, and a ninth fiber optic coupling mirror 75 that are sequentially arranged on the reflected light path. The half-wave plate 72 and the quarter-wave plate 73 together constitute a phase modulation component.

[0061] In a specific embodiment, the first polarizer 22 in the pre-selection module and the second polarizer 74 in the post-selection module are both linear polarizers. Their function is to ensure that the incident light of the sensing device is linearly polarized light after passing through the pre-selection first polarizer 22, and the linear polarizer through which the incident light passes is defined as pre-selection, and the half-wave plate, quarter-wave plate, and linear polarizer through which the outgoing light passes are defined as post-selection. Among them, the angle between the orthogonal direction of the polarization direction of the pre-selection first polarizer and the polarization direction of the post-selection second polarizer is the post-selection angle. The phase difference between the two polarized light beams can be adjusted by rotating the half-wave plate and the quarter-wave plate, so that the post-selection state parameter κ associated with the post-selection angle can satisfy the weak value amplification condition in weak measurement. Different post-selection angles will cause corresponding changes in the post-selection state parameter κ and also change the weak value amplification factor, thereby achieving the amplification of useful signals without increasing the system noise and obtaining the phase difference through detection.

[0062] In this embodiment, for the acoustic signal sensing part, the first reflective transducer 53 and the second reflective transducer 63 are both composed of diaphragm transducers. The diaphragm transducers used can be flywheel-type vibrating diaphragms, or E-type diaphragms, square diaphragms, pendant diaphragms, or composite diaphragms, etc., which are used to convert the measured acoustic signal (emitted by the acoustic signal source 11) into a deformation or displacement signal of the diaphragm, thereby introducing a corresponding optical phase change in the measurement optical path. The first optical time delay device 51 and the second optical time delay device 52 respectively correspond to the first transducer 53 and the second transducer 63, generating different delay times, so that there is a time delay between the optical phase signals of the two sensing channels, forming a time differential effect. The other settings of the two sensing channels are the same, and the distances between the first transducer 53 and the second transducer 63 and the acoustic signal source 11 are the same.

[0063] The photodetector 8 detects the asymmetric interference optical signal, converts the light intensity change into an electrical signal, the data acquisition module 9 converts the voltage signal output by the photodetector 8 into a digital signal, and the data processing module 10 processes the digital signal transmitted by the data acquisition module 9 to extract useful information and recover the acoustic signal within the working bandwidth.

[0064] Acoustic signal measurement based on asymmetric interference pre-time difference mainly involves the narrowband light source 1 emitting the same beam of light. After passing through the pre-selected first polarizer 22, linearly polarized light is formed, and then it is transmitted through the three-port fiber optic circulator 3 to the polarization beam splitter prism 42, where it is divided into two beams of light with orthogonal polarization states. The first beam of light is transmitted to the first transducer 53 and then reflected to the first optical time delay device 51, generating a controllable time delay τ1. Then it is reflected to the polarization beam splitter prism 42 to be combined with the second beam of light. The second beam of light is transmitted to the second transducer 63 and then reflected to the second optical time delay device 61, generating a controllable time delay τ2. Then it is reflected to the polarization beam splitter prism 42 to be combined with the second beam of light. When combining the beams, there is a controllable time delay τ = τ2 - τ1 between the two beams of light, thus forming a time difference. The combined light is then phase and polarization state modulated by the post-selection module 7 to form an asymmetric interference at the incident end of the photodetector 8. The photodetector then converts the light intensity change signal into an electrical signal, and then it passes through the data acquisition module 9 to reach the data processing module 10, which processes the data to recover the acoustic signal within the working bandwidth. The entire working process of this acoustic signal measurement and sensing system includes two parts: acoustic transduction and optical sensing:

[0065] Acoustic transduction (i.e., sound signal - mechanical deformation or displacement): For example, in a diaphragm transducer, the sound signal causes the diaphragm to vibrate, resulting in displacement of the diaphragm. The key characteristics of this process are the acoustic sensitivity and frequency characteristics of the diaphragm, that is, the relationship between the displacement of the vibrating diaphragm and the natural frequency and the relevant parameters of the diaphragm. Since the diaphragm generates displacement due to the sound signal, the light reflected from the transmitting fiber back to the receiving fiber will be modulated by the corresponding optical phase change.

[0066] Optical sensing (i.e., optical phase change - electrical signal - digital signal): Through the interference detection optical path, the optical phase change to be measured is converted into a current signal by the photodetector, and then the acoustic signal waveform is restored through subsequent electronics processing and algorithm processing.

[0067] For the convenience of understanding by those skilled in the art, the following briefly introduces asymmetric interference:

[0068] In the actual application process, it is necessary to establish a phase measurement model based on linear weak value amplification: First, perform pre-selection on the polarization state of a single-frequency coherent light beam, and at the same time express the initial state |Ψ i > as:

[0069]

[0070] In the above formula, |H> and |V> represent the horizontal polarization state and the orthogonal polarization state of the light beam respectively. After passing through the polarization beam splitting system, the initial state is divided into two light beams of these two polarization states. After passing through the sensing system, a small phase difference α will be generated between the two linearly polarized light beams with orthogonal polarization states, and then reflected back to the polarization beam splitting system for beam combination. At this time, the state |φ> of the system can be expressed as:

[0071]

[0072] In the above formula, |H> and |V> represent the horizontal polarization state and the vertical polarization state of the light beam respectively. In this system, α is the phase difference caused by different time delays between the two light beams with perpendicular polarization states in the two sensing channels, |Ψ i > represents the initial state of the system, represents the polarization state of the signal.

[0073] After that, the following post-selection is performed on the light:

[0074]

[0075] In the above formula, ± represents two post-selection states symmetric about the 45° linear polarization direction, m represents the final state selected through the post-selection step in the system, κ is the post-selection parameter, whose value can be a real number or a complex number, is related to the light polarization direction and the amplitude size, and can be set by adjusting the angle between the polarization direction of the pre-selection linear polarizer and the polarization direction of the post-selection linear polarizer, or can also be set by adjusting the phase and the polarization adjustment component.

[0076] After the post-selection, the state of the system will become:

[0077]

[0078] In the above formula, represents the observable weak value of the system. The magnitude of the weak value is related to the post-selection parameter κ. The smaller the post-selection parameter, the larger the corresponding weak value amplification factor. Therefore, by constructing appropriate pre-selection and post-selection, when the pre-selection and post-selection states are close to orthogonal, the post-selection parameter will approach the minimum value, and the observable weak value will be significantly amplified. This is the so-called weak value amplification effect.

[0079] Finally, a photodetector is used to detect the light intensity of the light beam after passing through the post-selection. The light intensity result can be expressed as:

[0080]

[0081] In the above formula, I0 represents the initial intensity of the light beam. When the values of α and κ are at their minimums, the measured light intensity value I has a linear increasing relationship with the phase α. Therefore, the phase α can be deduced inversely from the detected light intensity value, that is, the phase difference between the return light beams of the two sensing channels. This phase difference is caused by the different time delays generated by the time delay device for the return light beams of the two channels.

[0082] Figure 3 The flow chart of the conversion and transmission of the acoustic signal among the modules in this measurement system is shown. Among them, the acoustic wave signal P(t) is generated by the sound source, and then the acoustic wave signal acts on the first diaphragm transducer and the second diaphragm transducer, and is respectively converted into the vibration displacement signals of the diaphragms (illustrated by the displacement of the center point) x1(t) and x2(t). Then, the incident optical signals are respectively modulated and converted into optical signals E1(t) and E2(t). After that, they respectively pass through the first optical time delay device and the second optical time delay device to generate different time delays τ1 and τ2, and then the signals are converted into the first optical signal and the second optical signal:

[0083]

[0084] Among them, E0 is the amplitude of the optical field, ω is the angular frequency of the light wave; φ(t) is the phase term, and the signal to be measured (acoustic signal) is included in φ(t).

[0085] After the two light beams are combined by the polarization beam splitting system and form an asymmetric interference at the incident end of the photodetector, the total light intensity of the signal after the asymmetric interference can be obtained from formulas (1)-(5) as:

[0086] I(t) = I0sin 2 κ(1 + Δφ(t,τ)|A w |) (7)

[0087] In the above formula, I0 represents the initial intensity of the light beam, τ is the time delay τ = τ2 - τ1, Δφ(t,τ) represents the time difference term of the phase difference, Δφ(t,τ) = φ(t) - φ(t - τ), and κ represents the post-selection parameter.

[0088] In the technical solution of this embodiment, the time difference term Δφ(t,τ) = φ(t) - φ(t - τ), and its corresponding Laplace transform is H(s) = 1 - e -sτ , substituting s = j2πf into it, its transfer function can be obtained as:

[0089] H(j2πf) = 1 - e -j2πfτ (8)

[0090] Its amplitude response is:

[0091]

[0092] For Equation (8), when the frequency f in the low-frequency band is very small, the approximate relationship sin(x)≈x can be satisfied, and we can obtain:

[0093] |H(j2πf)|≈2πfτ (10)

[0094] At this time, the amplitude response decays linearly with f, and low-frequency signals are significantly suppressed.

[0095] When f increases, ∣H(jf)∣ increases with sin(πfτ), showing a high-pass characteristic.

[0096] This transfer function H(s) shows active suppression of low-frequency noise in the frequency domain while retaining a linear response to the acoustic signals in the working frequency band.

[0097] After subsequent signal acquisition, the inverse of the transfer function is used to solve for φ(t) to be measured.

[0098] Adopting the above low-frequency noise suppression scheme based on pre-time difference, introducing the noise suppression process in the optical interference stage before photoelectric detection can avoid low-frequency noise from entering the subsequent signal link and can better suppress the influence of low-frequency noise on the signal-to-noise ratio of photoelectric sensing and subsequent analog-to-digital conversion.

[0099] In some embodiments, the time delay τ is optimized. According to the minimum frequency (f min ) of the target acoustic signal frequency band and the power spectrum characteristics of low-frequency noise, the time difference component τ of the sensor system is set to satisfy:

[0100]

[0101] Thus, while retaining the effective signal, low-frequency noise outside the working frequency band is filtered out.

[0102] In some embodiments, the above pre-time difference low-frequency noise suppression scheme is combined with the asymmetric interference technique: Equation (11) is for an ideal situation, and in actual measurement, an operable approach is to reasonably design the time delay τ according to the requirements of the transfer function and the measured acoustic signal to better suppress the noise signals in the non-working frequency band. However, since the actual signal to be measured (signal frequency f s >>1 / 2πτ) is proportional to the value of τ after time difference; if the set value of τ is very small, better suppression of low-frequency signals can be achieved, but this also results in a very small phase after time difference. The asymmetric interference technique has a weak value amplification effect and can measure a smaller phase compared to classical interference. Therefore, by combining the asymmetric interference technique and through the pre-time difference processing, better suppression of low-frequency noise in the non-working frequency band can be achieved.​

[0103] The photodetector detects the optical intensity signal. As known from the previous text, where Δφ(t, τ) = φ(t) - φ(t - τ) is the actually measured optical phase signal, the method of calculating the frequency and amplitude of the acoustic signal based on the optical intensity is not limited and is implemented in any achievable manner in the prior art. For example:

[0104] The output signal of the photodetector is:

[0105]

[0106] where β is the responsivity of the photodetector, I0 represents the initial intensity of the light beam, κ represents the post-selection parameter, |A w | represents the observable weak value. The output signal of the photodetector is preprocessed to filter out the DC component and retain the AC component V AC (t):

[0107]

[0108] where the amplitude of the AC component V AC (t).

[0109] Considering the existence of noise, the objective function J(φ) is defined as the sum of the squares of the differences between the estimated value and the actual observed value V AC (t), that is:

[0110]

[0111] In order to find an estimated value of φ(t) that minimizes the objective function J(φ) The optimal solution φ(t) is obtained by iterative solution and is the acoustic signal within the working bandwidth.

[0112] FIG. 4(A) and FIG. 4(B) show a schematic diagram of a second embodiment of the polarization splitting system of the acoustic signal measurement device based on asymmetric interference pre-time difference according to the present invention; as shown in FIG. 4(A), the dashed line with an arrow shows the propagation path of the light beam. Among them, the two light beams (i.e., horizontally polarized light and vertically polarized light) split by the fiber optic polarization beam splitter 4' are respectively incident on the first acoustic signal sensing channel 5 and the second acoustic signal sensing channel 6. After receiving the signals modulated by the transducer and the time delay generated by the optical time delay device, the two polarized light beams are combined by the fiber optic polarization combiner 4" and then enter the post-selection module of the first embodiment described above. As shown in FIG. 4(B), the dashed line with an arrow shows the propagation path of the light beam. Among them, the light passing through the pre-selection module enters the non-polarizing semi-reflective and semi-transmissive beam splitter 42' through the fiber optic coupling mirror 41'. The light transmitted (or reflected) from the non-polarizing semi-reflective and semi-transmissive beam splitter 42' is split into two parallel-propagating polarized light beams with orthogonal polarization directions (e.g., horizontally polarized light and vertically polarized light) after passing through the birefringent crystal 42". These two polarized light beams are respectively incident on the fiber optic coupling mirror 43 and the subsequent first acoustic signal sensing channel, and the fiber optic coupling mirror 44 and the subsequent second acoustic signal sensing channel, and then are respectively reflected and return along the original path to the birefringent crystal 42" to be combined. After the combined light returns and is incident on the non-polarizing semi-reflective beam splitter 42', half of the light is reflected and enters the fiber optic coupling mirror 41" for transmission to the post-selection for subsequent measurement.

[0113] Figure 5 shows a schematic diagram of an alternative embodiment of the post-selection module according to the present invention. In Figure 5 this, the post-selection component includes a linear polarizer 74' and an electro-optic modulator (or magneto-optic modulation crystal) 72'. The dashed arrow in the figure is the spatial light propagation direction. In this alternative embodiment, the Figure 2 quarter-wave plate and half-wave plate in

[0114] are replaced with an electro-optic modulator (or magneto-optic modulation crystal) to achieve precise phase compensation in the post-selection process in an electrically controlled manner.

[0115] The measurement method provided in this embodiment suppresses the non-working frequency band noise signal at the physical end of sensor signal acquisition by introducing optical differential detection means and moving the time difference processing forward to the optical interference stage. In this way, the low-frequency disturbances outside the frequency band and the system self-drift noise are not directly detected by the detector, realizing the suppression of low-frequency noise, further reducing the system noise, improving the recognition sensitivity of weak acoustic signals, and thus enhancing the signal-to-noise ratio of the sensor system and the detection ability of weak signals. The time difference component is a higher-order small quantity of the original signal to be measured. The present invention uses a high-precision asymmetric interference measurement technique to measure the higher-order small quantity. Based on the weak value amplification effect of asymmetric interference, a high signal-to-noise ratio and high-sensitivity measurement of the higher-order small quantity is performed, so that the sensor system can set a smaller time difference component to obtain a better detection signal-to-noise ratio.

[0116] By using the measurement system of this embodiment, the dependence on high-precision frequency-stabilized lasers and thermostatic optical paths can be reduced, and the system complexity and cost can be lowered. It has a certain inhibitory effect on environmental disturbances such as temperature drift and mechanical vibration, and is applicable to non-ideal environments such as field stations and industrial sites.

[0117] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered by the scope of the claims and the description of the present invention.

Claims

1. An acoustic signal measurement device based on asymmetric interference lead time difference, characterized in that: include: A light source for emitting a light beam; A front selection module, used for converting the light beam emitted by the light source into linearly polarized light; A polarization beam splitting system for splitting linearly polarized light into two component beams with mutually orthogonal polarization states; The acoustic transducer sensing part includes an optical time delay device and a transducer. The optical time delay device is used to generate different time delays for two component light beams, and the transducer is used to convert the acoustic signal into mechanical deformation or displacement, and is also used to reflect the two component light beams; the transducer has a consistent acoustic signal frequency response function; The post-selection module modulates the phase and polarization state of the two reflected component beams to satisfy the weak value amplification condition; A photoelectric detector is used to detect the light intensity of an asymmetric interference signal formed by the two post-selected component light beams at the input end of the photoelectric detector, and convert the output into an electrical signal; A data acquisition module, used for converting the electrical signal output by the photoelectric detector into a digital signal; The data processing module is used to process the digital signal and restore the acoustic signal within the working bandwidth.

2. The acoustic signal measuring device based on asymmetric interference lead time difference according to claim 1, characterized in that: A light source, a front selection module, a three-port optical fiber circulator, a polarization splitter system, and an acoustic signal sensing part are arranged in sequence on the incident light path; an acoustic signal sensing part, a polarization splitter system, a three-port optical fiber circulator, a rear selection module, and a photodetector are arranged in sequence on the reflected light path.

3. The acoustic signal measuring device based on asymmetric interference lead time difference according to claim 1, characterized in that: The weak value amplification condition that needs to be satisfied by the post-selection is: The phase and polarization state of the returning light beam are modulated so that the polarization direction of the returning light beam after the post-selection is nearly orthogonal to the polarization direction of the returning light beam after the pre-selection.

4. The acoustic signal measuring device based on asymmetric interference lead time difference according to claim 2, characterized in that: The front selection module comprises: an optical fiber, a first optical fiber coupling mirror, a first polarizer, and a second optical fiber coupling mirror which are sequentially arranged on the incident light path.

5. The acoustic signal measuring device based on asymmetric interference lead time difference according to claim 2, characterized in that: The polarization splitting system includes two optical paths, a third optical fiber coupling mirror, a polarization splitting prism, and a fourth optical fiber coupling mirror are sequentially arranged on one optical path, and a third optical fiber coupling mirror, a polarization splitting prism, and a fifth optical fiber coupling mirror are sequentially arranged on the other optical path; the polarization splitting prisms are the same polarization splitting prism.

6. The acoustic signal measuring device based on asymmetric interference lead time difference according to claim 2, characterized in that: The acoustic signal sensing part includes a first acoustic signal sensing channel and a second acoustic signal sensing channel. The first acoustic signal sensing channel is provided with a first optical time delay, a sixth optical fiber coupling mirror, and a first reflective transducer in sequence on the incident light path. The second acoustic signal sensing channel is provided with a second optical time delay, a seventh optical fiber coupling mirror, and a second reflective transducer in sequence on the incident light path.

7. According to the acoustic signal measuring device based on asymmetric interference lead time difference according to claim 6, the reflective transducer includes a diaphragm transducer; the diaphragm transducer includes a flywheel-type vibration film, a corrugated diaphragm, a circular diaphragm, a cantilever diaphragm or a composite diaphragm.

8. The acoustic signal measuring device based on asymmetric interference lead time difference according to claim 2, characterized in that: The post-selection module includes an eighth fiber coupling mirror, a half wave plate, a quarter wave plate, a second polarizer, and a ninth fiber coupling mirror arranged in sequence on the reflected light path; the half wave plate and the quarter wave plate together constitute a phase modulation component.

9. According to the acoustic signal measurement device based on asymmetric interference lead time difference as described in claim 2, the polarization splitting system includes a fiber polarization beam splitter and a fiber polarization beam combiner; the post-selection module includes a linear polarizer, and an electro-optic modulator or a magneto-optical modulation crystal.

10. An acoustic signal measurement method based on asymmetric interference lead time difference, characterized in that: The method of measuring an acoustic signal using the acoustic signal measuring device according to any one of claims 1 to 9 comprises: The light beam emitted by the light source passes through the front selectively to form linearly polarized light; The linearly polarized light is divided into two component light beams with mutually orthogonal polarization states by polarization splitting; the two component light beams are passed through different optical time delay devices to generate different time delays in the optical path; Using a transducer to convert the acoustic signal into mechanical deformation or displacement, so that the two reflected component light beams produce optical path or phase changes and carry acoustic signal information; The two component light beams carrying the acoustic signal information enter the post-selection again through polarization splitting, and the phase and polarization state of the optical signal carrying the acoustic signal information are modulated through the post-selection; The two post-selected component beams form an asymmetric interference signal at the interference point; The light intensity of the asymmetric interference signal is obtained by photoelectric detection, and the acoustic signal within the working bandwidth is calculated based on the light intensity.

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