A high sensitivity acoustic wave sensing system and method
By combining AOM continuous optical heterodyne detection with suspended micro-nano optical fiber, the problems of mechanical resonance, packaging damping and signal fading of fiber optic acoustic wave sensors have been solved, and stable, lock-free, and highly sensitive detection of high-frequency ultrasound has been achieved.
Patent Information
- Application Number
- CN202610302443.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-12
- Publication Date
- 2026-07-24
AI Technical Summary
Existing fiber optic acoustic sensors suffer from problems such as mechanical resonance frequency limitation, poor high-frequency response, packaging damping, signal fading, and insufficient high-frequency response, making it difficult to effectively detect ultrasonic signals with frequencies higher than 20kHz.
A high-sensitivity acoustic wave sensing system based on AOM continuous optical heterodyne detection and suspended micro-nano fiber is adopted, including a narrow linewidth laser, beam splitter, acousto-optic modulator, suspended micro-nano fiber sensing probe, optical coupler and IQ demodulation module. The system directly senses the acoustic wave signal through the suspended micro-nano fiber and combines it with IQ demodulation technology to eliminate mechanical resonance and encapsulation damping, thereby achieving stable detection of high-frequency signals.
It achieves wideband detection without mechanical resonance limitations, encapsulation damping, or signal fading, and can respond to ultrasonic waves ranging from infrasound to MHz level. It has an infinite dynamic range and high sensitivity, and can continuously capture high-frequency transient acoustic signals.
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Figure CN122448340A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of fiber optic sensing technology, and in particular to a high-sensitivity acoustic wave sensing system and method. Background Technology
[0002] Fiber optic acoustic sensors are widely used in fields such as medical diagnosis, industrial micro-vibration detection, underwater acoustic detection, and structural health monitoring due to their advantages such as resistance to electromagnetic interference, corrosion resistance, small size, and high sensitivity.
[0003] Currently, most mainstream fiber optic acoustic sensors adopt a "diaphragm" or "cantilever beam" structure, which utilizes the resonance of a physical diaphragm under sound pressure to drive the deformation of the optical fiber, thereby modulating the optical signal. However, this type of structure has inherent defects: the diaphragm has a mechanical resonant frequency, resulting in poor high-frequency response and difficulty in effectively detecting ultrasonic signals with frequencies higher than 20kHz; at the same time, the diaphragm material is prone to aging, exhibits mechanical hysteresis, and lacks long-term stability.
[0004] Another type of existing technology is the fiber optic Fabry-Perot (FP) cavity probe. Although these probes are small and compact, they are mostly reflective structures, extremely sensitive to the wavelength of the light source, and difficult to directly integrate with heterodyne detection technology, resulting in a complex demodulation system that is susceptible to low-frequency noise.
[0005] In recent years, micro- and nano-fibers have attracted attention due to their extremely low bending stiffness, strong evanescent field characteristics, and high sensitivity. However, existing technologies often use polymer-modified molecular weighted seismic materials (PDMS) to encapsulate micro- and nano-fibers for mechanical protection. While this encapsulation protects the fiber, the polymer absorbs weak sound waves, introducing mechanical damping, which leads to a significant decrease in the sensor's response sensitivity to extremely weak sound waves (especially airborne sound waves).
[0006] In signal demodulation, traditional Mach-Zehnder (MZI) interferometers often employ homodyne detection. Homodyne detection is highly susceptible to interference from ambient temperature drift and laser 1 / f noise in the low-frequency range, leading to signal fading and necessitating the introduction of complex piezoelectric ceramic feedback frequency stabilization systems. However, feedback systems suffer from limited dynamic range and are prone to lock-up issues. Furthermore, while pulsed distributed fiber optic sensing systems can achieve distributed measurements, they suffer from sampling blind spots caused by pulse intervals, making it impossible to continuously and in real-time capture high-frequency transient acoustic signals. Summary of the Invention
[0007] The main objective of this application is to propose a high-sensitivity acoustic wave sensing system and method based on AOM continuous optical heterodyne detection and suspended micro / nano optical fiber, so as to solve the problems of mechanical resonance limitation, encapsulation damping, signal fading and insufficient high-frequency response in the prior art.
[0008] To achieve the above objectives, one aspect of this application provides a high-sensitivity acoustic wave sensing system, comprising: Narrow linewidth lasers are used to output continuous coherent light. The beam splitter, whose input end is connected to the output end of the narrow linewidth laser, is used to split the continuous coherent light into two paths, which enter the reference arm and the sensing arm respectively. An acousto-optic modulator (AOM), disposed in the reference arm, operates in continuous wave mode and is used to perform fixed-frequency frequency shifting on the passing optical signal, with an output frequency of [missing value]. The local oscillator; A suspended micro / nano fiber optic sensing probe, disposed within the sensing arm, is used to modulate external acoustic wave signals into phase changes transmitted through light, with an output frequency of [frequency value missing]. The phase of the signal light is modulated by the sound wave; An optical coupler, whose two input ends are respectively connected to the output ends of the reference arm and the sensing arm, is used to combine the local oscillator light and the signal light to form interference light; A photodetector, connected to the output of the optical coupler, is used to convert the interference light into light with a center frequency of [missing value]. Beat frequency electrical signal; The IQ demodulation module is connected to the output terminal of the photodetector and is used to perform quadrature demodulation on the beat frequency electrical signal to extract the phase change caused by the acoustic signal.
[0009] In some embodiments, the suspended micro / nano fiber optic sensing probe includes: The U-shaped suspension bracket has an upward-opening U-shaped groove; Micro-nano optical fiber is made of standard single-mode optical fiber with thermal tapering, with both ends being non-tapered thick ends and the middle being tapered thin end; The non-tapered thick end is fixed to both sides of the U-shaped suspended bracket, and the tapered thin end is completely suspended above the U-shaped groove, without contacting any solid or encapsulation material.
[0010] In some embodiments, the micro / nano optical fiber is subjected to axial pretension during encapsulation, so that it is in a taut “optical string” shape in a suspended state, in order to enhance the linearity of the vibration response to sound waves.
[0011] In some embodiments, the waist region diameter of the micro / nano optical fiber is The length of the waist region is .
[0012] In some embodiments, the frequency shift amount of the acousto-optic modulator 10MHz 200MHz, preferably 80MHz.
[0013] In some embodiments, the IQ demodulation module includes: The digital local oscillator signal generation unit is used to generate a local oscillator frequency of... orthogonal signals and ; A mixing unit is used to multiply the beat frequency electrical signal with the quadrature signal respectively to obtain the mixed in-phase component and quadrature component; A low-pass filter is used to filter out high-frequency components in the output signal of the mixer unit to obtain baseband in-phase signal and baseband quadrature signal; The phase calculation unit is used to extract the instantaneous phase based on the baseband in-phase signal and the baseband quadrature signal through arctangent operation; An unwinding unit is used to unwind the instantaneous phase to eliminate phase jumps; A high-pass filter is used to filter out the low-frequency environmental drift component in the instantaneous phase and output a clean acoustic signal phase.
[0014] In some embodiments, the phase modulation of the suspended micro / nano fiber optic sensing probe originates from the synergistic effect of the following three physical effects: Sound pressure drives the suspended optical fiber to undergo geometric deformation, changing the physical optical path. Sound pressure induces a photoelastic effect in quartz materials, altering the material's refractive index. Sound waves alter the density of the surrounding air, modulating the effective refractive index through the evanescent field of micro / nano optical fibers.
[0015] To achieve the above objectives, another aspect of this application proposes a high-sensitivity acoustic wave sensing method, applied to the aforementioned high-sensitivity acoustic wave sensing system, comprising the following steps: A narrow-linewidth laser outputs continuous coherent light, which is split into two paths by a beam splitter; The acousto-optic modulator in the reference arm applies a fixed frequency to the optical signal. Frequency shifting of the output local oscillator light; The suspended micro-nano fiber optic sensing probe in the sensing arm is subjected to external sound waves, which modulate the phase of the passing optical signal and output signal light. The local oscillator light and the signal light are combined at the optical coupler to form interference light, which is then converted by the photodetector to a center frequency of [frequency value missing]. Beat frequency electrical signal; The IQ demodulation module performs quadrature demodulation on the beat frequency electrical signal to extract the phase change caused by the acoustic signal.
[0016] In some embodiments, the IQ demodulation module performs quadrature demodulation on the beat frequency electrical signal to extract the phase change caused by the acoustic signal, including: Generate two orthogonal digital local oscillator signals and ; The beat frequency electrical signal is mixed with two local oscillator signals to obtain in-phase and quadrature components. High-frequency components after mixing are filtered out by a low-pass filter to obtain baseband in-phase and baseband quadrature signals; The instantaneous phase is calculated based on the baseband signal using arctangent calculation. The instantaneous phase is unwound to eliminate phase jumps; The low-frequency environmental drift component is filtered out by a high-pass filter, and the phase of the output sound wave signal is obtained.
[0017] In some embodiments, the method does not require piezoelectric ceramic feedback control, and directly filters out low-frequency phase drift caused by ambient temperature through the high-pass filter, thereby achieving stable detection that never loses lock.
[0018] Compared with the prior art, this application has the following beneficial effects: 1) No mechanical resonance limitation, flat and wide frequency response: Using transmission-type suspended micro-nano optical fiber as the sensing element, the traditional diaphragm or cantilever beam structure is abandoned, which fundamentally eliminates the limitation of mechanical resonance frequency and can effectively respond to broadband signals from infrasound to MHz-level ultrasound.
[0019] 2) Unencapsulated damping, high sensitivity: The suspended structure eliminates the mechanical damping and sound absorption effect of the polymer encapsulation material. The micro-nano optical fiber interacts directly with the sound field, and the evanescent field is extremely sensitive to changes in the surrounding medium, which significantly improves the response sensitivity to weak airborne sound waves.
[0020] 3) No signal fading and unlimited dynamic range: AOM continuous optical heterodyne detection is used to shift the acoustic signal to a high-frequency carrier in the MHz range. Combined with IQ demodulation and digital high-pass filtering, low-frequency phase noise caused by ambient temperature drift is directly filtered out. No PZT feedback control is required, which fundamentally solves the signal fading problem of traditional zero-difference interferometers and achieves stable detection that never loses lock, with unlimited dynamic range.
[0021] 4) No sampling blind zone, capable of continuously capturing transient signals: Adopting a continuous optical working mode, unlike pulse-type distributed fiber optic sensing systems, there is no sampling blind zone caused by pulse intervals, enabling continuous and real-time capture of high-frequency transient acoustic signals.
[0022] 5) Multi-physics field synergistic enhancement and strong detection capability: The phase modulation of the suspended micro-nano fiber comes from the synergistic effect of geometric deformation, photoelastic effect and evanescent field modulation. The superposition of the three makes the probe's response sensitivity to weak sound waves much higher than that of ordinary optical fibers. Attached Figure Description
[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following description is provided with accompanying drawings of the relevant technical solutions in the embodiments of this application or the prior art. It should be understood that the accompanying drawings described below are only for the purpose of clearly illustrating some embodiments of the technical solutions of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.
[0024] Figure 1 This is a structural block diagram of the high-sensitivity acoustic wave sensing system provided in the embodiments of this application; Figure 2 This is a schematic diagram of the overall optical path of the high-sensitivity acoustic wave sensing system based on AOM continuous optical heterodyne detection and suspended micro / nano optical fiber provided in the embodiments of this application. Figure 3 This is a schematic diagram of the structure of the suspended micro / nano fiber optic sensing probe provided in the embodiments of this application; Figure 4 The following is a simulation result diagram of the system provided in this application for detecting weak acoustic signals, where (a) is the signal fading phenomenon of a conventional MZI interferometer under environmental drift, and (b) is the acoustic demodulation signal based on AOM heterodyne detection; Figure 5 This is a flowchart of the high-sensitivity acoustic wave sensing method provided in the embodiments of this application. Detailed Implementation
[0025] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. The step numbers in the following embodiments are set only for ease of explanation, and there is no limitation on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.
[0026] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.
[0027] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.
[0028] Furthermore, in the description of this invention, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.
[0029] Before providing a detailed description of the embodiments of this application, some of the nouns and terms involved in the embodiments of this application will be explained first. The nouns and terms involved in the embodiments of this application are subject to the following interpretations.
[0030] 1) An acousto-optic modulator (AOM) is an optical device that uses the acousto-optic effect to rapidly modulate the intensity, frequency, direction, or phase of a laser beam.
[0031] 2) Mach–Zehnder usually refers to the Mach–Zehnder interferometer (MZI) or devices based on its principles, such as the Mach–Zehnder modulator (MZM). It is a core optical device that uses the interference effect of light to perform high-precision measurement or signal modulation.
[0032] 3) Fiber Fabry-Pérot is a fiber optic structure based on the Fabry-Pérot interference principle, which is widely used in sensing, communication and laser fields.
[0033] To address the problems of existing technologies, this application aims to propose a novel sensing system without diaphragms, polymer damping, or signal fading. By combining AOM continuous optical heterodyne with suspended micro / nano optical fibers, it solves the pain points of existing technologies in detecting weak low-frequency signals and high-frequency ultrasonic signals. This application utilizes the extremely low inertia of micro / nano optical fibers and the high-frequency carrier of AOM to achieve a wideband response from infrasound to ultrasound. The innovations of this application are as follows: 1) Structural innovation: Abandoning the traditional diaphragm sensitization and PDMS full encapsulation, a U-shaped suspended micro-nano fiber optic probe is designed. The extremely low bending stiffness and strong evanescent field of the micro-nano fiber are used to directly sense sound waves, realizing undamped intrinsic detection.
[0034] 2) Methodological Innovation: Unlike existing pulsed distributed detection (such as φ-OTDR), this application adopts continuous light (CW) AOM heterodyne detection. The AOM not only acts as a frequency shifter to generate high-frequency carriers (such as 80MHz), but also shifts the acoustic signal to the high-frequency low-noise region, completely solving the problems of low-frequency noise and operating point drift (signal fading) of MZI interferometers.
[0035] like Figure 1 As shown, this embodiment provides a high-sensitivity acoustic wave sensing system, specifically including: Narrow linewidth lasers are used to output continuous coherent light. The beam splitter, whose input end is connected to the output end of the narrow linewidth laser, is used to split the continuous coherent light into two paths, which enter the reference arm and the sensing arm respectively. An acousto-optic modulator (AOM), disposed in the reference arm, operates in continuous wave mode and is used to perform fixed-frequency frequency shifting on the passing optical signal, with an output frequency of [missing value]. The local oscillator; A suspended micro / nano fiber optic sensing probe, disposed within the sensing arm, is used to modulate external acoustic wave signals into phase changes transmitted through light, with an output frequency of [frequency value missing]. The phase of the signal light is modulated by the sound wave; An optical coupler, whose two input ends are respectively connected to the output ends of the reference arm and the sensing arm, is used to combine the local oscillator light and the signal light to form interference light; A photodetector, connected to the output of the optical coupler, is used to convert the interference light into light with a center frequency of [missing value]. Beat frequency electrical signal; The IQ demodulation module is connected to the output terminal of the photodetector and is used to perform quadrature demodulation on the beat frequency electrical signal to extract the phase change caused by the acoustic signal.
[0036] In one embodiment, the system employs a transmission Mach-Zehnder (MZI) interferometer structure, as detailed below: a) Light source: Continuous wave (CW) narrow linewidth laser.
[0037] b) Reference arm (modulation arm): A coherent acousto-optic modulator (AOM) is connected in series and is normally open. It performs a fixed-frequency shift (e.g., shift amount) on the optical signal. ), without pulse modulation.
[0038] c) Sensing arm (signal arm): A series suspended micro / nano fiber optic sensing probe, the phase of the optical signal is modulated by the acoustic wave.
[0039] d) Detection: The two beams are combined at the coupler, and the center frequency of the photodetector output is... Continuous beat frequency signal.
[0040] As an optional embodiment, the structure of the suspended micro / nano fiber optic sensing probe is as follows: a) Micro / nano fiber: formed by thermally tapering standard single-mode fiber, with a waist diameter of [missing information]. , length is .
[0041] b) U-shaped suspended support: The probe base is designed as a U-shaped groove structure or a hollow frame. The non-tapered section (thick end) of the micro-nano fiber is fixed on both sides of the support, while the tapered section (thin end) is completely suspended above the U-shaped groove and does not come into contact with any solid or colloid.
[0042] c) Pretension control: A weak axial pretension is applied to the micro-nano fiber during packaging, so that it exhibits a "fiber string" vibration mode under the action of acoustic waves, thereby maximizing the sound pressure-deformation conversion efficiency.
[0043] d) Multiphysics field sensitization mechanism: phase modulation of this structure The effect stems from three synergistic factors: ① Sound pressure drives the suspended optical fiber to undergo geometric deformation and vibration, altering the physical optical path; ② Sound pressure induces the photoelastic effect in the quartz material, changing its refractive index; ③ Sound waves alter the surrounding air density, modulating the effective refractive index through the strong evanescent field of the micro / nano optical fiber. The combined effect of these three factors makes the probe's response sensitivity to weak sound waves far higher than that of ordinary optical fibers.
[0044] In one embodiment, the anti-interference demodulation method is as follows: the output signal is Phase extraction is achieved using the orthogonal demodulation (IQ Demodulation) technique. Due to carrier frequency (e.g., 80MHz) is much higher than the ambient temperature drift frequency (<10Hz) and the sound wave frequency (20Hz-20kHz). The ambient drift term can be perfectly separated by a digital filter (filtered out as an extremely low frequency component), thus achieving stable detection without ever losing lock without using piezoelectric ceramic (PZT) feedback control.
[0045] Below, in conjunction with Figures 2-4 This application provides a detailed description of the high-sensitivity acoustic wave sensing system based on AOM continuous optical heterodyne detection and suspended micro / nano optical fiber, along with specific application examples. This embodiment aims to demonstrate how the system achieves high-sensitivity, fading-free detection of low-frequency, weak acoustic waves through hardware integration and algorithm processing.
[0046] (1) Construction of the optical sensing system See Figure 2 This embodiment provides a high-sensitivity acoustic wave sensing system based on AOM continuous optical heterodyne detection and suspended micro / nano optical fiber, the specific structure of which is as follows: 1.1) Light source selection: A distributed feedback (DFB) narrow-linewidth fiber laser with a center wavelength of 1550nm was selected, with a linewidth of less than 3kHz and an output power of 10mW. The narrow linewidth characteristic ensures coherence during long-distance transmission and reduces the phase noise floor.
[0047] 1.2) Optical beam splitting: The light output from the laser passes through an optical isolator (ISO, to prevent backlight damage to the laser) and then enters the first optical coupler (C1, with a splitting ratio of 50:50), where it is split into two paths of equal energy, which enter the reference arm and the sensing arm respectively.
[0048] 1.3) Reference arm (modulation): An optical fiber coupled acousto-optic modulator (AOM) is connected in series in the reference arm.
[0049] This AOM operates in continuous wave mode, not pulse mode. The frequency is provided by an RF driver. The sinusoidal drive signal. The optical signal frequency shifts overall after passing through the AOM, from its original... Become , which is the local oscillator (LO) of the system.
[0050] 1.4) Sensing Arm (Detection): Connected to a self-made suspended micro / nano fiber optic sensing probe (see Section (2) for details). The frequency of the optical signal transmitted by this arm remains constant. Unchanged, but its phase It will be modulated in real time by the external sound wave field.
[0051] 1.5) Signal combining and detection: The ends of the two optical fibers are connected to a second optical coupler (C2, splitting ratio 50:50) for combining. The combined optical signal enters an InGaAsPIN photodetector (PD) with a bandwidth of 200MHz. Due to the 80MHz frequency difference between the two beams, the electrical signal output by the detector is a beat frequency interference signal with a center frequency of 80MHz.
[0052] 1.6) IQ demodulation module: The analog voltage signal output by the photodetector is connected to the high-speed data acquisition card (the sampling rate is set to 200MS / s) and real-time digital signal processing is performed in the FPGA. For details, please refer to Section (3).
[0053] (2) Fabrication and packaging of suspended micro / nano fiber optic probes See Figure 3 The suspended micro / nano fiber optic probe is the core sensing element of this system, and its fabrication process is as follows: 2.1) Nanofiber drawing Standard single-mode fiber (SMF-28) was selected, and after the coating was stripped, it was thermally tapered using an oxyhydrogen flame melting tapering machine. By controlling the tapering parameters, a fiber with a waist diameter of [missing information] was fabricated. The uniform waist length is Micro- and nano-sized optical fibers. Optical fibers of this diameter have extremely strong evanescent fields and extremely low bending stiffness, and are extremely sensitive to weak airflow and sound pressure.
[0054] 2.2) Suspension Support Design The U-shaped groove support is made of quartz or low-expansion-coefficient glass. The opening width of the U-shaped groove is slightly larger than the waist length of the micro / nano fiber (e.g., 16 mm), and the depth is greater than 2 mm to ensure that the fiber does not touch the bottom surface when suspended.
[0055] 2.3) Pre-tensioned packaging (critical process) The tapered micro / nano fiber was transferred onto a U-groove support. Under microscopic monitoring, a high-precision micro-displacement platform was used to clamp the non-tapered regions (thicker ends) of the fiber. Before fixing, a slight axial tensile displacement (approximately) was applied to both ends of the fiber. This creates pretension in the suspended area. The purpose of pretension is to prevent the optical fiber from sagging due to gravity and to keep it in a taut "string"-like state, thus improving its linearity in response to high-frequency sound waves. The thicker end of the optical fiber is fixed to the platforms on both sides of the bracket using UV-curing adhesive. After the adhesive has fully cured, the clamps are released, completing the probe encapsulation.
[0056] 2.4) Multiphysics Sensitization Mechanism The phase modulation of this probe originates from the synergistic effect of three factors: a) Geometric deformation: Sound pressure drives the suspended optical fiber to vibrate micro-vibrations, changing the physical optical path; b) Photoelastic effect: Sound pressure causes stress changes in quartz materials, altering the material's refractive index; c) Evanescent field modulation: Sound waves change the density of the surrounding air, and the effective refractive index is modulated by the strong evanescent field of micro-nano optical fibers.
[0057] The combination of these three factors makes the probe's response sensitivity to weak sound waves far higher than that of ordinary optical fibers.
[0058] (3) Demodulation process of heterodyne signal (algorithm implementation) The analog voltage signal output by the photodetector is fed into a high-speed data acquisition card (sampling rate set to 200MS / s) and processed in real time on an FPGA or computer. The processing flow is as follows: 3.1) Signal Model: The expression of the acquired digitized signal is:
[0059] in For carrier frequency.
[0060] 3.2) Quadrature down-conversion (IQ Demodulation): Generate two digital local oscillator signals: and The collected signal respectively with and Multiplication (mixing). The harmonics are filtered out using a digital low-pass filter (LPF) to obtain the in-phase component. and orthogonal components .
[0061] 3.3) Phase Extraction: The instantaneous phase is calculated using the four-quadrant arctangent function.
[0062] 3.4) Phase Unwrap: For Perform unwinding to eliminate The phase transitions result in a continuous phase curve. This phase curve includes "ambient temperature drift (large amplitude at low frequencies)" and "acoustic signal (small amplitude at high frequencies)".
[0063] 3.5) Anti-drift filtering: Design a digital high-pass filter. Pass the dewound phase through this filter to directly filter out the extremely low-frequency drift components caused by changes in ambient temperature. Result: Outputs a pure sound wave signal. .
[0064] (4) System performance verification and working results 4.1) Verification of anti-drift performance like Figure 4 As shown, when a slow phase drift (drift amount exceeding π) simulating an ambient temperature change is applied to the sensing arm, Figure 4 Image (a) shows that the traditional zero-difference interferometer exhibits signal fading, with the output waveform distorted or even disappearing. Meanwhile... Figure 4 As shown in Figure (b), thanks to the high-frequency carrier and high-pass filtering introduced by the AOM, the waveform of the acoustic signal output by the system in this embodiment remains stable. The phenomenon of "signal fluctuating" or "complete disappearance (dead zone)" common in traditional zero-difference interferometers does not occur, which verifies the characteristic of the system never losing lock in principle.
[0065] 4.2) High sensitivity characteristics Compared to traditional PDMS fully encapsulated probes, the suspended micro / nano fiber in this embodiment eliminates the mechanical damping and sound absorption effects of the encapsulation material. Theoretical analysis and design expectations indicate that this structure can significantly improve the response to weak airborne sound waves and effectively capture faint whisper-level signals that are imperceptible to the human ear.
[0066] 4.3) Wideband response capability (covering ultrasound) This system possesses a wideband detection capability from infrasound to ultrasound. Physically, the suspended micro / nano optical fiber exhibits extremely low mass and inertia, resulting in a very high mechanical response frequency. In terms of demodulation, the 80MHz high-frequency carrier provided by AOM offers ample bandwidth margin for broadband signal demodulation. The system can not only cover the audible sound frequency band of 20Hz-20kHz, but also achieve distortion-free, high signal-to-noise ratio detection of ultrasonic signals in the 20kHz to MHz range (such as industrial partial-amplitude ultrasound and medical photoacoustic signals).
[0067] See Figure 5 Based on the aforementioned high-sensitivity acoustic wave sensing system, this embodiment also provides a high-sensitivity acoustic wave sensing method, comprising the following steps: Step S1: The narrow linewidth laser outputs continuous coherent light, which is split into two paths by the first optical coupler; Step S2: The acousto-optic modulator in the reference arm performs a frequency shift of 80MHz on the optical signal and outputs local oscillator light; Step S3: The suspended micro-nano fiber optic sensing probe in the sensing arm is subjected to external sound waves, which modulate the phase of the passing optical signal and output signal light. Step S4: The local oscillator light and the signal light are combined at the second optical coupler to form interference light, which is then converted into a beat frequency electrical signal with a center frequency of 80MHz by the photodetector. Step S5: The IQ demodulation module performs quadrature demodulation on the beat frequency electrical signal to extract the phase change caused by the acoustic signal.
[0068] Specifically, step S5 includes: generating two orthogonal digital local oscillator signals; mixing the beat frequency signal with the two local oscillator signals respectively; obtaining baseband in-phase and baseband quadrature signals through a low-pass filter; calculating the instantaneous phase through arctangent operation; unwinding the instantaneous phase; and filtering out low-frequency environmental drift components through a high-pass filter to output the phase of the acoustic signal.
[0069] This method eliminates the need for piezoelectric ceramic feedback control and directly filters out low-frequency phase drift caused by ambient temperature through a high-pass filter, achieving stable detection that never loses lock.
[0070] In summary, compared with the prior art, this application has at least the following advantages: 1) Compared to diaphragm / FP sensors: This application uses transmissive suspended micro / nano optical fibers, which eliminate the mechanical resonance limitations of diaphragms, resulting in a flatter frequency response; it also eliminates end-face reflectors, allowing for greater optical path tolerance and simpler fabrication. Without the mechanical resonance limitations of diaphragms, the frequency response is flat and wide, effectively responding to high-frequency ultrasound above 20kHz.
[0071] 2) Compared to PDMS packaged sensors: The suspended structure eliminates the mechanical damping of the packaging material, and the micro-nano optical fiber interacts directly with the sound field, improving the response sensitivity to weak airborne sound waves.
[0072] 3) Compared to conventional interferometers / PID frequency stabilization: Utilizing AOM heterodyne detection eliminates the need for complex PZT feedback circuits, avoids the "lock-off" problem caused by feedback loop saturation, offers an infinite dynamic range, and effectively avoids the low-frequency intensity noise (RIN) of the laser. It also boasts an infinite dynamic range, and its MHz-level carrier bandwidth is sufficient to support distortion-free demodulation of high-frequency ultrasonic signals.
[0073] 4) Compared to distributed pulse systems: It uses continuous light to operate, eliminating sampling blind spots caused by pulse intervals, and can continuously and in real time capture high-frequency transient acoustic signals.
[0074] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," or "some embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0075] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
[0076] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.
Claims
1. A high-sensitivity acoustic wave sensing system, characterized in that, include: Narrow linewidth lasers are used to output continuous coherent light. The beam splitting module, whose input end is connected to the output end of the narrow linewidth laser, is used to split the continuous coherent light into two paths, which enter the reference arm and the sensing arm respectively. An acousto-optic modulator, disposed in the reference arm, operates in continuous wave mode and is used to perform fixed-frequency frequency shifting on the passing optical signal, with an output frequency of [frequency value missing]. The local oscillator; A suspended micro / nano fiber optic sensing probe, disposed within the sensing arm, is used to modulate external acoustic wave signals into phase changes transmitted through light, with an output frequency of [frequency value missing]. The phase of the signal light is modulated by the sound wave; An optical coupler, whose two input ends are respectively connected to the output ends of the reference arm and the sensing arm, is used to combine the local oscillator light and the signal light to form interference light; A photodetector, connected to the output of the optical coupler, is used to convert the interference light into light with a center frequency of [missing value]. Beat frequency electrical signal; The IQ demodulation module is connected to the output terminal of the photodetector and is used to perform quadrature demodulation on the beat frequency electrical signal to extract the phase change caused by the acoustic signal.
2. The high-sensitivity acoustic wave sensing system according to claim 1, characterized in that, The suspended micro / nano fiber optic sensing probe includes: The U-shaped suspension bracket has an upward-opening U-shaped groove; Micro-nano optical fiber is made of standard single-mode optical fiber with thermal tapering, with both ends being non-tapered thick ends and the middle being tapered thin end; The non-tapered thick end is fixed to both sides of the U-shaped suspended bracket, and the tapered thin end is completely suspended above the U-shaped groove, without contacting any solid or encapsulation material.
3. The high-sensitivity acoustic wave sensing system according to claim 2, characterized in that, The micro-nano optical fiber is subjected to axial pretension during packaging, so that it is in a taut "optical string" shape in a suspended state, in order to enhance the linearity of the vibration response to sound waves.
4. The high-sensitivity acoustic wave sensing system according to claim 2, characterized in that, The waist diameter of the micro / nano optical fiber is The length of the waist region is .
5. The high-sensitivity acoustic wave sensing system according to claim 1, characterized in that, The frequency shift amount of the acousto-optic modulator 10MHz 200MHz.
6. The high-sensitivity acoustic wave sensing system according to claim 1, characterized in that, The IQ demodulation module includes: The digital local oscillator signal generation unit is used to generate a local oscillator frequency of... orthogonal signals and ; A mixing unit is used to multiply the beat frequency electrical signal with the quadrature signal respectively to obtain the mixed in-phase component and quadrature component; A low-pass filter is used to filter out high-frequency components in the output signal of the mixer unit to obtain baseband in-phase signal and baseband quadrature signal; The phase calculation unit is used to extract the instantaneous phase based on the baseband in-phase signal and the baseband quadrature signal through arctangent operation; An unwinding unit is used to unwind the instantaneous phase to eliminate phase jumps; A high-pass filter is used to filter out the low-frequency environmental drift component in the instantaneous phase and output a clean acoustic signal phase.
7. The high-sensitivity acoustic wave sensing system according to claim 1, characterized in that, The phase modulation of the suspended micro / nano fiber optic sensing probe originates from the synergistic effect of the following three physical effects: Sound pressure drives the suspended optical fiber to undergo geometric deformation, changing the physical optical path. Sound pressure induces a photoelastic effect in quartz materials, altering the material's refractive index. Sound waves alter the density of the surrounding air, modulating the effective refractive index through the evanescent field of micro / nano optical fibers.
8. A high-sensitivity acoustic wave sensing method, applied to the system described in any one of claims 1 to 7, characterized in that, Includes the following steps: The narrow linewidth laser outputs continuous coherent light, which is split into two paths by a beam splitter module; The acousto-optic modulator in the reference arm applies a fixed frequency to the optical signal. Frequency shifting of the output local oscillator light; The suspended micro-nano fiber optic sensing probe in the sensing arm is subjected to external sound waves, which modulate the phase of the passing optical signal and output signal light. The local oscillator light and the signal light are combined at the optical coupler to form interference light, which is then converted by the photodetector to a center frequency of [frequency value missing]. Beat frequency electrical signal; The IQ demodulation module performs quadrature demodulation on the beat frequency electrical signal to extract the phase change caused by the acoustic signal.
9. The high-sensitivity acoustic wave sensing method according to claim 8, characterized in that, The IQ demodulation module performs quadrature demodulation on the beat frequency electrical signal to extract the phase change caused by the acoustic signal, including: Generate two orthogonal digital local oscillator signals and ; The beat frequency electrical signal is mixed with two local oscillator signals to obtain in-phase and quadrature components. High-frequency components after mixing are filtered out by a low-pass filter to obtain baseband in-phase and baseband quadrature signals; The instantaneous phase is calculated based on the baseband signal using arctangent calculation. The instantaneous phase is unwound to eliminate phase jumps; The low-frequency environmental drift component is filtered out by a high-pass filter, and the phase of the output sound wave signal is obtained.
10. The high-sensitivity acoustic wave sensing method according to claim 8, characterized in that, The method does not require piezoelectric ceramic feedback control. It directly filters out low-frequency phase drift caused by ambient temperature through the high-pass filter, achieving stable detection that never loses lock.