Optical microcavity sound pressure detection method based on electro-optical heterodyne frequency shift and frequency locking

Abstract

The invention provides an optical microcavity sound pressure detection method based on electro-optical heterodyne frequency shift and frequency locking. A device comprises a tunable laser light source module, a sound pressure sensing module and a signal acquisition and demodulation module. The invention discloses a sound pressure detection method based on an optical microcavity, and the method comprises the steps: locking two tunable lasers with different frequencies to corresponding optical frequency combs through an electro-optical frequency shifter, injecting the two laser frequency combs with different frequencies into the optical microcavity, detecting an optical resonance signal through a photoelectric detector, and carrying out the detection of the sound pressure. And an optical heterodyne demodulation scheme is combined to invert a sound pressure signal of the optical microcavity. Complex modulation driving and demodulation equipment is not needed, the mapping relation between the sound pressure signal and the deformation of the optical microcavity is established, and rapid and high-precision detection of the sound pressure signal is achieved.

Description

Technical Field

[0002] This invention relates to the field of fiber optic sensing technology, specifically an optical microcavity acoustic pressure detection method based on electro-optic heterodyne frequency shifting and locking. Background Technology

[0004] Acoustic emission (AE) testing, as an important non-destructive testing technique, plays a crucial role in materials science, mechanical engineering, and structural health. In recent years, whispering-gallery mode (DMM) optical microcavities have provided a novel detection platform for AE testing due to their ultra-high quality factor and extremely small mode volume. DMM microcavities can efficiently couple acoustic signals into optical modes, enabling highly sensitive acoustic pressure (AP) detection by detecting changes in the optical modes. Traditional DMM AP detection methods typically rely on directly detecting the drift of the microcavity's resonant frequency. This method is susceptible to interference from environmental noise and laser frequency drift, making it difficult to achieve high-precision AP measurements. To address this issue, researchers have proposed various solutions, such as utilizing dual-microcavity structures or introducing reference optical paths. However, these methods often increase system complexity and cost, limiting their practical application. Electro-optic frequency shifting and locking technology, as a mature laser frequency stabilization technique, can effectively suppress laser frequency drift and improve frequency stability. Introducing electro-optic frequency shifting and locking technology into DMM AP detection holds promise for overcoming the shortcomings of traditional methods and achieving highly sensitive and stable AP detection. Therefore, developing a microcavity acoustic pressure detection method based on electro-optic frequency shifting and locking technology has significant research and application value. Summary of the Invention

[0006] To address the technical problem, this invention provides an optical whispering-gallery mode microcavity acoustic pressure detection method based on electro-optic frequency shifting and locking technology. The sensing and detection system has a compact structure, simple process, low cost, high sensitivity, and can realize remote signal transmission.

[0007] To realize the optical microcavity acoustic pressure detection method based on electro-optic heterodyne frequency shifting and locking provided by the present invention, the method includes: a tunable laser source module, an acoustic pressure sensing module, and a signal acquisition and demodulation module. The tunable laser source module includes a tunable laser, a coupler, a first electro-optic frequency shifter, a second electro-optic frequency shifter, an erbium-doped fiber amplifier, and an erbium-doped fiber amplifier, used to generate two optical comb signals with similar frequencies and to manipulate the optical comb spectrum. The acoustic pressure sensing module consists of a signal generator, a power amplifier, and an optical resonant cavity structure. The signal generator emits an acoustic pressure signal of a specific frequency, which is amplified by the power amplifier and applied to the optical resonant cavity structure for acoustic pressure signal detection.

[0008] The signal acquisition and demodulation module consists of a coupler, a coherent receiver, a detector, and an oscilloscope. The coupler transmits a reference signal to the coherent receiver, and another signal is received by the photodetector. The third optical signal from the coupler is coherently received with the signal obtained from the optical resonant cavity structure. The heterodyne signals from the two optical frequency combs obtained from the optical resonant cavity structure are demodulated. The sound pressure signal of the optical microcavity structure is retrieved by using the light emitted from the tunable laser, which is modulated into a dual optical comb by two electro-optic frequency shifters.

[0009] As a further improvement to the above scheme, the first and second optical frequency combs are optical frequency combs with adjustable repetition frequency differences, and their frequency difference matches the acoustic pressure response frequency band of the optical microcavity. The frequency shifting range of the first and second electro-optic frequency shifters covers the acoustic resonant frequency range of the optical microcavity, and the laser frequency locking state is adjusted in real time through feedback control.

[0010] As a further improvement to the above scheme, the optical microcavity is a hollow whispering-gallery style microcavity with adjustable cavity length or radius of curvature to enhance the photoacoustic coupling effect. The heterodyne demodulation can be achieved using a lock-in amplifier or mixer, with its reference signal frequency synchronized with the driving frequency of the electro-optic frequency shifter. The spectral characteristics of the sound pressure signal are extracted using a fast Fourier transform, and the sound pressure amplitude is retrieved by combining it with calibration data.

[0011] An optical microcavity acoustic pressure detection method based on electro-optic heterodyne frequency shifting and locking, characterized by comprising the following steps:

[0012] Step 1: Adjust the output frequency of the tunable laser and lock it to the specified frequency of the first optical frequency comb and the second optical frequency comb through the first electro-optic frequency shifter and the second electro-optic frequency shifter, respectively.

[0013] Step 2: Combine the locked dual-frequency laser beam and inject it into the optical resonant cavity structure, and use a coherent receiver and photodetector to collect the resonant light signal output by the microcavity;

[0014] Step 3: Demodulate the sound pressure signal by using a heterodyne demodulation oscilloscope to separate the components containing sound pressure information;

[0015] Step 4: Perform Fourier transform analysis on the demodulated signal to extract the spectral amplitude of the sound pressure signal, and use the pre-stored calibration curve to deduce the sound pressure value of the optical microcavity.

[0016] As a further improvement to the above scheme, frequency difference scanning of dual-frequency lasers is achieved by dynamically adjusting the driving frequency of the electro-optic frequency shifter, covering the acoustic resonant frequency band of the optical microcavity.

[0017] Therefore, the proposed optical microcavity acoustic pressure detection method based on electro-optic heterodyne frequency shifting and locking achieves enhanced acoustic pressure signal sensitivity by optimizing the measurement system architecture and signal processing mechanism. First, this method effectively overcomes the measurement error problems caused by laser frequency drift and environmental noise interference in traditional acoustic pressure detection by introducing a highly stable frequency reference system composed of dual electro-optic frequency shifters and an optical frequency comb. The frequency-locked optical signal generated by the dual optical comb structure enables the system to maintain extremely high frequency stability in complex environments, thereby raising the accuracy of acoustic pressure detection to a new level. Second, the system employs a signal processing strategy combining heterodyne demodulation and Fourier transform, which not only effectively separates the low-frequency signal components containing acoustic pressure information but also accurately extracts the acoustic pressure amplitude through frequency domain analysis, significantly improving the reliability and sensitivity of signal demodulation, especially suitable for detecting high-frequency and weak acoustic emission signals. This method has strong compatibility and can be adapted to various sensing structures such as Fabry-Perot cavities or whispering-gallery mode optical microcavities. By adjusting the cavity length or radius of curvature, the photoacoustic coupling efficiency can be further optimized, enhancing the signal conversion and transmission quality. This invention has broad application potential in fields such as industrial non-destructive testing, large-scale structural health assessment, and aerospace equipment condition monitoring. In summary, this invention not only achieves high-precision, high-stability, and high-sensitivity sound pressure detection at the technical level, but also demonstrates outstanding advantages at the engineering level, including compact structure, low cost, convenient operation, and strong scalability. It is an advanced sensing solution that combines innovation and practicality. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the optical microcavity acoustic pressure detection system based on electro-optic heterodyne frequency shifting and locking in the embodiment.

[0020] Figure 2 This is a front view of the heterodyne dual optical comb source resonant cavity structure in the embodiment;

[0021] Figure 3 This is a side view of the heterodyne dual optical comb source resonant cavity structure in the embodiment. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the embodiments of this invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other. The invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0024] like Figure 1The diagram shows a system structure of an optical microcavity acoustic pressure detection method based on electro-optic heterodyne frequency shifting and locking. By constructing an acoustic pressure detection demodulation system, acoustic pressure parameter measurement based on electro-optic heterodyne frequency shifting and locking is achieved. It includes a tunable laser 1, a coupler 2, an electro-optic frequency shifter 3, an arbitrary waveform generator 4, an electro-optic frequency shifter 5, an erbium-doped fiber amplifier 6, an erbium-doped fiber amplifier 7, a coupler 8, a signal generator 9, a power amplifier 10, a resonant cavity structure 11, a coupler 12, a coherent receiver 13, a detector 14, and an oscilloscope 15.

[0025] The light output from the tunable laser 1 is split into three beams by the coupler 2. Two of these beams are locked to the corresponding frequencies of the first and second optical frequency combs by the first electro-optic frequency shifter 3 and the second electro-optic frequency shifter 5, respectively. The signals are amplified by the erbium-doped fiber amplifier 7 and the erbium-doped fiber amplifier 6, and then the two optical frequency combs of different frequencies are mixed by the fiber coupler 8. The mixture is then sent into the resonant cavity structure 11 via a single-mode fiber. Inside the resonant cavity structure 11, the light is coupled into the whispering-gallery mode optical cavity in the form of an evanescent field by the fiber taper. The cavity light field that meets the resonance condition reaches the coupler 12 through the output end of the fiber taper. The coupler 12 splits the light into two paths. The first path is detected by the photodetector 14 and then recorded by the oscilloscope 15. The laser beam obtained from the coupler 2 is used as the intrinsic signal and is received by the coherent receiver 13 along with the signal from the coupler 12, and then recorded by the oscilloscope 15.

[0026] In the sensing system, the tunable laser 1, coupler 2, electro-optic frequency shifter 3, electro-optic frequency shifter 4, erbium-doped fiber amplifier 6, erbium-doped fiber amplifier 7, coupler 8, resonant cavity structure 11, coupler 12, detector 14, and coherent receiver 13 are connected by optical fibers. The arbitrary waveform generator 4 is connected to the electro-optic frequency shifter 3 and electro-optic frequency shifter 5 by electrical cables. The oscilloscope 15 is connected to the detector 14 and coherent receiver 13 by electrical cables. The oscilloscope 15 records the transmission spectrum and performs heterodyne demodulation on the output signal of the coherent receiver 13. The Fourier transform-processed demodulated signal is then subjected to spectral analysis. The sound pressure signal of the optical microcavity is retrieved by modulating the light emitted by the tunable laser back into a dual optical comb using two electro-optic frequency shifters.

[0027] Furthermore, such as Figure 2 As shown, this is a front view of the heterodyne dual-comb source resonant cavity structure 11 in the optical microcavity acoustic pressure detection system based on electro-optic heterodyne frequency shifting and locking. The dual-comb source 11-1 inside the tapered optical fiber is coupled into the hollow resonant cavity structure 11-2 by the evanescent field coupling. The two ends of the hollow resonant cavity structure 11-2 are fixed by single-mode optical fiber 11-3.

[0028] Furthermore, such as Figure 3The figure shows a side view of the heterodyne dual-comb source resonant cavity structure 11 in the optical microcavity acoustic pressure detection system based on electro-optic heterodyne frequency shifting and locking.

[0029] This embodiment presents an optical microcavity acoustic pressure detection method based on electro-optic heterodyne frequency shifting and locking. An electro-optic frequency shifter modulates a tunable laser to obtain two difference-frequency optical frequency combs. These two frequency-differential laser combs are injected into the optical microcavity. A photodetector detects the optical resonance signal, and the acoustic pressure signal of the optical microcavity is retrieved using an optical heterodyne demodulation scheme. Unlike traditional acoustic pressure detection methods that directly detect the drift of the microcavity resonant frequency in whispering-gallery mode microcavities, the electro-optic frequency shifting and locking technique effectively suppresses laser frequency drift and improves frequency stability. Introducing electro-optic frequency shifting and locking technology into whispering-gallery mode microcavity acoustic pressure detection is expected to overcome the shortcomings of traditional methods and achieve high-sensitivity and high-stability acoustic pressure detection.

[0030] The above description is merely an illustration of preferred embodiments of the present invention and is not intended to limit the scope of protection of the present invention. Without departing from the spirit and essence of the present invention, those skilled in the art can make various modifications and alterations based on the present invention, and all such modifications and alterations should fall within the scope defined by the claims of the present invention.

Claims

1. An optical microcavity acoustic pressure detection method based on electro-optic heterodyne frequency shifting and locking, characterized in that, include: Tunable laser source module, sound pressure sensing module, and signal acquisition and demodulation module; The tunable laser source module includes a tunable laser 1, a coupler 2, a first electro-optic frequency shifter 3, a second electro-optic frequency shifter 5, an erbium-doped fiber amplifier 6, and an erbium-doped fiber amplifier 7. The tunable laser 1 is split into three optical signals by the coupler 2, which are then processed by the outputs of the first electro-optic frequency shifter 3 and the second electro-optic frequency shifter 5 to generate corresponding frequencies for the first and second optical frequency combs, respectively. The first electro-optic frequency shifter 3 and the second electro-optic frequency shifter 5 are controlled by a signal generator 4. The two beams of light are converged by the coupler 8 and injected into the sound pressure sensing module. The sound pressure sensing module comprises a signal generator 9, a power amplifier 10, and an optical resonant cavity structure 11. The signal generator 9 emits... A sound pressure signal of a specific frequency is amplified by a power amplifier and used for sound pressure signal detection in an optical resonant cavity structure 11. The signal acquisition and demodulation module consists of a coupler 12, a coherent receiver 13, a detector 14, and an oscilloscope 15. The coupler 12 transmits the SI signal to the coherent receiver 13, and another signal is received by the photodetector 14. The third optical signal from the coupler 2 is coherently received with the signal obtained from the optical resonant cavity structure 11. The heterodyne signals of the two optical frequency combs obtained from the optical resonant cavity structure 11 are demodulated. The light emitted by the tunable laser is modulated into a dual optical comb by two electro-optic frequency shifters, and the sound pressure signal of the optical microcavity structure is then retrieved.

2. The microcavity acoustic pressure detection device according to claim 1, characterized in that: The first optical frequency comb and the second optical frequency comb are optical frequency combs with adjustable repetition frequency differences. Their frequency difference matches the acoustic pressure response frequency band of the optical resonant cavity structure 11. The frequency shifting range of the first electro-optic frequency shifter 3 and the first electro-optic frequency shifter 5 covers the acoustic resonance frequency range of the optical resonant cavity structure 11, and the laser frequency locking state is adjusted in real time through feedback control.

3. The microcavity acoustic pressure detection device according to claim 1 or 2, characterized in that: The optical resonant cavity structure 11 is a hollow whispering-gallery mode microcavity with adjustable cavity length or radius of curvature to enhance the photoacoustic coupling effect. The heterodyne demodulation can be achieved by using a lock-in amplifier or mixer, with its reference signal frequency synchronized with the driving frequency of the electro-optic frequency shifter. The spectral characteristics of the sound pressure signal are extracted by fast Fourier transform, and the sound pressure amplitude is retrieved by combining the calibration data.

4. A detection method based on the microcavity acoustic pressure detection device according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Adjust the output frequency of the tunable laser 1 and lock it to the specified frequencies of the first and second optical frequency combs using the first electro-optic frequency shifter 3 and the second electro-optic frequency shifter 5, respectively. Step 2: Combine the locked dual-frequency laser beams and inject them into the optical resonant cavity structure 11. Use the coherent receiver 13 and photodetector 14 to collect the resonant optical signal output from the microcavity. Step 3: Demodulate the sound pressure signal using the signal detected by the heterodyne demodulation oscilloscope 15 and separate the components containing sound pressure information. Step 4: Perform Fourier transform analysis on the demodulated signal, extract the spectral amplitude of the sound pressure signal, and deduce the sound pressure value of the optical microcavity by combining it with the pre-stored calibration curve.

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