Cavity optical force vibration sensor, measuring device and measuring method

Abstract

The present invention discloses a cavity optical force vibration sensor, a measuring device, and a measuring method. These sensors are applied to the field of vibration measurement technology. To address the low measurement accuracy of existing vibration sensors, the present invention utilizes the optomechanical coupling principle of a cavity optical force micro-opto-electromechanical system to achieve optical measurement of vibration states. Infrared light emitted by a laser enters a polarization controller via a single-mode optical fiber, generating laser light with arbitrary polarization directions. This laser light is then coupled via a V-shaped micro-concave optical fiber into a photonic crystal microcavity within a vacuum cavity. The microcavity's outgoing light, carrying optomechanical coupling information, enters a photodetector via an attenuator. A spectrum analyzer reads and analyzes the vibration information of the silicon micromechanical oscillator and the piezoelectric ceramic oscillator, and a computer reads and analyzes the coupled optical information.

Description

Technical Field

[0001] The present invention belongs to the technical field of vibration measurement, and in particular relates to a vibration sensor, a measuring device and a measuring method. Background Art

[0002] Vibration sensor technology, which measures and monitors the mechanical vibration of an object, has widespread applications in numerous fields, including machinery manufacturing, construction engineering, the automotive industry, aerospace, medical equipment, earthquake monitoring, and consumer electronics. Vibration sensors include piezoelectric, resistive, capacitive, inductive, and photoelectric types. However, existing vibration sensor technologies generally suffer from high noise, low accuracy, narrow bandwidth, and weak resistance to electromagnetic interference.

[0003] In recent years, MOEMS (micro-opto-electromechanical systems) technology based on cavity optomechanical systems has received widespread attention. This technology combines the advantages of MEMS (micro-electromechanical systems) and optical measurement, and can achieve high-precision measurement of physical quantities such as force, displacement, mass, acceleration, angular velocity, gravitational waves, close to the thermal noise limit. It also has excellent anti-electromagnetic interference performance. It is a rapidly developing new sensor technology with great potential. However, the existing technology has not yet applied MOEMS based on cavity optomechanical systems to the design and manufacture of vibration sensors. Summary of the Invention

[0004] To solve the above technical problems, the present invention proposes a cavity optical force vibration sensor, a measuring device and a measuring method, which utilize the optomechanical coupling principle of a cavity optical force micro-opto-electromechanical system to realize optical measurement of the vibration state.

[0005] One of the technical solutions adopted by the present invention is: a cavity optical force vibration sensor, comprising: a silicon micromechanical oscillator structure, a photonic crystal microcavity structure;

[0006] The silicon micromechanical oscillator structure includes: a front fixed mass block, a movable detection mass block, and a rear fixed mass block; the movable detection mass block is connected to the front fixed mass block and the rear fixed mass block via a U-shaped cantilever beam; tenon structures are respectively provided at the front and rear of the movable detection mass block to engage with mortise structures at corresponding positions of the front fixed mass block and the rear fixed mass block, with a gap provided between the tenon structures and the mortise structures; the silicon micromechanical oscillator structure comprises, from top to bottom, a first silicon layer, a SiO2 layer, and a second silicon layer, and further includes an etching hole penetrating the first silicon layer;

[0007] The photonic crystal microcavity structure includes: a front photonic crystal microcavity structure and a rear photonic crystal microcavity structure. The photonic crystal microcavity structure is arranged in the mortise and tenon structure gap between the movable detection mass block and the front fixed mass block and the rear fixed mass block. When the movable detection mass block vibrates along the y-axis, the cavity length of the photonic crystal microcavity structure will change in conjunction.

[0008] The second technical solution adopted by the present invention is: a measurement device based on a cavity optical force vibration sensor, comprising: an optical path system, a circuit system and a piezoelectric ceramic vibrator;

[0009] The optical path system includes: a laser, a polarization controller, a vacuum cavity, a cavity optical force vibration sensor, a V-shaped micro-concave optical fiber and an optical attenuator;

[0010] The piezoelectric ceramic vibrator is arranged below the cavity optical force vibration sensor;

[0011] The laser light emitted by the laser enters the polarization controller through the optical fiber to obtain laser light with any polarization direction. The laser light with any polarization direction is coupled into the photonic crystal microcavity structure of the cavity optical force vibration sensor in the vacuum cavity through the V-shaped micro-concave optical fiber. When the piezoelectric ceramic vibrator below the cavity optical force vibration sensor is driven by a sinusoidal signal, the movable detection mass block of the cavity optical force vibration sensor generates periodic linear displacement along the y-axis, and the laser light carrying the optical force coupling information enters the optical attenuator.

[0012] The circuit system includes: a photoelectric detector, a spectrum analyzer, a data collector, and a computer; the light output by the optical attenuator enters the photoelectric detector; the electrical signal output by the photoelectric detector enters the spectrum analyzer and the data collector respectively; and the data collector is also connected to the computer.

[0013] The third technical solution adopted by the present invention is: a measurement method based on a cavity optical force vibration sensor, comprising:

[0014] S1: Test the optical resonance characteristics; adjust the position of the V-shaped optical fiber to couple it with the photonic crystal microcavity of the cavity optical force vibration sensor, so that the laser output is swept near the characteristic frequency of the photonic crystal microcavity. The optical resonance characteristic transmission curve collected by the data acquisition device can be obtained in the computer;

[0015] S2: Conduct mechanical resonance characteristic test; adjust the laser output frequency according to the optical resonance characteristic transmission curve information, drive the cavity optical force vibration sensor into the mechanical resonance mode, and observe the power spectrum of the low-frequency modulated electrical signal from the spectrum analyzer;

[0016] S3: Perform vibration signal test; when the piezoelectric ceramic vibrator under the cavity optical force vibration sensor is driven by a sinusoidal signal, the movable detection mass block of the cavity optical force vibration sensor generates periodic linear displacement on the y-axis, thereby changing the cavity length of the photonic crystal microcavity and modulating the optical resonant frequency; at this time, the power signal at the corresponding vibration frequency of the piezoelectric ceramic vibrator can be observed on the spectrum analyzer. By changing the frequency and amplitude of the piezoelectric ceramic vibrator driving signal, the corresponding changes can be read on the spectrum analyzer, thereby obtaining information such as the sensitivity, frequency response range, and amplitude range of vibration detection.

[0017] Beneficial effects of the present invention: Compared with the existing technology, the present invention uses the optomechanical coupling principle of the cavity optical force micro-opto-electromechanical system to realize optical measurement of vibration state, which has the characteristics of high sensitivity, wide frequency response range, and strong anti-electromagnetic interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a top view of the cavity optical force vibration sensor provided by the present invention;

[0019] Figure 2 This is a left view of the cavity optical force vibration sensor provided by the present invention;

[0020] Figure 3 This is a diagram showing the structure of the cavity optical force vibration sensor measurement device provided by the present invention;

[0021] Figure 4 This is a mechanical spectrum measured by a spectrum analyzer at a vibration frequency of 6 kHz for the piezoelectric ceramic provided by the present invention.

[0022] Explanation of the accompanying symbols: P is the optical path system, E is the circuit system, 1 is the cavity optical force vibration sensor, 2 is the laser, 3 is the polarization controller, 4 is the vacuum cavity, 5 is the V-shaped micro-concave optical fiber, 6 is the piezoelectric ceramic vibrator, 7 is the optical attenuator, 8 is the photodetector, 9 is the spectrometer, 10 is the data acquisition device, 11 is the computer, 1a is the front fixed mass block, 1b is the movable detection mass block, 1c is the rear fixed mass block, 1d is the front photonic crystal microcavity structure, 1e is the rear photonic crystal microcavity structure, 1f is the air slot in 1d, 1g is the air slot in 1e, 1h is the U-shaped cantilever beam, and 1i is the corrosion hole. DETAILED DESCRIPTION

[0023] To facilitate those skilled in the art to understand the technical content of the present invention, the present invention is further explained below with reference to the accompanying drawings.

[0024] like Figure 1 As shown, the cavity optical force vibration sensor proposed in the present invention is composed of a silicon micromechanical oscillator structure and a photonic crystal microcavity structure.

[0025] The micromechanical oscillator measures 102 μm × 143 μm × 250 μm and exhibits left-right and front-back symmetry. The silicon micromechanical oscillator structure consists of a front fixed mass 1a, a movable proof mass 1b, and a rear fixed mass 1c. The movable proof mass is connected to the front and rear fixed masses via a U-shaped cantilever beam 1h. Tenons are located at the front and rear of the movable proof mass 1a, respectively, and fit into corresponding mortises on the front and rear fixed masses 1a and 1c. A 0.5 μm gap is provided between the tenons and mortises to allow vibration of the movable proof mass 1b.

[0026] like Figure 2 As shown, the cavity optical force vibration sensor in this embodiment is manufactured on a SOI substrate with a top silicon layer by micro-nano processing technology. The thickness of the top silicon layer in this embodiment is 250 nm.

[0027] The silicon micromechanical oscillator structure is provided with an etched hole 1i that penetrates the top silicon layer. This facilitates the removal of the intermediate SiO2 layer of the SOI (Silicon-On-Insulator) using HF gas after chip lithography. This allows the entire cavity optical force vibration sensor to be suspended in the air. The movable proof mass 1b has an effective modal mass of 5.6397 ng and a fundamental mode resonant frequency of 72980 Hz.

[0028] The photonic crystal microcavity structure includes a front photonic crystal microcavity structure 1d and a rear photonic crystal microcavity structure 1e, which constitute differential measurement, and are arranged at the junction of the tenon and the mortise. Each photonic crystal microcavity structure 1d is composed of two two-dimensional photonic crystals and an air slot with a width of 100nm, and the air slot is arranged between the two two-dimensional photonic crystals. Both two-dimensional photonic crystals can be obtained by etching periodically arranged circular air holes on the top silicon layer, and point defects are set near both sides of the center of the air slot, that is, a part of the air hole is translated to generate a photonic band gap, forming a microcavity, thereby confining light of a specific frequency inside the microcavity to produce resonance. The resonant frequency of the photonic crystal microcavity is determined by the width of the air slot and the range of the point defect; in this embodiment, the resonant frequency of the photonic crystal microcavity is 193.79THz.

[0029] like Figure 3As shown, the measurement device of the cavity optical force vibration sensor consists of a laser 2, a polarization controller 3, a vacuum chamber 4, a cavity optical force vibration sensor 1, a piezoelectric ceramic vibrator 6, an optical attenuator 7, a photodetector 8, a spectrometer 9, a data acquisition unit 10, and a computer 11. The infrared light emitted by the laser 2 enters the polarization controller 3 via a single-mode optical fiber, where it can be converted into laser light of arbitrary polarization direction. This laser light is coupled into the photonic crystal microcavity of the cavity optical force vibration sensor 1 in the vacuum chamber 4 via a V-shaped micro-concave optical fiber 5. The microcavity-emitted light, carrying the optomechanical coupling information, enters the photodetector 8 via an optical attenuator 7 (attenuated as needed). The vibration information of the silicon micromechanical vibrator and the piezoelectric ceramic vibrator is read and analyzed by the spectrometer 9, and the coupled optical information is read and analyzed by the computer 11.

[0030] The electrical signal after photoelectric conversion by the photoelectric detector 8 contains low-frequency and high-frequency parts. The low-frequency signal enters the spectrum analyzer 9 to extract the vibration information emitted by the micromechanical vibrator and the piezoelectric ceramic vibrator, and the high-frequency signal enters the computer 11 through the data acquisition device 10 to extract the optical signal after photomechanical coupling.

[0031] like Figure 4 The figure shows the mechanical spectrum measured by the spectrum analyzer when the vibration frequency of the piezoelectric ceramic is 6kHz. Figure 4 The frequency and amplitude of the micromechanical oscillator resonance signal and the piezoelectric ceramic vibration signal can be seen in the figure. By changing the amplitude of the vibration drive signal of the piezoelectric ceramic, Figure 4 The vibration amplitude of the piezoelectric ceramic in the sensor changes accordingly, and the vibration detection sensitivity at the corresponding frequency can be derived based on this change relationship. Tests have shown that the frequency response range of the vibration sensor embodiment is 500Hz to 66kHz, greater than 60kHz; the sensitivity is 35.22mV / g at 500Hz and 126.58mV / g at 6kHz, with equivalent frequency test sensitivities of 0.039mg / Hz and 0.0026mg / Hz, respectively. Over the entire frequency response range, the equivalent frequency test sensitivity is less than 0.04mg / Hz; and the dynamic range of the vibration detection amplitude is greater than 50dB.

[0032] It should be noted that according to the theory of cavity optomechanical coupling system, the light field a in the photonic crystal cavity and the displacement y of the micromechanical oscillator in the y direction respectively satisfy the following motion equations:

[0033]

[0034]

[0035] Where i represents an imaginary number, a(t) represents the light field in the photonic crystal cavity, represents the first derivative of a(t), y(t) represents the displacement, represents the first derivative of y(t), represents the second derivative of y(t), △=ω l -ω c is the laser detuning rate, ω l With ω c are the laser angular frequency and the microcavity resonance angular frequency, g OM is the optomechanical coupling ratio, defined as κ is the total cavity coupling ratio, κ e is the external coupling rate, κ i is the internal dissipation rate, κ = κ e +κ i . a in (t) is the laser input light field, and the corresponding input light power is γ i is the damping coefficient, ω m is the mechanical resonant frequency, F th is the thermal noise equivalent force, m y is the effective modal mass of the mechanical oscillator when it vibrates in the y direction, is the reduced Planck constant, n c (t)=|a(t) 2 is the number of photons in the cavity.

[0036] It should be noted that mechanical motion is coupled to the optical system through the optical-mechanical coupling interaction, causing the optical resonance frequency to shift. By setting the laser detuning near the microcavity resonance frequency, the mechanical motion will cause the laser output power to change. The output optical power P modulated by the mechanical motion m It can be expressed as:

[0037]

[0038] Where η represents the actual loss rate from the optical cavity to the detector, T represents the normalized transmittance, and the above formula is transformed into the frequency domain

[0039]

[0040] χ m (ω)A(ω) represents the Fourier transform of y(t);

[0041] It should be noted that the above optical power can be measured by a balanced photodetector with switchable transimpedance gain, and the spectral density can be calculated using a spectrum analyzer, thereby achieving vibration measurement.

[0042]

[0043] Among them, PSD ESA (ω) is the power spectral density, g ti is the photodetector gain.

[0044] In actual vibration measurement, the measurement process includes the following steps:

[0045] S1: Test the optical resonance characteristics; adjust the position of the V-shaped optical fiber so that it is coupled with the photonic crystal microcavity of the cavity optical force vibration sensor, so that the laser sweeps the output near the characteristic frequency of the photonic crystal microcavity. The optical resonance characteristic transmission curve collected by the data collector can be obtained in the computer; in this embodiment, the resonant frequency of the photonic crystal microcavity is 193.79THz, corresponding to a wavelength of approximately 1548nm, and the laser scanning frequency range is set to 1500nm to 1600nm.

[0046] S2: Conduct mechanical resonance characteristic test; adjust the laser output frequency according to the optical resonance characteristic transmission curve information, drive the cavity optical force vibration sensor into the mechanical resonance mode, and observe the power spectrum of the low-frequency modulated electrical signal from the spectrum analyzer;

[0047] S3: Perform vibration signal test; when the piezoelectric ceramic vibrator under the cavity optical force vibration sensor is driven by a sinusoidal signal, the movable detection mass block of the cavity optical force vibration sensor generates periodic linear displacement on the y-axis, thereby changing the cavity length of the photonic crystal microcavity and modulating the optical resonant frequency; at this time, the power signal at the corresponding vibration frequency of the piezoelectric ceramic vibrator can be observed on the spectrum analyzer. By changing the frequency and amplitude of the piezoelectric ceramic vibrator driving signal, the corresponding changes can be read on the spectrum analyzer, thereby obtaining information such as the sensitivity, frequency response range, and amplitude range of vibration detection.

[0048] Those skilled in the art will appreciate that the embodiments described herein are intended to aid the reader in understanding the principles of the present invention, and it should be understood that the scope of the present invention is not limited to such specific descriptions and embodiments. Various modifications and variations are readily apparent to those skilled in the art. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to be included within the scope of the claims.

Claims

1. A cavity optical force vibration sensor, characterized in that: The cavity optical force vibration sensor comprises: a silicon micromechanical oscillator structure and a photonic crystal microcavity structure; The silicon micromechanical oscillator structure includes: a front fixed mass block, a movable detection mass block, and a rear fixed mass block; the movable detection mass block is connected to the front fixed mass block and the rear fixed mass block via a U-shaped cantilever beam; tenon structures are respectively provided at the front and rear of the movable detection mass block to fit into mortise structures at corresponding positions of the front fixed mass block and the rear fixed mass block, with a gap provided between the tenon structure and the mortise structure; The photonic crystal microcavity structure includes: a front photonic crystal microcavity structure and a rear photonic crystal microcavity structure. The photonic crystal microcavity structure is arranged in the mortise and tenon structure gap between the movable detection mass block and the front fixed mass block and the rear fixed mass block. When the movable detection mass block vibrates along the y-axis, the cavity length of the photonic crystal microcavity structure will change in conjunction.

2. The cavity optical force vibration sensor according to claim 1, characterized in that: The cavity optical force vibration sensor is arranged on the top silicon layer of the SOI substrate.

3. The cavity optical force vibration sensor according to claim 2, characterized in that: A plurality of etching holes are arranged on the silicon micromechanical oscillator structure; the etching holes penetrate through the top silicon layer of the SOI substrate.

4. The cavity optical force vibration sensor according to claim 3, characterized in that: When in use, hydrogen fluoride gas corrodes SiO2 in the middle layer of the SOI substrate through the etching holes, so that the cavity optical force vibration sensor is suspended in the air.

5. The cavity optical force vibration sensor according to claim 4, characterized in that: The front photonic crystal microcavity structure is the same as the rear photonic crystal microcavity structure, specifically including two two-dimensional photonic crystals and an air groove between the two two-dimensional photonic crystals.

6. The cavity optical force vibration sensor according to claim 5, characterized in that: Both two-dimensional photonic crystals are obtained by etching periodically arranged circular air holes on the top silicon layer, and point defects are set near both sides of the center of the air groove.

7. A measurement device based on a cavity optical force vibration sensor, characterized in that: include: Optical path system, circuit system and piezoelectric ceramic vibrator; The optical system comprises: a laser, a polarization controller, a vacuum cavity, the cavity optical force vibration sensor according to any one of claims 1 to 6, a V-shaped micro-dimpled optical fiber, and an optical attenuator; The piezoelectric ceramic vibrator is arranged below the cavity optical force vibration sensor; The laser light emitted by the laser enters the polarization controller through the optical fiber to obtain laser light with any polarization direction. The laser light with any polarization direction is coupled into the photonic crystal microcavity structure of the cavity optical force vibration sensor in the vacuum cavity through the V-shaped micro-concave optical fiber. When the piezoelectric ceramic vibrator below the cavity optical force vibration sensor is driven by a sinusoidal signal, the movable detection mass block of the cavity optical force vibration sensor generates periodic linear displacement along the y-axis, and the laser light carrying the optical force coupling information enters the optical attenuator. The circuit system includes: a photoelectric detector, a spectrum analyzer, a data collector, and a computer; the light output by the optical attenuator enters the photoelectric detector; the electrical signal output by the photoelectric detector enters the spectrum analyzer and the data collector respectively; and the data collector is also connected to the computer.

8. The measurement device based on the cavity optical force vibration sensor according to claim 7, characterized in that: The electrical signal after photoelectric conversion by the photoelectric detector contains low-frequency and high-frequency parts. The low-frequency part enters the spectrum analyzer to extract the vibration information emitted by the micromechanical vibrator and the piezoelectric ceramic vibrator, and the high-frequency part enters the computer through the data acquisition device to extract the optical signal after photomechanical coupling.

9. A measurement method based on a cavity optical force vibration sensor, characterized in that: include: S1: Test the optical resonance characteristics; Adjust the position of the V-shaped micro-concave optical fiber so that it is coupled with the photonic crystal microcavity of the cavity optical force vibration sensor according to any one of claims 1 to 6, so that the laser is swept and output near the characteristic frequency of the photonic crystal microcavity, and the optical resonance characteristic transmission curve collected by the data collector can be obtained in the computer; S2: Conduct mechanical resonance characteristic test; adjust the laser output frequency according to the optical resonance characteristic transmission curve information, drive the cavity optical force vibration sensor into the mechanical resonance mode, and observe the power spectrum of the low-frequency modulated electrical signal from the spectrum analyzer; S3: Perform vibration signal test; when the piezoelectric ceramic vibrator under the cavity optical force vibration sensor is driven by a sinusoidal signal, the movable detection mass block of the cavity optical force vibration sensor generates periodic linear displacement on the y-axis, thereby changing the cavity length of the photonic crystal microcavity and modulating the optical resonant frequency; at this time, the power signal at the corresponding vibration frequency of the piezoelectric ceramic vibrator can be observed on the spectrum analyzer. By changing the frequency and amplitude of the piezoelectric ceramic vibrator driving signal, the corresponding changes can be read on the spectrum analyzer, thereby obtaining the sensitivity, frequency response range, and amplitude range information of the vibration detection.

Images