Fano resonance-based high-sensitivity acoustic sensor and measurement method

Abstract

The invention relates to an optical acoustic sensor, in particular to a high-sensitivity acoustic sensor based on Fano resonance and a measuring method. The problem that an existing optical acoustic sensor is low in sensitivity is solved. A high-sensitivity acoustic sensor based on Fano resonance comprises a 1550nm laser, a phase modulator, a first polarization controller, a conical optical fiber, a CaF2 crystal resonant cavity, a second polarization controller, a photoelectric detector, an oscilloscope and a computer. The emergent end of the 1550nm laser is connected with the head end of the conical optical fiber through the phase modulator and the first polarization controller in sequence; the conical optical fiber is coupled with the CaF2 crystal resonant cavity; the tail end of the conical optical fiber is connected with the incident end of the photoelectric detector through the second polarization controller; the signal output end of the photoelectric detector is connected with the signal input end of the oscilloscope; the signal output end of the oscilloscope is connected with the signal input end of the computer. The method is suitable for acoustic signal measurement in the fields of industry, traffic, environmental protection, medical treatment and the like.

Description

Technical Field

[0001] The present invention relates to an optical acoustic sensor, and in particular to a high-sensitivity acoustic sensor based on Fano resonance and a measurement method thereof. Background Art

[0002] Optical acoustic sensors are widely used in the measurement of acoustic signals in industrial, transportation, environmental protection, medical and other fields due to their advantages such as small size, light weight, and low cost. Under the existing technical conditions, optical acoustic sensors generally work based on Lorentz resonance spectra. However, in practical applications, due to the poor response ability of Lorentz resonance spectra to acoustic signals, the existing optical acoustic sensors have the problem of low sensitivity. Based on this, it is necessary to invent a high-sensitivity acoustic sensor based on Fano resonance and a measurement method thereof to solve the problem of low sensitivity of existing optical acoustic sensors. Summary of the Invention

[0003] In order to solve the problem of low sensitivity of existing optical acoustic sensors, the present invention provides a high-sensitivity acoustic sensor based on Fano resonance and a measurement method thereof.

[0004] The present invention is implemented by adopting the following technical solutions: A high-sensitivity acoustic sensor based on Fano resonance includes a 1550 nm laser, a phase modulator, a first polarization controller, a tapered fiber, a CaF 2 crystal resonator, a second polarization controller, a photodetector, an oscilloscope, and a computer; the output end of the 1550 nm laser is sequentially connected to the head end of the tapered fiber through the phase modulator and the first polarization controller; the tapered fiber is coupled with the CaF 2 crystal resonator; the tail end of the tapered fiber is connected to the input end of the photodetector through the second polarization controller; the signal output end of the photodetector is connected to the signal input end of the oscilloscope; the signal output end of the oscilloscope is connected to the signal input end of the computer.

[0005] It further includes a signal generator, a power amplifier, a horn, and a standard sound level meter; the signal output end of the signal generator is connected to the signal input end of the power amplifier; the signal output end of the power amplifier is connected to the signal input end of the horn; both the horn and the standard sound level meter are located beside the CaF 2 crystal resonator.

[0006] It further includes a lock-in amplifier and a PID controller; the signal output end of the photodetector is connected to the signal input end of the lock-in amplifier; the signal output end of the lock-in amplifier is connected to the signal input end of the PID controller; the signal output end of the PID controller is connected to the modulation end of the 1550 nm laser.

[0007] The 1550 nm laser adopts a continuously tunable narrowband laser.

[0008] The diameter of the tapered optical fiber is 2 μm; the CaF 2 crystal resonator has a diameter of 5 mm and a height of 0.2 mm; the coupling state between the tapered optical fiber and the CaF 2 crystal resonator is under-coupling or critical coupling or over-coupling, and the coupling state can be adjusted by a six-dimensional adjustment mount.

[0009] A high-sensitivity acoustic measurement method based on Fano resonance, which is realized based on a high-sensitivity acoustic sensor according to the present invention, and the method is realized by the following steps: First, control the sensor to enter the working mode; the working mode is specifically: a 1550 nm laser emits pump light, and the pump light sequentially passes through a phase modulator, a first polarization controller, a tapered optical fiber, CaF 2 crystal resonator, tapered optical fiber, and a second polarization controller and is incident on a photodetector, and then is converted into an electrical signal by the photodetector; the electrical signal is transmitted to an oscilloscope and is converted into a transmission spectrum by the oscilloscope; the transmission spectrum is displayed on the oscilloscope on the one hand and transmitted to a computer on the other hand; by adjusting the polarization angles of the first polarization controller and the second polarization controller, the transmission spectrum is presented as a Fano transmission spectrum with an asymmetric waveform; In the working mode, when an acoustic signal acts on the CaF 2 crystal resonator, the voltage at the resonance frequency of the Fano transmission spectrum changes; the computer monitors the voltage change in real time and substitutes the voltage change into the acoustic pressure measurement equation of the sensor, and thus calculates the acoustic pressure; the acoustic pressure measurement equation of the sensor is expressed as follows: Δ V = A · f ·(Δ T / Δ f )·(Δ q / Δ θ )· P ; In the formula: Δ V represents the voltage change; P represents the acoustic pressure; A represents the change rate of the radius and refractive index of the CaF 2 crystal resonator; f represents the resonance frequency of the CaF 2 crystal resonator; Δ T / Δ f represents the slope of the first-order derivative linear region of the Fano transmission spectrum; θ represents the polarization angle; q represents the asymmetry factor of the Fano transmission spectrum, and its magnitude is determined by the polarization angle θ ; A, f , Δ T / Δ f , θ , q are all known quantities.

[0010] The method further includes using a signal generator, a power amplifier, a horn, and a standard sound level meter to determine whether the performance indicators of the sensor meet the requirements; the specific steps are as follows: First, control the sensor to enter the working mode; In the working mode, the signal generator outputs a sine wave signal, the sine wave signal is transmitted to the horn through the power amplifier, and is converted into a sound signal by the horn; on the one hand, the sound signal acts on the CaF 2 crystal resonator, causing the voltage at the resonance frequency of the Fano transmission spectrum to change, and on the other hand, acting on the standard sound level meter; the computer monitors the voltage change in real time; the standard sound level meter monitors the sound pressure in real time; Then, on the one hand, calculate the sensitivity test value of the sensor according to the voltage change and the sound pressure, and on the other hand, calculate the sensitivity standard value of the sensor; the specific calculation formula is as follows: S 1 = Δ V / P ; S 2 = A · f · (Δ T / Δ f ) · (Δ q / Δ θ ); In the formula: S 1 represents the sensitivity test value of the sensor; S 2 represents the sensitivity standard value of the sensor; Δ V represents the voltage change; P represents the sound pressure; A represents the rate of change of the radius and refractive index of the CaF 2 crystal resonator; f represents the resonance frequency of the CaF 2 crystal resonator; Δ T / Δ f represents the slope of the first-order derivative linear region of the Fano transmission spectrum; θ represents the polarization angle; q represents the asymmetry factor of the Fano transmission spectrum, and its magnitude is determined by the polarization angle θ ; A , f , Δ T / Δf , θ , q are all known quantities; Then, compare the sensitivity test value of the sensor with the sensitivity standard value of the sensor, and judge whether the performance index of the sensor meets the requirements according to the comparison result: if the sensitivity test value of the sensor coincides with the sensitivity standard value of the sensor, it indicates that the performance index of the sensor meets the requirements; if the sensitivity test value of the sensor does not coincide with the sensitivity standard value of the sensor, it indicates that the performance index of the sensor does not meet the requirements.

[0011] This method also includes using a lock-in amplifier and a PID controller to achieve frequency tracking and locking of a 1550nm laser; the specific steps are as follows: In the working mode, the electrical signal is synchronously demodulated by the lock-in amplifier and then transmitted to the PID controller; the PID controller adjusts the output frequency of the 1550nm laser in real time according to the demodulation result, so that the output frequency of the 1550nm laser is consistent with the resonance frequency of the CaF 2 crystal resonator, thereby achieving frequency tracking and locking of the 1550nm laser.

[0012] Compared with the existing optical acoustic sensor, the present invention does not work based on the Lorentz resonance spectrum, but works based on the Fano transmission spectrum, thereby having the advantage of high sensitivity. Specifically, because the Fano transmission spectrum has a super strong response ability to acoustic signals (it can be seen from Figures 2 to 4 that: the Lorentz resonance spectrum has a symmetric waveform, and the Fano transmission spectrum has an asymmetric waveform. Compared with the slope of the linear region of the first derivative of the Lorentz resonance spectrum, the slope of the linear region of the first derivative of the Fano transmission spectrum is larger. Therefore, compared with the response ability of the Lorentz resonance spectrum to acoustic signals, the response ability of the Fano transmission spectrum to acoustic signals is stronger), the present invention has ultra-high sensitivity. On this basis, because the CaF 2 crystal resonator has 10 -11 g anti-acceleration and low noise interference, the present invention has good stability.

[0013] The present invention effectively solves the problem of low sensitivity of the existing optical acoustic sensor and is applicable to the measurement of acoustic signals in the fields of industry, transportation, environmental protection, medical treatment, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic structural diagram of the present invention.

[0015] Figure 2 is a schematic diagram of the Lorentz resonance spectrum.

[0016] Figure 3 is a schematic diagram of the Fano transmission spectrum.

[0017] Figure 4 It is a schematic diagram comparing the slope of the linear region of the first derivative of the Lorentz resonance spectrum with the slope of the linear region of the first derivative of the Fano transmission spectrum.

[0018] In the figure: 1 - 1550nm laser, 2 - phase modulator, 3 - first polarization controller, 4.1 - tapered fiber, 4.2 - CaF 2 crystal resonator, 5 - second polarization controller, 6 - photodetector, 7 - oscilloscope, 8 - computer, 9 - signal generator, 10 - power amplifier, 11 - horn, 12 - standard sound level meter, 13 - lock-in amplifier, 14 - PID controller. Specific implementation mode

[0019] A high-sensitivity acoustic sensor based on Fano resonance includes a 1550nm laser 1, a phase modulator 2, a first polarization controller 3, a tapered fiber 4.1, and CaF 2 crystal resonator 4.2, a second polarization controller 5, a photodetector 6, an oscilloscope 7, and a computer 8; the output end of the 1550nm laser 1 is sequentially connected to the head end of the tapered fiber 4.1 through the phase modulator 2 and the first polarization controller 3; the tapered fiber 4.1 is coupled with the CaF 2 crystal resonator 4.2; the tail end of the tapered fiber 4.1 is connected to the incident end of the photodetector 6 through the second polarization controller 5; the signal output end of the photodetector 6 is connected to the signal input end of the oscilloscope 7; the signal output end of the oscilloscope 7 is connected to the signal input end of the computer 8.

[0020] It also includes a signal generator 9, a power amplifier 10, a horn 11, and a standard sound level meter 12; the signal output end of the signal generator 9 is connected to the signal input end of the power amplifier 10; the signal output end of the power amplifier 10 is connected to the signal input end of the horn 11; both the horn 11 and the standard sound level meter 12 are located beside the CaF 2 crystal resonator 4.2.

[0021] It also includes a lock-in amplifier 13 and a PID controller 14; the signal output end of the photodetector 6 is connected to the signal input end of the lock-in amplifier 13; the signal output end of the lock-in amplifier 13 is connected to the signal input end of the PID controller 14; the signal output end of the PID controller 14 is connected to the modulation end of the 1550nm laser 1.

[0022] The 1550nm laser 1 adopts a continuously tunable narrowband laser.

[0023] The diameter of the tapered fiber 4.1 is 2μm; the CaF 2 crystal resonator 4.2 has a diameter of 5mm and a height of 0.2mm; the tapered fiber 4.1 and the CaF2 The coupling state between the crystal resonator 4.2 is under-coupling or critical coupling or over-coupling, and the coupling state can be regulated by a six-dimensional adjustment mount.

[0024] A high-sensitivity acoustic measurement method based on Fano resonance, which is realized based on a high-sensitivity acoustic sensor according to the present invention, and the method is realized by the following steps: First, control the sensor to enter the working mode; the working mode is specifically: the 1550 nm laser 1 emits pump light, and the pump light sequentially passes through the phase modulator 2, the first polarization controller 3, the tapered optical fiber 4.1, the CaF 2 crystal resonator 4.2, the tapered optical fiber 4.1, the second polarization controller 5 and is incident on the photodetector 6, and then is converted into an electrical signal by the photodetector 6; the electrical signal is transmitted to the oscilloscope 7 and is converted into a transmission spectrum by the oscilloscope 7; the transmission spectrum is displayed on the oscilloscope 7 on the one hand and transmitted to the computer 8 on the other hand; by adjusting the polarization angles of the first polarization controller 3 and the second polarization controller 5, the transmission spectrum is presented as a Fano transmission spectrum with an asymmetric waveform; In the working mode, when an acoustic signal acts on the CaF 2 crystal resonator 4.2, the voltage at the resonance frequency of the Fano transmission spectrum changes; the computer 8 monitors the voltage change in real time and substitutes the voltage change into the acoustic pressure measurement equation of the sensor, and thus calculates the acoustic pressure; the acoustic pressure measurement equation of the sensor is expressed as follows: Δ V = A · f ·(Δ T / Δ f )·(Δ q / Δ θ )· P ; In the formula: Δ V represents the voltage change; P represents the acoustic pressure; A represents the change rate of the radius and refractive index of the CaF 2 crystal resonator 4.2; f represents the resonance frequency of the CaF 2 crystal resonator 4.2; Δ T / Δ f represents the slope of the linear region of the first derivative of the Fano transmission spectrum; θ represents the polarization angle; q represents the asymmetry factor of the Fano transmission spectrum, and its magnitude is determined by the polarization angle θ ; A , f , Δ T / Δ f ,θ , q are all known quantities.

[0025] This method further includes using a signal generator 9, a power amplifier 10, a speaker 11, and a standard sound level meter 12 to determine whether the performance indicators of the sensor meet the requirements; the specific steps are as follows: First, control the sensor to enter the working mode; In the working mode, the signal generator 9 outputs a sine wave signal. The sine wave signal is transmitted to the speaker 11 through the power amplifier 10 and is converted into a sound signal by the speaker 11; on the one hand, the sound signal acts on the CaF 2 crystal resonator 4.2, causing the voltage at the resonance frequency of the Fano transmission spectrum to change, and on the other hand, acting on the standard sound level meter 12; the computer 8 monitors the voltage change in real time; the standard sound level meter 12 monitors the sound pressure in real time; Then, on the one hand, calculate the sensitivity test value of the sensor based on the voltage change and the sound pressure, and on the other hand, calculate the sensitivity standard value of the sensor; the specific calculation formulas are as follows: S 1 =Δ V / P ; S 2 = A · f ·(Δ T / Δ f )·(Δ q / Δ θ ); In the formula: S 1 represents the sensitivity test value of the sensor; S 2 represents the sensitivity standard value of the sensor; Δ V represents the voltage change; P represents the sound pressure; A represents the rate of change of the radius and refractive index of the CaF 2 crystal resonator 4.2; f represents the resonance frequency of the CaF 2 crystal resonator 4.2; Δ T / Δ f represents the slope of the linear region of the first derivative of the Fano transmission spectrum; θ represents the polarization angle; q represents the asymmetry factor of the Fano transmission spectrum, and its magnitude is determined by the polarization angle θ ; A , f , Δ T / Δ f , θ ,q All are known quantities; Then, compare the sensitivity test value of the sensor with the sensitivity standard value of the sensor, and judge whether the performance index of the sensor meets the requirements according to the comparison result: if the sensitivity test value of the sensor coincides with the sensitivity standard value of the sensor, it indicates that the performance index of the sensor meets the requirements; if the sensitivity test value of the sensor does not coincide with the sensitivity standard value of the sensor, it indicates that the performance index of the sensor does not meet the requirements.

[0026] This method further includes using a lock-in amplifier 13 and a PID controller 14 to achieve frequency tracking and locking of the 1550 nm laser 1; the specific steps are as follows: In the working mode, the electrical signal is synchronously demodulated by the lock-in amplifier 13 and then transmitted to the PID controller 14; the PID controller 14 adjusts the output frequency of the 1550 nm laser 1 in real time according to the demodulation result, so that the output frequency of the 1550 nm laser 1 is consistent with the resonance frequency of the CaF 2 crystal resonator 4.2, thereby achieving frequency tracking and locking of the 1550 nm laser 1.

[0027] Although the specific implementation manners of the present invention have been described above, those skilled in the art should understand that these are only examples, and the protection scope of the present invention is defined by the appended claims. Without departing from the principle and essence of the present invention, those skilled in the art can make various changes or modifications to these implementation manners, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A high-sensitivity acoustic sensor based on Fano resonance, characterized in that: The invention comprises a 1550nm laser (1), a phase modulator (2), a first polarization controller (3), a tapered optical fiber (4.1), a CaF2 crystal resonant cavity (4.2), a second polarization controller (5), a photodetector (6), an oscilloscope (7), and a computer (8); the output end of the 1550nm laser (1) is connected to the head end of the tapered optical fiber (4.1) through the phase modulator (2) and the first polarization controller (3) in sequence; the tapered optical fiber (4.1) is coupled to the CaF2 crystal resonant cavity (4.2); the tail end of the tapered optical fiber (4.1) is connected to the incident end of the photodetector (6) through the second polarization controller (5); the signal output end of the photodetector (6) is connected to the signal input end of the oscilloscope (7); and the signal output end of the oscilloscope (7) is connected to the signal input end of the computer (8).

2. A high-sensitivity acoustic sensor based on Fano resonance according to claim 1, characterized in that: It also includes a signal generator (9), a power amplifier (10), a loudspeaker (11), and a standard sound level meter (12); the signal output end of the signal generator (9) is connected to the signal input end of the power amplifier (10); the signal output end of the power amplifier (10) is connected to the signal input end of the loudspeaker (11); and the loudspeaker (11) and the standard sound level meter (12) are both located beside the CaF2 crystal resonant cavity (4.2).

3. A high-sensitivity acoustic sensor based on Fano resonance according to claim 1, characterized in that: It also includes a phase-locked amplifier (13) and a PID controller (14); the signal output end of the photodetector (6) is connected to the signal input end of the phase-locked amplifier (13); the signal output end of the phase-locked amplifier (13) is connected to the signal input end of the PID controller (14); and the signal output end of the PID controller (14) is connected to the modulation end of the 1550nm laser (1).

4. The high-sensitivity acoustic sensor based on Fano resonance according to claim 1, characterized in that: The 1550nm laser (1) is a continuously tunable narrow-band laser.

5. The high-sensitivity acoustic sensor based on Fano resonance according to claim 1, characterized in that: The diameter of the tapered optical fiber (4.1) is 2 μm; the diameter of the CaF2 crystal resonant cavity (4.2) is 5 mm and the height is 0.2 mm; the coupling state between the tapered optical fiber (4.1) and the CaF2 crystal resonant cavity (4.2) is under-coupling, critical coupling or over-coupling, and the coupling state can be regulated using a six-dimensional adjustment frame.

6. A high-sensitivity acoustic measurement method based on Fano resonance, the method being implemented based on the high-sensitivity acoustic sensor based on Fano resonance as claimed in claim 1, characterized in that: This method is implemented by the following steps: First, the sensor is controlled to enter a working mode; the working mode is specifically as follows: a 1550nm laser (1) emits pump light, which is sequentially incident on a photodetector (6) via a phase modulator (2), a first polarization controller (3), a tapered optical fiber (4.1), a CaF2 crystal resonant cavity (4.2), a tapered optical fiber (4.1), and a second polarization controller (5), and then converted into an electrical signal via the photodetector (6); the electrical signal is transmitted to an oscilloscope (7), and converted into a transmission spectrum via the oscilloscope (7); the transmission spectrum is displayed on the oscilloscope (7) on the one hand, and transmitted to a computer (8) on the other hand; by adjusting the polarization angles of the first polarization controller (3) and the second polarization controller (5), the transmission spectrum is presented as a Fano transmission spectrum with an asymmetric waveform; In the working mode, when the acoustic signal acts on the CaF2 crystal resonant cavity (4.2), the voltage at the resonant frequency of the Fano transmission spectrum changes; the computer (8) monitors the voltage change in real time, and substitutes the voltage change into the sound pressure measurement equation of the sensor, thereby calculating the sound pressure; the sound pressure measurement equation of the sensor is expressed as follows: D V = A · f ·(D T / D f )·(D q / D θ ); P ; Where: Δ V Indicates the voltage change; P Indicates sound pressure; A represents the rate of change of the radius and refractive index of the CaF2 crystal resonant cavity (4.2); f Indicates the resonant frequency of the CaF2 crystal resonator (4.2); Δ T / Δ f represents the slope of the linear region of the first-order derivative of the Fano transmission spectrum; θ represents the polarization angle; q The asymmetry factor of the Fano transmission spectrum is determined by the polarization angle θ Decide; A , f , Δ T / Δ f , θ , q All are known quantities.

7. A high-sensitivity acoustic measurement method based on Fano resonance according to claim 6, characterized in that: The method further comprises using a signal generator (9), a power amplifier (10), a speaker (11), and a standard sound level meter (12) to determine whether the performance index of the sensor meets the requirements; the specific steps are as follows: First, control the sensor to enter working mode; In the working mode, the signal generator (9) outputs a sine wave signal, which is transmitted to the speaker (11) via the power amplifier (10) and converted into an acoustic signal via the speaker (11); the acoustic signal acts on the CaF2 crystal resonant cavity (4.2) on the one hand, causing the voltage at the resonant frequency of the Fano transmission spectrum to change, and on the other hand, acts on the standard sound level meter (12); the computer (8) monitors the voltage change in real time; and the standard sound level meter (12) monitors the sound pressure in real time; Then, on the one hand, the sensitivity test value of the sensor is calculated according to the voltage change and the sound pressure, and on the other hand, the sensitivity standard value of the sensor is calculated; the specific calculation formula is as follows: S 1=D V / P ; S 2= A · f ·(D T / D f )·(D q / D θ ); Where: S 1 represents the sensitivity test value of the sensor; S 2 represents the standard value of sensor sensitivity; Δ V Indicates the voltage change; P Indicates sound pressure; A represents the rate of change of the radius and refractive index of the CaF2 crystal resonant cavity (4.2); f Indicates the resonant frequency of the CaF2 crystal resonator (4.2); Δ T / Δ f represents the slope of the linear region of the first-order derivative of the Fano transmission spectrum; θ represents the polarization angle; q The asymmetry factor of the Fano transmission spectrum is determined by the polarization angle θ Decide; A , f , Δ T / Δ f , θ , q All are known quantities; Then, compare the sensitivity test value of the sensor with the sensitivity standard value of the sensor, and judge whether the performance indicators of the sensor meet the requirements based on the comparison result: if the sensitivity test value of the sensor is consistent with the sensitivity standard value of the sensor, it indicates that the performance indicators of the sensor meet the requirements; if the sensitivity test value of the sensor is inconsistent with the sensitivity standard value of the sensor, it indicates that the performance indicators of the sensor do not meet the requirements.

8. A high-sensitivity acoustic measurement method based on Fano resonance according to claim 6, characterized in that: The method also includes using a phase-locked amplifier (13) and a PID controller (14) to achieve frequency tracking and locking of the 1550nm laser (1); the specific steps are as follows: In the working mode, the electrical signal is synchronously demodulated by the phase-locked amplifier (13) and then transmitted to the PID controller (14); the PID controller (14) adjusts the output frequency of the 1550nm laser (1) in real time according to the demodulation result, thereby making the output frequency of the 1550nm laser (1) consistent with the resonance frequency of the CaF2 crystal resonant cavity (4.2), thereby achieving frequency tracking and locking of the 1550nm laser (1).

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