A high-sensitivity acoustic sensor based on fano resonance and a measuring method

Abstract

The present application relates to optical acoustic sensor, specifically a kind of high sensitivity acoustic sensor based on fano resonance and measurement method.The present application solves the problem of low sensitivity of existing optical acoustic sensor.A kind of high sensitivity acoustic sensor based on fano resonance, including 1550nm laser, phase modulator, first polarization controller, tapered optical fiber, CaF2 Crystal resonant cavity, second polarization controller, photodetector, oscilloscope, computer;The exit end of 1550nm laser is sequentially connected with the first end of tapered optical fiber through phase modulator, first polarization controller;Tapered optical fiber is coupled with CaF2 Crystal resonant cavity;The tail end of tapered optical fiber is connected with the incident end of photodetector through second polarization controller;The signal output end of photodetector is connected with the signal input end of oscilloscope;The signal output end of oscilloscope is connected with the signal input end of computer.The present application is suitable for the measurement of acoustic signal in the fields of industry, transportation, environmental protection, medical treatment and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical acoustic sensor, in particular to a high-sensitivity acoustic sensor based on Fano resonance and a measuring method. BACKGROUND

[0002] Optical acoustic sensors are widely used in the fields of industry, transportation, environmental protection, medical treatment and the like for measuring acoustic signals due to their small size, light weight and low cost. Under the existing technical conditions, optical acoustic sensors are generally based on Lorentz resonance spectrum for operation. However, in practical applications, the response capability of the Lorentz resonance spectrum to acoustic signals is poor, resulting in the problem of low sensitivity of the existing optical acoustic sensors. Therefore, it is necessary to invent a high-sensitivity acoustic sensor based on Fano resonance and a measuring method to solve the problem of low sensitivity of the existing optical acoustic sensors. SUMMARY

[0003] The present application provides a high-sensitivity acoustic sensor based on Fano resonance and a measuring method to solve the problem of low sensitivity of the existing optical acoustic sensors.

[0004] The present application is implemented by using the following technical solutions:

[0005] The high-sensitivity acoustic sensor based on Fano resonance comprises a 1550nm laser, a phase modulator, a first polarization controller, a tapered optical fiber, a CaF2 crystal resonant cavity, a second polarization controller, a photodetector, an oscilloscope and a computer. The outgoing end of the 1550nm laser is connected with the first end of the tapered optical fiber through the phase modulator and the first polarization controller in sequence. The tapered optical fiber is coupled with the CaF2 crystal resonant cavity. The tail end of the tapered optical fiber is connected with the incoming end of the photodetector through the second polarization controller. The signal output end of the photodetector 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.

[0006] The high-sensitivity acoustic sensor based on Fano resonance further comprises a signal generator, a power amplifier, a loudspeaker and a standard sound level meter. The signal output end of the signal generator is connected with the signal input end of the power amplifier. The signal output end of the power amplifier is connected with the signal input end of the loudspeaker. The loudspeaker and the standard sound level meter are located on the side of the CaF2 crystal resonant cavity.

[0007] The high-sensitivity acoustic sensor based on Fano resonance further comprises a lock-in amplifier and a PID controller. The signal output end of the photodetector is connected with the signal input end of the lock-in amplifier. The signal output end of the lock-in amplifier is connected with the signal input end of the PID controller. The signal output end of the PID controller is connected with the modulation end of the 1550nm laser.

[0008] The 1550nm laser is a continuous tunable narrowband laser.

[0009] The diameter of the tapered fiber is 2 microns; the diameter of the CaF2 crystal resonant cavity is 5 mm, and the height is 0.2 mm; the coupling state between the tapered fiber and the CaF2 crystal resonant cavity is under-coupling, critical coupling or over-coupling, and the coupling state can be regulated by using a six-dimensional adjustment frame.

[0010] A high-sensitivity acoustic measurement method based on Fano resonance, which is realized based on the high-sensitivity acoustic sensor based on Fano resonance, and is realized by the following steps:

[0011] First, the sensor is controlled to enter the working mode; the working mode is specifically that the 1550nm laser emits pump light, the pump light is sequentially incident to the photodetector through the phase modulator, the first polarization controller, the tapered fiber, the CaF2 crystal resonant cavity, the tapered fiber and the second polarization controller, and then converted into an electrical signal through the photodetector; the electrical signal is transmitted to the oscilloscope and converted into a transmission spectrum through the oscilloscope; the transmission spectrum is displayed on the oscilloscope on one hand, and transmitted to the computer on the other hand; by regulating 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;

[0012] In the working mode, when the acoustic signal acts on the CaF2 crystal resonant cavity, 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, so as to calculate the acoustic pressure; the acoustic pressure measurement equation of the sensor is expressed as follows:

[0013] Δ V = A · f ·(Δ T / Δ f )·(Δ q / Δ θ )· P ;

[0014] In the formula: Δ V represents the voltage change; P represents the acoustic pressure; A represents the change rate of the radius and the refractive index of the CaF2 crystal resonant cavity; f represents the resonance frequency of the CaF2 crystal resonant cavity; 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, which is determined by the polarization angle θ ; A 、 f 、Δ T / Δ f 、θ , q are known quantities.

[0015] The method further comprises judging whether the performance index of the sensor meets the requirement by using a signal generator, a power amplifier, a loudspeaker and a standard sound level meter; the specific steps are as follows:

[0016] Firstly, the sensor is controlled to enter a working mode;

[0017] In the working mode, the signal generator outputs a sine wave signal, the sine wave signal is transmitted to the loudspeaker through the power amplifier, and the loudspeaker converts the sine wave signal into an acoustic signal; the acoustic signal acts on the CaF2 crystal resonant cavity on one hand, so that the voltage at the resonance frequency of the Fano transmission spectrum changes, and acts on the standard sound level meter on the other hand; the computer monitors the voltage change in real time; the standard sound level meter monitors the sound pressure in real time;

[0018] Then, on 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:

[0019] S 1=Δ V / P ;

[0020] S 2= A · f ·(Δ T / Δ f )·(Δ q / Δ θ );

[0021] 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 change rate of the radius and the refractive index of the CaF2 crystal resonant cavity; f represents the resonance frequency of the CaF2 crystal resonant cavity; 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, which is determined by the polarization angle θ ; A , f , Δ T / Δ f , θ , q are known quantities;

[0022] Then, the sensitivity test value of the sensor is compared with the sensitivity standard value of the sensor, and whether the performance index of the sensor meets the requirement is judged according to 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 index of the sensor meets the requirement; if the sensitivity test value of the sensor is not consistent with the sensitivity standard value of the sensor, it indicates that the performance index of the sensor does not meet the requirement.

[0023] The method further comprises using a phase-locked amplifier and a PID controller to realize frequency tracking and locking of the 1550nm laser; the specific steps are as follows:

[0024] In the working mode, the electric signal is transmitted to the PID controller after synchronous demodulation by the phase-locked amplifier; 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 CaF2 crystal resonant cavity, thereby realizing frequency tracking and locking of the 1550nm laser.

[0025] Compared with the existing optical acoustic sensor, the present application no longer works based on the Lorentz resonance spectrum, but works based on the Fano transmission spectrum, thereby having the advantage of high sensitivity. Specifically, since the Fano transmission spectrum has super strong response capability to the acoustic signal (through Figures 2-4 It can be seen that: the Lorentz resonance spectrum has a symmetrical waveform, and the Fano transmission spectrum has an asymmetrical 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 capability of the Lorentz resonance spectrum to the acoustic signal, the response capability of the Fano transmission spectrum to the acoustic signal is stronger, so that the present application has super high sensitivity. On this basis, since the CaF2 crystal resonant cavity has 10 -11 g acceleration resistance and low noise interference, the present application has good stability.

[0026] The present application effectively solves the problem of low sensitivity of the existing optical acoustic sensor, and is suitable for acoustic signal measurement in the fields of industry, transportation, environmental protection, medical treatment and the like. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a structural schematic diagram of the present application.

[0028] Figure 2 is a schematic diagram of the Lorentz resonance spectrum.

[0029] Figure 3 is a schematic diagram of the Fano transmission spectrum.

[0030] Figure 4Figure 1 is a schematic diagram of the slope of the linear region of the first derivative of the Lorentzian resonance spectrum versus the slope of the linear region of the first derivative of the Fano transmission spectrum.

[0031] In the figure: 1-1550nm laser, 2-phase modulator, 3-first polarization controller, 4.1-tapered fiber, 4.2-CaF2 crystal resonant cavity, 5-second polarization controller, 6-photodetector, 7-oscilloscope, 8-computer, 9-signal generator, 10-power amplifier, 11-horn, 12-standard sound level meter, 13-phase lock amplifier, 14-PID controller. DETAILED DESCRIPTION

[0032] A high-sensitivity acoustic sensor based on Fano resonance comprises a 1550nm laser 1, a phase modulator 2, a first polarization controller 3, a tapered 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 first end of the tapered fiber 4.1 through the phase modulator 2 and the first polarization controller 3 in sequence. The tapered fiber 4.1 is coupled to the CaF2 crystal resonant cavity 4.2. The tail end of the tapered fiber 4.1 is connected to the input 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.

[0033] It also comprises 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. The horn 11 and the standard sound level meter 12 are both located beside the CaF2 crystal resonant cavity 4.2.

[0034] It also comprises a phase lock 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 lock amplifier 13. The signal output end of the phase lock 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.

[0035] The 1550nm laser 1 is a continuous tunable narrowband laser.

[0036] The diameter of the tapered fiber 4.1 is 2μm. The diameter of the CaF2 crystal resonant cavity 4.2 is 5mm, and the height is 0.2mm. The coupling state between the tapered 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 adjusted by a six-dimensional adjustment frame.

[0037] The application discloses a high-sensitivity sound measurement method based on Fano resonance, and relates to the field of sound measurement.

[0038] Firstly, the sensor is controlled to enter a working mode; the working mode is specifically as follows: the 1550nm laser 1 emits pump light, the pump light is sequentially incident to the photodetector 6 through the phase modulator 2, the first polarization controller 3, the tapered optical fiber 4.1, the CaF2 crystal resonant cavity 4.2, the tapered optical fiber 4.1 and the second polarization controller 5, and then is converted into an electric signal through the photodetector 6; the electric signal is transmitted to the oscilloscope 7 and is converted into a transmission spectrum through the oscilloscope 7; the transmission spectrum is displayed on the oscilloscope 7 on one hand and is transmitted to the computer 8 on the other hand; the polarization angles of the first polarization controller 3 and the second polarization controller 5 are adjusted so that the transmission spectrum is a Fano transmission spectrum with an asymmetric waveform;

[0039] In the working mode, when the sound signal acts on the CaF2 crystal resonant cavity 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 a sound pressure measurement equation of the sensor, so that the sound pressure is calculated; the sound pressure measurement equation of the sensor is expressed as follows:

[0040] Δ V = A · f ·(Δ T / Δ f )·(Δ q / Δ θ )· P ;

[0041] In the formula, Δ V represents the voltage change; P represents the sound pressure; A represents the change rate of the radius and the refractive index of the CaF2 crystal resonant cavity 4.2; f represents the resonance frequency of the CaF2 crystal resonant cavity 4.2; Δ T / Δ f represents the slope of a linear region of a first derivative of the Fano transmission spectrum; θ represents the polarization angle; q represents an asymmetry factor of the Fano transmission spectrum, and the size of the asymmetry factor is determined by the polarization angle θ ; A 、 f 、Δ T / Δ f 、 θ 、 q are known quantities.

[0042] The method further comprises judging whether the performance index of the sensor meets the requirement by using the signal generator 9, the power amplifier 10, the loudspeaker 11 and the standard sound level meter 12; the specific steps are as follows:

[0043] Firstly, the sensor is controlled to enter a working mode;

[0044] In the working mode, the signal generator 9 outputs a sine wave signal, the sine wave signal is transmitted to the loudspeaker 11 through the power amplifier 10, and the loudspeaker 11 converts the sine wave signal into an acoustic signal; the acoustic signal acts on the CaF2 crystal resonant cavity 4.2 on one hand, so that the voltage at the resonance frequency of the Fano transmission spectrum changes, and acts on the standard sound level meter 12 on the other hand; the computer 8 monitors the voltage change in real time; the standard sound level meter 12 monitors the sound pressure in real time;

[0045] Then, on 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:

[0046] S 1=Δ V / P ;

[0047] S 2= A · f ·(Δ T / Δ f )·(Δ q / Δ θ );

[0048] 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 change rate of the radius and the refractive index of the CaF2 crystal resonant cavity 4.2; f represents the resonance frequency of the CaF2 crystal resonant cavity 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, which is determined by the polarization angle θ ; A 、 f 、Δ T / Δ f 、 θ 、 q ,

[0049] Then, the sensitivity test value of the sensor is compared with the standard sensitivity value of the sensor, and whether the performance index of the sensor meets the requirement is judged according to the comparison result: if the sensitivity test value of the sensor is consistent with the standard sensitivity value of the sensor, it indicates that the performance index of the sensor meets the requirement; if the sensitivity test value of the sensor is not consistent with the standard sensitivity value of the sensor, it indicates that the performance index of the sensor does not meet the requirement.

[0050] The method further comprises frequency tracking and locking of the 1550nm laser 1 by using the phase-locked amplifier 13 and the PID controller 14; the specific steps are as follows:

[0051] In the working mode, the electric signal is transmitted to the PID controller 14 after synchronous demodulation by the phase-locked amplifier 13; the PID controller 14 adjusts the output frequency of the 1550nm laser 1 in real time according to the demodulation result, so that the output frequency of the 1550nm laser 1 is consistent with the resonance frequency of the CaF2 crystal resonant cavity 4.2, thereby realizing frequency tracking and locking of the 1550nm laser 1.

[0052] Although the specific embodiments of the present application are described above, those skilled in the art should understand that these are only illustrative, the protection scope of the present application is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present application, and these changes and modifications all fall within the protection scope of the present application.

Claims

1. A high-sensitivity acoustic measurement method based on Fano resonance, characterized in that: The method is realized based on a high-sensitivity acoustic sensor based on Fano resonance, and the sensor 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 outgoing end of the 1550nm laser (1) is connected with the first 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 with the CaF2 crystal resonant cavity (4.2); the tail end of the tapered optical fiber (4.1) is connected with the incoming end of the photodetector (6) through the second polarization controller (5); the signal output end of the photodetector (6) is connected with the signal input end of the oscilloscope (7); and the signal output end of the oscilloscope (7) is connected with the signal input end of the computer (8); The sensor further comprises a phase-locked amplifier (13) and a PID controller (14); the signal output end of the photodetector (6) is connected with the signal input end of the phase-locked amplifier (13); the signal output end of the phase-locked amplifier (13) is connected with the signal input end of the PID controller (14); and the signal output end of the PID controller (14) is connected with the modulation end of the 1550nm laser (1); The method is realized by the following steps: First, the sensor is controlled to enter a working mode; the working mode is specifically that the 1550nm laser (1) emits pump light, the pump light is incident to the photodetector (6) through the phase modulator (2), the first polarization controller (3), the tapered optical fiber (4.1), the CaF2 crystal resonant cavity (4.2), the tapered optical fiber (4.1), and the second polarization controller (5) in sequence, and then is converted into an electric signal by the photodetector (6); the electric 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) and is transmitted to the computer (8); the polarization angles of the first polarization controller (3) and the second polarization controller (5) are adjusted so that the transmission spectrum presents a Fano transmission spectrum with an asymmetric waveform; In the working mode, when an acoustic signal acts on the CaF2 crystal resonant cavity (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 the voltage change is substituted into an acoustic pressure measurement equation of the sensor, so that the acoustic pressure is calculated; 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 ; wherein: Δ V represents the voltage variation; P represents the sound pressure; A represents the rate of change of the radius and the refractive index of the CaF2 crystal resonator (4.2); f represents the resonance frequency of the CaF2 crystal resonator (4.2); Δ T / Δ f represents the slope of the linear region of the first derivative of the Faraday transmission spectrum; θ represents the polarization angle; q represents the asymmetry factor of the Faraday transmission spectrum, whose magnitude is determined by the polarization angle θ ; A , f , Δ T / Δ f , θ , q are known quantities; The method further comprises frequency tracking and locking of the 1550nm laser (1) by using the phase-locked amplifier (13) and the PID controller (14); the specific steps are as follows: In the working mode, the electric signal is transmitted to the PID controller (14) after being synchronized demodulated by the phase-locked amplifier (13); the PID controller (14) adjusts the output frequency of the 1550nm laser (1) in real time according to the demodulation result, so that the output frequency of the 1550nm laser (1) is consistent with the resonance frequency of the CaF2 crystal resonant cavity (4.2), thereby realizing the frequency tracking and locking of the 1550nm laser (1).

2. The high sensitivity acoustic measurement method based on Fano resonance according to claim 1, characterized in that: The high-sensitivity acoustic sensor based on Fano resonance further comprises 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 with the signal input end of the power amplifier (10); the signal output end of the power amplifier (10) is connected with the signal input end of the loudspeaker (11); the loudspeaker (11) and the standard sound level meter (12) are both located beside the CaF2 crystal resonant cavity (4.2).

3. The high sensitivity acoustic measurement method based on Fano resonance according to claim 1, characterized in that: The 1550nm laser (1) is a continuous tunable narrowband laser.

4. The high sensitivity acoustic measurement method based on Fano resonance according to claim 1, characterized in that: The diameter of the tapered optical fiber (4.1) is 2μm; the diameter of the CaF2 crystal resonant cavity (4.2) is 5mm and the height is 0.2mm; 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 by using a six-dimensional adjustment frame.

5. The high sensitivity acoustic measurement method based on Fano resonance according to claim 2, characterized in that: The method further comprises judging whether the performance index of the sensor meets the requirements by using the signal generator (9), the power amplifier (10), the loudspeaker (11), and the standard sound level meter (12); 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 sinusoidal signal, the sinusoidal signal is transmitted to the loudspeaker (11) by the power amplifier (10), and is converted into an acoustic signal by the loudspeaker (11); the acoustic signal acts on the CaF2 crystal resonant cavity (4.2) on one hand, causing the voltage at the resonance frequency of the Fano transmission spectrum to change, and acts on the standard sound level meter (12) on the other hand; 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 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 = 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 standard value of the sensitivity of the sensor; Δ V represents the voltage change amount; P represents the sound pressure; A represents the change rate of the radius and the refractive index of the CaF2 crystal resonant cavity (4.2); f represents the resonance frequency of the CaF2 crystal resonant cavity (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, which is determined by the polarization angle θ ; A , f , Δ T / Δ f , θ , q are known quantities; Then, the sensitivity test value of the sensor is compared with the sensitivity standard value of the sensor, and whether the performance index of the sensor meets the requirements is judged according to 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 index of the sensor meets the requirements; if the sensitivity test value of the sensor is not consistent with the sensitivity standard value of the sensor, it indicates that the performance index of the sensor does not meet the requirements.

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