A photoacoustic spectroscopy gas detection device of F-P cavity

Abstract

The application relates to the technical field of gas detection, and discloses a photoacoustic spectroscopy gas detection device of an F-P cavity. The device forms a new voltage waveform signal by using the waveform voltage signals respectively emitted by a superposition function generator and a lock-in amplifier to provide a driving current for a pump laser, emits pump laser to a Fabry-Perot cavity through the pump laser, emits detection laser to the Fabry-Perot cavity through a fiber circulator, generates an acoustic signal, and processes the acoustic signal through interference in the Fabry-Perot cavity. The interference signal is converted into an electric signal through a photodetector, the electric signal is demodulated into a photoacoustic signal for representing gas concentration through the lock-in amplifier, and the input voltage signal of the detection laser is modulated according to the electric signal feedback through a proportional-integral-derivative controller to tune the wavelength of the detection laser, so that the photoacoustic signal error detected by the lock-in amplifier is minimized, and the sensitivity of the photoacoustic spectroscopy gas detection is improved.

Description

Technical Field

[0001] This invention relates to the field of gas detection technology, and in particular to a photoacoustic spectroscopy gas detection device with an FP cavity. Background Technology

[0002] Over the past two decades, photoacoustic spectroscopy for gas detection has made significant progress, offering advantages such as high sensitivity, fast response, and wide dynamic range. In photoacoustic spectroscopy, the gas sample being measured is excited by a light source. If the laser source is a pump source, this will cause localized heating of the gas molecules (along the pump beam). If the pump beam is modulated with a sine wave, square wave, or pulse, it will generate acoustic waves with periodic temperature gradients. A Fabry-Perot interferometer (FPI) is commonly used to detect the photoacoustic signal and study the accuracy of gas detection. During detection, the concentration of the gas sample is proportional to the amplitude of the acoustic waves generated by the photoacoustic effect. However, in current technologies, the sensitivity of photoacoustic spectroscopy for gas detection is not high enough, leading to inaccurate final gas detection results. Summary of the Invention

[0003] This invention provides a photoacoustic spectroscopy gas detection device with an FP cavity, which solves the technical problem of low sensitivity in photoacoustic spectroscopy gas detection.

[0004] In view of the above, the first aspect of the present invention provides a photoacoustic spectroscopy gas detection device with an FP cavity, comprising: a function generator, a lock-in amplifier, an adder, a laser driver, a pump laser, a Fabry-Perot cavity, an optical fiber circulator, a probe laser, a photodetector, and a proportional-integral-differential controller;

[0005] The function generator is connected to the adder and is used to send a sawtooth waveform voltage signal to the adder;

[0006] One end of the lock-in amplifier is connected to the adder and is used to send a sinusoidal voltage signal to the adder;

[0007] The adder is connected to the laser driver and is used to superimpose the sawtooth waveform voltage signal and the sine wave voltage signal into a new voltage waveform signal, which is then output to the laser driver.

[0008] The laser driver is connected to the pump laser and is used to provide a driving current to the pump laser according to the new voltage waveform signal;

[0009] The pump laser is used to emit pump laser light into the Fabry-Perot cavity, and after interacting with the gas to be tested in the Fabry-Perot cavity, it generates an acoustic signal through a photoacoustic effect.

[0010] The fiber optic circulator is connected to the probe laser, the Fabry-Perot cavity, and the photodetector, respectively. The probe laser is used to emit a probe laser that passes through the fiber optic circulator into the Fabry-Perot cavity.

[0011] The Fabry-Perot cavity interferes with the acoustic signal, and the output interference signal passes through the fiber optic circulator to the photodetector; the photodetector is connected to the lock-in amplifier and the proportional-integral-differential controller respectively, and is used to convert the interference signal into an electrical signal and send it to the lock-in amplifier and the proportional-integral-differential controller respectively;

[0012] The lock-in amplifier is also used to demodulate the electrical signal into a photoacoustic signal for characterizing the gas concentration;

[0013] The proportional-integral-derivative controller is connected to the probe laser and is used to modulate the input voltage signal of the probe laser according to the feedback of the electrical signal, so as to tune the wavelength of the probe laser.

[0014] Preferably, the pump laser is a mid-infrared pump laser.

[0015] Preferably, the detection laser is a distributed feedback diode laser with a center wavelength of 1550nm and an output power of 10mW.

[0016] Preferably, the Fabry-Perot cavity includes a first Fabry-Perot mirror, a second Fabry-Perot mirror, and an anti-resonance fiber optic gas chamber;

[0017] The anti-resonance fiber optic air chamber has sleeves on both sides, and anti-resonance hollow optical fibers are installed inside the sleeves. The anti-resonance hollow optical fibers are connected to the anti-resonance fiber optic air chamber. The bottom of the anti-resonance fiber optic air chamber has an air inlet and an air outlet. The first Fabry-Perot mirror and the second Fabry-Perot mirror are respectively located on both sides of the anti-resonance fiber optic air chamber, and the first Fabry-Perot mirror and the second Fabry-Perot mirror are arranged in parallel.

[0018] Preferably, the anti-resonance hollow optical fiber is provided with an optical fiber cladding, a hollow capillary layer and a hollow core from the outside to the inside. The hollow capillary layer includes a plurality of hollow capillaries, which are disposed in the hollow core and arranged along the inner wall of the hollow core. The optical fiber cladding is made of borosilicate glass material, and the hollow capillaries are made of silicon material.

[0019] Preferably, a prism is provided in the optical path between the pump laser and the Fabry-Perot cavity.

[0020] As can be seen from the above technical solutions, the present invention has the following advantages:

[0021] This invention uses superimposed waveform voltage signals from a function generator and a lock-in amplifier to form a new voltage waveform signal, providing a driving current for the pump laser and modulating its wavelength. Simultaneously, the pump laser emits a pump laser into a Fabry-Perot cavity, and a probe laser emits a probe laser that travels through an optical fiber circulator to the Fabry-Perot cavity. This probe laser interacts with the gas to be measured in the Fabry-Perot cavity, generating an acoustic signal. The Fabry-Perot cavity then performs interference processing on the acoustic signal. A photodetector converts the interference signal into an electrical signal, which is then demodulated by the lock-in amplifier into a photoacoustic signal characterizing the gas concentration. Furthermore, a proportional-integral-derivative (PID) controller modulates the input voltage signal of the probe laser based on the feedback of the electrical signal, thus tuning the probe laser's wavelength. This minimizes the error in the photoacoustic signal detected by the lock-in amplifier and improves the sensitivity of photoacoustic spectroscopy gas detection. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of an FP cavity photoacoustic spectroscopy gas detection device provided in an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of the Fabry-Perot cavity provided in an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the anti-resonance hollow optical fiber provided in an embodiment of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] For easier understanding, please refer to Figure 1 The present invention provides a photoacoustic spectroscopy gas detection device with an FP cavity, comprising: a function generator 3, a lock-in amplifier 4, an adder 2, a laser driver 1, a pump laser 11, a Fabry-Perot cavity 9, an optical fiber circulator 8, a probe laser 7, a photodetector 5, and a proportional-integral-differential controller 6.

[0027] Function generator 3 is connected to adder 2 and is used to send sawtooth waveform voltage signals to adder 2;

[0028] One end of the lock-in amplifier 4 is connected to the adder 2 and is used to send a sinusoidal voltage signal to the adder 2;

[0029] The voltage signals generated by function generator 3 and lock-in amplifier 4 can be set by the user.

[0030] Adder 2 is connected to laser driver 1 and is used to superimpose the sawtooth waveform voltage signal and the sine wave voltage signal into a new voltage waveform signal and output it to laser driver 1.

[0031] The laser driver 1 is connected to the pump laser 11 and is used to provide drive current to the pump laser 11 according to the new voltage waveform signal;

[0032] Pump laser 11 is used to emit pump laser into Fabry-Perot cavity 9, and after interacting with the gas to be measured in Fabry-Perot cavity 9, it generates an acoustic signal through photoacoustic effect.

[0033] Among them, the pump laser 11 adopts a mid-infrared pump laser.

[0034] In one example, a prism 10 is provided in the optical path between the pump laser 11 and the Fabry-Perot cavity 9.

[0035] The fiber optic circulator 8 is connected to the probe laser 7, the Fabry-Perot cavity 9, and the photodetector 5, respectively. The probe laser 7 is used to emit a probe laser that passes through the fiber optic circulator 8 into the Fabry-Perot cavity 9.

[0036] Among them, the detection laser 7 is a distributed feedback diode laser with a center wavelength of 1550nm and an output power of 10mW.

[0037] The probe laser is transmitted to the anti-resonance fiber gas chamber in the Fabry-Perot cavity 9 via fiber optic circulator 8 and ordinary optical fiber through a docking coupling method.

[0038] The Fabry-Perot cavity 9 performs interference processing on the acoustic signal, and the output interference signal passes through the fiber optic circulator 8 to the photodetector 5. The photodetector 5 is connected to the lock-in amplifier 4 and the proportional-integral-differential controller 6 respectively, and is used to convert the interference signal into an electrical signal and send it to the lock-in amplifier 4 and the proportional-integral-differential controller 6 respectively.

[0039] Among them, the photodetector 5 is selective for wavelength, and only detected laser light with a wavelength of 1550nm, but could not detect mid-infrared pump light.

[0040] Lock-in amplifier 4 is also used to demodulate the electrical signal into a photoacoustic signal for characterizing gas concentration;

[0041] The concentration of the gas sample is proportional to the amplitude of the photoacoustic signal.

[0042] The proportional-integral-derivative controller 6 is connected to the probe laser 7 and is used to modulate the input voltage signal of the probe laser 7 according to the feedback of the electrical signal, so as to tune the wavelength of the probe laser 7.

[0043] Because laser wavelengths exhibit wavelength drift—different driving voltage amplitudes correspond to slight differences in wavelength—the detection results are optimal at the center wavelength. Therefore, to ensure minimal error in the final detected photoacoustic signal related to gas concentration, a proportional-integral-differential controller 6 modulates the input voltage signal of the probe laser 7. The quadrature point and any amplitude drift point corresponding to the voltage signal are corrected by the voltage signal modulated by the probe laser 7, thereby achieving laser wavelength locking. After wavelength locking, the final photoacoustic signal detected by the lock-in amplifier 4 has minimal error.

[0044] Specifically, the electrical signal received by the proportional-integral controller is feedback information from the photodetector, which can provide feedback on the laser wavelength, facilitating a one-to-one correspondence between wavelength and photoacoustic signal. The amplitude of the photoacoustic signal can be displayed in the lock-in amplifier. By scanning a certain range of wavelengths, the maximum value of the photoacoustic signal corresponding to each wavelength is determined, thus finding the voltage signal corresponding to the maximum photoacoustic signal. This voltage signal corresponds to the most suitable laser wavelength, where the error is minimized.

[0045] This embodiment provides a photoacoustic spectroscopy gas detection device with an FP cavity. A new voltage waveform signal is formed by superimposing the waveform voltage signals emitted by the function generator 3 and the lock-in amplifier 4, respectively, to provide a driving current for the pump laser 11 and modulate its wavelength. Simultaneously, the pump laser 11 emits a pump laser into the Fabry-Perot cavity 9, and the probe laser 7 emits a probe laser that passes through the fiber optic circulator 8 into the Fabry-Perot cavity 9. The probe laser interacts with the gas to be measured in the Fabry-Perot cavity 9, generating an acoustic signal. The Fabry-Perot cavity 9 performs interference processing on the acoustic signal, and the photodetector 5 converts the interference signal into an electrical signal. The lock-in amplifier 4 demodulates the electrical signal into a photoacoustic signal for characterizing the gas concentration. Furthermore, the proportional-integral-derivative controller 6 modulates the input voltage signal of the probe laser 7 based on the feedback of the electrical signal to tune the wavelength of the probe laser 7. This minimizes the error of the photoacoustic signal detected by the lock-in amplifier 4 and improves the sensitivity of photoacoustic spectroscopy gas detection.

[0046] In one specific embodiment, such as Figure 2 As shown, the Fabry-Perot cavity 9 includes a first Fabry-Perot mirror 91, a second Fabry-Perot mirror 92, and an anti-resonance fiber optic air cell 97;

[0047] The anti-resonance fiber optic air chamber 97 has sleeves 93 on both sides, and anti-resonance hollow optical fibers 94 are installed inside the sleeves 93. The anti-resonance hollow optical fibers 94 are connected to the anti-resonance fiber optic air chamber 97. The bottom of the anti-resonance fiber optic air chamber 97 has an air inlet 95 and an air outlet 96. The first Fabry-Perot mirror 91 and the second Fabry-Perot mirror 92 are respectively located on both sides of the anti-resonance fiber optic air chamber 97, and the first Fabry-Perot mirror 91 and the second Fabry-Perot mirror 92 are arranged in parallel.

[0048] Among them, such as Figure 3 As shown, the anti-resonance hollow optical fiber 94 is provided with an optical fiber cladding 941, a hollow capillary layer 942, and a hollow core 943 from the outside to the inside. The hollow capillary layer 942 includes a plurality of hollow capillaries, which are disposed in the hollow core 943 and arranged along the inner wall of the hollow core 943. The optical fiber cladding 941 is made of borosilicate glass, and the hollow capillaries are made of silicon.

[0049] Among them, the outer cross-sectional area of ​​the anti-resonance hollow fiber 94 is 0.0675 mm². 2 The cross-sectional area of ​​the core is twice that of the inner ring. There are eight hollow capillaries, and the inner diameter of the hollow core 943 is 122 μm. The hollow capillaries are arranged around the hollow core 943 inside the optical fiber. The overlap between the outer glass layer of the optical fiber and the light passing through the core is minimal. According to the principle of anti-resonance fiber, when incident light propagates in the optical fiber, the light will be scattered at the outer glass layer. Due to the existence of scattering, quantum sound waves, i.e., phonon noise, will be generated. Since the materials of the optical fiber glass and capillaries are different, the phonon noise cannot resonate during propagation, which can greatly reduce the noise and make it have a good noise reduction effect, eliminating the interference of phonons from the glass.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A photoacoustic spectroscopy gas detection device with an FP cavity, characterized in that, include: Function generator, lock-in amplifier, adder, laser driver, pump laser, Fabry-Perot cavity, fiber optic circulator, probe laser, photodetector, and proportional-integral-differential controller; The function generator is connected to the adder and is used to send a sawtooth waveform voltage signal to the adder; One end of the lock-in amplifier is connected to the adder and is used to send a sinusoidal voltage signal to the adder; The adder is connected to the laser driver and is used to superimpose the sawtooth waveform voltage signal and the sine wave voltage signal into a new voltage waveform signal, which is then output to the laser driver. The laser driver is connected to the pump laser and is used to provide a driving current to the pump laser according to the new voltage waveform signal; The pump laser is used to emit pump laser light into the Fabry-Perot cavity, and after interacting with the gas to be tested in the Fabry-Perot cavity, it generates an acoustic signal through a photoacoustic effect. The fiber optic circulator is connected to the probe laser, the Fabry-Perot cavity, and the photodetector, respectively. The probe laser is used to emit a probe laser that passes through the fiber optic circulator into the Fabry-Perot cavity. The Fabry-Perot cavity performs interference processing on the acoustic signal, and the output interference signal passes through the fiber optic circulator to the photodetector. The photodetector is connected to the lock-in amplifier and the proportional-integral-differential controller respectively, and is used to convert the interference signal into an electrical signal and send it to the lock-in amplifier and the proportional-integral-differential controller respectively; The lock-in amplifier is also used to demodulate the electrical signal into a photoacoustic signal for characterizing the gas concentration; The proportional-integral-derivative controller is connected to the probe laser and is used to modulate the input voltage signal of the probe laser according to the feedback of the electrical signal, so as to tune the wavelength of the probe laser.

2. The photoacoustic spectroscopy gas detection device with an FP cavity according to claim 1, characterized in that, The pump laser is a mid-infrared pump laser.

3. The photoacoustic spectroscopy gas detection device with an FP cavity according to claim 1, characterized in that, The detection laser is a distributed feedback diode laser with a center wavelength of 1550nm and an output power of 10mW.

4. The photoacoustic spectroscopy gas detection device with an FP cavity according to claim 1, characterized in that, The Fabry-Perot cavity includes a first Fabry-Perot mirror, a second Fabry-Perot mirror, and an anti-resonance fiber optic gas chamber; The anti-resonance fiber optic air chamber has sleeves on both sides, and anti-resonance hollow optical fibers are installed inside the sleeves. The anti-resonance hollow optical fibers are connected to the anti-resonance fiber optic air chamber. The bottom of the anti-resonance fiber optic air chamber has an air inlet and an air outlet. The first Fabry-Perot mirror and the second Fabry-Perot mirror are respectively located on both sides of the anti-resonance fiber optic air chamber, and the first Fabry-Perot mirror and the second Fabry-Perot mirror are arranged in parallel.

5. The photoacoustic spectroscopy gas detection device with an FP cavity according to claim 4, characterized in that, The anti-resonance hollow optical fiber is provided with an optical fiber cladding, a hollow capillary layer and a hollow core from the outside to the inside. The hollow capillary layer includes a plurality of hollow capillaries, which are disposed in the hollow core and arranged along the inner wall of the hollow core. The optical fiber cladding is made of borosilicate glass material, and the hollow capillaries are made of silicon material.

6. The photoacoustic spectroscopy gas detection device with an FP cavity according to claim 1, characterized in that, A prism is provided in the optical path between the pump laser and the Fabry-Perot cavity.

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