All-fiber cantilever beam type photoacoustic spectrometry gas detection system based on microwave photon technology

Abstract

The invention discloses an all-fiber cantilever beam type photoacoustic spectrometry gas detection system based on a microwave photon technology, which belongs to the field of photoacoustic spectrometry gas detection and comprises an F-P (Fabry-Perot) fiber sensor, a pump laser, an MZM (Mach Zehnder Modulator) modulator, a vector network analyzer, a coupler, a variable optical attenuator, a photoelectric detector and a reflector, the pump laser is connected with the input end of the MZM modulator, the output end of the MZM modulator is connected with the coupling input end of the coupler, the first output end of the coupler is connected with the reflector through the variable optical attenuator, and the coupling output end of the coupler is connected with the vector network analyzer through the photoelectric detector. According to the all-fiber cantilever beam type photoacoustic spectrometry gas detection system based on the microwave photon technology, the problems that a traditional diaphragm type F-P interference cantilever beam is large in size, low in sensitivity and greatly affected by temperature are solved, and the signal-to-noise ratio of a detection signal is increased; in addition, the establishment of the microwave photonic link enhances the resolution and speed of signal detection.

Description

Technical Field

[0001] The invention relates to the technical field of photoacoustic spectroscopy gas detection, and in particular to an all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology. Background Art

[0002] The advent of the fourth industrial revolution has led to a high degree of cross-fertilization and integration of various traditional disciplines, giving birth to emerging fields such as artificial intelligence, nanotechnology, quantum technology, the Internet of Things, and the Industrial Internet of Things. Due to the demand for information perception in the above fields, the requirements for sensing technology have been further improved, such as sensor sensitivity, size, power consumption, and remote monitoring. Since the invention of lasers and optical fibers in the 1960s, optical fiber communications and related technologies have achieved great success, which has greatly improved the means and methods of human communication. Relying on optical communications and computer science and technology, the role of information in all aspects of human life has reached an immeasurable degree. Stimulated and driven by the development of optical communication technology, the research and development of optical fibers and related equipment has made great progress. Since the material of the optical fiber itself is quartz, compared with cables, optical fibers have strong anti-electromagnetic interference ability, small size, light weight, and chemical corrosion resistance. Optical fibers can not only transmit information obtained by sensors with low loss, high speed and large bandwidth, but also can be used as sensors themselves. Optical fiber sensing technology has been applied to many fields such as industry, transportation, and security. However, the current fiber optic sensing technology is still limited by optical measuring instruments such as spectrometers in terms of sensing speed and sensing resolution. Microwave photonics, as an emerging fusion discipline, combines the advantages of optics and microwaves. It has the advantages of fast speed, high resolution and large bandwidth, and can therefore achieve high-speed, high-sensitivity and high-resolution sensing.

[0003] Sound waves are mechanical waves that are generated by the vibration of objects and propagate through gases, liquids and solids. With the development of industrial production and the improvement of people's living standards, people have an increasing demand for the study of sound waves. The measurement of sound wave frequency and intensity and the restoration of sound wave signals are the basis for studying sound waves. According to the different properties of sound waves, sound waves can be classified, and different classifications correspond to different applications and research fields. Sound waves can be divided into sub-sound waves, audible sound waves and ultrasonic waves according to the frequency.

[0004] Photoacoustic spectroscopy is an absorption spectroscopy method that has important applications in the field of trace gas detection. This method uses the absorption peak of a substance to identify the substance or to enhance the photoacoustic effect. The intensity of the photoacoustic signal is proportional to the incident light intensity and the concentration of the gas. The concentration of the gas can be obtained by measuring the sound pressure. Therefore, the sound pressure sensor is one of the keys to the entire system.

[0005] The prior art can refer to the patent with announcement number CN114046868B, which discloses a high-sensitivity microwave interference vibration real-time monitoring system, wherein after the microwave interference electrical signal is brought into the Michelson interference mathematical model, the power of the second and fourth harmonics in the Michelson interference mathematical model is compared, or the power of the first and third harmonics in the Michelson interference mathematical model is compared to determine the phase change caused by the vibration signal, and based on the phase change, the intensity of the vibration signal is calculated. Summary of the invention

[0006] The purpose of the present invention is to provide an all-fiber cantilever photoacoustic spectroscopy gas detection system based on microwave photon technology, which overcomes the problems of large volume, low sensitivity and great temperature influence of traditional diaphragm-type FP interference cantilever, and improves the signal-to-noise ratio of the detection signal.

[0007] To achieve the above-mentioned object, the present invention provides an all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology, comprising an FP fiber sensor, wherein the FP fiber sensor comprises a fiber base and a fiber cantilever beam arranged above the fiber base, wherein the fiber base comprises a fiber core and a cladding arranged around the fiber core, an optical fiber segment is arranged between the fiber cantilever beam and the cladding, and a nanostructure and a transfer layer are arranged on the upper surface of the fiber cantilever beam and the end away from the support.

[0008] Preferably, the optical fiber segment is configured to be hollow, the nanostructure is configured to be hexagonal, and the transfer layer thickness of the nanostructure is 500 μm.

[0009] Preferably, one end of the optical fiber cantilever beam is combined with the optical fiber segment, one end of the optical fiber cantilever beam away from the optical fiber segment is suspended above the cladding, and the optical fiber cantilever beam is parallel to the end face of the cladding.

[0010] Preferably, the optical fiber cantilever is completed using a femtosecond laser.

[0011] Preferably, it also includes a pump laser, an MZM modulator, a vector network analyzer, a coupler, an adjustable optical attenuator, a photodetector and a reflector, wherein the pump laser is connected to the input end of the MZM modulator, the output end of the MZM modulator is connected to the coupling input end of the coupler, the first output end of the coupler is connected to the reflector through the adjustable optical attenuator, and the coupling output end of the coupler is connected to the vector network analyzer through the photodetector; the MZM modulator transmits the reference light with adjusted intensity to the reflector; after receiving the reference light with adjusted intensity, the reflector transmits the reference reflected light to the coupler through the adjustable optical attenuator.

[0012] Preferably, the photoelectric detector detects the microwave interference optical signal to obtain a microwave interference electrical signal; and the vector network analyzer analyzes the microwave interference electrical signal.

[0013] Preferably, firstly, a FP optical fiber sensor is constructed, and the light intensity of the FP sensor is expressed as:

[0014]

[0015] Wherein, R1 and R2 are the reflectivity of the mirror respectively.

[0016] Preferably, according to the Michelson interference mathematical model, the light intensity at the photodetector is described as:

[0017] I=A1Mcos[2πf(t+L c / c+2(nL S +(n+Δn)(L F-P +ΔL F-P )) / c)]

[0018] …+A2Mcos[2πf(t+L c / c+2nL R / c)]

[0019] Where A1 and A2 are the optical powers of the reflected optical signal, M and f are the amplitude and frequency of the microwave signal, t is the time, and L is c L is the length that the optical signal and the electrical signal travel together. S is the length of the sensor arm, L R is the length of the reference arm, n is the refractive index of the optical fiber, and c is the speed of light in vacuum;

[0020] The delay difference of the microwave signal after passing through two paths is expressed as:

[0021] ΔT0=2n(L S +(n+Δn)(L F-P +ΔL F-P )-L R / c)

[0022] The corresponding phase difference is expressed as:

[0023]

[0024] The spectrum intensity A of microwave interference is expressed as:

[0025]

[0026] The microwave interference spectrum is obtained by a vector network analyzer, and an extreme frequency is selected as the RF signal to modulate the electro-optic modulator, and finally the relationship curve between the RF intensity and the measured value is obtained:

[0027] I(Δn,ΔL F-P )∝DC+cos(2π·f RF (ΔT0(Δn,ΔL F-P ))).

[0028] Therefore, the present invention adopts the above-mentioned all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology, which has the following beneficial effects:

[0029] (1) Developing fiber cantilever beams by laser direct writing, which overcomes the problems of large volume, low sensitivity and great temperature influence of traditional diaphragm-type FP interference cantilever beams;

[0030] (2) Microwave interference method is used to improve the signal-to-noise ratio of the detection signal.

[0031] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of a photoelectric detector of an embodiment of an all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology of the present invention;

[0033] Figure 2 It is a system schematic block diagram of an embodiment of the all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology of the present invention;

[0034] Figure 3 It is a transmission spectrum and relationship fitting diagram under different length differences of an embodiment of the all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology of the present invention;

[0035] Figure 4 It is a schematic diagram of transmission spectra under different light intensity ratios of an embodiment of the all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology of the present invention;

[0036] Reference numerals

[0037] 1. Pump laser; 2. FP fiber sensor; 21. Fiber base; 211. Fiber core; 212. Cladding; 22. Fiber cantilever beam; 3. Fiber segment; 4. MZM modulator; 5. Adjustable optical attenuator; 6. Reflector; 7. Vector network analyzer; 8. Photodetector; 9. Coupler. DETAILED DESCRIPTION

[0038] The following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Reference Figure 1-Figure 4 The present invention discloses an all-fiber cantilever photoacoustic spectroscopy gas detection system based on microwave photon technology, comprising an FP fiber sensor 2, the FP fiber sensor 2 comprising an optical fiber base 21 and an optical fiber cantilever beam 22 arranged above the optical fiber base 21, the optical fiber base 21 comprising a fiber core 211 and a cladding 212 arranged outside the fiber core 211, an optical fiber segment 3 is arranged between the optical fiber cantilever beam 22 and the cladding 212, and the upper surface of the optical fiber cantilever beam 22 and the end away from the pillar are both provided with nanostructures and transfer layers. The optical fiber cantilever beam 22 is completed by femtosecond laser.

[0040] The fiber segment 3 is set to be hollow and serves as the FP cavity. The nanostructure is set to be hexagonal, and the thickness of the nanotransfer layer is 500 μm, which increases the surface area of ​​the fiber cantilever beam 22, while the higher porosity in the nanostructure reduces the value of the effective Young's modulus.

[0041] One end of the optical fiber cantilever beam 22 is combined with the optical fiber segment 3 , and one end of the optical fiber cantilever beam 22 away from the optical fiber segment 3 is suspended above the cladding 212 . The end surface of the optical fiber cantilever beam 22 and the cladding 212 are parallel.

[0042] The Young's modulus of the microcantilever is also an important performance parameter. Simply put, the operation of the microcantilever mainly depends on the bending of the beam, and as the Young's modulus decreases, the bending degree of the beam will also increase. Therefore, the sensitivity of the system detection can be significantly improved by reducing the Young's modulus of the beam. However, for microcantilever beams made of isotropic materials, they have a fixed Young's modulus, so the design of microcantilever beams with this structure has certain limitations. As for nanoarrays, since the nanochannels are arranged unidirectionally and have anisotropic properties, the Young's modulus under this structure is not a unique material property, and its value can also be controlled by changing the size of the nanochannels.

[0043] The sensitivity of the micro-cantilever beam is directly related to the structural dimensions of the micro-cantilever beam. In order to improve the sensitivity of the micro-cantilever beam sensor, the thickness and width of the micro-cantilever beam structure should be increased and the length of the micro-cantilever beam should be reduced.

[0044] The elastic coefficient is an important parameter to measure the performance of a micro cantilever. In order to accurately measure tiny forces, the elastic coefficient of the micro cantilever must be as small as possible. Reducing the length of the micro cantilever and increasing the thickness of the micro cantilever can increase the elastic coefficient.

[0045] When the micro-cantilever works in the dynamic mode, the sensing principle is: the mass attached to the micro-cantilever will change the initial resonant frequency of the micro-cantilever. Then, as long as the change in the resonant frequency of the micro-cantilever is detected, the size of the additional mass can be accurately obtained according to the formula of the undamped first-order natural frequency of the micro-cantilever. In MEMS biosensors, a micro-cantilever with a beam-mass block structure is usually used. Compared with a rectangular micro-cantilever with equal cross-section, its advantage is that it can absorb more samples to be detected and improve the sensitivity of detection. Therefore, it is of great significance to study the influence of the size of the additional mass block on the initial resonant frequency of the micro-cantilever and find the change law between the two.

[0046] like Figure 2 The system also includes a pump laser (PUMP) 1, an MZM modulator 4, a vector network analyzer (VNA) 7, a coupler (OC) 9, an adjustable optical attenuator (OA) 5, a photodetector (PD) 8 and a reflector 6. The pump laser 1 is connected to the input end of the MZM modulator 4, the output end of the MZM modulator 4 is connected to the coupling input end of the coupler 9, the first output end of the coupler 9 is connected to the reflector 6 through the adjustable optical attenuator 5, and the coupling output end of the coupler 9 is connected to the vector network analyzer 7 through the photodetector 8; the MZM modulator 4 transmits the reference light with adjusted intensity to the reflector 6; after receiving the reference light with adjusted intensity, the reflector 6 transmits the reference reflected light to the coupler 9 through the adjustable optical attenuator 5.

[0047] A pump laser 1 is a device that uses an external light source to excite a laser material to generate laser light. It is a key component in a laser and is mainly used to provide energy to excite the laser material. In a pump laser, the energy of an external light source (such as a laser diode or a fiber laser) is converted into the energy required to excite the laser material.

[0048] The function of the pump laser 1 is to provide the energy required to excite the laser material, so that the atoms or molecules in the laser material are excited and enter an excited state. These excited atoms or molecules will return to the ground state in a short time and release energy in the process. This energy release process is called stimulated radiation, and this radiation is coherent light, that is, laser.

[0049] The MZM modulator 4 modulates the signal by changing the phase or amplitude of the optical signal. The basic structure of the MZM modulator 4 consists of two grating couplers, two phase shift modulators and a fiber coupler. It uses the interference effect of light to achieve the modulation function. When the optical signal passes through the MZM modulator 4, it first enters the grating combiner, and then is divided into two light beams, which enter two phase shift modulators for phase or amplitude modulation. Finally, the two light beams are combined again and then output through the coupler 9.

[0050] The adjustable optical attenuator 5 is used to adjust the intensity of the reference light and transmit the reference light with adjusted intensity to the reflector 6; after receiving the reference light with adjusted intensity, the reflector 6 transmits the reference reflected light to the coupler 9 through the adjustable optical attenuator 5. By adjusting the intensity of the reference light, the contrast of the microwave interference is increased, thereby improving the vibration signal measurement sensitivity; and / or by selecting and loading a microwave signal with a set single frequency onto a laser signal, vibration measurement is performed using the laser signal loaded with the microwave signal, thereby improving the vibration signal measurement sensitivity.

[0051] The coupler 9 is used to split the laser signal loaded with the microwave signal into two paths, one of which is transmitted as reference light to the adjustable optical attenuator 5 .

[0052] First, build a FP optical fiber sensor. The light intensity of the FP sensor is expressed as:

[0053]

[0054] Among them, R1 and R2 are the reflectivity of the mirror respectively. It can be seen from the formula that the wavelength-related intensity is a trigonometric function curve related to the FP cavity refractive index and cavity length. When the FP cavity refractive index or cavity length changes, the function curve will be disturbed. Therefore, the wavelength at a certain extreme point is selected as the pump wavelength.

[0055] According to the Michelson interference mathematical model, the light intensity at the photodetector 8 is described as:

[0056]

[0057] Where A1 and A2 are the optical powers of the reflected optical signal, M and f are the amplitude and frequency of the microwave signal, t is the time, and L is c L is the length that the optical signal and the electrical signal travel together. S is the length of the sensor arm, L R is the length of the reference arm, n is the refractive index of the optical fiber, and c is the speed of light in vacuum;

[0058] The delay difference of the microwave signal after passing through two paths is expressed as:

[0059] ΔT0=2n(L S +(n+Δn)(L F-P +ΔL F-P )-L R / c) (3)

[0060] The corresponding phase difference is expressed as:

[0061]

[0062] The spectrum intensity A of optical microwave interferometry (OCMI) is expressed as:

[0063]

[0064] It can be seen that the microwave interference spectrum is a trigonometric function related to ΔT0. The microwave interference spectrum is obtained by a vector network analyzer (VNA), and a certain extreme frequency is selected as the RF signal to modulate the electro-optical modulator, and finally the relationship curve between the RF intensity and the measured value is obtained.

[0065] I(Δn,ΔL F-P )∝DC+cos(2π·f RF (ΔT0(Δn,ΔL F-P ))) (6).

[0066] According to formula (6), since the change of external sound pressure causes the change of FP cavity length and thus causes the change of output light intensity, the method of detecting light intensity can be used to realize sound detection.

[0067] Therefore, the present invention adopts the above-mentioned all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology, which overcomes the problems of large volume, low sensitivity and great temperature influence of traditional diaphragm-type FP interference cantilever beam, and improves the signal-to-noise ratio of the detection signal.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. An all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology, including an FP fiber sensor, characterized in that: The FP optical fiber sensor includes an optical fiber base and an optical fiber cantilever beam arranged above the optical fiber base, the optical fiber base includes a fiber core and a cladding arranged outside the fiber core, an optical fiber segment is arranged between the optical fiber cantilever beam and the cladding, and the upper surface of the optical fiber cantilever beam and the end away from the support are both provided with a nanostructure and a transfer layer.

2. The all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology according to claim 1 is characterized in that: The optical fiber segment is configured to be hollow.

3. The all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology according to claim 1 is characterized in that: The nanostructure is arranged in a hexagonal shape, and the thickness of the nanotransfer layer is 500 μm.

4. The all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology according to claim 1 is characterized in that: One end of the optical fiber cantilever beam is combined with the optical fiber segment, one end of the optical fiber cantilever beam away from the optical fiber segment is suspended above the cladding, and the optical fiber cantilever beam is parallel to the end surface of the cladding.

5. The all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology according to claim 1 is characterized in that: The optical fiber cantilever beam is completed by using a femtosecond laser.

6. The all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology according to claim 1 is characterized by: The invention also includes a pump laser, an MZM modulator, a vector network analyzer, a coupler, an adjustable optical attenuator, a photodetector and a reflector. The pump laser is connected to the input end of the MZM modulator, the output end of the MZM modulator is connected to the coupling input end of the coupler, the first output end of the coupler is connected to the reflector through the adjustable optical attenuator, and the coupling output end of the coupler is connected to the vector network analyzer through the photodetector; the MZM modulator transmits the reference light with adjusted intensity to the reflector; after receiving the reference light with adjusted intensity, the reflector transmits the reference reflected light to the coupler through the adjustable optical attenuator.

7. The all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology according to claim 6 is characterized in that: The photoelectric detector detects the microwave interference optical signal to obtain the microwave interference electrical signal; the vector network analyzer analyzes the microwave interference electrical signal.

8. The all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology according to claim 7 is characterized in that: First, build a FP optical fiber sensor. The light intensity of the FP sensor is expressed as: Among them, R1 and R2 are the reflectivity of the mirror respectively.

9. The all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology according to claim 8 is characterized in that: According to the Michelson interference mathematical model, the light intensity at the photodetector is described as: I=A1Mcos[2πf(t+L c / c+2(nL S +(n+Δn)(L F-P +ΔL F-P )) / c)] …+A2Mcos[2πf(t+L c / c+2nL R / c)] Where A1 and A2 are the optical powers of the reflected optical signal, M and f are the amplitude and frequency of the microwave signal, t is the time, and L is c L is the length that the optical signal and the electrical signal travel together. S is the length of the sensor arm, L R is the length of the reference arm, n is the refractive index of the optical fiber, and c is the speed of light in vacuum.

10. The all-fiber cantilever beam photoacoustic spectroscopy gas detection system based on microwave photon technology according to claim 9 is characterized in that: The delay difference of the microwave signal after passing through two paths is expressed as: ΔT0=2n(L S +(n+Δn)(L F-P +ΔL F-P )-L R / c) The corresponding phase difference is expressed as: The spectrum intensity A of microwave interference is expressed as: The microwave interference spectrum is obtained by a vector network analyzer, and an extreme frequency is selected as the RF signal to modulate the electro-optic modulator, and finally the relationship curve between the RF intensity and the measured value is obtained: I(Δn,ΔL F-P )∝DC+cos(2π·f RF (ΔT0(Δn,ΔL F-P )))。

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