Diaphragm type optical fiber liquid level sensing demodulation device and method based on microwave photon technology

Abstract

The invention provides a diaphragm type optical fiber liquid level sensing demodulation device and method based on a microwave photon technology, and the device comprises a broadband light source, a circulator, a diaphragm type optical fiber liquid level sensor, an erbium-doped optical fiber amplifier, a polarization controller, a DC power supply, a radio frequency source, an electro-optical modulator, a dispersion compensation optical fiber, a photoelectric detector and a power meter. The broadband light source is connected with a first port of the circulator, a second port of the circulator is connected with the diaphragm type optical fiber liquid level sensor, a third port of the circulator is connected with the erbium-doped optical fiber amplifier, the erbium-doped optical fiber amplifier is connected with the polarization controller, and the polarization controller is connected with the input end of the electrooptical modulator. The radio frequency source is connected with the modulation input of the electro-optical modulator, the direct current power supply is connected with the bias voltage input of the electro-optical modulator, the output of the electro-optical modulator is connected with the photoelectric detector through the dispersion compensation optical fiber, and the photoelectric detector is connected with the power meter, so that the measurement range is expanded while the sensing sensitivity and the resolution ratio are improved.

Description

Technical Field

[0001] The invention relates to the field of optoelectronic technology, and in particular to a diaphragm type optical fiber liquid level sensing demodulation device based on microwave photon technology and a diaphragm type optical fiber liquid level sensing demodulation method based on microwave photon technology. Background Art

[0002] In the related technology, the diaphragm-type optical fiber FP (Fabry-Perot) sensor not only has the advantages of small size, light weight, anti-electromagnetic interference, and suitability for long-distance transmission compared to electrical sensors, but the optical fiber diaphragm-type FP interferometer also does not require redundant optical components such as couplers in its own demodulation optical path, so the structure is more compact, easier to miniaturize and make into a sensor probe, and is widely used in the measurement of static parameters such as humidity, liquid level, temperature, pressure, or dynamic parameters such as sound waves.

[0003] Existing diaphragm-type optical fiber liquid level sensors mostly use lighter and thinner polymer diaphragms. Even if they can accurately perform liquid level tests under relatively ideal conditions, due to the characteristics of the material itself, they are easy to break and deform, so it is difficult to carry out multiple practical applications and only remain in the laboratory stage. In addition, in actual life and production, there are often many scenarios that require long-distance and other complex scene liquid level tests, such as flammable and explosive, large-sized containers such as aircraft oil tanks. However, when the existing optical fiber interferometer type liquid level sensor is working, its periodic interference spectrum in the light domain limits the measurement range of the sensor, which is not suitable for long-distance practical application measurements. Therefore, multi-point measurement and other methods are used for actual applications, which relatively increases the difficulty of measurement and application costs. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems in the above-mentioned technology to a certain extent. To this end, the first purpose of the present invention is to propose a diaphragm-type optical fiber liquid level sensor demodulation device based on microwave photon technology, which performs signal demodulation through microwave photon filtering technology, and corresponds the wavelength shift of interference light caused by the pressure change caused by the liquid level change in the optical domain to the passband center frequency shift of the microwave photon filter in the microwave domain, so as to improve the resolution and sensitivity, and break the periodicity of its interference spectrum, thereby significantly increasing the measurement range.

[0005] The second object of the present invention is to provide a diaphragm type optical fiber liquid level sensing demodulation method based on microwave photon technology.

[0006] To achieve the above-mentioned purpose, the first embodiment of the present invention proposes a diaphragm-type optical fiber liquid level sensor demodulation device based on microwave photon technology, comprising a broadband light source, a circulator, an optical fiber liquid level sensor, an erbium-doped optical fiber amplifier, a polarization controller, a DC power supply, a radio frequency source, an electro-optic modulator, a dispersion compensation optical fiber, a photodetector and a power meter, wherein the broadband light source is connected to the first port of the circulator, and the second port of the circulator is connected to the diaphragm-type optical fiber liquid level sensor, so that the light emitted by the broadband light source is output to the diaphragm-type optical fiber liquid level sensor through the second port of the circulator, so as to obtain corresponding interference light according to the change of the cavity length of the diaphragm-type optical fiber liquid level sensor; the third port of the circulator is connected to the erbium-doped optical fiber amplifier, and the interference light is output to the erbium-doped optical fiber amplifier through the third port of the circulator to perform optical power amplification; the erbium-doped optical fiber amplifier and the polarization controller The optical fiber is connected to the photodetector to control the polarization state of the interference light after optical power amplification by using the polarization controller; the polarization controller is connected to the input of the electro-optic modulator, the radio frequency source is connected to the modulation input of the electro-optic modulator, and the DC power supply is connected to the bias input of the electro-optic modulator to input the interference light after polarization state control into the electro-optic modulator, and modulate the interference light according to the bias applied by the DC power supply and the electrical signal with the passband center frequency of the microwave photon filter generated by the radio frequency source to obtain a modulated optical signal; the output of the electro-optic modulator is connected to the photodetector through the dispersion compensating optical fiber, and the modulated optical signal is transmitted to the photodetector through the dispersion compensating optical fiber to convert the modulated optical signal into an electrical signal; the photodetector is connected to the power meter to measure the power of the electrical signal by using the power meter, and the corresponding liquid level change is obtained according to the power change of the electrical signal.

[0007] According to the diaphragm-type optical fiber liquid level sensor demodulation device based on microwave photon technology provided by an embodiment of the present invention, since there is a linear relationship between the frequency shift of the passband center and the change of the cavity length in the FP cavity, when the cavity length of the liquid in the FP cavity changes, the microwave photon filter is used to convert the wavelength shift of the interference spectrum into the offset of the passband center frequency in the frequency domain, thereby improving the sensing sensitivity and resolution while also significantly expanding its measurement range.

[0008] In addition, the diaphragm type optical fiber liquid level sensing demodulation device based on microwave photon technology proposed in the above embodiment of the present invention may also have the following additional technical features:

[0009] Optionally, the diaphragm type optical fiber liquid level sensor includes an optical fiber ceramic ferrule, a first sleeve, a second sleeve and a silver-plated PET film, wherein the silver-plated PET film is bonded to the end face of the first sleeve, the second sleeve is inserted into the first sleeve, and the optical fiber ceramic ferrule is inserted into the second sleeve, and nested assembly is performed using epoxy resin AB glue.

[0010] Optionally, the end face of the optical fiber ceramic ferrule serves as the first reflection surface, the silver-plated surface of the silver-plated PET (polyethylene terephthalate) film serves as the second reflection surface, and an air cavity is formed between the first reflection surface and the second reflection surface.

[0011] Optionally, the cavity length change of the optical fiber liquid level sensor is obtained according to the following formula:

[0012]

[0013]

[0014] h=h0-Δd0

[0015]

[0016] Wherein, R1 represents the reflection coefficient of the first reflection surface; R2 represents the reflection coefficient of the second reflection surface; φ represents the phase difference caused by the optical path difference after the light is reflected once in the FP cavity; R FP represents the reflection spectrum of double-beam interference; h represents the cavity length of the FP cavity; λ0 represents the wavelength of the incident light; h0 represents the initial cavity length of the FP cavity; Δd0 represents the deformation amount generated at the center of the constant elastic film; p represents the lateral pressure difference on the constant elastic film; R0 represents the effective radius of the constant elastic film; d represents the thickness of the diaphragm; γ represents the Poisson's ratio of the material; E represents the Young's modulus of the material; FSR represents the free spectral range of the interference spectrum; λ1 and λ2 represent the wavelengths of the peak and trough of two adjacent interference peaks of the spectrum, respectively; L cav represents the cavity length of the standard FP interferometer; n0 represents the refractive index of the medium.

[0017] Optionally, the passband center frequency of the microwave photon filter is obtained; the radio frequency source is made to modulate the electrical signal of the passband center frequency to the electro-optical modulator; the demodulation loop is output to the power meter, and the offset direction of the passband center frequency of the single-passband microwave photon filter is determined by the change of the passband center frequency power value on the power meter; if the power value at the passband center frequency decreases, it is determined that the passband moves to the high frequency, otherwise it shifts to the low frequency, the change of the center frequency corresponds to the change of the liquid level, and the increase or decrease of the power count value is used to obtain the change result of the measured liquid level.

[0018] To achieve the above-mentioned purpose, the second embodiment of the present invention proposes a diaphragm-type optical fiber liquid level sensor demodulation method based on microwave photon technology, and the demodulation method is applied to the above-mentioned demodulation device; the demodulation method: outputs the light emitted by the broadband light source to the diaphragm-type optical fiber liquid level sensor through the second port of the circulator, so as to obtain the corresponding interference light according to the change of the cavity length of the diaphragm-type optical fiber liquid level sensor; the third port of the circulator outputs the interference light to the erbium-doped fiber amplifier to perform optical power amplification; a polarization controller is used to control the polarization state of the interference light after the optical power amplification; the interference light after polarization state control is input to the electro-optical modulator, and modulated according to the bias voltage applied by the DC power supply and the electrical signal with the passband center frequency of the microwave photon filter generated by the radio frequency source to obtain a modulated optical signal; the modulated optical signal is transmitted to the photodetector through the dispersion compensation optical fiber to convert the optical signal into an electrical signal; a power meter is used to measure the power of the electrical signal, and the corresponding liquid level change is obtained according to the power change of the modulated electrical signal.

[0019] In addition, the diaphragm type optical fiber liquid level sensing demodulation method based on microwave photon technology proposed in the above embodiment of the present invention may also have the following additional technical features:

[0020] Optionally, the diaphragm type optical fiber liquid level sensor includes an optical fiber ceramic ferrule, a first sleeve, a second sleeve and a silver-plated PET film, wherein the silver-plated PET film is bonded to the end face of the first sleeve, the second sleeve is inserted into the first sleeve, and the optical fiber ceramic ferrule is inserted into the second sleeve, and nested assembly is performed using epoxy resin AB glue.

[0021] Optionally, the end face of the optical fiber ceramic ferrule serves as a first reflection surface, the silver-plated surface of the silver-plated PET film serves as a second reflection surface, and an air cavity is formed between the first reflection surface and the second reflection surface.

[0022] Optionally, the cavity length change of the optical fiber liquid level sensor is obtained according to the following formula:

[0023]

[0024]

[0025]

[0026] Wherein, R1 represents the reflection coefficient of the first reflection surface; R2 represents the reflection coefficient of the second reflection surface; φ represents the phase difference caused by the optical path difference after the light is reflected once in the FP cavity; R FPrepresents the reflection spectrum of double-beam interference; h represents the cavity length of the FP cavity; λ0 represents the wavelength of the incident light; h0 represents the initial cavity length of the FP cavity; Δd0 represents the deformation amount generated at the center of the constant elastic film; p represents the lateral pressure difference on the constant elastic film; R0 represents the effective radius of the constant elastic film; d represents the thickness of the film; γ represents the Poisson's ratio of the material; E represents the Young's modulus of the material; FSR represents the free spectral range of the interference spectrum; λ1 and λ2 represent the wavelengths of the peak and trough of two adjacent interference peaks of the spectrum, respectively; L cav represents the cavity length of the standard FP interferometer; n0 represents the refractive index of the medium.

[0027] Optionally, the passband center frequency of the microwave photon filter is obtained; the radio frequency source is made to modulate the electrical signal of the passband center frequency to the electro-optical modulator; the demodulation loop is output to the power meter, and the offset direction of the passband center frequency of the single-passband microwave photon filter is determined by the change of the passband center frequency power value on the power meter; if the power value at the passband center frequency decreases, it is determined that the passband moves to the high frequency, otherwise it shifts to the low frequency, and the change of the center frequency corresponds to the change of the liquid level, so that the change result of the measured liquid level is obtained by increasing or decreasing the power count value. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a structural schematic diagram of a diaphragm-type optical fiber liquid level sensing demodulation device based on microwave photon technology according to an embodiment of the present invention;

[0029] Figure 2 Schematic diagram of the structure of a diaphragm type optical fiber liquid level sensor according to an embodiment of the present invention.

[0030] Figure 3 The figure is a flow chart of a membrane type optical fiber liquid level sensing demodulation method based on microwave photon technology according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0032] In order to better understand the above technical solution, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0033] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0034] Figure 1 FIG. 1 is a schematic diagram of a membrane type optical fiber liquid level sensing demodulation device based on microwave photon technology according to an embodiment of the present invention. Figure 1 As shown, the diaphragm-type optical fiber liquid level sensing demodulation device based on microwave photon technology includes a broadband light source 1, a circulator 11, a diaphragm-type optical fiber liquid level sensor 2, an erbium-doped optical fiber amplifier 3, a polarization controller 4, a DC power supply 5, a radio frequency source 6, an electro-optic modulator 7, a dispersion-compensating optical fiber 8, a photodetector 9 and a power meter 10.

[0035] Among them, the broadband light source 1 is connected to the first port of the circulator 11, and the second port of the circulator 11 is connected to the diaphragm-type optical fiber liquid level sensor 2, so that the light emitted by the broadband light source 1 is output to the optical fiber liquid level sensor 2 through the second port of the circulator 11, and the light reflected from the first end face of the optical fiber liquid level sensor interferes with the light transmitted from the first end face to the second end face and then reflected to the first end face, and the corresponding interference light is obtained according to the change of the cavity length of the optical fiber liquid level sensor 2; the third port of the circulator 11 is connected to the erbium-doped fiber amplifier 3, and the interference light is output to the erbium-doped fiber amplifier 3 through the third port of the circulator 11 to perform optical power amplification; the erbium-doped fiber amplifier 3 is connected to the polarization controller 4, so that the polarization state of the interference light after optical power amplification is controlled by the polarization controller 4; The polarization controller 4 is connected to the input of the electro-optic modulator 7, the radio frequency source 6 is connected to the modulation input of the electro-optic modulator 7, and the DC power supply 5 is connected to the bias input of the electro-optic modulator 7, so as to input the interference light after polarization state control to the electro-optic modulator 7, and modulate the electric signal with the passband center frequency of the microwave photon filter generated by the bias applied by the DC power supply 5 and the radio frequency source 6 to obtain a modulated light signal; the output of the electro-optic modulator 7 is connected to the photodetector 9 through the dispersion compensation optical fiber 8, and the modulated light signal is transmitted to the photodetector 9 through the dispersion compensation optical fiber 8 to convert the modulated light signal into an electrical signal; the photodetector 9 is connected to the power meter 10, so as to use the power meter 10 to measure the power of the electrical signal, and obtain the corresponding liquid level change according to the power change of the electrical signal.

[0036] That is to say, the broadband light source 1, the circulator 11, the diaphragm-type optical fiber liquid level sensor 2, the erbium-doped optical fiber amplifier 3, the polarization controller 4, the DC power supply 5, the radio frequency source 6, the electro-optic modulator 7, the dispersion compensation optical fiber 8, the photodetector 9 and the power meter 10 are connected in sequence to form a liquid level detection loop, the broadband light source 1 is connected to the first port of the circulator 11, the second port of the circulator 11 is connected to the diaphragm-type optical fiber liquid level sensor 2, the third port of the circulator 11 is connected to the erbium-doped optical fiber amplifier 3, and then the polarization controller 4 is connected to the output end of the erbium-doped optical fiber amplifier 3, and the polarization state of its light beam is adjusted by the polarization controller 4. The polarization controller 4 is connected to the electro-optic modulator 7 connected to the radio frequency source 6. At this time, the electro-optic modulator 7 has a DC power supply 5 to apply a bias to it, and is connected to the radio frequency source 6 to modulate it. Finally, the output of the electro-optic modulator 7 is connected to the photodetector 9, and the photodetector 9 is connected to the power meter 10 to realize detection.

[0037] It should be noted that general microwave photon sensing systems are usually observed on network analyzers, but the introduction of network analyzers will result in high actual application costs, and network analyzers are too large to be used for liquid level measurement in complex environments. Therefore, this device uses a radio frequency source and a power meter to replace the role of the network analyzer in the microwave photon sensing system. This can minimize the measurement cost, and replacing the role of the network analyzer in the sensing loop can better meet the liquid level detection in various environments, and has a wide range of application scenarios. In addition, when the center frequency of a single passband is determined, an RF source is used to modulate an electrical signal with the passband center frequency onto an electro-optical modulator. Subsequently, the corresponding liquid level change detection can be performed by observing the change in electrical power on the power meter.

[0038] As an embodiment, the diaphragm type optical fiber liquid level sensor includes an optical fiber ceramic ferrule 12, a first sleeve 13, a second sleeve 14 and a silver-plated PET (polyethylene terephthalate) film 15, wherein the silver-plated PET film 15 is bonded to the end surface of the first sleeve 13, the second sleeve 14 is inserted into the first sleeve 13, and the optical fiber ceramic ferrule 12 is inserted into the second sleeve 14 for nested assembly.

[0039] That is to say, Figure 2As shown, the liquid level sensor is an optical fiber diaphragm type Fabry-Perot cavity liquid level sensor made of a new material, wherein the first sleeve 13 and the second sleeve 14 are made of acrylic material, so that the optical fiber ceramic ferrule 12 can be nested and assembled therewith, and the first sleeve 13 and the second sleeve 14 have different sizes, the inner diameter of the first sleeve 13 is slightly larger than the outer diameter of the second sleeve 14, and the inner diameter of the second sleeve 14 is slightly larger than the size of the optical fiber ceramic ferrule 12. The first sleeve 13 first uses AB epoxy resin glue to bond the diaphragm to the sleeve end face, the second sleeve 14 is inserted into the first sleeve 13 with the diaphragm, and the optical fiber ceramic ferrule 12 is inserted into the second sleeve 14. The cavity length of the Fabry-Perot cavity is adjusted on the optical precision adjustment frame by observing the spectrometer. After the cavity length is determined, the three are finally bonded again using AB epoxy resin.

[0040] It should be noted that the diaphragm type fiber optic liquid level sensor is assembled from a sleeve made of acrylic material, a diaphragm made of PET material, and a fiber optic ceramic ferrule. It is simple to prepare, low in cost, and highly repeatable, so its application scenarios are very wide.

[0041] As an embodiment, the end face of the optical fiber ceramic ferrule is used as the first reflection surface, the silver-plated surface of the silver-plated PET film is used as the second reflection surface, and an air cavity is formed between the first reflection surface and the second reflection surface.

[0042] That is to say, from the perspective of the diaphragm-type optical fiber Fabry-Perot liquid level sensor, the end face of the optical fiber ceramic ferrule 12 can be used as the first reflection surface, and the second reflection surface is made of silver-plated PET (polyethylene terephthalate) film material, and there is an air cavity between the two end faces.

[0043] It should be noted that the PET film material is coated with a reflective film on its surface, the purpose of which is to enhance the reflection of the PET film to the light beam and improve the contrast of its interference spectrum, so as to achieve good observation of the interference spectrum when the liquid level changes; in terms of the material properties itself, PET material is a transparent polymer material with excellent heat resistance, corrosion resistance, tensile strength and rigidity; acrylic material is an important plastic polymer material developed earlier, with good transparency, chemical stability and weather resistance. Acrylic is usually manufactured using injection molding, extrusion or injection molding processes, which can make acrylic produced in different shapes and sizes while maintaining its superior physical properties, so acrylic has good processing performance; from the perspective of preparation, acrylic and PET materials are both relatively common materials, so the cost of preparing diaphragm-type optical fiber liquid level sensors is greatly reduced, and they have good repeatability and can be widely used in a variety of optical fiber diaphragm sensing measurement fields, and have a very broad application prospect.

[0044] As a specific embodiment, the light emitted by the broadband light source 1 is output from the second port through the three-port circulator 11 to the diaphragm-type optical fiber liquid level sensor 2. The pressure change caused by the liquid level change causes the cavity length of the Fabry-Perot cavity to change, and the interference light carrying the cavity length change information is reflected to the second port, and is output from the third port of the three-port circulator 11 to the subsequent detection loop; the interference light output from the third port of the three-port circulator 11 first passes through the erbium-doped fiber amplifier 3 to amplify the optical power, then enters the polarization controller 4 to control the polarization state of the transmission light beam, and then is connected to the electro-optic modulator 7 to which the bias is applied by the DC power supply 5. The electro-optic modulator is simultaneously connected to the radio frequency source 6, and the radio frequency source emits an electrical signal with a passband center frequency. The optical signal output by the electro-optic modulator 7 is then connected to the dispersion compensation optical fiber 8, and then the dispersion compensation optical fiber 8 is connected to the photodetector 9, and the photodetector 9 converts the modulated optical signal into an electrical signal. The output end of the photodetector 9 is finally connected to the power meter 10, and the liquid level is monitored by observing the power value change on the power meter 10.

[0045] Among them, the PET-EFPI (PET diaphragm optical fiber liquid level sensor) based on Fabry-Perot interference, because the incident light beam has a low reflectivity when entering the reflection surface of the FP interferometer, the incident light beam can only have a small amount of reflection in the resonant cavity, and double-beam interference occurs at this time. The reflection spectrum expression of double-beam interference is:

[0046]

[0047] Where: R1, R2 are the reflection coefficients of the two reflection end faces, φ is the phase difference caused by the optical path difference after the light is reflected once in the FP cavity, which is expressed as

[0048]

[0049] Where: h is the cavity length of the FP cavity; λ0 is the wavelength of the incident light.

[0050] Assuming the initial cavity length of the FP cavity is h0, then:

[0051] h=h0-Δd0

[0052] When the pressure generated by the liquid in the liquid cavity acts on the constant elastic film, the magnitude of the elastic deformation is related to the pressure difference it is subjected to, that is, the height of the liquid level. According to the principle of elastic mechanics, assuming that the constant elastic film is subjected to pressure p, the deformation generated at the center of the film is

[0053]

[0054] Where: p is the lateral pressure difference on the constant elastic film; R0 is the effective radius of the constant elastic film; d is the thickness of the film; γ is the Poisson's ratio of the material; E is the Young's modulus of the material.

[0055] For the selected material, γ and E are known quantities. From the above formula, we can see that by choosing different d and R0, we can determine the sensitivity and measurement range of the sensor. When these two parameters are determined, Δd0 is proportional to the pressure p.

[0056] When broadband light source 1 is selected as the light source, interference peaks of different frequencies will appear. At this time, the free spectral range (FSR) of the interference spectrum is expressed as:

[0057]

[0058] Among them, λ1 and λ2 are the wavelengths of the peak and trough of two adjacent interference peaks in the spectrum. The FSR value is read from the spectrum, from which the cavity length of the standard FP interferometer can be calculated:

[0059]

[0060] In other studies on liquid level sensing using FP interferometer structures, the relationship between the wavelength corresponding to the peak / trough of the interference spectrum and the change in liquid level is usually monitored, that is, wavelength demodulation. However, when the sensitivity of the liquid level sensor 2 is high and the liquid level change response range is wide, the multi-cycle wavelength offset within the wide liquid level change range cannot be identified in the interference spectrum. Therefore, this application combines microwave photon filtering technology, uses a diaphragm-type optical fiber liquid level sensor as a spectrum segmentation device for the filter, and uses dispersion-compensating optical fiber as a dispersion medium to achieve a single-passband frequency response, converting the wavelength change in the optical domain into a change in the center frequency of the passband in the electrical domain; avoiding the periodic limitation of the spectral interference signal and expanding the measurement range; by monitoring the change in the passband center frequency of the single-passband microwave photon filter, the change in the liquid level can be observed more intuitively; the expression of the passband center frequency is as follows:

[0061]

[0062] Among them, D and L refer to the dispersion value of the dispersion device and the length of the dispersion medium, and Δω is the change in the free spectral range (FSR) of the interference spectrum. It can be seen from the formula that the position of the passband center frequency is determined by the dispersion coefficient (D) of the dispersion-compensating fiber, the length (L) of the dispersion-compensating fiber, and the FSR (Δω) of the interference spectrum. By setting the values ​​of these three parameters, different filter responses at the passband center frequency positions can be obtained, that is, the passband can be tunable:

[0063]

[0064] When the liquid level changes, the cavity length of the sensor changes. Since the air cavity is kept closed, the refractive index n is constant, that is, the change of the passband center frequency under the same external conditions only depends on the change of the cavity length L, that is:

[0065]

[0066] When the diaphragm-type optical fiber liquid level sensor is applied to the position of the spectrum splitter, changes in external parameters will cause changes in the interference fringes, thereby causing changes in the position of the microwave photon filter passband. By tracking the passband center frequency, the sensing quantity to be measured can be obtained. The offset tracking of the passband center requires determining the passband center frequency of the single-passband microwave photon filter. After determining the passband center frequency, the RF source then modulates the electrical signal of this frequency to the electro-optical modulator. The final demodulation loop output is output to the power meter. By observing the change in the passband center frequency power value on the power meter, the offset direction of the single-passband microwave photon filter passband center frequency is determined. If the power value at the center frequency decreases, it is determined that the passband moves to the high frequency, otherwise it shifts to the low frequency, and finally the sensing of the liquid level change is realized.

[0067] In summary, the present application aims at actual liquid level measurement, and uses low-cost silver-plated PET film and acrylic sleeve for bonding, and finally assembles the ceramic ferrule and its film-sleeve structure to form the liquid level sensor of the present application; wherein the end face of the flat-head ceramic ferrule and the end face of the stainless steel film form an FP cavity, and when the liquid level changes, the pressure at the same level as the diaphragm-type optical fiber liquid level sensor changes, and the pressure acts on the diaphragm, causing the diaphragm to undergo a certain deformation, thereby changing the optical path difference of the interference light beam, and the purpose of detection is achieved by observing the offset of the interference spectrum of the spectrometer in the sensing loop, or by the displacement of the center frequency of the single-passband filter in the microwave photon loop, and at the same time, the microwave photon filtering technology is used for signal demodulation to correspond the wavelength offset of the light domain to the passband frequency offset of the microwave domain, which can improve the resolution and sensitivity; and the periodic interference spectrum of the light domain limits the measurement range of the sensor, and the use of the single-passband microwave photon filtering technology can break the periodicity of its interference spectrum, significantly increase the measurement range, and is suitable for long-distance liquid level detection.

[0068] In order to implement the above embodiment, Figure 3 As shown, the embodiment of the present invention also proposes a membrane type optical fiber liquid level sensor demodulation method based on microwave photon technology, and the demodulation method is applied to the above demodulation device; the demodulation method comprises the following steps:

[0069] S101, outputting the light emitted by the broadband light source to the diaphragm type optical fiber liquid level sensor through the second port of the circulator, so as to obtain corresponding interference light according to the change of the cavity length of the diaphragm type optical fiber liquid level sensor.

[0070] S102, the third port of the circulator outputs interference light to an erbium-doped fiber amplifier for optical power amplification.

[0071] S103, using a polarization controller to control the polarization state of the interference light after the optical power amplification.

[0072] S104, inputting the interference light after polarization state control into the electro-optic modulator, and modulating it according to the bias voltage applied by the DC power supply and the electrical signal with the passband center frequency of the microwave photon filter generated by the radio frequency source, so as to obtain a modulated optical signal.

[0073] S105, the modulated optical signal is transmitted to the photodetector through the dispersion compensation optical fiber to convert the modulated optical signal into an electrical signal.

[0074] S106, using a power meter to measure the power of the electrical signal, and obtaining a corresponding liquid level change according to the power change of the electrical signal.

[0075] As an embodiment, the diaphragm type optical fiber liquid level sensor includes an optical fiber ceramic ferrule, a first sleeve, a second sleeve and a silver-plated PET film, wherein the silver-plated PET film is bonded to the end face of the first sleeve, the second sleeve is inserted into the first sleeve, and the optical fiber ceramic ferrule is inserted into the second sleeve, and the nested assembly is performed by epoxy resin AB glue.

[0076] As an embodiment, the end face of the optical fiber ceramic ferrule serves as the first reflection surface, the silver-plated surface of the silver-plated PET film serves as the second reflection surface, and an air cavity is formed between the first reflection surface and the second reflection surface.

[0077] As an embodiment, the cavity length change of the optical fiber liquid level sensor is obtained according to the following formula:

[0078]

[0079]

[0080] h=h0-Δd0

[0081]

[0082] Wherein, R1 represents the reflection coefficient of the first reflection surface; R2 represents the reflection coefficient of the second reflection surface; φ represents the phase difference caused by the optical path difference after the light is reflected once in the FP cavity; R FPrepresents the reflection spectrum of double-beam interference; h represents the cavity length of the FP cavity; λ0 represents the wavelength of the incident light; h0 represents the initial cavity length of the FP cavity; Δd0 represents the deformation amount generated at the center of the constant elastic film; p represents the lateral pressure difference on the constant elastic film; R0 represents the effective radius of the constant elastic film; d represents the thickness of the film; γ represents the Poisson's ratio of the material; E represents the Young's modulus of the material; FSR represents the free spectral range of the interference spectrum; λ1 and λ2 represent the wavelengths of the peak and trough of two adjacent interference peaks of the spectrum, respectively; L cav represents the cavity length of the standard FP interferometer; n0 represents the refractive index of the medium.

[0083] As an embodiment, the passband center frequency of the microwave photon filter is obtained; the radio frequency source is made to modulate the electrical signal of the passband center frequency to the electro-optical modulator; the demodulation loop output is output to the power meter, and the offset direction of the passband center frequency of the single-passband microwave photon filter is determined by the change of the passband center frequency power value on the power meter; if the power value at the passband center frequency decreases, it is determined that the passband moves to the high frequency, otherwise it shifts to the low frequency, the change of the center frequency corresponds to the change of the liquid level, and the increase or decrease of the power count value is used to obtain the change result of the measured liquid level.

[0084] It should be noted that the device adopted by the diaphragm type optical fiber liquid level sensor demodulation method based on microwave photonic technology in this embodiment is the aforementioned diaphragm type optical fiber liquid level sensor demodulation device based on microwave photonic technology, so the aforementioned explanation of the embodiment of the diaphragm type optical fiber liquid level sensor demodulation device based on microwave photonic technology is also applicable to the diaphragm type optical fiber liquid level sensor demodulation method based on microwave photonic technology in this embodiment, and will not be repeated here.

[0085] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0086] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0087] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0088] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0089] It should be noted that in the claims, any reference signs placed between brackets shall not be construed as limiting the claims. The word "comprising" does not exclude the presence of components or steps not listed in the claim. The word "a" or "an" preceding a component does not exclude the presence of a plurality of such components. The invention may be implemented by means of hardware comprising several different components and by means of a suitably programmed computer. In a unit claim enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third etc. does not indicate any order. These words may be interpreted as names.

[0090] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0091] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

[0092] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0093] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0094] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0095] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily referring to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0096] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A diaphragm-type optical fiber liquid level sensing demodulation device based on microwave photon technology, characterized in that: It includes a broadband light source, a circulator, a diaphragm-type optical fiber liquid level sensor, an erbium-doped optical fiber amplifier, a polarization controller, a DC power supply, a radio frequency source, an electro-optic modulator, a dispersion-compensating optical fiber, a photodetector and a power meter, among which: The broadband light source is connected to the first port of the circulator, and the second port of the circulator is connected to the optical fiber liquid level sensor, so that the light emitted by the broadband light source is output to the diaphragm type optical fiber liquid level sensor through the second port of the circulator, so as to obtain corresponding interference light according to the change of the cavity length of the diaphragm type optical fiber liquid level sensor; The third port of the circulator is connected to the erbium-doped fiber amplifier, and the interference light is output to the erbium-doped fiber amplifier through the third port of the circulator to perform optical power amplification; The erbium-doped fiber amplifier is connected to the polarization controller so as to use the polarization controller to control the polarization state of the interference light after the optical power amplification; The polarization controller is connected to the input of the electro-optic modulator, the radio frequency source is connected to the modulation input of the electro-optic modulator, and the DC power supply is connected to the bias input of the electro-optic modulator, so as to input the interference light after polarization state control to the electro-optic modulator, and modulate the electric signal with the passband center frequency of the microwave photon filter generated by the radio frequency source according to the bias voltage applied by the DC power supply and the radio frequency source, so as to obtain a modulated optical signal; The output of the electro-optic modulator is connected to the photodetector through the dispersion-compensating optical fiber, and the modulated optical signal is transmitted to the photodetector through the dispersion-compensating optical fiber to convert the modulated optical signal into an electrical signal; The photoelectric detector is connected to the power meter so as to measure the power of the electrical signal with the power meter and obtain the corresponding liquid level change according to the power change of the electrical signal.

2. The diaphragm type optical fiber liquid level sensing demodulation device based on microwave photon technology as claimed in claim 1, characterized in that: The optical fiber liquid level sensor includes an optical fiber ceramic ferrule, a first sleeve, a second sleeve and a silver-plated PET film, wherein the silver-plated PET film is bonded to the end face of the first sleeve, the second sleeve is inserted into the first sleeve, and the optical fiber ceramic ferrule is inserted into the second sleeve, and nested assembly is performed using epoxy resin AB glue.

3. The diaphragm type optical fiber liquid level sensing demodulation device based on microwave photon technology as claimed in claim 2, characterized in that: The end face of the optical fiber ceramic ferrule serves as a first reflection surface, the silver-plated surface of the silver-plated PET film serves as a second reflection surface, and an air cavity is formed between the first reflection surface and the second reflection surface.

4. The diaphragm type optical fiber liquid level sensing demodulation device based on microwave photon technology as claimed in claim 3 is characterized in that: The change in cavity length of the diaphragm-type optical fiber liquid level sensor is obtained according to the following formula: h=h0-Δd0 Wherein, R1 represents the reflection coefficient of the first reflection surface; R2 represents the reflection coefficient of the second reflection surface; φ represents the phase difference caused by the optical path difference after the light is reflected once in the FP cavity; R FP represents the reflection spectrum of double-beam interference; h represents the cavity length of the FP cavity; λ0 represents the wavelength of the incident light; h0 represents the initial cavity length of the FP cavity; Δd0 represents the deformation amount generated at the center of the constant elastic film; p represents the lateral pressure difference on the constant elastic film; R0 represents the effective radius of the constant elastic film; d represents the thickness of the film; γ represents the Poisson's ratio of the material; E represents the Young's modulus of the material; FSR represents the free spectral range of the interference spectrum; λ1 and λ2 represent the wavelengths of the peak and trough of two adjacent interference peaks of the spectrum, respectively; L cav represents the cavity length of the standard FP interferometer; n0 represents the refractive index of the medium.

5. The diaphragm type optical fiber liquid level sensing demodulation device based on microwave photon technology as claimed in claim 4, characterized in that: By acquiring the passband center frequency of the microwave photon filter; making the radio frequency source modulate the electrical signal with the passband center frequency to the electro-optical modulator; the demodulation loop outputs to the power meter, and the offset direction of the passband center frequency of the single-passband microwave photon filter is judged by the change of the passband center frequency power value on the power meter; if the power value at the passband center frequency decreases, it is judged that the passband moves to the high frequency, otherwise it shifts to the low frequency, and the change of the center frequency corresponds to the change of the liquid level, so that the change result of the measured liquid level is obtained by increasing or decreasing the power count value.

6. A diaphragm type optical fiber liquid level sensing demodulation method based on microwave photon technology, characterized in that: The demodulation method is applied to the demodulation device according to any one of claims 1 to 5; the demodulation method comprises: Outputting the light emitted by the broadband light source to the diaphragm-type optical fiber liquid level sensor through the second port of the circulator, so as to obtain corresponding interference light according to the change of the cavity length of the diaphragm-type optical fiber liquid level sensor; The third port of the circulator outputs the interference light to an erbium-doped fiber amplifier for optical power amplification; A polarization controller is used to control the polarization state of the interference light after the optical power amplification; The interference light after polarization state control is input into the electro-optic modulator, and modulated according to the bias voltage applied by the DC power supply and the electrical signal with the passband center frequency of the microwave photon filter generated by the radio frequency source, so as to obtain a modulated optical signal; The modulated optical signal is transmitted to a photodetector via a dispersion-compensating optical fiber to convert the modulated optical signal into an electrical signal; A power meter is used to measure the power of the electrical signal, and a corresponding liquid level change is obtained according to the power change of the electrical signal.

7. The diaphragm type optical fiber liquid level sensing demodulation method based on microwave photon technology as claimed in claim 6 is characterized in that: The diaphragm-type optical fiber liquid level sensor comprises an optical fiber ceramic ferrule, a first sleeve, a second sleeve and a silver-plated PET film, wherein the silver-plated PET film is bonded to the end face of the first sleeve, the second sleeve is inserted into the first sleeve, and the optical fiber ceramic ferrule is inserted into the second sleeve, and nested assembly is performed using epoxy resin AB glue.

8. The diaphragm type optical fiber liquid level sensing demodulation method based on microwave photon technology as claimed in claim 7, characterized in that: The end face of the optical fiber ceramic ferrule serves as a first reflection surface, the silver-plated surface of the silver-plated PET film serves as a second reflection surface, and an air cavity is formed between the first reflection surface and the second reflection surface.

9. The diaphragm type optical fiber liquid level sensing demodulation method based on microwave photon technology as claimed in claim 8, characterized in that: The change in cavity length of the diaphragm-type optical fiber liquid level sensor is obtained according to the following formula: h=h0-Δd0 Wherein, R1 represents the reflection coefficient of the first reflection surface; R2 represents the reflection coefficient of the second reflection surface; φ represents the phase difference caused by the optical path difference after the light is reflected once in the FP cavity; R FP represents the reflection spectrum of double-beam interference; h represents the cavity length of the FP cavity; λ0 represents the wavelength of the incident light; h0 represents the initial cavity length of the FP cavity; Δd0 represents the deformation amount generated at the center of the constant elastic film; p represents the lateral pressure difference on the constant elastic film; R0 represents the effective radius of the constant elastic film; d represents the thickness of the film; γ represents the Poisson's ratio of the material; E represents the Young's modulus of the material; FSR represents the free spectral range of the interference spectrum; λ1 and λ2 represent the wavelengths of the peak and trough of two adjacent interference peaks of the spectrum, respectively; L cav represents the cavity length of the standard FP interferometer; n0 represents the refractive index of the medium.

10. The diaphragm type optical fiber liquid level sensing demodulation method based on microwave photon technology as claimed in claim 9, characterized in that: By acquiring the passband center frequency of the microwave photon filter; making the radio frequency source modulate the electrical signal with the passband center frequency to the electro-optical modulator; the demodulation loop outputs to the power meter, and the offset direction of the passband center frequency of the single-passband microwave photon filter is judged by the change of the passband center frequency power value on the power meter; if the power value at the passband center frequency decreases, it is judged that the passband moves to the high frequency, otherwise it shifts to the low frequency, and the change of the center frequency corresponds to the change of the liquid level, so that the change result of the measured liquid level is obtained by increasing or decreasing the power count value.

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