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

Abstract

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

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optoelectronic technology, 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

[0002] In the related art, the diaphragm type optical fiber F-P (Fabry-Perot) sensor not only has the advantages of small volume, light weight, anti-electromagnetic interference, and suitability for long-distance transmission compared with electrical sensors, but also has a more compact structure and is easier to realize miniaturization and manufacturing into a sensing probe because the diaphragm type F-P interferometer does not need couplers and other redundant optical components in the demodulation optical path, and is widely used in the measurement of static parameters such as humidity, liquid level, temperature, pressure, and dynamic parameters such as acoustic waves.

[0003] Existing diaphragm type optical fiber liquid level sensors mostly use light and thin polymer diaphragms, which can accurately test the liquid level in an ideal environment, but due to the characteristics of the material itself, they are prone to breakage and deformation, making it difficult to be used multiple times in practical applications and only remaining in the laboratory stage. In addition, in actual life and production, there are often many scenarios that require long-distance and complex scene liquid level testing, such as flammable and explosive, large-sized containers such as aircraft fuel tanks. However, the periodic interference spectrum of the optical domain limits the measurement range of the sensor when the existing optical fiber interferometer type liquid level sensor is working, and is not suitable for long-distance practical application measurement. Therefore, multi-point measurement and other methods are used for practical application, which relatively increases the difficulty and cost of measurement. SUMMARY

[0004] The present application aims to at least solve one of the above technical problems in the art. To this end, the first object of the present application is to provide a diaphragm type optical fiber liquid level sensing demodulation device based on microwave photon technology, which demodulates signals through microwave photon filtering technology, maps the interference wavelength shift caused by the pressure change due to the liquid level change in the optical domain to the microwave photon filter passband center frequency shift in the microwave domain, to improve the resolution and sensitivity, and break the periodicity of the interference spectrum, thereby significantly increasing the measurement range.

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

[0006] To achieve the above object, the first aspect of the present application provides a diaphragm type optical fiber liquid level sensing demodulation device based on microwave photon technology, comprising a broadband light source, a circulator, an optical fiber liquid level sensor, an erbium-doped fiber amplifier, a polarization controller, a direct current power supply, a radio frequency source, an electro-optical modulator, a dispersion compensation fiber, a photoelectric detector and a power meter, wherein 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, 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, and the corresponding interference light is obtained according to the cavity length change of the diaphragm type optical fiber liquid level sensor; a third port of the circulator is connected with the erbium-doped fiber amplifier, the interference light is output to the erbium-doped fiber amplifier through the third port of the circulator, so as to perform optical power amplification; the erbium-doped fiber amplifier is connected with the polarization controller, so that the polarization state of the interference light after optical power amplification is controlled by using the polarization controller; the polarization controller is connected with the input of the electro-optical modulator, the radio frequency source is connected with the modulation input of the electro-optical modulator, and the direct current power supply is connected with the bias input of the electro-optical modulator, so that the interference light after polarization state control is input to the electro-optical modulator, and the modulation light signal is obtained according to the bias voltage applied by the direct current power supply and the electrical signal with the passband center frequency of the microwave photon filter generated by the radio frequency source; the output of the electro-optical modulator is connected with the photoelectric detector through the dispersion compensation fiber, the modulation light signal is transmitted to the photoelectric detector through the dispersion compensation fiber, so as to convert the modulation light signal into an electrical signal; and the photoelectric detector is connected with the power meter, so that the power of the electrical signal is measured by using the power meter, and the corresponding liquid level change is obtained according to the power change of the electrical signal.

[0007] The diaphragm type optical fiber liquid level sensing demodulation device based on microwave photon technology provided by the embodiment of the present application has a linear relationship between the frequency shift of the passband center and the change of the cavity length in the F-P cavity, so that when the cavity length of the liquid in the F-P cavity changes, the wavelength shift of the interference spectrum is converted into the shift of the passband center frequency in the frequency domain by using the microwave photon filter, so that the sensing sensitivity and resolution are improved, and the measurement range is obviously expanded.

[0008] In addition, the diaphragm type optical fiber liquid level sensing demodulation device based on microwave photon technology provided by the above-mentioned embodiment of the present application can have the following additional technical features:

[0009] Optionally, the diaphragm type optical fiber liquid level sensor comprises a fiber ceramic ferrule, a first sleeve, a second sleeve and a silver-coated PET film, wherein the silver-coated PET film is bonded to the end face of the first sleeve, the second sleeve is inserted into the first sleeve, and the fiber ceramic ferrule is inserted into the second sleeve, and the nested assembly is achieved by epoxy AB glue.

[0010] Optionally, the end face of the fiber ceramic ferrule serves as a first reflecting surface, and the silver-coated surface of the silver-coated PET (polyethylene terephthalate) film serves as a second reflecting surface, and the first reflecting surface and the second reflecting surface are separated by an air cavity.

[0011] Optionally, the cavity length change of the 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 reflecting surface; R2 represents the reflection coefficient of the second reflecting surface; φ represents the phase difference caused by the optical path difference after the light is reflected once in the F-P cavity; R FP represents the reflection spectrum of double-beam interference; h represents the cavity length of the F-P cavity; λ0 represents the wavelength of the incident light; h0 represents the initial cavity length of the F-P cavity; Δd0 represents the deformation amount generated at the center of the constant elastic film; p represents the lateral pressure difference borne by 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 respectively represent the wavelengths of the two adjacent interference peak and trough of the spectrum; L cav represents the cavity length of the standard F-P 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 modulates the electrical signal of the passband center frequency to the electro-optical modulator; the demodulation loop outputs to the power meter, and the power value change of the passband center frequency on the power meter is used to judge the shift direction of the single-passband microwave photon filter at the passband center frequency; if the power value at the passband center frequency decreases, it is judged that the passband moves to high frequency, otherwise it shifts to low frequency; the change of the center frequency corresponds to the change of the liquid level, and the increase or decrease of the power meter value is used to obtain the measurement result of the change of the liquid level.

[0018] To achieve the above object, the second aspect of the present application provides a diaphragm type optical fiber liquid level sensing demodulation method based on microwave photon technology, which is applied to the above-mentioned demodulation device; the demodulation method comprises the following steps: outputting light emitted by a broadband light source to a diaphragm type optical fiber liquid level sensor through a second port of a circulator, so as to obtain corresponding interference light according to the cavity length change of the diaphragm type optical fiber liquid level sensor; outputting the interference light to an erbium-doped fiber amplifier through a third port of the circulator, so as to perform optical power amplification; controlling the polarization state of the interference light after optical power amplification by using a polarization controller; inputting the interference light after polarization state control to an electro-optical modulator, and modulating the interference light according to the bias voltage applied by a direct current power supply and the electrical signal with the passband center frequency of the microwave photon filter generated by a radio frequency source, so as to obtain a modulated optical signal; transmitting the modulated optical signal to a photoelectric detector through a dispersion compensation fiber, so as to convert the optical signal into an electrical signal; measuring the power of the electrical signal by using a power meter, and obtaining the corresponding liquid level change 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 according to the above-mentioned embodiments of the present application can have the following additional technical features:

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

[0021] Optionally, the end face of the fiber ceramic ferrule serves as a first reflecting surface, the silver-coated surface of the silver-coated PET film serves as a second reflecting surface, and the first reflecting surface and the second reflecting surface are separated by an air cavity.

[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 reflecting surface; R2 represents the reflection coefficient of the second reflecting surface; φ represents the phase difference caused by the optical path difference after the light is reflected once in the F-P cavity; R FPThe reflection spectrum represents the double-beam interference; h represents the cavity length of the F-P cavity; λ0represents the wavelength of the incident light; h0represents the initial cavity length of the F-P cavity; Δd0represents the deformation amount generated in the center of the constant-elasticity film; p represents the lateral pressure difference borne by the constant-elasticity film; R0represents the effective radius of the constant-elasticity 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; λ1and λ2respectively represent the wavelengths of the peaks and troughs of two adjacent interference peaks of the spectrum; L cav h represents the cavity length of the standard F-P interferometer; n0represents the refractive index of the medium.

[0027] Optionally, the center frequency of the single-pass microwave photonic filter is obtained; the radio frequency source modulates the electrical signal of the center frequency to the electro-optical modulator; the demodulation loop outputs to the power meter, and the change of the power value at the center frequency of the power meter is used to determine the direction of the shift of the center frequency of the single-pass microwave photonic filter; if the power value at the center frequency decreases, it is determined that the center frequency moves to the high frequency, and vice versa; the change of the center frequency corresponds to the change of the liquid level, and the change of the liquid level is obtained by the increase or decrease of the power meter value. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 FIG. 1 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 application;

[0029] Figure 2 FIG. 2 is a structural schematic diagram of a diaphragm type optical fiber liquid level sensor according to an embodiment of the present application.

[0030] Figure 3 FIG. 3 is a flow schematic diagram of a diaphragm type optical fiber liquid level sensing demodulation method based on microwave photon technology according to an embodiment of the present application. DETAILED DESCRIPTION

[0031] Embodiments of the present application are described in detail below with reference to the accompanying drawings, in which the same or similar elements or elements having the same or similar functions are denoted by the same or similar reference numerals throughout. The embodiments described below by reference to the accompanying drawings are exemplary and are intended to explain the present application, and should not be understood as limiting the present application.

[0032] In order to better understand the above technical solutions, exemplary embodiments of the present application will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present application are shown in the accompanying drawings, it should be understood that the present application 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 application and to fully convey the scope of the present application to those skilled in the art.

[0033] In order to better understand the above technical solutions, the above technical solutions will be described in detail below in combination with the drawings in the specification and specific embodiments.

[0034] Figure 1 A structural 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 application is shown in FIG. 1, which includes a broadband light source 1, a circulator 11, a membrane type optical fiber liquid level sensor 2, an erbium-doped fiber amplifier 3, a polarization controller 4, a direct current power supply 5, a radio frequency source 6, an electro-optical modulator 7, a dispersion compensation fiber 8, a photoelectric detector 9, and a power meter 10. Figure 1

[0035] 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 membrane 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, the light reflected from the first end face of the optical fiber liquid level sensor 2 and the light transmitted from the first end face to the second end face and then reflected to the first end face interfere with each other, and the corresponding interference light is obtained according to the cavity length change of the optical fiber liquid level sensor 2; the third port of the circulator 11 is connected to the erbium-doped fiber amplifier 3, so that the interference light is output to the erbium-doped fiber amplifier 3 through the third port of the circulator 11 for 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-optical modulator 7, the radio frequency source 6 is connected to the modulation input of the electro-optical modulator 7, and the direct current power supply 5 is connected to the bias input of the electro-optical modulator 7, so that the interference light after polarization state control is input to the electro-optical modulator 7, and the interference light is modulated according to the bias voltage applied by the direct current power supply 5 and the electrical signal with the center frequency of the passband of the microwave photon filter generated by the radio frequency source 6, so as to obtain a modulated light signal; the output of the electro-optical modulator 7 is connected to the photoelectric detector 9 through the dispersion compensation fiber 8, so that the modulated light signal is transmitted to the photoelectric detector 9 through the dispersion compensation fiber 8, so as to convert the modulated light signal into an electrical signal; and the photoelectric detector 9 is connected to the power meter 10, so that the power of the electrical signal is measured by the power meter 10, and the corresponding liquid level change is obtained according to the power change of the electrical signal.

[0036] ​That is, the broadband light source 1, the circulator 11, the membrane type optical fiber liquid level sensor 2, the erbium-doped fiber amplifier 3, the polarization controller 4, the direct current power supply 5, the radio frequency source 6, the electro-optical modulator 7, the dispersion compensation optical fiber 8, the photoelectric detector 9 and the power meter 10 are sequentially connected to form a liquid level detection loop, the broadband light source 1 is connected with the first port of the circulator 11, the second port of the circulator 11 is connected with the membrane type optical fiber liquid level sensor 2, the third port of the circulator 11 is connected with the erbium-doped fiber amplifier 3, then the polarization controller 4 is connected with the output end of the erbium-doped fiber amplifier 3, the polarization state of the light beam is adjusted through the polarization controller 4, the polarization controller 4 is connected with the electro-optical modulator 7 connected with the radio frequency source 6, at this time, the electro-optical modulator 7 has the direct current power supply 5 to apply a bias voltage to it, and the radio frequency source 6 is connected to it for modulation, finally the output of the electro-optical modulator 7 is connected with the photoelectric detector 9, and the photoelectric detector 9 is connected with the power meter 10 to realize detection.

[0037] It should be noted that, generally, the microwave photon sensing system is usually observed on the network analyzer, but the introduction of the network analyzer will cause the actual application cost to be relatively high, and the network analyzer is too large in size, and it is difficult to be used for liquid level measurement in complex environment, therefore, the radio frequency source and the power meter are used to replace the network analyzer in the microwave photon sensing system. In this way, the measurement cost can be maximized, and the replacement of the network analyzer in the sensing loop can better meet the liquid level detection in various environments, and has a wide application scenario. In addition, in the case of determining the center frequency of the single passband, the radio frequency source is used to modulate the electrical signal with the passband center frequency to the electro-optical modulator, and subsequent only needs to observe the change of the electrical power on the power meter to detect the corresponding liquid level change.

[0038] As an embodiment, the membrane 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 face 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, as Figure 2As shown, the liquid level sensor is a fiber film Fabry-Perot cavity liquid level sensor made of new materials, wherein the first sleeve 13 and the second sleeve 14 are made of acrylic material, so that the fiber ceramic ferrule 12 can be nested and assembled with them, the sizes of the first sleeve 13 and the second sleeve 14 are different, 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 fiber ceramic ferrule 12, the first sleeve 13 is first used to bond the diaphragm on the end face of the sleeve by AB epoxy resin glue, the second sleeve 14 is inserted into the first sleeve 13 with the diaphragm bonded thereon, the fiber ceramic ferrule 12 is inserted into the second sleeve 14, the cavity length of the Fabry-Perot cavity is observed and adjusted on the optical precision adjusting frame, and after the cavity length is determined, the three are finally bonded by using AB epoxy resin.

[0040] It should be noted that the diaphragm type fiber liquid level sensor is assembled by the sleeve made of acrylic material and the diaphragm and the fiber ceramic ferrule made of PET material, which is simple to prepare, low in cost, high in repeatability, and therefore has a very wide application scenario.

[0041] As an embodiment, the end face of the fiber ceramic ferrule serves as the first reflecting surface, the silver-plated surface of the silver-plated PET film serves as the second reflecting surface, and the first reflecting surface and the second reflecting surface are air cavities.

[0042] That is, from the diaphragm type fiber Fabry-Perot liquid level sensor, the end face of the fiber ceramic ferrule 12 can serve as the first reflecting surface, and the second reflecting surface is a silver-plated PET (polyethylene terephthalate) film material, and the two end faces are air cavities.

[0043] It should be noted that the PET film material is plated with a reflective film on its surface, which aims to enhance the reflection of the PET film to the light beam and improve the contrast of the interference spectrum, so as to achieve good observation of the interference spectrum when the liquid level changes; from the properties of the material 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 early, which has good transparency, chemical stability and weather resistance, and the manufacturing of acrylic usually adopts injection molding, extrusion or injection molding process, which can produce acrylic in different shapes and sizes while maintaining its superior physical properties, so acrylic has good processing performance; from the preparation point of view, acrylic material and PET material are relatively common materials, so the cost of preparing the diaphragm type fiber liquid level sensor is greatly reduced, which has good repeatability and can be widely used in various fiber diaphragm type sensing and measuring fields, and has very broad application prospects.

[0044] As a specific embodiment, the light emitted by the broadband light source 1 is output from the second port of the three-port circulator 11 to the membrane optical fiber liquid level sensor 2, and the pressure change caused by the liquid level change changes the cavity length of the Fabry-Perot cavity, and the interference light carrying the cavity length change information is reflected to the second port, and then 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, and then enters the polarization controller 4 to control the polarization state of the transmission beam, and then enters the electro-optical modulator 7 biased by the direct current power supply 5, the electro-optical modulator is simultaneously connected to the radio frequency source 6, the radio frequency source emits an electrical signal with a passband center frequency, and the optical signal output by the electro-optical modulator 7 is then connected to the dispersion compensation fiber 8, and then the dispersion compensation fiber 8 is connected to the photodetector 9, the photodetector 9 converts the modulated optical signal into an electrical signal, and finally the output end of the photodetector 9 is connected to the power meter 10, and the liquid level is monitored by observing the power value change on the power meter 10.

[0045] Wherein, the PET-EFPI (PET membrane optical fiber liquid level sensor) based on Fabry-Perot interference, when the reflectivity of the incident light beam entering the F-P interferometer is low, the incident light beam can only have a few reflections in the resonant cavity, at this time, double-beam interference occurs, and the reflection spectrum expression of the double-beam interference is:

[0046]

[0047] In the formula: R1 and R2 are the reflection coefficients of the two reflection end faces respectively, and φ is the phase difference caused by the optical path difference after the light is reflected once in the F-P cavity, which is expressed as

[0048]

[0049] In the formula: h is the cavity length of the F-P cavity; and λ0 is the wavelength of the incident light.

[0050] Set the initial cavity length of the F-P cavity as h0, then:

[0051] h = h0- Δd0

[0052] When the liquid in the liquid cavity acts on the constant elastic membrane, the size of the elastic deformation is related to the pressure difference it bears, that is, related to the height of the liquid level. According to the principle of elasticity, assuming that the constant elastic membrane is subjected to a pressure p, the deformation amount of the center of the membrane is

[0053]

[0054] where p is the lateral pressure difference on the elastic membrane, R0 is the effective radius of the elastic membrane, d is the thickness of the membrane, γ is the Poisson's ratio of the material, and E is the Young's modulus of the material.

[0055] For the selected material, γ and E are known quantities. By selecting different d and R0, the sensitivity and measurement range of the sensor can be determined according to the above formula. When both parameters are determined, Δd0 is proportional to the pressure p.

[0056] When a broadband light source 1 is selected as the light source, interference peaks of different frequencies will appear, and the free spectral range (FSR) of the interference spectrum is represented as:

[0057]

[0058] where λ1 and λ2 are the wavelengths of the peaks and troughs of two adjacent interference peaks in the spectrum, respectively. The value of FSR can be read from the spectrum, and the cavity length of the standard F-P interferometer can be calculated accordingly:

[0059]

[0060] In other studies on liquid level sensing using F-P interferometer structures, the relationship between the wavelengths corresponding to the peaks / troughs of the interference spectrum and the liquid level change is usually monitored, i.e., wavelength demodulation. However, when the sensitivity of the liquid level sensor 2 is high and the response range of the liquid level change is wide, the wavelength shift of multiple periods within the wide liquid level change range cannot be identified in the interference spectrum. Therefore, in combination with microwave photon filtering technology, a diaphragm type fiber optic liquid level sensor is used as a spectral splitting device for the filter, and a dispersion compensation fiber is used as a dispersion medium to realize a single passband frequency response, converting the wavelength change in the optical domain to the center frequency change of the passband in the electrical domain. This avoids the limitation of the periodicity of the spectral interference signal and expands the measurement range. By monitoring the change of the center frequency of the single passband microwave photon filter passband, the change of the liquid level can be more directly observed. The expression of the passband center frequency is as follows:

[0061]

[0062] where D and L represent the dispersion value of the dispersion device and the length of the dispersion medium, and Δω is the free spectral range (FSR) of the interference spectrum. According to the formula, the position of the passband center frequency is determined by the dispersion coefficient (D) of the dispersion compensation fiber, the length (L) of the dispersion compensation fiber, and the FSR (Δω) of the interference spectrum. By setting the sizes of these three parameters, different filter responses with different positions of the passband center frequency can be obtained, i.e., the passband can be tuned:

[0063]

[0064] When the liquid level changes, the cavity length of the sensor changes, and 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 membrane optical fiber liquid level sensor is applied to the position of the spectrum divider, the change of the external parameter will cause the change of the interference fringes, thereby causing the change of the passband position of the microwave photon filter, and the sensing to be measured can be obtained by tracking the passband center frequency. The tracking of the shift of the passband center requires determining the passband center frequency of the single-passband microwave photon filter. After the passband center frequency is determined, the radio frequency source is used to modulate the electrical signal of the frequency to the electro-optical modulator. Finally, the demodulation loop is output to the power meter, and the shift direction at the passband center frequency of the single-passband microwave photon filter is determined by observing the change of the power value of the passband center frequency on the power meter. If the power value at the center frequency decreases, it is determined that the passband moves to the high frequency, and vice versa. Finally, the sensing of the change of the liquid level is realized.

[0067] In summary, the application is aimed at the actual liquid level measurement, and the silver-plated PET film and the acryl sleeve are bonded at a low cost. Finally, the ceramic ferrule is assembled with the film-sleeve structure to construct the liquid level sensor of the application. The end surface of the flat-end ceramic ferrule and the end surface of the stainless steel film form an F-P cavity. When the liquid level changes, the pressure at the same horizontal height of the membrane optical fiber liquid level sensor changes. The membrane is deformed by the action of the pressure, thereby changing the optical path difference of the interference light beam. The purpose of detection is realized by observing the shift of the interference spectrum of the spectrometer in the sensing loop or the shift of the center frequency of the single-passband filter in the microwave photon loop. The wavelength shift in the optical domain is corresponded to the passband frequency shift in the microwave domain by using the signal demodulation of the microwave photon filtering technology, so that the resolution and the sensitivity are improved. The periodic interference spectrum in the optical domain limits the measurement range of the sensor, and the single-passband microwave photon filtering technology is used to break the periodicity of the interference spectrum, thereby significantly increasing the measurement range and being suitable for long-distance liquid level detection.

[0068] In order to realize the above-mentioned embodiments, as Figure 3 shown in the figure, the embodiment of the application also proposes a membrane optical fiber liquid level sensing demodulation method based on the microwave photon technology, which is applied to the demodulation device mentioned above. The demodulation method comprises the following steps:

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

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

[0071] S103, the polarization state of the interference light after optical power amplification is controlled by using a polarization controller.

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

[0073] S105, the modulated light signal is transmitted to a photoelectric detector through a dispersion compensation fiber, so as to convert the modulated light signal into an electrical signal.

[0074] S106, the power of the electrical signal is measured by using a power meter, and the corresponding liquid level change is obtained according to the power change of the electrical signal.

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

[0076] As an embodiment, the end face of the fiber ceramic ferrule serves as a first reflecting surface, the silver-coated surface of the silver-coated PET film serves as a second reflecting surface, and the first reflecting surface and the second reflecting surface are separated by an air cavity.

[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 reflecting surface; R2 represents the reflection coefficient of the second reflecting surface; φ represents the phase difference caused by the optical path difference after the light is reflected once in the F-P cavity; R FPThe reflection spectrum represents the double-beam interference; h represents the cavity length of the F-P cavity; λ0represents the wavelength of the incident light; h0represents the initial cavity length of the F-P cavity; Δd0represents the deformation amount generated in the center of the constant-elasticity film; p represents the lateral pressure difference borne by the constant-elasticity film; R0represents the effective radius of the constant-elasticity 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; λ1and λ2respectively represent the wavelengths of the peaks and troughs of two adjacent interference peaks of the spectrum; L cav h represents the cavity length of the standard F-P interferometer; n0represents the refractive index of the medium.

[0083] As an embodiment, the center frequency of the passband of the microwave photon filter is obtained; an electrical signal of the center frequency of the passband is modulated to an electro-optical modulator by a radio frequency source; the output of the demodulation loop is connected to a power meter, and the change of the power value of the center frequency of the passband on the power meter is used to determine the direction of the shift of the center frequency of the single-passband microwave photon filter; if the power value of the center frequency decreases, it is determined that the passband moves to a high frequency, and vice versa; the change of the center frequency corresponds to the change of the liquid level, and the increase or decrease of the power meter value is used to obtain the change result of the measured liquid level.

[0084] It should be noted that the device used by the film type optical fiber liquid level sensing demodulation method based on the microwave photon technology in the embodiment is the aforementioned film type optical fiber liquid level sensing demodulation device based on the microwave photon technology, and therefore the aforementioned explanations and descriptions of the embodiments of the film type optical fiber liquid level sensing demodulation device based on the microwave photon technology are also applicable to the film type optical fiber liquid level sensing demodulation method based on the microwave photon technology in the embodiment, which will not be described herein again.

[0085] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can 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 application is described in reference to the accompanying drawings, which use the legend: 100 - method, 200 - device (system), 300 - computer program product. Figure 1 one or more functions specified in the flow or flows and / or blocks. Figure 1 one or more functions specified in the flow or flows and / or blocks.

[0087] These computer program instructions can also be stored in a computer- readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instructions which implement the flow Figure 1 one or more functions specified in the flow or flows and / or blocks. Figure 1 one or more functions specified in the flow or flows and / or blocks.

[0088] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the flow Figure 1 one or more functions specified in the flow or flows and / or blocks. Figure 1 one or more functions specified in the flow or flows and / or blocks.

[0089] It should be noted that the use of any of the terms "first", "second" or the like does not connote any order, quantity, or importance, but rather are used to distinguish one element from another. It should also be noted that the terms "comprising", "including", "containing", and / or "having" are intended to be open-ended terms. Further, the singular forms "a", "an" and / or "the" are intended to include one or more, unless expressly specified otherwise.

[0090] While the preferred embodiments of the application have been described, additional variations and modifications can be made to the embodiments described and illustrated herein, without departing from the spirit and scope of the application. Accordingly, it is intended that all subject matter contained in the above description be interpreted as illustrative only and basis for claims.

[0091] Obviously, various modifications and changes can be made to the present application by those skilled in the art without departing from the spirit and scope of the application. Accordingly, it is intended that all such modifications and changes be included in the present application only as far as they come to be within the scope of the claims and their equivalents.

[0092] In the description of the present application, it is to be understood that the terms "first", "second", "third" and the like, merely mean different instances of the same thing, and do not imply relative importance or a number of the indicated technical features. Thus, a feature defined with "first", "second", "third" can include one or more of the features. In the description of the present application, the meaning of "plurality" is two or more, unless specifically defined otherwise.

[0093] In the present application, unless specifically defined and limited otherwise, the terms "mounting", "connection", "connecting", "fixed", and the like, should be interpreted broadly, for example, can be fixed connection, can be detachable connection, or integral; can be mechanical connection, can be electrical connection; can be directly connected, can be indirectly connected through intermediate media, can be internal communication of two elements or interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0094] In the present application, unless specifically defined and limited otherwise, the first feature "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through intermediate media. Moreover, the first feature "above", "over" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or only means that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "under" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or only means that the horizontal height of the first feature is less than that of the second feature.

[0095] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present application, the illustrative description 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 can be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or features of different embodiments or examples described in the present application without contradiction.

[0096] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and that variations, modifications, substitutions and changes can be made by those skilled in the art without departing from the scope of the present application.

Claims

1. A diaphragm type optical fiber liquid level sensing demodulation device based on microwave photon technology, characterized in that, The system comprises a broadband light source, a circulator, a membrane type fiber liquid level sensor, an erbium-doped fiber amplifier, a polarization controller, a direct current power supply, a radio frequency source, an electro-optical modulator, a dispersion compensation fiber, a photoelectric detector and a power meter, wherein, the broadband light source is connected with a first port of the circulator, a second port of the circulator is connected with the fiber liquid level sensor, so that the light emitted by the broadband light source is output to the membrane type fiber liquid level sensor through the second port of the circulator, and the corresponding interference light is obtained according to the cavity length change of the membrane type fiber liquid level sensor; a third port of the circulator is connected with the erbium-doped fiber amplifier, so that the interference light is output to the erbium-doped fiber amplifier through the third port of the circulator for optical power amplification; the erbium-doped fiber amplifier is connected with the polarization controller, so that the polarization state of the interference light after the optical power amplification is controlled by the polarization controller; the polarization controller is connected with the input of the electro-optical modulator, the radio frequency source is connected with the modulation input of the electro-optical modulator, and the direct current power supply is connected with the bias input of the electro-optical modulator, so that the interference light after the polarization state control is input to the electro-optical modulator, and the interference light is modulated according to the bias voltage applied by the direct current power supply and the electrical signal with the passband center frequency of the microwave photon filter generated by the radio frequency source, so that the modulated light signal is obtained; the output of the electro-optical modulator is connected with the photoelectric detector through the dispersion compensation fiber, so that the modulated light signal is transmitted to the photoelectric detector through the dispersion compensation fiber, and the modulated light signal is converted into an electrical signal; the photoelectric detector is connected with the power meter, so that the power of the electrical signal is measured by the power meter, and the corresponding liquid level change is obtained according to the power change of the electrical signal; The fiber liquid level sensor comprises a fiber ceramic ferrule, a first sleeve, a second sleeve and a silver-coated PET film, wherein the silver-coated PET film is bonded to the end face of the first sleeve, the second sleeve is inserted into the first sleeve, and the fiber ceramic ferrule is inserted into the second sleeve, and the components are assembled by epoxy AB glue.

2. The membrane optical fiber liquid level sensor demodulation device based on microwave photon technology according to claim 1, characterized in that, The end face of the fiber ceramic ferrule serves as a first reflecting surface, the silver-coated surface of the silver-coated PET film serves as a second reflecting surface, and the first reflecting surface and the second reflecting surface are separated by an air cavity.

3. The membrane optical fiber liquid level sensor demodulation device based on microwave photonics technology according to claim 2, characterized in that, The cavity length change of the membrane type fiber liquid level sensor is obtained according to the following formula: h = h0- Δd0 wherein R1 represents the reflection coefficient of the first reflecting surface; R2 represents the reflection coefficient of the second reflecting surface; φ represents the phase difference caused by the optical path difference after the light is reflected once in the F-P cavity; R FP represents the reflection spectrum of the double-beam interference; h represents the cavity length of the F-P cavity; λ0 represents the wavelength of the incident light; h0 represents the initial cavity length of the F-P cavity; Δd0 represents the deformation amount generated at the center of the constant-elasticity film; p represents the lateral pressure difference borne by the constant-elasticity film; R0 represents the effective radius of the constant-elasticity 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 respectively represent the wavelengths of the peaks and troughs of two adjacent interference peaks of the spectrum; L cav represents the cavity length of the standard F-P interferometer; n0 represents the refractive index of the medium.

4. The membrane optical fiber liquid level sensor demodulation device based on microwave photon technology according to claim 3, characterized in that, The passband center frequency of the microwave photon filter is obtained, the radio frequency source modulates the electrical signal with the passband center frequency to the electro-optical modulator, the demodulation loop output is connected with the power meter, the power value change of the passband center frequency on the power meter is used to determine the shift direction of the single-passband microwave photon filter passband center frequency, if the power value at the passband center frequency decreases, it is determined that the passband moves to high frequency, otherwise it shifts to low frequency, the change of the center frequency corresponds to the change of the liquid level, and the change of the measured liquid level is obtained by the increase or decrease of the power meter value.

5. 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 as claimed in any one of claims 1-4; the demodulation method comprises: 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 to obtain corresponding interference light according to the cavity length change 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; The polarization state of the interference light after optical power amplification is controlled by using a polarization controller; The interference light after polarization state control is input to an electro-optical modulator and modulated according to the bias voltage applied by a direct current power supply and the electrical signal with the passband center frequency of the microwave photon filter generated by a radio frequency source to obtain a modulated light signal; The modulated light signal is transmitted to a photoelectric detector through a dispersion compensation optical fiber to convert the modulated light signal into an electrical signal; The power of the electrical signal is measured by using a power meter, and the corresponding liquid level change is obtained according to the power change of the electrical signal.

Images