Liquid level measuring system based on optical carrier microwave ring-down optical fiber cavity

Abstract

The invention discloses a liquid level measuring system based on an optical carrier microwave ring-down optical fiber cavity, which is characterized in that an electro-optical modulator modulates a laser signal according to a modulation signal to obtain optical carrier microwaves and transmits the optical carrier microwaves to an optical fiber in a liquid level sensor; different hydraulic pressures corresponding to different liquid levels enable the bending degrees of the optical fibers to be different, so that the intensity attenuation degrees of the optical carrier microwaves after passing through the optical fibers are different; the optical carrier microwaves are continuously and circularly transmitted in the ring-down optical fiber cavity, the intensity of the optical carrier microwaves is attenuated when the optical carrier microwaves pass through the optical fiber every time, the optical carrier microwaves are circularly transmitted in the ring-down optical fiber cavity to form resonance signals, and the resonance signals are converted into electric signals; and the network analyzer obtains a ring-down signal according to the amplitude-frequency signal and the phase-frequency signal of the electric signal, and determines the liquid level of the liquid level sensor according to the light propagation duration or the light transmission distance when the ring-down signal is attenuated to a corresponding threshold value. According to the invention, the liquid level measurement resolution and the measurement range can be improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of liquid level measurement, and particularly relates to a liquid level measurement system based on an optical microwave decaying optical fiber cavity. BACKGROUND

[0002] Liquid level sensors have been widely used in many fields, such as industrial safety production, marine operation detection, water conservancy and hydropower, oil liquid level detection, and aerospace, etc. The accuracy and resolution of liquid level detection are of great significance to safety production, etc. At present, there is a liquid level sensor based on hydraulic pressure for liquid level detection (for example, a patent with the application number 202310926445.1 and the invention name "a liquid level sensor, a liquid level monitoring device and a method"). The liquid level sensor utilizes hydraulic pressure acting on an optical fiber in a hydraulic sensor, causing the optical fiber to stretch. The stretching of the optical fiber grating will cause the reflection wavelength to change. According to the transmitted light information output after the optical fiber grating, the liquid level information is determined. Although this scheme can also achieve liquid level measurement based on hydraulic pressure, the optical fiber grating can only stretch enough to cause the reflection wavelength to change when the hydraulic pressure changes need to be large enough. Therefore, the hydraulic pressure resolution is low, and the stretching length of the optical fiber grating is limited. When the stretching length of the optical fiber grating reaches the limit, it will not be able to continue to measure, so the measurement range is small. It can be seen that the liquid level measurement system based on hydraulic pressure for liquid level detection has the problems of low liquid level resolution and small measurement range. SUMMARY

[0003] The application provides a liquid level measurement system based on an optical microwave decaying optical fiber cavity to solve the problems of low liquid level resolution and small measurement range of the liquid level measurement system based on hydraulic pressure for liquid level detection.

[0004] According to a first aspect of an embodiment of the application, a liquid level measurement system based on an optical microwave decaying optical fiber cavity is provided, which comprises a laser, an electro-optical modulator, a network analyzer, a decaying optical fiber cavity, and a photoelectric detector. The decaying optical fiber cavity is provided with a liquid level sensor. The electro-optical modulator modulates the laser signal output by the laser according to the modulation signal provided by the network analyzer to obtain an optical microwave and transmit it to the optical fiber in the liquid level sensor. Different liquid pressures corresponding to different liquid levels cause different bending degrees of the optical fiber, so that the intensity attenuation degree of the optical microwave after passing through the optical fiber is different.

[0005] The optical microwave continuously circulates within the decaying fiber cavity, with its intensity attenuating each time it passes through the fiber. After reaching equilibrium through this circulatory transmission, a resonant signal is formed. This resonant signal is transmitted to the photodetector for photoelectric conversion, generating an electrical signal. The network analyzer obtains the decaying signal based on the amplitude and phase frequencies of this electrical signal. It then determines the liquid level of the level sensor based on the light propagation time or light transmission distance at which the decaying signal decays to the corresponding threshold.

[0006] Optionally, the ring-down fiber cavity includes a first coupler, a liquid level sensor, and a second coupler. The two input terminals of the electro-optic modulator are respectively connected to the modulation signal output terminals of the laser and the network analyzer, and its output terminal is connected to the first input terminal of the first coupler. The output terminal of the first coupler is connected to one end of the optical fiber in the liquid level sensor, and the other end of the optical fiber is connected to the input terminal of the second coupler. The first output terminal of the second coupler is connected to the input terminal of the network analyzer through the photodetector, and its second output terminal is connected to the second input terminal of the first coupler.

[0007] Optionally, the liquid level sensor includes a column with openings at both ends. The left and right ends of the column are sealed with thin films. The optical fiber is disposed in the column in the form of an optical fiber loop and is fixedly connected to the two thin films. In the initial state before being inserted into the liquid, the planes of the thin films at both ends of the column and the plane of the optical fiber loop are flat, and the planes of the two thin films are perpendicular to the plane of the optical fiber loop. When the hydraulic sensor is vertically inserted into the liquid, the planes of the two thin films are perpendicular to the liquid surface and enter the liquid. After vertical insertion into the liquid, under the action of hydraulic pressure, the two thin films deform towards the inside of the column, thereby causing the optical fiber loop to bend.

[0008] Optionally, in the initial state before liquid insertion, the fiber optic ring is rectangular, with its left and right sides fixedly connected to two films respectively; after vertical insertion into the liquid, under hydraulic pressure, the fiber optic ring is converted into a fiber optic ring with arc-shaped sides; the fiber optic ring is located at least at the middle position of the two films in the vertical direction.

[0009] Optionally, the left and right ends of the column extend outward to form annular platforms. Each annular platform is on the same plane as the corresponding end. The two annular platforms are provided with corresponding matching through holes. The lowering rope is inserted into the matching through holes on the two annular platforms so that the liquid level sensor can be smoothly lowered into the liquid through the lowering rope, and the liquid level sensor can be kept vertical during the lowering process.

[0010] The column contains multiple layers of fiber optic rings, with one free end of each layer connected to the other. The other free end of the uppermost or lowermost fiber optic ring passes through a through hole on the column or a through hole on the annular platform. After passing through the through hole on the column or the through hole on the annular platform, the through hole or through hole is sealed to prevent liquid from flowing into the column.

[0011] Optionally, the network analyzer obtains the ring-down signal based on the amplitude and phase frequency signals of the electrical signal, and determines the specific liquid level of the liquid level sensor based on the light propagation time or light transmission distance at which the ring-down signal decays to a corresponding threshold.

[0012] The network analyzer converts the amplitude-frequency signal of the electrical signal from dB to amplitude form, unwraps the phase-frequency signal of the electrical signal, and performs inverse Fourier transform on the converted amplitude-frequency signal and the unwrapped phase-frequency signal to obtain the time-domain oscillation signal.

[0013] The liquid level of the liquid level sensor is determined by the light propagation time or light transmission distance when the decaying signal decays to 1 / e of the electrical signal.

[0014] Optionally, it also includes a first optical amplifier and a second optical amplifier, a circulator and a fiber optic grating. The first optical amplifier is located between the output of the electro-optic modulator and the first input of the first coupler. The other end of the optical fiber in the liquid level sensor is connected to the input of the second optical amplifier, and the output of the second optical amplifier is connected to the input of the second coupler.

[0015] Optionally, it also includes a circulator and a fiber Bragg grating. The output of the second optical amplifier is connected to the first end of the circulator, the second end of the circulator is connected to the fiber Bragg grating, and the third end is connected to the input of the second coupler. The reflected wavelength of the fiber Bragg grating is the same as the wavelength of the laser signal, so as to filter out signals of other wavelengths except for the signal corresponding to that wavelength.

[0016] Optionally, the liquid level is 0, and the liquid level increases closer to the bottom. When measuring the liquid level, if the depth of the container to be measured is known, and the liquid in the container to be measured will gradually decrease or increase, the liquid level sensor is lowered to the bottom of the container to be measured. Based on the size of the liquid level at the bottom of the container to be measured and the shape and volume of the container to be measured, the amount of liquid currently stored in the container to be measured can be obtained.

[0017] When measuring liquid level, if it is necessary to detect the position of the liquid surface, the liquid level sensor is lowered to any position in the liquid. The vertical distance between the liquid surface and the lowered position is obtained by subtracting the liquid level of the sensor from the lowered distance.

[0018] Optionally, it also includes an optical time-division multiplexer, wherein the output of the first coupler is connected to the input of the optical time-division multiplexer, and each output of the optical time-division multiplexer is connected to the input of the second coupler through a liquid level sensor.

[0019] The beneficial effects of this invention are:

[0020] 1. In this invention, when detecting liquid level based on hydraulic pressure, a laser signal is first modulated using a modulation signal. The modulated optical microwave is then transmitted to the optical fiber within the liquid level sensor for liquid level detection. The optical microwave enables faster response speed for liquid level detection, significantly reducing the requirements for the light source and making the liquid level detection system less susceptible to phase and polarization effects. Furthermore, the hydraulic pressure causes the optical fiber within the liquid level sensor to bend, resulting in intensity attenuation of the optical microwave each time it passes through the fiber. This attenuation process cyclically occurs within the decaying fiber cavity until a resonant signal is formed. Therefore, even if the optical fiber emits... The smaller the degree of bending of the optical fiber, the smaller the intensity attenuation of the optical microwaves passing through the fiber. During the cyclic transmission of the optical microwaves within the decaying fiber cavity, the intensity attenuation can continuously accumulate and increase. Therefore, this invention has a high resolution for liquid level. Furthermore, this invention determines the liquid level based on the degree of bending of the optical fiber, not the amount of fiber tension. Compared to the amount of fiber tension, the range of fiber bending is wider. Therefore, this invention has a wider liquid level measurement range. Moreover, compared to the influence of liquid level on fiber bending, the influence of temperature on fiber bending is negligible. Therefore, this invention also has good temperature insensitivity.

[0021] 2. The liquid level sensor of the present invention includes a column, the left and right ends of which are sealed with thin films, so that the optical fiber is located in the sealed space in the form of an optical fiber ring, which is not affected by the external liquid. The left and right corresponding parts of the optical fiber ring are fixedly connected to two thin films respectively. Under the action of hydraulic pressure, both thin films are concave towards the inside of the column, and the two cause the optical fiber ring to bend. The bending amount of the optical fiber ring is determined by the degree of concavity of the two thin films. Therefore, under the same hydraulic pressure, the bending amount of the optical fiber in the liquid level sensor of the present invention is greater, thereby improving the liquid level detection resolution.

[0022] 3. In the initial state before liquid insertion, the fiber optic ring is rectangular, with its left and right ends fixedly connected to two films, ensuring a strong connection between the fiber optic ring and the two films. Under hydraulic pressure, the fiber optic ring transforms into a ring with arc-shaped sides, resulting in a larger bending amount. When measuring liquid level, after the film is inserted perpendicularly to the liquid surface, the indentation at the middle position in the vertical direction is deeper. This invention places the fiber optic ring at this middle position, achieving the maximum bending amount under the same hydraulic pressure, thereby further improving the resolution of liquid level detection.

[0023] 4. The present invention extends annular platforms outward from the left and right ends of the column. Corresponding matching through holes are set on the two annular platforms. After the rope is lowered through the matching through holes, it can ensure that the hydraulic sensor is smoothly lowered into the liquid and remains vertical during the lowering process. The present invention sets multiple layers of optical fiber rings in the column, and the planes of each layer of optical fiber rings are parallel. This can further improve the curvature of the optical fiber rings under the same hydraulic pressure, thereby improving the liquid level detection resolution.

[0024] 5. By setting up a first optical amplifier and a second optical amplifier, the inherent loss of optical microwave can be compensated. By setting up a circulator and a fiber optic grating, other wavelength signals with different wavelengths than the optical microwave can be filtered out, such as spontaneous emission noise introduced by the optical amplifier.

[0025] 6. When the depth of the container to be tested is known, the present invention can obtain the current liquid volume stored in the container by lowering the liquid level sensor to the bottom of the container and based on the liquid level at the bottom of the container and the shape and volume of the container; the present invention can also realize liquid level detection.

[0026] 7. The present invention provides an optical time-division multiplexer, so that each output terminal of the optical time-division multiplexer is connected to a liquid level sensor, and optical microwaves are sequentially provided to each liquid level sensor, thereby enabling sequential measurement of the liquid level in multiple different containers to be tested. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of an embodiment of the liquid level measurement system based on an optically-borne microwave ring-down fiber cavity according to the present invention;

[0028] Figure 2 This is a front perspective view of an embodiment of the hydraulic sensor of the present invention;

[0029] Figure 3 (a) and (b) show the initial state of the fiber optic ring before it is inserted into the liquid and the detection state after it is inserted into the liquid, respectively. Figure 2 Top view;

[0030] Figure 4 yes Figure 2 Side view;

[0031] Figure 5 This is a schematic diagram of the amplitude frequency signal and phase frequency signal after processing according to the present invention;

[0032] Figure 6 This is a schematic diagram of the waveform of the decaying signal of the present invention;

[0033] Figure 7 This is a schematic diagram of another embodiment of the liquid level measurement system based on an optically mounted microwave oscillation fiber cavity according to the present invention. Detailed Implementation

[0034] To enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, and to make the above-mentioned objectives, features and advantages of the embodiments of the present invention more apparent and understandable, the technical solutions in the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0035] In the description of this invention, unless otherwise specified and limited, it should be noted that the term "connection" should be interpreted broadly. For example, it can be a mechanical connection or an electrical connection, or it can be a connection between two internal components. It can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above term according to the specific circumstances.

[0036] See Figure 1 This is a schematic diagram of an embodiment of the liquid level measurement system based on an optically carried microwave decaying fiber cavity according to the present invention. The system may include a laser UNLL, an electro-optic modulator EOM, a network analyzer VNA, a ring-down fiber cavity 1, and a photodetector PD. A liquid level sensor is installed within the ring-down fiber cavity 1. The electro-optic modulator EOM modulates the laser signal output from the laser UNLL based on the modulation signal provided by the network analyzer VNA, obtaining optically carried microwaves, which are then transmitted to the optical fiber within the liquid level sensor. Different liquid levels correspond to different hydraulic pressures, causing varying degrees of bending in the optical fiber, resulting in different intensities of the optically carried microwaves as they pass through it. The optically carried microwaves continuously circulate within the ring-down fiber cavity, experiencing intensity attenuation each time they pass through the fiber. After reaching equilibrium through this circulation, a resonant signal is formed. This resonant signal is transmitted to the photodetector PD for photoelectric conversion, generating an electrical signal. The network analyzer VNA obtains the ring-down signal based on the amplitude and phase frequencies of this electrical signal. The VNA determines the liquid level at the liquid level sensor based on the propagation time or transmission distance of the light when the ring-down signal attenuates to a corresponding threshold.

[0037] In this embodiment, the ring-down fiber cavity may include a first coupler C1, a liquid level sensor, and a second coupler C2. The two inputs of the electro-optic modulator EOM are respectively connected to the modulation signal outputs of the laser UNLL and the network analyzer VNA, and its output is connected to the first input of the first coupler C1. The output of the first coupler C1 is connected to one end of the optical fiber in the liquid level sensor, and the other end of the optical fiber is connected to the input of the second coupler C2. The first output of the second coupler C2 is connected to the input of the network analyzer VNA through the photodetector PD, and its second output is connected to the second input of the first coupler C1. The laser UNLL can be an ultra-narrow linewidth laser, the modulation signal output by the network analyzer can be a broadband electrical signal of 2.68-2.82 GHz, and the first coupler C1 and the second coupler C2 can be fiber couplers with splitting ratios of 20:80 and 90:10, respectively.

[0038] Combination Figures 2 to 4 As shown, the liquid level sensor may include a column 1 (e.g., a cylinder) with openings at both ends. The left and right ends of the column 1 are sealed with thin films 2. The optical fiber is disposed inside the column 1 in the form of an optical fiber loop 3 and is fixedly connected to the two thin films 2. In the initial state before being inserted into the liquid, the planes of the thin films 2 at both ends of the column 1 and the planes of the optical fiber loop 3 are flat, and the planes of the two thin films 2 are perpendicular to the plane of the optical fiber loop 3. When the hydraulic sensor is vertically inserted into the liquid, the planes of the two thin films 2 are perpendicular to the liquid surface and enter the liquid. After being vertically inserted into the liquid, under the action of hydraulic pressure, the two thin films 2 deform towards the inside of the column 1, thereby causing the optical fiber loop 3 to bend. In its initial state without liquid insertion, the fiber optic ring 3 is rectangular, with its left and right sides fixedly connected to two films 2 respectively. After vertical insertion into the liquid, under hydraulic pressure, the fiber optic ring 3 transforms into a ring with arc-shaped sides, where the left and right sides are inwardly concave arc segments, and the front and back sides are outwardly curved arc segments. The fiber optic ring 3 can be positioned at least at the midpoint of the two films 2 in the vertical direction. The films can be polydimethylsiloxane (PDMS) films.

[0039] The liquid level sensor of the present invention includes a column, with the left and right ends of the column sealed with thin films, so that the optical fiber is located in the form of an optical fiber loop in the sealed space, unaffected by the external liquid. The left and right corresponding parts of the optical fiber loop are fixedly connected to two thin films respectively. Under hydraulic pressure, both films are concave towards the inside of the column, and both cause the optical fiber loop to bend. The amount of bending of the optical fiber loop is determined by the degree of concavity of the two films. Therefore, under the same hydraulic pressure, the amount of bending of the optical fiber in the liquid level sensor of the present invention is greater, thereby improving the liquid level detection resolution.

[0040] In the initial state before liquid insertion, the fiber optic ring is rectangular, with its left and right ends fixedly connected to two thin films, ensuring a strong connection between the fiber optic ring and the two films. Under hydraulic pressure, the fiber optic ring transforms into a ring with curved sides, resulting in a larger bending amount. When measuring liquid level, after the film is inserted perpendicularly to the liquid surface, the indentation at the middle position in the vertical direction is deeper. This invention positions the fiber optic ring at this middle position, achieving the maximum bending amount under the same hydraulic pressure, thereby further improving the resolution of liquid level detection.

[0041] In addition, the left and right ends of the column 1 can each extend outward to form annular platforms 4. Each annular platform 4 is on the same plane as the corresponding end. The two annular platforms 4 are provided with corresponding matching through holes 5. The lowering rope is passed through the matching through holes 5 on the two annular platforms 4 to smoothly lower the liquid level sensor into the liquid and ensure that the liquid level sensor remains vertical during the lowering process. The column 1 can be provided with multiple layers of fiber optic rings 3 (not shown in the figure). One free end of each layer of fiber optic ring 3 is connected to each other. The other free end of the uppermost or lowermost fiber optic ring 3 passes through the through hole on the column 1 or the through hole 5 on the annular platform 4. After passing through the through hole on the column 1 or the through hole 5 on the annular platform 4, the through hole or through hole is sealed to prevent liquid from flowing into the column 1.

[0042] This invention extends annular platforms outward from both ends of the column. Corresponding through holes are provided on the two annular platforms. After the rope is lowered through the matching through holes, it can ensure that the hydraulic sensor is smoothly lowered into the liquid and remains vertical throughout the lowering process. This invention also sets up multiple layers of fiber optic rings inside the column. The planes of each layer of fiber optic rings are parallel, which can further increase the curvature of the fiber optic rings under the same hydraulic pressure, thereby improving the resolution of liquid level detection.

[0043] The network analyzer obtains the ring-down signal based on the amplitude and phase frequencies of the electrical signal. It determines the liquid level of the level sensor based on the light propagation time or light transmission distance at which the ring-down signal decays to a corresponding threshold. Specifically, this includes: the network analyzer converts the amplitude frequency signal of the electrical signal from decibels (dB) to an amplitude value, unwinds the phase frequency signal of the electrical signal, and compares the converted amplitude frequency signal with the unwound phase frequency signal (e.g.,...). Figure 5 Perform an inverse Fourier transform on the signal (as shown) to obtain the time-domain oscillation signal, such as... Figure 6 As shown, the liquid level of the level sensor is determined by the light propagation time or light transmission distance when the decaying signal attenuates to 1 / e of the electrical signal. The liquid level at the surface can be 0, and the level increases closer to the bottom.

[0044] When measuring liquid level, if the depth of the container to be measured is known, and the liquid level inside the container gradually decreases or increases, the liquid level sensor is lowered to the bottom of the container. As the liquid level increases, the hydraulic pressure at the bottom of the container increases, resulting in a higher liquid level. Conversely, as the liquid level decreases, the hydraulic pressure at the bottom of the container decreases, resulting in a lower liquid level. Therefore, based on the liquid level at the bottom of the container and the shape and volume of the container, the current amount of liquid stored in the container can be obtained. This invention, when the depth of the container is known, allows the determination of the current amount of liquid stored in the container by lowering the liquid level sensor to the bottom and considering the liquid level at the bottom of the container and the shape and volume of the container.

[0045] When measuring liquid level, if it is necessary to detect the position of the liquid surface, the liquid level sensor can be lowered to any position within the liquid. Subtracting the liquid level from the lowered distance gives the vertical distance between the liquid surface and the lowered position. Therefore, this invention can also achieve liquid surface position detection.

[0046] As can be seen from the above embodiments, when detecting liquid level based on hydraulic pressure, the present invention first modulates the laser signal using a modulation signal, and then transmits the modulated optical microwave to the optical fiber in the liquid level sensor for liquid level detection. The optical microwave allows for faster response speed in liquid level detection, significantly reducing the requirements for the light source, and also makes the liquid level detection system less susceptible to phase and polarization effects. When the hydraulic pressure causes the optical fiber in the liquid level sensor to bend, the optical microwave experiences intensity attenuation each time it passes through the fiber. This attenuation process cyclically occurs within the decaying fiber cavity until a resonant signal is formed within the cavity. Therefore, it is evident that… Because the degree of bending of the optical fiber is relatively small, the intensity attenuation of the optical microwave passing through the fiber is also relatively small. During the cyclic transmission of the optical microwave in the decaying fiber cavity, the intensity attenuation can continuously accumulate and increase. Therefore, this invention has a high resolution for liquid level. In addition, this invention determines the liquid level based on the degree of bending of the optical fiber, not the amount of stretching. Compared with the amount of stretching, the range of variation of the amount of bending is wider. Therefore, the liquid level measurement range of this invention is wider. Moreover, compared with the influence of liquid level on the amount of bending, the influence of temperature on the amount of bending is negligible. Therefore, this invention also has good temperature insensitivity.

[0047] See Figure 7 This is a schematic diagram of another embodiment of the liquid level measurement system based on an optically carried microwave oscillation fiber cavity according to the present invention. Figure 7 and Figure 1The difference in the illustrated embodiment is that it may also include a first optical amplifier EDFA1, a second optical amplifier EDFA2, a circulator Cir, and a fiber optic grating FBG. The first optical amplifier EDFA1 is located between the output of the electro-optic modulator EOM and the first input of the first coupler C1. The other end of the optical fiber in the liquid level sensor is connected to the input of the second optical amplifier EDFA2. The output of the second optical amplifier EDFA2 is connected to the first end of the circulator Cir. The second end of the circulator Cir is connected to the fiber optic grating FBG, and the third end is connected to the input of the second coupler C2. The reflected wavelength of the fiber optic grating FBG is the same as the wavelength of the laser signal, so as to filter out signals of other wavelengths besides the signal corresponding to that wavelength.

[0048] This invention can compensate for the inherent loss of optical microwaves by setting up a first optical amplifier and a second optical amplifier. By setting up a circulator and a fiber optic grating, it can filter out other wavelength signals that are different from the wavelength of the optical microwaves, such as spontaneous emission noise introduced by the optical amplifier.

[0049] Additionally, the present invention may include an optical time-division multiplexer (not shown in the figure), the output of which can be connected to the input of the optical time-division multiplexer, and each output of the optical time-division multiplexer connected to the input of the second coupler via a liquid level sensor. The present invention configures the optical time-division multiplexer such that each output of the optical time-division multiplexer is connected to a liquid level sensor, sequentially providing optically carried microwaves to each liquid level sensor, thereby enabling sequential measurement of the liquid levels in multiple different containers under test.

[0050] As can be seen from the above embodiments, when detecting liquid level based on hydraulic pressure, the present invention first modulates the laser signal using a modulation signal, and then transmits the modulated optical microwave to the optical fiber in the liquid level sensor for liquid level detection. The optical microwave allows for faster response speed in liquid level detection, significantly reducing the requirements for the light source, and also makes the liquid level detection system less susceptible to phase and polarization effects. When the hydraulic pressure causes the optical fiber in the liquid level sensor to bend, the optical microwave experiences intensity attenuation each time it passes through the fiber. This attenuation process cyclically occurs within the decaying fiber cavity until a resonant signal is formed within the cavity. Therefore, it is evident that… Because the degree of bending of the optical fiber is relatively small, the intensity attenuation of the optical microwave passing through the fiber is also relatively small. During the cyclic transmission of the optical microwave in the decaying fiber cavity, the intensity attenuation can continuously accumulate and increase. Therefore, this invention has a high resolution for liquid level. In addition, this invention determines the liquid level based on the degree of bending of the optical fiber, not the amount of stretching. Compared with the amount of stretching, the range of variation of the amount of bending is wider. Therefore, the liquid level measurement range of this invention is wider. Moreover, compared with the influence of liquid level on the amount of bending, the influence of temperature on the amount of bending is negligible. Therefore, this invention also has good temperature insensitivity.

[0051] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0052] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is defined solely by the appended claims.

Claims

1. A liquid level measurement system based on an optically-borne microwave ring-down fiber cavity, characterized in that, The device includes a laser, an electro-optic modulator, a network analyzer, a ring-down fiber cavity, and a photodetector. A liquid level sensor is installed inside the ring-down fiber cavity. The electro-optic modulator modulates the laser signal output by the laser based on the modulation signal provided by the network analyzer to obtain optical microwaves, which are then transmitted to the optical fiber inside the liquid level sensor. Different liquid levels correspond to different hydraulic pressures, causing the optical fiber to bend to different degrees, thus resulting in different degrees of intensity attenuation of the optical microwaves after passing through the optical fiber. The optical microwave continuously circulates within the decaying fiber cavity, and its intensity decreases each time it passes through the fiber. After reaching equilibrium through its circulatory transmission within the decaying fiber cavity, it forms a resonant signal. This resonant signal is then transmitted to the photodetector for photoelectric conversion, generating an electrical signal. The network analyzer obtains the oscillation signal based on the amplitude and phase frequency signals of the electrical signal, and determines the liquid level of the liquid level sensor based on the light propagation time or light transmission distance of the oscillation signal attenuated to the corresponding threshold.

2. The liquid level measurement system based on an optically carried microwave ring-down fiber cavity according to claim 1, characterized in that, The ring-down fiber cavity includes a first coupler, a liquid level sensor, and a second coupler. The two inputs of the electro-optic modulator are respectively connected to the modulation signal outputs of the laser and the network analyzer, and its output is connected to the first input of the first coupler. The output of the first coupler is connected to one end of the optical fiber in the liquid level sensor, and the other end of the optical fiber is connected to the input of the second coupler. The first output of the second coupler is connected to the input of the network analyzer through the photodetector, and its second output is connected to the second input of the first coupler.

3. The liquid level measurement system based on an optically carried microwave ring-down fiber cavity according to claim 1 or 2, characterized in that, The liquid level sensor includes a column with openings at both ends. The left and right ends of the column are sealed with thin films. The optical fiber is disposed in the column in the form of an optical fiber loop and is fixedly connected to the two thin films. In the initial state before being inserted into the liquid, the planes of the thin films at both ends of the column and the plane of the optical fiber loop are flat, and the planes of the two thin films are perpendicular to the plane of the optical fiber loop. When the hydraulic sensor is vertically inserted into the liquid, the planes of the two thin films are perpendicular to the liquid surface and enter the liquid. After vertical insertion into the liquid, under the action of hydraulic pressure, the two thin films deform towards the inside of the column, thereby causing the optical fiber loop to bend.

4. The liquid level measurement system based on an optically carried microwave ring-down fiber cavity according to claim 3, characterized in that, In its initial state before liquid insertion, the fiber optic ring is rectangular, with its left and right sides fixedly connected to two thin films respectively. After vertical insertion into the liquid, under hydraulic pressure, the fiber optic ring transforms into a fiber optic ring with arc-shaped sides. The fiber optic ring is located at least at the midpoint of the two thin films in the vertical direction.

5. The liquid level measurement system based on an optically carried microwave ring-down fiber cavity according to claim 4, characterized in that, The column extends outward from its left and right ends to form annular platforms. Each annular platform is on the same plane as its corresponding end. The two annular platforms are provided with corresponding matching through holes. The lowering rope is inserted into the matching through holes on the two annular platforms to smoothly lower the liquid level sensor into the liquid and ensure that the liquid level sensor remains vertical during the lowering process. The column contains multiple layers of fiber optic rings, with one free end of each layer connected to the other. The other free end of the uppermost or lowermost fiber optic ring passes through a through hole on the column or a through hole on the annular platform. After passing through the through hole on the column or the through hole on the annular platform, the through hole or through hole is sealed to prevent liquid from flowing into the column.

6. The liquid level measurement system based on an optically carried microwave ring-down fiber cavity according to claim 1, characterized in that, The network analyzer obtains the oscillation signal based on the amplitude and phase frequency signals of the electrical signal. Based on the light propagation time or light transmission distance at which the oscillation signal decays to a corresponding threshold, it determines the specific liquid level at which the liquid level sensor is located, including: The network analyzer converts the amplitude-frequency signal of the electrical signal from dB to amplitude form, unwraps the phase-frequency signal of the electrical signal, and performs inverse Fourier transform on the converted amplitude-frequency signal and the unwrapped phase-frequency signal to obtain the time-domain oscillation signal. The liquid level of the liquid level sensor is determined by the light propagation time or light transmission distance when the decaying signal decays to 1 / e of the electrical signal.

7. The liquid level measurement system based on an optically carried microwave ring-down fiber cavity according to claim 2, characterized in that, It also includes a first optical amplifier and a second optical amplifier, a circulator and a fiber optic grating. The first optical amplifier is located between the output of the electro-optic modulator and the first input of the first coupler. The other end of the optical fiber in the liquid level sensor is connected to the input of the second optical amplifier, and the output of the second optical amplifier is connected to the input of the second coupler.

8. The liquid level measurement system based on an optically carried microwave ring-down fiber cavity according to claim 7, characterized in that, It also includes a circulator and a fiber Bragg grating. The output of the second optical amplifier is connected to the first end of the circulator, the second end of the circulator is connected to the fiber Bragg grating, and the third end is connected to the input of the second coupler. The reflected wavelength of the fiber Bragg grating is the same as the wavelength of the laser signal, so as to filter out signals of other wavelengths except for the signal corresponding to that wavelength.

9. The liquid level measurement system based on an optically carried microwave ring-down fiber cavity according to claim 1, characterized in that, The liquid level is 0, and the liquid level increases closer to the bottom. When measuring the liquid level, if the depth of the container to be measured is known, and the liquid in the container will gradually decrease or increase, the liquid level sensor is lowered to the bottom of the container to be measured. Based on the size of the liquid level at the bottom of the container to be measured and the shape and volume of the container, the amount of liquid currently stored in the container to be measured can be obtained. When measuring liquid level, if it is necessary to detect the position of the liquid surface, the liquid level sensor is lowered to any position in the liquid. The vertical distance between the liquid surface and the lowered position is obtained by subtracting the liquid level of the sensor from the lowered distance.

10. The liquid level measurement system based on an optically carried microwave ring-down fiber cavity according to claim 1, characterized in that, It also includes an optical time-division multiplexer, the output of the first coupler is connected to the input of the optical time-division multiplexer, and each output of the optical time-division multiplexer is connected to the input of the second coupler through a liquid level sensor.

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