A fiber optic liquid level sensor capable of identifying the direction of liquid flow

Abstract

The present invention discloses an optical fiber liquid level sensor capable of distinguishing the flow direction of liquid, comprising: a first optical fiber jumper, a second optical fiber jumper, a first single-mode optical fiber, a second single-mode optical fiber, a first tubular hollow-core optical fiber and a second tubular hollow-core optical fiber, wherein the first optical fiber jumper, the first single-mode optical fiber, the first tubular hollow-core optical fiber, the second tubular hollow-core optical fiber, the second single-mode optical fiber and the second optical fiber jumper are connected in sequence. The optical fiber liquid level sensor of the present invention uses the anti-resonance light guiding principle of light, constructs two different anti-resonance light guiding conditions by compounding two sections of hollow-core optical fibers with different air core diameters, and can realize micron-level precision monitoring of liquid level changes in the optical fiber axis by comparing the changes in the intensity of different types of resonance peaks generated by the detection light beam in the optical fiber sensor, and can distinguish the flow direction of liquid at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of liquid level sensing equipment, and in particular to an optical fiber liquid level sensor capable of identifying the flow direction of liquid. Background Art

[0002] Microfluidics is a technology for transporting fluids in microchannels (usually with sizes ranging from hundreds of micrometers to hundreds of nanometers). It is widely used in chemical synthesis, drug development, bioanalysis, microelectronics and other fields. Liquid level monitoring in microfluidic devices is conducive to the precise control and evaluation of liquid flow, but liquid level detection in microfluidic devices requires sensors with small size, high sensitivity and the ability to identify the direction of liquid flow. Traditional mechanical liquid level sensors are large in size, low in sensitivity, and cannot automatically record liquid level information, making them inconvenient to operate. Traditional electrical liquid level sensors can realize automatic data collection, but they still have the disadvantages of large size and low sensitivity. At the same time, electrical sensors have greater safety risks when measuring the liquid level of flammable and conductive liquids. Therefore, both traditional mechanical and electrical liquid level sensors are difficult to meet the liquid level detection needs in microfluidic devices. Fiber optic liquid level sensors are based on optical methods and are inherently safe. They have the advantages of light weight, small size, high sensitivity, resistance to electromagnetic interference, corrosion resistance, and ease of remote control and measurement. They are expected to solve the problem of liquid level detection in microfluidic devices. However, the reported fiber optic liquid level sensors still have the problem of low sensitivity and inability to distinguish the direction of liquid flow. Summary of the invention

[0003] The embodiment of the present invention provides an optical fiber liquid level sensor capable of identifying the flow direction of liquid, aiming to solve the problem that the liquid level sensor in the prior art method has low measurement sensitivity and cannot determine the flow direction of liquid.

[0004] The embodiment of the present invention provides an optical fiber liquid level sensor capable of identifying the flow direction of liquid, which includes: a first optical fiber jumper, a second optical fiber jumper, a first single-mode optical fiber, a second single-mode optical fiber, a first tubular hollow-core optical fiber, and a second tubular hollow-core optical fiber;

[0005] The input end of the first optical fiber jumper is connected to a broadband light source, the output end of the first optical fiber jumper is connected to the input end of the first single-mode optical fiber, the broadband light source is used to provide broadband light, the first optical fiber jumper is used to introduce the broadband light into the first single-mode optical fiber, the output end of the first single-mode optical fiber is connected to the second tubular hollow-core optical fiber through the first tubular hollow-core optical fiber, the second tubular hollow-core optical fiber is connected to the input end of the second single-mode optical fiber, and the output end of the second single-mode optical fiber is connected to the input end of the second optical fiber jumper;

[0006] The first single-mode optical fiber includes a first single-mode optical fiber core and a first silica cladding, and the second single-mode optical fiber includes a second single-mode optical fiber core and a second silica cladding; the first silica cladding covers the first single-mode optical fiber core, and the second silica cladding covers the second single-mode optical fiber core;

[0007] The first tubular hollow core optical fiber comprises a first air core and a third silica cladding, wherein the third silica cladding covers the first air core; the second tubular hollow core optical fiber comprises a second air core and a fourth silica cladding, wherein the fourth silica cladding covers the second air core;

[0008] The third quartz cladding forms a first radial Fabry-Perot resonant cavity, and the fourth quartz thin layer forms a second radial Fabry-Perot resonant cavity; the broadband light propagates in the first radial Fabry-Perot resonant cavity and excites to generate a first type of resonant peak, and propagates in the second radial Fabry-Perot resonant cavity and excites to generate a second type of resonant peak;

[0009] The output end of the second optical fiber jumper is connected to the spectrometer, and the second optical fiber jumper is used to introduce the optical signal after the broadband light is modulated by the first and second radial Fabry-Perot resonant cavities into the spectrometer.

[0010] The optical fiber liquid level sensor capable of identifying the direction of liquid flow, wherein the connection between the first tubular hollow-core optical fiber and the output end of the first single-mode optical fiber, the connection between the first tubular hollow-core optical fiber and the second tubular hollow-core optical fiber, and the connection between the second tubular hollow-core optical fiber and the input end of the second single-mode optical fiber are all core alignment fusion splicing.

[0011] The optical fiber liquid level sensor capable of identifying the flow direction of liquid, wherein the diameter of the first air core is larger than the diameter of the first single-mode optical fiber core, and the diameter of the second air core is larger than the diameter of the second single-mode optical fiber core.

[0012] The optical fiber liquid level sensor capable of identifying the flow direction of liquid, wherein the thickness of the third quartz cladding is different from the thickness of the fourth quartz cladding.

[0013] In the optical fiber liquid level sensor capable of identifying the flow direction of liquid, the refractive index of the first air core is smaller than the refractive index of the third quartz cladding, and the refractive index of the second air core is smaller than the refractive index of the fourth quartz cladding.

[0014] The above-mentioned optical fiber liquid level sensor capable of distinguishing the direction of liquid flow comprises a first optical fiber jumper, a second optical fiber jumper, a first single-mode optical fiber, a second single-mode optical fiber, a first tubular hollow-core optical fiber and a second tubular hollow-core optical fiber, wherein the first optical fiber jumper, the first single-mode optical fiber, the first tubular hollow-core optical fiber, the second tubular hollow-core optical fiber, the second single-mode optical fiber and the second optical fiber jumper are connected in sequence. The above-mentioned optical fiber liquid level sensor capable of distinguishing the direction of liquid flow utilizes the principle of anti-resonance light guiding of light, and constructs two different anti-resonance light guiding conditions by compounding two sections of hollow-core optical fibers with different air core diameters (different quartz cladding thicknesses). By comparing the changes in the intensity of different types of resonance peaks generated by the detection light beam in the optical fiber sensor, the liquid level change monitoring along the optical fiber axis with micron-level precision can be realized, and the direction of liquid flow can be distinguished at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0016] Figure 1 A structural diagram of an optical fiber liquid level sensor capable of identifying the flow direction of liquid provided by an embodiment of the present invention;

[0017] Figure 2 A cross-sectional structural diagram of an optical fiber liquid level sensor capable of identifying the flow direction of liquid provided by an embodiment of the present invention;

[0018] Figure 3 Another cross-sectional structural diagram of the optical fiber liquid level sensor capable of identifying the flow direction of liquid provided by an embodiment of the present invention;

[0019] Figure 4 A schematic diagram of the propagation path of the detection light beam of the optical fiber liquid level sensor capable of identifying the flow direction of liquid provided by an embodiment of the present invention;

[0020] Figure 5 A schematic diagram of the effect of the optical fiber liquid level sensor capable of identifying the flow direction of liquid provided by an embodiment of the present invention;

[0021] Figure 6 A schematic diagram of the effect of the optical fiber liquid level sensor capable of identifying the flow direction of liquid provided by an embodiment of the present invention;

[0022] Figure 7 A schematic diagram of the effect of an optical fiber liquid level sensor capable of identifying the flow direction of liquid provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0025] It should also be understood that the terms used in the present specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an" and "the" are intended to include plural forms unless the context clearly indicates otherwise.

[0026] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0027] See also Figures 1 to 4As shown in the figure, an optical fiber liquid level sensor capable of distinguishing the flow direction of liquid comprises: a first optical fiber jumper 1, a second optical fiber jumper 2, a first single-mode optical fiber 3, a second single-mode optical fiber 4, a first tubular hollow-core optical fiber 5 and a second tubular hollow-core optical fiber 6; the input end of the first optical fiber jumper 1 is connected to a broadband light source, the output end of the first optical fiber jumper 1 is connected to the input end of the first single-mode optical fiber 3, the broadband light source is used to provide broadband light, the first optical fiber jumper 1 is used to introduce the broadband light into the first single-mode optical fiber 3, the output end of the first single-mode optical fiber 3 is connected to the second tubular hollow-core optical fiber 6 through the first tubular hollow-core optical fiber 5, the second tubular hollow-core optical fiber 6 is connected to the input end of the second single-mode optical fiber 4, and the output end of the second single-mode optical fiber 4 is connected to the input end of the second optical fiber jumper 2 The first single-mode optical fiber 3 includes a first single-mode optical fiber core 31 and a first silica cladding 32, and the second single-mode optical fiber 4 includes a second single-mode optical fiber core 41 and a second silica cladding 42; the first silica cladding 32 covers the first single-mode optical fiber core 31, and the second silica cladding 42 covers the second single-mode optical fiber core 41; the first tubular hollow-core optical fiber 5 includes a first air core 51 and a third silica cladding 52, and the third silica cladding 52 covers the first air core 51; the second tubular hollow-core optical fiber 6 includes a second air core 61 and a fourth silica cladding 62, and the fourth silica cladding 62 covers the second air core 61; the refractive index of the first air core 51 is less than the refractive index of the third silica cladding 52, and the refractive index of the second air core 61 is less than the refractive index of the fourth silica cladding 62.

[0028] The optical fiber liquid level sensor capable of distinguishing the flow direction of liquid provided in this embodiment is a liquid level sensor based on a composite of two hollow core optical fibers with different air core diameters. The specific structure is as follows: Figure 1 As shown, Figure 1 It is a structural schematic diagram of the optical fiber liquid level sensor capable of distinguishing the flow direction of liquid, wherein the first optical fiber jumper 1 is connected to the first single-mode optical fiber 3 core pair, the first single-mode optical fiber core 31 is connected to the first air core 51, the first air core 51 is connected to the second air core 61, the second air core 61 is connected to the second single-mode optical fiber core 41, and the second single-mode optical fiber 4 is connected to the second optical fiber jumper 2 core pair. The third quartz cladding 52 forms a first radial Fabry-Perot resonant cavity, and the fourth quartz cladding 62 forms a second radial Fabry-Perot resonant cavity; the broadband light propagates in the first radial Fabry-Perot resonant cavity and excites the generation of a first type of resonant peak, and propagates in the second radial Fabry-Perot resonant cavity and excites the generation of a second type of resonant peak; the output end of the second optical fiber jumper is connected to a spectrometer, and the second optical fiber jumper is used to introduce the optical signal after the broadband light is modulated by the first and second radial Fabry-Perot resonant cavities into the spectrometer.

[0029] Among them, due to the reflection and refraction of the first radial Fabry-Perot resonant cavity, the first type of anti-resonance light guiding effect can be generated when the incident broadband light passes through the first air core 51; reflection and refraction will also occur in the second radial Fabry-Perot resonant cavity, and the second type of anti-resonance light guiding effect can be generated when the incident light passes through the second air core 61. The above broadband light source (broad-spectrum light) propagates and excites the first type of resonance peak under the condition of the first type of anti-resonance light guiding effect, and propagates and excites the second type of resonance peak under the condition of the second type of anti-resonance light guiding effect. There are differences in the central wavelength and free spectral range of the first type of resonance peak and the second type of resonance peak. The generated optical signal can be introduced into the spectrometer to display the first type of resonance peak and the second type of resonance peak on the spectrometer.

[0030] In a specific implementation process, when the liquid level moves along the first tubular hollow-core fiber 5 to the second tubular hollow-core fiber 6, the first tubular hollow-core fiber 5 is immersed, causing the resonance condition of the first radial Fabry-Perot resonant cavity to change, and the intensity of the first type of resonance peak excited by it changes, while the second tubular hollow-core fiber is not immersed in the air, and the intensity of the second type of resonance peak excited by it is almost unchanged; when the liquid level moves along the second tubular hollow-core fiber to the first tubular hollow-core fiber, the second tubular hollow-core fiber is immersed, causing the resonance condition of the second radial Fabry-Perot resonant cavity to change, and the intensity of the second type of resonance peak excited by it changes, while the first tubular hollow-core fiber is not immersed in the air, and the intensity of the first type of resonance peak excited by it is almost unchanged. Therefore, it can be used to identify the direction of the fluid immersion level sensor and measure the actual liquid level on the outer surface of the sensor at the same time.

[0031] In a specific embodiment, the connection between the first tubular hollow-core optical fiber 5 and the output end of the first single-mode optical fiber 3, the connection between the first tubular hollow-core optical fiber 5 and the second tubular hollow-core optical fiber 6, and the connection between the second tubular hollow-core optical fiber 6 and the input end of the second single-mode optical fiber 4 are all core-aligned fusion splicing. During fusion splicing, the collapse of the third quartz cladding 52 of the first tubular hollow-core optical fiber 5 and the fourth quartz cladding 62 of the second tubular hollow-core optical fiber 6 is avoided as much as possible. Other interfaces can be connected by fusion splicing or flanges.

[0032] The first quartz cladding 32 is coated on the outside of the first single-mode optical fiber core 31, the third quartz cladding 52 is coated on the outside of the first air core 51, the fourth quartz cladding 62 is coated on the outside of the second air core 61, and the second quartz cladding 42 is coated on the outside of the second single-mode optical fiber core 41. When the incident light passes through the third quartz cladding 52 and the first air core 51, a first type of anti-resonance light guiding effect is formed, and when the incident light passes through the fourth quartz cladding 62 and the second air core 61, a second type of anti-resonance light guiding effect is formed; the radial cross-sections of the first optical fiber jumper 1, the first single-mode optical fiber 3, the first tubular hollow-core optical fiber 5, the second tubular hollow-core optical fiber 6, the second single-mode optical fiber 4 and the second optical fiber jumper 2 are all circular, wherein the radial cross-section of the first tubular hollow-core optical fiber 5 is as shown in FIG. Figure 2 As shown, the radial cross section of the second tubular hollow core optical fiber 6 is as follows Figure 3 As shown; the broadband light source couples the incident light into the optical fiber liquid level sensor through the first optical fiber jumper 1. Since the refractive index of the third quartz cladding 52 is greater than the refractive index of the first air core 51, the incident light is reflected and refracted multiple times in the first air core 51 and the third quartz cladding 52 of the first tubular hollow core optical fiber 5; then the incident light is coupled into the second tubular hollow core optical fiber 6, reflected and refracted multiple times in the second air core 61 and the fourth quartz cladding 62, and finally coupled into the second single-mode optical fiber core 41. The specific propagation optical path is as follows: Figure 4 As shown. Specifically, the third quartz cladding 52 of the first tubular hollow-core optical fiber 5 forms a first radial Fabry-Perot resonant cavity. When the incident light passes through the air core 51 of the first hollow-core optical fiber 5, if the wavelength of the incident light meets the resonance condition of the first radial Fabry-Perot resonant cavity, the incident light will be greatly leaked in the air core 51, forming a first type of strong resonance peak in the transmission spectrum. Otherwise, when the anti-resonance condition is met, the incident light will be confined in the air core 51 and continue to propagate forward. Similarly, when the incident light passes through the air core 61 of the second hollow-core optical fiber 6, if the wavelength of the incident light meets the resonance condition of the second radial Fabry-Perot resonant cavity, the incident light will be greatly leaked in the hollow core 61, forming a second type of strong resonance peak in the transmission spectrum. Otherwise, when the anti-resonance condition is met, the incident light will be confined in the air core 61 and continue to propagate forward.

[0033] In a specific embodiment, the refractive index of the first air core 51 is less than the refractive index of the third silica cladding 52, and the refractive index of the second air core 61 is less than the refractive index of the fourth silica cladding 62. Specifically, the refractive indexes of the first air core 51 and the second air core 61 are both 1.0, the refractive indexes of the first silica cladding 32, the second silica cladding 42, the third silica cladding 52 and the fourth silica cladding 62 are all 1.447, and the refractive indexes of the first single-mode fiber core 31 and the second single-mode fiber core 41 are both 1.45. This design can ensure that the incident light forms an anti-resonance light guiding effect after entering the first tubular hollow core fiber 5 and the second tubular hollow core fiber 6.

[0034] In a specific embodiment, the total length of the first tubular hollow-core optical fiber 5 can be set to 2-10 mm, and the total length of the second tubular hollow-core optical fiber 6 can be set to 1-5 mm. In order to make the resonance peak quality displayed in the spectrometer higher, the lengths of the first tubular hollow-core optical fiber 5 and the second tubular hollow-core optical fiber 6 can be set within a certain length range, and the ratio of the lengths of the first tubular hollow-core optical fiber 5 and the second tubular hollow-core optical fiber 6 can also be set within a certain ratio range, such as the ratio of the lengths of the first tubular hollow-core optical fiber 5 and the second tubular hollow-core optical fiber 6 can be set to 1.5-2.8; specifically, the length of the first tubular hollow-core optical fiber 5 can be set to 4.5 mm, and the length of the second tubular hollow-core optical fiber 6 can be set to 2 mm.

[0035] In a specific embodiment, the diameter of the first air core 51 is greater than the diameter of the first single-mode optical fiber core 31, and the diameter of the second air core 61 is greater than the diameter of the second single-mode optical fiber core 41. The diameter of the first air core 51 is greater than the diameter of the second air core 61.

[0036] In a specific embodiment, the outer diameters of the first quartz cladding 32 and the second quartz cladding 42 are equal, and the outer diameters of the third quartz cladding 52 and the fourth quartz cladding 62 are equal.

[0037] In a specific embodiment, the diameter of the first air core 51 can be set to 30-50 μm, and the diameter of the second air core 61 can be set to 20-50 μm. Specifically, the diameter of the first air core 51 is designed to be 30 μm, and the diameter of the second air core 61 can be correspondingly set to be 20 μm, so as to ensure that the diameter of the first air core 51 is different from the diameter of the second air core 61 (or the thickness of the quartz cladding of the two hollow core optical fibers is different). Specifically, the outer diameters of the first quartz cladding 32 and the second quartz cladding 42 can be set to 125 μm, and the outer diameters of the third quartz cladding 52 and the fourth quartz cladding 62 can be set to 126 μm, that is, in the specific application process, the outer diameter of the third quartz cladding 52 can be set to be slightly larger than the outer diameter of the first quartz cladding 32. This design can ensure that the thickness of the third quartz cladding is less than the thickness of the fourth quartz cladding, and can ensure that the incident light forms different anti-resonance light guiding effects after entering the first tubular hollow core optical fiber 5 and the second tubular hollow core optical fiber 6.

[0038] In order to verify the function of the optical fiber liquid level sensor in the embodiment of this case to calibrate the direction of liquid flow and measure the liquid level on the outer surface of the sensor in actual application, this case designs a set of control experiments using the optical fiber liquid level sensor in the opposite direction of liquid flow, such as Figure 5 As shown, dip-30 represents the first type of resonance peak, dip-20 represents the second type of resonance peak, the optical fiber liquid level sensor is fixedly placed in a transparent plastic hose, water is used as the liquid to be measured, the change of the liquid level is controlled by a constant flow pump connected to the plastic hose, and an optical microscope is used to measure the liquid level on the outer surface of the optical fiber liquid level sensor. The forward flow direction of the liquid is set as the liquid flowing from the first tubular hollow-core optical fiber to the second tubular hollow-core optical fiber, and the reverse flow direction of the liquid is set as the liquid flowing from the second tubular hollow-core optical fiber to the first tubular hollow-core optical fiber, as shown in the attached figure. Figure 5 As shown in Figures (a) and (b), when the liquid flows forward, the first tubular hollow-core fiber is immersed from the forward liquid level of 0μm, and the intensity of dip-30 gradually weakens, while the second tubular hollow-core fiber is not immersed, and the intensity of dip-20 does not change significantly. When the first tubular hollow-core fiber is completely immersed, and the second tubular hollow-core fiber is gradually immersed, as shown in the attached figure, Figure 5 As shown in Figures (c) and (d), the intensity of dip-30 did not change significantly, while the intensity of dip-20 gradually weakened. Figure 6 As shown in Figures (a) and (b), when the liquid flows in the reverse direction, the second tubular hollow-core fiber is immersed from the reverse liquid level of 0μm, and the intensity of dip-20 gradually weakens, while the first tubular hollow-core fiber is not immersed, and the intensity of dip-30 does not change significantly. When the second tubular hollow-core fiber is completely immersed, and the first tubular hollow-core fiber is gradually immersed, as shown in the attached figure, Figure 6As shown in Figures (c) and (d), the intensity of dip-20 does not change significantly, while the intensity of dip-30 gradually weakens. The intensity of dip-30 and dip-20 changes with the change of liquid level; in order to make the correlation between the liquid level and the change of resonance peak intensity obtained in the experiment clearer, as shown in the attached figure, Figure 7 As shown, the intensity change of the resonance peak in the forward and reverse flow directions of the liquid and the liquid level are recorded and linearly fitted, and the highest liquid level sensitivities of dip-30 and dip-20 in the forward and reverse flow directions of the liquid are obtained to be 0.005dB / μm and 0.014dB / μm respectively. Assuming that the resolution of the spectrometer for the change in the intensity of the resonance peak is 0.01dB, the detection accuracy of the liquid level sensor can reach 2 microns. It can be seen that the liquid level sensor has extremely high liquid level sensitivity. The optical fiber liquid level sensor of the hollow-core optical fiber with two sections of composite air cores of different diameters (inconsistent cladding thickness) proposed in the embodiment of this case ensures the detection accuracy of liquid level sensing and the reliability of the sensor operation. The first type of resonance peak and the second type of resonance peak can also be used as the calibration of the liquid flow direction during the operation of the optical fiber liquid level sensor in this embodiment, so that the liquid level measurement and the identification of the liquid flow direction can be carried out simultaneously.

[0039] The optical fiber liquid level sensor capable of distinguishing the flow direction of liquid provided in the embodiment of the present invention comprises a first optical fiber jumper, a second optical fiber jumper, a first single-mode optical fiber, a second single-mode optical fiber, a first tubular hollow-core optical fiber and a second tubular hollow-core optical fiber, wherein the first optical fiber jumper, the first single-mode optical fiber, the first tubular hollow-core optical fiber, the second tubular hollow-core optical fiber, the second single-mode optical fiber and the second optical fiber jumper are connected in sequence. The above-mentioned optical fiber liquid level sensor capable of distinguishing the flow direction of liquid uses the principle of anti-resonance light guiding of light to compound two hollow-core optical fibers with different diameters of air cores, and constructs two different types of resonance conditions, so that the incident broadband light generates different types of resonance peaks under the two resonance conditions and appears in the spectrometer. Since the optical fiber liquid level sensor uses two different types of hollow-core optical fibers, it is equivalent to compounding two sensors, and the change of the liquid level in the axial direction of the optical fiber and the detection of the flow direction of the liquid can be realized by comparing the changes in the intensity of different types of resonance peaks generated by the detection light beam in the optical fiber sensor; the hollow-core optical fiber is selected to prepare the liquid level sensor, which simplifies the preparation process of the liquid level sensor and reduces the preparation cost. At the same time, the micron-level liquid level detection accuracy can be achieved, which greatly improves the accuracy of liquid level detection.

[0040] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. An optical fiber liquid level sensor capable of identifying the flow direction of liquid, characterized in that: include: A first optical fiber jumper, a second optical fiber jumper, a first single-mode optical fiber, a second single-mode optical fiber, a first tubular hollow-core optical fiber, and a second tubular hollow-core optical fiber; The input end of the first optical fiber jumper is connected to a broadband light source, the output end of the first optical fiber jumper is connected to the input end of the first single-mode optical fiber, the broadband light source is used to provide broadband light, the first optical fiber jumper is used to introduce the broadband light into the first single-mode optical fiber, the output end of the first single-mode optical fiber is connected to the second tubular hollow-core optical fiber through the first tubular hollow-core optical fiber, the second tubular hollow-core optical fiber is connected to the input end of the second single-mode optical fiber, and the output end of the second single-mode optical fiber is connected to the input end of the second optical fiber jumper; The first single-mode optical fiber includes a first single-mode optical fiber core and a first silica cladding, and the second single-mode optical fiber includes a second single-mode optical fiber core and a second silica cladding; the first silica cladding covers the first single-mode optical fiber core, and the second silica cladding covers the second single-mode optical fiber core; The first tubular hollow core optical fiber comprises a first air core and a third silica cladding, wherein the third silica cladding covers the first air core; The second tubular hollow core optical fiber comprises a second air core and a fourth silica cladding, wherein the fourth silica cladding covers the second air core; The third quartz cladding forms a first radial Fabry-Perot resonant cavity, and the fourth quartz cladding forms a second radial Fabry-Perot resonant cavity; the broadband light propagates in the first radial Fabry-Perot resonant cavity and excites to generate a first type of resonant peak, and propagates in the second radial Fabry-Perot resonant cavity and excites to generate a second type of resonant peak; The output end of the second optical fiber jumper is connected to the spectrometer, and the second optical fiber jumper is used to introduce the optical signal after the broadband light is modulated by the first and second radial Fabry-Perot resonant cavities into the spectrometer; The diameter of the first air core is larger than the diameter of the first single-mode optical fiber core; the diameter of the second air core is larger than the diameter of the second single-mode optical fiber core; there are differences in the central wavelength and free spectral range of the first type of resonance peak and the second type of resonance peak. By introducing the generated optical signal into the spectrometer, the first type of resonance peak and the second type of resonance peak can be displayed on the spectrometer.

2. The optical fiber liquid level sensor capable of identifying the flow direction of liquid according to claim 1, characterized in that: The connection between the first tubular hollow-core optical fiber and the output end of the first single-mode optical fiber, the connection between the first tubular hollow-core optical fiber and the second tubular hollow-core optical fiber, and the connection between the second tubular hollow-core optical fiber and the input end of the second single-mode optical fiber are all core alignment fusion splicing.

3. The optical fiber liquid level sensor capable of identifying the flow direction of liquid according to claim 1, characterized in that: The thickness of the third quartz cladding layer is different from the thickness of the fourth quartz cladding layer.

4. The optical fiber liquid level sensor capable of identifying the flow direction of liquid according to claim 1, characterized in that: The refractive index of the first air core is lower than that of the third silica cladding, and the refractive index of the second air core is lower than that of the fourth silica cladding.

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