CN107907491B - Optical fiber sensor and detection platform and method thereof - Google Patents
Optical fiber sensor and detection platform and method thereof Download PDFInfo
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- CN107907491B CN107907491B CN201711297513.3A CN201711297513A CN107907491B CN 107907491 B CN107907491 B CN 107907491B CN 201711297513 A CN201711297513 A CN 201711297513A CN 107907491 B CN107907491 B CN 107907491B
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Abstract
The invention discloses an optical fiber sensor, a detection platform and a detection method thereof, which belong to the technical field of optical fiber sensing. It may increase the sensitivity of the sensor. The platform comprises a support, the support is composed of a vertical surface and a horizontal surface, the vertical surface is provided with a fixing part for fixing the optical fiber probe, and the horizontal surface is provided with a cavity for bearing a container. Aiming at the problem of low detection sensitivity of the optical fiber sensor in the prior art, the common tapered optical fiber string is processed, so that the sensitivity of the tapered optical fiber sensor can be improved.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to an optical fiber sensor, a detection platform and a detection method thereof.
Background
Detection and analysis of temperature and liquid parameters are widely used in the petroleum, chemical, pharmaceutical, food and environmental monitoring industries, where detection of liquids includes a number of parameters such as composition, refractive index, concentration, surface tension, turbidity, pH, viscosity, and the like of the liquid. The liquid component detection method has a plurality of methods, besides the traditional physicochemical method, the spectrophotometry method, the liquid chromatography method and the like are widely applied, but most of the liquid detection methods have single functions, low detection efficiency and high cost. Fiber optic sensors have become a more practical method of measuring the refractive index and concentration of liquids, and microfibers have been increasingly found and widely used because of their sensitivity similar to fiber bragg grating-based sensors, while being relatively inexpensive to manufacture and relatively easier to manufacture (typically only requiring a fusion splicer). Recently, many microfiber structures have been reported, such as a Microfiber Loop Resonator (MLR), a Microfiber Coil Resonator (MCR), a microfiber knot resonator, a microfiber mach-zehnder interferometer (MMZI), and the like.
In the existing detection platforms, the sensitivity of the optical fiber sensor is improved by properly changing the optical fiber structure. It has been found that there are several methods used in changing the structure of the optical fiber: the sensitivity of the optical fiber sensor can be improved to a certain extent by tapering the common optical fiber, increasing the length of the evanescent field, or increasing a plurality of cone structures (evanescent fields), or changing the straight tapered optical fiber structure into a U-shaped probe structure, changing the transmission mode of light waves in the optical fiber into a reflection mode, and the like.
The paper Refractive Index Sensing With Mach-Zehnder Interferometer Based on Concatenating Two Single-Mode Fiber Tapers published on IEEE PHOTONICS TECHNOLOGY LETTERS, VOL.20, NO. on 4 and 15 of 2008, zhaoning Tian and the like research the high sensitivity characteristic of a tapered optical fiber string with a linear structure and are used for detecting the refractive index of liquid.
The paper Inline Microfiber Mach-Zehnder Interferometer for High Temperature Sensing, ali Abdulhadi Jasim published in IEEE SENSORS JOURNAL, VOL.13, NO.2 in 2013 and the like research the high temperature sensitivity characteristic of a tapered optical fiber string sensor based on Mach-Zehnder interference, and the common optical fiber is tapered to form a cone structure, and then the cone structure is tapered.
The paper Microcontroller-based instrumentation system for measurement of refractive index of liquid using bare, tapered and bent fibre as sensor, shakuntala Laskar published in 2013, 9 and 17-opt, which is based on a Microcontroller system, uses a bent cone-shaped multimode fiber sensor with a cladding removed, and bends the fiber into a U shape on a tapered section to form a probe so as to detect the refractive index of liquid; the paper mainly relates to the design of circuits, selection of components and connection.
Because the optical fiber is extremely easy to break, and the optical fiber of the evanescent field part is finer and more sensitive; therefore, no matter the linear type cone pulling structure or the U-shaped probe structure, the longer evanescent field of the sensor has the problem of inconvenient cleaning after one-time liquid detection is finished, and the cone pulling area is damaged during cleaning to influence the next liquid detection. The U-shaped structure is added to the tapered section, so that the processing difficulty is high, the requirement on consistency of tapered areas at two sides is high, the structure is complex, the packaging and the use of the sensor are more difficult, the realization difficulty in the actual operation is high, the popularization and the use are not realized, and the cost is high; in addition, when the tapered optical fiber with the linear structure is used for detecting small-scale trace liquid, the tapered optical fiber cannot be fully contacted with the liquid, and the detection is difficult; the optical fiber sensor with the structure cannot be popularized and used in occasions with higher sensitivity requirements.
Disclosure of Invention
1. Technical problem to be solved by the invention
Aiming at the problem of low detection sensitivity of an optical fiber sensor in the prior art, the invention provides an optical fiber sensor, a detection platform and a detection method thereof. The processing method is used for processing the common tapered optical fiber string, so that the sensitivity of the tapered optical fiber sensor can be improved.
2. Technical proposal
In order to solve the problems, the technical scheme provided by the invention is as follows:
the optical fiber sensor comprises an optical fiber probe, and further comprises a tapering region, wherein one end of the sensing region is sequentially connected with one tapering region and the incidence region, and the other end of the sensing region is sequentially connected with the other tapering region and one end of the optical fiber end. It may increase the sensitivity of the sensor.
Preferably, the tapering area include tapering area I and tapering area II, tapering area I one end be connected with sensing area one end, tapering area I other end be connected with the incidence district, tapering area II one end be connected with the sensing area other end, tapering area II other end be connected with the optic fibre end section.
Preferably, the fiber-optic probe comprises a cladding and a fiber core, wherein the fiber core is arranged in the cladding.
Preferably, a layer of metal film is arranged on the end face of the optical fiber end section, and a layer of metal film is arranged on the tapering region. It can obviously enhance the light intensity of the sensing area and is beneficial to improving the sensitivity.
Preferably, the sensing area is U-shaped.
Preferably, the sensing area comprises a sensing area I and a sensing area II, the sensing area II is U-shaped, one end of the sensing area II is sequentially connected with one sensing area I, the tapering area and the incident area, and the other end of the sensing area II is sequentially connected with the other sensing area I and the tail section of the optical fiber.
Preferably, the metal film is a gold film or a palladium-gold film.
The optical fiber sensor detection platform comprises a support, wherein the support is composed of a vertical surface and a horizontal surface, the vertical surface is provided with a fixing part for fixing the optical fiber probe, and the horizontal surface is provided with a cavity for bearing a container.
Preferably, the container is positioned in the concave hole, and the bottom of the container is communicated with the water filling port and the water outlet.
A detection method of an optical fiber sensor comprises the following steps:
A. respectively fixing two ends of the optical fiber sensor on the support of the optical fiber sensor detection platform;
B. the incidence area of the optical fiber probe is connected with a broadband light source and a spectrum analyzer through an optical fiber coupler; the broadband light source emits a light source, the light source passes through an incidence area, a sensing area and an optical fiber end section of the optical fiber probe, forms reflection through the end surface of the optical fiber end section, returns in an original path, finally reaches the spectrum analyzer through the optical fiber coupler, and the spectrum analyzer measures light source data;
C. and (3) temperature detection: placing the detection platform in an environment to be detected, and calculating the temperature according to the measurement result of the spectrum analyzer;
D. and (3) liquid detection: closing the water outlet, introducing liquid to be detected into the container through the water inlet until the liquid covers the sensing area of the optical fiber probe, and calculating liquid parameters according to the measurement result of the spectrum analyzer.
3. Advantageous effects
Compared with the prior art, the technical scheme provided by the invention has the following beneficial effects:
(1) According to the optical fiber sensor, the common tapered optical fiber string is processed, so that the sensitivity of the tapered optical fiber sensor can be improved;
(2) According to the optical fiber sensor detection platform, the water injection port and the water outlet are arranged on the transparent vessel, so that the liquid to be detected is prevented from sedimentation in the detection process, and the accuracy of a detection result is ensured; meanwhile, the U-shaped probe is cleaned in time, so that the liquid to be detected is detected more efficiently; therefore, the platform has simple operation process, can rapidly realize multiple sampling, has strong practicability and is convenient to clean;
(3) According to the optical fiber sensor detection method, the test temperature for detecting the liquid parameters is 25 ℃, the conical optical fiber string is very sensitive to the temperature, the temperature change can influence the detection result, the liquid is detected under the constant temperature condition (generally about 25 ℃ at room temperature) in the test, the ideal result can be better obtained, and the sensitivity of the interferometer to the temperature is greatly reduced;
(4) According to the detection method of the optical fiber sensor, two free ends (namely the optical fiber incidence area and the optical fiber end section) of the optical fiber probe are fixed by the two fixing clamping pieces on the bracket, so that uniform stress is ensured, and the influence of stress factors on cross sensitivity of liquid concentration detection of the sensor is reduced;
(5) The optical fiber sensor detection method has the advantages of small size, simple manufacturing process and higher sensitivity to temperature, pressure, refractive index and the like; the operation process is simple, multiple groups of samples can be rapidly realized, and experimental steps are greatly simplified; the manufacturing cost is lower.
Drawings
FIG. 1 is a schematic illustration of a fiber optic probe;
FIG. 2 is a second schematic diagram of a fiber optic probe;
FIG. 3 is a schematic diagram of a fiber optic sensor testing platform according to the present invention;
fig. 4 is a schematic view of a container.
Reference numerals in the schematic drawings illustrate:
100. an optical fiber probe; 11. an incidence area; 101. a cladding layer; 102. a fiber core; 12. a sensing region; 13. an optical fiber end section; 14; a tapering region; 121. a sensing region I; 122. a sensing region II; 141. the cone pulling area I; 142. a cone pulling area II; 1. a bracket; 2. a fixing part; 3. a container; 4. a bread board; 5. a broadband light source; 6. a spectrum analyzer; 8. a pit; 9. a water filling port; 10. and a water outlet 15 and an optical fiber coupler.
Detailed Description
For a further understanding of the present invention, the present invention will be described in detail with reference to the drawings and examples.
Example 1
The optical fiber sensor consists of an optical fiber probe 100, and comprises an incidence area 11, a sensing area 12, an optical fiber end section 13 and a tapering area 14, wherein one end of the sensing area 12 is sequentially connected with the tapering area 14 and the incidence area 11, and the other end of the sensing area 12 is sequentially connected with the other tapering area 14 and one end of the optical fiber end section 13.
The incident area 11 and the optical fiber end section 13 are of unprocessed optical fiber structures, the tapering area 14 and the sensing area 12 are processed, and when a liquid medium is placed in the sensing area 12, an evanescent field (formed around the tapering area 14 and the tapering area) interacts with the medium through absorption and scattering. In tapered fibers, a large portion of the evanescent wave travels in the cladding region and is therefore more sensitive to changes in the surrounding medium. The penetration depth of the evanescent wave, the sensing core diameter and the sensing length of the uniform sensing area are main influencing factors of the tapered optical fiber evanescent wave sensor. The sensitivity of the sensor depends on the amount of light reflection and the penetration depth of the evanescent field in the sensing region. To improve the sensitivity of the sensor, the configuration of the tapered fiber optic train is changed to a U-shaped probe shape, with the angle to the core/cladding interface normal at the outer surface of the bending region decreasing as light enters the bending region. The reduction of the value of the angle of the light in the sensing region increases the penetration depth and the number of evanescent ray reflections per unit length N, increasing the sensitivity of the sensor.
Example 2
An optical fiber sensor is further improved on the basis of embodiment 1, wherein the tapering region 14 comprises a tapering region I141 and a tapering region II142, one end of the tapering region I141 is connected with one end of the sensing region 12, the other end of the tapering region I141 is connected with the incident region 11, one end of the tapering region II142 is connected with the other end of the sensing region 12, and the other end of the tapering region II142 is connected with the optical fiber end section 13.
The optical fiber probe 100 comprises a cladding 101 and a fiber core 102, wherein the fiber core 102 is arranged in the cladding 101; the end face of the optical fiber end section 13 is provided with a layer of metal film, the tapering region 14 is provided with a layer of metal film, and the tapering region I141 and the tapering region II142 are respectively provided with a layer of metal film.
The metal film is gold film or palladium gold film, gold film is adopted, when the gold film is plated on the tapered optical fiber, the original projection measurement mode is changed into the reflection measurement mode, the electromagnetic field enhancement effect of the sensing area 12 can be utilized more effectively, the light output by the optical fiber sensing head passes through the sensing area again after being reflected, and the light returns to the original optical fiber and is finally received by the photoelectric detector, namely, the sensing length of the sensing area 12 is doubled and increased, meanwhile, the light intensity of the sensing area 12 can be enhanced obviously, and the sensitivity is improved.
A manufacturing method of an optical fiber sensor comprises the following steps:
A. the ordinary standard single mode fiber (SMF, core 102 and cladding 101 diameters of 60um and 125um respectively) is stripped of the cladding 101 and cleaned of the surface, the desired fiber taper is heated and tapered until the desired taper region 14 structure is obtained, and the taper parameters of the tapered fiber are controlled by special operating software.
B. And coating the tapered optical fiber.
C. The coated tapered optical fiber is bent to form a U-shaped structure, and the optical fiber probe 100 is manufactured.
Example 3
An optical fiber sensor is further improved on the basis of embodiment 1 or 2, wherein the sensing region 12 is U-shaped. As shown in fig. 1. Compared with the optical fiber sensor taking the tapering structure as the sensing area 12 in the prior art, the U-shaped sensing area 12 is convenient to clean, does not damage the tapering structure (tapering area I141 and tapering area II 142) and can be repeatedly used.
Example 4
An optical fiber sensor is further improved on the basis of any one of embodiments 1-3, wherein the sensing area 12 comprises a sensing area I121 and a sensing area II122, the sensing area II122 is U-shaped, one end of the sensing area II122 is sequentially connected with one sensing area I121, the tapering area 14 and the incident area 11, and the other end of the sensing area II122 is sequentially connected with the other sensing area I121 and the optical fiber end section 13. As shown in fig. 2, the sensing region I121 is a raw fiber structure.
Principle of detecting liquid parameters and temperature in this embodiment:
when a medium is placed in the sensing region 12, the evanescent field (which is formed around the tapered region 14 and itself) interacts with the medium by absorption and scattering. In the tapering region 14, a large part of the evanescent wave travels in the cladding 11 and is therefore more sensitive to changes in the surrounding medium. The penetration depth of the evanescent wave, the sensing core diameter and sensing length of the uniform sensing region are the main contributors to the sensitivity of the fiber optic probe 100.
The penetration depth is:
where λ is the wavelength of the light source, θ is the angle between the light rays striking the surface of the core 102 and the normal to the interface of the cladding 101, n co N, the refractive index of the core 102 cl Is the refractive index of the cladding 101. Defining the distance from the surface of the fiber core 102 to the position where the electromagnetic field amplitude is reduced to 1/e of the electromagnetic field amplitude of the surface of the fiber core 102 as the penetration depth d of evanescent waves of the fiber probe 100 p 。
As can be seen from equation 1, the penetration depth d decreases as the value of θ decreases p Will increase; the number of ray reflections per unit length N is defined as:
for a given type of fiber, N depends on the value of θ. Under the condition of total reflection, a standing wave field is generated in the fiber core 102 and decays exponentially to the cladding 101, and the intensity E (x) of the evanescent field is:
where x is the distance between the boundary from the surface of the core 102 to the penetration depth, E 0 Is the field strength at the interface of the core 102 and the cladding 101.
The common optical fiber is tapered into a tapered optical fiber with smaller diameter by a tapering technology, namely a tapering region 14 in the application, and the tapered optical fiber string comprises two tapering regions 14, which are formed by seamlessly connecting one taper body with a distance of a few centimeters and then manufacturing a second taper body. Wherein the taper has a uniform waist of a few millimeters long with less loss of characteristics (< 0.1 dB).
As shown in fig. 1 and 2, when the transmitted light enters the tapered region I141, a small fraction of the light in the evanescent field of the fiber is not guided by the core 102, but instead is guided by the cladding 101, as the cladding modes are excited and propagate in the region of the cladding 101. The portion that is not tapered is an interference region where interference between the core 102 and the cladding 101 can be achieved. Since the reference path of the transmitted light is along the core 102 and the sensing path is associated with a particular excited cladding mode, the need to have two physical fiber branches is reduced. When the guided mode that keeps traveling in the core 102 and the guided mode that the non-guided mode propagates through the cladding 101 meet, interference occurs, and the two modes accumulate differentially to create an optical path delay. A portion of the transmitted light in the cladding modes is coupled back into the core 102 at the tapered region II 142.
The sensitivity of the fiber optic sensor depends on the number of light reflections and the depth of penetration of the evanescent field at the sensing region 12. To further improve the sensitivity of the sensor, this embodiment changes the non-processed sections of two adjacent tapered regions 14 to a U-shape, as shown in fig. 1 and 2, with the sensing region 12 of the fiber optic sensor having a shape of a semicircle of fixed curvature. In the case of a U-shaped probe, as light enters the bending region of the sensing region 12 of the fiber optic sensor, the angle with the normal to the core 102/cladding 102 interface at the outer surface of the bending region decreases. The meridian is:
where θ represents the angle at which light is transmitted to the outer surface of the curved core 102, h is the distance the ray from the core 102/cladding 101 interface enters the entrance of the U-shaped structure, and R is the bend radius of the U-shaped structure. According to equations (1), (2), the decrease in the value of the angle of light in the sensing region 12 increases the penetration depth and the number of evanescent light reflections per unit length N.
For those skilled in the art, the optical fiber sensor formed by directly manufacturing the U-shaped structure on the unprocessed optical fiber has low sensitivity, poor performance and low cost performance, and those skilled in the art generally cannot think of the optical fiber sensor adopting the structure, and the technical prejudice exists for those skilled in the art in that the optical fiber sensor adopts the product of the structure, so that the thought of directly processing the unprocessed optical fiber sensor into the U-shaped structure is available for those skilled in the art.
The angle of ray propagation in a straight-line structured probe is constant, and the number of ray reflections is inversely proportional to the radius of the core 102 and depends only on the radius. However, in a U-shaped structure, the angle of ray propagation is not constant, but is continuously decreasing. A decrease in the propagation angle will thus cause an increase in the penetration depth. Bending of the fiber can result in increased light loss and evanescent field penetration depth, and in a U-shaped structure, the greater the absorption coefficient, the higher the fiber sensitivity.
The platform has the advantages of simple operation process, high practicality, convenient cleaning and good realization of the related detection of small-volume liquid, and can rapidly realize multiple sampling.
Example 5
The optical fiber sensor detection platform comprises a support 1, wherein the support 1 is composed of a vertical surface and a horizontal surface, the vertical surface is provided with a fixing part 2 for fixing the optical fiber probe 100 in any one of embodiments 1-3, and the horizontal surface is provided with a concave hole 8 for bearing a container 3.
As a further improvement of the embodiment, the container 3 is positioned in the concave hole 8, and the bottom of the container 3 is communicated with the water filling port 9 and the water outlet 10.
The fixing part 2 is a fixing clamping piece, the fixing clamping piece is used for fixing the optical fiber probe 100 on the vertical surface of the bracket 1, the container 3 is a transparent vessel, the transparent vessel is placed in the concave hole 8, the inner side of the transparent vessel is carved with a leveling line, and the bottom end of the transparent vessel is provided with a water filling port 9 and a water outlet 10; by observing the transparent vessel, the quantity of the solution can be intuitively known, and whether the liquid to be detected is stored and fully contacted with the sensing area 12 is judged.
Example 6
A detection method of an optical fiber sensor comprises the following steps:
A. fixing both ends of an optical fiber sensor according to any one of embodiments 1 to 4 on a bracket 1 of an optical fiber sensor detection platform according to embodiment 5, respectively;
B. the incidence zone 11 of the optical fiber probe 100 is connected with the broadband light source 5 and the spectrum analyzer 6 through the optical fiber coupler 15; the broadband light source 5 emits light, the light passes through the optical fiber coupler 15, the incidence area 11, the sensing area 12 and the optical fiber end section 13 of the optical fiber probe 100, is reflected by the end surface of the optical fiber end section 13, returns in the original path, passes through the optical fiber end section 13, the sensing area 12 and the incidence area 11 of the optical fiber probe 100 in sequence, and then reaches the spectrum analyzer 6 through the optical fiber coupler 15, and the spectrum analyzer 6 measures the light source data;
C. and (3) temperature detection: placing the detection platform in an environment to be detected, and calculating the temperature according to the measurement result of the spectrum analyzer 6;
D. and (3) liquid detection: closing the water outlet 10, introducing liquid to be detected into the container 3 through the water filling port 9 until the liquid covers the sensing area 12 of the optical fiber probe 100, and calculating liquid parameters according to the measurement result of the spectrum analyzer 6.
Example 7
An optical fiber sensor detection platform is improved on the basis of the embodiment 5 and comprises a bread board 4 and a bracket 1, wherein the bread board 4 is a solid aluminum bread board, and two boards are generally used for experimental design: the universal plate and the bread plate are welded, and the device cannot be moved after the universal plate is fixed; the bread board can be used for randomly inserting or extracting the device, and is very suitable for assembly, debugging and training.
The bread board 4 is provided with a bracket 1, and the bracket 1 is provided with a fixing clamping piece 2 for fixing two free ends (an incidence area 11 and an optical fiber end section 13) of the optical fiber probe 100, so that the uniform stress is ensured, and the cross sensitivity influence caused by stress factors is reduced. The incident end of the fiber optic probe 100 is connected to the broadband light source 5 and the spectrum analyzer 6 via the fiber optic coupler 15, as shown in fig. 3.
Besides the fixing clamping piece 2 capable of fixing the optical fiber probe 100, the support 1 is also provided with a horizontal plane capable of placing the container 3, a pit 8 with the diameter of 5cm is drilled on the horizontal plane, the size of the pit 8 is matched with the size of the container 3 (transparent vessel is used in the embodiment), namely, the transparent vessel can be fixedly embedded into the pit 8, and other size values can be selected in specific design. The transparent vessel for containing the liquid to be measured is embedded in the transparent vessel and is fixed, and the liquid to be measured is placed in the transparent vessel. For the quantity of control liquid that awaits measuring, the transparent container inboard is carved with the level line, and the setting of water injection port 9 and delivery port 10 is convenient for avoid the liquid that awaits measuring to take place to subside in the testing process, and the injection and the emission of liquid of being convenient for simultaneously, repeatedly used many times, the practicality is stronger.
The water injection port 9 and the water outlet 10 on the transparent vessel are arranged, so that the sensing area 12 of the optical fiber probe 100 can be cleaned in time in the detection process, and the liquid to be detected can be detected more efficiently; therefore, the platform is simple in operation process, can rapidly realize multiple sampling, and is high in practicality and convenient to clean.
Example 8
As shown in fig. 1-4, the detection method of the optical fiber sensor of the present embodiment is further improved on the basis of embodiment 7, and includes the following steps:
A. selecting a bread board 4, and fixing the bracket 1 on the bread board 4;
B. a pit 8 is drilled on the bracket 1, a transparent vessel is embedded into the pit 8 and is fixed, and a water injection port 9 and a water outlet 10 are closed;
C. the two free ends of the optical fiber probe 100 are respectively fixed on the bracket 1 by using the fixing clamping pieces; before measurement, moving the fixed optical fiber probe 100 to penetrate into the transparent vessel to a certain depth, and after measurement begins, fixing the fixed optical fiber probe, wherein the solution to be measured in the transparent vessel is ensured to be the same;
D. opening a water injection port 9 of the transparent vessel, and injecting liquid to be detected to an inner level line; opening the water outlet 10, adjusting the flow rate of the two water outlets, ensuring that the liquid amount in the transparent vessel is unchanged and the liquid is in a flowing state in the detection process so as to avoid sedimentation; detecting, namely detecting parameters of the liquid to be detected; closing the water filling port 9, keeping the water outlet 10 open, and discharging the liquid to be measured; opening a water filling port 9, injecting clean water for cleaning, discharging the clean water after cleaning is completed, and closing the water filling port 9 and a water outlet 10;
E. in step D, after the data detection for one liquid is completed, the signal of the optical fiber probe 100 is transmitted to the spectrum analyzer 6 through the optical fiber connector;
F. repeating the step D, E to detect a plurality of liquids;
as a further improvement, the test temperature for detecting the liquid parameter is 25 ℃.
Example 9
The detection method of the optical fiber sensor of the embodiment is improved on the basis of embodiment 6, and the temperature detection range is as follows: 5-45 ℃. The detection principle is as follows:
the spectrum analyzer 9 can measure the output light intensity I of the optical fiber, expressed as:
wherein I is co ,I cl ,Representing the light intensity of the core 102, the cladding 101, and the phase difference therebetween, respectively, the phase difference can be expressed as:
wherein n is co ,n cl Indicating the effective refractive index of the core 102 and cladding 101, the difference between the two being Δn eff When (when)The time interference is the smallest and corresponds to the wavelength lambda n.min ＝2Δn eff L/(2n+1), n is an integer, and Δn is due to L eff Is influenced by the thermal expansion effect and the thermo-optical effect of the optical fiber, lambda n.min With temperature, thus according to a specific lambda in the transmission spectrum n.min The drift amount of (c) can realize the sensing measurement of the ambient temperature.
Example 10
The method for detecting the optical fiber sensor in the embodiment comprises the following steps:
A. the optical fiber sensor detection platform is built, the test temperature for detecting the liquid parameters is 25 ℃, the reason for this is that the tapered optical fiber is very sensitive to the temperature, the temperature change can influence the detection result, the liquid is detected under the constant temperature condition in the test, generally at the room temperature of 25 ℃, the ideal result can be better obtained, and the sensitivity of the optical fiber probe 100 of the tapered optical fiber string to the temperature is greatly reduced;
B. a concave hole 8 is formed in the bracket 1, a transparent vessel is embedded into the concave hole, the transparent vessel is fixed, and a water injection port 9 and a water outlet 10 of the transparent vessel are closed;
C. opening a water injection port 9 of the transparent vessel, injecting liquid to be detected to an inner level line, opening a water outlet 10, strictly controlling the flow rate of the two water ports, ensuring that the liquid amount in the transparent vessel is always maintained at the inner level line, and simultaneously, the liquid is in stable and dynamic state;
D. the sensor (the sensing area 12) is fully contacted with the liquid, and the same standard ensures the same liquid pressure as long as the liquid is contacted, so that the liquid is detected; after the parameters of the liquid to be detected are detected in the detection process, the water injection port 9 of the transparent vessel is closed, the liquid is discharged, and then the cleaning work is carried out;
E. in step D, after each data test for a fluid is completed, the signal on the fiber optic probe 100 is transmitted to the spectrometer via the fiber optic connector. The optical fiber connector connects a free end (an incidence area 11) of the sensor with the spectrum analyzer 6, the spectrum analyzer 6 detects spectrograms of the sensor on different liquid concentrations, the spectrum change has a corresponding relation with the refractive index, the spectrum analyzer 6 transmits data to a computer, and the computer processes the data to obtain the liquid concentration;
F. step D, E is repeated for the detection of multiple liquids.
Example 11
The optical fiber sensor detection platform comprises a bracket 1, a fixing clamping piece, a transparent vessel and a bread board 4, wherein the bracket 1 is arranged on the bread board 4; two fixing clamping pieces are arranged on the bracket 1, and fixing clamping piece grooves are formed in the fixing clamping pieces; besides the fixed clamping pieces, the support 1 is also provided with an experimental device for placing the transparent vessel, a pit is formed in the device, the diameter of the pit 8 is 5cm, the size of the pit 8 is matched with that of the transparent vessel, namely, the transparent vessel can be fixedly embedded into the pit 8, and other values can be selected; the transparent vessel is placed in the concave hole 8, a leveling line is measured and carved in the transparent vessel 3, and the bottom is provided with a water filling port 9 and a water outlet 10.
Aiming at the problem that the liquid detection platform in the prior art is complex in operation of detecting one liquid at a time, the invention provides an optical fiber sensor, a detection platform and a detection method thereof. The structure of the conical light string is changed into a U-shaped probe, so that the conical optical fiber structure is changed into a compact structure, the sensitivity is improved, the test is easy, and the concentration change of small-volume liquid is realized.
The invention and its embodiments have been described above by way of illustration and not limitation, and the invention is illustrated in the accompanying drawings and described in the drawings in which the actual structure is not limited thereto. Therefore, if one of ordinary skill in the art is informed by this disclosure, the structural mode and the embodiments similar to the technical scheme are not creatively designed without departing from the gist of the present invention.
Claims (5)
1. An optical fiber sensor is composed of an optical fiber probe (100) and comprises an incidence area (11), a sensing area (12) and an optical fiber end section (13), and is characterized by further comprising a tapering area (14), wherein one end of the sensing area (12) is sequentially connected with one tapering area (14) and the incidence area (11), and the other end of the sensing area (12) is sequentially connected with one end of the other tapering area (14) and one end of the optical fiber end section (13);
the cone pulling area (14) comprises a cone pulling area I (141) and a cone pulling area II (142), one end of the cone pulling area I (141) is connected with one end of the sensing area (12), the other end of the cone pulling area I (141) is connected with the incident area (11), one end of the cone pulling area II (142) is connected with the other end of the sensing area (12), and the other end of the cone pulling area II (142) is connected with the optical fiber end section (13);
the optical fiber probe (100) comprises a cladding (101) and a fiber core (102), wherein the fiber core (102) is arranged in the cladding (101);
a layer of metal film is arranged on the end face of the optical fiber end section (13), and a layer of metal film is arranged on the tapering region (14);
the sensing area (12) is U-shaped, the sensing area (12) comprises a sensing area I (121) and a sensing area II (122), the sensing area II (122) is U-shaped, one end of the sensing area II (122) is sequentially connected with one sensing area I (121), a tapering area (14) and an incidence area (11), and the other end of the sensing area II (122) is sequentially connected with the other sensing area I (121) and an optical fiber end section (13).
2. The optical fiber sensor according to claim 1, wherein the metal film is a gold film or a palladium-gold film.
3. The optical fiber sensor detection platform comprises a support (1), and is characterized in that the support (1) is composed of a vertical surface and a horizontal surface, the vertical surface is provided with a fixing part (2) for fixing the optical fiber probe (100) according to claim 1, and the horizontal surface is provided with a concave hole (8) for bearing a container (3).
4. A fiber sensor testing platform according to claim 3, wherein the container (3) is located in the cavity (8), and the bottom of the container (3) is communicated with the water filling port (9) and the water outlet (10).
5. The detection method of the optical fiber sensor is characterized by comprising the following steps of:
A. fixing both ends of an optical fiber sensor according to claim 1 on a bracket (1) of an optical fiber sensor detection platform according to claim 3;
B. the incidence area (11) of the optical fiber probe (100) is connected with the broadband light source (5) and the spectrum analyzer (6) through the optical fiber coupler (15); the broadband light source (5) emits light, the light passes through an incidence area (11), a sensing area (12) and an optical fiber end section (13) of the optical fiber probe (100), the light passes through the end face of the optical fiber end section (13) to form reflection, the light returns in the original path, and finally reaches the spectrum analyzer (6) through the optical fiber coupler (15), and the spectrum analyzer (6) measures the light source data;
C. and (3) temperature detection: placing the detection platform in an environment to be detected, and calculating the temperature according to the measurement result of the spectrum analyzer (6);
D. and (3) liquid detection: closing the water outlet (10), introducing liquid to be detected into the container (3) through the water filling port (9) until the liquid covers the sensing area (12) of the optical fiber probe (100), and calculating liquid parameters according to the measurement result of the spectrum analyzer (6).
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| CN109405759A (en) * | 2018-11-14 | 2019-03-01 | 深圳市迈步机器人科技有限公司 | Fibre optical sensor, deformation detecting device, detection method and data glove |
| CN112833928B (en) * | 2020-12-31 | 2022-12-06 | 桂林电子科技大学 | Cascade macrobend and alternative single mode-multimode fiber structure temperature refractive index sensor |
| CN114235755A (en) * | 2021-12-18 | 2022-03-25 | 桂林电子科技大学 | Point type measurement SPR sensor based on U-shaped conical plastic optical fiber |
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