CN117906651A - Multi-core optical fiber Fabry-Perot sensor based on photo-thermal effect - Google Patents
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Abstract
The invention discloses a multi-core optical fiber Fabry-Perot sensor based on a photo-thermal effect, which comprises an optical fiber (1), a photo-thermal conversion material (2), a multi-core optical fiber connector (3), a circulator (4) and an optical fiber probe (5); the invention mainly utilizes the photoetching technology to write out a photo-thermal conversion material (2) on the end face of an optical fiber (1) at the tail end of an optical fiber probe (5), when excitation light (6) is focused on the photo-thermal conversion material (2), the photo-thermal conversion material (2) can generate photo-thermal effect, bubbles (7) are generated in liquid, a photoelectric detector (9) is connected with a sensing fiber core (103) through a multi-core optical fiber connector (3) and a circulator (4), when the optical fiber probe (5) is inserted into a micro-channel (8), liquid with different flow rates is introduced into the micro-channel (8), the position or shape of the bubbles (7) generated on the end face of the optical fiber (1) can be changed due to water flow impact, the length of a Fabry-Perot interference cavity can be changed, the intensity information or wavelength information of a received reflection signal (17) can be changed, so that the flow rate detection is realized, when the flow rate direction is different, the direction of the bubbles (7) is shifted or deformed can be changed, and the flow direction of the reflection signal (17) in the sensing fiber core (103) can be judged by analyzing and demodulating the flow direction; the sensor can be used for multi-parameter real-time monitoring in multiple fields of industrial production, basic medicine, biological analysis and the like.
Description
Field of the art
The invention relates to a multi-core optical fiber Fabry-Perot sensor based on a photo-thermal effect, belonging to the field of optical fiber sensing.
(II) background art
The optical fiber Fabry-Perot sensor is a high-precision measuring device based on the optical interference principle. The main components of the device are two reflectors and a light transmission medium, wherein the light transmission medium is usually formed by optical fibers. When light enters the sensor from the end, the light is reflected back and forth between the two reflectors, and an interference phenomenon is formed. When the external environment changes, such as temperature, pressure, vibration and the like, the length, refractive index and the like of the light transmission medium can be changed, so that the rule of interference phenomenon is influenced, and the external environment is measured. Because the optical fiber Fabry-Perot sensor is based on the optical interference principle, the sensitivity of the optical fiber Fabry-Perot sensor to the external environment is very high, and the micro-variation measurement can be realized. The optical fiber sensor is not affected by electromagnetic interference, so that the optical fiber Fabry-Perot sensor has advantages in some environments with strong electromagnetic interference. The optical fiber Fabry-Perot sensor has a relatively simple structure and is easy to process and integrate. The optical fiber Fabry-Perot sensor can realize measurement of various parameters such as temperature, pressure, displacement, speed and the like. The optical fiber sensor has the capability of transmitting optical signals in long distance, so that remote measurement can be realized.
The photothermal effect is a phenomenon that the temperature of a substance increases after absorbing light energy. This phenomenon mainly occurs during light absorption of the material, when photons interact with electrons in the material, which absorb light energy and convert it into heat energy, thereby causing the temperature of the material to rise. The photothermal effect is widely used in many fields, such as solar collectors, photothermal power generation, photothermal therapy, and the like. In solar collectors, the photo-thermal effect is used to convert sunlight into thermal energy, powering various energy conversion processes. In photo-thermal power generation, the photo-thermal effect is used for converting sunlight into electric energy, and a new way is provided for the development and utilization of renewable energy sources. In photothermal therapy, the photothermal effect is used to convert laser energy into thermal energy for precise ablation and ablation of diseased tissue.
The photoinitiator is a substance capable of initiating chemical reaction under the action of light and is widely applied to the photo-curing technology. Photoinitiators are largely classified into free radical type and cationic type. The radical photoinitiator can absorb energy and decompose to generate radicals under the irradiation of ultraviolet light, and the radicals can initiate the polymerization reaction of unsaturated resin. Cationic photoinitiators initiate polymerization by means of cations generated under the action of light. Photoinitiators play a critical role in the photo-curing technology. First, it is capable of absorbing ultraviolet light energy and converting it into chemical energy, thereby initiating polymerization of unsaturated resins. And secondly, the photoinitiator can improve the curing speed of unsaturated resin, shorten the production period and improve the production efficiency. In addition, the photoinitiator can also control the curing degree and the curing depth, so that the ideal curing effect is obtained.
In the field of optical fiber sensing, sensing technologies that are highly sensitive, miniaturized, and capable of performing multi-parameter measurements are constantly being pursued and explored. With the forward development of sensing technology, fiber optic fabry-perot sensors of various structures and functions are continuously emerging.
The invention patent with the publication number of CN110595517A mainly comprises a light source, a multimode optical fiber splitter, a sapphire optical fiber, a lens coupling system, a single-mode optical fiber and a light detector. Light emitted by the light source sequentially passes through the multimode fiber splitter, the multimode fiber and the sapphire fiber FP sensor, is reflected and interfered at two ends of the sapphire fiber FP cavity to form an interference signal, and is returned to the multimode fiber splitter, and then is coupled to the single-mode fiber through the coupling lens, and then the light signal is received by the light detector. But the manufacturing cost of the sensor is too high. The invention patent with publication number CN110160571A is a Fabry-Perot sensor based on silicon core optical fiber and a preparation method thereof. The sensor is composed of a common single mode fiber, an optical fiber fusion end face, a silicon core optical fiber and a polishing end face, wherein the fusion end face is formed after an input optical fiber and a silicon core optical fiber are fused, the silicon core optical fiber is composed of a silicon core optical fiber cladding and a silicon core optical fiber core, the polishing end face is formed by polishing the silicon core optical fiber end face, and the fusion end face and the polishing end face form two mirror faces of a silicon core optical fiber Fabry-Perot cavity. But the sensor has limited application scenes and is complex to manufacture. The invention patent with the authorization number of CN108120460A is an optical fiber Fabry-Perot sensor, a manufacturing method and a testing device thereof, wherein the sensor comprises a first optical fiber and a second optical fiber which are opposite, a first end face of the first optical fiber, which faces to one side of the second optical fiber, is a concave curved surface, a microcavity is formed by butt joint of the first end face and a second end face of the second optical fiber, which faces to one side of the first optical fiber, and the microcavity is a stable cavity; the concave curved surface of the first end face is obtained through carbon dioxide laser treatment, and a curved surface area with a first numerical value being a short axis diameter is an equivalent ellipsoid by taking an intersection point of the central axis of the first optical fiber and the first end face as a center, so that the optical fiber Fabry-Perot sensor has good mode matching. But the sensor is complicated in manufacturing process and high in cost.
The invention provides a multi-core optical fiber Fabry-Perot sensor based on photo-thermal effect, which has the characteristics of being capable of realizing multi-parameter sensing, high in sensitivity, simple to prepare and high in integration level. The bubble generated on the end face of the optical fiber is constructed into a composite method Fabry-Perot cavity, and the bubbles are caused to displace or deform by the action of external physical quantity, so that the monitoring of different physical quantities is realized; in addition, the micro-channel structure design, the selection of the photo-thermal conversion material, the shape design of the photo-thermal conversion material and the like can be corresponding to lasers with different wavelengths, so that the sensor can adapt to detection of different external environments and different physical quantities, the application scene and the application range of the sensor can be further improved, and the sensor provided by the invention has greater advantages compared with the prior art.
(III) summary of the invention
Aiming at the defects of the prior art, the invention aims to provide a multi-core optical fiber Fabry-Perot sensor based on the photo-thermal effect. The sensor is characterized in that a photo-thermal film is inscribed on the end face of an optical fiber excitation fiber core (102) or coated on the end face of the optical fiber excitation fiber core, excitation light (6) is transmitted to a photo-thermal conversion material (2) through the optical fiber excitation fiber core (102), the photo-thermal conversion material (2) can generate photo-thermal effect in liquid, so that a bubble (7) can be generated on the end face of an optical fiber (1), a composite Fabry-Perot interference cavity is formed between the end face of the optical fiber (1) and the front surface and the rear surface of the bubble (7), external physical quantity acts on the bubble (7), so that the bubble (7) is offset or deformed, and the cavity length of the sensor is changed, so that the sensing purpose is achieved.
The purpose of the invention is realized in the following way:
As shown in fig. 1, the sensor is a compound fabry-perot cavity formed by the end face of an optical fiber (1) and the front and rear surfaces of a bubble (7), the bubble (7) is a photothermal conversion material (2) transmitted to the end face of the optical fiber (1) by excitation light (6) through an excitation fiber core (102), the photothermal conversion material (2) generates a photothermal effect, and the bubble (7) is generated in a liquid environment. The sensing fiber core (103), the detection light (10) and the photoelectric detector (9) are connected through the circulator (4) and the multi-core fiber connector (3), the detection light (10) is transmitted to the end face of the optical fiber (1) in the sensing fiber core (103) to generate first reflected light (11) and first transmitted light (12), then the first transmitted light (12) is transmitted in liquid to reach the front surface of the bubble (7), second reflected light (13) and second transmitted light (14) are generated on the front surface of the bubble (7), the second transmitted light (14) is continuously transmitted to the rear surface of the bubble (7) in the bubble (7) to generate third reflected light (15), the first reflected light (11), the second reflected light (13) and the third reflected light (15) generate composite Fabry-Perot interference to generate a reflected signal (17), when the external physical quantity is changed, the bubble (7) is caused to generate offset or deformation, the length of the Fabry-Perot cavity generates the reflected signal (17) to change the length of the optical fiber core, and the thermal signal (17) is finally analyzed based on the change of the wavelength of the reflected signal (17) in the sensing fiber core.
The optical fiber (1) used in the multi-core optical fiber Fabry-Perot sensor based on the photo-thermal effect is a single mode optical fiber, a multimode optical fiber or other optical fibers.
The optical fiber (1) used in the multi-core optical fiber Fabry-Perot sensor based on the photo-thermal effect is a three-core optical fiber, a four-core optical fiber, a five-core optical fiber or other multi-core optical fibers.
The photo-thermal conversion material (2) in the multi-core optical fiber Fabry-Perot sensor based on the photo-thermal effect is a photoetching material, a metal-medium composite material or other materials with photo-thermal conversion performance.
The photoetching material used in the multi-core optical fiber Fabry-Perot sensor based on the photo-thermal effect is a free radical photoinitiator, a cationic photoinitiator or other photoetching materials such as metal oxyates.
The photo-thermal conversion material (2) in the multi-core optical fiber Fabry-Perot sensor based on photo-thermal effect is a dot array, a strip array, a dot and strip combined array or other patterning arrays.
The holographic optical tweezers platform is used for focusing excitation light (6) to the fiber end of the optical fiber (1), and the spatial light modulator is used for realizing single-path writing, double-path writing or multi-path writing in the adopted writing mode.
When the excitation light (6) is used for generating the bubble (7) on the end face of the optical fiber (1), the attachment position of the bubble (7) is on the photo-thermal conversion material (2) or the end face of the optical fiber (1), when the bubble is attached to the photo-thermal conversion material (2), the sensor is a composite Fabry-Perot interference cavity formed by the end face of the optical fiber (1), the front surface of the bubble (7) and three reflecting surfaces of the rear surface of the bubble (7), and when the bubble (7) is attached to the end face of the optical fiber (1), the sensor is a Fabry-Perot interference cavity formed by the end face of the optical fiber (1) and the two reflecting surfaces of the rear surface of the bubble (7).
The fiber core of the optical fiber (1) in the multi-core optical fiber Fabry-Perot sensor based on the photo-thermal effect is round, triangular, quadrilateral or other polygons.
By simplifying the multi-core optical fiber Fabry-Perot sensor based on the photo-thermal effect into a three-layer high-reflection film structure of an optical fiber end face and the front and rear surfaces of bubbles, a composite Fabry-Perot interference cavity is formed by the three-layer high-reflection film, the optical path distribution condition of the three-layer film structure is analyzed, and corresponding mathematical description is given below.
The multiple hybrid FPIs and the silica cavity FPIs formed by the connection SMFI between M2 and M3 will not contribute to the interference spectrum because their cavity length is larger than the coherence length of the light source. Thus, the four mirror model is reduced to a superposition of two separate FPI spectra. The reflection signal (17) of the proposed sensor can be expressed as:
Wherein I 1、I2、I3 and I 4 are the intensities of light reflected by the four reflective surfaces M1, M2, M3 and M4, respectively; l S and L R are the cavity lengths of SFPI and MFPI, respectively; n a is the refractive index of air.
In order to produce the vernier effect, the optical paths of the two FPIs need to be very close, but not exactly equal. This can be achieved by making the cavity lengths of the two FPIs slightly different, since the two FPIs have the same refractive index. Using the vernier effect, the envelope function of the reflected signal (17) can be expressed as:
where a is the amplitude of the envelope function.
By utilizing the vernier effect, the sensitivity of the sensor can be greatly improved by tracking the envelope displacement of the sensor. The envelope offset of the entire sensor can be expressed as SFPI wavelength offset multiplied by the amplification factor of the vernier effect M, and the expression can be written as:
Where Δλ is the resonant wavelength shift of a single FPI-based sensor as a function of strain; m represents a magnification factor, which is related to the optical lengths of SFPI and MFPI. It can be seen that the envelope displacement Δλ C of the sensor is M times the wavelength displacement of a single FPI, and therefore the sensor has a higher strain sensitivity than a single FPI-based fiber optic sensor.
The invention has the beneficial effects that:
The invention provides a multi-core optical fiber Fabry-Perot sensor based on photo-thermal effect according to the requirements of the modern sensing field and inheriting the advantages of the existing sensor. The composite method Fabry-Perot interference cavity composed of the optical fiber end face and the front and rear surfaces of the bubble is beneficial to the deformation or position change of the bubble (7) caused by the action of different physical quantities on the bubble (7) outside, so that the cavity length of the Fabry-Perot cavity is changed, the intensity information or wavelength information of a reflection signal (17) received by a photoelectric detector (9) is changed, and the sensing purpose can be achieved. The invention has simple preparation and high integration level, can realize detection and analysis of different environments and different physical quantities, and overcomes the defects of complex detection technology, low detection efficiency, limited application range and the like in the prior art.
(IV) description of the drawings
Fig. 1 is a multi-core fiber fabry-perot sensor based on photo-thermal effects. The sensor comprises an optical fiber (1), a thermal conversion material (2), a multi-core optical fiber connector (3), a circulator (4) and an optical fiber probe (5).
Fig. 2 is a schematic diagram of the optical fiber (1) cleaving process. In the figure, (1) is an optical fiber, (203) is an optical fiber clamping tool, and (204) is an optical fiber cutter.
Fig. 3 is a schematic view of the processing of the photothermal conversion material (2). Fig. 3 (a) is a holographic optical tweezers platform structure comprising excitation light (6), micro-channels (8), LEDs (301), objective lens (302) and mirror (303); fig. 3 (b) shows a writing process of writing the photothermal conversion material (2) on the end face of the optical fiber (1) by the excitation light (6).
Fig. 4 is a schematic diagram of the number of cores of an optical fiber (1), wherein (1) is an optical fiber, (101) is an optical fiber cladding, (102) is an excitation core, and (103) is a sensing core. FIG. 4 (a) is a four-core optical fiber; FIG. 4 (b) is a five-core optical fiber; FIG. 4 (c) is a six-core optical fiber; fig. 4 (d) is a seven-core optical fiber.
Fig. 5 is a schematic diagram of the core shape of an optical fiber (1), wherein (1) is an optical fiber, (101) is an optical fiber cladding, (102) is an excitation core, and (103) is a sensing core. FIG. 5 (a) is a circular core; FIG. 5 (b) is a triangular core; FIG. 5 (c) is a rectangular core; fig. 5 (d) is a pentagonal core.
Fig. 6 is a schematic diagram of the shape of the photothermal conversion material (2), wherein (2) is the photothermal conversion material, (101) is the optical fiber cladding, (102) is the excitation core, and (103) is the sensing core. Fig. 6 (a) is circular; fig. 6 (b) is triangular; fig. 6 (c) is rectangular; fig. 6 (d) is pentagonal.
Fig. 7 is a schematic diagram of the position of the bubble (7), wherein (1) is an optical fiber, (2) is a photothermal conversion material, and (7) is a bubble. FIG. 7 (a) is a schematic view showing bubbles (7) attached to the photothermal conversion material (2); fig. 7 (b) is a schematic view showing the attachment of bubbles (7) to the end face of the optical fiber (1).
Fig. 8 is a schematic diagram of a multi-core optical fiber fabry-perot Luo Liusu and a direction sensor based on photo-thermal effect, (1) an optical fiber, (101) an optical fiber cladding, (102) an excitation fiber core, (103) a sensing fiber core, (2) a photo-thermal conversion material, (3) a multi-core optical fiber connector, (4) a circulator, and (5) an optical fiber probe.
(Fifth) detailed description of the invention
The invention is further elucidated below by way of example with reference to the accompanying drawings.
The preparation process of the multi-core optical fiber Fabry-Perot sensor based on the photo-thermal effect mainly comprises the following three steps:
And step 1, processing a micro-channel. A glass substrate of suitable dimensions is prepared, and micro-channels (8) are written on one of the glass substrates by means of a femtosecond processing technique.
And 2, optical fiber treatment. As shown in fig. 3, the prepared optical fiber (1) is stripped of the coating layer on the outside of the optical fiber by a stripper, cleaned with alcohol, fixed by an optical fiber clamp (203), and cut and flattened by a cutter (204). The cleaned optical fiber (1) is inserted into an optical fiber probe (7).
And 3, inscribing the photo-thermal structure. The prepared photoinitiator solution is dropped on the end face of the optical fiber, excitation light (6) is focused on the end face of the optical fiber (1) through a holographic optical tweezers platform, and the required photo-thermal conversion structure (2) is inscribed by changing the focusing position of the laser.
The invention is further illustrated below in conjunction with specific examples.
Example 1: a multi-core optical fiber Fabry-Perot sensor based on photo-thermal effect is used for detecting the external flow velocity and the flow velocity direction.
As shown in fig. 8, the sensor comprises an optical fiber (1), a photo-thermal conversion material (2), a multi-core optical fiber connector (3), a circulator (4) and an optical fiber probe (5), wherein the optical fiber (1) comprises an optical fiber cladding (101), an excitation fiber core (102) and a sensing fiber core (103); referring to the steps 1-3 of the preparation process, after the micro-channel (8) is processed by using the femtosecond, the processed multi-core optical fiber (1) is inserted into the optical fiber probe (5), the photo-thermal conversion material (2) is written on the optical fiber (1) at the tail end of the optical fiber probe (5) by using the photoetching technology, the exciting light (6) is transmitted to the photo-thermal conversion material (2) at the end face of the optical fiber (1) by the exciting fiber (102), the photo-thermal conversion material (2) generates a photo-thermal effect, a bubble (7) is generated on the end face of the optical fiber (1), a compound Brillouin interference cavity is formed by the end face of the optical fiber (1), the front surface of the bubble (7) and the rear surface of the bubble (7), the detecting light (10) is connected and injected into the sensing fiber core (103) by the circulator (4) and transmitted to the end face of the optical fiber, the light source generates first reflected light (11) and first transmitted light (12) at the end face of the optical fiber (1), then the first transmitted light (12) reaches the front surface (7) in the liquid, the second light (14) is transmitted to the second surface (14) and the second light (14) is reflected at the front surface (7) and the second light (14) is further transmitted at the front surface (14) and the second light (14) is reflected at the front surface (14) and the second light is continuously reflected at the front surface (14) The second reflected light (13) and the third reflected light (15) generate a composite Fabry-Perot interference, a reflected signal (17) is generated, and the reflected signal (17) is received by the photodetector (9). When the optical fiber probe (5) is inserted into the micro-channel (8), and when the liquid (16) is injected into the micro-channel (8), the impact force of the liquid (16) enables the position of the bubble (7) to deviate in the same direction as the flowing direction of the liquid, so that the intensity information or wavelength information of the reflected signal (17) received by the photoelectric detector (9) is changed, the signal of the sensing fiber core (103) in the same direction as the deviation direction of the bubble (7) is enhanced, the reflected signal (17) of the sensing fiber core (103) in the opposite direction is weakened, and the flow speed direction are judged, so that the multi-core optical fiber Fabry-Perot Luo Liusu flow sensor based on the photo-thermal effect is finally realized.
Claims (7)
1. The invention provides a multi-core optical fiber Fabry-Perot sensor based on photo-thermal effect, which is characterized in that: the sensor comprises an optical fiber (1), a photo-thermal conversion material (2), a multi-core optical fiber connector (3), a circulator (4) and an optical fiber probe (5), wherein the optical fiber (1) comprises a cladding (101), an excitation fiber core (102) and a sensing fiber core (103); the photo-thermal conversion material (2) is inscribed on the end face of the optical fiber (1) at the tail end of the optical fiber probe (5) by utilizing the photoetching technology, the exciting light (6) is connected with the sensing fiber core (103) of the optical fiber (1) through the multi-core optical fiber connector (3), the photo-thermal conversion material (2) is transmitted to the end face of the optical fiber (1) through the exciting fiber core (102), the photo-thermal conversion material (2) can generate photo-thermal effect, a bubble (7) is generated on the end face of the optical fiber (1), three reflecting surfaces of the end face of the optical fiber, the front surface of the bubble and the back surface of the bubble form a compound Fabry-Perot interference cavity, the detecting light (10) and the photoelectric detector (9) are connected with the sensing fiber core (103) of the optical fiber (1) through the multi-core optical fiber connector (3) and the circulator (4), the detecting light (10) can generate first reflected light (11) and first transmitted light (12) at the end face of the optical fiber (1), then the first transmitted light (12) can be transmitted to the front surface of the bubble (7) in liquid, second reflected light (13) and second transmitted light (14) are generated on the front surface of the optical fiber (7), the second reflected light (14) is generated in the front surface of the bubble (7), and the second reflected light (15) is continuously reflected in the compound light (15) and the third reflected light (15) can generate first reflected light, generating a reflected signal (17), wherein the reflected signal (17) is transmitted to a photoelectric detector (9) through a multi-core optical fiber connector (3) and a circulator (4); when the optical fiber probe (5) is inserted into the micro-channel (8), the size and the direction of the deflection or deformation of the bubble (7) can be changed along with the different flow rates of the liquid in the micro-channel (8), so that the intensity information or the wavelength information of the reflection signal (17) received by the photoelectric detector (9) can be changed along with the change, the flow rate and the flow rate direction can be judged by solving and analyzing the interference signals in different sensing fiber cores (103), and finally the multi-core optical fiber Fabry-Perot sensor based on the photo-thermal effect is realized.
2. The photo-thermal effect based multi-core fiber fabry-perot sensor of claim 1, wherein: the optical fiber (1) is a three-core optical fiber, a four-core optical fiber, a five-core optical fiber or other multi-core optical fiber.
3. The photo-thermal effect based multi-core fiber fabry-perot sensor of claim 1, wherein: the optical fiber (1) used is a single mode optical fiber, a multimode optical fiber or other optical fibers.
4. The photo-thermal effect based multi-core fiber fabry-perot sensor of claim 1, wherein: the photo-thermal conversion material (2) is a photo-etching material, a metal-dielectric composite material or other materials with photo-thermal conversion performance.
5. The photo-thermal effect based multi-core fiber fabry-perot sensor of claim 1, wherein: the photoetching material is free radical photoinitiator, cationic photoinitiator or metal oxide salt and other photoetching materials.
6. The photo-thermal effect based multi-core fiber fabry-perot sensor of claim 1, wherein: the photothermal conversion material (2) is a dot array, a stripe array, a combined dot and stripe array or other patterned array.
7. The photo-thermal effect based multi-core fiber fabry-perot sensor of claim 1, wherein: the core of the optical fiber (1) is round, triangular, quadrilateral or other polygonal.
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