Optical fiber temperature sensor, system and manufacturing method thereof

Abstract

The invention relates to the technical field of optical fiber sensing, and discloses an optical fiber temperature sensor, a system and a manufacturing method thereof, and the sensor comprises a sensor probe and a packaging structure used for packaging the sensor probe. The sensor probe comprises an optical fiber coating layer, an optical fiber cladding layer, a fiber core and a grating; the optical fiber cladding comprises a bare optical fiber area, a transition area and a gentle area; one end of the bare fiber area is connected with the fiber coating layer, one end of the transition area is connected with the other end of the bare fiber area, and the other end of the transition area is connected with the gentle area; the fiber core is located in the fiber cladding, and the grating is located on the fiber core; the diameter of the transition area is gradually reduced from the bare fiber area to the gentle area; the diameter of the gentle area is gradually reduced from the end close to the transition area. After the optical fiber temperature sensor provided by the invention passes through the transition area and the gentle area, the diameter of the optical fiber can be reduced to more than ten microns, the fiber core can be reduced to be within 2 microns, ultrafast temperature response can be realized, the process is simple, the cost is relatively low, and the reliability is high.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature sensors, and particularly relates to an optical fiber temperature sensor, a system and a manufacturing method thereof. Background Art

[0002] As a new generation of temperature sensing technology, the working principle of an optical fiber temperature sensor is to monitor the changes in the wavelength, intensity, and phase of the light transmitted by the optical fiber with the external temperature, so as to achieve temperature measurement. Compared with traditional electronic temperature sensors such as thermocouples and the monitoring method of thermal radiation represented by non-contact temperature measurement, the optical fiber temperature sensor has the following advantages: First, all-optical transmission, which can be free from electromagnetic interference and still work normally in a strong magnetic environment, and is suitable for extreme scenarios such as high-voltage substations and nuclear industries; Second, the materials for preparing optical fiber sensors are generally oxides or single crystals, which have lower chemical activity than metal materials and have strong corrosion resistance, and can work in strong acid or strong alkali environments for a long time, and are suitable for the petrochemical industry; Third, optical fiber sensors are small in size and high-temperature resistant, and are often used for distributed in-situ temperature measurement, with high measurement accuracy and small error, and can achieve regional miniaturized measurement. Based on the above technical advantages, optical fiber sensors overcome the deficiencies of traditional temperature measurement devices and show good application prospects in many fields such as manufacturing, medical treatment, energy, aerospace, and deep-sea exploration.

[0003] For a rapidly changing temperature field, the response speed of the sensor will affect the accuracy of the measurement result. First, the thermocouples widely used in the market have a large temperature measurement range and high resolution, but they are not corrosion-resistant and require inert metal or ceramic sleeves for protection, which delays the thermal equilibrium with the external temperature, resulting in a slow response speed. Secondly, for a blackbody cavity based on Kirchhoff's blackbody radiation law, some people replace the opaque cavity with a transparent cavity and use the opaque liquid to be measured as the new cavity. Although the response speed can be effectively improved, it is limited by the characteristics that the object to be measured needs to be opaque and fluid, which is not conducive to the dynamic monitoring of the surface temperature of the aircraft and has a small applicable range. Finally, the fiber optic temperature sensor based on a Bragg grating is a common fiber optic temperature sensor, but its 125um cladding diameter (ordinary single-mode fiber) delays the heat conduction of the temperature, making the response time of the fiber Bragg grating temperature sensor as high as 136ms, and even higher with the encapsulation structure, making it difficult to meet the dynamic temperature measurement of objects with rapid temperature changes. Therefore, for the above problems, how to design a fast-response fiber optic temperature sensor has become a research hotspot.

[0004] In recent years, in response to the problem of improving the response speed of fiber optic temperature sensors, some solutions have been proposed. For example, by reducing the size of fiber Bragg gratings, using special coating materials, etc., the temperature sensitivity of fiber optic temperature sensors is improved, and thus the response speed of the sensors is increased to a certain extent. However, these methods often have problems such as complex processes, high costs, and poor reliability, making it difficult to achieve large-scale applications. For example, in the application with the application number CN201821843082.6 and the invention name "Fiber Optic Temperature Sensor and Temperature Measurement System" designed by adhering a single crystal of gallium arsenide to the end of an optical fiber, the sensor structure is to adhere a tiny single crystal of gallium arsenide to the end face of a bare optical fiber, and a highly reflective insulating coating is applied on the other side of the single crystal of gallium arsenide. A single crystal of gallium arsenide is a semiconductor, and its working principle is the intrinsic absorption of photons by internal electrons. When light irradiates the single crystal of gallium arsenide, the light with a wavelength less than the absorption edge wavelength λ will be absorbed, while the light with a wavelength greater than λ can pass through the gallium arsenide crystal and then be reflected by the high-reflection coating to a photodetector. The bandgap width of the single crystal of gallium arsenide directly determines the absorption edge wavelength of the crystal, and it is very sensitive to the surrounding environmental temperature, thus enabling rapid temperature detection, with a minimum response time of up to 5 ms, fully meeting the temperature detection requirements for explosives or chip temperature rise. However, its disadvantages are also obvious. The sensitivity is too high, resulting in a narrow temperature measurement range, generally between -40 and 260 °C. A wider temperature measurement range requires a light source with a larger bandwidth, which undoubtedly increases the cost and is not suitable for high-temperature rapid monitoring. In addition, the size and bonding process of the single crystal of gallium arsenide have a greater impact on the performance, making it difficult to ensure consistency.

[0005] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0006] In view of the above deficiencies of the existing technology, the purpose of the present invention is to provide a fiber optic temperature sensor, a system and a manufacturing method thereof to solve the problems of complex processes, high costs, and poor reliability existing in the existing fiber optic temperature sensors.

[0007] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a fiber optic temperature sensor, which includes a sensor probe and a packaging structure for packaging the sensor probe; the sensor probe includes: an optical fiber coating layer, an optical fiber cladding layer, a core and a grating; The optical fiber cladding layer includes a bare optical fiber area, a transition area and a gentle area; One end of the bare optical fiber area is connected to the optical fiber coating layer, one end of the transition area is connected to the other end of the bare optical fiber area, and the other end of the transition area is connected to the gentle area; The core is located within the optical fiber cladding layer, and the grating is located on the core; The diameter of the transition region gradually decreases from the bare optical fiber region towards the gentle region; The diameter of the gentle region gradually decreases from one end close to the transition region.

[0008] In a further setting of the present invention, the transition region is conical; the length of the transition region is 480 - 520 microns, and the diameter of the transition region is 20 - 130 microns.

[0009] In a further setting of the present invention, the gentle region is conical; the length of the gentle region is 180 - 220 microns, and the diameter of the gentle region is 13 - 18 microns.

[0010] In a further setting of the present invention, the diameter of the core in the gentle region is less than 2 microns.

[0011] In a further setting of the present invention, the encapsulation structure includes a ceramic ferrule and a mesh metal sleeve; one end of the sensor probe is inserted into the ceramic ferrule, and the mesh metal sleeve is sleeved on the other end of the sensor probe.

[0012] In a further setting of the present invention, the optical fiber cladding passes through the ceramic ferrule, and one end of the optical fiber cladding connected to the ceramic ferrule is fixed with a curing adhesive.

[0013] In a second aspect, the present invention provides an optical fiber temperature sensing system, which includes a grating demodulator, a computer terminal, and the above-mentioned optical fiber temperature sensor; The grating demodulator is connected to the computer terminal and is used to generate a resonance signal and input it to the computer terminal; The optical fiber temperature sensor is located on one side of the grating demodulator and is used to adjust the drift of the spectral center frequency according to the change of temperature; The computer terminal is used to obtain temperature data according to the resonance signal.

[0014] In a further setting of the present invention, the grating demodulator includes: a laser, an electro-optic modulator, a circulator, a photodetector, an amplifier, a filter, and a coupler; The laser is located on the light input side of the electro-optic modulator; The electro-optic modulator is located on the first light input side of the circulator; the optical fiber temperature sensor is located on the second light input side of the circulator; The circulator is located on the light input side of the photodetector; The photodetector, the amplifier, the filter, the coupler, and the electro-optic modulator are electrically connected in sequence; The coupler is also electrically connected to the computer terminal.

[0015] Thirdly, the present invention also provides a manufacturing method for manufacturing the optical fiber temperature sensor as described above, which includes: Pre-drawing a single-mode optical fiber by a fusion splicer, and simultaneously stretching the single-mode optical fiber in the left and right directions in reverse by a motor when the fusion splicer discharges; Re-drawing the single-mode optical fiber thinner by heating with a hydrogen-oxygen flame; Disconnecting the single-mode optical fiber to obtain two optical fibers with microcone structures; Using the femtosecond laser technology point-by-point method to inscribe a uniform fiber Bragg grating in the gentle area.

[0016] A further setting of the present invention further includes the step of: Installing a packaging structure on the obtained microcone optical fiber.

[0017] An optical fiber temperature sensor, system and its manufacturing method provided by the present invention. The optical fiber temperature sensor includes a sensor probe and a packaging structure for packaging the sensor probe; the sensor probe includes: an optical fiber coating layer, an optical fiber cladding layer, a core and a grating; the optical fiber cladding layer includes a bare optical fiber area, a transition area and a gentle area; one end of the bare optical fiber area is connected to the optical fiber coating layer, one end of the transition area is connected to the other end of the bare optical fiber area, and the other end of the transition area is connected to the gentle area; the core is located inside the optical fiber cladding layer, and the grating is located on the core; the diameter of the transition area gradually decreases from the bare optical fiber area towards the gentle area; the diameter of the gentle area gradually decreases from one end close to the transition area. The optical fiber cladding layer of the optical fiber temperature sensor provided by the present invention has a transition area and a gentle area. After passing through the transition area and the gentle area, the diameter of the optical fiber can be reduced to more than a dozen micrometers, and the core can be reduced to within 2 micrometers. The grating is arranged in the gentle area, enabling the optical fiber probe to have the ability to sense the external temperature. The core being reduced to within 2 micrometers can make the temperature induction faster, thereby achieving an ultra-fast temperature response. Compared with the existing optical fiber temperature sensors, it not only has a simple process, low cost, but also high reliability. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0019] Figure 1 It is a schematic structural diagram of the optical fiber temperature sensor in the present invention.

[0020] Figure 2 It is a schematic structural diagram of the sensor probe of the optical fiber temperature sensor in the present invention.

[0021] Figure 3 It is the schematic diagram of the fiber optic temperature sensing system in the present invention.

[0022] Figure 4 It is the flow schematic diagram of the manufacturing method of the fiber optic temperature sensor in the present invention.

[0023] Figure 5 It is the flow chart of the manufacturing method of the fiber optic temperature sensor in an embodiment of the present invention.

[0024] Figure 6 It is the microscopic image of the short tapered fiber structure under a 20x objective lens in an embodiment of the present invention.

[0025] Figure 7 It is the microscopic image of the femtosecond laser written grating in a fiber with a diameter of 16um and then under a 50x objective lens in an embodiment of the present invention.

[0026] Figure 8 It is the time constant measured by the fiber with a diameter of 125um in an embodiment of the present invention.

[0027] Figure 9 It is the time constant measured by the fiber with a diameter of 16um in an embodiment of the present invention.

[0028] Each label in the attached drawings: 10, fiber optic temperature sensor; 11, sensor probe; 111, fiber coating layer; 112, fiber cladding; 1121, bare fiber area; 1122, transition area; 1123, gentle area; 113, fiber core; 114, grating; 121, ceramic ferrule; 122, mesh metal sleeve; 123, curing glue; 20, grating demodulator; 21, laser; 22, electro-optic modulator; 23, circulator; 24, photodetector; 25, amplifier; 26, filter; 27, coupler; 30, computer terminal. Detailed implementation manners

[0029] The present invention provides a fiber optic temperature sensor, a system and a manufacturing method thereof. To make the purpose, technical solution and effect of the present invention clearer and more definite, the following further describes the present invention in detail with reference to the attached drawings and by way of examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] In the embodiments and the scope of the patent application, unless otherwise specifically defined in the text for articles, the words "a", "an", "the", and "said" may also include plural forms. If there are descriptions involving "first", "second", etc. in the embodiments of the present invention, such descriptions of "first", "second", etc. are only for descriptive purposes and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first", "second" may explicitly or implicitly include at least one such feature.

[0031] It should be further understood that the term "comprising" used in the specification of the present invention means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or their groups. It should be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to other elements, or there may also be intermediate elements. In addition, the "connection" or "coupling" used here may include wireless connection or wireless coupling. The phrase "and / or" used here includes all or any unit and all combinations of one or more of the associated listed items.

[0032] Those skilled in the art of the present technology can understand that, unless otherwise defined, all terms used here (including technical terms and scientific terms) have the same meaning as the general understanding of those of ordinary skill in the art to which the present invention pertains. It should also be understood that terms such as those defined in a general dictionary should be understood as having a meaning consistent with the meaning in the context of the prior art, and will not be interpreted with an idealized or overly formal meaning unless specifically defined as here.

[0033] In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0034] Please also refer to Figures 1 to 2 , the present invention provides a preferred embodiment of an optical fiber temperature sensor.

[0035] In some embodiments, as Figure 1 associated with Figure 2 shown, wherein Figure 2 is Figure 1Enlarged view of area A in the figure. The present invention provides an optical fiber temperature sensor 10, which includes a sensor probe 11 and a packaging structure for packaging the sensor probe 11; the sensor probe 11 includes: an optical fiber coating layer 111, an optical fiber cladding layer 112, a core 113 and a grating 114; the optical fiber cladding layer 112 includes a bare optical fiber area 1121, a transition area 1122 and a gentle area 1123; one end of the bare optical fiber area 1121 is connected to the optical fiber coating layer 111, one end of the transition area 1122 is connected to the other end of the bare optical fiber area 1121, and the other end of the transition area 1122 is connected to the gentle area 1123; the core 113 is located within the optical fiber cladding layer 112, and the grating 114 is located on the core 113; the diameter of the transition area 1122 gradually decreases from the bare optical fiber area 1121 towards the gentle area 1123; the diameter of the gentle area 1123 gradually decreases from one end close to the transition area 1122.

[0036] In this embodiment, the optical fiber temperature sensor 10 is composed of a sensor probe 11 and a packaging structure. The packaging structure is used to package the sensor probe 11 to protect the sensor probe 11 from damage. The optical fiber cladding layer 112 is obtained by removing the coating layer from a single-mode optical fiber, and the core 113 is located within the optical fiber cladding layer 112.

[0037] The optical fiber cladding layer 112 includes a bare optical fiber area 1121, a transition area 1122 and a gentle area 1123. The bare optical fiber area 1121 is obtained by directly removing the optical fiber coating layer 111. The transition area 1122 is located on one side of the bare optical fiber area 1121. The transition area 1122 is pre-drawn by a fusion splicer, which can reduce the optical fiber diameter from more than one hundred micrometers to dozens of micrometers, for example, from 100 micrometers to 20 micrometers, to form an initial tapered structure, thereby achieving a larger taper angle and being beneficial to reducing the total length of the probe. The gentle area 1123 is located on one side of the transition area 1122. The gentle area 1123 is further thinned by oxyhydrogen flame heating technology, and the diameter of dozens of micrometers can be further thinned to more than a dozen micrometers. This change in the optical fiber diameter can achieve an ultra-fast temperature response, and at the same time make the tip part of the tapered optical fiber probe smoother, which is beneficial to the consistency of the temperature response of the grating 114. The grating 114 is obtained by point-by-point writing of a uniform fiber Bragg grating in the gentle area 1123 by femtosecond laser direct writing technology, enabling the optical fiber probe to have the ability to sense the external temperature.

[0038] It should be understood that generally, the smaller the diameter of an object, the faster the temperature induction. According to the heat conduction theory, the thermal response time of a sensor is proportional to its cross-sectional size. Therefore, reducing the core diameter to less than 2 μm can significantly shorten the thermal response time of the sensor. The thermal time constant τ of a cylinder (such as a micro-optical fiber) immersed in a fluid can be described as follows: ; Where ρ is the density of the object, r is the radius of the object, c is the specific heat capacity of the object, and h is the heat transfer coefficient between the fluid and the surface of the cylinder. Therefore, reducing the diameter of the sensor is crucial for achieving a short response time of the sensor. Since the optical fiber is drawn very thin, it becomes extremely sensitive to the external temperature and can achieve a rapid response to temperature. By drawing the optical fiber thin, the problem that the traditional fiber Bragg grating has a slow response time and cannot quickly monitor temperature changes is effectively solved. Moreover, by designing a short conical structure, it has high reliability, a stable and simple structure, providing a reliable and economical solution for rapid temperature monitoring.

[0039] In the above technical solution, the present invention adopts a compact short conical optical fiber structure design. By rapidly drawing the optical fiber in a critical molten state, the diameter of the optical fiber changes sharply, forming an optical fiber structure with a large cone angle and a short cone length (the structural parameters of the tapered optical fiber can be precisely controlled by controlling the drawing speed ratio and the heating duration), which can significantly reduce the heat conduction time of the optical fiber temperature sensor. Enhance the heat conduction efficiency, reach thermal equilibrium with the measured object faster, so that the response time of the temperature can be effectively shortened to more than ten milliseconds or even lower. In addition, by breaking through the preparation of the fiber optic microcone grating, through the femtosecond laser direct writing technology, the position of the laser focus in the fiber optic microcone is precisely controlled, and the grating structure is prepared point by point in the microcone as a temperature sensitive element. By changing the grating period, the reflection wavelength can be flexibly controlled, and the relationship between the grating reflection wavelength and the temperature is established to realize temperature sensing measurement. The optical fiber temperature sensor provided by the present invention has a higher response rate than the traditional fiber Bragg grating temperature sensor, and has a simple process, does not require a sensitizing material, has a low cost and high reliability. At the same time, it has many other advantages of the fiber Bragg grating temperature sensor, can adapt to various complex measurement environments, is suitable for real-time temperature measurement under extreme conditions such as the surface of high-speed aircraft and the transient temperature monitoring of high-speed flow fields, and has important scientific significance and engineering application value.

[0040] In some embodiments, as Figure 2 shown, the transition region 1122 is in a conical shape; the length of the transition region 1122 is 480 - 520 microns, and the diameter of the transition region 1122 is 20 - 130 microns.

[0041] In this embodiment, to ensure the compactness of the fiber optic temperature sensor 10, the length of the transition region 1122 is set to be 40 - 520 micrometers. For example, it can be 480 micrometers, 500 micrometers, 520 micrometers, etc. In this embodiment, the length of the transition region 1122 can be 200 micrometers. In the transition region 1122, the diameter of the fiber optic cladding 112 is 20 - 130 micrometers, that is, in the transition region 1122, the maximum diameter of the fiber optic cladding 112 is 130 micrometers, and the minimum diameter is 20 micrometers. The diameter of the fiber optic cladding 112 in the transition region 1122 decreases sharply from the maximum to dozens of micrometers. In this embodiment, the diameter of the fiber optic cladding 112 in the transition region 1122 decreases from 125 micrometers to 20 micrometers.

[0042] In some embodiments, as Figure 2 shown, the gentle region 1123 is conical in shape; the length of the gentle region 1123 is 180 - 220 micrometers, and the diameter of the gentle region 1123 is 13 - 18 micrometers.

[0043] In this embodiment, in the gentle region 1123, the diameter of the fiber optic cladding 112 changes slowly. The length of the gentle region 1123 is 180 - 220 micrometers. For example, it can be 180 micrometers, 200 micrometers, 220 micrometers, etc. In this embodiment, the length of the gentle region 1123 is 200 micrometers. In the gentle region 1123, the diameter of the fiber optic cladding 112 will be slowly tapered to 13 - 18 micrometers. In this embodiment, the diameter of the fiber optic cladding 112 in the gentle region 1123 is 16 micrometers. In the gentle region 1123, the diameter of the fiber core 113 in the gentle region 1123 will be tapered to less than 2 micrometers, so that the fiber optic temperature sensor 10 can become very sensitive to the external temperature and can achieve a rapid response to temperature.

[0044] In some embodiments, as Figure 2 shown, the encapsulation structure includes a ceramic ferrule 121 and a mesh metal sleeve 122; one end of the sensor probe 11 is inserted into the ceramic ferrule 121, and the mesh metal sleeve 122 is sleeved on the other end of the sensor probe 11.

[0045] Furthermore, the fiber optic cladding 112 passes through the ceramic ferrule 121, and one end of the fiber optic cladding 112 connected to the ceramic ferrule 121 is fixed with a curing adhesive 123.

[0046] In this embodiment, to protect the optical fiber probe, the micro-tapered fiber structure can be inserted into the ceramic ferrule 121, and the ultraviolet curing glue can be further used to fix the tail end of the optical fiber to the ceramic ferrule 121. The sensor probe 11 is sleeved with a mesh metal sleeve 122 to protect the sensor probe 11 while ensuring heat conduction.

[0047] In some embodiments, as Figure 3 shown, the present invention provides an optical fiber temperature sensing system, which includes a grating demodulator 20, a computer terminal 30, and the optical fiber temperature sensor 10 described above; the grating demodulator 20 is connected to the computer terminal 30 for generating a resonance signal and inputting it to the computer terminal 30; the optical fiber temperature sensor 10 is located on one side of the grating demodulator 20 for adjusting the drift of the spectral center frequency according to the change of temperature; the computer terminal 30 is used to obtain temperature data according to the resonance signal.

[0048] In this embodiment, the general optical fiber temperature sensor 10 system mainly consists of three core parts: a sensor probe 11, a grating demodulator 20, and a computer terminal 30. An optical fiber jumper is used to connect the optical fiber temperature sensor 10, and the other end of the jumper is connected to a certain channel of the grating demodulator 20. When the system works, the laser 21 built in the grating demodulator 20 emits laser light (broadband light source) within a specific wavelength range, which is transmitted to the optical fiber temperature sensor 10 through the jumper. The grating 114 in the optical fiber temperature sensor 10 reflects the optical signal carrying temperature information, which is then collected and analyzed by the grating demodulator 20. The temperature change is accurately calculated by detecting the drift amount of the center wavelength of the grating 114, and finally the processed temperature data is displayed on the computer terminal 30 in real time. The optical fiber temperature sensor 10 provided by the present invention has the advantages of high versatility and easy reuse, can be compatible with the existing grating demodulator 20, and has a simple preparation method, low process and accuracy requirements.

[0049] In some embodiments, as Figure 3 shown, the grating demodulator 20 includes: a laser 21, an electro-optic modulator 22, a circulator 23, a photodetector 24, an amplifier 25, a filter 26, and a coupler 27; the laser 21 is located at the light input side of the electro-optic modulator 22; the electro-optic modulator 22 is located at the first light input side of the circulator 23; the optical fiber temperature sensor 10 is located at the second light input side of the circulator 23; the circulator 23 is located at the light input side of the photodetector 24; the photodetector 24, the amplifier 25, the filter 26, the coupler 27, and the electro-optic modulator 22 are electrically connected in sequence; the coupler 27 is also electrically connected to the computer terminal 30.

[0050] In this embodiment, the demodulation system composed of the laser 21, electro-optic modulator 22, circulator 23, photodetector 24, amplifier 25, filter 26, coupler 27, fiber optic temperature sensor 10 and computer terminal 30 is an opto-electronic oscillator (OEO), which has an optical path part A and a circuit / radio frequency part B. Integrating photonics and microwave technologies, through the conversion of opto-electronic signals, it can effectively shorten the temperature response time and improve the resolution of temperature measurement. The OEO opto-electronic oscillator has a resonant cavity that combines optical and electrical circuits, and can map optical signals to the frequency spectrum of microwave signals. Its main advantages are strong signal-to-noise ratio, high resolution and fast demodulation rate.

[0051] The working principle of the fiber optic temperature sensor system is as follows: Without considering the access of the sensor probe 11, the photodetector 24 continuously converts optical signals into electrical signals, which are amplified by the amplifier 25 and fed back to optical signal modulation. Due to the time delay effect of the loop, the components with a fixed frequency are amplified, while other frequency components are lost. After multiple cycles, a frequency comb with a fixed frequency interval is formed in the system. The interval of the frequency comb is related to the time delay, which is determined by the length of the transmission fiber in the loop. The longer the fiber length, the narrower the interval. Subsequently, under the action of the filter 26, most frequencies can be filtered out, and only one working frequency component is retained. The opto-electronic oscillator resonates very quickly (up to the microsecond level, mainly affected by the time delay), and a stable resonant signal can be formed in a short time. The access of the sensor probe 11 mainly affects the drift of the center frequency of the spectrum. When the sensor probe 11 senses temperature changes, it will cause the center wavelength of the reflection spectrum of the grating 114 to drift. This drift is manifested as a significant frequency change in the frequency domain, which can significantly improve the sensitivity and resolution. Due to the access of the amplifier 25, the optical signal is continuously amplified and reaches a stable state, enabling the OEO system to detect weak spectra. At the same time, the fast and stable resonance enables the system to demodulate dynamic signals, thus realizing fast and high-precision measurement of the temperature response of the fiber optic microcone grating.

[0052] In some embodiments, as Figure 4 shown, the present invention also provides a manufacturing method for manufacturing the fiber optic temperature sensor as described above, which includes the steps of: S100. Pre-draw a single-mode fiber using a fusion splicer, and simultaneously stretch the single-mode fiber in the left and right directions by a motor when the fusion splicer discharges; Specifically, please combine Figure 5, when preparing the fiber optic temperature sensor, a standard ordinary single-mode fiber is used as the base material. In this embodiment, the fiber cladding diameter of the single-mode fiber is 123 microns, and the core diameter is 9 microns. During the preparation process, considering the length of the heated area of the fiber and the limitations of arc discharge, the flame diameter ejected by the burner of the oxyhydrogen flame is about 1 cm, which is not conducive to the preparation of the short-tapered fiber structure. The discharge interval of the electrode rod of the fusion splicer is in the micron range, but the arc discharge will directly fuse the fiber with a thinner diameter, forming a spherical end face. Therefore, when pre-drawing the single-mode fiber, as in Figure 5 In step S1, while using the arc discharge of the fusion splicer, drive the motors on both sides to stretch in the reverse direction, so that the fiber diameter is reduced from 125 microns to dozens of microns, for example, reduced to 30-40 microns, to form an initial tapered structure, which can achieve a larger taper angle, that is, a transition zone can be formed, which is beneficial to reducing the total length of the probe.

[0053] S200. Heat the single-mode fiber with the oxyhydrogen flame to draw it thinner again; Specifically, please combine with Figure 5 In step S2, after forming the initial tapered structure, the fiber is drawn thinner again by the oxyhydrogen flame heating technology, and the fiber diameter can be further stretched from dozens of microns to more than a dozen microns, for example, 16 microns, that is, a gentle zone can be formed. This method can avoid the risk of directly fusing the fiber by arc discharge, and at the same time, the tip part of the tapered fiber probe can become smoother, which is beneficial to the consistency of the fiber grating temperature response.

[0054] S300. Disconnect the single-mode fiber to obtain two fibers with microcone structures; Specifically, please combine with Figure 5 In step S3, after the fiber diameter is drawn thinner to more than a dozen microns, the fiber is cut off, and two microtapered fibers can be obtained.

[0055] S400. Use the femtosecond laser technology point-by-point method to write a uniform fiber Bragg grating in the gentle zone; Specifically, please combine with Figure 5 In step S4, after forming the gentle zone, under the movement of the displacement stage, use the femtosecond laser direct writing technology point-by-point method to write a uniform fiber Bragg grating (Fiber Bragg Grating, FBG) in the gentle zone part of the tip, so that the sensor probe has the ability to sense the external temperature.

[0056] S500. Install a packaging structure on the obtained microtapered fiber.

[0057] Specifically, please combine with Figure 5, in order to protect the fiber optic probe, the micro-tapered fiber structure can be inserted into the ceramic ferrule, and ultraviolet curable glue can be further used to fix the tail end of the fiber to the ceramic ferrule. The sensor probe is then sleeved with a mesh metal sleeve to protect the sensor probe while ensuring heat conduction.

[0058] In the above technical solution, during the preparation process, considering the length of the heated area of the optical fiber and the limitations of arc discharge, the flame diameter ejected from the burner of the oxy-hydrogen flame is about 1 cm, which is not conducive to the preparation of the short-tapered fiber structure. The discharge interval of the electrode rod of the fusion splicer is in the micron order, but the disadvantage is that the arc discharge will directly fuse the optical fiber with a thinner diameter, forming a spherical end face. Therefore, combining the advantages and disadvantages of arc discharge and oxy-hydrogen flame heating, a three-step method of "pre-drawing - fine drawing - grating writing" is used to prepare the micro-tapered fiber grating. By controlling the relevant parameters of the fiber drawing taper system and the laser processing system, the drawing of the short-tapered fiber structure with a length of 1-2 mm and the writing of the fiber grating are realized. It can be found from the entire preparation process that the present invention has the advantages of simple process and low cost, and has potential application value.

[0059] Please refer to Figures 5 to 9 , after experimental verification, an ultra-fast temperature response fiber optic sensor designed by the present invention can reduce the response time to 4.75 ms, effectively solving the problem of slow response speed of fiber gratings. By fiber drawing taper, the diameter is reduced to 16 um, and the length of the tip flat area is 150 um, which is suitable for grating writing on it, such as Figure 6 shown. Then, using the femtosecond laser direct writing method, a 100x objective lens and an oil immersion processing method are used to write a grating with a length of 110 um point by point. The processed image is as shown in Figure 7 shown. Finally, using the method of controlling the CO2 laser by an optical switch to quickly heat the fiber grating to test the time constant, the time constants of the fiber grating with a fiber diameter of 125 um and the fiber grating with a fiber diameter of 16 um are tested. The grating demodulator is used to test the spectral curve in real time and find the peak in real time. The laser is irradiated for 2-3 s (to ensure reaching thermal equilibrium). The two groups of measured data are processed to obtain the first-order time constant τ (the time required for the central wavelength to drop from the highest value (red dotted line) to 63.2% (green dotted line) of the lowest value (red dotted line) after removing the heat source), as shown in Figure 8 and Figure 9 shown. It can be seen that the time constant τ of the fiber grating with a fiber diameter of 125 um is 136 ms (3729 - 3593), while the time constant τ of the fiber grating with a fiber diameter of 16 um is 4.75 ms (4126.5 - 4121.75). The results show that the time constant τ of the fiber grating is reduced by 2 orders of magnitude, and the experimental results well verify the temperature sensing performance of the present invention.

[0060] In summary, a fiber optic temperature sensor, a system and a manufacturing method thereof provided by the present invention have the following beneficial effects: The micro-tapered fiber grating is prepared by a three-step method of "pre-drawing - fine drawing - grating inscription". After passing through the transition zone and the gentle zone, the diameter of the fiber can be reduced to more than a dozen micrometers, and the core can be reduced to within 2 micrometers. The grating is arranged in the gentle zone, enabling the fiber optic probe to sense the external temperature. Reducing the core to within 2 micrometers can make the temperature sensing faster, thereby achieving an ultra-fast temperature response. Compared with the existing fiber optic temperature sensors, it not only has a simple process, low cost, but also high reliability.

[0061] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. An optical fiber temperature sensor, characterized in that, It includes a sensor probe and a packaging structure for encapsulating the sensor probe; the sensor probe includes: an optical fiber coating layer, an optical fiber cladding layer, a core, and a grating; The optical fiber cladding layer includes a bare optical fiber region, a transition region, and a gentle region; One end of the bare optical fiber region is connected to the optical fiber coating layer, one end of the transition region is connected to the other end of the bare optical fiber region, and the other end of the transition region is connected to the gentle region; The core is located within the optical fiber cladding layer, and the grating is located on the core; The diameter of the transition region gradually decreases from the bare optical fiber region towards the gentle region; The diameter of the gentle region gradually decreases from one end close to the transition region.

2. The optical fiber temperature sensor according to claim 1, wherein The transition region is conical; the length of the transition region is 480 - 520 microns, and the diameter of the transition region is 20 - 130 microns.

3. The optical fiber temperature sensor according to claim 1, characterized in that, The gentle region is conical; the length of the gentle region is 180 - 220 microns, and the diameter of the gentle region is 13 - 18 microns.

4. The optical fiber temperature sensor according to claim 3, wherein, The diameter of the core in the gentle region is less than 2 microns.

5. The optical fiber temperature sensor according to claim 1, characterized in that, The packaging structure includes a ceramic ferrule and a mesh metal sleeve; one end of the sensor probe is inserted into the ceramic ferrule, and the mesh metal sleeve is sleeved on the other end of the sensor probe.

6. The optical fiber temperature sensor according to claim 5, characterized in that The optical fiber cladding layer passes through the ceramic ferrule, and one end of the optical fiber cladding layer connected to the ceramic ferrule is fixed with a curing adhesive.

7. An optical fiber temperature sensing system, characterized in that, It includes a grating demodulator, a computer terminal, and the fiber optic temperature sensor according to any one of claims 1 - 6; The grating demodulator is connected to the computer terminal and is used to generate a resonant signal and input it to the computer terminal; The fiber optic temperature sensor is located on one side of the grating demodulator and is used to adjust the drift of the spectral center frequency according to the change in temperature; The computer terminal is used to obtain temperature data based on the resonant signal.

8. The fiber optic temperature sensing system according to claim 7, wherein The grating demodulator includes: a laser, an electro - optical modulator, a circulator, a photodetector, an amplifier, a filter, and a coupler; The laser is located at the incident light side of the electro - optical modulator; The electro - optical modulator is located at the first incident light side of the circulator; the fiber optic temperature sensor is located at the second incident light side of the circulator; The circulator is located at the incident light side of the photodetector; The photodetector, the amplifier, the filter, the coupler, and the electro - optical modulator are electrically connected in sequence; The coupler is also electrically connected to the computer terminal.

9. A manufacturing method for manufacturing an optical fiber temperature sensor as described in any one of claims 1-6, characterized in that, It includes: Pre - stretch a single - mode optical fiber using a fusion splicer, and simultaneously stretch the single - mode optical fiber in the left - right direction in reverse by a motor when the fusion splicer discharges; Heat the single - mode optical fiber with a hydrogen - oxygen flame to make it thinner again; Disconnect the single - mode optical fiber to obtain two optical fibers with micro - cone structures; Use the femtosecond laser technology point - by - point method to write a uniform fiber Bragg grating in the gentle region.

10. The manufacturing method according to claim 9, characterized in that, It further includes steps: Install a packaging structure on the obtained micro - cone optical fiber.

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