Optical fiber temperature sensor, system and manufacturing method thereof

Abstract

The present invention relates to the field of optical fiber sensing technology, and discloses an optical fiber temperature sensor, system, and manufacturing method thereof. The sensor includes a sensor probe and a packaging structure for packaging the sensor probe; the sensor probe includes: an optical fiber coating, an optical fiber cladding, a fiber core, and a grating; the optical fiber cladding includes a bare fiber region, a transition region, and a flat region; one end of the bare fiber region is connected to the optical fiber coating, one end of the transition region is connected to the other end of the bare fiber region, and the other end of the transition region is connected to the flat region; the fiber core is located in the optical fiber cladding, and the grating is located on the fiber core; the diameter of the transition region gradually decreases from the bare fiber region toward the flat region; the diameter of the flat region gradually decreases from the end closest to the transition region. The optical fiber temperature sensor provided by the present invention can reduce the diameter of the optical fiber to more than ten microns after passing through the transition region and the flat region, and the fiber core can be reduced to less than 2 microns, thereby achieving ultrafast temperature response, with not only simple process, low cost, but also high reliability.

Description

Technical Field

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

[0002] Fiber optic temperature sensors, a new generation of temperature sensing technology, measure temperature by monitoring the wavelength, intensity, and phase of light transmitted through optical fibers as it changes with ambient temperature. Compared to traditional electronic temperature sensors like thermocouples and thermal radiation monitoring methods, such as non-contact temperature measurement, fiber optic temperature sensors offer the following advantages: First, their all-optical transmission is immune to electromagnetic interference and can operate even in strong magnetic environments, making them suitable for extreme scenarios such as high-voltage substations and the nuclear industry. Second, fiber optic sensors are typically made of oxides or single crystals, which are less chemically active than metals and offer strong corrosion resistance. They can operate in strong acidic or alkaline environments for extended periods, making them suitable for the petrochemical industry. Third, fiber optic sensors are compact and high-temperature resistant, making them commonly used for distributed in-situ temperature measurement. They offer high accuracy, low error, and the ability to perform regional, miniaturized measurements. These advantages overcome the shortcomings of traditional temperature measurement devices and demonstrate promising application prospects in a wide range of fields, including manufacturing, healthcare, energy, aerospace, and deep-sea exploration.

[0003] For rapidly changing temperature fields, the sensor's response speed can affect the accuracy of measurement results. First, widely used thermocouples offer a wide temperature measurement range and high resolution. However, they are not corrosion-resistant and require protection from inert metal or ceramic sheathing, which delays thermal equilibrium with the ambient temperature, resulting in a slow response. Furthermore, some researchers have employed a blackbody cavity based on Kirchhoff's blackbody radiation law by replacing the opaque cavity with a transparent one, using the opaque liquid being measured as the new cavity. While this approach effectively improves response speed, it is limited by the requirement that the measured object possess both opacity and fluidity, making it unsuitable for dynamic monitoring of aircraft surface temperatures and limiting its applicability. Finally, fiber Bragg grating (FBG)-based temperature sensors are common, but their 125µm cladding diameter (common single-mode fiber) slows thermal conduction, resulting in a response time of up to 136ms. This can be even higher due to the packaging structure, making it difficult to measure the dynamic temperature of rapidly changing objects. Therefore, addressing these issues, designing a fast-response fiber optic temperature sensor has become a hot topic of research.

[0004] In recent years, several approaches have been proposed to improve the response speed of fiber optic temperature sensors. For example, by reducing the size of the fiber Bragg grating (FBG) and using special coating materials, the sensor's sensitivity to temperature is increased, thereby improving the sensor's response speed to a certain extent. However, these approaches often suffer from complex processes, high costs, and poor reliability, making them difficult to implement on a large scale. For example, patent application number CN201821843082.6, entitled "Fiber Optic Temperature Sensor and Temperature Measurement System," utilizes a gallium arsenide single crystal bonded to the end of an optical fiber. The sensor structure consists of bonding a tiny gallium arsenide single crystal to the end face of a bare optical fiber and applying a highly reflective insulating coating to the other side. Gallium arsenide single crystals are semiconductors that operate based on the intrinsic absorption of photons by electrons within them. When light strikes a gallium arsenide single crystal, light with wavelengths less than the absorption edge wavelength λ is absorbed, while light with wavelengths greater than λ can pass through the gallium arsenide crystal and is reflected by the highly reflective coating to a photodetector. The bandgap width of a GaAs single crystal directly determines its absorption edge wavelength, making it highly sensitive to ambient temperature. This allows for rapid temperature detection, with response times as low as 5ms, fully sufficient for detecting temperature rises in explosives or chips. However, its shortcomings are also significant. Its high sensitivity results in a narrow temperature measurement range, typically between -40°C and 260°C. A wider temperature measurement range requires a wider-bandwidth light source, which undoubtedly increases costs and makes it unsuitable for rapid high-temperature monitoring. Furthermore, the size and bonding process of the GaAs single crystal significantly impact its performance, making consistency difficult to ensure.

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

[0006] In view of the above-mentioned deficiencies in the prior art, an object of the present invention is to provide an optical fiber temperature sensor, a system and a manufacturing method thereof, so as to solve the problems of the existing optical fiber temperature sensors such as complex process, high cost and poor reliability.

[0007] The technical solutions of the present invention are as follows:

[0008] In a first aspect, the present invention provides an optical fiber 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, a fiber core and a grating;

[0009] The optical fiber cladding includes a bare optical fiber region, a transition region and a flat region;

[0010] One end of the bare 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 fiber area, and the other end of the transition area is connected to the flat area;

[0011] The fiber core is located in the fiber cladding, and the grating is located on the fiber core;

[0012] The diameter of the transition zone gradually decreases from the bare optical fiber zone toward the flat zone;

[0013] The diameter of the flat zone gradually decreases from one end close to the transition zone.

[0014] According to a further configuration of the present invention, the transition zone is cone-shaped; the length of the transition zone is 480-520 microns, and the diameter of the transition zone is 20-130 microns.

[0015] According to a further configuration of the present invention, the flat area is cone-shaped; the length of the flat area is 180-220 microns, and the diameter of the flat area is 13-18 microns.

[0016] According to a further configuration of the present invention, the diameter of the fiber core in the flat region is less than 2 microns.

[0017] According to a further configuration of the present invention, 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.

[0018] According to a further configuration of the present invention, the optical fiber cladding is passed through the ceramic ferrule, and one end of the optical fiber cladding connected to the ceramic ferrule is fixed by using a curing adhesive.

[0019] In a second aspect, the present invention provides an optical fiber temperature sensing system, which includes a grating demodulator, a computer terminal and the optical fiber temperature sensor described above;

[0020] The grating demodulator is connected to the computer terminal and is used to generate a resonance signal and input it into the computer terminal;

[0021] The optical fiber temperature sensor is located on one side of the grating demodulator and is used to adjust the drift of the spectrum center frequency according to temperature changes;

[0022] The computer terminal is used to obtain temperature data according to the resonance signal.

[0023] According to a further configuration of the present invention, the grating demodulator comprises: a laser, an electro-optical modulator, a circulator, a photodetector, an amplifier, a filter and a coupler;

[0024] The laser is located at the light entrance side of the electro-optical modulator;

[0025] The electro-optical modulator is located at the first light input side of the circulator; the optical fiber temperature sensor is located at the second light input side of the circulator;

[0026] The circulator is located on the light incident side of the photodetector;

[0027] The photodetector, the amplifier, the filter, the coupler and the electro-optical modulator are electrically connected in sequence;

[0028] The coupler is also electrically connected to the computer terminal.

[0029] In a third aspect, the present invention further provides a method for manufacturing the optical fiber temperature sensor as described above, comprising:

[0030] The single-mode optical fiber is pre-drawn by a fusion splicer. When the fusion splicer is discharged, the motor simultaneously stretches the single-mode optical fiber in the left and right directions.

[0031] The single-mode optical fiber is further thinned by heating with an oxyhydrogen flame;

[0032] The single-mode optical fiber is split to obtain two optical fibers with micro-taper structures;

[0033] A femtosecond laser technique is used to write a uniform fiber Bragg grating in the flat area point by point.

[0034] A further embodiment of the present invention further comprises the steps of:

[0035] A packaging structure is installed on the obtained micro-taper optical fiber.

[0036] Provided by the present invention are an optical fiber temperature sensor, system, and manufacturing method thereof, an optical fiber temperature sensor comprising a sensor probe and a packaging structure for encapsulating the sensor probe; the sensor probe comprising: an optical fiber coating, an optical fiber cladding, a fiber core, and a grating; the optical fiber cladding comprising a bare fiber region, a transition region, and a flat region; one end of the bare fiber region is connected to the optical fiber coating, one end of the transition region is connected to the other end of the bare fiber region, and the other end of the transition region is connected to the flat region; the fiber core is located within the optical fiber cladding, and the grating is located on the fiber core; the diameter of the transition region gradually decreases from the bare fiber region toward the flat region; and the diameter of the flat region gradually decreases from the end closest to the transition region. The optical fiber cladding of the optical fiber temperature sensor provided by the present invention has a transition zone and a flat zone. After passing through the transition zone and the flat zone, the diameter of the optical fiber can be reduced to more than ten microns, and the fiber core can be reduced to less than 2 microns. The grating is arranged in the flat zone, which enables the optical fiber probe to sense the external temperature. The reduction of the fiber core to less than 2 microns can make temperature sensing faster, thereby achieving ultra-fast temperature response. Compared with existing optical fiber temperature sensors, it not only has a simple process and low cost, but also has high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary personnel in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0038] Figure 1 It is a structural schematic diagram of the optical fiber temperature sensor in the present invention.

[0039] Figure 2 It is a structural schematic diagram of the sensor probe of the optical fiber temperature sensor in the present invention.

[0040] Figure 3 It is a schematic diagram of the optical fiber temperature sensing system in the present invention.

[0041] Figure 4 It is a flow chart of the manufacturing method of the optical fiber temperature sensor in the present invention.

[0042] Figure 5 FIG. 4 is a flow chart of a method for manufacturing an optical fiber temperature sensor in one embodiment of the present invention.

[0043] Figure 6 FIG. 1 is a microscopic image of a short tapered optical fiber structure under a 20x objective lens in one embodiment of the present invention.

[0044] Figure 7 This is a microscopic image taken under a 50x objective lens after a femtosecond laser directly writes a grating in an optical fiber that has been thinned to a diameter of 16 μm in one embodiment of the present invention.

[0045] Figure 8 It is the time constant measured for an optical fiber with a diameter of 125 μm in one embodiment of the present invention.

[0046] Figure 9 It is the time constant measured for an optical fiber with a diameter of 16 μm in one embodiment of the present invention.

[0047] The marks in the accompanying drawings are: 10, optical fiber temperature sensor; 11, sensor probe; 111, optical fiber coating; 112, optical fiber cladding; 1121, bare optical fiber area; 1122, transition area; 1123, flat 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 DESCRIPTION

[0048] The present invention provides an optical fiber temperature sensor, system, and manufacturing method thereof. To further clarify the objectives, technical solutions, and advantages of the present invention, the present invention is further described below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0049] In the embodiments and patent claims, unless otherwise specified herein, the words "a," "an," "the," and "the" may include plural forms. If the embodiments of the present invention include descriptions of "first," "second," etc., such descriptions are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly specifying the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one of such features.

[0050] It should be further understood that the term "comprising" used in the description of the present invention refers to the presence of the 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 groups thereof. It should be understood that when an element is said to be "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or there can be intermediate elements. In addition, "connected" or "coupled" as used herein can include wireless connections or wireless couplings. The term "and / or" as used herein includes all or any units and all combinations of one or more of the items listed in association.

[0051] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0052] In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the fact that ordinary technicians in this field can implement them. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0053] Please also see Figures 1 to 2 , the present invention provides a preferred embodiment of an optical fiber temperature sensor.

[0054] In some embodiments, as Figure 1 and Figure 2 As shown, Figure 2 for Figure 1 In the enlarged view at point A, 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 111, an optical fiber cladding 112, a fiber core 113 and a grating 114; the optical fiber cladding 112 includes a bare fiber area 1121, a transition area 1122 and a flat area 1123; one end of the bare fiber area 1121 is connected to the optical fiber coating 111, one end of the transition area 1122 is connected to the other end of the bare fiber area 1121, and the other end of the transition area 1122 is connected to the flat area 1123; the fiber core 113 is located in the optical fiber cladding 112, and the grating 114 is located on the fiber core 113; the diameter of the transition area 1122 gradually decreases from the bare fiber area 1121 toward the flat area 1123; the diameter of the flat area 1123 gradually decreases from the end close to the transition area 1122.

[0055] In this embodiment, the optical fiber temperature sensor 10 comprises a sensor probe 11 and a packaging structure. The packaging structure is used to encapsulate the sensor probe 11 and protect it from damage. The optical fiber cladding 112 is obtained by removing the coating layer of a single-mode optical fiber, and the fiber core 113 is located within the optical fiber cladding 112.

[0056] The optical fiber cladding 112 includes a bare fiber region 1121, a transition region 1122, and a flat region 1123. The bare fiber region 1121 is obtained by directly removing the optical fiber coating 111. The transition region 1122 is located on one side of the bare fiber region 1121. The transition region 1122 is pre-drawn by a fusion splicer, which can reduce the optical fiber diameter from more than 100 microns to tens of microns, for example, from 100 microns to 20 microns, forming an initial tapered structure, thereby achieving a larger cone angle, which is beneficial for reducing the total length of the probe. The flat region 1123 is located on one side of the transition region 1122. The flat region 1123 is further thinned by hydrogen-oxygen flame heating technology, which can further thin the optical fiber from a diameter of tens of microns to more than ten microns. This change in optical fiber diameter can achieve ultra-fast temperature response, while making the tip of the tapered optical fiber probe more flat, which is beneficial for the consistency of the temperature response of the grating 114. The grating 114 is obtained by writing a uniform fiber Bragg grating point by point in the flat area 1123 using a femtosecond laser direct writing technique, so that the fiber optic probe has the ability to sense the external temperature.

[0057] It is important to understand that, generally speaking, the smaller the diameter of an object, the faster the temperature sensing. According to heat conduction theory, the thermal response time of a sensor is proportional to its cross-sectional size. Therefore, reducing the fiber core diameter to below 2μm can significantly shorten the sensor's thermal response time. For a cylindrical object immersed in a fluid (such as a microfiber), the thermal time constant τ can be described as follows:

[0058] ;

[0059] 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 cylindrical surface. Therefore, reducing the sensor diameter is crucial to achieving a short response time. Because the optical fiber is stretched very thin, it becomes very sensitive to the external temperature, enabling rapid temperature response. This thinning of the optical fiber effectively addresses the slow response time of traditional fiber Bragg gratings and their inability to quickly monitor temperature changes. The short tapered structure offers high reliability, stability, and simplicity, providing a reliable and economical solution for rapid temperature monitoring.

[0060] In the above technical solution, the present invention adopts a compact short-tapered optical fiber structure design. By rapidly drawing the optical fiber in the critical molten state, the optical fiber diameter changes dramatically, forming an optical fiber structure with a large cone angle and short cone length (the structural parameters of the tapered optical fiber can be precisely controlled by controlling the drawing speed ratio and the heating time). This can significantly reduce the heat conduction time of the optical fiber temperature sensor. The heat conduction efficiency is enhanced, and thermal equilibrium with the object being measured is reached more quickly, thereby effectively shortening the temperature response time to more than ten milliseconds or even lower. In addition, a breakthrough is made in the preparation of optical fiber micro-cone gratings. Through femtosecond laser direct writing technology, the position of the laser focus within the optical fiber micro-cone is precisely controlled. The grating structure is prepared point by point within the micro-cone as a temperature-sensitive element. Changing the grating period can flexibly control the reflection wavelength, establish the relationship between the grating reflection wavelength and temperature, and realize temperature sensing measurement. The fiber optic temperature sensor provided by the present invention has a higher response rate than traditional fiber optic Bragg grating temperature sensors, and has a simple process, does not require sensitization materials, is low in cost and highly reliable. It also has many other advantages of fiber optic Bragg grating temperature sensors, can adapt to various complex measurement environments, and is suitable for real-time temperature measurement under extreme conditions such as transient temperature monitoring of high-speed aircraft surfaces and high-speed flow fields. It has important scientific significance and engineering application value.

[0061] In some embodiments, as Figure 2 As shown, the transition zone 1122 is cone-shaped; the length of the transition zone 1122 is 480-520 microns, and the diameter of the transition zone 1122 is 20-130 microns.

[0062] In this embodiment, to ensure the compactness of the optical fiber temperature sensor 10, the length of the transition region 1122 is set to 40-520 microns, for example, 480 microns, 500 microns, 520 microns, etc. In this embodiment, the length of the transition region 1122 is 200 microns. In the transition region 1122, the diameter of the optical fiber cladding 112 is 20-130 microns. That is, in the transition region 1122, the maximum diameter of the optical fiber cladding 112 is 130 microns and the minimum diameter is 20 microns. The diameter of the optical fiber cladding 112 in the transition region 1122 decreases dramatically from the maximum diameter to tens of microns. In this embodiment, the diameter of the optical fiber cladding 112 in the transition region 1122 decreases from 125 microns to 20 microns.

[0063] In some embodiments, as Figure 2 As shown, the flat area 1123 is cone-shaped; the length of the flat area 1123 is 180-220 microns, and the diameter of the flat area 1123 is 13-18 microns.

[0064] In this embodiment, the diameter of the optical fiber cladding 112 changes slowly within the flat region 1123. The length of the flat region 1123 is 180-220 microns, for example, 180 microns, 200 microns, and 220 microns. In this embodiment, the length of the flat region 1123 is 200 microns. Within the flat region 1123, the diameter of the optical fiber cladding 112 slowly tapers to 13-18 microns. In this embodiment, the diameter of the optical fiber cladding 112 within the flat region 1123 is 16 microns. Within the flat region 1123, the diameter of the fiber core 113 is tapered to less than 2 microns, thereby making the optical fiber temperature sensor 10 highly sensitive to external temperature and enabling rapid temperature response.

[0065] In some embodiments, as Figure 2 As shown, the packaging 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 .

[0066] Furthermore, the optical fiber cladding 112 is passed through the ceramic ferrule 121 , and one end of the optical fiber cladding 112 connected to the ceramic ferrule 121 is fixed by using a curing adhesive 123 .

[0067] In this embodiment, to protect the optical fiber probe, a micro-tapered optical fiber structure can be inserted into a ceramic ferrule 121, and a UV-curable adhesive can be further used to secure the tail end of the optical fiber to the ceramic ferrule 121. The sensor probe 11 is sheathed with a mesh metal sheath 122 to protect the sensor probe 11 while ensuring thermal conductivity.

[0068] In some embodiments, as Figure 3 As 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, and is used to generate a resonance signal and input it to the computer terminal 30; the optical fiber temperature sensor 10 is located on one side of the grating demodulator 20, and is used to adjust the drift of the spectrum center frequency according to the change of temperature; the computer terminal 30 is used to obtain temperature data according to the resonance signal.

[0069] In this embodiment, the universal fiber optic temperature sensor 10 system is primarily composed of three core components: a sensor probe 11, a grating interrogator 20, and a computer terminal 30. An optical fiber jumper is used to connect the fiber optic temperature sensor 10, with the other end of the jumper connected to a channel of the grating interrogator 20. When the system is operating, the laser 21 built into the grating interrogator 20 emits laser light (a broadband light source) within a specific wavelength range, which is transmitted via the jumper to the fiber optic temperature sensor 10. The grating 114 in the fiber optic temperature sensor 10 reflects the light signal carrying temperature information, which is then collected and analyzed by the grating interrogator 20. The temperature change is accurately calculated by detecting the center wavelength drift of the grating 114, and the processed temperature data is ultimately displayed in real time on the computer terminal 30. The fiber optic temperature sensor 10 provided by the present invention has the advantages of high versatility and ease of multiplexing. It is compatible with existing grating interrogators 20, has a simple preparation method, and has low process and precision requirements.

[0070] In some embodiments, as Figure 3 As shown, the grating demodulator 20 includes: a laser 21, an electro-optical 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-optical modulator 22; the electro-optical 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-optical modulator 22 are electrically connected in sequence; the coupler 27 is also electrically connected to the computer terminal 30.

[0071] In this embodiment, the demodulation system, comprised of a laser 21, an electro-optical modulator 22, a circulator 23, a photodetector 24, an amplifier 25, a filter 26, a coupler 27, an optical fiber temperature sensor 10, and a computer terminal 30, is an optoelectronic oscillator (OEO). This system comprises an optical path A and a circuit / RF section B. It integrates photonics and microwave technologies, effectively shortening temperature response time and improving temperature measurement resolution through photoelectric signal conversion. The OEO features a resonant cavity that combines both optical and circuit components, enabling it to map optical signals onto the frequency spectrum of microwave signals. Its primary advantages include a strong signal-to-noise ratio, high resolution, and fast demodulation speed.

[0072] The fiber optic temperature sensor system operates as follows: Regardless of the presence of sensor probe 11, photodetector 24 continuously converts optical signals into electrical signals, which are then amplified by amplifier 25 and fed back into the optical signal for modulation. Due to the time delay in the loop, fixed frequency components are amplified while other frequency components are lost. After multiple cycles, the system forms a frequency comb with fixed frequency spacing. The spacing 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, the narrower the spacing. Subsequently, filter 26 filters out most frequencies, retaining only the operating frequency component. The optoelectronic oscillator resonates very quickly (up to microseconds, primarily due to time delay), forming a stable resonant signal in a short period of time. The presence of sensor probe 11 primarily affects the drift of the center frequency of the spectrum. When sensor probe 11 senses temperature changes, it causes the center wavelength of the grating 114's reflection spectrum to shift. This shift manifests as a significant frequency change in the frequency domain, significantly improving sensitivity and resolution. Due to the access of the amplifier 25, the optical signal will continuously gain and reach a stable state, so that the OEO system can detect weak spectra. At the same time, the fast and stable resonance enables the system to demodulate dynamic signals, thereby achieving fast and high-precision fiber micro-cone grating temperature response measurement.

[0073] In some embodiments, as Figure 4 As shown, the present invention also provides a method for manufacturing the optical fiber temperature sensor as described above, which comprises the steps of:

[0074] S100, using a fusion splicer to pre-draw the single-mode optical fiber, and when the fusion splicer discharges, the motor simultaneously stretches the single-mode optical fiber in the left and right directions;

[0075] Specifically, please combine Figure 5When preparing the optical fiber temperature sensor, a standard ordinary single-mode optical fiber is used as the basic material. In this embodiment, the optical fiber cladding diameter of the single-mode optical fiber is 123 microns and the core diameter is 9 microns. During the preparation process, considering the length of the heated area of ​​the optical fiber and the limitations of arc discharge, the diameter of the flame ejected by the oxyhydrogen flame is about 1 cm, which is not conducive to the preparation of short-tapered optical fiber structures. The discharge range of the electrode rod of the fusion splicer is on the micron level, but arc discharge will directly melt the optical fiber with a smaller diameter, forming a spherical end face. Therefore, when pre-drawing the single-mode optical fiber, such as Figure 5 In step S1, the arc discharge of the fusion splicer is used while driving the motors on the left and right sides to stretch in opposite directions, so that the diameter of the optical fiber is reduced from 125 microns to tens of microns, for example, to 30-40 microns, to form an initial conical structure. A larger cone angle can be achieved, that is, a transition zone can be formed, which is beneficial to reducing the total length of the probe.

[0076] S200, drawing the single-mode optical fiber thinner again by heating with an oxyhydrogen flame;

[0077] Specifically, please combine Figure 5 In step S2, after forming the initial tapered structure, the optical fiber is further thinned by oxyhydrogen flame heating technology, which can further stretch the optical fiber diameter from tens of microns to more than ten microns, for example, 16 microns, so that a flat zone can be formed. This method can avoid the risk of arc discharge directly melting the optical fiber. At the same time, the tip of the tapered optical fiber probe can also become smoother, which is conducive to the consistency of the temperature response of the fiber Bragg grating.

[0078] S300, disconnecting the single-mode optical fiber to obtain two optical fibers with micro-cone structures;

[0079] Specifically, please combine Figure 5 In step S3, after the optical fiber diameter is thinned to more than ten microns, the optical fiber is cut to obtain two micro-tapered optical fibers.

[0080] S400, using femtosecond laser technology to write a uniform fiber Bragg grating in the flat area point by point;

[0081] Specifically, please combine Figure 5 In step S4, after the flat area is formed, a femtosecond laser direct writing technique is used to write a uniform fiber Bragg Grating (FBG) point by point on the flat area of ​​the tip while the translation stage is moving, so that the sensor probe has the ability to sense the external temperature.

[0082] S500 , installing a packaging structure on the obtained micro-taper optical fiber.

[0083] Specifically, please combine Figure 5To protect the fiber probe, a micro-tapered fiber structure can be inserted into a ceramic ferrule, and a UV-curable adhesive can be used to secure the fiber's tail end to the ceramic ferrule. The sensor probe is sheathed with a mesh metal sleeve to protect the sensor probe while ensuring thermal conductivity.

[0084] In the above technical solution, because it is necessary to consider the length of the heated area of ​​the optical fiber and the limitations of arc discharge during the preparation process, the diameter of the flame ejected by the oxyhydrogen flame is about 1 cm, which is not conducive to the preparation of short-tapered optical fiber structures, and the discharge range of the electrode rod of the fusion splicer is on the micron level, but the disadvantage is that the arc discharge will directly melt the optical fiber with a thinner diameter, forming a spherical end face. Therefore, combining the advantages and disadvantages of arc discharge and oxyhydrogen flame heating, a three-step method of "pre-drawing-fine drawing-grating writing" is adopted to prepare micro-tapered fiber gratings. By controlling the relevant parameters of the optical fiber taper system and the laser processing system, the drawing of a short-tapered optical fiber structure with a length of 1-2 mm and the writing of the optical fiber grating are achieved. 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.

[0085] See also Figures 5 to 9 After experimental verification, the ultrafast temperature response fiber sensor designed by the present invention can reduce the response time to 4.75ms, effectively solving the problem of slow response speed of fiber Bragg grating. By tapering the fiber, the diameter is reduced to 16um, and the length of the flat area at the tip is 150um, which is suitable for writing gratings on it. Figure 6 Then, using the femtosecond laser direct writing method, a 100x objective lens and oil immersion processing were used to write a grating with a length of 110 μm point by point. The processed image is shown as follows: Figure 7 Finally, a method for testing the time constant by using an optical switch to control a CO2 laser to rapidly heat a fiber Bragg grating (FBG) was used to test the time constants of fiber Bragg gratings with a fiber diameter of 125 μm and a fiber Bragg grating with a fiber diameter of 16 μm. A grating demodulator was used to test the spectrum curve in real time and to find the peak in real time. The laser was irradiated for 2-3 seconds (to ensure thermal equilibrium). After data processing, the two sets of measured data were used to obtain the first-order time constant τ (the time required for the center wavelength to drop from the highest value (red dashed line) to 63.2% (green dashed line) of the lowest value (red dashed line) after removing the heat source). Figure 8 and Figure 9 As shown, it can be seen that the time constant τ of the fiber Bragg grating with a fiber diameter of 125um is 136ms (3729-3593), while the time constant τ of the fiber Bragg grating with a fiber diameter of 16um is 4.75ms (4126.5-4121.75). The results show that the time constant τ of the fiber Bragg grating is reduced by 2 orders of magnitude. The experimental results well verify the temperature sensing performance of the present invention.

[0086] In summary, the optical fiber temperature sensor, system, and manufacturing method provided by the present invention have the following beneficial effects:

[0087] The micro-cone fiber Bragg grating is prepared by a three-step method of "pre-drawing-fine drawing-grating writing". After passing through the transition zone and the flat zone, the diameter of the optical fiber can be reduced to more than ten microns, and the core can be reduced to within 2 microns. The grating is set in the flat zone, which enables the optical fiber probe to sense the external temperature. The reduction of the core to within 2 microns can make the temperature sensing faster, thereby achieving ultra-fast temperature response. Compared with existing optical fiber temperature sensors, it not only has a simple process and low cost, but also has high reliability.

[0088] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. An optical fiber temperature sensor, characterized in that: It 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, a fiber core and a grating; The optical fiber cladding includes a bare optical fiber region, a transition region and a flat region; One end of the bare 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 fiber area, and the other end of the transition area is connected to the flat area; The fiber core is located in the fiber cladding, and the grating is located on the fiber core; The diameter of the transition zone gradually decreases from the bare optical fiber zone toward the flat zone; The diameter of the flat zone gradually decreases from one end close to the transition zone; The flat area is cone-shaped; the length of the flat area is 180-220 microns, and the diameter of the flat area is 13-18 microns; The transition zone is pre-drawn by a fusion splicer, which can reduce the fiber diameter from over 100 microns to tens of microns, forming an initial tapered structure. The flat zone is further thinned by oxyhydrogen flame heating technology, which can further thin the fiber diameter from tens of microns to more than ten microns. The diameter of the fiber core in the flat zone is less than 2 microns. 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; The grating is obtained by writing a uniform fiber Bragg grating point by point in the flat area using a femtosecond laser direct writing technique; The optical fiber temperature sensor uses standard single-mode optical fiber as a basic material.

2. The optical fiber temperature sensor according to claim 1, characterized in that The transition zone is cone-shaped; the length of the transition zone is 480-520 microns, and the diameter of the transition zone is 20-130 microns.

3. The optical fiber temperature sensor according to claim 1, wherein: The optical fiber cladding is passed through the ceramic ferrule, and one end of the optical fiber cladding connected to the ceramic ferrule is fixed by using curing glue.

4. A fiber optic temperature sensing system, characterized in that: It comprises a grating demodulator, a computer terminal and the optical fiber temperature sensor according to any one of claims 1 to 3; The grating demodulator is connected to the computer terminal and is used to generate a resonance signal and input it into 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 spectrum center frequency according to temperature changes; The computer terminal is used to obtain temperature data according to the resonance signal.

5. The optical fiber temperature sensing system according to claim 4, characterized in that: 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 light entrance side of the electro-optical modulator; The electro-optical modulator is located at the first light input side of the circulator; the optical fiber temperature sensor is located at the second light input side of the circulator; The circulator is located on the light incident 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.

6. A method for manufacturing the optical fiber temperature sensor according to any one of claims 1 to 3, characterized in that: include: The single-mode optical fiber is pre-drawn by a fusion splicer. When the fusion splicer is discharged, the motor simultaneously stretches the single-mode optical fiber in the left and right directions. The single-mode optical fiber is further thinned by heating with an oxyhydrogen flame; The single-mode optical fiber is split to obtain two optical fibers with micro-taper structures; A femtosecond laser technique is used to write a uniform fiber Bragg grating in the flat area point by point.

7. The manufacturing method according to claim 6, characterized in that Also includes the steps: A packaging structure is installed on the obtained micro-taper optical fiber.

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