Optical fiber temperature sensor

Abstract

The present invention discloses an optical fiber temperature sensor, comprising: a temperature sensing probe; the temperature sensing probe comprises a single-mode optical fiber, a microcapillary and a glass bulb; the single-mode optical fiber is fused to the top of the microcapillary, the bottom of the microcapillary is fused to the top of the glass bulb, and the glass bulb is filled with a sensitizing liquid; the cavity between the upper cross section of the single-mode optical fiber and the liquid surface of the sensitizing liquid in the microcapillary is an interference cavity. Compared with the traditional temperature sensing structure of the all-optical fiber structure, the present invention effectively improves the sensitivity, can be used in high-precision temperature monitoring, and can change the temperature sensing range by changing the filling liquid in the thermometer structure, thereby expanding the sensing field and effectively improving the practicality of the device.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber temperature sensing, and more particularly to an optical fiber temperature sensor. Background Art

[0002] In the fiber optic temperature sensor, the fiber optic sensing probe is the most important structure. Temperature sensing uses the characteristics of various optical fiber properties (phase, polarization, intensity, etc.) that change with temperature to measure temperature.

[0003] Although the existing fiber optic temperature sensor probe has the characteristics of integrated sensing and sensing, the traditional all-fiber sensing structure is limited by its own characteristics, such as low thermo-optical coefficient and low expansion coefficient, which makes it insensitive to temperature changes in the surrounding environment and difficult to obtain a high-precision sensing effect. Although there are sensitivity enhancement methods in the prior art, such as chemically corroding the optical fiber to achieve a specific structure or filling the optical fiber micro-nano structure with sensitivity enhancement materials, these methods are relatively cumbersome or costly to implement.

[0004] Therefore, how to provide an optical fiber temperature sensor with a simple structure and high sensing accuracy is a problem that technical personnel in this field need to solve urgently. Summary of the invention

[0005] In view of this, the present invention provides an optical fiber temperature sensor, which aims to solve the problem of low sensing accuracy of the all-optical fiber sensing structure in the prior art and high cost for improving the accuracy.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] An optical fiber temperature sensor comprises: a temperature sensing probe;

[0008] The temperature sensing probe comprises a single-mode optical fiber, a microcapillary tube and a glass bubble;

[0009] The single-mode optical fiber is fused to the top of the microcapillary tube, the bottom end of the microcapillary tube is fused to the top of the glass bubble, and the glass bubble is filled with a sensitizing liquid;

[0010] The cavity between the upper end cross section of the single-mode optical fiber and the liquid surface of the sensitizing liquid in the microcapillary is an interference cavity.

[0011] Preferably, it further comprises a laser, a coupler, a demodulation circuit and a temperature display, wherein the coupler is connected to the single-mode optical fiber, and the demodulation circuit is electrically connected to the coupler and the temperature display respectively;

[0012] The signal light emitted by the laser enters the coupler and is introduced into the interference cavity through the single-mode optical fiber. The optical signal after entering the interference cavity returns to the coupler and enters the demodulation circuit to generate an electrical signal, which is transmitted to the temperature display. The temperature display converts the electrical signal into an actual temperature value and displays it according to the corresponding relationship between the thermal expansion change of the sensitizing liquid, the change in the cavity length of the interference cavity and the change in the spectrum.

[0013] Preferably, it further comprises a light source controller, and the light source controller is electrically connected to the laser.

[0014] Preferably, it also includes a light source controller, and the laser is a semiconductor laser with a wavelength of 1550nm.

[0015] Preferably, the diameter of the microcapillary tube is the same as that of the single-mode optical fiber, and the diameter of the upper opening of the glass bubble is the same as that of the microcapillary tube.

[0016] Preferably, the sensitizing liquid is ethanol.

[0017] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a fiber optic temperature sensor, in which the optical temperature probe adopts a traditional thermometer structure and fuses a single-mode optical fiber above the microcapillary. Compared with the traditional all-optical fiber structure, the temperature sensing structure effectively improves the sensitivity and can be used for higher-precision temperature monitoring. The temperature sensing range can be changed by changing the filling liquid in the thermometer structure, thereby expanding the sensing field and effectively improving the practicability of the device. In addition, the sensing structure is simple, the preparation process is very convenient, the materials are cheap and easy to obtain, the overall cost of the device is low, and the problems existing in the prior art are solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0019] Figure 1 The accompanying drawing is a schematic structural diagram of a temperature sensing probe in an optical fiber temperature sensor provided by the present invention;

[0020] Figure 2 The accompanying drawing is a schematic diagram of the overall structural framework of an optical fiber temperature sensor provided by the present invention;

[0021] Figure 3 The accompanying drawing is a schematic diagram of a quantitative analysis process provided by an embodiment of the present invention;

[0022] Figure 4 The accompanying drawing is a schematic diagram of the experimental system structure framework provided by an embodiment of the present invention;

[0023] 1-single mode optical fiber, 2-micro capillary, 3-glass bubble, 4-sensitizing liquid. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The embodiment of the present invention discloses an optical fiber temperature sensor, such as Figure 1 As shown, it includes: a temperature sensing probe;

[0026] The temperature sensing probe comprises a single-mode optical fiber 1, a microcapillary 2 and a glass bulb 3;

[0027] The single-mode optical fiber 1 is fused to the top of the microcapillary 2, and the bottom end of the microcapillary 2 is fused to the top of the glass bubble 3, and the glass bubble 3 is filled with a sensitizing liquid 4;

[0028] The cavity between the upper end cross section of the single-mode optical fiber 1 and the liquid surface of the sensitizing liquid 4 in the microcapillary 2 is an interference cavity.

[0029] In order to further implement the above technical solution, Figure 2 As shown, it also includes a laser, a coupler, a demodulation circuit and a temperature display, the coupler is connected to the single-mode optical fiber 1, and the demodulation circuit is electrically connected to the coupler and the temperature display respectively;

[0030] The signal light emitted by the laser enters the coupler and is introduced into the interference cavity through the single-mode optical fiber 1; the optical signal after entering the interference cavity returns to the coupler and enters the demodulation circuit to generate an electrical signal, which is transmitted to the temperature display. The temperature display converts the electrical signal into an actual temperature value and displays it according to the corresponding relationship between the thermal expansion change of the sensitizing liquid 4, the change in the cavity length of the interference cavity and the change in the spectrum.

[0031] In order to further implement the above technical solution, a light source controller is also included, and the light source controller is electrically connected to the laser.

[0032] In order to further implement the above technical solution, it also includes a light source controller, and the laser is a semiconductor laser with a wavelength of 1550nm.

[0033] In order to further implement the above technical solution, the diameter of the microcapillary 2 is the same as that of the single-mode optical fiber 1 , and the diameter of the upper opening of the glass bubble 3 is the same as that of the microcapillary 2 .

[0034] In order to further implement the above technical solution, the sensitizing liquid 4 is ethanol.

[0035] The preparation process of this embodiment is:

[0036] First, use a wire stripper to scrape off a small section of the outer coating of a microcapillary 2, wipe the exposed part clean with an ethanol solution with a concentration of more than 95%, and cut a small section of about 30 mm with a fiber optic cutter. Place the two end ports of the cut microcapillary 2 in a fiber end face cleaning box and polish them to ensure that the ports are smooth and flat.

[0037] The glass bulb 3 is fixed to a hard thin rod with glue to ensure the stability of the glass bulb 3 during welding. By pushing the thin rod, the open end of the glass bulb 3 is moved to the discharge position of the optical fiber welding machine and clamped. At the same time, the microcapillary 2 is placed in the other side and clamped. The two ends are welded together with the optical fiber welding machine, and then the glue at the adhesion between the thin rod and the glass bulb 3 is cleaned by chemical corrosion to prepare the thermometer structure.

[0038] Select a section of single-mode optical fiber 1 that matches the size of the microcapillary 2, use a wire stripper to remove the protective layer of the single-mode optical fiber 1, and clean, cut, and polish the processed single-mode optical fiber 1 in turn before use. Fill the prepared thermometer structure with alcohol solution (the type and concentration of the liquid can be adjusted according to the application environment). After filling, let it stand and observe the liquid level until it drops to the theoretically appropriate height and fuse it with the previously processed single-mode optical fiber 1 to prepare a fiber optic sensor probe.

[0039] The working principle of this embodiment is:

[0040] When light enters the fiber temperature probe structure from the single-mode fiber 1, it first encounters the cross section of the single-mode fiber 1 and secondly the liquid surface of the alcohol solution in the microcapillary 2. These two end faces reflect the light for the first and second time respectively. The light reflected twice will enter the coupler in the subsequent system and interfere. The two interfaces constitute a Fabry-Perot interferometer cavity. In the thermometer structure, due to the thermal expansion of the liquid, the temperature change can be amplified by the filling of the liquid. The temperature change directly affects the cavity length of the Fabry-Perot interferometer cavity. In interference, the cavity length is an important parameter. The function of the entire thermometer structure is to amplify the modulation effect of the temperature change on the light beam, which is directly manifested as an increase in the sensitivity of the probe to temperature sensing.

[0041] like Figure 3As shown, according to the above principle, the key lies in the theoretical analysis of the quantitative analysis of the thermal expansion of the specified liquid and the corresponding relationship between the change in the cavity length of the interference cavity and the change in the spectrum. First, the change in the cavity length of the interference cavity caused by temperature is theoretically analyzed, and the influence of the change in cavity length on the interference spectrum is analyzed by ZEMAX simulation software. After continuously optimizing the experimental parameters, the proposed optical fiber temperature sensing structure is prepared, and the experimental system is built for experiments. The experimental data is processed and analyzed, and finally the expected temperature sensing sensitivity is obtained.

[0042] During the experiment, the sensitivity of the temperature sensor probe is analyzed by measuring the drift of the interference spectrum wavelength. Figure 4 As shown in the figure, the experimental system first requires a semiconductor laser controlled by a power supply. The emitted light reaches the Fabry-Perot interferometer through a coupler. The two beams of returning signal light enter the coupler and interfere. The interference spectrum formed can be seen through the spectrometer. At the same time, the optical fiber probe is placed in a heatable constant temperature furnace. By changing the temperature in the furnace, the liquid surface changes due to the thermal expansion of the liquid, which is equivalent to directly changing the cavity length of the interference cavity. The change in cavity length here will have an important impact on the interference spectrum. The drift of the spectrum with temperature changes can be seen directly on the spectrometer. The sensitivity of this temperature sensor probe is measured by analyzing the data. Considering the boiling point of alcohol under standard atmospheric pressure, the temperature range of the experiment is controlled at 20℃-65℃ to prevent the evaporation of ethanol from causing the liquid column to be faulted. In the constant temperature furnace, the temperature rises from 20℃ to 65℃ in steps of 5℃. Each time, the experimental data is measured after the temperature is constant for 3 minutes. A total of 10 experimental data are obtained. These 10 experimental data are analyzed by Origin software to obtain the linear relationship between temperature and spectrum drift, and the sensitivity of the proposed optical fiber sensor probe is obtained.

[0043] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0044] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An optical fiber temperature sensor, characterized in that: include: Temperature sensor probe; The temperature sensing probe comprises a single-mode optical fiber, a microcapillary tube and a glass bubble; The single-mode optical fiber is fused to the top of the microcapillary tube, the bottom end of the microcapillary tube is fused to the top of the glass bubble, and the glass bubble is filled with a sensitizing liquid; The cavity between the upper end cross section of the single-mode optical fiber and the liquid surface of the sensitization liquid in the microcapillary is an interference cavity; It also includes a laser, a coupler, a demodulation circuit and a temperature display, wherein the coupler is connected to the single-mode optical fiber, and the demodulation circuit is electrically connected to the coupler and the temperature display respectively; The signal light emitted by the laser enters the coupler and is introduced into the interference cavity through the single-mode optical fiber; The optical signal after entering the interference cavity returns to the coupler and enters the demodulation circuit to generate an electrical signal, which is transmitted to the temperature display. The temperature display converts the electrical signal into an actual temperature value and displays it according to the corresponding relationship between the thermal expansion change of the sensitizing liquid, the change of the cavity length of the interference cavity and the change of the spectrum; The preparation process of the optical fiber temperature sensor is as follows: Use wire strippers to remove the outer coating of a microcapillary tube, wipe it with an ethanol solution with a concentration of more than 95%, and cut it into 30mm sections with a fiber optic cutter. Place the two ends of the cut microcapillary tube in a fiber end face cleaning box and polish them for later use; The glass bulb is fixed to a hard thin rod with glue, and the open end of the glass bulb is moved to the discharge position of the optical fiber fusion splicer by pushing the thin rod and clamped, and a spare microcapillary is placed on the other side and clamped, and the optical fiber fusion splicer is used to perform fusion splicing, and the glue at the adhesion of the thin rod and the glass bulb is cleaned with a chemical corrosive agent to prepare a thermometer structure; Select a single-mode optical fiber that matches the size of the microcapillary, use a wire stripper to remove the protective layer of the single-mode optical fiber, clean, cut, and polish it for later use; The thermometer structure is filled with alcohol solution, and after filling, it is left to stand and the liquid level is observed until it drops to a preset height, and then fused with a spare single-mode optical fiber to prepare a fiber optic sensor probe.

2. The optical fiber temperature sensor according to claim 1, characterized in that: It also includes a light source controller, which is electrically connected to the laser.

3. The optical fiber temperature sensor according to claim 1, characterized in that: The laser is a semiconductor laser with a wavelength of 1550nm.

4. The optical fiber temperature sensor according to claim 1, characterized in that: The diameter of the microcapillary is the same as that of the single-mode optical fiber, and the diameter of the upper opening of the glass bubble is the same as that of the microcapillary.

5. The optical fiber temperature sensor according to claim 1, characterized in that: The sensitizing liquid is ethanol.

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