A candied haws-shaped optical fiber temperature sensor

Abstract

The invention discloses a candied haws shaped optical fiber temperature sensor, the sensor comprises a candied haws shaped optical fiber, the candied haws shaped optical fiber comprises a tapered optical fiber and a plurality of polymer microspheres sequentially connected in series and wrapped on the tapered optical fiber. The candied haws shaped optical fiber temperature sensor provided by the invention realizes highly sensitive temperature sensing detection by connecting a plurality of polymer microspheres in series on the optical fiber, and the sensor has the advantages of high sensitivity, rapid integration, small size, compact structure and low cost.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensing, and in particular relates to a candied haws-shaped optical fiber temperature sensor. Background Art

[0002] Fiber optic temperature sensors can achieve highly sensitive sensing and detection of ambient temperature and have been widely used in many fields such as power systems, construction, aerospace, and marine development. Fiber optic temperature sensing structures mainly include non-interference and interference types. The non-interference fiber optic temperature sensing structure is mainly prepared using Bragg gratings, and its sensitivity is between 7-11pm / ℃. The preparation process of this type of sensing structure is complicated, the required equipment is expensive, and the structural sensitivity is not high. The interference fiber optic temperature sensing structure has the advantages of simple production and high temperature sensing sensitivity. It is usually prepared by etching a microcavity in the optical fiber, drawing an optical fiber cone, and fusing different types of optical fibers.

[0003] At present, some new thermosensitive functional materials are prepared into microstructures and integrated with optical fibers to further improve the sensitivity and mechanical strength of optical fiber temperature sensing structures, such as liquid crystal, polydimethylsiloxane, etc. Although the sensitivity of such optical fiber temperature sensing structures has been significantly improved, the integration and sensitivity of optical fiber temperature sensors still need to be improved. Researching and realizing a highly sensitive, low-cost, compact, highly integrated, and easy-to-implement optical fiber sensor still has high research and application value. Summary of the invention

[0004] Based on the above technical problems, the present invention provides a candied haws-shaped optical fiber temperature sensor, which realizes highly sensitive temperature sensing detection by connecting multiple polymer microspheres in series on the optical fiber. The sensor has the advantages of high sensitivity, rapid integration, small size, compact structure and low cost.

[0005] The present invention provides a candied haws-shaped optical fiber temperature sensor, which comprises a candied haws-shaped optical fiber. The candied haws-shaped optical fiber comprises a tapered optical fiber and a plurality of polymer microspheres which are sequentially connected in series and wrapped around the tapered optical fiber.

[0006] In the present invention, the optical fiber temperature sensor is composed of a tapered optical fiber and a plurality of polymer microspheres sequentially connected in series and wrapped around the tapered optical fiber. When light is transmitted through the plurality of polymer microspheres, the light beam will be split and converged multiple times, thereby forming a Mach-Zehnder interferometer. As the temperature changes, it can produce very obvious interference fringes, thereby achieving high-sensitivity measurement of the external temperature.

[0007] Preferably, the number of the polymer microspheres is 4-8, preferably 6.

[0008] In the present invention, the plurality of polymer microspheres continuously excite part of the light in the optical fiber core into the optical fiber cladding to form a multi-order cladding mode, and the remaining part is still transmitted in the tapered optical fiber, so that the fundamental mode in the tapered optical fiber and the various order cladding modes in the cladding are continuously coupled into the tapered optical fiber by the following polymer microspheres to interfere with the original tapered optical fiber mode; therefore, when the number of optical fiber microspheres is less than 4, the effective interference length is small and is not enough to form an interference spectrum that is effectively sensitive to the external ambient temperature. When the number of optical fiber microspheres is greater than 8, a longer tapered optical fiber is required, which will result in a large loss of the projected interference spectrum of the sensor structure, which is not conducive to sensing detection.

[0009] Preferably, the plurality of polymer microspheres are spaced evenly on the tapered optical fiber, preferably at a spacing of 100-150 μm.

[0010] In the present invention, the spacing can ensure that more polymer microspheres are obtained within a certain interference length and the quality of the polymer microspheres is guaranteed.

[0011] Preferably, the plurality of polymer microspheres are of equal size, and their diameters are preferably 600-700 μm.

[0012] In the present invention, the diameter of the polymer microspheres can not only ensure the effective excitation of the multi-order modes, but also make the surface where the microspheres and the optical fiber meet as flat as possible, thereby reducing transmission loss.

[0013] Preferably, the tapered optical fiber is obtained by fusion taper technology.

[0014] In the present invention, the tapered optical fiber can increase the penetration depth range of the evanescent field of light, so that the light transmitted in the transmission area is more susceptible to the influence of the external environment.

[0015] Preferably, the length of the tapered optical fiber is 1-5 mm, preferably 2-3 mm.

[0016] Preferably, the candied haws-shaped optical fiber is prepared by the following method:

[0017] Photocurable adhesive is applied to multiple locations on the tapered optical fiber, and the photocurable adhesive at each location forms polymer microspheres on the tapered optical fiber. After light curing, the candied haws-shaped optical fiber is obtained.

[0018] Preferably, the photocurable adhesive is a photoresist, preferably SU-8 photoresist.

[0019] In the present invention, the photoresist, especially the SU-8 photoresist, has effective thermal expansion coefficient and thermo-optic coefficient characteristics, which improves the sensitivity of the interference spectrum formed in the optical fiber temperature sensor to the external environment temperature and improves its temperature sensing sensitivity.

[0020] Preferably, the optical fiber sensor further comprises a broadband light source and a spectrometer;

[0021] The broadband light source, the candied haws-shaped optical fiber and the spectrometer are sequentially connected to each other by means of optical fiber fusion splicing.

[0022] Preferably, after the light emitted by the broadband light source is input into the candied haws reed-shaped optical fiber, it excites a cladding mode that is sensitive to the external temperature, generates Mach-Zehnder interference with the core mode in the candied haws reed-shaped optical fiber, and is then output to the spectrometer.

[0023] In the present invention, when the external environment temperature changes, the wavelength position of the interference attenuation peak will change accordingly, and the external environment temperature can be measured by detecting the wavelength value of the interference attenuation peak of the transmitted light on the spectrometer.

[0024] The specific working principle of the sensor of the present invention is as follows:

[0025] The tapered optical fiber integrates multiple polymer microspheres to form a candied haws-shaped optical fiber temperature sensor. The incident light is divided into two beams on one side of the tapered optical fiber. The two beams are transmitted forward in the tapered optical fiber and the polymer microspheres respectively, and coupled and superimposed on the other side of the tapered optical fiber to form the transmission interference spectrum of the structure. The light beam transmitted in the tapered optical fiber is the core mode, and the light beam transmitted in the polymer microsphere is the cladding mode. The core mode and the cladding mode form an optical path difference when the transmitted light is transmitted, so the phase difference generated after a certain distance of transmission is It can be expressed as:

[0026]

[0027] In formula (1), n core is the effective refractive index of the core mode, n clad is the effective refractive index of the cladding mode, L is the interference length, λ is the wavelength of the light source, and m is the interference order.

[0028] The multiple polymer microspheres integrated into the tapered optical fiber are preferably made of polymer with a high thermo-optic coefficient of 10 -4 / ℃ level and high thermal expansion coefficient of α SU-8 =48ppm / ℃ SU-8 photoresist is applied to the fiber. The effective refractive index and interference length of the candied haws-shaped optical fiber thus formed will be modulated with changes in ambient temperature. According to formula (1), the phase difference between the core mode and the cladding mode changes, which ultimately changes the intensity of the transmission interference spectrum of the gourd-shaped optical fiber structure. The temperature sensing test is achieved by recording the change in the interference peak intensity in the transmission interference spectrum, and it is found that the temperature depends on the number and volume of the polymer microspheres and the fineness of the tapered optical fiber structure.

[0029] The beneficial effects of the present invention are as follows:

[0030] (1) In the present invention, a candied-haws-shaped optical fiber temperature sensing structure based on polymer microspheres is prepared by using simple fusion taper and ultraviolet light curing technology. The structure has a small size and high sensitivity.

[0031] (2) In the present invention, a tapered optical fiber is prepared by melt-drawing a taper technique, and then a plurality of polymer microspheres are uniformly dotted on the tapered optical fiber. Under the premise of controlling the spacing and diameter of the polymer microspheres, the polymer microspheres on the tapered optical fiber are exposed to light by ultraviolet light curing technology to be cured and integrated with the optical fiber, thereby obtaining a candied haws-shaped optical fiber temperature sensing structure.

[0032] (3) In the present invention, the incident light is divided into two beams on one side of the tapered optical fiber. The two beams are transmitted forward in the tapered optical fiber and the polymer microspheres respectively, and are coupled and superimposed on the other side of the optical fiber cone to form the transmission interference spectrum of the structure: it can be observed that the high-frequency peak is modulated in the low-frequency peak of the transmission interference spectrum. The interference spectrum of the structure is Fourier transformed to filter out the high-frequency peak to obtain a low-frequency interference spectrum and the interference peak A near 1475nm after filtering is monitored. When the ambient temperature varies between 30°C and 55°C, the interference spectrum of the structure has a good response to temperature, and its sensitivity can be as high as 0.1182dB / °C.

[0033] (4) In the present invention, the obtained optical fiber temperature sensor has the advantages of easy integration of polymer microspheres, easy production, and low cost, and has broad application prospects in power systems, construction industry, aerospace industry, and marine development fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the structure of the candied haws-shaped optical fiber temperature sensor of the present invention;

[0035] Figure 2 The interference spectrum of the candied haws-shaped optical fiber temperature sensor of the present invention at 30°C;

[0036] Figure 3 It is a spectrum diagram of the interference spectrum diagram of the present invention after Fourier transformation;

[0037] Figure 4 This is the interference spectrum of the interference spectrum of the present invention after high-frequency filtering. DETAILED DESCRIPTION

[0038] Hereinafter, the present invention will describe the technical solution in detail through specific embodiments, but it should be clearly stated that these embodiments are for illustration only and are not to be construed as limiting the scope of the present invention.

[0039] Example

[0040] This embodiment provides an optical fiber magnetic field sensor based on magnetic polymer microspheres, which is prepared by the following method:

[0041] (1) Take two single-mode optical fibers (SMF-28e+) of the same length, with a core diameter of 8 μm and a cladding diameter of 125 μm; use fiber pliers to strip off the coating of about 1 cm at the ends of the two single-mode optical fibers, and after exposing the fiber cladding, use lens paper dipped in alcohol to wipe off the remaining debris on the fiber, and place the exposed fiber cladding on the fiber cleaver to cut the end face flat;

[0042] (2) The optical fiber with the flattened end face is placed into the V-grooves on both sides of the optical fiber fusion splicer (KL-300T); the debris on the optical fiber end face is cleaned by manual cleaning discharge, and then the two optical fibers are fused together by manual discharge. The manual discharge time is 300ms, the manual supplementary discharge timing is 880ms, and the current intensity is 61bit; while manually discharging, a constant external force is applied to pull the optical fiber to move uniformly to both sides at a certain speed. After multiple discharges, a tapered optical fiber with uniform thickness and a length of 2.3±0.1mm can be obtained;

[0043] (3) The tapered optical fiber is taken out from the fusion splicer and fixed on a sample holder with a hollow middle, and then placed under a fiber precision cutting CCD system (XDC-10A-530H); an appropriate amount of liquid polymer material (SU-8 photoresist) is taken and applied to six locations on the tapered optical fiber at equal intervals using a dispensing instrument. Due to the effect of surface tension, the liquid polymer material wrapped around the tapered optical fiber forms polymer microspheres, which are cured after irradiation with an ultraviolet light source (UVLED, XP104, provided by Yuntong Electronic Technology Co., Ltd.) for 40 seconds, thereby preparing a candied haws-shaped optical fiber temperature sensor.

[0044] In the above embodiment, the liquid polymer material SU-8 photoresist is composed of polymer monomers and photoinitiators. Under ultraviolet light irradiation, the photoinitiator in the polymer material absorbs photons to generate active acid H + The active acid can open the chemical bonds contained in the polymer monomers and reorganize them with the chemical bonds of other monomers to solidify the polymer microspheres. The SU-8 photoresist has good light transmittance, high chemical corrosion resistance, strong biocompatibility, and a large thermal expansion coefficient. The same method is used to prepare six equally spaced polymer microspheres on the optical fiber cone, thus forming a candied haws-shaped optical fiber sensing structure.

[0045] The candied haws-shaped optical fiber temperature sensor obtained by the present invention is referred to Figure 1 See Figure 1 It can be seen that the surface of the polymer microspheres is smooth and yellow and transparent. The polymer microspheres are evenly and regularly arranged on the tapered optical fiber, forming a candied haws-shaped optical fiber sensing structure with the tapered optical fiber. The length of the tapered optical fiber is 2.3 mm, the distance between every two polymer microspheres is 125 μm, and the diameter of the polymer microspheres is 625 μm.

[0046] The candied haws-shaped optical fiber was connected to a broadband light source (SC-5-FC, Wuhan Anyang Laser Technology Co., Ltd.) and a spectrometer (AQ6370D, Yokogawa Test and Measurement Co., Ltd.) in sequence by optical fiber fusion splicing, and then placed in a temperature control box (Kingjo, CK-80G). The incident light was coupled to the transmission spectrum formed in the optical fiber after passing through the candied haws-shaped optical fiber. The transmission spectrum of the sensor structure at room temperature was measured. Figure 2 From Figure 2 It can be seen that the interference spectrum is composed of the superposition of low-frequency interference peaks and high-frequency interference peaks. Since the high-frequency interference peak is not conducive to data collection and processing in the sensor test, high-frequency filtering is performed on the high-frequency signal in the interference spectrum.

[0047] First, the interference spectrum is Fourier transformed, and the obtained spectrum is referenced Figure 3 As shown, from Figure 3 In the spectrum shown, we can see that there are two characteristic peaks. The frequencies corresponding to peak A and peak B are x=0.00432 (Hz) and y=0.00862 (Hz) respectively. Then low-pass filtering is performed to allow the low-frequency signal to pass through. The interference spectrum after filtering is shown in Figure 2. Figure 4 As shown, from Figure 4 It can be clearly seen in the interference spectrum shown that there are three low-frequency characteristic peaks in the interference spectrum when the wavelength measurement range is 900-1600nm, and the high-frequency peak is filtered out.

[0048] Temperature sensing characteristics test

[0049] A temperature test device was built to conduct experimental research on the above-mentioned candied haws-shaped optical fiber temperature sensor. The device system consists of a broadband light source, a spectrometer, and a programmable temperature control box. The candied haws-shaped optical fiber is connected to the broadband light source and the spectrometer respectively and placed on the sample rack.

[0050] The temperature of the temperature control box is changed from 30℃ to 55℃ at intervals of 5℃. The transmission spectrum at each temperature is measured and recorded. The spectrum shows that there are multiple interference peaks in the spectral measurement range, which have good response characteristics to temperature. The minimum intensity value of the interference peak A at each temperature is recorded. It can be seen that as the temperature increases, the minimum intensity value of the interference peak in the transmission spectrum increases. The minimum intensity value of the interference peak A is linearly fitted. From the fitting results, it can be seen that the temperature sensitivity of the candied haws-shaped optical fiber temperature sensor is 0.1182dB / ℃, and the linear correlation coefficient is 0.9823.

[0051] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A candied haws-shaped optical fiber temperature sensor, characterized in that: The sensor comprises a candied haws-shaped optical fiber, which comprises a tapered optical fiber and a plurality of polymer microspheres sequentially connected in series and wrapped around the tapered optical fiber; The candied haws-shaped optical fiber is prepared by the following method: Applying light-curing glue at multiple locations on the tapered optical fiber, so that the light-curing glue at each location forms polymer microspheres on the tapered optical fiber, and after light curing, the candied haws-shaped optical fiber is obtained; The tapered optical fiber is obtained by fusion taper technology; The plurality of polymer microspheres are spaced evenly on the tapered optical fiber; The number of the polymer microspheres is 4-8, and the sizes of the multiple polymer microspheres are equal, and the diameters thereof are 600-700 μm.

2. The candied haws-shaped optical fiber temperature sensor according to claim 1, characterized in that: The number of the polymer microspheres is 6.

3. The candied haws-shaped optical fiber temperature sensor according to claim 1, characterized in that: The spacing between the plurality of polymer microspheres on the tapered optical fiber is 100-150 μm.

4. The candied haws-shaped optical fiber temperature sensor according to claim 1, characterized in that: The length of the tapered optical fiber is 1-5 mm.

5. The candied haws-shaped optical fiber temperature sensor according to claim 1, characterized in that: The length of the tapered optical fiber is 2-3 mm.

6. The candied haws-shaped optical fiber temperature sensor according to claim 4, characterized in that: The light-curing adhesive is a photoresist.

7. The candied haws-shaped optical fiber temperature sensor according to claim 4, characterized in that: The photocurable adhesive is SU-8 photoresist.

8. The candied haws-shaped optical fiber temperature sensor according to any one of claims 1 to 7, characterized in that: The device for testing the optical fiber temperature sensor is composed of a broadband light source, a spectrometer and a programmable temperature control box; The broadband light source, the candied haws-shaped optical fiber and the spectrometer are sequentially connected to each other by means of optical fiber fusion splicing.

9. The candied haws-shaped optical fiber temperature sensor according to claim 8, characterized in that: When the light emitted by the broadband light source is input into the candied haws-shaped optical fiber, it excites the cladding mode that is sensitive to the external temperature, and undergoes Mach-Zehnder interference with the core mode in the candied haws-shaped optical fiber, and is then output to the spectrometer.

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