CN-121577188-B - Optical fiber temperature sensor based on double-FP parallel structure

Abstract

The application belongs to the technical field of temperature sensing, and particularly relates to an optical fiber temperature sensor based on a double-FP parallel structure, which is characterized in that the optical fiber temperature sensor is formed by connecting a reference interferometer and a sensing interferometer in parallel, wherein the reference interferometer consists of a first single-mode optical fiber, an hollow fiber and a second single-mode optical fiber, and the sensing interferometer consists of a third single-mode optical fiber, a PDMS cavity and a fourth single-mode optical fiber; the free spectrum range of the sensing interferometer is similar to but not equal to the free spectrum range of the reference interferometer by controlling the optical path lengths of the PDMS cavity and the hollow optical fiber to be similar but not equal, so that the vernier effect of the output spectrum is excited to form an envelope formed by fine stripes. The optical fiber temperature sensor has the advantages of high sensitivity, high linearity, large detection range, good repeatability and good reversibility, and meanwhile, the size of the optical fiber sensing probe is in the micrometer level, so that the optical fiber temperature sensor is suitable for detecting the temperature in a narrow space.

Inventors

• LIU QIANG
• ZHANG JIAWEI
• SU LI

Assignees

• 东北大学秦皇岛分校

Dates

Publication Date

20260505

Application Date

20260127

Claims (4)

1. 1. The optical fiber temperature sensor based on the double-FP parallel structure is characterized by comprising a reference interferometer and a sensing interferometer which are connected in parallel, wherein the reference interferometer comprises a first single-mode optical fiber, a hollow optical fiber and a second single-mode optical fiber, and the sensing interferometer comprises a third single-mode optical fiber, a PDMS cavity and a fourth single-mode optical fiber; The free spectrum range of the sensing interferometer is similar to but not equal to the free spectrum range of the reference interferometer by controlling the optical path lengths of the PDMS cavity and the hollow optical fiber to be similar but not equal to each other, so that the vernier effect of the output spectrum is excited to form an envelope formed by fine stripes; the optical path lengths of the PDMS cavity and the hollow optical fiber are controlled to be similar but unequal in the following way: Preparing a reference interferometer according to the length of a preset hollow fiber, and calculating the optical path length of the hollow fiber based on the refractive index of air; Calculating a length reference value of the PDMS cavity based on the optical path length of the hollow optical fiber and the refractive index of PDMS near 1550nm wavelength; Performing optical fiber alignment on the third and fourth single-mode optical fibers on a glass slide, reserving an air cavity with a specific length, observing and confirming the end face alignment condition in a microscope, and performing optical calibration, wherein the specific length of the air cavity is similar to but not equal to the calculated length reference value of the PDMS cavity; One side of the circulator is connected with a double-FP parallel structure, two lines on the other side are respectively connected with a spectrometer and a super-continuous light source, and after a vernier effect is generated on a spectrum appearing on the spectrometer, a free spectrum range near 1550 nm is calculated; Respectively dripping UV glue on the third single mode fiber and the fourth single mode fiber, and curing by an ultraviolet lamp to fix the two sections of single mode fibers on a glass slide; The bubble-removed PDMS solution was dropped between two sections of single-mode fiber, then placed in a dry box at 80 ℃ for 40 minutes and then removed, and the actual length of the PDMS cavity was measured and confirmed under a microscope.
2. 2. The optical fiber temperature sensor based on the dual FP parallel structure according to claim 1, wherein the preparing the reference interferometer according to the preset length of the hollow fiber comprises: Cutting the end surfaces of the first single-mode optical fiber, the hollow-core optical fiber and the second single-mode optical fiber in order by using a high-precision optical fiber cutter, and ensuring that the end surfaces are vertical, smooth and burr-free so as to reduce welding loss; placing the cut first single-mode optical fiber and hollow optical fiber into an optical fiber fusion splicer to align with an axis, and carrying out fusion splicing according to low discharge intensity and short discharge time so as to prevent collapse of the hollow optical fiber; after the end face of the fusion splice was checked and confirmed to be flat by a microscope, the fusion splice was cut to a predetermined length of the hollow fiber, and a second single mode fiber was fusion spliced at the other end of the hollow fiber in the same manner to construct a reflection plane.
3. 3. The dual FP parallel structure based fiber optic temperature sensor of claim 1, wherein the PDMS solution is configured by: Selecting PDMS raw material with the model of Dow Corning DC184, respectively extracting a certain amount of PDMS raw material and auxiliary curing agent by using a syringe, mixing the PDMS raw material and the auxiliary curing agent in a new centrifuge tube according to the mass ratio of 10:1, and then placing the mixture into the centrifuge for 30 to 60 minutes until bubbles in the solution disappear, thus obtaining the PDMS solution.
4. 4. The optical fiber temperature sensor based on the double-FP parallel structure according to claim 1, wherein before preparing a reference interferometer and a sensing interferometer, a fiber stripper is used for removing a coating layer of each single-mode fiber, a flame is used for removing a coating layer of a hollow fiber, and an end face is cleaned by absolute ethyl alcohol, so that the end face of each fiber is clean.

Description

Optical fiber temperature sensor based on double-FP parallel structure Technical Field The application belongs to the technical field of temperature sensing, and particularly relates to an optical fiber temperature sensor based on a double-FP parallel structure. Background The temperature sensor is used as a key device in a modern measurement and control system, is widely applied to the fields of industry, medical treatment, civil engineering, aerospace, geological exploration and the like, and provides accurate and reliable temperature monitoring and control means for various industries. The optical fiber sensing technology uses optical fibers as sensitive elements and information transmission media, and has been widely used for measuring physical parameters such as temperature, pressure, refractive index, etc. due to the advantages of small volume, high sensitivity, electromagnetic interference resistance, fast response speed, etc. The Fabry-Perot (F-P) interferometer (FPI) is a sensing structure which causes interference fringe drift through cavity length change, thereby realizing high-precision measurement of physical quantities such as temperature and the like, and has the characteristics of simple structure, easy signal demodulation, easy encapsulation and the like. A basic Fabry-Perot cavity is composed of a cavity formed between two reflecting surfaces, and light is reflected between two planes for multiple times to form sharp interference fringes. When external parameters such as pressure and temperature change, the cavity length of the resonant cavity may change, or the Refractive Index (RI) of the medium in the cavity may change, and both may cause adjustment of the optical path difference of the beam in the cavity, and may be reflected in the interference spectrum of the sensor. By accurately demodulating the interference spectrum and analyzing the changes of the characteristics such as peak position, intensity distribution and the like in the spectrum, the accurate detection and measurement of external parameters can be realized. FPIs can be broadly classified into intrinsic type fabry-perot interferometers (IFPI) and extrinsic type fabry-perot interferometers (EFPI) according to the principle of multi-beam interferometers, and typically IFPI is used for temperature measurement. In order to further improve the sensing sensitivity, a vernier effect can be introduced, and by constructing a double-cavity or multi-cavity interference structure, interference spectrums with slightly different free spectrum ranges can be overlapped to form an amplified envelope, so that multiplication and amplification of micro-wavelength variation are induced. In the temperature sensor of the Fabry-Perot interferometer based on the photosensitive polymer material, disclosed in the prior art, the photosensitive resin blended with PDMS is solidified on the end face of a single-mode fiber to form a microscale polymer cavity, so that an FPI structure which is compact in structure, low in cost and easy to prepare is realized. The temperature response of the device is mainly derived from the significant thermal expansion effect of the photopolymer and the doped PDMS, and the sensing sensitivity is improved by regulating the concentration of the PDMS. The experimental results show that the sensor only shows a temperature sensitivity of up to-1.18 nm/°c over the range of 20-110 ℃ when the concentration of PDMS is 30%. It can be seen that the FPI fiber temperature sensor has a large lifting space in terms of temperature sensitivity. Disclosure of Invention In view of the above, the application aims to provide an optical fiber temperature sensor based on a double-FP parallel structure, which has the advantages of high sensitivity, high linearity, large detection range, good repeatability and good reversibility, and the size of an optical fiber sensing probe is in the micrometer level, so that the optical fiber temperature sensor is suitable for detecting the temperature in a narrow space. The application provides an optical fiber temperature sensor based on a double-FP parallel structure, which consists of a reference interferometer and a sensing interferometer which are connected in parallel, wherein the reference interferometer consists of a first single-mode optical fiber, a hollow optical fiber and a second single-mode optical fiber, and the sensing interferometer consists of a third single-mode optical fiber, a PDMS cavity and a fourth single-mode optical fiber; The free spectrum range of the sensing interferometer is similar to but not equal to the free spectrum range of the reference interferometer by controlling the optical path lengths of the PDMS cavity and the hollow optical fiber to be similar but not equal, so that the vernier effect of the output spectrum is excited to form an envelope formed by fine stripes. Further, the optical path lengths of the PDMS cavity and the hollow fiber are controlled to be similar bu