Study on the performance of polarization maintaining fiber temperature sensor based on tilted fiber grating

Highlights

• A high integration polarization interference fiber temperature sensor is proposed.

• The sensor integrates an in-fiber polarizer based on 45° tilted fiber Bragg grating.

• Kalman filter is used to improve the accuracy and stability of the sensor.

• The accuracy and resolution of the sensor reach ±0.1 °C and 0.01 °C respectively.

• The feasibility of the sensor in transformer temperature monitoring is proved.

Abstract

A novel functional-type high integration polarization interference fiber temperature sensor based on 45° tilted fiber Bragg grating in-fiber polarizer (TFBG-PIF-TS) is proposed. The accuracy, resolution, stability, linearity and sensitivity of the prototype are tested and compared with PT100, 18B20 as well as polarizing plate based polarization interferometric fiber temperature sensor (PP-PIF-TS). The feasibility of the scheme in the transformer winding temperature monitoring is verified. The results show that the accuracy and resolution of TFBG-PIF-TS reach ±0.1 °C and 0.01 °C respectively, which has higher resolution, better integration and reliability, and has simple structure, strong anti-vibration and anti-electromagnetic interference abilities. Therefore, the proposed scheme can meet the needs of high voltage, strong magnetic field and other passive precise temperature measurement occasions.

Introduction

As a new type of temperature sensor, optical fiber temperature sensor has many advantages such as passivity, high measurement accuracy, anti-electromagnetic interference, safety explosion-proof, insulation and fire resistance [1], [2], [3]. It is widely used in metallurgy, transportation, petrochemical, electric power, nuclear energy and other special occasions where active temperature sensor is difficult to be applied.

At present, the mature optical fiber temperature sensors can be divided into two types according to their working principles: transmission-type and functional-type. The transmission-type optical fiber temperature sensor is equipped with temperature sensitive materials in the sensor probe, while the optical fiber only plays the role of transmitting light. Li et al. [4] introduced a temperature measurement scheme based on semiconductor absorption theory and spectral analysis method, where the temperature was measured by detecting the wavelength of the optical absorption edge. Shen et al. [5] proposed a kind of optical fiber temperature sensor based on ZnO composite graphene, and discussed the sensitivity in the range of 30–48 °C. Fitzpatrick et al. [6] introduces a fluorescent fiber optic sensor, which provides a practical method for temperature measurement in harsh electrical environment. In general, the transmission-type optical fiber temperature sensor has the characteristics of low cost and low price, but it has the problems of narrow measurement range (about 100 °C), low accuracy (greater than 1 °C) and short transmission distance (less than 20 m).

The functional optical fiber temperature sensor is based on the characteristics that the wavelength, phase and polarization of light vary with temperature, and the optical fiber is used as the temperature sensing component. Yang as well as Luo et al. [7], [8] use fiber Bragg grating (FBG) as temperature sensing components, Failleau et al. [9], [10], [11], [12] proposed the distributed optical fiber temperature sensor based on Raman/Brillouin scattering effect, Ma et al. [13] fabricated the temperature sensor by filling liquid crystal in the microstructure fiber, and tested the sensitivity of the sample in the range of 265–295 k. It can be seen that the existing mature functional-type optical fiber temperature sensor has wide measurement range and long transmission distance, but the system structure and demodulation scheme are complex and expensive, and the accuracy is also low (about 1 °C).

As a result, we propose a functional-type polarization interference optical fiber temperature sensor (PIF-TS), which is based on the temperature birefringence effect of polarization maintaining (PM) fiber [14], [15]. By detecting the energy change of interference field caused by the phase difference of polarized light to obtain the information of temperature, and using single-mode (SM) fiber to realize long-distance signal transmission, the scheme has excellent performances of simple structure, low cost, high precision, fast response speed, high resolution and long transmission distance.

The polarizer can convert non polarized light or low polarized light into high polarization beam, which is important for applications in fiber communication and sensing, and is the key component of PIF-TS. The traditional bulk optic polarizer uses optical fiber collimator to realize coupling with fiber, all this discrete components need to be bonded through adhesive process, which is susceptible to vibration and temperature, and is bulky and difficult to be integrated into optical fiber temperature probe. Compared with bulk optic polarizers, in-fiber polarizers are more desirable in fiber systems owing to their light weight, low insertion loss, and high coupling efficiency. Bao et al. [16] proposed a graphene based broadband optical fiber polarizer, whose out-coupled light in the telecommunication band shows a strong s-polarization effect with an extinction ratio of 27 dB. However, due to the bonding (deposition) structure, the scheme is limited to low power operation and suffers from thermal and mechanic stability problems. Kopp and Yang et al. [17], [18] proposed the chiral fiber grating based circular polarizer, which is formed by twisting a non-centric fiber to achieve the operation to circular polarized light. However, the chiral fiber gratings need specifical fiber with an asymmetric structure, which may also limit its application in all-fiber systems.

Fiber grating is formed in the core of the fiber by UV induced refractive index modulation, without physical modification of the fiber, so as to maintain high mechanical strength and sustainable to high operation power. Lim et al. [19] proposed a simple mathematical model to explain the formation of grating structure in photosensitive germane-silica fibers written by KrF excimer laser and phase-mask, and observed the variation of local refractive index of optical fiber during the process of writing. Fiber gratings have many uses. Yan et al. [20], [21], [22] proposed a 45° tilted fiber Bragg grating (TFBG), which has strong polarization dependent loss (PDL) effect, and can achieve high performance in-fiber polarizers with high polarization extinction ratio and wide bandwidth.

On this basis, we designed a high integration PIF-TS based on 45° TFBG in-fiber polarizer (TFBG-PIF-TS), which adopts all fiber fusion mode, and has no air gap and glue filling in the probe. The performance and engineering application feasibility of TFBG-PIF-TS were tested and compared with PT100 and 18B20. Compared with the existing mature temperature sensing schemes, TFBG-PIF-TS not only has higher accuracy and resolution, but also has better security and long-term operation reliability.