Optical High Temperature Sensor Research Articles

Fiber optic high temperature sensor based on ZnO composite graphene temperature sensitive material

The working temperature of the cable is particularly important for the safe operation of the power system, which requires high temperature detection for its working environment, but the sensitivity of the ordinary optical fiber temperature sensor in the high temperature state cannot meet this demand. For this purpose, an optical fiber high temperature sensor based on ZnO composite graphene temperature sensitive material is developed in this paper. MMF-TSCF-MMF temperature sensing unit is composed of two sections of multimode fiber (MMF) and a tapered seven core fiber (TSCF). Three different shapes of ZnO@Gr (ZnO composite graphene) temperature-sensitive materials were prepared by hydrothermal method. The experimental results show that the sensor has high stability and good interference effect. Meanwhile, the wavelength sensitivity reached 0.33268 nm/°C in a temperature measurement range of 89–98 °C. The fiber sensor is used for precision temperature measurement of cable temperature in fields such as electrical engineering due to its high temperature sensitivity, small size and low cost.

A high sensitivity optical thermometry on the basis of the intensity ratio between the fluorescence and phosphorescence in lutecium porphyrin

An optical thermometry was performed utilizing the intensity ratio between the fluorescence and the phosphorescence of lutecium hematoporphyrin (Lu-HMME). In spite of the large energy level difference between the singlet first excited state (S1) and the triple first excited state (T1), the emission intensities of the two channels were on the same order of magnitude, and the resulted luminescence intensity ratio was confirmed to follow the Boltzmann distribution law. The huge difference in population was made up by the intrinsic properties of Lu-HMME that the transition probability of the S1 state is several orders of magnitude higher than that of T1. Based on this, Lu-HMME is a candidate for optical high-temperature sensors with high relative sensitivity and good temperature resolution.

Residual-stress-induced helical long period fiber gratings for sensing applications.

We demonstrate a high-efficiency grating fabrication system, which can be used to inscribe a high-quality helical long period fiber grating (HLPFG) on single-mode fiber by means of hydrogen-oxygen flame. Such the HLPFG can be produced in enormous quantities with a uniform grating parameters and good reproducibility of grating inscription. Possible mechanisms for refractive index modulation in the HLPFG can be attributed to residual stress concentration by solidifying the periodic twisting stress under a fused status of optical fiber. Moreover, the HLPFG exhibits an excellence performance of high temperature sensing with a high sensitivity of ~132.8 pm/°C and a measuring range from room temperature to 900 °C. Comparing to the traditional LPFG fabricated by CO2 laser or arc discharge technique, the HLPFG has a low the bending and tensile strain sensitivity of 1.94 nm/(1/m) and 1.41 pm/με, respectively. So the proposed HLPFG could have a great potential in special applications as optical high-temperature sensors.

Effect of crystallinity on the optical thermometry sensitivity of Tm3+/Yb3+ codoped LiNbO3 crystal

Under 980nm excitation, optical temperature sensing properties based on the upconversion emissions of Tm3+ in LiNbO3 polycrystal and single crystal are studied in the temperature range of 323–773K. It is observed the 3F2,3 and 3H4 levels of Tm3+ are thermally coupled levels in both LiNbO3 polycrystal and single crystal, suggesting that the Tm3+-doped LiNbO3 crystals possess potential application in optical thermometry. Moreover, the crystallinity of host material greatly affects the optical thermometry sensitivity. The splitting degrees of upconversion emission spectra are changed with the crystallinities of LiNbO3 crystals, smaller splitting degree can result in higher absolute sensitivity. By optimizing the Tm3+ and Yb3+ ion concentrations, LiNbO3 single crystal is promising for optical high temperature sensor. These results reveal that the higher crystallinity of sensing material is beneficial to improve the sensitivity and resolution of optical temperature sensor.

Fabrication of high-temperature temperature sensor based on dielectric multilayer film on Sapphire fiber tip

A high-temperature temperature sensor based on dielectric ZrO2 / Al2O3 / ZrO2 (ZAZ) three-layer film structure on sapphire fiber tip with potential for low-cost batch production was fabricated. A fiber optic high-temperature sensor based on the principle of Fabry-Perot structure is proposed. The ZAZ three-layer film sensing element was deposited on the tip of a polished sapphire fiber using physical vapor deposition (PVD). Due to exceptionally small size, the as-prepared temperature sensor based on sapphire fiber tip can be used as an embedded sensor in harsh environments. And experimental result shows that the sensor based on sapphire fiber has a very high correlation with environment temperature; the correlation coefficient was measured to be 99.79%. The sensitivity of temperature reaches 1.8×10−5/°C when the environment temperature changes from 100.9°C to 1111.0°C.

Up-conversion luminescence of Er3+ and Yb3+ co-doped CaBi2Ta2O9 multifunctional ferroelectrics

Er 3+ and Yb 3+ co-doped CaBi 2 Ta 2 O 9 (CBT)-based bismuth layered-structure oxides were synthesized by a simple solid-state reaction method. Their up-conversion (UC) luminescence, dielectric and ferroelectric properties were investigated. Two strong green emission bands centered at 526 and 547 nm and a weak red emission band centered at 658 nm were obtained under a 980 nm laser excitation at room temperature. These emission bands originated from the radiative relaxation of Er 3+ from 2 H 11/2, 4 S 3/2, and 4 F 9/2 levels to the ground state 4 I 15/2, respectively. At the meantime, the fluorescence intensity ratio (FIR) variation of two green UC emissions at 526 and 547 nm has been studied as a function of temperature in the range of 153–603 K. The maximum sensor sensitivity obtained was 39 × 10-4 K-1 at 590 K, which indicated that Er 3+/ Yb 3+ co-doped CBT ceramic is a promising candidate for applications in optical high temperature sensor.

Research Status and Development Prospect of Optical Fiber High-Temperature Sensors

Accurate temperature measurement needs in both research and industry have become more demanding and traditional temperature measurement technologies are struggling to keep up. Optical fiber thermometers have many unique advantages and are an option with much potential in the area of high temperature measurement. Research shows that fiber optic temperature sensors are capable of making accurate and precise measurements in a wide range of harsh conditions where other measurement technologies cannot and are a cost effective option in situations where traditional measurement technologies are currently used. Several typical high temperature fiber optic sensors are discussed in detail, focusing on the principle of operation, advantageous characteristics, and recent research developments, with the aim of aiding in further work with fiber optic thermometers.

Optical High Temperature Sensor Based on Enhanced Green Upconversion Emissions in Er3+–Yb3+–Li+ Codoped TiO2 Powders

The Er3+-Yb3+-Li+ codoped TiO2 powders have been prepared by sol-gel method. The strong enhancement of green and red upconversion emissions were obtained for Er3+-Yb3+ codoped TiO2 by additional Li+ codoping and investigated using 976 nm semiconductor laser diode excitation. The enhanced upconversion emissions by the addition of Li+ resulted from the formation of Li compound with lower crystal field symmetry. The fluorescence intensity ratio (FIR) of green upconversion emissions from the transitions of 2H(11/2) --> 4I(15/2) and 4S(3/2) --> 4I(15/2) of Er3+ in the Er3+-Yb3+-Li+ codoped TiO2 has been studied as a function of temperature in the range of 300-925 K, and the maximum sensitivity was determined to be 0.0025 K(-1). Er3+-Yb3+-Li+ codoped TiO2 material with the highest operating temperature up to 925 K, has higher temperature sensitivity and fluorescence efficiency being a promising candidate for applications in optical high temperature sensor.

Optical thermometry through infrared excited green upconversion emissions in Er3+–Yb3+ codoped Al2O3

Fluorescence intensity ratio (FIR) variation of green upconversion emissions at 523 and 545nm in the Er3+–Yb3+ codoped Al2O3 has been studied as a function of temperature using a 978nm semiconductor laser diode as an excitation source. In the temperature range of 295–973K, the maximum sensitivity and the temperature revolution derived from the FIR technique are approximately 0.0051K−1 and 0.3K, respectively. The Er3+–Yb3+ codoped Al2O3 material with the highest operating temperature up to 973K, the higher temperature revolution, and the fluorescence efficiency indicated that it is promising for applications in optical high temperature sensor.

Optical high temperature sensor based on green up-conversion emissions in Er 3+ doped Al 2O 3

Er 3+ doped Al 2O 3 has been prepared by a non-aqueous sol–gel method using aluminum isopropoxide as precursor, acetylacetone as chelating agent, nitric acid as catalyzer, and hydrated erbium nitrate as a dopant in an isopropanol environment. The fluorescence intensity ratio (FIR) of the green up-conversion emissions at the wavelengths of about 523 and 545 nm in the Er 3+ doped Al 2O 3 was studied as a function of temperature over a wide temperature range of 295–773 K, using a 978 nm semiconductor laser diode (LD) as an excitation source. The maximum sensitivity and the temperature resolution derived form the FIR of the green up-conversion emissions are approximately 0.0052 K −1 and 0.3 K, respectively. It is demonstrated that the prototype optical high temperature sensor based on the FIR technique from the green up-conversion emissions in the Er 3+ doped Al 2O 3 is promising for applications in high temperature measurement.

Single-crystal sapphire-based optical high-temperature sensor for harsh environments

An optical temperature-sensing instrument based on broadband polarimetric differential interferometry (BPDI) technology is developed for ultrahigh temperature measurement in chemically corrosive environments. A single-crystal sapphire disk with inherent birefringence is employed as a sensing element in this instrument. Absolute temperature information is obtained and the measurement results are relatively immune to optical source power fluctuations and transmission fiber losses. Other advantages of this sensor are its mechanical simplicity, high resolution, and great accuracy over a wide measurement range.